EFFECTS OF LOCAL LIQUID STRUCTURE ON ORIENTATIONAL RELAXATION - 2-ETHYLNAPHTHALENE, NEAT AND IN SOLUTION

The rotational dynamics of 2-ethylnaphthalene have been studied using subpicosecond transient grating optical Kerr effect techniques. Botb t he neat liquid and a series of dilutions in carbon tetrachloride were examined. The neat liquid was studied over a temperature range of 2-10 0-degrees-C, and the 1 M solution was studied from -30 to +25-degrees- C. After ultrafast librational dynamics have decayed, there remains (> 2 ps) in the neat liquid a triple-exponential decay of the orientation al anisotropy. The slower two decays exhibit hydrodynamic temperature dependences, corresponding to rotational diffusion. The fastest decay is not hydrodynamic, being temperature independent from 2 to 40-degree s-C. This decay is attributed to the relaxation dynamics of local stru ctures in the liquid and is not present in all but the highest concent ration (5 M) solution.