FROM QUANTUM-STATE-SPECIFIC DYNAMICS TO REACTION-RATES - THE DOMINANTROLE OF TRANSLATIONAL ENERGY IN PROMOTING THE DISSOCIATION OF D(2) ONCU(111) UNDER EQUILIBRIUM CONDITIONS

We have calculated the rate of adsorption of isotropic D2 gas on a Cu( 111) surface, using recently determined differential adsorption probab ilities, as a function of translational energy, angle of incidence, an d surface temperature for molecules in each vibrational-rotational sta te. If the D2 gas is at the same temperature, T, as the surface, the m ean probability of dissociation per collision, [S0], is calculated to increase rapidly with temperature. Arrhenius plots of [S0] vs. 1/T are in good qualitative agreement with measurements for hydrogen dissocia tion on Cu, but display a distinct curvature over the range 300-1000 K . A detailed analysis of this temperature dependence reveals that the increase in [S0] with T is due almost entirely to the increase in tran slational energy of the incident molecules. Increases in the populatio ns of vibrationally or rotationally excited molecules are relatively u nimportant, as are the changes in the adsorption with surface temperat ure.