Raman Spectrum of Diamond

The first- and second-order Raman spectra of diamond were studied using the 4880 \AA{} and 5145 \AA{} lines of an Ar ion laser and the 6328 \AA{} line of a He-Ne laser. The spectra were recorded at room, liquid-nitrogen, and liquid-helium temperatures. In addition to the second-order spectrum previously reported by Krishnan, a new weaker second-order spectrum was observed in the range 1600-2100 ${\mathrm{cm}}^{\ensuremath{-}1}$. Polarization studies were carried out on both the first- and second-order spectra. From such studies it was established that the 1332-${\mathrm{cm}}^{\ensuremath{-}1}$ Raman line is the zone-center optical phonon with ${\ensuremath{\Gamma}}^{(25+)}$ (${F}_{2g}$) symmetry. The prominent features in both the second-order Raman spectra reported here and the second-order infrared spectra are interpreted in terms of the critical points of the phonon dispersion curves established from neutron spectroscopy and on the basis of space-group selection rules.

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