Ultrafast Vibrational Dynamics of Water Interfaces Revealed by Time-Resolved Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy

Abstract

Molecular-level understanding of interfaces is of crucial importance in many fundamental and applied sciences. Vibrational sum frequency generation (VSFG) spectroscopy has intrinsic interface-selectivity and has been widely utilized to study molecular structures and dynamics at interfaces. However, conventional VSFG spectroscopy measures the intensity of the signal, providing only information about the square of second-order nonlinear susceptibility, |χ⁽²⁾|². Recently, we developed multiplex heterodyne-detected (HD-) VSFG spectroscopy. This HD-VSFG spectroscopy enables us to measure the imaginary part of χ⁽²⁾, Imχ⁽²⁾, which can be directly compared to infrared absorption and Raman spectra. Moreover, we have extended the HD-VSFG spectroscopy to time-resolved (TR-) HD-VSFG spectroscopy and two-dimensional (2D) HD-VSFG spectroscopy by combining with the pump-probe technique. This review describes development of these time-resolved HD-VSFG methods and their applications to the water interfaces.