Temperature Dependence of the Rate Constants of H and D-Atom Additions to C2H4, C2H3D, C2D4, C2H2, and C2D2

Abstract

Abstract The high pressure limiting rate constants of H and D-atom additions to C2H4, C2H3D, C2D4, C2H2, and C2D2 have been measured in the temperature range from 206 to 461 K by means of the pulse radiolysis-resonance absorption method. Practically no isotope effects due to the deuteration of ethylene and acetylene could be observed. The rate constants were compared with those calculated by the activated complex theory using the potential energy surfaces provided by the ab initio calculations. Concerning the isotope effects, very poor agreement was obtained between theory and experiment. This seems to suggest that the assumptions on which the activated complex theory is based have to be reconsidered when it is applied to such reactions as H+C2H4→C2H5 and H+C2H2→C2H3.