Liquid water reorientation

Tabic I. Reorientational relaxation times Tf (in psec) of the Q (r) for two-body and three-body liquid water models. The value of is taken from Jonas, J. deFries, T. Wilbur, D. J. J. Chem. Phvs. 1976, 582. 

The NMR rotational reorientation time of liquid water at 25 °C is 2.5 10-12 sec and the dielectrid relaxation time of liquid water is 8 1(T12 sec173). 

Third, the success of the composite HC-SD model described in Section IX implies the idea that liquid water presents as if a solution of two components. The main one comprises 95% of molecules (librators), which reorient rather freely in a deep potential well and are characterized by a broken H-bond. The second component comprises 5% of molecules, which are H-bonded and perform fast vibration. Molecules of the first group live much longer than those of the second group. Thus a physical sense of the HC model is clarified in Section X as that describing dielectric response of dipoles with broken H-bonds. 

This is a crude assumption. However, it appears that a quantum picture of discrete rotational lines, placed in the submillimeter wavelength range (ca. from few to 150 cm-1), is essentially determined by a form of a molecule only for a gas. In the case of a liquid, discrete spectrum is not revealed, since separate rotational lines overlap due to strong intermolecular interactions, which become of primary importance. So, due to these interactions and the effect of a tight local-order cavity, in which molecules reorient, the maximum of the absorption band, situated in the case of vapor at 100 cm-1, shifts in liquid water to... 

Co-condensed EtOH-water mixtures reveal the formation of distinct EtOH hydrate phases in different temperature domains. A hydrate 1 appears in the 130 K - 163 K range depending on the EtOH content. It is proposed to have a cubic lattice similar to that of the clathrate type I. Hydrate 2 is found to crystallize at 158 K or 188 K-193 K in correlation with the absence or the presence of ice Ic and EtOH content. Its composition seems to correspond to the monohydrate. The deposited solids undergo crystallization 10 K lower in comparison to frozen aqueous solutions. This reflects the remarkable ease with which water molecules initiate molecular rearrangement at low temperature. This seems most likely due to EtOH generating defects that facilitate the water reorientation . This may also reflect the generation of clusters (in the vapour phase before deposition) having a different nature relative to those encountered in the liquid solutions. These unusual structures may have implications in atmospheric chemistry or astrophysics. 

The dynamics of the molecular rotation of 2-pyridone in toluene, carbon tetrachloride, methanol, and water have been investigated at 305 K by 13C and 2H NMR spectroscopy. Both chemical shifts and relaxation times show that it forms stable hydrogen-bonded complexes in methanol and in water, reorienting as a complete unit and taking with it two solvent molecules. These solvated species are stable within the liquid-state temperature range, and reorient according to the hydrodynamic law as indicated by the 14N line width measurements (85MRC460). 

We shall prove below that the isotopic dependence of the vibrational contribution As(v) on the permittivity e(v) is small, unlike the ID of the reorientation contribution 0r(v). It appears that the relaxation time td differs in HW from that in OW, since td strongly depends not only on the structure of liquid water but also on the strength of an individual hydrogen bond (a detailed analysis of dependence of td on water structure is given by Agmon [18]. 

In Figure 9 we depict the frequency dependences of the partial absorption coefficients aq(v) and a (v) pertinent to two harmonic-vibration modes. These frequency dependences are calculated from formulas (A6), (21) [24], (25), (28), and (29). When the above-mentioned coupling is accounted for (solid lines in Fig. 9), the spectral functions are taken from Eq. (Al). On the other hand, when the coupling is neglected (open circles in Fig. 9), then Lq and L are found from Eq. (19). We see from Fig. 9a that for both cases the calculated partial absorption a (v) practically coincide. The same assertion is valid also for the partial absorption ocq(v) depicted in Fig. 8b. Hence, there is no practical need to account for the coupling between the harmonic reorientation and vibration of HB molecules for calculation of spectra in liquid water. However, the effect of such coupling becomes noticeable (being, however, a rather small) in the case of ice, where the absorption lines are much narrower. 

We do not consider the low-frequency spectra for ice, since the contribution to complex permittivity of rigid reorienting dipoles is calculated from the simplified expression (A29), which is applicable only in the high-frequency approximation. Indeed, the ice permittivity is found for v > 0.1 cm-1 (see Figs. 20a,b and 24a), while for liquid water Eq. (4) is used, applicable also in the relaxation region. 

When the membrane is placed in liquid water, rearrangement and a phase-transition occur. This could be due to surface rearrangements wherein the fluorocarbon-rich skin of the membrane is repelled from the interface between the water and membrane. What this means is that in order to minimize the energy of the system the side chains and backbone of the polymer reorient so that the chains are now arranged at the membrane/ water interface. This hypothesis agrees with the data that show that the water contact angle on the membrane surface becomes more hydrophilic after the membrane is placed in liquid water [32]. The presence of liquid water also results in the removal of a vapor-liquid meniscus, which could also aid in the above rearrangements [28]. 

Woessner DE (1964) Molecular reorientation in liquids. Deuteron quadrupole relaxation in liquid deuterium oxide and perdeuterobenzene. J Chem Phys 40 2341-2348 Xenides D, Randolf BR, Rode BM (2006) Hydrogen bonding in liquid water an ab initio QM/MM MD simulation study. J Mol Liquids 123 61-67 Yalkowsky SH, Baneijee S (1992) Aqueous solubility. Dekker, New York Yalkowsky SH, Valvani SC (1980) Solubility and partitioning I solubility of nonelectrolytes in water. J Pharm Sci 69 912-922... 

Fig. 25.5. Aclivalion energy ( ,) vs. relaxation time t for various materials at 300 K (for symbols see Figs 25.3 and 25.4). Dashed lines Join values corresponding to higher temperature. Polyatomic ion reorientation, water reorientation proton and ion jump domains are shown. The value for liquid H2O (white cross) is shown. The same picture is observed for V2O5. l.bH O gels containing various types of cation (HjO, Li , Na, K, Ba ). In this case intra-site motions give rise to low activated relaxations ...

The relaxation time can be deduced from the Debye-like drcular arc. A plot of T values versus the inverse of temperature (10 /r) (Fig. 25.4) allows a measure of activation energy (Fig. 25.5). The separation of domains already discussed above is clearly visible, from fast reorientational motions of dipolar polyatomic ions such as HX04 and HjO" to slow reorientation of NH4 ions. Motions of water molecules cover a broad region they are slow in gel, medium in superionic materials (e.g. HUP) and fast in liquid water. 

In order to look at the effect of water on the structure of both hydrophobic and hydrophilic room-temperature ionic liquids, SFG measurements were taken at water partial pressures of 5 X 10 Torr and 20 Torr. Results showed that ionic liquid behaviour at the surface differed depending on whether the ionic liquid was hydrophobic or hydrophilic. For hydrophobic ionic liquids, the imidazolium ring reorients towards the surface normal upon addition of water, while for hydrophilic ionic liquids, the ring remains flat on the surface. The process was found to be reversible, with the tilting of the cation attributed to the interaction of water with C(2)—H. Moreover, for water-miscible ionic liquids, water molecules were said to be... 

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