title: Observation of orientation-dependent electron transfer in molecule-surface collisions.
abstract: Molecules typically must point in specific relative directions to participate efficiently in energy transfer and reactions. For example, Förster energy transfer favors specific relative directions of each molecule's transition dipole [Förster T (1948) Ann Phys 2(1-2):55-75] and electron transfer between gas-phase molecules often depends on the relative orientation of orbitals [Brooks PR, et al. (2007) J Am Chem Soc 129(50):15572-15580]. Surface chemical reactions can be many orders of magnitude faster than their gas-phase analogs, a fact that underscores the importance of surfaces for catalysis. One reason surface reactions can be so fast is the labile change of oxidation state that commonly takes place upon adsorption, a process involving electron transfer between a solid metal and an approaching molecule. By transferring electrons to or from the adsorbate, the process of bond weakening and/or cleavage is initiated, chemically activating the reactant [Yoon B, et al. (2005) Science 307(5708):403-407]. Here, we show that the vibrational relaxation of NO--an example of electronically nonadiabatic energy transfer that is driven by an electron transfer event [Gadzuk JW (1983) J Chem Phys 79(12):6341-6348]--is dramatically enhanced when the molecule approaches an Au(111) surface with the N atom oriented toward the surface. This represents a rare opportunity to investigate the steric influences on an electron transfer reaction happening at a surface.
authors.affiliation: Institut für Physikalische Chemie, Georg-August-Universität Göttingen, 37077 Göttingen, Germany.
authors.forename: Nils
authors.initials: N
authors.lastname: Bartels
authors.forename: Kai
authors.initials: K
authors.lastname: Golibrzuch
authors.forename: Christof
authors.initials: C
authors.lastname: Bartels
authors.forename: Li
authors.initials: L
authors.lastname: Chen
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Auerbach
authors.forename: Alec M
authors.initials: AM
authors.lastname: Wodtke
authors.forename: Tim
authors.initials: T
authors.lastname: Schäfer
mesh_terms: D002384:Catalysis; D004579:Electron Transport; D008670:Metals / Q000737:chemistry; D008956:Models, Chemical; D008968:Molecular Conformation; D009569:Nitric Oxide / Q000737:chemistry; D010084:Oxidation-Reduction; D013499:Surface Properties; D014732:Vibration
chemical_list: D008670:Metals; D009569:Nitric Oxide
keywords: dynamics at surfaces; orientation of molecules; rotational rainbow