OD Band Research Articles

Depth profiling of implanted D in silicates: Contribution of solar wind protons to water in the Moon and terrestrial planets

The solar wind protons implanted in silicate material and combined with oxygen are considered crucial for forming OH/H O on the Moon and other airless bodies. This process may also have contributed to hydrogen delivery to planetary interiors through the accretion of micrometre-sized dust and planetesimals during early stages of the Solar System. This paper experimentally investigates the depth distribution of solar wind protons in silicate materials and explores the mechanisms that influence this profile. We simulated solar wind irradiation by implanting 3 keV D ions in three typical silicates (olivine, pyroxene, and plagioclase) at a fluence of sim 1.4 × 10 ions/cm . Fourier transform infrared spectroscopy was used to analyse chemical bond changes, while transmission electron microscopy (TEM) characterised microstructural modifications. Nanoscale secondary ion mass spectrometry (NanoSIMS) was employed to measure the D/ O ratio and determine the depth distribution of implanted deuterium. The newly produced OD band (at 2400–2800 cm –1 ) in the infrared spectrum reveals the formation of O–D bonds in the irradiated silicates. The TEM and NanoSIMS results suggest that over 73<!PCT!> of the implanted D accumulated in fully amorphous rims with a depth of 70 nm, while 25<!PCT!> extended inwards to sim 190 nanometres, resulting in partial amorphisation. The distribution of these deuterium particles is governed by the collision processes of the implanted particles, which involve factors such as initial energy loss, cascade collisions, and channelling effects. Furthermore, up to 2<!PCT!> of the total implanted D penetrated the intact lattice via diffusion, reaching depths ranging from hundreds of nanometres to several micrometres. Our results suggest that implanted solar wind protons can be retained in silicate interiors, which may significantly affect the hydrogen isotopic composition in extraterrestrial samples and imply an important source of hydrogen during the formation of terrestrial planets.

Infrared spectroscopic analysis of hydrogen-bonding interactions in cryopreservation solutions

BackgroundIn this study we investigated hydrogen bonding interactions in hydrated and frozen solutions of different cryoprotective agents (CPAs) including dimethyl sulfoxide, glycerol, ethylene glycol, propylene glycol, and trehalose. We also investigated the effect of CPAs on ice crystal growth during storage and correlated this with storage stability of liposomes. MethodsFTIR spectroscopy was used to study hydrogen bonding interactions in CPA solutions in H2O and D2O, and their thermal response was analyzed using van ’t Hoff analysis. The effect of CPAs on ice crystal growth during storage was investigated by microscopy and correlated with storage stability of liposomes encapsulated with a fluorescent dye. ResultsPrincipal component analyses demonstrated that different CPAs can be recognized based on the shape of the OD band region only. Chemically similar molecules such as glycerol and ethylene glycol closely group together in a principal component score plot, whereas trehalose and DMSO appear as condensed separated clusters. The OH/OD band of CPA solutions exhibits an overall shift to higher wavenumbers with increasing temperature and changed fractions of weak and strong hydrogen interactions. CPAs diminish ice crystal formation in frozen samples during storage and minimize liposome leakage during freezing but cannot prevent leakage during frozen storage. ConclusionsCPAs can be distinguished from one another based on the hydrogen bonding network that is formed in solution. DMSO-water mixtures behave anomalous compared to other CPAs that have OH groups. CPAs modulate ice crystal formation during frozen storage but cannot prevent liposome leakage during frozen storage.

Infrared Spectroscopy on Equilibrated High-Density Amorphous Ice.

High-density (HDA) and low-density amorphous ices (LDA) are believed to be counterparts of the high- and low-density liquid phases of water, respectively. In order to better understand how the vibrational modes change during the transition between the two solid states, we present infrared spectroscopy measurements, following the change of the decoupled OD-stretch (vOD) (∼2460 cm–1) and OH-combinational mode (vOH + v2, vOH + 2vR) (∼5000 cm–1). We observe a redshift from HDA to LDA, accompanied with a drastic decrease of the bandwidth. The hydrogen bonds are stronger in LDA, which is caused by a change in the coordination number and number of water molecules interstitial between the first and second hydration shell. The unusually broad uncoupled OD band also clearly distinguishes HDA from other crystalline high-pressure phases, while the shape and position of the in situ prepared LDA are comparable to those of vapor-deposited amorphous ice.

Hydrogen defects in feldspars: kinetics of D/H isotope exchange and diffusion of hydrogen species in alkali feldspars

Diffusion of hydrogen in natural alkali feldspars (Eifel sanidine and adularia from unknown locality) containing strongly bonded OH defects was investigated by D/H isotope exchange in the T range 600–1050 °C at ambient pressure and at elevated pressures up to 8 kbar. Runs at 1 atm were performed in a fused silica tube connected to a liquid D2O reservoir at room temperature. In the high- pressure experiments samples were sealed with D2O in gold capsules and processed up to 4 kbar in externally heated pressure vessels using Ar/D2O as the pressure medium. Experiments at 6–8 kbar were performed in an internally heated gas pressure vessel using the double capsule technique to minimize isotopic contamination by the pressure medium. Diffusion coefficients were determined either by measuring concentration-distance profiles of OH and OD with an IR microscope or by measuring the total exchange of oriented plates after various run durations using a macroscopic IR technique. Both methods gave consistent data. D/H interdiffusion, DD/H, is almost identical in the adularia and in the sanidine implying that the chemical composition and the degree of Al/Si disorder have minor influence on the hydrogen isotope exchange in alkali feldspars. Furthermore, no effect of crystallographic orientation was found for DD/H in both feldspars. DD/H in sanidine, however, depends on the thermal pre-treatment. Heating for several days at 900 °C leads to a lowering of D by a factor of 2.3, indicating a corresponding decrease in mobile hydrogen species. Data for sanidine pre-annealed at 900 °C are well described in the T range 600–1050 °C by DD/Hm2/s=6.9·10-6exp-162kJ/molR·T\\documentclass[12pt]{minimal}\t\t\t\t\\usepackage{amsmath}\t\t\t\t\\usepackage{wasysym}\t\t\t\t\\usepackage{amsfonts}\t\t\t\t\\usepackage{amssymb}\t\t\t\t\\usepackage{amsbsy}\t\t\t\t\\usepackage{mathrsfs}\t\t\t\t\\usepackage{upgreek}\t\t\t\t\\setlength{\\oddsidemargin}{-69pt}\t\t\t\t\\begin{document}$$~D_{{{\\text{D/H}}}} \\left( {{\\text{m}}^{2} {\\text{/s}}} \\right) = 6.9 \\cdot 10^{{ - 6}} \\exp \\left( {\\frac{{ - 162{\\text{~kJ}}/{\\text{mol}}}}{{R \\cdot T}}} \\right)$$\\end{document}The diffusivity is strongly enhanced by water pressures (PH2O), i.e., in the range of 0–2 kbar. At PH2O = 2 kbar the following equation applies in the T-range of 645–800 °C: DD/Hm2/s=1.2·10-6exp-131kJ/molR·T\\documentclass[12pt]{minimal}\t\t\t\t\\usepackage{amsmath}\t\t\t\t\\usepackage{wasysym}\t\t\t\t\\usepackage{amsfonts}\t\t\t\t\\usepackage{amssymb}\t\t\t\t\\usepackage{amsbsy}\t\t\t\t\\usepackage{mathrsfs}\t\t\t\t\\usepackage{upgreek}\t\t\t\t\\setlength{\\oddsidemargin}{-69pt}\t\t\t\t\\begin{document}$$~D_{{D/H}} \\left( {{\\text{m}}^{2} /{\\text{s}}} \\right) = 1.2 \\cdot 10^{{ - 6}} \\exp \\left( {\\frac{{ - 131~{\\text{kJ}}/{\\text{mol}}}}{{R \\cdot T}}} \\right)$$\\end{document}Experiments with D2O/CO2 mixture of ratio 1:1 gave smaller exchange rates compared to pure D2O fluids, confirming that that not the pressure but the water fugacity leads to the increase in the mobility of hydrogen species. At 720 °C and pressures of 4–8 kbar, chemical diffusivities of H2O, tilde{D}_{{{text{H}}_{2} {text{O}}}}, were determined by fitting the weighted sum of the absorbances of the OH and the OD band vs. distance. The tilde{D}_{{{text{H}}_{2} {text{O}}}} values are similar to those reported by Kronenberg et al. (Geochim Cosmochim Acta 60:4075–4094, 1996) for dehydration of Kristallina adularia at ambient pressure. It is concluded that in both cases high concentrations of H2O molecules on interstitial sites govern the transport of hydrogen. Comparison of D/H interdiffusion to O diffusion in sanidine (Freer et al. in Phil Mag A75:485–503, 1997) implies that not only interstitial H2O but also protons contribute to the transport of hydrogen under hydrothermal conditions. On the other hand, the high DD/H at ambient pressure is attributed to an interdiffusion of protons and Na+, which is supported by Na tracerdiffusion data for sanidine (Wilangowski et al. in Defect Diffus Forum 363:79–84, 2015). A basic conclusion of this research is that hydrogen storage capacity and hydrogen diffusion in feldspars are largely determined by extrinsic defects, such as substitutional defects (i.e., Al3+ + H+ for Si4+) and associates of water molecules with vacancies. The bonding of hydrogen species to the defects can vary greatly, depending on the genesis of the feldspars, so that quantitative predictions are difficult.

Efficient Original-Destination Bandwidth: A Novel Model for Arterial Traffic Signal Coordination

This paper proposes an efficient origin-estimation bandwidth (OD band) model, which provides dedicated progression bands for arterial traffic based on the real-time dynamic matrix of their estimated OD pairs. The innovations of the OD band model are as follows: First, the dynamics of through and turning-in/out traffics are analyzed based on the matrix of their estimated OD pairs, and used to generate the traffic movement sequence at continuous intersections; Second, the end-time of green interval for lag-lag phase sequence at continuous intersections is determined according to the relevant constraints, the relationship between the start/end-time of green interval and the minimum/maximum green intervals; Third, the bandwidths of the two directions of the artery ware produced, after being weighted by their traffic demands. The intuitiveness, convenience, and feasibility of the OD band model were fully demonstrated through a case study. Overall, the OD band model helps to produce bi-directional progression bands for traffic with many turning movements on the artery, and enables the through and turning-in/out traffics to proceed through continuous intersections, when the signals at those intersections are green.

Study protocol for a randomised controlled trial of carvedilol versus variceal band ligation in primary prevention of variceal bleeding in liver cirrhosis (CALIBRE trial)

IntroductionLiver cirrhosis is the fifth largest cause of adult deaths, and a major complication, variceal bleeding is associated with a 1-year mortality of 40%. There is uncertainty on the first-line...

Computational Vibrational Spectroscopy of HDO in Osmolyte-Water Solutions.

The IR absorption and time-resolved IR spectroscopy of the OD stretch mode of HDO in water was successfully used to study osmolyte effects on water H-bonding network. Protecting osmolytes such as sorbitol and trimethylglycine (TMG) make the vibrational OD stretch band red-shifted, whereas urea affects the OD band marginally. Furthermore, we recently showed that, even though sorbitol and TMG cause a slow-down of HDO rotation in their aqueous solutions, urea does not induce any change in the rotational relaxation of HDO in aqueous urea solutions even at high concentrations. To clarify the underlying osmolyte effects on water H-bonding structure and dynamics, we performed molecular dynamics (MD) simulations of a variety of aqueous osmolyte solutions. Using the vibrational solvatochromism model for the OD stretch mode and taking into account the vibrational non-Condon and polarization effects on the OD transition dipole moment, we then calculated the IR absorption spectra and rotational anisotropy decay of the OD stretch mode of HDO for the sake of direct comparisons with our experimental results. The simulation results on the OD stretch IR absorption spectra and the rotational relaxation rate of HDO in osmolyte solutions are found to be in quantitative agreement with experimental data, which confirms the validity of the MD simulation and vibrational solvatochromism approaches. As a result, it becomes clear that the protecting osmolytes like sorbitol and TMG significantly modulate water H-bonding network structure, while urea perturbs water structure little. We anticipate that the computational approach discussed here will serve as an interpretive method with atomic-level chemical accuracy of current linear and nonlinear time-resolved IR spectroscopy of structure and dynamics of water near the surfaces of membranes and proteins under crowded environments.

Simultaneous spectral and temporal analyses of kinetic energies in nonequilibrium systems: theory and application to vibrational relaxation of O-D stretch mode of HOD in water.

A time series of kinetic energies (KE) from classical molecular dynamics (MD) simulation contains fundamental information on system dynamics. It can also be analyzed in the frequency domain through Fourier transformation (FT) of velocity correlation functions, providing energy content of different spectral regions. By limiting the FT time span, we have previously shown that spectral resolution of KE evolution is possible in the nonequilibrium situations [Jeon and Cho, J. Chem. Phys. 2011, 135, 214504]. In this paper, we refine the method by employing the concept of instantaneous power spectra, extending it to reflect an instantaneous time-correlation of velocities with those in the future as well as with those in the past, and present a new method to obtain the instantaneous spectral density of KE (iKESD). This approach enables the simultaneous spectral and temporal resolution of KE with unlimited time precision. We discuss the formal and novel properties of the new iKESD approaches and how to optimize computational methods and determine parameters for practical applications. The method is specifically applied to the nonequilibrium MD simulation of vibrational relaxation of the OD stretch mode in a hydrated HOD molecule by employing a hybrid quantum mechanical/molecular mechanical (QM/MM) potential. We directly compare the computational results with the OD band population relaxation time profiles extracted from the IR pump-probe measurements for 5% HOD in water. The calculated iKESD yields the OD bond relaxation time scale ∼30% larger than the experimental value, and this decay is largely frequency-independent if the classical anharmonicity is accounted for. From the integrated iKESD over intra- and intermolecular bands, the major energy transfer pathways were found to involve the HOD bending mode in the subps range, then the internal modes of the solvent until 5 ps after excitation, and eventually the solvent intermolecular modes. Also, strong hydrogen-bonding of HOD is found to significantly hinder the initial intramolecular energy transfer process.

Gas-discharge source of the noncarcinogenic UV radiation based on the mixture of helium and heavy-water (D2O) vapor

The spectrum of radiation and the results of optimization are presented for a UV lamp that works on the He-D2O mixture and is pumped using a repetitively pulsed barrier discharge. The dependences of the radiation intensity of the OD (X-A) band with the wavelength λ ≈ 309 nm on the partial pressure of the heavywater vapor, working voltage across the working capacitor of the high-voltage modulator, and repetition rate of the current pulses are studied.

Optical characteristics of an electric-discharge source of ultraviolet radiation based on a mixture of argon with heavy water (D2O) vapor

The optical characteristics of a barrier discharge in a mixture of heavy water vapor with argon in the wavelength region 200–315 nm are presented. The dependence of the radiation intensity of the OD (A → X) band at λ = 309 nm on the partial pressure of the D2O vapor is studied, the mechanism of hydroxyl formation in the plasma is considered, and optimal compositions of pollution-free and inexpensive mixtures based on Ar-D2O are determined for application in UV lamps, which are promising for use in photomedicine.

HDO INFRARED DETECTION SENSITIVITY AND D/H ISOTOPIC EXCHANGE IN AMORPHOUS AND CRYSTALLINE ICE

The sensitivity of the OD stretching band as a probe to detect HDO in astrophysical ice is discussed based on IR laboratory spectra of HDO molecules embedded in H2O ice. This band is extremely broad and tends to disappear into the absorption continuum of H2O for low-temperature amorphous samples. Detectable HDO/H2O ratios with this technique may range from a few percent for amorphous samples to a few per thousand in crystalline ice. These relatively high upper limits and the appreciable dependence of the band shape on temperature, which would complicate the interpretation of data from many lines of sight, decisively limit the usefulness of the technique for HDO detection in astronomical observations. The process of isotopic H/D exchange in mixed ice of H2O/D2O is also studied through the evolution of the OD band in IR spectra. Isotopic exchange starts at ~120 K and is greatly accelerated at 150 K, as crystallization proceeds in the ice. Annealed amorphous samples prove to be more favorable for isotope exchange than samples directly formed in crystalline phase. The annealing process seems to favor a polycrystalline ice morphology with a higher defect activity. These morphology differences can be of relevance for deuterium fractionation in astronomical environments.

Hydrogen bonding in aqueous solution of NaClO4

The ternary system NaClO4–H2O–D2O has been studied, using the Raman spectroscopy. Analysis of the uncoupled OD band of HDO clearly shows that the contour of the band consists of two components only. A new approach has been developed for the quantitative evaluation of the mole fraction of bonded OD groups as a function of perchlorate concentration. It is practically impossible to measure the absolute intensity of Raman scattering. Nevertheless, it is feasible to obtain the specific coefficients of scattering per bonded OD group from the ratio of integrated intensities of the components. For this purpose, the concept of negative ‘phantom’ concentration was introduced, at which all the OD groups must be bonded. As a result, the concentration dependence of the mole fraction of bonded OD groups has been derived. It was found that the infinite network of hydrogen bonds in bulk water ceases to exist at a mole fraction of NaClO4 above ∼0.03–0.035. At higher concentration of perchlorate only residual finite clusters of water molecules can take place. However, the infinite percolation in the system remains. The important fact resulting from the data treatment is that the average number of hydrogen bonds per water molecule in pure water is 2.6 ± 0.2.

H-Bonding of Zeolite Hydroxyls with Weak Bases: FTIR Study of CO and N2Adsorption on H-D-ZSM-5

Adsorption of CO (13CO) and 15N2 at 100 K on H-ZSM-5 samples has been followed by FTIR spectroscopy. For better interpretation of the spectra, experiments with H-D-ZSM-5 and D-ZSM-5 were also carried out. It was established that zeolite bridging hydroxyls displaying at 100 K a band at 3616 cm−1 formed 1:1 adducts with CO, and as a result, the band disappeared, and two new bands at 3306 and 3415 cm−1 emerged at its expense. These two bands changed in concert together with a carbonyl band at 2175 cm−1. Experiments with H-D-ZSM-5 and D-ZSM-5 indicated that the OD band due to bridging deuteroxyls (2667 cm−1) was shifted, upon CO adsorption, again to two IR bands (at 2460 and 2568 cm−1). However, the shift is smaller than expected from the OH → OD isotopic shift factor, which indicates a smaller acidity of OD groups as compared with OH. In addition, the difference in the positions of the two bands (calculated again on the basis of the isotopic shift factor), as well as their relative intensities, deviate from those observed for the OH bands. The results exclude the phenomenon to be due to heterogeneity of the bridging OH/OD groups and indicate a spectral origin. It was concluded that the appearance of two shifted bands was due to Fermi resonance with the second excitation mode of δ(OH). At high CO equilibrium pressure solvatation occurs, and the band at 3306 cm−1 is shifted to lower frequencies. Simultaneously, a shift of the carbonyl band to 2172 cm−1 was observed. At intermediate CO coverages, AlOH···CO complexes are also formed. It is clearly demonstrated that the CO-induced shift of the AlO−H band at 3667 cm−1 is ∼−190 cm−1, and the often reported higher values are due to confusion with the 3415 cm−1 band described above. The AlOD groups have been found to manifest a lower acidity than that of AlOH. Here again, solvatation occurred at high CO coverages. Another effect observed at high CO coverages is the interaction of CO with silanol groups. Two kinds of interaction are unambiguously distinguished: (i) the well documented CO-induced shift of isolated silanols (3745 cm−1) to 3650 cm−1 and (ii) a shift of silanols absorbing in the 3730−3710 cm−1 region to 3580 cm−1. No solvatation was evidenced in this case. Experiment on low temperature adsorption of 15N2 confirmed that the bridging OH(OD) groups of H-ZSM-5 were homogeneous. Upon 15N2 adsorption, the 3616 cm−1 OH band shifted by 118 cm−1, and the respective OD band at 2667 cm−1, by 81 cm−1. Solvatation was detected at high coverages. The 15N2 induced shift of AlO−H modes was found to be 77 cm−1, and for AlO−D, 51 cm−1. Here again, two kinds of interaction with two different silanols were established. A good correlation between the shifts produced by the two probe molecules of different OH and OD groups was found.

Systematic Study of Hydration Patterns of Phosphoric(V) Acid and Its Mono-, Di-, and Tripotassium Salts in Aqueous Solution

Fourier transform infrared (FTIR) spectroscopy of the OD band of HDO molecules has been applied to perform a systematic study of various phosphate forms in the order of decreasing protonation: H3PO4, KH2PO4, K2HPO4, K3PO4. HDO isotopically diluted in H2O has been prepared by adding adequate amounts of D2O to aqueous solutions in ordinary water. The difference spectra procedure has been applied to remove the contribution of bulk water and thus to separate the spectra of solute-affected HDO. The position at maximum of the principal anion-affected HDO band for potassium phosphates moves in the order KH2PO4 (2478 cm(-1))>K2HPO4 (2363 cm(-1))>K3PO4 (2301 cm(-1)), that is, decreases with increasing solute basicity and charge. The number of moles of water affected by one mole of solute (N) equals 11.0, 13.8 and 16.2, respectively. Phosphoric acid affects statistically 13.9 water molecules and appears to be a "structure making" solute in water. The isotopic substitution with deuterium occurs also on the phosphate anions and phosphoric acid. The thus formed P-O-D groups interact with water molecules via strong hydrogen bonds and the relative strength of this interaction increases with increasing solute acidity. The plausible assignments of OD bands of HDO have been confirmed by calculating equilibrium structures of small aqueous clusters of the studied individual utilizing density functional theory. Further interpretation of the energetic and structural properties of hydrating water is enabled by calculating intermolecular interaction energy of water and probability distributions for interatomic oxygen-oxygen distance.

Water structure and its influence on the flotation of carbonate and bicarbonate salts

Interfacial water structure is a most important parameter that influences the collector adsorption by salt minerals such as borax, potash and trona. According to previous studies, salts can be classified as water structure makers and water structure breakers. Water structure making and breaking properties of salt minerals in their saturated brine solutions are essential to explain their flotation behavior. In this work, water structure making–breaking studies in solutions of carbonate and bicarbonate salts (Na 2CO 3, K 2CO 3, NaHCO 3 and NH 4HCO 3) in 4 wt% D 2O in H 2O mixtures have been performed by FTIR analysis of the OD stretching band. This method reveals a microscopic picture of the water structure making/breaking character of the salts in terms of the hydrogen bonding between the water molecules in solution. The results from the vibrational spectroscopic studies demonstrate that carbonate salts (Na 2CO 3 and K 2CO 3) act as strong structure makers, whereas bicarbonate salts (NaHCO 3 and NH 4HCO 3) act as weak structure makers. In addition, the changes in the OD band parameters of carbonate and bicarbonate salt solutions are in agreement with the viscosity characteristics of their solutions.

Hydration of the hydrogen ion in aqueous solutions from intensity of the OD band of HDO

The OD band of HDO has been studied in partly deuterated aqueous solutions of acids: hydrochloric, sulfuric, nitric, trifluoroacetic, and perchloric. Composition of the hydrogen ion is determined. Observations are made on hydration of the perchlorate and trifluoroacetate ions.

Fourier transform-IR and 1 H NMR studies on the structure of water solubilized by reverse aggregates of calcium bis(2-ethylhexyl) sulfosuccinate in organic solvents

The structure of water solubilized by reverse aggregates of calcium bis(2-ethylhexyl) sulfosuccinate in deuterobenzene and toluene has been probed by Fourier transform-IR and 1 H NMR spectroscopies. The ν OD band of solubilized HOD (4% D 2 O in H 2 O) has been recorded as a function of the [water]/[surfactant] molar ratio, W/S. Curve fitting of this band showed the presence of a main peak at 2550 ± 13 cm -1 and a small one at 2405 ± 15 cm -1 . As a function of increasing W/S, the frequency of the main peak decreases, its full width at half-height increases, and its area increases linearly. The 1 H NMR chemical shift of solubilized H 2 O-D 2 O mixtures at W/S = 18.1 has been measured as a function of the deuterium content of the aqueous nanodroplet. These data were used to calculate the so-called fractionation factor of the aggregate-solubilized water, the value of which was found to be unity. The results of both techniques show that reverse aggregate-solubilized water, although different from bulk water, does not seem to coexist in layers of different degrees of structure, as suggested, for example by the two-state water-solubilization model.

Hydration Sphere of Tetrabutylammonium Cation. FTIR Studies of HDO Spectra

The hydration of tetrabutylammonium cation (Bu4N+) has been studied in aqueous solutions of Bu4NBr, Bu4NCl, and Bu4NF salts by means of the FTIR method. Isotopically diluted HDO in H2O has been applied by using the stretching vibration OD band as a probe of the solutes' hydration. The spectra have been analyzed in a way that led to removal of the contribution of the bulk water and thus to the separation of the spectra for salt-affected HDO. In several steps of a curve-fitting procedure the Bu4N+- and the respective anion-affected OD bands have been refined from the salt-affected HDO spectra. The Bu4N+-affected OD band profile and the bulk spectrum have been converted to a probability distribution function of interatomic O···O distances for influenced water, by the use of a correlation curve. Comparison of the band for HDO affected by cation with that of the bulk water, as well as the derived respective distributions of O···O distances, leads to the conclusion that ”iceberg formation” is a wrong expression...

FTIR study of hydration of dodecatungstosilicic acid

The dehydration of H4SiW12 O40·15.6 H2O was studied in situ in the IR chamber. On evacuation at room temperature the departure of most loosely bonded water characterized by bands at 3550 and 1616 cm−1 was observed. In the remaining hexahydrate the band at 3445 cm−1 was ascribed to the hydrogen bond between the Od oxygen atom of the Keggin unit and dioxonium H5O2+ ion, the presence of which is manifested by the 1710 and 1100 cm−1 vibrations. All these bands vanish in the case of anhydrous H4SiW12O40, in which the band at 3106 cm−1 ascribed to the hydrogen bond between neighbouring HPA anions Od−H+−Oc is still present. The dehydration of hexahydrate is accompanied by splitting of the W=Od band into 987 and 1010 cm−1 reflecting the change of the kind of hydrogen bond in which the Od oxygen atom is involved. Based on the above results it was concluded that protons forming oxonium ions in hydrated solid heteropoly acid are more strongly bonded than those in anhydrous one which are forming hydrogen bonds between neighbouring Keggin units.

Deuterium Tracer Studies on Hydrotreating Catalysts. 2. Contribution of the Hydrogen of the Alumina Support to H-D Exchange

H-D isotopic exchange between H2and D2was carried out at 80°C in a recycling reactor under a pressure of 2 bar over unsupported MoS2as well as on alumina supported Mo or NiMo sulfide catalysts. H2-D2experiments carried out over a commercial NiMo/Al2O3catalyst, to which were mixed different amounts of the alumina support, and over a series of Mo/Al2O3catalysts containing different amounts of Mo (4.4 to 14.8 wt%) showed that part of the exchangeable hydrogen detected by isotopic dilution came from the added alumina or from the support. This amount of hydrogen on the alumina was estimated for each series, to be respectively 22.1×10−4and 17.8×10−4mol H·g−1. Since under the same conditions H-D exchange between H2and D2did not occur at an appreciable rate on the alumina alone, it is concluded that hydrogen atoms from structural hydroxyl groups of the alumina or from hydroxyl groups resulting from the dissociation of H2S were able to migrate from grain to grain and to exchange with H2(D2) dissociated on the sulfide active phase. The hydrogen atoms supposedly migrate as protons by jumping from oxygen to oxygen atoms on the alumina surface or are conveyed through the gas phase by H2S (the “shuttle molecule”) which can adsorb dissociatively both on the alumina support and on the active phase. D2adsorption followed by FTIR under similar conditions confirmed that the presence of the sulfide phase was necessary, under the conditions of the experiments, to make the isotopic exchange between H2(D2) in the gas phase and the hydroxyls of the alumina possible. OD bands were difficult to detect on sulfided alumina alone, even after 5 h of exposure to D2, whereas a strong OD band appeared very rapidly on sulfided NiMo/Al2O3. These results are considered as being in favour of a heterolytic splitting of H2on sulfide catalysts.