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Is liquid water's relaxation rate strongly dependent on temperature, and does anyone have a link to a good online article with the dependency equation? Thanks!

asked Dec 22 '11 at 14:45

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plshelp
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Indeed, there is a strong temperature dependence. If we are to speak about the normal hydrogenated water (not the heavy water) the main source of relaxation arises from the dipole-dipole interactions of protons with: 1) each other 2) protons from other molecules. In water the distance between the protons is relatively small and thus a solid water creates even a Pake-powder pattern, with splitting ~ 30 kHz. Other molecules induce only a broadening of the solid spectrum. Hence the relaxation will be governed by the intramolecular dipolar interaction with D~30kHz, T^(-1) ~ D^(2) This interaction is modulated mainly by the mobility of the water molecules: even in liquid water these are quasi-isotropic jumps of the O-H bond orientation over tetrahedral lattice. In H2O these jumps have the activation barrier of ~ 13 kJ/mol. Thus the temperature dependence will be quite pronounced already. But the situation is even more difficult as at high temperatures the signs of formation of a 5-molecules complex begin to influence the relaxation. This process actually occurs in liquid water and it is characterized by the activation barrier of ~ 40-50 kJ/mol. So it affects the spin relaxation only at high temperatures (above 70 C if i recall correctly) If you are interested in the subject: the very first papers are the seria of nice works by Hindman and co-authors. It is pretty old already, and purely liquid NMR. In 1889 Wittebort and co-authors published a very nice solid-state 1H and 2H NMR paper on water dynamics in ice, in which experimental evidences and spectra simulations are given. The latter study correlates with Hindman findings. Another hint about water -since the main relaxation mechanism is the water microscopic mobility, one could expect that the temperature dependence of the spin relaxation will be correlated with the temperature dependence of the viscosity. The subject is nicely shown in Hindman papers, it is indeed impressive. To obtain the curve of the spin-lattice relaxation TD one just have to scale by a constant numerical factor the TD of the viscosity.

If you wish a formula the Hindman paper is for you - there the TD is fitted by a simple two-lorenzian approximation with two characteristic Arrhenius correlation times, one for the solo jumping and another for the mobility in a complex.

Hope it helped =)

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answered Dec 27 '11 at 03:39

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Daniil K
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updated Dec 27 '11 at 03:41

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The dominant relaxation mechanism for pure water magnetization at low and intermediate magnetic fields is the dipolar relaxation mechanism described in the earlier note by Daniil.

However, in Biomolecular NMR studies of water solutions, (which are usually carried out by using high magnetic fields and high-Q probes), other relaxation mechanisms may dominate, e.g., radiation damping. See the earlier discussion on radiation damping in this forum.

For some relevant data (but no equation) see the following paper: Journal of magnetic resonance. Series B 112 (2), 200. Note: the spectra described in this publication were for a solution of water containing a protein (not for pure water).

It is advisable to identify all the significant relaxation mechanisms before fitting the data to available equations.

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answered Jan 15 '12 at 09:57

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sekhar Talluri
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updated Jan 15 '12 at 09:58

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Asked: Dec 22 '11 at 14:45

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