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Concept
Dihydrogen cation
Summary
The dihydrogen cation or hydrogen molecular ion is a cation (positive ion) with formula H2+. It consists of two hydrogen nuclei (protons) sharing a single electron. It is the simplest molecular ion.
The ion can be formed from the ionization of a neutral hydrogen molecule (H2) by electron impact. It is commonly formed in molecular clouds in space by the action of cosmic rays.
The dihydrogen cation is of great historical, theoretical, and experimental interest.
Historically it is of interest because, having only one electron, the equations of quantum mechanics that describe its structure can be solved approximately in a relatively straightforward way, as long as the motion of the nuclei and relativistic and quantum electrodynamic effects are neglected. The first such solution was derived by Ø. Burrau in 1927, just one year after the wave theory of quantum mechanics was published.
The theoretical interest arises because an accurate mathematical solution, taking into account the motion of all constituents, is feasible. The accuracy has steadily improved over more than half a century, eventually resulting in a theoretical framework allowing ultra-high-accuracy predictions for the energies of the rotational and vibrational levels in the electronic ground state, which are mostly metastable.
In parallel, the experimental approach to the study of the cation has undergone a fundamental evolution with respect to earlier experimental techniques used in the 1960s and 1980s. Employing the most advanced techniques, the rotational and vibrational transitions can be investigated in extremely fine detail. The transition frequencies can be measured and the results can be compared with the theoretical predictions. This makes the dihydrogen cations another family of systems relevant for the determination of fundamental constants of atomic and nuclear physics, after the hydrogen atom family and the helium atom family.
Bonding in H2+ can be described as a covalent one-electron bond, which has a formal bond order of one half.
Official source
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