X-irradiated single crystals of Ph₃SeBr, Ph₂SeBr₂, and Ph₂SeCl₂ have been studied by ESR spectroscopy. In each crystal a radical species exhibiting anisotropic hyperfine interaction with the halogen nuclei has been trapped. The g tensors, the magnetic hyperfine tensors to the halogen nuclei, and the ⁸¹Br quadrupolar interaction tensors have been determined. The ⁷⁷Se magnetic hyperfine tensor has also been obtained for the radical species trapped in Ph₂SeBr₂ and Ph₂SeCl₂. These tensors lead to the identification of Ph₂SeHal. The spin distribution is discussed; the unpaired electron lies probably in a Se-Hal σ* orbital which is oriented perpendicularly to the CSeC plane. The spin distribution seems to be very sensitive to the nature of the host matrix.