Symmetric Raman Tensor Contributes to Chiral Vibrational Sum-Frequency Generation from Binaphthyl Amphiphile Monolayers on Water: Study of Electronic Resonance Amplitude and Phase Profiles

Heterodyne-detected vibrationally electronically doubly resonant chiral sum-frequency generation (HD-DR chiral SFG) spectra were observed for the first time on mono layers. Langmuir monolayers of R- and S-binaphthyl amphiphiles on water exhibited complex chiral vibrational sum frequency generation (VSFG) spectra whose amplitudes were approximately the same, but whose phases were different by pi. By comparing the electronic resonance profiles of the chiral VSFG signal amplitude and phase with simulations based on a nonadiabatic resonance Raman theory, we concluded that the chiral VSFG signals from the monolayers originated not from the antisymmetric Raman tensor but from the symmetric one. This is the first experimental evidence that the symmetric Raman tensor indeed contributes to the chiral VSFG signals from oriented monolayer systems.