The second order Raman spectrum of diamond

Abstract

Using an exceptional1y colourless plate of diamond of the ultra-violet transparent type and the λ2536.5 resonance radiation of mercury as exciter, the author has photographed the second order Raman spectrum of diamond with greatly increased intensity and much better resolved than any recorded hitherto. The spectrum exhibits ten distinct Raman lines with frequency shifts 2176, 2190, 2225, 22531 2299, 2330, 2430, 2460, 2502 and 2666 cm^-1. The frequency shifts of the first five lines, in particular, correspond very closely with the positions of a set of five absorption peaks observed by Robertson, Fox and Martin while exploring the absorption band in the region 4-4.8 μ with the aid of a concave grating of the echelette type. Of the ten observed second order Raman lines, the more intense and prominent ones have been identified as octaves of the prominent lattice frequencies of diamond appearing in the luminescence and absorption spectra. These facts are irreconcilable with the consequences of the Born lattice dynamics. They can, however, be satisfactorily explained on the basis of the Raman dynamics of crystal lattices. The relative intensities of the second order Raman lines, as well as the ratios of the intensities of the Stokes, the anti-Stokes and the octave of the principal Raman shift of 1332 cm^-1 have been estimated by photographic photometry.