Electron-spectroscopy studies of clean thorium and uranium surfaces. Chemisorption and initial stages of reaction withO2, CO, and CO2

The adsorption of ${\mathrm{O}}_2$, CO, and C${\mathrm{O}}_2$ on the thorium (111) crystal face and on polycrystalline $\alpha$-uranium has been investigated by x-ray photoelectron spectroscopy, Auger electron spectroscopy (AES), and secondary-ion mass spectroscopy (SIMS) at 300 K. Oxygen adsorption on both metals resulted in the formation of the metal dioxide. CO and C${\mathrm{O}}_2$ adsorption on Th(111) produced species derived from atomic carbon and oxygen; the presence of molecular CO was also detected. Only atomic carbon and oxygen were observed on uranium. Elemental depth profiles by AES and SIMS indicated that the carbon produced by the dissociation of CO or C${\mathrm{O}}_2$ diffused into the bulk of the metals to form a carbide, while the oxygen remained on their surfaces as an oxide.