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5 Quality of results

The IRON Project's aim is to produce high quality collision data for a wide range of electron induced transitions in positive ions. We outline the steps taken in the present work which justify our belief that the results given here are the most reliable ones at present available to those in search of rate coefficients for Fe+22. We first of all went to some trouble in order to obtain a good target model. Our confidence in it stems from the good agreement it affords between the theoretical energy levels and observational data (see Table 3). Furthermore, on comparing the length gauge oscillator strengths listed in Table 7 with those we have obtained using the velocity gauge, we find that in all cases except two, their ratio lies between 1.03 and 1.77. Only for the transitions 1-3 and 7-5 does the ratio exceed 2, but not by a great deal: $f_{\rm V}(1-3)/f_{\rm L}(1-3) 
= 2.56$ and $f_{\rm V}(7-5)/f_{\rm L}(7-5) = 3.53$. Although close agreement between the length and velocity f-values is not an absolute guarantee that the oscillator strengths are the correct ones, it is obviously desirable that the ratio $f_{\rm L}/f_{\rm V}$ should not deviate from unity a lot. As regards the collision calculation, we have made use of the R-matrix method in both the Breit-Pauli and LS-coupling modes. The Belfast-London-Meudon suite of programs has been developed over many years by a great number of scientists. The present programs, which are based on approximations that take into account much of the collision physics responsible for resonance scattering and relativistic effects, are widely considered as the most elaborate and satisfactory ones in existence for this type of calculation. With increasing energy, more and more partial waves need to be calculated. In order to ensure convergence of the expansion we let the partial wave quantum number J extend up to J = 35.5. This applies only to collision energies greater than 12.9843 Ry with respect to the ground state; for energies between 3.1521 and 12.9843 Ry we limited J to 5 and then did a top-up by estimating the contributions from higher partial waves. As mentioned earlier, we used OmeUps in order to estimate collision strengths at much higher energies than could be reached by the R-matrix codes. This procedure gives added reliability to the high temperature results in Table 9.


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