McCoy, Anne B. and Fry, Juliane L. and Francisco, Joseph S. and Mollner, Andrew K. and Okumura, Mitchio (2005) Role of OH-stretch/torsion coupling and quantum yield effects in the first OH overtone spectrum of cis-cis HOONO. Journal of Chemical Physics, 122 (10). Art. no. 104311. ISSN 0021-9606 http://resolver.caltech.edu/CaltechAUTHORS:MCCjcp05
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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 acid). 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 zeta basis set, at the structure optimized using the triple zeta basis set (CCSD(T)/cc-pVQZ//CCSD(T)/cc-pVTZ). 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 CCSD(T)/cc-pVTZ and QCISD/AUG-cc-pVTZ (QCISD—quadratic configuration interaction with single and double excitation and AUG-augmented with diffuse functions) level of theory/basis, respectively. The OH-stretch vibration depends strongly on the torsional angle, and the torsional potential possesses a broad shelf at ~90°, 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 2nuOH region. These differences are attributed to the fact that several of the experimentally accessible states do not have sufficient energy to dissociate to OH+NO2 and therefore are not detectable in an action spectrum. Scaling of the intensities of transitions to these states, assuming D0=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 Delta n=0 transitions (where n is the HOON torsion quantum number) that are blue shifted relative to the origin band, while the large peak near 7000 cm^–1 is assigned to a series of Delta 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.
|Additional Information:||©2005 American Institute of Physics (Received 24 November 2004; accepted 21 December 2004; published online 11 March 2005) This work was supported by the California Air Resources Board (Contract No. 03-333), the National Science Foundation (NSF Grant Nos. CHE-0200968 and ATM-0432377), and the National Aeronautics and Space Administration Upper Atmospheric Research Program (NASA Grant No. NGT-11657). Experiments were performed in the laboratory of Professor Paul O. Wennberg, and the authors gratefully acknowledge his support and interest. J.L.F. and A.K.M. acknowledge support of NSF Graduate Research Fellowships and a NASA Earth System Science Fellowship. The authors thank the NASA Jet Propulsion Laboratory Supercomputing Project for computer time. They thank Stanley P. Sander, John F. Stanton, Amit Sinha, and Marsha I. Lester for helpful discussions and for sharing unpublished results prior to publication.|
|Subject Keywords:||bonds (chemical); hydrogen compounds; librational states; coupled cluster calculations; ab initio calculations; potential energy surfaces; molecular moments; bond lengths; vibrational states; molecular configurations; photodissociation; spectral line intensity; photoexcitation; infrared spectra|
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|Deposited By:||Archive Administrator|
|Deposited On:||24 Dec 2005|
|Last Modified:||26 Dec 2012 08:43|
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