Ultrafast Dynamics in Solution: Wavepacket Motion and the Cage Effect in Iodine

Abstract

In a recent series of experiments at Caltech,1 65-90 fs tunable laser pulses are used to pump I2, both in the gas phase and in Ar solution, from the ground state to the electronically excited B state. The dynamics of I2 in the B state is then monitored by a time-delayed probe pulse which excites the I2 molecule further, to the f or E state. Absorption or fluorescence resulting from the probe pulse is measured as a function of delay time between the two pulses. The dynamics of the wavepacket on the B state is governed by the shape of the potential and the nature of the solvent environment. The initial pumped packet is influenced by the coherent nature of the pump pulse and the Franck-Condon overlaps between the initial thermal distribution of the ground state and the B state vibrational manifold.