Infrared Action Spectroscopy and Dissociation Dynamics of the HOOO Radical

Abstract

The HOOO radical has long been postulated to be an important intermediate in atmospherically relevant reactions and was recently deemed a significant sink for OH radicals in the tropopause region. In the present experiments, HOOO radicals are generated in a pulsed supersonic expansion by the association of O(2) and photolytically generated OH radicals, and the spectral signature and vibrational predissociation dynamics are investigated via IR action spectroscopy, an IR-UV double resonance technique. Rotationally resolved IR action spectra are obtained for trans-HOOO in the fundamental (nu(OH)) and overtone (2nu(OH)) OH stretching regions at 3569.30 and 6974.18 cm(-1), respectively. The IR spectra exhibit homogeneous line broadening, characteristic of a approximately 26-ps lifetime, which is attributed to intramolecular vibrational redistribution and/or predissociation to OH and O2 products. In addition, an unstructured feature is observed in both the OH fundamental and overtone regions of HOOO, which is likely due to cis-HOOO. The nascent OH X(2)Pi, v = 0 or v = 1, products following vibrational predissociation of HOOO, nu(OH) or 2nu(OH), respectively, have been investigated using saturated laser-induced fluorescence measurements. A distinct preference for population of Pi(A') Lambda-doublets in OH was observed and is indicative of a planar dissociation of trans-HOOO in which the symmetry of the bonding orbital is maintained.

Perspective: Water cluster mediated atmospheric chemistry

“…However, the atmospheric importance of this radical water complex depends on its stability, which is currently under investigation. [103][104][105] Progress in understanding the structure and stability of radical-water complexes points to remaining fundamental issues needed to assess the role of water radical complexes in atmospheric chemistry.…”

An Evaluation of Gas Phase Enthalpies of Formation for Hydrogen-Oxygen (HxOy) Species

“…HO 3 has been termed an "elusive" radical [160,164,167,169] with regard to detection, molecular structure, vibrational frequencies, and enthalpy of formation -from both experimental and theoretical points of view. The first measurement of its gas phase enthalpy of formation was derived indirectly from correlations in electron transfer efficiencies of the positive ion HO 3 + with the ionization energies of a series of neutral electron donors by Speranza (1996) [165].…”

“…More recently, Lester and coworkers [161][162][163][164] measured the vibrational predissociation of HO 3 putting an upper limit on its bond dissociation energy D 0 (HO-OO) moving the estimate for the enthalpy of formation upward by about (10 to 15) kJ mol −1 . In 2010, Le Picard et al [160], using a spectroscopic kinetic/equilibrium measurement at low temperatures (87 K to 100 K), determined the bond dissociation energy (D 0 ) relatively precisely (reportedly within about 0.5 kJ mol −1 ) and thus, pinned down the enthalpy http://dx.doi.org/10.6028/jres.121.005 The earlier "high" enthalpies of formation from theory were because of the inability of the single reference methods employed to properly treat HO 3 due to significant spin contamination and the multi-reference character of the wavefunctions (see discussion in references in Table 8).…”

Molecular dynamics study of the hydration of the hydroxyl radical at body temperature

“…On the basis of the fundamental stretching vibration of the isolated OH molecule and its first overtone, 3568 cm À1 and 6971 cm À1 , 29 The O-H equilibrium separation, R e , has been set at 0.975 Å , which is the bond-length of the isolated radical obtained in the DFT calculations described below. On the basis of the fundamental stretching vibration of the isolated OH molecule and its first overtone, 3568 cm À1 and 6971 cm À1 , 29 The O-H equilibrium separation, R e , has been set at 0.975 Å , which is the bond-length of the isolated radical obtained in the DFT calculations described below.…”