Ionization and Electron Capture Cross Sections for Single-Electron Removal from Biological Molecules by Swift Ion

Abstract

We have studied ionization and electron capture cross sections for single-electron removal from biological molecules (adenine, cytosine, guanine, thymine, and uracil) by proton impact at energies ranging from 30 keV/amu to 10 MeV/amu. In this investigation, the three-body distorted wave method is used. The calculations are based on the independent electron model. For electron capture process, distortion in the final channel related to the Coulomb continuum states of the active electron and the projectile in the field of residual target ion is included. In case of ionization, we take all the pair-wise Coulomb interactions, which treat all interactions on equal footing in the final channel. Moreover, the asymptotic Coulomb logarithmic phase for the relative motion of two colliding nuclei is included in the initial channel. In both processes, the molecular character of the biological target is assumed to be a linear combination of their atomic orbitals (LCAO) and, for all cases, the different atomic orbitals are described with the Roothaan-Hartree-Fock (RHF) approximation. We have also calculated the total capture cross sections using simple Bragg’s additivity rule. For electron capture, the contributions to the TCS from the core orbitals of the molecule have also been explicitly analyzed. The double differential cross sections (DDCS) for electron emission as well as the total cross sections for single ionization of only uracil molecule with fast proton impact are also calculated. The results for capture and ionization cross sections are compared with other theoretical calculations and existing experimental data. We find that our calculated results are in quite better agreement with available experimental data than the other theoretical results.