ABSOLUTE OSCILLATOR-STRENGTHS FOR THE PHOTOABSORPTION, PHOTOIONIZATION AND IONIC PHOTOFRAGMENTATION OF SILICON TETRAFLUORIDE .1. THE VALENCE SHELL

Absolute photoabsorption oscillator strengths (cross sections) for the valence shell of silicon tetrafluoride have been measured using dipole (e, e) spectroscopy in the equivalent photon energy range 10-100 eV at an energy resolution of almost-equal-to 1 eV fwhm. A high-resolution (0.048 eV fwhm) photoabsorption oscillator strength spectrum of silicon tetrafluoride has also been determined using a high-resolution dipole (e, e) spectrometer in the equivalent photon energy range 10-50 eV. Absolute oscillator strengths for the discrete features in the pre-ionization edge region of the high resolution spectrum have been obtained and their spectral assignments are discussed. Photoionization time-of-flight mass spectra have been collected using dipole (e, e + ion) coincidence spectroscopy from the first ionization potential up to 100 eV. Photoion branching ratios and photoionization efficiencies have been determined from the TOF mass spectra, and these have been used along with the measured absolute photoabsorption oscillator strengths to obtain the absolute partial photoionization oscillator strengths for production of the molecular and dissociative fragment ions. The ionic photofragmentation branching ratios differ substantially from previously published results (Lablanquie et al., J. Chem. Phys. 90 (1989) 7078; Imamura et al., J. Chem. Phys. 94 (1991) 4936). Absolute electronic state partial photoionization oscillator strengths have also been derived using the measured absolute photoabsorption oscillator strengths and photoionization efficiencies along with photoelectron branching ratios for the electronic states of silicon tetrafluoride reported in an earlier PES study (Yates et al., J. Chem. Phys. 83 (1985) 4906). The results are compared with MS-X-alpha calculations. The dipole induced breakdown for silicon tetrafluoride is also discussed.