Electron capture in low-energy collisions of Sn³⁺ ions with H₂ and D₂

We report experimental single-electron-capture cross sections for Sn³⁺ ions impacting on H₂ and D₂ molecules at low projectile energies, ranging from 0.8 to 153 eV/u. The data were obtained in a crossed-beam-type experiment with a decelerated Sn³⁺ ion beam and a H₂ (D₂) gas target. Charge-state resolved Sn ion currents are measured with a retarding field analyzer. After an extensive description of the setup and measurement procedure, we present and discuss the results in comparison to model calculations. Ab initio calculations of potential energy curves, including spin-orbit interactions, are performed and used to fit a four-state diabatic model. The experimental and theoretical single-electron-capture cross sections show good agreement and are found to have values in the range of 20–45 × 10⁻¹⁶ cm² with a shallow maximum around 10 eV/u. We do not observe a significant difference between the cross sections for H₂ and D₂, as hinted at in our previous work at energies of 80–400 eV/u.