Rotational Lattice Vibrations of Tetramethyl- and Tetramethyl-d12-pyrazine Crystals

Abstract

Abstract The low-frequency Raman bands of the tetramethyl- and tetramethyl-d12-pyrazine crystals and their hydra ted crystals were studied at various temperatures between 4.2 and 298 K. The isotopic factors and the temperature effects on the frequencies of the Raman bands indicate that the low-frequency Raman bands observed in the crystal are to be ascribed to the rotational lattice vibrations. A smooth curve of the plot of the Raman frequency versus temperature suggests that no apparent temperature-induced phase transition takes place in the tetramethylpyrazine crystal. Classification of the rotational lattice vibrations into symmetry species was made based on the polarization behavior of the Raman bands. It was also observed that tetramethylpyrazine hydrates quite easily with a trace of moisture in the air.