Time-resolved kinetic studies of the N2+ + N2 association reaction

Abstract

In this work, we apply a technique in which N2+ ions are formed by resonance enhanced multiphoton ionisation (REMPI) and monitored by laser-induced fluorescence (LIF) to measure reaction kinetics. Using this approach, we are able to measure pressure-dependent rate constants for the N2+ + N2 + M → N4+ + M association reaction over the pressure ranges 1–13 Torr N2 and 10–950 Torr He. In these ranges we find evidence for fall-off behaviour in the kinetics. Constraining the high pressure limiting rate constant (k∞) to the ion-induced dipole capture rate constant for N2+ + N2 collisions (8.3 × 10−10 cm3 s−1), we extract low pressure limiting rate constants (ko) and fall-off broadening parameters (Fcent). For M = He, we find ko = 2.02(±0.20) × 10−29 cm6 s−1 and Fcent = 0.465(±0.024) and for M = N2 we find ko = 5.83(±0.40) × 10−29 cm6 s−1 and Fcent = 0.517(±0.117). Both the low pressure limiting rate constants and the observed fall-off behaviour are analysed using statistical treatments for the reaction based upon the formation of a linear N4+ energised adduct. These treatments are found to interpret our data very satisfactorily.