si2

Si2 is the diatomic molecule consisting of two silicon atoms. It is a transient species that is not stable under ordinary conditions but has been observed in high-temperature silicon vapors, plasmas, and combustion environments. The molecule arises from the association of two silicon atoms and exhibits a covalent Si–Si bond that is weaker than typical silicon–silicon bonds in bulk materials, reflecting the limited orbital overlap in the diatomic configuration.

Experimental and theoretical studies have identified several low-lying electronic states for Si2, and its ground state has been a subject of ongoing investigation; spectroscopic data indicate multiple transitions in the visible to near-infrared region in gas-phase samples. Bond lengths reported for Si2 are significantly longer than a typical Si–Si single bond in bulk compounds, consistent with a relatively weak and highly anisotropic bond. Si2 thus serves as a benchmark system in computational chemistry for testing methods in open-shell and multi-reference electronic structure, and it provides insight into silicon cluster formation during vapor-phase synthesis and in plasmas.

In astrochemistry and materials science contexts, Si2 contributes to the understanding of silicon bonding mechanisms during vapor deposition and the initial stages of silicon-based nanostructure growth. Its study helps illuminate fundamental aspects of silicon bonding, cluster formation, and the challenges of characterizing open-shell diatomic species in high-energy environments.