Collision Strengths for Electron Excitation of Coronal Ions

Abstract

Using general purpose computer programmes developed by Drs. Eissner and Nussbaumer at University College London for the solution of atomic structure and atomic collision problems, collision strengths have been obtained for transitions between terms of the ground and first few excited configurations of ions of interest in studies of the solar corona. The atomic structure programme is written in a configuration interaction representation and uses a scaled Thomas-Fermi potential as described by Eissner and Nussbaumer (1969). The bound state wave functions generated by the structure programme are used by the collision programme (Eissner, 1970) to calculate the R-matrix solution of the collision problem by means of the distorted wave approximation (Saraph et al., 1969). This approximation should be valid for highly ionized ions such as exist in the corona and this prediction is fully confirmed where comparison can be made with calculations using the more rigorous but more time-consuming close coupling method (Burke et al., 1966; Petrini, 1969).

Fundamental Spectroscopic Data

“…A detailed paper deals with theoretical methods for excitation of hydrogenic ions (211). The Coulomb-Born or the distorted wave approximation is valid in many cases and has been applied for Ca IT (212), for C ill, N IV, 0 V (213) for the Li isoelectronic ions (215), for Si XII (216), for N V, Si XII, Fe XIII, Fe XV, Fe xvn (217,218) and for C III (190). Measurements have been made of different cross sections in N V, 0 VI, Ne vrn (219), in N V (220), in N IV, 0 v, Ne VII, Si IX (221) Ar VIII (222), Ne Vill (223), and Ne vn (225).…”