A1 Refereed original research article in a scientific journal
Ortho-para conversion in solid hydrogen, catalyzed by molecular oxygen impurities
Authors: Shevtsov V, Scherbakov A, Malmi P, Ylinen E, Punkkinen M
Publisher: PLENUM PUBL CORP
Publication year: 1996
Journal:: Journal of Low Temperature Physics
Journal name in source: JOURNAL OF LOW TEMPERATURE PHYSICS
Journal acronym: J LOW TEMP PHYS
Volume: 104
Issue: 3-4
First page : 211
Last page: 235
Number of pages: 25
ISSN: 0022-2291
DOI: https://doi.org/10.1007/BF00754095
Abstract
Ortho-para conversion in solid hydrogen with small amounts of molecular oxygen as impurity (0.01-0.5%) was studied by NMR in the temperature range 4.2-7 K. The observed conversion rate was substantially greater than that of the natural conversion process in pure solid H-2 and revealed a strong dependence on temperature and the oxygen content in the sample. Obviously, the conversion is catalyzed by the large paramagnetic moments of O-2 impurities. Since the influence of O-2 is of very short range, the overall rate of the catalyzed conversion in the sample is determined by the relative diffusion of ortho-H-2 and the O-2 impurities. The diffusion coefficient was found to obey and Arrhenius behaviour D(T) = 3(2). 10(-11). exp[96(8)T] cm(2)s(-1). This temperature dependence is interpreted in terms of vacancy-particle exchange by quantum tunneling through the intervening barrier.
Ortho-para conversion in solid hydrogen with small amounts of molecular oxygen as impurity (0.01-0.5%) was studied by NMR in the temperature range 4.2-7 K. The observed conversion rate was substantially greater than that of the natural conversion process in pure solid H-2 and revealed a strong dependence on temperature and the oxygen content in the sample. Obviously, the conversion is catalyzed by the large paramagnetic moments of O-2 impurities. Since the influence of O-2 is of very short range, the overall rate of the catalyzed conversion in the sample is determined by the relative diffusion of ortho-H-2 and the O-2 impurities. The diffusion coefficient was found to obey and Arrhenius behaviour D(T) = 3(2). 10(-11). exp[96(8)T] cm(2)s(-1). This temperature dependence is interpreted in terms of vacancy-particle exchange by quantum tunneling through the intervening barrier.
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