Spin-lattice magnetic relaxation times

Spin-lattice magnetic relaxation times T. on nuclei were measured at 25.15 MHz and 62.5 MHz using Jeol PS 100 and Bruker WP 250 spectrometers respectively. DMS0-d6 was used as an external lock. Tj was obtained from the 180 -t-90 sequence with an accuracy of 1 7,. 

The local dynamics of polymer chains can be studied by C NMR through measurements of J e spin-lattice magnetic relaxation time, T. The spin of a given relaxes by dipolar relaxation... 

In this paper we have investigated the segmental motions of bulk polybutadiene, in a temperature range hig r than (Tg + 60K), by using fluorescence anisotropy decay, and C spin-lattice magnetic relaxation time, Tp... 

Take a moment to look back at Figure 2.10. It shows how the magnitude of the z-component net magnetization vector M, when displaced from its Boltzmann equilibrium value, always recovers exponentially back to this equilibrium value at a rate determined by Th the spin-lattice (longitudinal) relaxation time. In this case, we will label this value Mq, the equilibrium magnitude of M in the magnetic field. Since the magnitude of M at any time (M,) is solely dependent on the difference between the populations of the up and down spin states, we can recast Eq. (2.9) in the form... 

There are several experimental tools available for the determination of the H-H distance and the degree of the H-H bonding interaction. Neutron diffraction studies provide an accurate measure of the H-H distance. The measurement of the spin-lattice proton relaxation time, Ti, for an tf -V 2 complex or the proton-deuteron couphng constant, Jhd. for the corresponding isotopically substituted rf -WT) complex via H nuclear magnetic resonance (NMR) spectroscopy provides a quantitative measure of the H-H distance. The frequency of the v(H-H) stretching band, as determined by Raman or infrared (IR) spectroscopy of / -H2 complexes provides semiquantitative information about the strength of the H-H interaction. 

After application of the RF energy the magnetization has components in the. r-y plane, and these also decay at least as fast as the spin - lattice relaxation returns the magnetization to the z-axis. However, x-y magnetization can also be lost by other processes, which cause the x-y magnetism to dephase to give a net x-y magnetization of zero. The rate constant in the x-y plane for this process is 7%, the spin - spin or transverse relaxation time. Such relaxation involves transfer of... 

For a vibrating crystal lattice, the interatomic distances are modulated at the frequency of the lattice vibration to produce an oscillating magnetic field. Suitable vibration with the frequency at the Larmor frequency of the electrons will induce a flip of the elecfron spin. The corresponding relaxation time can be simplified as... 

Figure Bl.13.2. Spin-lattice and spin-spm relaxation rates (R and/ 2> respectively) for a carbon-13 spin directly bonded to a proton as a fiinction of correlation time at the magnetic fields of 7 and 14 T.

If the strength of the saturating RF, A B2, and the spin-lattice relaxation time, Jj, are known, then can be measured, again free of magnetic field inliomogeneities. 

Here Ti is the spin-lattice relaxation time due to the paramagnetic ion d is the ion-nucleus distance Z) is a constant related to the magnetic moments, i is the Larmor frequency of the observed nucleus and sis the Larmor frequency of the paramagnetic elechon and s its spin relaxation time. Paramagnetic relaxation techniques have been employed in investigations of the hydrocarbon chain... 

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