Rydberg—valence mixing in the C 1s excited states of CH4 probed by electron spectroscopy

The C1s → ndt2 Rydberg series and the ν = 1 vibrational levels of the symmetric mode (ν1) in the dominant C1s → npt2 series are clearly identified in the C 1s high-resolution electron-yield spectrum of CH4. In the resonance Auger electron spectra the participant Auger decay rate following the C1s → 3sa1, 3pt2 and 3dt2 excitations are 5.5%, 2.5%, and 3.7% of the total Auger decays, respectively, indicating that these Rydberg states do not have so strongly mixed valence character. The ordering of the valence contribution as 3sa1 > 3dt2 > 3pt2 is consistent with the theoretical prediction.