bluuebunny/crossref_metadata_2025_split huggingface dataset:
Unified Orbital Treatment of Ethylene
Authors: Mueller C. R. 
Published: April 2005

Quantum-mechanical calculations of the properties of pi and sigma bonds in ethylene were carried out using atomic, molecular, and semilocalized orbital methods. Theoretical values were obtained for binding, and singlet-triplet separation energies. The polarizabilities of these bonds were also calculated, as were the charge distributions.
The electronic structure of the π bond was found to be largely localized contrary to the assumptions of molecular orbital theory, but the sigma bond was found to have molecular orbital structure.
On the basis of calculations of bond polarizability it was concluded that π bond accounts for about 90 percent of total bond polarizability. This result is due to the sp2 hybridization of the sigma bond.
The results of extended orbital treatments of π-electron systems are also discussed.
Mass Spectrometric Study of the Molecular Sublimation of Graphite
Authors: Honig Richard E. 
Published: April 2005

The emission of neutral and charged carbon molecules from spectroscopically pure graphite has been studied by rate of vaporization experiments in a 180° mass spectrometer. Small filaments (diameter: 0.015 in.), heated by ac up to 2600°K, yielded neutral particles which were converted into positive ions by bombardment with low-energy electrons. C3+, C2+, and C1+ ions were found. Although the effects of fragmentation and of differences in ionization cross sections may not be negligible, it is believed that carbon vapor consists largely of C3 molecules. Graphite was found to emit negative ions containing from one to eight carbon atoms. C2—, C4—, and C3— were the most abundant species, in that order. A search was made for carbon particles emitted as positive ions, but none were found.
Heats of activation were obtained for the neutrals and the more abundant negative ions from the slopes of logp vs 1/T plots. Identical heats measured for C1 and C3 (178±10 kcal/mole at 2400°K) suggest that these two species may sublime at rates that are interdependent. Thus, this value may not be representative of the true heat of sublimation of C1. For C2, a heat of 199±20 kcal/mole was measured at 2400°K. Electron affinities have been computed for C1, C2, and C3, and estimated bond energies deduced for C2 and C3. Some of the earlier measurements of the heat of sublimation of graphite, obtained from rates of vaporization and equilibrium effusion, but without mass analysis, have been reinterpreted, taking into account the complex character of the sublimation processes.
Ion-Exchange and Adsorption Column Kinetics with Uniform Partial Presaturation
Authors: Vermeulen Theodore , Hiester Nevin K. 
Published: April 2005

The available mathematical solutions for fixed-bed concentration histories apply primarily to one-component systems in adsorption and to two-component systems in ion exchange. Thomas has developed explicit general relations for the saturation of an adsorbent bed initially free of saturating component by a fluid phase containing only this component; as well as for the converse elution situation.
These results are extended here to cases of mixed binary feeds (in ion exchange), and cases of columns that are uniformly partially saturated prior to the run under study. New definitions of the dimensionless parameters that characterize the sorption processes render the existing numerical framework applicable for evaluating this broadened range of operating conditions. From the theoretical standpoint, these new parameters clarify the mathematical interrelationships between adsorption and ion exchange, between saturation and elution, and between sorption of trace components and sorption of gross or bulk components. A method is suggested for calculating physical-adsorption operations which do not conform to Langmuir isotherms.
Calculation procedures based upon this approach are illustrated by an idealized but representative example.
Mechanism of Formation of the Quinonoid Hydrocarbon CH2:C6H4:CH2
Authors: Levy M. , Szwarc M. , Throssell J. 
Published: April 2005

Para-xylyl radicals were generated by pyrolysing para-xylyl bromide in the presence of toluene or of para-xylene. Investigation of their behavior led to the conclusion that the quinonoid hydrocarbon CH2:C6H4:CH2 is formed by the disproportionation process. Further information about this reaction was secured by studying the pyrolysis of ω, ω′ dibromo para-xylene (Br·CH2·C6H4·CH2·Br). Semiquantitative treatment of the data indicates that the activation energy of the dissociation process CH2·C6H4·CH3→CH2:C̀6H6:CH2+His of the order 70 kcal/mole. Consequently, the dissociation process is too slow to account for the formation of the quinonoid hydrocarbon, at temperatures below 1100°K. We therefore attribute the formation of the quinonoid hydrocarbon to the disproportionation reaction.
Reinvestigation of the pyrolysis of benzyl bromide confirmed the past results and particularly the value for D(C6H5·CH2–Br). It was shown that the rate constant for the decomposition of para-xylyl bromide is essentially equal to the rate constant for the decomposition of benzyl bromide, and it appears that the rate constant for the decomposition of ω, ω′ dibromo para-xylene is higher by statistical factor of 2 from the rate constant of the decomposition of para-xylyl bromide.
Sedimentation Potential and Velocity of Solid Spherical Particles
Authors: Booth F. 
Published: April 2005

The electrical effects accompanying the steady fall of solid charged spherical particles under gravity in an electrolyte are examined theoretically. For a single particle falling in an infinite electrolyte, it is shown that, owing to fluid flow round the particle, the double layer field is modified. The effect in the double layer region is complicated, but outside this region a field is set up of the same form as that which would arise from a dipole fixed at the center of the particle with its axis vertical. A general expression is given for this dipole field in the case of nonconducting particles. The calculations extend previous work in that no restriction on the relative dimensions of the particle size and the double-layer thickness is imposed.
It is shown that the interaction between the charge on the particle and the modified field alters the sedimentation velocity of the particle. The calculations show that in practical cases the effect might, in favorable circumstances, reduce the velocity by a few percent.
The analysis is extended to suspensions containing a large number of particles uniformly distributed.
Studies on a Group of Silicon Carbide Structures
Authors: Mitchell Richard S. 
Published: April 2005

Morphological and structural details of silicon carbide type 141R are given. This polymorph, having a structure represented by the zigzag sequence 3333333333333332, is a member of the `3...2' rhombohedral series proposed by Ramsdell [Am. Mineralogist 32, 64 (1947)].
A detailed study of the `3...2' series is undertaken, resulting in an empirical mechanism which can be used for the direct determination of the structure of any member of this series. Using this means the structure of the new polymorph 393R is suggested.
Transport Properties of Gases Obeying a Modified Buckingham (Exp-Six) Potential
Authors: Mason Edward A. 
Published: April 2005

A large number of the Chapman and Cowling collision integrals have been calculated for gases obeying a modified Buckingham potential, [open phi](r)=ε1−6/α[6αeα(1−r/rm)−(rmr)6].The results are tabulated over a large temperature range, kT / ε from 0 to 200, and for four values of the parameter α, 12, 13, 14, and 15. The treatment was entirely classical, and no corrections for quantum effects were made. The results should be applicable to most simple, nonpolar gases, and may be used to obtain information about intermolecular forces from the observed temperature dependence of gaseous transport properties.
The second approximation to the thermal diffusion ratio and the third approximation to the coefficient of ordinary diffusion have been derived according to the method of Chapman and Cowling.
Evaluation of the potential parameters for specific substances and applications of the results will be published later.
The Infrared and Raman Spectra of Formaldehyde-d1 Vapor
Authors: Davidson D. W. , Stoicheff B. P. , Bernstein H. J. 
Published: April 2005

The infrared spectrum of HDCO vapor has been investigated in the region 2.5μ—25μ and all six fundamentals have been observed. Four of the fundamentals have also been observed in the Raman spectrum of the vapor.
The perpendicular component of an hybrid band at 3.5μ and the pure rotational Raman spectrum were resolved and analyzed. The rotational constant (A—B̄) for the symmetric top approximation was found to be 5.47±0.03 cm-1. This value, combined with the rotational constants of H2CO obtained by Dieke and Kistiakowsky, yields approximate molecular dimensions for the ground state of formaldehyde.
Theory of Ignition Considered as a Thermal Reaction
Authors: Hicks Bruce L. 
Published: April 2005

The history of a family of exothermally reactive solids is studied theoretically with the help of analytical and numerical calculations. The different members of this family of nonisothermal solids are obtained, by changing scales and values of parameters, from the basic model which describes a zero-order reaction of a semi-infinite slab of material subjected at its surface to heat transfer from a gas.
For low initial temperatures of the solid, the heat transfer rate determines the ignition time while for high initial temperatures, this heating parameter is less important than the initial temperature, which controls the adiabatic ignition time. For the model used, the ignition time is generally quite sensitive to the duration of the external heating. Within the solid, it is found that the inner boundary of the region in which the chemical heat production is negligible moves inward along a diffusional type of path x ∝ t½ but that the point of maximum temperature, which develops after interruption of the external heating, follows a much different path. An analytical, approximate method of estimating minimum ignition time was tested by making comparison with numerical integrations and is probably accurate to 25 percent in the ignition time.
The computational side of the theory presented here may be regarded as essentially complete for practical purposes until greater accuracy and detail are required by more critical applications than are now in prospect. Meaningful utilization of the computations in practical applications will not however be possible until reliable measurements have been made of certain of the parameters for the solid—namely, activation energy, frequency factor and thermal conductivity—and for the external heating— namely, gas temperature and heat transfer coefficient.
In the course of the computations, many mathematical questions arose which are fundamental to the investigation of this and more realistic models of ignition but which remain to be answered.
Rotation in Solid Mixtures of Neohexane and Cyclopentane from 20°K to Their Melting Points
Authors: Aston J. G. , Bolger Bouwe , Trambarulo Ralph , Segall H. 
Published: April 2005

Studies of the broadening of the proton spin resonance line have been made for solid solutions of neohexane and cyclopentane.
A convenient apparatus for control of temperatures from 10°K to room temperature for such studies is described.
The ``complex'' of one mole of neohexane with two moles of cyclopentane rotates in the solid state down to 65°K. In solid solutions with cyclopentane in excess of the complex, the complex rotates independently of the cyclopentane down to 66°K. The complex has no effect on the lower rotational transition of the cyclopentane which apparently nucleates.
Network Theory of the Gel Point and the ``Incestuous'' Polymerization of Diallyl Phthalate
Authors: Gordon Manfred 
Published: April 2005

The status of the gel point equation, advanced by Flory, Stockmayer, and Walling for polyfunctional reactions, is briefly discussed. Two complicating factors in the chain polymerization of divinyl compounds, to which this equation has been applied, are reviewed: the admixture of a monovinyl compound of comparable reactivity, and the ``incestuous'' tendency for the two double bonds in a divinyl compound to enter the same polymerization chain. Contrary to the treatment by Simpson and co-workers, these two factors are found to demand different theoretical approaches. The progress of polymerization enriches the monomer mixture in the monovinyl compound, while the incestuous tendency remains constant. Kinetic derivations are given for the gel point condition in both cases. The gel point in the ``incestuous'' polymerization of diallyl phthalate is calculated to lie at conversions 40 percent higher than estimated by Simpson and co-workers, and much better agreement is thus achieved with their experimental measurements.
A simple network theory suffices to predict the gel point in two chain polymerization reactions. Substantial delays of the gel point, predicted by Walling's theory of diffusion control in such reactions, are not encountered.
The Crystal and Molecular Structure of B5H11
Authors: Lavine Louis R. , Lipscomb William N. 
Published: April 2005

The molecular structure of B5H11 has been determined from 299 x-ray diffraction maxima which have been analyzed by three-dimensional Fourier and least-squares methods. There are four molecules in a monoclinic unit cell, in the space group P21/n, having parameters a=6.76, b=8.51, c=10.14A, and β=94.3°.
Although no molecular symmetry is demanded by the space group, the molecular dimensions indicate C8 symmetry for the isolated molecule. The boron skeleton is a fragment of the icosahedronlike arrangement in B10H14, and can also be derived from the tetragonal pyramid in B5H9 by opening up one of the basal B–B bonds. The apex boron BI is ``singly'' bonded to two hydrogens, one of which HVII, is very weakly bonded to the two outer borons BIII. Each BIII is ``singly'' bonded to two hydrogen atoms. Each of the remaining two borons BII is ``singly bonded'' to one hydrogen atom, and there are three bridge hydrogens, one bridging the BII–BII bond and two bridging the BII–BIII bonds. Molecular parameters are two BI–BIII=1.865, two BII–BIII=1.75, two BI–BII=1.72, one BII–BII=1.77A, seven B–H=1.07, six B–H (bridge) =1.24A, one BI–HVII=1.00 and two BIII–HVII=1.67A. The BIII–BI–BIII angle is 107°. Bond angles to hydrogen strongly resemble those in the other known boron hydrides.
Further Studies on the Reaction of Cyclopentane with Mercury-6(3P1) Atoms
Authors: Beck P. W. , Kniebes D. V. , Gunning H. E. 
Published: April 2005

A further investigation has been made of the reaction of cyclopentane with Hg6(3P1) atoms at 29.30±0.01°C, under static conditions. Analyses, using mass spectrometric techniques, confirm that the only direct products of the reaction are hydrogen, bicyclopentyl, and cyclopentene. No evidence was found for decomposition of the cyclopentane ring.
The kinetics of the reaction can be satisfactorily explained in terms of the following general mechanism:(1) cyclo CnH2n+Hg6(3P1)→cyclo CnH2n−1+H+Hg6(1S0),(2) H+cyclo CnH2n→H2+cyclo CnH2n−1,(3) 2(cyclo CnH2n−1)→cyclo CnH2n−2+cyclo CnH2n,(4) 2(cyclo CnH2n−1)→bicyclo C2nH4n−2,(5) H+cyclo CnH2n−2→cyclo CnH2n−1.Reaction (5) can be ignored at high substrate pressures or low extents of decomposition. The limiting high-pressure values for the quantum yields of cyclopentane disappearance, hydrogen formation, and cyclopentene formation are 0.90, 0.49, and 0.078, respectively.
From the steady-state treatment of the mechanism coupled with the quantum yield data, the ratio k4/k3, the ratio of the rates of recombination to disproportionation for cyclopentyl radicals, was determined to be 5.3.
Carbon-13 Isotope Effect in the Thermodecomposition of Nickel Carbonyl
Authors: Bernstein Richard B. 
Published: April 2005

The C12–C13 fractionation factor in the decomposition of gaseous nickel carbonyl has been measured from 30—105°C, using samples of normal isotope abundance. Assuming that the rate-determining step is the rupture of a Ni–C bond, the rate constants are defined as follows: Ni(CO)4→ lim Ni(CO)3·    +CO  k1,Ni(CO)3C*O−|→Ni(CO)3·   +C*Ok2,→Ni(CO)2C*O·+COk3.The C12 enrichment of the first fraction of CO from decomposition gives, over the temperature range studied, k1/(k2+k3)=1.0222−6.7×10−5t(∘C).
The intramolecular and intermolecular isotope effects are defined as k3/3k2 and k1/4k2, respectively. The magnitude of the intramolecular effect was assumed to be given by the square root of the usual reduced mass ratio, with a value of 1.0345. Thus the intermolecular effect calculated from the data becomes, k1/4k2=1.0481−6.7×10−5t(∘C).
A theoretical estimate of the magnitude of the intermolecular effect was made using the method of Bigeleisen. Isotopic shifts in vibrational frequencies were computed, and the usual assumptions regarding the vibrations of the activated complex were made. The calculated isotope effect was somewhat smaller than that observed.
Isotope Effect in Continuous Ultraviolet Absorption Spectra: Methyl Bromide-d3 and Chloroform-d
Authors: Gordus Adon A. , Bernstein Richard B. 
Published: April 2005

A comparison of the continuous ultraviolet absorption spectra of CH3Br and CD3Br indicated a nearly constant shift of +280±50 cm—1 upon deuterium substitution. In the case of CHCl3 and CDCl3 the shift was less than the uncertainty of ±50 cm—1. These results are interpreted in terms of the Herzberg-Goodeve picture involving the carbon-halogen bond rupture.
The ultraviolet absorption spectra of CCl4, CFCl3, CH2Cl2, CF2Cl2, and CHFCl2 are also reported.
Analysis of the Near Ultraviolet Absorption Spectrum of Acetylene
Authors: Innes K. Keith 
Published: April 2005

The absorption spectrum of acetylene in the region 1970—2470A has been photographed in the fourth and fifth orders of a twenty-one-foot grating spectrograph with absorbing paths of 0.007 to 70 m-atmos.
It has been possible to extend the arguments which led King and Ingold to conclude that in the upper electronic state the molecule is bent and has C2h symmetry. The upper electronic state is Au or, possibly Ag.
The effective moment of inertia Ia of the excited state is small, causing sub-band separations of 50 to 150 cm—1. These sub-bands all have P, Q, and R branches, are well resolved, and have the appearance of bands of diatomic molecules. The following rotational constants of the upper state are derived: A0=12.94,  B0=1.1247,  C0=1.0297 cm−1. If the C–H distance is assumed to be between 1.070 and 1.090A, one finds rcc=1.388A,  [open phi]CCH=120∘. Ground-state combination differences are in agreement with precise values derived from infrared data. Some new lower state B values are obtained.
The O–O vibrational transition is shown to be at 42 197.69 cm—1. The sub-bands form ν4″ progressions and ν3′ progressions. Analysis gives two upper state vibrational frequencies ν3(CCH)=1047.70 cm−1  and  ν2(CC)=1389 cm−1. The following lower state vibrational constants are obtained: ω40=608.26,  x44=+3.29, g44=+0.17 cm−1. The fundamental frequency ν4″ is the sum of these constants, that is, 611.72 cm—1.
The Effect of Oxygen on the Photoconductivity of Anthracene. II
Authors: Chynoweth A. G. 
Published: April 2005

The photoconductivity in the surface layers of crystalline anthracene has been found to increase considerably over its vacuum level when it is measured in the presence of oxygen or air. Replacing the oxygen by nitrogen or argon causes no such increase. The increased photoconductivity is attributed to the photooxidation of the surface, both the light and the oxygen being necessary to produce the effect. No reaction takes place in the dark. The oxide formed is fairly unstable and dissociates in the dark. Its rate of dissociation is considerably increased when the crystal is illuminated in the absence of oxygen. The experiments indicate that the peroxide is formed by a two-stage process, the highly unstable intermediate product being formed very rapidly while the final peroxide is formed much more slowly. The nature of the intermediate product is not known for certain. The end product is very likely the oxide formed by an oxygen bridge across the 9, 10 carbon atoms of the anthracene molecule. Apparently, both the oxidation products modulate the photocurrent solely by their effect on the mean free path of the carriers; the intermediate product producing a relatively large increase while the end product produces a smaller decrease in the mean free path.
It is suggested that the technique of photoconductivity measurements might prove to be useful in the study of the kinetics of certain photochemical reactions.
Symbolic Structural Formulas for Boron Hydrides
Authors: Platt John R. 
Published: April 2005

A structural convention is proposed, intended to serve the same function for boron hydrides that the standard valence bond convention serves for organic compounds. It involves the auxiliary concept of the ``valence cone,'' which is the cone swept out by three tetrahedral orbitals rotating about the fourth as an axis. The known open boron hydrides BnHn+p then appear to be even-electron molecules with the boron atoms approximately in a close-packed equilateral-triangular network on the convex surface formed by their overlapping valence cones; with n single B–H bonds normal to this surface; and with p (even) added peripheral hydrogen in the surface located so that every boron atom has neighbors in all three sectors of its valence cone. As long as this network does not form a complete polyhedron, we may represent it on paper by a flat triangular network having the same topology.
This prescription gives uniquely and correctly the structures and formulas for the known B2, B4, B5, B6, and B10 hydrides and predicts other possible open compounds up to B11. It would be consistent with the existence of closed inert polyhedral hydrides BnHn up to B12H12 and with chains and lattices of such polyhedra.
Inter- and Intramolecular Energy Transfer Processes. 4. Hydrogen-Hydrocarbon Systems
Authors: Moodie Margaret M. , Reid C. 
Published: April 2005

Extensive experiments have confirmed our earlier conclusion that long-range energy transfer does not occur between pairs of molecules in solution. Evidence is brought forward to show that the transfer of excitation energy from terphenyl to diphenyl hexatriene under x-ray bombardment in liquid scintillators must be due to a short-range process which occurs after the formation of a molecular complex between diphenyl hexatriene and either a positive terphenyl ion or a very highly excited terphenyl molecule.
Results of experiments in heterogeneous systems, in which transfer of excitation energy from adsorbed component to host crystal, and vice versa sometimes occurs, are summarized.
Effect of Pressure on Diffusion in Polymer Solutions
Authors: Emery A. H. , Tung L. H. , Drickamer H. G. 
Published: April 2005

Diffusion measurements have been made using two molecular weights of polysulfide polymer at 25°C and 59°C in toluene solution. One isotherm for the low molecular weight was obtained in chloroform solution.
The results indicate that there are two mechanisms of motion in solution. At low pressure the dominant mode involves the expulsion of a solvent molecule from the coiled polymer. At high pressure the motion is segmental.