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A Microfluidic Approach for the Study of Ice and Clathrate Hydrate Crystallization
Published on: August 18, 2022
Hydrogen nuclear spin relaxation in hydrogen-ice clathrate
Lasitha Senadheera1, Mark S Conradi
1Department of Physics, Washington University, One Brookings Drive, Saint Louis, Missouri 63130, USA.
The Journal of Physical Chemistry. A
|August 20, 2008
Summary
Hydrogen-2 (H2) in deuterium-oxide (D2O) ice clathrates exhibits unique relaxation dynamics. Nuclear magnetic resonance (NMR) reveals temperature-dependent relaxation times influenced by phonon interactions and molecular hopping.
Area of Science:
- Solid-state physics
- Materials science
- Quantum chemistry
Background:
- Previous studies identified line broadening in H2 clathrate spectra due to intramolecular dipolar interactions.
- Understanding molecular dynamics in clathrate hydrates is crucial for various scientific fields.
Purpose of the Study:
- To investigate the relaxation dynamics of H2 molecules within D2O ice clathrates.
- To elucidate the mechanisms governing H2 rotational transitions and molecular mobility.
Main Methods:
- Proton nuclear magnetic resonance (NMR) spectroscopy was employed.
- Measurements included spin-lattice relaxation time (T1), spin-lattice relaxation time in the rotating frame (T1rho), and spin-spin relaxation time (T2).
Main Results:
- T1 relaxation time showed a minimum at 10 K, attributed to resonant rotational transitions driven by a two-phonon process.
- T2 relaxation was largely temperature-independent, consistent with intermolecular interactions.
- T1rho revealed an additional slow-motion relaxation source above 85 K, linked to H2 hopping between clathrate cages.
- Ortho-para conversion of H2 was significantly slower in clathrates than in bulk solid H2.
Conclusions:
- The rotational dynamics of H2 in D2O clathrates are governed by phonon-mediated processes and cage hopping.
- H2 molecular mobility and ortho-para conversion are restricted within the clathrate structure.
- NMR relaxation measurements provide valuable insights into guest molecule dynamics in clathrate hydrates.
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