Migration coupling

H shift more readily occurs with loss of nitrogen.22 Excited diazirines decay by fluorescence, carbene formation, or 1,2-H(D) migration coupled with N2 loss. C-D bonds are stronger than C-H bonds, so that deuteration retards the latter pathway and therefore RIES, leading to an increase in both fluorescence and carbene formation from 35-d6 22... 

Let us first discuss the properties of migration coupling in the first type of systems. Here, the solution of Laplace s equation for any homogeneous situation yields a linear dependence of on z, i.e. with boundary condition 14b and the origin of the z-axis, z = 0 at the CE,... 

Note that Eq. 4b in Ref. [42] is identical to Eq. 4a and thus it is correct. However, the term that is claimed to describe the migration coupling does not vanish in a homogeneous situation and its interpretation is thus erroneous. 

Fig. 32. Illustration of front motion in a bistable system due to the interplay of homogeneous dynamics and migration coupling (see text).

If the distance between the WE and the CE is equal or larger than the length of the WE in the pattern forming direction, then the migration coupling is long-range or... 

Fig. 33. Schematic representation of the potential distribution in the electrolyte as a result of an inhomogeneous distribution of the electrode potential, DL, and the effect of migration currents induced by the inhomogeneous potential distribution on the local temporal evolution of the potential (a) for the case that the length of the WE is much smaller than the distance between the WE and the CE and (b) for the case that the length of the WE is much larger than the distance between the WE and the CE. The length of the arrows in the representations below the potential distributions indicate how the contribution of the migration couplings to the temporal evolution of DL changes as a function of distance from the disturbance. (x, z spatial coordinates parallel and perpendicular to the WE, respectively. The electrode is assumed to be one-dimensional and the electrolyte two-dimensional.)...

Fig. 34. Illustration showing why nonlocal coupling leads to accelerated front motion. The arrows indicate the contribution of the migration coupling on the temporal evolution of the double layer at a certain distance from the interface (e.g. the inflection point) for different potential distributions.

Because a and ji not only enter the local dynamics, but determine also the migration coupling, a variation of these two parameters leads to a shift of the curve along the ordinate, as well as to a change in the form of the curve. 

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