Kinetics and dynamics of vibrationally state resolved ion–molecule reactions: 14N+2(v=1 and 2) and 15N+2(v=0, 1, and 2) with 14N2

Abstract

Vibrationally state-selected measurements of the kinetics and dynamics of 14N+2(v=1 and 2) and 15N+2(v=0, 1, and 2) in collisions with 14N2 are made using a selected ion flow tube (SIFT), laser induced fluorescence (LIF) technique at thermal energies. Kinetics are measured by monitoring the LIF signal amplitudes of N+2(v) as a function of 14N2 concentration, added after ion injection. By comparison with the known N+2(v=1)+Ar rate, the 15N+2(v=0)+14N2 rate constant is found to be one-half of the Langevin collision rate, or 4.2±0.2×10−10 cm3 molecule−1 s−1. This suggests that the reaction proceeds via an N+4 energized adduct in which charge is shared on a time scale shorter than the adduct lifetime. The removal rates of 14N+2(v=1 and 2) reactions by 14N2 are also found to proceed at one-half of the Langevin collision rate. Thus product channels that remove vibrational energy from the ion upon dissociation of the adduct account for 50% of the collision probability. The removal rates of 15N+2(v=1 and 2) with 14N2 are 21%–26% faster than those for 14N+2(v=1 and 2); this is attributed to the channel that cannot be observed in collisions of 14N+2(v) with 14N2 in which both charge and vibrational energy are transferred between the collision partners. This pathway is also observed directly by the appearance of 14N+2(v=1 and 2) product states. For this channel to proceed, vibrational energy transfer between the two highest frequency modes of the N+4 energized adduct must occur on a time scale comparable to the adduct lifetime.