Temperature Dependence of the Zeeman Effect in the Nuclear Quadrupole Resonance in Chloranil

TLDR: In this paper, the nuclear quadrupole resonance of Cl35 and its Zeeman effect have been observed in chloranil between 78° and 373°K and a broad phase transition centered near 100°K is examined.

Abstract: The nuclear quadrupole resonance of Cl35 and its Zeeman effect have been observed in chloranil between 78° and 373°K. Effects of thermal expansion appear negligible hence the Bayer theory is used with the measured temperature dependence of the pure quadrupole frequencies and the field‐gradient asymmetries to yield room‐temperature rigid‐body libration amplitudes of 〈θx2〉 = 18×10—3 rad2, 〈θy2〉 = 〈θz2〉 = 0, where x is along the molecular normal. A broad phase transition centered near 100°K is examined. The results suggest that the potential well V(θx) has a double minimum and that the transition occurs when the molecules have sufficient torsional energy to override the barrier.