Nonadiabatic transitions at the limit of almost-adiabatic perturbations with random motion along the terms

Conclusions The investigation carried out has shown that in the diffusion approximation, which is valid when the effective length of the free path =v_ov is much smaller than the dimension of the nonadiabatic region, an adiabatic limit is achieved only under the condition v_v 1. This case cannot be described when (4) is assumed to be valid for , since this equation is fulfilled only when v_v 1. It is perfectly natural that the use of Eq. (4) produces a strong interaction between the terms of the quantum subsystem, i.e., we do not attain an adiabatic limit. In the work it was shown that at the adiabatic limit the rate of transitions between the terms decreases rapidly with increasing v_v.The condition v_v 1 strongly restricts the region for the applicability of (4) and, therefore, of (12). In this sense, expression (21) is a significant generalization of (14), since it was obtained only under the. assumption and V_D 1. However, the range of parameters which satisfy these inequalities corresponds to a fairly narrow group of processes; therefore, it would be of interest to also investigate the region of a. This question will be the subject of the next report.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 17, No. 1, pp.3–9, January–February, 1981.In conclusion, we express our sincerest thanks to I. V. Aleksandrov, S. Ya. Umanskii, and M. Ya. Ovchinnikova for numerous and useful discussions.     

Order and disorder in mixed metal linear chains: The homo and heterobimetallic EDTA (M(H2O)4OIOII)[M′(EDTA)] · 6H2O complexes (M = Mg,Mn, Co,Zn and Ni; M′ = Co,Ni, Cu and Zn)

Summary Polymetallic solid solutions of the ethylenediaminetetracetic acid (EDTA) and six divalent metal ions exist in the range: MgMnCoZnNiCu(EDTA) · 6H₂O where + + + + + =2, 01, 0,,2, 0, 1.This type of structure is characterized by the presence of two different octahedral carboxylate-bridged coordination sites forming infinite zig-zag chains. Visible and i.r. spectra and t.g.a. analysis show that there is occupational preference for the two coordination sites in the crystalline structure.Due to this preference, and also to the structural features, the heterobimetallic MM(EDTA) · 6H₂O compounds constitute a structurally new class of materials which can be described as ordered alternating-heterobimetallic polymeric coordination complexes.     

Transference numbers of aqueous HCl up to 15 mol-kg−1 at 25°C: A systematization and reassessment

Ion-transfer parameters of aqueous hydrochloric acid over a wide molality range have been re-investigated taking the concurrent solventtransfer into due account. In this context, the transference numbers for the hydrogen ion _H and for water _w have been determined from 10^–2 to 15 mol-kg^–1, together with the corresponding infinite-dilution values _H ^o and _w ^o , by processing a set of nearly a hundred emf measurements (some twenty of them new for this work) on HCl concentration cells with transference with both cation-reversible and anion-reversible electrode pairs.     

Über die Diffusion von Makromolekeln in Lösung

Zusammenfassung Polyisobuten (PIB) und Polyphenylvinylketon (PPVK) wurden mit 2 s-Impulsen von 15 MeV-Elektronen oder 25 ns-Lichtblitzen (=347 nm) in verdünnter Lösung in der Hauptkette abgebaut. Die dem kurzzeitigen Abbau folgende Separierung der Molekelfragmente wurde anhand der Änderung der Streulichtintensität (LSI) untersucht. Relaxationszeiten (LSI) > 10 s wurden gemessen. Die Zeit (S), in der eine Kettenspaltung erfolgt, beträgt im Falle des PPVK etwa 0,1 s. Auch für PIB ist (S) (LSI), da in Gegenwart von Cyclohexen zwar der Abbau stark inhibiert wird, (LSI) jedoch unbeeinflußt bleibt. (LSI) wird daher durch die Diffusion der Fragmente bestimmt. Parameterstudien bestätigen dies: (LSI) steigt linear mit der Mikroviskosität an. Im Falle des PIB nimmt (LSI) mit steigender Polymerkonzentration ab. (LSI) hängt nur geringfügig vom mittleren MolekulargewichtM ab ((LSI) M^0,2, im Falle des PPVK und (LSI)M ^0,3 im Falle des PIB). Daher wird geschlossen, daß (LSI) nicht der translatorischen, sondern der Entknäuelungs-diffusion zuzuordnen ist. Dies wird bestätigt durch die signifikante Abhängigkeit von (LSI) von der Knäueldichte. (LSI) steigt nämlich an, wenn man die Knäueldichte von PIB-Molekeln durch Zusatz vonn-Propanol zun-Hexanlösungen erhöht.

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Summary Polyisobutene (PIB) and polyphenylvinylketone (PPVK) were degraded in the main chain in dilute solutions by irradiation with 15 MeV electrons or 25 ns light flashes ( = 347 nm). The separation of the fragments of the macromolecule following the rapid degradation was monitored by measuring the change of the light scattering intensity (LSI). Relaxation times (LSI), > 10 s were found. The time for establishing a chain scission is ca. 0.1 s in the case of PPVK. Also for PIB (S) (LS)) since in the presence of cyclohexene the degradation is strongly inhibited whereas (LSI) remains constant. Therefore, (LSI) corresponds to the diffusion of the fragments. Further evidence for this was obtained by other studies: (LSI) increases linearly with microviscosity. In the case of PIB (LSI) decreases with increasing polymer concentration. (LSI) depends only weakly on the average molecular weightM. ( (LSI) M ^0.2 for PPVK and (LSI)M ^0.3 for PIB). Thus it is concluded that (LSI) does not correspond to translatory diffusion but to disentanglement diffusion. This is furthermore evidenced by the significant dependency of (LSI) on coil density. (LSI) increases by increasing the coil density whenn-propanol is added to n-hexane solutions containing PIB.

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Mit 8 Abbildungen und 1 Tabelle     

Information theory of optimization in chromatography: Optimum peak separation and dependency on peak area

Summary If a peak (j=2) moves along the time axis of a chromatogram with no change in the position ₁ of the other peak (j=1) or in areas A₁ and A₂, the optimum separation, _s, is defined as the resolution R_s which provides the maximum information, called FUMI, among all possible positions ₂ of the peak (₂₁). This paper demonstrates that optimum separation, _s, of chromatographic peaks critically depends on the peak areas. As the area ratio A₂/A₁ of overlapped peaks increases, greater separation (higher resolution R_s) is needed to obtain maximum information. The quantitative relationship between _s and A₂/A₁ is derived by computer simulation.     

Acidity and activity of H-mordenite in m-xylene isomerization

The dependence of the activity of H-mordenites prepared from a natural mordenite on the nature and strength of the acid groups present was studied. The superior catalytic activity and stability of the H(Ag)–MOR zeolite compared with other H-forms is explained on the basis of NH₃ adsorption and IR measurements.

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H-, . H(Ag)–MOP H- NH₃ .

     

Influence of mobility of medium on dynamics of metallotropy in tin-containing 2-R-oxyphenoxyls

The rate of intramolecular migration of the triphenylstannyl group in 3,6-ditert-butyl-2(triphenylstannyl) oxyphenoxyl decreases with increasing viscosity of the medium. A linear relationship _ex=·_c is observed between the characteristic time of stannotropy _ex and the correlation time for reorientational motions of the radical _c within a range of temperature variation no greater than 30°C. The parameter depends on the medium; this is explained by the possibility of complexation of the radical with the solvent.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 781–786, April, 1990.     

Correlation between solvent-reorganization dynamics and the kinetics of metallotropy in polar media

The kinetics of metallotropy of the 3,6-di-tert-butyl-2-(triphenylstannyl)oxyphenoxyl radical has been studied by ESR. The correlation between chemical exchange time _ex, solvent polarity, and longitudinal relaxation time of the solvent corresponds to the model of a process controlled by molecular dynamics. A linear relation between _ex and correlation time _c for reorientation movements of the radical is found: _ex = · _c. The coefficient depends on the dielectric properties of the solvent.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 410–413, March, 1994.This work was supported by the Russian Foundation for Basic Research, project No. 93-03-4372.     

Effect of electric field strength and exposure time on epoxy and high density polyethylene measured by positron annihilation lifetime

Using the positron annihilation lifetime technique, the annihilation parameters have been measured for epoxy and high density polyethylene (HDPE) as a function of AC electric field strength and the exposure time. The lifetime spectra have been resolved into three components, the longest component (I₃₃) is attributed to the pick-off annihilation of o-Ps in the amorphous regions. The intermediate one (I₂₂) is due to the annihilation of free positrons, while the shorter component (I₁₁) stems from self annihilation of p-Ps. In HDPE, the o-Ps parameters ₃ andI ₃ are measured as a function of electric field strengths in the range from 10 to 100 kV/cm exposed for 24 hours. A decrease inI ₃ of 8% is observed from zero to 50 kV/cm followed by an increase of the same order from 50 to 100 kV/cm. By investigating the effect of the exposure time from 2 to 24 hours at 16 and 50 kV/cm, the effect is confirmed and is attributed to the inhibition of o-Ps formation at lower field strength. In epoxy, the effect or exposure time onI ₃ at 166 and 133 kV/cm shows a similar behavior as in HDPE. At 133 kV/cmI ₃ decreases by only 2.5%. On the other hand, the changes in ₃ occur at short exposure times. Again at large times the saturation is obtained. These effects are attributed to the expansion of free volume (increase of ₃) competing at longer exposure times with other phenomena, such as liberation of free radicals, which reduce the o-Ps intensityI ₃ through the conversion to p-Ps. The reactions between o-Ps and free radicals might also lead to free positrons, which could explain the increase ofI ₂ and the decrease of ₃ at longer exposure times.     

Vibrational isotope effect of linear and planar molecules: Deuterated bromoethenes

Linear (planar) molecules A and B which are identical except for isotopic substitutions at the atomic sites are considered. Stretching (bending, out-of-plane) frequencies _k and normal modes _k of the isotopically perturbed molecule B are expressed in terms of stretching (bending, out-of-plane) frequencies _i and the corresponding normal modes _i of the unperturbed molecule A. Complete specification of the unperturbed normal modes is not required. All that is needed are stretching (bending, out-of-plane) amplitudes | _i of the normal modes _i at those sites that are affected by isotopic substitution. The rule which interlaces frequencies _k of molecule A with frequencies _i of molecule B is derived. Given two isotopic molecules A and B that differ by a single isotopic substitution at site , the inversion relation is derived. This relation expresses unperturbed stretching (bending, out-of-plane) amplitudes at the site in terms of stretching (bending, out-of-plane) frequencies of molecules A and B . As an example, out-of-plane vibrations of deuterated bromoethene were considered. In the simplest method 12 out-of-plane frequencies of four polydeuterated bromoethenes were calculated from 12 out-of-plane frequencies of bromoethene and three monodeuterated bromoethenes. Standard deviation of thus calculated frequencies from experimental frequencies is =2.74 cm^–1. In another method, 15 out-of-plane frequencies of four polydeuterated bromoethenes and selected monodeuterated bromoethene are calculated from 9 out-of-plane frequencies of bromoethene and the remaining two monodeuterated bromoethenes. Depending on which monodeuterated bromoethene is selected (1-, cis- or trans-), standard deviation of thus obtained frequencies from experimental frequencies is 1=2.84 cm^–1, c=2.96 cm^–1 and t=2.72 cm^–1.     

Transient photocapacitance study in 4-nitro-4′-aminodiphenyl layers

In 4-nitro-4-aminodiphenyl (NAD) layers the photocapacitance (PhC) transients were investigated. PhC spectral distribution as well as the temperature dependences of time constants (under/_on/or after/_off/illumination) have been measured. The photocapacitance spectral distribution possesses maxima at 350, 500, and 750 nm. It was shown that _on (T) is of exponential form while _off (T) is more complicated. The values of thermal activation energies (0.65±0.05) eV of both time constants coincide. The mechanism of photocapacitance process has been disclosed in NAD layers.     

Thermal decomposition of rare earth complexes with o-aminobenzoic acid

The conditions of thermal decomposition of La, Ce(III), Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu anthranilates have been studied. The anhydrous La, Ce(III), Pr(III), Nd and Sm anthranilates decompose in one step directly to the oxides Ln₂O₃, CeO₂ or Pr₆O₁₁. The monoand dihydrated anthranilates of the remaining rare earths first lose crystallization water when heated, and then decompose exothermally to the oxides Ln₂O₃ or Tb₄O₇.

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Zusammenfassung Die Bedingungen der thermischen Zersetzung der Anthranilate von La, Ce(III), Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb und Lu wurden untersucht. Die wasserfreien Anthranilate von La, Ce(III), Pr(III) und Nd zersetzen sich in einem Schritt direkt zu den Oxiden Ln₂O₃, CeO₂ und Pr₆O₁₁. Die ein oder zwei Kristallwasser enthaltenden Anthranilate der übrigen seltenen Erdmetalle werden beim Erhitzen zunächst dehydratisiert und danach exotherm zu den Oxiden Ln₂O₃ und Tb₄O₇ abgebaut.

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, . , , Ln₂O₃, CeO₂ Pr₆O₁₁. - Ln₂O₃ Tb₄O₇.

     

Photophysical properties of (η2-C60)Pd(PPh3)2 complex in benzene. Picosecond and nanosecond laser photolysis

Absorption spectra of the photoexcited (²-C₆₀)Pd(PPh₃)₂ complex in benzene were obtained by picosecond and nanosecond laser photolysis. The spectra are compared with those observed for photoexcited states of fullerene C₆₀ and charge-transfer states of C₆₀ complexes with ternary amines. The relaxation kinetics of excited (²-C₆₀)Pd(PPh₃)₂ complex has three components with characteristic lifetimes ₁ = 43 ps, ₂ = 1500 ps, and ₃ = 1.17 s. The results are discussed in terms of the four-level scheme of the excited complex.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1163–1166, May, 1996.     

Die Kobaltecke im Dreistoffsystem Kobalt-Molybdän-Bor

Zusammenfassung Im Dreistoffsystem Kobalt–Molybdän–Bor werden die Gleichgewichte um die Phasen (Cr₂₃C₆-Strukturtyp) und CoMoB (Struktur unbekannt) untersucht. In von 800°C abgeschreckten Legierungen liegt die Zusammensetzung von bei Co_21,7Mo_1,3B₆.

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The equilibria in the ternary system cobalt–molybdenum–boron were investigated in the region around (Cr₂₃C₆ structure) and CoMoB (unknown structure). In alloys quenched from 800°C the composition of is found at Co_21.7Mo_1.3B₆.

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Mit 5 Abbildungen     

Modelling of quantitative DTA equipment I. Electric analog approach

For an electric model, relationships have been established as a function of the DTA baseline shift, the intensity of the signal, the slope of the leading edge, the heating rate, the thermal resistance of the heating disc built into the DTA apparatus, the contact resistance between the disc and the sample holders, and the heat resistance between the two measuring sites. Some of the relationships obtained supported knowledge acquired earlier by other approaches, and some furnished new information. The limits of use of this simple model are indicated.

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Zusammenfassung Unter Anwendung eines elektrischen Modells wurden Zusammenhänge als Funktion der Verschiebung der Basislinie der DTA, der Signalintensität, der Steile der Leitkante, der Aufheizgeschwindigkeit, des Wärmewiderstandes der in das DTA-Gerät eingebauten Heizscheibe, des Kontaktwiderstandes, zwischen Scheibe und Probenbehälter und des Wärmewiderstandes zwischen den beiden Meßstellen ermittelt. Ein Teil der erhaltenen Zusammenhänge bestätigte von anderen Annäherungen her bereits vorliegende Kenntnisse, ein anderer Teil lieferte neue Informationen. Auf die Grenzen und der Nutzen dieses einfachen Modells wurden hingewiesen.

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Résumé A l'aide d'un modèle électrique, on a établi des relations décrivant l'influence de la dérive de la ligne de base ATD, de l'intensité du signal, de la pente du bord du pic, de la vitesse de chauffage, de la résistance thermique du disque de chauffage incorporé dans l'appareil ATD, de la résistance de contact entre le disque et les porte-échantillons et enfin, de la résistance thermique entre les deux points de mesure. Une partie des relations obtenues confirme les connaissances déjà acquises par d'autres approches, l'autre partie fournit des renseignements nouveaux. Les limites d'utilisation de ce modèle simple sont indiquées.

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, , , , , , , . , — . .

     

Dioxygen evolution from aqueous acid solutions of ruthenium complexes with nitrogen-containing ligands

Some peculiarities of reduction of one-electron oxidants, Ru(bpy) ₃ ³⁺ and Ru(bpy)₂(py) ₂ ³⁺ , in the absence of catalysts (when oxidation of the oxidant's ligands occurs) and in their presence (when also oxidation of water to dioxygen occurs) are discussed. Both oxidation reactions are thought to have a common intermediate.

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Ru(bpy) ₃ ³⁺ Ru(bpy)₂(py) ₂ ³⁺ ( -) ( ). , .

     

Valence state and coordination number of molybdenum supported on SiO2 or MgO during the oxidation of propylene

The nature of the species occurring during the oxidation of propylene on molybdenum oxides supported on silica or magnesia has been investigated by diffuse reflectance spectroscopy. The reaction was performed in the uv cell itself. The oxidation occurs on partially reduced solids and the selectivity for acrolein is related to tetrahedral Mo⁵⁺.

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, , . . . Mo⁺⁵.

     

Determination of the kinetic parameters of polyvinylchloride

Kinetic equations proposed in the literature for thermal decomposition reactions may be approximated at low conversions by the relation: ^b=Dp(x). This equation reveals three kinds of behaviour under isothermal conditions, as evidenced in the thermal dehydrochlorination of Polyvinylchloride. The kinetic parameters were determined with a computing program and its performances were tested. The calculation method was applied to some Polyvinylchloride macromodels.

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Zusammenfassung In der Literatur vorgeschlagene kinetische Gleichungen für thermische Zersetzungsreaktionen können bei niedrigen Konversionen mit der Gleichung ^b=Dp(x) genähert werden. Diese Gleichung offenbart unter isothermen Bedingungen drei Verhaltensweisen, wie an der thermischen Dehydrochlorierung von Polyvinylchlorid bewiesen wird. Die kinetischen Parameter wurden mittels eines Computerprogrammes ermittelt und ihre Leistungsfähigkeit überprüft. Das Rechenverfahren wurden an einigen Polyvinylchloridmakromodellen getestet.

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, , ^b =Dp(x). , . , . .

     

Quantum-chemical study of the optical properties of MgO surface hydroxy groups

Cluster models of MgO surface OH groups have been studied by the semi-empirical CNDO method. The calculated stretching vibration frequencies of OH bonds and localized electron excitation energies on the OH-groups are shown to depend on the oxygen atom coordination.

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OH- MgO. , OH- , OH-, .