A new low-symmetry S = 1 electron spin resonance center, with lines that were well-separated from the g = 2 position, was observed in electron-irradiated type-IIa diamond. Six groups of lines, R1a to R1f, were also observed. These had the same symmetry as R1; but with slightly smaller D values. The 13C hyperfine structure of R1 was analyzed and possible models for R1 were considered.

M.A.Lea-Wilson, J.N.Lomer: Philosophical Magazine A, 1996, 74[3], 685-95