Motional Averaging of Nuclear Resonance in a Field Gradient

TL;DR

This paper challenges traditional views on nuclear-spin decoherence in field gradients, showing that temperature dependence varies between liquids and gases, and introduces a detailed theory including position autocorrelation effects.

Contribution

It presents a new theoretical framework explaining the opposite temperature behaviors of linewidth in liquids and gases.

Findings

Linewidth increases with temperature in liquids.

Linewidth decreases with temperature in gases.

A detailed dephasing model explains the observed behaviors.

Abstract

The traditional view of nuclear-spin decoherence in a field gradient due to molecular self-diffusion is challenged on the basis of temperature dependence of the linewidth, which demonstrates different behaviors between liquids and gases. The conventional theory predicts that in a fluid, linewidth should increase with temperature; however, in gases we observed the opposite behavior. This surprising behavior can be explained using a more detailed theoretical description of the dephasing function that accounts for position autocorrelation effects.