O2/PD(111) - CLARIFICATION OF THE CORRESPONDENCE BETWEEN THERMAL-DESORPTION FEATURES AND CHEMISORPTION STATES

The system O2/Pd(111) has been probed with electron energy loss spectroscopy and thermal desorption spectrometry. The coincidence of three peaks in thermal desorption and the O-O region of the EEL spectrum has been noted previously and a one-to-one correspondence between the states resolved in EELS and the desorption features has been assumed. We show that this assumption is incorrect. The lowest binding energy state correlates with the highest frequency vibrational state. The lowest vibrational frequency state acts as a precursor to dissociation. The two higher temperature thermal desorption features both arise from the remaining state.