Magnetic Hyperfine and Quadrupole Interactions of F‐Centres in NaCl as Measured by ENDOR

The hyperfine and quadrupole interactions of F‐centres in NaCl were investigated by the ENDOR method. The constants of hyperfine interactions with nuclei of coordination shells I to X surrounding the vacancy have been determined. The quadrupole interaction with nuclei of shells II, IV, VI, and VIII has been recorded and measured. General expressions for ENDOR frequencies are given in single‐particle approximation, allowance being made for the deviation of the nuclear spin quantization axis from the direction of the constant magnetic field H₀ and for corrections due to second order perturbation theory. The angular dependence of ENDOR spectra has been investigated in detail and fully explained on the basis of theoretical formulae. The constants were determined at T = 20, 77, and 300 °K.