Excited-state proton transfer of 3-hydroxybenzoic acid and 4-hydroxybenzoic acid

The excited-state proton transfer of 3-hydroxybenzoic acid and 4-hydroxybenzoic acid was studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses. The excited-state reactions were identified in aqueous media as a function of the pH value. Apart from the well-known inversion of the ordinary dissociation properties of these compounds, new species were found which exist only in the excited-state resulting from a temporal and reversible annihilation of the aromatic bond system. These species and their reaction mechanisms were detected by their absorption and fluorescence spectra.     

Syntheses and spectroscopic characterization of uranium(VI) silicate minerals

In this study, the secondary uranium(VI) silicate minerals boltwoodite, sodium boltwoodite and uranophane were synthesized. Sodium boltwoodite was successfully obtained by the following new reaction procedure. Their analytical characterization was carried out by means of inductively coupled plasma mass spectrometry and atomic absorption spectroscopy, scanning electron microscopy, X-ray powder diffraction, differential thermal analysis combined with thermogravimetry and infrared spectroscopy. Furthermore, the fluorescence behaviour was measured using time-resolved laser fluorescence spectroscopy. Herewith, the fluorescence properties of the three silicious uranyl phases were determined at room temperature.     

First fluorescence spectroscopic investigation of Am(III) complexation with an organic carboxylic ligand, pyromellitic acid

For the first time Am(III) complexation with a small organic ligand could be identified and characterized with time-resolved laser-induced fluorescence spectroscopy (TRLFS) at room temperature and trace metal concentration. With pyromellitic acid (1,2,4,5-benzene-tetracarboxylic acid, BTC) as ligand spectroscopic characteristics for the Am-BTC complex system were determined at pH 5.0, an ionic strength of 0.1 M (NaClO4) and room temperature. The fluorescence lifetimes were determined to be 23.2±2.2 ns for Am3+(aq) and 27.2±1.2 ns for the Am-BTC 1:1 complex; the emission maximum for the 5D1-(7)F1 transition is 691 nm for both species. The complex stability constant for the Am-BTC 1:1 complex was calculated to be logβ110=5.42±0.16.     

Hydrodynamic and mass transfer characteristic of a novel grid-structured plastic packing

The hydraulic and mass transfer characteristic of a novel grid-structured plastic packing is presented. The geometry of this structured packings differ substantially from conventional corrugated structured packings resulting in an open structure which enables a free exchange of vapour and liquid also in horizontal direction. The hydraulic performance has been measured by air–water experiments in a 440 mm diameter column, the mass transfer characteristic has been determined with the absorption system ammonia–air–water. Is is shown that the grid-structured plastic packing is highly efficient, particularly in terms of the hydraulic capacity compared with random plastic packings. Beside this, the main advantage of the packing is the easy handling and installation as well as the low investment costs compared to the well-known conventional corrugated structured packings.     

Complex formation of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses

The complex formation of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid (vanillic acid) was studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses using the fluorescence properties of 4-hydroxy-3-methoxybenzoic acid. A 2:1 complex of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid was found. The stability constant of this complex was determined to be logbeta(210) = 7.33 +/- 0.10 at an ionic strength of 0.1 mol/l (NaClO(4)) and at 21 degrees C. The determination of the stability constant required an investigation of the excited-state proton transfer of 4-hydroxy-3-methoxybenzoic acid over the whole pH range. It was realized that 4-hydroxy-3-methoxybenzoic acid undergoes excited-state reactions only at pH values below 5. At pH values above 5 stability constants can be determined without kinetic calculation of the proton transfer.     

Complexation of uranium(VI) with aromatic acids such as hydroxamic and benzoic acid investigated by TRLFS

The complex formation of uranium(VI) with salicylhydroxamic, benzohydroxamic, and benzoic acid was investigated by time-resolved laser-induced fluorescence spectroscopy (TRLFS). We observed in all three systems a decrease in the fluorescence intensity with increasing ligand concentration. All identified complexed uranyl species are of the type M_pL_qH_r. In the uranium(VI)-salicylhydroxamate system a 1: 1 complex with a stability constant of log β ₁₁₁ = 17.34±0.06 and a 1: 2 complex with a stability constant of log β ₁₂₂ = 35.0±0.11 was identified. Also in the uranium(VI)-benzohydroxamate system the stability constants are determined to be log β ₁₁₀ = 7.92±0.11 and log β ₁₂₀ = 16.88±0.49. In the uranium(VI)-benzoate system only a 1: 1 complex is existent with a stability constant of log β ₁₁₀ = 3.56±0.05.     

Fractal-Generated Turbulence in Opposed Jet Flows

The opposed jet configuration presents a canonical geometry suitable for the evaluation of calculation methods seeking to reproduce the impact of strain and re-distribution on turbulent transport in reacting and non-reacting flows. The geometry has the advantage of good optical access and, in principle, an absence of complex boundary conditions. Disadvantages include low frequency flow motion at high nozzle separations and comparatively low turbulence levels causing bulk strain to exceed the turbulent contribution at small nozzle separations. In the current work, fractal generated turbulence has been used to increase the turbulent strain and velocity measurements for isothermal flows are reported with an emphasis on the axis, stagnation plane and the distribution of mean and instantaneous strain rates. Energy spectra were also determined. The instrumentation comprised hot-wire anemometry and particle image velocimetry with the flows to both nozzles seeded with 1  $\upmu$ m silicon oil droplets providing a relaxation time of ? 3 $\upmu$ s. It is shown that fractal grids increase the turbulent Reynolds number range from 48–125 to 109–220 for bulk velocities from 4 to 8 m/s as compared to conventional perforated plate turbulence generators. Low frequency motion of the order 10 Hz could not be completely eliminated and probability density functions were determined for the location of the stagnation plane. Results show that the fluctuation in the position of the stagnation plane is of the order of the integral length scale, which was determined to be 3.1±0.1 mm at the nozzle exits through the use of hot-wire anemometry. Flow statistics close to the fractal plate located upstream of the nozzle exit were also determined using a transparent glass nozzle.     

New trlfs laboratory at the CTU in Prague

Early in 2006, construction and equipment of a new TRLFS (Time-Resolved Laser-induced Fluorescence Spectroscopy) laboratory was accomplished at the Czech Technical University in Prague, Czech Republic. In this contribution, the system is described in detail, the results of the first measurements obtained in the new laboratory for a standard UO ₂ ²⁺ - SO ₄ ²⁻ system are presented, and the future research plans are outlined.     

Calculation of the vibronic spectrum of excitonic luminescence in AgBr:I

The radiative decay of an exciton bound to a substitutional iodine ion in AgBr is investigated theoretically. The vibronic spectrum showing multiphonon replicas is calculated under the assumptions of linear electron-phonon coupling. The experimental intensity of the one-phonon spectrum as a function of frequency could satisfactorily be reproduced only by considering coupling coefficients up to fifth neighbors. This result indicates that the bound exciton influences the dynamics of the lattice over an extended neighborhood of the iodine.