amidogen

Amidogen, or the amidogen radical, refers to the chemical radical NH2. It is a triatomic, neutral species with one nitrogen atom bonded to two hydrogen atoms and one unpaired electron, giving it a bent geometry and a doublet ground state. As a highly reactive intermediate, amidogen is typically short-lived under normal conditions and is mainly studied in gas-phase kinetics, combustion chemistry, and laboratory spectroscopy.

Formation and occurrence: In the laboratory, NH2 is generated by photolysis or discharge of ammonia (NH3) or by hydrogen abstraction from ammonia and related species. In combustion and plasma environments, amidogen appears transiently during the decomposition and oxidation of nitrogen- and hydrogen-containing compounds and participates in a network of radical reactions.

Reactions and role: Amidogen participates in reactions with common radicals such as O2, NO, H, and OH. Examples include NH2 + O2 → NH + HO2 and NH2 + NO → NH + NO2. Through these rapid reactions, NH2 influences nitrogen-oxide chemistry and flame kinetics, contributing to chain-branching steps and affecting the formation or destruction of NHx species and NOx depending on conditions.

Detection and spectroscopy: NH2 is detected and characterized using laser-based techniques such as laser-induced fluorescence (LIF) and cavity ring-down spectroscopy, as well as electron spin resonance in certain laboratory contexts. Its spectroscopic signatures and reaction rates are incorporated into detailed kinetic models of combustion and nitrogen-chemistry processes.

Name and context: The term amidogen is the IUPAC-style name for the NH2 radical; it is also referred to as the amidogen radical or, in older literature, as the amino radical. Related species include imidogen (NH) and various amide substituents in larger molecules.