Reaction mechanisms and energy disposal in the [C2H2:OCS](+) system: A mode-selective differential cross section study

Charge transfer and S-atom transfer have been studied for reaction of both charge states of the [C2H2:OCS](+) system. Reactions have been studied as a function of six different modes of reactant nuclear motion, including relative motion and nine levels of five vibrational modes for the two reactant ions. Integral cross section measurements provide information on how total reactivity and product branching are affected by different forms of reactant excitation. Detailed insight into the reaction mechanism is obtained from differential scattering measurements the first ever for mode-selectively excited reactants. The S-transfer reaction is found to be nearly identical for the two reactant charge states, which appear to be coupled by charge transfer in the collision entrance channel. In both charge states S transfer is dominated by two distinct direct scattering mechanisms, rebound and glancing/stripping, each of which are affected by collision energy and vibrational state. At collision energies below 0.5 eV, complex-mediated scattering becomes an important mechanism as well. It appears that the cis-trans symmetry of the C2H2+ bending vibration strongly affects formation of [C2H2:OCS](+) complexes. Charge transfer goes by very different mechanisms in the two charge states. For C2H2++OCS, long-range electron hopping is the dominant mechanism, while for OCS++C2H2 the dominant mechanism requires impulsive collisions. (C) 1996 American Institute of Physics.