ARH

ArH refers to argon hydride, the diatomic species consisting of one argon atom bonded to one hydrogen atom. In chemistry discussions, ArH can denote the neutral diatomic radical ArH as well as its ionized form ArH+. The neutral ArH radical is relatively short-lived under ordinary conditions and is typically studied in specialized laboratory environments or in inert-matrix experiments, whereas ArH+ is observed more readily in reactive environments and in space.

In astrochemistry, ArH+ has been detected in the diffuse interstellar medium through rotational transitions in the submillimeter range, observed with space- and ground-based telescopes. Its presence is notable because it tends to form in regions where hydrogen is mostly atomic and the molecular fraction is low, making ArH+ a potential tracer of the ionization environment and the cosmic-ray ionization rate. The chemistry of ArH+ involves ion-molecule processes, and its abundance helps constrain models of interstellar gas composition and ionization balance.

Laboratory studies of ArH focus on both the neutral radical and the cation. The neutral ArH radical is challenging to observe in the gas phase and is typically accessed via cryogenic matrix isolation or advanced spectroscopic techniques. ArH+ can be produced in discharge or ion-trap setups and studied by infrared and rotational spectroscopy, as well as by quantum-chemical calculations that illuminate its electronic structure and bonding characteristics. ArH is part of a broader family of noble-gas hydrides, which illustrates the limited but intriguing bonding behavior of noble gases. See also: argonium, noble gas hydrides.