An anomaly in the infrared absorption spectrum of synthetic diamond

Abstract
Careful measurements of infrared spectra of synthetic diamonds bring to light two apparently contradictory observations. On the one hand, it is shown that there is an excellent correlation between the strengths of the nitrogen-induced absorption at 1130 cm−1 and of the local-mode absorption peak at 1344 cm−1. On the other hand, our results confirm another earlier report that, whilst the 1130 cm−1 band is shifted towards lower wavenumbers by the incorporation of 15N into the crystals, the 1344 cm−1 peak is unaffected. This suggests that nitrogen atoms do not participate in the 1344 cm−1 vibration. It is difficult to understand the second observation in the light of the first. A small peak at ∼ 2688 cm−1 in the absorption of one of the specimens studied is thought to be the first overtone of the 1344 cm−1 vibration.