Selective determination of extremely low-levels of the thorium series in environmental samples by a new delayed coincidence method

An attempt was made to apply a delayed coincidence method for the absolute determination of trace quantities of the thorium series. This method is based on selective counting of the relatively short lived nuclide²¹⁶Po (half-life 145 ms) in the thorium series members. For this purpose, a list mode time analyzing system combined with a liquid scintillation counter was assembled by means of a conventional microcomputer. A multiple time analysis was employed in the processing and data compilation of delayed coincidences to distinguish them from the true coincidences due to random events.From a time spectrum, the decay component of²¹⁶Po (145 ms) can be selectively measured. Absolute activities of its progenitors,²²⁴Ra and²²⁸Th as well as²²⁰Rn, can be determined even in the presence of the background radiations of the almost equivalent activity-strength of concomitant uranium series.     

The valence orbital ionization potential of the first transition-metal atoms and ions

The 3d, 4s and 4p valence orbital ionization potentials (VOIP) are determined for the atoms and the ions with the electron configuration 3d 4s p , using the Anno-Teruya values of the average energies of the configurations and the experimental ionization potentials. Not all the configurations of this type are treated for lack of the data. As far as the data are available, a quadratic equation in terms of the atomic number Z is fitted to the VOIP's of an isoelectronic series: VOIP=A ₀+A ₁ Z+A ₂ Z ². The coefficients A ₀'s, A ₁'s and A ₂'s thus obtained are analysed in the light of Slater's simple expression for the total energy of an atom with the idea of screening effect due to inner electrons.

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Zusammenfassung Mit den Anno-Teruya-Werten für die durchschnittliche Energie der Konfigurationen und den experimentellen Ionisationspotentialen werden für Atome und Ionen der Konfigurationen 3d 4s p die 3d-, 4s- und 4p-VOIPs bestimmt. Mangels verfügbarer Daten werden nicht alle Konfigurationen dieses Typs behandelt. Sofern Daten verfügbar sind, wird den VOIPs einer isoelektronischen Reihe eine in der Kernladungszahl Z quadratische Gleichung angepa\t: VOIP=A ₀+A ₁ Z+A ₂ Z ². Dies aus dieser Gleichung gewonnenen RegelmÄ\igkeiten in den Koeffizienten A ₀, A ₁ und A ₂ werden mit der einfachen Slaterformel für die Gesamtenergie eines Atoms als Abschirmeffekte der inneren Elektronen erklÄrt.

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Résumé Les potentiels d'ionisation des orbitales de valence (VOIP) 3d, 4s et 4p sont déterminés pour les atomes et les ions de configuration électronique 3d 4s p en utilisant les valeurs de Anno-Teruya des énergies moyennes des configurations et les potentiels d'ionisation expérimentaux. Par suite d'absence de données toutes les configurations de ce type ne sont pas étudiées. Dans la mesure des données existantes, une relation quadratique en fonction du numéro atomique Z est ajustée pour les VOIP d'une série isoélectronique: VOIP=A ₀+A ₁ Z+A ₂ Z ². Les coefficients A ₀, A ₁ et A ₂ ainsi obtenus sont analysés à la lumière des expressions simples de Slater pour l'énergie totale d'un atome avec l'idée d'un effet d'écran dû aux électrons internes.

     

A Cocatalyst that Stabilizes a Hydride Intermediate during Photocatalytic Hydrogen Evolution over a Rhodium‐Doped TiO2 Nanosheet

The hydrogen evolution reaction using semiconductor photocatalysts has been significantly improved by cocatalyst loading. However, there are still many speculations regarding the actual role of the cocatalyst. Now a photocatalytic hydrogen evolution reaction pathway is reported on a cocatalyst site using TiO₂ nanosheets doped with Rh at Ti sites as one‐atom cocatalysts. A hydride species adsorbed on the one‐atom Rh dopant cocatalyst site was confirmed experimentally as the intermediate state for hydrogen evolution, which was consistent with the results of density functional theory (DFT) calculations. In this system, the role of the cocatalyst in photocatalytic hydrogen evolution is related to the withdrawal of photo‐excited electrons and stabilization of the hydride intermediate species; the presence of oxygen vacancies induced by Rh facilitate the withdrawal of electrons and stabilization of the hydride.     

NMR characterization of α- and β-mannopyranurono-2,6-lactones

Determining the stereochemistry at the anomeric position of glycosides is imperative in chemical synthesis. As for 1,2-cis-β-glycosides such as β-mannosides, ¹³C-¹H coupling constants, ¹J_CHs, are conventionally used when glycosides are in an ordinary chair conformation. In this work, we searched for appropriate criteria to determine the stereochemistry of products in a recently developed glycosylation reaction using 2,6-lactones. As a result, we found that α-glycosides exhibited vicinal coupling constants of around 3.0?Hz?at the anomeric proton, as well as a long-range coupling between protons at C-1 and C-5, whereas β-glycosides had coupling constants of 1.2?Hz?at most. These figures are expected to be useful for future assignments. In addition, the observations obtained from this study revealed the conformation of glycosides with a 2,6-lactone moiety.