title: Inverse velocity dependence of vibrationally promoted electron emission from a metal surface.
abstract: 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.
authors.affiliation: Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, CA 93106-9510, USA.
authors.forename: N H
authors.initials: NH
authors.lastname: Nahler
authors.forename: J D
authors.initials: JD
authors.lastname: White
authors.forename: J
authors.initials: J
authors.lastname: Larue
authors.forename: D J
authors.initials: DJ
authors.lastname: Auerbach
authors.forename: A M
authors.initials: AM
authors.lastname: Wodtke