共查询到20条相似文献,搜索用时 62 毫秒
1.
N. Hattori H. Hirata H. Okabayashi M. Furusaka C. J. O'Connor R. Zana 《Colloid and polymer science》1999,277(1):95-100
The microstructure of the normal micelles formed by dimeric surfactants with long spacers, [Br−(CH3)2N+(C
m
H2
m
+1)-(CH2)
S
-(C
m
H2
m
+1)N+(CH3)2Br−, m = 10 and s = 8, 10 and 12], has been investigated by small-angle neutron scattering and compared with previously reported results for
micelles of the same dimeric surfactants with shorter spacers (m = 10 and s = 2, 3, 4 and 6). It was found that for dimeric surfactants with long spacers (s = 8 and 10), both micellar growth and variation in shape occur to only a small extent, if at all, compared with dimeric surfactants
with short spacers. However, for the dimeric surfactant with the longest spacer, s = 12, the extent of micellar growth and shape variation is also large. These results are due to the differences in conformation
of dimeric surfactants with short spacers (s = 2–6) compared with that of the surfactants with long spacers (s = 8–12).
Received: 15 June 1998 Accepted: 22 July 1998 相似文献
2.
Seiichiro Ten-no Suehiro Iwata Sourav Pal Debashis Mukherjee 《Theoretical chemistry accounts》1999,102(1-6):252-261
Employing separate cluster ansatz in time-independent and time-dependent wave-operators, coupled-cluster (CC) response theory
is generalized to multireference (MR) expansion spaces. For state energies, this corresponds to the MR secular problem with
an arbitrary similarity-transformed effective Hamiltonian, H˜=Ω−1
HΩ. The effective Hamiltonian can be generated via size-extensive CC methods. Thus the states in MR linear response theory
(MRLRT) maintain the usual CC core-extensive properties. We have used the Gelfand unitary group basis of the spin-adapted
configurations to construct the matrix of H˜ in the MR excitation space. As a preliminary application, the CC singles and
doubles effective Hamiltonian is applied to excitation and photoionization energies of the CH+ and N2 molecules, and is compared with experimental results and results from other numerical procedures including conventional CC
linear response theory (CC-LRT), MR and full configuration interaction (MRCI and FCI) methods. The numerical results indicate
that MRLRT reproduces valence and external excited states quantitatively, combining the best features of CC-LRT and MRCI.
Received: 2 July 1998 / Accepted: 28 August 1998 / Published online: 11 November 1998 相似文献
3.
High-level ab initio electronic structure theories have been applied to investigate the detailed reaction mechanism of the
spin-forbidden reaction CH(2∏) + N2 → HCN + N(4S). The G2M(RCC) calculations provide accurate energies for the intermediates and transition states involved in the reaction,
whereas the B3LYP/6-311G(d,p) method overestimates the stability of some intermediates by as much as about 10 kcal/mol. A few new structures have been
found for both the doublet and quartet electronic states, which are mainly involved in the dative pathways. However, due to
the higher energies of these structures, the dominant mechanism remains the one involving the C
2 intersystem-crossing step. The C
2 minima on the seam of crossing (MSX) structures and the spin-orbit coupling between the doublet and quartet electronic states
are rather close to those found in previous studies. Vibrational frequencies orthogonal to the normal of the seam which have
been applied in a separate publication to calculate the rate of the CH(2∏) + N2 → HCN + N(4S) reaction with a newly proposed nonadiabatic transition-state theory for spin-forbidden reactions have been calculated at
the MSX from first principles.
Received: 23 June 1998 / Accepted: 21 September 1998 / Published online: 8 February 1999 相似文献
4.
The microstructure of the micelles formed in aqueous solution by gemini surfactants with aromatic spacers, [Br(CH3)2N+(C
m
H2
m
+1)-(Ph)-(C
m
H2
m
+1)N+(CH3)2Br, m=8 and Ph = o-, m- or p-phenylenedimethylene] has been examined by small-angle neutron scattering. Aggregation of the gemini surfactants with an
o-phenylenedimethylene spacer brings about formation of premicelles and small micelles at concentrations below the second critical
micelle concentration, while above this concentration marked micellar growth and variation in shape occurs. It is suggested
that the minimum aggregate formed at this critical micelle concentration may be the trimer or tetramer and that this result
supports the mechanism of “gemini → submicelle → assembly” for micellar growth.
Received: 8 September 1998 Accepted in revised form: 27 November 1998 相似文献
5.
Superdelocalizability, S
r, defined by Fukui et al. as a variant of reactivity indices in the Hückel molecular orbital scheme for conjugated hydrocarbon
molecules is reinvestigated with particular emphasis on its behavior for infinitely large π-electronic systems. Surprisingly,
almost all the S
r values of polyacetylene are found to diverge with the size of molecule, while all the S
r values of comb polyene converge to certain values. Similarly, the S
r values of linear polyacene diverge, while those of zigzag polyacene converge. Whether the superdelocalizability for a series
of periodic polymers converges or diverges can be predicted, respectively, if the density of states of the infinitely large
π-electron network is shown to have non-zero or zero gap at the Fermi level. The behavior of atom-atom polarizability defined
by Coulson et al. is also checked and discussed.
Received: 27 July 1998 / Accepted: 9 September 1998 / Published online: 23 February 1999 相似文献
6.
Bernd Hartke 《Theoretical chemistry accounts》1998,99(4):241-247
By an application to small silicon clusters Si
N
(with N = 4,5,7,10) it is shown that truly global geometry optimization on an ab initio or density functional theory level can be achieved, at a computational cost of approximately
1–5 traditional local optimization runs (depending on cluster size). This extends global optimization from the limited area
of empirical potentials into the realm of ab initio quantum chemistry.
Received: 24 February 1998 / Accepted: 6 March 1998 / Published online: 17 June 1998 相似文献
7.
Raman scattering spectra and molecular conformations of bis(quaternaryammonium bromide)-water systems 总被引:1,自引:0,他引:1
The dimeric bis(quaternaryammonium bromide) surfactants, [Br−(CH3)2N+(C
m
H2
m
+1)—(CH2)
s
—(C
m
H2
m
+1)N+(CH3)2Br−, s = 2, 3 and m = 4, 6, 10 and 12, s = 6 and m = 8, 10, 12], have been synthesized and the phase maps of the sm6-8-water, sm6-10-water and sm6-12-water binary systems have
been determined (sm6-8 implies s = 6, m = 8). In order to examine the molecular structures of these solid samples and of their dimeric surfactant-water binary systems,
Raman spectra of the simple dimeric surfactants, sm2-4 and sm3-4, in which crystal structures of the trans- and cis-type conformations
have been determined by single-crystal X-ray diffraction analysis, have been investigated, and Raman bands characteristic
of these skeletal structures were found in the skeletal deformation region. On the basis of these characteristic Raman bands
for the two conformations, it has been concluded that the dimeric surfactants, sm6-8, sm6-10 and sm6-12 also take up a cis-type
conformation in the crystalline state. Furthermore, it has been found that the Raman bands in the C—H stretching, skeletal
stretching and CH2 scissoring regions are sensitive to phase structure.
Received: 21 July 1998 Accepted in revised form: 9 November 1998 相似文献
8.
Peter Botschwina 《Theoretical chemistry accounts》1998,99(6):426-428
On the basis of large-scale coupled cluster calculations including connectedz triple substitutions in a perturbative way,
the geometrical parameters of the D
3
h
saddle point of the Walden inversion reaction Cl− + CH3Cl′→ ClCH3 + Cl′− are predicted to be R
s
(C—Cl) = 2.301 ? and r
s
(C—H) = 1.069 ?. The barrier height with respect to the reactants is recommended to be 11.5 ± 1.0 kJ mol−1. Connected triple substitutions lower the barrier height by almost a factor of 2, but have very little influence on the geometric
structure of the saddle point.
Received: 26 June 1998 / Accepted: 15 July 1998 / Published online: 28 September 1998 相似文献
9.
Colloidal dispersions of nanometer-sized platinum colloids were prepared by ethanol reduction of PtCl6
2− in the presence of poly(N-vinylformamide) (PNVF), poly(N-vinylacetamide) (PNVA) or poly(N-vinylisobutyramide) (PNVIBA) and analyzed by UV-vis spectroscopy and transmission electron microscopy. The dispersion stability
of each colloid to the presence of added KCl was determined by a stirring and centrifugation procedure. The platinum colloid
stabilized by PNVF (PNVF-Pt) was the most stable and its critical flocculation concentration was not observed up to the highest
electrolyte concentration employed (4.0 M). The stability of the platinum colloids stabilized by poly(N-isopropylacrylamide) (PNIPAAm) and poly(vinylpyrrolidone) (PVP) was also examined. The sequence of polymer-stabilized platinum
colloids in increasing order of dispersion stability was found to be PNIPAAm-Pt < PNVIBA-Pt < PVP-Pt < PNVA-Pt < PNVF-Pt.
Received: 25 August 1998 Accepted in revised form: 14 January 1999 相似文献
10.
Ilona Šperlingová Ludmila Dabrowská Vladimír Stránský Šárka Dušková Jan Kučera Monika Tvrdíková Milon Tichy 《Analytical and bioanalytical chemistry》2010,397(2):433-438
Ethylene glycol monobutyl ether (EGBE), an industrial solvent, is absorbed by the body not only by inhalation but also by
dermal absorption (liquid or vapour). EGBE is metabolized to butoxyacetic acid (BAA). Pooled freeze-dried urine candidate
reference material (RM) was prepared from urine obtained from persons occupationally exposed to EGBE. This material has the
advantage of containing butoxyacetic acid in both the free and conjugated (glutamine and glycine) forms, as found in native
urine. In all GC method modifications used, acid hydrolysis was used to release BAA from its conjugated form. The amount of
butoxyacetic acid in homogeneity and stability testing was measured by GC after derivatisation with N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide. Detection was by MS in EI mode, in the authors’ laboratory. For interlaboratory comparison of the
reference material GC methods with MS, FID, and ECD were used. Different extraction solvents (dichloromethane–isopropanol
2:1, ethyl acetate, or dichloromethane) and derivatisation reagents (trimethylsilyldiazomethane, N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide) were used. Using ANOVA (at the statistical level α = 0.05) no changes were found in the concentration of butoxyacetic acid during fifteen month isochronous stability testing,
or in homogeneity testing. The uncertainty contributions were u
h = 8.8 mg L−1 and u
s = 6.5 mg L−1. The concentration of butoxyacetic acid in freeze-dried urine RM was evaluated from the results of eight laboratory data
sets within an interlaboratory comparison by use of the interactive statistical software IPECA. The contribution to total
uncertainty derived from interlaboratory comparison was u
i = 12.7 mg L−1. The reference value (c = 273 ± 33 mg L−1) is an unweighted arithmetic average of accepted results. The value is traceable to the pure butoxyacetic acid (98% w/w; Acros Organic #257760010) used as calibrant. The uncertainty given is combined expanded uncertainty derived from the results
from interlaboratory comparison, and from homogeneity and stability tests (k = 2). The reference material will be used to verify method performance in the biological monitoring of occupational exposure
to EGBE. 相似文献
11.
Thomas Enevoldsen Jens Oddershede Stephan P. A. Sauer 《Theoretical chemistry accounts》1998,100(5-6):275-284
We present correlated calculations of the indirect nuclear spin-spin coupling constants of HD, HF, H2O, CH4, C2H2, BH, AlH, CO and N2 at the level of the second-order polarization propagator approximation (SOPPA) and the second-order polarization propagator
approximation with coupled-cluster singles and doubles amplitudes – SOPPA(CCSD). Attention is given to the effect of the so-called
W
4 term, which has not been included in previous SOPPA spin-spin coupling constant studies of these molecules. Large sets of
Gaussian basis functions, optimized for the calculation of indirect nuclear spin-spin coupling constants, were used instead
of the in general rather small basis sets used in previous studies. We find that for nearly all couplings the SOPPA(CCSD)
method performs better than SOPPA.
Received: 6 July 1998 / Accepted: 8 September 1998 / Published online: 23 November 1998 相似文献
12.
Joëlle Rault-Berthelot Marie Madeleine Granger 《Journal of Solid State Electrochemistry》1999,3(5):293-298
The physicochemical properties and electrochemical behaviour of products obtained by anodic oxidation of 2-aminofluorene
in CH2Cl2 + 0.2 M Bu4NBF4 are presented together with the oxidation conditions.
Received: 8 January 1998 / Accepted: 21 September 1998 相似文献
13.
Melvyn P. Melrose 《Theoretical chemistry accounts》2000,104(5):392-397
It is argued that the preservation of algebraic equivalence between the Allen and Laidler bond-energy schemes for nonconjugated
alkenes logically determines that the Allen scheme should apply to a classical structure of a conjugated hydrocarbon exactly
as it stands, i.e. no additional parameters are needed. Extending the requirement of equivalence to conjugated alkenes implies
that, in the Laidler scheme, the bond energy of the pure single CC bond in a conjugated system is a combination of the bond-energies
of the semiconjugated and normal CC single bonds: E(Cd—Cd)=2E(Cd—C)−E(C—C). This result is a deduction and is not an independent hypothesis. The equivalence of the two schemes for conjugated
hydrocarbons is demonstrated numerically, by calculating the resonance energies of some selected molecules by both methods.
Received: 5 December 1999 / Accepted: 5 March 2000 / Published online: 5 June 2000 相似文献
14.
Olaf Baake Peter S. Hoffmann Andreas Klein Beatrix Pollakowski Burkhard Beckhoff Marina L. Kosinova Nadeshda I. Fainer Veronica S. Sulyaeva Valentina A. Trunova Wolfgang Ensinger 《Analytical and bioanalytical chemistry》2009,395(6):1901-1909
Films of BC
x
N
y
were produced in a plasma-enhanced chemical vapor deposition process using trimethylborazine as precursor and with H2, He, N2, and NH3, respectively, as auxiliary gas. These films deposited on Si(100) wafers or fused quartz glass substrates were characterized
chemically by X-ray photoelectron spectroscopy and by synchrotron radiation-based total-reflection X-ray fluorescence combined
with near-edge X-ray absorption fine structure. Independent of the auxiliary gas, the B–N bonds are dominating. Furthermore,
B–C and N–C bonds were identified. Oxygen, present in the bulk (in contrast to the surface layer of some nanometers, where
molecular oxygen and/or water are absorbed) as an impurity, is bonded to boron or to carbon, respectively. The relation of
boron and nitrogen changes with the character of the auxiliary gas: c
B/c
N ≈ 4:3 (for H2 and He) and c
B/c
N ≈ 1 (for N2 or NH3). Furthermore, physical properties such as the refractive index and the optical band-gap energy were determined. 相似文献
15.
Kenzi Hori Nobuhisa Saitoh Shinjiro Kobayashi Tsugio Kitamura 《Theoretical chemistry accounts》1999,102(1-6):244-251
β, γ-Substituted γ-halo allylalkoxide ions decompose to form a halogen ion, formaldehyde, and an alkyne under mild conditions,
for example at room temperature. The E isomer does not differ from the Z isomer in terms of activation energy. We attempted
to shed light on the mechanism of the reaction by using ab initio molecular orbital calculations. The observed propensity
was confirmed by the present calculation on model molecules, γ-chloro allylalkoxide ions. We conducted further calculations
and compared the alkoxide results with a similar reaction of β-haloacrylate ions that release carbon dioxide instead of formaldehyde.
This similar reaction needs heating as high as 150°C. The activation energy of the acrylate ions (36–39 kcal mol−1) was calculated to be about 10 kcal mol−1 higher than that of the alkoxide ions. The activation energy of the E acrylate ion is smaller by 0.8 kcal mol−1 than that of the Z isomer at the MP2/6-31+G**//RHF/6-31+G* level of theory. This is consistent with experimental results.
While the ready deprotonation from the carboxylic group does not activate the acrylate ion very much, the alkoxide ion is
destabilized to a great degree in the process of anion formation. The difficulty in deprotonation that proceeds from the neutral
molecule is seen in the difference in the activation energies for the decomposition of the corresponding anions. Therefore,
the pK
a of a hydroxy or a carboxylic group plays the leading role in determining the magnitude of activation energies of allyl halides
with a negatively charged fragment.
Received: 2 July 1998 / Accepted: 9 September 1998 / Published online: 8 February 1999 相似文献
16.
Explicitly correlated MBPT-R12 and coupled cluster [up to CCSD(T)-R12] methods have been used in calculations of various
(vibrationless) electrical properties for the LiH molecule, including the dipole and quadrupole moments, dipole and quadrupole
polarizability tensors, dipole hyperpolarizability tensors, and the second dipole hyperpolarizability tensors. Generally,
with extension of the basis set the R12 method did not lead to faster convergence for the calculated properties towards the
basis limit. Nevertheless, R12 calculations serve as useful indicators to judge the reliability of the results, and substantially
help in determining the accuracy. Results obtained with the 11s8p6d5f/9s8p6d5f basis and CCSD(T)-R12 calculated within this work should be close to the basis set limit.
Received: 8 June 1998 / Accepted: 23 July 1998 / Published online: 7 October 1998 相似文献
17.
The accuracy of employing effective core polarization potentials (CPPs) to account for the effects of core-valence correlation
on the spectroscopic constants and dissociation energies of the molecules B2, C2, N2, O2, F2, CO, CN, CH, HF, and C2H2 has been investigated by comparison to accurate all-electron benchmark calculations. The results obtained from the calculations
employing CPPs were surprisingly accurate in every case studied, reducing the errors in the calculated valence D
e values from a maximum of nearly 2.5 kcal/mol to just 0.3 kcal/mol. The effects of enlarging the basis set and using higher-order
valence electron correlation treatments were found to have only a small influence on the core-valence correlation effect predicted
by the CPPs. Thus, to accurately recover the effects of intershell correlation, effective core polarization potentials such
as the ones used in the present work provide an attractive alternative to carrying out computationally demanding calculations
where the core electrons are explicitly included in the correlation treatment.
Received: 11 May 1998 / Accepted: 27 July 1998 / Published online: 28 October 1998 相似文献
18.
Jun-ichi Aihara 《Theoretical chemistry accounts》1999,102(1-6):134-138
A very simple but general index of kinetic stability, T, is proposed for π-electron systems, which is defined as a highest occupied molecular orbital (HOMO)- lowest unoccupied molecular orbital (LUMO)
energy separation multiplied by the number of conjugated atoms. This new index can be justified by relating it to the approximate
form of the superdelocalizability, an index of chemical reactivity defined by Fukui et al. It is best suited for predicting
the kinetic stability of fullerenes. All isolable fullerene isomers have T values larger than 13.
Received: 24 June 1998 / Accepted: 3 September 1998 / Published online: 17 December 1998 相似文献
19.
Peter Klampfer Primož Benkič Maja Ponikvar Ana Rahten Antonija Lesar Adolf Jesih 《Monatshefte für Chemie / Chemical Monthly》2003,134(1):1-9
Summary. Hydrazinium(+2) fluoroarsenate(III) fluoride was prepared by the reaction of hydrazinium(+2) fluoride and liquid arsenic
trifluoride. N2H6AsF4F is stable at 273 K, but decomposes slowly at room temperature. N2H6AsF4F crystallizes in the orthorhombic space group Pnn2 with a = 774.0(2) pm, b = 1629.2(4) pm and c = 436.6(1) pm; V = 0.5506(3) nm3, Z = 4 and d
c
= 2.461 g cm−3. The structure consists of N2H6
2+ cations, AsF4
− anions, and F− anions and is interconnected by a hydrogen bonding network. Distorted trigonal-bipyramidal AsF4
− units are very weakly interconnected and form chains along the b axis. Bands in the Raman spectrum are assigned to the vibrations of N2H6
+2 cations and AsF4
− anions.
Corresponding author. E-mail: adolf.jesih@ijs.si
Received April 18, 2002; accepted July 15, 2002 相似文献
20.
High-level ab initio calculations with large basis sets are reported for silene, H2C=SiH2. Correlated harmonic force fields are obtained from coupled cluster CCSD(T) calculations with the cc-pVQZ basis (cc-pVTZ
for H) while the anharmonic force fields are computed at the MP2/TZ2Pf level. There is excellent agreement with the available
experimental data, in particular the equilibrium geometry and the fundamental vibrational frequencies. Many other spectroscopic
constants are predicted for the C
2
v
isotopomers of silene.
Received: 27 May 1998 / Accepted: 23 July 1998 / Published online: 9 October 1998 相似文献