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31.
32.
采用密度分离、脱灰处理和逐级化学提取等间接方法,考察了铁岭煤中Pb, Cr, Co, Ni, V五个重金属元素的宏观结合形态,并在Φ25mm小型石英流化床反应装置上考察了上述五个重金属元素在热解过程中的挥发行为。研究发现,铁岭煤中Pb, Cr, Co, Ni, V均主要与非黄铁矿类矿物质相伴生, 且高达40%~60%赋存在硅酸盐类矿物质中。Pb的碳酸盐结合态和有机束缚的离子可交换态600℃前即可分解转化,而其硫化物和硫酸盐结合态在较高的热解温度下才能分解挥发;Co、Ni的硫化物和硫酸盐结合态在高温下可部分转换为有机结合的离子可交换态;而Cr、V的硫化物和硫酸盐结合态在高温下部分转化生成了新的热稳定相。在500℃~900℃范围内,Pb属半挥发性元素,Cr, Co, Ni, V属难挥发性元素。微量元素的挥发性极大地受其伴生环境、共存活泼元素等的影响,硅铝酸盐类矿物质对重金属元素的挥发有一定的抑制作用。  相似文献   
33.
用密度泛函理论研究了氧原子与氟代甲基自由基的反应.反应中出现的所有物种的平衡构型用B3LYP方法在6-311++G(2d, 2p)基组水平上进行了优化,同时对各物种进行了频率分析;在同一理论水平上计算了各反应通道的势能面变化,分析了反应物、中间体、过渡态、产物的振动模式随反应途径的变化关系,阐明了该多通道反应的反应机理.  相似文献   
34.
In order to understand the dynamics of chemical reactions in general, detailed information on electronic, structural and kinetic properties is required. The key questions on how chemical reactions actually occur can in many cases only be answered in terms of information obtained from kinetic studies. In conventional kinetic studies of chemical reactions in solution, the variables usually selected include concentration, acidity, solvent, and temperature. In recent years, pressure has become an additional selected variable in such studies. It enables the measurement of the volume of activation and the construction of reaction volume profiles and thus assists in the elucidation of the underlying mechanism; it also completes the comprehension of reaction kinetics by adding another kinetic parameter that the suggested reaction mechanism must account for. Furthermore, the volume of activation is the only transition state property that can be correlated with the corresponding ground state property in an experimentally simple manner. In this paper, the insights so gained in our understanding of the dynamics of reactions involving coordination complexes will be presented. Such reactions are of fundamental interest to chemists since they often form the basis of catalytic, biological, environmental and energy related processes. Any additional information that will add to the understanding of the reaction dynamics is therefore of exceptional importance.  相似文献   
35.
The Schiff base N,N'-ethylenebis(pyridoxylideneiminato) (H(2)pyr(2)en, 1) was synthesized by reaction of pyridoxal with ethylenediamine; reduction of H(2)pyr(2)en with NaBH(4) yielded the reduced Schiff base N,N'-ethylenebis(pyridoxylaminato) (H(2)Rpyr(2)en, 2); their crystal structures were determined by X-ray diffraction. The totally protonated forms of 1 and 2 correspond to H(6)L(4+), and all protonation constants were determined by pH-potentiometric and (1)H NMR titrations. Several vanadium(IV) and vanadium(V) complexes of these and other related ligands were prepared and characterized in solution and in the solid state. The X-ray crystal structure of [V(V)O(2)(HRpyr(2)en)] shows the metal in a distorted octahedral geometry, with the ligand coordinated through the N-amine and O-phenolato moieties, with one of the pyridine-N atoms protonated. Crystals of [(V(V)O(2))(2)(pyren)(2)].2 H(2)O were obtained from solutions containing H(2)pyr(2)en and oxovanadium(IV), where Hpyren is the "half" Schiff base of pyridoxal and ethylenediamine. The complexation of V(IV)O(2+) and V(V)O(2) (+) with H(2)pyr(2)en, H(2)Rpyr(2)en and pyridoxamine in aqueous solution were studied by pH-potentiometry, UV/Vis absorption spectrophotometry, as well as by EPR spectroscopy for the V(IV)O systems and (1)H and (51)V NMR spectroscopy for the V(V)O(2) systems. Very significant differences in the metal-binding abilities of the ligands were found. Both 1 and 2 act as tetradentate ligands. H(2)Rpyr(2)en is stable to hydrolysis and several isomers form in solution, namely cis-trans type complexes with V(IV)O, and alpha-cis- and beta-cis-type complexes with V(V)O(2). The pyridinium-N atoms of the pyridoxal rings do not take part in the coordination but are involved in acid-base reactions that affect the number, type, and relative amount of the isomers of the V(IV)O-H(2)Rpyr(2)en and V(V)O(2)-H(2)Rpyr(2)en complexes present in solution. DFT calculations were carried out and support the formation and identification of the isomers detected by EPR or NMR spectroscopy, and the strong equatorial and axial binding of the O-phenolato in V(IV)O and V(V)O(2) complexes. Moreover, the DFT calculations done for the [V(IV)O(H(2)Rpyr(2)en)] system indicate that for almost all complexes the presence of a sixth equatorial or axial H(2)O ligand leads to much more stable compounds.  相似文献   
36.
The normal mode frequencies and corresponding vibrational assignments of phosphirane in are examined theoretically using the GAUSSIAN 98 set of quantum chemistry codes. All normal modes were successfully assigned to one of nine types of motion (C–C stretch, P–C stretch C–H stretch, P–H stretch, CH2 scissors, CH2 wag, CH2 rock, CH2 twist, and P–H wag) predicted by a group theoretical analysis. Comparing the vibrational frequencies with IR and Raman spectra available in the literature, a set of scaling factors are derived. Predicted infrared and Raman intensities are reported.  相似文献   
37.
We report a theoretical study of the ground electronic state of BiH3. The potential energy surface (PES) is obtained from coupled cluster CCSD(T) calculations with a large basis set (289 contracted Gaussian functions). The previously available quartic force field (P4) is extended by adding the dominant quintic and sextic stretching terms to yield improved potential functions in symmetry coordinates (P6) and Morse-type coordinates (M4). Second-order rovibrational perturbation calculations on the P4-PES and full variational calculations on the P6-PES and M4-PES yield almost identical vibrational term values which is rationalized by considering the local mode behavior of BiH3 and the Morse-type character of the M4-PES. The remaining deviations between the computed and observed vibrational term values must thus be caused by imperfections in the CCSD(T) surface. A refinement of this ab initio surface by a restrained fit to experimental data allows an essentially perfect reproduction of the observed vibrational term values. Variational calculations on this refined surface provide predictions for several overtone and combination bands that have not yet been observed. Dedicated to Hermann Stoll on the occasion of his 60th birthday  相似文献   
38.
The gas‐phase reactions of XH? (X=O, S) + CH3Y (Y=F, Cl, Br) span nearly the whole range of SN2 pathways, and show an intrinsic reaction coordinate (IRC) (minimum energy path) with a deep well owing to the CH3XH???Y? (or CH3S????HF) hydrogen‐bonded postreaction complex. MP2 quasiclassical‐type direct dynamics starting at the [HX???CH3???Y]? transition‐state (TS) structure reveal distinct mechanistic behaviors. Trajectories that yield the separated CH3XH+Y? (or CH3S?+HF) products directly are non‐IRC, whereas those that sample the CH3XH???Y? (or CH3S????HF) complex are IRC. The IRCIRC/non‐IRC ratios of 90:10, 40:60, 25:75, 2:98, 0:100, and 0:100 are obtained for (X, Y)=(S, F), (O, F), (S, Cl), (S, Br), (O, Cl), and (O, Br), respectively. The properties of the energy profiles after the TS cannot provide a rationalization of these results. Analysis of the energy flow in dynamics shows that the trajectories cross a dynamical bifurcation, and that the inability to follow the minimum energy path arises from long vibration periods of the X?C???Y bending mode. The partition of the available energy to the products into vibrational, rotational, and translational energies reveals that if the vibrational contribution is more than 80 %, non‐IRC behavior dominates, unless the relative fraction of the rotational and translational components is similar, in which case a richer dynamical mechanism is shown, with an IRC/non‐IRC ratio that correlates to this relative fraction.  相似文献   
39.
Taking place within more extensive work that focuses on hybrid methods in aeroacoustics, the present study is devoted to the data transfer operations that are to be performed between two stages of a hybrid calculation. More precisely, the article focuses on two typical operations that usually accompany such data transfer, which are (i) the sampling rate reduction and (ii) the interpolation of the unsteady perturbations to be transmitted from one stage to the other. First part of the paper analyzes the two main issues of such operations, which are the spuriousing and the aliasing phenomena. For doing so, the usual notions of the interpolation theory are revisited before they are synthesized within an original approach. The here proposed formalism allows to understand better both the spuriousing and the aliasing phenomena, as well as to accurately predict the impact of the latter on the data to be transmitted in terms of signal degradation. Second part of the paper provides an illustration and a validation of these theoretical developments via a direct application to a typical aerodynamic noise problem (aeroacoustic emission by a 2D cylinder cross flow). There, it is further shown how the here proposed formalism can help in improving aeroacoustics hybrid calculations by predicting (and thus possibly minimizing) the bias to be induced on the acoustic extrapolation stage because of the aliasing and/or spuriousing effects inherited from the sampling rate reduction and/or interpolation of CFD data—which is likely to occur in any hybrid scenario. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
40.
Coordination compounds of copper have been invoked as major actors in processes involving the reduction of molecular oxygen, mostly with the generation of radical species the assignment for which has, so far, not been fully addressed. In the present work, we have carried out studies in solution and on surfaces to gain insights into the nature of the radical oxygen species (ROS) generated by a copper(II) coordination compound containing a thioether clip‐phen derivative, 1,3‐bis(1,10‐phenanthrolin‐2‐yloxy)‐N‐(4‐(methylthio)benzylidene)propan‐2‐amine (2CP‐Bz‐SMe), enabling its adsorption/immobilization to gold surfaces. Whereas surface plasmon resonance (SPR) and electrochemistry of the adsorbed complex indicated the formation of a dimeric CuI intermediate containing molecular oxygen as a bridging ligand, scanning electrochemical microscopy (SECM) and nuclease assays pointed to the generation of a ROS species. Electron paramagnetic resonance (EPR) data reinforced such conclusions, indicating that radical production was dependent on the amount of oxygen and H2O2, thus pointing to a mechanism involving a Fenton‐like reaction that results in the production of OH..  相似文献   
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