24 Pages


By(595) (449.5) (490.5)

Several spectral lines whose frequencies exhibited a strong dependence on s have been found in the simulated Raman spectra. If s=1.1, two distinct lines in the frequency interval between the E2(high) and LO modes appear. Frequencies of these lines are 557 and 624 cm−1. Analysis of atomic displacements has shown that the mode at 624 cm−1 corresponds to the ν3 vibration of an isolated MgN4 tetrahedron, whereas the mode at 557 cm−1 is a combination of ν3 with the ν4 “umbrella” vibration of the MgN4 tetrahedron. It can be supposed that they correspond to the Raman lines observed at 565 and 622 cm−1.