TEMPERATURE-DEPENDENCE OF NITROGEN DISSOCIATION ON METAL-SURFACES

The effect of crystal temperature on the dissociation dynamics of nitr ogen on a catalytic metal surface is studied. The framework is a nonad iabatic mechanism when the nitrogen crosses from the physisorption pot ential energy surface to a dissociative chemisorption potential. Withi n this framework the quantum dynamics is solved in three degrees of fr eedom including surface vibrational excitation. In general, surface vi brations promote the dissociation. However, if the nonadiabatic coupli ng potential is peaked at a restricted geometry, exciting the surface vibrations can hinder dissociation. This effect is maximized for the N -2/Fe mass ratio which leads to a negative temperature effect on the d issociation. For higher surface metal masses this effect disappears (N -2/Ru) and even reverses to a positive temperature effect for the N-2/ Re mass ratio. (C) 1995 American Institute of Physics.