NMR study of the pressure effects on the molecular dynamics in the disordered, crystalline phase of neopentane

The NMR proton spin–lattice relaxation times T1 have been measured in the disordered crystalline phase of neopentane as a function of pressure and temperature. The molecular reorientation and self-diffusion contributions to the observed relaxation time are separated and the activation parameters are calculated for the two processes, respectively. The over-all molecular reorientation has a very weak pressure dependence whereas the self-diffusion exhibits a strong pressure dependence. The interesting result that the activation volume for self-diffusion is close to the molecular volume in neopentane is discussed in terms of the diffusion mechanism. The data enable us to estimate the modulated portion of the second moment attributable to the over-all molecular reorientation.