Is it possible to have a diatomic molecule of sodium in gaseous state?

Already I know that hydrogen, all the halogens, nitrogen and oxygen forms diatomic molecules. But I am confused about $\ce{Na}$? So I would like to know about that.

• I haven't seen any cases approving $\ce{Na2}$'s existence, but $\ce{Li2}$ exists for sure. en.wikipedia.org/wiki/Dilithium Jun 10 '15 at 8:16
• The molecule $\ce{Na2}$ is well known in the gas phase (and $\ce{ Li2, K2}$), and has been studied since approx 1929! The ground state has a (long) bond length of $0.3078$ nm, vibrational frequency of $159 \pu{cm^{-1}}$ and rotational constant $0.1547 \pu{cm^{-1}}$. At least four excited state are known. Feb 9 '17 at 16:14

According to molecular orbital theory, disodium should be stable in the gas phase, with a bond order of one. The molecular orbital diagram is the same for all the alkali metals since they all have one valence electron in an $s$ orbital.
NIST chemistry webbook has a small page on disodium and quotes an enthalpy change of formation of $142.07~\mathrm{kJ~mol^{-1}}$ which is moderately endothermic.
The disodium molecule $$\ce{Na2}$$ has first been observed by M. Polanyi and collaborators in the diluted flame of sodium vapor and chlorine $$\ce{Cl2}$$. When sodium metal is heated in a vacuum, it gets vaporized. If now a tiny amount of gas $$\ce{Cl2}$$ is sent into this vapor, the famous yellow flame of $$\ce{Na}$$ is produced at the point where both gases are in contact to one another. This diffusion flame is due to three consecutive reactions. First : $$\ce{Na + Cl2 -> NaCl + Cl}$$ Then the chlorine atom cannot react with atomic sodium $$\ce{Na}$$ since there is no third body to remove the reaction energy. So the $$\ce{Cl}$$ atom does react with the dimer $$\ce{Na2}$$ in the reaction $$\ce{Cl + Na2 -> NaCl + Na'}$$ and this reaction is exothermic enough to produce an excited $$\ce{Na'}$$ atom. Sorry ! this $$\ce{Na'}$$ should have been printed as $$\ce{Na}$$ with a star, but my keyboard refuses to print this symbol (*) in index. Now this excitation energy ir reemitted as the yellow D-line of sodium ($$\pu{589.89 nm}$$) $$\ce{Na' -> Na + h\nu }$$ This was the first proof that the dimer $$\ce{Na2}$$ exists in the sodium vapor.