===== The Detection of Chloronium, H2Cl+, in the Interstellar Medium ===== Chloronium has been detected in absorption with the //Herschel// satellite toward the star-forming regions NGC 6334I and Sagittarius B2(S):\\ D. C. Lis, J. C. Pearson, D. A. Neufeld, et al.\\ **[[https://doi.org/10.1051/0004-6361/201014959|//Herschel///HIFI Discovery of Interstellar Chloronium (H₂Cl⁺)]]**\\ //Astron. Astrophys.// **521**, (2010) Art. No. L9.\\ Three transitions have been detected toward NGC 6334I which show broadening by Cl hyperfine splitting and no recognizable absorption caused by spiral arm clouds. The 2₁₂ –1₀₁ transition of //ortho//-H₂Cl⁺ has been observed near 781.6 and 780.05 GHz for the ³⁵Cl and ³⁷Cl isotopologs, respectively. The 1₁₁ –0₀₀ transition of //para//-H₂³⁵Cl⁺ was observed near 485.4 GHz.\\ The absorption features near 485.4 and 780.05 GHz were both affected by emission features from dimethyl ether. A preliminary model for this molecule permitted accounting for these emmsion features in the analyses. This is a clear example that features by so-called "weed" species can affect "flowers" even in the case of //Herschel// observations. The recent report on the rotational spectroscopy of dimethyl ether by C. P. Endres et al., //Astron. Astrophys.// **504**, (2009) 635, were instrumental.\\ The 1₁₁ –0₀₀ transition of //para//-H₂³⁵Cl⁺, observed toward Sgr B2(S), displays absorption features of spiral arm clouds. More recently, H₂Cl⁺ has turned out to be rather widespread. The 1₁₁ –0₀₀ transition of the //para// species was observed with the //Herschel// satellite for both ³⁵Cl and ³⁷Cl isotopologs in absorption toward the strong contiunuum sources W31C and Sgr A (+50 km/s cloud). The transition was seen in emission in Orion S and in the photon-dominated region Orion Bar by:\\ D. A. Neufeld, E. Roueff, R. L. Snell, et al.\\ **[[https://doi.org/10.1088/0004-637X/748/1/37|//Herschel// Observations of Interstellar Chloronium]]**\\ //Astrophys. J.// **748**, (2012) Art. No. 37. ---- Contributor(s): H. S. P. Müller; 10, 2010; 3, 2012 ----