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

Abstract

Absorption lines arising from the 2s2 2p 2P ground state of C II havebeen observed in the UV spectra of planetary nebulae, H II regions,and diffuse H I interstellar clouds. Attention is presently givento the results of R-matrix calculations of electron excitation ratesfor the 2s2 2p 2P1/2-2s2 2p 2P3/2 fine structure transition in CII, which are used to obtain density-sensitive population ratiosfor the ranges of electron and neutral hydrogen densities applicableto H I and H II regions. The results obtained are found to implyelectron density estimates 40-60 percent smaller than those calculatedby Smeding and Pottasch (1979).