Picosecond anti-Stokes Raman excitation profiles as a method for investigating vibrationally excited transients

A method for estimating vibrational quantum numbers of vibrationally excited transients in solution is proposed. In this method, we calculate anti-Stokes Raman excitation profiles (REPs) which are characteristic of the initial vibrational states involved in the Raman process, and compare them with observed anti-Stokes intensities. We have applied this method to vibrationally hot molecules of canthaxanthin in the S₀ state and those of trans-stilbene in the S₁ state. For canthaxanthin, it has been found that the vibrationally excited transients are for the most part on the v = 1 level of the C = C stretching mode, and that excess vibrational energy is statistically distributed among all intramolecular vibrational modes. As for S₁ stilbene, vibrational transients are shown to be mostly on the v = 1 level for two vibrational modes examined, while the excess vibrational energy is probably localised on the olefinic C = C stretching mode.