Non-exponential correlation functions in supercooled liquids

31P NMR is used to investigate phosphoric and phosphonic acid esters in their supercooled regimes. The NMR is dominated by chemical shift tensors which are large compared to the homonuclear dipolar coupling between the phosphorous nuclei. The chemical shift tensor originates from the electronic distribution in the PR4 tetrahedron and thus is intramolecular. The motion of the molecules is probed by the reorientation of the tensor with respect to the magnetic field. This means that only the rotational part of the glass transition is monitored. T1, T2, line shape and stimulated echo are studied, covering a wide range of accessible correlation times. The correlation function of the stimulated echo is similar to the one of the spin alignment experiment for deuterons and a corresponding analysis in the time domain can be performed (author). 12 refs.; 6 figs