THE LIFETIME AND ENERGY OF THE (2)PI(G) SHAPE RESONANCE OF N-2 ADSORBED ON AG(111) - THE ROLE OF THE SUBSTRATE ELECTRONIC-STRUCTURE

Using the (2) Pi(g) resonance of N-2 adsorbed on Ag(111) as a test cas e, we explore the influence of the substrate electronic states upon th e calculated resonance behavior of an adsorbed molecule. The calculati on of the resonance lifetime and energy is performed by a recently dev eloped layer KKR calculation in which the substrate scattering is full y incorporated. This approach allows the effect of the substrate elect ronic states to be included or neglected, thus permitting a quantitati ve estimate the influence of substrate scattering upon resonance forma tion in adsorbed molecules. For the (2) Pi(g) (2.3 eV) shape resonance of N-2 physisorbed on Ag(111), the screening of the negative ion stat e by the metallic substrate is found to be the primary cause of the ob served lifetime reduction and energy shift relative to the free molecu le. However, the effect of screening rapidly diminishes as the resonan ce energy is increased, and the scattering of the trapped electron amo ng the substrate atoms becomes important in determining the resonance lifetime. In contrast to previous theoretical studies based upon the e mpty crystal approximation, we demonstrate that the lifetime of a mole cular negative ion can be increased upon adsorption. The implications of these results for the accuracy of prior models of resonance behavio r are discussed.