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Performance of Binary-Encounter Bethe (BEB) Theory for Electron-Impact Ionization Cross-Sections of Molecules Containing Heavy Elements (Z > 10)

Published

Author(s)

Gregory Scott, Karl Irikura

Abstract

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 the correct equation is used, BEB predictions are as good for heavier-element molecules as for light-element molecules. The error in the published calculations was to neglect the kinetic-energy correction for molecular orbitals that are dominated by atomic orbitals with n > 2. 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.
Citation
Surface and Interface Analysis
Volume
37

Keywords

ab initio, cross section, effective core potential, electron impact, ionization, pseudopotential, theory

Citation

Scott, G. and Irikura, K. (2005), Performance of Binary-Encounter Bethe (BEB) Theory for Electron-Impact Ionization Cross-Sections of Molecules Containing Heavy Elements (Z > 10), Surface and Interface Analysis (Accessed February 28, 2024)
Created December 19, 2005, Updated October 12, 2021