Electron Spin Resonance of γ-Irradiated KH2PO4

ESR spectra of γ-irradiated KDP were measured at both X- and K-bands. The radical was ascertained to be ·OPO 3 H - which resulted from the loss of a hydrogen atom from a H 2 PO 4 - ion. The principal values of g -tensor of the radical were determined to be 2.054, 2.007 and 2.003, and those of A -tensor to be 36.8, 33.8 and 33.0 Gauss. From the analysis of the anisotropic g -tensor, it was concluded that the PO 4 tetrahedron in the radical was rotated by about 13° around the c -axis from the original position. The spectrum for the irradiated DKDP can be explained consistently with the present result if the unpaired electron is distributed equally on four oxygens.