Very often hydrochloric acid is employed in acidification operations aiming to dissolve the mineral matrix in petroleum wheel operations, which always require intense use of corrosion inhibitors. This work presents an evaluation of common indicators, phenolfthaleine, fluorescein, methylene blue, alizarine S and methyl orange, as corrosion inhibitors for carbon steel in HCl 15% w/v at temperatures of 26, 40 and 60 ºC. Fluorescein and methyl orange show excelent corrosion inhibition efficiencies at 26 ºC; however at 60 ºC only fluorescein shows good corrosion inhibition when employed with alcohol and/or formaldehyde. For the fluorescein 1% w/v + formaldehyde 0.6% w/v mixture we present polarization and impedance curves and adsorption isotherms.

O espectro NEXAFS do naftaleno foi analisado sob a aproximação do estado final. Cálculos ROHF/SCF foram realizados para os estados localizados do caroço, segundo o procedimento de Bagus-Schaffer para cada canal de excitação. Cálculos CI foram realizados com excitações simples e duplas do carbono 1s para os dez orbitais virtuais de menor energia. As energias e forças do oscilador foram calculadas e o espectro final foi gerado por convolução de picos gaussianos com 0,5 eV de largura a meia altura, com ponderação estatística dos canais. Os resultados teóricos mostram excelente concordância com o espectro NEXAFS de alta resolução, obtido no BESSY II. Trabalho se encontra em andamento de modo a controlar de maneira adequada o problema do colapso variacional em nível CI através da metodologia MEG-CI, desenvolvida para o tratamento de estados de simetria quebrada. Esta metodologia oferece uma forma clara e transparente de considerar o problema da relaxação, da energia de correlação e da especificidade orbital necessária para o problema da predição do espectro NEXAFS de compostos poliaromáticos.

The near-edge X-ray absorption fine structure (NEXAFS) spectrum of naphthalene was analysed theoratically using the final state approximation rule. ROHF/SCF calculations were carried out for a localized core-hole cationic state under the Bagus-Schaffer scheme for each channel of inequivalent excitations. CI calculations were performed allowing single and double excitations from carbon 1s electrons to the first ten virtual orbitals. The energies and oscillator strengths were calculated. The final spectrum was generated by convolution of Gaussian peaks with 0.5 eV as FWHM of the statistically-averaged calculated transitions. The theoretical result shows remarkable agreement with the experimental high-resolution NEXAFS data measured at BESSY II. Work is in progress to get better control of the variational wave function collapse problem at CI level through the use of symmetry breaking core-hole excited states (MEG-CI). This methodology might offer a clear and transparent way to take into account the relaxational and correlation energy, the virtual orbital specificity and the required restricted configuration interaction needed to the NEXAFS prediction problem.

Este trabalho apresenta uma investigação teórico-experimental dos espectros infravermelho/Raman de diversos metais representativos coordenados com 1,3-ditiol-2-tiona-4,5-ditiolato (dmit), a saber [NEt4]2[Zn(dmit)2], [NEt4][Sb(dmit)2] e [NEt4][Bi(dmit)2]. Os espectros IV/Raman de todos os sólidos e também o espectro IV em solução do composto [NEt4]2[Zn(dmit)2] foram registrados de 4000 a 100 cm-1. Duas regiões foram claramente identificadas: abaixo de 380 cm-1 os modos apresentaram forte contribuição metal-ligante, e acima, os modos indicaram majoritária contribuição do ligante. Os espectros IV/Raman do NEt4Br também foram registrados. As bandas vibracionais foram atribuídas a partir da análise de compostos relacionados, de publicações prévias e comparadas com amplo conjunto de cálculos ab initio realizados com diversos ECPs (SBK, Sttutgart), conjunto de bases (com e sem funções d) e metodologias (RHF, DFT e MP2). As geometrias, freqüências e intensidades foram calculadas e comparadas com as freqüências experimentais visando atribuições seguras. Assim, uma excelente concordância foi obtida para diversas bandas experimentais.

This work reports a theoretical-experimental investigation of the infrared/Raman vibrational spectra of several metal 1,3-dithole-2-thione-4,5-dithiolate (dmit) complexes; [NEt4]2[Zn(dmit)2], [NEt4][Sb(dmit)2] and [NEt4][Bi(dmit)2]. IR/Raman spectra of all the solids and the solution IR spectrum of [NEt4]2[Zn(dmit)2] were recorded from 4000 to 100 cm-1. Two regions were clearly identified: below 380 cm-1, the modes presented significant metal-ligand contributions, and above, the modes indicated major ligand contributions. IR/Raman spectra of NEt4Br have also been recorded. The vibrational bands have been assigned starting from the analysis of related compounds, of previous published spectra and compared to several ECPs (SBK, Stuttgart), basis sets (with and without functions d) and methodologies (RHF, MP2 and DFT). Geometries, frequencies and intensities were calculated and compared to the experimental frequencies seeking secure assignment. Thus, an excellent agreement was obtained for several experimental bands.

Four different pseudopotentials and three methodologies were employed in the calculation of the geometry and the frequencies of metal complexes like [M(NH3)2X2] [X=halogen, M=Zn, Cd], and [Hg(NH3)2]Cl2. The vibrational assignments were carefully checked and compared to the theoretically calculated ones. Graphical procedures were employed to estimate family errors and their average behavior. The calculated results show the SBK-X basis set with the best results for the geometries and calculated frequencies, for individual species and statistical results. Its use is recommend, mainly if the neighborhood atoms are described with similar pseudopotentials. Excellent results were also obtained with the Hay and Wadt pseudopotential.

We analyse vibrational frequencies of 168 compounds with the AM1 model concerning its experimentally observed gaseous frequencies. Stretching of CH, NH, OH and CO bonds, its related bending frequencies, and the CC frame movements are the studied vibrations. The results show problems with the AM1 vibrational splittings. Often symmetric stretching frequencies, like in CH3, CH2 and NH3, appear switched with the corresponding antisymmetrical ones. Among the studied vibrations many stretchings are overestimated, while bendings oscillate around experimental values. Fluorine stretchings, NN, OO, CH, double and triples CC bonds and cyclic hydrocarbon breathing modes are always overestimated while torsions, umbrella modes and OH/SH stretching are, in average, underestimated. Graphical analysis show that compounds with the lowest molecular masses are the ones with the largest difference to the experimental values. From our results it is not possible to fit confortably the calculated frequencies by a simple linear relationship of the type, n(obs)=a*n(AM1). Better aggreement is obtained when different curves are adjusted for the stretching and bending modes, and when a complete linear function is used. Among our studies the best obtained statistical results are for CH, NH and OH. The conclusions obtained in this work will improve the AM1 calculated frequencies leading to accurate results for these properties.

Desde a descoberta de dois estado meta-estáveis gerados por excitação ótica do nitroprussiato de sódio cristalino, Na2Fe(CN)5NO.2H2O (SNP), exibindo longa meia-vida a temperaturas abaixo de 160 K, grande esforço vem sendo realizado no sentido de entender a estrutura eletrônica de sistemas correlatos. Apesar deste esforço, a natureza dos orbitais de fronteira e dos processos de excitação eletrônica de baixa energia são, ainda hoje, controversos. Cálculos iniciais EHT mostram que o HOMO possuia caráter do orbital 3d metálico, enquanto o LUMO possuia uma contribuição dominantemente p* (NO). Entretanto, cálculos INDO definiram o orbital metálido d como orbital de valência interna com vários elétron-volts em energia de Koopmans. O espectro vertical foi estimado através de cálculos HF/Cl-SD com bases de qualidade double-zeta e potenciais de caroço. As energias de Koopmans para os resultados ab initio estão de acordo com os resultados de Bottomley e Grein, e atribuem as primeiras excitações a processos de transferência de carga (TC) do trans-cyano para os ligantes nitrosila. Forças de oscilador foram calculadas e os resultados mostraram intensidades comparáveis com os resultados experimentais. A energia de excitação para o processo de transferência de carga metal ® NO, 8e ® 13e (d xz,d yz p* NO) foi estimada em 4.52 eV e exibindo intensa banda de absorção. A segunda excitação de transferência de carga, 1b2 ®13e (d xy ® p* NO), apontada por trabalhos prévios como uma típica banda de transferência de carga (TC) mostra uma pequena intensidade em 5.04 eV. Nos cálculos foi observado que o ordenamento SCF é muito independente do conjunto de base utilizado para o metal. Bases metálicas de caráter mínimo mostram resultados em grande concordância com os resultados EHT, enquanto as bases double-zeta empurram os orbitais d metálicos para os orbitais de valência interna. O ordenamento das energias HF foi empregado no sentido de interpretar resultados de experimentos fotoquímicos e de termoanálise do SNP e os resultados parecem mostrar boa concordância com as propriedades calculadas.

Since the discovering of two photoexcited metastable states of crystalline sodium nitroprusside, Na2Fe(CN)5NO.2H2O (SNP), showing rather long lifetimes at temperatures below 160 K, much effort has been devoted toward the study of its electronic structure. Despite this tremendous effort the nature of the frontier orbitals and the related low energy excitations remains controversial. Early calculations, EHT, showed the HOMO as mainly the metallic 3d orbital while the LUMO had a major p* (NO) contribution. However INDO calculations, clearly set the metal d orbital many electron-volts deep in core. The vertical electronic spectrum have been estimated through ab initio HF/CI-SD with a double-zetaF quality basis set. The ab initio results support Bottomley and Greins interpretations and assign the first electronic transitions to ligand-to-ligand charge-transfer excitation from trans-cyano to nitrosyl ligands. The corresponding oscillator strengths have been calculated showing comparable intensity with the experimental results. The excitation energy of the metal ® NO charge-transfer transition, 8e ® 13e (d xz,d yz ® p* NO) have been estimated to be at 4.52 eV and show a rather intense absorption band. The second CT excitation, 1b2 ® 13e (d xy ® p* NO), pointed by previous works as a typical CT band, exhibits a small intensity at 5.04 eV. In the calculations it was observed that SCF orbital ordering are rather dependent on the metal basis set used. Metallic minimal basis set show results in close agreement with EHT early calculations while double-zeta basis set pushes the metallic d orbitals deep away from the HOMOs. The HF orbital ordering has been used to interpret photochemical and thermoanalysis experiments on SNP and the results seem to fit properly with the calculated properties.