EXCITATION OF 31,3D AND 41,3F LEVELS OF HELIUM BY DIRECT ELECTRON IMPACT AND 41P-]41,3F COLLISIONAL TRANSFER

Excitation of the 3D1,3 and 4F1,3 levels of helium by electron impact has been studied by time-resolved spectroscopy of the 3D1→2P1(λ6678) and 3D3→2P3(λ5876) transitions. (Excitation of the 4F1 and 4F3 levels are observed as cascade components under time resolution.) Cross sections are estimated for the direct excitation of these levels by 38-, 50-, and 100-eV electron impact. Excitation of the 4F levels by direct electron impact are much larger than predicted by the Born approximation but much smaller than implied by previous experimental measurements. Direct excitation of the 3D1 and 4F1 by 100-eV electron impact is in excellent agreement and satisfactory agreement, respectively, with preliminary close-coupling approximation calculations. The collisional transfer 4P1→4F3 is much smaller relative to the 4P1→4F1 transfer than has previously been suggested. © 1969 The American Physical Society.