Minerais Pesados da formação Resende (Bacia de Resende, Estado do Rio de Janeiro)

A Formação Resende é o principal registro litoestratigráfico da bacia de Resende, que está inserida no segmento central do Rifte Continental do Sudeste do Brasil, apresentando a maior extensão e o maior volume de material entre as unidades na bacia. Esta unidade possui idade do Eoceno-Oligoceno e é composta por sedimentos de origem fluvial (arenitos arcoseanos médios a grossos com estratificação cruzada acanalada, siltitos, argilitos e conglomerados finos a médios, maciços ou com estruturas cruzadas) e de leques aluviais (lamitos arenosos e brechas clasto-suportadas). O principal recurso mineral extraído da unidade é água, sendo o principal aquífero da região. O presente trabalho tem como objetivo identificar e descrever os minerais pesados presentes nas rochas sedimentares da Formação Resende. Foram analisadas amostras de sete pontos ao longo da bacia, envolvendo as seguintes etapas: quarteamento; separação granulométrica; separação densimétrica; separação magnética; separação eletromagnética; identificação e descrição em estereomicroscópico; e estimativa de frequência. A mineralogia básica encontrada foi ilmenita, granada incolor, granada rosa, granada vermelha, turmalina, monazita cristalina, monazita terrosa, monazita caramelo opaca, cianita, estaurolita, apatita, rutilo, muscovita, biotita, hidrobiotita, zircão, quartzo e feldspato, todos apresentado angulosidade. Esses minerais no entanto não se apresentam distribuídos de forma equânime ao longo da Formação Resende. Comparando esses dados com a bibliografia pequisada pode-se confirmar a proposta de diversos autores que o embasamento proximal da bacia serviu como principal fonte de sedimentos para a bacia, mas não foi possível determinar qual da bordas teve maior influência, se a borda norte ou sul

Infrared spectrum of formamide in the solid phase

Infrared spectra of solid formamide are reported as a function of temperature. Solid formamide samples were prepared at 30 K and then annealed to higher temperatures (300 K) with infrared transmission spectra being recorded over the entire temperature range. The NH2 vibrations of the formamide molecule were found to be particularly very sensitive to temperature change. The IR spectra revealed a phase change occurring in solid formamide between 155 and 165 K. Spectral changes observed above and below the phase transition may be attributed to a rearrangement between formamide dimers and the formation of polymers is proposed at higher temperatures

A quantitative analysis of OCN- formation in interstellar ice analogs

The 4.62 micron absorption band, observed along the line-of-sight towards various young stellar objects, is generally used as a qualitative indicator for energetic processing of interstellar ice mantles. This interpretation is based on the excellent fit with OCN-, which is readily formed by ultraviolet (UV) or ion-irradiation of ices containing H2O, CO and NH3. However, the assignment requires both qualitative and quantitative agreement in terms of the efficiency of formation as well as the formation of additional products. Here, we present the first quantitative results on the efficiency of laboratory formation of OCN- from ices composed of different combinations of H2O, CO, CH3OH, HNCO and NH3 by UV- and thermally-mediated solid state chemistry. Our results show large implications for the use of the 4.62 micron feature as a diagnostic for energetic ice-processing. UV-mediated formation of OCN- from H2O/CO/NH3 ice matrices falls short in reproducing the highest observed interstellar abundances. In this case, at most 2.7% OCN- is formed with respect to H2O under conditions that no longer apply to a molecular cloud environment. On the other hand, photoprocessing and in particular thermal processing of solid HNCO in the presence of NH3 are very efficient OCN- formation mechanisms, converting 60%--85% and ~100%, respectively of the original HNCO. We propose that OCN- is most likely formed thermally from HNCO given the ease and efficiency of this mechanism. Upper limits on solid HNCO and the inferred interstellar ice temperatures are in agreement with this scenario.Comment: 13 pages, 13 figures, to be published in A&

Modelling Catalyst Surfaces Using DFT Cluster Calculations

We review our recent theoretical DFT cluster studies of a variety of industrially relevant catalysts such as TiO2, γ-Al2O3, V2O5-WO3-TiO2 and Ni/Al2O3. Aspects of the metal oxide surface structure and the stability and structure of metal clusters on the support are discussed as well as the reactivity of surfaces, including their behaviour upon poisoning. It is exemplarily demonstrated how such theoretical considerations can be combined with DRIFT and XPS results from experimental studies

A 3-5μ\mum VLT spectroscopic survey of embedded young low mass stars II; OCN−^-

The 4.62$\mu$m (2164.5 cm$^{-1}$) `XCN' band has been detected in the $M$-band spectra of 34 deeply embedded young stellar objects (YSO's), observed with high signal-to-noise and high spectral resolution with the VLT-ISAAC spectrometer, providing the first opportunity to study the solid OCN$^-$ abundance toward a large number of low-mass YSO's. It is shown unequivocally that at least two components, centred at 2165.7 cm$^{-1}$ (FWHM = 26 cm$^{-1}$) and 2175.4 cm$^{-1}$ (FWHM = 15 cm$^{-1}$), underlie the XCN band. Only the 2165.7-component can be ascribed to OCN$^-$, embedded in a strongly hydrogen-bonding, and possibly thermally annealed, ice environment based on laboratory OCN$^-$ spectra. In order to correct for the contribution of the 2175.4-component to the XCN band, a phenomenological decomposition into the 2165.7- and the 2175.4-components is used to fit the full band profile and derive the OCN$^-$ abundance for each line-of-sight. The same analysis is performed for 5 high-mass YSO's taken from the ISO-SWS data archive. Inferred OCN$^-$ abundances are $\leq$ 0.85 % toward low-mass YSO's and $\leq$ 1 % toward high-mass YSO's, except for W33 A. Abundances are found to vary by at least a factor of 10--20 and large source-to-source abundance variations are observed within the same star-forming cloud complex on scales down to 400 AU, indicating that the OCN$^-$ formation mechanism is sensitive to local conditions. The inferred abundances allow quantitatively for photochemical formation of OCN$^-$, but the large abundance variations are not easily explained in this scenario unless local radiation sources or special geometries are invoked. Surface chemistry should therefore be considered as an alternative formation mechanism

Etude par spectrométrie IRTF de la réactivité de l'acide isocyanique (HNCO) avec des glaces composées d'eau et d'ammoniac: Production spontanée de l'ion OCN- dans le milieu interstellaire

The interstellar ices are mainly composed of CO, H2O, NH3, .... Under a luminous flow coming from stars (λ > 120 nm) these ices are subjected to photochemical processing and can evolve to the formation of new and more complex products. Among them, the isocyanic acid (HNCO) is found which we have studied the reactivity with H2O, NH3 and NH3/H2O ices. We have shown that it was been at the origin of the OCN- formation. This ion can be characterised by ISO spectra of protostellar sources, from its band at 4,62 μm (2167 cm-1). A spontaneous production of OCN-, in agreement with the temperature range (10 - 100 K) which ices evolve, is produced when HNCO and NH3 in excess are codeposed at 10 K. A salt analogous at NH4+OCN- is formed at above 160 K. Quantum calculations have shown that solvation of NH3 molecule in direct interaction with HNCO by three other NH3 molecules, plays an important role into the NH4+ and OCN- formation process and confirm the spontaneous character of this reaction. The UV irradiation (λ > 120 nm) of solid HNCO leads to the OCN- formation but also carbonyl compounds as formaldehyde, formamide, and urea. The comparison of the primary photoproducts spectrum with ISO spectrum of NGC7538 IRS9 or W33A ices, could give a tentative attribution for the bands located at 1700 cm-1 and 1470 cm-1.Les glaces interstellaires sont composées de CO, H2O, NH3, .... Soumis à un flux lumineux émanant des étoiles (λ > 120 nm) ces glaces peuvent évoluer vers la formation de molécules plus complexes. Parmi celles-ci, on trouve l'acide isocyanique (HNCO) dont nous avons étudié la réactivité avec des glaces de H2O, de NH3, de NH3/H2O. Nous avons montré qu'il pouvait être à l'origine de la formation de l'ion OCN-. Cet ion peut être caractérisé sur les spectres ISO de sources protostellaires, par sa bande dite "XCN" à 4,62 μm (2167 cm-1). Une production spontanée de l'ion OCN- cohérente avec le domaine de température (10 - 100 K) dans lequel évoluent ces glaces, se produit entre HNCO et NH3 en excès codéposés à 10 K. Un sel analogue à NH4+OCN- est formé au-delà de 160 K. Des calculs quantiques ont montré que la solvatation d'une molécule de NH3 directement liée à HNCO par trois autres molécules de NH3, joue un rôle important dans le processus de formation de NH4+ et OCN- et confirment le caractère spontané de cette réaction. L'irradiation UV (λ > 120 nm) de HNCO solide a conduit à la formation de OCN- mais aussi de composés carbonylés tels que le formaldéhyde, le formamide, et l'urée. La comparaison du spectre des photoproduits primaires avec le spectre ISO des glaces NGC7538 IRS9 ou W33A, permet de donner une tentative d'attribution pour les bandes situées à 1700 cm-1 et 1470 cm-1

Tungsten behavior under proton flux and high temperature

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Tentative identification of urea and formamide in ISO-SWS infrared spectra of interstellar ices

Laboratory experiments involving vacuum ultraviolet (VUV) irradiation of solid isocyanic acid (HNCO) at 10 K, followed by infrared spectroscopy (FTIR), are used to interpret the complex spectra associated with Interstellar Medium (ISM) dust grains, particularly the spectra associated with the icy phase observed toward dense molecular clouds. The comparison of the infrared spectra of the photolysis products with spectra recorded from the protostellar source NGC 7538 IRS9 shows that the “unexplained" 1700 cm-1 feature can be attributed to the contribution of several species H2CO (formaldehyde), HCONH2 (formamide) and H2NCONH2 (urea) mixed with H2O as the main contributor. Urea, formaldehyde and NH$_4^+$OCN- (ammonium cyanate) may also contribute to a band at 1470 cm-1, widely observed in many protostellar infrared sources and which remains up to now poorly explained in numerous ISO-SWS spectra. Isocyanic acid could be a precursor of formamide and urea in interstellar ices