  This is a preliminary acount of a theory for Raman scattering by
current-carrying molecular junctions. The approach combines a non-equilibrium
Green's function (NEGF) description of the non-equilibrium junction with a
generalized scattering theory formulation for evaluating the light scattering
signal. This generalizes our previous study (Phys. Rev. Lett. 95, 206802
(2005); J. Chem. Phys. 124, 234709 (2006)) of junction spectroscopy by
including molecular vibrations and developing machinery for calculation of
state-to-state (Raman scattering) fluxes within the NEGF formalism. For large
enough voltage bias we find that the light scattering signal contains, in
addition to the normal signal associated with the molecular ground electronic
state, also a contribution from the inverse process originated from the excited
molecular state as well as an interference component. The effect of coupling to
the electrodes and of the imposed bias on the total Raman scattering as well as
its components are discussed. Our result reduces to the standard expression for
Raman scattering in the isolated molecule case, i.e. in the absence of coupling
to the electrodes. The theory is used to discuss the charge transfer
contribution to surface enhanced Raman scattering for molecules adsorbed on
metal surfaces and its manifestation in the biased junction.
