COMBINED NEUTRON-DIFFRACTION AND COMPUTER-SIMULATION STUDY OF LIQUID DIMETHYL-SULFOXIDE

The structure of liquid dimethylsulphoxide (DMSO) at 25-degrees-C is e xplored using a combination of neutron diffraction with isotope substi tution and computer simulation techniques. The potentials used in the computer simulation consist of Coulomb and 6-12 Lennard-Jones interact ions for each of the carbon, oxygen, and sulfur sites on the molecule. To interpret the neutron diffraction data most effectively, it is nec essary to refine both the molecular internal structure and the intermo lecular contributions to the measured structure factors at the same ti me in order to separate the intermolecular terms correctly, because th ere is a large degree of overlap between intramolecular and intermolec ular distances. This renders the data far more sensitive to the interm olecular forces than if this analysis were not performed. Direct compa rison of neutron diffraction data and computer simulation results indi cates that existing models of the molecular force field give a sensibl e description of the liquid structure, although there are some discrep ancies which are not fully understood at this time. The question of wh ether this material can be regarded as an associated liquid, as it is frequently referred to, is discussed. All tests for association that h ave so far been applied to both the diffraction data and the computer simulation results do not indicate a highly ordered molecular associat ion in the liquid.