REACTIONS OF CH3- A LOW-PRESSURE HIGH-PRESSURE STUDY( WITH C2N2, CH2CHCN, AND HC3N )

The association of CH3+ with the three molecules C2N2, CH2CHCN, and HC CCN has been examined using ion cyclotron resonance (ICR) and selected ion flow tube (SIFT) techniques at room temperature. In each reaction , the mean lifetime of the complex (CH3 . N=C-R(+)) formed in the ass ociation has a major influence on the outcome of the reaction and the product channels that are observed using ICR and SIFT. Termolecular ra te coefficients are reported for the association of CH3+ + C2N2 for th e bath gases M = He, Ar, N-2, and C2N2. k(3) = 8.2 x 10(-24) cm(6) s(- 1) (M = C2N2). In each system the association product channel occurs i n competition with exothermic bimolecular channels. The complex lifeti mes in all three systems are in the range 30-70 mu s. Very rapid ion-m olecule association reactions have been observed in several systems of hydrocarbons and nitriles, and the implications for Titan ion chemist ry are discussed briefly.