A1 Refereed original research article in a scientific journal
High-temperature limit for the O-2-catalyzed ortho-para conversion rate in solid hydrogen
Authors: Shevtsov V, Malmi P, Ylinen E, Punkkinen M
Publisher: KLUWER ACADEMIC/PLENUM PUBL
Publication year: 1999
Journal:: Journal of Low Temperature Physics
Journal name in source: JOURNAL OF LOW TEMPERATURE PHYSICS
Journal acronym: J LOW TEMP PHYS
Volume: 114
Issue: 5-6
First page : 431
Last page: 444
Number of pages: 14
ISSN: 0022-2291
DOI: https://doi.org/10.1023/A:1021802220741
Abstract
Ortho-para conversion in solid hydrogen doped with small concentration of molecular oxygen (100 and 1000 ppm) was studied by pulsed NMR in the temperature range 4.2-10.9 K. Conversion rate was mainly determined by the paramagnetic oxygen impurities. The catalyzed conversion rate constant increases with temperature in the range 4.2-8 K and becomes independent of temperature above 8 K. The high-temperature limit is 1.15(8) s(-1). The catalyzed conversion rate was shown to become temperature independent when the ortho-H-2 diffusion time tau d falls below the conversion time tau(cc) in the first coordination sphere of O-2 impurity. The obtained value of tau(cc) = 10.5(8)s was used to identify the position of O-2 in H-2 lattice as substitutional. The temperature dependence of the ortho-H-2 diffusion rate near the high temperature limit was determined.
Ortho-para conversion in solid hydrogen doped with small concentration of molecular oxygen (100 and 1000 ppm) was studied by pulsed NMR in the temperature range 4.2-10.9 K. Conversion rate was mainly determined by the paramagnetic oxygen impurities. The catalyzed conversion rate constant increases with temperature in the range 4.2-8 K and becomes independent of temperature above 8 K. The high-temperature limit is 1.15(8) s(-1). The catalyzed conversion rate was shown to become temperature independent when the ortho-H-2 diffusion time tau d falls below the conversion time tau(cc) in the first coordination sphere of O-2 impurity. The obtained value of tau(cc) = 10.5(8)s was used to identify the position of O-2 in H-2 lattice as substitutional. The temperature dependence of the ortho-H-2 diffusion rate near the high temperature limit was determined.
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