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Ortho-to-Para Ratio in Interstellar Water on the Sight line toward Sagittarius B2(N)

Lis, Dariusz C. and Bergin, Edwin A. and Schilke, Peter and van Dishoeck, Ewine F. (2013) Ortho-to-Para Ratio in Interstellar Water on the Sight line toward Sagittarius B2(N). Journal of Physical Chemistry A, 117 (39). pp. 9661-9665. ISSN 1089-5639.

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The determination of the water ortho-to-para ratio (OPR) is of great interest for studies of the formation and thermal history of water ices in the interstellar medium and protoplanetary disk environments. We present new Herschel observations of the fundamental rotational transitions of ortho- and para-water on the sightline toward Sagittarius B2(N), which allow improved estimates of the measurement uncertainties due to instrumental effects and assumptions about the excitation of water molecules. These new measurements, suggesting a spin temperature of 24–32 K, confirm the earlier findings of an OPR below the high-temperature value on the nearby sightline toward Sagittarius B2(M). The exact implications of the low OPR in the galactic center molecular gas remain unclear and will greatly benefit from future laboratory measurements involving water freeze-out and evaporation processes under low-temperature conditions, similar to those present in the galactic interstellar medium. Given the specific conditions in the central region of the Milky Way, akin to those encountered in active Galactic nuclei, gas-phase processes under the influence of strong X-ray and cosmic ray ionization also have to be carefully considered. We summarize some of the latest laboratory measurements and their implications here.

Item Type:Article
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URLURL TypeDescription DOIArticle
Lis, Dariusz C.0000-0002-0500-4700
van Dishoeck, Ewine F.0000-0001-7591-1907
Additional Information:© 2013 American Chemical Society. Received: December 14, 2012; Revised: May 8, 2013; Published: May 8, 2013. HIFI has been designed and built by a consortium of institutes and university departments from across Europe, Canada, and the United States under the leadership of SRON Netherlands Institute for Space Research, Groningen, The Netherlands and with major contributions from Germany, France, and the US. Consortium members are: Canada: CSA, U. Waterloo; France: CESR, LAB, LERMA, IRAM; Germany: KOSMA, MPIfR, MPS; Ireland, NUI Maynooth; Italy: ASI, IFSI-INAF, Osservatorio Astrofisico di Arcetri-INAF; Netherlands: SRON, TUD; Poland: CAMK, CBK; Spain: Observatorio Astronómico Nacional (IGN), Centro de Astrobiologa (CSICINTA); Sweden: Chalmers University of Technology − MC2, RSS & GARD; Onsala Space Observatory; Swedish National Space Board, Stockholm University − Stockholm Observatory; Switzerland: ETH Zurich, FHNW; USA: Caltech, JPL, NHSC. Support for this work was provided by NASA through an award issued by JPL/Caltech.
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Issue or Number:39
Record Number:CaltechAUTHORS:20131204-140624558
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Official Citation:Ortho-to-Para Ratio in Interstellar Water on the Sightline toward Sagittarius B2(N) Dariusz C. Lis, Edwin A. Bergin, Peter Schilke, and Ewine F. van Dishoeck The Journal of Physical Chemistry A 2013 117 (39), 9661-9665
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42834
Deposited By: Tony Diaz
Deposited On:05 Dec 2013 00:43
Last Modified:03 Oct 2019 06:02

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