Electron Excitation Cross Sections for the S II Transitions 3s23p3 4So --> 3s23p3 2Do, 2Po, and 3s3p4 4P
Experimental and theoretical collisional excitation cross sections are reported for the transitions 3s23p3 4So --> 3s23p3 2Do, 2Po, and 3s3p4 4P in S II. The transition wavelengths (energies) are 6716 Å (1.85 eV), 4069 Å (3.05 eV), and 1256 Å (9.87 eV), respectively. In the experiments, use is made of the energy-loss merged-beams method. The metastable fraction of the S II beam was assessed and minimized. The contribution of elastically scattered electrons was reduced by the use of a lowered solenoidal magnetic field and a modulated radio-frequency voltage on the analyzing plates and by retarding grids to reject the elastically scattered electrons with larger Larmor radii. For each transition, comparisons are made among experiments, the new 19 state R-matrix calculation, and three other close-coupling calculations.