th  - 1987 - 51st ENC Conference

WF40
NONAXIALLT SYMMETRIC DIPOLAR COUPLINGS IN SOLIDS AND LIQUID CRYSTALS
m
T.P. Jarvie, A.M. Thayer, a J.M. Mlllar m
, M. Luzar and A. Pines
University of California, Berkeley
Small amplitude motions in solids can induce an asymmetry in the
dipolar coupling of two spln I=I/2 nuclei. In contrast to hlgh-field
NMR, such subtle motlonal effects are readily observed in the zero field
NMR spectrum. Experimental examples can be found in the llbratlonal
motions of the water molecules In a polyerystalllne hydrate, the proton
Jumps In a hydrogen-bonded carboxyllc acid dimer, and the diffusive Jumps
of a probe molecule in an unaligned blaxlal smectlc E liquid crystal
phase. An interesting experimental result shows that the presence of a
nonzero asymmetry parameter in the dlpolar coupling produces a quenching
effect of the coupling to small residual or local fields in analogy to a
spin I=I system (I) in zero field.
I. G.W. Leppelmeler and E.L. Harm, Phys. Rev. Iqi, 72~ (1966).