State-selective electron capture by slow S³⁺recoil ions in H, H₂and He

Abstract

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, H, 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+(*Po) 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 H, the majority of channels also involve 3s to 3p 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.

State Selective Electron Capture in the Collision of S3+ Ions in Atomic Hydrogen and Helium

“…Such a basis set shows a quite good agreement with experiment [17] for the atomic energy levels with a discrepancy in the range 0.01-0.14 eV (Table I). [6] and the 15.8 eV value given by the NIST Database [13], although the set of molecular calculations appears to be globally in good accordance with the tabulated energies as shown in Table II. …”

“…Astrophysical implications of this collisional system have been widely highlighted [4,5]. Previous calculations of the potential energy curves and couplings have been performed in relation with the translational energy experiments of Wilson et al [6] in the 2-9 keV energy range using ab-initio MCSCF-CI configuration interaction methods based on the CIPSI algorithm [8]. …”

“…Second row ions, such as silicon and sulfur play an important role in the reactions occurring in the interstellar medium [4,5], nevertheless, relatively few studies have been devoted to charge transfer processes involving sulfur ions [6][7][8][9][10][11][12]. Experimental measurements using the translational energy spectroscopy technique have been carried out by Wilson et al [6] on state-selective electron capture by S 3+ ions in H, H 2 and He at impact energies within the range 2.4-9.0 keV.…”

“…Experimental measurements using the translational energy spectroscopy technique have been carried out by Wilson et al [6] on state-selective electron capture by S 3+ ions in H, H 2 and He at impact energies within the range 2.4-9.0 keV. They show evidence of an S 2+ triplet state, identified as the S 2+ (3s 2 3p3d) 3 F° level, lying 15.03 eV above the S 2+ ground state in agreement with atomic data [13], which appears to be the dominant capture state in the S 3+ + H collision system over the entire range of impact energies investigated.…”

Atomic data for x-ray astrophysics

“…with H, H 2 and He (Wilson et al, 1990a). Using similar techniques, Kimura et al (1987) have studied highly stripped Ne, O, N and C in collisions with H and H 2 , and Kamber et al (1996) have studied N 3+ colliding with H 2 , He, Ne, and Ar.…”