Chemically Assisted Precompression of Hydrogen Molecules in Alkaline-Earth Tetrahydrides

Miriam Pena Alvarez*, Jack Binns, Miriam Marques , Mikhail A. Kuzovnikov, Philip Dalladay-Simpson, Chris J Pickard, Graeme J. Ackland, Eugene Gregoryanz, Ross T. Howie*

*Corresponding author for this work

Research output: Contribution to journalLetterpeer-review

Abstract

Through a series of high pressure diamond anvil experiments, we report the synthesis of alkaline earth (Ca, Sr, Ba) tetrahydrides, and investigate their properties through Raman spectroscopy, X-ray diffraction, and density functional theory calculations. The tetrahydrides incorporate both atomic and quasi-molecular hydrogen, and we find that the frequency of the intramolecular stretching mode of the H𝛿−2 units downshifts from Ca to Sr and to Ba upon compression. The experimental results indicate that the larger the host cation, the longer the H𝛿−2 bond. Analysis of the electron localization function (ELF) demonstrates that the lengthening of the H–H bond is caused by the charge transfer from the metal to H𝛿−2 and by the steric effect of the metal host on the H–H bond. This effect is most prominent for BaH4, where the precompression of H𝛿−2 units at 50 GPa results in bond lengths comparable to that of pure H2 above 275 GPa
Original languageEnglish
Article number13
Pages (from-to)8447-8454
Number of pages8
JournalThe Journal of Physical Chemistry Letters
Volume2022
Early online date2 Sep 2022
DOIs
Publication statusE-pub ahead of print - 2 Sep 2022

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