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arXiv · 2506.13169

Hydrogen bond symmetrization in high-pressure ice clathrates

Lorenzo Monacelli·Maria Rescigno·Alasdair Nicholls·Umbertoluca Ranieri·Simone Di Cataldo·Livia Eleonora Bove
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Abstract

Hydrogen bond symmetrization is a fundamental pressure-induced transformation in which the distinction between donor and acceptor sites vanishes, resulting in a symmetric hydrogen-bond network. While extensively studied in pure ice, most notably during the ice VII to ice X transition, this phenomenon remains less well characterized in hydrogen hydrates. In this work, we investigate hydrogen bond symmetrization in the high-pressure phases of hydrogen hydrate (H2-H2O and H2-D2O) through a combined approach of Raman spectroscopy and first-principles quantum atomistic simulations. We focus on the C2 and C3 filled-ice phases, using both hydrogenated and deuterated water frameworks. Our results reveal that quantum fluctuations and the interaction between the encaged H2 molecules and the host lattice play a crucial role in driving the symmetrization process. Remarkably, we find that in both C2 and C3 phases, hydrogen bond symmetrization occurs via a continuous crossover at significantly lower pressures than in pure ice, without any change in the overall crystal symmetry. These findings provide new insight into the quantum-driven mechanisms of bond symmetrization in complex hydrogen-bonded systems under extreme conditions.

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Lorenzo Monacelli, Maria Rescigno, Alasdair Nicholls, Umbertoluca Ranieri, Simone Di Cataldo, Livia Eleonora Bove. 2025-06-16. Hydrogen bond symmetrization in high-pressure ice clathrates. https://arxiv.org/abs/2506.13169

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