SOME OBSERVATIONS ON THE THERMOCHEMISTRY AND KINETICS OF PEROXY-RADICALS

Recent studies from one laboratory over the past decade of the equilib rium reaction [GRAPHICS] for seven different radicals have led to disc repancies in six cases in Delta H-1 degrees of From 3 to 7 kcal/mol wh en compared to estimates from group additivity. These studies have uti lized flash photolysis to generate R(.) radicals and have measured the decay of [R(.)] by mass spectrometry using near threshold photoioniza tion. This decay was fitted to a double-exponential rate expression, O nly one additional reaction was introduced in addition to 1 and -1, na mely, the wall decay (w) of R(.) radicals, measured in the absence of O-2. Reexamination of the differential equations has shown that they a re not compatible with the reported data and in fact lead to negative values of K-1 and k(1), It has not been possible using the equation gi ven by the authors of the papers under consideration to derive K-1 fro m k(w) and the exponents of the double-exponential decay. It is shown that HO2. elimination is important for EtO(2)(.), iPrO(2)(.), and tBuO (2)(.) at the temperatures used, If this is the only additional reacti on, it is further shown that the authors' values of Delta H-1 are stil l not compatible with their equations.