Infrared overtone spectroscopy and unimolecular decay dynamics of peroxynitrous acid

Abstract

Peroxynitrous acid (HOONO) is generated in a pulsed supersonic expansion through recombination of photolytically generated OH and NO(2) radicals. A rotationally resolved infrared action spectrum of HOONO is obtained in the OH overtone region at 6971.351(4) cm(-1) (origin), providing definitive spectroscopic identification of the trans-perp (tp) conformer of HOONO. Analysis of the rotational band structure yields rotational constants for the near prolate asymmetric top, the ratio of the a-type to c-type components of the transition dipole moment for the hybrid band, and a homogeneous linewidth arising from intramolecular vibrational energy redistribution and/or dissociation. The quantum state distribution of the OH (nu=0,J(OH)) products from dissociation is well characterized by a microcanonical statistical distribution constrained only by the energy available to products, 1304+/-38 cm(-1). This yields a 5667+/-38 cm(-1) [16.2(1) kcal mol(-1)] binding energy for tp-HOONO. An equivalent available energy and corresponding binding energy are obtained from the highest observed OH product state. Complementary high level ab initio calculations are carried out in conjunction with second-order vibrational perturbation theory to predict the spectroscopic observables associated with the OH overtone transition of tp-HOONO including its vibrational frequency, rotational constants, and transition dipole moment. The same approach is used to compute frequencies and intensities of multiple quantum transitions that aid in the assignment of weaker features observed in the OH overtone region, in particular, a combination band of tp-HOONO involving the HOON torsional mode.

Rotational spectral studies of O(1D) insertion reactions with methane and ethylene: Methanol and vinyl alcohol in a supersonic expansion

“…The resultant O( 1 D) underwent collisions with other molecules in the fused silica tube, where methanol was formed from O( 1 D) insertion into methane. As shown by Lester and coworkers [6,7], initiating the laser-induced chemistry in the fused silica tube before the expansion helps to promote product formation and stabilization through collisions. Use of a UV-grade fused silica cylindrical lens to focus the laser light onto the tube was found to increase methanol product yield as compared to the use of a spherical lens for focusing the laser light; this arrangement is the same as that used by Lester and coworkers in recent studies [66].…”

“…All studies were performed with the gas samples at room temperature; previous studies using this type of source determined that the gas temperature in the capillary tube dropped by 3 K [7]. We therefore assume that the gas in the capillary can be approximated to be at room temperature.…”

“…The Ar/O 3 /O 2 /CH 4 gas mixture was delivered via a pulsed valve (Parker Hannifin, Series 9) into a 3 cm long, 1 mm inner diameter UV-grade fused silica capillary tube (Wilmad Glass) before it was supersonically expanded into the vacuum chamber. The fused silica tube was attached to the valve faceplate with epoxy (TorrSeal); the design of the source was based on that used by Lester and coworkers [6,7]. The valve was driven at a repetition rate of 56 Hz with an on duration of 2-4 ms. An effective pumping speed at the valve of ∼250 L s −1 was maintained using a rotary vane + roots blower pumping system.…”

“…We have adapted the supersonic expansion photolysis source design of Lester and coworkers [6,7] to produce O( 1 D), which then reacts with a precursor molecule to form the target species. We are utilizing the structure-specificity of millimeter/submillimeter rotational spectroscopy to monitor the reactants and products throughout the experiment.…”

Rotational spectroscopy and dipole moment of cis-cis HOONO and DOONO

“…6 Recent kinetics and spectroscopy experiments have found both the direct and indirect evidence for HOONO production in the OH + NO 2 reaction, 2,[6][7][8] and the vibrational spectroscopy of HOONO is a subject of continued study. [9][10][11][12] The current best estimate of the HOONO / HONO 2 branching ratio is 0.075± 0.020͑2͒ at 295 K and 20 Torr. 2 Recent spectroscopic modeling suggests an upward adjustment of this branching ratio by approximately 25%.…”