Theoretical assignments of the electronic spectrum of acetylene

Non empirical calculations of energies and properties of some excited states of acetylene are presented. A frozen core approximation is used and excitations to , and MO's are taken into account. Both valence and Rydberg states are considered. Assignments of the UV and electron impact spectra are proposed and some questions are raised.     

On the change of thermal parameters in a glass during a Na/Tl ion-exchange-characterized by DTA measurements

The Na/Tl exchange is investigated in two silicate glasses (Na₂O·2SiO₂ and crown-flint KF₃) by estimation of concentration or refractive index profiles, resp. (c _Tl(x) orn(x)). The forms of the profiles are discussed in connection with changes of the glass transition temperature T_g owing to an increase of Tl₂O contents, determined by DTA on homogeneous glass samples. During the Na/Tl exchange the local and temporal enlargement of the Tl₂O content causes a drastic decrease ofT _g(x, t) values and of the viscosity (x, t), which yields a remarkable acceleration of the Na/Tl interdiffusion.

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Zusammenfassung Der Na/Tl-Austausch wird in zwei Silicatgläsern (Na₂O.2SiO₂ und Kron-Flintglass KF3) anhand der Bestimmung von Konzentrations- oder Brechzahlprofilen (c _Tl(x) odern(x)) untersucht. Die Profilformen werden im Zusammenhang mit Änderungen der Glastransformations-TemperaturT _g bei steigendem Tl₂O-Gehalt diskutiert, die mittels DTA an homogenen Glasproben bestimmt wurden. Während des Na/Tl-Austausches verursacht die lokale und zeitliche Erhöhung des Tl₂O-Gehaltes ein drastisches Absinken derT _g(x, t)-Werte bzw. der Viskosität (x, t), das zu einer bemerkenswerten Beschleunigung der Na/Tl-Interdiffusion führt.

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(Na₂O.2SiO₂ «») Na/Tl ₁(x) 321in(x). , , . Na/Tl _g(, t) i (x,t), Na/Tl .

     

Ionization potentials of halides. Substituent effects in Cl-, Br-, and I-centered radical cations

The first vertical ionization potentials (I) of halides HalX (Hal = Cl, Br, I; X is an inorganic or organic substituent) are linearly related to the inductive (_I), resonance (_R ⁺), and polarizability () constants of the substituents X (I = a + b_I + c_R ⁺ + d). As the atomic number of the Hal element in the Hal^·+X radical cations increases, the inductive interaction is strengthened while the polarizability interaction is weakened. Conjugation remains virtually independent of the Hal atom. The resonance _R ⁺-constants of the MX₃ (M = Si, Ge, Sn, Pb) substituents bound to the Hal^·+ radical cation centers were first calculated.     

Interpretation of AC Conductivity of Lightly Doped Conducting Polymers in Terms of Hopping Conduction

The ac conduction of most disordered materials shows a regime of constant dc conductivity (0) at low frequencies and a crossover to a frequency-dependent regime of the type A ^s at high frequencies. We discuss the physical origin of this behavior and the interpretation of the onset frequency of excess ac conduction, _c , in terms of models for hopping conduction of polaronic carriers in a disordered medium. We emphasize the central role of the critical hopping rate in the percolation lattice for determining both (0) and _c . We show the behavior of () for lightly doped polypyrrole samples at different stages of doping, and we discuss the significance of frequency dispersion effects for electrochemical measurements.     

Intensity of the η(C≡C) Bands in the IR Spectra of Acetylene Derivatives and σR 0 Constants of Organosilicon,Organogermanium, and Organotin Substituents

The integral absorptivities of shape-characteristic (CC) bands in the IR spectra of 66 acetylene derivatives RCCX (R = H, Me₃M; X are inorganic and organic substituents) are related by a common linear equation to the _R ⁰ constants of the R and X substituents. The _R R⁰ constants of 10 Alk₃M substituents were calculated. The _R ⁰, _R , and _R ⁺ constants of Me₃M substituents were analyzed. The positive _R ⁰ values (0.12, 0.06, and 0.04 for R = Si, Ge, and Sn, respectively) suggest that in the ground electronic state of Me₃MCCX molecules the resonance acceptor effect of the Me₃M substituents (d, conjugation) prevails over donor (, conjugation). The first effect attenuates and the second enhances as the atomic number of M increases.     

Charge control in the formation of complexes of phenol with unsaturated compounds containing organometallic substituents from group IV

The resonance donor effect of the , conjugation of R₃M and R₃MCH₂ (M = Si, Ge, Sn; R is an alklyl group) substituents with the triple bond in compounds R₃MC=CX and R₃MCH₂CCX (X = H, R) changes on passing from isolated molecules to their H-complexes. A partial ⁺ charge on the triple bond enhances , conjugation; a partial ^– charge on the triple bond has practically no effect on the resonance properties of R₃M substituents, whereas the , conjugation of R₃MCH₂ substituents diminishes owing to the effect of negative direct resonance interaction. The effect of , conjugation on the effective negative charges of the carbon atoms in the -CC- fragments was estimated quantitatively.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1041–1046, June, 1994.This work was supported by the Russian Fundation for Basic Research (Grant 93-03-18372).     

Predissociation lifetime of the 1σ g 2 2σ g diabatic state of He 2 + : a one-channel approach

Summary This work is concerned with the application of a one-channel model to obtaining predissociation lifetimes and transition rates in a system of crossing diabatic states. The calculation focuses on the first shape resonance of the 1 _g ² 2 _g diabatic state of He ₂ ⁺ , which is relatively stable with respect to tunneling. This resonance predissociates as a result of the 1 _g ² 2 _g state being crossed by the 1 _g 1 _u ² dissociative diabatic state near the resonance level. We have estimated its predissociation lifetime to be of the order of 10^–11 s.     

The UV spectra of arsines and arsine selenides

Short-wavelength n_Se ^* and long-wavelength n_Se ^* bands are observed in the UV spectra of saturated trialkylarsine selenides in the near-UV region. The n_x ^* band in going from arsine selenides to arsine sulfide and then to arsine oxides is shifted hypsochromically, as in the corresponding phosphorus compounds. The n_x ^* band is only slightly sensitive to the chalcogen. Saturated trialkylarsines, in contrast to alkylphosphines, absorb in the near UV region (the n_As ^* band is at 208 nm).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 940–942, April, 1990.     

Steady state catalytic properties and oxygen binding energy of cadmium-molybdenum catalysts in methanol oxidation

On normal cadmium molybdate the products of methanol oxidation are primarily CO₂ and H₂. After the introduction of excess MoO₃ to reach Mo/Cd=1.2, methanol is oxidized to formaldehyde and carbon monoxide via a consecutive scheme. The oxygen binding energy in the steady state for the first sample is by 30 kcal/mol higher than that for the second catalyst. The activation energies of methanol conversion are 11.5 and 20 kcal/mol, respectively.

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CO₂ H₂. MoO₃ Mo/Cd=1, 2 . 1- 30 / , , , , 11,5 20 /.

     

Use of EGD for the characterization of fining processes of glass melt

The control and optimization of the glass-making process is a serious problem in glass production. An EGD procedure involving high-temperature vacuum extraction and total pressure measurement allows determination of the fining state (Läuterzustand) and fining behaviour (Läuterverhalten). The fining state is characterized by the contents of CO₂, N₂ and other gases from the batch reactions, and gas inclusions. Oxygen evolved in a second step is characteristic for the fining behaviour.

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Zusammenfassung Die Kontrolle und Optimierung des Gasgehaltes von Glasschmelzen ist eine wichtige Voraussetzung für eine gleichbleibende Qualität der Glasprouktion. Eine EGD-Technik mit Hilfe der Hochvakuumheißextraktion und Gasdruckmessung erlaubt, den Läuterzustand und das Läuterverhalten einer Glasprobe zu bestimmen. Der Läuterzustand wird durch die Gase aus den Gemengereaktionen und Gemengeeinschlüssen (CO₂, N₂ u. a.) bestimmt. Das Läuterverhalten ergibt sich aus der Menge des in einer zweiten Stufe extrahierbaren Sauerstoffs.

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. , , . , , , . , , .

     

Effect of α-methylstyrene of the curing behaviour of vinyl ester resins

The curing behaviour of bismethacryloxy derivative of diglycidyl ether of bisphenol A (vinyl ester resin) containing styrene as the reactive diluent (40% w/w) was studied using gel point determination method and DSC. Seven samples of styrene/-methylstyrene in the ratio 400, 355, 3010, 2515, 2020, 1525 and 040 were studied. Delayed curing was observed in samples containing increasing proportions of -methylstyrene. The energy of activation decreased from 869 kJ mol^–1 to 333 kJ mol^–1 as the concentration of -methylstyrene increased in the formulations. However, no difference in thermal stability was observed by replacement of styrene by -methylstyrene. It was concluded that in vinyl ester resin samples 10–15% -methylstyrene and 30-25% styrene can be used as reactive diluent.

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Zusammenfassung Mittels DSC und Bestimmung der Gelierungstemperatur wurde das Aushärteverhalften des Bismethakryloxyderivaten des Diglycidyläthers von Bisphenol A (Vinylesterharz) mit 40 Gewichtsprozenten Styrol als reaktives Streckmittel untersucht. Es würden sieben Proben mit einem Styrol/-Methylstyrol Verhältnis von 400, 355, 3010, 2515, 2020, 1525 und 040 untersucht. Mit steigendem Anteil an -Methylstyrol konnte eine Verzögerung der Aushärtung sowie ein Absinken der Aktivierungsenergie von 869 kJ · mol^–1 auf 333 kJ · mol^–1 beobachtet werden. Der Ersatz von Styrol durch -Methylstyrol veränderte jedoch die thermische Stabilität in keiner Weise. Vinylesterharzproben mit 10–15% -Methylstyrol und 30–25% Styrol können als reaktive Streckmittel in Vinylesterharzen verwendet werden.

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- - , 40 .% . /-, 400, 355, 3010, 2515, 2020, 1525 040. - . - 869 333 · ^–1. , .. , , 10–15% - 30–25% .

     

Interaction of styrene with triphenylphosphinecobalt complexes

The interaction of the cobalt phosphine complexes Co(N₂)(PPh₃)₃, HCo(N₂)(PPh₃)₃ and H₃Co(PPh₃)₃ with styrene yields mono and dinuclear complexes identified by the ESR method. A paramagnetic complex, Co(PPh₃) (styrene)₂, is one of the intermediates in the catalytic hydrogenation of styrene.

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Co(N₂)(PPh₃)₃, HCo(N₂)(PPh₃)₃ H₃Co(PPh₃)₃ . , Co(PPh₃) ()₂.

     

Thermal and some other properties of the complexes crystallizing from the system Ni(II)-en-[Ni(CN)4]2−-H2O

Seven complex compounds exhibiting the compositions Ni(en)₃Ni(CN)₄·H₂O (I), Ni(en)₃Ni(CN)₄ (II),-Ni(en)₂Ni(CN)₄ (III), Ni(en)Ni(CN)₄·2H₂O (IV), Ni(en)Ni(CN)₄ (V), Ni(en)₂Ni(CN)₄ · 2.5H₂O (VI) and-Ni(en)₂Ni(CN)₄ (VII) were prepared from the system Ni-en-[Ni(CN)₄]^2–-H₂O. These compounds were examined by the methods of infrared spectroscopy, X-ray powder diffractometry, UV-VIS reflectance spectroscopy, and also by the measurement of magnetic moments. The thermal stability, the stoichiometry of thermal decomposition and the mutual transformations were investigated with a derivatograph. The reactions proceeding according to the following schemes were observed if the system was heated to appropriate temperature: (I)(II)(III)(V)(IV) and (VI)(VII)(III)(V)(IV) Process (VII)(III) represents isomerization. The reversibility of the process (V)(IV) is due to the high hygroscopicity of the anhydrous complex. The changes in structure in the course of the individual processes are discussed.

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Zusammenfassung Aus einem System Ni-en-[Ni(CN)₄]^2–-H₂O wurden sieben Komplexe der Formeln Ni(en)₃Ni(CN)₄·H₂O (I), Ni(en)₃Ni(CN)₄ (II),-Ni(en)₂Ni(CN)₄ (III), Ni(en)Ni(CN)₄·2H₂O (IV), Ni(en)Ni(CN)₄ (V), Ni(en)₂Ni(CN)₄ · 2.5H₂O (VI) und-Ni(en)₂Ni(CN)₄ (VII) hergestellt. Diese Verbindungen wurden mittels IR-Spektroskopie, Röntgenpulverdiffraktometrie, UV-Reflexionsspektroskopie und durch Messungen des magnetischen Momentes untersucht. Die Wärmestabilität, die Stöchiometrie des thermischen Zerfalles und die gegenseitigen Umwandlungen wurden mittels eines Derivatographen untersucht. Wird das System auf geeignete Temperaturen erhitzt, kann der Reaktionsverlauf durch folgendes Schema dargestellt werden: (I)(II)(III)(V)(IV) und (VI)(VII)(III)(V)(IV).Der Prozeß (VII)(III) verkörpert eine Isomerisierung. Die Umkehrbarkeit von Prozeß (V)(IV) ist auf die ausgeprägten Hygroskopieeigenschaften des wasserfreien Komplexes zurückzuführen. Es werden die im Ablaufe der einzelnen Prozesse vorgehenden Strukturveränderungen besprochen.

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Ni- -[No(N)]² -₂ Ni(en)₃Ni(CN)₄ · ₂ (I), Ni(en)₃Ni(CN)₄ (II),-Ni(en)₂Ni(CN)₄ (III), Ni(en)Ni(CN)₄-2H₂O (IV), Ni(en)Ni(CN)₄ (V), Ni(en)₂Ni(CN)₄ · 2,5H₂O (VI) -Ni(en)₂Ni(CN)₄ (VII). , , - , . , . (I)(II)(III)(V)(IV) (VI)(VII)(III)(V)(IV). (VII)(III) . (V)(IV) . .

     

Kinetics and mechanism of homogeneous catalytic oxidation of pyrocatechol in aqueous solutions containing Cu(II) and histidine

Kinetic studies of pyrocatechol oxidation by oxygen in weakly acidic aqueous solutions containing pyrocatechol, Cu(II) ions and histidine, indicate that the reaction involves mixed copper-pyrocatechol histidine complexes. The proposed mechanism of the process agrees with the kinetic relationships obtained.

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, , Cu(II) . , . , -.

     

Molecular isotope exchange of14CO in surface carbonyl complexes of rhodium

Molecular isotope exchange of CO with¹⁴CO for Rh₆(CO)₁₆/Sn(II)–SiO₂, Rh₆(CO)₁₆/Al₂O₃, Rh(I)(CO)₂/Al₂O₃, Rh₄(CO)₁₂/Al₂O₃ carbonyl complexes of rhodium has been studied. Estimates of the activation energies and a mechanism of the CO exchange are suggested.

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, (Rh₆(CO)₁₆/Sn(II)–SiO₂, Rh₆(CO)₁₆/Al₂O₃, Rh^I(CO)₂/Al₂O₃, Rh₄(CO)₁₂/Al₂O₃), ¹⁴CO. CO .

     

Kinetic data on the interaction between triplet anthraquinone and 2-naphthol in oxygen

During the photooxidation of ethylbenzene in the presence of 2-naphthol a new interaction has been found between the sensitizer anthraquinone and the inhibitor. The quantum yield and the kinetics of this interaction have been investigated in the temperature interval of 28–98°C.

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-, , 28–98°C , .

     

Studies on the V?Ti?O system obtained by thermal decomposition of vanadyl and titanyl oxalates in argon atmosphere

The V–Ti–O system as a product of thermal decomposition of vanadyl and titanyl oxalates at 873 and 1173 K in argon atmosphere was studied by X-ray diffraction and infrared spectroscopy. The results obtained, the analysis and surface measurement data suggest that a V³⁺–V⁴⁺–Ti⁴⁺–O solid solution is formed. Spectroscopic measurements reveal the presence of a V=O bond in the system obtained at 873 K.

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V–Ti–O, 873 1173 - . , , V⁺³–V⁺⁴–O . V=O , 873 .

     

Mechanism of homogeneous catalysis of isotope exchange during interaction of dihydrogen with alkaline solutions

The mechanism of hydrogen isotope exchange in aqueous alkaline solutions (AAS) of D₂ has been studied using Interacting Bonds Method (IBM) data obtained for hydrogen interaction with the molecular ion H₃O ₂ ^– . Models for the activated and metastable intermediate complexes are described.

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- D₂ (). () H₃O ₂ ^– . .

     

Diffusion Conductivity of Electrode Processes under Conditions of Natural Convection

The diffusion conduction = di/d (where i is the current and is the overvoltage) in reversible system [Fe(CN)₆]^3–/4– is measured by the electrochemical impedance method under isothermal and nonisothermal conditions of natural convection. Platinum disk electrodes 3 mm and 20 m in diameter are used. For a macroelectrode under isothermal conditions, passes through a maximum near equilibrium and tends to zero at 0. Under nonisothermal conditions and for a microelectrode under isothermal conditions, achieves a maximum near equilibrium. These data correlate with the dependence of the diffusion layer thickness and quantitatively agree with theory.     

The thermal behaviour of solvates in the LiCI(MgCl2, AlCl3) water-1,4-dioxane systems

The thermal behaviour of the solvates and mixed solvates in the LiCl(MgCl₂, AlCl₃)-water-1,4-dioxane systems was investigated by means of DTA measurements of the melting behaviour and by quasi-isothermal and quasi-isobaric investigations of the thermal decomposition processes.The compounds melt incongruently. The positions of the melting points and the processes of thermal decomposition confirm the assumption that 1,4-dioxane is bonded in the first coordination sphere in the mixed solvate of lithium, but in the cases of magnesium and aluminium chloride it is bonded via hydrogen-bonds and not directly to the cations. Only for the lithium and magnesium compounds does the decomposition of the anhydrous solvates result in anhydrous chlorides.

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Zusammenfassung Das thermische Verhalten der Solvate und Mischsolvate der Systeme LiCl, (MgCl₂, AlCl₃)-Wasser-1,4 Dioxan wurde mit Hilfe von DTA-Messungen zum Schmelzverhalten, und quasi-isothermen und quasi-isobaren Untersuchungen zum Ablauf der thermischen Zersetzung Untersucht. Die Verbindungen schmelzen inkongruent. Die Lage der Schmelzpunkte und der Verlauf der thermischen Zersetzung bekräftigen die Vorstellungen, daß 1,4 Dioxan im Mischsolvat des Lithiums in der ersten Koordinationsphäre direkt am Kation, hingegen bei Magnesium und Aluminium über Wasserstoffbrücken gebunden ist. Die Zersetzung der wasserfreien Solvate führt nur im Fall der Lithium- und Magnesiumverbindungen zu den wasserfreien Chloriden.

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( , )--1,4- , - - — . . , 1,4- . , , . .

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The valuable assistance of Dr. Frahghänel in the separation of the solid phase by means of the hightemperature centrifuge is gratefully acknowledged.