Ph₃AsBr is trapped in an X-irradiated single crystal of Ph₃As⁺CH₃Br^-. The g-tensor, the ⁷⁵As and ⁷⁹Br magnetic hyperfine tensors and the ⁷⁹Br quadrupolar interaction tensor are obtained at room temperature. They show that the structure of this arsoranyl radical is intermediate between the trigonal bipyramidal and the C_3v-symmetry structure. By the detection of several additional radical species, especially at 77 K, some steps of the radiation mechanism are elucidated.