Temperature dependence of nitrogen dissociation on metal surfaces

The effect of crystal temperature on the dissociation dynamics of nitrogen on a catalytic metal surface is studied. The framework is a nonadiabatic mechanism where the nitrogen crosses from the physisorption potential energy surface to a dissociative chemisorption potential. Within this framework the quantum dynamics is solved in three degrees of freedom including surface vibrational excitation. In general, surface vibrations promote the dissociation. However, if the nonadiabatic coupling potential is peaked at a restricted geometry, exciting the surface vibrations can hinder dissociation. This effect is maximized for the N₂/Fe mass ratio which leads to a negative temperature effect on the dissociation. For higher surface metal masses this effect disappears (N₂/Ru) and even reverses to a positive temperature effect for the N₂/Re mass ratio.