ELASTIC AND INELASTIC PROCESSES IN H-KILO-ELECTRON-VOLT REGIME(+CH4 COLLISIONS IN THE LOW)

Electron capture and direct elastic scattering in collisions of H+ ion s with CH4 molecules are studied by using a molecular representation w ithin a fully quantum-mechanical approach below 1.5 keV. Calculations are carried out at two different molecular configurations: (i) C-3v sy mmetry, in which H+ approaches along the direction of a C-H in CH4, an d (ii) C-2v symmetry, in which H+ approaches along a bisector of a H-C -H bond angle. We find that electron capture in the C-2v symmetry conf iguration takes place preferentially over that in the C-3v symmetry co nfiguration at scattering angles below 15 degrees at 1.5 keV, and that the situation reverses at larger scattering angles. Hence, interferen ces arising from these molecular configurations on differential cross sections for electron capture and elastic scattering processes are pre sent but weak, except for angles near the crossing. Accordingly, the t otal cross section for the C-2v symmetry is larger by more than an ord er of magnitude, because in this symmetry H+ can penetrate deep inside the electron distribution of the CH4 molecule, causing a strong inter action. In addition, angular dependence in the differential cross sect ion is quite different for the two molecular configurations at all ene rgies studied.