bluuebunny/crossref_metadata_2025_split huggingface dataset:
United-Atom Model for Molecules of the Type XHn
Authors: Gáspár R. , Tamássy-Lentei I. , Kruglyak Yuri 
Published: January 2005

A united-atom model is used for the variational treatment of the systems HF, F—, O—, O— —, OH, OH—, H2O, and H3O+. This model utilizes one-electron wave functions which are centered on the single heavy nucleus in each system.
The Hamiltonian is the correct one for the atoms in their true positions. Energies, equilibrium nuclear separations, and dissociation energies are calculated, as well as proton affinities of F—, O— —, O—, OH—, and H2O. The calculated values are in good agreement with experimental results.
Absorption of Ultrasonic Waves in Pure Methylcyclohexane
Authors: Pedinoff M. E. 
Published: January 2005

The ultrasonic pulse technique has been extended to lower frequencies by the use of solid dielectric transducers and has been used here for the determination of the anomalous absorption of sound in methylcyclohexane over a frequency range of approximately 150 to 3500 kc/sec.
The liquid studied, methylcyclohexane, has a large anomalous sound absorption which can be attributed to the irreversible perturbation of an equilibrium between two of its rotational isomers by the sound wave. The theoretical relationship between anomalous ultrasonic absorption and irreversibly perturbed monomolecular equilibria is used in conjunction with an experimental evaluation of the temperature dependance of the anomalous absorption per wavelength and the ultrasonic relaxation frequency to obtain the free energy difference between the two isomers and the activation energy barrier between these two states.
Values of 1.9 kcal per mole for the free enthalpy difference between the isomers, and 6.4 kcal per mole for the activation enthalpy of the higher energy state indicate that a monomolecular reaction between the polar substituted and the equatorial substituted chair configurations of methylcyclohexane is responsible for the ultrasonic absorption anomaly. Values for the entropy differences between the low energy, high energy, and activated states yield insight into the nature and structure of the activated state.
Diffusion of Hydrogen and Deuterium in Fused Quartz
Authors: Lee R. W. , Frank R. C. , Swets D. E. 
Published: January 2005

A mass spectrometer was used to record the transfer of hydrogen and deuterium through hollow, thinwalled cylinders of fused quartz over the temperature range of 300–1000°C. Steady-state gas permeation measurements resulted in permeability values which agree well with the literature; however, results of transient experiments which provide a direct means of measuring diffusion coefficients did not agree with so-called ``normal'' diffusion. The deviation from normal diffusion increases with increasing temperature.
Measurements were made of the temperature variation in the rate of release of deuterium from fused quartz resulting from replacement by dissolved hydrogen. A chemical exchange between the diffusing molecules (H2 or D2) and one or more species of trapped gas within the fused quartz is thought to be the principal cause of the nondiffusion-like character of the high-temperature gas transport.
Activation energies were calculated for the permeability (H2:8.88 kcal/mole. D2:9.05 kcal/mole), diffusion (H2:10.37 kcal/mole D2:10.52 kcal/mole), and chemical exchange (15.5 kcal/mole) mechanisms. Experimental solubilities were compared with the so-called normal solubilities (Sn=permeability/diffusion coefficient) and were found to exceed the normal to a greater extent with increasing temperature.
Heat Capacities and Thermodynamic Functions of YH2 and YD2 from 5° to 350°K and the Hydrogen Vibration Frequencies
Authors: Flotow Howard E. , Osborne Darrell W. , Otto Klaus 
Published: January 2005

The heat capacities of pure YH2 and YD2 were measured by an adiabatic method from 5° to 350°K. The compounds were found by x-ray analyses to consist of a single phase, with the yttrium atoms in face-centered cubic positions. Below 16°K the heat capacities of the two compounds are equal within experimental error, between 16° and 90°K the heat capacity of the hydride is about 0.02 cal deg—1 mole—1 greater than that of the deuteride, and at higher temperatures that of the deuteride becomes appreciably greater. The difference in the heat capacities above 100°K is ascribed to a single optical vibration of the hydrogen atoms, whose frequency is shifted upon isotopic substitution. The difference in the heat capacities of YH2 and YD2 in the temperature range 100° to 350°K is fitted to ±0.02 cal deg—1 mole—1 with Einstein heat capacity functions and a frequency of 1030±30 cm—1 for YH2 and 1030/√2 for YD2. These results are compared with those obtained by inelastic neutron scattering experiments.
The values obtained for the heat capacity, entropy, enthalpy and Gibbs free-energy function for YH2 at 298.15°K are 8.243±0.016 cal deg—1 mole—1, 9.175±0.018 cal deg—1 mole—1, 1403±3 cal mole—1 and —4.470±0.009 cal deg—1 mole—1, respectively. The corresponding values for YD2 are 10.773±0.022, 10.294±0.021, 1659±3 and —4.729±0.010. The enthalpy of formation of YH2 minus the enthalpy of formation of YD2 is calculated to be 0.78±0.08 kcal mole—1 at 0°K and 0.55±0.08 kcal mole—1 at 298.15°K.
Second Virial Coefficient for the Spherical Shell Potential
Authors: De Rocco Andrew G. , Hoover William G. 
Published: January 2005

Values of the second virial coefficient for the three-parameter spherical shell potential are tabulated over wide ranges of temperature and shell size. The potential, which is not new, results from the interaction of two spherical surfaces having uniform distributions of Lennard-Jones (6–12) sites.
An objective comparison is made between the tabulated values and the literature values for second virial coefficients, from which the potential parameters for twenty compounds are determined. Generally, the spherical shell potential generates a better fit than does the parent Lennard-Jones potential. The potential parameters found are in good agreement with expectations based upon density and interatomic distance data.
Vibrational Spectrum and Structure of Single Crystals of K3Co(CN)6
Authors: Jones Llewellyn H. 
Published: January 2005

The polarized infrared absorption spectra of single crystals of K3Co(CN)6 have been observed from 5000 to 280 cm—1. By combining this data with Raman and crystal structure data of other authors, most of the fundamental frequencies have been assigned. Force constants have been calculated using the recently derived resonance interaction valence force potential function which reduces the number of interaction terms in accord with theories of bonding. The primary stretching force constants are: FCN=16.8 md/A and FCoC=1.8 md/A.
It is shown that the observed spectrum cannot be satisfactorily explained with a Urey-Bradley force field.
Configuration Interaction Study of the Lithium Hydride Molecule
Authors: Ebbing Darrell D. 
Published: January 2005

A set of orbitals in elliptical coordinates has been used as basis in a self-consistent field configuration interaction (SCF–CI) study of the electronic structure of the ground state (1Σ+) of the lithium hydride molecule. The importance of various configurations is studied, and it is found that those configurations are most important which have either the inner-shell molecular orbital or the valence-shell molecular orbital doubly occupied. The results of each configuration interaction calculation have been analyzed into contributions to the inner-shell and outer-shell correlation energies, and in this way the importance of various orbitals is studied and related to correlation effects. It appears that LiH could be well described by a product of electron-pair wave functions.
A study of the numerical stability of the calculations shows that considerable care must be exercised in the choice of a basis in order for the results to be meaningful. Instability of a calculation is due to near linear dependency of the orbital basis.
The best total energy obtained, using 53 configurations formed from a basis of 7σ and 3π orbitals, is —8.04128H at an internuclear distance of 2.99B. This should be compared with the experimental energy of —8.0703H. The dipole moment was calculated to be 5.96D, and the ratio of dipole moment to dipole derivative is μe/(δμ/δr)ere=1.53 (experimental values are 5.88D and 1.8±0.3, respectively).
Electronic and Ionic Conductivity in Single Crystals of MgO
Authors: Mitoff S. P. 
Published: January 2005

The electrical conductivity and relative fractions of ionic and electronic conductivity of single crystals of MgO were measured between 1000° and 1500°C. The results resolve conflicting observations of electronic and ionic conductivity of previous investigations in that MgO is shown to exhibit both kinds of conductivity in this temperature range. The nature of the charge carriers depends on temperature, the surrounding oxygen pressure, and the purity of the crystal.
The following conditions favor predominant electronic conductivity: (1) high temperatures (&gt;1300°C), (2) high (1 atm) or very low (&lt;10—6 atm) oxygen partial pressures, (3) contamination, specifically Li, was found to increase the relative electronic fraction. Conversely, low temperatures (&lt;1300°C), intermediate (10—4 to 10—5) oxygen partial pressures, and probably high purity favor predominant ionic transport. The electronic conductivity observed at the higher temperatures most likely results from point defects created in thermodynamic equilibrium.
Radiolysis of Methylcyclohexane. II. Liquid Phase Inhibition by Benzene
Authors: Freeman G. R. 
Published: January 2005

The effect of benzene on the radiolysis of liquid methylcyclohexane (MCH) has been studied over the benzene concentration range from 0.25 to 100 mole %. The dominant effect of benzene at low concentrations appears to be one of hydrogen atom scavenging. At higher concentrations, the transfer of energy (excitation or ionization) from activated MCH to benzene also becomes important.
As in the liquid cyclohexane system, there seem to be two major reactive species in γ-irradiated MCH. One species, C7H14′, decomposes to produce ``cold'' hydrogen atoms that can be scavenged by benzene. The other species, C7H14″ or C7H14+, produces hydrogen by a mechanism that is not subject to atom scavenging but which can be inhibited by an energy transfer process. The 100-ev yields of the activated species in pure MCH are G(C7H14′) = 1.8±0.3 and G(C7H14″) = 3.0∓0.3. These compare with the cyclohexane yields G(C6H12′) = 2.4±0.3 and G(C6H12″) = 3.0∓0.3.
Reaction mechanisms have been proposed and tested against the experimental data.
Mechanism of Atom Recombination by Consecutive Vibrational Deactivations
Authors: Benson Sidney W. , Fueno Takayuki 
Published: January 2005

The process of atom recombination in the presence of foreign gases, M, not forming complexes with the atoms, is considered in terms of a cascade model in which deactivation occurs by small increments, essentially by one quantum at a time. This leads to an equation for the termolecular recombination rate constant: kr=λZK*G(T), where K* is the equilibrium constant for species X2* in equilibrium with X atoms, Z is the collision frequency of these species with M, and λ, assumed to be unity, is the probability that such species will be de-excited in a collision with M to the top vibrational level of X2, the diatomic molecule. The quantity G(T) is essentially the reciprocal of the number of vibrational states within a range of kT of the dissociation threshold.
Methods are given for the calculation of K*, G(T), and Z from physical data for the X2 and M molecules without any undetermined parameters. The use of Morse functions yields values of kr in excellent agreement with available experimental data for H2, N2, O2, Br2, and I2 over the range 300° to 2000°K (6000°K for O2) with argon as M.
The temperature dependence of kr is not simple and varies between light and heavy molecules. On the average and almost independently of the potential function used, it is in the range of T—1.
It does not appear as though contributions from other electronic states beyond the ground state are significant in the recombination process.
Initial Stages of the Chlorine Atom Induced Polymerization of Acetylene
Authors: Wijnen M. H. J. 
Published: January 2005

The initial stages of the chlorine atom induced polymerization of acetylene have been investigated. The photolysis of phosgene was used as a source of chlorine atoms. The following main reaction products were observed: carbon monoxide, vinyl chloride, 1-chloro-1,3-butadiene, benzene, and polymer. Small to trace amounts of monochloroacetylene and monochlorobenzene were also detected.
A qualitative examination of the formation and distribution of these products indicates that they are formed in the initial stages of the chlorine atom initiated polymerization of acetylene.
The data are compared with those obtained in other free radical induced polymerization reactions of acetylene.
Electron-Spin-Resonance Studies of DPPH Solutions
Authors: Ueda Hisashi , Kuri Zenichiro , Shida Shoji 
Published: January 2005

The effects of impurities on the ESR of DPPH in various solutions were studied. The broad quintet spectrum usually obtained with DPPH solutions becomes well resolved after dissolved gases are removed. Addition of tertiary hydroperoxides to DPPH solutions gives a triplet spectrum, which further splits into 17 lines after subsequent degassing in the case of t-butyl hydroperoxide. From an analysis of this spectrum, a determination was made of the spin-density distribution of the unpaired electron in a species electronically analogous to biphenylaminium ion.
An aerated DPPH solution of xylene loses its paramagnetic nature in time, but regeneration of the quintet ESR spectrum of DPPH is observed if this solution is mixed with the so-called lophine-x compound solution kept in the dark, and then irradiated by sunlight. The interpretation of this phenomenon is that the lophine-x compound, when irradiated by sunlight, has an odd electron which shifts onto the nonparamagnetic DPPH—O2 reaction product regenerating DPPH as a result. This is, therefore, a radical transfer reaction and is one of the few chemical reactions giving evidence for the radical nature of the lopine-x compound when photochemically excited.
Molecular Dimensions in Crystalline Polymers
Authors: Tobolsky A. V. , Gupta V. D. 
Published: January 2005

In this paper we calculate from theoretical considerations the molecular dimensions of polymer chains in partially crystalline polymers existing in any state of orientation. Our theory also applies to isolated molecules in solution which have helical and random coil regions within the same molecule.
The treatment is based on two probability parameters and the mathematical method of the Markoff chain.
Photolysis of Acetone in the Presence of HI and the Decomposition of the Acetyl Radical
Authors: O'Neal Edward , Benson Sidney W. 
Published: January 2005

Acetone over a range of pressures and temperatures (1.2–15 cm Hg; 126–295°C) was photolyzed with light of 3130 A in the presence of small amounts of hydrogen iodide. The primary process was found to be the C–C split to form acetyl and methyl radicals. Hydrogen iodide acted as an excellent radical ``trap'' for these radicals. No spontaneous decomposition of acetyl radicals was observed. Relative rates of methyl radical reactions with iodine and hydrogen iodide were measured. Complications due to surface effects in these reactions are considered.
Kinetic constants for the reactions CH3+HI→CH4+I(1); CH3+I2→CH3I+I(2) are E1—E2=1.3±0.5 kcal, A2/A1=2.4, and log(k1/k2) = —0.38–1300/4.575T.
Above 200°C the acetyl radical decomposition is measurable and the rate constant is observed to be pressure dependent. The pressure dependence is treated by an approximate method related to the Hinshelwood-Lindemann equation and the high- and low-pressure limiting rate constants are given by logk∞=10.3–15 000/4.575T sec—1, logk0=11.5–12 000/4.575T (l/mole-sec). The number of vibrational modes S contributing to the decomposition is 4.5 and the lifetime of the excited acetyl radical is t∼10—8 sec. The abnormally low frequency factor of the high-pressure rate constant implies a nonadiabatic decomposition of the acetyl radical. From the kinetic constants, the heat of formation of the acetyl radical is found to be ΔHf0 (CH3CO)—6.2 kcal and the values of the appropriate bond dissociation energies in a series of acetyl derivatives are tabulated.
Near-Ultraviolet Absorption Spectrum of Tetrolaldehyde
Authors: Muirhead J. S. , Howe J. A. 
Published: January 2005

The near-ultraviolet absorption spectrum of tetrolaldehyde vapor has been examined. The weak absorption appearing in the 300–400-mμ region has been assigned as the n→π* transition, and a vibrational analysis places the 0–0 transition at 26 620 cm—1 and yields a value for the C=O stretch frequency in the π* state of 1036 cm—1.
Two other regions of absorption are observed in the 200–300-mμ range, and one of these with center at 47 333 cm—1 is tentatively assigned as the N→V transition. The second of these appears as weak structure on the long wavelength edge of the first and may arise from a space forbidden π→π* transition.
Dielectric Relaxation in Liquid Alcohols and Diols
Authors: Sagal Matthew W. 
Published: January 2005

The temperature dependence of the dielectric relaxation time has been investigated from —5° to 50°C for ethanol—cyclohexane solutions from 1.0 to 0.25 mole fraction ethanol. The previously observed maximum in the relaxation time around equimolar composition is explained by a hydrogen-bonded switching mechanism.
Measurements of dielectric relaxation from 5° to 50°C have been carried out on three isomeric butanediols which differ in the separation of the two OH groups along the carbon skeleton. The differences in relaxation times among the three isomers can be explained by the switching mechanism suggested by the results for the ethanol—cyclohexane solutions.
The dielectric relaxation times of n-butanol from 5° to 50°C have also been determined. The chain-length dependence of the dielectric relaxation time of the normal aliphatic alcohols is discussed in terms of the proposed mechanism.
Effect of Anharmonic Vibrations on the Bond Lengths of Polyatomic Molecules. I. Model of Force Field and Application to Water
Authors: Kuchitsu Kozo , Bartell L. S. 
Published: January 2005

The detailed information on molecular force fields required for precise determinations of molecular structure is only rarely available for polyatomic molecules. A model of the force field is therefore proposed from which the cubic potential constants may be estimated from commonly available data. The potential energy is represented by a modified, anharmonic Urey-Bradley field in which the stretching and nonbonded potentials are assumed to have the Lippincott and Buckingham forms, respectively, and in which stretch-stretch interactions are included.
The model is applied to H2O and D2O, for which exceptionally complete spectroscopic data are available for comparison, and is found to give cubic constants in satisfactory agreement with experiment. The cubic constants thus estimated are used to evaluate the effect of zero-point vibrations on the internuclear distances and rotational constants of water by a first-order perturbation treatment. The resultant mean distances and mean amplitudes are in good agreement with those of Reitan's second-order treatment using the experimental cubic constants, and the rotation-vibration constants α agree satisfactorily with Benedict's experimental values.
Higher Ionization Potentials of NO2
Authors: Tanaka Y. , Jursa A. S. 
Published: January 2005

The spectrographic method of observing Rydberg series has been used to investigate higher ionization potentials of NO2. The most significant result was the determination of a new ionization potential at 18.87 ev. Four Rydberg series which converged to this limit were identified.
Other ionization potentials at 11.62 and 12.3 ev are discussed. No evidence was obtained which would indicate the existence of an ionization potential at 13.98 ev reported by others, nor was there any indication of an ionization potential at 17.5 ev, which is predicted theoretically.
Absorption Spectra of Gaseous Species Formed at Flash-Heated Solid Surfaces
Authors: Nelson L. S. , Kuebler N. A. 
Published: January 2005

A method is described for recording the absorption spectra of gaseous atoms and molecules produced at strongly heated solid surfaces. A very intense pulse of light from a capacitor discharge lamp falls on light-absorbing grids placed in the absorption path of a spectrograph. The diameter of the grid windings is sufficiently small that their temperatures rise several thousand degrees very rapidly. The gaseous thermal species that are formed in the optical path arise from the following reactions: (1) vaporization of the grid material; (2) vaporization of coatings applied to the grids; and (3) reactions of the grids with a surrounding gas. Flash spectroscopic recording is used.
The following illustrations of the technique are presented: the formation of atomic tungsten by the vaporization of tungsten grids; the formation of AlCl by the evaporation of AlCl3 from carbon grids; and the formation of CH3, CD3, and CF2 by the reaction of heated carbon grids with CH4, CD4, and CF4, respectively.
Flash heating compares favorably with flash photolysis as a way to produce labile species for kinetic absorption spectroscopy. Parent molecules need not absorb in the near ultraviolet since the dissociative processes that occur are thermal rather than photolytic. Container problems for high-temperature studies are virtually eliminated because of the pulse nature of the experiment.
Polyhedral Clathrate Hydrates. III. Structure of the Tetra n-Butyl Ammonium Benzoate Hydrate
Authors: Bonamico M. , Jeffrey G. A. , McMullan R. K. 
Published: January 2005

The compound (n-C4H9)4N·C6H5COO·39½H2O forms tetragonal crystals with four molecules in the unit cell. The water structure is a hydrogen-bonded clathrate framework, in the cavities of which are located the tetra alkyl ammonium cations. The oxygen atoms of the benzoate anions are hydrogen-bonded to the water framework and form part of the polyhedral structure. This structure contains 10 pentagonal dodecahedra, 16 tetrakaidecahedra, and four pentakaidecahedra per unit cell. The 20 larger polyhedra are occupied by the 16 alkyl and four benzyl groups with a statistical disorder over two sets of equivalent cation and anion positions. There is evidence of additional hydrogen-bonded water inside some of the dodecahedra which are distorted due to the presence of the ions.
The clathrate framework is iso-structural with that of other salts in this series, which have a very similar tetragonal lattice but differ in containing five tetra n-butyl ammonium salt molecules per unit cell.
Thermal Reactions of Isobutyl Radicals
Authors: Jackson W. M. , McNesby J. R. , Darwent B. deB. 
Published: January 2005

Deuterium labeled isobutane (CH3)3CD was pyrolyzed to generate (CH3)3C and CH2CD(CH3)2 radicals. The competition between reactions (5) and (6) was studied by isotopic analysis of the hydrogen, methane, and isobutene fractions. CH2CD(CH3)2→CH2=C(CH3)2+DCH2CD(CH3)2→CH2=CDCH3+CH3.
Reaction (5) was found to be of negligible importance relative to reaction (6) up to 540°C and it is concluded that previous estimates of k5/k6 (in the nondeuterated species) are too high by at least an order of magnitude. The expulsion of molecular hydrogen by isobutyl or t-butyl does not occur in competition with other unimolecular reactions of these radicals.