MOLECULAR-DYNAMICS NEAR THE GLASS-TRANSITION - A 2-DIMENSIONAL C-13 NMR-STUDY OF 1,3,5-TRI-ALPHA-NAPHTHYLBENZENE

Solid state C-13 NMR spectroscopy has been applied to investigate the time scale and the geometry of rotational motions near the glass trans ition of the low-molar-mass van der Waals glass former 1,3,5-tri-alpha -naphthylbenzene (T-g = 342 K). Two-dimensional C-13 exchange spectra were taken between 347 and 372K. With the principal values of the C-13 chemical shift tensors determined from C-13 CP/MAS spectra and static one-dimensional C-13 spectra, the two-dimensional spectra are interpr eted according to the isotropic rotational diffusional model to yield mean correlation times tau(0) in the range 10 ms less than or equal to tau(0) less than or equal to 50 s, and a log-Gaussian distribution of correlation times with a width of 1.5 decades. The mean correlation t imes agree with scaled viscosity data and with results from photon cor relation spectroscopy.