Concentration-Dependent Frequency Shifts and Raman Spectroscopic Noncoincidence Effect of the CO Stretching Mode in Dipolar Mixtures of Acetone/Dimethyl Sulfoxide. Experimental, Theoretical, and Simulation Results

Abstract

The nu(C=O) Raman band frequencies of acetone have been analyzed to separate the contributions of the environmental effect and the vibrational coupling to the gas-to-liquid frequency shifts of this band and to elucidate the changes in these two contributions upon dilution in DMSO. We have measured the frequencies of the nu((12)C=O) band in acetone/DMSO binary mixtures, the nu((13)C=O) band of the acetone-(13)C=O present as a natural abundance isotopic impurity in these mixtures, and both the nu((12)C=O) and nu((13)C=O) bands in the acetone-(12)C=O/acetone-(13)C=O isotopic mixtures at infinite dilution. These frequencies are compared with those of the nu((12)C=O) band in the acetone/CCl(4) binary mixtures measured previously. We have found the following three points: (i) The negative environmental contribution for the nu((12)C=O) oscillator of acetone completely surrounded by DMSO is reduced in magnitude by +5.5 cm(-1) and +7.8 cm(-1) upon the complete substitution of DMSO with acetone and CCl(4) molecules, respectively, indicating the progressive reduction of the attractive forces exerted by the environment on the nu((12)C=O) mode of acetone. (ii) In DMSO and other solvents, the contribution of the vibrational coupling to the frequency of the isotropic Raman nu((12)C=O) band of acetone becomes progressively more negative with increasing acetone concentration up to a value of -5.5 cm(-1), while the contribution to the frequency of the anisotropic Raman band remains approximately unchanged. The only difference resides in the curvatures of the concentration dependencies of these contributions which depend on the relative solute/solvent polarity. (iii) The noncoincidence effect (separation between the anisotropic and isotropic Raman band frequencies) of the nu(C=O) mode in the acetone/DMSO mixtures exhibits a downward (concave) curvature, in contrast to that in the acetone/CCl(4) mixtures, which shows an upward (convex) curvature. This result is supported by MD simulations and by theoretical predictions and is interpreted as arising from the reduction and enhancement of the short-range orientational order of acetone in the acetone/DMSO and acetone/CCl(4) mixtures, respectively.

Concentration‐dependent Raman study of noncoincidence effect in the NH2 bending and CO stretching modes of HCONH2 in the binary mixture (HCONH2 + CH3OH)

“…The NCE separation  nc expressed by Eqn (1) for the (C O) stretching mode in acetone/DMSO mixtures exhibited a downward (concave) curvature in contrast to that in the acetone/CCl 4 mixtures, in which an upward (convex) curvature was exhibited. These results were interpreted by Giorgini et al 12 as arising from the reduction and enhancement of short-range orientational order of acetone in acetone/DMSO and acetone/CCl 4 mixtures, respectively. As argued on the basis of their studies by Wang Although Wang and McHale,13 McHale, 14,15 and Mirone and Fini 17 have done a good deal of theoretical work on the NCE, in all these theoretical studies the attention has been mainly devoted to the most common case of dipole-dipole resonant energy transfer in polar liquids.…”

“…11 The stretching vibration of a polar bond in such molecules is, in fact, coupled through a transition dipole-transition dipole (TD-TD) interaction. In a very recent study, Giorgini et al 12 studied the Raman spectroscopic NCE of the C O stretching mode in dipolar mixtures of acetone C dimethylsulphoxide (DMSO) and also measured the concentration dependence of the wavenumber shifts for the C O stretching mode. The NCE separation  nc expressed by Eqn (1) for the (C O) stretching mode in acetone/DMSO mixtures exhibited a downward (concave) curvature in contrast to that in the acetone/CCl 4 mixtures, in which an upward (convex) curvature was exhibited.…”

Concentration-dependent frequency shifts of the CS stretching modes in ethylene trithiocarbonate studied by Raman spectroscopy

“…These effects lead to the spectral change of both the isotropic and anisotropic Raman components of the reference vibrational mode of solute molecule. [18][19][20][21] This phenomenon of the isotropic and anisotropic Raman bands (and also the IR band in some cases) of the same vibrational mode that appear at different frequency positions can be called noncoincidence effect (NCE). The peak frequency shifts of both the isotropic and anisotropic Raman spectra with the change of reference molecule concentration provide useful information regarding the solute-solvent interaction and intermolecular forces.…”

Raman and DFT study of hydrogen‐bonded 2‐ and 3‐chloropyridine with methanol

“…Raman spectroscopy is especially suited to study these interactions in liquid phases because of many reasons, such as (1) it is possible to isolate the isotropic component in a 90°s cattering geometry experimental setup, (2) precise understanding can be obtained by concentrating on characteristic Raman modes, when measurements are done at high resolution and (3) with the aid of accurate density functional theory (DFT) results in addition to the experimental results, knowledge at molecular level and even at atomic level can be developed. Because of the above excellent features, polarized Raman spectroscopy 1 -21 has been widely used to study the effect of intermolecular interactions in associated liquid mixtures.…”

“…1,7 On introducing a solvent to a liquid reference system, the isolated active oscillator of some normal mode is perturbed. The perturbation may cause a change in the vibrational quantum state leading to a well-known phenomenon, the population relaxation.…”