Ultrafast intramolecular and caging dynamics in solvents from frequency-domain experiments

A summary of results on the resonance Raman study of I2 in CCl4 and liq. Xe is presented. No discrete fluorescence can be obsd. upon excitation in the bound parts of the B state and instead a resonance Raman spectrum shows up superimposed on a broad fluorescence background. In the time-dependent picture, the resonance Raman spectrum is a signature of the excited state dynamics before the wavepacket decays by dephasing and/or depopulation. The latter is caused by solvent-induced curve crossing events to the purely repulsive B, a and a' states and the spectra deliver information about their time and location. From a Landau-Zener treatment, the matrix elements are derived for the crossing from B to B which plays a central role in the dynamics at very early times. The broad fluorescence background is due to incoherent returns of the fragments within the observation window. Structures show up in the resonance Raman overtone intensities for excitation in the continuum part of the B state and are attributed to coherent recoils of fragments in the solvent cage. [on SciFinder (R)]