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Novel insights into the mechanism of the ortho/para spin conversion of hydrogen pairs: Implications for catalysis and interstellar water

Limbach, H. H. and Buntkowsky, G. and Mathes, J. and Gründemann, S. and Pery, T. and Walaszek, B. and Chaudret, B. (2006):
Novel insights into the mechanism of the ortho/para spin conversion of hydrogen pairs: Implications for catalysis and interstellar water.
7, In: Chemphyschem, (3), pp. 551-554, [Online-Edition: http://apps.webofknowledge.com/full_record.do?product=WOS&se...],
[Article]

Abstract

The phenomenon of exchange coupling is taken into account in the description of the magnetic nuclear spin conversion between bound ortho- and para-dihydrogen. This conversion occurs without bond breaking, in contrast to the chemical spin conversion. It is shown that the exchange coupling needs to be reduced so that the corresponding exchange barrier can increase and the given magnetic interaction can effectively induce a spin conversion. The implications for related molecules such as water are discussed. For ice, a dipolar magnetic conversion and for liquid water a chemical conversion are predicted to occur within the millisecond timescale. It follows that a separation of water into its spin isomers, as proposed by Tikhonov and Volkov (Science 2002, 296, 2363), is not feasible. Nuclear spin temperatures of water vapor in comets, which are smaller than the gas-phase equilibrium temperatures, are proposed to be diagnostic for the temperature of the ice or the dust surface from which the water was released.

Item Type: Article
Erschienen: 2006
Creators: Limbach, H. H. and Buntkowsky, G. and Mathes, J. and Gründemann, S. and Pery, T. and Walaszek, B. and Chaudret, B.
Title: Novel insights into the mechanism of the ortho/para spin conversion of hydrogen pairs: Implications for catalysis and interstellar water
Language: English
Abstract:

The phenomenon of exchange coupling is taken into account in the description of the magnetic nuclear spin conversion between bound ortho- and para-dihydrogen. This conversion occurs without bond breaking, in contrast to the chemical spin conversion. It is shown that the exchange coupling needs to be reduced so that the corresponding exchange barrier can increase and the given magnetic interaction can effectively induce a spin conversion. The implications for related molecules such as water are discussed. For ice, a dipolar magnetic conversion and for liquid water a chemical conversion are predicted to occur within the millisecond timescale. It follows that a separation of water into its spin isomers, as proposed by Tikhonov and Volkov (Science 2002, 296, 2363), is not feasible. Nuclear spin temperatures of water vapor in comets, which are smaller than the gas-phase equilibrium temperatures, are proposed to be diagnostic for the temperature of the ice or the dust surface from which the water was released.

Journal or Publication Title: Chemphyschem
Volume: 7
Number: 3
Uncontrolled Keywords: exchange coupling hydrogen interstellar chemistry spin conversion water chemistry induced polarization magnetic-resonance molecular-hydrogen h-2 nmr complexes exchange proton
Divisions: 07 Department of Chemistry
07 Department of Chemistry > Physical Chemistry
Date Deposited: 27 Oct 2014 20:44
Official URL: http://apps.webofknowledge.com/full_record.do?product=WOS&se...
Additional Information:

025XL Times Cited:42 Cited References Count:27

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