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101.
T. V. Magdesieva I. V. Zhukov L. G. Tomilova E. V. Chernykh K. P. Butin 《Russian Chemical Bulletin》1997,46(12):2036-2043
The electrochemical potentials of seven redox transitions for green forms and eight redox transitions for blue forms of neutral
octa-tert-butylsubstituted diphthalocyanine cornplexes of lanthanides Pct
2Ln (Ln=Pr, Sm, Dy, and Lu) in solutions were measured by cyclic voltammetry and rotating disc electrode techniques. The spectroelectrochemical
investigation of the products of two-electron oxidation and reduction of the green form of Pct
2Lu was performed. The frontier molecular orbitals, total charge densities, total spin densities, electrostatic potentials,
and heats of ion formation for (Pc2Y)
m+,n−
(m=0, 1, 2 and 3;n=1, 2, 3 and 4), which can model the products of the redox transitions of the diphthalocyanines under study, were calculated
using the semiempirical ZINDO/1 method. The calculations for (Pc2Y)
m+,n−
and absorption spectra show that the electron changes in all redox transitions of the green forms of Pct
2Ln are mainly localized on the ligands.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya No. 12, pp. 2149–2156, December, 1997. 相似文献
102.
Two solid phase transitions of [Cd(H2O)6](BF4)2 occurring on heating at TC2=183.3 K and TC1=325.3 K, with 2 K and 5 K hysteresis, respectively, were detected by differential scanning calorimetry (DSC). High value of entropy changes indicated large orientational disorder of the high temperature and intermediate phase. Nuclear magnetic resonance (1H NMR and 19F NMR) relaxation measurements revealed that the phase transitions at TC1 and TC2 were associated with a drastic and small change, respectively, of the both spin-lattice relaxation times: T1(1H) and T1(19F). These relaxation processes were connected with the “tumbling” motions of the [Cd(H2O)6]2+, reorientational motions of the H2O ligands, and with the iso- and anisotropic reorientation of the BF4− anions. The cross-relaxation effect was observed in phase III. The line width and the second moment of the 1H and 19F NMR line measurements revealed that the H2O reorientate in all three phases of the title compound. On heating the onset of the reorientation of 3 H2O in the [Cd(H2O)6]+2, around the three-fold symmetry axis of these octahedron, causes the isotropic reorientation of the whole cation. The BF4− reorientate isotropically in the phases I and II, but in the phase III they perform slow reorientation only about three- or two-fold axes. A small distortion in the structure of BF4− as well as of [Cd(H2O)6]2+ is postulated. The temperature dependence of the bandwidth of the O-H stretching mode measured by Fourier transform middle infrared spectroscopy (FT-MIR) indicated that the activation energy for the reorientation of the H2O did not change much at the TC2 phase transition. 相似文献
103.
V. Ya. Kavun N. A. Didenko A. B. Slobodyuk I. A. Tkachenko A. V. Gerasimenko N. F. Uvarov V. I. Sergienko 《Journal of Structural Chemistry》2005,46(5):839-847
The mobility of fluoride and ammonium ions (180–480 K) in compounds K2? n (NH4)nZrF6 (0.2 ≤ n ≤ 1.70) was investigated by 19F and 1H NMR. Correlations have been found between the composition of the cation sublattice, the character of ion motions, and phase transition temperature in these compounds. The hightemperature modifications with n ≥ 0.85 of the compounds are characterized by translational diffusion of fluoride and ammonium ions and by uniaxial anisotropy of the 19F magnetic shielding tensor. The electrophysical characteristics of these compounds were studied in the temperature range 300–480 K. 相似文献
104.
The iterative difference-dedicated CI method (IDDCI) has been applied to determine excitation energies in small systems for
which benchmark FCI and other high-level calculations exist. Transitions to excited singlet and triplet states in Be and vertical
transitions in CH+, BH and CH2 are reported. The deviations from FCI results are lower than 0.1 eV and compare advantageously with SDCI including size-consistency
corrections, (SC)2SDCI, and with coupled cluster calculations including the effect of triples, especially for the states which have a predominant
double excitation character. The IDDCI procedure has been speeded up by using smaller subspaces for optimizing the molecular
orbitals.
Received: 17 January 1997 / Accepted: 31 July 1997 相似文献
105.
Tatsuhiko Kashimura Tomoya Ikezaki Yusuke Ohta Satoshi Yabushita 《Journal of computational chemistry》2019,40(2):482-499
One of the most spectacular yet unsolved problems for the ICN -band photodissociation is the non-statistical spin-rotation F1 = N + 1/2 and F2 = N − 1/2 populations for each rotation level N of the CN fragment. The F1/F2 population difference function f(N) exhibits strong N and λ dependences with an oscillatory behavior. Such details were found to critically depend on the number of open-channel product states, namely, whether both I (2P3/2) and I (2P1/2) are energetically available or not as the dissociation partner. First, in the asymptotic region, the exchange and dipole-quadrupole inter-fragment interactions were studied in detail. Then, as the diabatic basis, we took the appropriate symmetry adapted products of the electronic and rotational wavefunctions for the F1 and F2 levels at the dissociation limits. We found that the adiabatic Hamiltonian exhibits Rosen–Zener–Demkov type nonadiabatic transitions reflecting the switch between the exchange interaction and the small but finite spin-rotation interaction within CN at the asymptotic region. This non-crossing type nonadiabatic transition occurs with the probability 1/2, that is, at the diabatic limit through a sudden switch of the quantization axis for CN spin S from the dissociation axis to the CN rotation axis N . We have derived semiclassical formulae for f(N) and the orientation parameters with a two-state model including the 3A′ and 4A′ electronic states, and with a four-state model including the 3A′ through 6A′ electronic states. These two kinds of interfering models explain general features of the F1 and F2 level populations observed by Zare's group and Hall's group, respectively. © 2018 Wiley Periodicals, Inc. 相似文献
106.
Liping Li 《Journal of solid state chemistry》2007,180(10):2896-2904
Highly crystalline one-dimensional (1D) α-MnO2 nanostructures were synthesized by a hydrothermal method. All samples were characterized by X-ray diffraction, transmission electron microscope, thermogravimetric and differential scanning calorimeter, and infrared spectroscopy. During the formation reactions, the tunnel structure of 1D α-MnO2 was simultaneously modified by NH4+ species and water molecules. The amount of NH4+ species that were trapped in the tunnels is almost independent on the reaction temperature, while the total water content increased with the reaction temperature. The average diameter of α-MnO2 nanorods increased from 9.2 to 16.5 nm when the reaction temperature increased from 140 to 220 °C. 1D α-MnO2 was destabilized by a subsequent high-temperature treatment in air, which is accompanied by a structural transformation to 1D Mn2O3 of a cubic structure. At low temperatures, all 1D α-MnO2 nanorods showed two magnetic transitions that were characterized by a decreased Néel temperature with rod diameter reduction. According to the effective magnetic moments experimentally measured, Mn ions presented in the nanorods were determined to be in a mixed valency of high spin state Mn4+/Mn3+. 相似文献
107.
Kevin E. Bassler Kazuo Sasaki Robert B. Griffiths 《Journal of statistical physics》1991,62(1-2):45-88
Certain features in Frenkel-Kontorova and other models of phases with a one-dimensional modulation can be analyzed by assuming parallel interfaces separating sets of lattice planes belonging to two different phases, and treating the free energy to create interfaces, as well as the interaction of two, three, or more interfaces, as phenomenological parameters. A strategy employed by Fisher and Szpilka for interacting defects can be extended to the case of interfaces, allowing a systematic study of the phase diagram by ignoring all interface interactions, and then successively taking into account pair, triple, and higher-order terms. The possible phase diagrams which can occur near the point where =0 include: various sorts of endpoints analogous to critical endpoints, an accumulation point of first-order transitions and triple points, and a self-similar structure which we call an upsilon point, which turns out to be an accumulation point of an infinite number of segments of first-order transition lines, each of which terminates in two upsilon points. 相似文献
108.
Christian Borgs Roman Kotecký Salvador Miracle-Solé 《Journal of statistical physics》1991,62(3-4):529-551
Recently, Borgs and Kotecký developed a rigorous theory of finite-size effects near first-order phase transitions. Here we apply this theory to the ferromagneticq-state Potts model, which (forq large andd2) undergoes a first-order phase transition as the inverse temperature is varied. We prove a formula for the internal energy in a periodic cube of side lengthL which describes the rounding of the infinite-volume jumpE in terms of a hyperbolic tangent, and show that the position of the maximum of the specific heat is shifted by
m
(L)=(Inq/E)L
–d
+O(L
–2d
) with respect to the infinite-volume transition point
t
. We also propose an alternative definition of the finite-volume transition temperature
t
(L) which might be useful for numerical calculations because it differs only by exponentially small corrections from
t
. 相似文献
109.
We present a study of finite-size effects in a model exhibiting a first-order temperature-driven symmetry-breaking structural phase transition in theL
× cylindrical geometry in theL
limit. Exact studies demonstrate the applicability of our scaling ansatz even in the one-dimensional limit, making this model ideal for studying finite-size effects. The scaling ansatz, similar to the previously developed ansatz for field-driven transitions, demonstrates that latent heat is crucial in driving these transitions. This ansatz is supported by a 2×2 phenomenological transfer matrix based upon the symmetries of the system; this produces an analytic free energy which has the scaling form. Order parameter probability distributions show that the high- and low-temperature phases coexist only in a small finite-size-affected regime near the bulk transition temperature; this regime vanishes exponentially fast asL
diverges. 相似文献
110.
Thermal analysis methods are well-established techniques in research laboratories of pharmaceutical industry. The robustness
and sensitivity of instrumentation, the introduction of automation and of reliable software according to the industrial needs
widened considerably the areas of applications in the last decade. Calibration of instruments and validation of results follow
the state of the art of cGMP as for other analytical techniques. Thermal analysis techniques are especially useful for the
study of the behavior of the poly-phasic systems drug substances and excipients and find a unique place for new delivery systems.
Since change of temperature and moisture occur by processing and storage, changes of the solid state may have a considerable
effect on activity, toxicity and stability of compounds. Current requirements of the International Conference of Harmonisation
for the characterization and the quantitation of polymorphism in new entities re-enforce the position of thermal analysis
techniques. This challenging task needs the use of complementary methods. Combined techniques and microcalorimetry demonstrate
their advantages. This article reviews the current use of thermal analysis and combined techniques in research and development
and in production. The advantage of commercially coupled techniques to thermogravimetry is emphasized with some examples.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献