Desorption and C–H dissociation rate constants for C2 hydrocarbons on Ni, Pd and Pt

We have employed the normalized bond index-reactive potential, function (NBI-RPF) in molecular dynamics simulations of the desorption and C-H dissociation rate constants for C-2 hydrocarbons on fcc(lll) surfaces of Ni, Pd and Pt. The simulations yield Arrhenius preexponential factors, which together with activation barriers obtained from the unity bond index-quadratic exponential potential (UBI-QEP) method, complete the specification of the Arrhenius rate constants. Comparisons between the calculated and the available experimentally determined rate constants indicate good agreement. The calculations provide rate constants for the two different C-H bond dissociations in vinyl, while experiments were unable to distinguish between them. The values of the Arrhenius preexponentials obtained for the desorption of the C-2 hydrocarbons cluster in a narrow range, which is consistent with the traditional use of a single value for the desorption preexponential for all small molecules. The C-H dissociation preexponentials span a range of three orders of magnitude. For the dissociation of a given C-H bond in the periodic metal series, a general trend is that the preexponential decreases with increasing activation barrier. (C) 1998 Published by Elsevier Science B.V. All rights reserved.