Buntkowsky, G. ; Walaszek, B. ; Adamczyk, A. ; Xu, Y. ; Limbach, H. H. ; Chaudret, B. (2006)
Mechanism of nuclear spin initiated para-H-2 to ortho-H-2 conversion.
In: Physical Chemistry Chemical Physics, 8 (16)
Artikel, Bibliographie
Kurzbeschreibung (Abstract)
In this paper a quantitative explanation for a diamagnetic ortho/para H-2 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.
| Typ des Eintrags: | Artikel |
|---|---|
| Erschienen: | 2006 |
| Autor(en): | Buntkowsky, G. ; Walaszek, B. ; Adamczyk, A. ; Xu, Y. ; Limbach, H. H. ; Chaudret, B. |
| Art des Eintrags: | Bibliographie |
| Titel: | Mechanism of nuclear spin initiated para-H-2 to ortho-H-2 conversion |
| Sprache: | Englisch |
| Publikationsjahr: | 2006 |
| Titel der Zeitschrift, Zeitung oder Schriftenreihe: | Physical Chemistry Chemical Physics |
| Jahrgang/Volume einer Zeitschrift: | 8 |
| (Heft-)Nummer: | 16 |
| URL / URN: | http://apps.webofknowledge.com/full_record.do?product=WOS&se... |
| Kurzbeschreibung (Abstract): | In this paper a quantitative explanation for a diamagnetic ortho/para H-2 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. |
| Freie Schlagworte: | parahydrogen-induced polarization molecular-hydrogen complexes state nmr-spectroscopy situ phip-nmr homogeneous hydrogenation magnetic-resonance oxidative addition stereoselective hydrogenation pairwise addition line-shapes |
| Zusätzliche Informationen: | 032KB Times Cited:32 Cited References Count:56 |
| Fachbereich(e)/-gebiet(e): | 07 Fachbereich Chemie 07 Fachbereich Chemie > Eduard Zintl-Institut > Fachgebiet Physikalische Chemie |
| Hinterlegungsdatum: | 27 Okt 2014 20:38 |
| Letzte Änderung: | 28 Mai 2019 10:41 |
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