Electron spin resonance of SeO43- and SeO3- radicals in KDP single crystal

X-ray irradiation of KDP-K 2 SeO 4 mixed crystal is shown to produce SeO 4 3- and SeO 3 - radicals. The ESR spectrum of SeO 4 3- has well-resolved proton hyperfine structure which exhibits the "quintet to triplet" transition as seen on AsO 4 4- radical in KDA. This radical may be used as a new "probe" to study the proton dynamics of KDP. The tensors of hyperfine interaction with Se 77 for these radicals are evaluated from the angular dependence of ESR spectra of the radicals. The principal values of the hyperfine tensor of SeO 4 3- are as follows, T // =3389 MHz and T ⊥ =3178 MHs in the paraelectric phase, and T 1 =3055 MHz, T 2 =2986 MHz and T 3 =3490 MHz in the ferroelectric phase.