# DISSOCIATION DYNAMICS OF VIBRATIONALLY EXCITED TRANS-PERP HOONO

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 Title: DISSOCIATION DYNAMICS OF VIBRATIONALLY EXCITED TRANS-PERP HOONO Creators: Konen, Ian M.; Pollack, Ilana B.; Li, Eunice X. J.; Lester, Marsha I. Issue Date: 2004 Publisher: Ohio State University Abstract: Peroxynitrous acid (HOONO) is formed by the reaction of OH and $NO_{2}$ in conjunction with the more stable isomer, nitric acid ($HONO_{2}$). Determination of the HOONO binding energy is essential for atmospheric models to correctly budget these two reactive radical species. We have used an infrared pump-ultraviolet probe technique to obtain an accurate measurement of the binding energy of the trans perp (tp) conformer. The OH ($v = 0$) rotational state distribution resulting from vibrational predissociation of tp-HOONO ($2\nu_{OH}$) was measured by saturated laser induced fluorescence, and found to be consistent with a statistical model. A dissociation energy of 16.2 kcal/mol was obtained from the best fit of the data to a prior distribution, and is complemented by the value inferred from the highest energy channel with observable population. This information, combined with an ab initio calculation of 3.4 kcal/mol for the relative conformational $stability,^{a}$ provides an estimate of 19.6 kcal/mol for the binding energy of the more stable cis-cis (cc) conformer. Additional insight into the decay dynamics is provided by the $0.2 cm^{-1}$ linewidth observed in the IR spectrum. A discussion is presented on the likely origin of this homogeneous broadening (corresponding to a 30 ps lifetime) in terms of intramolecular vibrational redistribution (IVR) and unimolecular dissociation. Description: $^{a}$Bean, B. D. et al., J. Phys. Chem. A 107, 6974 (2003). Author Institution: Department of Chemistry, University of Pennsylvania URI: http://hdl.handle.net/1811/21449 Other Identifiers: 2004-TI-02