Cr(110) oxidation probed by carbon monoxide chemisorption

High resolution electron energy loss spectroscopy of chemisorbed carbon monoxide is used to distinguish between (1) an annealed, oxidized Cr(110) surface, (2) an intermediate, subsurface Cr(110) oxide, and (3) oxygen-dosed Cr(110). On the annealed oxide, weak signals are observed from both the dissociation-precursor (α 1−CO) and the terminally-bonded (α 2−CO) molecular CO binding states but only after relatively high CO exposures, reflecting greatly reduced sticking probabilities. However, on the surface with subsurface oxygen, both binding states are sequentially populated with sticking probabilities comparable to that of clean Cr(110); also, an increase in v CO from ~1975 to 2035 cm −1 is observed at high coverages of terminally-bonded α 2−CO. Both the annealed-oxide and subsurface-oxide CO chemisorption results are in contrast to the selective poisoning of only α 1−CO by chemisorbed atomic oxygen on Cr(110). Comparisons among the three oxygen containing surface (1) show how vibrational spectroscopy of chemically-inequivalent molecular binding states may be used as a probe of surface oxidation and (2) provide insights into the oxygen-CO surface chemistry.