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

• Published in: Science (American Association for the Advancement of Science) Vol. 321; no. 5893; pp. 1191 - 1194
• Main Authors: Nahler, N.H, White, J.D, LaRue, J, Auerbach, D.J, Wodtke, A.M
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 29-08-2008; The American Association for the Advancement of Science
• Subjects: Approximation; Atomic and molecular collision processes and interactions; Atomic and molecular physics; Chemistry; Electron emission; Electron transfer; Electrons; Energy; Exact sciences and technology; Lasers; Metal surfaces; Metals; Molecular excitation; Molecules; Physics; Scattering of atoms, molecules and ions; Theory; Velocity; Work functions; Inorganic compounds; Nitric oxide; Electron autodetachment; Laser induced fluorescence; Molecule-surface impact; Diatomic molecules; Electron emission; Vibrationally excited state
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1160040

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(X²π[fraction one₋half], 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.