In this project, supported by the Physical Chemistry Program of the Chemistry Division, Profs. M. Alexander of the University of Maryland and P. Dagdigian of Johns Hopkins University will pursue a joint theoretical-experimental effort to determine how molecular collisions and photodissociations are affected by molecular energy states. In particular, since molecular energy states are rarely the idealized, independent states used in the initial stages of theoretical formulations, the interactions between them play a signifant role in determining the details of the collision and photodissociation processes. Several prototypical free radical molecules, including di-and triatomic monohydride species, will be investigated. The theoretical portion of this project (M. Alexander) involves the development of new methods to elucidate the mechanism of molecular collisions and photodissociation. The experimental portion (P. Dagdigian) involves the determination of cross sections for inelastic collisions in which molecules undergo energy changes. Also to be determined are the distributions over the internal energy states of a molecular fragment that results from the photodissociation of the parent molecule. %%% Molecular energies are considered in the main to be the result of translational, rotational, vibrational and electronic motions, with the latter being made up of orbital and spin contributions. This separation of the total energy into independent contributions is, however, only an idealized first step in the conceptual model of molecular structure and dynamics, and allowing for interactions between these motions is necessary in order to account for the observed molecular properties. Photodissociations and collisions between molecules are also affected by these interactions, which are particularly evident in open shell (free radical) molecules. The investigations to be carried out in this research will contribute to the understanding of these processes and will assist in establishing the limits of validity of the fundamental Born-Oppenheimer approximation to open shell molecules.
