Dication

Template:Short description Template:Distinguish A dication is any cation, of general formula X²⁺, formed by the removal of two electrons from a neutral species.

Diatomic dications corresponding to stable neutral species (e.g. Template:Chem formed by removal of two electrons from H₂) often decay quickly into two singly charged particles (H⁺), due to the loss of electrons in bonding molecular orbitals. Energy levels of diatomic dications can be studied with good resolution by measuring the yield of pairs of zero-kinetic-energy electrons from double photoionization of a molecule as a function of the photoionizing wavelength (threshold photoelectrons coincidence spectroscopy – TPEsCO). The Template:Chem dication is kinetically stable.

An example of a stable diatomic dication which is not formed by oxidation of a neutral diatomic molecule is the dimercury dication Template:Chem. An example of a polyatomic dication is Template:Chem, formed by oxidation of S₈ and unstable with respect to further oxidation over time to form SO₂.

Many organic dications can be detected in mass spectrometry for example Template:Chem (a Template:Chem complex) and the acetylene dication Template:Chem.<ref>Template:Cite journal</ref> The adamantyl dication has been synthesized.<ref>Template:Cite journal</ref> The adamantane dication

Divalent metals

Template:Periodic table (micro) Some metals are commonly found in the form of dications when in the form of salts, or dissolved in water. Examples include the alkaline earth metals (Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Ra²⁺); later 3d transition metals (V²⁺, Cr²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺); group 12 elements (Zn²⁺, Cd²⁺, Hg²⁺); and the heavy members of the carbon group (Sn²⁺, Pb²⁺).

Presence in space

Multiply-charged atoms are quite common in the Solar System in the so-called Solar wind. Among these, the most abundant dication is He²⁺. However, molecular dications, in particular CO₂²⁺, have never been observed so far though predicted to be present for instance at Mars.<ref>Template:Cite journal</ref> Indeed, this ion by means of its symmetry and strong double bounds is more stable (longer lifetime) than other dications. In 2020, the molecular dication CO₂²⁺ has been confirmed to be present in the atmosphere of Mars<ref>Template:Cite journal</ref> and around Comet 67P.<ref>Template:Cite journal</ref>