THEORY OF TRANSIENT ANISOTROPY IN MOLECULAR PHOTODISSOCIATION

In this paper, we examine how vector properties of photodissociation with a coherent laser pulse evolve in time during and after the excitation process. In particular, we define and explore the transient anisotropy parameter beta(t). We apply our formulation to the case of the predissociation of the NaI molecule. We predict that under certain conditions, beta(t) displays a beating phenomenon, in which the system oscillates periodically between a parallel-type and a perpendicular-type angular distribution. Depending on the excitation pulse, this ''vectorial'' beating may be accompanied by a faster beating similar to the ''scalar'' vibrational beating observed in the past in the NaI system. It is shown that the transient anisotropy beating may be used to obtain experimentally the time-dependent average interfragment separation, and that different J states are characterized by different interfragment separation curves.