krar

KrAr is a diatomic van der Waals complex consisting of a krypton atom bound weakly to an argon atom. It is part of the family of noble-gas dimers and serves as an example of ultraweak intermolecular interaction. In experiments, KrAr is produced under cryogenic conditions either by co-deposition of Kr and Ar in inert matrices or by stabilization in cold gas mixtures and studied by high-resolution spectroscopy such as infrared and microwave transitions. The observed bond is characterized by a very shallow potential well, with binding energy of only a few wavenumbers (a few cm−1) and a bond length around 3.2 to 3.5 angstroms. The molecule is not bound at room temperature and is maintained in controlled environments where weak dispersion forces dominate.

Theoretical work using ab initio quantum chemistry and potential energy surface calculations supports a weak attraction with minor contributions from induction, primarily governed by dispersion forces. KrAr helps test computational methods for weakly bound systems and contributes to understanding noble-gas clustering and the transition from gas-phase dimers to condensed phases. Related species include ArKr, Kr2, and other mixed noble-gas clusters, which together illuminate the behavior of ultraweak interactions among noble gases.

Overall, KrAr is of interest in physical chemistry and chemical physics as a benchmark system for studying van der Waals interactions, molecular spectroscopy at cryogenic temperatures, and the development of accurate potential energy surfaces for noble-gas complexes.