Hydroxyl groups at the surfaces of NtO ( 100)) N10 ( 111) , and Cr203 ( 111) have been studled usmg different surface sensttlve spectroscopies The OH groups are readdy formed by the mteractlon of the oxide surfaces Hrlth the residual gas atmosphere or by dosing of water They can be removed by annealmg at temperatures T>, 600 K (NIO) or T> 540 K (Cr,O,) OH does not bond to regular NtO( 100) sites so that for a cleaved NlO( 100) single crystal surface no OH adsorption could be observed For the more defect contammg NIO( lOO)/Nl( 100) film the existence of OH could be venfied by Isotope exchange wtth OD As mdlcated by TDS (thermal desorption spectroscopy) of an NO adsorbate, OH groups fully block the ( 111) onented surface of N10 for NO adsoorptlon which mdlcates that OH groups bond to regular NlO( 111) surface sites For Cr203( 111) thermal decomposition of water at defect sates and photochemIcal dlssoclatlon IS observed The latter path seems to mvolve water molecules m the second layer and leads most ltkely to an occupation of regular surface sites