| Abstract
| - Time-domain Raman measurement of the excited state of a polyatomic molecule was demonstrated for thefirst time. Time-resolved impulsive stimulated Raman scattering (TR-ISRS) measurements were carried outfor trans-stilbene in solution, and resonantly enhanced signals due to the S1 state were observed under theresonance condition with the Sn ← S1 absorption. The observed signal consisted of a spike-like feature aroundthe time origin, an oscillatory component with a period of ∼0.12 ps, and a slowly decaying traditional transient-grating (TG) signal. A Fourier transform analysis clarified that the oscillatory ISRS component was attributedto an in-plane bending vibration of S1trans-stilbene (ν24, 285 cm-1). The origin of the TG signals was examinedby three-pulse absorption measurements, and it was concluded that the transient grating was created reflectingtwo relaxation processes following the Sn ← S1 excitation: the vibrational cooling process of S1trans-stilbeneand the loss of the S1 population. The present study demonstrated that time-resolved time-domain Ramanspectroscopy can provide spectral information about low-frequency tetrahertz motions of the excited-state,which cannot be accessed by ordinary time-resolved frequency-domain Raman spectroscopy.
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