Small-molecule weak-coupling case

It is important to point out that the limits of the intermediate case may be defined only in an operational way and depend on the accuracy of experiment. If the S-I2 and /1-/2 couplings are weak, the I2 continuum may be neglected and, in the first approximation, the system may be considered as a small molecule. On the other hand, a strong /j-lj coupling dissolves the /j levels in the I2 continuum. Therefore, deviations fi-om the statistical behavior may be insignificant. The interaction with the environment (collisions) shifts the same molecule from one case to another a small molecule collisionally coupled to the kinetic energy continua behaves as an intermediate or statistical system (see below Section III,E,2). 

The spin half nuclei 1H, 13 C and 15N, in the absence of chemical exchange and in diamagnetic molecules, give spectra with very narrow lines which are easy to resolve especially at high magnetic fields at least for small molecules, but the low abundances of 13C and especially 15N lead to weak signals. This inherent low sensitivity can be overcome by pulse FT techniques and accumulation, or in some cases by indirect detection (the inverse mode) most commonly with as the observed nucleide. In solution this requires the presence of a 7 H- N) coupling. 

With a large and small molecule linjit, there must also be an intermediate case. There are a number of possible manifestations of the intermediate case, so one interesting choice is discussed, 6) There may be situations in which the weakly coupled states 14>w I are sufficiently dense that on the time scales of real experiments, the 4>w behave, as an effective continum for decay of the zeroth... 

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