Effect of lattice vibrations on the NMR second moment. I. Intramolecular contribution

The effect of average librational motion of rigid molecules in the solid on the second moment of the NMR spectral line is investigated. The intramolecular contribution to the second moment is corrected for these motions by representing <cos₂θ> in terms of the libration tensor employing the formalism put forward by Schomaker and Trueblood. It is possible, with the aid of the equations derived here, to evaluate the motional correction of the intramolecular contribution to the second moment, for both single crystal and powder samples, using the relevant crystallographic positional and thermal parameters of the molecule in question.