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We report electron attachment (EA) measurements for the parent anion radical formation from coenzyme Q0 (CoQ0) at low electron energies (

We report electron attachment (EA) measurements for the parent anion radical formation from coenzyme Q0 (CoQ0) at low electron energies (

We investigate dissociative electron attachment to 5-fluorouracil (5-FU) employing a crossed electron-molecular beam experiment and quantum chemical calculations. Upon the formation of the 5-FU− anion, 12 different fragmentation products are observed, the most probable dissociation channel being H loss. The parent anion, 5-FU−, is not stable on the experimental timescale (~140 µs), most probably due to the low electron affinity of FU; simple HF loss and F− formation are seen only with a rather weak abundance. The initial dynamics upon electron attachment seems to be governed by hydrogen atom pre-dissociation followed by either its full dissociation or roaming in the vicinity of the molecule, recombining eventually into the HF molecule. When the HF molecule is formed, the released energy might be used for various ring cleavage reactions. Our results show that higher yields of the fluorine anion are most probably prevented through both faster dissociation of an H atom and recombination of F− with a proton to form HF. Resonance calculations indicate that F− is formed upon shape as well as core-excited resonances. [ABSTRACT FROM AUTHOR]

This work aims to detect the discharge products and study the decomposition characteristics of C5F10O/N2 gas mixture under pulsed discharge. Discharge tests are carried out on three kinds of gas mixtures with different contents of C5F10O (3.3%, 10%, and 30%). Electron attachment mass spectrometry (MS) is proposed to detect discharge products after negative ionization, and the results are compared with that in gas chromatography (GC) MS. The discharge products are detected and the formation pathways of the main decomposition products are deduced. The results show that the densities of some products increase with the number of discharge pulses. There are differences on the types of products and the cumulative effect of discharge in the three kinds of gas mixtures. Furthermore, these discharge products are able to characterize the discharge accumulation effects in power switchgear, such as insulation degradation. [ABSTRACT FROM AUTHOR]

Metronidazole belongs to the class of nitroimidazole molecules and has been considered as a potential radiosensitizer for radiation therapy. During the irradiation of biological tissue, secondary electrons are released that may interact with molecules of the surrounding environment. Here, we present a study of electron attachment to metronidazole that aims to investigate possible reactions in the molecule upon anion formation. Another purpose is to elucidate the effect of microhydration on electron-induced reactions in metronidazole. We use two crossed electron/molecular beam devices with the mass-spectrometric analysis of formed anions. The experiments are supported by quantum chemical calculations on thermodynamic properties such as electron affinities and thresholds of anion formation. For the single molecule, as well as the microhydrated condition, we observe the parent radical anion as the most abundant product anion upon electron attachment. A variety of fragment anions are observed for the isolated molecule, with NO2− as the most abundant fragment species. NO2− and all other fragment anions except weakly abundant OH− are quenched upon microhydration. The relative abundances suggest the parent radical anion of metronidazole as a biologically relevant species after the physicochemical stage of radiation damage. We also conclude from the present results that metronidazole is highly susceptible to low-energy electrons. [ABSTRACT FROM AUTHOR]

We have used a crossed electron molecular beam setup to investigate the behavior of the anticancer drug temozolomide (TMZ) upon the attachment of low-energy electrons (0–14 eV) in the gas phase. Upon a single electron attachment, eight anionic fragments are observed, the most intense being an anion with mass of 109 u at a resonance energy of 0 eV. Quantum chemical calculations suggest that this ion is generated after the tetrazine ring opens along a N–N bond and its fragments leave the molecule, forming an imidazole-carboxamide species. This ion represents the most abundant fragment, with further fragments following from its dissociation. The tetrazine ring cleavage reaction forming N2 is thus the driving force of TMZ reactivity upon electron attachment.

Using a multi-term solution of the Boltzmann equation and Monte Carlo simulation technique we study behaviour of the third-order transport coefficients for electrons in model gases, including the ionisation model of Lucas and Saelee and modified Nessâ€"Robson model of electron attachment, and in real gases, including N2 and CF4. We observe negative values in the E / n 0-profiles of the longitudinal and transverse third-order transport coefficients for electrons in CF4 (where E is the electric field and n 0 is the gas number density). While negative values of the longitudinal third-order transport coefficients are caused by the presence of rapidly increasing cross sections for vibrational excitations of CF4, the transverse third-order transport coefficient becomes negative over the E / n 0-values after the occurrence of negative differential conductivity. The discrepancy between the two-term approximation and the full multi-term solution of the Boltzmann equation is investigated for electrons in N2 and CF4. While the accuracy of the two-term approximation is sufficient to investigate the behaviour of the third-order transport coefficients in N2, it produces large errors and is not even qualitatively correct for electrons in CF4. The influence of implicit and explicit effects of electron attachment and ionisation on the third-order transport tensor is investigated. In particular, we discuss the effects of attachment heating and attachment cooling on the third-order transport coefficients for electrons in the modified Nessâ€"Robson model, while the effects of ionisation are studied for electrons in the ionisation model of Lucas and Saelee, N2 and CF4. The concurrence between the third-order transport coefficients and the components of the diffusion tensor, and the contribution of the longitudinal component of the third-order transport tensor to the spatial profile of the swarm are also investigated. For electrons in CF4 and CH4, we found that the contribution of the component of the third-order transport tensor to the spatial profile of the swarm between approximately 50 Td and 700 Td, is almost identical to the corresponding contribution for electrons in N2. This suggests that the recent measurements of third-order transport coefficients for electrons in N2 may be extended and generalized to other gases, such as CF4 and CH4. [ABSTRACT FROM AUTHOR]

We report a combined experimental and theoretical investigation of dissociative electron attachment (DEA) to the nucleobase uracil. Using ion momentum imaging experiments employing a DEA reaction microscope we have measured 3-dimensional momentum distributions of specific anionic fragments following DEA to uracil by 6 eV electrons. From the measured anion fragment kinetic energy we determine the possible dissociation pathways and the total kinetic energy release. We employ electronic structure and electron scattering calculations to determine the probability for electron attachment in the molecular frame. Combining these calculations with the imaging measurements, we reveal several key features of the coupled electronic and nuclear dynamics of DEA.

The application of an electric field to a flame modifies the flame characteristics due to the collective motion of charged particles generated within the flame. The applied field mobilises electrons and ions depending on their polarity, leading to localised regions of space charge with sufficient density to either locally amplify or shield the applied electric field. A fundamental understanding of the local electric field is essential for both electrically and plasma-assisted combustion, because it determines electric body force as well as electron temperature. In this work, we propose a method, which is independent of gas composition and temperature, to measure the local electric field using electric field induced second harmonic generation (E-FISH). We successfully apply this method to a laminar nonpremixed counterflow flame by applying modulated direct current (DC) electric field with a microsecond duration zero volt pulse. Electric potential and space charge distribution are also deduced from the measured electric field. Furthermore, we show the importance of electron attachment to O 2 forming O 2 − by changing the polarity of the applied DC electric field. When the anode is in the oxygen stream, a region of negative charge is obtained near the anode, whereas, when the anode is in the fuel stream, no region of negative charge is found. We also find the qualitative trends of the measured electric fields reasonably agree with previously reported one-dimensional modelling results. The limitations of the methodology are addressed, and we show that the ability to modulate the DC voltage on sub-microsecond timescales is required for accurate quantitative measurements. [ABSTRACT FROM AUTHOR]

Charge accumulation has always been a problem for the safe operation of gas insulated switchgear (GIS)/gas insulated transmission line (GIL) both under AC and DC. It is of great significance to investigate the behaviour of surface charge under high voltage. In this study, the charge distribution characteristics and accumulation mechanism on insulator surface in air and heptafluorobutyronitrile/carbon dioxide (C(4)F(7)N/CO(2)) mixtures under AC voltage are studied via the means of surface potential measurement and inversion algorithm, combined with the improved method of controlling the truncated phase of AC voltage. The results show that under the needle–plate electrode structure, charge distribution on the insulator surface presents a three-tier concentric circle structure both in air and C(4)F(7)N/CO(2) gas mixtures, and the charge composition of the innermost circle is closely related to the truncated phase of AC voltage. Under the same amplitude of voltage, the range of charge distribution on insulator surface in C(4)F(7)N/CO(2) mixtures is smaller than that in air, with the negative charges domination. It is suggested that the characteristic of charge distribution in C(4)F(7)N/CO(2) mixtures is related to the larger electron attachment cross-section of C(4)F(7)N gas in a wide range of electron energy distribution.

Laser dissociation spectroscopy of I−·adenine (I−·A) and ·adenine (·A) has been utilised for the first time to explore how the anion identity impacts on the excited states. Despite strong photodepletion, ionic photofragmentation is weak for both clusters, revealing that they decay predominantly by electron detachment. The spectra of I−·A display a prominent dipole-bound excited state in the region of the detachment energy which relaxes to produce deprotonated adenine. In contrast, near-threshold photoexcitation of ·A does not access a dipole-bound state, but instead displays photofragmentation properties associated with ultrafast decay of an adenine-localised π→π* transition. Notably, the experimental electron detachment onset of ·A is around 4.7 eV, which is substantially lower than the expected detachment energy of an ion-dipole complex. The low value for ·A can be traced to initial ionisation of the adenine followed by significant geometric rearrangement on the neutral surface. We conclude that these dynamics quench access to a dipole-bound excited state for ·A and subsequent electron transfer. ·A represents an important new example of an ionic cluster where ionisation occurs from the neutral cluster component and where photodetachment initiates intra-molecular hydrogen atom transfer. [ABSTRACT FROM AUTHOR]

We report the results of an experimental study of electron ionization of large helium nanodroplets doped with formic acid (FA). Several homologous series of cluster anions are observed, including [FAn-H]−, undissociated FAn−, and these ions complexed with one or more H2O. Some major features resemble those observed upon sputtering of frozen FA films but they differ significantly from results obtained by electron attachment to bare FA clusters in the gas phase. The FAn− and (H2O)[FAn-H]− series show abrupt onsets above n = 2 and 5, respectively. A prominent resonance in the anion yield occurs at 22.5 eV due to the formation of an intermediate He−*. Also observed are homologous series of [FA-H]− or [FA2-H]− complexed with helium. The cation chemistry is dominated by the production of protonated formic acid clusters, [FAnH]+, but various other homologous cluster ion series are observed as well. [ABSTRACT FROM AUTHOR]

Abstract The role of the ionic wind effects on modifying flame dynamics was demonstrated by detailed computational models. Full three-dimensional simulations were conducted to reproduce and describe the response of a laminar premixed methane–air Bunsen flame subjected to a transverse DC electric field at saturation condition. The chemical kinetic mechanism employed a methane–air skeletal mechanism with an optimized ionization model to predict the positive and negative ions that are important for generating the electric currents. Given the strong dependence of the ionic wind on the amount of charged species created by chemi-ionization, the ion production rate was optimized to match the measured saturation current. The simulation successfully reproduced the flame tilt toward the cathode. The ionic winds blowing from the flame toward the electrodes in both rightward and leftward directions were also captured. The calculated flow field is qualitatively consistent with the PIV experimental data. Accurate description of the three-body electron attachment to oxygen and the charge transfer reactions generating heavy anions was found to be critical in simulating the flame–electric field interaction. This is a first demonstration of the ionic wind effect by full three-dimensional simulations. Further investigation by both experiment and modeling are required in future work to address quantitative differences. [ABSTRACT FROM AUTHOR]