Contribution of Fermi and Darling–Dennison resonances to the formation of Raman spectra of water and water–ethanol solutions

Abstract

As a result of the experimental study of water Raman spectra and water–ethanol solutions, it was established that Fermi resonance and Darling–Dennison resonance make significant contribution to the formation of Raman spectra. Basing on the analysis of the spectra using optimization algorithms, the coupling constants W and the contributions of Fermi resonance to spectra in water and aqueous ethanol solutions at various temperatures were calculated. The contribution of the resonance of Darling–Dennison to the formation of the spectra of solutions was analyzed. It was established that Fermi and Darling–Dennison resonances manifested stronger in a 20% solution of ethanol in water in comparison with pure water. These resonances weakened with increasing temperature. This effect was explained from the point of view of strength of hydrogen bonds. Copyright © 2017 John Wiley & Sons, Ltd.

OH Stretching Dynamics in Hydroxide Aqueous Solutions

“…The literature on this topic is extremely abundant, and its inclusion here is out of the scope of this report. The assignment of each individual Gaussian to a particular vibration or overtone, to the stretching vibration of a particular kind of water molecules, as for instance non-hydrogen bonded or tetrahedrally bonded, in a high-density or in a low-density environment , and so on, is more questionable, although sometimes useful, to rationalize the information hidden in the Raman spectra. As already stated, the OH stretching band of hydroxides in water is the superposition of the contribution due to the H 2 O vibrations with the additional stretching contribution due to the OH – ions (see Figure A), the latter being a sharp band at ν̃ OH – between ∼3610 and ∼3640 cm –1 , depending on the solute concentration .…”

The strength of the OH-bend/OH-stretch Fermi resonance in small water clusters

“…The results compare favorably with coupling constants reported in the literature, which are mostly r30 cm À1 for the water monomer 12,13,[23][24][25] (our estimate is close to 30 cm À1 , Section 4.2) and Z50 cm À1 for water in aggregates or the condensed phase. 10,[17][18][19][20][21][22]28 The results hint at a trend towards a larger effective coupling constant for the smaller and more strained cyclic trimer and tetramer compared to the pentamer. The accurate anharmonic modeling of Raman spectra and investigation of trends with regard to ring size is a next logical step in the investigation of small water clusters, and we hope that this work can motivate such research in the quantum chemical community.…”

“…A good number of experimental and theoretical works have been published that quantify the strength of the OH-bend/OH-stretch Fermi resonance for water under various conditions. For liquid water 10,17–19 and water ice, 20–22 reported coupling constants fall mainly into the range 50 to 100 cm −1 , while the coupling constant for the isolated water molecule is smaller, with values mostly reported close to 30 cm −1 or below. 12,13,23–25 Johnson and coworkers 26,27 reported spectroscopic coupling constants of 30 ± 5 and 33 cm −1 for water in Br − ·H 2 O and Cl − ·H 2 O·(CCl 4 ) n complexes, respectively, and Tabor et al reported a value‡‡Note that comparison of these Fermi coupling constants is complicated by the choice of coordinates, e.g.…”

Recent advances in linear and nonlinear Raman spectroscopy. Part XII

“…It was found that the Fermi and Darling–Dennison resonances grew stronger in a 20% solution of ethanol in water in comparison with pure water. These resonances weakened with increasing temperature, and this effect was explained on the basis of the strength of hydrogen bonds …”

“…These resonances weakened with increasing temperature, and this effect was explained on the basis of the strength of hydrogen bonds. [189] 17 | PHARMACEUTICAL, FOOD, AND FORENSIC APPLICATIONS Applications of Raman spectroscopy in the areas of pharmaceuticals, food safety, and forensics is gaining increasing importance as the power of Raman to identify properties of substances at the molecular level is realized and put into practice. Particularly important are portable and handheld Raman devices that facilitate the in situ application of Raman in these vital areas.…”