Kr2

Kr2 is a diatomic molecule consisting of two krypton atoms. Krypton is a noble gas, so Kr2 is not formed by a typical covalent bond. Instead, the two atoms are held together by very weak van der Waals forces, making Kr2 a van der Waals dimer. Because of the weakness of the interaction, Kr2 exists only under extreme conditions, such as very low temperatures, low pressures, or within cryogenic or matrix isolation environments, and it is typically short-lived under ordinary laboratory conditions.

Formation of Kr2 occurs in cryogenic gas expansions, in clusters of rare gas atoms, or when krypton is isolated in inert matrices at low temperature. In solid krypton, Kr2 can be stabilized transiently, but it remains a weakly bound species with little chemical reactivity. The bond length is large compared with covalent bonds, and the interaction energy is tiny, reflecting the dominance of dispersion forces between the closed-shell krypton atoms.

Kr2 has been studied primarily through spectroscopic methods, including infrared and Raman spectroscopy in cryogenic matrices and various forms of electronic spectroscopy. The observed features are weak and require sensitive, matrix-assisted techniques to distinguish them from background signals. The molecule serves as a model system for understanding intermolecular forces in noble gas dimers and for testing theoretical descriptions of van der Waals interactions.

In context, Kr2 sits among noble gas dimers as a fundamentally weakly bound species, illustrating how noble gases can form transient partners without conventional chemical bonding. See also krypton, noble gas chemistry, van der Waals molecule, matrix isolation spectroscopy.