ELEMENTARY ARRHENIUS PARAMETERS IN THE CO-FOR-ETHYLENE DISSOCIATIVE SUBSTITUTION OF CR(CO)(5)(C2H4)

Gas-phase samples of Cr(CO)(5)(C2H4) are prepared in situ by laser irr adiation of quantitative mixtures of Cr(CO)(6), CO, and C2H4 In the pr esence of CO and C2H4, Cr(CO)(5)(C2H4) decays thermally to re-form Cr( CO)(6) by the mechanism of dissociative substitution. Systematic study of the rate of this reaction as a function of partial pressures of CO and C2H4 yields the elementary high-pressure limiting thermal rate co nstant for unimolecular dissociation of Cr(CO)(5)(C2H4) (k(1)) and the relative rate constant for recombination of Cr(CO)(5) with CO and C2H 4 (k(2)/k(3)) Measurements of k(1) and k(2)/k(3) extended over a range of precisely controlled temperatures determine Arrhenius parameters r eflecting energetic and statistical properties of these elementary rat e processes.