ELECTRONIC MECHANISM OF THE SURFACE-ENHANCED RAMAN-SCATTERING

Electronic mechanism of the surface enhanced Raman scattering (SERS) i s investigated by an ab initio molecular orbital theory. The time-depe ndent Hartree-Fock method is used to calculate the polarizability of t he surface-molecule interacting system. For representing the surface e ffect, we use small solid dusters Ag-2 Ag-10, K-2 Pd-2, and MgO. The p resent method succeeds in describing the enhancement of the Raman inte nsity for the adsorbed CO molecule. The maximum intensity of the Ag10C O system is calculated to be seven orders of magnitude larger than tha t of the free CO molecule. Furthermore, the wavelength dependence of t he Raman intensity calculated by the Ag10CO system agrees with the exp erimental spectrum. The electronic mechanism of the SERS is due to the resonance transitions, in which the surface polarization and the surf ace-molecule interaction are very important. This mechanism explains t he orientation- and distance-dependencies in the surface-adsorbate int eracting systems. (C) 1995 American Institute of Physics.