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DY: Fachverband Dynamik und Statistische Physik

DY 36: Focus Session: Water – from Atmosphere to Space V (joint session CPP/DY)

DY 36.4: Vortrag

Mittwoch, 11. März 2026, 11:45–12:00, ZEU/0260

Cooperative molecular dynamics and nuclear quantum effects in bulk water — •Margarita Russina — Helmholtz-Zentrum Berlin for Materials and Energy, Berlin, Germany

The cooperative dynamics in water remain difficult to access due to the lack of long-range order and the short lifetimes of molecular correlations. Neutron scattering is well suited to probe such phenomena on the nanoscale but has been hindered by the weak coherent signal of H2O. Using a novel neutron polarization-analysis approach, we directly measure the coherent scattering in H2O and D2O with high accuracy [1]. Beyond self-diffusion and molecular rotation, we identify a picosecond cooperative process in liquid water, likely associated with rearrangements of several neighboring molecules and the reorganization of hydrogen bonds. This process may act as a precursor to large-scale molecular transport. In the intermediate wave-vector range Q < 1 1/Å, the coherent signal in H2O is enhanced compared to the expectation for rigid, noninteracting, randomly oriented molecules. Since this Q-range corresponds to distances of several molecular spacings, our results provide evidence that intermolecular correlations in water extend beyond short-range correlations and involve more distant neighbors, giving rise to cooperative dynamical fluctuations. Such an enhancement can be rationalized by correlated preferential molecular orientations, hydrogen-bond rearrangements, and nuclear quantum effects. In contrast, D2O follows a more hydrodynamic behavior consistent with reported differences in the molecular bonding and symmetry of H2O and D2O. [1] M. Russina et al., J. Phys. Chem. Lett. (2025).

Keywords: liquid water; Cooperative molecular dynamics; Nuclear quantum effects; Coherent neutron scattering; Hydrogen-bond network