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.