FEMTOSECOND PHOTOASSOCIATION - COHERENCE AND IMPLICATIONS FOR CONTROLIN BIMOLECULAR REACTIONS

A theoretical analysis of the recent femtosecond photoassociation spec troscopy (FPAS) experiment on mercury [U. Marvet and M. Dantus, Chem. Phys. Lett. 245, 393 (1995)] is presented. It is shown that when a the rmal distribution of diatom collision pairs is excited from a free to a bound electronic state on a time scale shorter than molecular vibrat ion, an ensemble of coherent wave packets is produced. The dynamics of these wave packets created by the photoassociation pulse can be obser ved by firing a second probe pulse at variable time delays, and the de pletion of the first excited bound state by the probe pulse is detecte d via fluorescence of the remaining population. Simulations of the FPA S experiment, using both wave packet propagation techniques and pertur bation theory, clearly show the vibrational dynamics of the photoassoc iated transients. It is also demonstrated how the FPAS technique may b e used as a tool for controlling the energy, impact parameter, and ori entation in bimolecular reactions. (C) 1997 American Institute of Phys ics.