Threshold photoelectron spectroscopy of CF₄ up to 60.5 eV

The threshold photoelectron spectrum of CF₄ up to 60.5 eV has been recorded using synchrotron radiation and a penetrating-field electron spectrometer of high resolution. Our results confirm the broad spectral features of the X ²T₁, A²T₂ and B̃ 2E state bands of CF₄⁺ reported previously with He I PES. The influence of autoionizing super-excited states of CF₄ has been observed as an extension of the high-energy tail of the B ²E state, as a structured band in the energy region between the B ²E and C̃ ²T₂ states, and as additional vibrational structure extending the D̃ ²A₁ state band. Improved spectra of the C̃ ²T₂ and D̃ ²A₁ states have been obtained as a consequence of the high resolution of this study. The overall electronic state band profiles observed here up to about 26eV agree with a recently published low-resolution threshold photoelectron spectrum of CF₄ [Creasey et al., Chem. Phys., 174 (1993) 441]. Between 26 and 60.5 eV a continuum-like background was observed with some broad-band features superimposed on it. One broad peak, centered on 40.3 eV, is tentatively assigned to the formation of the Ẽ ²T₂ and F̃ ²A₁ states of CF₄⁺, but the formation of the double-charged ion, CF₄²⁺, may also be involved.