Electron impact excitation of OII fine-structure levels

TL;DR

This paper calculates accurate collision strengths for forbidden transitions among the lowest fine-structure levels of O II using the R-matrix method, providing data for electron temperatures from 100 to 100,000 K and assessing previous results.

Contribution

The study offers new, precise collision strength data for O II's fine-structure levels, confirming the validity of established optical line ratios and correcting previous inaccuracies.

Findings

Validated the Seaton and Osterbrock scaling for O II optical ratios

Provided comprehensive plasma diagnostic diagrams

Highlighted and corrected errors in earlier data

Abstract

Effective collision strengths for forbidden transitions among the 5 energetically lowest finestructure levels of O II are calculated in the Breit-Pauli approximation using the R-matrix method. Results are presented for the electron temperature range 100 to 100 000 K. The accuracy of the calculations is evaluated via the use of different types of radial orbital sets and a different configuration expansion basis for the target wavefunctions. A detailed assessment of previous available data is given, and erroneous results are highlighted. Our results reconfirm the validity of the original Seaton and Osterbrock scaling for the optical O II ratio, a matter of some recent controversy. Finally we present plasma diagnostic diagrams using the best collision strengths and transition probabilities.