Time-resolved studies of photoinitiated reactions in binary and larger (N2O)m(HI)n(m 1, n 1) complexes

Abstract

Under gas-phase conditions, reaction of fast hydrogen atoms with N₂O lead mainly to OH(X²Π)+ N₂(X¹∑) products via a 1,3 hydrogen-shift mechanism involving the HNNO intermediate. In complexes formed by using supersonic expansions, the reaction mechanism is less clear. In this paper, OH build-up times are reported for photoinitiated reactions in complexes of the form (N₂O)_m(HI)_n with m 1 and n 1. The build-up times vary from many hundreds of fs under conditions that encourage the formation of larger complexes (i.e. the highest stagnation pressures) down to ⩽ 100 fs for the lowest stagnation pressures. We conclude that in binary complexes OH is produced on timescales below 100 fs. This rules out the participation of a long-lived intermediate such as HNNO. Comparisons are made with the analogous CO₂–HI system, in which reactions in larger complexes either yield the same lifetimes as do binary complexes or are inhibited, presumably because of the relatively large H + CO₂ entrance channel barrier.