title: Theoretical analysis of peroxynitrous acid: characterization of its elusive biradicaloid (HO...ONO) singlet states.
abstract: Various high levels of theory (DFT, QCISD, BD(TQ), and CASSCF) have been applied to the characterization of two higher-lying biradicaloid singlet states of peroxynitrous acid. A singlet minimum (cis-2) was located that had an elongated O-O distance of 2.17 A and was only 14.4 kcal/mol [UB3LYP/6-311+G(3df,2p)] higher in energy than its cis-peroxynitrous acid ground-state precursor. A trans metastable higher-lying singlet (trans-2) was 12.8 kcal/mol higher in energy than ground-state HO-ONO. Complete active space calculations [CAS(12,10)/6-311+G(d,p)] predicted the optimized geometries of these cis and trans metastable singlets to be quite close to those obtained with the DFT method. Geometry optimization of both cis- and trans-2 within the COSMO solvent model suggest that both exist as energy minima in polar media with elongated O-O distances of 2.14 and 2.09 A. Both cis- and trans-2 exist as hydrogen-bonded complexes with several water molecules. These collective data suggest that solvated forms of cis-2.3H2O and trans-2.3H2O represent the elusive higher-lying biradicaloid minima that have been previously advocated (J. Am. Chem. Soc. 1996, 118, 3125) as the metastable forms of peroxynitrous acid (HOONO*).
authors.affiliation: Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA. rbach@udel.edu
authors.forename: Robert D
authors.initials: RD
authors.lastname: Bach
authors.forename: Olga
authors.initials: O
authors.lastname: Dmitrenko
authors.forename: Carlos M
authors.initials: CM
authors.lastname: Estévez
mesh_terms: D005609:Free Radicals / Q000737:chemistry; D008958:Models, Molecular; D030421:Peroxynitrous Acid / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D005609:Free Radicals; D030421:Peroxynitrous Acid