ArCO2He

ArCO2He is a weakly bound van der Waals triatomic cluster consisting of an argon atom, a carbon dioxide molecule, and a helium atom. It is not a conventional chemical compound with covalent bonds; rather, it is a transient, noncovalent association stabilized by dispersion forces and the quadrupole moment of CO2.

Formation and environment: Such complexes are typically produced in cold, dilute gas-phase conditions, for example in supersonic expansions or cryogenic matrix isolation, where collisions permit the assembly of three-body clusters from Ar, CO2, and He.

Structure: The CO2 molecule remains linear within the complex. Argon interacts with CO2 through dispersion and quadrupole interactions, creating a shallow potential well that holds the Ar near CO2. A helium atom is weakly bound to the Ar–CO2 complex, often occupying a secondary site around the Ar. The overall geometry is determined by the balance of Ar–CO2 and He–Ar interactions and is characterized by large interatomic separations typical of van der Waals clusters.

Spectroscopic studies: ArCO2He has been investigated with high-resolution spectroscopy, including microwave and infrared methods, and with mass spectrometry of cold clusters. Observables include very small rotational constants and low binding energies, consistent with a weakly bound three-body system. Data contribute to understanding three-body interactions and energy transfer in cold environments.

See also: van der Waals complex, argon–carbon dioxide complex, helium–rare gas complexes.