RESONANCES IN TOTAL CROSS SECTIONS FOR METASTABLE EXCITATION OF NOBLE GASES BY ELECTRON IMPACT

Total cross sections for excitation by electron impact of metastable states in the noble gases helium, neon, argon, krypton, and xenon have been measured as a function of impact energies. A 180°spherical monochromator was used to obtain incident beams of electrons with energy resolutions between 0.035 and 0.050 eV. Metastable atoms were detected in the scattering chamber by electron ejection from a metal surface. The detector was biased negatively to repel scattered electrons, and was electrostatically shielded from the incident electron beam. The cross sections were measured for impact energies up to 5 eV above the metastable thresholds. Several narrow resonances associated with negative-ion states were observed, and where possible their shapes and positions on the energy scale were compared with similar results obtained by different techniques. © 1968 The American Physical Society.