Excited-state vibrational coherence of solution-phase molecules observed in the third-order optical process using extremely short pulses

Abstract

Excited-state vibrational coherence of solution-phase polyatomic molecules was studied by two different time-domain spectroscopic methods. Raman-active low-frequency vibrations in the excited state of trans-stilbene were observed by transient impulsive stimulated Raman scattering spectroscopy. In transient absorption spectroscopy with a 40-fs resolution, a different vibrational mode of the same excited state was observed as a 'beat' in the pump-induced absorption signal. The selection of the vibrational modes was discussed by noting the difference in the third-order optical processes relevant to the two spectroscopies. The vibrational coherence of a 'reacting' excited state was also observed for ultrafast photodissociation of diphenylcyclopropenone.