Two-photon Dissociation Study of Carbon Disulfide in Acetonitrile at 266 nm

Using laser flash photolysis/transient absorption technique for the study of two photon photodissociation of carbon disulfide in acetonitrile solution at 266 nm, the transient UV-Vis absorption spectrum of Rydberg state CS2 （6sσg） within 240-370 nm and subsequent dissociation product CS （α^3П） with the maximum absorption at 260 nm were directly observed. The lifetime of CS （α^3П） in the nitrogen and oxygen saturated solution is also studied in our experiment.     

Theoretical Study of Weakly Bound Dimers between Hydrogen Fluoride and Some Polar Molecules

Weakly bound linear and bent dimers, FH—X (where X = CO, OC, CNH, NCH, N₂O and ON₂), are investigated using the DFT B3LYP and ab initio MP2 methods with the same basis sets (6–311++G(3df,2pd)). The strengths of the H—C or H—N H‐bonds in dimers FH—CO, FH—CNH, and FH—N₂O are compared with those of the H—O or H—N H‐bonds in dimers FH—OC, FH—NCH, and FH—ON₂. The results obtained for the H‐bond distances, the elongation effect of the HF bond, the red shift of the HF stretching frequency, and the energy difference between the dimer and the charge transfer reveal that the H‐bonds of the first group of dimers are stronger than those of the second. The Gibbs energies calculated for the six dimer formations indicate that the weakly bound dimers are unstable at room temperature (T = 298 K) (FH—X's → FH + X's, ΔG < 0).     

Electroconductivity of the calcium oxide-ethylene glycol-water system

The electroconductivity of calcium oxide-ethylene glycol (EG) and calcium oxide-EG-water systems is measured in wide ranges of temperatures and compositions. With increasing temperature, the conductivity of the former system passes through a maximum, which shifts to lower temperatures with increasing electrolyte concentration. Thermodynamic characteristics of the calcium hydroxy glycolate association in EG are estimated using the Lee-Wheaton equation. The conductivity of the latter system decreases with increasing EG content. Its dependence on the limiting high-frequency conductivity of the mixed solvent is analyzed. The activation energy for conduction in both systems decreases with increasing temperature and electrolyte concentration.     

Three polymorphs of 3‐(3‐phenyl‐1H‐1,2,4‐triazol‐5‐yl)‐2H‐1‐benzopyran‐2‐one formed from different solvents

The polymorphic study of 3‐(3‐phenyl‐1H‐1,2,4‐triazol‐5‐yl)‐2H‐1‐benzopyran‐2‐one, C₁₇H₁₁N₃O₂, was performed due to its potential biological activity and revealed three polymorphic modifications in the triclinic space group P, the monoclinic space group P2₁ and the orthorhombic space group Pbca. These polymorphs have a one‐column layered type of crystal organization. The strongest interactions between the molecules of the studied structures is stacking between π‐systems, while N—H…N and C—H…O hydrogen bonds link stacked columns forming layers as a secondary basic structural motif. C—H…π hydrogen bonds were observed between neighbouring layers and their role is the least significant in the formation of the crystal structure. Packing differences between the polymorphic modifications are minor and can be identified only using an analysis based on a comparison of the pairwise interaction energies.     

Low dielectric thermoset. II. Synthesis and properties of novel 2,6‐dimethyl phenol–dipentene epoxy

A 2,6‐dimethyl phenol–dipentene adduct was synthesized from dipentene (DP) and 2,6‐dimethyl phenol, and then a 2,6‐dimethyl phenol–DP epoxy was synthesized from the reaction of the resultant 2,6‐dimethyl phenol–DP adduct and epichlorohydrin. The proposed structures were confirmed by Fourier transform infrared, elemental analysis, mass spectra, NMR spectra, and epoxy equivalent weight titration. The synthesized 2,6‐dimethyl phenol–DP adduct was cured with 4,4‐diamino diphenyl methane, phenol novolac, 4,4‐diamino diphenyl sulfone, and 4,4‐diamino diphenyl ether. The thermal properties of the cured epoxy resins were studied with differential scanning calorimetry, dynamic mechanical analysis, dielectric analysis, and thermogravimetric analysis. These data were compared with those for the bisphenol A epoxy system. The cured 2,6‐dimethyl phenol–DP epoxy exhibited a lower dielectric constant (ca. 3.1), a lower dissipation factor (ca. 0.065), a lower modulus, lower thermal stability (5% degradation temperature = 366–424 °C), and lower moisture absorption (1.21–2.18%) than the bisphenol A system but a higher glass‐transition temperature (ca. 173–222 °C) than that of bisphenol A system. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4084–4097, 2002     

Synthesis, linear, and quadratic-nonlinear optical properties of octupolar D3 and D2d bipyridyl metal complexes

A series of D3 (Fe(II), Ru(II), Zn(II), Hg(II)) and D2d (Cu(I), Ag(I), Zn(II)) octupolar metal complexes featuring different functionalized bipyridyl ligands has been synthesized, and their thermal, linear (absorption and emission), and nonlinear optical (NLO) properties were determined. Their quadratic NLO susceptibilities were determined by harmonic light scattering at 1.91 microm, and the molecular hyperpolarizability (beta0) values are in the range of 200-657 x 10(-30) esu for octahedral complexes and 70-157 x 10(-30) esu for tetrahedral complexes. The octahedral zinc(II) complex 1 e, which contains a 4,4'-oligophenylenevinylene-functionalized 2,2'-bipyridine, exhibits the highest quadratic hyperpolarizability ever reported for an octupolar derivative (lambdamax=482 nm, beta1.91(1 e)=870 x 10(-30) esu, beta0(1 e)=657 x 10(-30) esu). Herein, we demonstrate that the optical and nonlinear optical (NLO) properties are strongly influenced by the symmetry of the complexes, the nature of the ligands (donor endgroups and pi linkers), and the nature of the metallic centers. For example, the length of the pi-conjugated backbone, the Lewis acidity of the metal ion, and the increase of ligand-to-metal ratio result in a substantial enhancement of beta. The contribution of the metal-to-ligand (MLCT) transition to the molecular hyperpolarizability is also discussed with respect to octahedral d6 complexes (M=Fe, Ru).     

Measurements and Utilization of Consistent Gibbs Energies of Transfer of Single Ions: Towards a Unified Redox Potential Scale for All Solvents

Utilizing the “ideal” ionic liquid salt bridge to measure Gibbs energies of transfer of silver ions between the solvents water, acetonitrile, propylene carbonate and dimethylformamide results in a consistent data set with a precision of 0.6 kJ mol⁻¹ over 87 measurements in 10 half-cells. This forms the basis for a coherent experimental thermodynamic framework of ion solvation chemistry. In addition, we define the solvent independent - and the values that account for the electronating potential of any redox system similar to the value of a medium that accounts for its protonating potential. This scale is thermodynamically well-defined enabling a straightforward comparison of the redox potentials (reducities) of all media with respect to the aqueous redox potential scale, hence unifying all conventional solvents′ redox potential scales. Thus, using the Gibbs energy of transfer of the silver ion published herein, one can convert and unify all hitherto published redox potentials measured, for example, against ferrocene, to the scale.     

基于迭代小波变换的光谱信号本底扣除方法研究

本底会对光谱分析结果产生很大的干扰作用,为获取特征峰的有效信息,必须首先去除本底。该文提出了一种基于小波变换的本底扣除算法,通过对光谱及后续光谱迭代进行小波变换,利用逼近系数估计本底,直到本底收敛。提出了判断多次估计的本底最大误差是否足够小的收敛准则。利用该算法去除本底后,即可进行特征峰信息的提取。分别利用仿真光谱和实验能量色散X射线荧光光谱对算法进行了验证,并与传统小波变换和多项式拟合法进行了对比。结果表明,该算法能够更准确扣除光谱本底,对其他光谱的本底扣除也具有借鉴意义。     

用透射电镜和火焰原子吸收法分析大气总悬浮颗粒物

以大气总悬浮颗粒物为主要研究对象,用透射电镜观察其形貌,污染特征明显;用火焰原子吸收法测定其水溶性常规元素K、Na、Ca和Mg。K、Na、Ca和Mg的检出限分别为0.105、0.124、0.259和0.237mg/kg,线性相关系数不低于0.9979,加标回收率为90.0%～95.0%,测定结果的相对标准偏差为0.6%～2.1%(n=6)。     

GROMACS: fast, flexible, and free

This article describes the software suite GROMACS (Groningen MAchine for Chemical Simulation) that was developed at the University of Groningen, The Netherlands, in the early 1990s. The software, written in ANSI C, originates from a parallel hardware project, and is well suited for parallelization on processor clusters. By careful optimization of neighbor searching and of inner loop performance, GROMACS is a very fast program for molecular dynamics simulation. It does not have a force field of its own, but is compatible with GROMOS, OPLS, AMBER, and ENCAD force fields. In addition, it can handle polarizable shell models and flexible constraints. The program is versatile, as force routines can be added by the user, tabulated functions can be specified, and analyses can be easily customized. Nonequilibrium dynamics and free energy determinations are incorporated. Interfaces with popular quantum-chemical packages (MOPAC, GAMES-UK, GAUSSIAN) are provided to perform mixed MM/QM simulations. The package includes about 100 utility and analysis programs. GROMACS is in the public domain and distributed (with source code and documentation) under the GNU General Public License. It is maintained by a group of developers from the Universities of Groningen, Uppsala, and Stockholm, and the Max Planck Institute for Polymer Research in Mainz. Its Web site is http://www.gromacs.org.