bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electronic Properties of Carbons and of Their Interstitial Bisulfate Compounds
Authors: Kmetko E. A. 
Published: January 2005

The conductivity of graphite increases when it is oxidized into graphite bisulfate, this being the result of the expulsion of resonance electrons by the negative ions and the resulting creation of excess holes in the π-band. This study concerns the electronic properties of the bisulfate compounds formed by the oxidation of carbons in sulfuric acid, the range of heat-treatment of carbons extending from 1400°C (baked carbons) to 3000°C (polycrystalline graphite). The resistivities of all samples thus treated decrease with increase in the degree of oxidation. The rate of decrease in resistance depends upon the heat-treatment, the rate being increasingly greater for samples treated to higher temperatures. The curve of the Hall constant of unoxidized carbons versus the heat-treatment temperature H has a sharp positive peak at about H=2000°C. The curve rapidly drops on either side of the peak, the coefficient becoming negative and exhibiting a minimum around H=1400°C.
The thermoelectric power of all samples studied becomes more positive with oxidation, with maxima appearing for lamellar compounds. The rate of the initial rise is greater for higher heat-treatment temperatures. The temperature coefficient of resistance depends strongly upon the ion concentration, changing from negative to positive for carbons heat-treated above 2000°C. On the other hand, the coefficients remain negative and are remarkably independent of ion concentration for carbons treated to temperatures below 2000°C.
The results are in general consistent with the electronic model for carbons proposed by Mrozowski whereby the Fermi level is initially depressed during devolatilization of the hydrocarbon material by the formation of a large number of excess holes (heat-treatments below 1400°C) and later steadily rises with the growth of the crystallites towards the top of the π band, the growth of the crystal planes resulting also in a steady decrease of the energy gap between the π and conduction bands. The negative Hall coefficient for baked carbons indicates the π band to be so depleted that the Fermi level drops at least partially below the inflection curve. At room temperature the conduction is therefore semi-metallic in nature for carbons treated to H&lt;2000°C in contrast with cases for which H&gt;2000°C where the number of excess holes is relatively small and the current is carried mainly by the holes and electrons thermally activated into the conduction band.
Some Thermal Reactions of the Higher Iron Carbides
Authors: Cohn Ernst M. , Hofer L. J. E. 
Published: January 2005

One of the undesirable side reactions of the Fischer-Tropsch synthesis is deposition of carbon. To ascertain whether thermal reactions of iron carbides might cause this deposition and to learn more about the nature of iron carbides, the transition from hexagonal close-packed (h.c.p.) iron carbide to Hägg iron carbide and the reaction of higher iron carbide with metallic iron to form cementite have been studied in a copper- and alkali-promoted iron catalyst by means of a magnetic balance.
The transition from h.c.p. to Hägg iron carbide is heterogeneous, with no apparent change of the compositions of both carbides, nor any detectable solubility of one carbide in the other. The data confirm the narrow range of composition of Hägg carbide and the fact that it contains somewhat more iron than corresponds to the formula Fe2C.
The synthesis of cementite from metallic iron and higher iron carbide proceeds via Hägg carbide and only above about 320°C. It does not go to completion up to 440°C; above that temperature, decomposition of Hägg carbide into cementite and free carbon is sufficiently rapid to prevent completion of the synthesis.
The data show that deposition of carbon on iron catalysts during the Fischer-Tropsch synthesis is not caused by thermal reactions of iron carbides, unless h.c.p. iron carbide should contain more carbon than Hägg iron carbide. A possible explanation of the apparent stabilizing effect of copper on h.c.p. iron carbide is given.
The Infrared and Raman Spectra of SiH2Cl2
Authors: Hawkins Janet A. , Wilson M. Kent 
Published: January 2005

An investigation of the infrared spectrum of gaseous SiH2Cl2 and the Raman spectrum of liquid SiH2Cl2 results in the following fundamental assignment: ν1(a1)=2200 cm−1,ν2(a1)=953 cm−1,ν3(a1)=531 cm−1,ν4(a1)=188 cm−1,ν5(a1)=710 cm−1,ν6(b1)=2200 cm−1,ν7(b1)=810 cm−1,ν8(b2)=877 cm−1,ν9(b2)=592 cm−1.
Thermodynamic functions for SiH2Cl2 were calculated with the usual assumptions. The infrared spectrum of gaseous CH2Cl2 and the infrared and Raman spectrum of liquid CH2Cl2 were remeasured.
A Semi-Empirical Theory of the Electronic Spectra and Electronic Structure of Complex Unsaturated Molecules. I.
Authors: Pariser Rudolph , Parr Robert G. 
Published: January 2005

A semi-empirical theory is outlined which is designed for the correlation and prediction of the wavelengths and intensities of the first main visible or ultraviolet absorption bands and other properties of complex unsaturated molecules, and preliminary application of the theory is made to ethylene and benzene.
The theory is formulated in the language of the purely theoretical method of antisymmetrized products of molecular orbitals (in LCAO approximation), including configuration interaction, but departs from this theory in several essential respects. First, atomic orbital integrals involving the core Hamiltonian are expressed in terms of quantities which may be regarded as semi-empirical. Second, an approximation of zero differential overlap is employed, and an optional uniformly charged sphere representation of atomic π-orbitals is introduced, which greatly simplify the evaluation of electronic repulsion integrals and make applications to complex molecules containing heteroatoms relatively simple. Finally, although the theory starts from the π-electron approximation, in which the unsaturation electrons are treated apart from the rest, provision is included for the adjustment of the σ-electrons to the π-electron distribution in a way which does not complicate the mathematics.
Electronic energy levels in the theory are expressed in terms of ionization potentials of atoms, resonance integrals of bonds, Coulomb repulsion integrals between two π-electrons on the same atom and between two π-electrons on different atoms, and penetration integrals between π-electrons and neutral atoms. Preliminary applications to ethylene and benzene in which only the carbon-carbon resonance integral is treated as an empirical quantity show that the theory can reproduce the results of the purely theoretical method with very little labor. The reasonableness of considering all of the above quantities as semi-empirical is pointed out, however, and it is through a detailed examination and exploitation of this in the second paper of this series that correction for the inadequacies of the π-electron approximation is made and improved agreement with experiment is attained.
The Asymmetric Rotor. XI. Hydrogen Sulfide Absorption in the Regions 8700 cm−1 and 11 000 cm−1
Authors: Innes K. Keith , Cross Paul C. , Bair Edward J. 
Published: January 2005

By the use of a 21-foot grating spectrograph and absorbing paths of up to 350 feet, sixty lines in the region from 10 870 cm−1 to 11 100 cm−1 have been measured and analyzed as the rotational structure of an A-type band. It may be identified as the lower component of the resonating pair (nσ, nπ, nδ)=(131), (311).
Most of the more than eighty hydrogen sulfide absorption lines measured between 8560 and 8830 cm−1 have been assigned to an A-type band identified as the lower component of the (121), (301) resonating pair. Several additional lines definitely not due to water appear to indicate the existence of a superimposed B-type band having about the same upper state parameters, presumably the lower component of the pair (211), (031). In cm−1, ν0=8697.3    A*=10.29   B*=8.75    C*=4.48ν0=11008.78  A*=10.197  B*=8.559  C*=4.411.
Excited Electronic States and Molecular Vibrations of Thiophosgene
Authors: Duchesne Jules 
Published: January 2005

The most general vibration potential function of the lower excited electronic state of thiophosgene is computed and interpreted in terms of theory. It is shown that the π* antibonding orbital is not far from being localized in the CS bond and that the sulfur lone pair electrons play a great part in the angular rigidity of the molecule. A general rule for the behavior of the sign of the cross terms is formulated.
A preliminary study of the next excited state is undertaken and a correlation between some properties of the molecular orbitals of both states is made.
Specific Heat of Diamond at Low Temperatures
Authors: DeSorbo Warren 
Published: January 2005

Specific heat data on diamond at temperatures between 20° and 300°K are reported. Comparisons of the data have been made with the predictions of the Debye theory. The deviation of the specific heat from the value given by the three-dimensional continuum theory in the low temperature region can be qualitatively described in terms of a superposition of a simple Einstein frequency. It has been found that variations that occur in expressing reduced characteristic temperatures as a function of reduced temperatures for diamond are qualitatively similar to those of the face-centered cubic metals Al, Cu, and Ag.
The values of entropy, enthalpy, and free energy have been determined and tabulated at integral values of temperature from 25° to 300°K. The entropy of diamond at 298.16°K is 0.568±0.005 cal/g-atom/deg.
Electron Deficient Compounds. VII. The Structure of the Trimethylaluminum Dimer
Authors: Lewis Paul H. , Rundle R. E. 
Published: January 2005

The trimethylaluminum dimer has a bridge structure with a skeletal symmetry of D2h within the accuracy of a structure determination by x-ray diffraction of single crystals. Bridge bonds, Al–C, equal 2.24A, vs Al–C bonds of 1.99A for the exterior, ``normal'' methyls. The bridge angle Al–C–Al=70°, the exterior angle C–Al–C=124°.
It is shown that a simple model provides the right order of magnitude for the heat of dimerization and indicates the relative importance of Al–C and Al–Al bonds. It is suggested that the sharp bridge angle required for good bridge bonding leads to metal-metal repulsions which should increase as the size of the metal increases. This probably plays a role in the instability and nature of polymers of the heavier trialkyl-metal compounds.
Electron Impact Studies of the Vinyl Ion and Radical
Authors: Field F. H. 
Published: January 2005

The appearance potentials of the vinyl ion as produced by electron impact from eight different compounds have been measured. The corresponding values of the heat of formation of the vinyl ion vary from 274 to 292 kcal/mole, with an average value of 281.5 kcal/mole. It is pointed out that no definitive explanation for the variation can be given.
The heat of formation of the vinyl radical is found to be 82.3 kcal/mole, which leads to a value of 122 kcal/mole for the first C–H bond dissociation energy in ethylene. The ionization potential of the vinyl radical is 200.5 kcal/mole=8.69 ev.
Nuclear Magnetic Relaxation of Nonuniform Systems
Authors: Broersma S. 
Published: January 2005

The relationship between the relaxation time measured for a heterogeneous system and the relaxation times and concentrations of the components is discussed. In general, the value of the ``average'' relaxation time observed is dependent upon the method of measurement. When the relaxation effects are completely averaged out within the time of measurement, the system behaves as a single phase while the relaxation time is determined by the time average (or mass average) of 1/T. If no averaging takes place at all the signal strength is determined by the sum of the magnetizations of the components, each with its own relaxation time.
In the transition case one should use the concept ``amount of relaxation during time t'', ∫0t dt′/T. Two examples of this transition have been examined experimentally. They are determined by the phenomena of diffusion and adsorption, both of which are able to delay the completion of the ``relaxation life cycle.'' The protons in hydrocarbons mixed with paramagnetic salt crystals, exhibit the properties of a two phase system; also dilute solutions of paramagnetic ions in water. In principle it is possible to obtain information about self-diffusion in liquids, hydration of ions, dispersivity of solid paramagnetic material.
Instrumental techniques used in the detection of the signal are described.
Raman Spectra of Hydrogen Peroxide in Condensed Phases. I. The Spectra of the Pure Liquid and Its Aqueous Solutions
Authors: Taylor Robert C. , Cross Paul C. 
Published: January 2005

The Raman spectrum of liquid 99.5% H2O2 has been obtained at 30° and −40°C and compared with the spectrum of 90% D2O2 at −40°C. Three bands not previously reported were observed and their assignment, together with that of the remaining bands, is discussed.
Raman spectra were also obtained for aqueous solutions at 30° and −40°C over the complete concentration range. The interpretation is qualitatively in agreement with the results of other work which indicate that the addition of hydrogen peroxide to water results in more extensive hydrogen bonding and an increased degree of order in the solutions.
Vibrational Spectra of OsF6 and PtF6
Authors: Weinstock Bernard , Claassen Howard H. , Malm John G. 
Published: January 2005

Infrared absorption spectra of gaseous OsF6 and PtF6 from 6–50μ and the Raman spectrum of liquid OsF6 are reported. These are interpreted in terms of the octahedral point group Oh, and the six fundamental frequencies are determined. Their values and symmetry species are for OsF6 733 (a1g), 632 (eg), 720 (f1u), 268 (f1u), 252 (f2g), and 230 (f2u); for PtF6 655 (a1g), 601 (eg), 705 (f1u), 273 (f1u), 242 (f2g), and 211 (f2u). Thermodynamic functions, including electronic contributions, are calculated for the ideal gaseous state of both compounds.
A comparison of the details of the vibrational spectra of eleven hexafluorides reveals certain characteristic features for OsF6 and ReF6. Since only these two molecules have appropriately degenerate electronic ground states these differences are interpreted as evidence of a Jahn-Teller effect.
Quantum Mechanical Cell Model of the Liquid State. I
Authors: Levelt J. M. H. , Hurst R. P. 
Published: January 2005

In this paper the cell model for the liquid state, as proposed by Lennard-Jones and Devonshire, is recast in terms of quantum statistical mechanics. A method is developed by which the energy levels and wave functions in the liquid cell can be determined to any prescribed accuracy. Thus, in the present work, no additional approximations are introduced which are not inherent in the cell model. When a sufficient number of energy levels is obtained, the partition function and thus the thermodynamic properties are derived.
A method is devised by which from a knowledge of the wave function, the derivative of the corresponding energy with respect to the volume may be obtained. This derivative is required for the evaluation of the pressure.
The theory is applied to H2 and D2 at a density near that of the crystals at 0°K. The corresponding classical Lennard-Jones and Devonshire thermodynamic functions are obtained and compared with the results of the present theory. The calculations involved were performed on a Bendix G—15D computer.
The quantized cell theory predicts that for hydrogen and deuterium experimentally detectable differences in energy, entropy, and specific heat must persist at temperatures as high as − 150°C.
Estimation of Molecular Parameters of C/H Fragments
Authors: Cowperthwaite M. , Bauer S. H. 
Published: January 2005

In this paper, we have assembled the molecular constants needed for the computation of the thermodynamic functions and the standard heats of formation for most of the low molecular-weight CmHn species which may be present in equilibrium at very high temperatures under a variety of external conditions. In the literature, the essential data are recorded for only 34 of the 73 species considered, and for those which are listed thermodynamic functions are given for the lower third of the temperature range included in our computations.
In order to arrive at an estimate for each of the 39 molecular fragments the following steps were used: (a) assign to each fragment a formal electronic configuration (this establishes the framework for the analogies to be sought and fixes its ground-state electronic degeneracy); (b) select several paths for dissociation which, when followed, generate the species under consideration in going from one molecule of known structure to another; and (c) estimate the bond dissociation energies from known simple dissociations, corrected for nonlocalized electron interactions. These corrections are relatively small and have been obtained by comparing similar reactions for known species. The success of this procedure is demonstrated by the good agreement found between a few predicted and experimental heats of formation. The self-consistency of the method is proven by the close check between estimates made for the heats of formation for many species following independent paths.
Radial Distribution of Electrons in the Ammonia and Hydrogen Sulfide Molecules
Authors: Banyard K. E. 
Published: January 2005

The model of ``floating'' hydrogen electron densities has been applied in detail to the molecules NH3 and H2S, both of the form XHn. In this way it has been shown that a reasonable radial distribution of electrons within these molecules may be obtained fairly easily from a knowledge of the molecular rotational magnetic moment which, in turn, is based on molecular beam or Zeeman effect microwave observations.
Some measure of the accuracy of these molecular electron densities has been obtained by calculating the coherent x-ray scattering factor and comparing it with the corresponding experimental values. Included in the present calculations for H2S is a determination of the paramagnetic contribution to the molar diamagnetic susceptibility. In addition, values of the molar diamagnetic susceptibility have been found for NH3 and H2S which are in good agreement with the experimental results.
Second Virial Coefficients of Argon, Krypton, and Argon-Krypton Mixtures at Low Temperatures
Authors: Fender B. E. F. , Halsey G. D. 
Published: January 2005

Second virial coefficients of argon between 80–125°K, and krypton (105–140°K), have been measured. The experimental values are 5–15% larger in magnitude than those calculated from 12–6 or exp—6 potential functions by the substitution of parameters assigned to describe high-temperature virial coefficients. Second virial coefficients calculated from the potential-distance relationship proposed by Guggenheim and McGlashan are within 1% of the experimental values for argon, but are about 4% smaller in magnitude than the measured krypton coefficients.
Argon-krypton mixed virial coefficients have been determined between 105–125°K. These experimental results are best expressed by a 12–6 potential energy parameter combining rule ε12=2ε1ε2/ε1+ε2.
Monte Carlo Calculation of Triatomic Dissociation Rates. I. N2O and O3
Authors: Bunker Don L. 
Published: January 2005

A very fast digital computer was used to simulate the motion of nonrotating triatomic molecules. Starting configurations were selected by a weighted random procedure which leads to correctly averaged dissociation rate constants vs energy. Trajectories were followed for 90 026 starting configurations representing various harmonic and anharmonic models of N2O and O3.
The conventional normal-mode description is very poor for all models studied; nevertheless, harmonic models give rise to large numbers of ``uninteresting'' molecules. The computations support a random gap assumption for anharmonic models only. It is concluded that calculations based on harmonic models give unrealistic rate constants below a pressure of about 100 atm for these molecules, and that the computed results are best described by a modified Rice—Kassel type of theory with a generalized postulate of limited molecular anharmonicity.
Potential Energy as a Function of Internal Rotation in CFClBr–CFClBr by NMR Measurements
Authors: Thompson Douglas S. , Newmark Richard A. , Sederholm Charles H. 
Published: January 2005

The NMR spectrum of CFClBr–CFClBr is reported as a function of temperature from 177° to 300°K. The high-temperature spectrum is analyzed in terms of a superposition of the spectra of the meso and dl isomers, each in rapid rotation about the C–C bond; the low-temperature spectrum on the basis of a superposition of the spectra of the three rotamers of each of the two isomers. The gauche coupling constant between fluorine atoms in this compound is 21.5±0.5 cps. Chemical shifts for the fluorine atoms were different for the three rotamers. Fluorine atoms gauche to one fluorine and one chlorine atom are at the highest field, and fluorine atoms gauche to one fluorine and one bromine atom are at the lowest field.
By observing the relative areas of peaks at low temperature, relative energies of the three potential minima for each isomer are calculated. High-temperature areas determined the relative amounts of the two isomers. Using, in addition, chemical shift data from the low-temperature spectra, spectra of this mixture of isomers have been calculated as a function of temperature assigning various potential barriers to internal rotation. By comparing the calculated spectra with those observed at various temperatures, several of the potential barriers to internal rotation have been assigned. In each isomer, the three potential minima vary by at most 450 cal/mole. The potential maxima which can be measured are all approximately 10.0±0.5 kcal/mole above the potential minima.
Raman Spectral Studies of Molten Potassium Bisulfate and Vibrational Frequencies of S2O7 Groups
Authors: Walrafen G. E. , Irish D. E. , Young T. F. 
Published: January 2005

Raman intensities and frequencies of molten potassium bisulfate, obtained in the temperature range of about 300° to 700°C, provide evidence for the reactions 2HSO4−→S2O72−+H2O and S2O72−→SO42−+SO3. Between 300° and 620°C the HSO4− concentration, inferred from Raman intensities, decreases rapidly. Simultaneously, the S2O72− concentration increases and becomes maximal at 500°C. Above 500°C the S2O72− concentration decreases, and Raman lines of SO42− appear. Analyses of gaseous and solidified products indicate that the production of SO42− is accompanied by the evolution of SO3.
Raman frequencies and polarizations of HSO4− ion obtained at temperatures ranging from the melting point to 620°C have been compared with the corresponding quantities obtained from studies of aqueous solutions. Differences observed are discussed in terms of hydrogen bonding. Raman spectra of molten potassium bisulfate obtained at ∼620°C provide vibrational frequencies of S2O72−. The number of Raman frequencies observed, polarizations of the Raman bands, and comparisons of the Raman frequencies with infrared frequencies of the corresponding solid exclude structures of the dihedral point groups and favor a structure of C2 symmetry (a slightly distorted C2v structure). Vibrational assignments for frequencies of S2O72− were made, and a comparison of those frequencies with frequencies of the related species HS2O7− and H2S2O7 indicates many close correspondences.