Femtosecond polarisability anisotropy relaxation and solvation dynamics The cases of aniline and methanol
Abstract
The polarisability anisotropy relaxation dynamics of liquid methanol and aniline are measured by means of the femtosecond optically heterodyne detected optical Kerr effect. The data are converted to a frequency domain spectral density and analysed in terms of contributions from diffusional reorientation and vibrational dynamics. For aniline a high frequency librational component of Gaussian form makes a large contribution. This is assigned to strong intermolecular interactions in the liquid. In methanol the dynamics are dominated by ultrafast relaxation, in good agreement with simulation. Using these data the solvation dynamics are calculated and compared with experimental measurement. Similarities and differences are discussed. Calculation reproduces the general form of the observations, but predicts a number of features which are not observed. It is suggested that the coupling strength between solvent modes and solute dipole needs to be taken into account.