SELECTIVE VIBRATIONAL EXCITATIONS IN PROTON-WATER COLLISIONS - A STUDY BASED ON CI CALCULATIONS

Earlier experimental investigations of inelastic and charge-transfer s cattering of protons by water molecules at collision energy up to abou t 50 eV (Friedrich et al. J. Chem. Phys. 1987, 87, 5256) are examined via an accurate computational study of several features of various gro und- and excited-state electronic potential energy surfaces (PES's). H ighly correlated calculations of representative 'cuts' of the multidim ensional PES's are able to show the preferential dynamical coupling to either bending or stretching vibrational motions depending on the dir ection of proton approach and on the existence of curve-crossing regio ns leading to nonadiabatic charge-transfer processes, in general agree ment with experiments. The general implications of our results on low- energy ion-molecule reactions are discussed for the H3O+ system, for w hich a rather detailed analysis of valence forces and of unimolecular breakup pathways had been Previously carried out in our group (Giantur co, F. A.; et al. J. Chem. Phys. 1994, 101, 3952).