Raman scattering from nonequilibrium molecular conduction junctions.

Raman scattering is a potentially important probe of structure, dynamics, and thermal properties of single-molecule conduction junctions. We combine a nonequilibrium Green's function description of the junction with a generalized scattering theory of the Raman process, which provides the first theoretical description of Raman scattering from such systems. The voltage dependence of the Raman flux shows a characteristic behavior at the conductance threshold resulting from (a) partial populations in the ground and excited molecular levels that give rise to two scattering pathways as well as interference between them and (b) junction heating that affects the Raman intensities. Comparing "effective temperatures" obtained from Raman scattering and heat balance serves to establish the integrity of this concept for nonequilibrium junctions.