Spin Exchange and Spin-Lattice Relaxation Induced by Mechanical Rotation of Solids

Abstract

Measurements with spin‐echo apparatus have shown that mechanical rotation of a sample in the static magnetic field decreases the proton T₁ in solid chlorobenzenes for particular proton magnetic resonance frequencies within the range 23.2–41 Mc/sec. The results are explained by the following model: magnetic coupling between protons and lattice is weak while the quadrupolar coupling of chlorine nuclei with the lattice is strong. Upon rotation of the sample, the angular dependence of the Zeeman splitting of the chlorine quadrupole levels enables the chlorine resonance frequencies to be brought into coincidence with that of the protons. The resulting spin exchange and energy transfer between protons and chlorine nuclei provides an indirect but nonetheless effective thermal contact of protons with the lattice, thereby reducing the proton T₁. The general question of anomalies in the dependence of T₁ upon resonance frequency is discussed briefly.