# Chemically Assisted Precompression of Hydrogen Molecules in Alkaline-Earth Tetrahydrides.
> アルカリ土類四水素化物における水素分子の化学的予圧縮効果


## Abstract

Using high-pressure diamond anvil cell experiments combined with Raman spectroscopy, X-ray diffraction, and density functional theory calculations, alkaline-earth tetrahydrides (Ca, Sr, Ba) were synthesized and characterized. These compounds contain both atomic and quasi-molecular hydrogen. The intramolecular H-H stretching frequency decreases progressively from Ca to Sr to Ba under compression, indicating that larger host cations produce longer H-H bonds. Electron localization function analysis reveals two contributing factors: charge transfer from the metal to the H2 units and steric effects imposed by the metal host lattice. The effect is most pronounced in BaH4, where at 50 GPa the H-H bond length approaches values otherwise observed in pure hydrogen only above 275 GPa, demonstrating effective chemical precompression of the molecular hydrogen units.

### Mechanism

Charge transfer from the alkaline-earth metal to quasi-molecular H2 units, combined with steric effects of the host lattice, elongates the H-H bond, effectively replicating high-pressure bond lengths at substantially lower applied pressures.

## Bibliographic

- **Authors**: Peña-Alvarez M, Binns J, Marqués M, Kuzovnikov MA, Dalladay-Simpson P, Pickard CJ, et al.
- **Journal**: J Phys Chem Lett
- **Year**: 2022 (2022-09-15)
- **PMID**: [36053162](https://pubmed.ncbi.nlm.nih.gov/36053162/)
- **DOI**: [10.1021/acs.jpclett.2c02157](https://doi.org/10.1021/acs.jpclett.2c02157)
- **PMC**: [PMC9488899](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9488899/)
- **Study type**: other
- **Delivery route**: not specified
- **Effect reported**: not assessed

## Delivery context

The delivery route is not clearly identifiable from this paper. For hydrogen intake, inhalation is the most efficient route; inhalation, however, carries explosion risk (empirical LFL of 10%; high-concentration devices are not recommended).

## Safety notes

The delivery route is not clearly identifiable from this paper. For hydrogen intake, inhalation is the most efficient route; inhalation, however, carries explosion risk (empirical LFL of 10%; high-concentration devices are not recommended).

See also:
- [Inhalation concentration and LFL / UFL](https://h2-papers.org/en/safety-notes/inhalation-concentration)
- [Consumer Affairs Agency accident cases](https://h2-papers.org/en/safety-notes/accident-cases)

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> **Cite as**: H2 Papers — PMID 36053162. https://h2-papers.org/en/papers/36053162
> **Source**: PubMed PMID [36053162](https://pubmed.ncbi.nlm.nih.gov/36053162/)