Vibronic theory for the x-ray absorption spectrum of CF₄ molecules

The C 1s x-ray absorption spectrum of CF₄ molecules is theoretically investigated by calculating the line shape quantum mechanically based upon a vibronic model. It is found that the main peak with a broad width is attributed to the transition of the C 1s core electron to the antibonding valence orbitals which are coupled with the C—F bond-stretching modes through the Jahn-Teller and the quasi-Jahn-Teller interactions. It is also clarified that the sharp asymmetric absorption line at the higher-energy side of the main band comes from the transition to the Rydberg states, where the interference effect between the Rydberg states and the vibronic state of the antibonding molecular orbitals leads to the asymmetric structure.