Yu Yokoyama

Anion coordination to uranyl ion and the luminescence lifetime of the uranyl complex

Abstract Nonexponential uranyl luminescence decay curves corresponding to the liminescence of different complex species was found in solutions containing very small amounts of fluoride or phosphate. The luminescence lifetimes of uranyl aquo ion, 1:1 and 1:2 uranyl fluoro complexes are determined to be 2.4, 75 and 150 μs, respectively (25°C, 0.1 M HClO 4 , μ = 1), The rate of formation of 1:1 uranyl fluoro complex in an excited state (UO 2 2+∗ + F − → UO 2 F +∗ ) is smaller than the rate of deactivation of uranyl aquo ion, but the equilibrium UO 2 F +∗ + F − ⇄ UO 2 F 2 ∗ is attained within the luminescence lifetimes of UO 2 F +∗ and UO 2 F 2 ∗ . Kinetic characteristics of complexes formed between UO 2 2+ and sulfate or phosphate was also discussed.

Quenching of uranyl luminescence by water molecule

Abstract The limetime of uranyl luminescence was measured in aqueous solution. The quenching of uranyl luminescence by water molecules was satisfactorily interpreted by an electron transfer mechanism in terms of oxidation-reduction potentials of uranyl ion and water molecule. The proposed mechanism could also explain the variation in the luminescence lifetime (and the quenching rate constant) with change in pH of the uranyl solution and in the degree of formation of uranyl complex with fluoride, sulfate and phosphate anion.

Electron transfer mechanism in quenching of uranyl luminescence by halide ions

Abstract The rate constants in quenching reaction of uranyl luminescence by halide ions were determined from luminescence lifetime measurement. The uranyl luminescence was quenched by iodide, bromide and chloride ions, but not by fluoride ion. An attempt was made to interpret quantitatively the difference in the quenching efficiency of halide ions in terms of free energy change accompanying redox reaction of the ions involved in quenching collision. It was found that quenching by iodide, bromide and chloride ions is favored energetically, whereas quenching by fluoride ion is impossible, showing that an electron transfer process plays an important role in the quenching by halide ions. In addition, description of the electron transfer process by a molecular orbital model is proposed.

Quenching mechanisms of uranyl luminescence by metal ions

Abstract The quenching reaction of uranyl luminescence by metal ions in a lower valence state such as Fe 2+ , Tl + and Ce 3+ is diffusion-controlled and the dominant process of the reaction is concluded to be an electron transfer from the quenchers to uranyl ion. In case of many transition metal and lanthanide ions including Ce(IV), MnO 4 − and Cr 2 O 7 2− , the electron transfer is impossible energetically and the energy transfer is predominant.

Activation of a gold electrode by electrochemical oxidation-reduction pretreatment in hydrochloric acid

Abstract Gold electrodes were activated for the oxidation of ascorbic acid by applying electrochemical oxidation-reduction cycles in hydrochloric acid. The electrode surfaces were examined by XPS, SEM, PXD and electrochemical techniques. The results indicate that the gold atoms on the electrode surface are rearranged to form a single-crystal-like surface by the electrochemical pretreatment. The active site must be either a (111) facet of gold, or the edges or peaks of the pyramid structure constructed from (111) facets. Heat treatment also activates the gold electrode.

Vibrational structures in the photoelectron spectrum of formic acid

Abstract He I photoelectron spectra of formic acid and its deuterium substituted derivatives have been measured. The first, second and fifth bands of each molecule exhibit very fine vibrational structures. The characters of molecular orbitals from which the photoelectron bands originate are discussed by the use of results of vibrational analyses and molecular orbital calculations.

Spectrophotometric determination of trace amounts of titanium(IV), zirconium(IV) and thorium(IV) With molybdophosphoric acid solution

Abstract Trace amounts of titanium(IV), zirconium(IV) and thorium(IV) ions were determined spectrophotometrically with molybdophosphoric acid solution. The method is based on the formation of the ternary heteropoly complex by reaction of the metal ion with molybdophosphoric acid, and the elimination of unreacted molybdophosphoric acid by extraction with n-butyl acetate. Beers law was obeyed over the range 1–7 p.p.m. of metal ion. These ternary heteropoly complexes have the composition of Me:P:Mo= 1:1:12. The formation constants increase in the order, molybdotitanophosphate, molybdothorophosphate, and molybdozirconophosphate.

XPS Study on the Charge Distribution in Chromium(0) Complexes

Binding energies of core electrons in Cr(C6H6)2, Cr(C6H6)(CO)3, and Cr(CO)6 were measured by means of X-ray photoelectron spectroscopic method in solid phase. By comparison with their UPS spectra observed in gasous phase, binding energies referred to vacuum level can be obtained. On the basis of this result, charge distribution in these complexes are estimated. The intramolecular relaxation energy of Cr(C6H6)2 is also discussed.

Inhibiting action of thallium(I) ion on uranyl photoreduction

Abstract The reaction rate of uranyl photoreduction in lactic acid solution is decreased in the presence of small amounts of thallium(I) ion. The inhibiting action of thallium(I) ion obeys the Stern-Volmer equation. The reaction mechanism of the uranyl photoreduction and the inhibiting action has been investigated in correlation with quenching of uranyl fluorescence. The results are: (1) In 1 N sulfuric acid, lactic acid quenches the uranyl fluorescence by collision and simultaneously initiates the uranyl photoreduction. (2) Inhibiting action of thallium(I) ion is also collisional. The collisional process is diffusion-controlled, having a rate constant of 5·2 × 109 M−1 sec−1 at 22°C. (3) Quenching by paramagnetic ions is not so significant compared with heavy metals.

Atomic absorption spectrometry by a pulse technique and measurement of half life of copper and magnesium vapours

Abstract A new technique is proposed to measure the absorption by atomic vapours in the atomic absorption spectrometry. Atomic vapours were produced in an absorption source, consisting of a hollow cathode lamp of Schuler-Gollnow type, by a pulsed discharge, and the absorption by a resonance line was observed with a pulse-gated photomultiplier within the intervals when the pulse discharge of the absorption source was interrupted. The experiments showed (1) that in these intervals atomic vapours of some elements existed in the atmosphere of the absorption source during a considerably long duration after emission spectra of the atoms had disappeared; the half-life periods of copper and magnesium were 132 ± 11 μsec and 72 ± 5 μsec in neon at 1.4 mm Hg, respectively, and (2) that atomic absorption spectrometry could be performed without any interference from the emission spectra of sample vapour by applying a gating pulse to the photomultiplier at an appropriate phase of the interruption period.