DECAY OF SINGLE AND DOUBLE-QUANTUM COHERENCES IN DEUTERATED GLASSY ORTHO-TERPHENYL

The decay of single and double quantum coherences in amorphous ortho-t erphenyl is studied by means of deuteron NMR echo experiments near and below the calorimetric glass transition temperature T-g. In perdeuter ated samples a Gaussian decay for these coherences is found at low tem peratures, in accord with theoretical predictions for random local dip olar fields. A method is proposed to extract information about slow mo tional processes from ordinary solid echo experiments below T-g. Partl y deuterated ortho-terphenyl does not show a Gaussian decay. Simple mo del calculations show that this observation indicates the importance o f correlations of the local dipolar fields in the presence of protons. (C) 1998 American Institute of Physics. [S0021-9606(98)51820-X].