bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effect of including polarization functions on the geometrical parameters calculated for benzene, fluorobenzene and cyanobenzene
Authors: Bock Charles W. , Trachtman Mendel , George Philip 
Published: December 2004

AbstractThe geometrical parameters for benzene, fluorobenzene, and cyanobenzene have been calculated using the 6–31G*(5D) and 6–31G** basis sets, and, in addition, the 6–31 + G*(5D) basis set in the case of fluorobenzene. Compared to previous results obtained using the 6‐31G basis set there are minor changes in the magnitude of the bond lengths and angles in the ring, but the relative values remain unaltered. The values for the ipso angles in fluorobenzene and cyanobenzene are again somewhat less than those reported from microwave and/or electron diffraction studies. The distortion of the ring is characterized as either an elongation or a flattening with respect to the F–C1 ⃛C4 and NCC1C4 axes, and the shape is characterized as either a broadening or a narrowing across the ring just below the F and Cn group, i.e., an increase or a decrease in the C2 ⃛C6 internuclear distance, relative of the C3 ⃛C5 distance.
Theoretically derived absorption and MCD spectral data for the cellular species produced in the hydrolysis of cis‐diamminedichloroplatinum(II)
Authors: Krogh‐Jespersen Mary‐Beth 
Published: December 2004

AbstractThe cellular species formed in the hydrolysis of cis‐Pt(NH3)2Cl2 (DDP), namely, cis‐[Pt(NH3)2XY]n+ (X, Y = Cl−, H2O, OH−; n = 0, 1, 2) have been investigated theoretically using the relativistic and nonrelativistic extended Huckel molecular orbital method. Molecular orbital (MO) results for trans‐DDP and its hydrolysis products are also reported for comparison. Transition energies, molar absorption coefficients (ϵ), and B terms from magnetic circular dichroism (MCD) derived from theory are presented for each of the species studied. The electronic absorption and MCD spectra of all the complexes are predicted to exhibit ligand field transitions arising primarily from excitations between the occupied Pt 5d orbitals and the unoccupied Pt 5d and 6pz orbitals, respectively. The 5d → 6pz transitions are expected to yield intense absorptions in the UV spectral region. Some intensity is generated in the d → d transitions as a result of the low symmetry of these complexes. Correlation of available experimental data with theory allows spectral assignments to be made and predicted. Substituent effects in the cis‐ and trans‐isomeric species are discussed. Finally, the applicability of the EHMO method to these systems is examined.
A parallel molecular dynamics strategy
Authors: Nguyen H. L. , Khanmohammadbaigi H. , Clementi E. 
Published: December 2004

AbstractThis article presents a strategy to perform molecular dynamics simulations using parallel processing techniques on a parallel‐distributed loosely coupled system consisting of IBM host computers (4341 and 4381) with attached scientific processors (FPS‐164). This substantially enhances our ability to perform fast and more realistic large scale many‐body trajectory simulations. A powerful extention of the computational range of molecular dynamics the parallel approach offers the opportunity to substantially reduce the simulation time to allow a longer simulation period to study more realistic models and larger systems. It is flexible and uses, for the most part, standard products and straightforward implementation with a broad range of applicability. The implementation of a simulation of water molecules with the inclusion of two‐ and three‐body interactions is discussed. Some considerations in the design and implementation of parallel programs on a loosely coupled system are also presented.
The through‐space transmission of 31P‐31P coupling constants
Authors: Diz A. C. , Contreras R. H. , Natiello M. A. , Gavarini H. O. 
Published: December 2004

AbstractInner projections of the polarization propagator (IPPP) are used to study several features of the throughspace transmission of 31P‐31P coupling constants. Cis‐1,2‐diphosphinoethylene is chosen as a model compound. INDO ground state wave functions are used, including two different second‐row parameterizations. Results obtained with a phosphorus spd basis set are also presented. It is found that the overlap of phosphorus lone‐pairs constitute an efficient coupling pathway. Results are discussed in terms of experimental values for similar compounds taken from the literature. Theoretical predictions are in line with experimental trends.
Interaction energy studies of pyrrolopyrimidine nucleoside antibiotics‐toyocamycin
Authors: Sanyal Nitish K. , Ojha Rajendra Prasad , Roychoudhury M. 
Published: December 2004

AbstractThe biological activity of toyocamycin has been examined on the basis of the model developed by Sanyal et al. for the incorporation of nucleoside analogs during transcription. Using the simplified formula of Claverie for intermolecular interactions, computations have been carried out on the pairing energy of toyocamycin base with the complimentary bases as well as on the interaction energy with nucleic acid base pairs. The results are compared with the results of similar computations with nucleic acids. On the basis of the model an attempt has been made to explain the mechanism of the biological action of toyocamycin.
An improved set of mndo parameters for sulfur
Authors: Dewar Michael J. S. , Reynolds Charles H. 
Published: December 2004

AbstractThe MNDO parameters for sulfur have been reoptimized. Calculations for a number of sulfur compounds indicate a very significant improvement. Inclusion of d AOs failed to correct the errors for compounds of sulfur in its higher valence states. Since d AOs are not included, the calculations are still confined to compounds of divalent sulfur.
Spatially constrained minimization of macromolecules
Authors: Bruccoleri Robert E. , Karplus Martin 
Published: December 2004

AbstractA structural minimization procedure which converges rapidly and restricts the atomic shifts is outlined. It is implemented by adding a harmonic penalty term for the displacements of atomic positions and resetting the reference coordinates with respect to which the constraints are computed during the minimization. The resetting serves to reduce the constraint energy of the minimized structure to negligible levels.
Rates of reaction of allyl radicals: A reassessment
Authors: Throssell J. J. 
Published: December 2004

AbstractValues of the rate constants for allyl‐radical abstraction from toluene and allyl‐radical recombination have been recalculated in the light of recent data on butene‐1 decomposition. The rate of recombination is in good agreement with that found by Van den Bergh and Callear [13] and the cross‐combination ratio for the allyl + methyl system has a “normal” value of almost 4. It is concluded that allyl radicals behave like alkyl radicals in respect of their rates of reaction with other radicals.
Carbon–nitrogen bond dissociation energy values in C‐nitrosocompounds
Authors: Carmichael P. J. , Gowenlock B. G. , Johnson C. A. F. 
Published: December 2004

AbstractMeasurements of the D(RNO) bond strength in some C‐nitrosocompounds have been made using an electron impact method. The appearance potential of the radical ion (R+) has been determined, the D(RNO) bond energy being obtained from the relation

The values obtained are: D(C6H5NO) = 41 kcal/mole, D(t‐C4H9NO) = 34 kcal/mole, D(t‐C5H11NO) = 36 kcal/mole and D(i‐C3H7NO) = 36.5 kcal/mole. These values are in good agreement with the numerous estimations of Benson and coworkers and confirm that the CN bond strength in C‐nitrosocompounds is very much less than in nitrocompounds or in amines.
Aquation of (N, Ndimethylformamide) pentaamminecobalt (III) perchlorate in aqueous perchlorate media
Authors: Reynolds Warren L. , Knoll Michael A. 
Published: December 2004

AbstractThe first‐order rate constants for aquation of Co(NH3)5(DMF)3+ were determined in aqueous perchlorate media. The rate constants were independent of hydrogen ion concentration and ionic strength, but decreased with increasing perchlorate ion concentration. Proton magnetic resonance studies showed that dimethylformamide was not hydrolyzed to formic acid and dimethylamine in the aquation step. Mass‐spectrometer studies showed that cobalt–oxygen bond breaking occurred in 98 percent, or more, of the aquation acts. Enthalpies and entropies of activation were determined. It was concluded that aquation occurred by an Id mechanism.
Shock tube studies of the N2O/Ar and N2O/H2/Ar systems
Authors: Dean Anthony M. 
Published: December 2004

AbstractN2O decay has been monitored via infrared emission for a series of mixtures containing N2O/Ar and N2O/H2/Ar. These mixtures were studied behind reflected shock waves in the temperature interval of 1950–3075°K with total concentrations ranging from 1.2 to 2.5 × 1018 molec/cm3. In all cases the N2O decayed exponentially, and a rate constant kobs was obtained. Runs without added H2 could be described by the following Arrhenius parameters: log A = −9.72 ± 0.08 (in units of cm3/molec · sec) and EA = 203.5 ± 3.6 kJ/mole. Addition of 0.01% and 0.1% H2 was observed to increase the decay rate; the largest increase occurred between 2250 and 2500°K with 0.1% H2, where kobs doubled.Mixtures with no added H2 were analyzed by numerical integration of the following reactions:
equation image
Quantitative agreement between calculations and observations were obtained with both high and low choices for k2 and k3.The additional reactions
equation image
were included in the analysis of the mixtures containing H2. Here agreement was obtained only when low values were assigned to k2 and k3. The combinations of k1 ← k3 which agreed with all the data were k1 = 3.25 × 10−10 exp (−215 kJ/RT) and k2 = k3 = 1.91 × 10−11 exp (‐105 kJ/RT).
Kinetics and mechanism of the silane decomposition
Authors: Newman C. G. , O'neal H. E. , Ring M. A. , Leska F. , Shipley N. 
Published: December 2004

AbstractThe homogeneous gas‐phase decomposition kinetics of silane has been investigated using the single‐pulse shock tube comparative rate technique (T = 1035–1184˚K, Ptotal ≈︁ 4000 Torr). The initial reaction of the decomposition SiH4 \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm SiH}_{\rm 4} \mathop \to \limits^1 {\rm SiH}_{\rm 2} + {\rm H}_{\rm 2} $\end{document} SiH2 + H2 is a unimolecular process in its pressure fall‐off regime with experimental Arrhenius parameters of logk1 (sec−1) = 13.33 ± 0.28–52,700 ± 1400/2.303RT. The decomposition has also been studied at lower temperatures by conventional methods. The results confirm the total pressure effect, indicate a small but not negligible extent of induced reaction, and show that the decomposition is first order in silane at constant total pressures. RRKM‐pressure fall‐off calculations for four different transition‐state models are reported, and good agreement with all the data is obtained with a model whose high‐pressure parameters are logA1 (sec−1) = 15.5, E1(∞) = 56.9 kcal, and ΔE0±0(1) = 55.9 kcal. The mechanism of the decomposition is discussed, and it is concluded that hydrogen atoms are not involved. It is further suggested that silylene in the pure silane pyrolysis ultimately reacts with itself to give hydrogen: 2SiH2 → (Si2H4)* → (SiH3SiH)* → Si2H2 + H2. The mechanism of H ⟷ D exchange absorbed in the pyrolysis of SiD4‐hydrocarbon systems is also discussed.
The reaction of methoxy radicals with nitric oxide and nitrogen dioxide
Authors: Batt L. , Rattray G. N. 
Published: December 2004

AbstractBy allowing dimethyl peroxide (10−4M) to decompose in the presence of nitric oxide (4.5 × 10−5M), nitrogen dioxide (6.5 × 10−5M) and carbon tetrafluoride (500 Torr), it has been shown that the ratio k2/k2′ = 2.03 ± 0.47: CH3O + NO → CH3ONO (reaction 2) and CH3O + NO2 → CH3ONO2 (reaction 2′). Deviations from this value in this and previous work is ascribed to the pressure dependence of both these reactions and heterogeneity in reaction (2). In contrast no heterogeneous effects were found for reaction (2′) making it an ideal reference reaction for studying other reactions of the methoxy radical. We conclude that the ratio k2/k2′ is independent of temperature and from k1 = 1010.2±0.4M−1 sec−1 we calculate that k2′ = 109.9±0.4M−1 sec−1. Both k2 and k2′ are pressure dependent but have reached their limiting high‐pressure values in the presence of 500 Torr of carbon tetrafluoride. Preliminary results show that k4 = 10.9.0±0.6 10−4.5±1.1/ΘM−1 sec−1 (Θ = 2.303RT kcal mole−1) and by k4 = 108.6±0.6 10−2.4±1.1/ΘM−1 sec−1: CH3O + O2 → CH2O + HO2 (reaction 4) and CH3O + t‐BuH → CH3OH + (t‐Bu) (reaction 4′).
The kinetics of the reactions of C2F5 radicals with Br2 and HBr
Authors: Evans Brian S. , Whittle Eric 
Published: December 2004

AbstractA mixture of Br2 + HBr + C2F5I was photolyzed in the vapor phase. The reaction

forms C2F5 radicals which are removed by
equation image

equation image
Competitive studies over the range of 74–146°C gave ratios of k10/k9, and these were combined with values obtained previously by different methods at higher temperatures upto 515°C to give

where θ = 2.303RT J/mol. A value is assigned to the activation energy E10, and this, with other data, leads to

at 25°C. This result is in excellent agreement with two previous independent determinations.
Kinetics of electrophilic brominations. Mechanistic significance of the third‐order term
Authors: Fukuzumi S. , Kochi J. K. 
Published: December 2004

AbstractThe rates of electrophilic bromination of various donors follow complex kinetics which include both first‐order and second‐order dependences on bromine, especially in the less polar solvents. The second‐order rate constant ks and the third‐order rate constant kt are evaluated for alkene bromination in carbon tetrachloride, and they are compared to those already listed for the electrophilic brominations of substituted styrenes, arenes, and metal carbonyls in the extant literature. Despite the varying magnitudes of the second– and third‐order rate constants for these diverse donors (and in different solvents), the ratio log(ks/kt) is remarkably invariant. The mechanistic implication of this unique observation is discussed in the context of charge transfer interactions which are common to the activated complexes in the electrophilic brominations of various donors.
Yields of O2(b1Σ) from reactions of HO2
Authors: Keyser L. F. , Choo K. Y. , Leu M. T. 
Published: December 2004

AbstractA discharge‐flow apparatus with resonance fluorescence and chemiluminescence detection has been used to monitor O2(b 1σ) production from several reactions of the HO2 radical at 300 K and 1‐torr total pressure. O2(b), HO2, and OH were observed when F atoms were added to H2O2 in the gas phase. Signal strengths of O2(b) were proportional to initial concentrations of H2O2 and HO2. These observations were analyzed by using a simple three step mechanism and a more complete computer simulation with 22 reaction steps. The results indicate that the F + HO2 reaction yields O2(b) with an efficiency of (3.6 ± 1.4) × 10−3. By monitoring [O2(b)] and [HO2] upon addition of an excess second reactant to HO2, O2(b) yields from the reactions of HO2 with O, Cl, D, H, and OH were found to be <1 × 10−2, <5 × 10−4, <2 × 10−3, <8 × 10−3, and <1 × 10−3, respectively. Yields of O2(b) from the HO2 ± HO2 reaction were found to be less than 3 × 10−2.
A kinetic study of the chlorination of tertiary alcoholamines in alkaline media
Authors: Antelo J. M. , Arce F. , Armesto J. L. , Garcia‐Verdugo A. , Penedo F. J. , Varela A. 
Published: December 2004

AbstractThe kinetics of the chlorination of various tertiary alcoholamines by hypochlorite have been studied in alkaline media. A reaction mechanism consistent with the experimental results is put forward, and a relationship is established between the rate constants and the polar parameter (Σσ*) of the substituents.
Bond dissociation energies and radical heats of formation in CH3Cl, CH2Cl2, CH3Br, CH2Br2, CH2FCl, and CHFCl2
Authors: Tschuikow‐Roux E. , Paddison S. 
Published: December 2004

AbstractAn analysis of thermochemical and kinetic data on the bromination of the halomethanes CH4–nXn (X = F, Cl, Br; n = 1–3), the two chlorofluoromethanes, CH2FCl and CHFCl2, and CH4, shows that the recently reported heats of formation of the radicals CH2Cl, CHCl2, CHBr2, and CFCl2, and the CH bond dissociation energies in the matching halomethanes are not compatible with the activation energies for the corresponding reverse reactions. From the observed trends in CH4 and the other halomethanes, the following revised ΔH°f,298 (R) values have been derived: ΔH°f(CH2Cl) = 29.1 ± 1.0, ΔH°f(CHCl2) = 23.5 ± 1.2, ΔHf(CH2Br) = 40.4 ± 1.0, ΔH°f(CHBr2) = 45.0 ± 2.2, and ΔH°f(CFCl2) = −21.3 ± 2.4 kcal mol−1. The previously unavailable radical heat of formation, ΔH°f(CHFCl) = −14.5 ± 2.4 kcal mol−1 has also been deduced. These values are used with the heats of formation of the parent compounds from the literature to evaluate CH and CX bond dissociation energies in CH3Cl, CH2Cl2, CH3Br, CH2Br2, CH2FCl, and CHFCl2.
Sensitivity analysis of the two kinetic states of the Belousov‐Zhabotinsky reaction
Authors: Györgyi L. , Deutsch T. , Kőrös E. 
Published: December 2004

AbstractA recently published kinetic model of the Belousov‐Zhabotinsky reaction was studied by the feature sensitivity analysis of the slow bromide consumption and slow bromide production periods of the relaxing‐type oscillatory system. The computed sensitivities allowed us to reveal the kinetic importance of the 17 individual reactions during the two, “kinetically homogeneous” states of the oscillation. Similarities and differences in the relative kinetic importances of the reaction steps were carefully studied when changing the magnitude of the rate constants (high set and low set). Of the 17 reactions examined, the attack of Ce4+ on malonic acid proved to be an essential step of the mechanism. Using the low set, there emerge more reactions which significantly affect the length of the two kinetic states.
Fortschritte auf dem Gebiete der „Thermit”︁‐Schweißung
Authors: Ahlert Wilhelm 
Published: December 2004

AbstractDie starke Affinität des Aluminiums zum Sauerstoff ermöglicht es, Schwermetalle, z. B. Eisen, aus ihren Oxyden zu reduzieren. Hieraus entwickelte Hans Goldschmidt die Aluminothermie und das „Thermit”︁‐Verfahren. Die chemischen und thermochemischen Grundlagen des Thermit‐Prozesses werden angegeben. Das auf aluminothermischem Wege aus seinen Oxyden gewonnene Eisen wird in statu nascendi durch Beigabe stahlbildender Zusätze zur Thermit‐Mischung veredelt. Für das „Thermit”︁‐Schweißverfahren ist neben der Ausführungstechnik die Metallurgie des Thermitstahles von größter Bedeutung. Man kann Thermitstähle von verschiedener Art und mit hohen Güteeigenschaften herstellen. Die Verschweißung von Straßenbahnschienen nach dem „thermit”︁‐Verfahren ist in der ganzen Welt üblich. Seit über 25 Jahren schweißen auch Eisenbahnen, allen voran die Deutsche Bundesbahn, ihre Schienen zu größeren Längen und teilweise lückenlos zusammen. Ein weiteres Anwendungsgebiet ist die konstruktive oder instandsetzende Schweißung großer Werkstücke aus gegossenem und geschmiedetem Stahl.
Bemerkungen zu reaktionsfähigen Grundier‐bzw. Rostschutzmitteln
Authors: Scheifele Bernhard F. H. 
Published: December 2004

AbstractReaktive Grundiermittel mit Gehalt an Säure reagieren mit dem metall unter Bildung einer unlöslichen komplexen Metallsalz‐Pigment‐Harzverbindung. Als Bindemittel weden außer Polyvinylbutyrat auch andere Mischpolymerisate bzw. Kunstharze herangezogen. Als reaktive Komponente dient i. allg. Phosphorsäure, als antikorrosives Pigment Zn‐chromat. Ein Zusatz an lamellaren Pigmenten (Al‐pulver, Glimmer, Talkum) verbessert die Haftfähigkeit und Undurchlässigkeit des Schutzfilmes. Die reaktiven grundiermittel werden in dünner Schicht aufgebracht und erfordern bei stärkerer Korrosionsbeanspruchung des Gesamtanstriches noch Abdeckung mit antikorrosiven Grundierfarben. Sie ergeben auf Fe, Al, Leichtmetallen, verzinktem Fe einen antikorrosiven Deckfilm u. einen haftfesten Verankerungsgrund für die nach‐folgenden Farbschichten.
Korrosionschemisches Repetitorium. Der Einfluß der Außen‐ und Elektrolytwiderstände auf die Arbeitsweise elektrochemischer Modellelemente mit einer leicht polarisierbaren Elektrode
Authors: Schwarz Wolfram 
Published: December 2004

AbstractEs wird dargestellt, wie die Widerstände im äußeren Stromkreis und im Elektrolyten die Potentiallage der Kathode, die Klemmspannung und ähnliche Größen beeinflusst. Abschließend wird ein Weg zur Aufnahme von Strom‐Spannungskurven in Elektrolyten mit geringer Leitfähigkeit gegeben und auf eine Variation der Bedingungen zur Erzielung von Porportionalität zwischen Strom und zu bestimmenden Stoff hingewiesen, die die Elementanordnung gleichzeitig in weitem Maße von dem Salzgehalt der Lösung unabhängig macht.
Über das Korrosionsverhalten von Eisen in hochkonzentrierter Salpetersäure
Authors: Fitzer Erich , Hohn Hans , Sekal Johann 
Published: December 2004

AbstractÜber den passiven Zustand von Eisen in Salpetersäure – Standversuche von Eisen in hochkonzentrierter Salpetersäure – Interkristalliner Zerfall von handelsüblichem Eisenblech in Hoko mit über 96 Gew. %HNO3 – Einfluß der Prüfbedingungen sowie der Vorbehandlung und der Zusammensetzung des Werkstoffes auf den interkristallinen Zerfall – Das Verhalten von Reinsteisen und von aufgekohltem Eisen gegenüber Hoko – Untersuchungen über die gasförmigen, gelösten und festen Zerfallsprodukte beim interkristallinen An‐griff von Eisen durch Hoko.
Der Werkstück‐Oberflächenschutz im Fabrikationsablauf des Maschinenbaus
Authors: Van Der Bruggen Burchard 
Published: December 2004

AbstractUngeschützte Werkstückoberflächen setzen in der Regel Rost an und verunreinigen schnell, insbesondere dort, wo es sich um rauhe Gußoberflächen handelt. Die Reinigung ist dann meist schwierig und auch teuer. Wirklich saubere Oberflächen werden aber auch dann nur selten erzielt.Mit dem Haftvermögen des ersten Farbauftrages steht oder fällt der Aufwand für die Lackierung. In den Fällen, in denen die mechanische Bearbeitung des Stückes bereits erfolgte, ist die Benutzung rationeller Farbauftrags‐Verfahren nur selten möglich. Ein frühzeitiger Oberflächenschutz des Gusses kann deshalb sehr vorteilhaft sein. Er senkt die Kosten für Oberflächenreinigung und erhöht die Haltbarkeit des Farbauftrages. Er verbessert außerdem die Arbeitshygiene und fördert die Sauberkeit im Betrieb.An zwei Beispielen werden der Aufwand und die Vorteile des Grundanstrichs im Fabrikationsablauf des Maschinenbaus aufgezeigt.
Einfluß von Feuchtigkeit und Wärme auf das druckelastische Verhalten von rohem und ölimprägniertem Preßspan
Authors: Köhler Walther 
Published: December 2004

AbstractIm Rahmen einer größeren Untersuchung wurde der Einfluß der verschiedensten herstellungstechnischen Faktoren, wie Aufbaustoffe, Oberflächenbeschaffenheit, Mahlungsgrad und Kalanderdruck sowie der verschiedensten verarbeitungstechnischen Faktoren, wie Wärme und Feuchtigkeit auf das druckelastische Verhalten von rohen und ölimprägnierten handelsüblichen sowie Spezial‐Cellulose‐Produkten geklärt.
Zur Anwendung der Schallemissionsanalyse beim Zugversuch an Nickel‐ und Nickeldispersionsschichten
Authors: Wagner E. , Broszeit E. , Schwalbe H. J. 
Published: December 2004

AbstractNickel‐Siliciumkarbid‐Dispersionsschichten werden durch galvanische Mitabscheidung feinster SiC‐Partikel in eine Nickelmatrix hergestellt und überwiegend für den Verschleißschutz eingesetzt. Zur Beurteilung des Verschleißverhaltens dieses Verbundwerkstoffs interessiert u. a., inwieweit Haftkräfte in der Grenzfläche zwischen beiden Phasen vorhanden sind, und wie sich die Haftung auf die Versagensmechanismen der Schicht bei kritischer mechanischer Beanspruchung auswirkt. Zur Beurteilung dieses Einflusses und des allgemeinen Einflusses von Dispersionsteilchen wurden einige Zugversuche mit begleitender SEA an Nickelschichten ohne und mit SiC‐Einlagerungen durchgeführt.