27,306 results on '"IONIZATION (Atomic physics)"'
Search Results
2. Real-Time Authentication of Camellia Oil by Rapid Evaporative Ionization Mass Spectrometry.
- Author
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Xiang, Jun, Liu, Qi, Jing, Huihua, and Chen, Xiaoqing
- Subjects
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MASS spectrometry , *CAMELLIAS , *VEGETABLE oils , *RAPESEED oil , *SUNFLOWER seed oil , *IONIZATION (Atomic physics) - Abstract
Camellia oil is a high-value product with rich nutrients. Recently, the adulteration of camellia oil has become an increasingly concerning issue related to human health. In this study, electric soldering iron coupled with rapid evaporative ionization mass spectrometry (REIMS) was employed for the identification and analysis of camellia oil without any sample preparation. REIMS technology coupled with chemometrics was applied to develop an analysis model for the authentication of camellia oil adulterated with soybean oil, peanut oil, rapeseed oil, sunflower oil, and corn oil (5–40%, v/v). The results showed that different types of vegetable oils could be classified using principal component analysis-linear discriminant analysis (PCA-LDA) with a correct classification of 93.8% in leave-20%-out cross-validation and 100% correctly identified in real-time recognition. The established prediction models were found to be particularly sensitive when the camellia oil samples were adulterated with 5–40% of other oils, indicating that REIMS could be a powerful tool for the authentication and adulteration analysis of camellia oil, particularly for cases where the adulteration levels are relatively high. In conclusion, the results provide valuable insights into the potential of REIMS for the rapid, accurate, and real-time authentication and adulteration analysis of camellia oil. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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3. The Effects of Particle LET and Fluence on the Complexity and Frequency of Clustered DNA Damage.
- Author
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Rezaee, Mohammad and Adhikary, Amitava
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DNA damage ,RADIOBIOLOGY ,PROTONS ,ELECTRONS ,IONIZATION (Atomic physics) - Abstract
Motivation: Clustered DNA-lesions are predominantly induced by ionizing radiation, particularly by high-LET particles, and considered as lethal damage. Quantification of this specific type of damage as a function of radiation parameters such as LET, dose rate, dose, and particle type can be informative for the prediction of biological outcome in radiobiological studies. This study investigated the induction and complexity of clustered DNA damage for three different types of particles at an LET range of 0.5–250 keV/µm. Methods: Nanometric volumes (36.0 nm
3 ) of 15 base-pair DNA with its hydration shell was modeled. Electron, proton, and alpha particles at various energies were simulated to irradiate the nanometric volumes. The number of ionization events, low-energy electron spectra, and chemical yields for the formation of °OH, H°, e a q − , and H2 O2 were calculated for each particle as a function of LET. Single- and double-strand breaks (SSB and DSB), base release, and clustered DNA-lesions were computed from the Monte-Carlo based quantification of the reactive species and measured yields of the species responsible for the DNA lesion formation. Results: The total amount of DNA damage depends on particle type and LET. The number of ionization events underestimates the quantity of DNA damage at LETs higher than 10 keV/µm. Minimum LETs of 9.4 and 11.5 keV/µm are required to induce clustered damage by a single track of proton and alpha particles, respectively. For a given radiation dose, an increase in LET reduces the number of particle tracks, leading to more complex clustered DNA damage, but a smaller number of separated clustered damage sites. Conclusions: The dependency of the number and the complexity of clustered DNA damage on LET and fluence suggests that the quantification of this damage can be a useful method for the estimation of the biological effectiveness of radiation. These results also suggest that medium-LET particles are more appropriate for the treatment of bulk targets, whereas high-LET particles can be more effective for small targets. [ABSTRACT FROM AUTHOR]- Published
- 2024
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4. Study on theoretical model for electrical explosion resistivity of Al/Ni reactive multilayer foil.
- Author
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Zehao Wang, Tao Wang, Pengfei Xue, Mingyu Li, and Qingxuan Zeng
- Subjects
CHEMICAL reactions ,MICROELECTROMECHANICAL systems ,VAPORIZATION ,IONIZATION (Atomic physics) ,PHASE transitions - Abstract
Al/Ni reactive multilayer foil (RMF) possesses excellent comprehensive properties as a promising substitute for traditional Cu bridge. A theoretical resistivity model of Al/Ni RMF was developed to guide the optimization of EFIs. Al/Ni RMF with different bilayer thicknesses and bridge dimensions were prepared by MEMS technology and electrical explosion tests were carried out. According to physical and chemical reactions in bridge, the electrical explosion process was divided into 5 stages: heating of condensed bridge, vaporization and diffusion of Al layers, intermetallic combination reaction, intrinsic explosion, ionization of metal gases, which are obviously shown in measured voltage curve. Effects of interface and grain boundary scattering on the resistivity of film metal were considered. Focusing on variations of substance and state, the resistivity was developed as a function of temperature at each stage. Electrical explosion curves were calculated by this model at different bilayer thicknesses, bridge dimensions and capacitor voltages, which showed an excellent agreement with experimental ones. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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5. Ising density functional theory for weak polyelectrolytes with strong coupling of ionization and intrachain correlations.
- Author
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Gallegos, Alejandro, Ong, Gary M. C., and Wu, Jianzhong
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DENSITY functional theory , *POLYELECTROLYTES , *ISING model , *ELECTROSTATIC interaction , *IONIZATION (Atomic physics) , *POLYMER structure - Abstract
We report a theoretical framework for weak polyelectrolytes by combining the polymer density functional theory with the Ising model for charge regulation. The so-called Ising density functional theory provides an accurate description of the effects of polymer conformation on the ionization of individual segments and is able to account for both the intra- and interchain correlations due to the excluded-volume effects, chain connectivity, and electrostatic interactions. Theoretical predictions of the titration behavior and microscopic structure of ionizable polymers are found to be in excellent agreement with the experiment. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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6. The missing hydrogen ion, part-1: Historical precedents vs. fundamental concepts.
- Author
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Robergs, Robert, O'Malley, Bridgette, Torrens, Sam, and Siegler, Jason
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HYDROGEN ions ,ORGANIC acids ,PHOSPHORYL group ,IONIZATION (Atomic physics) ,LACTATES - Abstract
The purpose of this review and commentary was to provide an historical and evidence-based account of organic acids and the biochemical and organic chemistry evidence for why cells do not produce metabolites that are acids. The scientific study of acids has a long history dating to the 16
th and 17th centuries, and the definition of an acid was proposed in 1884 as a molecule that when in an aqueous solution releases a hydrogen ion (Hþ). There are three common ionizable functional groups for molecules classified as acids: 1) the carboxyl group, 2) the phosphoryl group and 3) the amine group. The propensity by which a cation will associate or dissociate with a negatively charged atom is quantified by the equilibrium constant (Keq) of the dissociation constant (Kd) of the ionization (Keq = Kd ), which for lactic acid (HLa ) vs. lactate (La-) is expressed as: Keq = Kd = [HLa] [La] =[HLa] = 4 677.351 4 (ionic strength = 0.01 Mol-L-1 , T = 25 °C). The negative log10 of the dissociation pKd reveals the pH at which half of the molecules are ionized, which for HLa = 3.67. Thus, knowing the pKd and the pH of the solution at question will reveal the extent of the ionization vs. acidification of molecules that are classified as acids. [ABSTRACT FROM AUTHOR]- Published
- 2023
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7. GC-FTICR mass spectrometry with dopant assisted atmospheric pressure photoionization: application to the characterization of plastic pyrolysis oil.
- Author
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Mase, Charlotte, Maillard, Julien F., Piparo, Marco, Friederici, Lukas, Rüger, Christopher P., Marceau, Sabrina, Paupy, Benoit, Hubert-Roux, Marie, Afonso, Carlos, and Giusti, Pierre
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ATMOSPHERIC pressure , *ION cyclotron resonance spectrometry , *PHOTOIONIZATION , *MASS spectrometry , *DOPING agents (Chemistry) , *CHEMICAL ionization mass spectrometry , *IONIZATION energy , *IONIZATION (Atomic physics) - Abstract
Pyrolysis is a promising way to convert plastic waste into valuable resources. However, for downstream upgrading processes, many undesirable species, such as conjugated diolefins or heteroatom-containing compounds, can be generated during this pyrolysis. In-depth chemical characterization is therefore required to improve conversion and valorization. Because of the high molecular diversity found in these samples, advanced analytical instrumentation is needed to provide accurate and complete characterization. Generally, direct infusion Fourier transform mass spectrometry is used to gather information at the molecular level, but it has the disadvantage of limited structural insights. To overcome this drawback, gas chromatography has been coupled to Fourier transform ion cyclotron resonance mass spectrometry. By taking advantage of soft atmospheric pressure photoionization, which preserves molecular information, and the use of different dopants (pyrrole, toluene, and benzene), selective ionization of different chemical families was achieved. Differences in the ionization energy of the dopants will only allow the ionization of the molecules of the pyrolysis oil which have lower ionization energy, or which are accessible via specific chemical ionization pathways. With a selective focus on hydrocarbon species and especially hydrocarbon species having a double bond equivalent (DBE) value of 2, pyrrole is prone to better ionize low-mass molecules with lower retention times compared to the dopant benzene, which allowed better ionization of high-mass molecules with higher retention times. The toluene dopant presented the advantage of ionizing both low and high mass molecules. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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8. Applicability of the Suspension Effect in Estimation of Influence Exerted by Ionic Composition of Flotation Pulp on Apatite Surface.
- Author
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Artem'ev, A. V. and Mitrofanova, G. V.
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APATITE , *SURFACE properties , *FLOTATION , *ORES , *IONIZATION (Atomic physics) - Abstract
By means of determining the suspension effect, the authors studied the change in the surface properties of apatite under the action of reagents and ions present in flotation pulp during processing of apatite-bearing ore. It is shown that the ratio of acid–base centers of apatite surface change in interaction with ions HCO , CO , HPO , cations Ca and oleate ions in distilled water and in water after deionization to remove carbon dioxide. The change in apatite surface properties in alkaline water shows up as quantitative superiority of base centers. Such ionization of mineral surface favors adsorption of cations, for example, Ca , and sets background for more efficient interaction between anion-type agents. The data obtained from the studies of the suspension effect, correlate with the results of infrared spectroscopy of apatite treated by the appropriate agents. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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9. Spectroscopic Detection of Alfvénic MHD Waves in the Sunspot Chromosphere.
- Author
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Chae, Jongchul
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SOLAR chromosphere , *SUNSPOTS , *SOLAR wind , *IONIZATION (Atomic physics) , *OSCILLATIONS - Abstract
Alfvénic waves are regarded as an important process in understanding coronal heating, solar wind acceleration, and the fractionization of low first-ionization-potential (FIP) elements. Recently, significant progresses have been made in the detection of propagating Alfvénic waves in the solar chromosphere using two different methods: the imaging method and the spectroscopic method. The imaging method detects Alfvénic waves that oscillate in the direction perpendicular to the line of sight, and the spectroscopic method, those that oscillates in the line of sight direction. We have applied the spectroscopic method to the imaging spectral data taken by the FISS on GST at Big Bear. As a result, we detected a number of propagating Alfvénic wave packets, and found that there are two distinct groups: three-minute period waves, and ten-minute period waves. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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10. THEORETICAL STUDY OF THE PHOSPHATE UNITS STABILITY BY THE DFT B3LYP/6-311G QUANTUM METHOD.
- Author
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El Addali, A., El Boukili, A., Boudad, L., Taibi, M., and Guedira, T.
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PHOSPHATES ,DENSITY functional theory ,ELECTRIC potential ,REACTIVITY (Chemistry) ,IONIZATION (Atomic physics) - Abstract
The phosphate units have been theoretically investigated through density functional theory (DFT) calculations. Ionization potential (I), electron affinity (A), electrophilicity index (ω), chemical potential (µ), hardness (η), softness (S), and dipole moment (P) have been optimized. The obtained results revealed that the [PO
4 ]3- (Q0 ) units act as electron donors, while the [P4 O10 ]0 (Q3 ) unit acts as an electron acceptor. The passage from one unit to the other implies an increase in the number of bridging oxygens (BO) consistent with the variation of Mulliken charges. Moreover, the analysis of the optimized contours of the electrostatic potential has indicated that the electrophilic attack is more expected on the P-O-P bonds. The infrared and Raman spectra have been also predicted and the change of symmetric and asymmetric vibrational bands of the phosphate units with the number of bridging oxygens has been investigated. [ABSTRACT FROM AUTHOR]- Published
- 2023
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11. SWAG: The Maps.
- Author
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Ott, Jürgen, Meier, David S., Candelaria, Tierra, and Ward, Dylan
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STAR formation , *DYNAMICS , *TEMPERATURE , *IONIZATION (Atomic physics) , *STELLAR mass - Abstract
We present maps of the "Survey of Water and Ammonia toward the Galactic center" (SWAG). SWAG was observed over three years (∼550 h) with the Australia Telescope Compact Array (ATCA) and covers the entire Central Molecular Zone (CMZ) at about 26" or ∼1 pc resolution. The observed 21.2–25.6 GHz range contains tens of spectral lines and 4 GHz of continuum. Here, we present some final maps. These include multiple NH3 lines, radio recombination lines, shock tracers like HNCO and methanol (CH3OH), high resolution 22 GHz water masers, and a continuum map. The maps are the foundation for ongoing comprehensive temperature mapping of the CMZ, including the identification of heating mechanisms, the characterization of water maser sources as young stellar objects or AGB stars, as well as chemistry, dynamics, and star formation studies of the ISM in this unique environment. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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12. Fast prediction of electron-impact ionization cross sections of large molecules via machine learning.
- Author
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Zhong, Linlin
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IONIZATION (Atomic physics) , *ELECTRONS , *MACHINE learning , *MOLECULES , *SUPPORT vector machines , *KERNEL (Mathematics) - Abstract
The theoretical determination of electron-impact ionization cross section (Qion) for a molecule requires ab initio computation, which is time-consuming for large molecules. We propose a machine learning based method to construct a model for predicting Qion of large molecules without the high-cost ab initio calculation. The model is learned from the data composed of the calculated Qion of the small molecules with fewer constituent atoms and the electron numbers of the corresponding molecules in a train set by a support vector machine. The radial basis function is set as a kernel function to map data to a higher dimensional space. The grid search with 5-fold cross-validation is performed to find optimal hyperparameters in the learning model. The prediction on the test sets composed of CF4, C3F8, SF6, C6, C6F12, and C6F12O shows that this data-driven model can generate well-agreed Qion and has good generalization performance. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
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13. Terahertz radiation generation by three-color laser pulses in air filament.
- Author
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Vaičaitis, V., Balachninaitė, O., Morgner, U., and Babushkin, I.
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SUBMILLIMETER waves , *FEMTOSECOND pulses , *FREE electron lasers , *APERIODICITY , *IONIZATION (Atomic physics) - Abstract
We demonstrated terahertz (THz) radiation generated from a three-color laser-excited filament in air for a wide tuning range and various wavelength ratios of the pump laser pulses. As a pump source, the radiation of the femtosecond Ti:sapphire laser and infrared output of the optical parametric generator were used. It was found that the spectrum of generated THz pulses spans up to 50 THz, while the overall THz generation efficiency is of an order of magnitude larger than the one produced by two-color pulses in an analogous configuration. Our results support the idea that three-color pulses are more suitable for broadband THz generation, since the corresponding waveforms can produce faster free electrons in larger quantities. We have found that the conversion efficiency is significantly limited due to intensity clamping. The spectral broadening of THz radiation is explained by aperiodicity of ionization events in time. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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14. The dynamic expansion of leader discharge channels under positive voltage impulse with different rise times in long air gap: Experimental observation and simulation results.
- Author
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Cui, Yingzhe, Zhuang, Chijie, Zhou, Xuan, and Zeng, Rong
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EXPANSION of gases , *AIR gap (Engineering) , *INTERFEROMETRY , *WAVE analysis , *ELECTRODES , *NUMERICAL analysis , *IONIZATION (Atomic physics) - Abstract
In this paper, we observe the dynamic expansion process of positive leader channels under impulses with different rise times in a 1-m air gap using a Mach-Zehnder interferometry and a high-speed video camera. The thermal parameters describing the leader channel under a lightning and switching impulse are obtained through an analysis of interference fringes. The influences of different voltage waveforms on the dynamic expansion of leader channels are obtained. Firstly, the expansion rates of the channel radius are higher for shorter rise times. The average expansion rates are 72.30 ± 9.54, 28.09 ± 5.05, and 14.38 ± 3.02 m/s for the rise times of 1.2, 40, and 100 μs and the crest value of 425 kV for a 0.5-cm-diameter cone electrode; moreover, the temperatures at the centre of the leader channels are 5000–7000 K, 4000–6000 K, and 3000–4500 K, respectively. Secondly, the high-temperature region is larger for the shorter rise times. A numerical model was used to study the expansion of the leader channels, and the simulation results for the leader channel diameters showed good consistency with the experimental measurements. The continuous energy injection results in an over-pressure process in the leader channels and ultimately in their expansion. For a 1.2/50 μs waveform, the vibrational-translational relaxation (QVT) and the thermal dissociation (QD), which dominate the energy flow, are about one order of magnitude greater than that in a 100/2500 μs waveform. The convection loss and the ionization mechanism during the expansion process are also discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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15. Hollow cathode effect modified time-dependent global model and high-power impulse magnetron sputtering discharge and transport in cylindrical cathode.
- Author
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Cui, Suihan, Wu, Zhongzhen, Lin, Hai, Xiao, Shu, Zheng, Bocong, Liu, Liangliang, An, Xiaokai, Fu, Ricky K. Y., Tian, Xiubo, Tan, Wenchang, and Chu, Paul K.
- Subjects
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GLOW discharges , *SIMULATION methods & models , *MAGNETRON sputtering , *IONIZATION (Atomic physics) , *GLOBAL modeling systems , *PLASMA diffusion - Abstract
High-power impulse magnetron sputtering boasts high ionization, large coating density, and good film adhesion but suffers from drawbacks such as low deposition rates, unstable discharge, and different ionization rates for different materials. Herein, a cylindrical cathode in which the special cathode shape introduces the hollow cathode effect to enhance the discharge is described. To study the discharge performance of the cylindrical cathode, a hollow cathode effect modified time-dependent global model is established to fit the discharge current pulses. The simulation results indicate that the cylindrical cathode has relatively large Hall parameters of 24 (700 V) to 26 (1000 V). Compared to the planar cathode, the cylindrical cathode has a larger plasma density as a result of the hollow cathode effect. In addition, the ionization rate and ion return probability increase by about 3.0% and 4.3%, respectively. Particle transport derived from the plasma diffusion model shows that the magnetic field enables further diffusion of ions than atoms, resulting in nearly pure ion deposition on the substrate. The deposition rate and ion current measured experimentally support the simulation model and results, and this model provides a universal platform to simulate plasma systems with similar structures. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
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16. Low energy electron and positron impact differential cross sections for the ionization of water molecules in the coplanar and perpendicular kinematics.
- Author
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Singh, P., Purohit, G., Champion, C., Sébilleau, D., and Madison, D.
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LOW energy electron diffraction , *POSITRON impact ionization , *KINEMATICS , *COPLANAR waveguides , *IONIZATION (Atomic physics) , *BORN approximation - Abstract
We report here triply differential cross sections (TDCSs) for 81 eV electron and positron-impact ionization of the combined (1b1 + 3a1) orbitals of the water molecule by using the second-order distorted wave Born approximation (DWBA2) for ejection electron and positron energies of 5 eV and 10 eV and different momentum transfer conditions. The electron-impact TDCS will be compared with the experimental data measured by Ren et al. [Phys. Rev. A 95, 022701 (2017)] and with the molecular 3-body distorted wave (M3DW) approximation results in the scattering plane as well as the perpendicular plane. The DWBA2 results are in better agreement with the experiment than the M3DW results for the scattering plane, and the M3DW results are somewhat better for the perpendicular plane. This observation is explained in terms of collision interactions. The electron and positron TDCSs are indistinguishable in the scattering plane. In the perpendicular plane, the positron results are similar in shape, but smaller in magnitude. However, the difference reduces with increasing projectile scattering angle and increasing ejected electron energy. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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17. Total and partial electron impact ionization cross sections of fusion-relevant diatomic molecules.
- Author
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Huber, Stefan E., Mauracher, Andreas, Süß, Daniel, Sukuba, Ivan, Urban, Jan, Borodin, Dmitry, and Probst, Michael
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ELECTRON impact ionization , *DIATOMIC molecules , *PLASMA boundary layers , *PLASMA physics , *IONIZATION (Atomic physics) - Abstract
We report calculations of total (and absolute) electron-impact ionization cross sections (EICSs) for the fusion-relevant diatomic molecular species BeH, BeN, BeO, WH, WBe, WN, WO, O2, and N2 by means of the Deutsch-Märk and the binary-encounter-Bethe methods in the energy range from threshold to 10 keV. In addition, we discuss an empirical scheme to estimate partial cross sections from the total ones based on reaction energetics and empirical threshold laws and explore its accuracy by assessing available experimental data on total and partial EICSs. Finally, we also report parameters obtained by fitting the calculated cross sections to an expression commonly used in fusion edge plasma modeling. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
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18. Learning from model grids: Tracers of the ionization fraction in the ISM.
- Author
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Bron, Emeric, Roueff, Evelyne, Gerin, Maryvonne, Pety, Jérôme, Gratier, Pierre, Le Petit, Franck, Guzman, Viviana, Orkisz, Jan, de Souza Magalhaes, Victor, Gaudel, Mathilde, Palud, Pierre, Einig, Lucas, Bardeau, Sébastien, Chainais, Pierre, Chanussot, Jocelyn, Goicoechea, Javier, Hughes, Annie, Kainulainen, Jouni, Languignon, David, and Le Bourlot, Jacques
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INTERSTELLAR medium , *IONIZATION (Atomic physics) , *CHEMICAL processes , *ULTRAVIOLET radiation , *MOLECULAR clouds - Abstract
The ionization fraction in neutral interstellar clouds is a key physical parameter controlling multiple physical and chemical processes, and varying by orders of magnitude from the UV irradiated surface of the cloud to its cosmic-ray dominated central regions. Traditional observational tracers of the ionization fraction, which mostly rely on deuteration ratios of molecules like HCO+, suffer from the fact that the deuterated molecules are only detected in a tiny fraction of a given Giant Molecular Cloud (GMC). In [1], we propose a machine learning-based, semi-automatic method to search in a large dataset of astrochemical model results for new tracers of the ionization fraction, and propose several new tracers relevant in different ranges of physical conditions. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
19. Mapping the high ionization rate of the GC starburst Sgr B2 through low HCO+ /N2H+J=1-0 intensity ratios.
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Santa-Maria, Miriam G. and Goicoechea, Javier R.
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STARBURSTS , *IONIZATION (Atomic physics) , *GALACTIC nuclei , *GALACTIC center , *STAR formation - Abstract
We still do not understand which mechanisms dominate the heating and ionization of the extended molecular gas in galactic nuclei. The starburst Sgr B2, in the Galactic Center (GC), is an excellent template to spatially resolve the high-mass star-forming cores from the extended cloud environment, and to study the properties of the warm neutral gas in conditions likely prevalent in star-forming galaxies. We mapped ~1000 pc2 of Sgr B2 complex, using the IRAM 30m telescope, in the N2H+, HCO+J=1-0 and SiO J=2-1 line emission. The extended nature of the N2H+J=1-0 emission is remarkable. Compared to molecular clouds in the disk of the galaxy, the N2H+J=1-0 emission is not confined to cold and dense cores and filaments. This can be explained by the high ionization rate (ζ ≳10−15 s−1), leading to overabundant H+3, He+, and N2H+. The enhanced ionization rate is likely responsible of the much lower line intensity ratio RI =HCO+/N2H+J=1-0 observed in Sgr B2 (RI ≈ 2 ± 2), Arp 220 (RI ≈ 2), and NGC 253 (RI ≈ 5), compared to disk clouds such as Orion B (RI ≈ 24) and starburst galaxies such as M82 (RI ≈ 21). [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
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20. Non-thermal air plasma jets at atmospheric pressure: The flow-dependent propagation in the afterglow.
- Author
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Wu, Shuqun, Liu, Xueyuan, Mao, Wenhao, Chen, Wen, Liu, Chang, and Zhang, Chaohai
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ATMOSPHERIC pressure , *GAS flow , *IONIZATION (Atomic physics) , *PLASMA jets , *ELECTRIC fields - Abstract
With a bare pin-to-nozzle electrode configuration, an ac-driven non-thermal air plasma jet with a length of several centimeters is generated. Depending on the gas flow rate, the propagation speed of these plasma columns is in the range of 100–350 m/s, which is close to the gas flow velocity. This indicates that the propagation of the plasma jet is determined by the transport of long lifetime species by gas flow instead of the electron-impact excitation and ionization of molecules under a high electric field. In comparison to the N2, O2, and Ar plasma jets, the length of the air plasma jet is much shorter than that of the N2 plasma jet but longer than that of the O2 and Ar plasma jets. A simple kinetic model reveals that the N2 (A3Σ) metastable plays a crucial role in sustaining the length of the N2 and air plasma jets, whose lifetime is strongly dependent on the quenching effect of O2, O, and NO as well as the compensation from the three-body recombination of nitrogen atoms. Based on the flow-dependent mechanism of the plasma jet, a visually uniform air plasma brush with a width of 2.8 cm and a length of 1.6 cm and a visually uniform N2 plasma brush with a width of 4 cm and a length of 4.4 cm have been demonstrated. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
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21. Carboxylic acids in aqueous solutions: Hydrogen bonds, hydrophobic effects, concentration fluctuations, ionization, and catalysis.
- Author
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Gailus, Torsten, Krah, Holger, Kühnel, Volker, Rupprecht, Andreas, and Kaatze, Udo
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CARBOXYLIC acids , *AQUEOUS solutions , *HYDROGEN bonding , *HYDROPHOBIC interactions , *FLUCTUATIONS (Physics) , *IONIZATION (Atomic physics) , *CATALYSIS - Abstract
In the frequency range between 100 kHz and 2 GHz, ultrasonic absorption spectra have been measured for a series of carboxylic acids from formic to enanthic acid, including constitutional isomers. Also investigated have been the spectra for mixtures with water of short-chain formic, acetic, propionic, butyric, and isobutyric acid, in each case covering the complete composition range. The neat carboxylic acids feature two Debye-type relaxation terms with relaxation times between 5.6 and 260 ns as well as 0.14 and 1.4 ns, respectively, at room temperature. Depending on the composition, mixtures with water reveal an additional Debye relaxation term in the intermediate frequency range (acetic acid) or a term subject to a relaxation time distribution (propionic, butyric, and isobutyric acid). The relaxations of the neat acids are assigned to the equilibrium between monomers and single-hydrogen-bonded linear dimers and between linear and twofold-hydrogen-bonded cyclic dimers. The latter equilibrium is considerably catalyzed by hydronium and carboxylate ions. Several mixtures with water indicate one of the up to three Debye relaxations to reflect the protolysis of the organic acid. The term with underlying relaxation time distribution is due to noncritical fluctuations in the local concentrations. The Debye relaxations are evaluated to yield the parameters of the relevant elementary chemical reactions, such as the rate and equilibrium constants and the isentropic reaction volumes. A comparison of the correlation length of concentration fluctuations with data for other aqueous systems confirms the idea that the hydrophobic part of the organic constituent promotes the formation of a micro-heterogeneous liquid structure, whereas the hydrophilic moiety is of minor importance in this respect. The high-frequency limiting absorption suggests the equilibrium between conformers of linear dimers to contribute to the spectra well above the frequency range of measurements. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
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22. Hole transport in selenium semiconductors using density functional theory and bulk Monte Carlo.
- Author
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Mukherjee, Atreyo, Vasileska, Dragica, and Goldan, A. H.
- Subjects
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SELENIUM , *SEMICONDUCTORS , *IONIZATION (Atomic physics) , *ELECTRIC fields , *PHONONS - Abstract
Amorphous selenium is emerging as a viable large-area imaging detector with avalanche multiplication gain for low-light and low-dose radiation detection applications. A key feature of its avalanche process is that only holes become "hot" carriers and undergo impact ionization. Thus, understanding the transport of non-equilibrium hot holes in extended states is pivotal to all the device applications. One of the interesting aspects of elemental selenium is the similar general feature of the electronic structure for various phase modifications. This stems from the strikingly similar short-range order between the crystalline and amorphous phases of selenium. At high electric fields, hole mobility in amorphous selenium loses its activated behavior and saturates with transport shifted entirely from localized to extended states. Thus, we expect the general details of the extended-state hole-phonon interaction in the amorphous phase to be described by the band-transport lattice theory of its crystalline counterparts, namely, monoclinic and trigonal selenium. To that effect and due to the intrinsic meta-stability of the monoclinic phase and high trap density in prepared specimens, we study hole transport in crystalline trigonal selenium semiconductors using a bulk Monte Carlo technique to solve the semi-classical Boltzmann transport equation. We validated our transport model by showing the excellent match between experimentally calculated hole drift mobilities with that calculated using the bulk Monte Carlo technique. Furthermore, calculations of the field-dependent carrier energy showed that holes in selenium can break the thermal equilibrium and get hot at which point the rate of energy gain from the applied electric field exceeds that of energy loss from the lattice. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
23. Development of a new Geant4-DNA electron elastic scattering model for liquid-phase water using the ELSEPA code.
- Author
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Shin, W.-G., Bordage, M.-C., Emfietzoglou, D., Kyriakou, I., Sakata, D., Min, C. H., Lee, S. B., Guatelli, S., and Incerti, S.
- Subjects
- *
ELASTIC scattering , *POSITRON scattering , *IONIZATION (Atomic physics) , *MICRODOSIMETRY , *THERMAL conductivity - Abstract
This paper presents the calculation of new elastic scattering cross sections for the simulation of electron interactions in liquid water. The calculations are based on the "ELastic Scattering of Electrons and Positrons by neutral Atoms" code, which adopts a Dirac partial wave analysis. A Muffin-tin potential was used in order to account for the liquid-phase of water, and the optical parameters of the correlation-polarization and the inelastic absorption potentials were optimized against vapour-phase water data. The differential and total elastic scattering cross sections calculated in the present work show a global agreement with the experimental data. The impact of these elastic scattering cross sections on the transport of electrons in liquid water was evaluated by track-structure simulations of range, dose-point-kernel, microdosimetric spectra, and ionization clustering using the Geant4-DNA simulation toolkit. The results are compared against those obtained with the elastic scattering models already available in Geant4-DNA and are discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
24. Structure factors for tunneling ionization rates of molecules: General grid-based methodology and convergence studies.
- Author
-
Dnestryan, Andrey I., Tolstikhin, Oleg I., Madsen, Lars Bojer, and Jensen, Frank
- Subjects
- *
IONIZATION (Atomic physics) , *MOLECULAR structure , *ELECTRONIC structure , *HARTREE-Fock approximation , *QUANTUM chemistry , *INTEGRAL equations , *PHOTOELECTRONS - Abstract
We present a general methodology for evaluating structure factors defining the orientation dependence of tunneling ionization rates of molecules, which is a key process in strong-field physics. The method is implemented at the Hartree-Fock level of electronic structure theory and is based on an integral-equation approach to the weak-field asymptotic theory of tunneling ionization, which expresses the structure factor in terms of an integral involving the ionizing orbital and a known analytical function. The evaluation of the required integrals is done by three-dimensional quadrature which allows calculations using conventional quantum chemistry software packages. This extends the applications of the weak-field asymptotic theory to polyatomic molecules of almost arbitrary size. The method is tested by comparison with previous results and illustrated by calculating structure factors for the two degenerate highest occupied molecular orbitals (HOMOs) of benzene and for the HOMO and HOMO-1 of naphthalene. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
25. Pulse shape analysis of individual gamma events—Correlation to energy resolution and the possibility of its improvement.
- Author
-
Gridin, S., Onken, D. R., Williams, R. T., Swiderski, L., Mianowska, Z., Syntfeld-Kazuch, A., Moszynski, M., Gayshan, V., Vasiukov, S., and Gektin, A.
- Subjects
- *
OSCILLOSCOPES , *SCINTILLATORS , *IONIZATION (Atomic physics) , *ELECTRONIC instruments , *SCINTILLATION counters - Abstract
The measurement in 2014 of the nonproportionality of each decay component in CsI:Tl found opposite slopes of the fast and tail nonproportionality curves above about 10 keV. Somewhat earlier experiments on nonproportionality and resolution versus shaping time in NaI:Tl and CsI:Tl showed that proportionality and intrinsic resolution could be improved by including the slower "tail" component of the scintillation pulse. The observed opposing nonproportionality trends of fast and tail components constitute a basis for improvement of scintillator nonproportionality if they are added in a suitable linear combination. We examine whether combining the rise and decay components pulse by pulse with an algorithm of optimized proportions may also improve energy resolution. The premise is that a scintillation pulse carries more information about the particle stopping event than is conveyed in a simple measurement of the pulse height. In this work, we measured pulse shapes of individual gamma events in CsI:Tl and other scintillators using an eMorpho multichannel analyzer as a digital oscilloscope. Decomposition of every scintillation pulse into a rise and three exponential decay components allowed us to represent the pulse height spectrum as a linear combination of them. We found that energy resolution of CsI:Tl can be altered and improved through changing the weight of decay components in the linear combination. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
26. Photoionization of the iodine 3d, 4s, and 4p orbitals in methyl iodide.
- Author
-
Forbes, Ruaridh, De Fanis, Alberto, Bomme, Cédric, Rolles, Daniel, Pratt, Stephen T., Powis, Ivan, Besley, Nicholas A., Simon, Marc, Nandi, Saikat, Milosavljević, Aleksandar R., Nicolas, Christophe, Bozek, John D., Underwood, Jonathan G., and Holland, David M. P.
- Subjects
- *
IONIZATION (Atomic physics) , *METHYL iodide , *ORGANOIODINE compounds , *PHOTOELECTRON spectra , *MOLECULAR spectra - Abstract
Ionization of the I 3d, 4s, and 4p orbitals in methyl iodide (CH3I) has been studied by using synchrotron radiation to measure the total ion yield and by recording photoelectron spectra with linearly polarized radiation in two polarization orientations. The complete photoelectron spectrum of CH3I has been recorded at several photon energies, and bands due to the C 1s, I 3d, 4s, 4p, and 4d atomic-like orbitals, as well as the molecular orbitals, have been observed and assigned. In the vicinity of the I 3d5/2 and 3d3/2 ionization thresholds at 626.8 and 638.3 eV, respectively, the ion yield displays weak structure in the pre-edge region due to transitions into valence or Rydberg states, and, at higher energies, a shoulder and a broad maximum attributed to the I 3d5/2 → εf and the I 3d3/2 → εf shape resonances, respectively. The absorption spectrum calculated using time-dependent density functional theory, within the Tamm-Dancoff approximation, has allowed assignments to be proposed for the valence and Rydberg states. The Stieltjes imaging technique has been used to simulate the absorption spectrum above the ionization threshold and indicates that transitions into the f(l = 3) continuum channel dominate. This conclusion has been corroborated by a Continuum Multiple Scattering–Xα (CMS–Xα) calculation. The asymmetric broadening of the photoelectron bands associated with the I 3d orbital, due to post collision interaction, is taken into account in our experimental analysis. Experimentally derived photoelectron anisotropy parameters for the I 3d orbital are in good agreement with the theoretical predictions obtained with the CMS–Xα approach. The I 3d shake-up/shake-off photoelectron spectrum has been recorded, and assignments have been proposed for several of the satellites. The M4N45N45 and M5N45N45 Auger electron yields have been measured, and that for the M5N45N45 decay exhibits a maximum due to interchannel coupling between the 3d5/2 and 3d3/2 continua. The photoelectron band associated with the I 4p orbital has an unusual appearance. Based upon previous theoretical work for the analogous Xe 4p orbital, it appears that the initial I 4p−1 hole state decays rapidly through Coster-Kronig and super-Coster-Kronig transitions. This leads to a redistribution of the spectral intensity associated with the I 4p orbital and results in a photoelectron spectrum containing a single structured band together with an extended continuum. Another continuum is observed on the high binding energy side of the peak due to the 4s orbital, and we assign this to super-Coster-Kronig transitions into the 4p-14d−1 continuum. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
27. Auger electron angular distributions following excitation or ionization of the I 3d level in methyl iodide.
- Author
-
Forbes, Ruaridh, De Fanis, Alberto, Bomme, Cédric, Rolles, Daniel, Pratt, Stephen T., Powis, Ivan, Besley, Nicholas A., Nandi, Saikat, Milosavljevíc, Aleksandar R., Nicolas, Christophe, Bozek, John D., Underwood, Jonathan G., and Holland, David M. P.
- Subjects
- *
METHYL iodide , *AUGER electron spectroscopy , *EXCITATION spectrum , *IONIZATION (Atomic physics) , *MULTIPLE scattering (Physics) - Abstract
Auger electron spectra following excitation or ionization of the I 3d level in CH3I have been recorded with horizontally or vertically plane polarized synchrotron radiation. These spectra have enabled the Auger electron angular distributions, as characterized by the β parameter, to be determined. The I 3d photoionization partial cross section of CH3I has been calculated with the continuum multiple scattering approach, and the results show that in the photon energy range over which Auger spectra were measured, the I 3d cross section exhibits an atomic-like behavior and is dominated by transitions into the εf continuum channel. In this limit, the theoretical value of the alignment parameter (A20) characterizing the core ionized state in an atom becomes constant, independent of photon energy. This theoretical value has been used to obtain the Auger electron intrinsic anisotropy parameters (α2) from the β parameters extracted from our normal (non-resonant) molecular Auger spectra. The resulting anisotropy parameters for the M45N45N45 transitions in CH3I have been compared to those calculated for the corresponding transitions in xenon, and the experimental and theoretical results are in good agreement. Anisotropy parameters have also been measured for the M45N1N45, M45N23N45, and M45N45O23 transitions. For the M45N1N45 and M45N23N45 Auger decays in CH3I, the experimentally derived angular distributions do not exhibit the strong dependence on the final ionic state that is predicted for these transitions in xenon. Resonantly excited Auger spectra have been recorded at 620.4 and 632.0 eV, coinciding with the I 3d5/2 → σ* and 3d3/2 → σ* transitions, respectively. The resulting Auger electron angular distributions for the M4N45N45 and M5N45N45 decays were found to exhibit a higher anisotropy than those for the normal process. This is due to the larger photo-induced alignment in the neutral core excited state. For a particular Auger transition, the Auger electron kinetic energy measured in the resonantly excited spectrum is higher than that in the normal spectrum. This shift, due to the screening provided by the electron excited into the σ* orbital, has been rationalized by calculating orbital ionization energies of I 3d excited and I 3d ionized states in CH3I. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
28. Impact ionization in β-Ga2O3.
- Author
-
Ghosh, Krishnendu and Singisetti, Uttam
- Subjects
- *
IMPACT ionization , *IONIZATION (Atomic physics) , *ATOMIC physics , *MOLECULAR physics , *BAND gaps - Abstract
A theoretical investigation of extremely high field transport in an emerging wide-bandgap material β-Ga2O3 is reported from first principles. The signature high-field effect explored here is impact ionization. The interaction between a valence-band electron and an excited electron is computed from the matrix elements of a screened Coulomb operator. Maximally localized Wannier functions are utilized in computing the impact ionization rates. A full-band Monte Carlo simulation is carried out incorporating the impact ionization rates and electron-phonon scattering rates. This work brings out valuable insights into the impact ionization coefficient (IIC) of electrons in β-Ga2O3. The isolation of the Γ point conduction band minimum by a significantly high energy from other satellite band pockets plays a vital role in determining ionization co-efficients. IICs are calculated for electric fields ranging up to 8 MV/cm for different crystal directions. A Chynoweth fitting of the computed IICs is done to calibrate ionization models in device simulators. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
29. Impact ionization in β-Ga2O3.
- Author
-
Ghosh, Krishnendu and Singisetti, Uttam
- Subjects
IMPACT ionization ,IONIZATION (Atomic physics) ,ATOMIC physics ,MOLECULAR physics ,BAND gaps - Abstract
A theoretical investigation of extremely high field transport in an emerging wide-bandgap material β-Ga
2 O3 is reported from first principles. The signature high-field effect explored here is impact ionization. The interaction between a valence-band electron and an excited electron is computed from the matrix elements of a screened Coulomb operator. Maximally localized Wannier functions are utilized in computing the impact ionization rates. A full-band Monte Carlo simulation is carried out incorporating the impact ionization rates and electron-phonon scattering rates. This work brings out valuable insights into the impact ionization coefficient (IIC) of electrons in β-Ga2 O3 . The isolation of the Γ point conduction band minimum by a significantly high energy from other satellite band pockets plays a vital role in determining ionization co-efficients. IICs are calculated for electric fields ranging up to 8 MV/cm for different crystal directions. A Chynoweth fitting of the computed IICs is done to calibrate ionization models in device simulators. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
30. Numerical analysis of plasma structure observed in atmospheric millimeter-wave discharge at under-critical intensity.
- Author
-
Nakamura, Yusuke, Komurasaki, Kimiya, Fukunari, Masafumi, and Koizumi, Hiroyuki
- Subjects
- *
PLASMA gases , *MILLIMETER wave oscillators , *NUMERICAL analysis , *IONIZATION (Atomic physics) , *ELECTRON density , *MAXWELL equations , *BOLTZMANN'S equation , *SPHEROMAKS - Abstract
Atmospheric millimeter-wave discharge at intensity on the order of 1 GW/m2, which is lower than the critical intensity for breakdown by one order, was computed numerically using a tuning parameter to reproduce a wavelength-scale discrete plasmoid structure in a propagating ionization front observed in experiments. In this structure, the plasmoids line up along the
E field of the incident beam in the same pitch of 0.9λ. Computational results showed that the structure appears when the electron number density in the plasmoid is greater than the cutoff density of 2.5 × 1020/m3. Interference among an incident wave and reflection waves from a plasmoids produces fringes around the plasmoid. Neighboring plasmoids come to the enhanced point, which is placed at a distance of 0.9λ from the plasmoid center. This knowledge related to the structure is expected to be correct irrespective of the plasma modeling because the revealed forming mechanism is dependent only on the geometrical interference between the incident and reflection. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
31. Electron and positron scattering cross sections for propene.
- Author
-
Singh, Suvam, Gupta, Dhanoj, and Antony, Bobby
- Subjects
- *
ELECTRON scattering , *POSITRON scattering , *NUCLEAR cross sections , *PROPENE , *SCATTERING potentials , *NUCLEAR optical potentials , *IONIZATION (Atomic physics) - Abstract
The molecular R-matrix calculation is performed for the low energy electron scattering from propene to obtain total and rotational excitation cross sections. The rotational excitation cross sections are calculated for the transitions involving levels from j = 0 to j = 5. These cross sections are used for calculating their corresponding rate coefficients for the temperature range 30–5000 K. The rate coefficients at such temperatures have relevance in the interstellar medium as well as in the plasma environment. The spherical complex optical potential and complex scattering potential- ionization contribution methods are used for high energy calculation of the total cross section (Qtot) and ionization cross section (Qion), respectively, for both electron and positron scattering. The present Qtot results give reasonable agreement with previous experimental data. We have detected a π * shape resonance for electron scattering at 3.71 eV due to 2A″ scattering state, which is in accordance with the experimental results. However, no such resonance is observed in the positron scattering calculations. The cross sections reported here show good comparison with existing data, validating present calculations and its reliability. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
32. Phonon-assisted anti-Stokes excitation: Mechanism for the unusual temperature dependence of the Ce3+ luminescence in yttrium aluminum garnet.
- Author
-
Yan, Lin, Li, Bo, Song, Yunfei, Zhang, Wei, Wang, Zanhao, Lv, Zhe, Zheng, Xianxu, Wu, Qiang, and Yang, Yanqiang
- Subjects
- *
PHONONS , *LUMINESCENCE , *YTTRIUM aluminum garnet , *CERIUM , *VIBRONIC coupling , *IONIZATION (Atomic physics) , *CONDUCTION bands - Abstract
Luminescence emission spectra and decay kinetics of Ce3+ in YAG were investigated as a function of temperature (300–800 K) under excitation in the long wavelength tail of the lowest 4f–5d absorption spectrum. Both the anti-Stokes and Stokes emission intensity were found to exhibit an unusual non-monotonic temperature dependence compared to those commonly excited in the absorption band, where luminescence intensity decreases monotonically with increasing temperature. This phenomenon is well explained by a phonon-assisted anti-Stokes excitation model with strong vibronic interaction. It reveals that the intensity enhancement of Ce3+ anti-Stokes and Stokes emission is caused by the anti-Stokes excitation efficiency. Excitation efficiency is enhanced with increasing temperature, and thermal ionization of the 5d electron into the conduction band remains as the quenching mechanism of Ce3+ anti-Stokes and Stokes luminescence at high temperatures. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
33. Physics-informed machine learning for inorganic scintillator discovery.
- Author
-
Pilania, G., McClellan, K. J., Stanek, C. R., and Uberuaga, B. P.
- Subjects
- *
PHYSICS , *MACHINE learning , *SCINTILLATORS , *IONIZATION (Atomic physics) , *RARE earth metals - Abstract
Applications of inorganic scintillators—activated with lanthanide dopants, such as Ce and Eu—are found in diverse fields. As a strict requirement to exhibit scintillation, the 4
f ground state (with the electronic configuration of [Xe]4f n 5d 0) and 5d 1 lowest excited state (with the electronic configuration of [Xe]4f n −1 5d 1) levels induced by the activator must lie within the host bandgap. Here we introduce a new machine learning (ML) based search strategy for high-throughput chemical space explorations to discover and design novel inorganic scintillators. Building upon well-known physics-based chemical trends for the host dependent electron binding energies within the 4f and 5d 1 energy levels of lanthanide ions and available experimental data, the developed ML model—coupled with knowledge of the vacuum referred valence and conduction band edges computed from first principles—can rapidly and reliably estimate the relative positions of the activator’s energy levels relative to the valence and conduction band edges of any given host chemistry. Using perovskite oxides and elpasolite halides as examples, the presented approach has been demonstrated to be able to (i) capture systematic chemical trends across host chemistries and (ii) effectively screen promising compounds in a high-throughput manner. While a number of other application-specific performance requirements need to be considered for a viable scintillator, the scheme developed here can be a practically useful tool to systematically down-select the most promising candidate materials in a first line of screening for a subsequent in-depth investigation. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
34. A redshift mechanism of high-order harmonics: Change of ionization energy.
- Author
-
Yue, Shengjun, Fu, Silin, Li, Jinbin, Zhang, Xiao, Feng, Yongkang, Hu, Bitao, and Du, Hongchuan
- Subjects
- *
HARMONIC generation , *REDSHIFT , *IONIZATION (Atomic physics) , *HYDROGEN isotopes , *BORN-Oppenheimer approximation , *SPECTRUM analysis - Abstract
We theoretically study the high-order harmonic generation of H 2 + and its isotopes beyond the Born-Oppenheimer dynamics. It is surprising that the spectral redshift can still be observed in high harmonic spectra of H 2 + driven by a sinusoidal laser pulse in which the trailing (leading) edge of the laser pulse is nonexistent. The results confirm that this spectral redshift originates from the reduction in ionization energy between recombination time and ionization time, which is obviously different from the nonadiabatic spectral redshift induced by the falling edge of the laser pulse. Additionally, the improved instantaneous frequency of harmonics by considering the changeable ionization energy can deeply verify our results. Therefore, this new mechanism must be taken into account when one uses the nonadiabatic spectral redshift to retrieve the nuclear motion. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
35. Synergistic effects on microstructural evolution and hardening of the Hastelloy N alloy under subsequent He and Xe ion irradiation.
- Author
-
Gao, Jie, Huang, Hefei, Liu, Jizhao, Liu, Renduo, Lei, Qiantao, and Li, Yan
- Subjects
- *
MICROSTRUCTURE , *CHROMIUM-cobalt-nickel-molybdenum alloys , *IONIZATION (Atomic physics) , *CHROMIUM alloys , *MOLYBDENUM alloys , *TRANSMISSION electron microscopes , *NANOINDENTATION , *XENON , *HELIUM - Abstract
Synergistic effects in the evolution of He bubbles and dislocation loops in Hastelloy N alloy were investigated using transmission electron microscopy and nanoindentation. Results show that the sizes of both He bubbles and dislocation loops induced by the He and Xe irradiation were larger than those in the individual irradiation cases. The corresponding hardening degree of irradiated sample was also measured to be higher than the combined hardening value of two individual irradiation cases. The underlying physics controlling the synergistic effects have revealed that the vacancies are preferentially captured by pre-existed He bubbles as compared to their annihilation with the interstitial atoms during the subsequent Xe irradiation. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
36. Effect of the ionization wave velocity on the current and voltage of a gas-filled diode.
- Author
-
Belomyttsev, S. Ya., Grishkov, A. A., Shklyaev, V. A., and Ryzhov, V. V.
- Subjects
- *
DIODES , *ION acoustic waves , *INHOMOGENEOUS materials , *ELECTROMAGNETIC fields , *LORENTZ transformations , *CHARGE conservation , *IONIZATION (Atomic physics) - Abstract
Here, continuing our research in the breakdown of a gas diode with a highly inhomogeneous electric field, we present an analytical model which relates the diode current and voltage to the ionization wave velocity from cathode to anode in an axisymmetric statement. The model shows that the voltages cross- and lengthwise the diode can differ greatly and that the difference increases as the wave moves faster. This effect should be taken into account when analyzing subnanosecond pulsed breakdowns in a highly inhomogeneous electric field, otherwise a large discrepancy is possible between measured and actual diode voltages. The analytical model is based on charge conservation laws and Lorentz transforms for electric field strengths and coordinates, and it has been verified using the KARAT particle-in-cell (PIC) and X-Object Oriented Particle-in-cell PIC/Monte Carlo codes. The simulation results agree well with the analytical model developed. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
37. Coupled-cluster treatment of molecular strong-field ionization.
- Author
-
Jagau, Thomas-C.
- Subjects
- *
IONIZATION (Atomic physics) , *CARBON dioxide , *STARK effect , *STATIC electricity , *GAUSSIAN function - Abstract
Ionization rates and Stark shifts of H2, CO, O2, H2O, and CH4 in static electric fields have been computed with coupled-cluster methods in a basis set of atom-centered Gaussian functions with a complex-scaled exponent. Consideration of electron correlation is found to be of great importance even for a qualitatively correct description of the dependence of ionization rates and Stark shifts on the strength and orientation of the external field. The analysis of the second moments of the molecular charge distribution suggests a simple criterion for distinguishing tunnel and barrier suppression ionization in polyatomic molecules. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
38. <italic>NH2−</italic> in a cold ion trap with He buffer gas: <italic>Ab initio</italic> quantum modeling of the interaction potential and of state-changing multichannel dynamics.
- Author
-
Hernández Vera, Mario, Yurtsever, Ersin, Wester, Roland, and Gianturco, Franco A.
- Subjects
- *
SPATIAL analysis (Statistics) , *PHOTODETACHMENT , *IONIZATION (Atomic physics) , *SPATIAL systems , *CLUSTER analysis (Statistics) - Abstract
We present an extensive range of accurate
ab initio calculations, which map in detail the spatial electronic potential energy surface that describes the interaction between the molecular anion N H 2 − (1A1) in its ground electronic state and the He atom. The time-independent close-coupling method is employed to generate the corresponding rotationally inelastic cross sections, and then the state-changing rates over a range of temperatures from 10 to 30 K, which is expected to realistically represent the experimental trapping conditions for this ion in a radio frequency ion trap filled with helium buffer gas. The overall evolutionary kinetics of the rotational level population involving the molecular anion in the cold trap is also modelled during a photodetachment experiment and analyzed using the computed rates. The present results clearly indicate the possibility of selectively detecting differences in behavior between theortho - andpara -anions undergoing photodetachment in the trap. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
39. Vacuum ultraviolet photoionization cross section of the hydroxyl radical.
- Author
-
Dodson, Leah G., Savee, John D., Gozem, Samer, Shen, Linhan, Krylov, Anna I., Taatjes, Craig A., Osborn, David L., and Okumura, Mitchio
- Subjects
- *
PHOTOIONIZATION , *HYDROXYL group , *RADICALS (Chemistry) , *IONIZATION (Atomic physics) , *PHOTOCHEMISTRY - Abstract
The absolute photoionization spectrum of the hydroxyl (OH) radical from 12.513 to 14.213 eV was measured by multiplexed photoionization mass spectrometry with time-resolved radical kinetics. Tunable vacuum ultraviolet (VUV) synchrotron radiation was generated at the Advanced Light Source. OH radicals were generated from the reaction of O(1
D ) + H2O in a flow reactor in He at 8 Torr. The initial O(1D ) concentration, where the atom was formed by pulsed laser photolysis of ozone, was determined from the measured depletion of a known concentration of ozone. Concentrations of OH and O(3P ) were obtained by fitting observed time traces with a kinetics model constructed with literature rate coefficients. The absolute cross section of OH was determined to be σ(13.436 eV) = 3.2 ± 1.0 Mb and σ(14.193 eV) = 4.7 ± 1.6 Mb relative to the known cross section for O(3P ) at 14.193 eV. The absolute photoionization spectrum was obtained by recording a spectrum at a resolution of 8 meV (50 meV steps) and scaling to the single-energy cross sections. We computed the absolute VUV photoionization spectrum of OH and O(3P ) using equation-of-motion coupled-cluster Dyson orbitals and a Coulomb photoelectron wave function and found good agreement with the observed absolute photoionization spectra. [ABSTRACT FROM AUTHOR]- Published
- 2018
- Full Text
- View/download PDF
40. Doubly charged coronene clusters--Much smaller than previously observed.
- Author
-
Mahmoodi-Darian, Masoomeh, Raggl, Stefan, Renzler, Michael, Goulart, Marcelo, Huber, Stefan E., Mauracher, Andreas, Scheier, Paul, and Echt, Olof
- Subjects
- *
COMPLEX ions , *MASS spectrometry , *ELECTRON impact ionization , *IONIZATION (Atomic physics) , *HELIUM , *DENSITY functional theory , *ATOMIC clusters - Abstract
The smallest doubly charged coronene cluster ions reported so far, Cor152+, were produced by charge exchange between bare coronene clusters and He2+ [H. A. B. Johansson et al., Phys. Rev.A84, 043201 (2011)]. These dications are at least five times larger than the estimated Rayleigh limit, i.e., the size at which the activation barrier for charge separation vanishes. Such a large discrepancy is unheard of for doubly charged atomic or molecular clusters. Here we report the mass spectrometric observation of doubly charged coronene trimers, produced by electron ionization of helium nanodroplets doped with coronene. The observation implies that Cor32+ features a non-zero fission barrier too large to overcome under the present experimental conditions. The height of the barriers for the dimer and trimer has been estimated by means of density functional theory calculations. A sizeable barrier for the trimer has been revealed in agreement with the experimental findings. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
41. Potential of Microwave Heating and Plasma for Biosecurity Applications.
- Author
-
Taheri, Saeedeh, McFarlane, Dylan John, Mattner, Scott William, and Brodie, Graham Ian
- Subjects
MICROWAVE heating ,PLASMA gases ,BIOSECURITY ,IONIZATION (Atomic physics) ,PLASMA flow - Abstract
This review explores the use of microwave heating and microwave-generated plasma for biosecurity applications. Microwave heating has been shown to rapidly heat and kill a wide range of pests and pathogens. Examples of microwave thermal disinfestation of soils, grains, hay, and timber are presented and discussed. Microwave energy can also ionize various gasses, including air, to create plasma. Plasmas are described by many characteristics, such as temperature, degree of ionization, and density. In the "after glow" (cold plasma) of a plasma discharge, there are sufficient charged particles and excited atoms to generate elevated UV levels and ionize the surfaces of objects. Examples of cold plasma and plasma-activated water disinfestation of grains and other commodities are also presented and discussed. Brief comments on the scale-up of this technology have also been presented. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
42. Time delay in XUV/IR photoionization of H2O.
- Author
-
Serov, Vladislav V. and Kheifets, Anatoli S.
- Subjects
- *
PHOTOIONIZATION , *IONIZATION (Atomic physics) , *SCHRODINGER equation , *DENSITY functionals , *HYDROGEN , *FIELD ionization - Abstract
We solve the time-dependent Schrödinger equation describing a water molecule driven by a superposition of the extreme ultraviolet and IR pulses typical for a reconstruction of attosecond beating by interference of two-photon transitions experiment. This solution is obtained by a combination of the time-dependent coordinate scaling and the density functional theory with self-interaction correction. Results of this solution are used to determine the time delay in photoionization of the water and hydrogen molecules. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
43. Delayed avalanche breakdown of high-voltage silicon diodes: Various structures exhibit different picosecond-range switching behavior.
- Author
-
Brylevskiy, Viktor, Smirnova, Irina, Gutkin, Andrej, Brunkov, Pavel, Rodin, Pavel, and Grekhov, Igor
- Subjects
- *
SILICON diodes , *DIODES , *IONIZATION (Atomic physics) , *ELECTRIC potential , *SILICON - Abstract
We present a comparative study of silicon high-voltage diodes exhibiting þe effect of delayed superfast impact-ionization breakdown. þe effect manifests itself in a sustainable picosecondrange transient from þe blocking to þe conducting state and occurs when a steep voltage ramp is applied to þe p+-n-þ+ diode in þe reverse direction. Nine groups of diodes wiþ graded and abrupt pn-junctions have been specially fabricated for þis study by different techniques from different Si substrates. Additionally, in two groups of þese structures, þe lifetime of nonequilibrium carriers was intentionally reduced by electron irradiation. All diodes have identical geometrical parameters and similar stationary breakdown voltages. Our experimental setup allows measuring boþ device voltage and current during þe kilovolt switching wiþ time resolution better þan 50 ps. Alþough all devices are capable of forming a front wiþ kilovolt amplitude and 100 ps risetime in þe inseries load, þe structures wiþ graded pn-junctions have anomalously large residual voltage. þe Deep Level Transient Spectroscopy study of all diode structures has been performed in order to evaluate þe effect of deep centers on device performance. It was found þat þe presence of deeplevel electron traps negatively correlates wiþ parameters of superfast switching, whereas a large concentration of recombination centers created by electron irradiation has virtually no influence on switching characteristics. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
44. Lithium atoms on helium nanodroplets: Rydberg series and ionization dynamics.
- Author
-
Lackner, Florian, Krois, Günter, and Ernst, Wolfgang E.
- Subjects
- *
ELECTRONIC excitation , *ENERGY levels (Quantum mechanics) , *LITHIUM , *IONIZATION (Atomic physics) , *POLARIZATION (Electricity) - Abstract
The electronic excitation spectrum of lithium atoms residing on the surface of helium nanodroplets is presented and analyzed employing a Rydberg-Ritz approach. Utilizing resonant two-photon ionization spectroscopy, two different Rydberg series have been identified: one assigned to the nS(Σ) series and the other with predominantly nP(II) character. For high Rydberg states, which have been resolved up to n = 13, the surrounding helium effectively screens the valence electron from the Li ion core, as indicated by the apparent red-shift of Li transitions and lowered quantum defects on the droplet with respect to their free atom counterparts. For low n states, the screening effect is weakened and the prevailing repulsive interaction gives rise to strongly broadened and blue-shifted transitions. The redshifts originate from the polarization of nearby He atoms by the positive Li ion core. As a consequence of this effect, the ionization threshold is lowered by 116 ± 10 cm-1 for Li on helium droplets with a radius of about 40 Å. Upon single-photon ionization, heavy complexes corresponding to Li ions attached to intact helium droplets are detected. We conclude that ionization close to the on-droplet ionization threshold triggers a dynamic process in which the Li ion core undergoes a transition from a surface site into the droplet. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
45. Calculation of thermodynamic properties and transport coefficients of C5F10O-CO2 thermal plasmas.
- Author
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Xingwen Li, Xiaoxue Guo, Murphy, Anthony B., Hu Zhao, Jian Wu, and Ze Guo
- Subjects
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GAS mixtures , *THERMODYNAMICS , *IONIZATION (Atomic physics) , *THERMOPHYSICAL properties , *TEMPERATURE - Abstract
The thermodynamic properties and transport coefficients of C5F10O-CO2 gas mixtures, which are being considered as substitutes for SF6 in circuit breaker applications, are calculated for the temperature range from 300K to 30 000K and the pressure range from 0.05 MPa to 1.6 MPa. Special attention is paid on investigating the evolution of thermophysical properties of C5F10O-CO2 mixtures with different mixing ratios and with different pressures; both the mixing ratio and pressure significantly affect the properties. This is explained mainly in terms of the changes in the temperatures at which the dissociation and ionization reactions take place. Comparisons of different thermophysical properties of C5F10O-CO2 mixtures with those of SF6 are also carried out. It is found that most of the thermophysical properties of the C5F10O-CO2 mixtures, such as thermal conductivity, viscosity, and electrical conductivity, become closer to those of SF6 as the C5F10O concentration increases. The composition and thermophysical properties of pure C5F10O in the temperature range from 300K to 2000K based on the decomposition pathway are also given. The calculation results provide a basis for further study of the insulation and arc-quenching capability of C5F10O-CO2 gas mixtures as substitutes for SF6. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
46. Characterizing and optimizing a laser-desorption molecular beam source.
- Author
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Teschmit, Nicole, Długołeecki, Karol, Gusa, Daniel, Rubinsky, Igor, Horke, Daniel A., and Küpper, Jochen
- Subjects
- *
DESORPTION , *MOLECULAR beams , *IONIZATION (Atomic physics) , *LASER pulses , *FREE electron lasers - Abstract
The design and characterization of a new laser-desorption molecular beam source, tailored for use in x-ray free-electron laser and ultrashort-pulse laser imaging experiments, is presented. It consists of a single mechanical unit containing all source components, including the molecular-beam valve, the sample, and the fiber-coupled desorption laser, which is movable in five axes, as required for experiments at central facilities. Utilizing strong-field ionization, we characterize the produced molecular beam and evaluate the influence of desorption laser pulse energy, relative timing of valve opening and desorption laser, sample bar height, and which part of the molecular packet is probed on the sample properties. Strong-field ionization acts as a universal probe and allows detecting all species present in the molecular beam, and hence enables us to analyze the purity of the produced molecular beam, including molecular fragments. We present optimized experimental parameters for the production of the purest molecular beam, containing the highest yield of intact parent ions, which we find to be very sensitive to the placement of the desorbed-molecule plumes within the supersonic expansion. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
47. Geometric dependence of strong field enhanced ionization in D2O.
- Author
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McCracken, Gregory A., Kaldun, Andreas, Liekhus-Schmaltz, Chelsea, and Bucksbaum, Philip H.
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- *
GEOMETRIC approach , *IONIZATION (Atomic physics) , *LASER pulses , *LASER beams , *LASER ultrasonics , *MAGNETIZATION transfer - Abstract
We have studied strong-field enhanced dissociative ionization of D2O in 40 fs, 800 nm laser pulses with focused intensities of <1-3 × 1015W=cm² by resolving the charged fragment momenta with respect to the laser polarization. We that observe dication dissociation into OD+/D+ dominates when the polarization is out of the plane of the molecule, whereas trication dissociation into O+/D+/D+ is strongly dominant when the polarization is aligned along the D–D axis. Dication dissociation into O/D+/D+ and O+/D2+ is not seen nor is there any significant fragmentation into multiple ions when the laser is polarized along the C2v symmetry axis of the molecule. Even below the saturation intensity for OD+/D+, the O+/D+/D+ channel has higher yield. By analyzing how the laser field is oriented within the molecular frame for both channels, we show that enhanced ionization is driving the triply charged three body breakup but is not active for the doubly charged two body breakup. We conclude that laser-induced distortion of the molecular potential suppresses multiple ionization along the C2v axis but enhances ionization along the D–D direction. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
48. Radiation degradation prediction for InGaP solar cells by using appropriate estimation method for displacement threshold energy.
- Author
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Okuno, Y., Okuda, S., Akiyoshi, M., Oka, T., Harumoto, M., Omura, K., Kawakita, S., Imaizumi, M., Messenger, S. R., Lee, K. H., and Yamaguchi, M.
- Subjects
- *
SOLAR cells , *IRRADIATION , *ELECTRONS , *ENERGY dissipation , *IONIZATION (Atomic physics) , *ATOMIC physics - Abstract
InGaP solar cells are not predicted to be susceptible to displacement damage by irradiation with electrons at energies lower than 100 keV from non-ionizing energy loss (NIEL) calculations. However, it is recently observed that InGaP solar cells are shown to degrade by irradiation with 60 keV electrons. This degradation is considered to be caused by radiation defects but is not clear. In this study, the kind of the defects generated by electrons at energies lower than 100 keV is found by deep-level transient spectroscopy (DLTS). The result of DLTS indicates that the prediction of primary knock-on atoms by using the radiation damage model is different from the experiment. In order to suggest the generation mechanism of radiation defects, we propose a new displacement threshold energy (Ed) by using a new technique in which NIEL and the introduction rate of radiation defects are combined. The degradation prediction by using estimated Ed is found to agree well with the degradation of electric power of InGaP solar cells irradiated by low-energy electrons. From the theory of radiation defects, we propose a new obtaining process of suitable degradation prediction by the displacement damage dose method. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
49. Dissociative recombination of HCl+.
- Author
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Larson, Åsa, dos Santos, Samantha Fonseca, and Orel, Ann E.
- Subjects
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HYDROGEN chloride , *ELECTRON scattering , *SCHRODINGER equation , *RESONANT states , *RYDBERG states , *IONIZATION (Atomic physics) - Abstract
The dissociative recombination of HCl+, including both the direct and indirect mechanisms, is studied. For the direct process, the relevant electronic states are calculated ab initio by combining electron scattering calculations to obtain resonance positions and autoionization widths with multi-reference configuration interaction calculations of the ion and Rydberg states. The cross section for the direct dissociation along electronic resonant states is computed by solution of the time-dependent Schrüdinger equation. For the indirect process, an upper bound value for the cross section is obtained using a vibrational frame transformation of the elements of the scattering matrix at energies just above the ionization threshold. Vibrational excitations of the ionic core from the ground vibrational state, v = 0, to the first three excited vibrational states, v = 1, v = 2, and v = 3, are considered. Autoionization is neglected and the effect of the spin-orbit splitting of the ionic potential energy upon the indirect dissociative recombination cross section is considered. The calculated cross sections are compared to measurements. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
50. Bond dissociation energies of TiSi, ZrSi, HfSi, VSi, NbSi, and TaSi.
- Author
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Sevy, Andrew, Sorensen, Jason J., Persinger, Thomas D., Franchina, Jordan A., Johnson, Eric L., and Morse, Michael D.
- Subjects
- *
CHEMICAL bonds , *BOND number (Chemistry) , *GROUND state (Quantum mechanics) , *PHOTONS , *IONIZATION (Atomic physics) - Abstract
Predissociation thresholds have been observed in the resonant two-photon ionization spectra of TiSi, ZrSi, HfSi, VSi, NbSi, and TaSi. It is argued that because of the high density of electronic states at the ground separated atom limit in these molecules, the predissociation threshold in each case corresponds to the thermochemical bond dissociation energy. The resulting bond dissociation energies are D0(TiSi) = 2.201(3) eV, D0(ZrSi) = 2.950(3) eV, D0(HfSi) = 2.871(3) eV, D0(VSi) = 2.234(3) eV, D0(NbSi) = 3.080(3) eV, andD0(TaSi) = 2.999(3) eV. The enthalpies of formation were also calculated as Δf,0KH°(TiSi(g)) = 705(19) kJ mol-1, Δf,0KH°(ZrSi(g)) = 770(12) kJ mol-1, Δf,0KH°(HfSi(g)) = 787(10) kJ mol-1, Δf,0KH°(VSi(g)) = 743(11) kJ mol-1, Δf,0KH°(NbSi(g)) = 879(11) kJ mol-1, and Δf,0KH°(TaSi(g)) = 938(8) kJ mol-1. Using thermochemical cycles, ionization energies of IE(TiSi) = 6.49(17)eVand IE(VSi) = 6.61(15)eVand bond dissociation energies of the ZrSi- and NbSi- anions, D0(Zr-Si-) ≤ 3.149(15) eV,D0(Zr--Si) ≤ 4.108(20) eV,D0(Nb-Si-) ≤ 3.525(31) eV, andD0(Nb--Si) ≤ 4.017(39) eV, have also been obtained. Calculations on the possible low-lying electronic states of each species are also reported. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
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