Infrared spectroscopy and vibrationally mediated dynamics of peroxynitrous acid and reactant complexes of oxygen-deuterium with nitrogen, methane, and carbon monoxide

An infrared pump-ultraviolet probe technique is used to investigate the CH4-OD and OD-CO reactant complexes formed in the shallow attractive well in the entrance channel to reaction. Infrared radiation selectively excites the complex in the OD overtone region supplying sufficient energy to break the weak intermolecular bond and leading to vibrational predissociation and/or chemical reaction. Ultraviolet radiation then probes the OD fragments resulting from inelastic decay of the vibrationally activated complex. Changes in the spectroscopic constants and vibrational frequencies upon deuteration of the hydroxyl moiety are used to characterize the geometric structure, spectral shift, and intermolecular vibrations of these complexes. Deuteration is also used as a means of slowing down the rapid inelastic decay processes previously observed for vibrationally activated CH4-OH and OH-CO, as initially demonstrated by comparing the infrared spectroscopy and decay dynamics of the non-reactive OD-N2 complex to that previously characterized for OH-N2. Changes in the lifetime, OH/D product state distribution, and infrared action intensities upon OH/D overtone and intermolecular bending excitation are evaluated to provide further information about the overall decay rate and vibrational predissociation mechanism of each complex. The same high-resolution spectroscopy technique is used to investigate peroxynitrous acid (HOONO), a less stable isomer of nitric acid, in the gas phase under supersonic jet-cooled conditions. The rotational band contour observed in the experimental spectrum allows for definitive identification of the OH overtone transition of the trans-perp (tp) conformer of HOONO. Further analysis of the rotationally resolved band structure yields spectroscopic constants for tp-HOONO, the orientation of the transition dipole moment, and the decay rate of the initially prepared vibrational state. The nascent quantum state distribution of the OH fragments resulting from dissociation of vibrationally activated tp-HOONO firmly establishes its binding energy. The binding energy for the more stable cis-cis conformer is subsequently determined from its theoretically predicted increase in stability