Overtone Vibrational Dephasing in Liquids Studied by Femtosecond Fifth-Order Nonlinear Spectroscopy

We have directly observed vibrational dephasing of the first overtone bands in liquids by femtosecond fifth-order nonlinear spectroscopy for the first time to our knowledge. The overtone and fundamental dephasing processes have been studied for the C-D stretching of CDCl₃ and the sym-methyl stretching of CD₃I in neat liquid and in its binary mixture with CHCl₃. Simulations based on simple stochastic theory or perturbation theory for a harmonic oscillator do not explain both the overtone and fundamental dephasing simultaneously.