FEMTOSECOND CONTROL OF AN ELEMENTARY UNIMOLECULAR REACTION FROM THE TRANSITION-STATE REGION

We present a simple example of temporal control of the evolving dynami cs in a reactive system - a unimolecular reaction with two channels. U sing three femtosecond pulses, a wave packet is prepared, probed, and intercepted in the transition-state region. The femtosecond control pu lse intercepts the predissociative system at a fixed time and internuc lear separation, both determined by the 'window' of the laser pulse. E xperiments are performed on the NaI system which is a prototype for st udies of elementary nuclear motion and reaction dynamics along two pot entials, the covalent (Na+I) and the ionic (Na++I-) channels.