铜/硒二元团簇离子的形成和紫外光解

用串级飞行时间质谱仪结合激光直接溅射的方法产生了铜/硒二元团簇正负离子,正离子主要系列为(Cu₂Se)_nCu⁺和(Cu₂Se)_n⁺,负离子主要系列为(Cu₂Se)_nCuSe^-和(Cu₂Se)_nSe^-;研究了团簇正离子的紫外光解.结果表明,光解产物主要是一级谱中丰度较大的一些离子.用密度泛函方法(DFT)对Cu₃Se^-,Cu₃Se₂⁺的稳定构型及光解通道进行了理论计算,解释了实验中观察到的现象.     

铬/磷二元团簇的形成和光解

用532nm的Nd:YAG激光直接溅射铬/磷粉末混合物样品产生铬/磷团簇,并用串级飞行时间质谱仪研究了二元团簇的组份分布及紫外激光光解规律.实验表明,铬/磷极易形成富磷的二元团簇离子,CrP_m⁺团簇离子系列表现出明显的奇偶振荡效应,且CrP₄⁺,Cr_nP₈⁺(n=1～4),Cr₄P₉⁺,Cr₅P₁₁⁺,Cr₆P₁₂⁺和Cr₈P₁₄⁺等为质谱中丰度较大的离子,不随样品组成的变化而变化,光解时主要以失去中性P₂和P₄的方式进行解离,尝试对其电子结构进行推测.并与铬/硫二元团簇的形成和光解结果作简单对比.     

Micropore size analysis in hydrated cement paste by NMR

We present a time evolution of ¹H spin-lattice relaxation rates in the laboratory (1/T₁) and in the rotating (1/T_1ρ) frame of a synthetic cement paste. The typical results found for both rates allow us to follow the main hydration stages of the cement paste and the refinement of its microporosity. In particular the texturation of the porosity and the structuration of the surface of the material are evidenced on two model cement pastes. An interpretation in terms of fractal size distribution is considered as well as the effect of the curing temperature.     

多原子反应体系的高精度拟合势能面

本文介绍了近几年来我们组构建多原子反应体系的高精度拟合势能面的进展。我们基于神经网络(NN)方法,成功构建了多原子气相分子体系和气相分子在金属表面解离的一系列势能面。这些势能面的拟合精度相当高,并且经过了严格的量子动力学测试,能广泛应用到动力学研究中。我们还提出了一种新的置换不变势能面的拟合方法,即基本不变量神经网络方法(FI-NN)。基本不变量的使用极大地减少了神经网络输入层多项式的个数,有效提高了势能面的计算速度。     

Ultraviolet Photodissociation Dynamics of DNCO+hv→D+NCO: Two Competitive Pathways

Photodissociation dynamics of DNCO+hv→D+NCO at photolysis wavelengths between 200 and 235 nm have been studied using the D-atom Rydberg tagging time-of-flight technique. Product translational energy distributions and angular distributions have been determined. Nearly statistical distribution of the product translational energy with nearly isotropic angular distribution was observed at 210-235 nm, which may come from the predissociation pathway of internal conversion from S₁ to S₀ state followed by decomposition on S₀ surface. At shorter photolysis wavelengths, in addition to the statistical distribution, another feature with anisotropic angular distribution appears at high translational energy region, which can be attributed to direct dissociation on S₁ surface. Compared with HNCO, the direct dissociation pathway for DNCO photodissociation opens at higher excitation energy. According to our assignment of the NCO internal energy distribution, dominantly bending and a little stretching excited NCO was produced via both dissociation pathways.     

Infrared Photodissociation Spectroscopic and Theoretical Study of [Co(CO2)n]+ Clusters

The mass-selected infrared photodissociation (IRPD) spectroscopy was utilized to investigate the interactions of cationic cobalt with carbon dioxide molecules. Quantum chemical calculations were performed on the [Co(CO₂)_n]⁺ clusters to identify the structures of the low-lying isomers and to assign the observed spectral features. All the [Co(CO₂)_n]⁺(n=2-6) clusters studied here show resonances near the CO₂ asymmetric stretch of free CO₂ molecule. Experimental and calculated results indicate that the CO₂ molecules are weakly bound to the Co⁺ cations in an end-on con guration via a charge-quadrupole electrostatic interaction. The present IRPD spectra of [Co(CO₂)_n]⁺ clusters have been compared to those of Ar-tagged species ([Co(CO₂)_n]⁺-Ar), which would provide insights into the tagging effect of rare gas on the weakly-bounded clusters.     

Modulation of Conformational Preferences of Heteroaromatic Ethers and Amides through Protonation and Ionization: Charge Effect

Multiple approaches reveal the strong effects of a positive charge introduced by protonation or ionization on the conformation of o-heteroaromatic ethers and amides. The ethers and amides containing an ortho-N heteroatom are syn-preferring while those containing an ortho-O or ortho-S heteroatom are mostly anti-preferring. However, for all the monocyclic o-heteroaromatic ethers and amides, the protonated ones are all anti-preferring while the ionized ones are all syn-preferring. Interestingly, although both the protonation and ionization introduce a positive charge, they have such different effects on molecular conformation, very informative for understanding the origin of conformational preferences. Detailed analysis shows that the population of the introduced positive charge dictates the conformational preferences via electrostatic and orbital interactions. Compared to ortho-heteroatoms, meta-heteroatoms have weaker effect on conformational preference. Achieved by complete inductive method, the regularity of conformational preferences and switching provides easy ways to modulate conformers (by pH or redox), and makes this kind of ether or amide bond a conformational hinge applicable to design of functional molecules (drugs and materials) and modulation of molecular biological processes.     

O~++H_2→OH~++H反应的动力学研究

采用含时量子波包方法结合二阶分裂算符传播子对初始态为(v=0, j=0)的O~++H_2→OH~++H反应体系在0.01—1.00 eV的碰撞能范围内进行了态分辨理论水平上的动力学计算.对反应概率、积分截面、微分截面以及固定初始态的热速率常数等动力学信息进行了计算并与文献报道的实验和理论结果进行了比较.结果表明本文的理论结果与实验结果十分符合.从微分截面的散射信息可知,在低碰撞能范围内,插入反应机制在反应中占据主导地位.随着碰撞能的增加,反应机制逐渐由插入机制变为抽取反应机制.     

Electron Affinities of the Early Lanthanide Monoxide Molecules

The photoelectron imagings of LaO^-, CeO^-, PrO^-, and NdO^- at 1064 nm are reported. The well resolved photoelectron spectra allow the electron a±nities to be determined as 0.99(1) eV for LaO, 1.00(1) eV for CeO, 1.00(1) eV for PrO, and 1.01(1) eV for NdO, respectively. Density functional calculations and natural atomic orbital analyses show that the 4f electrons tend to be localized and suffer little from the charge states of the molecules. The photodetached electron mainly originates from the 6s orbital of the metals. The ligand field theory with the δ=2 assumption is still an effective method to analyze the ground states of the neutral and anionic lanthanide monoxides.