Analysis of intermolecular coordinate contributions to third-order ultrafast spectroscopy of liquids in the harmonic oscillator limit

The apparently - multicomponent subpicosecond intermolecular dynamics of ca rbon disulfide liquid are addressed in a unified manner in terms of an inho mogeneously broadened quantum mechanical harmonic oscillator model for a si ngle vibrational coordinate. For an inhomogeneously broadened (Gaussian) di stribution of oscillators, the model predicts naturally the bimodal charact er of the subpicosecond intermolecular dynamics of carbon disulfide liquid, and also the spectral evolution effects (spectral narrowing and saturation ) that are observed for solutions of carbon disulfide in weakly interacting alkane solvents. The unique dynamical signature of these low-frequency vib rational coordinates is determined largely by the physical constraints on t he coordinates (near equality of oscillator frequency, dephasing frequency, and inhomogeneous bandwidth), such that constructive and destructive inter ference effects play a dominant role in shaping the experimental observable .