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The CH~COOH radicals in ~,-irradiated glycine have been observed in two spectroscopically inequivalent forms by the ENDOR method. The first form (A) was induced by warming ~,-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 nuclearnuclear interaction of two ~-protons of CHzCOOH radicals is examined. The relative signs of proton hyperfine couplings were determined by comparison with experimental data.

Calculations using the self-consistent unrestricted Hartree-Fock-Roothan method are carried out in the MNDO approximation for a cluster of 35 host atoms of cubic Sic with a boron impurity. The equilibrium geometry and the hyperfine and quadrupole constants are obtained and compared with experimental values. The computed parameters reveal the main features of boron impurities in

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Comparison calculation of boron impurities, substituting for Si and C sites in cubic SiC, is performed in the framework of the cluster MNDO method. Impurity site preference, equilibrium geometry, potential energy surface, reorientation barriers, Franck-Condon shift, spin and charge density distribution and hyperfine parameters are under consideration. The reasonable values of all calculated parameters support the model of a Jahn-Teller centre with strong coupling for the B Si impurity. Calculations predict the B C impurity to be the effective-mass-like acceptor.