  It is suggested that the substitutional nitrogen in diamonds bonded to three
of the surrounding carbon atoms instead of four. This proposed electron
configuration of the defect is deduced from previous experiments and
theoretical considerations. Notably, the 1344 cm-1 band, characteristics of the
substitutional Nitrogen, is independent of the isotopic change of Nitrogen but
depend on the isotopic change of Carbon. The well established NV centre should
not be stable if Nitrogen is bounded to four of the surrounding Carbon.
Additional support comes from the substantially bigger size of the single
substitutional nitrogen atom indicating loan pair electron. The proposed
configuration of the substitutional Nitrogen was also tested by using a simple
force constant model. Replacing force constant of C-N with 2/3 C-C:1/3 C=C
reproduces the 1344 cm-1 band.
