Atomic data from the IRON Project. XXXII. On the accuracy of the effective collision strength for the electron impact excitation of the quadrupole transition in AR III
Abstract
Since te[Burgess et al. (1997)]{bur97} have recently questioned the accuracy of the effective collision strength calculated in the IRON Project for the electron impact excitation of the 3ssp23p sp4 \ sp1 D sp1 S quadrupole transition in Ar iii, an extended Rmatrix calculation has been performed for this transition. The original 24state target model was maintained, but the energy regime was increased to 100 Ryd. It is shown that in order to ensure convergence of the partial wave expansion at such energies, it is necessary to take into account partial collision strengths up to L=30 and to ``topup'' with a geometric series procedure. By comparing effective collision strengths, it is found that the differences from the original calculation are not greater than 25% around the upper end of the common temperature range and that they are much smaller than 20% over most of it. This is consistent with the accuracy rating (20%) previously assigned to transitions in this low ionisation system. Also the present hightemperature limit agrees fairly well (15%) with the CoulombBorn limit estimated by Burgess et al., thus confirming our previous accuracy rating. It appears that Burgess et al., in their data assessment, have overextended the lowenergy behaviour of our reduced effective collision strength to obtain an extrapolated hightemperature limit that appeared to be in error by a factor of 2.
 Publication:

Astronomy and Astrophysics Supplement Series
 Pub Date:
 December 1998
 DOI:
 10.1051/aas:1998455
 Bibcode:
 1998A&AS..133..245G
 Keywords:

 ATOMIC AND MOLECULAR DATA