Electron excitation cross sections for the 3s(2)3p(2) P-3 -> 3s3p(3) S-5(o) transition in S2+

Experimental and theoretical collisional excitation cross sections are repo rted for the 3s(2)3p(2) P-3-->3s3p(3) S-5(o) spin-forbidden transition in S 2+. Th, transition energies (wavelengths) are 7.171 eV (1728.9 Angstrom, J = 2 --> 2) and 7.237 eV (1713.1 Angstrom J = 2 --> 1). In the experimental approach, use is made of the electron energy-loss method with merged electr on and ion beams. The metastable fraction in the S2+ beam is assessed and m inimized. A novel "electronic aperture" is used to limit the trajectories o f elastically scattered electrons into the trochoidal electrostatic analyze r. Theoretically, the R-matrix method in a 17 state and a 27 state calculat ion is used to obtain cross sections from threshold to. 15.0 eV. Good agree ment is found between experiment and the results of the 27 state theory. Th e presence of two strong resonances near threshold (7.5-9.0 eV) and a third resonance above threshold (11.5 eV) is verified by experiment.