Mechanism of nuclear spin initiated para-H2 to ortho-H2 conversion

Physical Chemistry Chemical Physics : PCCP
Gerd BuntkowskyBruno Chaudret

Abstract

In this paper a quantitative explanation for a diamagnetic ortho/para H2 conversion is given. The description is based on the quantum-mechanical density matrix formalism originally developed by Alexander and Binsch for studies of exchange processes in NMR spectra. Only the nuclear spin system is treated quantum-mechanically. Employing the model of a three spin system, the reactions of the hydrogen gas with the catalysts are treated as a phenomenological rate process, described by a rate constant. Numerical calculations reveal that for nearly all possible geometrical arrangements of the three spin system an efficient spin conversion is obtained. Only in the chemically improbable case of a linear group H-X-H no spin conversion is obtained. The efficiency of the spin conversion depends strongly on the lifetime of the H-X-H complex and on the presence of exchange interactions between the two hydrogens. Even moderate exchange couplings cause a quench of the spin conversion. Thus a sufficiently strong binding of the dihydrogen to the S spin is necessary to render the quenching by the exchange interaction ineffective.

References

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Citations

Apr 11, 2009·Solid State Nuclear Magnetic Resonance·Bernadeta WalaszekGerd Buntkowsky
Aug 16, 2017·Physical Chemistry Chemical Physics : PCCP·M EmondtsP P M Schleker
May 6, 2016·Physical Chemistry Chemical Physics : PCCP·Monika HartlGünter Muhrer
Sep 12, 2018·Applied Spectroscopy·Andrew J ParrottAlison Nordon
Dec 22, 2006·Chemphyschem : a European Journal of Chemical Physics and Physical Chemistry·Omar DeebTamar Seideman
Sep 4, 2019·Chemphyschem : a European Journal of Chemical Physics and Physical Chemistry·Andreas B SchmidtJan-Bernd Hövener
May 10, 2013·Chemphyschem : a European Journal of Chemical Physics and Physical Chemistry·Torsten GutmannGerd Buntkowsky
Jul 28, 2013·Chemical Communications : Chem Comm·Marco KörnerGerd Buntkowsky
Sep 22, 2019·Nitric Oxide : Biology and Chemistry·Zs KolbertJ T Hancock
Mar 7, 2021·Plants·John T Hancock, Grace Russell
Aug 21, 2008·Journal of the American Chemical Society·Elena SartoriNicholas J Turro
May 11, 2021·Chemphyschem : a European Journal of Chemical Physics and Physical Chemistry·Ekaterina V PokochuevaIgor V Koptyug
Jan 15, 2015·The Journal of Physical Chemistry. a·Danila A BarskiyIgor V Koptyug
Apr 6, 2007·Journal of the American Chemical Society·Igor V KoptyugRenad Z Sagdeev

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