The Pressure Dependence of the Rate Constant for the t-Butoxy Radical Decomposition Reaction

A thermal decomposition of the tert-butoxy radical has been studied in the gas phase over the pressure range of 1-200 torr at using di-tert-butyl peroxide + trimethylsilane mixtures. The relative rate constants were obtained by studying the competitive reactions between tert-butoxy radical decomposition and hydrogen abstraction reaction from trimethylsilane The conventional RRKM calculations were carried out to compare the observed fall-off behavior of the decomposition rate constant with the theoretical predictions using reasonable values of input parameters. In all cases the calculated half-rate pressure were significantly higher than those observed. The failure of RRKM to reproduce the fall-off behavior led us to suggest that not all of vibrational modes contribute to excitation (leading to decomposition) on the same time scale.