  A many-body Green's function approach to the microscopic theory of
surface-enhanced Raman scattering is presented. Interaction effects between a
general molecular system and a spatially anisotropic metal particle supporting
plasmon excitations in the presence of an external radiation field are
systematically included through many-body perturbation theory. Reduction of the
exact effects of molecular-electronic correlation to the level of Hartree-Fock
mean-field theory is made for practical initial implementation, while
description of collective oscillations of conduction electrons in the metal is
reduced to that of a classical plasma density; extension of the former to a
Kohn-Sham density-functional or second-order M{\o}ller-Plesset perturbation
theory is discussed; further specialization of the latter to the random-phase
approximation allows for several salient features of the formalism to be
highlighted without need for numerical computation. Scattering and
linear-response properties of the coupled system subjected to an external
perturbing electric field in the electric-dipole interaction approximation are
investigated. Both damping and finite-lifetime effects of molecular-electronic
excitations as well as the characteristic fourth-power enhancement of the
molecular Raman scattering intensity are elucidated from first principles. It
is demonstrated that the presented theory reduces to previous models of
surface-enhanced Raman scattering and leads naturally to a semiclassical
picture of the response of a quantum-mechanical molecular system interacting
with a spatially anisotropic classical metal particle with electronic
polarization approximated by a discretized collection of electric dipoles.
