Arylsulfinyl radicals are key intermediates in sulfoxide chemistry. The parent molecule, phenylsulfinyl radical PhSO center dot, has been generated for the first time in the gas phase through high-vacuum flash pyrolysis of PhS(O)R = CF3 and Cl) at about 1000 K. Upon UV light irradiation (365 nm), PhSO center dot isomerizes to novel oxathiyl radical PhOS center dot in cryogenic matrices (2.8 K). Prolonged irradiation causes further isomerization of PhOS center dot to 2-hydroxyphenylthiyl radical, the formation of which has been also observed in the 193 nm laser photolysis of matrix-isolated 2-hydroxybenzenethiol. Concomitantly, ring-opening occurs during the UV photolysis of PhOS center dot and 2-hydroxybenzenethiol and forms an acyclic thioketoketene radical. Phenylsulfinyl radical reacts partially with molecular oxygen in the gas phase and yields phenyl radical Ph center dot and 0-500. Upon irradiation (365 nm), the isomeric oxathiyl radical also combines O-2 with immediate dissociation to phenoxy radical PhO center dot and SO2. The identification of the intermediates with IR and UV-vis spectroscopy is supported by quantum chemical computations at the B3LYP/def2-TZVPP and UCCSD(T)/aug-cc-pV(D+d)Z levels of theory. The isomerization of PhSO center dot has been discussed based on the computed potential energy profile and the comparison with the intensively explored photochemistry of phenylperoxy radical PhOO center dot.