Charge Transfer Processes in Ion-Molecule Collisions at Intermediate Energies; the Vibrational Effect, Isotope Effect, Isomer Effect, and Steric Effect

摘要

Charge transfer processes resulting from collisions of H+ ions with H2, HD, D2, CH2, CH4, C2H2, C2H4 and C2H6 molecules have been investigated in the energy range of 0.2 to 10.0 keV by using experimental as well as theoretical approaches. The initial growth rate method was employed for the experimental study of the dynamics and cross sections, while theoretical analysis based on a molecular-orbital expansion method for all these targets was carried out. The present results for the H2, HD and D2 molecules are found be in excellent accord with most of previous measurements above 1 keV and to show a conspicuous isotope effect, that is, the cross sections for three molecules differs in sizable amounts particularly below a few keV. For CmHn hydrocarbon targets (m 3), both experimental and theoretical results indicate that if the target is in a vibrationally excited state, then charge transfer processes sometimes become more favorable since these vibrationally excited states enforce an accidental resonant condition. This is a clear indication of the role of vibrational excited states for charge transfer, i.e., a temperature effect.