Nuclear magnetic resonance relaxation time in CH₂I₂
Date
1974
Authors
Peemoeller, Hartwig
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Measurements of spin-lattice relaxation time, T₁, of protons in oxygen-free samples of 100% CH₂I₂, 80% CH₂I₂ - 20% CD₂I₂, 60% CH₂I₂ - 40% CD₂I₂, 40% CH₂I₂ - 60% CD₂I₂ and of deuterons in oxygen-free samples of CD₂I₂ have been carried out between 7 - 100°c at a frequency of 4 Mc/sec using pulse techniques.
The intermolecular dipole-dipole, intramolecular dipole-dipole and spin-rotational contributions have been separated. The results show that both the intramolecular dipole-dipole and intermolecular dipole-dipole contributions are temperature dependent and the intramolecular dipole-dipole interaction is predominant in causing relaxation. The contributions due to intramolecular dipole-dipole and intermolecular dipole-dipole interactions are found to be 67.5% and 32.5% of the total relaxation respectively between 7 - 100°c. The intra- and intermolecular dipole-dipole contributions due to interactions between non-identical spins are 5% of the intramolecular dipole-dipole contribution and 24% of the intermolecular dipole-dipole contribution respectively. The spin-rotational contribution is zero over the temperature range studied. The intermolecular dipole-dipole contribution calculated using the Bloembergen, Purcell and Pound theory, modified by Gierer and Wirtz to take into .account the finite size of the molecules, agrees with the experimental value to within 22%. The activation energies of the intramolecular dipole-dipole and intermolecular dipole-dipole contributions are 3.14 ± 0.03 kcal/mole and 3.13 ± 0.03 kcal/mole respectively. The activation energy obtained from the deuteron T₁ data is 3.07 ± 0.02 kcal/mole.
The rotational motion of this molecule appears to be anisotropic and the microviscosity theory for rotational diffusion seems to apply here. The rotational correlation times calculated from the Debye - BPP expression (4πηa³/3kT) differ from the experimental values by a factor of about 15. The correlation time of translational motion is about 3 times that of rotational motion and it appears that the molecule reorientates substantially while moving by a distance of the order of one molecular diameter.