Surface-enhanced hyper-Raman scattering (SEHRS) provides complimentary information to surface-enhanced Raman scattering (SERS). If the near field is described accurately, SEHRS simulations can provide valuable information, such as molecular orientation to surfaces. While much progress has been made to understand the local electric fields generated from plasmonic nanoparticles, little has been done to understand how solvent affects the observed SEHRS signal. The Discrete Interaction Model / Quantum Mechanics (DIM/QM) method was developed in conjunction with molecular dynamics to simulate pyridine in a nanoparticle junction in aqueous solution. By using this method, perturbations from the solvent and the nanoparticles were included in all geometries, frequencies, and hyperpolarizabilities. In order to overcome the computational burden of explicit solvation, a reduced model was implemented. This reduced model included image dipoles and total near field contribution from atoms close to the analyte while only including the near field contribution from atoms farther away. The effect of the explicit solvent on the near field was investigated for SEHRS and compared to SERS and Raman calculations both with and without solvent. We find that the simple |E(ω)|<sup>4</sup>|E(2ω)|<sup>2 </sup>approximation does not hold for SEHRS. While the inclusion of solvent screens the Raman intensity, we find that including solvent increases the SERS and SEHRS intensity. We also see that including solvent changed which vibrational mode was most intense for pyridine’s Raman spectra, matching what was seen in experiment.

Simulating nonlinear surface-enhanced vibrational spectroscopy in aqueous solution

2019 Fall National Meeting

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