15min:

BRIDGET A. O'DONNELL, CRAIG MURRAY AND MARSHA I. LESTER, Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323.

Hydroxyl radicals (OH) are expected to form strong hydrogen bonds with water (H₂O), making complexes of OH with water important for a variety of systems, such as the gaseous environment of the atmosphere, the interface of water and/or ice, and the bulk regions of liquid water, snow, and ice. The study of binary OH-water complexes will shed new light on the intermolecular interaction between the OH radical and water molecule in these environments. In this study, the OH-H₂O complex is produced in the gas phase by the association of photolytically generated OH radicals with H₂O in the collisional region of a supersonic expansion. Infrared spectroscopy is used to identify a band at 3491 cm^-1, displaying a shift of --79 cm^-1 from its hydroxyl monomer, which is consistent with ab~initio predictions of the fundamental OH radical stretch of the complex. The rotationally structured band profile is modeled using a simulation based on an a-type transition for an open-shell complex with partially quenched orbital angular momentum. Following infrared excitation of OH-H₂O, the OH products of vibrational predissociation are detected by laser-induced fluorescence on the OH A ^{2 +}-- X ² (1,0) transition. By utilizing information from the OH product state distribution, an upper limit to the binding energy of the complex will be determined.