binary-encounter-Bethe Research Articles

Electron impact ionization cross-sections for few-electron uranium ions

Electron impact ionization cross sections for the U88+, U89+, U90+ and U91+ ions were calculated with the relativistic binary encounter Bethe model (RBEB), the modified RBEB (MRBEB) and the new MRBEB corrected by the ionic factor (MRBR–IF). Our results were compared with the available three sets of experimental data and the most used theoretical results. The MRBEB–IF results are the ones that better agree with the experimental data of the four analysed ions.

Vanadium fine-structure K-shell electron impact ionization cross sections for fast-electron diagnostic in laser–solid experiments

The K-shell electron impact ionization (EII) cross section, along with the K-shell fluorescence yield, is one of the key atomic parameters for fast-electron diagnostic in laser–solid experiments through the K-shell emission cross section. In addition, in a campaign dedicated to the modeling of the K lines of astrophysical interest (Palmeri et al. (2012)), the K-shell fluorescence yields for the K-vacancy fine-structure atomic levels of all the vanadium isonuclear ions have been calculated.In this study, the K-shell EII cross sections connecting the ground and the metastable levels of the parent vanadium ions to the daughter ions K-vacancy levels considered in Palmeri et al. (2012) have been determined. The relativistic distorted-wave (DW) approximation implemented in the FAC atomic code has been used for the incident electron kinetic energies up to 20 times the K-shell threshold energies. Moreover, the resulting DW cross sections have been extrapolated at higher energies using the asymptotic behavior of the modified relativistic binary encounter Bethe model (MRBEB) of Guerra et al. (2012) with the density-effect correction proposed by Davies et al. (2013).

Binary-Encounter-Bethe ionisation cross sections for simulation of DNA damage by the direct effect of ionising radiation.

DNA damage is of crucial importance in the understanding of the effects of ionising radiation. To refine existing DNA damage models, an approach using the Binary-Encounter-Bethe (BEB) cross sections was developed. The differential cross sections for ionisation of the molecular orbitals of the DNA bases, sugars and phosphates are calculated using the electron binding energy, the mean kinetic energy and the occupancy number of each orbital as parameters. The resulting cross section has an analytic form which is quite convenient to use for Monte-Carlo codes that randomly sample the energy loss occurring during an ionisation event. We also describe an algorithm to simulate the interactions of electrons with DNA in the radiation transport code RITRACKS using the integrated BEB cross section for the bases, sugar and phosphates.

Electron-impact study of SiN using the R-matrix method

We have carried out a comprehensive study of electron-impact on an open-shell SiN molecule by using the R-matrix method. Elastic (integrated and differential), momentum-transfer, excitation and ionization cross sections, along with efffective collision frequencies over a wide electron temperature range (100–100 000 K) have been presented. The target states are represented by including correlations via a configuration interaction formalism. The results of the static-exchange, one-state and 28-state close-coupling approximation are presented. Our study has detected a shape resonance, two core-excited and three Feshbach resonances in the 28-state model. All calculations are done in C 2v point group. We detect a stable bound state of SiN− of 1 A 1 symmetry having configuration ...7σ 2, 1π 4,2π 4 with a Vertical Electronic Affinity value of 2.86 eV which is in good agreement with the experimental (adiabatic) value of 2.949 ± 0.008 eV. The ionization cross sections are calculated using the Binary-Encounter-Bethe (BEB) Model in which molecular orbitals at self-consistent Hartree-Fock (HF) level are used to calculate kinetic and binding energies of the occupied molecular orbitals. For scattering calculations we have used partial waves up to l = 4 to represent continuum electron in our R-matrix approach. A Born top-up procedure is invoked for dipole-allowed transitions to account for the contribution of partial waves higher than l = 4 to obtain converged cross-sections.

Absolute cross sections for dissociative electron attachment to HCCCN

New absolute cross sections for dissociative electron attachment to HCCCN (cyanoacetylene or propiolonitrile) in the range of 0–10 eV electron energy are presented here, which have been determined from a new analysis of previously reported data (Graupner et al 2006 New J. Phys. 8 117). The highest cross sections are observed for the formation of CN− at 5.3 eV and CCCN− at 5.1 eV; approximately 0.06 Å2 and 0.05 Å2 respectively. As part of the re-analysis, it was necessary to determine absolute cross sections for electron-impact ionization of HCCCN with the binary-encounter Bethe method. These electron-impact ionization absolute cross sections for HCCCN are also presented here; the maximum value was found to be ∼6.6 Å2 at ∼80 eV.

Electron-impact total cross sections for inelastic processes for furan, tetrahydrofuran and 2,5-dimethylfuran

We report total inelastic, total ionisation and summed total excitation cross sections for electron scattering on furan, tetrahydrofuran (THF) and 2,5-dimethylfuran at energies between the ionisation threshold and 5 keV. We have employed the spherical complex optical potential formalism (SCOP) to calculate the total inelastic cross sections (Qinel) and have used complex scattering potential-ionisation contribution (CSP-ic) method to derive total ionisation cross sections (Qion) and summed total excitation cross sections (∑Qexc) from the calculated Qinel. We have also computed Qion for these molecules using binary-encounter-Bethe (BEB) approach. We have compared our total cross sections (TCS) with available experimental as well as previous theoretical results and have found good agreement. The results are presented graphically as well as numerically.

Electron-impact total cross sections for phosphorous triflouride

Various total cross sections for scattering of electrons by phosphorous triflouride (${\mathrm{PF}}_{3}$) using the $R$-matrix method for incident energies from 0.1$--$15 eV and using spherical complex optical potential formalism beyond ionization threshold of target to 5000 eV are reported. We performed close-coupling calculations using static exchange plus polarization model. We employed different target models in order to study their relative dependence on the total cross sections. Three important structures are revealed in the total-cross-section curve: one that corresponds to the Ramsauer-Townsend minimum at 0.33 eV, the second is a strong maximum of 100 \AA{}${}^{2}$ at 1 eV, the third is around 11 eV corresponding to negative ion formation as predicted by earlier study. The total ionization cross sections are computed using the complex scattering potential ionization contribution method and the binary encounter Bethe method. The electronic-excitation cross sections, momentum-transfer cross sections, and differential and ionization cross sections are our maiden efforts for this system. We have compared our total-cross-section results with available theoretical and experimental results.

Determination of subshell-resolvedL-shell-ionization cross sections of gold induced by 15–40-keV electrons

The $L$-subshell specific electron impact ionization cross sections, near the ionization threshold ($15<E<40$ keV) of gold are calculated from the measured production cross sections in this collaborative work between an experimental and a theoretical group. Calculations are performed using the distorted wave Born approximation formalism, and the modified relativistic binary encounter Bethe model to understand the data. The observed agreements and discrepancies between the two theoretical formalisms considered and the experimental data are reported.

Total ionization cross-sections for Si2, SiC, SiC2 and Si2C molecules

Total ionization cross-sections for Si2, SiC, SiC2 and Si2C molecules have been calculated by applying modified Binary Encounter Bethe (BEB) model by electron impact. The cross-sections are calculated in the energy range from ionization threshold to 2 keV. No measurements are available in the literature to the best of my knowledge for comparison. From theoretical side, very recently Spherical complex optical potential formalism has been employed for obtaining the total ionization cross sections for these molecules. The present results are compared with the available theoretical data.

Total ionization cross-sections for fluoro acetylene molecule

Total ionization cross-sections for Fluoro acetylene molecule is calculated by applying Binary Encounter Bethe (BEB) model by electron impact. The cross-sections are calculated in the energy range from ionization threshold to 2 keV. No experimental or theoretical work is reported in the literature to the best of my knowledge for comparison. Present work is a maiden attempt to find electron impact ionization cross section.

Electron-impact-ionization dynamics of five C2to C4perfluorocarbons

Perfluorocarbons (PFCs) are man-made compounds whose ion physics exhibit complex interplays between statistical and nonstatistical fragmentation and intramolecular rearrangement processes. One probe of such processes is the energy-dependent electron-impact-ionization cross section. Partial electron-impact-ionization cross sections are reported for the fragments arising from five C${}_{2}$ to C${}_{4}$ PFCs, namely, C${}_{2}$F${}_{6}$, C${}_{3}$F${}_{8}$, C${}_{3}$F${}_{6}$, CF${}_{2}$=CF-CF=CF${}_{2}$, and CF${}_{3}$-C\ensuremath{\equiv}C-CF${}_{3}$, over the energy range from threshold to \ensuremath{\sim}210 eV. Care was taken to maximize ion collection efficiency and to minimize discrimination against ions produced with high kinetic-energy release, and the measured cross sections have been calibrated using independent absolute total (gross) ionization efficiency curves measured previously in the same laboratory with an instrument that was designed to essentially have unit detection efficiency. Total ionization cross sections have also been modeled using the binary-encounter Bethe model, and the shortcomings of the model when applied to perfluorinated compounds are discussed. Analysis of the mass spectral fragmentation patterns in combination with ab initio energetics suggests that nonstatistical dissociative ionization processes play a significant role in the fragmentation dynamics of saturated PFCs. In contrast, unsaturated PFCs exhibit long-lived parent ions, which tend to undergo a higher degree of statistical dissociation following ionization, involving considerable intramolecular rearrangement.

Electron impact ionization cross sections of several ionization stages of Kr, Ar and Fe

Direct electron impact ionization cross sections for all ionization stages of Kr were calculated with the modified relativistic binary encounter Bethe model (MRBEB), and excitation–autoionization cross sections were evaluated using the first order many body theory (FOMBT) for Kr+, Kr5+, Kr6+, Kr10+, Kr15+ and Kr17+. Our results were compared to configuration-averaged distorted-wave (CADW) calculations, the widely used Lotz formula, and available experimental results. Comparison between direct ionization cross sections for the Ar and Fe isonuclear series was also done with the goal of assessing the versatility of the MRBEB model.

Electron impact ionization cross sections of beryllium and beryllium hydrides

We report calculated electron impact ionization cross sections (EICSs) for beryllium (Be) and some of its hydrides from the ionization threshold to 1 keV using the Deutsch-Mark (DM) and the Binary-Encounter-Bethe (BEB) formalisms. The positions of the maxima of the DM and BEB cross sections are very close in each case while the DM cross section values at the maxima are consistently higher. Our calculations for Be are in qualitative agreement with results from earlier calculations (convergent close-coupling, R matrix, distorted-wave and plane-wave Born approximation) in the low energy region. For the various beryllium hydrides, we know of no other available data. The maximum cross section values for the various compounds range from 4.0 × 10−16 to 9.4 × 10−16 cm2 at energies of 44 to 56 eV for the DM cross sections and 3.0 × 10−16 to 5.4 × 10−16 cm2 at energies of 40.5 to 60 eV for the BEB cross sections.

Total Ionization Cross Sections of $NO_2$, $CO$ and $CS$ Molecules Due to Electron Impact

The total cross sections for NO2, CO and CS have been calculated by Binary- Encounter-Bethe (BEB) method of Khare from threshold energy to 10 MeV due to elec- tron impact. This model has been developed by combining the useful features of Plane Wave Born Approximation (PWBA) and BEB model of Kim. It is shown that Bethe and Mott cross section terms differ from those of the Kim (BEB) method but their sums are very close to other. Results are presented with the help of graphs. Adequate com- parisons of collisional parameter have been made with other available experimental values. The calculated cross-sections are compared extensively with a number of all possible experimental data and theoretical results. PACS: 34.80 Gs

Hybrid Vlasov–Fokker–Planck–Maxwell simulations of fast electron transport and the time dependance of K-shell excitation in a mid-Z metallic target

Using a hybrid Vlasov–Fokker–Planck–Maxwell code coupled to calculations using a modified relativistic binary-encounter Bethe model of ionizing collisions we study the time and space dependence of Kα photon generation by a fast electron beam injected into a solid density copper plasma target. The electron beam is chosen to be representative of that expected to be generated by a picosecond duration, ∼1019 W cm−2 intensity laser. Kα photons are produced as electrons reflux laterally across the target and are slowed and thermalized by collisions with, and Ohmic heating of, the background fluid over a ∼10 ps timescale, which dictates the timescale for Kα emission. The results show reasonable agreement with recent experimental results in terms of both the yield and time dependance. We show how lateral expansion of the electrons can be imaged in the Kα radiation.

Electron-Impact study of S2 molecule using the R-Matrix method

We have employed the R-matrix method [1] to compute elastic (integrated and differential cross section DCS), momentum-transfer and excitation and ionization cross sections for electron impact on S2 molecule. We have calculated DCS, in correlated one-state model, by using the POLYDCS program of Sanna and Gianturco [2]. The data of momentum-transfer cross section, generated from DCS, is used to compute effective collision frequencies [3] over a wide electron temperature range (200-30000 K). The ionization cross sections are calculated in the binary-encounter Bethe (BEB) model [4] and compared with [5, 6].

New expression for the K-shell ionization

A new expression for the total K-shell ionization cross section by electron impact based on the relativistic extension of the binary encounter Bethe (RBEB) model, valid from ionization threshold up to relativistic energies, is proposed. The new MRBEB expression is used to calculate the K-shell ionization cross sections by electron impact for the selenium atom. Comparison with all, to our knowledge, available experimental data shows good agreement.

Electron-impact study of the B2molecule using theR-matrix method

The results of ab initio scattering calculations for low-energy electron collisions with the B${}_{2}$ molecule using the $R$-matrix method have been presented. The differential and momentum-transfer cross sections along with effective collision frequency over a wide electron temperature range (300--30 000 K) are computed at the one-state close-coupling level. In this work, 61-state close-coupling calculations are performed to compute the integral cross sections (elastic and excitations). We investigated five resonances: two in the excitation cross sections of $A{\phantom{\rule{0.16em}{0ex}}}^{3}\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\Pi}}_{u}$, two in the excitation cross sections of $a{\phantom{\rule{0.16em}{0ex}}}^{5}\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\Sigma}}_{u}^{\ensuremath{-}}$ and one in both $b{\phantom{\rule{0.16em}{0ex}}}^{1}\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\Delta}}_{g}$ and $c{\phantom{\rule{0.16em}{0ex}}}^{1}\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\Sigma}}_{g}^{+}$ excited states. The Born correction for the dipole-allowed transition ($X{\phantom{\rule{0.16em}{0ex}}}^{3}\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\Sigma}}_{g}^{\ensuremath{-}}$ to $A{\phantom{\rule{0.16em}{0ex}}}^{3}\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\Pi}}_{u}$) has been carried out to account for the contribution of partial waves higher than the $g$ wave ($l=4$) up to which the $R$-matrix scattering calculations are carried. We have detected a stable anionic bound state ${}^{2}\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\Pi}}_{u}$ of B${}_{2}^{\ensuremath{-}}$ having the configuration $1{\ensuremath{\sigma}}_{g}^{2}$ $2{\ensuremath{\sigma}}_{g}^{2}$ $1{\ensuremath{\sigma}}_{u}^{2}$ $2{\ensuremath{\sigma}}_{u}^{2}$ $1{\ensuremath{\pi}}_{u}^{3}$. The ionization cross sections are calculated in the binary-encounter Bethe model in which Hartree-Fock molecular orbitals at a self-consistent level are used to calculate kinetic and binding energies of the occupied molecular orbitals. We have also evaluated scattering length for electron-B${}_{2}$ collisions at the one-state close-coupling level (6.8${a}_{0}$) and at the static exchange plus polarization level (6.2${a}_{0}$).

Electron ionization of exotic molecular targets CN, C2N2, HCN, HNC and BF—Theoretical cross sections

Total ionization cross sections Qion of the electron impact on exotic but lesser known targets CN, C2N2, HCN, HNC and BF have been calculated at incident energies Ei from ionization threshold (IE) to 2keV, by employing the Complex potential ionization contribution (CSP-ic) method. Since most of the present results are new, comparable theoretical data are obtained by Additivity Rules and by generating the BEB (Binary Encounter Bethe) values through the Quantemol-N package. A good accord is found among the present and the other results, except in BF. Our ionization cross sections on HCN, HNC and BF are also compared with the available data on iso-electronic 14-electron systems N2, CO and C2H2. Moreover in e−–HCN scattering, the relative contributions of various allowed scattering channels are analyzed at the energy of the peak of ionization (70eV) and presented here as a bar chart. The present work is relevant due to importance in mass spectrometry and in planetary environments.

Cross section calculations for electron impact ionization and elastic scattering from cisplatin

Total cross section for single electron-impact ionization of cisplatin (H6N2Cl2Pt) molecule has been calculated with the binary-encounter-Bethe (BEB) model from the ionization threshold up to 5 keV. To obtain input data for the BEB calculations, geometric and electronic structures of the cisplatin have been studied with quantum chemical methods. Elastic cross section for electron collisions with cisplatin have also been evaluated using independent atom method with static-polarization model potential for incident energies ranging from 50 to 3000 eV. The obtained geometric structure of cisplatin is compared with available experimental and theoretical data. Calculated cross sections have been compared with related cross sections for selected purine and pirimidine bases.