A&A Supplement Series, Vol. 123, June II 1997, 575-580
Received September 25; accepted October 8, 1996
H.L. Zhang and A.K. Pradhan
Send offprint request: H.L. Zhang
Department of Astronomy, The Ohio State University, Columbus, OH 43210, U.S.A.
New collision strengths have been calculated for 990 transitions among 45 fine structure n=2 and n=3 levels of Fe XXII. The relativistic Breit-Pauli formulation of the R-matrix method was employed in the close coupling approximation, with radiation damping of autoionizing resonances included for the first time in the calculations of excitation rate coefficients. It is found that, at low temperatures, the relativistic effects considerably enhance rate coefficients for the intercombination transitions, and the radiation damping effect reduces those for a few transitions. It is also found that resonances due to coupling with the n=3 levels significantly enhance rate coefficients for the transitions to low-lying levels at intermediate and high temperatures, and for the transitions to the n=2 high-lying levels at all temperatures. It is expected that the new data, tabulated at a wide range of temperatures, would lead to a revision of the spectral diagnostics of Fe XXII in laboratory and astrophysical sources, in particular the X-ray spectra observed from solar flares and tokamaks.
keywords: atomic data -- Sun: flares -- X-rays: general