Ab initio study of charge transfer in low-energy Si3+ collisions with helium

Charge transfer cross sections for collisions of ground state Si3+(3s S-2) and excited state Si3+(3p P-2(o)) with atomic helium are presented for ener gies less than 250 eV u(-1). Using a fully quantum mechanical, molecular-or bital, close-coupling approach, the cross sections are calculated in a diab etic representation. Completely ab initio adiabatic potentials and nonadiab atic radial coupling matrix elements obtained with the spin-coupled valence -bond method are utilized. Rate coefficients for temperatures between 100 a nd 100 000 K and cross sections for collisions with isotopic He-3 are prese nted. Results for the reverse process, Si2+ + He+, are also given.