VIBRATIONAL PREDISSOCIATION SPECTROSCOPY OF PROTONATED MOLECULES

Author Institution: Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of TechnologyProtonated chlorine nitrate and protonated nitric acid have been proposed as important reactive intermediates in stratospheric chemistry. We report infrared spectra which reveal that both of these species can exist in two isomeric forms, depending on the site of Protonation, consistent with {ab initio} studies by Lee and Rice. The most stable isomers are weakly bound complexes, $NO_{2}^{+}(H_{2}O)$ and $NO_{2}^{+}(HOCl)$, formed by Protonation of the OH(CIO) group. These clusters readily predissociate upon absorption of one or two photons pumping the OH stretch bands. Protonation of a terminal O atom form higher energy covalently-bound species which must isomerize by a photon-induced intramolecular proton transfer in order to dissociate. These isomers can be distinguished by their infrared spectra and the conditions for their formation. Anomalous intensities in the IR spectrum of a related ionospheric species, protonated nitrous acid, suggest that dynamical effects (IVR or dissociation rates) may be important in determining intensities observed in two-photon predissociation spectra