Chemical-state effects in Auger electron spectroscopy

We have used Auger spectroscopy as a probe of local chemical environment both in the gas and condensed phases using a systematically chosen series of molecules H2O, CH3OH, (CH3)2O, CH4, C2H4, and C2H2. For the series of gas phase molecules, H2O, CH3OH, (CH3)2O, and CH4, where oxygen and carbon are, respectively, in similar bonding arrangements, characteristic fingerprint spectra (methanelike for C and waterlike for O) are shown to result. Additional fine structure, which is dependent on the specific molecular environment, appears on the spectra. In contrast, dramatic differences are observed for the series CH4, C2H2, and C2H4 in which major differences in hybridization exist at the carbon site. H2O, CH3OH, and (CH3)2O were studied both in the gas phase (electron excited) and in the condensed phase (x-ray excited). The O(KVV) (K level–valence–valence transition) and C(KVV) spectra are shown to be similar when comparing the gas–solid results only if the multilayer spectra are properly corrected for electron-loss effects. Some ’’solid-state’’ broadening is observed in the multilayer case. The degree of this broadening is found to be greater in the O(KVV) than for the C(KVV) and a new peak appears in the case of solid H2O which is not present in the gas phase. This is consistent with intermolecular bonding primarily at the oxygen site. These results demonstrate, along with the fingerprint correlations given above, that AES is sensitive to changes in the local environment.