Infra-Red Absorption Spectrum of Diamond

ONE of the crucial arguments put forward by Raman in support of 'tetrahedral' and 'octahedral' diamonds being associated with the Type I and Type II diamonds of Robertson, and Fox and Martin, was that the tetrahedral form should have a certain fundamental vibration frequency active in infra-red absorption and also in scattering, while for the octahedral form this same frequency should be inactive in absorption. Raman identified this frequency with the well-known scattering line at 1,332 cm. -1 and claimed that this frequency coincided with the infrared absorption “between 1350 and 1300 cm. -1 ” on Type I diamonds. One of the purposes of the paper by Willis and myself was to point out that this last was a serious mis-statement of fact, since the principal infra-red absorption maxima in this region of the spectrum lie at 1,286 cm. -1 and 1,376 cm. -1 , of which the former is much more intense than the latter.