Temperature study of intra‐ and inter‐molecular coupling and Fermi resonance constants in the Raman spectra of liquid water using Fourier deconvolution

Abstract

The structure of the Raman OH stretching band of water has been investigated from 4 to W0C using a Fourier deconvolution technique. The overlapped components in the isotropic and anisotropic spectra have been resolved. The information on the positions of the components in the deconvoluted spectra was used for calculation of the constants for intra-and inter-molecular coupling and Fermi resonance and for an estimation of the component frequencies according to the model presented. For the first time, the value of the asymmetric Fermi resonance constant and the temperature dependences of all coupling constants have been obtained. Their temperature behaviour is in good agreement with the data in the literature concerning the different phases of water. It was established that the intramolecular coupling constant increases and the intermolecular coupling constant decreases as the temperature increases. The Fermi resonance constant for symmetric components tends to decrease with increasing temperature. The decrease in the symmetric Fermi resonance interaction with increasing temperature is due to the increase in the distance between the unperturbed fundamental and overtone band positions. The asymmetric Fermi resonance constant tends to increase with increasing temperature and this determines the strengthening of the asymmetric Fermi resonance interaction, which exhibits a limiting value at high temperatures.

The Role of Fermi Resonance in Formation of Valence Band of Water Raman Scattering

“…To estimate the value W, the authors of [3,5] decomposed the valence band of isotropic water Raman spectrum into components (the curves of Gaussian shape or the components of Fourier deconvolution). If the difference of maximum frequencies Δ of two from these components and the ratio of their intensities R = I 1 /I 2 are determined, the values of Δ 0 and W will be found from system (1).…”

“…Many attempts (see, [1][2][3][4][5][6]) to determine contributions of intra-and intermolecular interactions and Fermi resonance (FR)-resonance between symmetric valence vibration v 1 and overtone of bending vibration 2v 2 of water molecule-did not lead to definite conclusions. Under FR energy transfers from vibration v 1 to overtone 2v 2 [1][2][3][4][5][6] occurs. This energy transfer can explain existence of the shoulder in low-frequency part (in the region 3300 cm −1 ) of water Raman valence band.…”

“…Contradiction in the opinions about the role of FR in vibrational spectra of water is connected with absence of precise methods of calculating frequencies and intensities of intramolecular vibrations in spectra of liquids. Nevertheless, different models of FR are discussed in literature [2][3][4][5], and different methods of calculation of FR quantitative characteristics are suggested [1][2][3][4][5][6][7][8][9].…”

“…According to the generally received model [1][2][3]5], the scheme of splitting of bands of intramolecular vibrations due to FR is presented in Figure 1. Valence vibrations of OH bond with "unperturbed" frequency v u are split into symmetric v s and antisymmetric v a components due to intramolecular interactions (V is the constant of intramolecular coupling).…”

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

“…One should note that according to the prevailing in the literature a few decades ago point of view, FR does not have any influence on the formation of water Raman stretching band. [26,27] The authors [28][29][30][31][32][33][34][35] suppose, that as a result of FR between the overtone of the bending vibration 2ν 2 ≈ 3240 cm À1 and the fundamental tone of symmetric stretching vibrations ν 1 of water molecules, pumping intensity of RS between vibrations ν 1 and 2ν 2 occurs. Exactly, this energy exchange explains the presence of intense low-wavenumber region near 3300 cm À1 in the spectrum of water Raman stretching band.…”