Chlorine-bearing molecules in molecular absorbers at intermediate
  redshifts
  We use observations of chlorine-bearing species in molecular absorbers at
intermediate redshifts to investigate chemical properties and
$^{35}$Cl/$^{37}$Cl isotopic ratios in the absorbing sightlines. Chloronium
(H$_2$Cl$^+$) is detected along three independent lines of sight in the z=0.89
and z=0.68 molecular absorbers located in front of the lensed quasars PKS
1830-211 and B 0218+357, respectively. Hydrogen chloride (HCl) was observed
only toward PKS 1830-211, and is found to behave differently from H$_2$Cl$^+$.
It is detected in one line of sight with an abundance ratio [H$_2$Cl$^+$]/[HCl]
$\sim 1$, but remains undetected in the other, more diffuse, line of sight,
with a ratio [H$_2$Cl$^+$]/[HCl]~$>17$. The absorption profiles of these two
chlorine-bearing species are compared to other species and discussed in terms
of the physical properties of the absorbing gas. Our findings are consistent
with the picture emerging from chemical models where different species trace
gas with different molecular hydrogen fraction. The $^{35}$Cl/$^{37}$Cl
isotopic ratios are measured in the different lines of sight and are discussed
in terms of stellar nucleosynthesis.
