The effects of vibrational mode, spin–orbit state, and collision energy on collision-induced dissociation and predissociation of OCS+

Abstract

We report the first study of the effects of mode specific vibrational excitation on collision-induced dissociation of a polyatomic cation. Resonance-enhanced multiphoton ionization was used to produce OCS+ ions with variable excitation in each of the three vibrational modes, in combination with either spin–orbit electronic state. Cross sections for fragmentation of the state-selected ions in collision with Xe and Ar atoms were measured over the collision energy range from 0.5 to 9.0 eV, using a guided ion beam tandem mass spectrometer. Both spin-allowed and spin-forbidden channels are observed for both collision partners, and the cross sections in both cases are enhanced by collision energy and all modes of vibrational excitation. Vibration is more effective than collision energy, but the effect is nonmode specific. The absolute magnitude of the dissociation cross sections and the relative vibrational effects are bigger for collisions with Xe than for Ar. The spin–orbit state of the primary ion has no effect on dissociation of ground vibrational state OCS+, but there appears to be some synergy between vibrational and spin–orbit excitation. The results are discussed in view of the electronic structure of OCS+ and possible scattering mechanisms.