Revisiting the Chlorine Abundance in Diffuse Interstellar Clouds from Measurements with the Copernicus Satellite

TL;DR

This study reanalyzed Copernicus satellite data to refine chlorine abundance measurements in diffuse interstellar clouds, revealing clearer relationships with molecular hydrogen and hydrogen columns.

Contribution

It provides an updated analysis of chlorine spectra using new laboratory data and high-resolution measurements, improving understanding of chlorine chemistry in interstellar clouds.

Findings

Clearer correlation between Cl I and H2 column densities

Refined chlorine abundance measurements

Confirmation of rapid Cl+ to Cl0 conversion in molecular regions

Abstract

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.