The interaction Of CO2 with the bare RuO2(110) surface, exposing unsaturated Ru and oxygen atoms, was studied using high-resolution electron energy-loss spectroscopy (HREELS) and thermal desorption spectroscopy (TDS). At 85 K, CO2 is found to adsorb only on coordinatively unsaturated Ru-cus sites giving rise to three different species: physisorbed CO2, chernisorbed CO2delta-, and CO2-CO2delta- dimers. A complete assignment of the vibrational spectra is reached which allows us to gain insight into the reactions involved. Upon annealing, two channels open up for physisorbed CO2: desorption or further reaction with chernisorbed CO2delta- forming CO2.CO2delta-dimers. At 175 K, a bidentate carbonate is observed because of the reaction Of CO2delta- with an O bridge. Further annealing induces a thermally activated conversion from the bidentate to a CO3delta- monodentate species. The latter is stable up to about room temperature and then decomposes into CO2 and O-ad. The adsorption geometries of the different species are discussed in detail. The activation Of CO2 to form a chemisorption bond occurs only on the Ru-cus site. This gives further evidence for the key role played by Ru-cus in the catalytic activity of the bare RuO2(110) surface.