Initial adsorption of oxygen molecules on the Si(1 1 0)-16 x 2 surface and subsequent modi. cation of the bonding states induced by mild (300 degrees C) annealing have been studied by synchrotron-radiation photoemission spectroscopy and scanning-tunneling microscopy. It has been shown that upon annealing, the intensity and the energy positions of the Si 2p suboxide components shift towards the values characteristic for the thermal oxide. This indicates the presence of a metastable chemisorption state of oxygen on the Si(1 1 0)-16 x 2 surface. (C) 2008 Elsevier B. V. All rights reserved.