Experimental information about the structure of a R₂PCl˙^- ion is obtained from the ESR study of an X-irradiated single crystal of 1,2-phenylenephosphorochloridite. The crystal structure of this compound is determined and is used to discuss the hyperfine interaction with ³¹P and ³⁵Cl. The unpaired electron is strongly localized in a P-Cl σ*-orbital and the radical anion is shown to thermally dissociate into a phosphinyl radical and a Cl^- ion. Ab initio calculations show that the geometry of PCl₃˙^- is of the planar T-shape type whereas H₂PCL˙^- adopts a pyramidal structure, which is in good agreement with the experimental results. The theoretical dissociation energy PH₂Cl^- → ṖH₂ + Cl^- is calculated to be ~7 kcal.