Single-Capture Cross Sections from Biological Molecules and Noble Gases by Bare Ion Impact

Abstract

In this work, we report theoretical electron capture cross sections for single-electron removal from molecules of biological interest and noble gases by bare ion (H + and H e 2+) impact at energies ranging from 25 to 10,000 keV/amu. We use a distorted wave (DW) method where the intermediate continuum state of the active electron with the target ion has been taken into account. This method is developed within the framework of the independent electron model taking particular care of the representation of the bound continuum target states. Two different approximations have been considered for molecular targets: molecular representation of the bound-state target wavefunction and Bragg's additivity rule. The molecular orbital for targets are described within the framework of the complete neglect of differential overlap (CNDO) method based on the linear combination of atomic orbital (LCAO) approximation. Using the DW method, we have also calculated the K-, Land M-shell electron capture in collisions of bare ions with three noble gases He, Ne, and Ar respectively. Contributions from different molecular orbitals and different shells to the total cross sections (TCS) are studied. The preference of electron capture occurs in accordance as the binding energy of the active electron in molecular orbital and atomic shell. The maximum contributions to TCS for SC comes from the less bound electrons in repetitive orbitals, whereas the tightly bound electrons dominate the TCS at higher projectile energy regime. Variation of TCS with impact energy are compared with the available experimental observation and other theoretical findings. We find that the present theoretical method is satisfactory in both intermediate and high-energy region for molecules as well as noble gas targets to give reliable outcomes compared to other theoretical methods.

Electron capture and ionization cross-section calculations for proton collisions with methane and the DNA and RNA nucleobases

“…a similar impact energy dependence, at least down to E = 50 keV where the CDW-EIS calculation terminates. The cross-section curve from[20] extends further down to E = 25 keV and indicates an even stronger increase toward low energies than the present CNDO calculation, which significantly overestimates the measurements in this region. We note thatPurkait et al also reported IAM-AR calculations in their work which for p-CH 4 collisions are in close agreement with their CNDO results.…”

“…The details of the calculations show that at low impact energies the resonant capture from H(1s) dominates, while capture from the carbon AOs gains relative importance toward higher energies. The differences in the orbital-specific cross sections and those between the gross populations and occupation numbers listed in IAM-PCM, IAM-AR, and CNDO: present calculations, CDW-EIS-CNDO [7], DW-CNDO [20]; experiments: Rudd83 [21], Toburen68 [22], Sanders03: [23].…”

“…a similar impact energy dependence, at least down to E = 50 keV where the CDW-EIS calculation terminates. The cross-section curve from [20] extends further down to E = 25…”

“…also includes two previous CNDO calculations; the calculation by Quinto and coworkers[7] uses the CDW-EIS model and the one by Purkait et al[20] a different distortedwave (DW) approach to calculate the AO-specific cross section contributions. Both works yield somewhat smaller cross section values than the present CNDO calculation, but show Total cross section for net capture in p-CH 4 collisions as a function of impact energy.IAM-PCM, IAM-AR, and CNDO: present calculations, CDW-EIS-CNDO[7], DW-CNDO[20]; experiments: Rudd83[21], Toburen68[22], Sanders03:[23]. a similar impact energy dependence, at least down to E = 50 keV where the CDW-EIS calculation terminates.…”