Abstract
We report the first extragalactic detection of chloronium (H2Cl+) in the z = 0.89 absorber in front of the lensed blazar PKS 1830-211. The ion is detected through its 1(11)-0(00) line along two independent lines of sight toward the North-East and South-West images of the blazar. The relative abundance of H2Cl+ is significantly higher (by a factor similar to 7) in the NE line of sight, which has a lower H-2/H fraction, indicating that H2Cl+ preferably traces the diffuse gas component. From the ratio of the (H2Cl+)-Cl-35 and (H2Cl+)-Cl-37 absorptions toward the SW image, we measure a Cl-35/Cl-37 isotopic ratio of 3.1(-0.2)(+0.3) at z = 0.89, similar to that observed in the Galaxy and the solar system.