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Mechanisms of dipolar ortho/para-H2O conversion in ice

Buntkowsky, G. and Limbach, H. H. and Walaszek, B. and Adamczyk, A. and Xu, Y. and Breitzke, H. and Schweitzer, A. and Gutmann, T. and Wächtler, M. and Frydel, J. and Emmler, T. and Amadeu, N. and Tietze, D. and Chaudret, B. (2008):
Mechanisms of dipolar ortho/para-H2O conversion in ice.
In: Zeitschrift Fur Physikalische Chemie-International Journal of Research in Physical Chemistry & Chemical Physics, pp. 1049-1063, 222, (7), [Online-Edition: http://apps.webofknowledge.com/full_record.do?product=WOS&se...],
[Article]

Abstract

In this paper a possible explanation for an unexpected ortho/para-water ratio in the gas clouds of comets is given. The description is based on the quantum-mechanical density matrix formalism and the spin temperature concept. Only the nuclear spin system is treated quantum-mechanically. Employing the model of a four spin system, created by two nearest neighbour water molecules, spin eigenstates and their dynamics under the influence of their mutual dipolar interactions are studied. It is shown that a fast conversion between ortho- and para-states occurs on a msec time scale, caused by the intermolecular homonuclear magnetic dipolar interaction. Moreover the spin eigenstates of water in an ice crystal are determined by magnetic dipolar interactions and are not given by normal ortho- and para-H2O states of gaseous water. As a result of this the spin temperature of gaseous water evaporated from ice depends strongly on its evaporation history and the ortho/para-ratio of water molecules are only an indirect measure of the temperature of ice crystals from where they descend. This result could explain the unexpected experimentally observed ortho/para-ratios in the clouds of comets.

Item Type: Article
Erschienen: 2008
Creators: Buntkowsky, G. and Limbach, H. H. and Walaszek, B. and Adamczyk, A. and Xu, Y. and Breitzke, H. and Schweitzer, A. and Gutmann, T. and Wächtler, M. and Frydel, J. and Emmler, T. and Amadeu, N. and Tietze, D. and Chaudret, B.
Title: Mechanisms of dipolar ortho/para-H2O conversion in ice
Language: English
Abstract:

In this paper a possible explanation for an unexpected ortho/para-water ratio in the gas clouds of comets is given. The description is based on the quantum-mechanical density matrix formalism and the spin temperature concept. Only the nuclear spin system is treated quantum-mechanically. Employing the model of a four spin system, created by two nearest neighbour water molecules, spin eigenstates and their dynamics under the influence of their mutual dipolar interactions are studied. It is shown that a fast conversion between ortho- and para-states occurs on a msec time scale, caused by the intermolecular homonuclear magnetic dipolar interaction. Moreover the spin eigenstates of water in an ice crystal are determined by magnetic dipolar interactions and are not given by normal ortho- and para-H2O states of gaseous water. As a result of this the spin temperature of gaseous water evaporated from ice depends strongly on its evaporation history and the ortho/para-ratio of water molecules are only an indirect measure of the temperature of ice crystals from where they descend. This result could explain the unexpected experimentally observed ortho/para-ratios in the clouds of comets.

Journal or Publication Title: Zeitschrift Fur Physikalische Chemie-International Journal of Research in Physical Chemistry & Chemical Physics
Volume: 222
Number: 7
Uncontrolled Keywords: ortho para-water spin temperature dipolar interaction comets ice parahydrogen-induced polarization transition-metal dihydrides situ phip-nmr homogeneous hydrogenation stereoselective hydrogenation magnetic-resonance spin polarization comet p/halley water masers complexes
Divisions: 07 Department of Chemistry
07 Department of Chemistry > Physical Chemistry
Date Deposited: 27 Oct 2014 20:37
Official URL: http://apps.webofknowledge.com/full_record.do?product=WOS&se...
Additional Information:

353IF Times Cited:23 Cited References Count:52

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