The E.S.R. spectrum of irradiated ammonium hypophosphite

Electron spin resonance spectra of irradiated crystals of ammonium hypophosphite (NH₄)⁺(H₂PO₂)^- indicate that the ionic radical H[Pdot]O₂ ^- is initially formed. The hyperfine interaction tensor of the phosphorus nucleus has the principal values 1698, 1228 and 1228 Mc/s. Interaction with the proton gives rise to an almost isotropic hyperfine coupling of 230 Mc/s. These results indicate that the species H[Pdot]O₂ ^- is irregular tetrahedral in shape, the unpaired electron occupying a hybrid σ orbital centred on the phosphorus nucleus.

There is evidence that the radical H[Pdot]O₂ ^- reacts with an adjacent H₂PO₂ ^- ion forming the species O₂[Pdot]-PHO₂ ⁼. The principal values of the hyperfine interaction tensors of the two phosphorus nuclei are 1365, 944, 921 Mc/s and 527, 362, 359 Mc/s respectively. The proton has an isotropic hyperfine coupling of 90 Mc/s. The spectra of irradiated deuterated crystals confirmed this analysis.