银硫二元团簇形成与光过程的硫敏化

采用激光烧蚀法和串级飞行时间质谱仪研究了银硫二元团簇离子的形成(银硫比例影响,尺寸大小范围,激光功率作用及紫外光解等).工作表明,带正电荷的团簇存在着两种不同的形式[(Ag_2S)_n·Ag]~+和[(Ag_2S)_(n-1)·Ag_3]~+.指出[(Ag_2S)]~+,[(Ag_2S)·Ag]~+和[(Ag_2S)·Ag_3]~+及其同系物是硫敏化中心作为光自由电子陷阱最可能存在的形式.     

AgnSm^±和AunSm^±的激光产生与质谱研究

以高能量密度的脉冲激光束在高真空中直接溅射银(金)粉与硫的混合物, 产生了丰富的银-硫和金-硫二元原子族正负离子, 记录了它们的飞行时间质谱。通过对这些簇离子的组成与分布的分析, 发现了它们的一些结构规律。银硫簇离子以离子键为主, Ag2S是它们的主要结构单元, 其中Ag11S5^+和Ag9S5^-特别稳定; 金硫簇离子基本上是共价结构, 金原子间相互成键, 构成簇离子的核, 硫原子则仅与核表面的金原子配位, 其中Ag6S14^+, Au5S6^-的稳定性比较突出。     

银硫二元团簇[Ag.(Ag~2S)~n]^+(n=3,4)的从头算研究

用abinitio分子轨道限制性Hartree-Fock(RHF)和密度泛函(DFT)方法对银硫二元团簇[Ag.(AgS)~n]^+(n=3,4)的结构进行研究.结果表明,具有环状结构的团簇最为稳定.得到了相应的几何构型和电子结构,并且对这两种团簇可为硫敏化中心自由电子深陷阱的存在形式作出合理解释。     

金-硫团簇负离子组成特征的探讨

报导了金/硫靶在静态二次离子质谱实验条件下形成的组成通式为Au1－15S0－5的团簇负离子.其中,Aun组成系列具有典型的奇数优势,属于金的一元团簇负离子.其余组成系列（Au1－15S1－5）则属于金 硫二元团簇负离子.研究发现,金 硫团簇负离子具有以下与组成密切相关的特征: （1）它们继承了金一元团簇负离子的奇数优势;（2）它们中硫原子数仅限于5,而金原子数则在较大范围变化;（3）它们完全没有多数其它金属与非金属（包括硫）二元团簇正/负离子共有的MenNn型组成优势;（4）它们以上组成特征及其它细节恰似碳 磷这样的典型非金属二元团簇正/负离子.基于这样的组成特征可提出,金 硫团簇负离子在构成上包含着相对完整的金一元团簇组件,在形成机制上源于金一元团簇与硫一元团簇（或称为:限于五原子的多硫单元）之间的再团簇化.关于再团簇化机制中的相互作用问题,即两类团簇间是依靠末端原子交叉成键还是依赖两类团簇中异种原子之间静电诱导力等“非共价键”作用的问题,则有待于今后研究证实.     

钪-硫团簇的形成和光解

报道了用激光直接溅射法产生钪硫团簇, 并用串级飞行时间质谱仪研究了所产生的团簇离子的分布及紫外激光光解规律。钪硫二元团簇正负离子都是由周边硫原子包围团簇骨架而构成的, 骨架是由包含着不同数目的Sc2S3这样的组份单元组成, 它们结合紧密, 构成了稳定的钒硫团簇的核心。稳定的团簇正离子为ScS(Sc2S3)n^+和Sc2S2(Sc2S3)n^+。稳定的团簇负离子为ScS2(Sc2S3)n^-,S3(Sc2S3)n^-, (Sc2S3)n^-。周边硫原子数目随样品中硫的摩尔含量的增加而增多, 它们结合较弱, 易于剥离。在紫外光解时往往以失去S2, S4, S6的方式解离。通过分析认为具有组份单元的Sc对于S团簇的结构可能是一种笼状结构。     

钽硫原子簇的形成及激光裂解的初步研究

报导用激光直接溅射的方法产生了大量的钽硫原子团簇离子Ta_nS_m~+(n≤9, m≤30),并用串级飞行时间质谱仪研究了所产生团簇离子的组成及紫外激光裂解规律。实验发现, 最稳定的团簇正离子往往具有Ta_nS_(2n+7)~+(n=1,2,…9)的组成, 相应的负离子具有, Ta_nS_(2n+3)~-(n=1,2,…9)的组成。各种团簇正离子的激光裂解的主要通道是连续的S_2消除过程, 且对于n=3,4,5的团簇, 主要光解产物还有Ta_3S_4~+或Ta_4S_6~+离子。据此推测出Ta_nS_m~+团簇离子的可能结构为在Ta原子周围有6个左右的S原子配位。Ta原子之间不存在直接的化学键,而较大团簇可能是以Ta_3S_4或Ta_4S_6为核心的结构。     

铅、硫团簇的形成、反应与光解

用激光直接溅射和串级溅射两种方法产生铅／硫二元团簇,并用串级飞行时间质谱仪研究了二元团簇的组份及光解规律,用激光直接溅射铜＋硫混合样品时,组成为PbnSn-1 和PbnSn-的团簇丰度最大,是二元团簇的结构骨架和稳定组份,而用激光串级溅射铅样品和硫样品,通过铅团簇与硫团簇的反应,则可得到PbnSm (n=1-3,m=0-9)和PbnSm-(n=1-7,m=0-9)。这两种二元团簇的产生方法对应两种不同的团簇形成机理。     

银硫团簇离子的形成与光解

银硫团簇离子的形成与光解于忠德，高振，张南，朱起鹤，孔繁敖（中国科学院化学研究所分子反应动力学国家重点实验室，北京１０００８０）本文首次报道用激光溅射方法产生了银硫团簇离子，并研究了部分团簇离子的紫外激光解离规律。由于银与铜都是具有满壳层ｄ电子结构的...     

银硫纳米簇合物的阴离子模板法合成、结构与发光性能

银硫纳米簇合物的形成,因涉及多个组分的组装过程,其合成富有挑战性.而阴离子模板法是一种简单有效的合成银硫纳米簇合物的方法,特别是在对银硫纳米簇合物结构的控制方面表现出独特的优越性.结合本课题的工作,我们综述了简单的球形阴离子(如卤素离子、S~(2-)等),三角形阴离子(如CO_3~(2-)、NO_3~-等)及复杂的多酸阴离子(如[W_6O_(21)]~(6-)、Mo_6O_(22)~(8-)等)为模板剂合成银硫纳米簇合物的研究进展,同时探索了合成的银硫纳米簇合物的结构和发光性能.     

铝硫二元团簇的组分及其光解规律

硫与金属元素所形成的二元团簇具有很多重要的特性,已受到人们的普遍重视.用激光-串级飞行时间质谱仪,我们曾研究了硫与过渡金属钽、铁等的二元团簇.最近我们选取主族金属元素铝,研究了铝硫团簇的形成及其光解,实验结果表明,与钽硫或铁硫团簇相比,铝硫团簇无论在其组份构成还是在其光解方面,都表现出鲜明的特有规律性.实验的主要参数如下:溅射用激光为Nd:YAG 二倍频,其输出强度控制在约10~7W·cm~(-2),激光的重复频率10Hz 样品位于激光束的焦点附近,由焦距f=50cm 的透镜调整其聚焦状     

Ag/Se二元团簇的形成以及Ag与Se团簇反应的研究

用飞行时间质谱仪研究了激光直接溅射Ag/Se混合样品产生的二元团簇以及团簇正离子的光解行为;并用串级溅射反应装置研究了Ag和Se正负离子产物.在直接溅射产生的Ag/Se二元团簇中,正离子主要系列是:[(Ag₂Se)_nAg⁺],[(Ag₂Se)_nAg₃⁺];负离子主要系列是:[(Ag₂Se)_nAgSe^-],[(Ag₂Se)_nAgSe₂^-],[(Ag₂Se)_nSe^-].团簇正离子的光解结果表明,同样条件下Ag/Se二元团簇正离子光解比率比Ag/S大.在Ag和Se样品串级溅射实验中,主要得到AgSe_n⁺(n=4～9)和AgSe_nSe^-(n=4～7)系列的产物,在AgSe_n⁺系列中,n=4,6时丰度较大.这表明串级溅射反应和直接溅射二元混合样品两种过程中成簇机理是不同的.     

Communication: CO oxidation by silver and gold cluster cations: identification of different active oxygen species

The oxidation of carbon monoxide with nitrous oxide on mass-selected Au(3)(+) and Ag(3)(+) clusters has been investigated under multicollision conditions in an octopole ion trap experiment. The comparative study reveals that for both gold and silver cations carbon dioxide is formed on the clusters. However, whereas in the case of Au(3)(+) the cluster itself acts as reactive species that facilitates the formation of CO(2) from N(2)O and CO, for silver the oxidized clusters Ag(3)O(x)(+) (n=1-3) are identified as active in the CO oxidation reaction. Thus, in the case of the silver cluster cations N(2)O is dissociated and one oxygen atom is suggested to directly react with CO, whereas a second kind of oxygen strongly bound to silver is acting as a substrate for the reaction.     

Formation of binary silver sulfide clusters and sulfur sensitization of photographic process

Formation of silver sulfide binary cluster ions,as well as the effects of silver and sulfur content proportion,the cluster size range,the influence of laser fluence,the UV laser photolysis,etc.,was studied with the laser ablation method and a tandem time-of-flight mass spectrometer.The results show that there exist two different forms of positively charge-bearing cluster ions;[(Ag2S)n Ag] + and [ (Ag2S)n-1 Ag3]+.The most possible forms of the sulfur sensitization centers acting as traps of photoelectrons are [Ag2S] +,[ Ag2S Ag] +,[ Ag2S Ag3]+ and the analogs.     

Structure, bonding, and linear optical properties of a series of silver and gold nanorod clusters: DFT/TDDFT studies

DFT/TDDFT calculations have been carried out for a series of silver and gold nanorod clusters (Ag(n), Au(n), n = 12-120) whose structures are of cigar-type. Pentagonal Ag(n) clusters with n = 49-121 and hexagonal Au(n) clusters with n = 14-74 were also calculated for comparison. Metal-metal distances, binding energies per atom, ionization potentials, and electron affinities were determined, and their trends with cluster size were examined. The TDDFT calculated excitation energies and oscillator strengths were fit by a Lorentz line shape modification, which gives rise to the simulated absorption spectra. The significant features of the experimental spectra for actual silver and gold nanorod particles are well reproduced by the calculations on the clusters. The calculated spectral patterns are also in agreement with previous theoretical results on different-type Ag(n) clusters. Many differences in the calculated properties are found between the Ag(n) and Au(n) clusters, which can be explained by relativistic effects.     

Reactions of mixed silver-gold cluster cations AgmAun + (m+n=4,5,6) with CO: radiative association kinetics and density functional theory computations

Near thermal energy reactive collisions of small mixed metal cluster cations Ag(m)Au(n) (+) (m+n=4, 5, and 6) with carbon monoxide have been studied in the room temperature Penning trap of a Fourier transform ion-cyclotron-resonance mass spectrometer as a function of cluster size and composition. The tetrameric species AgAu(3) (+) and Ag(2)Au(2) (+) are found to react dissociatively by way of Au or Ag atom loss, respectively, to form the cluster carbonyl AgAu(2)CO(+). In contrast, measurements on a selection of pentamers and hexamers show that CO is added with absolute rate constants that decrease with increasing silver content. Experimentally determined absolute rate constants for CO adsorption were analyzed using the radiative association kinetics model to obtain cluster cation-CO binding energies ranging from 0.77 to 1.09 eV. High-level ab initio density functional theory (DFT) computations identifying the lowest-energy cluster isomers and the respective CO adsorption energies are in good agreement with the experimental findings clearly showing that CO binds in a "head-on" fashion to a gold atom in the mixed clusters. DFT exploration of reaction pathways in the case of Ag(2)Au(2) (+) suggests that exoergicities are high enough to access the minimum energy products for all reactive clusters probed.     

How cationic gold clusters respond to a single sulfur atom

Results describing the interaction of a single sulfur atom with cationic gold clusters (Au(n) (+), n=1-8) using density functional theory are described. Stability of these clusters is studied through their binding energies, second order differences in the total energies, fragmentation behavior, and atom attachment energies. The lowest energy structures for these clusters appear to be three dimensional right from n=3. In most cases the sulfur atom in the structure of Au(n)S(+) is observed to displace the gold atom siting at the peripheral site of the Au(n) (+) cluster. The dissociation channels of Au(n)S(+) clusters follow the same trend as Au(n) (+) cluster, based on the even/odd number of gold atoms in the cluster, with the exception of Au(3)S(+). This cluster dissociates into Au and Au(2)S(+), signifying the relative stability of Au(2)S(+) cluster regardless of having an odd number of valence electrons. Clusters with an even number of gold atoms dissociate into Au and Au(n-1)(S)(+) and clusters with an odd number of gold atoms dissociate into Au(2) and Au(n-2)(S)(+) clusters. An empirical relation is found between the conduction molecular orbital and the number of atoms in the Au(n)S(+) cluster.     

Bimetallic silver-gold clusters by matrix-assisted laser desorption/ionization

Pure gold clusters (Aun+) were produced up to the cluster size of n = 100 by matrix-assisted laser desorption/ionization (MALDI). The mass spectrum of the resulting clusters showed alteration in the ion intensity at odd-even clusters size. On the other hand, intensity drops at cluster size predicted by the jellium model theory was also observed. Positively and negatively charged bimetallic silver-gold clusters were produced under MALDI conditions from the mixture of HAuCl4/silver trifluoroacetate and the 2-(4-hydroxyphenylazo)benzoic acid (HABA) matrix. A linear correlation was found between the intensity ratio of AunAgm+ to Au(n+1)Ag(m-1)+ cluster ions and the molar ratio of the gold to silver salt. It was observed that the composition and the distribution of the clusters can be varied with the molar ratio of the silver and gold salts. It was also found that the resulting cluster sizes obey the lognormal distribution.     

CO adsorption on pure and binary-alloy gold clusters: a quantum chemical study

We performed density-functional theory analysis of nondissociative CO adsorption on 22 binary Au-alloy (Au(n)M(m)) clusters: n=0-3, m=0-3, and m+n=2 (dimers) or 3 (trimers), M=Cu/Ag/Pd/Pt. We report basis-set superposition error corrections to adsorption energies and include both internal energy of adsorption (DeltaU(ads)) and Gibbs free energy of adsorption (DeltaG(ads)) at standard conditions (298.15 K and 1 atm). We found onefold (atop) CO binding on all the clusters except Pd2 (twofold/bridged), Pt2 (twofold/bridged), and Pd3 (threefold). In agreement with the experimental results, we found that CO adsorption is thermodynamically favorable on pure Au/Cu clusters but not on pure Ag clusters and also observed the following adsorption affinity trend: Pd>Pt>Au>Cu>Ag. For alloy dimers we found the following patterns: Au2>M Au>M2 (M=Ag/Cu) and M2>M Au>Au2 (M=Pd/Pt). Alloying Ag/Cu dimers with (more reactive) Au enhanced adsorption and the opposite effect was observed for PdPt dimers. The Ag-Au, Cu-Au, and Pd-Au trimers followed the trends observed on dimers: Au3>M Au2>M2Au>M3 (M=Ag/Cu) and Pd3>Pd2Au>PdAu2>Au3. Interestingly, Pt-Au trimers reacted differently and alloying with Au systematically increased the adsorption affinity: PtAu2>Pt2Au>Pt3>Au3. A strikingly different behavior of Pt is also manifested by the triplet spin state and onefold (atop) binding in Pt3-CO which is in contradiction with the singlet spin state and threefold binding in Pd3-CO. We found a linear correlation between CO binding energy (BE) and elongation of the CO bond. For Ag-Au and Cu-Au clusters, the increase in CO BE (and elongation of the C-O bond which is probably due to the back donation) is accompanied by the decrease in the cluster-CO distance suggesting that the donation (from 5sigma highest occupied molecular orbital in CO to cluster lowest unoccupied molecular orbital) mechanism also contributes to the BE. For Pd-Au clusters, the cluster-CO distance (and CO bond length) increases with increase in the BE, suggesting that the donation mechanism may not be important for those clusters. No clear trend was observed for Pt-Au clusters.