Ph3ÅsBr is trapped in an X‐irradiated single crystal of Ph3As+CH3Br−. The g‐tensor, the75As and79Br magnetic hyperfine tensors and the79Br quadrupolar interaction tensor are obtained at room temperature. They show that the structure of this arsoranyl radical is intermediate between the trigonal bipyramidal and theC3v‐symmetry structure. By the detection of several additional radical species, especially at 77 K, some steps of the radiation mechanism are el