Universität zu Köln

Lis, Dariusz C., Bergin, Edwin A., Schilke, Peter and van Dishoeck, Ewine F. (2013). Ortho-to-Para Ratio in Interstellar Water on the Sight line toward Sagittarius B2(N). J. Phys. Chem. A, 117 (39). S. 9661 - 9666. WASHINGTON: AMER CHEMICAL SOC. ISSN 1520-5215

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Abstract

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:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Lis, Dariusz C. UNSPECIFIED UNSPECIFIED UNSPECIFIED Bergin, Edwin A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Schilke, Peter UNSPECIFIED UNSPECIFIED UNSPECIFIED van Dishoeck, Ewine F. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-474226
DOI:	10.1021/jp312333n
Journal or Publication Title:	J. Phys. Chem. A
Volume:	117
Number:	39
Page Range:	S. 9661 - 9666
Date:	2013
Publisher:	AMER CHEMICAL SOC
Place of Publication:	WASHINGTON
ISSN:	1520-5215
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language HERSCHEL; PHOTODESORPTION; MOLECULES; AMMONIA; VAPOR; ICE Multiple languages Chemistry, Physical; Physics, Atomic, Molecular & Chemical Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/47422