Hai all, I need some help in understanding the calculation of total ionization cross section. As per the literatures, for a gas capable of multiple ionization, the total cross section is a charge-weighted sum of partial ionization cross sections. To be more elaborate, consider the case of Xenon. Upon electron impact, Xe can become Xe+ or Xe2+ or Xe3+ ..... , cross sections of which are respectively represented as σ1, σ2, σ3 .... etc. Then total ionization cross section for Xe will be calculated as σtotal = σ1+ (2*σ2) +(3*σ3)+....... . So my question is, why can't we just add the partial ionization cross section to calculate total ionization cross section instead of adding charge weighted sum ?