The first Born approximation and absolute scattering cross sections

The problem of bringing experimental electron-scattering cross sections to the absolute scale using the so-called Lassettre theorem is addressed. Experimental data that have been measured by electron-scattering experiments for different incident energies (in the range of 100 to 600 eV) and have been normalized on the basis of this theorem are compared with absolute cross sections that have been calculated within the first Born approximation by means of the complex-scaling method. The agreement is not found to be satisfactory even for the smallest values of momentum transfer. This, however, is a contradiction to Lassettre's theorem. A new normalization procedure for the experimental data is suggested that has yielded good agreement between the present calculated and the measured data even for a comparatively large range of momentum transfer. This indicates an extended range of validity of the first Born approximation. (Author)