The Tail-Broadening Parameter

The dispersion of the photocurrent transients is frequently described by the tail broadening parameter JF. defined by Schein (1992) as 

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Figure 20 The field dependencies of the tail-broadening parameter W.

Figure 22 The field dependence of the tail-broadening parameter W for different values of (o/kT) and I.

Band broadening and tailing can also be the result of column overloading and ionic interaction. In this discussion, we would like to exclude these possibilities. The actions discussed here include the column, the instrument and the chromatographic parameters. Table 37-1 summarizes the options to increase the theoretical plate number. 

These relationships are known as the Debye formulae. The Debye process has a relaxation time distribution, which is symmetrical around /niax= niax/2n and has a full width at half-maximum of 1.14 decades in frequency for the dielectric loss. In most cases, the half width of measured loss peaks is much broader than the predicted by eqn [26] and in addition, their shapes are asymmetric and with a high-frequency tail. This is the non-Debye (or nonideal) relaxation behavior found in many glass formers. In the literature, several empirical model funaions, mostly generalization of the Debye function, have been developed and tested which are able to describe broadened and/or asymmetric loss peaks. Among these empirical model functions, the most important are the Kohlrausch-Williams-Watts (KWW), Cole-Cole (CC), Cole-Davidson (CD), and the Havriliak-Negami (HN) function. The HN function, with two shape parameters, is the most commonly used funaion in the frequency domain. 

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