Low-energy Electron Impact Research Articles

R-matrix study for electron scattering of beryllium dihydride for fusion plasma

We report the integral elastic, differential, momentum transfer, dissociative electron attachment and electronic- and rotational excitation cross sections for low-energy electron impact on beryllium dihydride computed using the Quantemol-N interface for driving the UK molecular R-matrix code. The energy of the projectile electron is in the range 0.1–10 eV. The effect of multichannel coupling is investigated by calculating the cross sections with various target models by increasing the number of target states in the trial wave function of the entire scattering system. The cross sections converge for the calculation with more than 15-target states. The vertical excitation energies calculated with the present model give excellent agreement with the EOM-CCSD calculations. Collisional frequencies are determined using the momentum transfer cross section for a Maxwell–Boltzmann distribution. From the collisional frequency, the transport properties such as mean free path, diffusivity and mobility are calculated for the temperature range of 100 to 500 000 K. The cross section data and transport properties reported in this article are important for fusion plasma.

Low energy electron and positron impact differential cross sections for the ionization of water molecules in the coplanar and perpendicular kinematics.

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.

An ab initio investigation for elastic and electronically inelastic electron scattering from para-benzoquinone.

We report the results of ab initio calculations for elastic scattering and also for excitation of individual electronic states of para-benzoquinone (pBQ) by the impact of low-energy electrons. The calculations for elastic scattering were performed with the Schwinger multichannel method implemented with pseudopotentials (SMCPP) in the static-exchange (SE) plus polarization (SEP) approximation for energies up to 50 eV. The assignments for the resonance spectrum obtained in this study are, in general, in good agreement with previous results available in the literature. For electronic excitation by electron impact, the SMCPP method with N energetically open electronic states (N open ), at either the static-exchange (N open ch-SE) or the static-exchange-plus-polarisation (N open ch-SEP) approximation, was employed to calculate the scattering amplitudes using a channel coupling scheme that ranges from the 1ch-SEP up to the 89ch-SE level of approximation, depending on the energy of interest. Integral cross sections (ICSs) and differential cross sections (DCSs) were obtained for incident electron energies lying between 15 eV and 50 eV. The study focuses on the influence of multichannel coupling effects for electronically inelastic processes, more specifically, on how the number of excited states included in the open-channel space impacts upon the convergence of the cross sections at intermediate and higher energies. In particular, we found that the magnitude of DCS and ICS results for electronic excitation decreases as more channels are included in the calculations. To the best of our knowledge, there are no other experimental or theoretical ICS or DCS results for excitation into individual electronic states of pBQ available in the literature between 15 and 50 eV against which we might compare the present calculations.

Time-delayed mass spectrometry of the low-energy electron impact with a liquid beam surface.

We set up an experimental apparatus to investigate the low-energy electron impact with a liquid beam surface, in which a cylindrical liquid beam with a diameter of 25 μm emits as the laminar flow from a microjet and the positively charged ions produced by the electron-impact ionizations are detected with a linear time-of-flight mass spectrometer. We propose a time-delayed mass spectrometry for this apparatus to identify the cationic fragments produced on the liquid surface, in which the application of the ion extracting pulse is delayed with different time intervals after the electron beam pulse. Sensitivity and specificity of the present methodology are demonstrated by the combinational experiments of the gas-phase and liquid ethanol. In comparison with the gas-phase experiments, the ion peaks become much broader in the mass spectra of the liquid beam, primarily due to the molecular evaporation and diffusion. After delaying with about 2 μs, we find that the hydrocarbon ions are ultimately the predominant products in the mass spectra of the liquid ethanol and they are proposed to be produced on the liquid surface. Above observations are in line with the widely accepted picture of the molecular orientation on the liquid surface; namely, the ethanol's CH3-CH2- group on the liquid surface prefers to be oriented outside. Therefore, we demonstrate a new mass spectrometry to explore the molecular structures of the liquid surface.

Formation of CO2 from formic acid through catalytic electron channel.

Low energy electrons can initiate and control chemical reactions through resonant attachment forming an electron-molecule compound state. Recently, it has been theoretically shown that free electrons can also act as catalysts in chemical reactions. We investigate this novel concept for the case of conversion of formic acid into CO2. Resonant production of CO2 from cold formic acid films by low energy electron impact is observed using Fourier transform infrared spectroscopy. The resonant peak observed at 6 eV is identified as the catalytic electron channel. The experimental results are augmented with the ab initio quantum chemical calculations.

On the influence of low-energy ionizing radiation on the amino acid molecule: Valine case

New data on the valine molecule (C5H11NO2) fragmentation under the low-energy electron-impact are presented. These data are related to the formation of ionized products due to the ionizing radiation influence on the above amino acid molecule. A series of the fragments produced are identified by applying an extensive DFT-theory approach. The results obtained allowed the principal pathways of the valine molecule fragmentation to be found. The absolute appearance energies of some fragments are both measured experimentally and calculated theoretically. The experimental and theoretical data are compared and analysed.

Dissociation of dicyclohexyl phthalate molecule induced by low-energy electron impact.

Experimental investigation of electron ionization (EI) of and electron attachment (EA) onto dicyclohexyl phthalate (DCHP) was carried out using a crossed electron and molecular beam technique. Formation of positive and negative ions by EI and EA with the corresponding dissociation processes was studied and discussed. Due to a low ion yield of the parent positive ion, we were not able to estimate the ionization energy of DCHP. However, we estimated the appearance energies for the protonated phthalate anhydride (m/z 149) to be 10.5 eV and other significant ionic fragments of m/z 249 [DCHP-(R-2H)]+, m/z 167 [DCHP-(2R-3H)]+, and m/z 83 [C6H11]+. The reaction mechanisms of the dissociative ionization process were discussed. In the case of negative ions, we estimated the relative cross sections for a transient negative ion (TNI) and for several detected ions. At low electron energies (close to 0 eV), the TNI of DCHP molecules was the dominant ion, with products of dissociative EA dominating in broad resonances at 7.5 and 8.5 eV.

低エネルギー電子－分子衝突過程における電子・解離イオン同時計数実験

低エネルギー電子－分子衝突過程における電子・解離イオン同時計数実験

Hydrogen rearrangements in the fragmentation of anthracene by low-energy electron impact

We have measured mass spectra for positive ions produced by low-energy electron impact on anthracene using a reflectron time-of-flight mass spectrometer. The electron impact energy has been varied from 0 to 100 eV in steps of 0.5 eV. Ion yield curves of most of the fragment ions have been determined by fitting groups of adjacent peaks in the mass spectra with sequences of normalized Gaussians. Appearance energies for all these ions have been determined, and we report the first direct measurement of the triple ionization energy of anthracene at 45.5 +/- 0.5 eV. The groups of fragments containing 8-13 carbon atoms provide evidence for hydrogen rearrangements during the fragmentation, involving retention or loss of one or two additional hydrogen atoms. Groups of fragments with 6 and 7 carbon atoms clearly show the presence of doubly-charged fragments. The smaller fragments with 1-4 carbon atoms all show broadened peaks, and these fragments may be partly or mostly due to energetic charge-separation fragmentations of doubly-charged anthracene.

Differential cross sections for excitation of H2 by low-energy electron impact

Experimental and theoretical differential cross sections (DCS) for the electron-impact excitation of molecular hydrogen to the , , , , and the states are presented at incident energies near to threshold. The experimental DCSs were taken at incident energies of 14, 15, 16 and 17.5 eV and for scattering angles from 10° to 130°. The theoretical DCSs are from the convergent close-coupling method which has recently successfully modeled differential electron scattering from H2 when compared with available experiment at energies of 17.5 eV and above.

Low-energy electron impact cross-sections and rate constants of $$\hbox {NH}_2$$ NH 2

This systematic study reports various electron impact cross-sections, rate constants and transport properties of $$\hbox {NH}_2$$ radical in the low-energy limit. The collision study is based on R-matrix formalism and involves the use of various scattering models employing different active spaces. Both electron excited inelastic cross-sections and resonances are found influenced by correlation and polarization effects. The non-relativistic molecular bremsstrahlung radiation cross-section for soft photons, binary encounter Bethe model-based ionization cross-sections and a few molecular properties of the target radical are also reported. The present calculations are found to be in agreement with the available results. This theoretical study provides a pathway to understand collision dynamics and generates data required in various fields of applied physics.

Cross sections for electron collision with fluoroacetylene: A comparative study with acetylene and difluoroacetylene along with fluorination

Low energy electron impact cross sections of fluoroacetylene (HCCF) are investigated using the R-matrix method. The best target model, which gave good target properties in comparison with literature values, is used for the final scattering calculation. The fluorination effect on the various elastic, momentum transfer, differential, excitation and ionization cross section is studied by comparing the present results with the recent theoretical results of difluoroacetylene (FCCF) and acetylene (HCCH). This is the first reported detailed investigation of cross sections for HCCF along with the fluorination effect.

Positive ion mass spectrometry for fragmentation of anthracene by low energy electron impact

SynopsisWe have studied the fragmentation of anthracene molecules induced by low energy electron impact. A reflectron time-of-flight mass spectrometer has been used to mass resolve and detect positively charged fragments. Using computer controlled data acquisition, mass spectra have been measured as a function of electron impact from 5 to 100 eV. The mass spectra show clear indications of double and triple ionization. Ion yield curves and appearance energies for most of the positive ions have been extracted from the data.

Positive ion mass spectrometry for fragmentation of 5-fluorouracil by low energy electron impact

SynopsisFragmentation of 5-fluorouracil in the gas phase has been studied using low energy electron impact. Positive ions have been mass resolved and detected using a reflectron time-of-flight mass spectrometer. Mass spectra have been measured as a function of electron impact from 5 to 100 eV, and ion yield curves and appearance energies for most of the positively charged fragments have been extracted.

Measurements of Lα, Lβ, Lγ and M X-ray production cross sections of Os, Ir and Pt by low-energy electron impact: Comparisons of experiment with theory

Experimental determinations of Lα, Lβ, Lγ and M X-ray production cross sections and their ratios for Os (Z=76), Ir (Z=77) and Pt (Z=78) by electron impact at incident energies of 6–30keV are presented. Thin films of the studied elements deposited on thick carbon substrates were employed as targets in the experiments. Enhancements in L- and M-shell characteristic X-ray production due to electron-scattering effects in the double-layer structure target were corrected by means of Monte Carlo simulations. Comparisons were made between the measured Lα, Lβ, Lγ and M X-ray production cross sections and their ratios with the DWBA and PWBA-C-Ex theories and with other experimental data in the literature. In the case of L-subshells, the measured data of Os and Pt agree well with the theoretical values within the experimental uncertainties, but appreciable discrepancies between the experiment and theory exist for Ir; in the case of the M-shell, measured data for Ir show good agreement with theoretical values within the experimental uncertainties, but the measured results are somewhat lower than the theoretical values for Os and Pt. Finally, possible factors that could affect the comparisons between experiment and theory on cross-section ratios are discussed.

A theoretical study on collision mechanisms for low energy electron impact ionization of helium in the perpendicular geometry

Under the condition of ten different incident energies ranging from 3 eV to 80 eV above the ionization potential of helium and the outgoing electrons having equal energies, by making use of 3C model and modified 3C model, the triple differential cross sections of electron-impact single ionization of the ground state of helium in the perpendicular geometry are calculated. The result is compared with corresponding experimental result to systematically investigate the influences of various screening effects on the triple differential cross sections for helium. The collision mechanisms of the triple differential cross sections are explored. The result shows that the effects of dynamic screening in the final state can directly affect the structures of the triple differential cross sections at lower incident energy, which will unavoidably affect the angular distribution and relative amplitude of side peaks at angles =90 and =270. The screening effects of residual electron in the final state of He+ have a similar significant effect on the amplitude of triple differential cross section of helium and angular distributions and relative amplitudes of side peaks at angles =90 and =270. When the incident energy is over 84.6 eV, the screening effect of residual electron in the final state of He+ has a slight effect on the amplitude of triple differential cross section, which can be overlooked. But the effects of dynamic screening in the final state on side peaks at angles =90 and =270 need considering. In addition, by taking advantage of DS3C-Z model, the results of collision mechanism of various peaks at angles =180, =90 and =270 show that the middle peak at angle =180 is produced by a process called triple scattering mechanism and then the side peaks at angles =90 and =270 are produced by a process called double scattering mechanism. Such a collision mechanism has a direct influence on the generation and variation law of triple differential cross sections.

Excitation of the lowest electronic transitions in ethanol by low-energy electrons

We report absolute differential and integral cross sections for electronic excitation of ethanol, by low-energy electron impact. Cross sections for low-lying excited states were measured at incident electron energies from 9 to 20 eV and at scattering angles from through . Our results include cross sections for excitation of the and states as well as for the + and + cross section sums. Corresponding calculations were also performed using the Schwinger multichannel method, within an 11-channel close-coupling scheme.

Triple differential cross section for the near threshold single ionization of helium atoms for equal energy sharing

Low energy electron impact single ionization triple differential cross section (TDCS) results are reported for the helium atoms in the threshold regime at 1eV, 3eV and 5eV excess energy. TDCSs are calculated in the doubly symmetric kinematics for the coplanar to perpendicular emission of electrons. Present attempt to calculate TDCS in the second Born approximation and treating target polarization and post collision interaction is helpful to analyze the available measurements. The second order processes, target polarization and post collision interaction (PCI) have been found to be significant in describing the trends of TDCS and helpful to produce reasonably good agreement with measurements.

Investigations of L-shell x-ray production cross sections of In and Sn by low-energy electron impact

Results from the measurements of absolute L-shell x-ray production cross sections of In (Z = 49) and Sn (Z = 50) by the impact of electrons with energies in the range of 6–28 keV are presented. The experimental setup has been improved and thin films with thick aluminum substrates were used as targets in the experiments. The effect of directional and energy spreads of the incident electron beam within the films and the characteristic x-ray enhancement due to backscattered electrons and bremsstrahlung photons generated from the substrates were corrected by means of Monte Carlo simulations. The experimental results of In and Sn elements by electron and positron impacts were compared with the DWBA and PWBA-C-Ex theories. It was shown that the L-shell x-ray production cross sections of In and Sn elements by electron impact measured in this paper were in good agreement with the theoretical predictions within the uncertainties and that the discrepancies existed between the experimental results by positron impact, available in the literature, and the theoretical values. The influence of the atomic relaxation parameters (fluorescence yields and Coster–Kronig coefficients) has also been discussed.

Measurements of L-shell X-ray production cross-sections of Ag and Sb by low-energy electron impact

Abstract The total L-shell X-ray production cross-sections of Ag and Sb elements were measured by detecting the characteristic X-rays induced by the electron impact in the energy range of 6–28 keV. In this experiment, the thin films with thick aluminum substrates were used as the targets, and the experimental setup was improved. The influence of multiple scattering of electrons penetrating the targets films, electrons reflected from the thick aluminum substrates and bremsstrahlung photons produced when incident electrons impacted the targets were corrected by using the Monte Carlo method. The experimental results determined in this paper were compared with some theoretical models and other available experimental data in the literature. It was shown that the L-shell X-ray production cross-sections of Ag and Sb elements measured in this paper were in good agreement with the theoretical predictions within the uncertainties.