Solid hydrogen

About: Solid hydrogen is a research topic. Over the lifetime, 1317 publications have been published within this topic receiving 24678 citations.

The solid molecular hydrogens in the condensed phase: Fundamentals and static properties

Abstract: The molecular hydrogens (${\mathrm{H}}_{2}$, ${\mathrm{D}}_{2}$, HD, etc.) form the simplest of all molecular solids. The combination of the light mass, small moment of inertia, weak interactions, and the quasi-metastable ortho-para species result in a fascinating low-temperature behavior that can be understood to a large extent from considerations of first principles. After discussing single molecule properties and intermolecular interactions we discuss in detail the ortho-para properties, conversion and diffusion. This is followed by a description of the crystal structures and the orientational ordering phenomena. The thermodynamic properties are reviewed. The article is concluded with a discussion of the translational ground state of the solid and the effect of the large zero-point motion on the solid state properties. A large number of data are collected in tables and graphs to provide a reference source.

On the Possibility of a Metallic Modification of Hydrogen

Abstract: Any lattice in which the hydrogen atoms would be translationally identical (Bravais lattice) would have metallic properties. In the present paper the energy of a body‐centered lattice of hydrogen is calculated as a function of the lattice constant. This energy is shown to assume its minimum value for a lattice constant which corresponds to a density many times higher than that of the ordinary, molecular lattice of solid hydrogen. This minimum—though negative—is much higher than that of the molecular form. The body‐centered modification of hydrogen cannot be obtained with the present pressures, nor can the other simple metallic lattices. The chances are better, perhaps, for intermediate, layer‐like lattices.

Hydrogen-hydrogen bonding: a stabilizing interaction in molecules and crystals.

Abstract: Bond paths linking two bonded hydrogen atoms that bear identical or similar charges are found between the ortho-hydrogen atoms in planar biphenyl, between the hydrogen atoms bonded to the C1–C4 carbon atoms in phenanthrene and other angular polybenzenoids, and between the methyl hydrogen atoms in the cyclobutadiene, tetrahedrane and indacene molecules corseted with tertiary-tetra-butyl groups. It is shown that each such H–H interaction, rather than denoting the presence of “nonbonded steric repulsions”, makes a stabilizing contribution of up to 10 kcal mol−1 to the energy of the molecule in which it occurs. The quantum theory of atoms in molecules—the physics of an open system—demonstrates that while the approach of two bonded hydrogen atoms to a separation less than the sum of their van der Waals radii does result in an increase in the repulsive contributions to their energies, these changes are dominated by an increase in the magnitude of the attractive interaction of the protons with the electron density distribution, and the net result is a stabilizing change in the energy. The surface virial that determines the contribution to the total energy decrease resulting from the formation of the H–H interatomic surface is shown to account for the resulting stability. It is pointed out that H–H interactions must be ubiquitous, their stabilization energies contributing to the sublimation energies of hydrocarbon molecular crystals, as well as solid hydrogen. H–H bonding is shown to be distinct from “dihydrogen bonding”, a form of hydrogen bonding with a hydridic hydrogen in the role of the base atom.