共查询到20条相似文献,搜索用时 421 毫秒
1.
Milivoj Lovrić Michael Hermes Fritz Scholz 《Journal of Solid State Electrochemistry》1998,2(6):401-404
A solid-state redox reaction involving an insertion of ions is analyzed with respect to the influence of the concentration
of inserting ions in the solution phase. The voltammetric response is independent of the mass transfer in the solution provided
that z = (D
ss/D
aq)1/2
ρ/[C+]* is smaller than 0.1 (D
ss: diffusion coefficient of the cation C+ in the crystal; D
aq: diffusion coefficient of the cation C+ in the solution; ρ: density of the solid compound; [C+]*: concentration of cations in the bulk of the solution). In real cases this condition will be satisfied at solution concentrations
above 1 mol/l.
Received: 15 December 1997 / Accepted: 5 March 1998 相似文献
2.
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
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.
K. N. Semenenko V. V. Burnasheva N. A. Yakovleva E. A. Ganich 《Russian Chemical Bulletin》1998,47(2):209-212
The experimental data on the mechanism of hydride dispersion of intermetallic compounds of the LaNi5 type and the crystal structures of hydride phases based on these compounds were analyzed. A new approach was suggested and
substantiated, which allows one to consider hydride dispersion as a result of a redox process associated with the formation
of Hδ− hydride ions at concentrations of hydrogen in the solid hydrideC
H>-C
H
cr. The value ofC
H
cr is determined by the redox potential of the reaction Hδ++Mδ−⇌Hδ′−+Mδ′+.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 214–217, February, 1998. 相似文献
5.
Tomás Grygar 《Journal of Solid State Electrochemistry》1997,1(1):77-82
Pure goethites and Al-, Cr-, and Mn-goethites, as synthetic and natural products, were used to establish the conditions for
electrochemical reductive dissolution following surface reaction kinetics. In diluted perchloric acid and at reaction rate
coefficients of the order of 10−4s−1, the γ parameters in the kinetic equation J/N
0 = k(N/N
0)γ (where J is the reaction rate and N and N
0 are actual and total molar amounts of a solid reactant) were in the range expected for the shape-preserving dissolution of
the particles with a certain size and reactivity distribution function. The same range of γ was found using the dissolution
of goethites by a chemical reaction via oxalate-ferrous ion surface complexation. The importance of the charge transfer coefficient
to describe the iron oxide reactivitie
s was highlighted as it is sensitive to the synthetic route and also to the substitution of iron.
Received: 20 December 1996 / Accepted: 24 February 1997 相似文献
6.
A. Molina-Díaz A. Ruiz-Medina M. L. Fernández-de Córdova 《Fresenius' Journal of Analytical Chemistry》1999,363(1):92-97
A continuous flow-through solid phase spectrophotometric system was developed for the determination of ascorbic acid based
on the measurement of its intrinsic absorbance in the UV region when retained on a 1 mm Sephadex QAE A-25 anion exchanger
gel layer which is placed into an appropriate quartz flow-through cell, the absorbance exhibited by this solid phase being
monitored at 267 nm. A monochannel manifold was used, the sample (300, 600 or 1000 μL) being injected into the carrier solution
(acetate buffer). This solution also elutes the analyte after developing the analytical signal, and regenerates the resin
layer which, therefore, remains ready for the next sample. The linear dynamic range and other analytical parameters vary according
to the sample volume injected. Three calibration lines were established for 300, 600 and 1000 μL sample volume, which ranged
from 1.0 to 20.0, 0.5 to 10.0 and 0.2 to 6.0 μg mL–1, respectively. The detection limits were 0.04 (300 μL), 0.03 (600 μL) and 0.02 μg mL–1 (1000 μL), the sampling rates 28, 24 and 21 h–1, and the RSDs (n = 10) 0.87%, 1.08% and 0.90%, respectively. The amount of ascorbic acid in various samples (pharmaceuticals, sweets and urine)
were successfully determined with this method.
Received: 28 April 1998 / Revised: 3 June 1998 / Accepted: 30 June 1998 相似文献
7.
A. Molina-Díaz A. Ruiz-Medina M. L. Fernández-de Córdova 《Analytical and bioanalytical chemistry》1999,363(1):92-97
A continuous flow-through solid phase spectrophotometric system was developed for the determination of ascorbic acid based
on the measurement of its intrinsic absorbance in the UV region when retained on a 1 mm Sephadex QAE A-25 anion exchanger
gel layer which is placed into an appropriate quartz flow-through cell, the absorbance exhibited by this solid phase being
monitored at 267 nm. A monochannel manifold was used, the sample (300, 600 or 1000 μL) being injected into the carrier solution
(acetate buffer). This solution also elutes the analyte after developing the analytical signal, and regenerates the resin
layer which, therefore, remains ready for the next sample. The linear dynamic range and other analytical parameters vary according
to the sample volume injected. Three calibration lines were established for 300, 600 and 1000 μL sample volume, which ranged
from 1.0 to 20.0, 0.5 to 10.0 and 0.2 to 6.0 μg mL–1, respectively. The detection limits were 0.04 (300 μL), 0.03 (600 μL) and 0.02 μg mL–1 (1000 μL), the sampling rates 28, 24 and 21 h–1, and the RSDs (n = 10) 0.87%, 1.08% and 0.90%, respectively. The amount of ascorbic acid in various samples (pharmaceuticals, sweets and urine)
were successfully determined with this method.
Received: 28 April 1998 / Revised: 3 June 1998 / Accepted: 30 June 1998 相似文献
8.
9.
Kazunari Naka Hirofumi Sato Akihiro Morita Fumio Hirata Shigeki Kato 《Theoretical chemistry accounts》1999,102(1-6):165-169
The free-energy profile for the Menshutkin-type reaction NH3 + CH3Cl → NH3CH3
+ + Cl− in aqueous solution is studied using the RISM-SCF method. The effect of electron correlation on the free-energy profile is
estimated by the RISM-MP2 method at the HF optimized geometries along the reaction coordinate. Solvation was found to have
a large influence on the vibrational frequencies at the reactant, transition state and product; these vibrational frequencies
are utilized to calculate the zero-point energy correction of the free-energy profile. The computed barrier height and reaction
exothermicity are in reasonable agreement with those of experiment and previous calculations. The change of solvation structure
along the reaction path is represented by radial distribution functions between solute-solvent atomic sites. The mechanisms
of the reaction are discussed from the view points of solute electronic and solvation structures.
Received: 26 June 1998/Accepted: 28 August 1998 / Published online: 2 November 1998 相似文献
10.
M. Ehara P. Tomasello J. Hasegawa H. Nakatsuji 《Theoretical chemistry accounts》1999,102(1-6):161-164
The valence ionization spectrum of HCl is studied by symmetry-adapted-cluster configuration-interaction general-R and SD-R methods. The general-R method describes well the peak positions and intensities of seven satellite lines observed below the double ionization threshold.
The twinning shake-up states due to the (4σ)−1 state and the Rydberg states of HCl+ are correctly reproduced.
Received: 26 June 1998 / Accepted: 9 September 1998 / Published online: 8 February 1999 相似文献
11.
Tatiana Korona Bogumil Jeziorski Robert Moszynski Geerd H. F. Diercksen 《Theoretical chemistry accounts》1999,101(4):282-291
Symmetry-adapted perturbation theory is extended to the (quasi) degenerate, open-shell case. The new formalism is tested
in calculations of the interaction energies for a helium atom in the ground state interacting with an excited hydrogen atom.
It is shown that the method gives satisfactory results if the coupling with higher Rydberg states of the dimer is small, as
is the case for the A2Σ+,B2Π,E2Π,32Π, and 12Δ states of HeH. For the C2Σ+ state convergence of the method is very slow, but it can be improved by including the n=3 states in the model space.
Received: 3 June 1998 / Accepted: 9 September 1998 / Published online: 7 December 1998 相似文献
12.
D. Y. Kwok A. Leung A. Li C. N. C. Lam R. Wu A. W. Neumann 《Colloid and polymer science》1998,276(6):459-469
Low-rate dynamic contact angles of 22 liquids on a poly(n-butyl methacrylate) (PnBMA) polymer are measured by an automated axisymmetric drop shape analysis-profile (ADSA-P). It is found that 16 liquids yielded
non-constant contact angles, and/or dissolved the polymer on contact. From the experimental contact angles of the remaining
6 liquids, it is found that the liquid–vapor surface tension times cosine of the contact angle changes smoothly with the liquid–vapor
surface tension, i.e. γlv cos θ depends only on γlv for a given solid surface (or solid surface tension). This contact angle pattern is in harmony with those from other inert
and non-inert (polar and non-polar) surfaces [34–37, 45–47]. The solid–vapor surface tension calculated from the equation-of-state
approach for solid-liquid interfacial tensions [14] is found to be 28.8 mJ/m2, with a 95% confidence limit of ±0.5 mJ/m2, from the experimental contact angles of the 6 liquids.
Received: 12 September 1997 Accepted: 22 January 1998 相似文献
13.
The reaction between triplet methylene and nitric oxide, producing the formaldiminoxy (CH2NO) radical, and the subsequent decomposition and isomerization reactions of CH2NO have been studied using ab␣initio quantum chemical techniques that include the Gaussian-2 (G2), CASSCF and CASPT2 methods.
Stationary points on the potential energy surfaces were located at MP2/6-31G(d) and CASSCF/cc-pVDZ levels of theory, while the electronic energies were determined using G2, G2(MP2), QCISD(T)/cc-pVTZ,
RCCSD(T)/cc-pVTZ and CASPT2/cc-pVTZ approaches. G2 is believed to be reliable at equilibrium geometries, but the determination
of certain transition state geometries and energies requires a MCSCF-based approach. The calculations suggest that CH2NO (2A′) forms in a barrierless reaction and could readily decompose to H+HCNO. A subsequent abstraction reaction then results in
H2+CNO. No molecular elimination channel was found. An alternative pathway is the formation of CH2ON, which readily isomerizes to CH2NO.
Received: 8 May 1998 / Accepted: 11 August / Published online: 9 October 1998 相似文献
14.
Paul G. Mezey 《Theoretical chemistry accounts》1999,102(1-6):279-284
A simple proof is presented for a fundamental topological property of catchment regions of potential energy hypersurfaces:
each catchment region C(λ,i), representing a chemical species and its conformational range on the potential energy hypersurface, is simply k-connected for each dimension k=1,2,…3N−6−λ, where λ is the index of the catchment region. The consequences of this property on the structure of the fundamental
group of reaction mechanisms (the one-dimensional homotopy group of reaction paths) is discussed.
Received: 8 July 1998 / Accepted: 6 October 1998 / Published online: 23 February 1999 相似文献
15.
Yukio Kawashima Tomohiro Hashimoto Haruyuki Nakano Kimihiko Hirao 《Theoretical chemistry accounts》1999,102(1-6):49-64
The valence π → π
* excited states of anthracene and naphthacene are studied with multireference perturbation theory with complete active space
self-consistent field reference functions. The predicted spectra provide a consistent assignment of all one- and two-photon
spectra and T-T spectra of low-lying valence π → π
* excited states of anthracene and naphthacene. The present theory predicts the valence π → π
* excitation energies with an accuracy of 0.15 eV for anthracene and of 0.25 eV or better for naphthacene. The excited states
of anthracene and naphthacene are compared with those of benzene and naphthalene studied previously. The present calculations
predict that, going from anthracene to naphthacene, there is a symmetry reversal of the two lowest singlet state transitions,
but not for the triplet, just as indicated by the experimental data. Some general trends of polyacene excited states are discussed
based on the calculated results for benzene to naphthacene. Conclusive results obtained for anthracene and naphthacene can
be used as a model for understanding the excited states of larger polyacenes.
Received: 22 April 1998 / Accepted: 6 July 1998 / Published online: 28 September 1998 相似文献
16.
Adiabatic potential curves for the ground state and several low-lying excited states of the barium atom interacting with
Ne, Ar, Kr and Xe have been obtained from valence ab initio configuration-interaction calculations. Atomic cores are replaced
by scalar-relativistic l-dependent pseudopotentials, while core-polarization potentials are used for describing correlation contributions of the rare-gas
atoms and the Ba2+ cores. Implications of the resulting potential curves for the interpretation of experimental data are discussed, together
with first applications of the curves for calculating absorption profiles of the (6s
2)1S→(6p)1P Ba transition.
Received: 7 April 1998 / Accepted: 27 July 1998 / Published online: 12 October 1998 相似文献
17.
G. Xie S. P. Chen S. L. Gao X. X. Meng Q. Z. Shi 《Journal of Thermal Analysis and Calorimetry》2006,83(3):693-700
A novel solid complex, formulated as Ho(PDC)3
(o-phen), has been obtained from the reaction
of hydrate holmium chloride, ammonium pyrrolidinedithiocarbamate (APDC) and
1,10-phenanthroline (o-phen·H2O)
in absolute ethanol, which was characterized by elemental analysis, TG-DTG
and IR spectrum. The enthalpy change of the reaction of complex formation
from a solution of the reagents, ΔrHmθ (sol), and the molar heat capacity of the complex, cm,
were determined as being –19.161±0.051 kJ mol–1
and 79.264±1.218 J mol–1 K–1
at 298.15 K by using an RD-496 III heat conduction microcalorimeter. The enthalpy
change of complex formation from the reaction of the reagents in the solid
phase, ΔrHmθ(s), was calculated as
being (23.981±0.339) kJ mol–1 on the
basis of an appropriate thermochemical cycle and other auxiliary thermodynamic
data. The thermodynamics of reaction of formation of the complex was investigated
by the reaction in solution at the temperature range of 292.15–301.15
K. The constant-volume combustion energy of the complex, ΔcU, was determined as being –16788.46±7.74
kJ mol–1 by an RBC-II type rotating-bomb
calorimeter at 298.15 K. Its standard enthalpy of combustion, ΔcHmθ, and standard enthalpy of formation,
ΔfHmθ, were calculated to be –16803.95±7.74 and –1115.42±8.94
kJ mol–1, respectively. 相似文献
18.
Flow injection chemiluminescence determination of isoniazid with electrogenerated hypochlorite 总被引:4,自引:0,他引:4
Jiachu Huang Chengxiao Zhang Zhujun Zhang 《Fresenius' Journal of Analytical Chemistry》1999,363(1):126-128
A flow-injection chemiluminescence method for the determination of isoniazid based on the sensitizing effect of isoniazid
on the chemiluminescence generating luminol-hypochlorite reaction is described. The hypochlorite was electrogenerated on-line
by constant current electrolysis, thus, eliminating instability of hypochlorite solution prepared from commercially available
sodium hypochlorite. The calibration graph is linear in the range 1 × 10–8 to 1 × 10–6 g mL–1, and the detection limit is 6 × 10–9 g mL–1. The relative standard deviation for determination of 5 × 10–8 g mL–1 is 2.8%. The proposed method has been successfully applied to the determination of isoniazid in pharmaceutical preparations.
Reveived: 2 May 1998 / Revised: 27 July 1998 / Accepted: 7 August 1998 相似文献
19.
Hyo Weon Jang 《Theoretical chemistry accounts》1998,99(6):420-425
Novel parametrically energy-dependent boundary functions, F, combined with a finite L
2 basis set, permit accurate and efficient calculation of scattering wavefunctions for many energies. Both accuracy and efficiency
are achieved simultaneously because all the necessary integrals are energy-independent and also certain functionals, (H−E)|F>, in the Schr?dinger equation are allowed to satisfy desirable boundary conditions. In addition, slight modification of the
Schr?dinger equation in the boundary region is shown to be useful for improving the numerical accuracy when a cutoff-radius-truncated
basis set is used. The advantages of the present approaches are demonstrated for the one-dimensional Eckart barrier problem.
Received: 17 June 1998 / Accepted: 13 July 1998 / Published online: 18 September 1998 相似文献
20.
High-resolution energy spectra of electrons released in Penning ionization collisions of metastable rare gas atoms Rg*(ns) (Rg = He, Ne, Ar, Kr, Xe) with several open-shell and closed-shell atoms are analyzed to determine the well depth of the
potential energy curve which describes the respective autoionizing collision complex. We thereby elucidate trends in the chemical
interaction of Rg* with closed-shell target atoms A(ns
2) and establish a basis for detailed comparison with the respective interactions involving open-shell, ground state alkali
atoms A(ns). From electron energy spectra due to␣associative ionization (RgH+ formation) in Rg* + H(1s) collisions, we determine binding energies for the RgH+(1Σ) ground state potential (Rg = Ne, Ar, Kr, Xe) with uncertainties around 0.03 eV.
Received: 30 June 1998 / Accepted: 5 August 1998 / Published online: 28 October 1998 相似文献