2-Dimensional atomic arrangements of Te on Pt(111) whose coverage is higher than 0.25+

Presented is an in-situ electrochemical STM study on the structural evolution of Te layer on Pt(111) whose coverage is higher than 0.25. The irreversibly adsorbed oxygenated Te layer was reduced to a rectangular (2×3) adlayer of elemental Te (_Te=0.25). As additional Te was deposited underpotentially onto the Te-covered Pt(111) surface in a TeO₂-saturated 0.05 M H₂SO₄ solution, the surface structure of Te evolved from the rectangular (2×3) (_Te=0.25) to a rectangular c(2×3) (_Te=0.50) via a rectangular c(3×3) (_Te=0.33). The adsorbed elemental Te was mobile enough to compress the superlattice structure to denser ones, so that the resulting Te layer became electrochemically inactive in the potential range below 0.55 V.Dedicated to Professor György Horányi, Hungary, on the occasion of his 70th birthday.     

Kinetics of Methyl Iodide Tribosorption on the Solid-Phase Salt KI

It was found that the tribosorption of methyl iodide from the gas phase of a closed reactor onto a matrix of KI is described by the rate equation for a reversible first-order reaction v _g – v _{, g} = mv _ts ^* exp(–_td D _sp), where v _g and v _{, g} are, respectively, the current and equilibrium amounts of methyl iodide in the gas phase; v _ts ^* is the equilibrium amount of methyl iodide tribosorbed per gram of salt; m is the mass of potassium iodide; _td is a constant, which characterizes the efficiency of tribodesorption (_td = 0.011 ± 0.005 g/J); and D _sp is the specific dose of mechanical energy absorbed by the KI powder. The value of v _ts ^* monotonically increased with increasing equilibrium partial pressure of methyl iodide and reached a maximum value of 25 mol/g. The lower limit of the constant _td, which characterizes the efficiency of tribosorption, was estimated at 0.1 g/J.     

Abhängigkeit der freien Enthalpie-Änderung von der Netzebenenzahl bei Bildung von Mikroparakristallen

Zusammenfassung Das anhand vieler sorgfältiger Reflexprofilanalysen abgeleitete ^*-Gesetz läßt sich auch thermodynamisch verstehen, wenn man die Fragilität der Valenzwinkel durch ein entsprechendes MuldenpotentialU einführt. Dies liefert in dem Ausdruck für die ÄnderungG der freien Enthalpie bei Teilchenbildung neben den bekannten, von der Teilchengröße unabhängigen zwei Termen für freie Oberflächenenergie und freie VolümenthalpieG _v einen dritten, mit der ZahlN der Netzebenen wachsenden Summanden. Diese sog. Volum-StörenthalpieA ₀g² N ist also auch abhängig von der relativen statistischen Varianzg der Abständed von Gitterbausteinen benachbarter Netzebenen. Durch Einführung des ^*-Gesetzes ergibt sich die Beziehung ¦G_v¦ /A ₀ K()=0.06 mitK()=356 g² /¯ d¦G_v¦=1–1–. Im Grenzfall=1 ist die kritische Keimgröße gleich der mittleren statistischen Größe der Mikroparakristalle. Dieser Fall wird für Metallschmelzen diskutiert.=0 stellt den anderen Grenzfall der Kristallbildung dar.Herrn Prof. Dr. K. Kobayashi zum 70. Geburtstag zugedacht.     

A Simplified version of the Pariser-Parr-Pople treatment of π-electron systems

The semi-empirical configuration interaction treatment due to Pariser and Parr and to Pople has been modified by reducing the set of electronic interaction integrals to ₁₁ and ₁₂ and by limiting the number of configurations to 10. Hückel MOs are used as basis functions. The dependence of the resonance integral _v on the interatomic distance R _v is simulated by making _v a quadratic function of the Hückel bond orders P _v .

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Zusammenfassung Eine Modifikation des semiempirischen CI-Verfahrens von Pariser, Parr und Pople wurde zur Behandlung von -Systemen herangezogen. Als Vereinfachung wurde der Grad der CI-Matrix auf zehn beschränkt und von den Elektronenwechselwirkungsintegralen nur ₁₁ und ₁₂ berücksichtigt. Hückel-MOs wurden als Basisfunktionen verwendet. Die Abhängigkeit des Resonanzintegrals _v vom interatomaren Abstand R _v wurde durch den Ansatz von _v als quadratische Funktion der Hückel-Bindungsordnung P _v angenähert.

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Résumé Le procédé semi-empirique de l'interaction de configuration selon Pariser, Parr et Pople a été modifié en réduisant l'ensemble des intégrales d'interaction électronique à ₁₁ et limitant le nombre des configurations à 10. Les fonctions de base sont des orbitales moléculaires selon Hueckel. La dépendance entre l'intégrale de résonance _v et la distance interatomique R _v est simulée en posant que _v est une fonction quadratique des ordres de liaisons P _v selon Hückel.

     

Critical behavior and interfacial tension of mixtures of propylene glycol and ethylene glycol oligomers

This investigation presents an analysis of the critical behavior of mixtures of oligomers of propylene glycol, PG₁₇, and ethylene glycol, EG_n, withn=3, 4, 5, 6.4, 8.7, 12.1 and 22.1. The critical coordinates, _c andT _c were determined from the phase diagrams. The critical compositions compare very well with the Huggins-Flory predictions. The interaction parameter _n is around one for EG₃, EG₄ and EG₅ and it increases up to two for the higher oligomers. The break in the interaction parameter also corresponds to a minimum in the critical temperature. The phase diagrams and the interfacial tension were used to get the critical exponents and , respectively. The data were analysed with two approaches. First, from the temperature dependence of the length of the tie-lines and of the interfacial tension up to the upper critical solution temperature, UCST. Second, with the data at 30°C using the critical temperature of the systems as the variable. The first method led to =0.39±0.05 in good agreement with the result of the second method, =0.37±0.04. The exponents for the interfacial tension, , determined with the first method for PG₁₇ with EG_6.4, EG_8.7 and EG_12.1 are =1.66±0.11, 1.46±0.25 and 1.73±0.18, respectively. The second method led to =1.17±0.14. The critical exponents are compared to mean field and ising-3D predictions.     

On theC v toC p conversion for solid linear macromolecules

TheC _v toC _p conversion for solid linear macromolecules via the Nernst-Lindemann equationC _p -C _v =A ₀,C _p ² T/T_m is discussed on hand of data for 10 crystals and seven glasses. An average value ofA ₀=(5.11±2.41) · 10^–3 mol K J^–1 was calculated if the mole is assumed to refer to heavy atoms only. ThisA ₀ is numerically equal to the original Nernst—Lindemann constant.

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Zusammenfassung An Hand von sich auf 10 Kristalle und 7 Gläser beziehenden Daten wird die Umrechnung vonC _v -inC _p -Werte für feste lineare Makromoleküle mittels der Nernst-Lindemann-GleichungC _p -C _v =A ₀ C _p ² T/T _m diskutiert. Ein Durchschnittswert vonA ₀=(5.11±2.41) · 10^–3 mol K J^–1 wurde unter der Annahme berechnet, daß sich das Mol nur auf schwere Atome bezieht. DieserA ₀-Wert ist numerisch gleich der ursprünglichen Nerns-Lindemann-Konstanten.

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10 , - C _v C _p , —C _p –C _v = _{0 p} ² / . , , ₀ (5.11±2.41) · 10^–3 · ^–1. ₀ — .

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Support by the National Science Foundation, Polymers Program (Grant No. DMR 83-17097) is gratefully acknowledged.     

Kinetics of Detonation Initiation in the Supersonic Flow of the H2 + O2 (Air) Mixture in O2 Molecule Excitation by Resonance Laser Radiation

The possibility of initiating detonation in the supersonic flow of the H₂ + O₂ (air) mixture behind the front of the inclined shock wave by O₂ molecule excitation to the O₂(a ¹_g) and O₂(b ¹·⁺ _g) states by laser radiation with a wavelength _I = 1.268 m and 762 nm is considered. Resonance laser radiation intensifies chain combustion due to the formation of new pathways for generating active atoms O^· and H^· and radicals OH and has a substantially nonthermal character. Even at low (3 kJ/cm²) energies of radiation with _I = 762 nm applied to the gas, detonation combustion can occur even at a distance of 1 m from the front at the gas temperature as high as 600 K.     

NMR Spectral Assignment of Per-substituted Key-Intermediates of β-Cyclodextrin and Implications in the Structures of the Derivatives

The compounds, 6-per-O-(t-butyldimethylsilyl)--cyclodextrin(1), 2,3-per-O-benzyl-6-per-O-(t-butyldimethylsilyl)--cyclodextrin(2), 2,3-per-O-benzyl--cyclodextrin (3),2,3,6-per-O-benzyl--cyclodextrin (4),2,3,6-per-O-benzoyl--cyclodextrin (5), are used as keyintermediates in the synthesis of selectively substituted -CD derivatives. Simple and assignable ¹H and ¹³C NMR spectra (chemical shifts and coupling constants) were obtained for compounds1–4 indicating C₇ symmetry, ⁴C₁ glucose conformation and major arrangement of H6, H6' atoms at the primary side. The derivative 5, however, gave very broad peaksat room temperature. The peaks could partially be assigned at 270 K, but the broadening was still present at 220 K. This implies that there exist several conformers of similar energyand C₁ symmetry that continuously interchange, since there is not a single type of stabilizing interaction thatpredominates. We attributed this phenomenon to the presence of the carbonyl group, which probablydisfavors - stacking and induces random arrangements of the aromatic rings.     

Darstellung,Thermisches Verhalten und Gitterparameter von Erbiumfluorooxalattetrahydrat ErFC2O4 · 4H2O

Zusammenfassung Erbiumfluorhydrat ErF₃ · 1.1 H₂O bildet in Oxalsäurelösungen Erbiumfluorooxalattetrahydrat ErFC₂O₄ · 4 H₂O. Das ErFC₂O₄ · 4 H₂O ist grobkristallin, unlöslich in verdünnten Säuren und Laugen und löslich in konzentrierter Schwefelsäure. Beim thermogravimetrischen Abbau bildet es die Verbindungen ErFC₂O₄ · 2 H₂O, ErFC₂O₄ · · H₂O, ErFC₂O₄, ErOF und ErO_1.5. Die Kristallstruktur des ErFC₂O₄ · 4 H₂O ist orthorhombisch mit den Gitterkonstantena=11.217±0.007 Å,b-13.046±0.008 Å,c=9.191±0.005 Å undZ=6.

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Erbium fluoride hydrate ErF₃ · 1.1 H₂O forms in solutions of oxalic acid erbium fluorooxalate tetrahydrate ErFC₂O₄ · 4 H₂O. The ErFC₂O₄ · 4 H₂O is coarse-crystalline, insoluble in diluted acids and bases and soluble in concentrated sulphuric acid. During thermal decomposition ErFC₂O₄ · 2 H₂O, ErFC₂O₄ · H₂O, ErFC₂O₄, ErOF and ErO_1.5 are formed. The crystal structure of ErFC₂O₄ · 4H₂O is orthorhombic, with lattice constantsa=11.217±0.007 Å,b=13.046±0.008, Å c=9.191±±0.005Å andZ=6.

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Résumé Le fluorure d'erbium hydraté (ErF₃ · 1.1 H₂O) forme dans l'acide oxalique fluorooxalate d'erbium tétrahydraté (ErFC₂O₄ · 4 H₂O), un précipité consistant à gros cristaux insoluble dans les acides et bases dilués, mais soluble dans l'acide sulfurique concentré. Au cours de sa décomposition thermique on obtient ErFC₂O₄ · 2 H₂O; ErFC₂O₄ · H₂O; ErFC₂O₄, ErOF et ErO_1.5. ErFC₂O₄ · 4 H₂O a une structure cristalline ortorhombique avec les paramètres suivants:a=11.217±0.007 Å,b=13.046±0.008 Å,c-9.191 ±0.005 Å,Z=6.

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ErF₃ · 1.1 H₂O, ErFC₂O₄ · 4H₂O. ErFC₂O₄ · 4H₂O, - , , . : ErFC₂O₄ · 2H₂O. ErFC₂O₄ · H₂O, ErFC₂O₄, ErOF ErO_1·5. ErFC₂O₄ · 4 H₂O a=11,217±0,007 Å,b=13,046±0,008 Å,c=9,191± 0,005 Å Z=6.

     

Bounds for reactivity indices

Lower and upper bounds are derived for bond number, localization energy and atom self-polarizability of alternant hydrocarbons. It is proved that in acyclic polyenes the maximal bond number is 1, 2 and 3, respectively for primary, secondary and tertiary carbon atoms.     

On subspectral acyclic molecular graphs

Based on the contraction and expansion of graphs, the subspectrality of acyclic molecular graphs is treated in a systematic way. The graphs containing eigenvalues 0, t 1 and ± 2 are discussed in detail, with emphasis on how to detect and construct the concealed species which can neither be recognized by symmetry considerations nor by the Heilbronner procedure. As a consequence, graphs and their counts have been given for species with numbers of vertices less than 16.Also known as Yuan-sun Kiang.     

Possibilities of applying the piloyan method of determination of decomposition activation energies in the differential thermal analysis of polynitroaromatic compounds and their derivatives

Piloyan activation energiesE as well as initals of exothermT _D of sevenN-monoalkyl and fiveN,N-dialkyl-2,4-dinitroanilines were determined. Relationships were found between the T_D values and R_f factors as well asE values and those R_M functions and also theET _D ^–1 term and R_M functions.

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Zusammenfassung Die AktivierungsenergienE nach Piloyan sowie die Anfangswerte der ExothermenT _D wurden für siebenN-Monoalkyl- und fünfN,N-Dialkyl-2,4-dinitroaniline bestimmt. Die Zusammenhänge zwischen denT _D-Werten und den papierchromatographischenR _f-Faktoren der gemessenen Dinitroaniline wurden abgeleitet und erörtert. Desgleichen wurden auch die Zusammenhänge zwischen denE-Werten und denR _M-Funktionen der Papierchromatographie abgeleitet und erörtert. Auch zwischen dem AusdruckE ·T _D ^–1 und denR _M-Funktionen wurde ein Zusammenhang gefunden.

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Résumé On a déterminé les températures initialesT _D de l'effet exothermique ainsi que les énergies d'activationE d'après la méthode de Piloyan, de sept N-mono alcoyl et cinqN,N-dialcoyl-2, 4-dinitroanilines. Une corrélation entre les valeursT _D et les facteursR _f de la Chromatographie sur papier des dinitroanilines étudiées a été trouvée et discutée, ainsi qu'entre les valeursE et les fonctionsR _M de la Chromatographie sur papier. Une relation entre le termeE ·T _D ^–1 et les fonctionsR _M a également été trouvée.

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E T _D N- N,N- -2,4- . _D R _f , E R _M. E. _D ^–1 R _M.

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The authors would like to thank Mrs. Anna Collàkovà for careful DTA measurements, and Dr. Ladislav Smolka for help in treatment of the measured results with the Wang 600 computer.     

Molecular structure of aniline in the gaseous phase: A concerted study by electron diffraction and ab initio molecular orbital calculations

The molecular structure of free aniline has been investigated by gas-phase electron diffraction and ab initio MO calculations at the HF and MP2 levels of theory, using the 6-31G^*(6D) basis set. Least-squares refinement of a model withC _s symmetry, with constraints from MP2 calculations, has led to an accurate determination of the C-C-C angle at theipso position of the benzene ring, =119.0±0.2 (where the uncertainty represents total error). This parameter provides information on the extent of the interaction between the nitrogen lone pair and the system of the benzene ring, and could not be determined accurately by microwave spectroscopy. The angles at theortho, meta, andpara positions of the ring are 120.3±0.1, 120.7±0.1, and 119.0±0.3, respectively. Important bond distances are r _g(C-C)=1.398±0.003 å andr _g(C-N) =1.407±0.003 å. The effective dihedral angle between the H-N-H plane and the ring plane, averaged over the large-amplitude inversion motion of the amino group, is ¦¦=44±4. The equilibrium dihedral angle is calculated to be 41.8 at the HF level and 43.6 at the MP2 level, in agreement with far-infrared spectroscopic information. The MO calculations predict that the differencer(C_ortho-C_meta) -r(C_ipso-C_ortho) is 0.008–0.009 å. They also indicate that the nitrogen atom is displaced from the ring plane, on the side opposite to the amino hydrogens. The displacement is 0.049 å at the HF level and 0.072 å at the MP2 level. The two calculations, however, yield very different patterns for the minute deviations from planarity of the ring carbons.     

Corrected values of osmotic and activity coefficients of aqueous NaTcO4 and HTcO4 at 25°C

Published isopiestic molalities for aqueous NaTcO₄ and HTcO₄ solutions at 25°C have been reexamined. Our calculations indicate that published smoothed values of the osmotic coefficients and mean molal activity coefficients _± of NaTcO₄ are substantially in error, by up to 100% for and 300% for _±. Published smoothed values of and _± for HTcO₄ solutions are in somewhat better agreement with the input data, but the reported are sometimes higher and sometimes lower than experimental values, by up to 6%. Consequently, we have reanalyzed isopiestic data for these two systems, and find that errors arose in representing the data mathematically. We report parameters for an extended form of the specific ion interaction equations and for Pitzer's equations, and corrected values of and _± are tabulated for aqueous NaTcO₄ and HTcO₄.     

Komplexbildung im System Ni2+—o-Methylbenzamidoxim

Zusammenfassung Die Komplexe des Ni²⁺ mit o-Methylbenzamidoxim wurden in neutraler und in alkalischer Lösung spektrophotometrisch untersucht. Die Bildungskonstanten sindK ₁=40 für 11 undK ₂=1,7·10² für 12 in neutraler Lösung und ₁ = =(3,92 ±0,2) · 10⁴für 11 und lgK = lg ₁ + lg ₂ = 3,45 ± ±0,15 für 12 bei 25° und =1 in alkalischer Lösung.

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Complex formation in the systemeNi ²⁺—o-methylbenzamide oxime

The complexes of Ni²⁺ with o-methylbenzamide oxime were investigated spectrophotometrically in neutral as well as in alkaline solution. The formation constants areK ₁=40 for 11 andK ₂=1.7·10² for 12 in the neutral solution and ₁ = =(3.92 ±0.2) · 10⁴ for 11 and lgK = lg ₁ + lg ₂ = 3.45 ± ±0.15 for 12 at 25° and =1 for the alkaline solution. *** DIRECT SUPPORT *** A3615139 00007

     

Fluorescent Molecular Sensing System Based on Tri-Pyrenes-Labeled γ-Cyclodextrin at the Hetero Rim

Fluorescent active host labeled at the upper and lower rims of -cyclodextrin, namely, mono-3^A-deoxy-3^A-pyrenebutylamido-6^X,Y-O-bis-pyrenebutylate-mono-altro--cyclodextrin (-3) has been synthesized as a chemosensor for steroidal guests using fluorescence spectra change upon a guest addition. The -3 shows monomer and excimer fluorescence, which results in an increase of the intensity of monomer and decrease of excimer fluorescence with a host–guest binding in the cyclodextrin cavity. The extent of monomer and excimer fluorescence variations of -3 was used as an indication for the sensing ability for the guests examined. The guest-induced fluorescence changes were measured for 10^–7 M solutions of -3. The sensing parameters (I_ex/I⁰_ex and I_mon/I⁰_mono) were used to describe the sensing ability of -3. The values of I_ex/I⁰_ex describe that -3 shows less selectivity for guests than that of mono-3^A-deoxy-3^A-pyrenebutylamido-6^X-O-mono-pyrenebutylate-mono-altro--cyclodextrin (-2), and the values of I_mon/I⁰_mono show that -3 shows higher sensitivity and selectivity than that of -2.     

Catalytic hydrogenation of carbon monoxide on RuFe/SiO2 catalysts

The H₂+CO reaction on silica supported Ru, Fe and RuFe catalysts prepared from metal carbonyl clusters has been investigated under atmospheric and 20 bar pressure. According to the change of selectivity values with temperature and with pressure, the participation of surface carbon proposed earlier by several authors seems to be confirmed by this work.

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H₂+CO Ru, Fe RuFe, , 20 . , , , .

     

Ruthenium clusters containing the [2.2] paracyclophane ligand: Recent developments in arene-cluster chemistry

In this article we review the synthesis, reactivity, and characterization of a number of clusters bearing the [2.2] paracyclophane ligand with nuclearities ranging from two to eight. Particular attention is focused on the different coordination modes that paracyclophane adopts; these being µ₁- ⁶, µ₂- ³ : ³, µ₃- ¹ : ² : ², and µ₃- ² : ² : ². Structural modifications which take place within the ring system on bonding in these various modes are also discussed.     

Simple screening method for the fast determination of clenbuterol in animal feeds

Summary A simple method for the determination of clenbuterol is described. It is extracted from the sample at pH 3 and then at pH 11, followed by partitioning the analyte into water at pH 3 and reextraction into ethyl acetate at pH 9. Clenbuterol is oxidized with KMnO₄ to clenbuteron for GC-determination. Recoveries for 0.01– 1.0 mg/kg were between 70% and 110% (standard deviation ±14%, n = 18).

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Eine einfache Screening-Methode zur schnellen Bestimmung von Clenbuterol in tierischen Futtermitteln