Temperature-dependent molecular dynamics of liquid carbon disulphide: Polarization-selected impulsive stimulated light-scattering data and Kubo line shape analysis

Abstract

Femtosecond time-resolved impulsive stimulated scattering (ISS) data from carbon disulphide at three temperatures are presented and analyzed in terms of molecular orientational motions which show weakly oscillatory, librational dynamics at short times (<1 ps) and rotational diffusion at longer times. The data are collected with a light polarization combination that eliminates signal due to electronic polarizabilities. Compared to ISS data reported earlier [S. Ruhman et al., Chem. Phys. Lett. 141, 16 (1987)], this permits improved examination of molecular motion at times shorter than 150 fs. The data also extend to longer times (several picoseconds) with good signal/noise ratios, permitting a more complete analysis of the molecular response. Finally, an improved analysis of the data is presented. Angular position correlation functions, which are determined from the data, are related to angular velocity correlation functions (AVCFs) through a Kubo line shape analysis. Approximate analytical models of liquid-state molecular dynamics which account for inhomogeneity and stochastic forces are then used to fit the AVCFs, rather than to fit the data itself as was done earlier. In the context of the models, we extract information about intermolecular torques and the extent of inhomogeneity in the torques.