Chetan Limbachiya

Calculations of elastic, ionization and total cross sections for inert gases upon electron impact: threshold to 2 keV

In this paper we report comprehensive calculations of total elastic (Qel), total ionization (Qion) and total (complete) cross sections (QT) for the impact of electrons on inert gases (He, Ne, Ar, Kr and Xe) at energies from about threshold to 2000 eV. We have employed the spherical complex optical potential (SCOP) formalism to evaluate Qel and QT and used the complex spherical potential-ionization contribution (CSP-ic) method to derive Qion. The dependence of QT on polarizability and incident energy is presented for these targets through an analytical formula. Mutual comparison of various cross sections is provided to show their relative contribution to the total cross sections QT. Comparison of QT for all these targets is carried out to present a general theoretical picture of collision processes. The present calculations also provide information, hitherto sparse, on the excitation processes of these atomic targets. These results are compared with available experimental and other theoretical data and overall good agreement is observed.

Screening-corrected electron impact total and ionization cross sections for boron trifluoride (BF3) and boron trichloride (BCl3)

In this paper, we report modified calculations for total elastic, total ionization and total (complete) cross sections for boron trifluoride (BF3) and boron trichloride (BCl3) upon electron impact at energies from around threshold to 2000 eV. We have proposed a model which allows screening correction due to the overlapping of atoms as seen by incident electrons in a complex molecule. We have employed the well-known spherical complex optical potential (SCOP) formalism to evaluate total elastic and total inelastic cross sections and hence total (complete) cross sections. The ionization cross sections were derived using the complex optical potential–ionization contribution (CSP-ic) method developed by us. The present results are compared with available experimental and other theoretical data wherever available and overall good agreement is observed. The present screening-corrected model shows improvement over the previous method especially at low energies. We also predict total elastic cross sections for these targets using this method.

Electron impact total cross section calculations for CH3SH (methanethiol) from threshold to 5 keV

We report calculated total elastic cross sections Qel, total ionisation cross sections, Qion, summed total excitation cross sections ∑Qexc and total cross sections QT for CH3SH upon electron impact for energies from ionisation threshold to 5 keV. We have employed Spherical Complex Optical Potential (SCOP) formalism to calculate total elastic cross section Qel, and total inelastic cross section Qinel and used Complex Scattering Potential – the ionisation contribution (CSP-ic) method to extract the ionisation cross sections, Qion, from the calculated Qinel. The calculated total cross sections are examined as functions of incident electron energy and are compared with available data wherever possible and overall good agreement is observed. In this work Qel, Qion, and ∑Qexc are reported for the first time for CH3SH in this energy range.

Ionization and excitation of some atomic targets and metal oxides by electron impact

We have calculated total inelastic and total ionization cross-sections for collisions of electrons on atomic targets oxygen (O), aluminium (Al) and copper (Cu) and metal oxides AlO and Al2O, at impact energies from near excitation threshold to 2000 eV. A complex (optical) energy-dependent interaction potential is used to derive total inelastic cross-sections resulting from ionization as well as excitation processes. The inelastic cross-sections are bifurcated into discrete and continuum contributions and total ionization cross-sections have been deduced therefrom. Our calculation also provides information, hitherto sparse, on the excitation processes in the atomic targets O, Al, Cu and metal oxides AlO, Al2O. Adequate comparisons are made with other theoretical and experimental data.

Electron impact ionization of H2O molecule in crystalline ice

Abstract The present work focuses on electron impact scattering in crystalline ice, which is an exotic solid. The major difference between crystalline form and amorphous form lies in its structure. Here we consider the H2O molecule to possess properties consistent with the ice structure. Our basic calculation rests on the complex optical potential for the e-molecule system, with the molecular charge density as an input. To examine a single scattering event in condensed phases, we build up a model scattering potential to determine total inelastic cross-section Qinel. Finally an estimate of the total ionization cross-section, Qion for H2O (free), H2O (amorphous) and H2O (ice) in the energy range from threshold to 2000 eV, is obtained through semi-empirical arguments.

Electron impact total and ionization cross-sections for DNA based compounds

This paper reports computational results of the total (complete) and total ionization cross- sections, for electron impact on Uracil (C4H4N2O2) and PO3OH for impact energies from the ionization threshold to 2 keV. The total cross-section is evaluated using quantum mechanical approach using Spherical Complex Optical Potential (SCOP) presented as sum of the elastic and inelastic cross-sections. The ionization cross-sections are extracted from total inelastic cross-section using Complex Optical Potential–ionization contribution (CSP-ic) method. The present results are, in general, found to be in good agreement with previous theoretical results. In absence of any theoretical or experimental data, present results for PO3OH will serve to fill the void in the data base and may also inspire the experimentalists for some measurements as it is very important target.

Electron impact ionization of water molecules in ice and liquid phases

Electron scattering processes in ice or water are known to occur in natural as well as man-made systems. But the processes are difficult to investigate in theory or in laboratory. We present our calculations on total ionization cross section (Qion) for collisions of electrons with H2O molecules in condensed matter (ice and liquid) forms, at impact energies from ionization threshold to 1000 eV, extendable to about 1 MeV. Our theoretical method determines the total inelastic cross section (Qinel) of electron impact on H2O (ice), by starting with the complex scattering potential partial wave formalism. Reasonable approximations are invoked to project out the ionization cross section of H2O molecule in ice (or liquid) form by using the Qinel as an input. Properties of the condensed phase H2O are incorporated together with bulk screening effects in the scattering echanism. Due to medium effects, the present Qion are found to be lower than the corresponding values for H2O in free or gaseous state. Macroscopic cross sections and electron mean free paths for the bulk medium are also calculated. This study has potential applications in radiation biology as well as chemistry and in planetary science and astrophysics.

Total cross-section calculations for electrons colliding with molecular nitrogen over an extensive energy range from meV to keV

We report a comprehensive study of the electron impact total cross-sections for molecular nitrogen for impact energies from 0.01 eV to 2000 eV. Ab initio calculations are performed using the R-matrix formalism at low impact energies (up to ∼15 eV), while the Spherical Complex Optical Potential formalism is utilised beyond this range. The two methods are consistent at the transition energy, which enables us to provide data for such an extensive range. The results obtained show overall good agreement with the available data.

Electron impact total cross sections for simple biomolecules (HCOOH and H2CO) over a wide energy range (meV to keV)

We present here total cross sections obtained as sum of elastic and electronic excitation cross sections below ionization threshold of the target and sum of elastic and inelastic cross sections above ionization threshold molecule. We employ two different codes, R matrix code through Quantemol N for low energies and Spherical Complex Optical Potential for intermediate and high energies.

Probing total cross sections for electron impact studies from meV to keV for H2S and PH3

In this paper we have computed total cross sections for H2S and PH3 using two different molecular codes, Quantemol N for low energy calculations and Spherical Complex Optical Potential for intermediate and high energies. The results are found to be in overall good agreement with available theoretical and experimental results.