Free H2O Molecules Research Articles

The orientation and vibrational states of H 2 O in synthetic alkali-free beryl

The polarized single-crystal Raman spectra of synthetic H2O-containing alkali-free beryl were recorded at room and low temperatures, and the polarized single-crystal IR spectra at room temperature. The H2O molecule in the channel cavities is characterized by a Raman-active symmetric stretching vibration (ν1) at 3607 cm−1 and an IR-active asymmetric stretch (ν3) at 3700 cm−1 at room temperature. At low temperatures this ν3 mode is observed in the Raman. Weak ν1 and ν3 modes of a second type of H2O are also observed in the Raman spectra but only at 5 K. The H⋯·H vector of the most abundant type of H2O is parallel to the channel axis of beryl along [0 0 0 1]. The components of the polarizability tensor of the ν1 mode of H2O are similar to, but not exactly the same as, those of a free H2O molecule. The Raman measurements indicate that the H2O molecule is rotationally disordered around [0 0 0 1]. External translation and librational modes of H2O could be observed as overtones with the internal H2O-stretching modes. In the case of the librational motions, normal modes could also be observed directly in the Raman spectra at ∼200 cm−1. The energies of the translational modes can be determined from an analysis of the overtones and are about 9 cm−1 in energy (i.e., Tz). The energies of the librational modes are about 210 cm−1 for Rx and 190 cm−1 for Ry.

Optical absorption spectra studies for amorphous Cu2O-Bi2O3 glass system

Infrared absorption spectra were measured in the spectral range 4000–200 cm−1 for the Cu2O-Bi2O3 glass system. Strong bands were observed around 436–477, 600–632, 700–715, 810–875, 975–1000, 1550–1610 and 3225–3510 cm−1 which are due to harmonics of the Bi-O-Bi stretching vibration, Cu-O stretching vibrations, O-Bi-O stretching vibrations, O-Bi-O bending vibrations, Bi-O stretching vibrations, free H2O normal-mode bending vibrations and free H2O molecules or OH− ions, respectively. Quantitative justification of these absorption bands shows that the values of the experimental wave number for most recorded absorption bands agree well with the theoretical ones. The optical absorption spectra were recorded for the same glass system in the spectral range 300–700 Nm. These records show that the absorption edge has a tail extending towards lower energies. The edge shifts towards lower energies with increasing Cu2O content. This shift is mostly related to the structural rearrangement and the relative concentrations of the glass basic units. By increasing the Cu2O content, the optical energy gap decreases, while the width of the localized states increases.

Cation influence on the structure and electron density of water in some Men+�H2O complexes

The cation influence on the water molecule in the Li+·H2O, Be2+·H2O, Mg2+·H2O and A13+·H2O complexes has been studied by means of quantum-mechanical ab initio calculations. A number of general trends are noted. (1) The calculated equilibrium water O-H distances increase with increasing binding energies, i.e. in the order Li+, Mg2+, Be2+, Al3+. The H-O-H angles differ by about ±1 ° from the calculated equilibrium angle for the free H2O molecule; the variation has no systematic trend. (2) The electron density redistribution accompanying the change in the internal H2O geometry in these complexes is considerably smaller than the redistribution brought about by the direct influence of the external field. (3) The harmonic O-H stretching force constant decreases with increased cation-water bonding. (4) The qualitative features of the density changes are very similar for the four complexes. The magnitudes of the interactions follow the relation Li+ < Mg2+ < Be2+≲ Al3+. An increased polarization of the H2O molecule occurs with electron migration from the H atoms towards the O atom and an accumulation of electron charge approximately at the centre of the Men+—O bond, especially in Be2+·H2O and A13+·H2O. An electron deficiency is found in the lone-pair region.

Depolarisation thermocurrents in frozen aqueous solutions of glucose

The dielectric behaviour of frozen aqueous solutions of glucose was studied by the depolarisation thermocurrent (DTC) method in the temperature range 85-250K and over a wide range of concentrations (0.005-1.5 mol. litre-1), to obtain information on the state of water in the solutions. Two predominant peaks were observed at temperatures of about 125-130 and 225K, respectively. The low-temperature DTC peak was studied in detail, using several techniques offered by the DTC method. The peak was attributed to polarisation of free and hydration H2O molecules. The results show the existence of a continuous transition from hydration to free H2O molecules in solutions with molar solute concentrations up to about 0.7 mol. litre-1, and the presence of only hydration H2O molecules in solutions with higher concentrations.

Dielectric studies of zeolite systems. Part 2.—Ag-X zeolite with dipolar and non-dipolar absorbates

Studies have been made over the range 6 Hz to 130 kHz and 170 to 450 K of dielectric absorptions in Ag-X zeolite evacuated at 10–5 Torr and 520 K and also with controlled contents of H2O, NH3, CH3CN or C6H6: adsorption isotherms were measured simultaneously. Introduction of a Teflon film with the compacted dielectric disc gave blocking-electrode conditions when the d.c. conductance was disturbingly large. In addition to this d.c. ionic conductance a separate dielectric absorption (I) was measured in the zeolite itself and further distinct processes, absorption II and III were characterized both in frequency and intensity (via Fuoss–Kirkwood parameters) and in activation enthalpy and entropy terms (via Eyring parameters). Processes I and II arise from ion-jumping within the lattice and are discussed in relation to their most probable mechanisms. Absorption III in Ag-X/H2O is due to H2O reorientation: it appears (sharply) at H2O contents above 160 molecules per unit cell and has an effective strength (µeff≈ 1.8 D) equivalent to that of the free H2O molecule.