Vibrational Dynamics in Liquid Water: A New Interpretation of the Infrared Spectrum of the Liquid

Abstract

In comparing the infrared spectra of liquid water and simple hydrates, two anomalies are noted which are apparently inexplicable in terms of presently acceptable theories of the liquid. These anomalies are explained in terms of a Maxwellian distribution of collisional interactions between water molecules, which when put in quantitative form reveals (1) that most molecules in the liquid are highly distorted by collisional perturbations, and (2) that there is a broad distribution of distortion among the molecules in the liquid. When translated into vibrational dynamics, these concepts lead to a continuum distribution of ν1 and ν3 modes of varying distorted molecules. It is shown that in its stretching motion, liquid water behaves dynamically as a continuum of OH bond oscillators of different frequencies, demonstrating both weak inter- and intramolecular vibrational interactions. A new interpretation of the infrared spectrum of liquid water is given in terms of this model, and other spectral evidence is offered in support of it.

Infrared studies of water in crystalline hydrates: NaClO4•H2O, LiClO4•3H2O, and Ba(ClO4)2•3H2O

“…This can be taken to indicate that weak hydrogen bonds between water molecules and perchlorate ions, similar to those in LiCI04.3H20, occur in NaC10,-H20 and BaCI04.3H,0. These stretching frequencies are unusually high for crystalline hydrates, the most common frequency range being 3300-3500 cm-' for OH and 2440-2560 cm-' for OD (5,16,(27)(28)(29)(30). These frequencies correspond closely to the high-frequency peaks in the spectra of HDO in aqueous solutions of perchlorate ions (4,(7)(8)(9)(10), showing that very similar weak hydrogen bonds occur in the crystalline hydrates and in solution.…”

An i.r. investigation on some calcium aluminate hydrates, CA2Al(OH)6+X−·yH2O (=3CaO·Al2O3·CaX2·nH2O, X− = univalent anion)

“…The formation of hydrogen bonds in crystal hydrates, liquid water and salt solutions leads to broadening and shifts towards smaller wave numbers of the absorption band [10][11][12][13][14][15][16][17][18]26]. So the broad absorption band due to interlayer water of the calcium aluminate hydrates is found at lower wave numbers in the direction X-=CIO4 -, J-, C103-, NO3-, Br-, CI-, BrO3-to JO3-.…”

“…There is evidence from the literature [10][11][12][13][14][15][16][17][18] that the interactions of water molecules in crystal hydrates with their surroundings are correlated with the positions of the absorption bands due to these water molecules.…”

The correlation between O—H stretching frequencies and hydrogen bond distances in a crystalline sugar monohydrate

“…In the general case of a hydrated crystal (17)(18)(19)(20) water is treated as a vibrationally distorted molecule. For a water molecule which occupies an asymmetric site, Can.…”