Theoretical Formulation and Simulation of Electronic Sum-Frequency Generation Spectroscopy

Abstract

Sum-frequency generation (SFG) spectroscopy is a powerful tool for not only identifying molecular species but also analyzing orientation configurations on a surface/interface. In this Article, we presented reformulation of the theoretical framework of electronic SFG spectroscopy, the signal of which could be greatly enhanced by tuning one or two incident beam frequencies resonant with electronic excited states. Simulated electronic SFG spectra resonant at the sum frequency of a pair of coumarin-derivative pH-indicator surfactant molecules, 4-methyl-7-hydroxycoumarin and its anionic counterpart (MHC/MHC-), floating on the water surface were carried out as a demonstration.