| Abstract
| - A time-domain method for simulating vibrational band profiles that simultaneously takes into account boththe diagonal and off-diagonal effects is developed and applied to the CO stretching bands of neat liquidacetone and the acetone/dimethyl sulfoxide (DMSO) binary liquid mixtures. By using this method, it is possibleto examine the influence of liquid dynamics on the noncoincidence effect (NCE), which arises from theoff-diagonal vibrational interactions, as well as the frequency shifts and band broadening, which are relatedto both the diagonal and off-diagonal effects. It is shown that the simulations for the CO stretching bandsof acetone in acetone/DMSO binary liquid mixtures on the basis of this method can reproduce theexperimentally observed concave curvature of the concentration dependence of the NCE and the unusuallylarge frequency shift of the anisotropic Raman band. The widths of the infrared, isotropic Raman, andanisotropic Raman bands calculated for neat liquid acetone are also in good agreement with those observed.Based on these calculations, the extent of delocalization of the CO stretching vibrational motions is examinedby referring to two quantitative measures of this property, one calculated in the frequency domain and theother in the time domain. It is shown that the extent of delocalization gets larger as the mole fraction ofacetone increases, the CO stretching vibrations being delocalized over a few tens of molecules in neatliquid acetone. It is also shown that the extent of delocalization is related to the quantity called NCEdetectability, which is the ratio between the magnitude of NCE and the bandwidth. It is therefore suggestedthat the extent of delocalization of vibrational motions may be estimated from observable features of Ramanband profiles.
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