Quantum effects and the local environment of water hydrogen: Deep inelastic neutron scattering study

Abstract

""A deep inelastic neutron scattering experiment, performed on D2O in the temperature range 276-292 K provides insight on changes of the local environment of the water deuteron around the temperature of maximum density. We have measured the deuteron average kinetic energy and momentum distribution and found that their temperature dependence closely follows that shown by the density of the bulk liquid. These findings suggest an anomalous behavior of both kinetic energy and momentum distribution, similar to that observed for H2O. However, in contrast to previous results on lightwater, no signatures of deuteron delocalization along the hydrogen bond have been observed for supercooled D2O. This indicates a different relevance of quantum effects in the two liquids. Data such as that discussed here, are crucial to assess the validity of existing electrostatic-based models to describe changes of the water intermolecular potential upon hydrogen bonding."

Temperature dependence of the zero point kinetic energy in ice and water above room temperature

“…Increased kinetic energy in the solid with respect to the liquid is also reported in Path Integral simulations of water using rigid models [54]. Such combined efforts should help to shed some light on the effects of isotopic substitution (H-D) or the behaviour of hE K ðTÞi in the region below room temperature or near the triple point, where the large discrepancies between experiments on water's protons and deuterons, and theories, are still unexplained [33,35]; we note, in passing, that indications of slight if not almost negligible differences in the deuteron kinetic energies were reported between room temperature liquid and solid heavy water close to the triple point [55], the solid showing in this case a slightly lower kinetic energy than the liquid. Values inferred from macroscopic thermodynamic free energy data on the proton kinetic energy in ice at 269 K and liquid water at 300 K predict a $ 0.5 meV increase from the solid to the liquid [56].…”

Isotope effects in liquid water probed by transmission mode x-ray absorption spectroscopy at the oxygen K-edge

“…In particular, the bulk structure of the liquid [1,2], the structure of water at interfaces [3], the thermodynamical properties of water [4], the translational and rotational motions in liquid water [5] and the hydrogen-bond (H-bond) environment [6,7] and its ultrafast dynamics [8] were investigated in light of these quantum effects. Such experimental results can serve as benchmark tests for theoretical treatments of quantum effects in hydrogen bonding (Hbonding) in water [9,10] and H-bonds in general [11].…”

Simulation of quantum zero-point effects in water using a frequency-dependent thermostat

“…In Fig. (13) we observe that for P ≤ 10, i.e. for P T ≤ 3000K goo(r) looses structure compared to the classical (P=1 bead) case.…”

“…However, the question of how much this effect will play a role in the liquid phase is still open. Experimentally, there are indications 13 that quantum effects might be different in low density and high density regions of liquid water. Understanding to which point this is correct will shed light on the question of how much the local environment of the proton will modify its kinetic energy.…”