Ion-molecule association in acrylonitrile

The association reactions of the acrylonitrile ion, CH2CHCN+, and the proto nated ion derived from acrylonitrile, CH2CHCNH+. with acrylonitrile (CH2CHC N) have been examined using ion cyclotron resonance (ICR) and flowing after glow selected ion flow drift tube (FA/SIFDT) techniques at room temperature . These techniques yield different results for these two systems that can b e rationalized by considerations of the lifetime of the collision complex. In the CH2CHCN+/CH2CHCN system, the measured reaction rate coefficients are : k(ICR) = 2.5 x 10(-9) cm(3) s(-1) with a single product channel (CH2CHCNH + + C3H2N) and k(SIFT) = 3.1 x 10(-9) cm(3) s(-1) (with a 30% product chann el to the adduct C6H6N6+) The rate coefficient and product distributions in the FA/SIFDT instrument are invariant with pressure in the range 0.25-0.75 Torr. In the CH2CHCNH+/CH2CHCN system, the measured rate coefficients are: k(ICR) = 9.2 x 10(-11) cm(3) s(-1) at a CH2CHCN pressure of 3.0 x 10(-4) T orr and k(SIFT) = 1.6 x 10(-9) cm(3) s(-1), where association is the only p roduct channel observed by each technique. The termolecular process corresp onding to this latter association has a measured reaction rate coefficient of k(3) = 1.2 x 10(-23) cm(6) s(-1) (for M = CH2CHCN) and k(3) = 8.1 x 10(- 25) cm(6) s(-1) (for M = He). Both systems were modelled: A double well pot ential model involving the formation of loosely bound and tightly bound com plexes was required to account for the kinetic behaviour of the CH2CHCN+/CH 2CHCN system whereas a single-well potential model satisfactorily accounted for the behaviour of the CH2CHCNH+/CH2CHCN system. (Int J Mass Spectrom 18 5/186/187 (1999) 663-672) (C) 1999 Elsevier Science B.V.