14N nuclear quadrupole resonance and proton spin–lattice relaxation study of phase transition in pyridazine perchlorate

The temperature dependence of the 14N nuclear quadrupole resonance frequencies in pyridazine perchlorate has been measured by double resonance. The results show that in the low temperature phase the pyridazinium ions are static, while in the high temperature phase the ions reorient around the normal to the plane of the ring between six equivalent orientations in agreement with the X-ray data. The 14N NQR data have been obtained for the protonated nitrogen position in the pyridazine ring for the first time. Temperature and frequency dependence of the proton spin–lattice relaxation time T 1 has been measured in both crystallographic phases. The results show the ionic mobility dominates T 1 in the low temperature phase. The activation energy for the ionic mobility is 240 meV. In the high temperature phase the pyridazine ring reorientation dominates the proton spin–lattice relaxation.