Many-body theory of surface-enhanced Raman scattering

TL;DR

This paper develops a comprehensive many-body Green's function framework for surface-enhanced Raman scattering, incorporating molecular-electronic interactions and metal plasmon effects to explain key phenomena from first principles.

Contribution

It introduces a systematic many-body approach to model surface-enhanced Raman scattering, bridging quantum molecular interactions with classical plasmonic responses.

Findings

Elucidates damping and lifetime effects on molecular excitations.

Derives the characteristic fourth-power Raman enhancement.

Shows the theory reduces to previous models and a semiclassical picture.

Abstract

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.