Electronic Spectra and the Mechanism of Complexing of Uranyl Nitrate in Water–Acetone Solutions

Based on the analysis of electronic absorption and luminescence spectra, the processes of complexing in an aqueous solution of uranyl nitrate hexahydrate (UO₂(NO₃)₂·6H₂O) on gradual addition of small amounts of acetone have been investigated. In a pure aqueous solution, uranyl exists as the UO₂·5H₂O complex. It is shown that addition of acetone to the solution leads to displacement of some water molecules from the first coordination sphere of uranyl and formation of uranyl nitrate dihydrate complexes, UO₂(NO₃)₂·2H₂O. It has been established that the stability of these complexes is determined by the decrease in both the water activity and the degree of hydration of uranyl and nitrate. This is the result of the local increase in the concentration of the molecules of acetone (due to its hydrophobicity) in those regions of the solution in which there are uranyl and nitrate ions. The experimental facts supporting the proposed mechanism are given.     

Infrared Spectra Interpretations of Clay-Adsorbed Water in Relation to the “Anomalous” Water Controversy

Abstract

The nature of surface adsorbed water has been the subject of countless investigations. Much of the discussion has centered around the degree and strength of H-bonding to surface groups and between adjacent water molecules.^1,2 Water condensed into glass or quartz capillaries sometimes has unusual properties. This unusual water has been referred to as “orthowater,”³ “anomalous water,”^4,5,6 and “polywater”^7,8 and was thought by some to be polymers of water formed by specific surface catalysis.^1–3 Several possible structures of “polywater” have been suggested which require formation of symmetrical or very strong H-bonds between water molecules.^4,6,7 Infrared spectra of polywater have been presented^7,8 and the strongest absorption band which appeared at 1595 cm^?1 was assigned to the symmetric O-H-O bond. However, more recent investigations suggest that the observed polywater bands may actually be SO₄ ^2-, -COOH^?, or HCO₃ ^? bands, impurities collected by surface diffusion,⁹ or bands of a HNO₃ solution formed by corona discharge.¹⁰ Other observers^11,12 suggest that polywater may be a hydrosol formed by surface contaminates.     

Vibronic excitation spectrum of alkali aluminometaphosphate glasses containing uranium

The absorption, excitation and emission spectra of metaphosphate glasses MPO₃.Al(PO₃)₃ (M = Li, Na, K) doped with 1 or 2 w.% of uranium oxide have been measured at room temperature. The spectra were compared with those of solid uranyl nitrate and its water solution. The excitation band of glasses peaking at about 420 nm shows a great deal of structure like that of the solution. The diffuse structure would be due to the electron vibronic transitions in the uranium centre of a molecular form (probably uranyl (UO₂)²⁺).     

Optical spectra of mixed anhydrous rare earth trihalides

The optical absorption spectra of 1 per cent Nd in LaCl₃ doped with Br and I have been investigated. Extra lines produced by replacing Cl ions by Br and I ions have been observed. Two contributions to the change of the energy of the absorption lines in different local environments can be separated; one which is due to the change of lattice spacing and another one which is due to the change of the ionicity of the anion.     

Self- and N2-broadened spectra of water vapor between 7.5 and 14.5 μm

Self- and N₂-broadened absorption spectra of water vapor have been measured in the infrared between 7.5 and 14.5 μm at 294, 311, 333 and 339 K. The so-called continuum aspect of the observed absorption coefficients is interpreted in terms of existing theoretical models.     

Absorption and Fluorescence Emission Attributes of a Fluorescent dye: 2,3,5,6-Tetracyano-p-Hydroquinone

Four cyano groups have been substituted on the aromatic ring of p-hydroquinone (2,3,5,6-tetracyanohydroquinone) in order to study the enhanced photoacidity of this molecule. The acid-base equilibria have been studied using absorption (for ground state pK_a) and fluorescence (excited state pK_a) spectra. Three distinct species (neutral, anionic and dianionic forms) were observed in the ground state and only two species (anionic and dianionic forms) were found in the excited state when studied at different pH/H_o in water. Absorption and emission characteristics were studied in various organic solvents, including protic and aprotic solvents. Deprotonation was also investigated using binary mixtures. It has been revealed that absorption and emission spectra are considerably changed with change in media. Proton transfer to the solvent has been observed in various solvents.     

Diode laser measurements of temperature-dependent collisional-narrowing and broadening parameters of Ar-perturbed H2O transitions at 1391.7 and 1397.8 nm

High-resolution absorption lineshapes of two H₂O transitions near 7185.60 and 7154.35 cm⁻¹ have been recorded in a heated static cell as a function of temperature (296-1100 K) and pressure (6-830 Torr) using two distributed-feedback diode lasers. The measured absorption spectra are least squares fit to both Voigt and Galatry profiles. Strong collisional-narrowing effects are observed in the Ar-broadened H₂O spectra at near-atmospheric pressure due to the relatively weak collisional broadening induced by Ar-H₂O collisions, while collisional narrowing is not significant for pure H₂O absorption lineshapes. Line strengths and self-broadening coefficients are inferred from the pure H₂O absorption spectra and compared with published data. Temperature dependences of the Ar-induced broadening, narrowing, and shift coefficients are determined using Galatry fits to the absorption data. The measured collisional-narrowing parameters have similar temperature dependence to the collisional-broadening coefficients.     

Calculation of absorption and resonance Raman cross sections of ClO2 in the gas‐phase and in solution: including Duschinsky effects

The time‐correlation function formalism has been used to calculate resonance Raman cross sections, excitation profiles, and electronic absorption spectra of the OClO molecule in the gas‐phase and in different solvents like cyclohexane, chloroform, and water. The multidimensional time domain integrals that arise in these calculations have been evaluated for the case in which an X²B₁ òA₁ electronic transition takes place between displaced‐distorted‐rotated harmonic potential energy surfaces. Ab initio calculations have been performed to provide the spectroscopic constants required for the evaluation of these integrals. The calculated absorption spectra and resonance Raman cross sections have been compared with the experimental results. Copyright © 2009 John Wiley & Sons, Ltd.     

Spectral and Photophysical Properties of α-carboline (1-Azacarbazole) in Aqueous Solutions

The absorption and fluorescence spectra of α-carboline, 9H-pyrido[2,3-b]indole, AC, in organic aprotic solvents containing different water proportions and in acid/base aqueous solutions inside and outside the pH range have been examined. In the organic aprotic solvents, the addition of increasing concentrations of water sequentially quenches and shifts to the red the fluorescence spectra of AC. These spectral changes have been rationalized assuming the formation, at the lower water concentrations, of a discrete ground state non-cyclic weakly fluorescent AC hydrate emitting at 376 nm that, upon increasing the water concentrations, evolves to a higher order AC poly hydrate emitting at 397 nm. The changes of the AC absorption spectra in aqueous acid/basic solutions indicate the existence of three ground state prototropic species; the pyridinic protonated cation, C (pK_a?=?4.10?±?0.05), the neutral, N (pK_a?=?14.5?±?0.2), and the pyrrolic deprotonated anion, A. Conversely, the changes of the AC fluorescence spectra in these media indicate the existence of four excited state species emitting at 376 nm, 397 nm, 460 nm and 465 nm. Since the emissions at 376 nm and 397 nm satisfactorily match those of the hydrates observed in the organic-water mixtures, they were consistently assigned to two differently hydrated ground state N species. The remaining emissions at 460 nm and 465 nm have been assigned without ambiguity, on the basis of their excitation spectra, to the C and A species, respectively. The excited-state pK_as of the prototropic species of AC have been estimated by using the Förster-Weller cycle.     

IR absorption spectrum (4200–3100 cm) of H2O and (H2O)2 in CCl4. Estimates of the equilibrium constant and evidence that the atmospheric water absorption continuum is due to the water dimer

IR absorption spectra, 4200–3100 cm⁻¹, of water in CCl₄ solutions are presented. It is shown that for saturated solutions significant amounts of water are present as dimer (ca. 2%). The IR spectra of the monomer and dimer are retrieved. The integrated absorption coefficients of the monomer absorption are significantly enhanced relative to the gas phase values. The dimer spectrum consists of 5 bands, of which 4 were expected from data from cold beams and cold matrices. The origin of the “extra” band is discussed. In addition it is argued that the dimer absorption bands intensities must be enhanced relative to the gas phase values. Based on recent calculations of band strengths, and observed frequency shifts relative to the gas phase, the intensity enhancement factors are estimated as well as the monomer/dimer equilibrium constant in CCl₄ solution at T=296 K (K_c=1.29 mol⁻¹ L). It is noted that the observed dimer spectrum has a striking resemblance with the water vapour continuum determined by Burch in 1985 which was recently remeasured by Paynter et al. and it is concluded that the atmospheric water absorption continuum in the investigated spectral region must be due to water dimer. Based on the newly published spectral data a revised value of the gas phase equilibrium constant is suggested (K_p=0.035 atm⁻¹ at T=296 K) as well as a value for the standard enthalpy of formation, ΔH⁰=15.4 kJ mol⁻¹.     

Infrared absorption and water structure in aerosol OT reverse micelles

Summary The structure of water in bis(2-ethylhexyl)sodium sulfosuccinate (AOT) micelles has been studied as a function of the [H₂O]/[AOT] ratio (W) by using the absorption IR due to O−H stretching modes in the 3800–3000 cm⁻¹ range. Three systems have been studied: water/AOT/carbon tetrachloride, water/AOT/n-heptane and water/AOT iso-octane. Experimental spectra are presented and discussed for the O−H stretching region both of H₂O and isotopically diluted HDO molecules in D₂O. We have restricted ourselves to the region of small amounts of water (0<W<20) where the properties of the systems change strongly with the water content. The results show that IR spectra can be expressed as sum of contributions from interfacial and bulk-like water. The fraction of water in the two “regions” within the water pool was evaluated as a function ofW. From the data a continuous variation appears in the water properties inside micellar cores rather than a two-steps hydration mechanism. The solubilization of water is described in terms of hydration of the AOT head group and Na⁺ counterions. The maximum hydration number of AOT was found to be 3.5. The same behaviour has been observed in the three solvents studied.     

Libratory modes of water molecules in tutton salts

The existence of rocking, wagging and twisting librations of different types of water molecules in tutton salts has been established from their ir spectra. These bands have been identified, following the intensity criterion of Miyazawa. The present assignments indicate that the bands due to libratory motion of H₂O III in NH₄Mn-, KNi-, KCo and KMn- and of H₂O I in KMn- and KCu- tutton salts are out-of-plane H-bonded. The strength of the hydrogen bonding is the weakest in the (NH₄)₂Fe(SO₄)₂.6H₂O.     

Infrared properties of the oxygen-deficient triperovskite YBa2Cu3Oy compound

Infrared absorption spectra have been evaluated for the YBa₂Cu₃O_y compound samples prepared after rapid cooling from various temperatures in order to maintain the composition existing at the quench temperature. The absorption spectra for the samples with tetragonal symmetry and the reflection spectra for the samples with the orthorhombic symmetry have been determined. The superconducting energy gap was evaluated for a orthorhombic sample.     

Fundamental absorption spectra of transition metal chlorides

The optical absorption spectra of MnCl₂, FeCl₂, CoCl₂, and NiCl₂ have been measured over the energy range from 2 to 30 eV. The gross features of the spectra, especially broad bands above 10eV, are alike in all of the four materials. The charge transfer bands due to the electronic transitions from the 3p level of chlorine to the 3d and 4s levels of metal ions and the band due to the 3d → 4s transition are assigned in the spectra.     

Spectral behavior study of 3-(4-dimethylamino-phenyl)-1-{6-[3-(4-dimethylamino-phenyl)-acryloyl]-pyridin-2-yl}-propanone

The photophysical properties such as singlet absorption, molar absorptivity, fluorescence spectra, fluorescence quantum yield (?_f) and transition dipole moment (μ₁₂) of 3-(4-dimethylamino-phenyl)-1-{6-[3-(4-dimethylamino-phenyl)-acryloyl]-pyridin-2-yl}-propanone (DMAPAPP) have been studied in different media. DMAPAPP exhibits a large red-shift in both absorption and emission spectra as the solvent polarity increases, indicating a large change in dipole moment of molecule upon excitation. The fluorescence quantum yield depends on the nature of the solvent. The absorption and emission spectra of DMAPAPP in dioxane–water mixture are also studied. The effect of different type of surfactants to determine their critical micellar concentration (CMC) and the microemulsion effect on the electronic absorption and emission spectra of DMAPAPP are recorded. The effect of acidity on the electronic absorption and emission spectra of DMAPAPP is studied to determine the pK_a and pK_a^? values.     

Energy spectrum and optical transitions in C80 fullerene isomers

The energy spectra of all isomers of the C₈₀ fullerene have been calculated in terms of the Schubin-Wonsowskii-Hubbard model. On this basis, their optical absorption spectra have also been calculated. The optical absorption spectra calculated for the endohedral Ca@C₈₀, Ba@C₈₀, and Sr@C₈₀ fullerenes with the I _h symmetry agree well with the experimental data. This circumstance allows us to conclude that the optical absorption spectra of other isomers (for which experimental data are unavailable) obtained in this work can be used for their identification.     

Photoluminescence and photoconductive characteristics of hydrothermally synthesized ZnO nanoparticles

In the present paper, ZnO nanoparticles (NPs) with particle size of 20–50 nm have been synthesized by hydrothermal method. UV-visible absorption spectra of ZnO nanoparticles show absorption edge at 372 nm, which is blue-shifted as compared to bulk ZnO. Photoluminescence (PL) and photoconductive device characteristics, including field response, light intensity response, rise and decay time response, and spectral response have been studied systematically. The photoluminescence spectra of these ZnO nanoparticles exhibited different emission peaks at 396 nm, 416 nm, 445 nm, 481 nm, and 524 nm. The photoconductivity spectra of ZnO nanoparticles are studied in the UV-visible spectral region (366–691 nm). In spectral response curve of ZnO NPs, the wavelength dependence of the photocurrent is very close to the absorption and photoluminescence spectra. The photo generated current, I_pc = (I_total - I_dark) and dark current I_dc varies according to the power law with the applied field I_pcαV^r and with the intensity of illumination I_pcαI_L ^r, due to the defect related mechanism including both recombination centers and traps. The ZnO NPs is found to have deep trap of 0.96 eV, very close to green band emission. The photo and dark conductivities of ZnO NPs have been measured using thick film of powder without any binder.     

Atomic Absorption Spectrometry of Fire-Extinguishing Aerosols

The process of extinguishing a propane-air flame by aerosols of salt solutions has been investigated with the use of an atomic absorption spectrometer. The method of comparing aerosols in terms of the extinguishing efficiency has been evaluated. The changes in the flame temperature and spectra at different jet heights under the influence of aerosols of water and K₂CO₃ and Al(NO₃)₃ solutions have been shown.     

Giant red shift of the absorption spectra due to nonstoichiometry in GdCoO<Subscript>3–δ</Subscript>

The GdCoO_3–δ perovskite is a semiconductor with the energy gap E _g ≈ 0.5 eV from electrical transport measurements. It reveals unusual optical absorption spectra without transparency window expected for semiconductors. Instead we have measured the narrow transmittance peak at the photon energy ε₀ = 0.087 eV. To reconcile the transport and optical data we have studied the effect of oxygen vacancies on the electronic structure of the GdCoO_3–δ. We have found that oxygen vacancies result in the in-gap states inside the charge-transfer energy gap of the GdCoO₃. It is a multielectron effect due to strong electron correlations forming the electronic structure of the GdCoO_3–δ. These in-gap states decrease the transparency window and result in a narrow absorption minimum. The predicted temperature dependence of the absorption spectra has been confirmed by our measurements.     

Goldanskii effect in quadrupole Mössbauer spectra of the 89 keV gamma ray of 156Gd

Unusual relative line intensities in the recoilless absorption spectra of the 89 keV gamma ray of ¹⁵⁶Gd in Gd₂Ti₂O₇ have been observed at various temperatures. The results prove that the unusual intensities are mainly due to lattice vibrational anisotropy.