Absolute oscillator strengths for the photoabsorption, photoionization and ionic photofragmentation of silicon tetrafluride. II. The Si 2p and 2s inner shells

Abstract

Using dipole (e, e) spectroscopy, absolute photoabsorption oscillator strengths (cross sections) for the Si 2p and 2s inner shells of silicon tetrafluoride have been obtained in the equivalent photon energy range 100–350 eV. The contribution of the valence shell to the total photoabsorption oscillator strength in the Si 2p and 2s inner shell regions has been estimated. Comparison of the present TRK sum-rule normalized photoabsorption data for SiF 4 with summed (Si+4F) atomic cross sections shows that normalization procedures based on atomic data are likely to be seriously in error in molecules where molecular (resonance) effects are strong. The high-resolution photoabsorption oscillator strength spectrum of silicon tetrafluoride has also been measured using a high-resolution dipole (e, e) spectrometer in the equivalent photon energy range 105–170 eV. Absolute oscillator strengths for the discrete transitions in the Si 2p pre-ede region have been obtained. Using dipole (e, e+ion) coincidence spectroscopy, photoionization time-of-flight mass spectra have been measured at ten selected energies corresponding to the valence ionization continuum, discrete transitions from the Si 2p orbitals to virtual valence and Rydberg orbitals, and at resonant and non-resonant energies in the Si 2p continuum. Absolute photoionization oscillator strengths for production of the molecular and dissociative fragment ions of silicon tetrafluride have been obtained at these energies using the the total absolute photoabsorption oscillator strengths, the photoionization efficiency and the ionic photofragmentation branching ratios obtained from the mass spectra. The ionic photogragmentation branching ratios differ substantialy from previously published results (Lablanqui et al., J. Chem. Phys. 90 (1989) 7078; Imamura et al., J. Chem. Phys. 94 (1991) 4936).