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.
- Anti-Stokes Raman scattering
- Resonance Raman excitation profiles
- Time-resolved Raman spectroscopy
- Vibrational relaxation