Ar2

Ar2, or the diatomic argon molecule, is a van der Waals dimer consisting of two argon atoms bound by weak dispersion forces. It is not a stable molecule at room temperature but can exist as a transient species in argon gas at low temperatures and can be stabilized in cryogenic matrices or ultracold environments.

The bonding in Ar2 is very weak and purely van der Waals in character. The electronic ground state is closed-shell, giving a singlet Sigma state (X1Σg+). The interaction creates a shallow potential well with a depth on the order of 100 cm−1 (about 0.01 eV) and an equilibrium internuclear distance near 3.8 Å. Because the well is shallow, the vibrational and rotational levels are sparse and lie at low energies, with transitions appearing in the far infrared.

Spectroscopic studies of Ar2 have probed its vibrational and rotational structure, providing insight into the van der Waals potential between two noble-gas atoms. The molecule has been observed in matrix isolation, in cold supersonic beams, and in ultracold or cryogenic environments. Its presence helps illuminate intermolecular forces in noble-gas systems and serves as a benchmark for theoretical potential energy surfaces.

In practice, Ar2 is inert and exists only in trace amounts under ordinary conditions. It is primarily of interest to researchers studying weak intermolecular interactions, van der Waals complexes, and the spectroscopy of noble gases.