Reactions of a C-60 monolayer with oxygen adatoms on the Pt(lll) surface were studied by a multitechnique surface science approach in the 100-1100 IC range. Temperature programmed desorption (TPD), x-ray photoelectron spectroscopy (XPS), ultraviolet (UV) photoelectron spectroscopy (UPS), and high resolution electron energy loss spectroscopy (HREELS) were used to determine the onset temperature for the initial reaction and to characterize the reaction intermediates and products. Unlike the reaction of C-60 With O-2(g), which begins at 370 K, reaction with oxygen adatoms on Pt(lll) begins below 100 K with the formation of C=O bonds with nu(CO) at 2134 cm(-1). At about 450, R-O-R species, where K=sp(2)-hybridized carbon atoms singly bonded to oxygen, with nu(CO)=1215 cm(-1), develop and become the dominant reaction intermediates at 700-800 K. Also at these temperatures, an intense peak develops in the HREELS spectra characteristic of polymerized C-60 at 1460 cm(-1). The reaction products decompose to liberate gas phase CO and CO2 and form graphitic carbon. A prominent difference between the intermediates of this reaction and that of C-60 with O-2(g) is the absence of vibrational peaks in the 1650-1750 cm(-1) region that arise from carbonyl groups. An R-O-R intermediate derived from the opening of pentagons in C-60 a structure that has not been observed experimentally before but has been suggested to be stable from theoretical calculations, is most consistent with our spectroscopic results.