The C 1s Auger decay spectrum of the CH4 molecule: the effects of vibrational fine structure, double excitations and shake-up transitions

Auger electron spectra of the methane molecule have been measured at various photon energies below and above the C 1s threshold. At energies corresponding to the higher Rydberg resonances the resonant Auger spectrum approaches the normal Auger spectrum both in form and peak position. Deviations from this trend are observed, however, when the core-to-Rydberg transition is accompanied by the excitation of vibrational modes. Auger spectra measured at the continuum resonance around 303 eV excitation energy display new decay features, which allows this resonance to be assigned to core-hole double excitations. Furthermore, above the C 1s threshold the satellite Auger features arising from the lowest shake-up initial states are identified.