External field effects on dielectronic recombination rate coefficients for oxygen atomic ions

Abstract

The effects of external electric fields on Ln =0 dielectronic recombination {DR) rate coefficients for O~+, q =1, . . . , 5 are calculated using a configuration-average distorted-wave approach. Fieldionization effects lead to a decrease in the DR rate coefficient while field-mixing effects lead to an increase in the DR rate coefficient. Overall, strong fields produce a significant decrease in the DR rate coefficient at the peak temperature, i.e. , by over a factor of 10 for several oxygen ions. The configuration-average distorted-wave results are also compared with the Burgess general formula II [A. Burgess (private communication)] that includes both field-mixing and ionization effects It . is found that this formula roughly models these effects, and some guidelines as to the range of validity of this simple-to-use formula are developed. In the limit of zero external electric fields, the distorted-wave approach is further compared with recent sophisticated configuration-mixing intermediate-couplingcalculations as well as with the Burgess general formula I [A. Burgess, Astrophys. J. 141, 1588 (1965)].

Experimental O VI dielectronic recombination rate coefficient and its enhancement by external electric fields

“…The theoretical results of Nussbaumer & Storey (1983), Krylstedt et al (1990), Romanik (1988), and the DR rate coefficient recommended by Arnaud & Rothenflug (1985), show a very good agreement with the experimental data at low temperatures. For other ions, e. g. C  no standard theory was found to match the experiment at low temperatures.…”

“…The results were compared to theoretical plasma rate coefficients. The data of Krylstedt et al (1990) and Romanik (1988) are not too far off from our experimental data over the whole temperature range. The discrepancies at low temperatures for these two calculations are below 70%.…”

“…Now the magnetic field significantly alters the recombination rate coefficient. Since the calculation of Krylstedt et al (1990) does not include a magnetic field the comparison in this case is only qualitative. Inclusion of the magnetic field significantly complicates the calculations and available theories are still far off the experiment (Böhm et al 2002).…”

“…Field effects are also included in the Burgess general formula II (GFII, dotted line, Fig. 6) which is given in Krylstedt et al (1990) for n max = 20. For temperatures T ≥ 5 × 10 5 K the experimental rate coefficient in a plasma in the presence of an electric field E ⊥ = 340 V/cm and a magnetic field B = 100 mT for DR including Rydberg states up to n = 19 is enhanced by about a factor of 1.8.…”

Dielectronic recombination ofO+

“…We present our final results in Table I. In fact, the general conclusions of Badnell and Pindzola [2] and of Krylstedt, Pindzola, and Badnell [17] that were based on relative results for 0+ remain largely unchanged, e.g. , the effect of alternative Auger channels, intermediate coupling, electric fields, and the accuracy of the Burgess general formula [18].…”