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1.
本文采用尺寸选择的负离子光电子能谱与高精度理论计算,对AlnC4-/0(n=2∽4))团簇的结构和成键性质进行了研究. Al2C4-团簇负离子的最稳定结构是一个C2v对称的平面结构,其中两个C2单元与两个铝原子分别相连. Al2C4-团簇负离子的次稳定结构是一个线型结构,两个铝原子位于C4线型结构两端,能量仅比最稳定结构高0.05 eV. 中性Al2C4团簇是一个线型结构. Al3C4-团簇负离子是一个平面结构,其中三个铝原子分别与两个C2单元相连. 而中性Al3C4团簇则是一个V字型结构. Al4C4-团簇负离子和中性Al4C4团簇均为C2h对称的平面结构,四个铝原子分别位于两个C2单元的末端. AlnC4-/0(n=2∽4))团簇负离子的自适应自然密度配分的分析结果表明这些团簇中铝原子与C2单元之间的化学键具有σ和π键特征.  相似文献   

2.
本文利用尺寸选择的负离子光电子能谱和理论计算探索Au_2Ge_n~(-/0)(n=1~8)团簇的结构演化和电子性质.通过比较理论模拟谱与实验谱,并使用CCSD(T)理论方法计算异构体的相对能量,从而确定金锗混合团簇的全局最小结构.本文发现Au_2Ge_n~(-/0)(n=1~8)团簇的两个Au原子具有较高的配位数和较弱的亲金相互作用.负离子团簇和中性团簇的最稳定结构分别处于自旋双重态和自旋单重态.除了Au_2Ge_4~(-/0)和Au_2Ge_5~(-/0),负离子团簇和中性团簇的全局最小结构具有相似的结构特点.Au_2Ge_1~(-/0)团簇是一个C_(2v)对称的V形结构,而Au_2Ge_2~(-/0)团簇是一个C_(2v)对称的双桥连结构.Au_2Ge_4~-负离子团簇是两个Au原子盖帽的Ge_4四面体结构,而Au_2Ge_4中性团簇是两个Au原子盖帽的Ge_4菱形结构.Au_2Ge_(5~8)~(-/0)团簇主要采用三棱柱、四棱柱、及五棱柱结构.Au_2Ge_6是一个C_(2v)对称的四棱柱结构,并表现出σ和π双键性质.  相似文献   

3.
利用光电子能谱及密度泛函理论计算对TiGen-(n=7~12)团簇的几何结构及电子特性等进行了系统研究. 对于TiGen-负离子及中性TiGen,在n=8时出现了钛原子半内嵌的船型结构;在n=9~11时,新增的锗原子加盖到这种船型结构上,逐步形成钛原子完全内嵌的结构. TiGe12- 团簇具有一种钛原子内嵌的变形六棱柱结构. 自然布居分析结果显示,对于n=8~12的TiGen-/0 团簇,随着内嵌结构的形成,有电子从锗原子转移到钛原子,说明其电荷转移方式与结构演变密切相关.  相似文献   

4.
采用密度泛函理论方法,研究了近年来实验报道的双金属纳米团簇Au2@Cu6的电子结构和成键特征. 一般认为,纳米团簇Au2@Cu6中(CuSH)6环和(Au2PH3)2两部分之间的相互作用可以看作是d10-σ闭壳相互作用. 然而,化学成键分析表明,两个部分之间存在一个十中心两电子(10c-2e)的多中心键. 将该结构与其他双金属纳米团簇M2@Cu6(M=Ag、Cu、Zn、Cd、Hg)做对比分析,结果表明除了d10-σ闭壳层相互作用外,多中心键也是配合物的电子结构稳定性的原因. 这一结果将为理解闭壳层相互作用提供有利的帮助.  相似文献   

5.
张蓓  保安  陈楚  张军 《物理学报》2012,61(15):153601-153601
本文采用基于自旋极化的密度泛函理论系统研究了ConCm± (n=1-5; m=1,2)团簇的几何结构和电子结构特性. 将ConC± (n=2-5)团簇中的一个Co替换为C原子, 个体的基态几何结构发生明显变化; 在ConC2± (n=1-5)团簇的生长序列中, 发现从n=3开始团簇中的两个C原子有彼此分离分布的趋势, 我们分析, 这是Co金属能够维持单壁碳纳米管(SCNTs)保持开口生长, 成为非常有效的一种催化剂的重要原因. 同时, 将ConC± (n=2-5)团簇中添加一个Co原子后系统的总磁矩出现大幅下降的趋势, 但仍保持奇偶交替的规律. 通过比较中性及带电的ConC以及ConC2 (n=1-5)团簇的碎裂能, 本工作发现: 由实验获取的SCNTs应均为带正电的体系, 这一结论与已有的实验模型拟合得很好.  相似文献   

6.
利用飞秒时间分辨光谱,可观测叠加在电子态动力学上的相干振动动力学. 从金团簇的相干振动中,不仅能提取电子与振动的耦合信息,也能得到力学性质和电子结构,进而有望实现微小质量探测等应用. 本文利用飞秒时间分辨的瞬态吸收探测了[Au25(SR)18]-团簇的相干振动动力学,通过对相干振动的频率、相位、波长分布的详细分析进一步揭示了其来源. 在[Au25(SR)18]-团簇的飞秒瞬态吸收动力学中可以观测到频率为40 cm-1和80 cm-1的两种振动,均来源于团簇中心Au13核的振动. 通过对相干振动的相位分析发现频率为80 cm-1的振动来自于对电子态之间吸收频率的调制,而频率为40 cm-1的振动来源于对电子态之间吸收强度的调制. 同时,研究发现[Au25(SR)18]-团簇相干振动的频率对其表面配体不敏感,该振动是来源于Au13核的本征性质.  相似文献   

7.
本文利用时间切片离子速度成像技术在134∽140 nm波段研究了OCS分子经由F 31Π里德堡态的真空紫外光解离动力学. 在选取的5个分别对应OCS(F 31Π, v1=0∽4)的伸缩振动激发的光解波长,实验测得了来自CO(X1Σ+)+S(1D2)产物通道的SS(1D2))实验影像,并获得了总平动能谱和CO(X1Σ+, v)共生产物的振动布居及角分布. 结果分析表明OCS分子解离生成CO(X1Σ+)+S(1D2)产物的过程经历了上态F 31Π 与C?v和Cs构型的下电子态间非绝热耦合过程. 实验结果显示了很强的波长相关性:OCS (F 31Π, v1)的较低转动激发态(v1=0∽2)和较高转动激发态(v1=3, 4)的CO(X1Σ+)产物的振动布居和角分布具有显著差异,表明该解离过程中具有不同的解离机理. 本结果提供了振动耦合可能对真空紫外光解离动力学产生关键作用的相关证据.  相似文献   

8.
本文采用密度泛函理论和波函数理论研究了M2Pt20/-团簇(M表示碱土金属元素)在气相中的几何结构和电子性质. 研究表明,拥有平面结构的D2h异构体比拥有较小二面角及较短Pt-Pt键长的C2v异构体更稳定. M(s,p)与Pt(5d)的相互作用和Pt-Pt共价键之间的相互竞争导致了这两种异构体在稳定性方面有所不同. M(s,p)与Pt(5d)的相互作用支持D2h异构体的平面结构;Pt-Pt共价键作用导致了C2v异构体的弯曲结构. Be2Pt2的单重态和三重态的势能曲线有两个不同的交点,但是Ra2Pt2和Ca2Pt2-的不同多重度的势能曲线间只有一个交点,这可能是由于三重态Ra2Pt2和四重态Ca2Pt2-较平坦的势能曲线造成的. 上述结果揭示了一个拥有最小原子数的二面角弯曲异构现象,并且为解释其他潜在的角度弯曲异构体提供了理论帮助.  相似文献   

9.
本文利用红外光解离光谱研究了一价钴阳离子与二氧化碳之间的相互作用. 通过密度泛函理论计算得到[Co(CO2)n]+团簇的几何结构,并且模拟了它们的振动光谱与实验数值进行比较. 研究结果表明,在[Co(CO2)n]+(n=2∽6)团簇中,钴阳离子通过电四极矩静电作用以端点结合的方式与二氧化碳中的氧原子结合在一起. 团簇的红外光谱都集中在二氧化碳反对称伸缩的波数附近,并且随着团簇尺寸的变化出现蓝移,最后把[Co(CO2)n]+的红外光解离光谱与稀有气体贴附的[Co(CO2)n]+-Ar的红外光解离光谱进行了比较.  相似文献   

10.
描述了包含共线的光电子速度成像仪,以及与双阀激光溅射团簇源联用的时间飞行质谱装置.为了避免预混气体,两个脉冲阀和一个反应通道被用来产生反应负离子.共线的光电子成像仪采用了改进的速度成像透镜系统,它的能量分辨率优于3%.此外还报道了Si4-团簇在532和355 nm,以及Si3C- 团簇在532 nm的光电子速度成像.从实验图像中可以获得光电子能谱和各向异性参数.从Si4-团簇能谱上获得了中性的Si4团簇的基态和第一激发态的振动频率分别为330和312 cm-1.初步的实验结果证明这套光电子成像装置对研究团簇负离子的电子结构以及光脱附动力学非常有效.  相似文献   

11.
In this paper we report the study of the perovskites La0.7Ca0.3Mn0.5Co0.5O3 and La0.8Sr0.2Mn0.5Co0.5O3 by neutron powder diffraction at various temperatures and magnetization measurements in zero applied field and at low cooling regimes. The replacement of half Mn by Co in La0.7Ca0.3MnO3 and La0.8Sr0.2MnO3 destroys their long-range ferromagnetism exhibiting a cluster glass ferromagnetic order similar to the one observed in many cobaltites.  相似文献   

12.
13.
High-purity powder specimens of AgCa2Mn2V3O12 and NaPb2Mn2V3O12 have been successfully synthesized by solid-state chemical reaction. The Rietveld refinements from X-ray powder diffraction data verified that these compounds have the garnet-type structure (space group , No. 230) with the lattice constant of a=12.596(2) Å for AgCa2Mn2V3O12 and a=12.876(2) Å for NaPb2Mn2V3O12. Calculation of the bond valence sum supported that Mn is divalent and V is pentavalent in these garnets. Estimation of the quadratic elongation and the bond angle variance showed that the distortions of the MnO6 octahedra and the VO4 tetrahedra are significantly suppressed. Our new results of AgCa2Mn2V3O12 and NaPb2Mn2V3O12 are compared to those of AgCa2M2V3O12 and NaPb2M2V3O12 (M=Mg, Co, Ni, Zn).  相似文献   

14.
This work reports on the phase formation during a solid-state reaction of Eu3+-doped garnets with the general formula A3B2Ge3O12 (A=Ca, Sr and B=Ga, In, Y) and their luminescent properties. It is shown by XRD and DTA/TG experiments that the garnet-phase formation is completed at 1100-1200 °C. Moreover, it turned out that the position of the oxygen to europium charge-transfer band and the intensity of the forbidden 4f-4f transitions of Eu3+ is dependent on the covalent interaction between the Eu3+ activator and the surrounding oxygen anions. The investigated red-emitting luminescent materials show high lumen equivalents and deep red emission at the same time, which makes them attractive for the application in LEDs (light emitting diodes), in particular for near UV-emitting LEDs.  相似文献   

15.
We have measured the resistivities of Al2O3-Bi2Sr1.8Ca1.2Cu2Oy and MgO-Bi2Sr1.8Ca1.2Cu2Oy composites with the nominal Bi2Sr1.8Ca1.2Cu2Oy volume fraction, 2212, ranging from 0.15 to 1.00. For the Al2O3-Bi2Sr1.8Ca1.2Cu 2Oy composites, we find for the samples with 2212≥0.6 that the superconducting transition temperature, Tc, is not disturbed by the addition of Al2O3. For 2212<0.3, no zero-resistivity state is observed. For the MgO-Bi2Sr1.8Ca1.2Cu2Oy composites, Tc is barely disturbed for the samples with ρ2212≥0.7. No superconducting state is observed for the samples with ρ2212<0.35. The variation of (300 K) with ρ2212 indicates a three-dimensional percolating Bi-Sr-Ca-Cu-O matrix occurring at ρ2212≈0.19 and ≈0.15 in Al2O3-Bi2Sr1.8Ca1.2 Cu2Oy and MgO-Bi2Sr1.8Ca1.2Cu2Oy, respectively. Both resistivity and magnetization measurements suggest that the reactions of Bi2Sr1.8Ca1.2Cu2Oy with MgO are weaker than with Al2O3.  相似文献   

16.
The silicates Ca3Sc2Si3O12, Ca3Y2Si3O12 and Ca3Lu2Si3O12, both undoped and doped with Pr3+ ions, have been synthesized by solid-state reaction at high temperature. The luminescence spectroscopy and the excited state dynamics of the materials have been studied upon VUV and X-ray excitation using synchrotron radiation. All doped samples have shown efficient 5d-4f emission upon direct VUV excitation of 5d levels, but only Ca3Sc2Si3O12:Pr3+ shows luminescence upon interband VUV or X-ray excitation. The VUV excited emission spectra of Ca3Y2Si3O12:Pr3+ and Ca3Lu2Si3O12:Pr3+ show features attributed to emission from two distinct sites accommodating the Pr3+ dopant. The decay kinetics of the Pr3+ 5d-4f emission in Ca3Sc2Si3O12:Pr3+ upon VUV excitation across the band gap are characterized by decay times in the range 25-28 ns with no significant rise after the excitation pulse. They appear to be faster upon X-ray irradiation than for VUV excitation. Weak afterglow components are attributed to defect luminescence.  相似文献   

17.
Attempts have been made to synthesize a few compositions Ce0.80La0.15Al0.05O1.90, Ce0.80Sm0.10Gd0.05Al0.05O1.90, and Ce0.80Gd0.10Sm0.05Al0.05O1.90 by citrate–nitrate auto-combustion method. The aim of the present investigation was to study the effect of co-doping and multiple doping on the ionic conductivity of CeO2 for its use as solid electrolyte in intermediate temperature solid oxide fuel cells. XRD patterns showed that all the samples have fluorite-type crystal structure similar to undoped ceria. Microstructures of thermally etched samples have been studied by scanning electron microscopy. Contributions of grains σ g and grain boundaries σ gb to the total conductivity σ T, have been determined using impedance analysis. Impedance measurements were made in the frequency range 1 Hz–1 MHz and temperature range 250–500 °C. Our experimental results show that multiple doping is more effective than co-doping for improving the oxide ion conductivity of ceria in the materials investigated in the present study.  相似文献   

18.
The infrared spectrum of isotopically pure CH279BrCl has been recorded at a resolution of 0.0023 cm−1 (FWHM) in the range 550-800 cm−1 with a Bruker IFS 120 HR Fourier transform spectrometer in Wuppertal. Here we report the full rotational analysis of the ν4 and ν5 fundamentals and of the hot-bands ν4+ν6ν6 and ν5+ν6ν6. Ground state combination differences were constructed for all bands, yielding improved ground state constants, up to quartic terms, as well as reliable rotational constants for the ν4, ν5, and ν6 states.  相似文献   

19.
Electrical and electrochemical properties of the 70Li2S·(30 − x)P2S5·xP2S3 and the 70Li2S·(30 − x)P2S5·xP2O5 (mol%) glass-ceramics prepared by the mechanical milling technique were investigated. Glass-ceramics with 1 mol% P2S3 and 3 mol% P2O5 showed the highest conductivity of 5.4 × 10− 3 S cm− 1 and 4.6 × 10− 3 S cm− 1, respectively. Moreover, these glass-ceramics showed higher electrochemical stability than the 70Li2S·30P2S5 (mol%) glass-ceramic. From the XRD patterns of the obtained glass-ceramics, trivalent phosphorus and oxygen were incorporated into the Li7P3S11 crystal. We therefore presume that the Li7P3S11 analogous crystals, which were formed by incorporating trivalent phosphorus and oxygen into the Li7P3S11 crystal, improve the electrical and electrochemical properties of the glass-ceramics. An all-solid-state cell using the 70Li2S·29P2S5·1P2S3 (mol%) glass-ceramic as solid electrolyte operated under the high current density of 12.7 mA cm− 2 at the high temperature of 100 °C. The cell showed an excellent cyclability of over 700 cycles without capacity loss.  相似文献   

20.
The substitutional effect of Ru on the magnetic and transport properties of double exchange ferromagnets, La0.7Sr0.3MnO3 and La0.5Sr0.5CoO3 has been investigated. It is found that substitution of 10% Ru at the Mn site of La0.7Sr0.3MnO3 decreases the Curie temperature by 20 K than that of the parent compound. However, a large decrease in the Curie temperature, ΔTc80 K and the system undergoes a transition from metallic state to insulating state is observed when 10% Ru is doped in La0.5Sr0.5CoO3. The marginal effect of Ru in the Mn–O–Mn sublattice in comparison to the Co–O–Co sublattice could be due to the magnetic exchange interaction between Mn and Ru by virtue of the fact that Ru exhibits variable valence states, Ru+4/Ru+5. The eg and t2g parentage of Ru+5 is similar to Mn+4 and therefore, Ru+5 ion appears to participate in the double exchange mediated ferromagnetic (FM) interaction. On the other hand, Ruthenium (IV) ion disrupts an intermediate spin state of cobalt (Co+3: t2g5eg1), forcing a double exchange FM state to anti-FM state.  相似文献   

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