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排序方式: 共有95条查询结果,搜索用时 12 毫秒
1.
Reed M. Izatt Gypzy C. Lindh Peter Huszthy Glen A. Clark R. L. Bruening Jerald S. Bradshaw James J. Christensen 《Journal of inclusion phenomena and macrocyclic chemistry》1989,7(5):501-509
The macrocycle-mediated fluxes of alkali, alkaline earth, and several transition metal cations have been determined and compared in a H2O-CH2Cl2-H2O liquid membrane system using four water-insoluble macrocycles containing a dialkylhydrogenphosphate moiety. Transport of alkali metal cations by these ligands was greatest from a source phase pH = 12 or above into an acid receiving phase (pH = 1.5). Very low fluxes were observed for the transport of the alkaline earth cations and all transition metal ions studied except Ag+ and Pb2+ which were transported reasonably well by these new macrocycles.Deceased: September 5, 1987. 相似文献
2.
The UV photodissociation (<5 eV) of diiodomethane (CH(2)I(2)) is investigated by spin-orbit ab initio calculations. The experimentally observed photodissociation channels in the gas and condensed phases are clearly assigned by multi-state second-order multiconfigurational perturbation theory in conjunction with spin-orbit interaction through complete active space-state interaction potential energy curves. The calculated results indicate that the fast dissociations of the first two singlet states of CH(2)I(2) and CH(2)I--I lead to geminate-radical products, CH(2)I (.)+I((2)P(3/2)) or CH(2)I (.)+ I*((2)P(1/2)). The recombination process from CH(2)I--I to CH(2)I(2) is explained by an isomerization process and a secondary photodissociation reaction of CH(2)I--I. Finally, the study reveals that spin-orbits effects are significant in the quantitative analysis of the electronic spectrum of the CH(2)I--I species. 相似文献
3.
Christopher W. McDaniel Jerald S. Bradshaw Kenneth H. Tarbet Gypzy C. Lindh Reed M. Izatt 《Journal of inclusion phenomena and macrocyclic chemistry》1989,7(5):545-548
Two new macrocyclic crown ethers containing one or two selenium donor atoms have been prepared. Diselena-18-crown-6 (2) was found to transport silver ions through a methylene chloride bulk membrane at about the same rate as the analogous dithia- (3) and diaza-18-crown-6 (4) compounds and transported lead ions about the same as dithia-18-crown-6 but better than diaza-18-crown-6. 相似文献
4.
Spin-orbit ab initio study of alkyl halide dissociation via electronic curve crossing 总被引:1,自引:0,他引:1
An ab initio study of the role of electronic curve crossing in the photodissociation dynamics of the alkyl halides is presented. Recent experimental studies show that curve crossing plays a deterministic role in deciding the channel of dissociation. Coupled repulsive potential energy curves of the low-lying n-sigma(*) states are studied including spin-orbit and relativistic effects. Basis set including effect of core correlation is used. Ab initio vertical excitation spectra of CH(3)I and CF(3)I are in agreement with the experimental observation. The curve crossing region is around 2.371 A for CH(3)I and CF(3)I. The potential curves of the repulsive excited states have larger slope for CF(3)I, suggesting a higher velocity and decreased intersystem crossing probability on fluorination. We also report the potential curves and the region of curve crossing for CH(3)Br and CH(3)Cl. 相似文献
5.
Reed M. Izatt Gypzy C. Lindh Jan F. Biernat Maria Bochenska Ronald L. Bruening Jerald S. Bradshaw James J. Christensen 《Journal of inclusion phenomena and macrocyclic chemistry》1989,7(5):487-499
The transport of alkali metal cations by several macrocycles possessing two sulfonamide groups as a part of an 18-, 20-, or 21-membered macroring has been studied. Some of these compounds were found to be more effective transport agents than the proton-ionizable pyridone- and triazole-containing crown ethers reported previously. The factors affecting transport, such as ring size, source and receiving phase pH, and the nature of the groups attached to the sulfonamide nitrogen atoms were examined. Also, extraction experiments by some of the ligands were performed. The behavior of sulfonamide type crowns in single and competitive transport of the alkali metal cations is explained. The mechanism of transport appears to be complex. Transport of one or two cations per molecule of the disulfonamide carriers occurs. Complexation of these cations appears to occur both within and outside the macrocycle cavity. Our results also suggest that kinetic factors may play a significant role in transport rates and selectivities.Deceased: September 5, 1987. 相似文献
6.
Daniel Roca‐Sanjuán Marcus Lundberg David A. Mazziotti Roland Lindh 《Journal of computational chemistry》2012,33(26):2124-2126
In the preceding paper results are presented, which are in serious conflict with state‐of‐the‐art ab initio method. Based on these new results the authors propose a new explanation of the reason for the preferential production of a phosphorescent state. Here we show that these controversial results are flawed, since the model use exclude biradical electron structures. © 2012 Wiley Periodicals, Inc. 相似文献
7.
8.
In self-consistent field (SCF) calculations the construction of the Fock matrix is most time-consuming step. The Fock matrix construction may formally be seen as a matrix-vector multiplication, where the matrix is the supermatrix,??ijkl, and the vector is the first-order density matrix, γij. This formalism should be optimal for vector machines. This is not, however, fully utilized in most programs running on computers with small core memory. The size of the ?? matrix, typically in the order of 106–108 elements, has forced programmers to implement other nonvectorizable methods. We will present a submatrixbased algorithm which will partition the supermatrix so that vectorizable methods can be employed. The method will also reduce the input/output. 相似文献
9.
M. Andersson C. Bargholtz Kj. Fransson L Holmberg K. Lindh L. M⇘rtensson I. Sitnikova P. E. Tegnér P. Thörngren Engblom G. Weiss K. Wilhelmsen Rolander 《Acta Physica Hungarica A》1997,6(1-4):37-43
The isobaric analogue state of the ground state of the halo nucleus6He,6Li* has been studied in a pionic fusion experiment at the CELSIUS storage ring facility in Uppsala, Sweden. This was the first of two proposed experiments with the aim to study the high momentum part of the wave functions of the halo nuclei6He and6Li (0+, T=1). The Li nuclei were produced in inverse kinematics reactions with alpha particles incident on a deuterium cluster jet target. The6Li ions were detected in a zero-degree spectrometer situated in the fourth quadrant of the CELSIUS ring. The measurement was done for three different beam energies corresponding to 5.4, 2.2 and 1.5 MeV above threshold in the c.m. The cross-sections slowly increase with beam energy from 95 nb at the lowest energy to about 250 nb at 5.4 MeV above threshold. 相似文献
10.
Ruijun Pan Zhaohui Wang Rui Sun Jonas Lindh Kristina Edström Maria Strømme Leif Nyholm 《Cellulose (London, England)》2017,24(7):2903-2911
The pore structure of the separator is crucial to the performance of a lithium-battery as it affects the cell resistance. Herein, a straightforward approach to vary the pore structure of Cladophora cellulose (CC) separators is presented. It is demonstrated that the pore size and porosity of the CC separator can be increased merely by decreasing the thickness of the CC separator by using less CC in the manufacturing of the separator. As the pore size and porosity of the CC separator are increased, the mass transport through the separator is increased which decreases the electrolyte resistance in the pores of the separator. This enhances the battery performance, particularly at higher cycling rates, as is demonstrated for LiFePO4/Li half-cells. A specific capacity of around 100 mAh g?1 was hence obtained at a cycling rate of 2 C with a 10 µm thick CC separator while specific capacities of 40 and close to 0 mAh g?1 were obtained for separators with thicknesses of 20 and 40 µm, respectively. As the results also showed that a higher ionic conductivity was obtained for the 10 µm thick CC separator than for the 20 and 40 µm thick CC separators, it is clear that the different pore structure of the separators was an important factor affecting the battery performance in addition to the separator thickness. The present straightforward, yet efficient, strategy for altering the pore structure hence holds significant promise for the manufacturing of separators with improved performance, as well as for fundamental studies of the influence of the properties of the separator on the performance of lithium-ion cells. 相似文献