Cationic Rydberg states observed in resonantly enhanced electron spectra of CS2

The inner valence electron spectrum of the CS2 molecule has been investigated in the binding energy range between 18.6 and 26.3 eV using synchrotron radiation for ionisation. Photon energies in the range from 67 to about 167 eV have been used, with particular focus on 166.70, 166.89 and 167.09 eV for which S2p electrons are resonantly transferred into Rydberg orbitals close to the ionisation threshold. From there, autoionisation takes the molecule into various cationic states characterized by two valence holes and a Rydberg spectator electron. Many new bands are observed which contain vibrational progressions with spacings around 120 meV in most cases. These are assigned as excitations of the totally symmetric stretching ν1 mode in the cationic state. The new bands reflect states in the cation that are close to the electronic states of the dication and assignments are made by comparison to double ionisation electron spectra.