Theoretical Studies on the Reaction Mechanism of AsCl3 with H2 in the Vapor Phase Epitaxy of GaAs

The reaction mechanism of AsCl3 with H2 has been studied by using the method of BHandHLYP in Density Functional Theory (DFT) at the 6-311G** basis set. The transition state of each reaction is verified via the analysis of vibration mode and Intrinsic Reaction Coordinate (IRC). Meanwhile,single-point energy has been calculated at the QCISD(T)/6-311G** level,and the zero-point energy correction has been made to the total energy and reaction energy barrier. It shows that AsCl3 reacts with H2 to first result in AsHCl2 which may incline to self-decompose and finally afford the product As2,or continue to react with H2 to provide the product AsH3. The computing result demonstrates that the former is the main reaction channel.     

Red‐Tuned Mn d–d Emission in Doped Semiconductor Nanocrystals

Light‐emitting Mn‐doped semiconductor nanocrystals have been extensively studied for the last three decades for their intense and stable Mn d–d emission. In principle, this emission should be fixed at 585 nm (yellow), but recent studies have shown that the emission can be widely tuned even to 650 nm (red). This is a spectacular achievement as this would make Mn‐doped nanocrystals efficient and tunable light emitters. Keeping these developments in view, the chemistry of the synthesis of these materials, their photophysical processes and the expected origins of their red emission are summarized in this Minireview. All the related important studies from 1992 onwards are chronologically discussed, and one particular case is elaborated on in detail. As these materials are potentially important for biology, and photovoltaic, sensing and light‐emitting devices, this Minireview is expected to help researchers investigating the chemistry, physics and applications of these materials.     

Direct Chemical Fine‐Tuning of Electronic Properties in Sc2Ir6−xPdxB

Crystal orbital Hamilton population (COHP) bonding analysis has predicted that ScPd₃B_0.5 is the least stable compound of the entire series Sc₂Ir_6?xPd_xB. Here, we report a systematic study of Sc₂Ir_6?xPd_xB (x=3, 5 and 6) by means of ¹¹B nuclear magnetic resonance (NMR), Knight shift (K) and nuclear spin‐lattice relaxation rate (1/T₁). NMR results combined with theoretical band structure calculations provide a measure of s‐ and non‐s‐character Fermi‐level density of states. We present direct evidence that the enhanced s‐state character of the Fermi level density of states (DOS) in ScPd₃B_0.5 reduces the strength of the B 2p and Pd 4d hybridized states across the entire Sc₂Ir_6?xPd_xB series. This hybridization strength relates to the opening of a deep pseudogap in the density of states of Sc₂IrPd₅B and the chemical bonding instability of ScPd₃B_0.5. This study is an experimental realization of a chemical fine‐tuning of the electronic properties in intermetallic perovskites.     

锌冶炼行业环境风险分级评价指标体系研究

在国内重金属突发性污染环境事件的高发态势的背景下,如何科学、合理、有效地对具有高环境风险的锌冶炼行业进行管理已成为我国环境风险管理工作急需解决的问题。本文在已有研究的基础上,对锌冶炼行业的环境风险要素分析后,基于突发性环境风险水平、累积性环境风险水平和选址敏感性水平三方面入手,选取了锌冶炼行业环境风险分级评价指标,构建了锌冶炼行业环境风险分级评价指标体系,为锌冶炼行业环境风险管理工作提供依据。     

Elements in the Sera of Preschool Children Living in Central Taiwan

This study assessed elemental concentrations in the serum of 154 preschool children in central Taiwan via instrumental neutron activation analysis （INAA）. A total of eight elements, Br, C1, Fe, Na, Rb, Sc, Se and Zn of sera for Taiwanese preschool children living at four residential areas： Taichung city, Taichung urban townships and in a remote area inhabited by two groups of aborigines, Atayal and Bunun were determined. Standard reference materials （tomato leaves, NIST-SRM 1570a, and lichen, IAEA-336） were used as quality control standards to crosscheck the accuracy. Residential area, socioeconomic status and gender were shown to significantly influence serum levels of the eight trace elements. Statistical analysis revealed several different gender patterns via the two-tailed student＇s test. A quantified index of agreement （AT） was used to classify these elements. Small AT indicated a close consistency, while large AT indicated a larger fluctuation, or less agreement, such that the correlation between the elements could be interpreted using a series of quantified indices at the serum levels of preschool children.     

Dependence on the electric power of the immersion-angle dependence of the resonant-frequency shift of a quartz crystal microbalance in a liquid

We have investigated the immersion-angle dependence of the series resonant-frequency shift, ΔF, of the quartz crystal microbalance, QCM, in a Newtonian liquid from the point of view of the supplied electric power level. In the low electric power levels, the immersion-angle dependence and the transition phenomenon of the ΔF are observed. However, when the higher electric power levels are supplied to the QCM, the region of the transition phenomenon of the ΔF decreases rapidly with an increase in the electric power level and disappears above 1.5 dBm. That is, above 1.5 dBm, the ΔF values have only the values of 90° immersion angle in all immersion angles. We suggest that the electric power is very important factor for the ΔF in a liquid.     

Theoretical study on the reaction mechanism for the hydrolysis of esters and amides under acidic conditions

The mechanisms underlying the hydrolysis of methyl acetate and acetamide under acidic conditions were investigated using the MP2/6-311+G(d,p)//MP2/6-31+G(d,p) level of theory. It was necessary to include two water molecules as reactants to obtain a tetrahedral (TD) intermediate for the A_AC2 mechanism that Ingold classified for the hydrolysis of methyl acetate. This mechanism includes two TS structures, one for the formation of the TD intermediate and the other for its decomposition. Since the activation energies were calculated to be 15.7 and 18.3 kcal mol⁻¹, the second step determines the rate of hydrolysis. The calculated value was close to that observed at ∼16 kcal mol⁻¹. It was confirmed that the A_AC2 mechanism had a barrier lower by 9.9 kcal mol⁻¹ than the A_AL2 mechanism. The A_AC2 mechanism is also applicable to the acid-catalyzed hydrolysis of acetamide. It is not the TD intermediate with which the NH₃⁺ moiety forms, but one further step is required to produce the final products, acetic acid and ammonium ion.     

Excited state properties, fluorescence energies, and lifetime of a poly(fluorene-pyridine) copolymer, based on TD-DFT investigation

The structural and electronic properties of the fluorene-pyridine copolymer (FPy)(n), (n = 1-4) were investigated theoretically by means of quantum mechanical calculations based on density functional theory (DFT) and time-dependent DFT (TD-DFT) using the B3LYP functional. Geometry optimizations of these oligomers were performed for the ground state and the lowest excited state. It was found that (FPy)(n) is nonplanar in its ground state, whereas a more pronounced trend toward planarity is observed in the S(1) state. Absorption and fluorescence energies have been extrapolated to infinite chain length making use of their good linearity with respect to 1/n. An extrapolated value of 2.64 eV is obtained for vertical excitation energy. The S(1)<--S(0) electronic excitation is characterized as a highest occupied molecular orbital to lowest unoccupied molecular orbital transition and is dominating in terms of oscillator strength. Fluorescence energies and radiative lifetime were calculated as well. The obtained results indicate that the fluorescence energy and radiative lifetime of (FPy)(n) are 2.16 eV and 0.38 ns, respectively. The decrease of fluorescence energy and radiative lifetime with the increase in the chain length is discussed.     

Benzodipyrrole‐based Donor–Acceptor‐type Boron Complexes as Tunable Near‐infrared‐Absorbing Materials

Benzodipyrrole‐based donor–acceptor boron complexes were designed and synthesized as near‐infrared‐absorbing materials. The electron‐rich organic framework combined with the Lewis acidic boron co‐ordination enabled us to tune the LUMO energy level and the HOMO–LUMO gap (i.e.,the absorption wavelength) by changing the organic acceptor units, the number of boron atoms, and the substituents on the boron atoms.