Pietzsch, A.; Niskanen, J.; Vaz da Cruz, V.; Büchner, R.; Eckert, S.; Fondell, M.; Jay, R.M.; Lu, X.; McNally, D.; Schmitt, T.; Föhlisch, A.: Cuts through the manifold of molecular H2O potential energy surfaces in liquid water at ambient conditions. Proceedings of the National Academy of Sciences of the United States of America : PNAS 119 (2022), p. e2118101119/1-6
10.1073/pnas.2118101119
Open Access Version
Abstract:
The fluctuating hydrogen bridge bonded network of liquid water at ambient conditions entails a varied ensemble of the underlying constituting H2O molecular moieties. This is mirrored in a manifold of the H2O molecular potentials. Subnatural line width resonant inelastic X-ray scattering allowed us to quantify the manifold of molecular potential energy surfaces along the H2O symmetric normal mode and the local asymmetric O–H bond coordinate up to 1 and 1.5 A, respectively. The comparison of the single H2O molecular potentials and spectroscopic signatures with the ambient conditions liquid phase H2O molecular potentials is done on various levels. In the gas phase, first principles, Morse potentials, and stepwise harmonic potential reconstruction have been employed and benchmarked. In the liquid phase the determination of the potential energy manifold along the local asymmetric O–H bond coordinate from resonant in- elastic X-ray scattering via the bound state oxygen 1s to 4a1 resonance is treated within these frameworks. The potential energy surface manifold along the symmetric stretch from resonant inelastic X-ray scattering via the oxygen 1s to 2b2 resonance is based on stepwise harmonic reconstruction. We find in liquid water at ambient conditions H2O molecular potentials ranging from the weak interaction limit to strongly distorted potentials which are put into perspective to established parameters, i.e., intermolecular O–H, H–H, and O–O correlation lengths from neutron scattering.