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25cm; line-height: 120%; }a:link { }Thestructure and dynamics of molecular liquids have been of interest fora long time. Intermolecular interactions, especially hydrogen bondingbrings about many interesting properties in self-associated liquids.Binary mixtures of two molecular liquids will have various suchinteractions that give rise to non-ideality.

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In some cases, when thisnon-ideality is large, we observe the formation of an azeotrope. Inthis study, we try to understand this non-ideality at a molecularlevel, using Optical Kerr Effect (OKE) spectroscopy, broadband (1-10THz) THz-Time domain spectroscopy (THz-TDS) along with temperaturedependent Nuclear Magnetic Resonance spectroscopy (NMR) of theazeotropic as well as other composition mixtures of benzene andmethanol.WithOKE spectroscopy we can probe both, the collective orientationaldiffusion and the intermolecular dynamics in liquids. From previousOKE studies and simulation on benzene and other molecular liquids, wecan see that the Reduced Spectral Densities (RSDs) lack distinctfeatures and can be broadly categorized into two broad categories,rectangular and triangular. This categorization depends mostly on themolecular shapes and not so much on the local structural orpolarizability changes. The benzene spectra show a bimodal character.Simulations have shown that while the high-frequency shoulder isattributed purely to rotational motion, the low-frequency mode hascontributions from the collective translational and the rotationalmodes.

The addition of polar methanol to benzene not only changes theshape of the RSD but also shifts it to lower frequencies. The bimodalcharacter of the RSD is less pronounced in the mixtures than inbenzene. The azeotrope and the manually mixed mixture have similar”triangular” RSDs. We did not observe a linear trend of the RSDswith the mole fraction of benzene. A detailed analysis of the RSDscan indicate the rate of structural fluctuations in thebenzene-methanol liquid mixtures.

Vibrationaland NMR studies have shown that the formation of the methanol benzeneazeotrope, weakens the hydrogen bond network. Intermolecular forcesbetween the benzene molecules have also been reduced significantly.Methanol disrupts the stacking of benzene which is also evident fromthe depression in the boiling points.

OKEspectroscopy along with other complementary techniques is a powerfultool that can be used to understand the ultrafast liquid statedynamics. The terahertz region gives us information on the vibrationsof a large number of atoms and molecules interacting with each other.These are the collective modes which are sensitive to bothintermolecular and intramolecular perturbations in the system.Studying these low-frequency modes can be useful, in investigatingthe intermolecular dynamics in a binary liquid system.