Chlorine chemistry in diffuse interstellar clouds

The results of recent observations of the column densities of chlorine species in diffuse interstellar clouds are inconsistent with the column densities predicted by model calculations. The use of new atomic and molecular data fails to decrease the discrepancy. It is speculated that the exothermic reaction Cl(+) yields HCl(+) + H may not be rapid at the low temperatures prevailing in diffuse interstellar clouds.