The thermal dissociation of N2O5 in N2

Abstract

The thermal decomposition of dinitrogen pentoxide (N2O5 → NO2 + NO3) has been studied in excess nitrogen between 4 × 1014 and 2.8 × 1019 molecules cm−3 and between 262 and 307 K. This reaction is an example of unimolecular reaction kinetics, catalyzed by inert gases M, and exhibiting effects of non‐equilibrium distributions over reacting energy states. Previous measurements of the limiting low‐pressure second‐order rate constant have been confirmed and extended to lower temperatures; with M = N2, the combined old and new data give ko′ = 6.1 × 10−6 exp [(− 9570 ± 200)/T] cm³ molecules−1 s−1. An estimate of the high‐pressure first‐order rate constant, k∞ = 1.78 × 1017 exp [(− 12540 ± 130)/T] s−1, was found to be lower than the previous value at 300 K, and the high‐pressure activation energy was found to be larger than the previous estimate. The problem of extrapolating unimolecular reaction data to low temperature is not simple; a general theoretical formula is presented, which can be used approximately to extrapolate these data to stratospheric conditions.