Thermal decomposition of HNO

Abstract

HNO and DNO were produced by flash photolysis of H₂, NO and D₂, NO mixtures, and their rates of decay were monitored from absorption in the ultraviolet. It was discovered that if the heterogeneous reaction is eliminated with suitable surface treatment, the residual homogeneous reaction is second order in HNO (or DNO), and its rate is independent of the NO or total pressures. The second-order rate coefficients were measured from 80 to 420 K, and were found to vary by only ∼10 fold for the 5 fold temperature change. From a comparison of the experimental results with semi-quantitative transition state theory, it is suggested that the HNO decomposition probably occurs by a simple bimolecular reaction over a potential energy barrier of ∼320 cm^–1, and with a substantial vibrational contribution to the entropy of activation above 130 K.