The pair correlation function of krypton in the critical region: theory and experiment

We present the results of high-precision measurements of the structure factor S(k) of krypton in the near-critical region of the liquid-vapour phase transition for values of k ranging from 1.5 up to 50 nm(-1). The experimental results are compared with a theoretical calculation based on the hierarchical reference theory (HRT) with an accurate potential which includes two- and three-body contributions. The theory is based on a new implementation of HRT in which we avoid the use of hard spheres as a reference system. With this soft-core formulation we find a generally good agreement with experiments both at large k, where S(k) probes the short-range correlations, as well as at small k, where critical fluctuations become dominant. Also, for the density derivative of the pair correlation function there is an overall good agreement between theory and experiment.