ENDOR studies of hydrogen bonding of the AsO^4-₄ centre in X-ray irradiated KH₂AsO₄

Abstract

We here report what we believe to be an important method for studying hydrogen bonding in systems containing a paramagnetic centre. The technique of electron-nuclear double resonance (ENDOR) has been applied to study the hydrogen-bond network around the AsO^4-₄ centre in X-ray irradiated KH₂AsO₄. ENDOR transitions from several sets of hydrogen nuclei surrounding the centre were observed at 4.2°K and the spectra for two sets of neighbouring nuclei are identified. The angular dependences for these spectra are fitted with a spin-Hamiltonian to obtain the isotropic and anisotropic magnetic hyperfine constants. The results are discussed in terms of the available spectroscopic and crystallographic data on KH₂AsO₄ and the order-disorder model of ferroelectrictricity in this class of crystals.