NMR spin-rotation relaxation and diffusion of methane

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dc.citation.articleNumber204504en_US
dc.citation.journalTitleThe Journal of Chemical Physicsen_US
dc.citation.volumeNumber148en_US
dc.contributor.authorSinger, P.M.en_US
dc.contributor.authorAsthagiri, D.en_US
dc.contributor.authorChapman, W.G.en_US
dc.contributor.authorHirasaki, G.J.en_US
dc.date.accessioned2018-09-11T20:40:46Zen_US
dc.date.available2018-09-11T20:40:46Zen_US
dc.date.issued2018en_US
dc.description.abstractThe translational diffusion-coefficient and the spin-rotation contribution to the 1H NMR relaxation rate for methane (CH4) are investigated using MD (molecular dynamics) simulations, over a wide range of densities and temperatures, spanning the liquid, supercritical, and gas phases. The simulated diffusion-coefficients agree well with measurements, without any adjustable parameters in the interpretation of the simulations. A minimization technique is developed to compute the angular velocity for non-rigid spherical molecules, which is used to simulate the autocorrelation function for spin-rotation interactions. With increasing diffusivity, the autocorrelation function shows increasing deviations from the single-exponential decay predicted by the Langevin theory for rigid spheres, and the deviations are quantified using inverse Laplace transforms. The 1H spin-rotation relaxation rate derived from the autocorrelation function using the “kinetic model” agrees well with measurements in the supercritical/gas phase, while the relaxation rate derived using the “diffusion model” agrees well with measurements in the liquid phase. 1H spin-rotation relaxation is shown to dominate over the MD-simulated 1H-1H dipole-dipole relaxation at high diffusivity, while the opposite is found at low diffusivity. At high diffusivity, the simulated spin-rotation correlation time agrees with the kinetic collision time for gases, which is used to derive a new expression for 1H spin-rotation relaxation, without any adjustable parameters.en_US
dc.identifier.citationSinger, P.M., Asthagiri, D., Chapman, W.G., et al.. "NMR spin-rotation relaxation and diffusion of methane." <i>The Journal of Chemical Physics,</i> 148, (2018) AIP: https://doi.org/10.1063/1.5027097.en_US
dc.identifier.doihttps://doi.org/10.1063/1.5027097en_US
dc.identifier.urihttps://hdl.handle.net/1911/102502en_US
dc.language.isoengen_US
dc.publisherAIPen_US
dc.rightsArticle is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.en_US
dc.titleNMR spin-rotation relaxation and diffusion of methaneen_US
dc.typeJournal articleen_US
dc.type.dcmiTexten_US
dc.type.publicationpublisher versionen_US
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