Surface enhanced Raman scattering from a single molecule adsorbed on a metal particle aggregate: A theoretical study

A methodology for the theoretical evaluation of Raman intensities for a molecule adsorbed on a metal particle aggregate, possibly in the presence of a solvent, is presented. The molecule is treated at the ab initio level, both in the evaluation of ground state electronic density and nuclear geometry, and in the evaluation of normal modes and Raman scattering factors. The whole metal aggregate, built by exploiting a Cluster-Cluster Aggregation (CCA) model, is described as an ensemble of polarizable dipoles. The metal particles nearest to the molecule are treated as a single complex shaped metal nanoparticle and the quasielectrostatic problem for the molecule-nanoparticle system is solved by using a Boundary Element Method (BEM). The solvent is modeled by using the Polarizable Continuum Model (PCM). Applications of the methodology to systems for which huge enhancements (10(13)-10(14)) of Raman intensities have been experimentally measured are given. (C) 2002 American Institute of Physics.