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1.
We investigate hydrogen isotope and nuclear quantum effects on geometries and binding energies of small protonated rare gas clusters (Rg $_n$ X $^ +$ , Rg = He,Ne,Ar, X = H,D,T, and $n$ = 1–3) with the any particle molecular orbital (APMO) MP2 level of theory (APMO/MP2). To gain insight on the impact of nuclear quantum effects on the different interactions present in the Rg $_n$ X $^ +$ systems, we propose an APMO/MP2 energy decomposition analysis scheme. For RgH $^ +$ ions, isotopic substitution leads to an increase in the stability of the complex, because polarization and charge transfer contributions increase with the mass of the hydrogen. In the case of Rg $_2$ H $^ +$ complexes, isotopic substitution results in a shortening and weakening of the rare gas‐hydrogen ion bond. For Rg $_3$ X $^ +$ complexes, the isotope effects on the rare gas binding energy are almost negligible. Nevertheless, our results reveal that subtle changes in the charge distribution of the Rg $_2$ X $^ +$ core induced by an isotopic substitution have an impact on the geometry of the Rg $_3$ X $^ +$ complex. © 2012 Wiley Periodicals, Inc.  相似文献   

2.
We investigate the dynamics of the detachment of single polyethylene (PE) chains from a strongly adsorbing surface in vacuum using a united atom model. Various statistical properties, including the mean‐square end‐to‐end distance 〈R2〉, the mean‐square radii of gyration , , the shape factor , the torsion angle distribution, the average surface adsorption energy , the average total energy , and the average force , are analyzed. The relationship between the average force and the pulling velocity v shows two distinctive regions: a weakly dependence region at Å/ps and a strongly dependence region at Å/ps. Remarkably, the PE chain manifests force hysteresis under sequential stretching and releasing. These investigations may provide some insights into the elastic behavior of adsorbed polymer chains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2322–2332, 2007  相似文献   

3.
The effect of a layer of electrochemically grafted 4‐diazo‐N,N‐diethylaniline (DEA) groups on the electron transfer kinetics of redox systems, displaying fast and slow heterogeneous electron transfer rate constants at edge and basal planes of carbon, was investigated. The properties of the modified electrode were characterized by cyclic voltammetry using four different inorganic redox systems (Fe(CN) , Co(phen) , Ru(NH3) , and IrCl in acidic, neutral, and basic media. Two distinct blocking behaviors and electrostatic effects were observed. More precisely, a strong blocking effect of the grafted layer on Fe(CN) and Co(phen) was found, whereas Ru(NH3) and IrCl showed to be rather unaffected by the presence of the DEA grafted layer.  相似文献   

4.
The Sturmian expansion of the generalized Dirac‐Coulomb Green function (Szmytkowski, J Phys B, 1997, 30, 825; erratum 1997, 30, 2747) is exploited to derive closed‐form expressions for electric $(\sigma_{E})$ and magnetic $(\sigma_{M})$ dipole shielding constants for the ground state of the relativistic hydrogen‐like atom with a point‐like and spinless nucleus of charge Ze. It is found that $\sigma_{E}=Z^{-1}$ (as it should be) and where $\gamma_{1}=\sqrt{1-(Z\alpha)^{2}}$ (α is the fine‐structure constant). This expression for $\sigma_{M}$ agrees with earlier findings of several other authors, obtained with the use of other analytical techniques, and is elementary compared to an alternative one presented recently by Cheng et al. (J Chem Phys 2009, 130, 144102), which involves an infinite series of ratios of the Euler's gamma functions. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012  相似文献   

5.
Stereo multiblock PLAs with different block lengths are synthesized by melt polycondensation of low‐molecular‐weight poly(L ‐lactic acid)/poly(D ‐lactic acid) blends with a wide variety of $\overline {M} _{{\rm w}} $ in the range of 1.1–5.2 × 103 g · mol–1. The average block length (νav) of the stereo multiblock PLAs increases with increasing $\overline {M} _{{\rm w}} $ of the blend and with the reaction temperature, whereas $\overline {M} _{{\rm w}} $ and PDI of the stereo multiblock PLAs increases with increasing $\overline {M} _{{\rm w}} $ of the blend, the reaction time, and the temperature. Stereo multiblock PLAs with νav > 7 are crystallizable to form stereocomplex crystallites, and the crystallinity and melting temperature of the stereo multiblock PLAs increases with increasing νav and $\overline {M} _{{\rm w}} $ of the stereo multiblock PLAs.

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6.
We present the solutions of the ro‐vibrational motion of a diatomic molecule with a spatially dependent mass by solving the Dirac equation with position‐dependent mass for repulsive vector $V(r)$ and attractive scalar $S(r)$ q‐deformed Morse potential for any $\kappa$ value, within the framework of Pekeris approximation of the spin‐orbitcoupling term. The relativistic energy spectra are obtained using theNikiforov‐Uvarov method and the two‐component spinor wavefunctions are obtained in terms of the Laguerre polynomials. It is found that there exist only negative energy states for bound states, and the energy values for a fixed value of $n_r$ increase with decrease in $\kappa$ . © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012  相似文献   

7.
The synthesis system for mesophase formation, using the diprotic anionic surfactant N‐myristoyl‐L ‐glutamic acid (C14GluA) as the structure‐directing agent (SDA) and N‐trimethoxylsilylpropyl‐N,N,N‐trimethylammonium chloride (TMAPS) as the co‐structure‐directing agent (CSDA), has been investigated and a full‐scaled synthesis‐field diagram is presented. In this system we have obtained mesophases including three‐dimensional (3D) micellar cubic Fm m, Pm n, Fd m, micellar tetragonal P42/mnm, two‐dimensional (2D) hexagonal p6mm and bicontinuous cubic Pn m, by varying the C14GluA/NaOH/TMAPS composition ratios. From the diagram it can be concluded that the mesophase formation is affected to a high degree by the organic/inorganic‐interface curvature and the mesocage–mesocage electrostatic interaction. Bicontinuous cubic and 2D‐hexagonal phases were found in the low organic/inorganic‐interface curvature zones, whereas micellar cubic and tetragonal mesophases were found in the high organic/inorganic‐interface curvature zones. Formation of cubic Fm m and tetragonal P42/mnm was favoured in highly alkaline zones with strong mesocage–mesocage interactions, and formation of cubic Pm n and Fd m was favoured with moderate mesocage–mesocage interactions in the less alkaline zones of the diagram.  相似文献   

8.
A novel sensor have been constructed by layer‐by‐layer hybridizing phosphomolybdate (POM) and poly(ferrocenylsilane) (PFS) on a cysteamine modified gold electrode. The properties and performance of the sensor have been measured by electrochemistry and atomic force microscopy in detail. The results showed that the constructed multilayers modified gold electrode combined the properties of POM and PFS, and exhibited good electrocatalytic ability to a series of inorganic ions, including BrO , IO , NO , Fe3+, ascorbic acid and SO . The well catalytic activity of the sensor was ascribed to the porous structure of hybrid POM‐PFS multilayer. The resulted sensor exhibited extremely fast amperometric response, low detection limit, high selectivity and wide linear range to these analyses.  相似文献   

9.
The photopolymerization of methyl, ethyl, butyl, and hexyl methacrylates in solution was studied. The effect of initial initiator and monomer concentrations on the time evolution of polymer concentration, , and PDI was examined. The reversible chain addition and β‐scission, and primary radical termination steps were included in the mechanism along with the classical steps. The rate equations were derived using continuous distribution kinetics and solved numerically to fit the experimental data. The regressed rate coefficients compared well with the literature data. The model predicted the instantaneous increase in and PDI to steady state values. The rate coefficients exhibited a linear increase with the size of alkyl chain of the alkyl methacrylates.

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10.
Hydrolyses of HC?CSO3SiMe3 ( 1 ) and CH3C?CSO3SiMe3 ( 2 ) lead to the formation of acetylenic sulfonic acids HC?CSO3H?2.33 H2O ( 3 ) and CH3C?CSO3H?1.88 H2O ( 4 ). These acids were reacted with guanidinium carbonate to yield [+C(NH2)3][HC?CSO3?] ( 5 ) and [+C(NH2)3][CH3C?CSO3?] ( 6 ). Compounds 1 – 6 were characterized by spectroscopic methods, and the X‐ray crystal structures of the guanidinium salts were determined. The X‐ray results of 5 show that the guanidinium cations and organosulfonate anions associate into 1D ribbons through ${{\rm R}{{2\hfill \atop 2\hfill}}}$ (8) dimer interactions, whereas association of these ions in 6 is achieved through ${{\rm R}{{2\hfill \atop 2\hfill}}}$ (8) and ${{\rm R}{{1\hfill \atop 2\hfill}}}$ (6) interactions. The ribbons in 5 associate into 2D sheets through ${{\rm R}{{2\hfill \atop 2\hfill}}}$ (8) dimer interactions and ${{\rm R}{{3\hfill \atop 6\hfill}}}$ (12) rings, whereas those in 6 are connected through ${{\rm R}{{1\hfill \atop 2\hfill}}}$ (6) and ${{\rm R}{{2\hfill \atop 2\hfill}}}$ (8) dimer interactions and ${{\rm R}{{4\hfill \atop 6\hfill}}}$ (14) rings. Compound 6 exhibits a single‐layer stacking motif similar to that found in guanidinium alkane‐ and arenesulfonates, that is, the alkynyl groups alternate orientation from one ribbon to the next. The stacking motif in 5 is also single‐layer, but due to interlayer hydrogen bonding between sulfonate anions, the alkynyl groups of each sheet all point to the same side of the sheet.  相似文献   

11.
The issues raised in the comment by Manz are addressed through the presentation of calculated atomic charges for NaF, NaCl, MgO, SrTiO $$_3$$ , and La $$_2$$ Ce $$_2$$ O $$_7$$ , using our previously presented method for calculating Hirshfeld‐I charges in solids (Vanpoucke et al., J. Comput. Chem. doi: 10.1002/jcc.23088). It is shown that the use of pseudovalence charges is sufficient to retrieve the full all‐electron Hirshfeld‐I charges to good accuracy. Furthermore, we present timing results of different systems, containing up to over 200 atoms, underlining the relatively low cost for large systems. A number of theoretical issues are formulated, pointing out mainly that care must be taken when deriving new atoms in molecules methods based on “expectations” for atomic charges. © 2012 Wiley Periodicals, Inc.  相似文献   

12.
A mathematical model was developed to account for the evolution of polymer product attributes in the emulsion polymerization of styrene. The effects of transfer agent, surfactant, initiator and temperature were investigated. Polymerization rate, and particle size decreased with increasing concentration of the transfer agent. The polymerization rate increased with increasing surfactant and initiator concentrations, while an increase in temperature led to a decrease of molecular weight but an increase of polymerization rate and particle size. Chain extension was successfully achieved in the presence of our RAFT agent. The model predictions compared well with our experimental results.

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13.
Picky ferryl : The complex [Fe(Tp)(BF)] (Tp=hydrotris(3,5‐diphenylpyrazolyl)borate; BF=benzoylformate) reacts with O2 to generate an oxidant (see picture; O red, pink; Fe yellow; N blue; C gray; H white) that oxidizes added hydrocarbons shape‐selectively. Discrimination derives from a cleft formed by two phenyl groups of the Tp ligand, favoring oblate spheroidal substrates.

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14.
A kinetic model is developed mimicking experimental results obtained via detailed kinetic investigation of Cu0‐mediated LRP processes of butyl acrylate in variable solvents at 50 °C. In all polymerizations, a pronounced offset in the $\overline {M} _{{\rm n}} $ versus conversion profile is observed. The kinetic modeling predicts that conventional FRP is responsible for a high molecular weight fraction of terminated polymer. The initial $\overline {M} _{{\rm n}} $ offset is congruent with a relatively slow establishment of the controlling equilibrium. Kinetic modeling and experiments demonstrate that the conversion versus time data cannot be adequately described by a first‐order kinetic analysis. For selected rate coefficients (ka, kd, and kdis_cu) a range is assigned, which affords a well controlled polymerization.

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15.
The crystal structure of Cs2BaTa6Br15O3 has been elucidated by using synchrotron X‐ray powder diffraction and absorption experiments. It is built from edge‐bridged octahedral [(Ta6${{\rm Br}{{{\rm i}\hfill \atop 9\hfill}}}$ ${{\rm O}{{{\rm i}\hfill \atop 3\hfill}}}$ )${{\rm Br}{{{\rm a}\hfill \atop 6\hfill}}}$ ]4? cluster units with a singular poor metallic electron (ME) count equal to thirteen. This leads to a paramagnetic behaviour related to one unpaired electron. The arrangement of the Ta6 clusters is similar to that of Cs2LaTa6Br15O3 exhibiting 14‐MEs per [(Ta6${{\rm Br}{{{\rm i}\hfill \atop 9\hfill}}}$ ${{\rm O}{{{\rm i}\hfill \atop 3\hfill}}}$ )${{\rm Br}{{{\rm a}\hfill \atop 6\hfill}}}$ ]5? motif. The poorer electron‐count cluster presents longer metal–metal distances as foreseen according to the electronic structure of edge‐bridged hexanuclear cluster. Density functional theory (DFT) calculations on molecular models were used to rationalise the structural properties of 13‐ and 14‐ME clusters. Periodic DFT calculations demonstrate that the electronic structure of these solid‐state compounds is related to those of the discrete octahedral units. Oxygen–barium interactions seem to prevent the geometry of the octahedral cluster to strongly distort, allowing stabilisation of this unprecedented electron‐poor Ta6 cluster in the solid state.  相似文献   

16.
17.
Based on Buckingham and Pople’s theory of magnetic double refraction, a theoretical expression is derived for a new Cotton–Mouton effect ${\phi _{{\rm{C}} - {\rm{M}}}^{(IB)} }$ in liquid induced by the crossed effect between the high dc magnetic field B0 and the nuclear magnetic moment ${m_z^{(I)} }$ . It contains temperature‐independent and ‐dependent parts. The latter is proportional to the product between anisotropy of polarizability and the nuclear magnetic shielding tensor. For this new effect ${\phi _{{\rm{C}} - {\rm{M}}}^{(IB)} }$ , its order in magnitude for a molecule with large polarizability anisotropy is estimated to be comparable to the nuclear‐spin‐induced optical Faraday rotation (NSOFR). In the multipass approach, ${\phi _{{\rm{C}} - {\rm{M}}}^{(IB)} }$ can be eliminated by time‐reversal symmetry arguments, but NSOFR is enhanced.  相似文献   

18.
The effect of adding various aluminum alkyls (R = Et, i‐Bu) on the polymerization of propylene is studied using a (2‐PhInd)2ZrCl2 pre‐catalyst. A mild deactivating effect is found upon addition of TIBA, whereas TEA shows a sharp deactivating effect. Increasing amounts of AlR3 results in a significant activity increase for TIBA, but an activity plateau for TEA. AlR3 imposes remarkably different effects on the molecular weight and stereochemical microstructure of polymers. As the TIBA concentration increases, $\overline {M} _{{\rm v}} $ increases at first, growing from 49 000 to 72 000, but subsequently drops to 40 000. For TEA, $\overline {M} _{{\rm v}} $ decreases sharply, plummeting from 49 000 to 17 000. Both TIBA and TEA increase the mmmm pentad content from 7.9 to 23.5% and 17.6%, respectively.

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19.
Pressure broadening and pressure shift of N2H+ rotational lines perturbed by collisions with He are studied for the first time using experiment and theory. Results are reported from measurements at 88 K for the rotational transitions ${j = 3 \leftarrow 2}$ , ${4 \leftarrow 3}$ , ${5 \leftarrow 4}$ and ${6 \leftarrow 5}$ with frequencies ranging from 0.28 to 0.56 THz. The agreement between experiment and theoretical data derived from close coupling calculations confirms the reliability of a theoretical framework used for state‐to‐state transition rates of interest in the interpretation of spectroscopic data from interstellar molecular clouds. The influence of hyperfine effects on shifts and widths of the rotational lines is discussed in detail. Although in principle possible, experiment and theoretical considerations lead to the conclusion that hyperfine effects only play a minor role.  相似文献   

20.
2‐Bromocyclohexanone is a model compound in which a 4JH2, H6 coupling constant is observed, whereas the corresponding 4JH2, H4 is absent. The observed long‐range coupling is not only a result of the known W‐type coupling, in the axial conformation, but also because of the less usual diaxial spin–spin coupling in the equatorial conformer. The carbonyl group plays a determining role in describing the coupling pathway, as concluded by natural bond orbital (NBO) analysis; although the and interactions in the axial conformer contribute for transmitting the spin information associated with the W‐type coupling, the strong and hyperconjugations in the equatorial conformer define an enhanced coupling pathway for 4JH2, H6, despite the inhibition of this coupling because of interaction and the large carbonyl angle. These findings provide the experimental evidence that orbital interactions contribute for the conformational isomerism of 2‐bromocyclohexanone. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

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