New Model for Electron-Impact Ionization Cross Sections of Molecules

Authors

W. Hwang, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
Y.-K. Kim, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
M. Eugene Rudd, University of Nebraska - LincolnFollow

Date of this Version

2-22-1996

Comments

Published in J. Chem. Phys. / Volume 104 / Issue 8. Issue Date: 22 February 1996. Copyright ©1996 American Institute of Physics. Used by permission.

Abstract

A theoretical model for electron-impact ionization cross sections, which has been developed primarily for atoms and atomic ions, is applied to neutral molecules. The new model combines the binary-encounter theory and the Bethe theory for electron-impact ionization, and uses minimal theoretical data for the ground state of the target molecule, which are readily available from public-domain molecular structure codes such as GAMESS. The theory is called the binary encounter Bethe (BEB) model, and does not, in principle, involve any adjustable parameters. Applications to 19 molecules, including H₂, NO, CH₂, C₆H₆, and SF₆, are presented, demonstrating that the BEB model provides total ionization cross sections by electron impact from threshold to several keV with an average accuracy of 15% or better at the cross section peak, except for SiF₃. The BEB model can be applied to stable molecules as well as to transient radicals.