Total Ionization Cross Sections for Electron Scattering from Atomic and Molecular Targets Using Quantum Mechanical Semi-Empirical Approach from Threshold to 400 eV

Abstract

Total ionization cross sections (σion) by electron impact are presented for a large class of atoms and molecules from the ionization threshold to the intermediate energy region where experimental data are available. A spherical complex optical potential (SCOP), averaged over all molecular orientations, is treated exactly in partial-wave analysis to yield elastic (σel), absorption (σabs) and total (σt) cross sections. The imaginary part of the SCOP takes into account the loss of flux due to inelastic (mainly the ionization) processes and yield the (σabs) quantity. We use σion(E) = p σabs(E) to determine the σion at an energy E, where p is a scaling factor for the corresponding target. In general, p is less than one and reflects the fraction of ionization cross section in the total inelastic channel. The SCOP term for each target is determined ab initio from target wavefunctions at the Hartree-Fock level. In particular, we present results on the σion for He, Ne, Ar, Kr, Xe, H2, N2, O2, F2, CO, NO, H20, H2S, CO2, N2O, NH3, C2H2, CH4, SiH4 and CF4 systems.