Intermolecular potentials from nuclear spin lattice relaxation in pure gases with octahedral symmetry

Abstract

Fluorine spin lattice relaxation times per unit density T ₁/ρ in pure SF₆, MoF₆, WF₆ and UF₆ gases are experimentally found to be proportional to T ^-1·5 where T is the temperature. These data can be analysed to obtain information on the anisotropic part of the intermolecular potential in these systems. Hard sphere, Lennard-Jones (6–12) and modified Buckingham (exp-6) potentials were used for the isotropic part of the intermolecular interaction. The analysis is made using the Bloom-Oppenheim theory, assuming that the correlation time of the spin rotation interaction can be approximated by the average lifetime of a molecule in the given J state. We have obtained the strengths of the repulsive and attractive terms in the anisotropic potential. From the strength of the attractive term in the anisotropic potential, the hexadecapole moments of all the four molecules are obtained. The hexadecapole moment of SF₆ obtained by us using the Lennard-Jones model is in good agreement with the values reported earlier, based on other techniques, while the values for MoF₆, WF₆ and UF₆ are reported for the first time.