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 S₁ state immediately after photoexcitation is studied by picosecond time-resolved anti-Stokes Raman spectroscopy with 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 from vibrationally excited transients with excess vibrational energy not thermally distributed in the molecule. Probe-wavelength dependence suggests that the vibrationally excited transients at 0 ps are mostly on the lowest excited vibrational levels, as far as the olefinic C = C stretching and the C-Ph stretching modes are concerned. The vibrational relaxation process of S₁ trans-stilbene is discussed on the basis of the observed results.