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          Institute: MPI für medizinische Forschung     Collection: Forschungsgruppe Prof. Dr. Haeberlen     Display Documents

ID: 23100.0, MPI für medizinische Forschung / Forschungsgruppe Prof. Dr. Haeberlen
The dynamics of ND+4 and NH3D+ groups in ammonium persulphate studied by deuteron nuclear magnetic resonance. I. Tunneling and stochastic reorientations at low temperatures
Translation of Title:The dynamics of ND<sup>+</sup><sub>4</sub> and NH<sub>3</sub>D<sup>+</sup> groups in ammonium persulphate studied by deuteron nuclear magnetic resonance. I. Tunneling and stochastic reorientations at low temperatures
Authors:Olejniczak, Zbigniew; Lalowicz, Z. T.; Schmidt, T.; Zimmermann, Herbert; Haeberlen, Ulrich; Schmitt, Heike
Date of Publication (YYYY-MM-DD):2002-06-15
Title of Journal:Journal of Chemical Physics
Journal Abbrev.:J. Chem. Phys.
Issue / Number:23
Start Page:10343
End Page:10355
Review Status:Peer-review
Audience:Experts Only
Intended Educational Use:No
Abstract / Description:We report on a single-crystal deuteron nuclear magnetic resonance (NMR) spectroscopy study of the low-temperature dynamics of ND&frac+4; and NH3D+ ions in the title compound. The most prominent feature of the dynamics of ND&frac+4; ions is uniaxial rotational (primary) tunneling of three deuterons about the N–D bond of the fourth. At T<25 K, the latter deuteron gets localized on the time scale of 10-3 s. We identify the direction of this unique N–D bond. The low-temperature limit of the primary tunneling frequency is 1.6 MHz. In the form of splittings of NMR resonances, our spectra also contain clear evidence of secondary tunneling which, again, is uniaxial. Again we say about which of the other three N–D bonds it takes place. The secondary tunneling frequency is only 4.5 kHz. The deuteron of NH3D+ ions gets localized at T<25 K. It can reside in any of the four sites available to the hydrogens of the ion. The dynamics of the three protons depends strongly on which site the deuteron occupies. If it is the site which was identified as unique for ND&frac+4; ions, the protons reorient stochastically with a rate k>106 s-1. Very likely, they also undergo tunneling but the stochastic reorientations erase any tunneling features from the spectra. By contrast, if the deuteron occupies any other site, stochastic reorientations of the protons are slow and (proton) tunneling on the scale of 105 Hz can be identified. Finally, isotopic ordering is observed. The single deuteron of NH3D+ ions goes preferentially into the site identified as unique. Energetically, the preference amounts to 1 meV.
Comment of the Author/Creator:One of the authors (Z.T.L.) gratefully acknowledges an Alexander-von-Humboldt fellowship for an extended stay at the MPI in Heidelberg in the fall of 1998. Participation of Z.T.L. and Z.O. in this project was partially supported by the State Committee for Scientific Research (Poland), Grant No. 2 P03B 07415. We are grateful to A. Birczy[n-acute]ski for providing numerical solutions of the Mathieu equation. We enjoyed most fruitful discussions with Professor Zeev Luz from the Weizmann Institute of Science, and with Dr. A. Detken, now at the ETH, Zürich.
External Publication Status:published
Document Type:Article
Communicated by:Wulf Kaiser
Affiliations:MPI für medizinische Forschung/Abteilung Biophysik
MPI für medizinische Forschung/Abteilung Molekulare Neurobiologie
MPI für medizinische Forschung/Forschungsgruppe Molekülkristalle
Identifiers:URI:http://ojps.aip.org/journals/doc/JCPSA6-ft/vol_116... [Fulltext HTML]
URI:http://ojps.aip.org/getabs/servlet/GetabsServlet?p... [Abstract]
URI:http://ojps.aip.org/getpdf/servlet/GetPDFServlet?f... [Fulltext PDF]
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