Calculation of electron impact ionization cross sections of DNA using the Deutsch-Mark and Binary-Encounter-Bethe formalisms

Electron impact ionization cross sections for fragments of the DNA, the bases adenine, cytosine, guanine and thymine and the sugar-phosphate backbone, have been calculated using the Deutsch-Mark (DM) and the Binary-Encounter-Bethe (BEB) formalism. The necessary molecular structure information was determined by ab initio calculations, which were performed with the Gaussian 98 system using the Hartree-Fock (HF) method with different basis sets. Comparison of the Koopmans ionization potentials of the four bases revealed good agreement with experimental measurements. The two algorithms yield similar total electron impact ionization cross sections but their predictions differ, when cross sections per molecular orbital are compared. (C) 2002 Elsevier Science B.V. All rights reserved.