The third- and fifth-order nonlinear Raman response of liquid CS2 calculated using a finite field nonequilibrium molecular dynamics method

A finite field molecular dynamics (MD) method has been developed to calculate the off-resonant Raman response of liquids. The method has been used to calculate the third- and fifth-order optical responses of CS2. From the third-order response, the intensity of third-order cascading processes has been estimated. The calculated ratio between the fifth-order intensity and the intensity of the third-order cascading processes supports experimental observations, claiming that two-dimensional Raman spectra are dominated by third-order cascading processes

Many-body effects in the stimulated Raman response of binary mixtures:A comparison between theory and experiment

The subpicosecond dynamics of binary mixtures of carbon disulfide and alkane have been studied using third-order time-resolved Raman techniques. Both the anisotropic and the isotropic responses were investigated. These depend differently on many-body contributions to the first-order susceptibility and probe different modes in the liquid. The anisotropic response is dominated by single molecule effects, whereas the isotropic response is completely determined by many-body contributions since the single molecule response vanishes. To interpret the experimental results, molecular dynamics simulations were performed on model mixtures. The effect of dilution on the subpicosecond response cannot be explained by many-body effects in the first-order susceptibility alone. Aggregation due to permanent quadrupole moments on the carbon disulfide molecules and density changes upon dilution are also inadequate explanations for the observed effect. Apparently the character of the many-body dynamics itself is modified by the change of the molecular force fields, when carbon disulfide molecules are replaced by alkanes.<br/

Interaction induced effects in the nonlinear Raman response of liquid CS2:A finite field nonequilibrium molecular dynamics approach

The third- and fifth-order time-domain Raman responses of liquid carbon disulfide have been calculated, taking local field effects into account through the dipole-induced dipole approximation to the polarizability. The third-order response is shown to be in excellent agreement with experimental data. The calculated two-dimensional shape of the fifth-order response is compared with recently reported experimental observations of what is claimed to be pure fifth-order response. Considerable discrepancies are observed which might be explained by contamination of the experimental results with sequential and especially parallel third-order cascaded Raman response. A new choice of polarization conditions is proposed, which increases the discrimination against these unwanted cascading effects, as compared to the previously discussed fully polarized and magic angle conditions

Liquid xenon as an ideal probe for many-body effects in impulsive Raman scattering

The collision induced effects in the third-order Raman response of liquid xenon have been studied both experimentally and theoretically. The effect of electron cloud overlap on the polarizability of xenon dimers was studied using accurate time-dependent density functional theory calculations. The dimer polarizabilities were used to fit parameters in a direct reaction field model that can be generalized to condensed phase systems. This model was employed in molecular dynamics simulations in order to calculate the impulsive Raman response of liquid xenon. Excellent agreement is found between the shape of the calculated and the measured anisotropic part of the response. The shape of this response is little affected by the electron overlap effects, but the intensity is strongly influenced by it. The shape of the isotropic response is predicted to be strongly dependent on electron overlap effects

The effect of induced multipoles on the fifth-order Raman response

In our previous work we developed the Finite Field method in order to calculate the fifth-order Raman response. The method was applied to calculate various polarization components of the two-dimensional response of liquid CS2. So far, all calculations relied on the dipole-induced dipole. Accurate time-dependent density functional theory calculations have shown that this model has big discrepancies, when molecules are close together as in the liquid. We now report results of investigations on the importance of multipole and electron overlap effects on the polarizability and the fifth-order Raman response. It is shown that these collision effects, especially the induced multipoles, are crucial in the description of the fifth-order response. The impact chi(mmzzzz)((5)) is found to be especially pronounced for the response that is solely due to interaction induced effects. The calculated response will be compared with various experimental results