Coulomb autoionisation of Li I quartet states above the Li+(1s2s)3S threshold

Four distinct structures are observed in the zero-degree projectile electron energy spectra of 300 keV lithium ions excited in C foils. The lowest single narrow peak has a centre mass energy of 140 meV and is attributed to Coulomb autoionisation of the Li I initial state. A second rather sharp peak has a centre of mass energy of 360 meV and originates from Coulomb autoionisation of the Li I state, decaying into the continuum. Finally, a third broader peak, centred at 610 meV, results from a rapidly autoionising transition. Theoretically the (1s2pnl) quartet levels of lithium are calculated within the framework of the saddle point technique and the complex-rotation method. The predicted resonance energies and widths are compared with experimental results. An attempt to assign similar excited states from collisions of keV C2+ with He gas is also presented. (author)