Revisiting the Chlorine Abundance in Diffuse Interstellar Clouds From Measurements With Thecopernicussatellite

We reanalyzed interstellar Cl i and Cl ii spectra acquired with the Copernicus satellite. The directions for this study come from those of Crenny & Federman and sample the transition from atomic to molecular-rich clouds where the unique chemistry leading to molecules containing chlorine is initiated. Our profile syntheses relied on up-to-date laboratory oscillator strengths and component structures derived from published high-resolution measurements of K i absorption that were supplemented with Ca ii and Na i D results. We obtain self-consistent results for the Cl i lines at 1088, 1097, and 1347 Å from which precise column densities are derived. The improved set of results reveals clearer correspondences with H 2 and total hydrogen column densities. These linear relationships arise from rapid conversion of Cl + to Cl 0 in regions where H 2 is present.