Dicopper and heteronuclear iron-copper peroxo complex formation: kinetics and thermodynamics

Quasireversible adducts of dioxygen with Cu(I) complexes are of interest as models for dioxygen transport proteins, for oxygen-dependent copper redox enzymes, and for low-molecular oxidation and oxygenation catalysts. Depending on ligand denticity and structural factors dioxygen binds in various geometries and metal:O2 ratios to the reduced copper centers. Kinetic investigations produce detailed mechanistic insight into the nature of coppers-dioxygen interaction. Heteronuclear FeO2Cu complexes with stabilities far beyond statistical expectation are obtained when 1:1 mixtures of suitable copper(I) complexes and appropriate Fe(II) porphyrins are treated with O2.     

Intercalation reaction kinetics: a TDPAC study of 2H-TaS2 intercalation

Summary We report on thein situ observation of the¹⁸¹Ta nuclear quadrupole interaction during electrointercalation of 2H-TaS₂ with hydrated gadolinium ions by means of time differential perturbed angular correlations (TDPAC). Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

The stoichiometry and kinetics of carbon combustion at low temperature: A surface complex approach

The stoichiometry and rate of carbon combustion at low temperature (673 K) were investigated. Oxidation and TPD experimental data provide quantification of gaseous products and stable surface complexes over a broad range of conversion. Our analysis distinguishes between surface complexes forming CO and CO₂ and has assumed a certain fraction of each complex type decomposes instantaneously upon formation, leaving the remainder on the surface as stable complexes, C(O) and C(O₂). This analysis suggests that a maximum of 25% of CO-complexes and 89% of CO₂-complexes are unstable upon formation. At low conversion, unstable complex formation is the dominant pathway for the CO product. As conversion increases, decomposition of stable CO-complexes eventually becomes the main source of CO. Formation of unstable CO₂-complexes is the dominant pathway for the CO₂ product at all times. The combustion rate is initially high due to a high availability of vacant active sites, decreases sharply as these sites are filled with stable complexes, and gradually increases as the stable complexes promote CO₂-complex formation, in turn, driving their decomposition. The dynamics of formation and decomposition of C(O) and C(O₂) dictates their ratio on the carbon surface at any moment, which may be measured by TPD. This work may help in developing new kinetic models of carbon combustion which can predict the stoichiometry as well as the rate.     

The low temperature water formation reaction on Pt(111): A static SIMS and TDS study

The formation of water by the reaction of preadsorbed oxygen with hydrogen on a Pt(111) surface has been characterized, using secondary ion mass spectroscopy, below the desorption temperature of H₂O (180 K). The concentration of chemisorbed water was monitored during the reaction by following the SIMS H₃O⁺ signal. Reaction profiles were measured over a temperature range of 120 to 153 K, and an H₂ pressure range of 10^-9 to 10^-6 Torr. Under all conditions the reaction profiles were characterized by an induction time, a region of rapid reaction, and finally a steady decline in the rate. In the rapid region, an overall activation energy of 2.9 ± 0.3 kcalmol^-1 and a half-order H₂ pressure dependence were observed. At low initial oxygen concentrations the induction time increased and the maximum rate decreased. The reaction was slow in the absence of gas phase hydrogen, even when the surface coverage of hydrogen was relatively high. Water and hydrogen thermal desorption spectra, measured after stopping the reaction by removal of gas phase hydrogen, were complex functions of the H₂ exposure, exhibiting several peaks between 170 and 400 K. However, after an exposure large enough to drive the reaction to completion, only one H₂O peak at 173 K and one H₂ peak at 350 K were observed. The results indicate that only a fraction of the total H(a) on the surface was readily available for reaction during H₂ exposure at T ? 153 K. the remainder either recombined to form H₂ or reacted with O(a) during the thermal desorption ramp. There is good evidence for a surface rearrangement during the induction period. A model is proposed which involves the formation of water clusters that accelerate the rate.     

Nuclear moment determination by Mössbauer effect detection of low temperature nuclear orientation (No/Me)

Absorption Mössbauer spectra were measured on low temperature (6–21 mK) oriented nuclei. For magnetic orientation this method allows the determination of the sign of the parent state magnetic moment. The method enables the determination of the parent state quadrupole coupling even for a polycrystalline sample. Signs of ground state magnetic moments for¹⁹¹Pt and¹⁹³Os, and electric quadrupole moments for¹²⁵Te^m and¹²⁹Te are determined.     

Electronic structure and spectra of [Cr(C6H6)2]+ and [Fe(C5H5)2]+

The high-resolution N.M.R. spectra of a series of bicyclo [2.2.1] heptanols are discussed. Three unusual features are observed: (a) relatively large ⁴ J's; (b) unequal J _endo-endo's and J _exo-exo's; and (c) unusual magnetic shieldings.

These are presented as empirical phenomena and only little attempt is made to discuss their implications.     

Zirconium-assisted reaction in low temperature atomic layer deposition using Bis(ethyl-methyl-amino)silane and water

The reaction of Bis(ethyl-methyl-amino)silane (BEMAS) and water in atomic layer deposition (ALD) became possible when Zr-containing species were adsorbed on the vacant sites of the surface after a pulse and purge of BEMAS. The growth rates of the Si(Zr)O_x films were 0.8-0.9 nm/cycle in the temperature range of 185-325 °C. This phenomenon probably originates from the highly reactive hydroxyl species generated by Zr atoms. From this point of view, transition metals make reactant gas molecules to be highly activated in the ALD processes of transition metal oxides and nitrides, which might be an important factor that determines the ALD characteristics.     

Film forming kinetics and reaction mechanism of γ-glycidoxypropyltrimethoxysilane on low carbon steel surfaces

The film forming kinetics and reaction mechanism of γ-GPS on low carbon steel surfaces was investigated by FTIR-ATR, AFM, NSS and theoretical calculation method. The results from experimental section indicated that the reaction of γ-GPS on low carbon steel surfaces followed the conventional reaction mechanism, which can be described as reaction (I) (Me (Metal)-OH + HO-Si → Me-O-Si + H₂O) and reaction (II) (Si-OH + Si-OH → Si-O-Si + H₂O). During film forming process, the formation of Si-O-Fe bond (reaction (I)) exhibited oscillatory phenomenon, the condensation degree of silanol monomers (reaction (II)) increased continuously. The metal hydroxyl density had significant influence on the growth mechanisms and corrosion resisting property of γ-GPS films. The results from theoretical calculation section indicated that the patterns of reaction (I) and reaction (II) were similar, involving a nucleophilic attack on the silicon center. The formation of Si-O-Fe bond (reaction (I)) was kinetically and thermodynamically preferred, which had catalytic effect on its condensation with neighboring silanol monomers (reaction (II)). Our DFT calculations were good consistent with the experimental measurements.     

The steady-state kinetics of the hydrogen-oxygen reaction on a Pt(111) surface at low and moderate pressures

The steady-state kinetics of the hydrogen-oxygen reaction on a Pt(111) surface is studied at low (10⁻⁵−10⁻⁴ Pa) and moderate (5–100 Pa) pressures of the stoichiometric mixture of the reagents. The moderate-pressure kinetics is analyzed on the basis of data obtained in the transient studies at low pressures. It is found that the reaction rate, extrapolated from low to moderate pressures, exceeds the measured rate by about an order of ten.     

茂金属配合物[(eat5-C5H4R)Mo(CO)3 ]2(R: SiMe3 ,Si2Me5)的电子结构研究

运用G98W ,采用Lanl2dz基组 ,对茂金属配合物 [(eat5 C5H4R)Mo(CO) 3 ]2 (R :SiMe3 ,Si2 Me5)进行从头算研究 ,探讨配合物结构单元的稳定性、分子轨道能量、原子净电荷布居规律 ,以及一些前沿分子轨道的组成特征等 ,结果表明 ,标题配合物结构在能量上是稳定的 ,作为结构单元而存在 .     

The low temperature specific heat of NpOs2 and NpRu2

Specific heat measurements on NpOs₂ show a peak at T_c = 7.9 ± 0.1 K, and γ = 90 mJ/(mol K²) above T_c. The magnetic entropy, 0.2 R 1n 2, supports previous arguments for itinerant ferromagnetism. The data for NpRu₂, supposedly a spin fluctuation compound, are fit below 10 K by C/T = γ + BT², with γ = 118 mJ/(mol K²) and B corresponding to θ_D = 174 K.     

Effect of ausforming temperature and strain on the bainitic transformation kinetics of a low carbon boron steel

The effect of ausforming temperature and strain on the bainitic transformation kinetics was investigated in a low carbon boron steel. A new mechanism, which is based on the competition between the increase in nucleation rate and the decrease in average volume of bainite sheaf after deformation, is proposed. The increase in nucleation rate is due to the decrease in boron concentration at the grain boundaries after small deformation and the formation of sub-grain boundaries at the grain interior after large deformation. The decrease in average volume of bainite sheaf is ascribed to the frequent impingement of bainite sub-units after deformation. The increase in nucleation rate after deformation results in the decrease in incubation time, which is confirmed from the experiment. The increase in nucleation rate overcomes the decrease in average volume of bainite sheaf, resulting in the increase in transformation velocity and volume fraction after small deformation. On the contrary, the decrease in the average volume of bainite sheaf overcomes the increase in nucleation rate after large deformation, leading to the decrease in transformation velocity and volume fraction of bainite.     

Raman study of (NH4)2CuCl4·2H2O—I: Dynamics and structure in low temperature phase

We report the results of a Raman scattering study of (NH₄)₂CuCl₄2H₂O at 300, 205 and 100°K, in order to elucidate the dynamics and phase transition in this double salt. A group theoretical calculation of the symmetry vectors, in the high temperature phase (D_4h¹⁴), is made and the various modes are identified. The deuterated compound (ND₄)₂CuCl₄·2D₂O has also been investigated to help in identifying the modes involving motion of the ammonium ions and water molecules. Through a careful analysis of the spectra at 100°K, the space group in the low temperature phase has been established as D_2d³. The important consequence of this result is that this leads to parallel spatial ordering of ammonium tetrahedra in this compound in the low temperature phase.     

铽掺钇配合物[(TbxY1-x)(HL)L'Cl·1/2H2O]的合成及荧光性质研究

以1,3,5-苯三甲酸根(BTC3-)为阴离子配体,1,10邻菲啰啉(phen)为中性配体,以不同摩尔比铽、钇离子为中心体,合成了系列铽掺钇配合物.经C,N,H元素分析,稀土总量络合滴定和铽、钇分量的测定推测配合物的组成为(TbxY1-x)(HL)L'C1·1/2H2O(x=0.10,0.30,0.50,0.70,0....     

Growth kinetics of low temperature single-wall and few walled carbon nanotubes grown by plasma enhanced chemical vapor deposition

Single-wall, double walled or few walled nanotubes (FWNT) are grown by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) at temperature as low as 600 °C. Most of these structures are isolated and self-oriented perpendicular to the substrate. The growth mechanism observed for single-wall and few walled (less than seven walls) nanotubes is the “base-growth” mode. Their grow kinetics is investigated regarding two parameters namely the growth time and the synthesis temperature. It is shown that nucleation and growth rate is correlated with the number of walls into FWNT. It also provides an evidence of a critical temperature for FWNT synthesis.     

Carbon-oxygen bond strength as a control of reaction kinetics: Phenol on Mo(110)

The reaction of phenol on Mo(110) has been studied using temperature programmed reaction and X-ray photoelectron spectroscopies. After desorption of multilayers and a weakly bound molecular species, decomposition produces the only reaction products observed: gaseous dihydrogen, surface carbon and surface oxygen. The O-H bond cleaves first at temperatures below 360 K to form surface phenoxide (C₆H₅O-), followed by C-H bond activation commencing at 370 K. C-O bonds are cleaved in the temperature range of 370 to 450 K. After annealing to 300 K, multiple species are detected on the surface by X-ray photoelectron spectroscopy. The cleavage of C-H bonds in the same temperature regime as C-O bonds is thought to lead to selective decomposition of phenol on Mo(110). The reaction of phenol is contrasted to that of a sulfur-containing analogue, benzenethiol, on the Mo(110) surface. The stability of the phenoxide intermediate with respect to carbon-heteroatom bond cleavage is greater than that of the corresponding phenyl thiolate formed from benzenethiol. Comparison of the reaction of phenol and benzenethiol demonstrates the importance of C-X (X = O,S) bond strength in determining the reactivity and selectivity of these molecules.