Vibrational Spectroscopy of Interfaces Based on Fourth- and Third-Order Time-Domain Raman Processes

Abstract

Vibrational spectroscopy of interfaces was developed by taking advantage of fourth- and third-order Raman processes. An example making use of the fourth-order Raman process is interface-specific vibrational spectroscopy using only visible light. An oxazine dye at an air-solution interface was irradiated with visible 16-fs pump and probe pulses. The fourth-order signal as a function of the pump-probe delay represents the Raman-active nuclear motion. The Fourier transform of the motion provided the vibrational spectrum from 0 to 1000 cm^-1 for the dye at the interface. An example making use of the third-order Raman process is vibrational spectroscopy of molecular films of submonolayer coverage. For a cresyl-violet dye of submonolayer coverage (4 × 10¹³ molecules cm^-2) on a fused silica, the observation of time-resolved reflectance due to the third-order Raman process provided the sensitivity six times higher than in time-resolved transmittance. The vibrational spectrum of the dye at the interface was obtained from 0 to 1000 cm^-1 by the Fourier transform of the reflection signal.