Temperature dependence of the14N quadrupole coupling constants in pyrazine

摘要

The frequency of the14N nuclear quadrupole resonances ngr;plus;and ngr;minus;in pyrazine has been measured at several temperatures between 4.2 and 324 K. Below 300 K, only one ngr;plus;line and one ngr;minus;line are seen, indicating the existence of a unique sort of crystalline site for nitrogen atoms in the crystal of pyrazine. At 27deg; and 35deg;C crystalline phase transitions are observed through a splitting of the lines and a discontinuity of the frequency of resonance. An interpretation of the temperature dependence of the resonance frequencies, ngr;plus;and ngr;minus;, between 4.2 and 300 K is proposed using Bayer's theory and the molecular motion frequencies reported by Ito and Shigeoka; however, the assignment of these frequencies to specific rotations about the different axes of symmetry of the molecule, which fits nuclear quadrupole resonance data, is different from that given by Ito and Shigeoka.