Proton-impact excitation of laser-excited lithium atoms

A time-dependent solution of the Schr\"odinger equation on a three-dimensional lattice is used to calculate proton-impact excitation cross sections for both the ground $(2s)$ and first excited $(2p)$ states of the neutral lithium atom. Total cross sections for the 2→s3l and 2→p3l excitations are compared with atomic-orbital close-coupling calculations at incident energies of 15--50 keV. In support of future experiments involving crossed ion, atom, and laser beams, total aligned cross sections for the 2p→σ3l and 2p→π3l excitations are presented over the same energy range. The ratio of aligned cross sections for certain excitations and incident energies is found to be almost a factor of 2.