Elastic and inelastic processes inH++CH4collisions in the low-kilo-electron-volt regime

Electron capture and direct elastic scattering in collisions of ${\mathrm{H}}^{+}$ ions with ${\mathrm{CH}}_4$ molecules are studied by using a molecular representation within a fully quantum-mechanical approach below 1.5 keV. Calculations are carried out at two different molecular configurations: (i) ${\mathit{C}}_{3\mathit{v}}$ symmetry, in which ${\mathrm{H}}^{+}$ approaches along the direction of a C-H in ${\mathrm{CH}}_4$, and (ii) ${\mathit{C}}_{2\mathit{v}}$ symmetry, in which ${\mathrm{H}}^{+}$ approaches along a bisector of a H-C-H bond angle. We find that electron capture in the ${\mathit{C}}_{2\mathit{v}}$ symmetry configuration takes place preferentially over that in the ${\mathit{C}}_{3\mathit{v}}$ symmetry configuration at scattering angles below 15° at 1.5 keV, and that the situation reverses at larger scattering angles. Hence, interferences arising from these molecular configurations on differential cross sections for electron capture and elastic scattering processes are present but weak, except for angles near the crossing. Accordingly, the total cross section for the ${\mathit{C}}_{2\mathit{v}}$ symmetry is larger by more than an order of magnitude, because in this symmetry ${\mathrm{H}}^{+}$ can penetrate deep inside the electron distribution of the ${\mathrm{CH}}_4$ molecule, causing a strong interaction. In addition, angular dependence in the differential cross section is quite different for the two molecular configurations at all energies studied.