Excitation and ionization of freon molecules. I. Absolute oscillator strengths for the photoabsorption (12–740 eV) and the ionic photofragmentation (15–80 ev) of CF 4

Abstract

Absolute photoabsorption oscillator strengths (cross sections) for the valence shell of CF 4 have been measured using dipole (e, e) spectroscopy in the equivalent photon energy range 12–200 eV. The present results are in good agreement with optical measurements obtained using synchrotron radiation in the range 12–70 eV and also with earlier reported oscillator strengths derived from electron impact measurements in the range 12–37 eV. Predicted values obtained by extrapolation of the valence shell continuum to high energies are in excellent agreement with published measurements obtained using X-ray characteristic lines and bremsstrahlung radiation. Carbon 1s and fluorine 1s photoabsorption spectra obtained by Bethe-Born conversion of earlier reported inner shell electron energy loss spectra of CF 4 have been placed on an absolute intensity scale by normalizing on atomic cross sections in the respective 1s photoionization continuum regions. The results are compared with bremsstrahlung measurements. The photoionization efficiency and also the ion photofragmentation branching ratios have been determined from time of flight mass spectra measured using dipole (e, e+ion) coincidence spectroscopy at equivalent photon energies ranging from the first ionization threshold up to 80 eV. Absolute partial oscillator strengths for molecular and dissociative photoionization have been derived. The nature of the dipole induced breakdown pathways of CF 4 is investigated by combining the present oscillator strength measurements for molecular and dissociative photoionization with previously published photoelectron data. On the basis of the present work, a revised set of absolute electronic state partial oscillator strengths for CF 4 are presented.