Zeeman Effect of ^<35>Cl NQR on A Low Temperature Phase of 2,4,6-Trichloronitrobenzene

^<35>Cl NQR frequencies in the title compound have been observed as a function of temperature in the range of 77 K to the melting point. A discontinuity in the NQR signals has been observed at 321 K, suggesting a phase transition. The Zeeman effect on resonance lines in the low temperature phase has been studied at room temperature. The asymmetry parameter for the Cl atom at 2- or 6-position is 0.094, whereas that for the Cl atoms at the 4-position is0.080. The angles between the C-Cl bonds are determined on the basis of the orientations of the axes of the electric field gradients. The phase transition is revealed to be accompanied with change in molecular shape.