A1 Refereed original research article in a scientific journal
Ortho-para conversion in solid hydrogen catalyzed by O-2 impurities
Authors: Shevtsov V, Malmi P, Ylinen E, Punkkinen M
Publisher: ELSEVIER SCIENCE BV
Publication year: 2000
Journal:: Physica B: Condensed Matter
Journal name in source: PHYSICA B
Journal acronym: PHYSICA B
Volume: 284
First page : 385
Last page: 386
Number of pages: 2
ISSN: 0921-4526
DOI: https://doi.org/10.1016/S0921-4526(99)02777-5
Abstract
The ortho-para conversion in solid H-2 doped with less than 0.1% of O-2 impurities is studied by pulsed NMR between 1.5 and 10.9 K. The rate of O-2-catalyzed conversion (CC) reveals remarkable temperature dependence with three distinct regions. For T > 8 K the CC rate is almost temperature independent and is limited by the conversion time tau(cc) = 10.5 s of the ortho-H-2 neighbors nearest to an O-2 impurity. Within 4.6 < T < 7 K the ortho-Hz diffusion (proceeding, most probably, via tunneling to nearby vacancy positions) determines the CC rate, resulting in an activation-type variation with temperature. However, at T < 4 K the temperature dependence of the rate becomes much weaker again, and that may be ascribed to another mechanism of ortho-H-2 diffusion. (C) 2000 Published by Elsevier Science B.V. All rights reserved.
The ortho-para conversion in solid H-2 doped with less than 0.1% of O-2 impurities is studied by pulsed NMR between 1.5 and 10.9 K. The rate of O-2-catalyzed conversion (CC) reveals remarkable temperature dependence with three distinct regions. For T > 8 K the CC rate is almost temperature independent and is limited by the conversion time tau(cc) = 10.5 s of the ortho-H-2 neighbors nearest to an O-2 impurity. Within 4.6 < T < 7 K the ortho-Hz diffusion (proceeding, most probably, via tunneling to nearby vacancy positions) determines the CC rate, resulting in an activation-type variation with temperature. However, at T < 4 K the temperature dependence of the rate becomes much weaker again, and that may be ascribed to another mechanism of ortho-H-2 diffusion. (C) 2000 Published by Elsevier Science B.V. All rights reserved.
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