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R. Kopitzky, H. Grothe, H. Willner:
"Chlorine Oxide Radicals, ClO_x x = 1-4, Studied by Matrix Isolation Spectroscopy.";
Chemistry - A European Journal, 8 (2002), 5601 - 5621.

Low pressure flash thermolysis of different precursor molecules containing a ClO, ClO3 or OClO3 group yield, when highly diluted in Ne or O2 and subsequent quenching of the products in a matrix at 5 or 15 K, the ClOx x = 1, 3, 4 radicals, respectively. If Ne or O2 gas is directed over solid ClO2 at -120°C and the resulting gas mixtures are immediately deposited as a matrix, a high fraction of (OClO)2 is trapped. This enables recording of the IR and UV spectra of weakly bonded (OClO)2 dimers and to study their photochemistry in detail. For Ne or O2 matrix isolated ClO radicals the vibrational wavenumbers and electronic transitions are only slightly affected in comparison to the gas phase. In this study strong evidence is found for long lived ClO in the electronically excited 21/2 state. A comprehensive IR study of Ne matrix isolated ClO3 (fundamentals at 1081, 905, 567, 476 cm1) yield (i) a reliable force field; (ii) a OClO bond angle of αe = 113.8±1° and (iii) a ClO bond length of 148.5±2 pm in accordance with predicted data from quantum chemical calculations. The UV/VIS spectrum of ClO3 isolated in a Ne matrix (λmax. at 32100 and 23150 cm1) agrees well with the photoelectron spectrum of ClO3 and theoretical predictions. The origin of the structured high energy absorption is at 22696 cm-1 and three fundamentals (794, 498, 280 cm-1) are detected in the C 2E state. By photolysis of ClO3 with visible light the complex ClO·O2 with ClO in the 21/2 state is formed. In an extended spectroscopic study of the elusive ClO4 radical, isolated in a Ne or O2 matrix, three additional IR bands, a more complete UV spectrum and a strong interaction with O2 are found. This leads to the conclusion that ClO4 exhibits C2v or Cs symmetry with a shallow potential minimum and forms with O2 the previously unknown peroxy radical O3ClOO2. All these results are discussed in the context of recent developments in the chemistry and spectroscopy of the important and interesting ClOx x = 1 to 4 family of radicals.

http://www3.interscience.wiley.com/cgi-bin/fulltext?ID=101525889&PLACEBO=IE.pdf