Energy dependence of the total cross section for electron scattering by N2 and CO molecules at energies above 1 keV

Recently, an analytical formula to reproduce total cross section data for electron scattering by diatomic molecules has been published by Liu and Sun (Phys. Lett. A 222 (1996) 233). This formula was derived by fitting available experimental data for intermediate and high energy to a one-parameter expression that the authors state to be based on the Born approximation. However, as discussed in the present Letter, the energy dependence of the total cross section for high energies, above 1 keV, given by this formula is in contradiction with the Born-Bethe theory. We also present in this Letter a method to calculate differential and integral elastic cross sections for e-N-2 and e-CO collisions in the energy range (0.1-10 keV) that gives results in agreement with the available experimental data. By combining these results with inelastic cross section data existing in the literature has been confirmed the applicability of an alternative expression for the total cross section for electron scattering by diatomic molecules, which can be used in the energy range (1-10 keV). The energy dependence given by this expression shows an asymptotic behaviour for increasing energy in better agreement with the Born-Bethe theory. (C) 2001 Elsevier Science B.V. All rights reserved.