Etats de valence 2Π et 2Δ des molécules isoélectroniques N 2 + , CN et CO+

Résumé On a calculé les courbes d'énergie potentielle de plusieurs états excités de N₂ ⁺, CN et CO⁺, en utilisant les fonctions d'onde LCAO MO SCF. Les valeurs calculées des constantes spectroscopiques et spin orbite sont en bon accord avec l'expérience. Notre calcul prévoit qu'on ne peut pas observer de transition ² -A ² dans CO⁺, et confirme que l'état supérieur de la transition récemment observée est un état ² et non ² .

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Potential energy curves have been calculated for several excited states of N₂ ⁺, CN and CO⁺, using LCAO MO SCF functions. Good agreement with experiment has been obtained for spectroscopic and spin orbit constants. From our calculation, ² -A ² transition in CO⁺ is predicted to be non observable, but we confirm that the upper state of the experimentally observed transition is ² _r and not ² .

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Zusammenfassung Für verschiedene angeregte Zustände der iso-elektronischen Moleküle N₂ ⁺, CN und CO⁺ wurden unter Verwendung von LCAO-MO-SCF-Funktionen die Potentialkurven berechnet. Für die spektroskopischen und die Spin-Bahn-Kopplungskonstanten wurde gute Übereinstimmung mit dem experimentellen Befund erreicht. Unseren Berechnungen nach sollte der ² -A ² -Übergang in CO⁺ nicht beobachtbar sein, während die Rechnung bestätigt, daß der obere Zustand des experimentell beobachteten Überganges ein ² _r -Zustand und nicht ein ² -Zustand ist.

     

Exact spin-pairing energies at the crossovers in octahedral d 4, d 5, d 6, and d 7 transition metal complexes

Exact spin-pairing energies are calculated by direct diagonalization of the relevant ligand field plus interelectronic repulsion matrices for the configurations d ⁴, d ⁵, d ⁶, and d ⁷ of octahedral transition metal ions. The results are presented in terms of /B as function of = C/B for the range of values =3.0 to 8.0. Comparison with the quantity resulting from a simplified approach in which configuration interaction is neglected or considered on an approximate basis only reveals significant differences. Useful estimates of spin-pairing energies are provided, in addition, on the basis of empirical magnetic and electronic spectral data.

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Zusammenfassung Exakte Spinpaarungsenergien für die Konfigurationen d ⁴, d ⁵, d ⁶ und d ⁷ oktaedrischer Übergangsmetallionen werden durch direkte Diagonalisierung der entsprechenden Matrizen des Ligandenfeldes sowie der Elektronenwechselwirkung berechnet. Die Ergebnisse für /B werden in Abhängigkeit von = C/B für den Wertebereich =3.0 bis 8.0 angegeben. Ein Vergleich mit der Größe , die bei einer vereinfachten Behandlung unter Vernachlässigung oder näherungsweiser Berücksichtigung der Konfigurationswechselwirkung erhalten wird, zeigt auffallende Unterschiede. Nützliche Abschätzungen der Spinpaarungsenergie werden außerdem unter Benutzung empirischer magnetischer und elektronenspektroskopischer Daten erhalten.

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Résumé Les énergies exactes de couplage de spin sont calculées par diagonalisation directe du champ de ligand correspondant en plus des matrices de répulsion électronique pour les configurations d ⁴, d ⁵, d ⁶ et d ⁷ des ions octaédriques des métaux de transition. Les résultats sont présentés en termes de /B en fonction de = C/B dan l'intervalle =3,0 à 8,0. On trouve des différences significatives par comparaison de avec les valeurs résultant d'une approche simplifiée sans interaction de configuration ou avec interaction de configuration approchée. De plus, des estimations des énergies de couplage de spin sont obtenues à partir de données empiriques magnétiques et spectrales.

     

A study of thermal decomposition of the solid-layered fluorocarbon,poly(carbon monofluoride)

Isothermal-thermogravimetric analyses were used to obtain kinetic data on the CF_x decomposition. Weight of samplevs. time curves were obtained for compounds having stoichiometries CF_0,61, CF_0.96, CF_1.08, and CF_1.12 for several different temperatures over the range 450–650° and in both a nitrogen atmosphere and in vacuum. A small percentage of fluorine in the atmosphere was shown to strongly inhibit thermal decomposition.These experimental results were fit to various theoretical models and it was found that a satisfactory fit was obtained by use of the Avrami equation, -In(1–)=(kt)ⁿ, where is the extent of reaction,k is an apparent rate constant, andn is an apparent reaction order. The valuen=2.0 was indicated which corresponds to planar growth of the decomposed phase.This information was combined with analytical data for the gaseous and solid products of decomposition to formulate a detailed mechanism.

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Zusammenfassung Isotherm-thermogravimetrische Analysen wurden durchgeführt um kinetische Daten über die Zersetzung von CF_x zu erhalten. Probengewicht-Zeit-Kurven wurden für Verbindungen mit stöchiometrischen Verhältnissen von CF_0.61, CF_0.96, CF_1.08 und CF_1.12 bei verschiedenen Temperaturen im Bereich von 450° bis 650°, in Stickstoff sowie im Vakuum aufgenommen. Ein geringer Prozentsatz an Fluor in der Atmosphäre wirkte stark inhibierend auf die thermische Zersetzung.Diese Versuchsergebnisse wurden verschiedenen theoretischen Modellen angepasst und es wurde gezeigt, dass mit Hilfe der Avrami-Gleichung -In (1–)=(kt)ⁿ eine befriedigende Anpassung möglich ist, wobei =Ausmaß der Reaktion, k=scheinbare Geschwindigkeitskonstante undn=scheinbare Reaktionsordnung ist. Der angedeutete Wertn=2.0 entspricht einer planaren Zunahme der zersetzten Phasen.Diese Information wurde mit analytischen Daten der gasförmungen und festen Zersetzungsprodukte kombiniert um einen Mechanismus in allen Einzelheiten zu formulieren.

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Résumé La TG isotherme a été utilisée pour obtenir des données cinétiques sur la décomposition de CF_x. Les courbes donnant le poids de l'échantillon en fonction du temps ont été energistrées à différentes températures, entre 450 et 650°, en atmosphère d'azote et sous vide, sur des composés de composition CF_0.61, CF_0.96 et CF_1.08. Un faible pourcentage de fluor dans l'atmosphèere s'est avéré inhiber considérablement la décomposition thermique.Ces résultats expérimentaux ont été confrontés à divers modèles mathématiques. On a trouvé un ajustement satisfaisant à l'aide de l'équation d'Avrami, -In (1–)=(kt)ⁿ, où es l'avancement de la réaction,k une constante de vitesse apparente etn un ordre de réaction apparent. La valeurn=2.0 correspond à une croissance dans le plan de la phase décomposée.Cette information a été combinée avec des données analytiques sur les produits de décomposition gazeux et solides, afin de formuler un mécanisme détaillé.

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- CF_x. — CF_0.61, CF_0.96, CF_1.08 F_1.12 450°–650°, , . . , -1(1–)= (kt)ⁿ, — , k — , n — . n=2, . , .

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Abstracted in part from the Ph. D. thesis of Peter Kamarchik, Jr. Rice University, Houston, Texas, May, 1976.

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This work was supported financially by the National Science Foundation, the U.S. Army Research Office (Durham), the National Aeronautics and Space Administration, and the Robert A. Welch Foundation. Liquid helium was provided under a grant from the Office of Naval Research.     

A calculation of the spin-orbit splitting of the X 2Π state of NO

Using Brion, Moser and Yamazaki's SCF LCAO MO the spin orbit splitting of the X ² state of NO has been calculated using various potentials. Experimentally W (² _3/2) –W (² _1/2) is known to be 122 cm^–1. Using an unscreened nuclear field we find a value of 328 cm^–1. Inclusion of screening due to electronic repulsions reduces this value to 283 cm^–1. Agreement with the experimental value may be obtained by reducing the orbital exponents in the 2 molecular orbital by 30% over the value given by Slater's rules.

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Zusammenfassung Die Spin-Bahn-Aufspaltung des X ² -Zustandes von NO wurde mit verschiedenen Potentialen unter Verwendung der SCF LCAO MOs von Brion, Moser und Yamazaki berechnet. Der experimentelle Wert für W (² _3/2) –W (² _1/2) beträgt 122 cm^–1. Die Rechnung mittels eines reinen Kernfeldes liefert den Wert 328 cm^–1 und unter Einschluß der Abschirmung durch die Elektronen 283 cm^–1. Übereinstimmung mit dem experimentellen Wert läßt sich erzielen, wenn man den Exponenten des 2-Zustandes 30% kleiner als nach den Slater Regeln macht.

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Résumé Avec les orbitals moléculaires SCF LCAO de Brion, Moses et Yamazaki, nous avons calculé le dédoublement spin-orbitale de l'état X ² de NO. La valeur expérimentale W (² _3/2) –W (² _1/2) est 122 cm^–1. Dans un champ nucléaire «sans écran» on trouve 328 cm^–1. L'inclu-sion de l'effet d'écran dû aux répulsions interélectroniques réduit cette valeur à 283 cm^–1. La valeur expérimentale s'obtient, si l'on réduit de 30% les exposants d'après Slater dans l'orbi-tale moléculaire 2.

     

Influence des charges nucléaires effectives σ et π sur les calculs LCAO-MO-SCF-π

Application of the LCAO-MO-SCF- method to conjugated hydrocarbons leads with the effective nuclear Slater's charges, Z_eff = Z_eff = 3.25 to electronic transitions higher than experimental ones by about 50%.We show that in the case of all trans linear polyenes and fulvene, one may obtain satisfying results by the same method, without any reference to experience, by taking Z_eff = 3.0 Z_eff = 3.55. There the effective nuclear charges are near of these of the valence state of carbon V ₄1s²t₁t₂t₃2pt_z:Z_eff = 2.971 Z_eff = 3.382 [10].     

Microcalorimetric studies of slag alkaline binders

Calorimetric measurements were carried out on the hydration of slag activated by sodium hydroxide, sodium carbonate and water glass at 60 °C. The results can be correlated with the mechanical properties of the cured cements. The studies confirmed the applicability of calorimetry in the testing of activators used in concrete technology.

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Zusammenfassung Die Hydratation von Schlacke bei 60 °C und Aktivierung mit Natriumhydroxid, Natriumcarbonat oder Wasserglas wurde durch kalorimetrische Messungen verfolgt. Die Ergebnisse lassen sich mit den mechanischen Eigenschaften der erhärteten Zemente korrelieren. Die Untersuchungen bestätigen die Brauchbarkeit der kalorimetrischen Methode zum Testen von Aktivatoren in der Betontechnologie.

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, 60° , . . , - .

     

Reduction by hydrogen transfer processes, II. Reduction of substituted derivatives of benzaldehyde

In the present paper, date are reported on transfer hydrogenation of aromatic aldehydes with commercial and synthetic Pd catalysts, based on SiO₂–AlPO₄ (2080 mass). Cyclohexenes and ,-unsaturated alcohols have been tested as hydrogen donors. The reaction products obtained upon reduction of benzaldehyde were benzyl alcohol and toluene (hydrogenation) and benzene and formaldehyde (hydrogenolysis), while methyl, ethoxycarbonyl and hydroxyl groups also present are not affected by the reaction. The selectivity towards each product depends on both the hydrogen donor and the catalyst used. When electron-donor substituents exist on the substrate, a decrease of the reaction rate towards the hydrogenolysis products is observed.

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, SiO₂–AlPO₄ (20–80 ). ,- . () (), , -, , . , . - , .

     

Kinetics of product formation in the initial phase of oxidative degradation of pentaerythritol tetraacetate

The kinetics of formation of acetic acid, methanol, methyl acetate and hydroperoxide in the autoxidation (463–503 K) and initiated oxidation (413 K) of pentaerythritol tetraacetate has been studied. A scheme for product formation is proposed.

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, , (463–503 ) (413 ) . .

     

Optimal double-configuration study of the lowest excited Π states of H2

Various levels of approximation (Hartree-Fock, configuration interaction and double-configuration Hartree-Fock method) are compared for extensive and limited exponent optimization of the atomic orbitals of the wavefunctions. The potential energy curves for the lowest-lying ¹ _u, ³ _u, ¹ _g, ³ _g states of the hydrogen molecule are presented. The shapes of the curves on the highest level of approximation, i.e. with the optimal double-configuration wavefunction, are basically in agreement with previous, more sophisticated and time-consuming work. The influence of the various approximations is also studied for several one-electron properties: charge distribution of the wavefunction along and perpendicular to the molecular axis, quadrupole moment and core attraction energy distribution. Differences arise to the work of Zemke et al. [1], who used a limited exponent optimization with a larger basis set, in the _g states where the orbitals are very diffuse. The differences concern magnitude and location of minima and maxima of potential curves, as well as considerable changes in one-electron properties which depend strongly on the spatial distribution of the orbitals.

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Zusammenfassung Verschiedene Approximationsstufen (Hartree-Fock, Konfigurationenwechselwirkung und Doppelkonfigurationen-Hartree-Fock-Methode) werden für ausgedehnte und begrenzte Exponentenoptimisierung von Atomorbitalen der Wellenfunktionen verglichen. Die Potentialkurven für die niedrigsten ¹ _u, ³ _u, ¹ _g, ³ _g Zustände des Wasserstoffmoleküls werden angegeben. Die Form der Kurven im Rahmen der besten Näherung, d. h. mit Doppelkonfiguration, stimmen im wesentlichen mit früheren aufwendigeren Rechnungen überein. Der Einfluß der verschiedenen Approximationen wird auch an einigen Einelektroneneigenschaften studiert: Ladungsverteilung der Wellenfunktion längs und senkrecht zur Molekülachse, Quadrupolmoment und Verteilung der Rumpfenergie. Unterschiede erscheinen zur Arbeit von Zemke et al. [1], die einen größeren Basissatz mit begrenzter Optimisierung verwandten, bei den _g Zuständen, wo die -Orbitale sehr diffus sind. Die Unterschiede betreffen Größe und Lage der Minima und Maxima der Potentialkurven sowie beträchtliche Änderungen in solchen Einelektroneneigenschaften, die stark von der räumlichen Verteilung der Orbitale abhängen.

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Résumé Comparaison de différents niveaux d'approximation (Hartree-Fock, interaction de configuration et Hartree-Fock à deux configurations) pour des optimisations étendues et limitées des orbitales atomiques de base. Calcul des courbes d'énergie potentielle pour les plus bas états ¹ _u, ³ _u, ¹ _g, ³ _g de la molécule d'hydrogène. Pour la fonction d'onde la plus raffinée: H.F. à deux configurations, la forme des courbes est en accord avec les résultats obtenus dans des travaux précédents plus complexes et plus coûteux. On étudie aussi l'influence des diverses approximations sur plusieurs propriétés monoélectroniques: distribution de charge le long de l'axe moléculaire et perpendiculairement à celui-ci, moment quadrupolaire et distribution de l'énergie d'attraction de coeur. On trouve des différences avec le travail de Zemke et al. (1), qui utilisent une plus grande base partiellement optimisée, pour les états _g où les orbitales sont très diffuses. Les différences concernent la grandeur et la position des extrema des courbes de potentiel, ainsi que des variations importantes des propriétés monoélectroniques qui dépendent fortement de la distribution spatiale des orbitales.

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On leave to: Institut für Theoretische Chemie, Universität Stuttgart.

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On leave to: Office of Computing Activities, National Science Foundation, Washington, D.C.     

Effect of water on hydrogen desorption from the surface of Rh/C catalysts

An increase in the number of titration cycles results in a considerable decrease in H_T and O_T values, which in turn, brings about a decrease in the amount of desorbed hydrogen. This shows that water, being a product of titration reaction, is adsorbed on the oxidized surface of rhodium and represents a kinetic-diffusive barrier for hydrogen titration.

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, H_T O_T, , , . , , , , , - .

     

Kinetics of oxidation of vanadium(III) by hydroxylamine in acid medium

The kinetics of oxidation of vanadium(III) by hydroxylamine have been investigated at high acidities in the temperature range 25–30 °C. Rates decreased with increasing acidity of the medium. Both NH₂OH and NH₃OH⁺ are capable of oxidizing V(III) in parallel reactions, the order being unity each in oxidant and reductant.

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(III) 25–30 °C. . NH₂OH NH₃OH⁺ V(III) , , .

     

Natural spin orbital analysis of diatomic molecular wave functions in terms of generalized diatomic orbitals

Starting from the demi-H ₂ ⁺ -model for Rydberg states, ab initio calculations of the energy and the wave function for some excited states of H₂ have been carried out with the help of diatomic orbitals. The potential curves and wave functions for the following states: 2¹ _g< ^/+ , 3¹ _g< ^/+ , 1³ _g< ^/+ , 2³ _g< ^/+ , 1¹ _u< ^/+ , 2¹ _u< ^/+ , 1³ _u< ^/+ , 2³ _u< ^/+ , 3³ _u< ^/+ , 1¹ _g , 1³ _g , 1¹ _u , and 1³ _u , have been calculated by a complete CI (configuration interaction) calculation in the sense that all configurations of the state symmetry have been used which can be formed from a given basis set. From the wave functions thus obtained the natural spin orbitals are calculated subsequently to the variational calculations. The dependence of the occupation numbers of the natural spin orbitals on internuclear distance is interpreted according to the model and is used for the explanation of the special features like double minima and maxima which occur in the potential curves of H₂. For the curves of the occupation numbers a non-crossing rule in analogy to that for potential curves is valid. The potential curves for the states 1³ _g and 1³ _u have been improved by the use of linear combinations of diatomic orbitals with different nuclear charges, which allow a flexible transition to linear combinations of atomic orbitals.Dedicated to Professor Iwan N. Stranski on the occasion of his 80th birthday.     

Formation of uranium mixed oxides from thermal decomposition of uranyl propionate complexes

Four new derivatives of uranium with propionic acid, ammonium and various divalent cations have been synthesized, whose general formula corresponds to NH₄M[UO₂(C₂H₅COO)₃]₃nH₂O, (M=Mn⁺⁺, Co⁺⁺, Ni⁺⁺ and Zn⁺⁺). These compounds have been studied by X-ray diffraction, differential thermal and thermogravimetric analysis, so as to identify the different solid phases isolated during heat treatment. The existence of a new double oxide of uranium and cobalt with fluorite type structure has also been shown.

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Zusammenfassung Vier neue Derivate des Urans mit Propionsäure, Ammonium und verschiedenen zweiwertigen Kationen wurden synthetisiert. Die allgemeine Formel ist: NH₄M[UO₂(C₂H₅COO)₃]₃nH₂O, (M=Mn⁺⁺, Co⁺⁺, Ni⁺⁺ und Zn⁺⁺). Diese Verbindungen wurden durch Röntgendiffraktion, Differentialthermoanalyse und thermogravimetrische Analyse untersucht um die während der Wärmebehandlung isolierten verschiedenen Festphasen zu identifizieren. Die Existenz eines neuen Doppeloxides von Uran und Cobalt mit einer Struktur von Fluorit-Typ wurde ebenfalls nachgewiesen.

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Résumé Quatre nouveaux dérivés de l'uranium avec l'acide propionique, l'ammonium et divers cations bivalents ont été synthétisés. Leur formule générale correspond à NH₄M[UO₂(C₂H₅COO)₃]₃ nH₂O, (M=Mn⁺⁺, Co⁺⁺, Ni⁺⁺ et Zn⁺⁺). Ces composés ont été examinés par diffraction des rayons X ainsi que par analyses thermique et thermogravimétrique afin d'identifier les différentes phases solides isolées pendant leur traitement thermique. L'existence d'un nouvel oxyde double d'uranium et de cobalt de structure type fluorine est également démontrée.

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, NH₄M[UO₂(C₂H₅COO)₃]₃ · n₂, M=Mn⁺⁺, Co⁺⁺, Ni⁺⁺ Zn⁺⁺. - , , , . .

     

Kinetic conversion of complex hydrocarbon mixtures in reforming on platinum/alumina catalysts

General forms of the kinetic equations for the conversion of various hydrocarbons in reforming of multicomponent gasoline fractions on platinum/alumina catalysts have been confirmed experimentally by using a gradientless method.

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Calorimetry for thermokinetic determinations

The possibilities of using direct calorimetric measurements for the determination of kinetic parameters of processes are discussed in terms of the choice of an appropriate method of reproduction of the course of changes in the heat power generated in time, i.e. thermokinetics. Such methods are presented and it is concluded that many of these methods permit reproduction of the thermokinetics in the same way as if the experimental thermal curve were obtained in a calorimetric system characterized by a time constant 100–200 times as large as that for the thermal inertia of this calorimetric system.

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Zusammenfassung Die Möglichkeiten zur Benutzung direkter kalorimetrischer Messungen zur Bestimmung kinetischer Parameter von Prozessen werden hinsichtlich der Wahl geeigneter Methoden zur Reproduzierung des Verlaufs der Änderungen der Wärmekraft mit der Zeit, d.h. zur Reproduzierung der Thermokinetik diskutiert. Solche Methoden werden angeführt und es wird die Schlussfolgerung gezogen, dass viele dieser Methoden die Reproduzierung der Thermokinetik auf gleiche Weise wie in den Fällen erlauben, in denen die thermische Kurve mit einem kalorimetrischen System erhalten wird, dessen Zeitkonstante um 100–200mal grösser als die des diskutierten Systems ist.

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. . . , , , 100–200 .

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Presented at the 2nd Czechoslovak Conference on Calorimetry, Liblice, Czechoslovakia, 1982.     

Determination of gaseous nitrogen in gas mixtures using low pressure microwave induced plasma emission spectrometry

A microwave induced plasma emission spectrometer operating at low energy (30 W) and low plasma gas pressure (2.510^-2 Pa) has been used for the quantitative measurement of molecular nitrogen in natural gases. The samples have been introduced into the plasma using a counterflow principle to produce emission spectra of diatomic molecular fragments in low excitation states (advantage: minimized interferences). The N₂ concentration has been determined by measuring the intensity of the N₂-line at 337.13 nm (C³_u-B³_g-system; (0,0)vibrational transition) and of the NH-line at 336.03 nm (A³_i-X^2--system; (0,0)-vibrational transition). A linear correlation between concentration and signal intensities has been obtained in the range of 0.00% to 14.24% (v/v). The method possesses a detection limit of 0.01 ppm (v/v) for the determination of N₂, and a reproducibility of 1.33% (RSD).     

Studies of the reactions of Br(2P3/2) and Br(2P1/2) with SiH4

Photobromination of SiH₄ under uv-irradiation at various wavelengths has been studied. Rate constants for the elementary reactions Br(²P_3/2)+SiH₄HBr+SiH₃ (k=3.2×10^–11 exp(–21.8±2.5)/RT, cm³/s) and Br^* (²P_1/2)+SiH₄HBr+SiH₃ (k^*=(3±1)×10^–13 cm³/s) have been determined in the temperature range from 300 to 415 K.

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- . Br(²P_3/2)+SiH₄HBr+SiH₃, k=3,2×10^–11 exp (–21,8±2,5)/RT ³/ Br^*(²P_1/2)+SiH₄HBr+SiH₃, k^*=(3±1)×10^{–13 3}/ 300–415 K.

     

Effect of thick fixed-charge layers on electrostatic interaction — a theoretical approach

The electrostatic interaction pressure of charged surface layers is considered qualitatively and quantitatively. In the case of mutual penetration of the surface layers in addition to Maxwell stress and osmotic resp. hydrostatic pressure an isotropic stress on the fixed charges carrying molecules of the surface layers has to be taken into account. The derivation of the pressure-distance equations is given starting from both thermodynamic/electrostatic and hydrostatic/electrostatic principles. A possible biological significance of the additional stress is discussed emphasizing its role in modifying the structure of surface layer molecules.List of symbols e ₀ elementary charge - k Boltzmann constant - n _i concentration of theith ionic species in the bulk solution - P hydrostatic pressure - P hydrostatic pressure in the bulk volume (× ) - P ^h integration constant, independent on ×:P ^h =P(h) - T absolute temperature - Z _i electrovalence of theith ionic species - thickness of the surface layer - , ₀ relative and absolute permittivities - II(×) osmotic pressure at position × - II osmotic pressure in the bulk solution (× ) - osmotic pressure in the symmetry plane of interacting identical surface layers (electric field strength equals zero) - integration constant, independent on ×: - _e ^h electrostatic component of the disjoining pressure _e ^h = _e (h) - (×) mobile charge density profile (cations and anions of the electrolyte) - (×) fixed charge density profile - ^t(x) total charge density profile ( ^t = +) - ¹(x) fixed charge density profile of one of the two surface layers ( ¹(×) 0 for 0×) - (×) electric potential profile     

Spectroscopic study of organosilicon derivatives of thiophene

It is shown that the chemical shifts of hydrogen atoms in the 3 position of the thiophene ring in the PMR spectra of 2-substituted thiophenes are linearly associated with the Hammett _n substituent constants. On the basis of this, it was concluded that silyl substituents in 2-silylthiophenes have electron-acceptor character. It was established that the degree of d–p conjugation between the d orbitals of the silicon atom and the p electrons of the thiophene ring depends on the nature of the other three substituents attached to the silicon atom. The data from the IR spectra of organosilylthiophenes that contain a Si-H bond also attest to the presence of d–p conjugation in these compounds.See [1] for communication I.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 911–915, July, 1972.     

Pulse photolysis of ditertbutyl peroxide in benzene

The method of pulse photolysis has been used to determine termination rate constants of primary peroxy radicals in benzene at 295 K. Radicals CH₃O ₂ ^. have been found to decay with the rate constant 2k₆=3.7×10⁸ M^–1 s^–1 and radicals (CH₃)₃ COOC(CH₃)CH₂O ₂ ^. with 2k₈=1.2×10⁸ M^–1 s^–1, the rate constant of cross-recombination for both radicals being 2.4×10⁸ M^–1 s^–1.

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295 K: CH₃O ₂ ^. 3,7·10⁸ (M·c)^–1, (CH₃)₃COOC(CH₃)₂CH₂O ₂ ^. =qt 1,2·10⁸ (M·c)^–1, 2,4·10⁸ (M·c)^–1.