A vibrational overtone photodissociation spectrum of HOONO formed in the reaction of OH with NO2 isreported. 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 notpossible without further spectroscopic information. The ratio HOONO/HONO2 formed in the reaction of OHwith NO2 is estimated to be about 5% at 253 K and 20 Torr.