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: (1s2s2)2S, 1s(2s2p3P)a2P, 1s(2s2p1P)b2P and (1s2p2)2D, angular distributions have been measured to yield relative substate populations. The a2P state has a remarkable alignment structure peaked at an impact energy 250 keV with Q(ML=0)/Q(ML=1)=7.5, not seen in the b2P state. The mechanism of a2P excitation is not yet clear.