화학공학소재연구정보센터
Journal of Chemical Physics, Vol.121, No.10, 4770-4780, 2004
H-2 nuclear magnetic resonance study of the molecular motion in cyanoadamantane. I. Supercooled plastically crystalline phase
The supercooled plastically crystalline phase (glassy crystal) of cyanoadamantane was investigated by multidimensional H-2 NMR (T>T-g). Although the orientationally disordered crystalline phase always coexisted with the orientationally ordered crystalline phase, we were able to single out the signal from the glassy crystal by selective excitation and it was possible to carry out line shape measurements and two-dimensional (2D) experiments (in frequency and time domain). The latter directly reveal sixfold jumps with an reorientation of the molecular C-3 axis via 90degrees angles, thus reflecting the symmetry of the lattice. The motion around the C-3 axis is found to be always fast. We can reproduce the line shape by random walk simulations properly taking into account these molecular motions. Both methods (line shape and 2D experiments) yield time constants which agree with those reported by other techniques. Refining the analysis a narrow distribution of correlation times is introduced to account for a weak stretching of the correlation function. We did not find any indication of a small angle process usually found in structural glasses. Thus, the motional process in the glassy crystal appears to be simple and quite different from that in structural glasses. (C) 2004 American Institute of Physics.