bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of Double-Layer Differential Capacitance in Electrolytes
Authors: Macdonald J. Ross , Barlow Carl A.
Published: January 2005

A theory of the double layer in uni-univalent unadsorbed electrolytes is developed and used to analyze Grahame's experimental measurements of differential capacitance for NaF in water at 0° to 85°C and KF in methanol at 25°C. Excellent agreement with experiment is obtained except in the region of strong anodic polarization; this disagreement is tentatively ascribed to specific adsorption of anions, an effect not quantitatively considered in the present work. Although the quantities calculated herein relate to the entire double layer as, of course, do Grahame's data, the Gouy—Chapman theory of the diffuse part of the double layer (without dielectric saturation) is adequate in the present situation for all concentrations considered and has been used throughout. Consequently, the degree of agreement between theory and experiment found reflects primarily upon the applicability of the present theory of the inner layer. In the absence of specific adsorption this region is taken to be a hexagonally close-packed charge-free monolayer of solvent, physically adsorbed on the mercury electrode by dipole image forces. Adsorption anisotropy can lead to some dielectric saturation in the inner layer even at the electrocapillary maximum, the point of zero electrode charge. Neglecting association in the monolayer, the inner-layer dielectric constant and its dielectric saturation properties are calculated under three situations—where dipole image contributions are neglected, where the monolayer dipoles are imaged in the mercury electrode only, and where they are additionally imaged in an equipotential plane on the other side of the layer. The last case leads to an infinite set of images and to infinite series which are summed. These treatments all lead to much smaller dielectric constants and saturation constants than are found for bulk solvent. Comparison with values of these constants obtained from fitting the theory to the experimental data using a digital computer yields reasonably close agreement. New equations for the dependence of inner-layer thickness, volume, and dielectric constant on pressure and electric field, are derived and applied. The electrostatic pressure in this region is shown to consist of a capacitor-plate compressive term and an electrostrictive term, the latter originating only from the distortional and not the orientational polarization of the inner layer. As with the dielectric properties, the compressibility of the inner region found from curve fitting is of the right order of magnitude for both water and methanol solvents. The hump which occurs in water at low temperatures and small anodic polarization is attributed to the interplay of specific adsorption and dielectric saturation. Finally, it is pointed out that the usual method of separation of the inner-layer capacitance from the total differential capacitance by assuming the former to be in series with the diffuse-layer capacitance is unjustified in regions of appreciable specific adsorption, where the inner layer is no longer charge free.
Calculation of Atomic Valence State Energies of B—, C, and N+ in BHn—, CHn, and NHn+, n = 1 to 4
Authors: Ellison Frank O.
Published: January 2005

A general procedure described previously for calculating atomic valence state energies is simplified and extended to calculation of the intra-atomic portion of resonance energies of two or more valence bond structures. The revised method is illustrated by its detailed application to the 1A1 state of CH2 (in which, however, the nuclei are displaced to a linear configuration). The atomic valence state and intra-atomic resonance energies of B—, C, and N+ in various electronic states of BHn—, CHn, and NHn+, respectively, are then given as a function of hybridization.
Calculation of p-Band Positions of Aromatic Polycyclic Hydrocarbons by Limited Configuration Interaction Method
Authors: Koutecký J. , Paldus J. , Zahradník R.
Published: January 2005

The positions of p-bands of 20 aromatic polycyclic hydrocarbons have been calculated by the semiempirical limited configuration interaction method in a π-electron approximation using Hückel's molecular orbitals. The agreement with experimental values is very good. The effect of the extent of configuration interaction has been studied. It has been demonstrated that the contribution of electron repulsion integrals is nearly constant within this class of hydrocarbons. The failure of the approximation of Hückel in the studies of spectra of compounds with conjugated double bonds belonging to different classes of hydrocarbons, has been explained by the fact that the contribution of electron repulsion integrals is larger with polyenes and considerably smaller with tropylium and its benzoderivatives. The usefulness of the approximation of Hückel within one class of compounds is demonstrated by a comparison of the experimental and theoretical (according to Hückel) positions of the lowest energy absorption maximum of the aromatic hydrocarbon derivatives.
Infrared Absorption Spectrum of CD4 at 4500 cm—1
Authors: Fox K. , Hecht K. T. , Meredith R. E. , Peters C. W.
Published: January 2005

A high-resolution infrared absorption spectrum is presented for the region of the first overtone of the triply degenerate vibrational fundamental ν3 of CD4. The measured lines between 4430 and 4550 cm—1 are reproduced and tabulated. Comparisons are made between the tetrahedral splittings in this spectrum and those in the spectra ν3 and ν1+ν4 of CH4.
Gas-Phase Radiolysis of Propane
Authors: Ausloos P. , Lias S.
Published: January 2005

The radiolysis of CH3CD2CH3 and of equimolar C3H3—C3D8 mixtures in the presence of radical scavengers has been investigated as a function of pressure from 0.35 to 6000 mm and as a function of temperature from 40° to 220°C.

In the presence of scavengers, hydrogen and methane are mainly produced by molecular elimination. Values for the ratio CH3D/CH4 were found to increase with pressure and with surface to volume ratio of the irradiation vessel. Ethane is mostly formed by a hydrogen transfer reaction such as C2H5++C3H8→C2H6+C3H7+.From the distribution of the isotopic ethanes formed in the radiolysis of CH3CD2CH3, it can be concluded that the hydrogen atoms in the CH3CD2+ ion undergo a rapid randomization prior to reaction with propane.

Ethylene can be accounted for by the occurrence of the following processes: (a) decomposition: C3H8*→CH4+C2H4, (b) ion molecule reactions, (c) decomposition of vibrationally excited propyl and/or ethyl radicals.

From a comparison of the radiolysis results with the mass spectral cracking pattern of propane and recent photochemical studies, it can be deduced that the decomposition of propane ion and of neutral excited propane molecules are responsible for the products. The relative importance of these two modes of decomposition depends on the pressure and the size of the reaction vessel.
Photosensitized Reaction between Hydrogen (2P) Atoms and Molecular Nitrogen
Authors: Tanaka Ikuzo , McNesby J. R.
Published: January 2005

The reaction between H(2P) atoms and molecular nitrogen has been studied. H(2P) atoms were produced by irradiating ground-state H(2S) atoms, generated in a microwave discharge, with Lyman-alpha radiation at 1216 Å (∼1014—1015 quanta sec—1). The interaction of H(2P) atoms with N2 produces ammonia but not hydrazine. Two alternative mechanisms of the primary reaction are proposed. The first involves transfer of electronic energy. H(2P)+N2(1Σ+g)→H(2S)+N2*;N2*→2N(4S).The second possibility is a chemical mechanism involving atom transfer. H(2P)+N2(1Σ+g)→NH(3πi)+N(4S).Ammonia is formed either by reaction of N with H or by reaction of NH with H or H2.
Direct Observation of Individual Adatoms: Nitrogen on Tungsten
Authors: Ehrlich Gert , Hudda F. G.
Published: January 2005

The utility of the field ion microscope for adsorption studies has been explored by examining the interaction of nitrogen with an atomically smooth tungsten surface. Individual nitrogen adatoms are shown to be visible, and it is demonstrated that adsorption fails to perturb the lattice permanently. In probing the room-temperature distribution of adsorbed material, the closely packed (110) is found to remain bare, even when exposed to nitrogen at p=2×10—6 mm for 2 hr. All the other planes, with the possible exception of the {100} and {130}, are irreversibly covered. Nitrogen, presumably in the form of atoms, is bound on the (110) only at T<190°K. Adsorption on this plane at higher temperatures is limited not by an activation barrier but rather by thermodynamics: the binding energy on the (110) is only 5.1 ev, compared with 6.7 ev elsewhere on the surface.
Inelastic Scattering from Atoms at Medium Energies. I. Bound States
Authors: Bonham Russell A.
Published: January 2005

The problem of computing differential scattering cross sections for the inelastic scattering of 10–80 kv electrons from atoms is treated. Expressions for the electron scattering factor for the excitation of bound states of atoms for small excitation energies are presented using the first Born approximation. The scattering factor and differential cross section for argon at 40 kv have been calculated neglecting spin and polarization effects. Both Hartree—Fock and Slater central-field wave functions were used in these calculations. Selection rules for electron excitation of bound states of atoms and the behavior of the total inelastic scattering intensity at small scattering angles are discussed. Approximate formulas for the first Born approximation total cross sections have also been derived.
Infrared Studies of Nitriles as Proton Acceptors in Hydrogen Bond Formation
Authors: Mitra Shashanka S.
Published: January 2005

The hydrogen-bond formation between phenol, methyl alcohol, and pyrrole as proton donors and acetonitrile, propionitrile, butyronitrile, acrylonitrile, 3-butenenitrile, and cyanogen bromide as proton acceptors has been studied by the infrared spectroscopic method. Spectra were recorded (CaF2 prism) for the OH and NH stretching modes in binary and ternary solutions. CCl4 was used as the solvent for the latter. In ternary solutions bands for both bonded and unbonded molecules were observed. Temperature dependent spectra were used to obtain the heat of formation of the hydrogen bonds. A correlation between the energy of formation and the corresponding frequency shift, Δν (=νfree—νassoc) could be made. In the binary system with a donor compound as solute and an acceptor compound as solvent, only one band corresponding to the bonded molecule was observed. The intensity of this band increased monotonically with the solute concentration, and no other band was observed even for a concentration of 4 moles/liter. The results indicate that the solute—nitrile interactions are stronger than solute—solute interactions, and that only one species of complex molecules is formed, which presumably is a single solute molecule bonded with a single nitrile molecule. A comparison shows that in every case the Δν measured in a weak ternary system was of considerably lower value than that in the corresponding binary system. This is explained as due to the environmental effect of the nitriles which are known to have very high dielectric constants (∼40).
Photo-ionization of Alkyl Free Radicals
Authors: Elder Fred A. , Giese Clayton , Steiner Bruce , Inghram Mark
Published: January 2005

Studies of the photo-ionization of the methyl, ethyl, propyl, and isopropyl radicals are reported. The radicals were prepared by pyrolysis of the appropriate alkyl nitrites, tetra-alkyllead compounds, and the dialkylmercury compounds. Secondary processes occurring in the energy range covered (7.2–11.7 ev) are discussed.

The appearance potentials for the methyl, ethyl, propyl, and isopropyl radicals, as measured by photo-ionization—mass spectrometric techniques are 9.82±0.04, ≤8.4, ≤8.1, and ≤7.5 ev, respectively. The adiabatic transition is accessible for the methyl radical only. Hence, the ionization potential of the ethyl, propyl, and isopropyl radicals cannot be determined by ordinary photon or electron impact experiments.
Nuclear Magnetic Resonance Study of Collagen Hydration
Authors: Berendsen Herman J. C.
Published: January 2005

The proton resonance signal of water in partially dried tendon shows three peaks for samples equilibrated in an atmosphere of 30%—80% relative humidity (R.H.). The outer-peak splitting (between 0.5 and 1 gauss) has the character of a proton-pair splitting with effective interactions in, or close to, the fiber direction, as concluded from the dependence of the absorption on the angle between the fiber direction and the magnetic field. Chainlike water structures, exhibiting certain proton-reorientation processes, are postulated. At 10% R.H. a narrow peak is observed, which is not angular dependent; this indicates rapid reorientation of water molecules. Above 80%—90% R.H., a single peak is observed, the width of which has a strong angular dependence. A structural relationship between collagen and water exists, by virtue of which the existence of water chains and, possibly, of three-dimensional water structures, could be stabilized.
Crystal Spectrum of Chromium Acetylacetonate and the Ligand Field in Trigonal Coordination Compounds
Authors: Piper T. S. , Carlin R. L.
Published: January 2005

The optical crystal spectrum of chromium acetylacetonate has been measured. The trigonal field splitting K is found to be +530 cm—1. The ionic model can account for the sign of the trigonal field and intensity ratios of Cr(C2O4)3—3 but not of the acetylacetonate. This failure is ascribed to covalency, particularly π covalency in the acetylacetonate ring.
Thermal-Diffusion—Column-Shape Factors for a Gas Composed of Rigid Spherical Molecules
Authors: Raman S. , Saxena S. C.
Published: January 2005

The thermal-diffusion—column-shape factors have been computed for a gas whose molecules interact as rigid spheres. These tabulations supersede the earlier results of Srivastava, which are based on incorrect theoretical expressions for the shape factors. The experimental data on helium and xenon are interpreted. Previous tabulations of shape factors according to the Lennard-Jones (12–6) and Maxwellian models are also considered. It is found that for both the gases the calculated values of separation factors are in better agreement with the experimental data for the inverse power model than the Lennard-Jones (12–6) potential; the improvement though small for helium is very pronounced for xenon.
Structure of Water and Hydrophobic Bonding in Proteins. I. A Model for the Thermodynamic Properties of Liquid Water
Authors: Némethy George , Scheraga Harold A.
Published: January 2005

The thermodynamic parameters of liquid water are derived by means of a statistical thermodynamic treatment, based on the ``flickering cluster'' model proposed by Frank and Wen. Various models proposed for the structure of liquid water are reviewed, and the advantages of the Frank—Wen model are pointed out. The hydrogen-bonded ice-like clusters of H2O molecules in equilibrium with non-hydrogen-bonded liquid are described quantitatively in terms of the molecular species participating in different numbers of hydrogen bonds in the clusters. Equations expressing the mole fractions of the various species in terms of the average cluster size are derived. The partition function derived for the description of liquid water is based on a distribution of the H2O molecules over five energy levels, corresponding to four, three, two, one, and no hydrogen bonds per molecule. The most probable values of the average cluster size, the mole fraction of non-hydrogen-bonded water, and the thermodynamic parameters are obtained from the partition function. The energy of the hydrogen bond and the molecular ``free volume'' of the unbonded molecules are introduced as adjustable parameters; they are shown to have physically reasonable magnitudes. The average cluster size ranges from 91 to 25 H2O molecules over the temperature range from 0° to 70°C, with the mole fraction of non-hydrogen-bonded molecules increasing from 0.24 to 0.39 over the same range of temperature. The calculated values of the free energy, enthalpy, and entropy of liquid water in this temperature range agree with experimental data to within an error of less than 3%. The calculated temperature dependence of cv is too large. The calculated results agree well with the radial distribution curve derived from x-ray diffraction data. The compressibility and the thermal expansion are considered in terms of two contributing forms in the liquid: the hydrogen-bonded clusters and the more closely packed molecules. The P—V—T data derived for the close-packed species from the model and from experimental data are shown to have physically reasonable magnitudes. Several other properties are discussed qualitatively on the basis of the model. The model can also be extended to provide an explanation of the properties of aqueous solutions of nonpolar substances.
Reliability of the Hellmann—Feynman Theorem for Approximate Charge Densities
Authors: Salem L. , Wilson E. Bright
Published: January 2005

A spherical atom in a uniform external field and the long-range interaction of two molecules are examples which illustrate the unreliability of the Hellmann—Feynman theorem when applied to systems described by approximate wave functions or charge densities. However, in the first case a wave function correct to first order in the perturbing field and in the second case a wave function correct to second order in the mutual interaction will yield the correct force.

For spherical atoms in an external field, the contribution of the continuum states to the electronic screening of the field is very large, 54% for hydrogen and about 72% for helium. From this case also one can evolve general considerations concerning the use of effective nuclear charges in electrostatic force calculations.

In the general case it is shown that for a system submitted to a given perturbation the wave function correct to order n, or the corresponding charge density, yields the force correct to order n and to order n only. This result leads to a brief comparison of the Hellmann—Feynman procedure and the variational method.
Radius of Gyration of Polymer Chains
Authors: Fixman Marshall
Published: January 2005

The probability distribution of the radius of gyration of unbranched polymer chains is discussed. The characteristic function of the distribution is presented in closed form, and calculations are the made of the semi-invariants, moments, and behavior of the probability at very large and very small values of the radius of gyration.
Dielectric Constants of Imperfect Gases. II. Carbon Dioxide and Ethylene
Authors: Johnston D. R. , Cole R. H.
Published: January 2005

Dielectric constants in the density range 0 to 4 moles/liter have been measured at temperatures between 25° and 75°C. Both gases show significant increases of the Clausius-Mossotti function with density attributable to pair interactions. In CO2, these are consistent with the theory of quadrupole-induced dipoles for a molecular quadrupole moment of about 5×10—26 esu cm2. In ethylene, the increased effect at higher temperatures is contrary to the theory, which is given in a more general form suitable at high temperatures for molecules such as ethylene, which lack axial symmetry. It is shown that for both gases the theory may be somewhat inaccurate at ordinary temperatures because effects of quadrupole coupling energies have not been adequately treated. Measurements of mixtures with a second gas of highly symmetrical molecules are proposed as a promising means of studying the questions raised by those results.
Infrared Spectra of Metal Chelate Compounds. VI. A Normal Coordinate Treatment of Oxalato Metal Complexes
Authors: Fujita Junnosuke , Martell Arthur E. , Nakamoto Kazuo
Published: January 2005

The infrared spectra of 10 oxalato complexes have been obtained in the frequency range 4000 to 300 cm—1. A normal coordinate treatment made on the 1:1, metal:ligand model of the chelate ring of tris-(oxalato)-Cr(III) resulted in the assignment of metal-oxygen stretching bands in the range between 600 and 300 cm—1 for various oxalato complexes. The force constants and the band assignments obtained are compared with those of the previous normal coordinate analysis based on the free oxalato ion. Relationships between the metal-oxygen and the carbon-oxygen stretching frequencies are discussed.
Infrared Spectra of Metal Chelate Compounds. VII. Normal Coordinate Treatments on 1:2 and 1:3 Oxalato Complexes
Authors: Fujita Junnosuke , Martell Arthur E. , Nakamoto Kazuo
Published: January 2005

Normal coordinate treatments have been made on the square planar 1:2 oxalato complex of Pt(II) and the octahedral 1:3 oxalato complex of Cr(III), and the results were compared with those obtained with simple 1:1 complexes. It was found that coupling between the ligands in the square planar 1:2 complex is small whereas coupling between the ligands in the octahedral 1:3 complex is appreciable. Observed differences of the spectra between 1:1 and 1:2 oxalato complexes of Pt(II) and between 1:1 and 1:3 oxalato complexes of Cr(III) and Co(III) are in good agreement with the results of these calculations.
C13 Splittings in Proton Magnetic Resonance Spectra. III. Formyl Compounds
Authors: Muller Norbert
Published: January 2005

Electron-coupled spin-spin interaction constants JC–H for a series of formyl compounds are presented and interpreted. It is concluded that JC–H is essentially independent of the polarity of the C–H bond and provides the best experimental measure of the hybridization of the carbon atomic orbital used in the bond. Some of the C–H bonds involve carbon orbitals of surprisingly high s character, especially in view of the available data on the bond lengths. It is suggested that the electrostatic interaction between the C–H proton and the π electron density may play an important part in fixing the lengths of these C–H bonds.
Heats of Solution of Alkali Metals in Liquid Ammonia at 25°
Authors: Gunn Stuart R. , Green LeRoy G.
Published: January 2005

Heats of solution in ammonia at 25° have been measured for Li, Na, and K at concentrations down to 0.005 M, and for Na in the presence of NaI. Dilution is endothermic, and the heat of dilution is greater in the presence of added Na ion; these results support the Becker-Lindquist-Alder theory of the solutions.
Diffraction of X Rays by Liquid Neon
Authors: Stirpe Dante , Tompson C. W.
Published: January 2005

X-ray diffraction patterns obtained from liquid neon at six conditions of temperature and pressure ranging from the triple point to the critical point were used to calculate the corresponding radial atomic distribution functions. Areas and locations of the first peaks in the distribution curves varied from 8.4 atoms at 3.18 A near the triple point, to 4.3 atoms at 3.26 A near the critical point. Experimental intensity patterns for temperatures nearest the triple and critical points were compared with intensity patterns calculated by the method used by Fournet. Small-angle scattering patterns obtained at 15 conditions of temperature and pressure near the critical point were used to calculate corresponding radii of gyration and characteristic functions.
Theory of Condensation of Liquids of One and Two Components
Authors: Cernuschi Felix , Segre Myriam
Published: January 2005

Cernuschi and Eyring's theory of condensation has been reconsidered, taking account of Kirkwood's criticisms, by the introduction of vibrations in the model. Variation of Einstein's frequency with temperature has been considered, following some works of Raman. With these modification results according with experiment are obtained, overcoming thus Kirkwood's objections.

The possibility of extending the model to the case of two components is then examined. The resulting formulas do not allow, because of their complexity, an analytic determination of the critical point. The equations can be simplified supposing that only one of the three previous interactions is different from zero. Numerical calculation has been done for the case of interaction between different particles. The critical curve is found by trial and error. The calculations made for three different concentrations of one of the components (parameter in the theory) shows that the exp(ε/kTc)—ε interaction energy decreases with such concentration.
Some Photochemical Reactions of O3 in the Gas Phase
Authors: Katakis D. , Taube H.
Published: January 2005

When a gaseous mixture containing O3 and CO2 of different isotopic composition is illuminated by uv light, the oxygen that is formed has undergone some exchange with CO2. The extent of this exchange has been studied as a function of initial O3 and CO2 pressure, and the influence of foreign gases on it was also studied. It is concluded that O1D is the intermediate which undergoes rapid exchange with CO2, and further that the reaction O1D+CO2⇌CO+O2does not provide the dominant mechanism for this exchange. The results suggest that at low total pressures exchange takes place by O*+CO2⇌O+CO2*and that at high total pressures, CO3 is formed as an intermediate.
Statistical Theory of Dielectric Fluids
Authors: Isihara A. , Hanks Russell V.
Published: January 2005

A formal cluster expansion theory of the dielectric constants and the susceptibilities of nonpolar fluids is developed and the deviation of the Clausius-Mossotti equation from experiments is discussed. Many-body polarization effects are considered in terms of diagrams. A chain-diagram approximation gives the susceptibilities in terms of the Fourier transforms of the Mayer f function and of the effective dipole interaction tensor.
Variational Calculation of Ethylene
Authors: Huzinaga S.
Published: January 2005

A variational treatment is applied to the lower electronic states of planar ethylene; specifically the 1Ag(N), 3B1u(T), and 1B1u(V) states are investigated. The problem is treated nonempirically by using the method of molecular orbitals within the framework of the π-electron approximation. Several new features are introduced. First, we use separate ζ values (orbital exponents) for the bonding and antibonding LCAO MO's. This brings about significant improvements in lowering the energy of the V state. As a result, the separation of the V and T states, which was too large in the conventional LCAO MO calculations, is now in much better agreement with the experiment. Extensive variations are made in the π-electron orbitals; three different σ-core potential fields are also examined. Zener's value of the effective charge for the σ-core electrons is shown to be an adequate choice for characterizing this core field. The effect of the four hydrogen atoms is also investigated.
Hydrogen-Deuterium Kinetic Isotope Effect at Very High Temperature
Authors: Johnston Harold S. , Tschuikow-Roux Eugene
Published: January 2005

The kinetic isotope effect for the reaction CF3+CH2D2→CF3H+CHD2 or CF3D+CH2D has been studied in a shock tube between 1000° and 2000°K where CF3 radicals were produced by thermal decomposition of CF3N2CF3. In the reaction zone gas compositions were: noble gases≫CH2D2≫CF3N2CF3; and in this way ratio of final products CF3H/CF3D was equal to the ratio of rate constants kH/kD. The data are represented empirically by lnkH/kD=ln1.400+0.42×106/T2. A London-Polanyi-Eyring-Sato potential energy surface was constructed, where Sato's parameter was fitted to give the correct activation energy, and the frequencies and zero-point-energy of the activated complex were then found from curvatures through the saddle-point of the potential energy surface. At very high temperatures activated complex theory predicts lnkH/kD=ln1.402+0.502×106/T2 —0.069×1012/T4, in fair agreement with experiment.
Paramagnetic Relaxation in Asphalt Solutions
Authors: Poindexter Edward H.
Published: January 2005

The relaxation time of the free-radical electrons in asphalt solutions at 18.6 gauss has been measured by a double-resonance technique. The relaxation time T1e is found to average below 1 μsec in solutions containing dissolved oxygen and about 15 μsec in degassed solutions. The finer variations in T1e with asphalt concentration may be qualitatively correlated with the viscosities of the solutions.
Microwave Absorption and Molecular Structure in Liquids. XLIV. Investigation of Dielectric Relaxation by an Interferometric Method for the Measurement of Dielectric Constant and Loss at 2.2-mm Wavelength
Authors: Vaughan W. E. , Lovell W. S. , Smyth C. P.
Published: January 2005

The theory and apparatus for an interferometric method for the measurement of the dielectric constant and loss of a liquid at 2.2-mm wavelength are described. The probable error of the dielectric constant measurements is 2%. The probable error of the loss measurements is 2–5%, increasing for high-loss materials. The dielectric constants and losses of chlorobenzene, phenyl ether, and benzophenone have been measured at 2.2-mm wavelength at temperatures between 21.5° and 60°. The results are examined in the light of existing lower-frequency data. The presence of a second dispersion region for benzophenone has been confirmed. The observed losses at 2.2-mm wavelength are slightly higher than extrapolation of lower-frequency data would predict.
Assignment of Electronic Transitions in Azo Dye Prototypes
Authors: Robin Melvin B. , Simpson William T.
Published: January 2005

Quantitative calculations of the absorption frequency, transition moment length, and polarization of the first strong absorption band in the series of compounds C6H5N=N(C6H4N=N)xC6H5 have been successfully carried out using a model employing delocalization of electronic excitation energy rather than delocalization of electrons. It is found that the compounds can be treated as azo-perturbed phenyl groups interacting with both an electrostatic force and through conjugation. Because of the electrostatic part of the interaction, there results a demonstrable heat of single bond isomerization in phenylazo-β-naphthalene, its conformational isomers possessing different colorband spectra.

The n—π* transition in the azo dyes is shown to be, in all probability, the low-frequency component of two previously degenerate n—π* bands which have split. The intensity and polarization of the formally forbidden, low-frequency n—π* band can be explained by assuming a mixing of the n—π* band with the strong, low-frequency band responsible for the color in azo dyes.

A high-frequency band found at 44 kk (the symbol kk used throughout this paper stands for kilokayser or 103 cm—1) having a constant intensity throughout the series of dyes investigated has been shown to be isolated within the end phenyl groups.
Vacuum Ultraviolet Photochemistry. II. Photolysis of Ethylene
Authors: Okabe H. , McNesby J. R.
Published: January 2005

The direct photolyses of CH2CD2 and trans-CHDCHD were carried out at room temperature in the vacuum ultraviolet region. Kr, Xe, and Hg resonance radiations were used for photolyses. Products at the Kr lines were mainly hydrogen, acetylene, ethane, and n-butane. The ratio of acetylene/hydrogen was 2.8±0.2 at 1236 A. The photolysis of CH2CD2 gives 40% H2, 40% HD, and 20% D2. The acetylene was 12% C2H2, 62% C2HD and 26% C2D2. The relative amounts of H2, HD and D2 depend upon whether a hydrogen molecule is eliminated from two (type I process) or one (type II process) carbon atom. The remaining vinylidene rapidly rearranges to acetylene.

The photolysis of trans-CHDCHD gives 17% H2, 73% HD, and 10% D2. This shows that hydrogen is formed from the trans as well as from the cis position and that the isotope effect for the type I process is slightly smaller than that for the type II process. Nearly free rotation of the molecule in its excited state is suggested. The percentages of the hydrogen isotopes produced are almost independent of exciting wavelength in both isotopic ethylenes. A comparison is made with Hg(3P1)-sensitized photolysis.
Infrared Spectrum and Thermodynamic Properties of Gaseous Sulfur Trioxide
Authors: Lovejoy R. W. , Colwell J. H. , Eggers D. F. , Halsey G. D.
Published: January 2005

The infrared spectrum of sulfur trioxide was obtained under prism resolution in the gaseous state and in xenon matrices at liquid-nitrogen temperature. In both cases a satisfactory vibrational assignment of the monomeric SO3 spectrum could be made on the basis of a simple D3h symmetry model. The observed gas phase fundamentals were v3(e′) = 1391, v4(e′) = 529, and v2(a2″) = 495 cm—1. The matrix fundamentals were essentially the same as those of the gas phase except that the v2(a2″) mode was shifted to 464 cm—1. A normal coordinate treatment of the SO3 molecule was carried out and potential constants were determined for both Urey-Bradley and simplified valence force fields. Three weak absorption bands of S3O9 were also detected in the gas-phase spectrum. From the temperature and pressure variation of the intensities of these bands it was estimated that for the trimerization reaction at 298°K, Kp was approximately 1 atm—2 and ΔH298° was approximately 30 kcal/mole of S3O9. The values of the thermodynamic properties of monomeric SO3 were computed for the ideal gaseous state using the rigid rotor harmonic oscillator approximation at 1 atm from 100° to 1500°K.
De-Excitation of Molecular Vibration by Collision
Authors: Bauer Ernest , Cummings F. W.
Published: January 2005

The reaction rate has been calculated for a vibrationally excited diatomic molecule to be de-excited by collision with another atom or molecule, the second particle carrying away the excess vibrational energy as kinetic energy. The quantum mechanical distorted wave method has been used in the ``modified wave number'' approximation, and the large amplitude of the vibrational motion is taken into account both in the choice of vibrational wave functions (Morse functions) and in the interaction potential. The calculation is performed for the process N2(a1Πg;v)+N2(X 1Σg+)⇒N2(a1Πg;v′<v)+N2(X 1Σg+)+kinetic energyfor the vibrational transitions v = 5 to v′ = 4, 3, 2, 1, 0, and for v = 2 to v′ = 0 and v = 1 to v′ = 0, for the temperature range 300–6000°K. The results show clearly that in a situation of this kind the collisional de-excitation of the molecular vibration proceeds in steps v—v′ = δv = 1, rather than δv>1.
Motion of Small Suspended Particles in Nonuniform Gases
Authors: Mason Edward A. , Chapman Sydney
Published: January 2005

The motion of small suspended particles in a gas or gas mixture containing gradients of temperature, pressure, or composition is derived as a special case of the Chapman-Enskog kinetic theory of gases, by formally treating the suspended particles as large molecules. Gas molecules colliding with the suspended particles are considered to rebound elastically, but a fraction f rebound in random directions and the remainder rebound specularly. The results check, in an indirect way, the calculations of Waldmann by a momentum transfer method on a slightly different model, in which the randomly rebounding molecules also have a random distribution of speeds. Significantly different results are predicted by the two models only in the presence of a temperature gradient (thermal diffusion), which has interesting implications concerning thermal diffusion in polyatomic gases.
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.
Microwave Absorption and Molecular Structure in Liquids. XLV. The Dispersion of Alkyl Halides at Millimeter Wavelengths
Authors: Vaughan W. E. , Lovell W. S. , Smyth C. P.
Published: January 2005

The dielectric constants and losses of selected n-alkyl bromides have been measured at 4.3- and 2.2-mm wavelength at various temperatures between 1° and 55°. In addition, n-octyl chloride, i-amyl bromide, and i-butyl bromide have been measured at 4.3 mm wavelength, and i-amyl bromide has been measured at 1.22 cm. The results are examined in the light of existing lower frequency data. Asymmetric plots of dielectric loss against dielectric constant are found. The nature of the distribution function which would produce such asymmetry is investigated. The losses at 2.2-mm wavelength are unexpectedly large and, consequently, lead to slightly smaller values of the optical dielectric constant than those previously obtained for these substances.
Nuclear Magnetic Resonance Study of the Diffusion of Hydrogen in Zirconium Hydride
Authors: Hon J. F.
Published: January 2005

Diffusion of hydrogen in two hydrides of zirconium, ZrH1.54 and ZrH1.99, has been studied by nuclear magnetic resonance methods. The activation energy for diffusion of hydrogen by a direct tetrahedral to tetrahedral site jump mechanism was found to be 0.54 ev in both compositions. A complex proton line shape was observed in ZrH1.99 over part of the temperature range covered in these measurements. A tentative explanation of this line shape results in an estimate of 0.65 ev for the activation energy for diffusion by an indirect tetrahedral to octahedral to tetrahedral site mechanism. The rigid lattice linewidth of the proton line in both hydrides was found to be too large to be accounted for by nuclear dipolar broadening.
Isotopic Fractionation of Nitrogen in the Nitrogen Oxide-Nitrate Exchange System
Authors: Stern Marvin J. , Kauder Lois Nash , Spindel W.
Published: January 2005

The single-stage fractionation factors for nitrogen exchange between nitric oxide and nitrate salt solutions were found to range from 1.073 at 25° to 1.056 at 70°. The experimental values are about 0.007 less than the values calculated from spectroscopic data, a result not unexpected, since the statistical-mechanical calculations do not take interactions in a condensed phase into account. Within the estimated experimental error of ±0.004, the isotope effect appears to be independent of the nature and degree of complexing of the nitrate ion in solution. Measurements were also made of the fractionation factors between nitric oxide and nitric acid solutions (1–12 M) over the temperature range 25–70°. The formation of additional oxy-nitrogen species in both phases introduces additional exchange reactions which lower the over-all isotope effect significantly. Due to the changes in the chemical compositions of the phases, the observed factors go through a maximum in the vicinity of 6 M nitric acid. The experimental effective fractionation factors are in general agreement with the values calculated from the chemical compositions of the systems and the partition function ratios for the chemical species involved.
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.
Estimation of the Mutual Diffusion Coefficient of Hydrogen Atoms and Molecules
Authors: Weissman Stanley , Mason E. A.
Published: January 2005

The mutual diffusion coefficient D12 of hydrogen atoms and molecules has been calculated from experimental data on the viscosity of mixtures of hydrogen atoms and molecules. The needed viscosity of pure atomic hydrogen was calculated from accurate experimental and theoretical potential energy curves. The resulting values of the viscosity are about 15% smaller than those estimated previously by Amdur from the mixture data, and the values of D12 about 30% greater than Amdur's estimate. Values of D12 calculated directly from the atom-molecule force law are in good agreement with those obtained from the mixture viscosity.
Critical Opalescence of Polystyrene in Cyclohexane Transmission Measurements
Authors: Debye P. , Woermann D. , Chu B.
Published: January 2005

In the vicinity of the critical point, angular dissymmetry of scattering is observed. Its amount is connected with the range of molecular forces. Integrated over all angles it reveals that the total scattering is less than that calculated according to Einstein. At the same time the scattered light is less blue than we would expect according to Rayleigh. This effect has been investigated on the system polystyrene-cyclohexane by measurements of the wavelength dependence of the total turbidity of the solution at its critical concentration as a function of the temperature. The interaction ranges as calculated from the data are in good agreement with values calculated from dissymmetry measurements.
Calculation of NMR Chemical Shifts
Authors: O'Reilly D. E.
Published: January 2005

A condition in the application of the total orbital angular momentum operator to generate a trial function for a variational calculation of chemical shifts is derived from the equation of continuity in a rotating coordinate system. Group-theoretical arguments are used to show that the origin for the angular momentum operator should be chosen at a center of symmetry or along an axis of symmetry if no center of symmetry is present. The method is applied to a hydrogen atom in an electric field and the results are compared to the exact solution. For multicenter problems, the trial function must be modified as required by invariance of the Schrödinger equation under translations. A modified function is proposed and an explicit formula for the chemical shift is derived, which is invariant to choice of origin. Application is made to the calculation of the chemical shifts of nuclei of ions in crystalline fields. Relationships of the variational method with perturbation methods are discussed.
Nuclear Magnetic Resonance Effects in Aqueous Solutions of 1–1 Electrolytes
Authors: Hindman J. C.
Published: January 2005

Experimental data on the effect of varying concentrations of salts of univalent diamagnetic ions on the proton resonance of water are given. A reference scale for the division of the infinite dilution shifts for the salts into contributions for the separate ions is discussed. Factors entering into the separate ion contributions are considered and a model is developed from which an attempt has been made to evaluate in a quantitative manner the magnitude of these factors. ``Effective'' hydration numbers are calculated from this model, which treats as ion-water complex as a molecular species. These hydration numbers for cations are very similar to estimates of ``primary'' hydration obtained from other sources. A decrease in effective hydration number with increasing cation radius is found. It is suggested from th data that of the halide ions, only the fluoride ion forms a hydrate in the chemical sense, the larger halide ions acting primarily to break down the water structure, the effect increasing with increasing anionic radius. These structural effects are expressed in terms of equivalent numbers of hydrogen-bonds made or broken. A structure-making effect is suggested for the lithium ion. Factors to be considered in the extension of the equations to the interpretation of concentration effects are discussed and evidence presented for different kinds of environmental changes occurringe in solutions of different salts.
Dissociation of Gaseous Diatomic Molecules: Classical Adiabatic Scattering Approach
Authors: Light John C.
Published: January 2005

The classical Liouville equation of a three-body system consisting of a harmonic oscillator and a free particle is resolved by an adiabatic approximation procedure based on the assumption that the collision time is much larger than the period of vibration of the oscillator. An integral formalism developed from the Liouville equation is used, and strong interactions can be treated. Numerical calculations of the rate of dissociation of homonuclear diatomic molecules are in good agreement with experimental results over large temperature ranges. The Lennard-Jones 6–12 potential is used, and comparisons between one and three-dimensional calculations are made.
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.