25 / 2026-03-04 16:10:03

Hydrogen-bond symmetrisation dynamics in planetary Ice Analogues

High-pressure NMR,Correlation Relaxometry,Hydrogen-Bond Symmetrization,Proton Mobility,Hydrogen-bonded molecular solids；

高压物理与材料科学 > 静高压物理与材料科学

          Hydrogen-bonded molecular solids are major constituents of planetary ice reservoirs composed of the cosmically abundant elements H–C–N–O(–F). Under compression, shortening of hydrogen bonds can strongly modify proton dynamics and may ultimately lead to hydrogen-bond symmetrisation, a process well studied in simple systems such as water but far less explored in complex molecular materials. Experimental probes capable of resolving hydrogen mobility in microscopic high-pressure samples remain limited.

         Here we investigate pressure-induced changes in hydrogen dynamics in a series of small hydrogen-bearing molecules representative of planetary ice analogues using NMR relaxometry mapping. Experiments were performed on trifluoroacetamide (TFA), melamine, formamide, and water to pressures up to 80 GPa.

         Across all investigated organic compounds, the relaxometry maps reveal a consistent sequence of pressure-induced changes. At intermediate compression, spectral signatures indicate the formation of imide-like structural motifs, suggesting pressure-driven rearrangements within the molecular framework. Upon further compression, near 40–50 GPa, an additional hydrogen-bearing spin population emerges in all systems, exhibiting markedly enhanced motional averaging compared with the more rigid proton environments of the surrounding lattice.

         The appearance of this highly mobile hydrogen sub-species is reproducible across chemically distinct systems. Despite substantial differences in molecular structure between TFA, melamine, and formamide, the additional signal emerges within a narrow pressure interval. This convergence suggests a common underlying physical mechanism largely independent of molecular structures.

The consistent pressure scale and the similarity of the dynamical signatures across both organic molecules and a water reference suggest that the observed high-mobility hydrogen populations are associated with strongly compressed hydrogen bonds approaching a symmetric configuration.

         These results demonstrate that two-dimensional correlation NMR provides a sensitive probe of hydrogen dynamics in microscopic high-pressure samples and reveals a common pressure-driven hydrogen mobility regime across diverse H–C–N–O(–F) molecular systems relevant to planetary ice chemistry.