Studying substituent number effects on vibrational energy transfer by time−resolved CARS spectroscopy

Vibrational energy transfer was a key property of chemical reactions that remains deeply understood. In this work, the detail information of vibrational energy transfer in aniline, N,N-dimethylaniline (DMA) and N,N-diethylaniline (DEA) were studied by femtosecond time-resolved coherent anti-Stokes Raman scattering (CARS) spectroscopy, respectively. Low frequency modes of aniline, DMA and DEA were collectively excited, the beats arising from vibrational couplings among these modes were described. With analysis of vibrational coupling, energy transfer flow from one mode to another was visualized. An investigation into the molecular structure and vibrational couplings can be found that vibrational energy transfer is related to vibrational mode symmetry. In addition, substituent groups play an important role in vibrational coupling and energy transfer of aniline, DMA and DEA. A decrease of the number of substituent vibrational modes involved in coupling and energy transfer efficiency with the increase of the amount of relative molecular mass ratio was found out.