Charge transfer processes in low-energy Na⁺–Na collisions

A comprehensive theoretical study of resonant and non-resonant charge transfer processes in the homonuclear Na⁺ + Na(3s) collision system is provided. The electronic structure of the quasi-molecular system is calculated using the multireference single- and double-excitation configuration interaction (MRD-CI) method under both one-electron (OEM) and thirteen-electron (TEM) models. The radial and rotational coupling matrix elements are obtained with careful inclusion of electron translation factors (ETFs). Based on these data, fully quantum-mechanical scattering calculations were performed using the fully quantum-mechanical molecular orbital close-coupling (QMOCC) method to derive state-selective and total cross sections for electron capture over a broad energy range (0.2–5600 eV/amu). The calculated resonant charge-transfer cross sections show excellent agreement with available theoretical and experimental results. Non-resonant processes, which involve electron capture into excited states of Na⁺, are found to become increasingly important above several keV/amu. This work provides the first theoretical predictions for non-resonant state-selective cross sections in this system, offering a valuable reference for future experimental and theoretical studies in atomic collision physics.