ABSOLUTE OSCILLATOR-STRENGTHS FOR PHOTOABSORPTION, PHOTOIONIZATION AND IONIC PHOTOFRAGMENTATION OF SULFUR-DIOXIDE .2. THE S-2P AND 2S INNER SHELLS

Absolute photoabsorption oscillator strengths (cross sections) for the S 2p and 2s inner shells of sulphur dioxide have been obtained using dipole (e, e) spectroscopy in the equivalent photon energy range 160-260 eV. Photoionization time-of-flight (TOF) mass spectra have been collected using dipole (e, e + ion) coincidence spectroscopy at 161, 170, 179, 188, 197 and 206 eV. These energies correspond to the valence ionization continuum (161 eV), S 2p discrete excitation (170 eV) and the S 2p continuum (179-206 eV) respectively. Combination of the photoabsorption oscillator strengths with the photoionization efficiency and the ionic photofragmentation branching ratios determined from the mass spectra yielded absolute photoion oscillator strengths for the molecular and dissociative photoionization channels at these energies. The photoabsorption oscillator strengths are compared with previously published experimental and theoretical work on the cross sections for atomic sulphur and oxygen, and are found to be in reasonably close agreement at photon energies above the molecular resonances. The photofragmentation processes involved in production of the observed ions in the TOF mass spectra are discussed.