Effect of vibrational interaction on the rate of dissociation of adsorbed molecules: ethene on a nickel surface

Abstract

The effect of vibrational interaction between an adsorbed molecule and the surface on the rate of dissociation of a bond in this molecule has been estimated quantitatively. The method described here and calculations performed for breaking a carbon–carbon bond in ethene adsorbed on Ni(111) or Fe(110) surfaces show that the catalytic effect of metal surfaces on bond dissociation in an adsorbed molecule comprises two components: a decrease in the bond order due to rearrangement of the electron density and the vibrational energy exchange. The latter effect changes the vibrational energy of the bond and the temperature dependence of the rate constant. In this way the macroparameters (activation energy and pre-exponential term) of the reaction determined by experimental measurements may be completely different from the microparameters (energy barrier height and frequency factor), characterizing the potential-energy surface of the reaction. The effective values of the macroparameters calculated for the Ni(111) surface are close to those obtained by experimental measurements.