= Molecular ion
In the <International Union of Pure and Applied Chemistry> (IUPAC) <mass spectrometry> convention, a <molecular ion> is formed by removing or adding one or more <Electrons> to a <molecule> without fragmentation of its molecular structure.<IUPAC Compendium of Chemical Terminology, fifth edition (Gold Book) by International Union of Pure and Applied Chemistry/molecular ion in mass spectrometry>[Gold Book, fifth edition, molecular ion in mass spectrometry: formation by electron removal or addition without fragmentation]{ref} For example, removing one <Electron> from intact <water> gives $\mathrm{H_2O^{\bullet+}}$: two <hydrogen> and one <oxygen> <chemical atom>, total <electric charge> $+e$, and an unpaired <Electron>, hence a <radical cation>. Atom inventory, net <electric charge>, and electronic state are separate pieces of information. <Hydronium>, $\mathrm{H_3O^+}$, has a different inventory; it is a <polyatomic ion>, rather than the <molecular ion> obtained by electron removal from <water>.
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