An investigation of nonequilibrium kinetic isotope effects in chemically activated vinyl radicals

Abstract

Abstract New experimental data have been obtained for H + C 2 H 2 , D + C 2 H 2 , H + C 2 D 2 , and D + C 2 D 2 at room temperature. Two previously described apparatus were used in order to measure the pressure dependence of the reactions. The absolute rate constants are compared to results from other laboratories. The present results and those of Payne and Stief are used to obtain the high‐pressure limiting rate constant at room temperature. When the activation energy from the work of Payne and Stief is considered, it is shown that the A factor for H + C 2 H 2 is too low by a factor of ∼20. If a transmission coefficient is introduced which is constant for all isotopic variations, the pressure dependence can be explained in terms of the randomly energized radicals. RRKM theory is then invoked to explain the observed statistical nonequilibrium kinetic isotope effects.