Orientational dynamics on glassformer 2 lsqb;Ca(NO3)2rsqb;sdot;3lsqb;KNO3rsqb;: A study by transient optical Kerr effect

摘要

The fast orientational dynamics of molten 2lsqb;Ca(NO3)2rsqb;sdot;3lsqb;KNO3rsqb; is investigated by timehyphen; resolved optical Kerr effect (OKE) with subpicosecond resolution in the temperature range 380ndash;620 K. Apart from the instantaneous electronic response and a very fast decay, the OKE intensity profiles show clearly the presence of a nonexponential decay. The simplest function which fits the experimental data is a biexponential with time constants ranging from 120 to 15 and 10 to 3 ps, respectively. The results are discussed in terms of an integrated correlation time tgr;cthat does not show a diverging behavior approaching the glass transition. At high temperatures tgr;cfollows a typical Arrhenius law with activation energy of 1.5 kcal/M. Different possible interpretations of the observed behavior (agr;ndash;bgr; bifurcation, domain size effect) are discussed. The main conclusion is that rotational motions are decoupled from translational ones even for temperatures well above the liquidndash;glass transition.