bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Fluorine Molecule. II. Energy Levels of F2 and F2+
Authors: Hijikata Katsunori
Published: January 2005

The same ASMO treatment as in Part I [K. Hijikata, J. Chem. Phys. 34, 221 (1961), preceding paper] is applied to the fluorine molecule with several pairs of effective nuclear charges, and the best value of the effective nuclear charge is determined for each state. The ground state 1Σg+ has De=2.02 ev, Re=1.437 A and the effective nuclear charge 2.58. It is found that the explanation for the effective nuclear charge of each state from the ``atomic point of view'' is difficult. The vertical excitation energies 1Σg+—1Πu, 1Σg+—3Πu, and 1Σg+—1Πg are calculated to be 4.49, 3.73, and 6.50 ev, respectively. The lower energy levels of the molecular ion F2+ are also calculated, showing that the ground state is 2Πg, that two more states appear to have potential minima, and that the higher energy levels of F2 calculated by ASMO are almost meaningless except 1Σu+. The energy level of this ionic state 1Σu+ at R=1.625 A is 10.8 ev above the minimum of 1Σg+. The energy diagram summarizing the calculations is shown. The discrepancy is indicated between the experimental and the theoretical ionization potentials.
Effect of Dissolved Oxygen on the Spin-Lattice Relaxation Time of Free Radicals in Petroleum Oils
Authors: Saraceno A. J. , Coggeshall N. D.
Published: January 2005

Electron paramagnetic resonance studies of free radicals in petroleum oils reveal that the presence of dissolved oxygen significantly affects the free radical spin-lattice relaxation time, T1. Changes in T1 can occur upon: (a) dilution with solvents, (b) exposure to light, (c) bubbling with oxygen, and (d) stripping of dissolved oxygen. In this investigation it is shown that these changes all result from the influence of dissolved oxygen. Dilution with ordinary cp solvents results in a decrease of T1. If the solvent is first stripped of dissolved oxygen, there will be no changes in T1. The effect is reversible, i.e., the value of T1 for free radicals in a petroleum oil may be arbitrarily decreased or increased by adding or removing dissolved oxygen, respectively. It was observed that free radicals in oil, or in oil in solution, experienced an increase in spin-lattice relaxation time when allowed to remain sealed in a quartz tube. This change was traced to the effect of light and appears to occur for wavelengths of the order of 5400 A and lower. It is concluded that this phenomenon is due to the photochemical takeup of dissolved oxygen whose presence decreases T1. This is based on the fact that T1 may be lowered to its original value merely by adding molecular oxygen to the petroleum oil. Depending upon the degree of saturation being effected, changes in T1 will be reflected as changes in ``apparent'' free radical content. The true free radical content was unchanged by the processes studied.
Infrared Spectrum and Force Field of Crystalline Hydrogen Peroxide
Authors: Miller R. L. , Hornig D. F.
Published: January 2005

The infrared spectrum of crystalline and vitreous hydrogen peroxide was studied from 300 cm—1 to 4000 cm—1. A normal coordinate analysis of the tetragonal crystal with four molecules/unit cell is given. The hydrogen bonds are only slightly weaker than in H2O but the O–H linewidths are only 80 cm—1. From the coupled motion of the torsion and the high-frequency libration, the torsional frequency in the gas is estimated to be about 230 cm—1.
Microwave Spectrum of cis-Difluoroethylene. Structures and Dipole Moments of Fluoroethylenes
Authors: Laurie Victor W.
Published: January 2005

The microwave spectrum of cis-difluoroethylene, HFC=CHF, has been investigated in the region 17–36 kMc. Observed rotational constants (Mc) for the ground vibrational state of C212H2F2 are a0=21103.31, b0=5930.35, c0=4622.27; for C13C12H2F2, a0=20752.10, b0=5900.17, c0=4586.92. From these constants a structure is obtained with rCC=1.324 A, rCF=1.337 A, rCH=1.080 A, <FCC=122°9′, and <HCC=121°16′. Rotational constants for v5=1 have also been determined. A dipole moment of 2.42 D is calculated from the Stark effect. Comparison with previously existing data for ethylene, vinyl fluoride, and vinylidene fluoride shows that there is a shortening of both the CF and the CC bonds with increasing fluorine substitution.
Structure of the Water Molecule in Solid Hydrated Compounds
Authors: McGrath J. W. , Silvidi A. A.
Published: January 2005

The proton-proton separations in hydrated water in 10 compounds have been measured by the Pake method using proton magnetic resonance. The mean value is 1.595±0.003 A with a range in values from 1.56 to 1.61 A. However, consideration of experimental error in individual values of the p-p separation indicates that this range does not prove that this separation varies between compounds. Thus it appears that intermolecular forces on the protons in the water molecule are not appreciable compared to intramolecular forces. The orientations of the water molecules have been determined for eleven compounds. In every instance the orientation appears to be determined by formation of hydrogen bonds between the water oxygen and the nearest pair of electronegative atoms.
Criticality Criteria for Various Configurations of a Self-Heating Chemical as Functions of Activation Energy and Temperature of Assembly
Authors: Parks John R.
Published: January 2005

In 1939 D. A. Frank-Kamenetsky proposed a criticality criterion that is a dimensionless constant that varies only with configuration of the self-heating chemical. In his studies of the equation equating power production as a function of temperature by the formula of Arrhenius and the power loss by conduction alone, he made a simplifying assumption. A Pace analog computer and an IBM 704 have been used to study the exact equation and it was found that the value of the F-K criticality criterion is a slowly varying function of E/RT0 in the range from infinity to 30 but becomes a sensitive function for values of E/RT0 less than 30.
Photoconduction Activation Energies in cis-trans Isomers of β-Carotene
Authors: Rosenberg Barnett
Published: January 2005

The activation energies for photoconduction have been measured in all trans and 15–15′ cis β-carotene powders and in β-carotene glass consisting of a mixture of isomers. The average values of a number of measurements of each are all trans, 0.37 ev; 15–15′ cis, 0.20 ev; isomerized glass, 0.19 ev. The values predicted by the triplet state theory of photoconduction are 0.35 (or 0.53), 0.18, and 0.18 ev, respectively. The larger activation energy (two or three vibrational quanta) of the all trans is attributed to the thermal energy necessary to allow an intersystem crossing from the first singlet excited state (about 2.6 ev) to the triplet state (about 3.0 ev). The activation energy of the cis-trans forms of the molecule (1 vibrational quanta) correspond to intersystem crossing from the ``cis peak'' state (about 3.5 ev) to the triplet state. The excitation spectrum of photoconduction in 15–15′ cis β-carotene and isomerized glass, peaks in the ``cis peak'' region, in agreement with this assignment. These results, that intersystem crossing occurs more readily from the cis peak state than the first singlet excited state, provide an explanation for the shape of the photocurrent excitation spectra in β-carotene and for the lack of phosphorescence in all trans lycopene as reported by Lewis and Kasha.
On the Solution of the Hartree-Fock Equation in Terms of Localized Orbitals
Authors: Adams William H.
Published: January 2005

The Hartree-Fock method is discussed with emphasis placed on the transformation properties of the Hartree-Fock equation. It is emphasized that the Hartree-Fock equation may be solved in terms of non-orthogonal one-electron functions, and that in some cases it may be more convenient to choose such solutions. Equations are developed which define the localized one-electron functions and it is shown how these equations may be solved. For a system of closed shell atoms or ions, it is suggested that the localized orbitals of each atom or ion can be expanded in terms of functions centered on its nucleus. This suggestion is based on the success of the ionic theory of crystals. Due to the symmetry of a crystal, it is suggested that use of the localized orbitals could lead to expressions for the first order, Hartree-Fock density matrix and the Hartree-Fock energy of a crystal, i.e., one could obtain the solution of the Hartree-Fock equation for a crystal.
Photochemical Studies in Flash Photolysis. II. Photolysis of Acetone with Filtered Light
Authors: Slagg N. , Marcus R. A.
Published: January 2005

Flash photolysis was studied in the absence of wavelengths below 200 mμ. Effects of acetone pressure, light intensity, added biacetyl, temperature, and wavelength were investigated. The results are consistent with primary acts postulated previously on the basis of low-intensity studies, but with the absence of complicating first-order secondary reactions at these high radical concentrations. Deactivation of excited molecules explains the pressure effect on the C2H6/CO ratio, for wall effects are absent under flash conditions. A hot radical mechanism is suggested by the data for methane formation. The effect of wavelength on C2H6/CO ratio in regions centered near 260, 280, and 295 mμ is rather striking, and the results are compared with trends in low-intensity studies in the same pressure region.
Electrical Conductivity of Near-Stoichiometric α-Nb2O5
Authors: Greener E. H. , Whitmore D. H. , Fine M. E.
Published: January 2005

The electrical conductivity of α-Nb2O5 monocrystalline and sintered specimens, measured under a constant ambient oxygen pressure and over the temperature range 300 to 900°C, exhibits an exponential temperature dependence with an activation energy of 1.65 ev. The isothermal conductivity, σ, of near-stoichiometric α-Nb2O5 is related to the ambient oxygen partial pressure, PO2, by the power law expression σ=const PO2—0.24±0.01. Both sets of observations may be rationalized on the basis that slightly-reduced α-Nb2O5 becomes a metal-excess, n-type semiconducting oxide containing oxygen vacancies capable of trapping electrons. A detailed analysis of the relation between conductivity and ambient oxygen pressure has indicated that the conductivity dependency may be ascribed to a mechanism whereby defect levels (due to oxygen ion vacancies with either one or two trapped electrons) are created and electrons are thermally excited from these levels into the conduction band.
Monte Carlo Computations on the Ising Model. The Body-Centered Cubic Lattice
Authors: Guttman Lester
Published: January 2005

The Monte Carlo method of computation has been used to obtain some equilibrium properties of bcc binary solid solutions whose atoms interact according to the Ising model. Four cases have been treated: (a) N=128, c=½, (b) N=1024, c=½, (c) N=1024, c=3/8, and (d) N=1024, c=¼ (N being the total number of atoms and c the fraction of one kind.) In all cases the heat capacity has a well-defined maximum. At the equiatomic composition, the height of this maximum is greater in the larger crystal. Discontinuities in thermodynamic properties were not observed, and it seems reasonable that the order-disorder transition in an infinite crystal would be characterized by an infinite heat capacity as calculated by Onsager and others for two-dimensional crystals. Comparison of the results with experimental properties of β-CuZn suggests a remarkable applicability of the Ising model to this system. The potentialities and limitations of the Monte Carlo method for systems with phase transitions are discussed.
Kinetics of Coordinate Bond Formation. IV. Kinetic Isotope Effect in the Reaction NH3+BF3
Authors: Kistiakowsky G. B. , Klots C. E.
Published: January 2005

An isotopic rate ratio, k′/k = 1.91±0.10, has been measured at room temperature for the reactions NH3 (ND3)+BF3 = NH3BF3(ND3BF3). A set of vibrational frequencies for the transition states is deduced which explains the observation by attributing to the transition state a large degree of charge transfer stabilization and a negligible activation energy.
Crystal Field Splitting and Covalent Bonding in Fe++ Silicate Garnets
Authors: Bloomfield Philip , Lawson A. W. , Rey Charles
Published: January 2005

A point-ion model and Slater free-ion wave functions have been used to calculate the crystal field splitting of the Fe++ ion 5D ground term in Fe3Al2(SiO4)3 garnet for various assumed charge distributions within the (SiO4)4— ion. The best fit with Clark's experimental data on absorption spectra is obtained with about 50% covalent bonding between Si and O, and with an effective nuclear charge for the Fe++ ion about 10% less than that given by Slater's rules. This estimate of the degree of covalency is consistent with that given by Pauling. The calculated pressure dependence of the optical absorption is in satisfactory agreement with the experiments of Balchan and Drickamer.
Analysis of Specific Heat Data for Zinc. Resolution of the Calorimetric and Elastic Θ0 Discrepancy
Authors: Garland C. W. , Silverman J.
Published: January 2005

The low-temperature heat capacity of zinc (in the normal state) has been expressed by Cv=γT+αT3+βT5 over the range from 0.15°K to about 8°K. The new parameters obtained are: γ=1.56×10—4 cal/deg2 mole, α=1.39×10—5 cal/deg4 mole, and β=2.44×10—7 cal/deg6 mole. The calorimetric Debye temperature, Θ0C, is found to be 322°K which is in reasonable agreement with the elastic value, Θ0E, of 328°K. The apparent disagreement between Θ0C and Θ0E values cited in the literature arises from the difficulty in analyzing the calorimetric data for a very anisotropic metal.
Infrared Spectra of Alkyldiboranes. V. Tri- and Tetramethyl- and Ethyldiboranes
Authors: Lehmann Walter J. , Wilson Charles O. , Shapiro I.
Published: January 2005

Frequency assignments are reported for the infrared spectra of tri- and tetramethyl- and ethyldiboranes, together with some of their boron-deuterated and B10 isotopic derivatives. Additionally, a Raman spectrum of tetramethyldiborane from sources in the literature is analyzed. In assigning some of the B–C stretching frequencies, use is made of the recently formulated Average Rule.
Capacitive Energy and the Ionization of Aromatic Hydrocarbons
Authors: Smith Felix T.
Published: January 2005

Large polynuclear aromatic molecules ionize like fragments of graphite, and their ionization potentials approach the sum of the graphite work function vgr and the electrostatic work of charging a conductor the size and shape of the molecule. The capacitive work for a single charge is u=e2/2C, where C is the molecular capacitance. In the limit of large size, the work to remove n electrons is Wn=nvgr+n2u. This limiting law implies a relation among successive ionization potentials and the electron affinity, which is well satisfied by anthracene and phenanthrene, and moderately well by naphthalene and even benzene. For larger molecules, C, and therefore u, can be estimated classically by assuming the conducting region is bounded by the carbon skeleton, and computed by analog measurements on metallic models; results are tabulated for a series of aromatics. The relation between the limiting law and more detailed quantal formulations is discussed, and the magnitude and trend of some expected deviations are explored with the help of a simple free electron picture.
Kinetics of Crystal Nucleation in Some Normal Alkane Liquids
Authors: Turnbull David , Cormia Robert L.
Published: January 2005

The crystal nucleation behavior of some normal alkane liquids—C16H34, C17H36, C18H38, C24H50, and C32H66—was investigated by the droplet technique. The relative undercoolings, 1—λ, (i.e., the actual undercooling in units of the absolute melting temperature) at which the crystal nucleation frequency in these liquids becomes 107 cm—3 sec—1 are 0.037 to 0.043, and almost an order of magnitude smaller than those for simple molecular substances. Crystal nucleation frequencies in droplets of C17H36 and C18H38 samples of very high purity were determined quantitatively. The frequencies were proportional to droplet volume and increased by a factor of 5000 to 8000 per 1° decrease in temperature. The results are satisfactorily described by the classical nucleation theory with values of the crystal nucleus - liquid interfacial tension σ, 7.2 erg-cm—2 for C17H36 and 9.6 erg-cm—2 for C18H38. The experimental pre-exponential factors in the nucleation expression agree with the theoretical values to well within the experimental uncertainty. The small relative undercooling and the weak glass-forming tendency in the high-molecular weight n-alkane liquids is satisfactorily explained by the hypothesis of nucleation of small segments of molecules.
Problems in Perturbation Theory Calculation of Diamagnetic Susceptibility and Nuclear Magnetic Shielding in Molecules. Illustration with the Hydrogen Atom
Authors: Snyder Lawrence C. , Parr Robert G.
Published: January 2005

The perturbation theory expressions for the diamagnetic susceptibility and nuclear magnetic shielding constants of atoms and molecules may be written as sums of ground state and excited state terms. The effects of truncations in the evaluation of the excited state terms are studied through a specially contrived application of these expressions to the hydrogen atom. When the origin of the vector potential is taken 1.4a0 away from the proton, computations of both properties show that the excited state part is comparable with the ground state part, that the continuum excited states contribute about as much as the discrete excited states, and that the first excited discrete state accounts for about a third of the whole excited-state contribution. The inference is made, for molecules, that truncation of conventional perturbation formulas by omission of continuum contributions will result in major errors and a dependence of computed properties on the origin taken for the vector potential. The average excited state energy required to make a correct sum rule estimate of the excited state part of the nuclear magnetic shielding constant of the hydrogen atom is calculated, and it is shown to depend strongly on the distance of the shielded position from the proton.
Electrochromism, a Possible Change of Color Producible in Dyes by an Electric Field
Authors: Platt John R.
Published: January 2005

Theoretical considerations suggest that the absorption and emission spectra of certain dyes may be shifted by hundreds of angstroms upon application of a strong electric field. The effect could be called ``electrochromism,'' in analogy to ``thermochromism'' and ``photochromism.'' The theory of the effect is outlined and is discussed in terms of compounds which might be expected to show it most strongly.
Paramagnetic Resonance Absorption in Naphthalene in Its Phosphorescent State
Authors: Hutchison Clyde A. , Mangum Billy W.
Published: January 2005

Paramagnetic resonance absorption has been observed in naphthalene in solid solution in a single crystal of durene when irradiated with light from an A-H6 mercury lamp. The fine structure of the spectrum at a frequency of ∼22.7×109 cps may be described by the spin-Hamiltonian H=|β|H·g·S+DSz2+E(Sx2−Sy2),,with S=1,g=2.0030±0.0004 (isotropic),D/hc=±0.1003±0.0006 cm−1,E/hc=∓0.0137±0.0002 cm−1.Observations at a different frequency, ∼9.7×109 cps, and also measurements on perdeuteronaphthalene are described by essentially the same parameters. The fine structure data identify the spectrum as arising from a triplet state and leave no doubt as to the triplet character of the phosphorescent state of naphthalene. The zero-field splitting of the triplet has its origin in the magnetic dipole-dipole interaction between the two unpaired electrons in the triplet state. These experimental results are in agreement with the theoretical estimates. Hyperfine structure has been observed and is interpretable on the basis of the anisotropic hyperfine interaction constants for a C–H fragment given by McConnell. The π-electron spin density on the α-carbons is found to be 0.209. The hyperfine structure results identify the spectrum as arising from naphthalene. In addition they show that the triplet state is 3B2u+ and that the naphthalene molecules are oriented in the crystals such that they are not only coplanar with the durene molecule which they replace but also have their long and short twofold axes in this plane parallel, respectively, to the long and short axes of durenes.
New Determinations of the Vibrational Constants of Li6F and Li6Cl35 by the Molecular Beam Electric Resonance Method
Authors: Moran T. I. , Trischka J. W.
Published: January 2005

New measurements of the vibrational constants of LiF and LiCl were stimulated by the hypothesis of Klemperer and Herschbach that disagreement between infrared and previous molecular beam values of these constants could be explained by a variation in the efficiency of the molecular beam detector with vibrational state. The new molecular beam results rule out this hypothesis because of their agreement with infrared results. These new values are 930±19 cm—1 for Li6F and 705±14 cm—1 for Li6Cl35. The agreement of these values with the infrared results leads to the conclusion that the vibrational states of molecules in the molecular beam source have a Boltzmann distribution. The relative detector efficiency for the vibrational states v=0 and v=1 did not vary when the total efficiency was changed over a range from 0.2 of the maximum value to the maximum. The ratio of the vibrational constants of Li6F and Li7F was found to be 1.06±0.01, in agreement with the value calculated from the ratio of the reduced masses. A rough measurement of the vibrational decay constant between the v=1 and v=0 states gave 65±40 sec—1.
Shock Tube Study of Vibrational Relaxation in the A 2Σ+ State of NO
Authors: Roth W.
Published: January 2005

Nonequilibrium NO γ-band emission has been observed behind incident shock waves in rare gas-air mixtures in the approximate temperature range, 5000–10 000°K. Vibrational relaxation times for collisional de-excitation of NO (A 2Σ+) were measured. The measured relaxation times were used to calculate P10, the probability for collisional de-excitation of the v′=1 level of the A 2Σ+ state; P10 ranges from about 3×10—5 at 5000°K to 3×10—4 at 10 000°K.
Second-Order Perturbation Theory of Helium-Like Ions
Authors: Gray B. F. , Whitehead R.
Published: January 2005

A method for calculating the Coulomb interaction between the electrons to the second order of approximation, due to Kessler, is examined and shown to require modification. This removes the discrepancy between the value obtained by Kessler and that obtained by Hylleraas and Midtdal using a variational method, although only very limited accuracy is obtainable.
Raman Intensities and the Structure of Some Oxyanions of Group VII
Authors: Chantry G. W. , Plane R. A.
Published: January 2005

In order to obtain information concerning bonding and to test a hypothesis concerning the non-existence of BrO4—, the absolute intensities and depolarization ratios have been determined for Raman lines of ClO3—, BrO3—, IO3—, IO4—, and H5IO6. From the data, values of ᾱx0′ are obtained. These show that ClO3— resembles previously studied ions in containing sufficient π bonding to achieve essential electrical neutrality. Values for the other oxyhalides are consistent with this interpretation; however, an independent criterion based on depolarization ratios (which are apparently greater for BrO3— and IO3— than for ClO3—) indicates that there is less π bonding in BrO3— and IO3— than in ClO3—. Since neither criterion can be applied rigorously to the present examples, it is difficult to decide which explanation is correct or wehther the truth lies intermediate between the two extremes.
Electronic Paramagnetic Relaxation Times in Potassium-Ammonia and Potassium-Deuteroammonia Solutions
Authors: Hutchison Clyde A. , O'Reilly Donald E.
Published: January 2005

The longitudinal and transverse paramagnetic relaxation times T1 and T2 for K–NH3 and K-ND3 solutions, have been measured over a range of concentrations and temperatures. T1 is found to be equal to T2 at the higher concentrations. At the lower concentrations, the values of T1 are found to be greater than those of T2, although at the very lowest concentrations studied they are again approaching each other in value with decreasing molarity. The product of the linewidth at zero rf field by the ratio of temperature to viscosity is found to be constant in both NH3 and ND3 over the temperature range studied.
Pressure Dependence of the Absolute Catalytic Efficiency of Surfaces for Removal of Atomic Nitrogen
Authors: Young Robert A.
Published: January 2005

By utilizing the nitrogen afterglow to monitor the exponentially decaying nitrogen atom concentration within a closed observation bulb, the low catalytic efficiency of four wall coatings is measured over a large pressure range. The catalytic efficiency of all surfaces is essentially independent of pressure.
Reaction of Nitrogen Atoms with Ozone
Authors: Chen Mei Chio , Taylor H. Austin
Published: January 2005

The reaction of ozonized oxygen and active nitrogen at room temperature has been shown to produce, almost exclusively, nitrous oxide. Rate measurements in a flow system have been analyzed as involving a primary reaction N+O3→NO+O2. Accepting present values for the specific rates of subsequent reactions of nitric oxide, the rate of the primary reaction is found to be 1010 ml/mole sec. This is several orders faster than the reaction of nitrogen atoms and oxygen molecules and many orders faster than the three-body recombination of atomic nitrogen and atomic oxygen, substantiating the Barth-Kaplan suggestion of the probable source of nitric oxide in the upper atmosphere.
Interaction Potentials of Simple Nonpolar Molecules with Graphite
Authors: Crowell A. D. , Steele R. B.
Published: January 2005

The interaction and zero-point energies of Ne, A, Kr, Xe, and CH4 molecules near a semi-infinite graphite lattice at the potential minimum have been calculated using lattice sums of a (6–12) potential with empirically determined potential constants and have been compared with recent experimental data. The significance of the results with respect to the possible role of charge-transfer no-bond mechanism for these systems is briefly discussed and it is concluded that dispersion forces alone are sufficient to account for the interaction energy.
Concentration Dependence of Polymer Chain Configurations in Solution
Authors: Yamakawa Hiromi
Published: January 2005

On the basis of the theory of fluids and of the fashion prevailing in the statistical thermodynamics of dilute chain polymer solutions, the segment distribution functions are formally derived as a power series in concentration. The mean-square radius of gyration and end-to-end distance at finite concentrations are calculated by using the general equations derived and introducing the modified random flight model. Evaluation is carried out up to the linear term in concentration. The coefficients of the linear terms are obtained as a power series in the excluded volume parameter, and also appropriate closed forms for those are proposed, which might be properly applied to good solvent systems. The results show that the polymer chain dimension decreases with increasing concentration. Then the concentration-dependent term in the intramolecular intensity function in light scattering is evaluated. It is pointed out that the separation of this term and the intermolecular correlation leads to the possibility of estimation of the polymer chain dimension at finite concentrations by light-scattering measurements. Finally, the Huggins constant k′ in the viscosity-concentration relation is phenomenologically calculated. The concentration dependence of polymer chain dimensions proves to explain satisfactorily the effect of solvent power on the k′ constant.
Heat Capacities and Thermodynamic Functions of ZrH2 and ZrD2 from 5 to 350°K and the Hydrogen Vibration Frequency in ZrH2
Authors: Flotow Howard E. , Osborne Darrell W.
Published: January 2005

The heat capacities of ZrH2 and ZrD2 were measured in an adiabatic type calorimeter from 5 to 350°K. X-ray analyses showed the hydrides consist of a single face-centered tetragonal phase. The data for both compounds below 11°K were found to fit the equation Cv=9.8×10—4T+464.6(T/θ)3 cal deg—1 mole—1, where θ=311.4, and this equation was used to extrapolate the heat capacities below 6°K. Between 20 and 100°K the Cp of ZrD2 averages 1% lower than that of ZrH2 but above 110°K the Cp of ZrD2 becomes increasingly greater than that of ZrH2. At 298.15°K the heat capacities and thermodynamic functions calculated from the data are Cp=7.396±0.015 cal deg—1 mole—1, S°=8.374±0.02 cal deg—1 mole—1, H°—H0°=1284.1±2 cal mole—1, and (F°—H0°)/T=—4.067±0.01 cal deg—1 mole—1 for ZrH2, and 9.631±0.019, 9.168±0.02, 1474.4±3, and —4.223±0.01, respectively, for ZrD2. The free energy of formation of ZrH2 at 298.15°K is —30.9±2 kcal mole—1 and that of ZrD2 is —31.2±2. On the assumption that the difference in the heat capacity between the two isotopic compounds arises from a triply degenerate hydrogen vibration, it was found that the difference in the temperature range 100 to 350°K could be satisfactorily fitted by the difference between two Einstein heat capacity functions with a frequency of 1190±30 cm—1 for ZrH2 and 1190/√2 cm—1 for ZrD2. This result is compared with the optical lattice vibration frequency found by neutron scattering experiments.
Luminescence during Annealing and Phase Change in Crystals
Authors: Johnson Noye M. , Daniels Farrington
Published: January 2005

The accepted definition of thermoluminescence is the thermal release of trapped electrons with accompanying optical transition. This interpretation presupposes an exposure to ionizing radiation in order to fill the electron traps. Other processes such as mechanical stress and chemical reaction can also serve to excite electrons, as observed in triboluminescence and chemiluminescence. It is proposed that some instances of luminescence during heating are produced by physical processes other than the release of previously trapped electrons. Evidence for this is provided by the correlation of certain glow-curve peaks with crystalline annealing, decomposition, and polymorphic transition. Measurements of annealing and polymorphic changes were made through x-ray diffraction. Attempts to interpret the thermal or radiation history of geological specimens by thermoluminescence must account for both radiation-induced and radiation-independent forms of light generation.
Effect of Inert-Gas Moderators on the (n, γ) Activated Reaction of I128 with CH4
Authors: Rack Edward P. , Gordus Adon A.
Published: January 2005

In the presence of a large excess of gaseous methane, 54.4±0.5% of I128 formed by (n, γ) activation was found to become stabilized in organic combination. The effects of inert-gas additives in moderating the reaction of I128 with CH4 were determined in an effort to ascertain the mechanism. The data, extrapolated to zero mole-fraction methane, indicate that xenon is capable of reducing the organic I128 to 11% whereas neon, argon, and krypton each reduce it to only about 36%. These data suggest that of the 54.4% organic I128, about 18.4% forms as a result of hot I128 reactions, 11% as a result of excited iodine atoms or I+ ions in the 3P2, 3P1, and/or 3P0 states, and 25% as a result of reactions of I+(1D2) ions.
Quantum Mechanics of Mobile Electrons in Conjugated Bond Systems. I. General Analysis in the Tight-Binding Formulation
Authors: Ruedenberg Klaus
Published: January 2005

The quantum-mechanical treatment is carried through for a set of electrons in a homonuclear conjugated bond system of arbitrary size, including electronic interaction and including all overlap effects between neighbors. All framework contributions are obtained by explicit integration over the framework Hamiltonian, including the effect of nonconjugated neighbor atoms and differentiating between different types of conjugated atoms (joint, nonjoints, etc.). Expressions are given for the ground-state energy, ionization potential, electron affinity, electronegativity, and for the configuration interaction matrix for the calculation of excited states, assuming singly excited configurations. The results take simple forms permitting instructive interpretations. The partial additivity of one-electron binding-energy contributions, obtained as eigenvalues of topological molecular orbitals, and the approximate validity of the ``neglect of differential overlap'' is proved.
Quantum Mechanics of Mobile Electrons in Conjugated Bond Systems. II. Augmented Tight-Binding Formulation
Authors: Ruedenberg Klaus
Published: January 2005

The analysis of homonuclear conjugated systems, which has been given within the limits of the tight-binding approximation in the first paper of this series, is extended to include the interactions between non-neighbor atoms and the variation in the interactions between neighbor atoms. Both kinds of interactions are included as perturbation effects on the tight-binding approximation. As a consequence, the formalism developed for the latter is not being complicated and the interpretations remain unchanged. Application to benzene and naphthalene illustrates the approach.
Quantum Mechanics of Mobile Electrons in Conjugated Bond Systems. IV. Integral Formulas
Authors: Ruedenberg Klaus
Published: January 2005

Formulas are established for all carbon and hydrogen penetration integrals occurring in the tight-binding approximation of the theory of mobile electrons. The orbital exponents of the penetrated shielding orbitals may differ from the orbital exponent of the penetrating 2pπ electrons. A simple correlation between kinetic energy integral and overlap integral is found.
Shock Tube Determination of Dissociation Rates of Oxygen
Authors: Rink John P. , Knight Herbert T. , Duff Russell E.
Published: January 2005

The rate of dissociation of oxygen in Xe–O2 mixtures was measured over a temperature range of 3000°K to 6000°K. An x-ray densitometer was used to measure the density during the dissociation process behind a shock wave. It was possible to match the experimental data with theoretical density profiles over a wide range of compositions and initial conditions. The reactions considered were O2+M⇌ lim krkd2 O+M,where M can be Xe, O2, or O. Considering these species as third bodies, the deduced recombination rates in cc2 mole—2 sec—1 were 4.7×1017 T—1, 1.6×1018 T—1, and 4.8×1018 T—1, respectively. The third-body efficiencies of O2 and O relative to Xe are 3 and 10. Experimental conditions were such that an accurate measurement of the exponent of the temperature could not be made. However, since the data showed it to be within the limits of —½ and —2, a value of —1.0 was arbitrarily chosen. The agreement between results reported here and previous work demonstrates the potential utility of this method for kinetic studies of other reactions.
A Calculation of the Potential Energy Curves for Some Electronic States of Carbon Monoxide
Authors: Lefebvre-Brion Hélène , Moser C. M. , Nesbet R. K.
Published: January 2005

The LCAO-MO SCF orbitals for the 1Σ+ ground state of carbon monoxide, constructed from 1s, 2s, and 2p atomic functions, have been calculated for 11 internuclear distances between 1.5 and 4.0 a.u. Using the unoccupied SCF orbitals a number of lower excited states have been calculated. The equilibrium distances, force constants, and ν00 energies have been calculated from the curves of E vs R for these various states. As these calculated curves do not separate at infinity into the atoms in their proper spectroscopic states, configuration interaction has been carried out with functions which cross the computed curves and separate into the atoms in their 3P states. The lower states of carbon monoxide seem to be divided into three classes: (a) those which are reasonably well represented by our functions, namely, X 1Σ+, e 3Σ—, a′ 3Σ+, A 1Π, and a 3Π; (b) those which are not at all well represented by our functions, namely, b 3Σ+, B 1Σ+, and C 1Σ+; (c) those states for which the experimental assignment may be in error, namely, d 3Π and F 1Π.
Madelung Constants for Several Structures
Authors: Johnson Quintin C. , Templeton David H.
Published: January 2005

Madelung constants are given for 38 structures, some of which are relatively complex. The Madelung constants for binary compounds are compared with an empirical rule previously formulated.
Positive and Negative Ion Formation in CCl3F
Authors: Curran R. K.
Published: January 2005

A mass spectrometer with an ion source utilizing nearly monoenergetic electrons was used to measure appearance potentials of positive and negative ions in CCl3F. Kinetic energy measurements were made on the negative ions. The results have lead to values for the ionization potentials of CCl3, CCl2F, and CClF. The C–F and C–Cl bond energies have been determined from measurements on the negative fluorine and chlorine ions. A value is given for the electron affinity of the CCl3 radical.
Kinetic Model for Solid-State Reactions
Authors: Carter R. E.
Published: January 2005

A model for solid-solid or solid-gas reactions between spherical particles and a fine powder or gas has been developed. The oxidation of uniformly sized nickel spheres has been shown to fit this model to 100% reaction. Previously reported models are inadequate because they do not meet the boundary conditions set down and because the volume of the product was assumed to equal that of one of the reactants. The inadequacy of earlier experimental results has been explained by the failure to experimentally meet the boundary conditions imposed.
Fluid Superposition Approximation and the Fourth Virial Coefficient
Authors: Cole G. H. A.
Published: January 2005

A new superposition approximation is given for relating the triplet distribution for a classical system of identical particles in interaction (fluid) to the pair distribution. The new approximation is based upon the well-known expression due to Kirkwood, but explicitly accounts for the particle density through a power series expansion. It is proposed that the coefficients of this expansion should be chosen in order to ensure internal consistency in the calculation of the virial coefficients of the pressure (when expressed in powers of the density) from either the pressure equation or the relative compressibility equation, and the necessary formulas are given. The equations are checked numerically for the ideal case of a gas of rigid spheres, as far as the fourth virial coefficient. The modified form of the original Kirkwood superposition approximation, which is the new approximation, is found for this case to be g(3)(r, s, t) = g(2)(r)g(2)(s)g(2)(t) [1+0.1014bn] where g(3) is the triplet distribution, g(2) the pair distribution, n the particle number density, and b is equal to four times the volume of each particle. The theory then leads to a fourth virial coefficient of value 0.2885b3 which is to be compared with the exact value 0.2869b3. This value is found to be a marked improvement on the values calculated by previous authors. The higher powers of n in the new superposition approximation necessary for the correct calculation of higher virial coefficients than the fourth are not considered in this paper.
Proton Resonance Line Shape for a Polycrystalline Aromatic Radical
Authors: Lefebvre Roland
Published: January 2005

A calculation is made of the resonance line shape for an in-plane proton of a polycrystalline aromatic radical in the case where the electron-proton hyperfine interaction is the only factor responsible for the resonance shift. Even with the inclusion of the anisotropic part of the electron-proton hyperfine interaction the position of the peak is linearly related to the unpaired π-electron density on the neighboring carbon atom, ρc. The relation is very close to the one found for the solution. The line shape is very symmetrical, with a width which increases for an increasing ρc. This behavior is in good agreement with the recent results of Gutowsky and collaborators.
Heat Capacity of Thulium from 15° to 360°K
Authors: Jennings L. D. , Hill Emma , Spedding F. H.
Published: January 2005

Thulium shows a lambda anomaly in its heat capacity near 55°K which is associated with magnetic ordering and which shows thermal hysteresis. In addition, there are anomalous changes in the slope of the heat capacity curve near 88°, 162°, and 180°K. These changes and the unexpectedly low value of the slope near room temperature complicate the analysis of the data, but there is evidence that the effective exchange integral in thulium is appreciably larger than that for neighboring rare earths. The results in the temperature range from 14° to 21°K support a T3 dependence of the magnetic specific heat as predicted by spin wave theory for an antiferromagnet. The thermodynamic functions are tabulated for the temperature range studied.
Role of Exchange Energy in Intermediate-Range Interactions
Authors: Ellison Frank O.
Published: January 2005

Computations have been made of the Coulomb and exchange parts of the interaction energies of a proton with a hydrogen atom and of two hydrogen atoms. It is found that the exchange energy becomes a more important and Coulomb energy becomes a less important fraction of the first-order interactions (i.e., interaction of ground-state atoms with no configuration interaction) as the internuclear distance is increased. It is also shown that the first-order contribution is necessary to bring the perturbation calculations of Coulson on H2+ and of Löwdin and Hirschfelder on H2 into good agreement with experiment for intermediate separations.
Diffusional Transport of Atomic Hydrogen through Molecular Hydrogen at Elevated Temperatures
Authors: Wise Henry
Published: January 2005

Changes in the transport properties of a gas mixture of atomic and molecular hydrogen were measured in a temperature range from 300° to 700°K. The steady-state distribution of atoms diffusing from a source towards a catalytically active surface was determined in a cylinder of finite length. The experimental parameter of interest is the diffusion Reynolds number which contains the ratio of interdiffusion coefficient to recombination coefficient. If the catalytic activity of the surface is known, one may relate the atom-concentration gradient to the diffusion coefficient. In the temperature region studied the change in the binary diffusion coefficient for the system H, H2 was evaluated. Based on the results obtained, the intermolecular force fields applicable to the atom-molecule encounters were examined.
On the Kinetic Theory of Dense Fluids. VI. Singlet Distribution Function for Rigid Spheres with an Attractive Potential
Authors: Rice Stuart A. , Allnatt Alan R.
Published: January 2005

A new integro-differential equation for the singlet distribution function in a model dense fluid is derived and solved. In the model considered, the pair interaction potential is represented as a rigid core plus a soft attraction. Interactions between two rigid cores are handled as in the theory of the dense rigid-sphere fluid, while interactions between the soft attractions are handled, following Kirkwood, in the Fokker-Planck approximation. The use of coarse graining in time to provide a time scale permitting the above separation, the relaxation in momentum space, the kinetic flux vectors, and the physical basis of the analysis are all discussed.
Vibrational Relaxation in Carbon Dioxide
Authors: Witteman W. J.
Published: January 2005

The vibrational excitation of a CO2 molecule in collision with another CO2 molecule is investigated. A derivation of the cross section by means of the method of the distorted waves and the rate of total energy transfer are presented. There are two relaxation processes with different relaxation times related to direct excitation of the bending mode and excitation in series of the valence mode. Experimental results obtained by the author, to be published separately, confirm this conclusion. The experimental relaxation time for the bending vibration was about one-half of the calculated value, which may be considered a fair agreement in view of the uncertainty involved in the interaction potential and of other approximations which had to be introduced into the calculations.
General Relation between Potential Energy and Internuclear Distance for Diatomic Molecules. III. Excited States
Authors: Lippincott E. R. , Steele D. , Caldwell P.
Published: January 2005

A previously proposed internuclear potential function has been used to calculate the dissociation energies for the excited states of a large number of diatomic molecules. From these results and the Wigner-Witmer rules the dissociation products are determined, and it is shown that in many cases it is possible to estimate independently, the dissociation energy of the ground state. The three- and five-parameter forms of the proposed function lead to nearly equal values for dissociation energies suggesting an equivalence of the two forms. This leads to a relation between the anharmonicity and the vibrational-rotational coupling constant which is slightly superior to the Pekeris relation. Equations derived from this relation are given relating the parameters a and b of the five-parameter functions to the anharmonicity or vibrational-rotational coupling constant. The parameter b and to a lesser extent a was found nearly constant for the excited states of all diatomic molecules.
ESR Line Shapes in Glasses of Copper Complexes
Authors: Neiman Robert , Kivelson Daniel
Published: January 2005

The study by Sands of ESR line shapes of polycrystalline copper complexes has been extended and various ``anomalies'' discovered in the line shapes. The spectrum of copper phthalocyanine dissolved in concentrated H2SO4 has been studied at 77°K. The M=−32 hyperfine line has a behavior very different from that discussed by Sands. Isotropic extra hyperfine structure, arising from the presence of the ligand nitrogens, is easily discernible even in the glass.
Ultraviolet Absorption Spectrum of Ammonia in Solid Argon at 4.2°K
Authors: Dressler K.
Published: January 2005

A series of absorption bands in the region 1600 to 1900 A has been observed in thin films of solid argon containing between 0.3% and 3% of ammonia. The bands are attributed to isolated NH3, and the absence of alternating bands in the observed vibrational progression shows that in the ground state only the J = 0 level is appreciably populated. Thermal equilibration of NH3 at 4.2°K involves the interconversion of nuclear spin species. It is suggested that the observed rapid equilibration is due to coupling between the proton spins and the spin of the nitrogen nucleus.
On the Theory of Condensation
Authors: Saitô Nobuhiko
Published: January 2005

A calculation based on the Bragg-Williams approximation in lattice gases is presented, which shows a connection between the Yang-Lee and Mayer theories of condensation through an analogy with image charges in a two-dimensional electrostatic problem. The main features of this calculation are presumed to be retained in an exact treatment of lattice gases and real gases. A determination of the singularities of Mayer's series is made by making use of the results of recent investigations of cluster integrals by the approximation of the diagram method. It is concluded to be very probable that Mayer's theory cannot locate the condensation point but determines instead the supersaturation limit. Further, there is no Derby hat region near the critical point.