Gas-Surface Vibrational Energy Transfer in the Transient Region of a Low-Pressure Unimolecular Reaction

Article abstract of DOI:10.1021/j100448a001

A technique has been developed, called the variable encounter method, for the study of gas-wall vibrational energy transfer in the transient region of a unimolecular reaction.The method was applied to the isomerization of cyclopropane to propylene.Molecules at room temperature were introduced into the hot reactor, and the accomodation to the final temperature of the reactor was monitored by measurement of the amount of reaction that occured at various intervals during the energy relaxation process.Specifically, the amount of reaction following some (variable) mean number of collisions, m, between gas and reactor wall was measured.Temperatures in the range 900-1125 K were employed.Reactors having m values of 2.6, 8.5, and 27.2 were used.The average probability of reaction per collision, <*>_c(m), for a given reactor, was deduced from the data and compared with a theoretical stochastic calculation based on both Gaussian and exponential models for the energy transfer probabilities.It is found that the efficiency of a seasoned quartz wall is greater than gas-gas collisions of substrate and that the efficiency declines with an increase of temperature.The steady state is closely approached (90percent) in a comparatively small number of gas-wall collisions - 10-20, approximately.