Molecular Dynamics and Energy Transfer in Pure Aniline and Rh101+/Aniline Mixed Solution Measured by Ultrafast Spectroscopy

Energy transfer is an important phenomenon of physicochemical systems vibrationally coupled to an environmental bath. For a condensed system, energy exchange from one mode to another is the first step of chemical reactions. In this work, we use femtosecond time- and frequency-resolved coherent anti-Stokes Raman scattering (CARS) spectroscopy technique to track molecular dynamics and energy transfer in pure aniline and its mixed solutions. In pure aniline, oscillatory structures in time- and frequency-resolved CARS spectra indicate that vibrational modes participate in the vibrational coupling, and the vibrational coupling process is necessary for energy transfer. In the Rh101(+)/aniline mixed solution, vibrational dynamics and energy transfer processes are not detected due to strong hydrogen interactions. By comparing the experimental results for the pure aniline and the Rh101(+)/anilinemixed solution, we find that energy transfer in the pure aniline depends mainly on the vibrational coupling; in the Rh101(+)/aniline mixed solution, hydrogen bonds act as the molecular damper, which leads to a faster decay in the vibrational dynamics.