A tunnelling model for activated adsorption at metal surfaces

The reaction rate for dissociative adsorption of N2 on stepped Ru(0001): Six-dimensional quantum calculations

“…At an energy of 0.1 eV below the threshold energy ͑1.15 eV͒, the reaction probability has already a value below 10 −5 . This result is in sharp contrast to the results of previous model calculations of the dissociation probability for N 2 on various metal surfaces, [66][67][68][69][70][71][72] where significant reaction probabilities ͑Ϸ10 −5 ͒ have been found for more than 0.3 eV below the barrier energy. Note that N͑E͒ is an upper bound to the initial state-selected reaction probabilities since it is the sum of all reaction probabilities.…”

“…[66][67][68][69][70][71][72] These calculations show a significant tunneling effect on the reaction probability. As discussed by Haase et al, 67 the results suggest that at room temperature the reaction is completely dominated by a tunneling mechanism, 67 which is quite surprising for a heavy-atom system.…”

“…The good agreement between the accurate quantum-mechanical result and the Wigner theory is a clear indication that the present system is close to the classical limit. The obstinacy of tunneling theories in the literature for N 2 on a plain metal surfaces [66][67][68][69][70][71][72] is presumably caused by the experimental observation of significant reaction probabilities at energies well below the barrier energy. This observation could be explained by a tunneling mechanism.…”

“…The effect of tunneling on the reaction rate is found to be almost negligible, which is in marked contrast to findings of previous model calculations. [66][67][68][70][71][72] Harmonic transition-state theory can be used to reliably predict the rate constant for dissociative adsorption of nitrogen on Ru and similar processes. While the present work has been restricted to a frozen Ru surface, future work 73 will include the effect of surface motion.…”

The effect of surface relaxation on the N2 dissociation rate on stepped Ru: A transition state theory study

“…The positions of the surface atoms were frozen, in order to reduce the computational effort. The strong tunneling effect found in previous model calculations [6][7][8][9][10][11] is not found. In contrast, the tunneling effect was very small above room temperature.…”