关键词: ion-atom collision, charge transfer, electron-excitation processes, quantum-mechanical molecular-orbital close-coupling (QMOCC) method

Abstract: We present a theoretical study of charge-transfer (CT) and electron-excitation (EX) processes in collisions of He$^+$ with Na(3s) and Na(3p) using the quantum-mechanical molecular-orbital close-coupling (QMOCC) method. Adiabatic potential curves together with the corresponding radial and rotational nonadiabatic couplings are calculated for both singlet and triplet spin manifolds. State-resolved results show that, for He$^+$-Na(3s) collisions, the CT process is mainly governed by long-range Demkov-type interactions, with electron capture predominantly populating the He(1s2s) triplet state, while excitation cross sections are smaller and occur at shorter internuclear distances. In the He$^+$-Na(3p) system, additional $\Pi$-symmetry channels participate in the dynamics, leading to dominant capture into the He(1s2p) state. Despite the different initial electronic configurations, the total CT cross sections for Na(3p) are comparable in magnitude to those for Na(3s), with $\Sigma $-symmetry channels contributing more efficiently than $\Pi $ channels. The calculated total CT cross sections for Na(3s) and Na(3p) are on the order of $10^{-18}$-$10^{-14}$ cm$^2$ and agree with the experimental data within deviations of about 5% and 10%-20% in the overlapping energy range. The present results show good agreement with available experimental and theoretical data, providing a comprehensive description of the state-resolved collision dynamics in the low- and intermediate-energy regimes.

Key words: ion-atom collision, charge transfer, electron-excitation processes, quantum-mechanical molecular-orbital close-coupling (QMOCC) method