Cathodic electroluminescence at the terbium(III)-doped oxide-covered tantalum electrode and its feasibility for the determination of hydrogen peroxide

Anodization of the tantalum electrode with a symmetric double-step potential, (i.e., sequential positive and negative potential pulses with intermittent zero potential pulses), but not with a conventional DC potential, in an electrolyte containing traces of terbium (III) produces a terbium (III)-doped oxide film on the electrode surface. The pulsed cathodic polarization of this doped electrode in the presence of hydrogen peroxide or peroxodisulfate generates sub-bandgap electroluminescence where the oxide-bound terbium (III) is the radiative recombination center. The detailed mechanism for this terbium(III)-based sub-bandgap electroluminescence is discussed, as is the possibility of using the electroluminescence for the determination of trace hydrogen peroxide in aqueous solution.     

Intrinsic and 1-aminonaphthalene-4-sulfonate-specific extrinsic lyoluminescences of X-ray irradiated sodium chloride

1-Aminonaphthalene-4-sulfonate (ANS)-specific extrinsic lyoluminescence (LL) of X-ray irradiated sodium chloride is observed at 425 nm when the irradiated salt is dissolved in an aqueous solution of ANS. The paper discusses, in detail, the mechanism of the ANS-specific LL and its analytical applicability. Also, the intrinsic LL of X-ray irradiated sodium chloride is studied. Hydrated electron as well as hole scavenger experiments support the proposal that in the case of the intrinsic LL of X-ray irradiated sodium chloride, trapped electrons (mainly F-center electrons) are released and hydrated whereas trapped holes (V-centers) remain surface-bound and are only partially hydrated before recombination occurs. These hydrated electrons and dissolving solid surface-bound hole centers, which are probably only partially hydrated, are able to act as reducing and oxidizing agents, respectively, in the luminophore oxidation-initiated reductive excitation pathway of ANS. Solution additives (halides and pseudohalides) show that in the chemiluminescence processes in question, oxidizing agents will follow the Marcus theory of electron transfer reactions. The LL method described allows the determination of ANS in the concentration range ≈10⁻¹¹ − 10⁻⁷ M. This suggests that aminonaphthalene derivatives can be used as label molecules in high sensitivity lyoluminobioaffinity assays.     

Color Tunability and Electrochemiluminescence of Silver Nanoclusters

Colorful clusters : Silver nanoclusters consisting of only a few atoms exhibit large chemical‐environment‐responsive shifts of their optical absorption and emission bands, that is, large solvatochromism (see picture). The photophysical characteristics and electrochemiluminescence of the Ag clusters give them remarkable advantages over larger nanoparticles in applications such as molecular sensing.

     

Ab initio and density functional theory reinvestigation of gas-phase sulfuric acid monohydrate and ammonium hydrogen sulfate

We have calculated the thermochemical parameters for the reactions H(2)SO(4) + H(2)O <--> H(2)SO(4).H(2)O and H(2)SO(4) + NH(3) <--> H(2)SO(4).NH(3) using the B3LYP and PW91 functionals, MP2 perturbation theory and four different basis sets. Different methods and basis sets yield very different results with respect to, for example, the reaction free energies. A large part, but not all, of these differences are caused by basis set superposition error (BSSE), which is on the order of 1-3 kcal mol(-1) for most method/basis set combinations used in previous studies. Complete basis set extrapolation (CBS) calculations using the cc-pV(X+d)Z and aug-cc-pV(X+d)Z basis sets (with X = D, T, Q) at the B3LYP level indicate that if BSSE errors of less than 0.2 kcal mol(-1) are desired in uncorrected calculations, basis sets of at least aug-cc-pV(T+d)Z quality should be used. The use of additional augmented basis functions is also shown to be important, as the BSSE error is significant for the nonaugmented basis sets even at the quadruple-zeta level. The effect of anharmonic corrections to the zero-point energies and thermal contributions to the free energy are shown to be around 0.4 kcal mol(-1) for the H(2)SO(4).H(2)O cluster at 298 K. Single-point CCSD(T) calculations for the H(2)SO(4).H(2)O cluster also indicate that B3LYP and MP2 calculations reproduce the CCSD(T) energies well, whereas the PW91 results are significantly overbinding. However, basis-set limit extrapolations at the CCSD(T) level indicate that the B3LYP binding energies are too low by ca. 1-2 kcal/mol. This probably explains the difference of about 2 kcal mol(-1) for the free energy of the H(2)SO(4) + H(2)O <--> H(2)SO(4).H(2)O reaction between the counterpoise-corrected B3LYP calculations with large basis sets and the diffusion-based experimental values of S. M. Ball, D. R. Hanson, F. L Eisele and P. H. McMurry (J. Phys. Chem. A. 2000, 104, 1715). Topological analysis of the electronic charge density based on the quantum theory of atoms in molecules (QTAIM) shows that different method/basis set combinations lead to qualitatively different bonding patterns for the H(2)SO(4).NH(3) cluster. Using QTAIM analysis, we have also defined a proton transfer degree parameter which may be useful in further studies.     

Hot electron-induced electrogenerated chemiluminescence of rare earth(III) chelates at oxide-covered aluminum electrodes

Aromatic Gd(III) and Y(III) chelates produce ligand-centered emissions during cathodic pulse polarization of oxide-covered aluminum electrodes, while the corresponding Tb(III) chelates produce metal-centered⁵D₄ →⁷F_j emissions. It was observed that a redox-inert paramagnetic heavy lanthanoid ion, Gd(III), seems to enhance strongly intersystem crossing in the excited ligand and direct the deexcitation toward a triplet-state emission, while a lighter diamagnetic Y(III) ion directs the photophysical processes toward a singlet-state emission of the ligand. The luminescence lifetime of Y(III) chelates was too short to be measured with our apparatus, but the luminescence lifetime of Gd(III) chelates was between 20 and 70 μs. The mechanisms of the ECL processes are discussed in detail. Preliminary results of electrogenerated triplet-state emission of one of the ligands used in this work have been published in a letter elsewhere [9].     

Activity determination without tracers in high-resolution alpha-particle spectrometry

High-resolution alpha spectrometry was applied for the activity determination of 10 reference sources containing different amounts of ²³⁸Pu, ²³⁹Pu, ²⁴⁰Pu and ²⁴²Pu. They were analyzed as blind sources using a novel spectrum analysis tool ADAM. The information needed in the spectrum unfolding was taken only from the spectrum under investigation, and no tracers were applied. Therefore, a Monte Carlo program AASI was used to compute geometrical detection efficiency of the measurement setup. All reported activities corresponded to those of the reference sources within expanded uncertainty. The developed tools can be used for the activity determination in nondestructive alpha spectrometry or when the radionuclide composition does not change during the sample processing.     

Standoff alpha radiation detection for hot cell imaging and crime scene investigation

Optical Review - This paper presents the remote detection of alpha contamination in a nuclear facility. Alpha-active material in a shielded nuclear radiation containment chamber has been localized...     

Competing Ising interactions and chaotic glass-like behaviour on a Cayley tree

For the Ising model on a Cayley tree with competing nearest neighbour coupling J and next nearest neighbour coupling J′, we find in addition to the expected paramagnetic, ferromagnetic and antiferromagnetic phases, an intermediate range of J′/J < 0 values where the local magnetization has chaotic oscillatory glass-like behaviour.     

First Principles Calculations for Hydrogenation of Acrolein on Pd and Pt: Chemoselectivity Depends on Steric Effects on the Surface

The chemoselective hydrogenation of acrolein on Pt(111) and Pd(111) surfaces is investigated employing density functional theory calculations. The computed potential energy surfaces together with the analysis of reaction mechanisms demonstrate that steric effects are an important factor that governs chemoselectivity. The reactions at the C=O functionality require more space than the reactions at the C=C functionality. Therefore the formation of allyl alcohol is more favorable at low coverage, while the reduction of the C=C bond and the formation of propanal becomes kinetically more favorable at higher coverage. The elementary reaction steps are found to follow different reaction mechanisms, which are identified according to terminology typically used in organometallic catalysis. The transition state scaling (TSS) relationship is demonstrated and the origin of multiple TSS lines is linked to variation of an internal electronic structure of a carbon skeleton.     

Heterogeneous multicomponent nucleation theorems for the analysis of nanoclusters

In this paper we present a new form of the nucleation theorems applicable to heterogeneous nucleation. These heterogeneous nucleation theorems allow, for the first time, direct determination of properties of nanoclusters formed on pre-existing particles from measured heterogeneous nucleation probabilities. The theorems can be used to analyze the size (first theorem) and the energetics (second theorem) of heterogeneous clusters independent of any specific nucleation model. We apply the first theorem to the study of small water and n-propanol clusters formed at the surface of 8 nm silver particles. According to the experiments the size of the two-component critical clusters is found to be below 90 molecules, and only less than 20 molecules for pure water, less than 300 molecules for pure n-propanol. These values are drastically smaller than the ones predicted by the classical nucleation theory, which clearly indicates that the nucleating clusters are too small to be quantitatively described using a macroscopic theory.