Excitation process in alkali-atom-He collisions in the keV energy range

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Abstract
The excitation of the ground state to the first excited state of an alkali atom (Li, Na, K, Rb, Cs) by collision with a He atom has been studied theoretically in the low keV collision energy regime. The electron translation factor corrected multichannel perturbed-stationary-state method was used assuming a straight-line trajectory for the heavy-particle motion. The molecular eigenstates and eigenvalues used in these calculations were generated from the l-dependent pseudo-potential method. Eight molecular states for the alkali-atom-He system (five Sigma states plus three Pi states) have been employed in the close-coupling calculations. The results for excitation into the first excited level of the alkali atom, in the LiHe and NaHe systems, show an improved agreement with experimental results, both qualitatively and quantitatively, over all the other available theoretical results. For the KHe system, the result shows a good accord with a peak observed at E approximately=25 keV, while the agreement in the peak at E approximately 3.5 keV is only qualitative.