Photoelectron study of the valence levels of CF4 and SiF4 from 20 to 100 eV

Abstract

Using monochromatized synchrotron radiation, the gas phase photoelectron spectra of the five valence orbitals of CF4 and SiF4 have been obtained from 21 to 100 eV photon energies. Branching ratios (BR) for both molecules, and partial cross sections (σ) for CF4, have been obtained from these spectra. The agreement between our σ values for CF4 and previous results is excellent. Theoretical branching ratios, partial cross sections, and β values have been obtained from MS Xα calculations, and compared with experiment. The generally good agreement between experiment and theory for SiF4 confirms the orbital assignment: 1t1<5t2<1e<4t2<5a1, in order of increasing binding energy. In contrast to the CF4 results which show little structure, five shape resonances are predicted for SiF4, at 3, 7, 13, 23, and 35 eV kinetic energies. The predicted resonance positions and intensities are in good agreement with experiment (e.g., for the 23 and 35 eV resonances), but the low energy resonance positions and intensities are usually not well reproduced experimentally. The radically different resonance features in CF4 and SiF4 are discussed.