Dilithium
Template:Short description Template:About Template:Chembox Dilithium, Li2, is a strongly electrophilic, diatomic molecule comprising two lithium atoms covalently bonded together. Li2 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.<ref>Chemical Bonding, Mark J. Winter, Oxford University Press, 1994, Template:ISBN</ref> The electron configuration of Li2 may be written as σ2.Template:Fact
Being the third-lightest stableTemplate:Fact 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,<ref name=LeRoy(A-X)>Template:Cite journal</ref> a-state,<ref name=Dattani(c-a)>Template:Cite journal</ref> A-state,<ref name=Gunton(A-X)>W. Gunton, M. Semczuk, N. S. Dattani, K. W. Madison, High resolution photoassociation spectroscopy of the 6Li2 A-state, https://arxiv.org/abs/1309.5870</ref> c-state,<ref name=Semczuk(c-a)>Template:Cite journal</ref> B-state,<ref name=Huang(B)>Template:Cite journal</ref> 2d-state,<ref name=Li(l,d)>Template:Cite journal</ref> l-state,<ref name=Li(l,d) /> E-state,<ref name=Jastrzebski(E)>Template:Cite journal</ref> and the F-state.Template:Huh<ref name=Pashov(F)>Template:Cite journal</ref> The most reliable of these potential energy curves are of the Morse/Long-range variety (see entries in the table below).<ref name=LeRoy(A-X) /><ref name=Dattani(c-a) /><ref name=Huang(B) /><ref name=Gunton(A-X) /><ref name=Semczuk(c-a) />
Li2 potentials are often used to extract atomic properties. For example, the C3 value for atomic lithium extracted from the A-state potential of Li2 by Le Roy et al. in <ref name=LeRoy(A-X) /> is more precise than any previously measured atomic oscillator strength.<ref name=Tang(C9,C11)>Template:Cite journal</ref> 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.
| Electronic state | Spectroscopic symbolTemplate:Huh | Term symbol | Bond length (pm) | Dissociation energy (cm−1) | Bound vibrational levels | References | ||
|---|---|---|---|---|---|---|---|---|
| 1 (Ground) | X | 11Σg+ | Template:Decimal cell<ref name=LeRoy(A-X) /> | Template:Decimal cell<ref name=LeRoy(A-X) /> | 39<ref name=LeRoy(A-X) /> | <ref name=LeRoy(A-X) /> | ||
| 2 | a | 13Σu+ | Template:Decimal cell<ref name=Dattani(c-a) /> | Template:Decimal cell<ref name=Dattani(c-a) /> | 11<ref name=Dattani(c-a) /> | <ref name=Dattani(c-a) /> | ||
| 3 | b | 13Πu | <ref name=Li(l,d) /> | |||||
| 4 | A | 11Σg+ | Template:Decimal cell<ref name=LeRoy(A-X) /> | Template:Decimal cell<ref name=LeRoy(A-X) /> | 118<ref name=LeRoy(A-X) /> | <ref name=LeRoy(A-X) /> | ||
| 5 | c | 13Σg+ | Template:Decimal cell<ref name=Dattani(c-a)/> | Template:Decimal cell<ref name=Dattani(c-a)/> | 104<ref name=Dattani(c-a)/> | |||
| 6 | B | 11Πu | Template:Decimal cell<ref name=Huang(B) /> | Template:Decimal cell<ref name=Huang(B) /> | 118<ref name=Huang(B) /> | |||
| 7 | E | 3(?)1Σg+ | <ref name=Jastrzebski(E) /> | |||||