锡苯和铅苯二聚反应的理论研究

采用密度泛函理论B3LYP方法,研究了锡苯和铅苯的[2+2],[4+2]及[4+4]二聚反应的微观机理和势能剖面,考察了Sn(Pb)原子上的2,4,6-三甲基苯基(Mes)取代基对反应势能剖面的影响.研究结果表明,所有反应均为协同过程,且大多数情况下,2个C—Sn(Pb)键同步形成.[2+2]和[4+2]反应在热力学和动力学上均比相应的[4+4]反应容易进行,而[4+2]反应在动力学上比相应的[2+2]反应有利.Sn(Pb)原子上的Mes取代基在热力学和动力学上均不利于反应的进行.铅苯的动力学稳定性与锡苯相当,但其热力学稳定性高于锡苯.     

Asymmetric Hydrosilylation of Aromatic Ketones Catalyzed by an Economical and Effective Copper-Diphosphine Catalytic System in Air

In the presence of the inexpensive and non‐toxic polymethylhydrosiloxane, the combination of copper(II) acetate and a chiral diphosphine displayed high catalytic efficiency in the asymmetric hydrosilylation of a series of aromatic ketones in air atmosphere and at room temperature. (R)‐1‐Arylethanols were obtained with up to 99% yield and 93% enantiomeric excess. Meanwhile, the electron effect and steric hindrance of substituents on the aromatic ring had an interesting influence on both the yields and enantioselectivities. Furthermore, a possible mechanism was presented to explain the influence of some key factors on the reaction.     

ICP-AES法测定高温合金中5种非金属元素

本文研究了快速测定高温合金中5种非金属元素(As、B、P、Se、Si)的分析方法,以满足高温合金行业对非金属元素检测的需求。利用王水和高氯酸对高温合金进行酸溶解,并系统研究了基体元素和共存元素对分析元素谱线的光谱干扰情况,同时进行了分析谱线的选择。5种非金属元素的检出限在5.5 ～ 11.9 ug/ml,5次数据的相对标准偏差(RSD,n=5)为0.9 % ～ 7 %,各元素的回收率在96 % ～ 102 %之间,该方法适用于高温合金中非金属元素的测定。     

Surface of room temperature ionic liquid [bmim][PF6] studied by polarization- and experimental configuration-dependent sum frequency generation vibrational spectroscopy

Understanding and control of the surface properties such as molecular orientations are of great importance in numerous applications of ionic liquids. However, there remain discrepancies among the previous experimental and theoretical studies on the surface orientation and structures of room temperature ionic liquids(RTIL) systems. In this article, the orientation of 1-butyl-3-methylimidazolium([bmin]) cation at the air/liquid interface of a characteristic RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate([bmim][PF6]), was investigated by the sum frequency generation vibrational spectroscopy(SFG-VS). Detailed polarization and experimental configuration analyses of the SFG-VS spectra showed the possibility of a small spectral splitting in the CH3 symmetric stretching region, which can be further attributed to the probable existence of multiple orientations for the interfacial [bmim] cations. In addition, the(N)–CH3 vibrations were absent, ruling out the prediction by several recent molecular dynamics simulations which state that portions of the [bmim] cations orient with a standing-up(N)–CH3 group at the ionic liquid surface. Hence, new realistic theoretical models have to be developed to reflect the complex nature of the ionic liquid surface.     

Observation and analysis of near-surface atmospheric aerosol optical properties in urban Beijing

Year-round measurements of the mass concentration and optical properties of fine aerosols(PM_2.5) from June 2009 to May 2010 at an urban site in Beijing were analyzed.The annual mean values of the PM_2.5 mass concentration,absorption coefficient（Ab）,scattering coefficient（Sc） and single scattering albedo（SSA）at 525 nm were 67±66μg/m³,64 ±62 Mm^-1,360 ±405 Mm^-1 and 0.82 ±0.09,respectively.The bulk mass absorption efficiency and scattering efficiency of the PM_2.5 at 525 nm were 0.78 m²/g and 5.55 m²/g,respectively.The Ab and Sc showed a similar diurnal variation with a maximum at night and a minimum in the afternoon,whereas SSA displayed an opposite diurnal pattern.Significant increases in the Ab and Sc were observed in pollution episodes caused by the accumulation of pollutants from both local and regional sources under unfavorable weather conditions.Aerosol loadings in dust events increased by several times in the spring,which had limited effects on the Ab and Sc due to the low absorption and scattering efficiency of dust particles.The frequency of haze days was the highest in autumn because of the high aerosol absorption and scattering under unfavorable weather conditions.The daily PM_2.5concentration should be controlled to a level lower than 64 μg/m³ to prevent the occurrence of haze days according to its exponentially decreased relationship with visibility.