A combined instantaneous normal mode and time correlation function description of the optical Kerr effect and Raman spectroscopy of liquid CS2

Abstract

The depolarized reduced Raman and corresponding optical Kerr effect (OKE) spectral density of ambient CS2 have been calculated by way of time correlation function (TCF) and instantaneous normal mode (INM) methods and compared with experimental OKE data. When compared in the reduced Raman spectrum form, where the INM spectrum is proportional to the squared polarizability derivative weighted density of states (DOS), the INM results agree nearly quantitatively (at all but the lowest frequencies) with the TCF results. Both are in excellent agreement with experimental measurements. The INM signal has a significant contribution from the imaginary INMs. Within our INM theory of spectroscopy the imaginary INMs contribute like the real modes, at the magnitude of their imaginary frequency. When only the real modes are allowed to contribute, and the spectrum is rescaled to account for the missing degrees of freedom, the results are much poorer, as has been observed previously. When the spectra are compared in their OKE form, the INM spectrum is found to lack the low-frequency spike which is associated with long time scale rotational diffusion, and it is not surprising that an INM theory would not capture such a feature. The results demonstrate that while the OKE and spontaneous depolarized Raman spectrum contain the same information, they clearly highlight different dynamical time scales. At higher frequencies (ω>25 cm−1) the INM OKE results are in excellent agreement with TCF and experimental results. The TCF results capture the low-frequency spike and are in agreement with experiment everywhere within the precision of the present calculations. The molecular contributions to the OKE signal are analyzed using INM methods.

Intermolecular Dynamics and Structure of Carbon Disulfide in Isoviscous Alkane Solutions: An Optical Kerr Effect Study

“…However, if II scattering is actually more important at lower frequencies than at higher frequencies, an increase in the importance of II scattering could cause a red shift in the spectrum. Third, simulations performed on CS 2 with a distributed polarizability model have done an excellent job in fitting experimental OKE spectra without going beyond the DID level of scattering, which suggests that higher-order multipole moments are probably not important contributors to the intermolecular spectrum, 40 although again different conclusions have been reached on the basis of other simulations. 37 Last, recent simulations suggest that negative cross-terms between single-molecule scattering and II scattering are much stronger than the pure contribution of II scattering in the intermolecular spectrum of CS 2 .…”

Ultrafast H2 and D2 rotational Raman responses in near critical CO2: An experimental and theoretical study of anisotropic solvation dynamics

“…The spontaneous rotational Raman scattering of H 2 in supercritical CO 2 has been reported in one prior experimental study. 4 Although the frequency domain spontaneous spectra and the corresponding impulsive OHD Raman responses are essentially related by a Fourier transform relationship, 23,24 the time resolved observations of these rotational resonances offer several advantages. First of all, pure rotational Raman cross sections are quite weak, hence, making electronically nonresonant rotational Raman measurements via a stimulated, as compared to a spontaneous, optical technique offers considerable signal/noise improvement.…”

The Effect of Induced Multipoles on the Fifth-order Raman Response

“…Similar models have been used in other studies of the third-and fifth-order Raman response. 35,50,51 The effect of overlapping electron clouds is taken into account in an approximate way by using the direct reaction field model (DRF). 43,46 In this model a set of screening functions damp the interaction as the atoms start overlapping, assuming that the electron clouds are well described by exponentially decaying densities.…”

“…Therefore the dynamics of liquids have been studied extensively experimentally applying, for example, third-order time resolved Raman techniques. [1][2][3][4][5][6] In the last decade substantial efforts have been made in order to measure, 7-15 model [16][17][18][19][20][21][22][23] and calculate [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] the fifth-order Raman response suggested by Tanimura and Mukamel. 16 Spectroscopies relying on this response should be able to distinguish between different relaxation mechanisms, which the lower order techniques cannot.…”

“…Normal mode approaches, [24][25][26][27][28][34][35][36][37] mode coupling methods [29][30][31][32][33] and the GLE approach 38 all belong to the first type and their success depends on whether the dynamic information they exclude is superfluous or not. The time correlation function method 25,26,28 and the finite field method 39,40 on the other hand both take all motion into account.…”