Quantitative studies of the photoabsorption, photoionization, and ionic photofragmentation of methyl fluoride at VUV and soft X-ray energies (7–250 eV) using dipole electron scattering and synchrotron radiation

Abstract

Absolute oscillator strengths (cross sections) for the valence shell photoabsorption of CH3F have been measured using low resolution (1 eV fwhm) dipole (e, e) spectroscopy in the equivalent photon energy range from 7 to 250 eV. In addition, high resolution (0.048 eV fwhm) dipole (e, e) spectroscopy has been used to study the valence shell region from 8 to 50 eV in more detail. The photoionization efficiency, ionic photofragmentation branching ratios and absolute partial oscillator strengths for molecular and dissociative photoionization have been determined for CH3F by dipole (e, e+ion) spectroscopy from the first ionization threshold to 100 eV. The major pathways of the ionic dipole induced breakdown scheme are predicted from these results. The electronic ion state branching ratios for the photoionization of CH3F were determined from photoelectron spectra recorded using monochromated synchrotron radiation at photon energies from 21 to 72 eV. The partial photoionization oscillator strengths for production of the electronic states of CH3F+ derived from the PES electronic ion state branching ratios and the present low resolution photoabsorption measurements are compared with estimates derived from the dipole induced breakdown scheme and the molecular and dissociative photoionization partial oscillator strengths. The two estimates of electronic state partial photoionization oscillator strengths are in good agreement only at higher photon energies. The differences at lower photon energies arise from errors in the photoelectron branching ratios due to the difficulties of assessing the steeply rising non-spectral background in the photoelectron spectra, particularly in the (1a1)−1 many-body region. Suggestions are made for improving the quantitative accuracy of PES measurements.