ON THE PARTIAL IONIZATION CROSS-SECTIONS FOR CF4 BY USE OF THE PULSED-ELECTRON-BEAM TIME-OF-FLIGHT METHOD

Recent measurements of the absolute partial ionization cross-sections for CF4 by two different experimental approaches are in generally good agreement except for the cross-sections for production of the doubly charged ions CF32+ and CF22+ which were in serious disagreement. We have recently remeasured the Ar2+/Ar+ ratio using the pulsed-electron-beam time-of-flight method and have uncovered several problems which caused a revision of our earlier work. Here we report a similar study for the CF4 molecule. Although one of the three error sources in the case of Ar was found to be unimportant in the case of CF4+ the main error, insufficient ion impact energy on the front surface of the detector, leads to an upward revision of most of our previous cross-sections. Our new results range from 5-15% larger than our previous values for the partial cross-sections. These results are in even better agreement with those reported by H. Poll, C. Winkler, D. Margreiter, V. Grill and T.D. Mark [Int. J. Mass Spectrom. Ion Processes, 112 (1992) 1], except for the CF32+/CF3+ and CF22+/CF3+ cross-section ratios which are approximately a factor of two higher than those of Poll et al. The cause of this remaining discrepancy is unknown.