Spin asymmetries in the low-energy electron impact excitation of 2S to 2P transitions in lithium atoms

Abstract

Crossed beams of spin-polarised lithium atoms and spin-polarised electrons with energies up to ten times the first excitation threshold have been used to measure the ratio of singlet to triplet scattering and to see the influence of exchange in excitation. The measured spin asymmetry in the intensity of the fluorescence radiation emitted perpendicular to the two beams shows substantial agreement with several close-coupling theories. Singlet scattering (A approximately=1) dominates near threshold but the asymmetry declines towards zero within about 4 eV, indicating equally large contributions thereafter from angle-integrated singlet and triplet scattering. Measurements of the spin asymmetry in the double differential cross section (DDCS) were also performed, using a hemispherical energy analyser at theta =65, 90 and 107.5'.