Herschel/HIFI discovery of interstellar chloronium (H$_2$Cl$^+$)
Creators: name: Lis, D. C.
name: Pearson, J. C.
name: Neufeld, D. A.
name: Schilke, P.
name: Müller, H. S. P.
name: Gupta, H.
name: Bell, T. A.
name: Comito, C.
name: Phillips, T. G.
name: Bergin, E. A.
name: Ceccarelli, C.
name: Goldsmith, P. F.
name: Blake, G. A.
name: Bacmann, A.
name: Baudry, A.
name: Benedettini, M.
name: Benz, A.
name: Black, J.
name: Boogert, A.
name: Bottinelli, S.
name: Cabrit, S.
name: Caselli, P.
name: Castets, A.
name: Caux, E.
name: Cernicharo, J.
name: Codella, C.
name: Coutens, A.
name: Crimier, N.
name: Crockett, N. R.
name: Daniel, F.
name: Demyk, K.
name: Dominic, C.
name: Dubernet, M. -L.
name: Emprechtinger, M.
name: Encrenaz, P.
name: Falgarone, E.
name: Fuente, A.
name: Gerin, M.
name: Giesen, T. F.
name: Goicoechea, J. R.
name: Helmich, F.
name: Hennebelle, P.
name: Henning, Th.
name: Herbst, E.
name: Hily-Blant, P.
name: Hjalmarson, Å.
name: Hollenbach, D.
name: Jack, T.
name: Joblin, C.
name: Johnstone, D.
name: Kahane, C.
name: Kama, M.
name: Kaufman, M.
name: Klotz, A.
name: Langer, W. D.
name: Larsson, B.
name: Bourlot, J. Le
name: Lefloch, B.
name: Petit, F. Le
name: Li, D.
name: Liseau, R.
name: Lord, S. D.
name: Lorenzani, A.
name: Maret, S.
name: Martin, P. G.
name: Melnick, G. J.
name: Menten, K. M.
name: Morris, P.
name: Murphy, J. A.
name: Nagy, Z.
name: Nisini, B.
name: Ossenkopf, V.
name: Pacheco, S.
name: Pagani, L.
name: Parise, B.
name: Pérault, M.
name: Plume, R.
name: Qin, S. -L.
name: Roueff, E.
name: Salez, M.
name: Sandqvist, A.
name: Saraceno, P.
name: Schlemmer, S.
name: Schuster, K.
name: Snell, R.
name: Stutzki, J.
name: Tielens, A.
name: Trappe, N.
name: van der Tak, F. F. S.
name: van der Wiel, M. H. D.
name: van Dishoeck, E.
name: Vastel, C.
name: Viti, S.
name: Wakelam, V.
name: Walters, A.
name: Wang, S.
name: Wyrowski, F.
name: Yorke, H. W.
name: Yu, S.
name: Zmuidzinas, J.
name: Delorme, Y.
name: Desbat, J. -P.
name: Güsten, R.
name: Krieg, J. -M.
name: Delforge, B.
Publisher: name: arXiv
Year: 2010
Subjects: subject: Astrophysics of Galaxies (astro-ph.GA)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: We report the first detection of chloronium, H$_2$Cl$^+$, in the interstellar medium, using the HIFI instrument aboard the \emph{Herschel} Space Observatory. The $2_{12}-1_{01}$ lines of ortho-H$_2^{35}$Cl$^+$ and ortho-H$_2^{37}$Cl$^+$ are detected in absorption towards NGC~6334I, and the $1_{11}-0_{00}$ transition of para-H$_2^{35}$Cl$^+$ is detected in absorption towards NGC~6334I and Sgr~B2(S). The H$_2$Cl$^+$ column densities are compared to those of the chemically-related species HCl. The derived HCl/H$_2$Cl$^+$ column density ratios, $\sim$1--10, are within the range predicted by models of diffuse and dense Photon Dominated Regions (PDRs). However, the observed H$_2$Cl$^+$ column densities, in excess of $10^{13}$~cm$^{-2}$, are significantly higher than the model predictions. Our observations demonstrate the outstanding spectroscopic capabilities of HIFI for detecting new interstellar molecules and providing key constraints for astrochemical models.
description: Accepted for publication in A&amp;A, HIFI Special Issue; 4 pages, 2 figures, 1 table