Spectroscopic study of low temperature interactions in metal-organic co-condensates

The results on spectroscopic study of low temperature interactions of metal atoms, small clusters and nanoparticles with different organic and inorganic substances in the temperature range 12-300 K are presented. Complexation and reactions of atoms and clusters of magnesium, samarium and silver with carbon dioxide, ethylene and some mesogenic cyanophenyls were studied by the technique of matrix isolation and low temperature co-condensation of metal and ligand vapors, low temperature UV-Vis, IR- and ESR-spectroscopy in combination with quantum chemistry calculations. It was shown that cryochemical reactions of metal particles of different sizes reflected the system's redundant energy.     

Spectroscopic study of the interactions of alkali fluorides with D-xylose.

The interactions of alkali fluorides with D-xylose have been studied by X-ray diffraction (XRD), infrared spectroscopy (IR), nuclear magnetic resonance (NMR, 1H and 13C) and atomic absorption spectrophotometry. KF and CsF form complexes with D-xylose in a 1:1 molar ratio. These complexes can be obtained by solid state milling the reactants in an agate mortar or from methanolic solutions of the sugar and the salt. LiF and NaF do not form complex with D-xylose. IR and XRD prove the identical nature of the complexes obtained by milling and from solution. IR spectra indicate strong perturbation of the OH stretching vibrations with considerable shifts to lower frequencies, which must be caused by strong hydrogen bond formation to the fluorine anion. The perturbations of C-O bond are weak, indicating that cation binding to the oxygen atoms is not the main interaction responsible for the complex formation. 1H NMR spectra of the D-xylose-KF complex dissolved in deuterium oxide is equal to that of pure D-xylose, indicating the destruction of the complex in solution. The complex is stable in DMSO, and 13C spectra of the complex in DMSO-d6 and in solid state (CPMAS) spectra are in accordance with the observed interactions in the IR spectra. As far as we know, this is the first report of a sugar-halide salt complex in which the anion instead of the cation provides the binding forces.     

Spectroscopic ellipsometry study of CVD molybdenum oxide films: effect of temperature

The optical properties of CVD MoO₃ films were studied by ellipsometry in the spectral range 280–820 nm. The films were deposited on silicon substrates by pyrolytic decomposition at atmospheric pressure of Mo(CO)₆ at 150 and 200 °C. To optimize the film structure, annealing was performed at temperatures of 300 and 400 °C. The refractive index for as-deposited MoO₃ films varies within 1.8–2.2 and the optical band gap energies in the range 2.87–2.98 eV. After annealing, the latter values slightly increase to 2.85–3.05 eV, depending on the annealing temperature. The band gap energies are typical for a polycrystalline material. Peaks in the spectral dependence of the absorption coefficient were observed. Their position and intensity are found to be affected by the process temperature. Electronic Publication     

Thermogravimetric study of magnetite reduction at low temperature

Results on hydrogen reduction of pure magnetite to iron at low temperature are reported as part of research on ammonia synthesis catalyst. Experimental work was carried out by thermogravimetry and by electron microscopy.The reduction has a typical S-shaped kinetic curve, with a poorly reproducible induction period. The slope of the reduction curve at 50% conversion (k _0.5) was found to depend on sample mass (2–50 mg), particle size, temperature (220–280C) and presence of moisture in the hydrogen .The results suggest both interparticle and intraparticle (through iron ash) diffusion to be slow. Morphological examinations of the sample at various reduction degrees support this interpretation.

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Zusammenfassung Die Ergebnisse der Reduktion von reinem Magnetit zu Eisen durch Wasserstoff bei niedrigen Temperaturen werden als Teil einer Forschungsarbeit über Katalysatoren zur Ammoniak-Synthese mitgeteilt. Die Versuche wurden mittels Thermogravimetrie und Elektronenmikroskopie durchgeführt.Die Reduktion verläuft nach einer typisch S-förmigen kinetischen Kurve, mit einer schlecht reproduzierbaren Induktionsperiode. Es wurde festgestellt, daß die Steile der Kurve bei 50% Konversion (k _0.5) von der Probenmenge (2–50 mg), der Teilchengröße, der Temperatur (220 bis 280) und der Feuchtigkeit des Wasserstoffes abhängt.Diese Ergebnisse lassen darauf schliessen, daß sowohl die interpartikuläre als auch die intrapartikuläre Diffusion (durch die Eisen-Asche) langsam ist. Diese Deutung wird durch morphologische Prüfung des Musters bei verschiedenen Reduktionsstufen unterstützt.

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Résumé On communique les résultats obtenus en réduisant par l'hydrogène à basse température la magnétite pure en fer, travail faisant partie de recherches sur les catalyseurs pour la synthèse de l'ammoniac. Les expériences ont été effectuées par thermogravimétrie et par microscopic électronique.La courbe cinétique de la réduction présente la forme en S type, avec une période d'induction peu reproductible. Il est apparu que la pente de la courbe de réduction, pour un taux de conversion de 50% (k _0.5) dépendait de la prise d'essai (2–50 mg), de la dimension des particules, de la température (220 à 280) et de la présence d'humidité dans l'hydrogène .Ces résultats permettent de conclure que les processus de diffusion sont lents, qu'ils soient de type interparticule ou intraparticule. L'examen morphologique des échantillons pour divers degrés de réduction a confirmé cette interprétation.

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, , . . S- , . , 50% (_0.5) (2–50 ), , (220–280) (₂)=1,2 ). , , , , . .

     

Conformational properties and photochemistry of tetrazolylpyridines in low temperature matrices. Spectroscopic evidence for the photochemical carbon-to-nitrogen rearrangement

The most stable conformers of 2-(tetrazol-1-yl)-, 3-(tetrazol-1-yl)- and 2-(tetrazol-5-yl)pyridines undergo photolysis in Ar matrices at cryogenic temperatures to yield pyridin-2-ylcarbodiimide or pyridin-3-ylcarbodiimide. Spectroscopic evidence of carbon-to-nitrogen rearrangement in the case of the 2-(tetrazol-5-yl)pyridine molecule is provided. For the latter molecule a second pathway leads to the 1-cyclopenta-2,4-dienylketenimine formation. The experimental findings are supported by extensive B3LYP/6-311++G(2d,2p) calculations.     

Spectroscopic investigations of solvent effect on chiral interactions

The spectrophotometric method was used to determine the mechanism of chiral interactions between a known chiral selector, tert-butyl carbamoylated quinine (t-BuCQN), and N-derivative amino acids (DNB-Leu). Results obtained on binding constants, free energy of binding (DeltaG), and difference in free energy of binding (DeltaDeltaG) values seem to suggest that there are three possible types of interactions between DNB-Leu and t-BuCQN: electrostatic interaction between the carboxylate group of the DNB-Leu and the ammonium group of the t-BuCQN, the donor-acceptor charge-transfer type of interaction between the (acceptor) aromatic group of the amino acid and the (donor) aromatic group of the t-BuCQN, and the hydrogen-bonding interaction between the amide group of the DNB-Leu and the carbonyl group of t-BuCQN. The strongest interaction will be observed if all of three interactions are in operation as in the case of DNB-Leu. The electrostatic interaction seems to play the dominant role in the interactions. While the charge-transfer interaction is relatively weaker, it seems, however, to be responsible for enantiomeric selectivity, namely, the closer the electron acceptor dinitrophenyl group is to the electron donor quinoline group, the higher is the enantiomeric selectivity. Specifically, in solvent with high polarity, both donor and acceptor are solvated by solvent molecules, thereby preventing them from being close. As a consequence, the interaction will be weaker and, hence, lower enantiomeric selectivity. Solvation will be less in less polar solvent which, in turn, leads to stronger interaction and higher enantiomeric selectivity.     

Quantum chemical study of low temperature oxidation mechanism of dibenzofuran

A density functional theory (DFT) study of the reaction of dibenzofuranyl radical with oxygen molecule has been made. The geometries, energies, and vibrational frequencies of the reactant, transition states, intermediates, and products have been calculated at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d) level of theory. The initial reaction of dibenzofuran (DBF) with molecular oxygen results in the formation of the 1-dibenzofuranylperoxy radical. The stability of this adduct toward decomposition at low to intermediate temperatures results in it undergoing several possible rearrangements. The lowest energy pathway with a barrier of 24.2 kcal/mol involves a rearrangement to the 1,1-dioxadibenzofuran radical. The next lowest energy pathway involves fission of the O-O linkage whose reaction energy was found to be 37.6 kcal/mol. Transition state theory (TST) calculations indicate that the lowest energy pathway should predominate at temperatures up to about 1200 K. Two other unimolecular reaction pathways with barriers of 45.5 and 91.1 kcal/mol have also been discovered. The latter pathway leads to the formation of a para-quinone (dibenzofuran quinone) which has been detected experimentally in the low-temperature oxidation of DBF [Marquaire, P. M.; Worner, R.; Rambaud, P.; Baronnet, F. Organohalogen Compd. 1999, 40, 519]. Our quantum calculations, however, do not support this latter pathway to quinone formation. Instead, the quinone is most probably formed as a consequence of recombination of the 1-dibenzofuranyloxy radical (produced by peroxy fission) with an O atom in the para position. Each of the unimolecular reaction pathways have been subjected to detailed quantum chemical investigation and transition states and intermediates leading to the final products (principally CO, CO2, and C2H2 with traces of benzofuran and benzene) have been identified. For certain stable intermediates, their possible reactions with molecular oxygen have been further investigated quantum chemically. The present work therefore presents a detailed quantum chemical investigation of the reaction pathways in the low-temperature oxidation mechanism of DBF. Since the dibenzofuran moiety is present in the polychlorinated DBFs, our conclusions should be generally applicable to this family of compounds.     

低温低内应力化学镀镍工艺的研究

化学镀广泛应用于非金属的电镀、电铸前的施加导电层。化学镀沉积层质量与其在零件上的附着力有着密切的关系 ,重视对化学镀沉积层内应力的研究 ,开发一个低温、低内应力的化学镀镍工艺 ,对于化学镀沉积层的推广应用有着十分重要的意义。本文采用正交实验方法对低温、低内应力化学镀镍工艺进行了系统研究 ,开发出了一个低温、低内应力的化学镀镍工艺。在实验过程中发现沉积层内应力同其在零件上的结合力具有密切关系并对其进行了初步探讨。1　实验方法1 1　正交实验根据探索性实验结果分析 ,影响化学镀镍层内应力σ和沉积层速率ｒ的主要因…     

Raman scattering study of the low temperature phase transitions in ammonium nitrate

The phase changes in polycrystalline ammonium nitrate and its fully deuterated analogue have been studied by Raman scattering. The phase V and IV transition was found to be associated with the softening and intensity decrease of a NO₃^? librational mode. The Raman line-width data suggest that the VII to V phase transition involves a change in the degree of orientational order of the ions without incurring a change in lattice structure.     

Spectroscopic study of Mentha oils

The visible fluorescence and excitation spectra of Mentha oils (Japanese mint oil, peppermint oil and spearmint oil) have been recorded. Different physical constants which are characteristic of the fluorescent molecules have been calculated for all three oils. Results reveal that the same group of organic compounds dominate in the oils of peppermint and spearmint, whereas some different compound is present in Japanese mint oil. It is also found that the fluorescence intensity of these oils is comparable to that of Rhodamine 6G dye in methanol solution. Our studies suggest that Mentha oils may be a useful lasing material in the 450–600 nm wavelength range.     

Spectroscopic study of germanium-containing compounds

Conclusions The values of C=0 in the IR spectra and the position of the band from the n ^* electronic transition in the UV spectra of the amides R¹CONR²R³ vary linearly with the inductive effect of the R¹ substituent (for R²=R³=H, Alk). This may indicate the absence of the intramolecular coordination Ge 0, where or. The substituent R¹=Ge(C₂H₅)₂ exhibits electron-acceptor properties besides a +I-effect.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 349–352, February, 1984.     

A semiclassical study of the thermal conductivity of low temperature liquids

The conventional classical energy current auto-correlation function has been extended into a quantum mechanical version and then approximated by the linearized semiclassical initial value representation approach. Comparison of the thermal conductivity to simulation results shows that about 15% quantum correction to the classical molecular dynamics results for liquid neon are quantitatively predicted. For liquid para-hydrogen the quantum effects are sufficiently large that the linearized semiclassical approach is only 20% accurate, while for both liquid He(4) and He(3) the thermal conductivity disagrees by a factor of 2, although exchange effects appear to play a minor role.     

Spectroscopic investigation of conjugated polymer/single-walled carbon nanotube interactions

Composite materials, based on single-walled carbon nanotubes and a poly(p-phenylene vinylene) derivative, show an interaction between the components capable of solubilising the nanotubes, which has not been otherwise achieved. Here these materials are characterised by electron microscopy, and optical and vibrational spectroscopy. The spectroscopic behaviour of the polymer is seen to be dramatically affected, which is attributed to conformational changes due to the effect of the nanotubes.     

Spectroscopic studies on the molecular interactions of curcumin and piperine

Monatshefte für Chemie - Chemical Monthly - The diarylheptanoid curcumin is the yellow coloring agent accumulated in the rhizome of the common spice turmeric (Curcuma longa L.). It has...     

Spectroscopic study of hydrogen bonding in aminoanthrapyridones

By an analysis of the IR spectra of solutions of aminoanthrapyridones in chloroform it was demonstrated that the primary and secondary amino groups in the 1 and 6 positions form an intermolecular hydrogen bond with the CO groups; the amino groups in the 6 position form a stronger hydrogen bond. An anomalous form of the absorption band of the stretching vibrations of the NH group was detected in the IR spectrum of 6-n-hexylamino-3-ethylanthrapyridone. The long-wave band in the electronic spectra of aminoanthrapyridone is related to the band of charge transfer of the unshared pair of electrons of the amino nitrogen atom to the π system of the rings.     

Pressure broadening study at low temperature: application to methane

We studied the R(0) line profile in the CH4 v4 band from room temperature to 188 K with N2 as a perturber, to 100 K with O2 as perturber, and from room temperature to 15 K using He as a perturber. The N2 and O2 measurements were performed over a total pressure range of 15-110 mbar, and for the He measurements the maximum sample pressure at 15 K was 1.10 mbar. Broadening parameters were determined, taking into account the confinement narrowing (Dicke effect), and narrowing parameters, deduced from the soft or hard collision model, are compared with the dynamic friction coefficient calculated values. We also obtained preliminary values for the temperature dependence of the N2, O2 and He line broadening parameters for this transition.