bluuebunny/crossref_metadata_2025 huggingface dataset:
Spin-Density Distribution in Nitrile Anion Radicals
Authors: Rieger Philip H. , Fraenkel George K.
Published: January 2005

Molecular-orbital calculations of the pi-electron spin densities in a series of aromatic and aliphatic nitrile anion radicals have been performed using the Hückel—LCAO method and the approximate configuration-interaction correction of McLachlan. Coulomb and resonance integrals for the nitrile group were estimated by comparing calculated spin densities with proton and carbon-13 hyperfine splittings obtained from electron-spin resonance measurements. The predicted spin densities were in generally good agreement with the experimental results, but for some of the compounds it is impossible to get an exact fit between theory and experiment within the framework of the simple valence-theory calculations if the sigma—pi interaction parameters relating splittings to spin densities are taken as fixed quantities. Semiempirical treatments of the N14 and C13 splittings in the cyano groups give excellent correlations of the experimental splittings with the calculated spin densities, and estimates have been made of some of the sigma—pi interaction parameters relating to the N14 splitting. Polarographic half-wave potentials have also been compared with calculated pi-electron energies. A discussion is given of the relation between the spin densities predicted by the valencebond and molecular-orbital theories.
Electron Spin Resonance Spectra of Carbonyl Anion Radicals
Authors: Rieger Philip H. , Fraenkel George K.
Published: January 2005

Electron spin resonance studies are reported on the anion radicals of single-ring aromatic ompounds containing aldehyde, acetyl, or amide groups, as well as other substituents. The radicals were generated by electrolytic reduction in N,N-dimethylformamide solution. Many of the radicals have spectra which indicate that the carbonyl group is locked in a conformation planar with the ring for times of the order of a microsecond or longer. The para dicarbonyls and the 3-cyanoacetophenone anion were found to be present in both the cis and trans modifications. A simple modification of conventional molecular-orbital theory has been used with considerable success to account for the loss of symmetry in the pi-electron spin density for compounds with a locked carbonyl group, and the calculated energy differences for the cis and trans isomers are in good agreement with experiment. Molecular-orbital calculations of spin densities were made for most of the radicals, often with excellent results, and comparisons are made with the predictions of valence-bond theory. The benzaldehyde, acetophenone, and 4-fluoroacetophenone anions have spectra with abnormally small ring-proton splitting constants, and no satisfactory explanation of these anomalous results has been found. The appearance or nonappearance in all the radicals but these three of twofold symmetry in the pattern of splitting constants is interpreted qualitatively in terms of competing effects determined by the bond order of the bond between the ring and the carbonyl group, and steric factors in the neighborhood of the carbonyl group. A number of features of the experimentally determined spin-density distributions have been correlated with the relative electron-withdrawing effects of the substituents.
Boron Hydrides: LCAO—MO and Resonance Studies
Authors: Hoffmann Roald , Lipscomb William N.
Published: January 2005

The results of an LCAO—MO calculation for the boron hydrides and hydride ions B2H6, B4H10, B5H9, B5H11, B6H10, B9H15, B10H14, B10H16, BH4—, B3H8—, B9H14—, B10H10—2, B10H14—2, B12H12—2 are reported. Charge distributions and overlap populations are calculated from the wavefunctions for real distances and for idealized molecules with all distances equal. The three-center bond theory is extended to incorporate unsymmetric equivalent structures with concomitant improvement in charge distributions. These are compared with the presumably better LCAO—MO charges. The valence structure of a new boron hydride, B18H22, is discussed.
NMR and Double Resonance Spectra of CH2F2 and CH3CHF2 in the Gas Phase
Authors: Flynn George W. , Baldeschwieler John D.
Published: January 2005

The methyl proton spectrum of CH3CHF2 in the gas phase consists of three broad peaks, with a sharp doublet superimposed on the central broad peak. The proton spectrum of CH2F2 also consists of three broad features, with a single sharp peak superimposed on the central broad peak. Proton—fluorine double resonance measurements show that the width of the broad features in the proton spectra is determined by fluorine relaxation processes, and that the broad peaks arise from transitions between states with K(F)=1, while the sharp lines must be assigned to transitions between states with K(F)=0. The relative widths of the broad peaks are consistent with the assumption that the collision-modulated spin—rotation interaction provides the dominant fluorine relaxation mechanism, but that this interaction is not important for proton relaxation. The addition of oxygen to CH3CHF2 causes the broadening of the sharp central doublet in the methyl proton spectrum. However, it is shown by double resonance that the dominant effect of the addition of oxygen to CH3CHF2 is to decrease the proton relaxation time, rather than to increase the fluorine singlet—triplet conversion rate.
Rotational Isomerism and Microwave Spectroscopy. II. The Microwave Spectrum of Butyronitrile
Authors: Hirota Eizi
Published: January 2005

The butyronitrile molecule has been confirmed by microwave spectroscopy to exist in two rotational isomers, trans and gauche. Rotational constants in the ground vibrational state are A=23 668.06, B=2268.16, C=2152.95 Mc/sec for the trans form and A=10 060.37, B=3267.63, C=2705.49 Mc/sec for the gauche form. Three sets of vibrational satellites have been found for each form.
Kinetics of the Gas-Phase Addition of HI to C2H4 and the Pyrolysis of Ethyl Iodide
Authors: Benson Sidney W. , Bose A. N.
Published: January 2005

The addition of HI to C2H4 yields C2H5I at low temperatures and C2H6+I2 at higher temperatures. From 289° to 331°C the rate law is mixed—second order with C2H6+I2 as products. The rate is independent of added I2 and has a specific rate constant k2 (units, liter/mole-sec): logk2=8.52−(28900/4.575T). The pyrolysis of C2H5I from 330° to 392°C goes by a first-order process to C2H4+C2H6+I2. The first-order rate constant is given by (units, sec—1): logku=13.66−(50000/4.575T).

If it is assumed that both processes have the same rate determining step, namely the reversible dissociation of C2H5I, they yield an equilibrium constant in good agreement with independently calculated values of Keq for this dissociation. Under these conditions k1, the specific rate constant for the unimolecular split of C2H5I into C2H4+HI is given by ku/2. Arguments are presented to show that this common path involves the four-center molecular transition state rather than a radical disproportionation. The latter, however, may account for as much as 20% of the pyrolysis at 392°C.
Mass Spectrometry of Ions in Glow Discharges. III. Nitrogen and Its Mixtures with Hydrogen and Oxygen
Authors: Knewstubb P. F. , Tickner A. W.
Published: January 2005

Ions in the negative glow and positive column of a dc glow discharge in nitrogen have been examined at a pressure of 0.4 mm and a current density of 0.03 mA/cm2. Mixtures of nitrogen with hydrogen (0.9%) and with oxygen (0.5% and 20%) were also used.

In addition to N2+ and N+, the ions N3+ and N4+ are prominent in the negative glow in pure nitrogen. They appear to be formed by N++2N2→N3++N2, N2++2N2→N4++N2, both of which proceed to an extent dependent on field strength.

With added hydrogen the ions N2H+ and NH4+ become important. N2H+ appears to be formed by at least two processes. The concentration of NH4+ is greatest in the tail of the negative glow where vibrational excitation is a possible factor and the residence time of ions is relatively long.

In the presence of oxygen the ions NO2+ and N2O+ appear, as well as O2+, but the most prominent oxygen-containing ion is NO+. The mechanism of formation of these ions is not definitely assigned but charge-transfer reactions may be important, as well as ion-molecule reactions which depend to some extent upon vibrational excitation, or upon residence time in the discharge.
Conversion of Cv[T, V(T)] to Cv[T, V(0°K)] with Application to Na and Cu
Authors: Overton William C.
Published: January 2005

The thermodynamic quantity E(T)= ∫ V0V(∂Cv/∂V)TdV=Cv[T,V(T)]−Cv[T,V(0∘K)]may be evaluated in terms of the thermal expansion and the coefficients, ai's, in the solid equation of state and their derivatives. Slater's procedure for E(T) is extended herein to the case in which the ai's are arbitrary functions of temperature and pressure. This E(T) is then transformed to a second equivalent form in terms of the bulk modulus and its temperature and pressure derivatives. It is seen that Cv[T, V(0)] may be determined entirely from experimental data. The lattice specific heat CL[T,V(0)]=Cv[T,V(0)]−Tγe[V(0)], this form being the physically correct way of calculating CL from electronic specific heat measured at low temperatures, is determined for Na and Cu. The CL[T, V(0)] of Na is compared with the Born—von Kármán theoretical Ctheoret calculated by C. B. Clark; this comparison indicating an anharmonic CL of the form Ctheoret (1+AT+BTn), (5<n<6), where A is only one-sixth that calculated by Leibfried and Ludwig for Cp[T, V(T)]. Comparison of CL[T, V(0)] of copper with theoretical specific heat calculated by the author shows quantitative agreement (within 0.2% from 50° to 300°K) thus indicating the adequacy of the central force model with nearest- and next-nearest-neighbor forces used.
One-Center Integrals of Extraordinary Functions
Authors: Snyder Lawrence C.
Published: January 2005

One-center integrals required in wave mechanical computations with the individual lobes of real spherical harmonics are discussed. Convenient formulas and tables are given for overlap, nuclear attraction, kinetic energy, and Coulomb repulsion integrals employed in the variational computation of a helium-atom ground-state wavefunction by the interaction of configurations built from Slater orbitals of the angular types s, px, py, and pz; and the extraordinary functions |px|, |py|, and |pz|.
Microwave Spectrum, Structure, and Dipole Moment of Carbonyl Fluoride
Authors: Laurie Victor W. , Pence Dallas T. , Jackson Robert H.
Published: January 2005

The microwave spectrum of carbonyl fluoride, COF2 has been investigated in the region 8–30 kMc. The following effective rotational constants have been obtained (Mc): C12O16F219C13O16F219C12O18F219a11813.4511814.6611813.48b11752.9911747.2710878.54c5880.915879.815653.32The structure calculated from these constants is rCF = 1.312 Å, rCO = 1.174 Å, ≰FCF = 108.0°. From measurements of the Stark effect the dipole moment is found to be 0.951±0.010 D.
Derivation of Physically Significant Nonbonded Interaction Constants in Hydrides by a Modified Urey—Bradley Analysis
Authors: Bartell L. S. , Kuchitsu Kozo
Published: January 2005

Previous Urey—Bradley (U.B.) analyses of vibrational spectra have suggested that intramolecular repulsions between atoms are generally large and similar, at a given distance, to intermolecular nonbonded interactions. Hydrogen, however, has been found to exhibit anomalously low intramolecular repulsions according to conventional U.B. analyses. In the present modified analysis completely general quadratic force fields, corrected for anharmonicity, are resolved into the sum of U.B. fields and additional interactions neglected in conventional U.B. analyses. The assumptions required for evaluation of the central force components are discussed. It is found for a series of hydrides that explicit inclusion of stretch—stretch interactions over and above those implied by nonbonded repulsions markedly alters the analysis and yields H···H interactions interpretable in terms of large repulsions entirely comparable with those calculated using intermolecular force laws. Such large repulsions are compatible with structural, thermochemical, and kinetic data. While they cannot be separated from effects of hybridization solely on the basis of quadratic force constants, they provide an alternative explanation for effects commonly ascribed to hybridization and more specialized interactions.
Work Function Changes Produced by Chemisorption on Surfaces with Different Types of Adsorption Sites
Authors: Crowell A. D. , Norberg A. L.
Published: January 2005

A simple model describing the changes in work function produced by chemisorption on a surface possessing two types of adsorption sites is presented. Equations for the change in work function as a function of the amount of gas adsorbed are given, and curves for the cases of CO and N2 adsorbed on the (113) plane of tungsten are compared with recent experimental results.
Effect of Inert Salts on Equilibrium and Rate Constants for Ionic Reactions
Authors: Gryder J. W.
Published: January 2005

Empirical evidence is given to show that individual ion activity coefficients can be written as logγt=Zt2G(S)+[ν1α1t+ν2α2t]C, where ν1 and ν2 are the number of ions of type 1 and 2 formed from one formula of the supporting electrolyte, C is the formal concentration of the electrolyte, Zt is the charge of the ion t, G(S) is a function of the medium only, α1t is a function of the ion-size parameter for ions 1 and t, and α2t is a similar function of the ions 2 and t. The equation is applicable only if the concentration of ion t is small in comparison to the concentration of electrolyte. Mayer's theory predicts that the above equation, when used to calculate experimentally observable quantities, should be correct to within good accuracy for ion-size parameters between 5.5 and 8.5 Å in a 1–1 supporting electrolyte and for higher-charged electrolytes at ionic strengths above about 0.2. Using this equation one can calculate the ratio of the rate constant for the bromacetate—thiosulfate reaction to that for the peroxydisulfate—iodide reaction at infinite dilution from data obtained in MgSO4, Mg(NO3)2, Na2SO4, and NaNO3 solutions at concentrations between 0.25 and 2F. The value obtained under these conditions is within experimental accuracy of the value obtained by extrapolation to infinite dilution from ionic strengths below 0.02.
Low-Energy Electron Diffraction Study of Silicon Surface Structures
Authors: Lander J. J. , Morrison J.
Published: January 2005

Low-energy electron diffraction data are presented for superstructures on the clean (100) and (111) surfaces of silicon, and for structures formed by a monolayer of iodine and a monolayer of phosphorus on the (111) surface. Conventionally defined structure factors, modified for atomic structures a few layers thick, have been used to analyze two of these structures with results which are very probably correct. Insufficient data are apt to be the most serious limitation of the technique in structure determination. Observed transitions for the clean surface structures are described and results are presented for transition temperatures and rates of reaction of the surfaces with iodine and with phosphorus as a function of temperature and pressure. Iodine appears to be adsorbed in the ionic state and the calculated Si–I distance is about 3.2 Å. The data show that the physical and chemical properties of a silicon surface at low temperatures depend very much on thermal, chemical, and mechanical history, and the models presented explain this in considerable detail. Multilayer adsorption of iodine and phosphorus, disordered transition structures, and etching effects were also observed. The stable clean silicon surface has silicide properties, and reaction with hydrogen, mercury, and molybdenum is limited to a few active sites under conditions accessible in this work.
Melting Curves of Five Metals under High Pressure
Authors: McDaniel Marvin L. , Babb Stanley E. , Scott Gene J.
Published: January 2005

Techniques have been developed for the determination of the melting curves of metals under pressure and are applied to five metals. These data are used to evaluate the constants appearing in the Simon equation, with and without approximate values of the corrections to be applied to the thermocouples. These corrections can make as much as 20% difference. The values of these constants are compared with the theoretical expressions of Gilvarry, and agreement is close.
Power-Series Solutions for Energy Eigenvalues
Authors: Secrest Don , Cashion K. , Hirschfelder Joseph O.
Published: January 2005

A numerical method is presented for rapidly calculating the energy eigenvalues of one-dimensional Schrödinger equations. It is applicable to systems for which the potential is either analytic or has no pole of order greater than two. The method is based on a power-series expansion of the wave function at large distances. With the use of high-speed computing machines the large number of terms required in the power series can be computed easily. The method is illustrated by obtaining energy eigenvalues for a number of one-dimensional systems with potentials of the type V=kx2n/2n. It is also applicable to a variety of systems of physical interest. As an example, an exact energy eigenvalue for a rotating Morse oscillator has been calculated. This is compared with that obtained from Pekeris' approximate analytical solution.
Luminescence of Solids Excited by Surface Recombination of Atoms. I. Luminescence Spectra
Authors: Sancier Kenneth M. , Fredericks William J. , Wise Henry
Published: January 2005

The luminescence spectra of the lumophors CaO, CaO:Mn, CaO:Bi, MgO, and MgO:Sb excited by heterogeneous recombination of nitrogen atoms were studied. The photoexcitation and photoemission spectra of CaO:Mn are compared with those of atom excitation. The spectra produced by atom excitation are found to be strongly dependent upon lumophor temperature and exposure time to atoms, whereas photoluminescence is not affected by these parameters. The results of atom-excited luminescence are discussed in terms of surface-adsorbed nitrogen atoms in weakly and in strongly bound states whose populations are strongly temperature dependent and subject to surface poisoning.
Vapor-Phase Radiolysis of Propane-d8 in the Presence of Other Hydrocarbons
Authors: Lias Sharon G. , Ausloos P.
Published: January 2005

The radiolysis of propane-d8 has been investigated in the presence of saturated and unsaturated hydrocarbons. Radical scavengers have been added in all experiments in order to prevent the production of hydrogen, methane, ethane, and ethylene by neutral thermal radical reactions. The formation of ethane could be ascribed mainly to the occurrence of the hydride-transfer reactions C2D5++C3D8→ lim k1C2D6+C3D7+and C2D5++RH→ lim k2C2D5H+R+.When RH=saturated hydrocarbon, the values of k2/k1 increase with increase in the molecular weight of RH. The observation that olefins and aromatic compounds lower the yield of ethane, but do not affect the rates of formation of molecular methane and ethylene, led to the conclusion that ethyl ions may add to the unsaturated hydrocarbons. Evidence has been obtained for a molecular elimination of hydrogen, methane, ethane, and ethylene from several of the hydrocarbons.
Magnetic Susceptibility of Ruthenium-Yttrium Oxide (Ru2O4·Y2O3) Powder
Authors: Rosset J. , Ray D. K.
Published: January 2005

Detailed analysis of the magnetic susceptibility of Ru2O4·Y2O3 powder shows that the Ru4+ ion experiences an appreciable trigonal field and some covalent bonding. Possible explanations have been given of the deviation of the experimental susceptibility data in the high-temperature region from theoretical models considered here.
Infrared Spectra of the Methyl Halides. II. Methyl Bromide near 4450 cm—1
Authors: Brown R. G. , Edwards T. H.
Published: January 2005

Three overlapping perpendicular bands of CH3Br are assigned in this work to ν2+ν4 at 4352.58, ν4+ν5 at 4446.03, and ν1+ν3+ν6 at 4482.39 cm—1. Of these, ν4+ν5 is relatively weak, and the analysis was based on directly measured frequencies of the sharp Q branches. The analyses of the other two bands were based on many individual lines in the P and R branches of the subbands.
Infrared Spectra of the Methyl Halides. III. Methyl Iodide Near 4400 cm—1
Authors: Brown R. G. , Edwards T. H.
Published: January 2005

At least four overlapping perpendicular bands of CH3I are observed in the 2.2 μ region. Two are assigned in this work to ν2+ν4 at 4302.14, and ν4+ν5 at 4438.99 cm—1. Two others are tentatively assigned to ν1+ν5 at 4489.54, and ν1+ν3+ν6 at 4467.04 cm—1. Several anomalous features are outlined, and empirical expressions are given.
Determination of Virial Coefficients from the Potential of Mean Force
Authors: Hoover William G. , Poirier Jacques C.
Published: January 2005

A relation between the potential of mean force at zero separation and the excess chemical potential is derived for ``hard'' molecules. Application to hard spheres shows that of the Percus—Yevick, Kirkwood, convolution, and Born—Green—Yvon integral equations, only the Kirkwood equation gives the correct third viral coefficient.
Potential Curves and Rotational Perturbations of CN
Authors: Fallon Robert J. , Vanderslice Joseph T. , Cloney Robert D.
Published: January 2005

Potential energy curves for the X 2Σ+, A Π322, A 2Π½, B 2Σ+, D 2Πi, and J 2Δi states of CN have been calculated from the experimental data by the Rydberg—Klein—Rees method. The resulting curves have been used to discuss qualitatively the rotational perturbations in the v=7 vibrational level of the Π322 electronic state.
Thermodynamic Study of Tin Sulfide and Lead Sulfide Using a Mass Spectrometer
Authors: Colin R. , Drowart J.
Published: January 2005

A mass-spectrometric investigation of the vapor in equilibrium with solid SnS, solid PbS, and a mixture of SnS and PbS has yielded the following reaction enthalpies: SnS(s)→SnS(g)ΔH2980=52.6±1.6 kcal/mole2SnS(s)→Sn2S2(g)56.5±5.0PbS(s)→PbS(g)55.7±1.62PbS(s)→Pb2S2(g)66.6±5.0      PbS(g)→Pb(g)+12S2(g)28.8±2.6Sn2S2(g)→2SnS(g)48.7±5.0Pb2S2(g)→2PbS(g)44.8±5.0      SnPbS2(g)→SnS(g)+PbS(g)46.5±5.0.The dissociation energies of gaseous SnS and PbS were determined to be D00(SnS) = 110.1±3.0 kcal/mole, D00(PbS) = 79.1±2.8 kcal/mole and are compared with the spectroscopically determined values.
Microwave Spectrum of Chlorine Dioxide. V. The Stark and Zeeman Effects
Authors: Tolles W. M. , Kinsey James L. , Curl R. F. , Heidelberg Robert F.
Published: January 2005

The Stark and Zeeman effects of ClO2 have been observed in the rotational spectrum of ClO2. The dipole moment resulting from the Stark-effect measurements is 1.784±0.01 D. The Zeeman effect was observed to fit the calculated spectrum for the interaction of a free electron with the magnetic field. The anisotropic components of the g factor are too small (about 1%) to be measured reliably with low magnetic fields.
Total Scattering Cross Sections of H2O and NH3
Authors: Kydd Paul H.
Published: January 2005

Molecular beam scattering experiments have been performed to determine the total scattering cross sections, Q, and the van der Waals constants, C, of H2O and NH3 beams in an effusive flow of H2O. CH2O–H2O was found to be 610±150×10—60 erg cm6 which is larger than the calculated value 313×10—60, as would be the case if short-range dipole—dipole forces, not included in the calculation, were effective. CNH3–H2O is smaller than calculated, 176±50×10—6 compared to 292×10—60, as though the dipole—dipole forces were altogether inactive. An attempt was also made to measure the temperature dependence of QH2O–H2O.
Generalized Form for Dispersion Interaction
Authors: Linder Bruno
Published: January 2005

A general treatment of dispersion interaction, based on the continuum model, is presented. Expressions are derived which relate the dispersion free energy of a molecule to the complex dielectric constant. Approximate relations are given for calculating the free energy from the static dielectric constant and mean absorption frequencies. The theory applies to homogeneous dielectrics, irrespective of composition or phase.
Quenching Interactions between Rare-Earth Ions
Authors: Van Uitert L. G. , Iida S.
Published: January 2005

Interactions between identical or nonidentical rare-earth ions that result in the quenching of fluorescence of Eu3+ or Tb3+ have been studied. Comparison of the intensities of emission of Eu3+ as a function of its concentration in various oxides indicates that interactions that result in the quenching of emission from the 5D0 levels of the Eu3+ ions are associated with pairing through intervening oxygen ions. Higher-lying levels appear to be quenched by interactions through anionic groups (e.g., WO42—). The quenching effects that a dissimilar rare-earth ion M has on the emission of Eu3+ or Tb3+ in the sodium rare-earth tungstates correlate with (1) the energy gap between the fluorescing level of the latter and the closest lower-lying level of M, and (2) the total orbital angular momentum of the ground state of M.
Distortion of Atomic Orbitals in Molecular Orbitals. II. Charge Shift and Charge Deformation of the Hydrogen Atom in H2+
Authors: Miller Robert L. , Lykos Peter G.
Published: January 2005

Distorted atomic orbitals are constructed to describe the electron charge cloud associated with an atom within a molecular orbital framework when it enters into molecule formation. These functions are obtained as a result of a variational calculation with respect to the energy on the lowest 2Σg+, 2Σu+, 2Πu, and 2Πg states of the hydrogen molecule ion. Both the scale of the orbital and the spatial symmetry of the charge cloud are allowed to adjust to the molecular environment in a manner suggested by variation-perturbation theory. The energies obtained are in good agreement with accurate theoretical values. Criteria are advanced for the selection of an appropriate basis for the description of distorted atomic orbitals.
Self-Diffusion and Impurity-Controlled Proton Relaxation in Liquid Ethane
Authors: Gaven J. V. , Stockmayer W. H. , Waugh J. S.
Published: January 2005

Self-diffusion in liquid ethane, under its own vapor pressure, has been studied over most of the liquid range between the triple point and the critical point by means of the spin-echo technique. The activation energy for self-diffusion increases markedly from approximately 0.5 kcal/mole at 100°K to 3.5 kcal/mole at 300°K. The Stokes—Einstein relation is not well satisfied with either a constant molecular radius or a radius proportional to the cube root of the molar volume. The results are well correlated by a free-volume expression in which the free volume, defined as an actual volume minus the volume of the hypothetical liquid at 0°K, replaces temperature as the independent variable. The value of the hypothetical 0°K liquid volume resulting in best fit of the experimental data is less than that determined by extrapolation of the liquid specific volume to 0°K or that based upon best fit of experimental liquid viscosity data, but it is between a value based on a hard-sphere radius determined from gas viscosity and one derived from the second virial coefficient.

Proton spin-lattice relaxation measurements on the liquid ethane sample over a similar temperature range indicate that the relaxation is controlled by mutual diffusion of ethane and small amounts of dissolved oxygen, although the situation is somewhat complicated by temperature dependence of the distribution of oxygen between the two phases.
Electron Affinity of Atomic Iodine
Authors: Steiner Bruce , Seman Michael L. , Branscomb Lewis M.
Published: January 2005

Photodetachment of I— ions has been observed in a crossed-beam experiment. The apparatus used was essentially similar to that in previous photodetachment experiments. Use of four Sharp Cut filters provided good ``effective'' resolution close to threshold but did not permit an independent determination of the behavior of the cross section as a function of wavelength. A step-function cross section, shown by Berry and co-workers to approximate closely the true cross section behavior, was used to provide an upper energy limit to the electron affinity shown to be close to the actual value. The value of the electron affinity thus determined, 3.076±0.005 eV, is in excellent agreement with the shock-wave determination of Berry, 3.078±0.005. The absolute magnitude of the cross section in the region 0.3 eV above threshold was determined to be 2.1±1.1×10—17 cm2.
Ionization Accompanying the Acetylene—Oxygen Reaction in Shock Waves
Authors: Hand Clifford W. , Kistiakowsky G. B.
Published: January 2005

A Langmuir probe was used to study the ionization produced during the oxidation of acetylene in shock waves. While the results were ambiguous at low applied potentials, positive probes were shown to measure approximately the free electron concentrations. These were found to be several orders of magnitude higher than those of thermodynamic equilibrium. The ionization behaves very similarly to the emission of short uv radiation from shock waves in acetylene—oxygen mixtures described by Kistiakowsky and Richards: after an induction period it rises exponentially and then decays. The values of the induction periods and of the exponential time constants agree with those obtained from uv emission studies. Emission of visible and near uv radiation has also been studied now and very similar results obtained. The temperature coefficient of the maximum ionization and maximum radiation intensities is the same, equivalent to 23 kcal/mole. The decay of ionization is second order. The mechanisms of chemiluminescence and chemi-ionization are discussed, and it is suggested that the following reactions are involved: C2H+O2→CO2+CH*,or C2H+O→CO+CH*;CH*→CH+hvCO+O→CO2+hv}  (visible and near uv),CH*+O→CO(A1π)+H,CO(A1π)→CO(X1Σ)+hv  (vacuum uv),CH*+O→HCO++e−  (ionization).The effect of small additions of lead tetramethyl and acetone on the kinetics of the reaction was investigated. Both additives reduce sharply the induction periods in the reaction, without affecting strongly the rate of exponential growth of the reaction rate as evidenced by ionization and radiation.
Electron Paramagnetic Resonance Studies of the ZnS-A and -B Centers
Authors: Kasai Paul H. , Otomo Yoshiro
Published: January 2005

Two photosensitive electron paramagnetic resonance signals A and B are found in self-activated ZnS phosphors of polycrystalline form. Both these signals appear at 77°K when illuminated with uv light, and can be quenched with visible light of longer wavelength. The center responsible for the A signal is a hole trap and is found to be the luminescent center of the self-activated emission. The atomic structure of this center is concluded to be an associate of zinc-ion vacancy and a coactivator ion at one of the nearest possible sites. The center responsible for the B signal is an electron trap. A simple sulfur vacancy is proposed to be the structure of this center. In one case, the A signal was traced using a crude single crystal. Owing to the crudeness of the crystal, the result is not complete, but is found to be sufficient enough to substantiate the accuracy of the powder pattern analysis. Also described in this report are the results of investigating the effects of oxygen incorporated into ZnS by both the electron paramagnetic resonance and the thermoluminescence techniques. One of the observed effects is that the incorporation of oxygen leads to formation of self-activated luminescent centers whose coactivator ions are not at the nearest possible sites.
Improved Rate Expression in the Quasi-Equilibrium Theory of Mass Spectra
Authors: Vestal Marvin , Wahrhaftig Austin L. , Johnston William H.
Published: January 2005

An improved continuous approximation to the number of states of a collection of harmonic oscillators of different frequencies has been developed and applied to the quasi-equilibrium theory of mass spectra. The classical approximation previously used in this theory has been shown to be invalid at low energies. The difficulties in the application of the quasi-equilibrium theory of mass spectra are to a great extent resolved by the use of this more reasonable approximation.
Temperature Dependence of the ESR Spectrum of Irradiated Oriented Polyethylene
Authors: Ohnishi Shun-ichi , Sugimoto Shun-ichi , Nitta Isamu
Published: January 2005

Temperature dependence of the ESR spectrum in irradiated polyethylene has been studied using stretched specimens. Among the observed spectra the septet spectrum with doublet substructure is known to be due to an ``allyl type'' –CH2–ĊH–CH=CH–CH2– radical. Although the spectrum observed at 142°C is such a septet (splitting 21.3 G) with doublet substructure (splitting 5.5 G), it changes with temperature in a complicated way. Positions of the peaks are displaced, and their apparent number changes, while the spectrum below — 180°C remains unchanged. Such changes were found completely reversible with temperature, and the magnitude of the over-all splitting as well as the outermost doublet remained constant. The analysis of this complicated temperature dependence has been carried out on the assumption that the hyperfine coupling constant of the β protons changes with temperature, while that of the α protons remains constant. By choosing an appropriate set of coupling constants (Aβ) of β protons, the observed spectrum could be reproduced. From the spectrum at — 180°C were deduced Aβ1 = 30 G and Aβ2 = 11 G. Such inequivalence of the coupling might suggest that the methylenic group in the ``allyl type'' radical should be twisted with respect to the nodal plane of the unpaired π electron. As the temperature rises, a hindered oscillation of the methylenic group will take place between two equivalent twisted positions with respect to the same nodal plane. Such behaviors have been interpreted using a theory of time-dependent phenomena and the activation energy was obtained to be 410 cal/mole, the frequency factor being 4.6×108 sec—1.
Absolute Infrared Intensities in Crystalline Benzene
Authors: Hollenberg J. Leland , Dows David A.
Published: January 2005

The infrared spectra of polycrystalline benzene and fully deuterated benzene have been examined under high resolution. All ``u'' fundamentals (except ν16 of C6D6) have been observed and most crystal multiplets have been resolved, many to the full extent predicted. Accurate frequencies at two low temperatures are presented.

Absolute intensities have been measured at two temperatures for all fundamentals observed. An interference method has been used to measure sample thickness. The results are compared to existing data on three phases of benzene. The sum of all integrated intensities for a given molecule is empirically found to be independent of state of aggregation, and a sum rule expressing this fact is derived and criticized.
Kinetics of Crystal Nucleation in Polyethylene
Authors: Cormia R. L. , Price F. P. , Turnbull D.
Published: January 2005

Observations of the freezing behavior of droplets of a linear polyethylene (Marlex-50) suspended in an inert medium have been made. It is possible to cool such suspensions of molten droplets to 85°—87°C before the majority of the droplets freeze, provided precautions are taken to minimize nucleation by the vessel walls. This indicates unambiguously that spherulites formed near 120°C (the usual crystallization range) are nucleated by heterogeneities in the melt. Analysis of experiments performed at various cooling rates indicate an end surface interfacial energy of rod-shaped nuclei of 168 ergs/cm2. This is similar to the estimates made of the fold-surface energy in crystals formed from dilute solution. The cooling-rate experiments also indicated that the transport processes in the production of the polymeric nucleus are similar to those involved in the production of nuclei of n-alkane crystals.
Evaluation of Lattice Sums in the Calculation of Crystal Spectra
Authors: Hexter R. M.
Published: January 2005

Transition dipole—transition dipole exciton interaction lattice sums are shown to be amenable to evaluation by the general procedure of Nijboer and de Wette [Physica 23, 309 (1957)]. The practical evaluation of lattice sums in certain cubic and tetragonal crystals is then discussed, with emphasis upon the importance of the manner in which the spectrum of a molecular solid is obtained. The particle size of a polycrystalline sample is shown to strongly affect the value of the lattice sum. For single crystals, the orientation of the crystal and its transition moment directions with respect to the electric vector of the exciting field is of importance. Specific formulas relating crystal field splittings to dipole derivatives (in vibrational spectra) and to oscillator strengths (in electronic spectra) are given and tested with a variety of vibrational transitions of various cubic crystals as well as with the deformation mode of N3— in the tetragonal alkali azides. The oscilator strength of the 1∏←1Σ+ transition of CO is calculated to be 0.148, using some recent data on this spectrum obtained by Dressler. Splittings in the related transition in solid N2 are also discussed.

The results indicate that several conclusions in earlier calculations based upon dipole coupling models have been in error due to inadequate summation procedures. The results also indicate that ``exciton packets'' extend to the boundaries of the crystallites of which a polycrystalline sample is composed. Limitations to the general applicability of the summation procedures presented here are also discussed.
Calorimetric Determination of Isothermal Entropy Changes in High Magnetic Fields at Low Temperatures. CoSO4·7H2O
Authors: Giauque W. F. , Lyon D. N. , Hornung E. W. , Hopkins T. E.
Published: January 2005

An apparatus has been described for the detailed calorimetric measurement of the entropy increase accompanying isothermal demagnetization from high magnetic fields. Integrated automatic heat input controlled by a helium gas thermometer, in thermal contact with the sample, divided by the selected temperature, gives a detailed description of the entropy increase. Investigation of a powdered sample of CoSO4·7H2O has shown that application of fields of the order of 100 kOe near 1°K extracts an entropy of R ln2 as an upper limit from the electronic system of this substance. No irreversible effects were found. The entropy was found to be a function of Hi/T, over the range 1.236 to 4.211°K and from 0 to 94 500 Oe. Hi refers to the magnetic field inside the sample. The resistance of a Pt(91–92%)—W(9–8%) alloy wire used for the noninductively wound calorimetric heater was investigated. The magnetoresistance was positive, very small, and linear with field at all fields. (1/R) (dR/dT) = —5×10—5 deg—1 and (1/R) (dR/dH) = +2.5×10—9 Oe—1, range 1.2 to 4.2°K and from 0 to 95 kOe. Equations for the effect of a magnetic field on the helium gas thermometer are given.
Use of Electrostatic Variation Principles in Molecular Energy Calculations
Authors: Schrader David M. , Prager Stephen
Published: January 2005

The Thomson and Dirichlet principles of electrostatics have been applied to the evaluation of electron-interaction terms occurring in molecular-energy calculations. A suitable choice of certain trial electric fields and electrostatic potentials permits these terms to be approximated both from above and from below. These approximate calculations of electronic interaction terms may often be considerably easier to perform than the exact evaluations required when molecular energies are obtained in the usual way through the minimum-energy principle. At the same time, when the upper and lower bounds obtained by the present method are properly inserted into the total-energy expression, the validity of the minimum-energy principle is preserved, so that any parameters appearing in the trial wave function can still be evaluated by the usual energy minimization procedure. For illustration, the method has been applied to the calculation of the ground-state energy of molecular hydrogen.
New Orthorhombic Phase in the Ru–B and Os–B Systems
Authors: Roof R. B. , Kempter C. P.
Published: January 2005

By the use of single crystal and polycrystalline x-ray diffraction techniques, isomorphous orthorhombic lattices (space group No. 59) have been found in the Ru-B and Os-B systems having lattice parameters of a0=4.6443±0.0003 Å, b0=2.8668±0.0008 Å, c0=4.0449±0.0004 Å and a0=4.6832±0.0001 Å, b0=2.8717±0.0002 Å, c0=4.0761±0.0001 Å, respectively. The probable empirical formulas are RuB2 and OsB2, with two formula weights per unit cell.
On the Ionization Potential of the CH2 Radical
Authors: Berkowitz J. , Wexler S.
Published: January 2005

A marked difference has existed between the ionization potential of the methylene radical as measured by flash photolysis (10.396 eV) and by mass spectrometry (11.75 eV). A reinvestigation of the mass spectrometric experiment, undertaken to resolve the discrepancy, did not confirm the value previously reported. No evidence could be obtained for the formation of CH2+ from CH2 formed by pyrolysis of CH2N2, although the formation of CH3+ from CH3 formed by pyrolysis of (CH3)2 Hg could be readily detected.
Effect of Pressure on Cyanine Spectra
Authors: Samara G. A. , Riggleman B. M. , Drickamer H. G.
Published: January 2005

The effect of high pressure has been measured on the electronic spectra of a number of cyanine dyes dissolved in cellulose acetate. In general, a red shift was observed with pressure, which varied in magnitude with the chain length and electronegativity of the end group. The results are discussed in terms of Olszewski's resonance barrier model.

The peaks tended to broaden with increasing pressure, and to decrease in height. There was no significant change in the total area under the peak.

For a few cyanines the spectra of the crystals were also measured to study the effect of pressure on the Davydoff splitting. The degree of splitting increased with increasing pressure as was to be expected. There was a redistribution of intensity among the different branches with increasing splitting.
Kinetic Theory of Dense Fluids. XII. Electronic and Ionic Motion in Liquid He4I and Liquid He3
Authors: Davis H. T. , Rice Stuart A. , Meyer Lothar
Published: January 2005

The mobilities of positive and negative charge carriers in liquid He3 and He4I are calculated and the resultant agreement with experiment is excellent. The negative carrier is taken to be an electron. Due to electrostriction and density fluctuations the effective mass of the electron is of the order of 100 electron masses. In addition, the disorder of the liquid leads to incoherences in the scattering of the electron from atomic pseudopotentials. The positive carrier is taken to be He2+. An extension of the theory of Rice and Allnatt, using the ideas introduced by Mazo and Kirkwood, leads to a formula for the mobility in terms of a quantum-mechanical temperature. Electrostriction increases the density about an ion and the dissipation arises about equally from the short-range repulsive forces and the Coulomb and van der Waals attractive forces. Both calculations involve only basic considerations and there are no adjustable parameters in the theory.

The computed effective mass of the negative carrier in He3 at 3.00°K and 2-atm pressure is 105 electron masses: The observed effective mass is 97 electron masses. For the negative carrier in He4I at 4.2°K and 1-atm pressure the computed and observed effective masses are 149 and 128 electron masses, respectively. In the case of the positive ion, the observed mobility at 2.2°K and 1-atm pressure in He4 is 5.6×10—2 cm2 V—1 sec—1 while the computed value is 5.2×10—2 cm2 V—1 sec—1.

The reader is referred to the Note added in proof for new comments and alternative interpretation of the electron effective mass.
Hydrogen—Deuterium Kinetic Isotope Effect, an Experimental and Theoretical Study over a Wide Range of Temperature
Authors: Sharp Terry E. , Johnston Harold S.
Published: January 2005

An experimental study of the kinetic isotope effect for the reactionCF3+CHD3–|→F3C–H–CD3→F3CH+···→F3C–D–CHD2→F3CD+···has been carried out between 300° and 700°K, and also the Arrhenius parameters k=A exp (—E/RT) were obtained for the individual reactions. An especial effort was made to avoid systematic errors, and the precision obtained was good.

These data were combined with those of Tschuikow-Roux who studied the essentially same reaction between 1000° and 1800°K, and a detailed test was made of activated complex theory utilizing the method of London—Polanyi—Eyring—Sato with corrections for quantum mechanical tunneling. Sato's parameter was evaluated from activation energy of an analogous reaction so that kH/kD and A provided an unambiguous, nonadjustable test of theory. Because reactants were identical for both reactions, all the kinetic isotope effect depended on differences in the two activated complexes. The vibrational frequencies of the two nine-atom models of the complex were evaluated by a computer, programmed to E. B. Wilson's FG-matrix methods, and the effect of replacing the full nine-atom model by simpler five-, four-, or three-atom models was tested.

The Arrhenius A factor was enormously sensitive (factor of 103) to number of atoms assigned to the model; the three- or four-atom models gave A factors much too high, but the five- or nine-atom models with tunneling corrections were in fairly good agreement with experiment from 300° to 1800°K.

It is judged that if one evaluates a potential-energy surface, carries out a full vibrational analysis, and applies a reasonable tunneling correction, then one has in activated complex theory an expression analogous in logic and in usefulness to the perfect-gas theory; that is, broad over-all predictions can be made (in spite of readily identified conceptual flaws) but fine points will always be missed. Any quantitative value in the simplified versions of the theory is open to grave doubt.
Reaction of Methyl-d3 Radicals with Isobutane, Isobutane-2-d, and Propane
Authors: Jackson W. M. , McNesby J. R. , Darwent B. deB.
Published: January 2005

The relative rates of abstraction by CD3 radicals of primary, secondary, and tertiary H atoms have been measured. Using a standard rate constant for abstraction of D from acetone-d6, the following rate constants are obtained:               k(mole−1cc sec−1)CD3+CD3COCD3→CD4+CD2COCD33.5×1010T12exp(−11 100/RT),(2)CD3+(CH3)3)CD→CD4+(CH3)3C0.88×1010T12exp(−9200/RT),(3)CD3+(CH3)3CD→CD3H+CH2–CD(CH3)24.38×1010T12exp(−11 100/RT),(4)CD3+(CH3)3CH→CD3H+(CH3)3C0.70×1010T12exp(−7600/RT).(10)Isotope effects obtained are, for secondary H and D in propane kH/kD=1.04exp(1400/RT),and for tertiary H and D in isobutane kH/kD=0.80 exp(1600/RT).These isotope effects are within experimental error of that given by the general expression for the deuterium isotope effect previously proposed kH/kD=exp(1500/RT),and are in excellent correspondence with the theoretical treatment of Johnston and Rapp.