  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.
