INFRARED ACTION SPECTROSCOPY OF THE OH-H$_{2}$O COMPLEX

Abstract

Hydroxyl radicals (OH) are expected to form strong hydrogen bonds with water (H$_2$O), 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-H$_2$O complex is produced in the gas phase by the association of photolytically generated OH radicals with H$_2$O in the collisional region of a supersonic expansion. Infrared spectroscopy is used to identify a band at 3491 \wn, displaying a shift of --79 \wn from its hydroxyl monomer, which is consistent with $\it ab~initio$ predictions of the fundamental OH radical stretch of the complex.} The rotationally structured band profile is modeled using a simulation based on an $\it a$-type transition for an open-shell complex with partially quenched orbital angular momentum.} Following infrared excitation of OH-H$_2$O, the OH products of vibrational predissociation are detected by laser-induced fluorescence on the OH {\it A,}$^2\Sigma^+$--{\it X,}$^2\Pi$ (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.