Surface-enhanced hyper-Raman scattering of Rhodamine 6G isotopologues: Assignment of lower vibrational frequencies

Jacob E Olson; Zhongwei Hu; Michael D Best; Lasse Jensen; Jon P Camden

doi:10.1063/5.0031679

Surface-enhanced hyper-Raman scattering of Rhodamine 6G isotopologues: Assignment of lower vibrational frequencies

J Chem Phys. 2021 Jan 21;154(3):034703. doi: 10.1063/5.0031679.

Authors

Jacob E Olson¹, Zhongwei Hu², Michael D Best³, Lasse Jensen², Jon P Camden¹

Affiliations

¹ Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556-5670, USA.
² Department of Chemistry, The Pennsylvania State University, 104 Chemistry Building, University Park, Pennsylvania 16802-4615, USA.
³ Department of Chemistry, University of Tennessee, 1420 Circle Drive, Knoxville, Tennessee 37996, USA.

PMID: 33499640
DOI: 10.1063/5.0031679

Abstract

We report a comprehensive experimental and theoretical study of the lower-wavenumber vibrational modes in the surface-enhanced hyper-Raman scattering (SEHRS) of Rhodamine 6G (R6G) and its isotopologue R6G-d4. Measurements acquired on-resonance with two different electronic states, S₁ and S₂, are compared to the time-dependent density functional theory computations of the resonance hyper-Raman spectra and electrodynamics-quantum mechanical computations of the SEHRS spectra on-resonance with S₁ and S₂. After accounting for surface orientation, we find excellent agreement between experiment and theory for both R6G and its isotopologue. We then present a detailed analysis of the complex vibronic coupling effects in R6G and the importance of surface orientation for characterizing the system. This combination of theory and experiment allows, for the first time, an unambiguous assignment of lower-wavenumber vibrational modes of R6G and its isotopologue R6G-d4.