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1.
碳原子簇的结构与质谱关联   总被引:1,自引:0,他引:1  
在自制的仪器上以脉冲激光蒸发和电离单质碳样品,可以产生各种大小的碳原子簇正负离子。这些原子簇的飞行时间质谱可以直接与Hückel规则、Euler定理等相关联。而由此分析得出,随着碳原子簇的增大,它们所经历的各种基本几何构型的转化。  相似文献   

2.
随着“足球烃”C_(60)及其他“球碳烃”的发现,以及对它们奇妙的结构与化学行为的不断揭示,碳原子簇的产生与研究已成为当前化学界的一个热门课题.Smalley等最近又将C_(60)中的一个碳原子以硼原子取代,成为Lewis酸,使这方面的研究更加深入。近二年来,我们在自制的装置上对碳原子簇的结构作了较为充分的研究后,又以独特的方式产生了链状构型的C_nB~-,记录了它们的负离子质谱。  相似文献   

3.
在自制的仪器上,以脉冲激光束在高真空中溅射适当的样品,产生了一系列合有1个VA族原子(N、P、As)或ⅢA族原子(B、Al)及13个以下碳原子的原子簇负离子。在实验记录的飞行时间质谱中,这些簇离子的信号强度均因其碳原子数的奇偶而发生交替变化.对实验结果的分析研究显示:这些簇离子均为直链构型.VA或ⅢA族原子位于链的一端,所有成簇原子的价键均得到满足.  相似文献   

4.
CnD-m簇离子的结构特性和形成动力学研究   总被引:2,自引:2,他引:0  
对较小碳原子簇负离子C-n结构的研究是从直链向单环乃至双环构型发展的.氢原子在碳原子簇中起着电子给予体的作用[1,2].但以往的研究未发现碳原子数的奇偶性和氢原子数目对簇离子构型的影响.我们以激光溅射氘代蒽样品,产生了丰富的碳/氢团簇负离子CnD-m...  相似文献   

5.
自从C_(60)被发现以来,人们普遍认为其具有非常稳定的结构,但我们最近在实验中发现,C_(60)在激光的作用下不仅能形成正负离子,还能进一步聚合成为更大的碳原子簇离子。 1 实验部分 实验在自制仪器上进行。实验中采用高纯C_(60)样品,溅射样品的脉冲激光束波长532nm、脉宽7ns、功率密度10~7W/cm~2。激光产生的正负离子以两台原位飞行时间质谱仪同时检测。实验在10~(-4)Pa真空下进行,实验过程中未引入任何气源。  相似文献   

6.
二元以至多元原子簇(包括铝氧原子簇)的产生与研究是当前十分活跃的领域.最近,我们在自制的装置上,以功率密度达10~8W·cm~(-2)的脉冲激光束(波长532nm)在10_4~-Pa 的真空中溅射AlN 样品时,在实验记录的正负离子质谱中出现的几乎都是铝原子簇离子;而当我们选择α-Al_2O_3为样品时,则观察到了一系列质量分布很广的二元铝氧原子簇负离子,如图1所示.图1的飞行时间质谱是连续100次记录的数据叠加的结果,图中各Al_nO_m~-分别以(n,m)  相似文献   

7.
激光法产生球烯负离子   总被引:3,自引:0,他引:3  
黄荣彬  高振 《应用化学》1993,10(3):60-62
C_(60)及其他具有封闭结构的球烯(Fullerene)的产生与研究是当今化学界的热门课题。我们在自制的仪器上,以脉冲激光束在高真空中溅射单质碳样品,产生球烯的正负离子。最近又在相同条件下记录了煤、稠环芳香烃等10余种有机物的负离子质谱,发现其中许多物质均能产生球烯负离子,且质谱特征十分相似,与以往观察的正离子质谱有明显不同。实验结果揭示了球烯负离子的激光产生与样品组成和结构的关联。 实验装置另文介绍。激光波长532nm,脉冲7ns,功率密度接近10~8W/cm~2。实验中通过  相似文献   

8.
根据出现在质谱中的各种大小的碳原子簇的相对丰度,分析了由激光产生的碳原子簇离子的统计分布,研究了这些统计分布与碳原子簇结构的关联。研究结果表明:相同构型的原子簇的相对丰度可以由同一条对数正态分布曲线来描述,由此能够获得碳原子簇构型的变化情况。质谱中分布曲线的数目对应于具有不同构型或不同结构稳定性的原子簇的数目。如果某些簇离子的谱峰明显地高出分布曲线,它们的结构应特别稳定,其成簇原子数就是所谓的“奇幻数”(magicnumber),例如在石墨质谱中的C_(60)就属于这种情况。原子簇的统计分布还与它们的生成过程有关,由此可能揭示出原子簇的产生机理。  相似文献   

9.
激光产生的碳原子簇负离子及其质谱研究   总被引:6,自引:0,他引:6  
自80年代中叶以来,Bloomfield等人以脉冲激光结合超声分子束的方式产生碳原子簇,尤其在Smalley等发现被认为具有足球形超稳定结构的C_(60)以来,碳原子簇的激光产生与研究已经吸引了越来越多的化学家的兴趣.然而迄今为止,研究的手段仍以质谱为主,而且多  相似文献   

10.
介绍直接用激光溅射芳香化合物固态样品产生的含氢磷原子团簇离子(C_nH~+_m),并用飞行时间质谱仪研究了其组成和结构.实验发现,在低质量区(n=32-56)得到了具有奇偶碳原子数的含氢磷原子簇,而在高质量区(n>100)除了得到纯碳原子簇以外,还得到了含氢碳原子簇.根据对实验结果的分析提出了两种结构模型:对低质量区的团簇,其结构为芳香基团与富勒烯笼状框架的复合体;对高质量区的团簇,其结构为蜗牛形与圆柱形的复合体.  相似文献   

11.
Two types of anion states are shown to coexist in nanometer-scale polyacene cluster anions. Naphthalene and anthracene nanoclusters having a single excess electron were produced in the gas-phase. Photoelectron spectra of size-selected cluster anions containing 2 to 100 molecules revealed that rigid "crystal-like" cluster anions emerge, greater than approximately 2 nanometers in size, and coexist with the "disordered" cluster anion in which the surrounding neutral molecules are reorganizing around the charge core. These two anion states appear to be correlated to negative polaronic states formed in the corresponding crystals.  相似文献   

12.
A hybrid density functional approach with very large basis sets was used for studying Ca2 through Ca19 and Zn3 through Zn11 neutral clusters and their cluster anions. Energetics, structure, and vibrational analysis of all these neutral clusters and cluster anions are reported. The calculated electron affinities are in excellent agreement with experiment displaying a characteristic kink at Ca10 and Zn10. This kink occurs because the 10-atom neutral cluster is very stable whereas the cluster anion is not. Additionally, the electron detachment binding energies (BEs) up to Ca6(-) and Zn6(-) were identified by analyzing the ground and excited states of the cluster anions and of their corresponding size neutral clusters. The theoretical BE is in very good agreement with experiment for both calcium and zinc cluster anions. The three main peaks in the spectrum correspond to BEs from the ground state of the cluster anion (doublet) to the ground state of the neutral cluster (singlet) and to the first triplet and quintet excited states of the neutral cluster. The calculated energy gap from the lowest BE peak to the second peak is in excellent agreement with experiment. The calculation reproduces very well the energy gap observed in Ca4(-) and Zn4(-), which is larger than those for other sizes and is indicative of the strong stability of the anion and neutral tetramers.  相似文献   

13.
A first-principles quantum chemistry method, based on the Kohn-Sham density-functional theory, is used to investigate the adsorption of CO and O2 on small gas-phase gold cluster anions. The saturated adsorption of carbon monoxide on gold cluster anions AuN- (N=2-7) is discussed. The adsorption ability of CO reduces with the increase of the number of CO molecules bound to gold cluster anions, resulting in saturated adsorption at a certain amount of absorbed CO molecules, which is determined by geometric and electronic properties of gold clusters cooperatively. The effect of CO preadsorption on the electronic properties of gold cluster anions depends on the cluster size and the number of adsorbed CO, and the vertical detachment energies of CO-adsorbed gold cluster anions show a few changes with respect to corresponding pure gold cluster anions. The results indicate that the impinging adsorption of CO molecules may lead to geometry structure transformation on Au3- cluster. For the coadsorption of CO and O2 on Au2-, Au3- isomers, Au4-, and Au6-, we describe the cooperative adsorption between CO and O2, and find that the O2 dissociation is difficult on gas-phase gold cluster anions even with the preadsorption of CO.  相似文献   

14.
Reactions of free silver anions Agn- (n = 1 - 13) with O2, CO, and their mixtures are investigated in a temperature controlled radio frequency ion trap setup. Cluster anions Agn- (n = 1 - 11) readily react with molecular oxygen to yield AgnOm- (m = 2, 4, or 6) oxide products. In contrast, no reaction of the silver cluster anions with carbon monoxide is detected. However, if silver cluster anions are exposed to the mixture of O2 and CO, new reaction products and a pronounced, discontinuous size dependence in the reaction behavior is observed. In particular, coadsorption complexes Agn(CO)O2- are detected for cluster sizes with n = 4 and 6 and, the most striking observation, in the case of the larger odd atom number clusters Ag7-, Ag9-, and Ag11-, the oxide product concentration decreases while a reappearance of the bare metal cluster signal is observed. This leads to the conclusion that carbon monoxide reacts with the activated oxygen on these silver clusters and indicates the prevalence of a catalytic reaction cycle.  相似文献   

15.
磷原子形成的奇数和偶数团簇离子的信号存在明显的强度差异. 当团簇离子尺寸n>25时, 奇数团簇离子的信号强度一般会远远超过其邻近的偶数团簇离子. 为更好地理解团簇尺寸对这一现象的影响, 本文通过真空中激光溅射红磷的方法, 利用质谱对磷团簇离子进行了研究和分析. 结果表明这种方法可以产生较大尺寸(n~500)的磷团簇离子. 进一步对团簇离子的强度分布进行分析表明: 随着正负离子团簇尺寸的增加, 奇/偶数离子强度差异都会逐渐减小. 根据它们的变化趋势, 可以预测: 当n>1000时, 奇/偶数离子强度交替的现象可能会消失. 这一结果正反映出团簇在从原子演变到凝聚态物质过程中的桥梁作用.  相似文献   

16.
Reaction kinetics of metal cluster ions under well defined thermal conditions were studied using a flow tube reactor in combination with laser vaporization. Aluminum anions and cations were reacted with oxygen, and several species which are predicted jellium shell closings, were found to have special stability. Metal alloy cluster anions comprised of Al, V and Nb were also seen to react with oxygen. Alloy clusters with an even number of electrons reacted more slowly than odd electron species, and certain clusters appeared to be exceptionally unreactive. Copper cation clusters were observed to associate with carbon monoxide with reactivities that approach bulk behavior at surprisingly small cluster size. These reactions demonstrate how the rate of reaction changes with cluster size.  相似文献   

17.
Attachment of free electrons to water clusters embedded in helium droplets leads to water-cluster anions (H2O)n(-) and (D2O)n(-) of size n > or = 2. Small water-cluster anions bind to up to 10 helium atoms, providing compelling evidence for the low temperature of these complexes, but the most abundant species are bare cluster anions. In contrast to previous experiments on bare water clusters, which showed very pronounced magic and anti-magic anion sizes below n = 12, the presently observed size distributions vary much more smoothly, and all sizes are easily observed. Noticeable differences are also observed in the stoichiometry of fragment anions formed upon dissociative electron attachment and the energy dependence of their yield. Spectroscopic characterization of these ultracold water-cluster anions promises to unravel the relevance of metastable configurations in experiments and the nature of the still controversial bonding sites for the excess electron in small water-cluster anions.  相似文献   

18.
The collisional electron detachment process of carbon cluster anions containing from 2 to 72 atoms was investigated on the collision with a MoS2 surface. The detachment efficiency was classified into several groups and is most likely to reflect the structures or the isomer contents of the incident cluster anions. The cluster anions produced via laser-vaporization of graphite showed quite a larger detachment efficiency than the fullerene C 60 - and its fragment anions. The major isomers of these cluster anions were suggested to be chains or rings.  相似文献   

19.
We carry out a systematic search for the atomic structures of silicon cluster cations and anions in the size range n=31-50 using density functional theory in the generalized-gradient approximation. The obtained lowest-energy candidates feature cagelike structures. We find that the computed binding energies and the dissociation pathways as well as the mobilities of our lowest-energy isomers of the cations are all in good agreement with the measured data from experiments. Furthermore, based on these isomers, we reveal that the steplike feature appearing in the measured high-resolution mobilities can be correlated with the corresponding fullerenes explicitly, which strongly support the notion that endohedral silicon fullerenelike structures are the most favored growth pattern for silicon clusters in the range n=31-50. Our calculation and analysis suggest that the proposed isomers are probably very close to the major-abundance isomers observed in experiments.  相似文献   

20.
We have measured the photoelectron-spectra of I? (H2O)n clusters in the size range n=1–60. We have found that the first six water molecules form a solvation layer with an average 0.35 eV electrostatic stabilization of the anion. At larger cluster sizes the electrostatic stabilization of water does not fit a continuous dielectric solvent. The most stable structures of the clusters consist of internally solvated anions. In the size range n=34–40 we have found evidence for existence of cluster structures with surface solvated anions.  相似文献   

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