Electron capture in collisions of S⁴⁺ with atomic hydrogen

Charge transfer processes due to collisions of ground state S⁴⁺(3s^{2 1}S) ions with atomic hydrogen are investigated for energies between 1 meV u^-1 and 10 MeV u^-1 using the quantum mechanical molecular-orbital close-coupling (MOCC), atomic-orbital close-coupling, classical trajectory Monte Carlo (CTMC) and continuum distorted wave methods. The MOCC calculations utilize ab initio adiabatic potentials and nonadiabatic radial coupling matrix elements obtained with the spin-coupled valence-bond approach. A number of variants of the CTMC approach were explored, including different momentum and radial distributions for the initial state, as well as effective charge and quantum-defect models to determine the corresponding quantum state after capture into final partially stripped S³⁺ excited classical states. Hydrogen target isotope effects are explored and rate coefficients for temperatures between 100 and 10⁶ K are also presented.