ABSTRACT
The recommended values are determined on the basis of the available experimental data. The method is absolute and has an accuracy of about 5–15%, though some earlier data can contain additional uncertainties in reading pressure connected with a pumping effect of the McLeod gauge. In this method, yields of different ionic species are measured using magnetic, quadrupole or time–;of–flight spectrometers, and the total ionization cross section is determined by summing partial ionization cross sections. The absolute values of cross sections can be deter–mined both directly, by measuring all the parameters entered into the expression for the doubly differential cross section, and by normalization to the available data on the absolute cross sections for elastic scattering or for ionization of atomic gases by electron impact. The original data involved in their determination were obtained using one of the versions of mass spectroscopy, by magnetic, quadrupole or time–of–flight spectrometers, with normalization to the known absolute values of total ionization cross sections.
