Infra-red absorption spectrum of diamond

Abstract

In his comments appended to our note on the above subject appearing in Nature of January 12, Dr. Sutherland ascribes to us the statement that the "principal infra-red frequency of diamond has been defined as the position of minimum absorption". This is not What we said, neither does it represent the actual facts of the case. The true position is that pointed out by Sir C. V. Raman, namely, that in the 8μ band of diamond, the infra-red absorption coefficient rises very steeply in passing through the fundamental vibration frequency of the lattice, namely, 1332 cm^-1. The accompanying absorption curves (A), (B), (C) and (D), carefully redrawn on a wave-number scale from the experimental results published by British observers3,4, demonstrate that this is the actual situation. A similar feature appears also in the infra-red emission spectrum (Curve E) of diamond. The 1332 cm^-1 frequency is indicated by the vertical line which, it will be seen, in each case cuts through the curve at or near the point where it is steepest. There can be no doubt, therefore, that the absorption associated with that frequency is an integral part of the 8μ band and that this latter has its primary origin in the infra-red activity of the fundamental lattice vibration. There remains no need for us to comment on the rest of Dr. Sutherland's note.