Orientational correlations in molecular liquid Sn I4

Abstract

The total scattering structure factor of liquid tin tetraiodide (Sn I4) has been interpreted by means of reverse Monte Carlo (RMC) modeling. From the sets of particle coordinates provided by RMC, which are consistent with experimental results within errors, partial radial distribution functions as well as correlation functions characterizing mutual orientations of molecules as a function of distance between molecular centers can be calculated. Interestingly and very much in contrast to liquids of symmetric X Cl4 molecules, the corner-to-face (or "Apollo")-type orientation of neighboring molecules has a significant (about 20%) occurrence in liquid Sn I4. Via comparison with a reference system, obtained by hard sphere Monte Carlo simulation, we demonstrate that intermolecular two-body correlations in liquid Sn I4 are determined largely by excluded volume (steric) effects; that is, intermolecular two-body interactions play only a minor role. On the other hand, as it is manifested in the large difference between the reference and "real" systems in terms of the orientational correlations, higher order interactions are indispensable. This feature can explain the extremely rich phase behavior of Sn I4 at high pressures. © 2008 American Institute of Physics.