The effects of different vibrational modes and collision energy on the reaction of acetylene cations with carbonyl sulfide

Abstract

Resonance-enhanced multiphoton ionization has been used to produce beams of vibrationally state-selected acetylene cations. The ions are formed with excitation in either the symmetric C–C stretch (ν2) or in a bending mode (ν5). Reactions with OCS have been studied in a guided ion-beam mass spectrometer. Absolute cross sections for the production of OCS+ and C2HnS+ (n=1,2) are reported for collision energies ranging from 80 meV to 5 eV. Charge transfer is observed to be enhanced by bending excitation, suppressed by C–C stretching vibration, and only weakly affected by collision energy. In contrast, the C2HnS+ channels are strongly collision energy dependent, with vibrational effects that vary with collision energy. The effects of bending and stretching excitation are qualitatively similar; however, the size of the effects are different and are not what would be expected on energetic grounds. These results are contrasted to the situation for reaction of mode selectively excited C2H+2 with methane.