13C,14N and15N ENDOR measurements on the single substitutional nitrogen centre (P1) in diamond

New ENDOR measurements on the single substitutional nitrogen centre in diamond are reported. The CW-ENDOR mechanism utilizes cross relaxation, and measurements have been made on both 14 N and 15 N, as well as the first detailed 13 C ENDOR study on the isotope at the natural abundance of 1.1%. The change in EPR intensity induced by driving the 13 C nuclear transitions was approximately equal to 100% of the EPR intensity of the appropriate 13 C hyperfine satellite. The assignment of 13 C hyperfine coupling matrices with specific sites is considered, and predictions made about the signs of some of the 13 C hyperfine interactions.