Inelastic differential electron scattering from metastable He(23S) atoms

Abstract
Differential cross sections have been measured for the electron impact excitation of the metastable He(23S) state to the individual states 23P, 33S, 33P, 33D and to the sum of the n=4 triplet states of helium. The contributions of the various n=3 sublevels were determined by a peak shape analysis. The experiments have been carried out in a crossed-beam configuration using a target metastable helium beam (density about 6*107 cm-3) produced in a differentially pumped cold cathode DC discharge source. The measurements have been performed for impact energies of about 15, 20 and 30 eV and for selected angles between 10 degrees and 40 degrees . The cross sections are very large at small scattering angles and decrease rapidly with increasing angle. The results of a multichannel eikonal calculation of the differential cross section by Flannery and McCann (1975) agree well with the shapes of the measured angular dependencies, but are typically a factor of two or three lower in absolute size.