Theory of the Effects of Exchange on the Nuclear Fine Structure in the Paramagnetic Resonance Spectra of Liquids

Abstract

A theory of the influence of exchange forces in liquids upon the nuclear hyperfine structure in paramagnetic ``spin resonance'' spectra is presented. Formulas are derived for two limiting cases: for the exchange J much larger than the hyperfine separation A, and for A≪J. It is found that as J increases the hyperfine lines broaden (exchange broadening) and start to shift towards the ``unsplit'' Zeeman frequency. For J≈A, the hyperfine lines have coalesced into a single broad line and for J>A the line narrows (exchange narrowing) about the ``unsplit'' Zeeman frequency. These calculations are discussed in considerable detail. The effect upon the spectrum of electronic-electronic and electronic-nuclear dipolar interactions and the effect of the rapid molecular motions in liquids have also been considered, as well as their interactions with the exchange forces.