Low-energy electron collisions with atomic sulfur: R-matrix calculation with non-orthogonal orbitals

The low-energy electron collision with neutral sulfur has been investigated using a modified R-matrix method based on the B-spline representation of t he scattering orbitals. Integral cross sections for elastic scattering and for excitation of the 3s(2)3p(4) D-1, S-1, (3)s(2)3p(3)4s(3,5)S degrees, P- 1,P-3 degrees, D-1,D-3 degrees, 3s(2)3p(3)3d D-3 degrees and 3s3p(5) P-3 de grees states in the LS coupling scheme are presented in the energy region f rom threshold to 50 eV. Accurate representation of target wavefunctions has been obtained on the basis of the non-orthogonal orbitals. The close-coupl ing expansion consists of the 27 spectroscopic bound and autoionizing targe t states. Calculations in three-, five- and 15-state close-coupling approxi mations and in the Born approximation have also been carried out to check t he convergence of excitation cross sections. The large influence of inclusi on of the 3s3p(5) P-3 degrees state in the close-coupling expansion was fou nd to be due to large exchange interaction at the 3s-3p excitation. The pre sent cross sections differ considerably from the existing results obtained in less elaborate calculations.