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doi: 10.1007/BF03173448pmid: N/A
The Raman spectra of diamonds of the ultra-violet transparent type have been investigated using the 2536 resonance line of mercury as exciter. Besides the well-known 1332 Raman line, ten others with frequency shifts 1925, 2175·5, 2245, 2267, 2300·5, 2467, 2495, 2518, 2609·5 and 2664·6 cm.−1 have been recorded. These new lines have been identified as the octaves and allowed combinations of some of the eight fundamental frequencies of oscillation of the diamond structure of which the existence is indicated by the Raman theory of crystal dynamics, but which are not themselves permitted to appear in light-scattering by reason of the selection rules.
doi: 10.1007/BF03173449pmid: N/A
The new view of crystal dynamics developed by Sir C. V. Raman indicates that the diamond lattice has eight distinct normal frequencies of vibration which comprise forty-five out of the forty-eight degrees of freedom of the atoms present in a group of eight lattice cells, while the remaining three degrees of freedom represent the elastic vibrations of lower frequency. These eight frequencies of atomic vibrations are actually observed in the Raman spectrum recorded by Dr. R. S. Krishnan and in the luminescence and the absorption spectra in the visible region investigated by Dr. P. G. N. Nayar and (Miss) Anna Mani. The modes corresponding to the observed frequencies and their respective degeneracies have been ascertained from the theoretical formulæ given by Bhagavantam and Chelam. The elastic constants have been calculated from the spectroscopic data with the aid of the same formulæ. The calculated and experimental values of the bulk modulus agree well. The thermal energy of diamond has been evaluated from the spectroscopically observed frequencies and the known degeneracies, the three degrees of freedom not covered by these frequencies being considered as an elastic spectrum for which a formula of the Debye type with greatly reduced characteristic temperature is an approximate representation. The theoretical and experimental results agree throughout the whole range of temperature and particularly well in the temperature range between 200 and 1100° K. where the thermal energy content is principally determined by the optical frequencies of vibration.
doi: 10.1007/BF03173452pmid: N/A
The paper deals with the study of the intensity of the Bragg reflections from the (111) planes of diamond, and its variation from specimen to specimen. The diamonds were chosen so as to include a variety exhibiting different types and intensity of fluorescence. The study brings out the following facts: (1) In blue-fluorescing diamonds, the intensity of X-ray reflection increases with intensity of fluorescence. (2) Yellow-fluorescent diamonds give greater intensity than the blue ones. (3) Among these, the intensity decreases with increasing intensity of yellow-fluorescence, and is largest for non-fluorescent diamonds. A discussion is given regarding these phenomena, and it is shown that they fit in with Sir C. V. Raman’s new theory of the structure of diamond.
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