Excitations through rotational and radial couplings in Li^+^-He collisions.

What is it about?

Double differential cross sections (DCS) have been measured over the wide center-of-mass angular range of 25 < Θ < 175° by analyzing velocities of the scattered particles at laboratory (lab) collision energies of 350 < E_lab_ < 2000 eV. In this collision system, strong two-electron (2e) excitations as well as one-electron (1e) excitations were observed. Furthermore, the excitations were mostly transitions into the He*(2p), Li*(2p), and He**(2p^2^) states due to rotational couplings. As the first, assuming rotational couplings between three states of ground ^1^Σ and excited ^1^Π and ^1^Δ states, angular dependences of experimental DCSs could be fairly reproduced by the model calculations. However, the 2e excitation at large angles Θ > 100° could not be reproduced because of the He**(2s2) excitation through the radial coupling. As the second, ab initio potential curves including 35 excited states were calculated by the multi-configuration self-consistent field method. Excitation probabilities P(Θ)i were calculated by considering 7 states (5Σ, 1Π, and 1Δ). The results were sufficiently well reproduced the experimental P(Θ)i for 1e and 2e excitations. These analyses gave valuable information on excitation processes through rotational and radial couplings.

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Why is it important?

The Li+-He collision system is simplest closed-shell system, and it supplies typical excitation processes occurring through rotational and radial couplings. The excitations observed in this system are most important to understand the excitation processes in the atomic collisions.

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