Revisiting the Chlorine Abundance in Diffuse Interstellar Clouds from
  Measurements with the Copernicus Satellite
  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 A from which
precise column densities are derived. The improved set of results reveals
clearer correspondences with H2 and total hydrogen column densities. These
linear relationships arise from rapid conversion of Cl^+ to Cl^0 in regions
where H2 is present.
