The effects of vibrational mode and collision energy on the reaction of formaldehyde cation with carbonyl sulfide

Abstract

The effects of collision energy (Ecol) and five different H2CO+ vibrational modes on the title reaction have been studied, including measurements of product ion recoil velocity distributions. A series of ab initio and Rice–Ramsperger–Kassel–Marcus calculations were used to examine properties of various complexes and transition states that might be important. Four product channels are observed. Proton transfer (PT) dominates at low Ecol, and is suppressed by Ecol but mildly enhanced by H2CO+ vibrational excitation. PT occurs by a direct mechanism at high energies, but appears to be mediated by reactantlike complexes at low energies. The other major low energy channel corresponds to H2+ transfer, and the majority of these product ions go on to eliminate CO, producing H2S+. Both H2+ transfer and H2S+ channels are strongly inhibited by Ecol and vibrational excitation, which is interpreted in terms of competition with other channels. Charge transfer occurs in short time scale collisions at all energies, and is strongly enhanced by Ecol and by vibrational excitation. The vibrational effects for all channels are mode specific.