Effect of Pressure on Molecular Motions of Bromobenzene and Toluene- d 3 in the Liquid State

The pressure dependences of the proton spin–lattice relaxation times have been measured at 30°C in liquid bromobenzene and its mixtures with bromobenzene-d5 up to 2.5 kbar, and in liquid toluene-d3 and its mixtures with toluene-d8 up to 4.5 kbar. The separation of the intramolecular and intermolecular contributions to proton dipolar relaxation allowed us to study the effect of pressure on reorientational and translational motions of the molecular liquids investigated. Activation volumes for the intramolecular and intermolecular T1; and the rotational and translational correlation times were calculated. The data obtained indicate that the molecular shape seems to play a decisive role on the degree of coupling between the rotational and translational motions of these two model liquids. The effect of the difference in the dipole moments on this coupling seems to be less important.