This research, part of the Experimental Physical Chemistry Program, is designed to provide insights into the structure and dynamics of transient molecular species involved in chemical reactions, spectroscopy of clusters and photodissociation dynamics of free radicals. This research is supported by a Presidential Young Investigator Award (PYI). The experiments will be carried out using molecular negative ion beams. A mass selected fast (3-5 KeV) ion beam is photodetached with a laser tuned just above the electron binding energy of the ions. This yields a fast beam of neutral radicals in their ground vibrational state. A second laser photodissociates the radicals, and a two particle position sensitive detector yields the masses as well as the center-of-mass angular and velocity distributions of the photofragments. These data are then interpreted to yield information on the structure and dynamics of the species studied.