ENDOR studies on the W7 di-nitrogen centre in brown diamond

A new technique, involved rapid and repeated sweeping of radio-frequency irradiation through a wide frequency range, has been used to enhance the ENDOR signal of the W7 di-nitrogen centre in diamond. This allowed the determination of the following magnetic hyperfine and electric quadrupole interaction parameters (expressed in MHz) for the two nitrogen atoms: A/sub /// (1) =121.39(3), A perpendicular to (1) =86.00(3), PA/sub /// (1) =2.55(3), P perpendicular to (1) =1.27(3), A 1 (2) =13.58(5), A 2 (2) =16.01(5), A 3 (2) =14.00(5), P 1 (2) =0.13(1), P 2 (2) =-0.13(1), P 3 (2) =0.000(5). The interactions for A (1) and P (1) are axially symmetrical about 111, but those for A (2) and P (2) have low symmetry, and their principal axes have no clear relationship with one another or with the crystal structure. Hence, the overall symmetry of the site is established as C 1 .