Femtosecond Coherent Anti-Stokes Raman Spectroscopy (fs-CARS) with Nitrobenzene and Nitomethane

Abstract

Time-resolved coherent anti-Stokes Raman Scattering (CARS) is a nonlinear spectroscopic tool, which has gained importance with the development of ultrafast lasers due to its ability to probe ultrafast dynamical processes in molecules. Apart from the time resolution, the superiority of CARS over spontaneous Raman scattering derives from its high signal generation ability and coherent, laser like, signal emission. In this contribution, we describe the development of an experimental facility for the time-resolved coherent anti-Stokes Raman scattering spectroscopy and its application to study the vibrational dynamics of molecules containing nitro (NO2) groups. fs-CARS experiments were carried out in neat liquids of nitrobenzene, nitromethane and their mixture. A detailed mapping of the dynamics initiated by the stimulated Raman process is achieved from the spectrum of the transient CARS signal. The CARS transient shows rich beating structure corresponding to frequencies as high as 10 THz. The Fourier transform of the transient allows accurate determination of the vibrational energy differences.This methodology is capable of providing the dephasing behaviour and spectral information of the molecular system at the same time.The results demonstrate that CARS spectroscopy with femtosecond time resolution and wavenumber-resolved detection is a powerful tool for the characterization of dynamics in the electronic ground state of molecules.