H-2 NUCLEAR-MAGNETIC-RESONANCE STUDY OF SUPERCOOLED TOLUENE - SLOW AND FAST PROCESSES ABOVE AND BELOW THE GLASS-TRANSITION

H-2-NMR spin-lattice relaxation times T-1 of phenyl ring deuterated to luene have been measured as a function of temperature (75-290 K) at La rmor frequencies between 13.8 and 55.8 MHz. The results are interprete d by assuming a Cole-Davidson rotational correlation time distribution for the alpha process dominating T-1 at temperatures down to about 20 K above the glass transition (T-g=117 K) and one further process at l ower temperatures. The latter is analyzed below T-g using a model with temperature dependent librational angles Delta Phi<13 degrees and mea n correlation times tau>10(-9) s. Self-diffusion coefficients are dete rmined at temperatures down to 136 K (D=1.5X10(-14) m(2) s(-1)) using a static field gradient H-1-NMR method. The product of D and the mean rotational correlation time shows a tendency to increase at the lowest temperatures. (C) 1996 American Institute of Physics.