Nuclear Magnetic Resonance Study of Electron-Coupled Internuclear Interactions in Thallium Chloride

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Abstract
Measurements are reported of the electron‐coupled nuclear exchange and pseudodipolar interactions in thallium chloride single crystals. The interaction parameters are obtained by combining second‐moment data for the nuclear magnetic resonance lines of the two abundant thalliumisotopes with measurements of the heat capacity of the whole system of spin—spin interactions. Spin‐decoupling experiments in which the 205Tl nuclear spins are decoupled first from the 203Tl spins, and then from the 203Tl and chlorine spins, help to determine the relative importance of Tl–Tl and Tl–Cl interactions. The results show that the Tl–Cl interaction is unmeasurably small, consistent with a calculation due to Yosida and Moriya. The exchange coupling constant between neighboring thallium nuclei is found to be 1.4 G. The pseudodipolar coupling has the opposite sign from that of the dipole—dipole interaction and is of approximately equal magnitude. The sign is that predicted from a simple two‐electron model. From the relative magnitudes of exchange and pseudodipolar terms, we infer that the wavefunctions of the valence electrons on the thallium atoms have about 35% s character.