H2O2–Ng dynamics predictions using an accurate potential energy surface

ABSTRACT

Based on ab initio calculations, our research group has built an analytical ground-state potential energy surface (PES) for hydrogen peroxide– noble gas (Ng) interactions, such as H₂O₂–He, H₂O₂–Ne, H₂O₂–Ar, H₂O₂–Kr, and H₂O₂–Xe complexes. From this PES, it was verified that the Ng presence does not affect the equilibrium values of the H₂O₂ dihedral angles. This happens because the H₂O₂ intramolecular barriers have much higher energies than the atom–bond interaction within these complexes. From this point of view, it is indeed reasonable to consider the H₂O₂ system as a rigid rotor, frozen at its equilibrium configuration. We present in this work the torsional motion for the H₂O₂ isolated system, the vibration–rotation energy levels and spectroscopic constants for hydrogen peroxide–noble gas by using the aforementioned PES. The predicted H₂O₂ torsional motions are in good agreement with both theoretical and experimental results available in the literature. Regarding H₂O₂–Ng ro-vibrational energies and spectroscopic constants, it is the first time that these calculations are presented in the literature. The current theoretical predictions are expected to be useful in the future experimental investigations.     

Electrosprayed NiCo<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles for long cycle life and high-power Li-ion battery anode

Electrospraying-based synthesis of NiCo₂O₄ (NCO-ES) nanoparticles that exhibit long cycle life and high rate capability is reported. The results are compared with a conventionally prepared NiCo₂O₄ sample by direct annealing (NCO-DA). The structure and morphology of NCO-ES and NCO-DA nanoparticles have been characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy to confirm the size, morphology, structure, and surface chemistry of the as-prepared samples. Electrochemical testing established that the NCO-ES sample displayed enhanced Li-ion storage performance. The NCO-ES delivered a discharge capacity of almost 370 mAh/g at the end of 50 cycles at 1C rate (890 mA/g) while only 180 mAh/g was retained for the NCO-DA sample at the same condition. At a high rate of 5C (4450 mA/g), NCO-ES electrodes delivered a stabilized specific capacity of 225 mAh/g with almost 100% Coulombic efficiency over 1000 cycles. Its rate capability and cycle life were found to be superior to NCO-DA electrodes. The nanoscale grain boundaries in the NCO-ES sample enhanced the lithium-ion diffusion and enabled high rate capability. The impedance analysis at different stages of lithiation/delithiation indicates a lower impedance and better kinetics as one of the reasons for better performance of the NCO-ES sample.     

Fluorescent Properties of a Hybrid Cadmium Sulfide-Dendrimer Nanocomposite and its Quenching with Nitromethane

A fluorescent hybrid cadmium sulphide quantum dots (QDs) dendrimer nanocomposite (DAB-CdS) synthesised in water and stable in aqueous solution is described. The dendrimer, DAB-G5 dendrimer (polypropylenimine tetrahexacontaamine) generation 5, a diaminobutene core with 64 amine terminal primary groups. The maximum of the excitation and emission spectra, Stokes’ shift and the emission full width of half maximum of this nanocomposite are, respectively: 351, 535, 204 and 212 nm. The fluorescence time decay was complex and a four component decay time model originated a good fit (χ = 1.20) with the following lifetimes: τ ₁ = 657 ps; τ ₂ = 10.0 ns; τ ₃ = 59.42 ns; and τ ₄ = 265 ns. The fluorescence intensity of the nanocomposite is markedly quenched by the presence of nitromethane with a dynamic Stern-Volmer constant of 25 M⁻¹. The quenching profiles show that about 81% of the CdS QDs are located in the external layer of the dendrimer accessible to the quencher. PARAFAC analysis of the excitation emission matrices (EEM) acquired as function of the nitromethane concentration showed a trilinear data structure with only one linearly independent component describing the quenching which allows robust estimation of the excitation and emission spectra and of the quenching profiles. This water soluble and fluorescent nanocomposite shows a set of favourable properties to its use in sensor applications.     

Disappearance of criticality in thermal ignition for a simple reactive viscous flow

Conditions for the disappearance of criticality for reactive plane-Poiseuille flow are obtained by means of a perturbation series in the viscous heating parameter; an approximation to the Arrhenius reaction-rate term proposed in this journal by Bazley and Wake is used.

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Résumé On cherche les conditions pour la disparition de la limite critique pour l'écoulement Poiseuille de réactif entre deux plans en utilisant une série de perturbation de termes d'un paramètre que représente les effets thermiques de la viscosité; nous employons une approximation proposée dans ce journal par Bazley et Wake qui simplifie le terme d'Arrhenius dans l'équation de la balance de chaleur.

     

Untersuchungen an Kristallhydraten anorganischer Salze, 8. Mitt. Interpretation der Schwingungsspektren vonM(BF4)2·6H2O fürM=Fe2+, Co2+, Ni2+

The infrared and Raman spectra were recorded in the range 4000–160 cm^–1 forM(BF₄)₂·6 H₂O whereM=Fe²⁺, Co²⁺, Ni²⁺. The spectroscopic data support the X-ray structural data in showing that in the crystal hydrates studied two kinds of hydrogen bonds are present: H₂O...H₂O and OH₂... F₄B^–. The energies and molecular force constants (f _OH and fH₂O) andr _OH for OH₂...F₄B^– were calculated for the three crystal hydrates. It was found that the bond OH₂... F₄B^– is comparatively weak, with mean energy 3.7–3.3 kcal/mol. Two types of water molecule with different structures are existing as the first are participating in H₂O...H–O–H...F₄B^– and the second in BF₄ ^–...H–O–H...F₄B^–.     

Ueber einige Methoden der Bestimmung der Salpeters?ure

Ohne Zusammenfassung     

Investigation of thermal decomposition reactions by means of thermal analysis and dielectric constant measurement

Dielectric constant measurements as a function of temperature and thermal analysis were performed in copper sulphate pentahydrate and sodium nitrite to study the nature of the decomposition reactions. The application of these combined techniques to the study of several possible mechanisms of thermal decomposition is advanced.