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Chapter: 3 Chemistry
    Section: 3.8 Molecular spectroscopy
        SubSection: 3.8.3 Nuclear spin relaxation time

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3.8.3 Nuclear spin relaxation time

When a material is in thermal equilibrium, the nuclear spins are either randomly oriented or have a distribution of orientations related to the crystal structure. This equilibrium distribution of nuclear spins may be altered by various re-orienting processes, but after such a process is removed the spin orientations (and hence the nuclear magnetization of the sample) will revert to their original equilibrium distribution exponentially with time. The time constant for this reversion is known as the spin-lattice relaxation time, τ. Relaxation times are usually temperature sensitive but are not very dependent on magnetic field. In the table a magnetic field of about 1 tesla (10 kilogauss) is assumed and the temperature T, or temperature range of the observations, is listed. The relaxation times in insulating diamagnetic materials are often very much reduced if paramagnetic impurities are present.

Nuclide

 Material

  τ/s

T/K

 

 

 

 

1H

   H2 (gas, 10 atm)

   0.015

293

1H

   H2 (liquid, 75% ortho)

   0.017

  20

1H

   H2O (liquid)

   2.8

293

1H

   H2O (solid)

   20

263

1H

   C6H6 (benzene, liquid)

   15

293

1H

   Polyethylene (solid)

   0.9

295

1D

   D2O (liquid)

   0.36

293

3He

   3He (liquid)

   550

   3

7Li

   LiF (solid)

   300

293

7Li

   Li (solid)

   45 /(T/K)

  1–300

13C

   C6H6 (benzene, liquid)

   23

310

13C

   Polyethylene (solid)

   0.24

298

17O

   H2O (liquid)

   0.0059

293

19F

   LiF (solid)

   120

293

23Na

   NaCl (solid)

   12

293

23Na

   Na (solid)

   4.9/(T/K)

  1–300

27Al

   Al (solid)

   1.82/(T/K)

  1–900

29Si

   Si (solid)

   2 × 104

293

31P

   P (white)

   20

300

31P

   P (red or black)

   300

300

35Cl

   NaCl (solid)

   6

293

51V

   V (solid)

   0.79/(T/K)

  20–290

63Cu

   Cu (solid)

   1.27/(T/K)

  1–300

69Ga

   GaAs (solid)

   0.27

293

109Ag

   Ag (solid)

   9/(T/K)

1–4

115In

   InSb (solid)

   0.05

298

127I

   KI (solid)

   0.04

293

195Pt

   Pt (solid)

   0.032 /(T/K)

  0.5–290

197Au

   Au (solid)

   4.0/(T/K)

1–4

 

 

 

 




References

A. Abragam (1961) The Principles of Nuclear Magnetism, Oxford University Press.

L.E.Drain

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