Ultrafast intramolecular and caging dynamics of I-2 in CCl4 from resonance Raman spectroscopy

The resonance Raman overtone progressions of I-2 in CCl4 following excitation in the bound and continuum parts of the B state are presented. It is shown that the Raman contribution from the bound part is damped by predissociation as that of an outgoing wavepacket crossing over to the purely repulsive B '' (1) Pi(1u), (3) Pi(2g), a (3) Pi(1g) and a' (3) Sigma(g)(-)(0) states. The Raman data deliver information about location and time of curve crossing events which is consistent with the previous results in liquid Xe and the femtosecond pump-probe studies in liquids. For excitation in the continuum part, the Raman overtone intensities show structures which are assigned to a coherent recoil of fragments in the cage. In addition, a broad structureless emission background appears for all excitation wavelengths shorter than 570 nm, which is assigned to incoherent recoils caused by vibrational relaxation and return of the I atoms in the Franck-Condon window of the B state to the ground state. (C) 1997 by John Whey & Sons, Ltd.