Y. S. Badyal

Electron distribution in water

The x-ray structure factor of water measured under ambient conditions with synchrotron radiation is compared with those predicted on the basis of partial structure factors describing the nuclear positions obtained by neutron diffraction and of different assumptions for the electron distribution. The comparison indicates that a charge of approximately 0.5 e is transferred from each hydrogen atom to the oxygen on the same molecule, implying an effective dipole moment of 2.9 D, in good agreement with theoretical estimates.

Quantum effects on the structure of water at constant temperature and constant atomic density

To explore quantum effects on the structure of liquid water, we have carried out high-energy x-ray diffraction measurements of quantum differences both under isothermal conditions at 24.5 °C and under isochoral conditions at 0.0997 atom/A3. The measured isothermal difference correlation function is approximately equivalent to an isochoric temperature differential (ITD) of 5.5 °C, reflecting the tendency of quantum effects to introduce more disorder into the liquid. The measured isochoral correlation function is about three times higher in amplitude and is approximately equivalent to an ITD of 19 °C. Since the isochoral measurements for H2O and D2O were made at temperatures 13.5 °C apart, the isothermal and isochoral functions are roughly consistent. The discrepancies are discussed with reference to data on the pressure dependence in the literature. They are comparable with differences in results obtained with different potential functions in path-integral molecular dynamics simulations. The present results lend further validity to the notion that quantum effects on the structure of liquid water are similar to those of thermal disorder, as long as the effects of differences in the equation-of-state of H2O and D2O are taken into account.To explore quantum effects on the structure of liquid water, we have carried out high-energy x-ray diffraction measurements of quantum differences both under isothermal conditions at 24.5 °C and under isochoral conditions at 0.0997 atom/A3. The measured isothermal difference correlation function is approximately equivalent to an isochoric temperature differential (ITD) of 5.5 °C, reflecting the tendency of quantum effects to introduce more disorder into the liquid. The measured isochoral correlation function is about three times higher in amplitude and is approximately equivalent to an ITD of 19 °C. Since the isochoral measurements for H2O and D2O were made at temperatures 13.5 °C apart, the isothermal and isochoral functions are roughly consistent. The discrepancies are discussed with reference to data on the pressure dependence in the literature. They are comparable with differences in results obtained with different potential functions in path-integral molecular dynamics simulations. The present result...

The structure of molten alkali carbonates studied by neutron diffraction and ab initio calculations

The total structure factors, S(Q), of pure molten and an equimolar mixture with , , were measured by neutron diffraction at 1013 K and 923 K, respectively. The results are generally consistent with the findings of previous MD simulations. The ion remains essentially unperturbed in the mixture. The real-space pair correlation functions are consistent with a close-packed, regular, planar, trigonal geometry for the ion in both and . There is some indication, also consistent with the findings of MD simulation, of a possible tightening of the local coordination of ions around in the presence of the larger, more weakly polarizing cation. Modelling the S(Q) data using structure factors calculated from monomer and dimer structures derived from ab initio quantum chemical calculations suggests that larger clusters are needed to realistically describe the melt local structure.

Structural analysis of a completely amorphous {sup 238}Pu-doped zircon by neutron diffraction.

The structure of a completely amorphous zircon was determined by time-of-flight neutron diffraction at Argonnes Intense Pulsed Neutron Source (IPNS). The sample of metamict zircon (ZrSiO{sub 4}), initially doped to 8.85 weight percent {sup 238}Pu, had been completely amorphized by alpha-recoil damage since its synthesis in 1981 at the Pacific Northwest National Laboratory (PNNL). The measured diffraction structure factor, S(Q), indicated a completely amorphous sample, with no signs of residual zircon microcrystallinity. The pair distribution function obtained indicated that the structure was that of an oxide glass, retaining the Si-0, Zr-0, and O-O bond lengths of crystalline zircon.