Low-temperature studies of the Raman X-ray reflections in crystals

Summary

The Raman reflections of X-rays by carborundum, rock-salt, sodium nitrate and penta-crythritol are obtained at liquid air temperature with a specially designed vacuum X-ray camera and their intensities, are compared with those at room temperature. For rock-salt an intermediate temperature of solid carbon dioxide and for carborundum two higher temperatures namely 600° and 900° T have also been employed. From the relative intensities of these reflections at various temperatures, the infra-red frequency active in the particular reflection is ascertained in each case making use of the following formula

Intensity$\propto {{e^{hv*\left| {k^T } \right.} + 1} \over {e^{hv*\left| {k^T } \right.} - 1}}$. These frequencies are about 800 cm.⁻¹ for carborundum, 160 cm.⁻¹ for rock-salt, 200 cm.⁻¹ for sodium nitrate and less than 100 cm.⁻¹ for penta-erythritol. They coincide with one or other of the low frequencies observed in the Raman effect or in the infra-red spectrum of the respective crystal. This new X-ray effect thus provides a novel method of evaluating the infra-red frequencies of crystals and is specially suitable for substances for which the methods of light scattering and infra-red spectro-scopy are inapplicable.