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Chlorine Oxide Radicals ClO x ( x =1–4) Studied by Matrix Isolation Spectroscopy
Author(s) -
Kopitzky Rodion,
Grothe Hinrich,
Willner Helge
Publication year - 2002
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20021216)8:24<5601::aid-chem5601>3.0.co;2-z
Subject(s) - chemistry , matrix isolation , radical , analytical chemistry (journal) , excited state , absorption spectroscopy , molecule , photochemistry , organic chemistry , atomic physics , physics , quantum mechanics
Low pressure flash thermolysis of different precursor molecules containing ‐ClO, ‐ClO 3 or ‐OClO 3 yield, when highly diluted in Ne or O 2 and subsequent quenching of the products in a matrix at 5 or 15 K, ClO x ( x =1, 3, 4) radicals, respectively. If Ne or O 2 gas is directed over solid ClO 2 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 IR and UV spectra of weakly bonded (OClO) 2 dimers and detailled studying of their photochemistry. For Ne or O 2 matrix isolated ClO radicals the vibrational wavenumbers and electronic transitions are only slightly affected compared with the gas phase. In this study strong evidence is found for long lived ClO in the electronically excited 2 Π 1/2 state. A comprehensive IR study of Ne matrix isolated ClO 3 (fundamentals at 1081, 905, 567, 476 cm −1 ) yield i) a reliable force field; ii) a OClO bond angle of α e =113.8±1° and iii) a ClO bond length of 148.5±2 pm in agreement with predicted data from quantum chemical calculations. The UV/Vis spectrum of ClO 3 isolated in a Ne matrix ( λ max at 32 100 and 23 150 cm −1 ) agrees well with the photoelectron spectrum of ClO 3 − and theoretical predictions. The origin of the structured high energy absorption is at 22 696 cm −1 and three fundamentals (794, 498, 280 cm −1 ) are detected in the C 2 E state. By photolysis of ClO 3 with visible light the complex ClO ⋅ O 2 with ClO in the 2 Π 1/2 state is formed. In an extended spectroscopic study of the elusive ClO 4 radical, isolated in a Ne or O 2 matrix, three additional IR bands, a complete UV spectrum and a strong interaction with O 2 are found. This leads to the conclusion that ClO 4 exhibits C 2v or C s symmetry with a shallow potential minimum and forms with O 2 the previously unknown peroxy radical O 3 ClO–O 2 . All these results are discussed in the context of recent developments in the chemistry and spectroscopy of the important and interesting ClO x ( x =1–4) family of radicals.