The radical Ph₂P(0)CH₂Cl^- is observed in 3 K X-ray irradiated crystals of (chloromethyl)diphenylphosphine oxide. The X-ray irradiation was carried out in the dark. The hyperfine coupling tensors were found to be A(³⁵Cl) = (40.4, 17.9, 16.1 G), A₁(¹H ) = (24.0, 17.2, 13.1 G), A₂(¹H) = (25.0, 16.4, 9.0 G), and A(³¹P) = (42.1, 33.6, 23.8 G). The g-tensor components are equal to 2.0021, 2.0040, and 2.0046. The maximium ³⁵Cl coupling and the minimum g value are located within 5° of the parent C-Cl bond direction. Upon thermal annealing to ~170 K, the anion decays and the Ph₂P(G)ĊH₂ radical appears. UV photolysis of the anion at 3 K results in the disappearance of the anion and the formation of Ph₂P(O)ĊH₂. Ph₂P(O)ĊH₂ decays above 230 K, giving rise to a room-temperature-stable species.