Theoretical study of intermolecular correlation effects on simple liquid properties obtained by x-ray diffraction

Abstract

This work reports a theoretical study of x-ray scattering from simple liquids when environmental effects are included. An instantaneous configuration-dependent scattering factor is defined for a molecule in a liquid. Using statistical mechanics and physical principles, an expression is derived that corrects the usual scattering equations for both coherent and incoherent radiation. Using the new results, scattering data from several states of liquid helium and liquid argon are analyzed. Comparison of correlated scattering factors and isolated molecule scattering factors indicate that corrections are significant only in the vicinity of the hard core radius and for values of the wave vector s≳0.5 Å−1. Incorporating correlation effects into scattering data for these liquids, the resultant radial distribution function peak is depressed an average of 1% and computed potential well depths lowered by an average of 5%. Although treatment of data in this manner leads to better coincidence with theoretical predictions, the accuracy with which data for simple liquids may be obtained at the present time may not warrant a complete treatment as presented here. However, indications are that in polar and oriented liquids it is unjustified to leave out environmental effects when an accurate treatment is desired.