THE INTERMOLECULAR HYDROGEN-HYDROGEN STRUCTURE OF CHAIN-MOLECULE LIQUIDS FROM NEUTRON-DIFFRACTION

Neutron diffraction isotopic substitution experiments on liquid n-deca ne (C10H22) and n-eicosane (C20H42) are described. The intermolecular H-H structure function h(HH)(Q) and the intermolecular H-H correlation function g(HH)(inter)(r) are obtained without recourse to models of t he intramolecular structure. The structure of the g(HH)(inter)(r) foun d at 2.5, 5.0, and 7.0 Angstrom corresponds to different shells in the H-H pair correlation function. In addition, g(HH)(inter)(r)<1 for a c onsiderable range, due to the screening of intermolecular correlations by intramolecular correlations. This ''correlation hole'' effect is a ccentuated by extrapolation of the structure functions to the expected infinite wavelength limit, and shows good agreement with values deter mined from small-angle neutron scattering (SANS) data. All of these fe atures are in good agreement with the results of molecular dynamics si mulations for the closely related system C13H28.