High spins Boltzmann distribution

For completeness, it is already mentioned here that the relatively high intensity of the origin hne II at T = 1.3 K (Figs. 13 and 16 a) is not in accordance with a Boltzmann distribution for two states which are separated by 7 cm. It will be pointed out in Sects. 4.2.7 and 4.2.8 that the emission from state II cannot be frozen out. This is a consequence of the relatively slow spin-lattice relaxation from state II to state I (compare also the Refs. [24,62,64,65]). 

The differences in population between the corresponding states can be calculated by assuming a Boltzmann distribution. For the electron spin, the ratio Ws,high/... 

In the thermal equilibrium with lattice the spin system is characterized by one single temperature (the temperatures a and jS coincide). In the general case any thermodynamic state of spin system in high temperature approximation can be described by two temperatures one for a Boltzmann distribution between the Zeeman levels, and a second one describing... 

Another technique for the study of reactions that is highly specific for radical processes is known as CIDNP, an abbreviation for chemically induced dynamic nuclear polarization." The instrumentation required for such studies is a normal NMR spectrometer. CIDNP is observed as a strong perturbation of the intensity of NMR signals in products formed in certain types of free radical reactions. CIDNP is observed when the normal population of nuclear spin states dictated by the Boltzmann distribution is disturbed by the presence of an unpaired electron. The intense magnetic moment associated with an electron causes a polarization of nuclear spin states, which is manifested by enhanced absorption or emission, or both, in the NMR spectrum of the diamagnetic product of a free radical reaction. The technique is less general than EPR spectroscopy because not all free radicals can be expected to exhibit the phenomenon. 

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