Excitation of autoionising Li I and He states in 20-500 keV Li+-He collisions

Autoionisation in 20-500 keV Li + -He collisions has been studied experimentally and absolute cross sections sigma (Li) and sigma (He) have been obtained. A double hump structure is observed for sigma (Li) against impact velocity, while sigma (He) declines surprisingly rapidly. For the four prominent Li lines: (1s2s 2 ) 2 S, 1s(2s2p 3 P) a 2 P, 1s(2s2p 1 P) b 2 P and (1s2p 2 ) 2 D, angular distributions have been measured to yield relative substate populations. The a 2 P state has a remarkable alignment structure peaked at an impact energy 250 keV with Q(M L =0)/Q(M L =1)=7.5, not seen in the b 2 P state. The mechanism of a 2 P excitation is not yet clear.