Electron–ion coincidence measurements: The neutral dissociation cross section for CF4

Abstract

Pulsed electron beam time-of-flight measurements of the electron energy loss spectrum of CF4 at scattering angles of 28°, 45°, 71°, 112°, and 135° were made at impact energies of 22, 25, and 34 eV in coincidence with positive ions. The angular-dependent elastic, total dissociation, ionization, and neutral dissociation cross sections were measured. The data were integrated over electron energy loss for each scattering angle. These angular dependent data were then fitted with various analytic functions and integrated over angle to obtain individual total cross sections. All cross-section data were placed on an absolute scale by matching to total cross-section measurements reported in the literature. The angular-dependent elastic cross section and the integrated cross sections for elastic and total dissociation were found to be in good agreement with literature values. Values obtained for the neutral dissociation cross section agree with the difference between previous separate measurements of total dissociation by Winters and Inokuti and total ionization by Bruce and Bonham, but are inconsistent with those of the direct measurements of Sugai et al. The total ionization cross sections agree to within the experimental uncertainties with literature values.