Ultrafast dynamics of the В state of I2 in condensed rare gases

The resonance Raman overtone progressions of I2 in liquid Xe following excitation of the В state are discussed and compared with similar data in solid Ar. It is shown that the Raman contribution from the В state is damped by predissociation within one recurrence and the Raman emission can be treated as that of an outgoing wave packet crossing over to purely repulsive B", a and a' states. The curve crossing can be localised in space and time from the Raman data. Predissociation to B" is important, especially for excitation near the bottom of the well. A Golden-Rule type of expression describes the data poorly and a Landau-Zener approach is used. The coupling is induced by the solvent and similarities between liquid Xe and solid Ar indicate that structural details of the surroundings are of minor importance since the transition occurs already during the first elongation. A broad emission background from resonance and vibrationally hot fluorescence is also observed. It is attributed to incoherent returns of the predissociated wave packets in the В state Franck-Condon region and to vibrational cooling.