Hydrogen atom catalyzed ortho-to-para conversion in solid molecular hydrogen
| Autor: | K. L. Fillmore, Aaron I. Strom, David T. Anderson |
|---|---|
| Rok vydání: | 2019 |
| Předmět: |
010302 applied physics
Materials science Physics and Astronomy (miscellaneous) Hydrogen Kinetics Photodissociation General Physics and Astronomy chemistry.chemical_element Infrared spectroscopy Hydrogen atom 01 natural sciences Catalysis chemistry Solid hydrogen 0103 physical sciences Physical chemistry Molecule 010306 general physics |
| Zdroj: | Low Temperature Physics. 45:676-688 |
| ISSN: | 1090-6517 1063-777X |
| Popis: | Infrared spectroscopy is used to investigate the process of molecular hydrogen ortho-to-para (o/p) conversion in solid hydrogen samples doped with small concentrations (10–50 ppm) of hydrogen atoms (H-atoms) as an impurity. The H-atoms are generated using the in situ 193 nm photolysis of N2O dopant molecules. For hydrogen crystals with relatively low initial ortho-H2 fractions (Xo ≤ 0.03), the o/p conversion kinetics at temperatures of 1.8 and 4.0 K follow kinetic equations developed previously for H-atom catalyzed o/p conversion. The measured atom catalyzed o/p conversion kinetics indicates the H-atoms are mobile under these conditions in agreement with previous ESR measurements. It has been proposed that the H-atoms diffuse by a quantum tunneling mechanism that is described as chemical diffusion. Detailed fits of the measured o/p conversion kinetic data allow the initial H-atom concentration after photolysis to be extracted assuming literature values for the H-atom recombination rate constant (H + H → H2). The measured o/p conversion kinetics show the observed o/p conversion is much less than expected based on the previously measured H-atom recombination rate constant and thus suggest that the H-atoms do not diffuse randomly through the crystal but rather diffuse preferentially in regions of high para-hydrogen content. The estimated H-atom concentrations from this study are consistent with previous ESR measurements but in conflict with kinetic studies of H-atom reactions with various dopants such as N2O. |
| Databáze: | OpenAIRE |
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