A vibrational overtone photodissociation spectrum of HOONO formed in the reaction of OH with NO2 is reported. Rich vibrational structure, consistent with the existence of several HOONO conformers, is observed. A tentative vibrational assignment of the observed bands is proposed although complete assignment is not possible without further spectroscopic information. The ratio HOONO/HONO2 formed in the reaction of OH with NO2 is estimated to be about 5% at 253 K and 20 Torr.