GAS-ADSORPTION STUDIES ON PU METAL BY PHOTOEMISSION SPECTROSCOPY

In the context of elucidating the role of the 5f electrons in the reac tivity of actinides, the adsorption of O2, CO2, CO and C2H4 on Pu meta l has been studied at 77 and 296 K by UPS and XPS. For 02 at 77 and 29 6 K, Pu2O3 is formed initially and followed by an oxidation to PuO2. P uO2 formation occurs at higher dosages (60 L) at 296 K than at 77 K. A t 77 K, CO2 is dissociated for low dosages (2 L). At higher exposures (> 4 L) new emission lines in UPS are observed and are attributed to c arbonate formation. For higher dosages (> 20 L) CO2 physisorbs. At 296 K, the behavior is similar to that at 77 K with the exception that ph ysisorbed CO2 is not observed. Low dosages (4 L) of CO at 77 K results in dissociation of the molecule. At higher dosages (> 6 L) chemisorbe d CO is detected. At 296 K, CO behaves in the same way as CO2 at this temperature. For both CO2 and CO, the dissociation of the gases is alw ays followed by the formation of some amount of PU2O3. For C2H4 at 77 and 296 K, dissociation of the gas is followed either by formation of PuC or chemisorbed C. The formation of some PuH2 is also observed. At 77 K, and high dosages (100 L), a very weak physisorbed phase of C2H4 can be observed. These results are quite different from those for U me tal, for which dissociation of the gases was observed at all temperatu res, and additionally at low temperatures CO2, CO and C2H4 are physiso rbed at exposures higher than 6 L. It is not yet, however, clear, how this large variety of surface reactivity in the actinide series is rel ated to the gradual localization of 5f electrons.