Three-body-potential contribution to the structure of krypton gas

The virial expansion for the inverse structure factor of a gas is known to involve coefficients which are a function of $q$ and $T$, and whose $q\to 0$ limits are the usual pressure virial coefficients. The authors have made careful measurements of the structure factor of krypton gas using improved neutron-diffraction techniques at 15 densities between 0.25 and 6.19×${10}^{27}$ ${\mathrm{a}\mathrm{t}\mathrm{o}\mathrm{m}\mathrm{s}/\mathrm{m}}^3$ at $T=297\mathrm{}$ K. The methods used are described, and the experimental errors are analyzed and found to be less than 1%. These data are compared to virial-expansion calculations based on the Barker et al. pair potential, to extract the first coefficient depending on the triplet potential. Some difference is found between this result and that predicted by the long-range triple-dipole (Axilrod-Teller) term.