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Effective collision strengths for forbidden transitions among the 3s23p3 fine-structure levels of Cl IIIIII
Authors:C A Ramsbottom  K L Bell  F P Keenan
Institution:Department of Applied Mathematics and Theoretical Physics, The Queen's University of Belfast, Belfast BT7 1NN; Department of Pure and Applied Physics, The Queen's University of Belfast, Belfast BT7 1NN
Abstract:Effective collision strengths for the 10 astrophysically important fine-structure forbidden transitions among the 4So, 2Do and 2Po levels in the 3s23p3 configuration of Cl  iii are presented. The calculation 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 are formed from the 3s23p3, 3s3p4, 3s23p23d and 3s23p24s configurations. The Maxwellian-averaged effective collision strengths are presented graphically for all 10 fine-structure transitions over a wide range of electron temperatures appropriate for astrophysical applications log  T (K)=3.3?log  T (K)=5.9]. Comparisons are made with the earlier seven-state close-coupling calculation of Butler & Zeippen, and in general excellent agreement 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 4So ground state level, particularly for the lowest temperatures considered. At the higher temperatures, the present data are the only reliable results currently available.
Keywords:atomic processes
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