Long-range pair potential from the low density S(k) of 4He around 6 K

The static structure factor S(k) of gaseous 4He at various densities along the T=6.13 K isotherm has been determined with the G4.1 diffractometer at LLB (Saclay, F). Thanks to the explored k-values (1<k/nm^-1<34), the long range behaviour of the interatomic interaction potential U(r^N) can be conveniently investigated. The resulting structure factors S(k) are presented and compared with previous determinations obtained at almost the same thermodynamic conditions using the D4B and D11 diffractometers at ILL (Grenoble, F). By means of a well known low-k expansion of the Fourier transform of the direct correlation function c(k), the London dispersion coefficient C6 of the r^-6 tail in U(r^N) has been experimentally evaluated for the first time and compared with the values present in literature.