State-selective electron capture by slow S3+ recoil ions in H, H2 and He

Translational energy spectroscopy has been used to study electron capture by slow S3+ ions from a recoil ion source. These ions are important in astrophysical plasmas. Cross sections for state-selective electron capture by S3+ ions in H, H2 and He have been determined at energies within the range 2.4-9.0 keV. The main excited product channels have been identified and their relative importance has been assessed. In the case of H and He a multichannel Landau-Zener model has been used to predict cross sections which have been compared with experiment. The presence of S3+(4P) metastable as well as S3+(2P0) ground-state ions in our primary beam has been clearly demonstrated. Electron capture by ground-state ions is dominated by 3p electron capture. For H and H2 the majority of channels also involve 3s excitation of the projectile core. Results obtained for all three collision systems provide clear evidence for a S2+(3s23p3d)3F0 state (missing from published tabulations), 15.03 eV above the ground state of S2+. The existence of this state was previously suggested by Dynefors and Martinson. (author)