LOCAL-STRUCTURE DYNAMICS IN LIQUIDS - NONHYDRODYNAMIC ORIENTATIONAL RELAXATION OF 2-ETHYL NAPHTHALENE

The rotational dynamics of 2-ethyl naphthalene have been studied from 2-degrees-C to 100-degrees-C using subpicosecond transient grating optical Kerr effect techniques. After ultrafast librational dynamics have decayed, there remains (> 3-4 ps) a triple-exponential decay of the orientational anisotropy. The slower two decays exhibit hydrodynamic temperature dependences, corresponding to rotational diffusion. The fastest decay is not hydrodynamic, being temperature independent from 2-degrees-C to 40-degrees-C. This decay is attributed to the relaxation dynamics of local structures in the liquid.