Computational Methods for Analyzing the Intermolecular Resonant Vibrational Interactions in Liquids and the Noncoincidence Effect of Vibrational Spectra
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In the liquid phase, vibrational dynamics and spectra of molecules are affected more or less by intermolecular interactions. There are two types of such effects. One of them is responsible for the modulation of the vibrational frequencies of each molecule, and is called “diagonal”. This effect is operating even for a solute molecule in a dilute solution, and gives rise to a solvation-induced vibrational frequency shift. This effect also induces vibrational dephasing, since the magnitude of the solvation-induced frequency shift is modulated as time evolves according to the liquid dynamics. The other type of the effects of intermolecular interactions on vibrational dynamics and spectra arises from the direct coupling of vibrational modes of different molecules in the system. It is called “off-diagonal”, because it is represented by the off-diagonal terms of the force constant matrix. This effect manifests itself most clearly in the resonant case, where the intrinsic frequencies of the interacting vibrational modes are sufficiently close to each other as compared with the magnitude of the coupling.
KeywordsVibrational Frequency Liquid Structure Time Correlation Function Rotational Relaxation Vibrational Dynamic
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