Helium collision cross-section with electrons

Calculations using the CDW-EIS model [38] are shown to be in good accord with 40-keV protons incident on molecular hydrogen and helium, and at this energy both theory and experiment show no evidence of any saddle-point enhancement in the doubly differential cross sections. However, for collisions involving 100-keV protons incident on molecular hydrogen and helium the CDW-EIS calculations [39] predict the existence of the saddle-point mechanism, but this is not confirmed by experiment. Recent CDW-EIS calculations and measurement for 80-keV protons on Ne by McSherry et al. [41] find no evidence of the saddle-point electron emission for this collision. 

If the electronic excitation energy of a metastable atom A exceeds the ionization potential of another atom B, their collision can lead to an act of ionization, the so-called Penning ionization. The Penning ionization usually proceeds through the intermediate formation of an unstable excited quasi molecule in the state of auto-ionization cross sections of the process can be very high. Cross sections for the Peniung ionization of N2, CO2, Xe, and Ar by metastable helium atoms He(2 S) with an excitation energy of 19.8 eV reach gas-kinetic... 

Fig. 2 Elastic differential cross section for scattering of electrons by cyclopropane panel) and helium atom (right panel). Collision energies are 2.6 eV (left panel) and 10 eV (right panel). Present calculations with exact exchange interaction are displayed by red curves while the local AAFEGE exchange model is shown by green curves. The results are compared to experimental data for cyclopropane [22] and helium [23], both displayed as circles in respective panels...

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