Trihydrogen oxide

Trihydrogen oxide is a predicted inorganic compound of hydrogen and oxygen with the chemical formula H3O. This is still a hypothetical compound, one of the unstable hydrogen polyoxides. It is forecasted that the compound could constitute a thin layer of metallic liquid around the cores of Uranus and Neptune, being the source of their magnetic fields. Calculations indicate the stability of H3O in solid, superionic, and fluid metallic states at the deep interior conditions of these planets.

Synthesis
Trihydrogen oxide has not been observed experimentally as of 2023, but its existence is predicted by calculation using the CALYPSO method. The compound should be stable in the pressure range 450–600 GPa and could be produced by the reaction:


 * 2H2O + H2 -> 2H3O

Physical properties
The compound is considered not a true molecular trihydrogen oxide compound. Instead, each oxygen atom is linked by a strong (covalent) bond to only two hydrogen atoms, as a water molecule, and there are molecules of dihydrogen inserted in the voids of the water molecules network. Structurally, it is thus a 2(H2O)*H2 stoichiometric combination.

At 600 GPa and 7000 K, the compound density is calculated to be 4.3 g/cm3. Molecular dynamics simulations were carried out at constant density for different temperatures:
 * At 1000 K, H3O is an orthorhombic crystalline solid (space group Cmca).
 * At 1250 K, this solid passes into a superionic state.
 * The compound liquefies at 5250 K, and the liquid should have metallic-like electrical conductivity.

In the Solar system
The magnetic fields of both Uranus and Neptune are special—non-dipolar and non-axisymmetric. This fact can be explained if the magnetic fields are produced by dynamo effect within a sufficiently thin conductive layer. However, the origin of the fields is still problematic because the cores of these planets are probably solid (thus too rigid), and the thick mantles of ice are too poorly conductive to create the effect.