Transient vibrational temperatures estimated from anti-Stokes and Stokes Raman intensities and vibrational cooling of electronically excited trans-stilbene in solution

To examine vibrational cooling of trans-stilbene in the S₁ state, transient temperatures of a few vibrational modes were estimated by analyzing transient anti-Stokes and Stokes Raman intensities. Vibrational temperatures obtained for the olefinic C=C and C-Ph stretches are 900 and 680 K, respectively, at 0 ps after photoexcitation (temporal resolution ca 5 ps). These values are higher than the equilibrium temperature (ca 550 K) calculated for a statistical distribution of excess vibrational energy. Ultrafast intermolecular energy flow (vibrational cooling) is discussed based on a model analysis. Copyright (C) 2000 John Wiley and Sons, Ltd.