Selective vibrational excitation and mode conservation in H++CO2/N2O inelastic and charge transfer collisions

Abstract

Total angular distributions and vibrationally resolved time-of-flight spectra have been measured for H++CO2/N2O at collision energies of 9.8 and 30 eV and scattering angles up to θ=15°. Results are available for the scattered protons as well as for H atoms from charge transfer collisions into the electronic ground states of CO+2/N2O+. For both systems, the H+ and H product channels exhibit practically identical total angular distributions with marked rainbow structures in the CO2 case. The time-of-flight distributions, on the other hand, reveal strongly selective excitation of the ν3 fundamental modes and their overtones for both target molecules and both product channels. In addition, at each scattering angle, the ν3 transition probability distributions for CO2 and N2O are remarkably similar to those for CO+2 and N2O+, respectively. The dominance of the ν3 mode excitation in the neutral molecules is in accord with what is expected from the combination of dipole- and valence-type interaction mechanisms on the lower H++CO2/N2O potential energy surfaces. Excitation of the same mode with nearly the same distributions in the charge transfer channel is explained by Franck–Condon selection rules, which favor transitions between identical vibrational states of either CO2 and CO+2 or N2O and N2O+.