FEMTOSECOND REAL-TIME PROBING OF REACTIONS .18. EXPERIMENTAL AND THEORETICAL MAPPING OF TRAJECTORIES AND POTENTIALS IN THE NAI DISSOCIATIONREACTION

We describe a method of tracking wave packet trajectories by probing b oth the temporal and spatial evolution of a coherent state prepared by a femtosecond laser pulse in real time. Application to the NaI dissoc iation reaction illustrates this technique, in which the direction of wave packet propagation within the quasi-bound A 0(+) potential is obs erved and correlated to the physical processes of extension and contra ction of the Na-I bond. From the combination of spatial and temporal i nformation observed from experiments, self-consistent potential energy functions for the A 0(+) state and the higher-lying state accessed by the probe laser pulse are constructed. The dynamics and the validity of the potentials so derived are tested via semiclassical and quantum- dynamical simulations of the wave packet motion, and comparisons with potentials obtained from other methods are drawn.