Abstract

The femtosecond optically heterodyne detected optical Kerr effect (OHD-OKE) is one of the best characterised and most widely applied techniques for the study of the ultrafast dynamics of liquids.¹ The method essentially yields the low frequency depolarised Raman spectrum of liquids, with excellent resolution in the 0 - 50 cm^–1 range, of importance in understanding intermolecular librational modes. The OHD-OKE data have been used to test simulations of liquid dynamics and to model ultrafast solvation dynamics and two-pulse echo experiments. Here we will describe our OHD-OKE studies of aniline and its methylated derivatives. The data recorded for pure aniline with a 50 fs time resolution are shown below (fig. 1). The data reveal an instantaneous component, an ultrafast decay, a weak oscillation at ca. 500 fs, followed by a slower, nonexponential decay. The assignment and analysis of these features and their relative significance in methylated anilines will be described. The analysis of the aniline data is of some significance because of a number of recent measurements of ultrafast reactions and solvation dynamics in which aniline was the solvent.² It is hoped that by contrasting the aniline OKE data with these experimental results we can shed some light on the role of the solvent dynamics in determining the rates of photochemical processes in solution.

© 1996 IEEE