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Vibrational phase relaxation

Advances in experiments have led us to a deeper understanding of microscopic processes that cause the vibrational phase relaxation. The coherent anti-Stokes Raman scattering (CARS) and photon echo spectroscopy are the time resolved experimental techniques, those have allowed systematic investigation of the temperature, density and concentration dependence of the vibrational phase relaxation in liquids. From the theoretical point of view it’s a great challenge to develop sophisticated theories and models and to compare the results with experimental studies.

We have been working on the theoretical and computer simulation studies of the vibrational phase relaxation in various molecular liquids. That includes liquid nitrogen, both along the coexistence line and the critical isochore, binary liquid mixture and liquid water. The focus of this work is to understand the dependence of the vibrational relaxation on the density, temperature, composition and the role of different interactions among the molecules. The density fluctuation of the solute particles in a solvent is studied systematically, where the computer simulation results are compared with the mode coupling theory (MCT). The classical density functional theory (DFT) is used to study the vibrational relaxation dynamics in molecular liquids with an aim to understand the heterogeneous nature of the dynamics commonly observed in experiments.

Some of the interesting results follow:

Raman linewidth of nitrogen

Figure caption:

The lambda-shaped Raman linewidth of nitrogen along the phase transition. The filled symbols represent the simulation points whereas the open circles denote the experimental results

The composition dependent Raman lineshape of the binary liquid mixture

Figure caption:

The composition dependent Raman lineshape of the binary liquid

Water: orientation

Figure caption:

A correlation between the O-H stretching frequency fluctuation and the orientation of a single water molecule