In this work a fully symmetrized quantum mechanical description of vibrational motion in terms of complex vibrational coordinates and complex basis wavefunctions is outlined, designed for studying vibrational level mixing and intramolecular vibrational energy redistribution (IVR) around CH stretch overtone states in benzene. Symmetrized local mode (LM) formalism has been applied to the CH stretch system, while the remaining benzene vibrations (including out-of-plane modes) were treated as normal modes (NM). Using the outlined approach a model calculation of the absorption spectrum of the first overtone state CH (n=2) at ∼6000 cm−1 has been carried out.
The vibrational level mixing at the second CH stretch overtone state CH(v=3) in benzene has been studied quantum mechanically using a completely symmetrized vibrational basis set in terms of a combined local mode/normal mode description. The employed symmetrized approach has helped to reduce the dimensionality of coupling Hamiltonian matrices and thus allowed for the inclusion of all 30 vibrational modes in the calculations. The absorption spectrum and dynamical intramolecular vibrational redistribution characteristics for initial excitation of a symmetrized local mode “bright” state in the CH(v=3) overtone manifold have been calculated and analyzed in connection with the degree of localization of the CH stretch overtone vibrational system in benzene.
The effect of the permanent electric-dipole moments of polar media on the two-photon resonance four-wave mixing (TPR FWM) as described by chi (3)( omega 4= omega 1- omega 2+ omega 3) is studied. The spectra corresponding to different processes of TPR FWM are modelled for a three-level system. It is demonstrated that the difference- and sum-frequency TPR FWM spectroscopy is sensitive to the difference between permanent dipole moments of the two levels coupled by the TPR.
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