Dirubidium is produced when rubidium vapour is chilled. The enthalpy of formation (ΔH) in the gas phase is 113.29 kJ/mol. In practice, an oven heated to 600 to 800K with a nozzle can squirt out vapour that condenses into dimers. The proportion of Rb in rubidium vapour varies with its density, which depends on the temperature. At 200° the partial pressure of Rb is only 0.4%, at 400 °C it constitutes 1.6% of the pressure, and at 677 °C the dimer has 7.4% of the vapour pressure (13.8% by mass).
The rubidium dimer has been formed on the surface of helium nanodroplets when two rubidium atoms combine to yield the dimer:
:Rb + Rb → Rb
Rb has also been produced in solid helium matrix under pressure.
Ultracold rubidium atoms can be stored in a magneto-optic trap and then photoassociated to form molecules in an excited state, vibrating at a rate so high they barely hang together. In solid matrix traps, Rb can combine with the host atoms when excited to form exciplexes, for example Rb(Π)He in a solid helium matrix.
Ultracold rubidium dimers are being produced in order to observe quantum effects on well-defined molecules. It is possible to produce a set of molecules all rotating on the same axis with the lowest vibrational level.