O estudo cinético da reação clorato-cloreto foi feito acompanhando-se a formação do ClO 2 • por espectroscopia UV-Vis. Para permitir comparação com resultados da literatura, a velocidade inicial foi medida após pequeno período de indução. The kinetics of chlorate-chloride reaction was studied following the formation of ClO 2 • by UV-Vis spectroscopy. For comparison with other results in the literature, the initial rate was measured after small induction period. The results show a special effect of a saturation profile for the initial chloride concentration, suggesting the formation of the intermediate Cl 2 O 3 2-. At low chloride concentration, the reaction orders for chlorate, chloride and H + were 1.03 ± 0.05, 1.02 ± 0.03 and 2.80 ± 0.03, respectively. These order values must be considered with care because they were calculated using the maximum rate values after induction period. In fact, the presence of this induction period indicates that the system is complex. Then, a mechanism was proposed to explain the experimental results, and includes the reaction between two ClOClO to form ClO 2 •. It was able to model the experimental curves at different [H + ] 0 and at low and high [Cl -] 0 .

The equilibrium geometries, vibrational frequencies, heat capacity, and heat of formation for compounds of general formula HBrOx were calculated by DFT (BP and pBP methods) with DN* and DN** numerical basis sets. The comparison of our HOBr calculated results with the HOBr experimental values points out that the BP and pBP methods are as good as other ab initio and DFT methods related in the literature employing extended basis sets. The calculated HBrOx total energy and heat of formation values, at 0 and 298.15 K, present the following order: HOBr < HBrO; HOOBr < HOBrO < HBrO2; HOOOBr < HOBrO2 < HOOBrO < HBrO3. The HBrOx heat of formation was calculated using isodesmic and homodesmic reactions and the results show that, in general, the use of these reactions gives similar results.Key words: HOBr, HBrO2, HBrO3, DFT, numerical basis.

Correlated ab initio investigations on the intermolecular and intramolecular potential energy surfaces in the ground electronic state of the O 2 − (X Π g 2) − HF (X Σ + 1) complex We present a matrix functional form to fit the nearly degenerated potential energy surface of the H 2 O-OH molecular complex. The functional form is based on second order perturbation theory, which allows us to define two diabatic states coupled together in the field of the surrounding water molecules. The fit reproduces faithfully the fine details of the potential energy surface (PES) like the crossings and the shallow barrier between the main and secondary minima. The explicit dependence of the model on polarization ensures its transferability to systems made of several water molecules. The potential is used to investigate the structural properties of the OH radical in solution by Monte Carlo simulation. The twin surface fit shows that the second PES is shifted above the ground state by typically 1600 cm −1 for the configurations explored at a temperature of 300 K and a density of 1.0 g/cm 3. The second PES has thus little influence on the structuring of water around the OH radical at such a temperature and density. Our study confirms that under these thermodynamic conditions, OH is a weak hydrogen acceptor.

O sal pentacianonitrosilrutenato(II) de potássio, em forma amorfa, foi sintetizado e caracterizado por espectroscopias UV, IR, difração de raios X e análise termogravimétrica. Amostras irradiadas por raios X revelam, por espectroscopia de Ressonância Paramagnética Eletrônica, a presença de complexos paramagnéticos de rutênio (I) e de radicais NO 2. Os parâmetros do hamiltoniano de spin medidos para o complexo [Ru(CN) 5 NO] 3-(g ⊥ = 2.0064, A ⊥ (14 N) = 60.7 MHz, g || = 1.999, A || (14 N) = 77.3 MHz) indicam uma captura eletrônica em um orbital molecular π* do grupo nitrosil com a participação de orbitais d xz and d yz do rutênio, como recentemente previsto por cálculos teóricos. Íons de prata, presentes como impurezas oriundas da rota sintética, são reduzidos a Ag(0) durante a irradiação e interagem com quatro nitrogênios equivalentes em um sítio distorcido, originando um espectro de RPE anisotrópico. Amorphous potassium pentacyanonitrosylruthenate (II) was synthesized and characterized by UV, IR, X-ray diffraction and thermogravimetric analysis. Electron Spin Resonance spectroscopy reveals the presence of paramagnetic ruthenate (I) complexes and NO 2 radicals in the X-irradiated diamagnetic salt. Spin-hamiltonian parameters of the [Ru(CN) 5 NO] 3complex (g ⊥ = 2.0064, A ⊥ (14 N) = 60.7 MHz, g || = 1.999, A || (14 N) = 77.3 MHz) support an electron capture in a π* molecular orbital of the nitrosyl group mixed with d xz and d yz ruthenium orbitals as recently predicted by theoretical calculations. Silver ions, present as impurities, are reduced to Ag(0) by X-irradiation and coordinate to four magnetically equivalent nitrogens in a distorted site, giving rise to a well resolved anisotropic ESR powder spectrum.

The geometrical structures and the vibrational spectra of the HOBr·(H2O)n clusters (n = 1–4) have been calculated at the DFT level of theory, using the pBP method and the DN* and DN** numerical basis sets. The results showed that the interaction involving the H of the HOBr and the O of the water molecule represent the preferred arrangements for these hydrated compounds. Both HOBr·H2O and HOBr·(H2O)2 clusters presented stable structures with syn and anti conformations, the syn being the most stable. The HOBr·(H2O)3 and the HOBr·(H2O)4 clusters have presented stable cyclic structures. In the HOBr·H2O and HOBr·(H2O)2 clusters, low-frequency stretching values could be assigned to hydrogen bonds, but the same could not be done so clearly for the HOBr·(H2O)3 and the HOBr·(H2O)4 cyclic clusters. The binding energies were also determinated for these HOBr hydrated clusters, showing that the addition of a water molecule to the HOBr·H2O and HOBr·(H2O)2 clusters increases the binding energy by approximately 4 kcal mol–1, while the addition of a water molecule to the HOBr·(H2O)3 cluster decreases this value by 4 kcal mol–1.Key words: DFT, numerical basis, HOBr·(H2O)n, clusters.

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Theory Theory C 1000 Geometrical and Virbrational DFT Studies of HOBr·(H 2 O) n Clusters (n = 1-4). -(SANTOS, C. M. P.; FARIA*, R. B.; DE ALMEIDA, W. B.; MACHUCA-HERRERA, J. O.; MACHADO, S. P.; Can. J. Chem. 81 (2003) 9, 961-970; Dep. Quim. Inorg., Inst. Quim., Univ. Fed. Rio de Janeiro,

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