Rn2

Rn2 is the diatomic molecule formed by two radon atoms (Rn). It is categorized as a van der Waals or weakly bound dimer of a noble gas. Compared with lighter noble gases, the polarizability is large, but the closed-shell structure yields only a very shallow potential well; consequently, Rn2 would be only metastable and exists primarily at ultracold temperatures or within a solid noble-gas matrix.

Formation and observation: In laboratory conditions using cryogenic cooling and careful purity, Rn2 can be formed via radiative association of two radon atoms or by trapping radon in a solid neon/argon matrix where dipole-induced interactions stabilize a dimer temporarily. Experimental evidence is indirect and relies on high-resolution spectroscopy or mass-sensitive detection under controlled conditions.

Properties: Bond length is expected to be long for a noble-gas dimer, reflecting weak interaction; bond energy is very small; the molecule is highly fragile and readily dissociates or is quenched by decay.

Radioactivity: All radon isotopes are radioactive, with half-lives ranging from milliseconds to several days; for the common radon-222, the half-life is 3.8 days. The radioactive decay of radon imposes a fundamental limit on the lifetime of Rn2 in addition to its dissociation, leading to practical challenges for observation.

Scientific significance: Rn2 provides a test case for theoretical models of noble-gas interactions at the heavy end of the periodic table and constraints on radon-based quantum chemistry. It also highlights safety considerations when studying radioactive noble-gas species in ultra-cold environments.