Ca. Ramsbottom et al., Effective collision strengths for forbidden transitions among the 3s(2)3p(3) fine-structure levels of ClIII, M NOT R AST, 307(3), 1999, pp. 669-676
Effective collision strengths for the 10 astrophysically important fine-str
ucture forbidden transitions among the S-4 degrees, D-2 degrees and P-2 deg
rees levels in the 3s(2)3p(3) configuration of Cl III are presented. The ca
lculation employs the multichannel R-matrix method to compute the electron-
impact excitation collision strengths in a close-coupling expansion, which
incorporates the lowest 23 LS target eigenstates of Cl III. These states ar
e formed from the 3s(2)3p(3), 3s3p(4), 3s(2)3p(2)3d and 3s(2)3p(2)4s config
urations. The Maxwellian-averaged effective collision strengths an presente
d graphically for all 10 fine-structure transitions over a wide range of el
ectron temperatures appropriate for astrophysical applications [log T(K) =
3.3 - log T(K) = 5.9]. Comparisons are made with the earlier seven-state cl
ose-coupling calculation of Butler & Zeippen, and in general excellent agre
ement is found in the low-temperature region where a comparison is possible
[log T(K) = 3.3 - log T(K) = 4.7], However, discrepancies of up to 30 per
cent are found to occur for the forbidden transitions which involve the S-4
degrees ground state level, particularly for the lowest temperatures consi
dered. At the higher temperatures, the present data are the only reliable r
esults currently available.