PNNL

Abstract

We record sequences of Raman spectra at a plasmonic junction formed by a gold AFM tip in contact with a silver surface coated with 4,4’-dimercaptostilbene (DMS). A 2D correlation analysis of the recorded trajectories reveals that the observable vibrational states can be divided into sub-sets. The first set comprises the totally symmetric vibrations of DMS (ag) that are neither correlated with each other nor to the fluctuating background, which is assigned to the signature of charge transfer plasmons tunneling through DMS. The second set consists of bu vibrations, which are correlated both with each other and with the continuum. Our findings are rationalized on the basis of the charge-transfer theory of Raman scattering, and illustrate how the tunneling plasmons modulate the vibronic coupling term from which the intensities of the bu states are derived.