Spectrum and structure of the HO 2 free radical

Abstract

In studies of the vacuum-ultraviolet photolysis of Ar:O 2:HCl and Ar:O 2:H 2O samples at 14°K the free radical HO 2 has been stabilized in considerably greater concentrations than in earlier experiments, in which the mercury-arc photolysis of HBr or of HI had been used to provide a source of H atoms. Appreciable concentrations of H 2O 2 and O 3 and, in the experiments using HCl as an H-atom source, of HOCl and ClOO were also stabilized. The infrared spectra of the mixed oxygen-isotopic species of DO 2 have been reported for the first time. The data for the four oxygen-isotopic species of HO 2 have been subjected to a normal coordinate analysis, using a four-constant valence-force field, and the calculated DO 2 frequencies have been compared with the observed values. The previous assignment of the 1389-cm −1 absorption as the OH deformation fundamental and of the 1101-cm −1 absorption as the oxygen-oxygen stretching fundamental has been definitively established. A satisfactory fit to the observed absorption pattern for the oxygen-isotopic species of DO 2 has been obtained for a valence angle of 105° ± 5°. The magnitudes of the two stretching force constants of HO 2 suggest that the electronic structure of HO 2 may approach that of O 2 −, lending some support to the previous identification of an electronic transition of HO 2 near that of O 2 −.