Production of Excitation and Ionization in Helium by Single-Electron Impact

Abstract

The production of excited He⁺ ions by single‐electron impact collisions with ground‐state helium atoms has been observed by the optical method. The absolute value of the cross section for the collision process yielding the n=4→n=3 transitions (4686 Å) in He⁺ was determined for incident electron energies ranging from 60 to 470 eV. The excitation—ionization cross section exhibited a single broad maximum at 200 eV with an onset at 75 eV. The peak value of the cross section was 4.2×10^—21 cm². Stepwise ionization and excitation was nowhere in evidence. The excitation—ionization function obtained at a number of gas pressures was independent of pressure. Light yield was proportional to the electron beam currents. Comparison with previous experimental work and with theoretical calculations were made.