Performance of binary-encounter-Bethe (BEB) theory for electron-impact ionization cross sections of molecules containing heavy elements (Z > 10)

The binary-encounter-Bethe (BEB) theory developed by Kim and coworkers has been successful for computing electron-impact ionization cross sections of many molecules. However, some recent publications have stated that BEB theory performs poorly for molecules that contain heavier elements such as chlorine and sulfur. We have found that the BEB calculations in those publications were performed incorrectly. When performed correctly, BEB predictions are as good for heavy-element molecules as for light-element molecules. We recommended recently that an alternative, less-confusing procedure be used for molecules that contain heavier elements. The alternative procedure, based upon effective core potentials (ECPs), does not require explicit kinetic energy corrections. For peak cross sections of a group of 18 molecules, the root-mean-square difference between BEB predictions and experimental values is 13%. Results are presented for CCl3CN, C2Cl6, C2HCl5, C2Cl4, both isomers Of C2H2Cl4, CCl4, TiCl4, CBr4, CHBr3, CH2Br2, GaCl, CS2, H2S, CH3I, Al(CH3)(3), Ga(CH3)(3), and hexamethyldisiloxane. Incorrect BEB calculations have been reported in the literature for several of these molecules. Published in 2005 by John Wiley & Sons, Ltd.