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Science 29 August 2008:
Vol. 321. no. 5893, pp. 1191 - 1194
DOI: 10.1126/science.1160040
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Reports

Inverse Velocity Dependence of Vibrationally Promoted Electron Emission from a Metal Surface

N. H. Nahler,1* J. D. White,1 J. LaRue,1 D. J. Auerbach,2 A. M. Wodtke1{dagger}

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(X2{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.

1 Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, CA 93106–9510, USA.
2 GRT Inc., 861 Ward Drive, Santa Barbara, CA 93111–2920, USA.

* Present address: Department of Chemistry, Durham University, South Road, Durham DH1 3LE, UK.

{dagger} To whom correspondence should be addressed. E-mail: wodtke{at}chem.ucsb.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
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