Tautomers of the nucleobases play fundamental roles in spontaneous mutations of DNA. Tautomers of neutral cytosine have been studied in the gas phase,b ut muchl ess is knownabout charged species.Here,wereport the observation and characterization of three tautomers of deprotonated cytosine anions,[ trans-keto-amino-N3H-H8b] (tKAN3H8b À ), [cis-keto-amino-N3H-H8a] (cKAN3H8a À ) and [keto-amino-H] (KAN1 À ), produced by electrospray ionization. Excited dipole-bound states (DBSs) are uncovered for the three anions by photodetachment spectroscopy. Excitations to selected DBS vibrational levels of cKAN3H8a À and tKAN3H8b À yield tautomer-specific resonant photoelectron spectra. The current study provides further insight into tautomerism of cytosine and suggests an ew method to study the tautomers of nucleobases using electrosprayionization and anion spectroscopy.