The Low-Energy Unimolecular Reaction Rate Constants for the Gas Phase, Ni+-Mediated Dissociation of the C-C σ Bond in Acetone

The time dependence of the gaseous unimolecular decomposition of the jet-cooled adduct ion, Ni+-OC(CH3)(2), was monitored through selective detection of the Ni+CO fragment ion. Various resolved amounts of energy in the range 15600-18800 cm(-1) were supplied to initiate the dissociation reaction through absorption of laser photons by the title molecular complex. First-order rate constants, k(E), ranged from 113000 to 55000 s(-1) and decreased with decreasing amounts of internal excitation. The energy used to initiate the reaction is well below that required to fragment C-C sigma bonds and indicates the necessity of the Ni+ cation to induce bond activation and fragmentation. These measurements are carried out in a unique apparatus and represent the first direct kinetic study of such catalytic type reactions.