The intermolecular hydrogen–hydrogen structure of chain–molecule liquids from neutron diffraction

Neutron diffraction isotopic substitution experiments on liquid n-decane (C10H22) and n-eicosane (C20H42) are described. The intermolecular H–H structure function hHH(Q) and the intermolecular H–H correlation function ginterHH(r) are obtained without recourse to models of the intramolecular structure. The structure of the ginterHH(r) found at 2.5, 5.0, and 7.0 Å corresponds to different shells in the H–H pair correlation function. In addition, ginterHH(r)<1 for a considerable range, due to the screening of intermolecular correlations by intramolecular correlations. This ‘‘correlation hole’’ effect is accentuated by extrapolation of the structure functions to the expected infinite wavelength limit, and shows good agreement with values determined from small-angle neutron scattering (SANS) data. All of these features are in good agreement with the results of molecular dynamics simulations for the closely related system C13H28.