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901.
The use of the pyN4 coordination cap to synthesize high‐nuclearity clusters supported by polycyanometallate units was explored. The heptanuclear bimetallic complexes 2 and 3 were obtained as their salts by reacting stoichiometric amounts of pyN4 and Ni(ac)2 with K3[Fe(CN)6] and K4[Mo(CN)8], respectively. The tetranuclear complex 4 formed as a by‐product in the synthesis of 3 . Temperature‐dependent magnetic susceptibility measurements carried out for 2 revealed that this compound behaves as a paramagnet over the whole range of temperatures. 相似文献
902.
903.
Frank M. Zimmermann 《Surface science》1997,390(1-3):174-185
Quantum state specific detection of photodesorbed molecules enables measuring their final state distributions in the translational and internal degrees of freedom, which contain a wealth of information about the desorption mechanism and dynamics. Vibrational state populations are of particular interest because of the information they contain about the lifetime and nature of the electronic excited states responsible for desorption. The measured vibrational distributions for nondissociative photodesorption of diatomic molecules tend to resemble Boltzmann distributions with temperatures of 600–1200 K for desorption from metal surfaces, and 1700–2000 K for semiconductors and oxides. Two-dimensional quantum dynamics calculations of the desorption process show that these vibrational distributions can be reproduced only if the intramolecular equilibrium bondlength in the electronic excited state is remarkably similar to that of the ground state. In particular, the results are inconsistent with a desorption mechanism in which the intramolecular bondlength change upon excitation is similar to that of electron capture in the gas phase. 相似文献
904.
乙基紫苏霉素硫酸盐的选择性远程DEPT和二维NMR研究 总被引:1,自引:1,他引:0
本文通过选择性远程DEPT和二维NMR实验研究了由紫苏霉素合成的乙基紫苏霉素硫酸盐的1H和13C NMR谱,推定其结构为(1),并且对其NMR谱峰归属作了确定。 相似文献
905.
906.
907.
硫酸锰铵结晶水的测定及热分析 总被引:2,自引:1,他引:1
合成了复盐硫酸锰铵,利用热重分析法(TG)、差示扫描量热法(DSC)、微商热重法(DTG)研究了它在氮气气氛中的热分解过程,确定了其结晶水的数目为7个,并通过Ka-West方法确定了化合物热分解反应的活化能(E)、反应级数(n)和频率因子(A)等动力学参数,用线性拟合的方法得到其相关系数均大于0.99,具有良好的动力学一致性,并运用等转化率法对热分析动力学参数进行了验证。 相似文献
908.
909.
We present results concerning the dynamical behavior of a Ni3+ adsorbate on a NiO(0 0 1) surface obtained by molecular dynamics simulations. In a first place, we examined at low temperature the position of the Ni3+ ion as an adatom on the surface and the corresponding modification of its local environment as reflected on the pair-wise radial distribution function. The calculation of the vibrational properties of the adatom by means of the phonon local density of states (LDOS) shows that there is an anisotropic behavior both in the two principal in-plane directions as well as in the direction normal to the surface in accordance with the structural results. We compare the phonon LDOS of the Ni3+ adatom with the corresponding results for the Ni2+ adatom and the Ni2+ surface cations.Static energetic calculations are indicative that the exchange of the Ni3+ ion with a surface Ni2+ ion could be favorable. Such a behavior is confirmed by results observed at temperatures higher than 700 K where the Ni3+ adsorbate is located on a substitutional position on the surface and not on adatom position. The exchange takes place through simple or double exchange mechanisms. The structural and dynamical behavior of the Ni3+ ion at the substitution position was investigated in the temperature range 700-2000 K through the calculation of the pair distribution function, the relaxed interlayer relative position (RIRP), mean-square displacements (MSDs) and phonon LDOS. Results show that in comparison with the Ni2+ surface ions the Ni3+ ion at substitution position is more tightly bound especially in the direction normal to the surface as is indicated by the local structure and the contraction it presents as well as its phonon LDOS. As temperature increases the binding of the Ni3+ ion becomes less important as reflected on the physical properties mentioned above. 相似文献
910.
Alexander Winkler 《Surface science》2006,600(15):3036-3044
The activity of supported Ni catalysts can easily be affected by high temperatures and oxidative atmosphere. In order to study the origin of this behaviour, we performed systematic LEED and XPS investigations on a model system prepared by physical vapour deposition of Ni on a thin epitaxial alumina film on NiAl(1 1 0). Annealing experiments showed that deposited Ni is thermally stable up to ∼370 K. Further annealing seems to lead first to changes in the island structure and then, at temperatures above ∼480 K, to diffusion of Ni through the alumina film. Analysis of the complex oxidation behaviour revealed that there is a competition between oxidation of the Ni deposit and of the NiAl support. The latter process is probably enabled by a solid state reaction at the interface which means that Ni catalyses the further oxidation of the support. While the surface of the deposited Ni clusters is easily oxidised, the further oxidation processes of the Ni particles and the support were found to be diffusion-controlled. 相似文献