Inverse velocity dependence of vibrationally promoted electron emission from a metal surface

N. H. Nahler, J. D. White, J. LaRue, D. J. Auerbach, A. M. Wodtke

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All previous experimental and theoretical studies of molecular interactions at metal surfaces show that electronically nonadiabatic influences increase with molecular velocity. We report the observation of a nonadiabatic electronic effect that follows the opposite trend: The probability of electron emission from a low- work function surface-Au(111) capped by half a monolayer of Cs- increases as the velocity of the incident NO molecule decreases during collisions with highly vibrationally excited NO(X-2 Pi(1/2), V = 18; V is the vibrational quantum number of NO), reaching 0.1 at the lowest velocity studied. We show that these results are consistent with a vibrational autodetachment mechanism, whereby electron emission is possible only beyond a certain critical distance from the surface. This outcome implies that important energy- dissipation pathways involving nonadiabatic electronic excitations and, furthermore, not captured by present theoretical methods may influence reaction rates at surfaces.

Original languageEnglish
Pages (from-to)1191-1194
Number of pages4
Issue number5893
Publication statusPublished - 29 Aug 2008

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