Vibrational Modes Of Water Research Articles

Terahertz Irradiation of Liquid Water Inhibits Methane Hydrate Formation

In the general effort toward a low carbon economy, natural gas (NG) may represent a viable solution in a transition scenario. NG is conveyed through pipelines where, under low temperatures and high pressures that are typically found under sea bottom conditions (1–4 °C and 6–8 MPa), ice-like solid gas hydrates may form, grow, accumulate, and eventually cause complete pipe plugging. To avoid such events, chemical inhibitors are generally added, which chemically disrupt the structure of water, preventing the formation and/or growth of hydrates. To identify alternative chemical-free approaches to hydrate inhibition, the effects of electromagnetic radiation in the terahertz (THz) domain are explored. In this paper, we show, for the first time, that hydrate formation is inhibited by irradiating the water/methane system with THz radiation in the spectral region between 1 and 5 THz. In addition, we show that this inhibition persists for many hours after switching off the irradiation. A tentative explanation of this phenomenon is given in terms of THz radiation interaction with vibrational modes of water in hydrate-like cages. The findings reported herein may be developed into a sustainable, chemical-free hydrate inhibition process.

Effect of fine-tuning pore structures on the dynamics of confined water

Confinement of water in sub-nanometer pores strongly alters its vibrational dynamics from that of bulk water. The effect of confinement can, furthermore, be finely tuned by small changes in the size and symmetry of the confining pore. Using inelastic neutron scattering (INS), we recently studied the dynamics of water confined in the channels of beryl and cordierite in which, at low temperatures, water shows similar behavior, indicating an absence of hydrogen bonds acting on the water molecule and a shallow water potential in the direction perpendicular to the channels. In addition, we observed multiple tunneling modes (between 0.66 and 14.7 meV) in the INS spectra of beryl due to transitions between the split ground-state of the water protons. Here, we present a study of (i) the effect of pressure on the dynamics of water in beryl, (ii) the dynamics of water in beryl containing alkali metals (which results in changing the orientation of the water molecule in the crystal), and (iii) the dynamics of water in cordierite at low energies. We found a shift in the tunneling and vibrational modes of water in beryl to higher energies at 22 kbar relative to 1 bar. No tunneling modes were observed for water in cordierite and type-II water in beryl. Therefore, we conclude that very small differences in the size and structure of the pores and the orientation of the water molecule in these minerals result in changes in the potential of the water protons and drastic changes in the confined water dynamics.

Unraveling the Coupled Processes of (De)hydration and Structural Changes in Na+-Saturated Montmorillonite

The coupled processes of (de)hydration and structural changes of a well characterized Na+-exchanged dioctahedral smectite with a low layer charge (0.26 mol(+)/formula unit) were studied by in situ transmission Fourier transform infrared spectroscopy. Therefore, a sample preparation technique based on the tethering by aggregation and growth method is extended to clay minerals to obtain a thin film of montmorillonite on a silicon wafer. After equilibration of the sample at 53% relative humidity, infrared measurements were done with a custom-made, heatable sample holder in an oxygen free atmosphere under N2 purging which allowed subsequent FTIR measurements. Using a very thin film, deviation of the Si–O phonon modes could be simultaneously studied with the vibrational modes of water. The structural changes in the 2:1 layer of the montmorillonite during dehydration can be recognized from the shift of longitudinal optical Si–O phonon mode. The accompanied decrease and shift of the bending vibration of water δ(...

Effect of the cation on the interactions between alkyl methyl imidazolium chloride ionic liquids and water.

A systematic study of the interactions between water and alkyl methyl imidazolium chloride ionic liquids at 298.2 K, based on activity coefficients estimated from water activity measurements in the entire solubility range, is presented. The results show that the activity coefficients of water in the studied ILs are controlled by the hydrophilicity of the cation and the cation-anion interaction. To achieve a deeper understanding on the interactions between water and the ILs, COSMO-RS and FTIR spectroscopy were also applied. COSMO-RS was used to predict the activity coefficient of water in the studied ionic liquids along with the excess enthalpies, suggesting the formation of complexes between three molecules of water and one IL molecule. On the basis of quantum-chemical calculations, it is found that cation-anion interaction plays an important role upon the ability of the IL anion to interact with water. The changes in the peak positions/band areas of OH vibrational modes of water as a function of IL concentration were investigated, and the impact of the cation on the hydrogen-bonding network of water is identified and discussed.

CHARACTERISTIC VIBRATIONAL MODES OF H2O ADSORBED MOLECULARLY AND DISSOCIATIVELY ON TITANIUM OXIDE CLUSTERS

To provide useful information on dissociation of water molecule on ( TiO2 )n clusters for experimental verification, we have calculated the infrared (IR) and Raman spectra of three possible states involved, namely molecularly adsorbed state, metastable state and dissociatively adsorbed state, using density functional theory at the B3LYP/6-311G(d) level. We find that the characteristic bands of H2O molecules below 2000 cm-1 in both IR and Raman spectra vanish upon both molecular and dissociative adsorption of H2O . In the high frequency range of 3600–4200 cm-1, the adsorption caused the single IR peak of water to split into two bands, while the dissociation removed the one at lower frequency and blue shifted slightly the higher frequency band. The two Raman peaks of the water molecule in the same high frequency range were slightly blue shifted upon adsorption but the one at lower frequency was removed upon dissociation, while the one at high frequency blue shifted slightly. The intensities of vibrational modes of water in 3600–4200 cm-1 are generally significantly enhanced upon both molecular and dissociative adsorption. Our results show clearly signatures of dissociation of water molecule into hydroxyl radical at the terminal site.

Infrared spectroscopic study of water in mesoporous silica under supercritical conditions

The structure of water under high temperature–pressure conditions in mesospace was investigated by measuring the infrared spectra of water in mesoporous silica. Absorption peaks attributed to OH-stretching vibration of water in mesoporous silica were detected at lower wavenumbers as compared with bulk water, and the absorption peak positions were dependent on pore diameter. For small pore diameters (3–20 nm), absorption peak positions of water were detected at lower wavenumbers (ca. 3,300 cm−1) at 400 °C, while for larger pore diameters (30–50 nm) the peaks were detected at higher wavenumbers (ca. 3,500 cm−1). We attribute these features to the effects of mesoporous silica surface structure on the structural and vibrational modes of water. Furthermore, absorption peak positions changed significantly at different pore sizes (20 and 30 nm), indicating that the structure of water in small pores approaches a more ice-like structure. Based on our experimental results, the structured water layer in mesoporous silica is estimated to be at least 10 nm thick, which is thicker than that previously documented in molecular dynamic simulation studies where the thickness of structured water was found to be two or three layers from the surface.

Cation–anion–water interactions in aqueous mixtures of imidazolium based ionic liquids

We have examined the cation–anion–water interactions in aqueous mixtures of imidazolium ionic liquids (ILs) over the whole composition range using FTIR spectroscopy. Changes in the peak positions or band areas of OH vibrational modes of water and CH vibrational modes of imidazolium cation as a function of IL concentration indicated a diminishing trend in hydrogen-bonding network of water and qualitative changes in solution structures. 1H NMR chemical shifts of C(2)H, HC(4)C(5)H and alkyl chain protons of imidazolium cation provided useful information about the comparative strength of cation–anion–water interactions.

Changes in vibrational modes of water and bioprotectants in solution

Inelastic neutron scattering (INS) measurements have been performed on trehalose and sucrose/H 2O mixtures at very low temperature as a function of concentration by using the TOSCA spectrometer at the ISIS Facility (DRAL, UK). The aim of this work is to investigate by INS the vibrational behaviour of water in presence of trehalose and sucrose in order to characterize the changes induced by these disaccharides on the H 2O hydrogen-bonded network. In particular, we obtained information about the effects of the two disaccharides in the translational, librational and bending spectral regions of ice. The disaccharide bioprotective effectiveness can be linked by the high destructuring effect emphasised by the analysis of the librational modes region. On the other hand, the analysis of the vibrational region corresponding to the ice bending modes show a high “crystallinity” degree which can justify the cryptobiotic action of disaccharides.

Biomedical applications of free-electron lasers

Tunable, pulsed radiation sources in the ultraviolet, visible, and infrared wavelength ranges offer novel opportunities for investigating laser-induced biomedical effects. Free-electron lasers (FELs) deliver continuously tunable, pulsed radiation in the infrared, providing the capability to selectively target radiation into the vibrational modes of water or other biopolymers. Experimental techniques for measuring the absorption spectra of biological samples are described. These spectra indicate wavelengths that potentially serve as the basis for laser-induced biomedical effects. Some practical considerations for infrared, visible, and UV spectroscopy of biological samples are summarized, and the connection between biomedical research and more fundamental investigations of vibrational energy transfer are emphasized.

Infrared and Raman spectra of potassium pentacyanonitrosylmanganate(I) dihydrate: K3[Mn(CN)5NO]� 2H2O

The infrared spectra of polycrystalline K/sub 3/(Mn(CN)/sub 5/NO) x 2H/sub 2/O at different degrees of deuteration were recorded between 4000 and 200 cm/sup -1/, both at room and low temperature. The room-temperature Raman spectrum of the isotopically normal powder was also obtained. The observed bands were assigned to the internal vibrational modes of the (Mn(CN)/sub 5/NO)/sup 3 -/ ion and to the internal and vibrational modes of water of hydration. In accordance with X-ray diffraction studies, the spectra showed the existence of two crystallographically distinct types of water molecules located in different sets of sites of C/sub 1/ symmetry.

Infrared studies of water in complexes

The intramolecular coupling of the OH stretching vibrational frequencies are studied in binary mixtures (H2O + bases) and ternary mixtures (H2O + bases + CCl4). For water molecules partially H bonded with bases (1:1 complexes) this coupling decreases rapidly with the acceptor strength, the C2ν symmetry changing to Cs. In 2:1 complexes the C2ν symmetry is re-established, ν3 and ν1 undergo similar frequency shifts referred to unperturbed H2O. The force constants and vibrational modes of water in 1:1 complexes are calculated approximately. This paper shows that the frequency region between the unperturbed ν3 and the unperturbed (ν3+ν1)/2 is useful in determining the content of non H bonded OH groups.