Dissociative recombination of HCl$^{\mathrm{+}}$, H$_{\mathrm{2}}$Cl$^{\mathrm{+}}$, DCl$^{\mathrm{+}}$, and D$_{\mathrm{2}}$Cl$^{\mathrm{+}}$ (300-500 K), and the astrophysical relevance.

A review by Neufeld and Wolfire$^{\mathrm{1}}$ pointed out the unique chemistry of chlorine in the interstellar medium (ISM), including (a) Cl is the only species in the ISM with an IE less than that of H atom, which allows Cl$^{\mathrm{+}}$ to survive among an abundance of H atoms; (b) those Cl$^{\mathrm{+}}$ can react with H$_{\mathrm{2}}$ to form HCl$^{\mathrm{+}}$ exothermically; and (c) HCl$^{\mathrm{+}}$ can in turn react with another H$_{\mathrm{2}}$ to form H$_{\mathrm{2}}$Cl$^{\mathrm{+}}$. Only in the past 6 years have HCl$^{\mathrm{+}}$ and H$_{\mathrm{2}}$Cl$^{\mathrm{+}}$ been observed in the ISM. Modeling the true quantities of chlorinated species in the ISM requires knowing dissociative recombination (DR) kinetics for HCl$^{\mathrm{+}}$ and H$_{\mathrm{2}}$Cl$^{\mathrm{+}}$. We have used a flowing afterglow apparatus to measure DR rate coefficients at 300-500 K for HCl$^{\mathrm{+}}$, H$_{\mathrm{2}}$Cl$^{\mathrm{+}}$, DCl$^{\mathrm{+}}$, and D$_{\mathrm{2}}$Cl$^{\mathrm{+}}$. For 300 K, we find 7.7 x 10$^{\mathrm{-8}}$ cm$^{\mathrm{3}}$/s (HCl$^{\mathrm{+}})$, 2.6 x 10$^{\mathrm{-7}}$ cm3/s (H$_{\mathrm{2}}$Cl$^{\mathrm{+}})$, and 1.1 x 10$^{\mathrm{-7}}$ cm$^{\mathrm{3}}$/s (D$_{\mathrm{2}}$Cl$^{\mathrm{+}})$, each with $\sim$ 35{\%} accuracy. The DR rate coefficient for DCl$+$ is too slow for us to measure, especially in the face of dealing with mixed H/D species formed in apparatus feedlines when introducing DCl. Novotn\'{y}, et al.$^{\mathrm{2}}$ have carried out storage ring measurements in Heidelberg on this problem and will soon report new results over a wide electron energy range and including neutral product information. \\ \\$1.$ D. A. Neufeld and M. G. Wolfire, Astrophys. J. \textbf{706}, 1594 (2009).\newline 2. O. Novotn\'{y}, et al., Astrophys. J. \textbf{777}, 54 (2013).