RELAXATION DYNAMICS IN ORTHOTERPHENYL - COMPARING BETA(K) FROM EXTENDED MODE-COUPLING THEORY AND PHENOMENOLOGICAL ANALYSES

Depolarized light scattering susceptibility spectra of orthoterphenyl (OTP) were analyzed using the idealized and extended versions of mode coupling theory (MCT). The extended MCT fits were combined with KWW fi ts to the alpha peaks to provide combined alpha-beta fits from which t he KWW stretching coefficient beta(K) was determined. beta(K) was foun d to be nearly independent of temperature, in agreement with the asymp totic prediction of MCT. The spectra were also analyzed with a five-fu nction phenomenological model developed by Patkowski et al. [J. Non-Cr yst. Solids 172-174 (1994) 52]. While this model gives excellent fits to the spectra, we found that it is not able to determine beta(K) uniq uely unless other parameters are artificially constrained. Here, and i n comparing light scattering and dielectric data for salol, we find th e claim that beta(K) approaches 1 at high temperatures not to be justi fied by the experimental data. (C) 1998 Elsevier Science B.V. All righ ts reserved.