The chemisorption of O atoms on graphite and
the thermal reduction of the oxidized surface were studied by
means of high energy resolution photoelectron spectroscopy
with synchrotron radiation. The C 1s and O 1s core levels and
the valence band spectra were used to identify the different
oxidizing surface species and to evaluate the extension of the
sp2 conjugation as a function of oxidation time and annealing
temperature. We found that epoxy groups are the dominant
species only at the low oxidation stage, and ethers and
semiquinones form as oxidation proceeds. The evolution of
the ether/epoxy ratio with increasing oxygen coverage provides evidence for the occurrence of C−C bond unzipping. Epoxy
groups are the functionalities with the lowest thermal stability and start to desorb around 370 K, strongly affecting the desorption
temperature of other functional groups. The ratio between ethers and epoxy groups determines the balance between epoxy−
epoxy and epoxy−ether reactions, the latter promoting the removal of C atoms from the C backbone. Adsorbate spectroscopy
during thermal annealing definitely proves the catalytic effect of the basal plane oxygen atoms on the desorption reactions.
