Electron solvation by polar molecules:The interaction of Na atoms with solid methanol films studied with MIES and density functional theory calculations

摘要

The interaction of Na atoms with CH_3OH films was studied with metastable impact electron spectroscopy (MIES) under UHV conditions.The films were grown at 90(+/-10) K on tungsten substrates and exposed to Na.Na-induced formation of methoxy (CH_3O) species takes place,and Na atoms become ionized.At small Na exposures the outermost solvent layer remains largely intact as concluded from the absence of MIES signals caused by the reaction products.However,emission from CH_3O,located at the film surface,occurs at larger exposures.In the same exposure range also Na species can be detected at the surface.The spectral feature from 3s Na ionization occurs at an energetic position different from that found for metals or semiconductors.The results are compared with density functional theory calculations [see Y.Ferro,A.Allouche,and V.Kempter,J.Chem.Phys.120,8683 (2004),preceding paper].Experiment and theory agree in the energetic positions of the main spectral features from the methanol and sodium ionization.The calculations suggest that the 3s Na emission observed experimentally originates from solvated 3s electrons which are located far from the Na core and become stabilized by solvent molecules.The simultaneous emergence of emission from CH_3O and from solvated 3s electrons suggests that the delocalization and,consequently,the solvation play an important role in the Na-induced formation of CH_3O from CH_3OH.