Molecular motion in liquid benzene by nuclear magnetic resonance |
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Authors: | JG Powles R Figgins |
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Institution: | The Physics Laboratories , University of Kent at Canterbury , Canterbury, England |
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Abstract: | The proton spin-lattice relaxation time, T 1, has been measured for a series of mixtures of benzene in perdeuterobenzene for the liquid in equilibrium with its vapour over the temperature range from below the normal freezing point up to the critical temperature. The two contributions to T 1 due to interactions within the molecule (T 1 intra) and between molecules (T 1 inter) have been separated and are found to be very different in magnitude and in variation with temperature. The variation and magnitude of T 1 inter correlates well with other translational motion dependent properties such as self diffusion and viscosity. The correlation of T 1 intra with other re-orientation dependent properties such as deuteron T 1 and Rayleigh scattering is poor. The observed variation in T 1 intra and in particular the broad maximum at higher temperatures is then interpreted as due to a combination of dipolar and spin-rotation effects. This interpretation results in good agreement between the activation energies for re-orientational molecular motion deduced from proton T 1 and deuteron T 1. It supports the Hubbard theory for the relation between the dipolar and spin-rotation correlation times τd and τsr. It gives a rough value, 3·8 kc/s, for the spin-rotation interaction constant for protons in benzene. Reasonable values for τd and τsr are predicted and for all temperatures τsr < τd as expected. There is clearly a considerable difference between the re-orientational and translational motion of the molecules in liquid benzene but the exact nature of the difference cannot be elucidated. |
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