A critical examination of data on the dissociative adsorption and associative desorption of hydrogen at copper surfaces

Abstract

The role of molecular rotation in activated dissociative adsorption on metal surfaces

Dissociation of H2 on Cu(100): Dynamics on a new two-dimensional potential energy surface

“…The idea that initial vibrational excitation enhances dissociation has been confirmed by recent experiments which measure the kinetic energies of desorbing H 2 in a state-selective manner. 8 Comparing our results for the thresholds with the results of the analysis by Michelsen and Auerbach, 41 we find that our 2-D results for the thresholds are too low, the vϭ1 threshold ͑0.14͒ by approximately 0.1 eV and our vϭ0 threshold by approximately 0.3 eV. However, it is known from comparisons of 2-D computational results with results of higher dimensionality calculations 27,38,53 that the 2-D thresholds are usually too low.…”

“…Originally, Anger et al 1 found no evidence in their experiments for vibrational enhancement of dissociation. However, in a careful analysis of their experiments Michelsen and Auerbach 41 found subtle deviations from normal energy scaling, which were well explained if a lower threshold for dissociation were assumed for vϭ1 H 2 than for vϭ0 H 2 . Their analysis puts the vϭ1 threshold at 0.26 eV and the vϭ0 threshold at approximately 0.55 eV.…”

“…Certainly, a barrier height of 0.9 eV seems too high when compared with the experimental results. 41 One reason for the discrepancy may be that White et al have used a coverage that could be too high. With the &ϫ& coverage they employ, the distance between H atoms of different H 2 molecules becomes ͱ4.8 2 ϩ(4.8Ϫr) 2 bohrs, compared to (9.6Ϫr) bohrs for the 2ϫ2 coverage.…”

“…Much work has been done to understand the mechanism of the dissociation and to investigate the effects of molecular vibration 33,36 and rotation. 28,39,40 A recent careful investigation 41 of available experimental results has put the threshold to dissociation for H 2 in its ground vibrational state at approximately 0.5 eV. The barrier height accessible through electronic structure calculations should then be of roughly the same size.…”

A note on the vibrational efficacy in molecule-surface reactions

“…The first theoretical [3][4][5][6][7] and experimental [8][9][10][11][12][13][14] studies related to the vibrational enhancement for specific molecule-surface systems were carried out on H 2 dissociation on Cu.…”