The arsonium cation is a positively charged polyatomic ion with the chemical formula . An arsonium salt is a salt containing either the arsonium cation, such as arsonium bromide and arsonium iodide, which can be synthesized by reacting arsine with hydrogen bromide or hydrogen iodide.[1] Or more commonly, as organic derivative such as the quaternary arsonium salts (CAS:, hydrate form) and the zwitterionic compound arsenobetaine.