Fine-structure population ratios for the 2P ground state of C II

Abstract

Results of R-matrix calculations of electron excitation rates for the |$2s^2\enspace 2p\enspace ^2P_{1/2}-2s^2\enspace 2p\enspace ^2P_{3/2}$| fine-structure transition in C II are used to derive density sensitive population ratios |$n(2s^2\enspace 2p\enspace ^2P_{3/2})/n(2s^2\enspace 2p\enspace ^2P_{1/2})$| for the ranges of electron and neutral hydrogen densities (⁠|$n_\text e=10^{-3}-10^3\enspace\text {cm}^{-3};\enspace n_\text H=0-1000\enspace\text {cm}^{-3}$|⁠) applicable to H I and H II regions. These are found to differ significantly from the earlier calculations of Smeding & Pottasch, and lead to electron density estimates between 40 and 60 per cent smaller.