TRITIUM NUCLEAR-MAGNETIC-RESONANCE STUDY OF T-2, HT, AND DT DISSOLVEDIN NEMATIC SOLVENTS

A tritium nuclear magnetic resonance study is carried out on the T-2, HT, and DT isotopomers of dihydrogen dissolved in various nematic phas es, including a zero-electric-field-gradient mixture. Ab initio calcul ations are performed to reproduce the observed dipolar couplings. With in the framework of the ''mean-field'' approximation, the results prov ide support for a picture in which two independent contributions to th e solute orientation can be distinguished. One contribution involves a liquid-crystal-dependent interaction between the mean solvent electri c-field gradient and the solute molecular quadrupole moment. The other contribution is of unknown origin; however, it is essentially identic al in all liquid crystals and it can be modeled adequately with a phen omenological mean-field interaction. A remarkable feature of this seco nd interaction is that it causes the average orientation of the asymme trical isotopomers, and especially of HT, to behave differently from t he symmetrical species.