Capturing interference variations of atomic motion in vibrational modes by non-resonant Raman images

Abstract

Non-resonant Raman imaging associated with vibrational modes provides an optical means to structure and function characterisation for a single molecule, where the interference between atomic motions in a vibrational mode plays an important role. Taking the [18]annulene as a proof-of-the-concept molecule, we present here a comprehensive study on the dependence of non-resonant Raman images on interference variations involving the phase and amplitude of atomic displacements in vibrational modes. Calculations demonstrate that constructive and destructive phase interferences contribute to the characteristic merging and repulsion of Raman patterns, respectively, which should be attributed to the same/opposite signs of Raman polarisability. In addition, the imaging characteristic by constructive and destructive interferences become more significant with the increase of plasmonic size. Moreover, Raman images are highly sensitive to the subtle variations of interference induced by molecular symmetry and element substitution, highlighting the importance of amplitude variations of interference in modes for Raman images to monitor molecular structure changes. Our findings propose the capability of Raman images toward capturing interference variations in modes, serving as good references for Raman imaging to characterise various molecules and their corresponding structure changes by analysing interference effects in vibrational modes.