NMR Spin—Lattice Relaxation in Solid Solutions of C6H6 and C6D6: Evidence for Concerted Motions by Adjacent Molecules

Abstract

The NMR spin—lattice relaxation time T₁ has been investigated as a function of isotopic substitution in cyrstalline benzene. 1,3,5‐C₆H₃D₃ and six solid solutions of C₆H₆ and C₆D₆ were studied between 140°K and the melting point. The concentration dependence of T₁ was used to separate the effects of intra‐ and intermolecular relaxation. The experimental intramolecular T₁ contribution agreed quite closely with that calculated from known molecular dimensions. Comparison of the intra‐ and intermolecular correlation times are shown to give information regarding the relative motion of neighboring molecules in the solid. Independent molecular ``jumps'' are found to be relatively unimportant in crystalline benzene, and a free‐volume model, leading to the simultaneous motion of adjacent molecules, is discussed.