Natural diamonds were studied by Fourier-transform infra-red spectroscopy, and it was shown that B2 centers in them form through intermediate stages, which were accompanied by the appearance of absorption bands with maxima near 1550 and 1526/cm. The concentration of interstitial C atoms in the centers responsible for these bands may be several times higher than the concentration of the interstitials in B2 defects.

Interstitial Carbon Showing up in the Absorption Spectra of Natural Diamonds. E.A.Vasilyev, V.I.Ivanov-Omskii, I.N.Bogush: Technical Physics, 2005, 50[6], 711-4