ⅥA族元素原子簇的电子结构研究

用势价基对ⅥA族Sx、Se_x、Te_x、Te_yS_r、Te_ySe_z等原子簇(x=4,6,8,10,12;y、z=2,3,4,6)作了从头算研究。结果表明:ⅥA族原子簇正离子体系,d轨道参与成键。随着正电价升高,原子簇构型由环链状向扭曲型、封闭多面体发展,而化学键则从一般的定域键向三中心键,多中心键变化。     

金原子簇催化应用的研究进展

在最近的10年里,原子精确的金原子簇(AunLm,L为有机配体)已经被证明是一种新型的纳米金催化剂.不同尺寸的AunLm催化剂表现出独特的电子和晶体结构,为关联催化性能和催化剂结构的内在关系及研究纳米金催化的化学反应机制提供了新的研究平台.在这篇综述中,主要介绍金原子簇催化剂在催化反应中的应用,如选择性氧化和加氢,及C—C偶联反应等,同时,也讨论金原子簇催化剂的尺寸效应、配体效应(例如,芳香族vs脂肪族)、杂金属掺杂(如铜、银、钯、铂)等.最后,在原子尺度上研究了金原子簇催化的反应机制以及结构-活性的构建关系.     

FeRhN原子簇几何结构和磁性

采用离散变分局域自旋密度泛函方法，对ＦｅＲｈＮ原子族（Ｎ＝２－６，１２，４２和５４）的几何结构和磁性进行了系统研究。发现小ＦｅＲｈＮ原子簇几何结构的相对稳定性同原子簇中的相邻原子间成键数目成正比，小ＦｅＲｈＮ原子簇的在态倾向于有较多近邻键合的高维几何结构。所讨论的所有ＦｅＲｈＮ原子簇比相应的ＲｈＲｈＮ原子簇的磁矩都大。因此，用Ｆｅ替换Ｒｈ后，铁确实能提高原子簇的磁矩。这个结论同相关的实验结果相一致     

原子簇的球势阱模型（一）──硼烷、金属羰合物及非金属原子簇结构

原子簇的球势阱模型（一）──硼烷、金属羰合物及非金属原子簇结构姚崇福（化学系）原子簇化学的发展极其迅速。国内外许多学者对它们进行了系统的研究，并提出多种结构规则［１－４］。对硼烷、金属羰合物等原子簇，均可得到满意的解释。但这些规则往往在不同程度上带有...     

原子簇NiBP稳定结构与成键性质的DFT研究

利用DFT方法在B3LYP/Lan12dz水平下对原子簇NiBP的单重态和三重态各种可能构型进行优化,计算结果表明:单重态有两个稳定构型,即具有Cs对称性的NiBP(1)(A)和Cv对称性的NiBP(1)(B);三重态也有两个稳定构型,即具有Cs对称性的NiBP(3)(A)和Cv对称性的NiBP(3)(D),原子簇NiBP(3)(A)是单、三重态中最稳定的构型;在原子簇中Ni,B,P原子间有强烈的相互作用.     

NixFe（x=1—5）原子簇稳定结构的DFT研究

用DFT(密度泛函理论)方法对原子簇NixFe(x=1-5)的几十种可能构型进行优化计算，并对这些优化构型的能量和稳定性进行了分析比较。结果表明，原子簇NixFe(x=1-5)变形空间对称构型最稳定，而且成键主要由Ni-Fe键提供。     

车前草中一种黄酮化合物的电喷雾多级串联质谱研究

利用电喷雾多级串联质谱技术研究了车前草药材中的一种黄酮化合物,根据其在负离子条件下表现出的特征质谱行为,提出了该化合物可能的电喷雾质谱碎裂规律。     

用正电子研究Ⅲ—Ⅴ族化合物半导体的缺陷谱

简要介绍了本科研组近年来用正电子湮没谱学研究Ⅲ－Ⅴ族化合物半导体缺陷的最新进展,包括原生样品中缺陷的种类、大小、电荷态、负离子缺陷、缺陷与杂质的相互作用、辐照以及形变引入的缺陷等,研究表明,在原生半导体材料中存在各种缺陷,经过辐照和璩 变化有单空位、双空位及孔洞形成;在重掺杂材料中,空位还补偿载流子,使载流子发生饱和。     

车前草中一种黄酮化合物的电喷雾多级串联质谱研究

利用电喷雾多级串联质谱技术研究了车前草药材中的一种黄酮化合物,根据其在负离子条件下表现出的特征质谱行为,提出了该化合物可能的电喷雾质谱碎裂规律.     

原子簇NiBP稳定结构与成键性质的DFT研究

利用DFF方法在B3LYP／Lanl2dz水平下对原子簇NiBP的单重态和三重态各种可能构型进行优化，计算结果表明：单重态有两个稳定构型，即具有Cs对称性的NiBP^[1](A)和Cv对称性的NiBP^[1](B)；三重态也有两个稳定构型，即具有Cs对称性的NiBP^[3](A)和Cv对称性的NiBP^[3](D)，原子簇NiBP^[3](A)是单、三重态中最稳定的构型；在原子簇中Ni，B，P原子间有强烈的相互作用．     

Formation of substitutionalmetallofullerenes by laser ablation of externally doped fullerenes C60Mx (M=Sm, Pt,Ni and Rh)

Photofragmentation study of metal fullerides C60Mx (M=Sm, Pt, Ni and Rh) by excimer laser ablation-TOF mass spectrometry shows that metallofullerenes C2nM and C2n+1M formed in both the positive and negative ionic medes.The isotopic distributions of the metallofullerenes C2nM and C2n+1M are consistent with the calculated spectra based on the natural abundance of isotopes of C and M, confirming the formation of metallofullerenes. The metal atom is supposed to be incorporated into the network of the fullerene cage to replace one carbon atom of the cage forming substitutional metallofullerene. Odd-numbered high carbon cluisters are observed in our laser ablation study of all the metal fullerides in the negative ion channel. Evolution of mass spectrum with irradiation laser shots shows that the formation of the substitutionally doped fullerenes is closely related to the production of metal carbide (MC). The structures, as well as formation mechanism, of metallofullerenes C2n+1Mand C2nM with even and odd numbers of total atoms respectively are discussed based on the structural optimization of the odd-numbered high carbon clusters.     

玻璃态碳的激光质谱研究

碳原子簇的结构多年来吸引着理论与实验化学家的兴趣。我们以脉冲激光作用于石墨和主要为石墨微晶的无定形碳(木炭,焦炭等),对所产生的碳原子簇离子的质谱加以分析,发现当碳原子数n=13时,碳原子簇的结构从链状向环状转化,为了进一步确定碳原子簇的结构规律,又选取了晶体构型不同的玻璃态碳为样品,以相同的方法研究。     

Formation of substitutional metallofullerenes by laser ablation of externally doped fullerenes C60M x (M=Sm, Pt, Ni and Rh)

Photofragmentation study of metal fullerides C₆₀M _x (M = Sm, Pt, Ni and Rh) by excimer laser ablation-TOF mass spectrometry shows that metallofullerenes C_2n M and C_2n+1M formed in both the positive and negative ionic modes. The isotopic distributions of the metallofullerenes C_2n M and C_2n+1M are consistent with the calculated spectra based on the natural abundance of isotopes of C and M, confirming the formation of metallofullerenes. The metal atom is supposed to be incorporated into the network of the fullerene cage to replace one carbon atom of the cage forming substitutional metallofullerene. Odd-numbered high carbon clusters are observed in our laser ablation study of all the metal fullerides in the negative ion channel. Evolution of mass spectrum with irradiation laser shots shows that the formation of the substitutionally doped fullerenes is closely related to the production of metal carbide (MC). The structures, as well as formation mechanism, of metallofullerenes C_2n+1M and C_2n M with even and odd numbers of total atoms respectively are discussed based on the structural optimization of the odd-numbered high carbon clusters.     

激光作用于稠环芳烃及其衍生物产生碳原子簇的负离子质谱研究

在自制的装置上以脉冲激光束作用于多种稠环芳烃及衍生物,产生各种大小的碳原子簇与它们的化合物,对这些簇负离子的质谱分析表明,其中质量较高的离子具有球烯(Fullerene)的空间封闭体构型,信号强度最突出的是C~-_(50),次为C~-n,而C~-(60)在实验记录的多数质谱中并不突出;质量较低的离子的构型则是直链状的,其组成为C~-_n和C_nX~-(X因样品的不同分别为N、B、H、P和OH),而C_nX~-因其杂原子X的组成的不同,n或者必须为偶数、或者必须为奇数;质量靠近样品分子量的离子则仍为环状构型,其中保留了较多数量的氢原子。     

第一性原理研究Au_n(n=2-11)团簇的结构和稳定性

从第一性原理出发,利用密度泛函理论中广义梯度近似对Aun(n=2-11)团簇进行了结构优化、能量和振动频率分析,得到了金团簇最低能量结构及亚稳态结构.计算结果表明,Aun(n=2-11)团簇的基态结构均为平面结构,Aun可通过Aun-1边戴帽一个原子生长而得,归咎于相对论效应引起的sd杂化.综合Aun团簇基态的平均结合能、离解能及二阶能量差分可知,n为偶数的Aun团簇的稳定性相对较高,并且Au6团簇的稳定性在所有团簇中是最突出的.     

强激光场中不同尺寸原子团簇的电离和光辐射

通过数值求解一维含时薛定谔方程 ,研究了在强激光场中原子及不同尺寸原子团簇的电离几率和光辐射现象。结果表明 ,当外场强度相同时 ,小尺寸原子团簇电离几率小于原子的电离几率 ,可以产生高频率的高次谐波。当原子团簇尺寸较大时 ,其电离几率大于原子的电离几率 ,原子团簇越大 ,电离几率也越大 ,大尺寸原子团簇更易吸收外场能量。     

Multiphoton ionization of pyrrole-water mixed clusters

Multiphoton ionization of the hydrogen-bonded pyrrole-water clusters ( C4H5 N)n H2O)m is studied with a reflectron?time of flight mass spectrometer at 355 nm. With increasing partial concentration of pyrrole in a gas mixture source, a series of poly-pyrrole-water binary-mixed cluster ions can be observed, including unprotonated cluster ions [(C4H5N)x (H2O)y]* , protonated cluster ions [(C4H5N)x (H2O)yH]* and dehydrogenated cluster ions [ ( C4 H4 N) ( C4 H5 N) x ( H2O) y ] + . Ab initio calculations of their structures, bond strengths, charge distributions and re action energies are carried out. Stable structures of these clusters are obtained from the calculations. A probable forma tion mechanism of the cluster ions [(C4H5N)x(H2O)y] + , [(C4H5N)x (H2O)y]H+ and [(C4H4N) (C4H5N)x (H2O)y]-is supposed to be the ionization of clusters followed by dissociation.     

原子团簇P+9的同分异构体预测

Ｐ８ 、 Ｐ＋９ 和 Ｐ＋２５是解释由激光产生的磷原子团簇正离子的质谱图的关键原子团簇, Ｐ＋２５ 可视为由 Ｐ８和 Ｐ＋９ 结合而生成的结构．使用分子图形软件设计出 １９ 种 Ｐ＋９ 的同分异构体,并进行分子力学、 Ｐ Ｍ ３ 半经验量子化学和 Ａ Ｄ Ｆ 密度泛函优化．所有的异构体模型中的磷原子均采用二、三和四配位成键．从各异构体成键能量的比较中可得知,具有平面和双键的结构较不稳定,某些对称性高的结构变形后更加稳定,最稳定的 Ｐ＋９ 构型是在楔状的 Ｐ８ 的侧下部增加一个磷原子所生成的结构．计算结果可为进一步设计大分子磷原子团簇正离子的结构并解释它们在激光质谱图上的尺寸分布打下基础．     

MSn_（10）（M=Sc,Ti,V,Cr,Mn,Fe,Co,Ni）团簇的稳定性和磁性研究

采用密度泛函理论（density functional theory,DFT）中的广义梯度近似（generalized gradient approximation,GGA）对Sn11团簇的4种同分异构体（对称性分别为D5h,D5d,D4h,D4d）的几何结构、电子结构计算研究,得出对称性为D5d的团簇最稳定.将Sn11团簇的中心原子替换成过渡金属原子成为MSn10（M=Sc,Ti,V,Cr,Mn,Fe,Co,Ni）团簇,对其稳定性和磁性进行了分析.在Sn11团簇中将中心原子替换成过渡金属原子后,束缚能都变小了,说明过渡金属原子的替换提高了原锡团簇的稳定性,其中NiSn10团簇的束缚能最小,稳定性最强.过渡金属原子都具有一定的磁性,当把这些原子掺入锡团簇后,过渡金属原子的磁性都有所减弱,其中MSn10（M=Sc,Ti,V,Ni）团簇的磁性完全消失,其原因在于掺杂后,团簇中各原子的电荷分布发生了变化.     

Observation of ligand effects during alkene hydrogenation catalysed by supported metal clusters

Homogeneous organometallic catalysts and many enzymes activate reactants through coordination to metal atoms; that is, the reactants are turned into ligands and their reactivity controlled through other ligands in the metal's coordination sphere. In the case of supported metal clusters, catalytic performance is influenced by the support and by adsorbed reactants, intermediates or products. The adsorbates are usually treated as ligands, whereas the influence of the supports is usually ascribed to electronic interactions, even though metal clusters supported on oxides and zeolites form chemical bonds to support oxygen atoms. Here we report direct observations of the structure of supported metal clusters consisting of four iridium atoms, and the identification of hydrocarbon ligands bound to them during propene hydrogenation. We find that propene and molecular hydrogen form propylidyne and hydride ligands, respectively, whereas simultaneous exposure of the reactants to the supported iridium cluster yields ligands that are reactive intermediates during the catalytic propane-formation reaction. These intermediates weaken the bonding within the tetrahedral iridium cluster and the interactions between the cluster and the support, while replacement of the MgO support with gamma-Al2O3 boosts the catalytic activity tenfold, by affecting the bonding between the reactant-derived ligands and the cluster and therefore also the abundance of individual ligands. This interplay between the support and the reactant-derived ligands, whereby each influences the interaction of the metal cluster with the other, shows that the catalytic properties of supported metal catalysts can be tuned by careful choice of their supports.