Onium Ions
From Mass Spec Terms
Positively charged higher-valency (higher-coordination) ions of the nonmetallic elements. More common types are the carbonium, oxonium, sulfonium, nitronium, diazonium, phosphonium, and halonium ions. Classical examples are the methonium ion CH5+, the hydrogenonium ion H3+ and and the hydronium ion H3O+
