Pump- And Probe-Wavelength Dependencies of Picosecond Anti-Stokes Raman Spectrum of Trans-Stilbene in the S1 State

Vibrational relaxation dynamics of trans-stilbene in the S 1 state immediately afterphotoexcitation is studied by picosecond time-resolved anti-Stokes Raman spectroscopywith several pump and probe wavelengths. Pump-wavelength dependence of the anti-Stokes spectrum indicates that, when pump photons with high excess energy(≈5200cm -1 ) are used, the anti-Stokes Raman bands at 0 ps delay time arise fromvibrationally excited transients with excess vibrational energy not thermally distributedin the molecule. Probe-wavelength dependence suggests that the vibrationally excitedtransients at 0 ps are mostly on the lowest excited vibrational levels, as far as the olefinicC═C stretching and the C–Ph stretching modes are concerned. The vibrationalrelaxation process of S 1 trans-stilbene is discussed on the basis of the observed results.