LIMITATIONS ON DISTINGUISHING BETWEEN REPRESENTATIONS OF RELAXATION DATA OVER NARROW FREQUENCY RANGES

In this article, we examine the ability to distinguish between relaxat ion functions with data over a limited range of frequency. It is demon strated that over these limited frequency ranges under a variety of co nditions, the Cole-Cole equation can be used to fit data generated by the Havriliak-Negami equation. These results show that discerning betw een several very different broad relaxation functions fit to data obta ined over narrow time or frequency ranges is nearly impossible within experimental accuracy. Therefore, the uniqueness of the fit parameters , and hence the ability to verify model predictions, is brought into q uestion. Furthermore, as this conclusion is drawn from comparison of e xact functions that experience no dispersion overlaps or instrumental systematic errors that can mask exact fits, the true situation with ex perimental data is even worse. The same conclusion can be applied to t ime domain data. [S0021-8979(98)00420-4].