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Detection of nascent O($^3P_j$, $j=2,1,0$) atoms using one-photon resonant excitation to the $3s\,^3S^o_1$ state at $\sim 130$ nm followed by near-threshold ionization, i. e., 1 + 1' resonance enhanced multi-photon ionization (REMPI), has been investigated. The aim was to achieve low ion recoil, improved sensitivity, and reliable angular momentum polarization information, with an as simple as possible laser setup. An efficient 1 + 1' scheme has been found where the VUV light for the first step 1 is generated by difference frequency ($2\omega_1 - \omega_2$) VUV generation by four wave mixing in Kr gas, and the ionization step 1' uses 2$\omega_2$ at 289 nm. The presented scheme induces 9 m/s recoil of the O$^+$ ion using a two-dye laser system, and zero recoil should be possible by generating 302 nm radiation with a third dye laser. While this approach is much more sensitive than a previous 1 + 1' scheme using 212.6 nm for the 1' step, we found that the relatively intense 289 nm radiation does not saturate the 1' step. In order to test the ability of this scheme to accurately determine branching ratios, fine structure yields, and angular distributions including polarization information, it has been applied to O$_2$ photodissociation around 130 nm with subsequent O($^3P_j$) fragment detection.

Helium is commonly used as a carrier gas in gas chromatography-tandem mass spectrometry (GC-MS/MS); however, there are growing concerns regarding its global shortage and the resulting limited supply and high cost. Using nitrogen as an alternative carrier gas in GC-MS/MS with the widely used electron ionisation (EI) technique leads to a significantly lower sensitivity; thus, in this study, we explored the use of atmospheric-pressure chemical ionisation (APCI) as the ionisation method and examined the applicability of GC-(APCI)MS/MS with nitrogen gas for the determination of pesticide residues. GC-(APCI)MS/MS using nitrogen provided slightly wider peaks, and poorer isomeric separation compared to those using helium under identical conditions; however, the peak intensities were comparable. GC-(APCI)MS/MS using nitrogen was validated for 166 pesticides in green tea at a spiking level of 0.01 mg/kg and was compared with the conventional GC-(EI)MS/MS using helium gas. Except dimethomorph and resmethrin, GC-(APCI)MS/MS showed satisfactory results that were comparable to those of GC-(EI)MS/MS for most compounds, with trueness in the range of 73%–95% and relative standard deviations of

Detectors using liquid xenon as target are widely deployed in rare event searches. Conclusions on the interacting particle rely on a precise reconstruction of the deposited energy which requires calibrations of the energy scale of the detector by means of radioactive sources. However, a microscopic calibration, i.e. the translation from the number of excitation quanta into deposited energy, also necessitates good knowledge of the energy required to produce single scintillation photons or ionisation electrons in liquid xenon. The sum of these excitation quanta is directly proportional to the deposited energy in the target. The proportionality constant is the mean excitation energy and is commonly known as $W$-value. Here we present a measurement of the $W$-value with electronic recoil interactions in a small dual-phase xenon time projection chamber with a hybrid (photomultiplier tube and silicon photomultipliers) photosensor configuration. Our result is based on calibrations at $\mathcal{O}(1-10 \, \mathrm{keV})$ with internal $^{37}$Ar and $^{83\text{m}}$Kr sources and single electron events. We obtain a value of $W=11.5 \, ^{+0.2}_{-0.3} \, \mathrm{(syst.)} \, \mathrm{eV}$, with negligible statistical uncertainty, which is lower than previously measured at these energies. If further confirmed, our result will be relevant for modelling the absolute response of liquid xenon detectors to particle interactions., Comment: 12 pages, 4 figures, 2 tables. v2: external crosstalk considered, NEST comparison and references added, typos corrected

The article reports the excitation of a helical argon atmospheric pressure plasma jet using a pulse modulated 13.56 MHz radiofrequency (RF) power source. This helical structure is observed in open ambient air which is far different from the conventional conical shape. This helical structure originates due to the periodic pressure variation in the discharge region caused by pulse modulated RF (2 kHz modulation frequency (fp)) and propagates downstream into the ambient air. The geometrical characteristics of the observed structure are explored using optical imaging. Moreover, the influence of various input parameters viz., duty cycle (D), gas flow rate (Q), and RF power (P) of the modulated pulse on the formation of helical structure are studied. These helical structures have an implication on the plasma jet chemical features (enhancement of reactive oxygen and nitrogen species (RONS)) as these are involved in increase in air entrainment into the ionization region desired for various plasma applications., 17 pages, 12 figures

The ionization equilibrium in a heterogeneous strongly nonideal smoky plasmas containing condensed particles and an easily ionized addition of cesium atoms in the gas phase is considered. To determine the charges of particles, the nonlinear Poisson-Boltzmann equation was used, and for the ionization of atoms of the gas phase, the Saha equation taking into account the effect of the displacement of the ionization equilibrium. The dependences of the concentration of electrons and particle charges, as well as the interface between the regions of positive and negative charges of particles, on the concentration of cesium atoms and the concentration of aluminum oxide particles are obtained.

The possibility of analyzing the amount of chlorine on the surface of stainless steel is investigated and a method for obtaining reproducible results by evening or eliminating the physicochemical features of surface ionization of a calibrant crystallized from a solution is described. It is shown that the main factor influencing the quality of calibration and analysis is the shape of the resulting drop and its size. It was also found that integrating the analytical signal over the entire drop is the most appropriate method for calibration and obtaining the most reproducible results. The main factors influencing the physicochemical characteristics of ionization and, as a consequence, the reproducibility of the calibration data are presented. It has been established that the method of calibration with the integration of a signal by a drop can be effectively used in the analysis of ultra-small amounts of chlorine on the surface of stainless steel in the range from 0.12 to 120 pmol/mm2. In this case, the proposed approach eliminates the physicochemical factors affecting the ionization efficiency, which limit the use of surface laser desorption/ionization for quantitative analysis.

In this paper we present our calculation of the ionization cross section by electron impact of C V, N VI, and O VII. Using the Flexible Atomic Code (FAC), we obtain the cross sections for the ionization of these ions from the ground state 11S, and from the unstable states 21S and 23S. Our results are in good agreement with those based on the Coulomb–Born (CB) approximation and the available measurements.

Experiments involving the irradiation of water contained within magnesium hydroxide and alumina nanoparticle sludges were conducted and culminated in observations of an increased yield of molecular hydrogen when compared to the yield from the irradiation of bulk water. We show that there is a relationship linking this increased yield to the direct nanoscale ionization mechanism in the nanoparticles, indicating that electron emission from the nanoparticles drives new radiative pathways in the water. Because the chemical changes in these sludges are introduced by irradiation only, we have a genuinely unstirred system. This feature allows us to determine the diffusivity of the dissolved gas. Using the measured gas production rate, we have developed a method for modelling when hydrogen bubble formation will occur within the nanoparticle sludges. This model facilitates the determination of a consistent radiolytic consumption rate coinciding with the observations of bubble formation. Thus, we demonstrate a nanoscale radiation effect directly influencing the formation of molecular hydrogen.

Polycyclic Aromatic Hydrocarbons (PAHs) are carbon-based molecules resulting from the union of aromatic rings and related species, which are likely responsible for strong infrared emission features (3.3, 6.2, 7.7, 8.6, 11.3 and 12.7 microns). In this work, using a sample of 50 Seyfert galaxies (DL300-400) as well as neutral species. By subtracting the spectrum of the central source from the total, we compare the PAH emission in the central vs extended region of a small sample of AGN. In contrast to the findings for the central regions of AGN-dominated systems, the PAH ratios measured in the extended regions of both type 1 and type 2 Seyfert galaxies can be explained assuming similar PAH molecular size distribution and ionized fractions of molecules to those seen in central regions of star-forming galaxies (100, Comment: 29 pages, 21 figures, 6 tables, MNRAS, accepted 2021 October 22

We report a dramatic reduction of operation voltage of a CuO nanowire-based ionization gas sensor due to the crystalline-to-amorphous phase transformation. The structural change is attributed to the ion bombardment and heating effect during the initial discharge, which brings about the formation of abundant nanocrystallites and surface states favoring gaseous ionization. The gas-sensing properties of the CuO nanowire sensor are confirmed by differentiating various types or concentrations of volatile organic compounds diluted in nitrogen, with a low detection limit at the ppm level. Moreover, a sensing mechanism is proposed on the basis of charge redistribution by electron-gas collision related to the specific ionization energy. The insightful study of the electrode microstructure delivers an exploratory investigation to the effect of gas ionization toward the discharge system, which provides new approaches to develop advanced ionization gas sensors.

We present 5--14~$\mu$m spectra at two different positions across the Orion Bar photodissociation region (PDR) obtained with the Infrared Spectrograph onboard the Spitzer Space Telescope and 3.3~$\mu$m PAH observations obtained with the Stratospheric Observatory for Infrared Astronomy (SOFIA). We aim to characterize emission from Polycyclic Aromatic Hydrocarbon (PAH), dust, atomic and molecular hydrogen, argon, sulfur, and neon as a function of distance from the primary illuminating source. We find that all the major PAH bands peak between the ionization front and the PDR front, as traced by H$_{2}$, while variations between these bands become more pronounced moving away from this peak into the face-on PDRs behind the PDR front and at the backside of the \HII\, region. While the relative PAH intensities are consistent with established PAH characteristics, we report unusual behaviours and attribute these to the PDR viewing angle and the strength of the FUV radiation field impinging on the PDRs. We determine the average PAH size which varies across the Orion Bar. We discuss subtle differences seen between the cationic PAH bands and highlight the photo-chemical evolution of carbonaceous species in this PDR environment. We find that PAHs are a good tracer of environmental properties such as the strength of the FUV radiation field and the PAH ionization parameter., Comment: 25 pages, 19 Figures. To be published in MNRAS

We report the spectroscopic observation of the jet-cooled para-ethynylbenzyl (PEB) radical, a resonance-stabilized isomer of C9H7. The radical was produced in a discharge of p-ethynyltoluene diluted in argon and probed by resonant two-color two-photon ionization (R2C2PI) spectroscopy. The origin of the D0(2B1)-D1(2B1) transition of PEB appears at 19,506 cm-1. A resonant two-color ion-yield scan reveals an adiabatic ionization energy (AIE) of 7.177(1) eV, which is almost symmetrically bracketed by CBS-QB3 and B3LYP/6-311G++(d,p) calculations. The electronic spectrum exhibits pervasive Fermi resonances, in that most a1 fundamentals are accompanied by similarly intense overtones or combination bands of non-totally symmetric modes that would carry little intensity in the harmonic approximation. Under the same experimental conditions, the m/z = 115 R2C2PI spectrum of the p-ethynyltoluene discharge also exhibits contributions from the m-ethynylbenzyl and 1-phenylpropargyl radicals. The former, like PEB, is observed herein for the first time, and its identity is confirmed by measurement and calculation of its AIE and D0-D1 origin transition energy; the latter is identified by comparison with its known electronic spectrum (J. Am. Chem. Soc.,2008,130, 3137-3142). Both species are found to co-exist with PEB at levels vastly greater than might be explained by any precursor sample impurity, implying that interconversion of ethynylbenzyl motifs is feasible in energetic environments such as plasmas and flames, wherein resonance-stabilized radicals are persistent.

This work outlines a new instructional laboratory experiment focused on the photoelectric effect and the determination of Planck's constant. The described laboratory system employs contemporary experimental techniques, including real-time data acquisition based on the use of Arduino boards. The basis of this experiment is to measure the associated turn-on voltages of a small neon bulb as it is illuminated with several different optical wavelengths. Six different LED and laser illumination sources were used with wavelengths ranging from UV (383 nm) to red (659 nm). A plot of the bulb's turn-on voltage as a function of the inverse of the excitation wavelength showed a linear relationship with a high correlation coefficient. Planck's constant was determined from this plot, yielding a value of h=7.4±1.1×10−34 J·s. Additionally, the system allows for experimental verification of the independence between excitation light intensity and the energy needed to ionize the gas inside the bulb.

A miniature ionization vacuum sensor (IVS) based on an on-chip SiOx-based tunneling electron source is reported. The vacuum sensor fabricated by microfabrication technologies exhibits a compact multilayered structure with overall dimensions of $13\times 9\times2.7$ mm3, where the electron source chip, Si layer of the electron collector, Si layer of the ion collector, and glass spacers between them are stacked together by an anodic bonding method. Electron impact ionization occurs in a semiclosed cavity through the electron and ion collector layers and glass spacers. Because of the compact structure, low working voltage of SiOx-based tunneling electron sources, and stable electron emission of the electron sources in a poor vacuum, a wide linear detection range from $1.3\times 10^{-2}$ to 133 Pa and a sensitivity of $8.3\times 10^{-4}$ Pa−1 have been demonstrated for the devices. These advantages, including miniature size, a detection range up to the rough vacuum regime, and the capability of batch fabrication with microfabrication technologies, make our IVSs promising in vacuum measurements.

We report electron diffraction of cationic argon nanoclusters embedded in superfluid helium droplets. Superfluid helium droplets are first doped with neutral argon atoms to form nanoclusters, and then the doped droplets are ionized by electrons. The much lower ionization energy of argon ensures that the positive charge resides on the Ar nanocluster. Using different stagnation temperatures therefore droplets with different sizes, we have been able to preferentially form a small ionic cluster containing 2 – 4 Ar atoms and a larger cluster containing 7 – 11 atoms. The fitting results of the diffraction profiles agree with structures reported from theoretical calculations, containing a cationic trimer core with the remaining atoms largely neutral. This work testifies to the feasibility of performing electron diffraction from ionic species embedded in superfluid helium droplets, dispelling the concern over the particle density in the diffraction region. However, the large number of neutral helium atoms surrounding the cationic nanoclusters poses a challenge for the detection of the helium solvation layer, and the detection of which awaits further technological improvements.

Even-parity Rydberg and autoionizing Rydberg spectrum of antimony have been calculated by relativistic multichannel theory, in which the ionic core dipole polarization effect due to the Rydberg ele...

We investigate the sputtering and ionization process that takes place during secondary ion mass spectrometry (SIMS) analysis in order to develop a better understanding of the underlying controls on elemental and molecular oxide secondary ion yields. Using data from a suite of uranium compounds that were sputtered with an O- primary beam on a NanoSIMS 50L, our goal is to understand whether a compound’s intrinsic properties, or processes operating at the sputtering site, exert the greatest influence over the relative abundances of uranium elemental and molecular oxide secondary ions observed during an analysis. While the observed 238U/238U16O and 238U/238U16O2 of the various compounds exhibit considerable overlap, there are relationships between the weighted mean 238U/238U16O and 238U/238U16O2 ratios for the various compounds and their enthalpies of formation. This reinforces the existing theory that the nature of the material being sputtered can influence relative ion yields (e.g. the SIMS matrix effect), but we also document significant evidence for the influence of processes operating at the sputtering site as a major factor. The existence of a strong relationship between the relative uranium molecular oxide production rate and the mass fractionation regimes taking place within an analysis, as well as the existence of sudden shifts in molecular oxide production rates taking place within an analysis, provide further evidence for the importance of processes related to the sputtering and ionization dynamics as exerting the most control over observed ion yields. Evaluation of our data within the context of existing models for secondary ion production during SIMS analysis highlights the need for additional models that consider the competing influences of a sample’s chemical and/or structural form, reactions taking place at the sputtering site, as well as the ionization and ion extraction dynamics of the various elemental and molecular oxide species.

In this study, the possibility of using a superhalogenide ion AlF4- extracted from Na3AlF6 based target materials for 26Al/27Al measurements by Accelerator Mass Spectrometry (AMS) was investigated. Determination of 26Al by usual mass spectrometric methods is generally hampered by the presence of the isobar 26Mg. However, the AMS method enables significant suppression of this interference, particularly by negative ion formation. After initial current tests in a caesium sputtering ion source of the Tandetron system, performance of the fluoride materials was analysed on the MILEA AMS system at ETH Zurich. The AlF4- current was used to evaluate the performance of the respective samples. Additives as PbF2 were tested to increase the extracted ion currents and samples containing MgF2 were used to investigate the presence of isobaric ions. Subsequently, the ionization efficiency of AlF4- was determined by recording the 27Al2+ current on the high energy side and the signals of 26Al2+ were investigated with the gas ionization detector.

The dynamics of charge-state fractions of Au- and U-ion beams, penetrating hydrogen plasmas, is investigated for 1.4 and 3.6 MeV/u ion energies and plasma electron temperatures T e = (0.6 − 3.0) eV and densities N e =(1016 − 1020) cm−3. Calculations of the fractions as a function of the plasma thickness are performed by solving the balance rate equations with calculated ionization and recombination rates including those for dielectronic recombination (DR). The DR rates are calculated by the recently created computer code DRIMP using the fully relativistic multi-configuration approach and the so-called shifted Maxwellian velocity distribution function. Calculated by this method DR rates of Au- and U-ion beams passing through a hydrogen plasma are presented for the first time. Using the results obtained, the temperatures T e and densities N e are found at which the equilibrium mean charges q of Au- and U-ion beams are maximal for hydrogen-plasma length L ≤ 100 cm. Dependencies of the plasma equilibrium thicknesses X e q on the initial charge q 0 of incident ions are investigated, and it is found that X e q values are minimal at q 0 ≈ q .

This work presents a systematic numerical investigation on the behaviors of electrons in the bullet in the Ar/O2 plasma jet in changing oxygen concentration and the applied voltage, based on a needle-plate discharge configuration and a 1-D particle-in-cell Monte-Carlo collision (PIC-MCC) method. The increase in oxygen concentration allows more electrons to be scattered toward the target, i.e., more electrons to most probably interact with the target, and induces a dramatic increase of reactive oxygen species (ROS), but leads to the decrease of the bullet velocity and average electron energy. In addition, there is a weak correlation between the electron density and ROS generation. When increasing the applied voltage, the electrons scattered toward the target decrease, however, the majority of these electrons, above 70%, are of energy higher than the threshold inducing a dissociative electron attachment (DEA) to water molecule, and meanwhile, there is an evident increase of high-energy electrons being able to excite water molecules. Also, there is a strong correlation between the electron density and ROS generation. The present results are also compared with those in the Ar/H2O plasma jets, indicating qualitative and quantitative differences.

It is known that, in the strong electric field, electrons undergo continuous acceleration [runaway electrons (REs)] even in dense media, receiving from the field more energy than lose via interactions with the ambient atomic particles. We, here, analyze the effect of the angular scattering of electrons in inelastic interactions on the runaway process. For this purpose, we developed a Monte Carlo (MC) code and, having carried out simulations of electron transport in the helium of atmospheric density, calculated the runaway rate at the field strengths of 50–300 kV cm−1. We show that different models of the electron scattering lead to a tenfold difference in the runaway rate magnitudes.

To examine the influence of radiative transitions on the performance of nonequilibrium seed-free argon plasma magnetohydrodynamic (MHD) generators, we developed MHD numerical simulation technique with a collisional-radiative (C-R) model, where neutral argon atoms with 45 discrete effective electronic excitation levels, singly ionized argon ions, and free electrons were considered under a two-temperature, low-magnetic Reynolds number MHD approximation. Furthermore, a so-called escape factor was implemented in the C-R model to consider the effects of radiation trapping by ground-state neutral atoms. Using the developed technique, we computed the performance characteristics of a nonequilibrium seed-free argon plasma MHD generator. The numerical results showed that the generator performance gets higher as the escape factor decreases, i.e., the optical thickness for radiative transitions to the ground state of neutral atoms increases. The numerical results also suggested that when the escape factor is $1.0\times 10^{-3}$ or less, the generator performance is almost the same as that for the escape factor of 0 corresponding to completely optical-thick plasma case for the radiative transitions to the ground state of neutral atoms. Furthermore, realistic escape factor values for resonance lines in the power generation channel were evaluated using a well-known estimation model. Consequently, the estimated values had the order of $10^{-4}$ . We also showed that under such relatively optically thick plasma cases, a collisional (C) model and a widely used global ionization-recombination rate model with no explicit consideration of electronically excited-state neutral atoms can reproduce the generator performance predicted by the C-R model with relatively good accuracy.

Neon cluster ions Ne$_s^+$ grown in pre-ionized, mass-to-charge selected helium nanodroplets (HNDs) reveal a strong enrichment of the heavy isotope $^{22}$Ne that depends on cluster size s and the experimental conditions. For small sizes the enrichment is much larger than previously reported for bare neon clusters grown in nozzle expansions and subsequently ionized. The enrichment is traced to the massive evaporation of neon atoms in a collision cell that is used to strip helium from the HNDs. We derive a relation between the enrichment of $^{22}$Ne in the cluster ion and its corresponding depletion factor $F$ in the vapor phase. The value thus found for $F$ is in excellent agreement with a theoretical expression that relates isotopic fractionation in two-phase equilibria of atomic gases to the Debye temperature. Furthermore, the difference in zero-point energies between the two isotopes computed from F agrees reasonably well with theoretical studies of neon cluster ions that include nuclear quantum effects in the harmonic approximation. Another fitting parameter provides an estimate for the size s$_i$ of the precursor of the observed Ne$_s^+$. The value is in satisfactory agreement with the size estimated by modeling the growth of Ne$_s^+$, and with lower and upper limits deduced from other experimental data. On the other hand, neon clusters grown in neutral HNDs that are subsequently ionized by electron bombardment exhibit no statistically significant isotope enrichment at all. The finding suggests that the extent of ionization-induced dissociation of clusters embedded in HNDs is considerably smaller than for bare clusters., 14 pages, 5 figures, supplementary material

Salinity tolerance of ambient electric arc ionization (AEAI) was evaluated by comparing electrospray ionization for various samples at NaCl concentrations from 0 to 1000 mmol/L. AEAI-mass spectrometry (AEAI-MS) exhibited an excellent signal intensity even at NaCl concentrations of 1000 mmol/L, while the ESI-MS had no signal because high salinity has a strong inhibitory effect on analytes. The sodium adduct was verified using LiCl instead of NaCl. AEAI-MS successfully quantified saline samples with an excellent quantitative ability (R2 ≥ 0.998). We also achieved some analytical samples in the buffer solution at a very high concentration and even in a saturated salt solution. Overall, AEAI-MS has protonated ions for most target analytes. In addition, the relationship between auxiliary temperature and the distance from the sample to the arc was investigated, and the results indicated that thermal desorption plays an important role in AEAI source.

In this article, a noninterceptive and high-accuracy beam position monitor, named Hi’Beam-A, has been designed for the accelerator of a heavy-ion therapy facility. The Hi’Beam-A consists of the detector subsystem and the readout subsystem. In the detector subsystem, the microchannel plate multiplies the ionized charge in the high vacuum chamber, and the novel Topmetal silicon pixel sensor directly collects the charge. The readout subsystem processes the data and calculates the beam position. Beam test results show that the Hi’Beam-A reaches an accuracy of $5~\mu \text{m}$ . This article will present the design, characterization, and beam test of Hi’Beam-A.

Using multi-electron–ion coincidence measurements combined with high level calculations, we show that double ionisation of SO2 at 40.81 eV can be state selective. It leads to high energy products, in good yield, via a newly identified mechanism, which is likely to apply widely to multiple ionisation by almost all impact processes.

Pulsed vacuum ultraviolet (VUV) radiation (80–180 nm) emitted by laser plasma produced on a metal target is used in mass spectrometry to ionize volatile organic compounds at atmospheric pressure. The parameters of light emitted by the laser plasma generated by a pulsed Nd:YAG laser radiation at a wavelength of 1064 nm, power density of about 70 GW/cm2, and pulse energy of 250 µJ have been determined using emission spectroscopy. During the first several nanoseconds, the plasma emission spectrum does not contain any pronounced spectral lines and can be described as the emission spectrum of a blackbody with a temperature of 5.5 × 104–105 K (the temperature depends on the ambient gas pressure). This radiation provides ionization of water, oxygen, and nitrogen molecules, as well as argon atoms. It is shown that the mechanisms of ionization of organic compounds under VUV irradiation in argon are based on the reaction of proton transfer from ionized water molecules and reactions of organic compounds with oxygen ions.

Multidevice capillary vibrating sharp-edge spray ionization (cVSSI) source parameters have been examined to determine their effects on conducting in-droplet hydrogen/deuterium exchange (HDX) experiments. Control experiments using select compounds indicate that the observed differences in mass spectral isotopic distributions obtained upon initiation of HDX result primarily from solution-phase reactions as opposed to gas-phase exchange. Preliminary studies have determined that robust HDX can only be achieved with the application of same-polarity voltage to both the analyte and the deuterium oxide reagent (D2O) cVSSI devices. Additionally, a similar HDX reactivity dependence on the voltage applied to the D2O device for various analytes is observed. Analyte and reagent flow experiments show that, for the multidevice cVSSI setup employed, there is a nonlinear dependence on the D2O reagent flow rate; increasing the D2O reagent flow by 100% results in only an ∼10–20% increase in deuterium incorporation for this setup. Instantaneous (subsecond) response times have been demonstrated in the initiation or termination of HDX, which is achieved by turning on or off the reagent cVSSI device piezoelectric transducer. The ability to distinguish isomeric species by in-droplet HDX is presented. Finally, a demonstration of a three-component cVSSI device setup to perform multiple (successive or in combination) in-droplet chemistries to enhance compound ionization and identification is presented and a hypothetical metabolomics workflow consisting of successive multidevice activation is briefly discussed.

Radiating amorphous In–Ga–Zn–O (a-IGZO) thin-film transistors (TFTs) with deep ultraviolet light (λ = 175 nm) is found to induce rigid negative threshold-voltage shift, as well as a subthreshold hump and an increase in subthreshold-voltage slope. These changes are attributed to the photo creation and ionization of oxygen vacancy states (VO), which are confined mainly to the top surface of the a-IGZO film (backchannel). Photoionization of these states generates free electrons and the transition from the neutral to the ionized VO is accompanied by lattice relaxation, which raises the energy of the ionized VO. This and the possibility of atomic exchange with weakly bonded hydrogen leads to metastability of the ionized VO, consistent with the rigid threshold-voltage shift and increase in subthreshold-voltage slope. The hump is thus a manifestation of the highly conductive backchannel and its formation can be suppressed by reduction of the a-IGZO film thickness or application of a back bias after radiation. These results support photo creation and ionization of VO as the main cause of light instability in a-IGZO TFTs and provide some insights on how to minimize the effect.

In electrostatic tandem charged particle accelerators, gas stripping targets are used to convert negative ions into positive ones. Partial ionization of the gas by ions leads to the formation of an undesirable beam of stripping gas ions in the accelerating channels. In this work, the current of a beam of argon ions produced in a tandem accelerator with vacuum insulation was measured by mass spectroscopy. It is shown that the current of argon ions is 2000 times smaller than the current of the proton beam. The reliability of the measurements is provided by visualization of an argon ion beam on the surface of a lithium target and is also confirmed by an experiment with increased gas injection and an estimate of the possible contribution of the proton beam. It is shown that such a small value of the argon ion current does not pose a danger either as a source of additional heating of a lithium target, or as an additional load of a high-voltage power supply, and therefore does not require the previously proposed means for its suppression.

The influence of electron-proton irradiation on the process of changing the surface structure of K‑208 glass, caused by the formation of gas-filled bubbles and their destruction, is studied by atomic-force microscopy (AFM). These phenomena are associated with the formation of hydrogen atoms H in the process of the recombination of protons with electrons injected into the glass and those that appeared in it during ionization. The migration of hydrogen atoms and their aggregation into H-clusters in the vicinity of glass structure defects leads to the formation of molecular hydrogen (H2) bubbles. The glass is exposed to electrons and protons with energies of 40 and 20 keV, respectively. Irradiation is carried out in a vacuum chamber with a residual pressure of 10–4 Pa. At a fixed value of the proton flux density φр = 5.5 × 1010 cm–2 s–1, the electron flux density φe varies in the range (0–16.8) × 1010 cm–2 s–1. It is shown that the size of the bubbles depends on the ratio of the parameters φe and φр. Analysis of the experimental data suggests that the destruction of a bubble occurs with a local decrease in the thickness of its cap to 10–20 nm, as a result of heating and growth in the direction normal to the surface under the pressure of the accumulating gas. It is also found that electrostatic discharges developing along the irradiated glass surface stimulate the destruction of bubbles.

Ionosorbed oxygen is the key player in reactions on metal-oxide surfaces. This is particularly evident for chemiresistive gas sensors, which operate by modulating the conductivity of active materials through the formation/removal of surface O-related acceptors. Strikingly though, the exact type of species behind the sensing response remains obscure even for the most common material systems. The paradigm for ab initio modeling to date has been centered around charge-neutral surface species, ignoring the fact that molecular adsorbates are required to ionize to induce the sensing response. Herein, we resolve this inconsistency by carrying out a careful analysis of all charged O-related species on three naturally occurring surfaces of SnO2. We reveal that two types of surface acceptors can form spontaneously upon the adsorption of atmospheric oxygen: (i) superoxide O2- on the (110) and the (101) surfaces and (ii) doubly ionized O2- on the (100) facet, with the previous experimental evidence pointing to the latter as the source of sensing response. This species has a unique geometry involving a large displacement of surface Sn, forcing it to attain the coordination resembling that of Sn2+ in SnO, which seems necessary to stabilize O2- and activate metal-oxide surfaces for gas sensing.

A gas-discharge magnetically insulated vircator containing two tubes, one of which is filled with low-pressure gas is proposed. Its particle-in-cell (PIC)/Monte Carlo (MC) simulation is carried out. The dynamics of free electrons, the dynamics of the virtual cathode (VC) as a whole, and gas ionization are calculated using the example of helium. It is shown that a squeezed state of the electron beam (distributed VC) arises in a gas-filled tube, effectively ionizing gas. It is found that at a pressure of helium of the order of several Pa, the degree of its ionization can reach several percent, which can be useful in creating a joint device “vircator-laser.” A high degree of ionization leads to charge and current compensation of the electron beam in the location of the squeezed state, and the distributed VC gradually dissolves. It is replaced by the two-beam state of the beam again, and repeated microwave generation, more powerful than in the vacuum case (the power increase is more than 6 times), occurs. In this case, the peak efficiency of repeated microwave generation reaches 15%. The frequency characteristics of the gas-discharge vircator which as it turned out differ insignificantly from the characteristics of the vacuum vircator were calculated.

The electrical degradation in AlGaN/GaN high-electron-mobility transistors (HEMTs) is examined under irradiation with 7.6-MeV carbon (C), 20-MeV oxygen (O), and 30-MeV fluorine (F) ions in situ . To characterize the radiation damage in the HEMTs, the ionizing dose $D_{i}$ , displacement dose $D_{d}$ , and number of vacancies versus the chip depth in the devices have been calculated for heavy ions. As expected, in all three types of HEMTs, the output current decreases more than 30% and threshold voltage positive shifts after the irradiation fluence of $4\times 10^{12}$ ions/cm2. The performance degradation of AlGaN/GaN HEMTs is caused by radiation-induced charged defects. Based on calculation and experimental results, it is shown that the nonionizing energy loss (NIEL) method is not suitable for estimating the degradation of AlGaN/GaN HEMTs either considering gallium vacancy or considering both gallium vacancy and nitrogen vacancy. In the same displacement damage dose, the threshold voltage degradation rate depends on the type of incident particles and independent of the channel length. The damage caused by carbon ions is the smallest and the damage caused by fluoride ions is the largest.

The ionization degree of hydrogen is crucial in the physics of the plasma in the solar chromosphere. It specifically limits the range of plasma temperatures that can be determined from the Hα line. Given that the chromosphere greatly deviates from the local thermodynamic equilibrium (LTE) condition, precise determinations of hydrogen ionization require the solving of the full set of non-LTE radiative transfer equations throughout the atmosphere, which is usually a formidable task. In many cases, it is still necessary to obtain a quick estimate of hydrogen ionization without having to solve for the non-LTE radiative transfer. Here, we present a simple method to meet this need. We adopt the assumption that the photoionizing radiation field changes little over time, even if physical conditions change locally. With this assumption, the photoionization rate can be obtained from a published atmosphere model and can be used to determine the degree of hydrogen ionization when the temperature and electron density are specified. The application of our method indicates that in the chromospheric environment, plasma features contain more than 10% neutral hydrogen at temperatures lower than 17,000 K but less than 1% neutral hydrogen at temperatures higher than 23,000 K, implying that the hydrogen temperature determined from the Hα line is physically plausible if it is lower than 20,000 K, but may not be real, if it is higher than 25,000 K. We conclude that our method can be readily exploited to obtain a quick estimate of hydrogen ionization in plasma features in the solar chromosphere.

The hydrocarboxyl radical (HOCO) is an important species in combustion and astrochemistry because it is easily converted to CO2 after hydrogen reduction. In this study, the formation mechanism of the HOCO radical in a CO-H2O system was investigated by direct ab initio molecular dynamics calculations. Two reactions were examined for HOCO formation. First, the reaction dynamics of the CO-H2O cluster cation, following the ionization of the neutral parent cluster CO(H2O)(n) (n = 1-4), were investigated. Second, the bimolecular collision reaction between CO and (H2O)(n)(+) was studied. In the ionization of the CO(H2O)(n) clusters (n = 3 and 4), proton transfer, expressed as CO(H2O)(n)(+) -> CO(OH)H3O+(H2O)(n-2), occurred within the (H2O)(n)(+) cluster cation, and the HOCO radical was yielded as a product upon addition of CO and OH. This reaction proceeds under zeropoint energy. Also, this radical was effectively formed from the collision reaction of CO with water cluster cation (H2O)(n)(+), expressed as CO + OH(H3O+)(H2O)(n-2) -> HOCO-H3O+ + (H2O)(n-2). If the intermolecular vibrational stretching mode is excited in the CO(H2O)(n) cluster (vibrational stretching between CO and the water cluster), the HOCO radical was detected after ionization when n = 2. The reaction mechanism was discussed based on the theoretical results.

To explore the role of hydrogen in radiation degradation of AlGaN/GaN high-electron-mobility transistors (HEMTs), the performance degradation of the hydrogen untreated and pretreated devices is compared under the exposure of carbon ions. The energy of carbon ions is chosen as 7.6 MeV, and the maximum fluence reaches $4 \times 10^{12}$ cm−2. By electrical character measuring, it is found that the positive shift of the threshold voltage and the decrease of the transconductance occur after to the irradiation. Hydrogen pretreatment accelerates the shift of threshold voltage and the decrease of the transconductance. The threshold voltage of the device is almost unchanged under 1-MeV electron irradiations. This means that the displacement damage leads to the shift of the threshold voltage. The height of Schottky barrier hardly changes in the hydrogen pretreated devices, showing that the ionization defects such as the formation of interface states under the gate are not the main cause of device degradation. Deep level transient spectrum (DLTS) results show that the irradiations cause the increase of gallium vacancies, and the hydrogen pretreatment inhibits its formation. According to the first principle calculation, the existence of hydrogen in GaN layer can reduce the formation energy of and the number of charges of the defects. It is speculated that hydrogen atoms participate in the evolution of radiation defects, which changes the types and number of defects in the devices.

The purpose of this article is to study the influence of different powers, pressures, frequencies, and gases on the electron density distribution in special structures. A simulation model is established, and the electronic density in a special capacitance coupled plasma (CCP) device is calculated over the power range of 0–10 kW, pressure range of 0–50 Pa, and frequency range of 13.56–300 MHz. The results show that the power is a logarithmic function of the electron density in helium and argon plasmas, and the peak value for the electron density occurs in the diffusion region. At a certain power, collisions between particles increase with increasing pressure, which leads to an increase in electron density. However, the high electron density region in the helium plasma is concentrated near the electrode, while the high density region in the argon plasma moves from the center of the device to the electrode with increasing gas pressure. At the same time, the increase in the power frequency increases the ionization rate, and energy is transferred to the electrons, which increases the electron density. However, the rate of increase in the electron density decreases with increasing power frequency at the same voltage and pressure. With increasing power frequency, the 2-D electron density distribution in the argon and helium plasmas is found to vary in a similar way to that found for increasing pressure.

The electron impact ionization of helium droplets doped with ethylene molecules and clusters yields diverse CXHY+ cations embedded in the droplets. The ionization primarily produces C2H2+, C2H3+, C2H4+, and CH2+, whereas larger carbocations are produced upon the reactions of the primary ions with ethylene molecules. The vibrational excitation of the cations leads to the release of bare cations and cations with a few helium atoms attached. The laser excitation spectra of the embedded cations show well resolved vibrational bands with a few wavenumber widths—an order of magnitude less than those previously obtained in solid matrices or molecular beams by tagging techniques. Comparison with the previous studies of free and tagged CH2+, CH3+, C2H2+, C2H3+, and C2H4+ cations shows that the helium matrix typically introduces a shift in the vibrational frequencies of less than about 20 cm−1, enabling direct comparisons with the results of quantum chemical calculations for structure determination. This work demonstrates a facile technique for the production and spectroscopic study of diverse carbocations, which act as important intermediates in gas and condensed phases.

The laser intensity dependence of the recoil energies from the Coulomb explosion of small argon clusters has been investigated by resolving the contributions of the individual charge states to the ion recoil energy spectra. Between $10^{14}$ and $10^{15}$ W/cm$^2$ the high-energy tail of the ion energy spectra changes its shape and develops into the well-known knee feature, which results from the cluster size distribution, laser focal averaging, and ionization saturation. Resolving the contributions of the different charge states to the recoil energies, the experimental data reveal that the basic assumption of an exploding homogeneously charged sphere cannot be maintained in general. In fact, the energy spectra of the high-$q$ show distinct gaps in the yields at low kinetic energies, which hints at more complex radial ion charge distributions developing during the laser pulse impact., Comment: 15 pages, 5 figures

Extensions have been made recently to the coronal approximation for the purpose of modelling line emission from carbon and oxygen in the lower solar atmosphere. The same modelling is used here for other elements routinely observed in the solar transition region: N, Ne, Mg, Si and S. The modelling includes the effects of higher densities suppressing dielectronic recombination and populating long-lived, metastable levels; the presence of metastable levels typically causes effective ionisation rates to increase and recombination rates to decrease. Processes induced by the radiation field, namely photo-ionisation and photo-excitation, have been included, along with charge transfer, which occurs when electrons are exchanged during atom-ion and ion-ion collisions. The resulting ion balances are shown, and indicate significant changes compared to the frequently-employed coronal approximation. The effect on level populations within ions caused by photo-excitation is also assessed. To give an illustration of how line emission could be altered by these processes, selected line contribution functions are presented at the end., Comment: Accepted in MNRAS, 15 pages, 13 figures

Wavelength and spatially resolved imaging and 2D plasma chemical modeling methods have been used to study the emission from electronically excited C2 radicals in microwave-activated dilute methane/hydrogen gas mixtures under processing conditions relevant to the chemical vapor deposition (CVD) of diamond. Obvious differences in the spatial distributions of the much-studied C2(d3Πg–a3Πu) Swan band emission and the little-studied, higher-energy C2(C1Πg–A1Πu) emission are rationalized by invoking a chemiluminescent (CL) reactive source, most probably involving collisions between H atoms and C2H radicals, that acts in tandem with the widely recognized electron impact excitation source term. The CL source is relatively much more important for forming C2(d) state radicals and is deduced to account for >40% of C2(d) production in the hot plasma core under base operating conditions, which should encourage caution when estimating electron or gas temperatures from C2 Swan band emission measurements. Studies at higher pressures (p ≈ 400 Torr) offer new insights into the plasma constriction that hampers efforts to achieve higher diamond CVD rates by using higher processing pressures. Plasma constriction is proposed as being inevitable in regions where the local electron density (ne) exceeds some critical value (nec) and electron–electron collisions enhance the rates of H2 dissociation, H-atom excitation, and related associative ionization processes relative to those prevailing in the neighboring nonconstricted plasma region. The 2D modeling identifies a further challenge to high-p operation. The radial uniformities of the CH3 radical and H-atom concentrations above the growing diamond surface both decline with increasing p, which are likely to manifest as less spatially uniform diamond growth (in terms of both rate and quality).

Analysis of neutral hydrogen $\lambda 21$ -cm profiles at high northern and southern Galactic latitudes reveals unexpected properties, connects unanticipated associations, and confirms the fundamental parameters of the interstellar medium. Gaussian decomposition of profiles from the second data release of the Galactic Arecibo $L$ -Band Feed Array (GALFA) confirms earlier results of a pervasive component with a linewidth of order 34 km s−1, consistent with the critical ionization velocity (CIV) of helium. The ratio of the column density of this component to the entire profile is proportional to the interstellar helium abundance. The results are comparable to the accepted value of the cosmic abundance, 0.085, in the southern Galactic hemisphere, but different for directions in the northern Galactic hemisphere. Normalizing to the cosmic abundance allows us to estimate how much HI is “missing” from the $\lambda 21$ -cm observations in the northern sky, confirming an asymmetry that has been known for decades. These CIV results also predict the volume density of interstellar electrons along different lines of site, which match values derived from pulsar dispersion measures and $\text{H}\alpha $ observations. These results provide strong support for the hypothesis that interstellar $\lambda 21$ -cm HI profile linewidths are modulated by the CIV plasma phenomenon.

On the basis of the Monte Carlo method and the many particles dynamics, the ionization and drift characteristics of electrons in a constant field drifting in helium with a certain amount of iron vapor are calculated. The main attention is paid to the study of the influence of iron vapor concentration on the characteristics of escaping electrons. The formulation of the problem involves the death of electrons on the wall and the balance between the birth of ionization and leaving the escape mode (whiz). The obtained results indicate a sharp change in the ionization characteristics when an easily ionizable additive in the form of iron vapor is added to helium. Starting with a fraction of a percent of the concentration of iron atoms in helium, due to the strong ionization of iron atoms, there is a strong change in the electron distribution function, which leads to a significant increase in the frequency of ionization and a non-monotonic dependence of the number of escaping electrons on the concentration of iron vapors.

We present the first space-borne observation of optical emissions of both neutral and ionized argon atoms resulting from a radio-frequency glow discharge (RF-GD) from a sounding rocket payload. The Observations of Electric-field Distributions in the Ionospheric Plasma — a Unique Strategy-C (OEDIPUS-C) payload was designed to separate into two sub-payloads on its up-leg. This separation permitted a number of two-point measurements, including those on radio wave propagation from the active dipole antennas on the upper sub-payload to the synchronized receiving dipoles on the lower sub-payload. A white-light video camera on the lower sub-payload recorded strong luminosity around the active dipoles during the first 15 s after sub-payload separation, when argon gas jets were providing propulsion to separate the two sub-payloads. Parts of the ejected argon appeared as a glowing volume where the large radio-frequency (RF) fields from the two active dipoles excited the optical emission, as the sub-payload separation increased from 2 to 55 m. The shape and intensity of the luminosity were well repeated as a function of the swept frequency (0.025–8.000 MHz), but their frequency dependences were distinctly different from those of sounder-accelerated electrons measured onboard, and deduced to result from the nonlinearity of the glow discharge. The observation is to our knowledge the first of its kind, and is interpreted in terms of a RF-GD energized by the strong near electric fields of the transmitting dipoles.