Electron-capture cross sections in collisions of ${\mathrm{He}}^{+}$ with several molecules

Abstract

Single-electron capture in ground state from several biologically relevant molecules by ${\mathrm{He}}^{+}$ has been studied theoretically by a three-body version of the distorted-wave (DW) approximation both in prior and post forms in the energy range from 60 to 8000 keV. Due to multi-electron targets, this approximation is developed within the framework of independent electron model taking into account the molecular character of the target and the simple Bragg’s additivity rule. The present formalism satisfies the proper boundary conditions. The interaction of the active electron with the incoming projectile ion has been approximated by a model potential containing a long-range part and a short-range part. The quantum-mechanical post and prior forms of the transition amplitude for charge exchange between ${\mathrm{He}}^{+}$ and molecules are derived in terms of one-dimensional real integral which can be computed numerically. A detailed analysis on the contributions to the total cross sections (TCSs) coming from different molecular orbitals has also been discussed. Moreover, the contribution of short-range potential to the TCS in prior form is analysed. The calculated cross sections are compared with the available experimental and theoretical results in the wide range of impact energies. Overall, numerical results for the TCS show good agreement with the available experimental findings particularly at intermediate energy region. From this investigation, we find that the additivity rule is to be limited to relatively high energies where the molecular character is insignificant. Finally, the dependence of TCS on the number of valance electrons of different target molecules is analysed at different collision energies.