Spectroscopic characterization of HOONO and its binding energy via infrared action spectroscopy

Francisco

et al. 2005

A joint theoretical and experimental investigation is undertaken to study the effects of OH-stretch/ HOON torsion coupling and of quantum yield on the previously reported first overtone action spectrum of cis-cis HOONO ͑peroxynitrous acid͒. The minimum energy path along the HOON dihedral angle is computed at the coupled cluster singles and doubles with perturbative triples level with correlation consistent polarized quadruple basis set, at the structure optimized using the triple basis set ͑CCSD͑T͒/cc-pVQZ//CCSD͑T͒/cc-pVTZ͒. The two-dimensional ab initio potential energy and dipole moment surfaces for cis-cis HOONO are calculated as functions of the HOON torsion and OH bond length about the minimum energy path at the CCSD͑T͒/cc-pVTZ and QCISD/ AUG-cc-pVTZ ͑QCISD-quadratic configuration interaction with single and double excitation and AUG-augmented with diffuse functions͒ level of theory/basis, respectively. The OH-stretch vibration depends strongly on the torsional angle, and the torsional potential possesses a broad shelf at ϳ90°, the cis-perp conformation. The calculated electronic energies and dipoles are fit to simple functional forms and absorption spectra in the region of the OH fundamental and first overtone are calculated from these surfaces. While the experimental and calculated spectra of the OH fundamental band are in good agreement, significant differences in the intensity patterns are observed between the calculated absorption spectrum and the measured action spectrum in the 2 OH region. These differences are attributed to the fact that several of the experimentally accessible states do not have sufficient energy to dissociate to OH+ NO 2 and therefore are not detectable in an action spectrum. Scaling of the intensities of transitions to these states, assuming D 0 = 82.0 kJ/ mol, is shown to produce a spectrum that is in good agreement with the measured action spectrum. Based on this agreement, we assign two of the features in the spectrum to ⌬n = 0 transitions ͑where n is the HOON torsion quantum number͒ that are blue shifted relative to the origin band, while the large peak near 7000 cm −1 is assigned to a series of ⌬n = + 1 transitions, with predominant contributions from torsionally excited states with substantial cis-perp character. The direct absorption spectrum of cis-cis HOONO ͑6300-6850 cm −1 ͒ is recorded by cavity ringdown spectroscopy in a discharge flow cell. A single band of HOONO is observed at 6370 cm −1 and is assigned as the origin of the first OH overtone of cis-cis HOONO. These results imply that the origin band is suppressed by over an order of magnitude in the action spectrum, due to a reduced quantum yield. The striking differences between absorption and action spectra are correctly predicted by the calculations.

Section: -4mentioning

confidence: 99%

Role of OH-stretch/torsion coupling and quantum yield effects in the first OH overtone spectrum of cis-cis HOONO

McCoy

Francisco

et al. 2005

“…Hippler, Nasterlack, and Striebel report the only experimental value, D 0 (cis-cis HOONO)ϭ83 kJ/mol, from a third-law analysis of the equilibrium constants over 430-490 K. 3 A refinement of the evaluation of this data is underway, and reanalysis of the high temperature data now gives D 0 (cis-cis HOONO)ϭ80.5 kJ/mol. 16 Pollack et al 17 have set an experimental upper limit on the trans-perp HOONO binding energy of 70.3 kJ/mol from the product internal energy distribution of the vibrational predissociation of jetcooled trans-perp HOONO. From this limit and the ab initio energy difference between cis-cis and trans-perp HOONO, they find an upper limit for the cis-cis HOONO dissociation energy, D 0 (cis-cis HOONO)р84.6 kJ/mol.…”

Section: Fig 1 Energy Level Diagram For the Ohϩnomentioning

confidence: 99%

“…Subsequently, Pollack et al definitively identified the first OH stretching overtone of supersonically cooled trans-perp HOONO from the rotational band contours detected with photodissociation action spectroscopy. 17 Though the band origin at 6971.4 cm Ϫ1 lies close to the strongest band seen by Nizkorodov and Wennberg, the band is expected to be substantially narrower even at room temperature.…”

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confidence: 99%

Cis-cis and trans-perp HOONO: Action spectroscopy and isomerization kinetics

Nizkorodov

Okumura

et al. 2004

The weakly bound HOONO product of the OHϩNO 2 ϩM reaction is studied using the vibrational predissociation that follows excitation of the first OH overtone (2 1 ). We observe formation of both cis-cis and trans-perp conformers of HOONO. The trans-perp HOONO 2 1 band is observed under thermal ͑223-238 K͒ conditions at 6971 cm Ϫ1 . We assign the previously published ͑warmer temperature͒ HOONO spectrum to the 2 1 band at 6365 cm Ϫ1 and 2 1 -containing combination bands of the cis-cis conformer of HOONO. The band shape of the trans-perp HOONO spectrum is in excellent agreement with the predicted rotational contour based on previous experimental and theoretical results, but the apparent origin of the cis-cis HOONO spectrum at 6365 cm Ϫ1 is featureless and significantly broader, suggesting more rapid intramolecular vibrational redistribution or predissociation in the latter isomer. The thermally less stable trans-perp HOONO isomerizes rapidly to cis-cis HOONO with an experimentally determined lifetime of 39 ms at 233 K at 13 hPa ͑in a buffer gas of predominantly Ar͒. The temperature dependence of the trans-perp HOONO lifetime in the range 223-238 K yields an isomerization barrier of 33Ϯ12 kJ/mol. New ab initio calculations of the structure and vibrational mode frequencies of the transition state perp-perp HOONO are performed using the coupled cluster singles and doubles with perturbative triples ͓CCSD͑T͔͒ model, using a correlation consistent polarized triple basis set ͑cc-pVTZ͒. The energetics of cis-cis, trans-perp, and perp-perp HOONO are also calculated at this level ͓CCSD͑T͒/ cc-pVTZ͔ and with a quadruple basis set using the structure determined at the triple basis set ͓CCSD͑T͒/cc-pVQZ//CCSD͑T͒/cc-pVTZ͔. These calculations predict that the anti form of perp-perp HOONO has an energy of ⌬E 0 ϭ42.4 kJ/mol above trans-perp HOONO, corresponding to an activation enthalpy of ⌬H 298 ‡0 ϭ41.1 kJ/mol. These results are in good agreement with statistical simulations based on a model developed by Golden, Barker, and Lohr. The simulated isomerization rates match the observed decay rates when modeled with a trans-perp to cis-cis HOONO isomerization barrier of 40.8 kJ/mol and a strong collision model. The quantum yield of cis-cis HOONO dissociation to OH and NO 2 is also calculated as a function of photon excitation energy in the range 3500-7500 cm Ϫ1 , assuming D 0 ϭ83 kJ/mol. The quantum yield is predicted to vary from 0.15 to 1 over the observed spectrum at 298 K, leading to band intensities in the action spectrum that are highly temperature dependent; however, the observed relative band strengths in the cis-cis HOONO spectrum do not change substantially with temperature over the range 193-273 K. Semiempirical calculations of the oscillator strengths for 2 1 (cis-cis HOONO) and 2 1 (trans-perp HOONO) are performed using ͑1͒ a one-dimensional anharmonic model and ͑2͒ a Morse oscillator model for the OH stretch, and ab initio dipole moment functions calculated using Becke, Lee, Yang, and Parr density functional theory ͑B3LYP͒,...

“…This work was followed in rapid succession by detection of the cis-cis 1 fundamental by Bean et al using cavity ringdown spectroscopy 16 and a high-resolution study of the trans-perp 2 1 band in a supersonically cooled molecular beam by Pollack et al 17 18 The vibrational frequencies and intensities calculated in this study enabled Lee and co-workers 11,13 to distinguish between the trans-perp and cis-cis conformers in their matrix IR spectra. McGrath and Rowland subsequently used G2, G2͑MP2͒, QCISD(T)/6-311G(d,p), and MP2 calculations with basis sets up to 6-311ϩG͑3df,2p͒ to improve characterization of the relative energetics of the three stable conformers.…”

mentioning

confidence: 99%

“…A combined submillimeter and infrared experiment could also be used to quantify the band strengths of the infrared transitions. 14,16,17 This research was performed at the Jet Propulsion Laboratory ͑JPL͒, California Institute of Technology, under contract with the National Aeronautics and Space Administra- …”

mentioning

confidence: 99%

Rotational spectrum of cis–cis HOONO

Drouin

Miller

2004

The pure rotational spectrum of cis-cis peroxynitrous acid, HOONO, has been observed. Over 220 transitions, sampling states up to JЈϭ67 and K a Јϭ31, have been fitted with an rms uncertainty of 48.4 kHz. The experimentally determined rotational constants agree well with ab initio values for the cis-cis conformer, a five-membered ring formed by intramolecular hydrogen bonding. The small, positive inertial defect ⌬ϭ0.075667(60) amu Å 2 and lack of any observable torsional splittings in the spectrum indicate that cis-cis HOONO exists in a well-defined planar structure at room temperature.