Details

Autor(en) / Beteiligte

• Liu, Xiao-Di
• Dalladay-Simpson, Philip
• Howie, Ross T.
• Zhang, Hui-Chao
• Xu, Wan
• Binns, Jack
• Ackland, Graeme J.
• Mao, Ho-Kwang
• Gregoryanz, Eugene

Titel

Counterintuitive effects of isotopic doping on the phase diagram of H₂–HD–D₂ molecular alloy

Ist Teil von

• Proceedings of the National Academy of Sciences - PNAS, 2020-06, Vol.117 (24), p.13374-13378

Ort / Verlag

Washington: National Academy of Sciences

Erscheinungsjahr

2020

Quelle

EZB Electronic Journals Library

Beschreibungen/Notizen

• Molecular hydrogen forms the archetypical quantum solid. Its quantum nature is revealed by behavior which is classically impossible and by very strong isotope effects. Isotope effects between H₂, D₂, and HD molecules come from mass difference and the different quantum exchange effects: fermionic H₂ molecules have antisymmetric wavefunctions, while bosonic D₂ molecules have symmetric wavefunctions, and HD molecules have no exchange symmetry. To investigate how the phase diagram depends on quantum-nuclear effects, we use high-pressure and low-temperature in situ Raman spectroscopy to map out the phase diagrams of H₂–HD–D₂ with various isotope concentrations over a wide pressure–temperature (P-T) range. We find that mixtures of H₂, HD, and D₂ behave as an isotopic molecular alloy (ideal solution) and exhibit symmetry-breaking phase transitions between phases I and II and phase III. Surprisingly, all transitions occur at higher pressures for the alloys than either pure H₂ or D₂. This runs counter to any quantum effects based on isotope mass but can be explained by quantum trapping of high-kinetic energy states by the exchange interaction.