Dilithium, Li<sub>2</sub>, is a strongly nucleophilic, diatomic molecule comprising two lithium atoms covalently bonded together. Li<sub>2</sub> has been observed in the gas phase.
It has a bond order of 1, an internuclear separation of 267.3 pm and a bond energy of 102 kJ/mol or 1.06 eV in each bond.
The electron configuration of Li<sub>2</sub> may be written as σ<sup>2</sup>.
Being the third-lightest stable neutral homonuclear diatomic molecule (after dihydrogen and dihelium), dilithium is an extremely important model system for studying fundamentals of physics, chemistry, and electronic structure theory.
It is the most thoroughly characterized compound in terms of the accuracy and completeness of the empirical potential energy curves of its electronic states. Analytic empirical potential energy curves have been constructed for the X-state, a-state, A-state, c-state, B-state, 2d-state, l-state, and the F-state.<!-- [Removing names of people who did the work / wrote the cited papers, because I've added their names in too many other places. If someone thinks it's helpful to include the names, they can put them back.] all by Robert J. Le Roy
This lithium oscillator strength is related to the radiative lifetime of atomic lithium and is used as a benchmark for atomic clocks and measurements of fundamental constants.
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! Electronic state !! Spectroscopic symbol !! Term symbol !!colspan=2 | Bond length (pm) !!colspan=2 | Dissociation energy (cm<sup>−1</sup>) !! Bound vibrational levels !! References
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| 1 (Ground) || X || 1<sup>1</sup>Σ<sub>g</sub><sup>+</sup> ||