Experimental and (first-order many-body) theoretical differential and integral cross sections for excitation of then=3states of He by electron impact at 29.2 and 39.7 eV

Abstract

Differential and integral electron scattering cross sections have been measured and calculated for the transitions $1{}_{}{}^1{}_{}{}^{}S\to 3{}_{}{}^1{}_{}{}^{}S, 3{}_{}{}^3{}_{}{}^{}S, 3{}_{}{}^3{}_{}{}^{}P$ and for the experimentally unresolved transitions $1{}_{}{}^1{}_{}{}^{}S\to 3{}_{}{}^1{}_{}{}^{}P, 3{}_{}{}^{1,3}{}_{}{}^{}D$ in helium. Measurements were made relative to both the $2{}_{}{}^3{}_{}{}^{}P$ and $2{}_{}{}^1{}_{}{}^{}P$ transitions at incident electron energies of 29.2 and 39.7 eV, and over the angular range 5-136°. The $n=3\mathrm{}$ relative differential cross sections (DCS) were normalized to the absolute scale by utilizing known normalized absolute DCS for the $2{}_{}{}^3{}_{}{}^{}P$ and $2{}_{}{}^1{}_{}{}^{}P$ transitions. The theoretical calculations were carried out in the first-order manybody theory of Csanak, Taylor, and Yaris. Comparisons are also made of the present measurements and calculations with other calculations carried out for the $3{}_{}{}^1{}_{}{}^{}S$, $3{}_{}{}^1{}_{}{}^{}D$, and $3{}_{}{}^1{}_{}{}^{}P$ states in the Born and several Ochkur-like approximations. The theoretical origins in several theories of the intriguing sharp minimum in the $1{}_{}{}^1{}_{}{}^{}S\to 3{}_{}{}^1{}_{}{}^{}S$ DCS are discussed.