State-selective single- and double-electron capture in collisions of low-energy S⁵⁺ ions with helium

Abstract State-selective single- and double-electron capture processes in collisions of S 5+ ions with helium at energies ranging from 50.8 keV to 100 keV were investigated using cold target recoil ion momentum spectroscopy (COLTRIMS). Q -value spectra and projectile scattering angle distributions were obtained. For single-electron capture, single electron capture into n = 3 states of the projectile ion is dominant. As the projectile energy increases, the contribution of single electron capture into n = 4 states is observed. Experimental relative cross-sections for single-electron capture into different projectile final states were compared with theoretical predictions based on the molecular orbital close-coupling (MOCC) method. In double-electron capture, two-electron populating into the 3s 2 3p and 3s3p 2 states of projectile dominates. The reaction window calculated from the classical molecular Coulombic barrier model can qualitatively explain the experimental results. The scattering angle distribution of the multi-peak structure of the double-electron capture process is observed. The database is openly available in Science Data Bank at https://doi.org/10.57760/sciencedb.j00113.00233 .