Vibrational excitation in H+(D+)-CO2collisions: mode selectivity and time effects

Abstract
Mode-resolved measurements are presented for vibrational excitation of CO2 by H+ and D+ ions in the energy range Ecm=15.100 eV. Under the present conditions of forward scattering (0+or-0.5 degrees ) the infrared-active 010 and 001 modes are predominantly excited, whereas previous measurements have shown very strong and selective excitation of the 00n3 series in the rainbow region. Various other excitations of higher harmonics and intercombination modes, although weak in their intensities, are identified in the spectra. The excitation processes are investigated as a function of the CM energy and the relative velocity of the colliding particles. Time effects are shown to play an important role, e.g. the intensity ratio of 010 to 001 excitation changes by a factor of 20 in the velocity range 5-12*104 m s-1. The importance of separating the influence of interaction and time effects in investigating the mode selectivity is stressed.