Vibrational energy redistribution of selectively excite liquid acetonitrile

Selective excitation of parent modes and detection of the intramolecular vibrational energy flow to daughter modes is proposed by the femtosecond time-resolved coherent anti-Stokes Raman scattering (CARS) spectroscopy. Vibrational modes of CCN bending at 379 cm −1 , CN stretching at 2253 cm −1 and CH stretching at 2943 cm −1 are excited, energy flow to relative higher frequency ones located outside the excitation range is described. The up-hill energy flow from lower frequency modes to higher ones is related to the vibrational symmetry and vibrational couplings. With analysis of quantum beats arising from vibrational coupling, the CCN bending at 379 cm −1 is a doorway mode which makes energy transfer from outside to inside of the acetonitrile molecule and the CC stretching mode at 917 cm −1 is stagnation-point of vibrational energy redistribution.