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

Differential and integral electron scattering cross sections have been measured and calculated for the transitions 1¹S-->3¹S, 3³S, 3³P and for the experimentally unresolved transitions 1¹S-->3¹P, 3^1,3D in helium. Measurements were made relative to both the 2³P and 2¹P transitions at incident electron energies of 29.2 and 39.7 eV, and over the angular range 5-136°. The n=3 relative differential cross sections (DCS) were normalized to the absolute scale by utilizing known normalized absolute DCS for the 2³P and 2¹P 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 3¹S, 3¹D, and 3¹P states in the Born and several Ochkur-like approximations. The theoretical origins in several theories of the intriguing sharp minimum in the 1¹S-->3¹S DCS are discussed.