Adsorbate spectra of rare-gas atoms on metal surfaces

Abstract

This paper is dedicated to Professor J. A. MorrisonCONSTANTINE MAVROYANNIS. Can. J. Chem. 66, 741 (1988).The optical excitation spectra of neutral rare-gas atoms physisorbed on metal surfaces have been considered. Emphasis has been given to the dynamic effects of the surface plasmons on the lifetimes of the adsorbed atoms. At low coverage and when the damping of the surface plasmons is much greater than the effective radiative damping, the spectral functions of the symmetric and antisymmetric modes consist of asymmetric Lorentzian lines, whose asymmetry depends on the strength of the surface plasmons. At this limit the relative intensities of the symmetric and antisymmetric modes take positive and negative values describing the physical processes of absorption (attenuation) and stimulated emission (amplification), respectively. Hence, the occasional disappearance of the spectral lines of the optical absorption is due to a cancellation process, which takes place between the frequency profiles arising from two nearby excited states of the adsorbed atom. The red shifted peak of the symmetric mode of the higher excited state and the blue shifted peak of the antisymmetric mode of the lower excited state of the atom cancel each other out provided that their frequency profiles nearly coincide. This may be a possible explanation of the persistence-extinction phenomenon that has been observed for a number of rare-gas substrate systems in the low coverage limit, where it has been proposed that a charge-transfer instability exists. Numerical results indicate that the peaks of excited Xe on A1 and excited Kr on Au vanish in the low coverage limit.CONSTANTINE MAVROYANNIS. Can. J. Chem. 66, 741 (1988).On a CtudiC les spectres d'excitation optique d'atomes de gaz rares neutres adsorb& physiquement sur des surfaces mCtalliques. On considkre principalement les effets dynarniques des plasmons de surface sur les temps de vie des atornes adsorb&. Lorsque la couverture est faible et que le ralentissement des plasmons de surface est beaucoup plus grand que le ralentissement radiatif effectif, les fonctions spectrales des modes symktriques et antisymktriques consistent en des raies asymCtriques de Lorentz dont l'asyrnktrie dkpend de la force des plasmons de surface. A cette lirnite, les intensites relatives des modes syrn&triques et antisymktriques prennent des valeurs positive et negative en dtcrivant respectivement les processus physiques d'adsorption (attenuation) et d'emission stirnulees (amplification). I1 s'en suit que la disparition occasionnelle des lignes du spectre d'absorption optique est due B une processus d'annulation qui prend place entre les profils de friquence qui proviennent de deux Ctats excites adjacents de l'atorne adsorbt. La raie deplacte vers le rouge du mode symetrique de 1'Ctat excite le plus eleve de l'atome et la raie dCplacte vers le bleu du mode antisymetrique de 1'Ctat excite le plus bas de l'atorne s'annulent lorsque leurs profils de frkquence coincident. Ceci est une explication possible du phenomkne ...