EFFECTIVE COLLISION STRENGTHS FOR ELECTRON-IMPACT EXCITATION OF SINGLY IONIZED SULFUR

The multichannel R-matrix method has been used to compute effective co llision strengths for electron impact excitation of the P-sequence ion S II. Included in the expansion of the total wave function are the lo west 18 LS target eigenstates of S II, consisting of twelve n = 3 leve ls with configurations 3s(2)3p(3), 3s3p(4), and 3s(2)3p(2)3d, and six n = 4 levels with configurations 3s(2)3p(2)4l (I = s, p). These 18 ion ic states correspond to 43 fine-structure levels, leading to a total p ossible 903 independent transitions (including all forbidden, semi-for bidden, and allowed). The effective collision strengths which are obta ined by averaging the electron collision strengths over a Maxwellian d istribution of velocities are tabulated for all fine-structure transit ions to include those between the n = 3 levels, those from the n = 3 t o n = 4 states, and those between the n = 4 levels, for electron tempe ratures, T, in the range log T(K) = 3.5 to log T(K) = 5.0. The present results are compared with a variety of other close-coupling data and some significant differences are found to occur. In particular we find that resonances converging to the high lying 3s(2)3p(2)nl levels enha nce the effective collision strength for many of the forbidden transit ions at low impact energies. (C) 1996 Academic Press, Inc.