The flowing afterglow technique has been used to study the reactions of HO2−and HC3− in the gas phase. The hydroperoxide ion reacts slowly with CO to form HO−, and oxidizes CO2, OCS, CS2, NO, SO2, CH3NCO, and CH3NCS in fast reactions to form CO3−, CO2S−, COS2−, NO2−, SO3−, CH3NCO2−, and CH3NCOS−, respectively. Reactions of HO2− with certain amides and esters provide synthetic routes for a number of interesting peracyl anions. One of these, the peroxyformate ion, HCO3−, reacts with CO and NO in slow oxidation reactions to form the formate ion HCO2−. It also forms HCO2− upon reaction with acetone and pivalaldehyde, perhaps by Baeyer–Villiger oxidation.