Herschel/HIFI discovery of interstellar chloronium (H2Cl+)

We report the first detection of chloronium, H2Cl+, in the interstellar medium, using the HIFI instrument aboard the Herschel Space Observatory. The 212-101 lines of ortho-H_235Cl+ and ortho-H_237Cl+ are detected in absorption towards NGC 6334I, and the 111-000 transition of para-H_235Cl+ is detected in absorption towards NGC 6334I and Sgr B2(S). The H2Cl+ column densities are compared to those of the chemically-related species HCl. The derived HCl/H2Cl+ column density ratios, ~1-10, are within the range predicted by models of diffuse and dense photon dominated regions (PDRs). However, the observed H2Cl+ column densities, in excess of 1013 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. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Table 1 and acknowledgments (page 5) are only available in electronic form at http://www.aanda.org

P. Hennebelle | K. Menten | H. Müller | P. Caselli | M. Pérault | T. Henning | D. Johnstone | P. Encrenaz | J. L. Bourlot | F. Petit | C. Joblin | J. Goicoechea | A. Tielens | D. Hollenbach | A. Fuente | M. Gerin | E. Bergin | T. Bell | J. Black | M. Kaufman | V. Ossenkopf | È. Roueff | J. Stutzki | S. Viti | Z. Nagy | C. Vastel | J. Cernicharo | D. Lis | G. Blake | F. Helmich | E. Falgarone | P. Martin | J. Murphy | M. Dubernet | S. Schlemmer | V. Wakelam | D. Li | P. Goldsmith | T. Phillips | C. Comito | N. Crockett | P. Schilke | S. Wang | E. Caux | S. Cabrit | C. Ceccarelli | F. Daniel | M. Emprechtinger | T. Giesen | H. Gupta | E. Herbst | W. Langer | S. Lord | S. Maret | G. Melnick | P. Morris | D. Neufeld | L. Pagani | J. Pearson | R. Plume | S. Qin | M. Salez | N. Trappe | F. D. Tak | H. Yorke | S. Yu | J. Zmuidzinas | A. Klotz | R. Liseau | A. Benz | J. Krieg | R. Snell | E. Dishoeck | R. Güsten | P. Saraceno | F. Wyrowski | B. Lefloch | B. Parise | C. Kahane | R. Gusten | K. Schuster | M. Benedettini | J. Pearson | C. Codella | A. Walters | Å. Hjalmarson | B. Larsson | A. Lorenzani | C. Dominic | M. Wiel | P. Hily-Blant | A. Bacmann | A. Sandqvist | Y. Delorme | A. Baudry | H. Muller | A. Coutens | A. Boogert | M. Kama | B. Nisini | S. Bottinelli | B. Delforge | S. Pacheco | A. Hjalmarson | K. Demyk | A. Castets | N. Crimier | M. P'erault | T. Jack | J. Desbat | J. Stutzki | T. Phillips | S. Yu | H. Gupta | A. Tielens | Shanshan Yu | F. V. D. Tak | C. Dominic | Di Li

[1]  P. Hennebelle,et al.  The distribution of water in the high-mass star-forming region NGC 6334 I , 2010, 1007.4226.

[2]  P. Hennebelle,et al.  Herschel/HIFI observations of spectrally resolved methylidyne signatures toward the high-mass star-forming core NGC 6334I , 2010, 1007.1539.

[3]  K. Menten,et al.  Herschel observations of ortho- and para-oxidaniumyl (H2O+) in spiral arm clouds toward Sagittarius B2(M) , 2010, 1007.0670.

[4]  S. Ott,et al.  Herschel Space Observatory - An ESA facility for far-infrared and submillimetre astronomy , 2010, 1005.5331.

[5]  M. Wolfire,et al.  THE CHEMISTRY OF INTERSTELLAR MOLECULES CONTAINING THE HALOGEN ELEMENTS , 2009, 0910.1927.

[6]  S. Schlemmer,et al.  Torsion-rotational spectra within the vibrational ground state , 2009 .

[7]  A. Benz,et al.  MULTIDIMENSIONAL CHEMICAL MODELING OF YOUNG STELLAR OBJECTS. II. IRRADIATED OUTFLOW WALLS IN A HIGH-MASS STAR-FORMING REGION , 2009 .

[8]  D. York,et al.  Chlorine in the Galactic Interstellar Medium: Revised f-Values with the Far Ultraviolet Spectroscopic Explorer and the Space Telescope Imaging Spectrograph , 2006 .

[9]  K. Menten,et al.  Millimeter Multiplicity in NGC 6334 I and I(N) , 2006, astro-ph/0605468.

[10]  Holger S. P. Müller,et al.  The Cologne Database for Molecular Spectroscopy, CDMS: a useful tool for astronomers and spectroscopists , 2005 .

[11]  C. Kramer,et al.  The Herschel-Heterodyne Instrument for the Far-Infrared (HIFI) , 2005, Infrared and Millimeter Waves, Conference Digest of the 2004 Joint 29th International Conference on 2004 and 12th International Conference on Terahertz Electronics, 2004..

[12]  Peter Schilke,et al.  Reconstructing reality: Strategies for sideband deconvolution , 2002 .

[13]  D. Lis,et al.  Atomic Oxygen Abundance in Molecular Clouds: Absorption toward Sagittarius B2 , 2001 .

[14]  S. Saito,et al.  Submillimeter-Wave Spectra of H2Cl+ and its Isotopic Species: Molecular Structure , 2001 .

[15]  K. Brooks,et al.  Ground-state OH observations towards NGC 6334 , 2000, astro-ph/0010399.

[16]  P. Mürtz,et al.  Measurement of high-frequency rotational transitions of H2O+ in its ground state by far-infrared laser magnetic resonance (LMR) spectroscopy , 1998 .

[17]  Holger S. P. Müller,et al.  THE COLOGNE DATABASE FOR MOLECULAR SPECTROSCOPY, CDMS , 2001 .

[18]  W. Langer,et al.  Hydrogen Chloride Detection in Orion A and Monoceros R2 and , 1996 .

[19]  J. Carlstrom,et al.  HCl Absorption toward Sagittarius B2 , 1995, The Astrophysical journal.

[20]  David L. Lambert,et al.  Vibrationally excited H2, HCl and NO+ in the diffuse clouds toward zeta Ophiuchi , 1995 .

[21]  T. Phillips,et al.  Hydrogen chloride in OMC-1 , 1995 .

[22]  J. Dickey,et al.  Cold atomic gas in the inner Galaxy , 1989 .

[23]  John H. Black,et al.  Comprehensive models of diffuse interstellar clouds : physical conditions and molecular abundances , 1986 .

[24]  G. Blake,et al.  Chemistry of Chlorine in Dense Interstellar Clouds , 1986 .

[25]  G. Blake,et al.  Chlorine in dense interstellar clouds : the abundance of HCl in OMC-1. , 1985 .

[26]  H. Müller,et al.  Submillimeter, millimeter, and microwave spectral line catalog. , 1985, Applied optics.

[27]  B. Draine Photoelectric heating of interstellar gas , 1978 .

[28]  J. Black,et al.  Hydrogen Chloride in Dense Interstellar Clouds , 1974 .

[29]  M. Jura Chlorine-bearing molecules in interstellar clouds , 1974 .

[30]  A. Dymanus,et al.  Magnetic properties and molecular quadrupole moment of HF and HCl by molecular-beam electric-resonance spectroscopy , 1973 .

[31]  Charles A. Burrus,et al.  One-to-Two Millimeter Wave Spectroscopy. II.H2S , 1953 .