Nuclear Magnetic Relaxation Study of the Anisotropy of Rotational Reorientation in Liquid Boron Trichloride

Abstract

Boron‐11 and chlorine‐35 nuclear magnetic relaxation measurements were used to determine the anisotropy of rotational reorientation in liquid BCl₃. If the classical diffusion model is used, then the ratio of the rotational diffusion constants parallel and perpendicular to the $C_3$ axis in ¹¹B³⁵Cl₃ is 0.75 + 0.25, independent of temperature in the range − 90 to 30°C. The error estimate includes the effect of uncertainties in the ¹¹B and ³⁵Cl quadrupole coupling constants for the liquid. It is also shown that the determination of the anisotropy of rotational motion in liquids from relaxation times dominated by a quadrupolar mechanism is very sensitive to errors in the nuclear quadrupole coupling constants. This problem is least serious when the motion is nearly isotropic, as in BCl₃.