ELECTRON-ION COINCIDENCE MEASUREMENTS - THE NEUTRAL DISSOCIATION CROSS-SECTION FOR CF4

Pulsed electron beam time-of-flight measurements of the electron energ y loss spectrum of CF4 at scattering angles of 28 degrees, 45 degrees, 71 degrees, 112 degrees, and 135 degrees were made at impact energies of 22, 25, and 34 eV in coincidence with positive ions. The angular-d ependent elastic, total dissociation, ionization, and neutral dissocia tion cross sections were measured. The data were integrated over elect ron energy loss for each scattering angle. These angular dependent dat a were then fitted with various analytic functions and integrated over angle to obtain individual total cross sections. All cross-section da ta were placed on an absolute scale by matching to total cross-section measurements reported in the literature. The angular-dependent elasti c cross section and the integrated cross sections for elastic and tota l dissociation were found to be in good agreement with literature valu es. Values obtained for the neutral dissociation cross section agree w ith the difference between previous separate measurements of total dis sociation by Winters and Inokuti and total ionization by Bruce and Bon ham, but are inconsistent with those of the direct measurements of Sug ai et al. The total ionization cross sections agree to within the expe rimental uncertainties with literature values. (C) 1998 American Insti tute of Physics.