ENDOR study of CH2COOH radicals in γ-irradiated single crystals of glycine

Abstract

The CH2COOH radicals in γ-irradiated glycine have been observed in two spectroscopically inequivalent forms by the ENDOR method. The first form (A) was induced by warming γ-irradiated crystals at 77 K up to 120–140 K, the second one (A′)—up to 140–300 K. The proton and nitrogen couplings are given for these two forms. The transition from A to A′ form was observed at 140–160 K. This transition is discussed in terms of a double-minimum potential curve for the hydrogen bond protons. The second-order effects are reduced to indirect nuclear-nuclear interaction terms giving rise to the splitting of ENDOR lines. The general expression for this interaction has been obtained. The indirect nuclear-nuclear interaction of two α-protons of CH2COOH radicals is examined. The relative signs of proton hyperfine couplings were determined by comparison with experimental data.