FEMTOSECOND REAL-TIME PROBING OF REACTIONS .13. MULTIPHOTON DYNAMICS OF IHGI

Real-time studies of the dynamics were performed on the reaction of Hg I2 in a molecular beam. Excitation was by either one or multi pump pho tons (311 nm), leading to two separate sets of dynamics, each of which could be investigated by a time-delayed probe laser (622 nm) that ion ized the parent molecule and the fragments by REMPI processes. These d ynamics were distinguished by combining the information from transient s taken at each mass (HgI2, HgI, I2, Hg, and I) with the results of pu mp (and probe) power dependence studies on each mass. A method of plot ting the slope of the intensity dependence against the pump-probe time delay proved essential. In the preceding publication, we detailed the dynamics of the reaction initiated by a one photon excitation to the A-continuum. Here, we present studies of higher-energy states. Multiph oton excitation accesses predissociative states of HgI2, for which the re are crossings into the symmetric and asymmetric stretch coordinates . The dynamics of these channels, which lead to atomic (I or Hg) and d iatomic (Hgl) fragments, are discussed and related to the nature of th e intermediates along the reaction pathway.