ELECTRON-IMPACT IONIZATION CROSS-SECTIONS OF MOLECULES .2. THEORETICAL DETERMINATION OF TOTAL (COUNTING) IONIZATION CROSS-SECTIONS OF MOLECULES - A NEW APPROACH

Cross sections for single ionization of molecules by electrons (threshold ≤ E ≤ 200 eV) have been calculated using a newly developed semiclassical formula. The formula is a combination of the classical binary encounter approximation, the Born-Bethe approximation and the additivity rule. This formula has been applied to H2, N2, O2, H2O, CO2, C2H2, NH3, CH4, CF4, C2H4, CH3OH, SF6, UF6, C2H6 and C6H6 and the cross sections obtained have been compared with results from the classical binary encounter approximation (Gryzinski formula), the semiclassical Jain-Khare approach, and reliable experimental data. The main advantage of the present treatment is that ionization cross sections can be described by a simple analytical formula (depending only on basic atomic properties), which yields results in better agreement with experimental data than the classical formulae. © 1990.