Electron impact ionization cross-sections of SF3 and SF5

We report experimental and theoretical studies of the total electron impact ionization cross-sections for the radicals SF3 and SF5. It is shown that for radicals with strongly polar fluoride bonds, the shielding of the attractive dipole interaction potential in the bonding region is important in a proper description of the collision process. The siBED model, which has incorporated the shielding factor, was found to provide cross-sections in agreement with recently re-analyzed experimental data for the species CFx, and NFx (x = 1-3), whereas the DM model and the BEB model, on the other hand, showed large discrepancies with experiment. These findings also hold for the two free radicals SF3 and SF5 studied here, providing further evidence on the importance of a proper shielding of the dipole potential. (C) 2004 Elsevier B.V. All rights reserved.