The scattering of light in diamond and its Raman spectrum
A detailed study of the scattering of light in diamond and its Raman spectrum has been made using the λ 2536·5 mercury resonance radiation as exciter. The seattered spectrum exhibits two pairs of Doppler-shifted components, one pair due to the longitudinal sound waves, and the other due to the two sets of transverse sound waves which have very nearly the same velocity. The velocities of the longitudinal and transverse sound waves estimated from the observed frequency shifts of the displaced components are in agreement with those calculated from the elastic constants of diamond. The directional dependence of sound velocity in diamond has been quantitatively verified. Contrary to expectation, the longitudinal Doppler components are found to be less intense than the transverse Doppler eomponents.
The second-order spectrum of diamond has been examined with a quartz spectrograph of high dispersion and resolution. It exhibits a whole series of sharply defined Raman lines the frequency shifts of which have been tabulated. The prominent ones which are 15 in number have been satisfactorily explained as octaves of combinations of six of the eight fundamental frequencies of vibration of the diamond lattice to be expected on the basis of the Raman theory, some of which are split due to the removal of degeneracy by anharmonicity and due to resonance effect.