Fine structure at the carbon 1s K edge in vapours of simple hydrocarbons

Electron yield spectra in the range of 280 <= hω/2π <= 300 eV which basically resemble the absorption spectra, have been measured for gaseous methane, ethane, ethylene, benzene and acetylene using synchrotron radiation. The spectra being fairly simple compared to the valence shell absorption are characterized by weak maxima for energies below the ionization threshold for C 1s for methane and ethane whereas additional strong resonances are observed in the spectra from molecules containing π-electrons. The nature of these excitations is discussed on the basis of their term values using information from XPS-measurements. (orig./HK)