Spin dynamics in liquid and rotationally disordered solid oxygen

摘要

The spin and nuclear dynamics of the liquid and plastic-solid phases of molecular oxygen are studied by means of inelastic neutron scattering. A detailed spectral analysis over wide energy- (0-18 meV) and momentum- (0.2-4.5 A~(-1)) transfer ranges permits a robust separation of magnetic and nuclear contributions to the dynamic structure factor. Reliable spin-exchange constants are obtained for both liquid and plastic phases, which are found to be remarkably similar to each other, with no evidence for long-range antiferromag-netic spin correlations beyond next-nearest neighbors. Analysis of the time scales involved in spin-Hip processes suggests that spin diffusion in these structurally disordered phases takes place within a lapse of time comparable to the lifetime of an O_4 unit in the liquid.