Experimental and (first-order many-body) theoretical differential and integral cross sections for excitation of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>n</mml:mi><mml:mo>=</mml:mo><mml:mn>3</mml:mn><mml:mn/></mml:math>states 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 $1^{1}S\ensuremath{\rightarrow}3^{1}S, 3^{3}S, 3^{3}P$ and for the experimentally unresolved transitions $1^{1}S\ensuremath{\rightarrow}3^{1}P, 3^{1,3}D$ 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\ifmmode^\circ\else\textdegree\fi{}. The $n=3$ 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 $1^{1}S\ensuremath{\rightarrow}3^{1}S$ DCS are discussed.