XE2

Xe2 is the diatomic molecule formed by two xenon atoms. It is a rare-gas dimer bound primarily by weak van der Waals forces, rather than a chemical covalent bond. The molecule is nonpolar and homonuclear, with a ground electronic state designated as X1Σg+.

Structure and bonding: The Xe–Xe distance is on the order of a few ångströms, commonly cited around 4 Å. The binding energy is very small compared with typical chemical bonds, reflecting its van der Waals character. The vibrational spectrum is likewise low in frequency, producing transitions in the far-infrared region. Xe2 exists predominantly at low temperatures or within stabilizing environments such as cryogenic matrices, where the weak attraction can be maintained long enough for study.

Formation and detection: Xe2 forms transiently in cryogenic gas expansions and in rare-gas matrices, where two xenon atoms can be brought into close proximity. It has been observed and characterized by high-resolution spectroscopy, including infrared, Raman, and microwave techniques, as well as through photoassociation experiments in ultracold or controlled environments.

Context and significance: Among noble-gas dimers, Xe2 is the heaviest and one of the better-studied examples of a van der Waals bound dimer. It serves as a benchmark for theoretical models of dispersion forces and many-body interactions in closed-shell systems. There are no practical chemical applications; Xe2 is primarily of interest in fundamental physical chemistry and molecular physics.

History: The Xe2 molecule was identified and investigated as part of the broader study of van der Waals molecules in the mid-to-late 20th century, aided by advances in spectroscopic techniques and cryogenic stabilization.