摘要:

AbstractSingle molecular experiments carried out in the group of Prof. Wild in ETH Zurich, as well as the experimental and theoretical studies of several research groups in Taiwan, have been summarized in this review. It is shown that with the contemporary technologies, single molecular experiments can be carried out under a broad range of physical conditions. These includes low and room temperatures; in vacuum, in solution, in the air, or with specific pressure applied on the sample; in applied direct‐current or alternating‐current electric fields; on molecules in solid matrices, in gel, or even functioning biomolecules in vitro. Theoretical efforts have been able to help identifying the interactions of single molecules with their surroundings that modulate their static or time‐resolved spectroscopic properties. The joint experimental and theoretical effort to develop the research techniques in single molecular experiments is shown to be fruitful, and future works in this direction are important for many fields in chemistry, physics, and bi

ISSN:0009-4536    

DOI:10.1002/jccs.200300075

出版商:WILEY‐VCH Verlag    

年代:2003

数据来源: WILEY

摘要:

AbstractThe geometric and electronic structures of clean TiC(001) surface were investigated using first principles calculations based on generalized gradient approximation density functional theory. The structural optimization of the surface shows that the C and Ti atoms on the top layer move outward and inward, respectively. The results of the band structure calculation indicate that the “active” surface states of TiC(001) surface located around 2.3 eV below Fermi level are originated from 2pzorbital of surface C atoms. Furthermore, the influence of the surface relaxation on the electronic structures, including the charge densities, work functions and surface core level shifts are also discussed in the pa

ISSN:0009-4536    

DOI:10.1002/jccs.200300076

出版商:WILEY‐VCH Verlag    

年代:2003

数据来源: WILEY

摘要:

AbstractDFT/B3LYP calculations were carried out for a boron‐nitride nanotube (BNNT) of zigzag (N,0) and armchair (N,N), where N = 4,5 and 6, respectively. From a calculated energy band, density of state and bond order, the electroconductivity and bonding character of BNNT were discussed and compared with that of a carbon nanotube (CNT

ISSN:0009-4536    

DOI:10.1002/jccs.200300077

出版商:WILEY‐VCH Verlag    

年代:2003

数据来源: WILEY

摘要:

AbstractTo understand the mechanism of ionic migration in the amorphous matrixes of polymer electrolytes is crucial for their applications in modern technologies. Here, molecular dynamics (MD) simulation was carried out to investigate the ionic conduction mechanism of a particular conjugated rigid‐rod polymer, sPBI‐PS(Li+). The backbone of this polymer is poly[(1,7‐dihydrobenzo[1,2‐d:4,5‐d']diimidazole‐2,6‐diyl)‐2‐(2‐sulfo)‐p‐phenylene]. The polymer has pendants of propane sulfonate Li+ionomer. The MD simulations showed that the main chains of sPBI‐PS(Li+) are in a layer‐like structure. The further detailed structure analysis suggested that the π‐electron of this polymer is not delocalized among aromatic rings. This agrees with the experimental result that sPBI‐PS(Li+) shows no electronic conductivity, and the conductivity of this polymer is mainly ionic. The calculated migration channels of lithium ions and electrostatic potential distributions indicated clearly that the polymer matrix is anisotropic for the migrations of ions. The migration of lithium ions along the longitudinal direction is more preferable than that along the transverse direction. The relaxations of the polymer host were found to play important roles in the transfer process of lithium ions. The hopping of lithium ions from one ‐SO3−1group to another correlated strongly with characteristic motions of ‐SO3

ISSN:0009-4536    

DOI:10.1002/jccs.200300078

出版商:WILEY‐VCH Verlag    

年代:2003

数据来源: WILEY

摘要:

AbstractThe potential energy surfaces for N‐methlyformamide(HCONHCH3) dissociation into HCO + NHCH3and CONHCH3+ H in the ground and lowest triplet states have been characterized with DFT, MP2 and CASSCF methods with the cc‐pVDZ basis set, while the S1potential energy surfaces for the dissociation reactions were determined by the CASSCF/cc‐pVDZ optimizations followed by MRSDCI single‐point calculations. The mechanism of the HCONHCH3photodissociation has been elucidated on the basis of the computed potential energy surfaces and surface crossing

ISSN:0009-4536    

DOI:10.1002/jccs.200300079

出版商:WILEY‐VCH Verlag    

年代:2003

数据来源: WILEY

摘要:

AbstractFace selectivity for the reactions of 5‐substituted (X)‐2‐dicyanomethyleneadamantanes with a Grignard reagent was examined usingab initiocalculation for the substituents (X=F, Cl, Br, OH, NH2, and CH3). The calculated syn/anti product ratio based on the results of transition state energies for the halide substituents are in good agreement with the available experimental results. In addition, the results of the natural bond orbital calculation suggest that the through‐bond Cieplak hyperconjugation effect, instead of the through‐space interaction suggested by the experimental results in a prior study, is the main factor in determining face selectivity for the halide substituents in the present study, while for (X=OH, NH2, and CH3) substituents, other interactions may have unnegligible effect

ISSN:0009-4536    

DOI:10.1002/jccs.200300080

出版商:WILEY‐VCH Verlag    

年代:2003

数据来源: WILEY

摘要:

AbstractThe mathematical modeling of the reactor in the TAP technique describes it as composed of zones of different diffusivity, and it makes the model linear by imposing boundary conditions of the continuity of concentration and flux at zone boundaries so as to be able to use a Fourier transformation technique to solve the equations. An alternative description of the reactor that uses a spatially non‐constant diffusivity to obviate the need to impose auxiliary boundary conditions in the regions where diffusivities change is proposed. The reactor equation is the mass balance equation without the simplification to the case of constant diffusivity, that is, without the diffusivity taken out of the differential operator. Computations based on it are compared with those of the linear model. The computed response curves of both models are similar, which indicates that the alternate model is equally good as a description of the reaction system. The alternate model is useful for modeling reactor systems with a variable cross‐sectional area or with temperature non‐unifo

ISSN:0009-4536    

DOI:10.1002/jccs.200300081

出版商:WILEY‐VCH Verlag    

年代:2003

数据来源: WILEY

摘要:

AbstractThe bifurcation analyses of the internal rotation of three different series of monorotor molecules are investigated in this paper. Our results indicate that the types of catastrophe and topological regions are related to the generic form of potential energy function and the critical points. Namely, when the double‐barrier energy function is represented as the third‐order generic polynomial of the reduced reaction coordinate, the process is isomorphic to the elementaryfoldcatastrophe. Similarly, when the triple‐barrier energy functions are represented as the fourth‐order generic polynomial of the reduced reaction coordinate, the process is isomorphic to the elementarycuspcata

ISSN:0009-4536    

DOI:10.1002/jccs.200300082

出版商:WILEY‐VCH Verlag    

年代:2003

数据来源: WILEY

摘要:

AbstractTime‐dependent wave packet calculations for the reaction H+HCl and its isotopic reactions are carried out on the potential energy surface (PES) of Bian and Werner (BW2) [Bain, W.; Werner, H.‐J.J. Chem. Phys.2000,112, 220]. Reaction probabilities for the exchanged and abstraction channels are calculated from various initial rotational states of the reagent. Those have then been used to estimate reaction cross sections and rate constants which also are calculated and explained by the zero‐point energy and the tunneling effect. The results of this work were compared with that of previous quasiclassical trajectory calculations and reaction dynamics experiments on the abstraction channel. In addition, the calculated rate constants are in reasonably good agreement with experimental measurements for both cha

ISSN:0009-4536    

DOI:10.1002/jccs.200300083

出版商:WILEY‐VCH Verlag    

年代:2003

数据来源: WILEY

摘要:

AbstractA ring‐stacking model for the fullerene growth mechanism has been analyzed using the semiempirical AM1 scheme. Following different routes, small fullerenes C28(Tdand D2), C26(D3h) and C24(D6d) have been constructed from monocyclic/polycyclic precursors and circumscribing them with appropriate carbon belts. The deformation energies (DE) and the average bond lengthsof the precursors have been computed. The DE values suggest that there is a chance of bond cleavage of the polycyclic precursors as the growth process proceeds towards the cage formation. On the other hand, the monocyclic precursors are found to have significantly lower deformation energies than the polycyclic precursors. Further analyzingvalues of the polycyclic and monocyclic cases at different stages, it is observed that thevalues of the polycyclic cases decrease gradually, depicting a shrink in the precursors which may be detrimental to the growth process, whereas monocyclic precursors tend to swell, corroborating the tendency of the system to grow, which may be conducive for the growth proces

ISSN:0009-4536    

DOI:10.1002/jccs.200300084

出版商:WILEY‐VCH Verlag    

年代:2003

数据来源: WILEY