C6 H5 S O2 radicals were produced upon irradiation of three flowing mixtures: C6 H5 S O2 Cl in N2, C6 H5 Cl and S O2 in C O2, and C6 H5 Br and S O2 in C O2, with a KrF excimer laser at 248 nm. A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to record the time-resolved infrared (IR) absorption spectra of reaction intermediates. Two transient bands with origins at 1087.7 and 1278.2 cm-1 are assigned to the S O2 -symmetric and S O2 -antisymmetric stretching modes, respectively, of C6 H5 S O2. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ and B3P86/aug-cc-pVTZ) predict the geometry and vibrational wave numbers of C6 H5 S O2 and C6 H5 OSO. The vibrational wave numbers and IR intensities of C6 H5 S O2 agree satisfactorily with the observed new features. Rotational contours of IR spectra of C6 H5 S O2 simulated based on predicted molecular parameters agree satisfactorily with experimental results for both bands. The S O2 -symmetric stretching band is dominated by a - and c -type rotational structures and the S O2 -antisymmetric stretching band is dominated by a b -type rotational structure. When C6 H5 S O2 Cl was used as a precursor of C6 H5 S O2, C6 H5 S O2 Cl was slowly reproduced at the expense of C6 H5 S O2, indicating that the reaction Cl+ C6 H5 S O2 takes place. When C6 H5 BrS O2 C O2 was used as a precursor of C6 H5 S O2, features at 1186 and 1396 cm-1 ascribable to C6 H5 S O2 Br were observed at a later period due to secondary reaction of C6 H5 S O2 with Br. Corresponding kinetics based on temporal profiles of observed IR absorption are discussed.