Diions

Diions are a proposed class of molecular ions characterized by a net charge and a bound configuration of two ionic centers within a single molecular framework. In theoretical chemistry and plasma physics, diions are envisioned as transient, doubly charged species formed by the pairing of two monovalent ions into a single bound complex. They are distinct from conventional multiply charged ions in that the two charge centers are spatially separated within a single molecular scaffold, potentially giving rise to unique spectroscopic and reactive properties.

The concept has appeared in studies of highly ionized molecules, ultrafast laser–driven chemistry, and strong-field plasmas. Theoretical models use ab initio and density functional theory to map potential energy surfaces and predict stable geometries, lifetimes, and possible dissociation channels. Predicted features include large dipole moments, characteristic vibrational transitions, and specific fragmentation pathways that reflect the two-center charge distribution.

Experimental evidence remains tentative. The short lifetimes of highly charged species, rapid fragmentation, and competition with simpler ionic channels make unambiguous detection difficult. Researchers have proposed strategies such as high-resolution mass spectrometry of highly ionized ensembles, cold ion traps with spectroscopy, and ultrafast pump–probe experiments to identify signature spectra or fragmentation that would indicate diion formation. If observed, diions would have implications for reaction dynamics in plasmas, interstellar chemistry, and the interpretation of ionized molecular spectra.

Diions are a topic of ongoing theoretical interest rather than established chemistry. The term is used mainly in speculative discussions and in certain modeling contexts; it is not a standard category in established chemical nomenclature.

See also: multiply charged ions; diatomic molecules; ionic bonding.