Bi2

Bi2 is the diatomic molecule formed by two bismuth atoms, with the chemical formula Bi2. It is a homonuclear diatomic species of the heavier pnictogens and is primarily studied in gas-phase chemistry, spectroscopy, and theoretical quantum chemistry. Bi2 is not a common compound found in everyday materials, but it appears under high-temperature conditions where elemental bismuth vaporizes and can be detected in molecular beams or plasmas.

Bi2 is typically formed by sublimation or evaporation of elemental bismuth and observed using spectroscopic techniques such as laser-induced fluorescence, absorption spectroscopy, or mass spectrometry under controlled, high-temperature or low-pressure environments. Its existence is important for understanding the behavior of heavy-element diatomic molecules and for testing high-level electronic structure methods that must account for relativistic effects in heavy atoms.

In terms of bonding, Bi2 is understood to possess a covalent Bi–Bi bond, which is relatively weak compared to bonds in lighter diatomic molecules. The bond is influenced by the large atomic radius of bismuth and relativistic effects that affect orbital overlap. Consequently, Bi2 often shows multiple low-lying electronic states and sensitively depends on the environment and excitation conditions.

Electronic structure studies of Bi2 rely on advanced quantum chemical calculations that incorporate relativistic corrections. The molecule serves as a benchmark system for methods dealing with heavy elements and for exploring how bond strength and electronic state ordering evolve in the heaviest main-group diatomics.

See also: As2, Sb2, Bi-containing clusters, bismuth chemistry.