bluuebunny/crossref_metadata_2025 huggingface dataset:
Purification and Single-Crystal Growth of Potassium Cyanide
Authors: Neubert Theodore J. , Susman Sherman
Published: January 2005

Reagent-grade KCN has been fashioned into nominally pure, low-strain, single crystals via a sequence of operations involving vacuum melting, zone refining and thermal-gradient growth of a monocrystal. Vacuum melting of KCN largely transforms oxygen-containing impurities (e.g., HCOO—, C2O4=, and CO3=) to OCN—. Zone refining removes the OCN— contamination with an effective working segregation coefficient of 0.7. Fe, Na, and Si are also readily removed. Molybdenum is a suitable container material.

Single crystals of KCN were grown under vacuum in a quartz, filtering-crystallizing device and strain minimized by freeing the crystalline boule from the ampoule walls prior to annealing slowly to room temperature. Samples cleaved from such a boule proved suitable for polarized-light experiments. They typically contained 10 ppm Na and trace quantities of OCN— impurity. A pure KCN crystal has no absorption bands in the visible or near-ultraviolet regions and begins to absorp strongly at 190 mμ. As the purity of KCN crystals decreases, the tail of the fundamental absorption shifts to lower energies. This shift is related to an increase in cyanate-ion contamination.
Crystallite Orientation in Materials Having Fiber Texture. II. A Study of Strained Samples of Crosslinked Polyethylene
Authors: Krigbaum W. R. , Roe R.-J.
Published: January 2005

Diffraction data obtained for a crosslinked polyethylene sample crystallized at fixed strain are utilized to demonstrate the practicality of the method of analysis for samples having fiber texture which was presented in a previous paper. Plane-normal distributions qi(ζi) reconstructed using data for twelve reflections reproduce the features of the measured distributions quite satisfactorily. The series termination error is only appreciable for planes having a sharply peaked distribution, and fortunately it then appears mainly as false oscillations of small amplitude in the low-density region, which do not distort the principal features of the distribution. As a test of the accuracy of plane-normal distributions constructed for unmeasured reflections, qi(ζi) was recalculated for the (200) plane with omission of the intensity data for this plane. Deviations from the experimental distribution are again trivial. Thus, the procedure permits one to calculate the plane-normal distributions for the (002) and (401) planes, for which experimental measurements are not feasible.

The crystallite orientation distribution G(ξ, φ) is calculated using the diffraction data for twelve reflections. This may be presented as a contour map or, if plotted in stereographic projection, as the inverse pole figure diagram. The most probable crystallite orientation for this sample, having relative elongation α=4.58, inclines the a, b, and c axes from the fiber direction by 41°, 90°, and 49°, respectively. The series termination error does not displace the peak positions, but it creates small areas of negative density in the low-density region. It is demonstrated that data for four planes suffice to reveal the qualitative aspects of the crystallite distribution. The approximate relation used to estimate the standard deviation of the truncated series is tested and verified.

Diffraction data were also obtained for three additional samples covering a range of elongation α from 2.20 to 6.67. The (h0l) plane-normals orient most strongly toward the fiber axis, the (h/l) ratio of the plane exhibiting the best alignment decreasing continuously as α is increased. The implication that the b axis tends to orient perpendicular to the fiber axis is verified by the plane-normal distribution, which becomes more sharply peaked about χ=90° as α is increased. The maximum in the a-axis distribution shifts from χ=0° to larger values of χ as α is increased, while the c-axis distribution undergoes a more complex transformation.
Anharmonic Forces and the Vapor-Pressure Ratio of Monatomic Isotopic Solids
Authors: Klein M. L.
Published: January 2005

An expression for the vapor pressure ratio of two monatomic anharmonic isotopic solids is derived for T≳θ. At constant volume the contribution of the anharmonicity can be represented by an effective shift in the normal mode frequencies; this shift differs from that appropriate to neutron scattering and the entropy in that at high temperatures φ3 (the third-order term in the expansion of the lattice potential energy) makes no contribution. The effect of thermal expansion can be represented by an additional frequency shift. Lattice vacancies may also contribute to the vapor-pressure ratio but this effect should be small. In the harmonic approximation the vapor pressure ratio can be related to the isotope separation factor; this relationship is discussed in some detail. The isotope separation factor is evaluated approximately for a fcc lattice with various interaction potentials, and compared with the experimental results for solid argon; it appears that the anharmonic contribution due to φ4 is important. A systematic method is proposed for the analysis of experimental data.
Chemiluminescent Nitric Oxide—Oxygen-Atom Reaction at Low Pressures
Authors: Reeves Robert R. , Harteck Paul , Chace William H.
Published: January 2005

The light emitting reaction NO+O→NO2+hv is shown to be second order in the pressure region of 3 to 20 μ. This would indicate that the major source of emission is a simple radiative combination of nitric oxide and oxygen atoms. In addition, any excitation and emission mechanism involving a third body would be too small to account for the light emission observed.
Cross-Section Measurements for the Quenching of the 2537-Å Resonance Radiation of Mercury
Authors: Bellas M. G. , Rousseau Yves , Strausz O. P. , Gunning H. E.
Published: January 2005

Quenching cross-section values have been obtained for 28 compounds. These include protiated, deuteriated, and halogenated hydrocarbons as well as some oxygen- and sulfur-containing species to which the nitrous oxide method had not been applied previously. The earlier reported H/D primary kinetic isotope effect of about 15 has been confirmed for n- and isobutane and cyclohexane, but cyclopropane exhibited no isotope effect. The relation between substrate structure and quenching cross section values is compatible with the postulated electrophilic character of the Hg 6(3P1) atom. Discrepancies with values based on fluorescence measurements indicate the complex nature of the energy-transfer mechanism.
Interactions between Ordinary Vibrations and Hindered Internal Rotation. II. Theory of Internal Rotation Fine Structure in Some Perpendicular Bands of Ethane-Type Molecules
Authors: Kirtman Bernard
Published: January 2005

A method for determining the barrier to internal rotation in ethane-type molecules from the fine structure of certain perpendicular vibrational bands is presented. This fine structure depends upon the degree of coupling between vibration and internal rotation which, in turn, is a function of the barrier height. By comparing observed and theoretical spectra it is possible to set an upper limit of 100 cal/mole for the barrier to internal rotation in dimethylacetylene. Application to other molecules is discussed.
Effect of 18O on the Infrared Absorption Intensity of the Phosphorus Oxychloride Symmetrical Vibrations
Authors: Laulicht I. , Pinchas S. , Sadeh D. , Samuel David
Published: January 2005

The infrared absorption of normal and 97 at. % 18O phosphorus oxychloride in the 4000–200 cm—1 region has been investigated for cyclohexane and other solutions. The relative integrated absorption of all their symmetrical (A1) bands was estimated by multiplying each molar index of absorbancy by the corresponding half-width. The respective normal and labeled compound F sums for the A1 species were found to disagree by about 5%. The origin of this discrepancy, as well as the different effect of a change of solvent on the half-width and integrated area of the P=16O and P=18O stretching bands is discussed.
Collisional Deactivation of Highly Vibrationally Excited Cyclopropane
Authors: Simons J. W. , Rabinovitch B. S. , Setser D. W.
Published: January 2005

Vibrationally excited cyclopropane molecules were produced by chemical activation at ≈100 kcal mole—1 above the ground level; methylene radicals were formed by photolysis of ketene at 3200 Å and were added to ethylene. Collisional deactivation has been studied at 298° and 423°K, with ethylene as the inert deactivator, and at 298° with He, Ar, and N2 as deactivators.

The average amount of energy removed by ethylene per collision was calculated on a stepladder model and found to be in excess of 10 kcal mole—1, and not higher than 14 kcal, from the present data. Nitrogen and argon appear to have lesser efficiency than ethylene. Helium is the most inefficient gas; it removes ≈ 6 kcal mole—1 per effective collision, with some evidence that an important fraction of collisions (≈ 0.67) are elastic, i.e., result in only a little or no energy transfer. This suggests that a bimodal distribution of collisional transition probabilities, or other distribution skewed toward smaller step sizes, may be more appropriate for helium, as also found previously in works by Kohlmaier and Rabinovitch.
Dielectric Relaxation in Alkylcyanides
Authors: Krishnaji  , Mansingh Abhai
Published: January 2005

The values of ε′ and ε″ have been measured for pure methyl, ethyl, n-propyl and n-butyl cyanides at 1.0 Mc/sec, 9.95, 20.8, and 32.0 kMc/sec. The relaxation time and the distribution parameters have been calculated from Cole-Cole plots. The value of dielectric relaxation time increases from methyl to n-butyl cyanides (3.8, 4.7, 6.2, 7.5×10—12 sec at 30°C) but the distribution parameter is decreasing with increasing chain length (0.14, 0.08, 0.02, 0.00, at 30°C). This indicates that probably there is rotation of the CN group around the C–CN bond. The cyanides are showing that the most probable enthalpies of activation are less than the corresponding free energies so that the most probable entropies of activation are negative. A recording-type dielectric measuring bench has been used for the microwave measurements.
Pressure Dependence of the Electrical Conductivity of Ag2HgI4
Authors: Weil Raoul , Lawson A. W.
Published: January 2005

The electrical conductivity of Ag2HgI4 is primarily ionic above the order—disorder transition temperature of 50°C. Below this critical temperature, there is an appreciable electronic component. The effect of pressure, at all temperatures, is initially to increase the conductivity. However, the conductivity passes through a maximum and decreases between 4000 and 6000 kg/cm2. This unusual pressure behavior is not explicable in terms of any simple model. A new phase, which is presumably an analog of that ocurring in AgI, appears above about 6000 kg/cm2. The conductivity in this phase is primarily electronic even at high temperatures. The data also suggest the possible existence of still another new phase between 4000 and 6000 kg/cm2. Despite the complicated pressure dependence, the temperature dependence has a simple activation energy at all pressures except in the immediate vicinity of the transition point.
Polyhedral Clathrate Hydrates. VIII. The Geometry of the Polyhedra
Authors: Allen K. W.
Published: January 2005

The geometry of the polyhedra important in the structures of clathrate hydrates—the tetrakaidecahedron, the pentakaidecahedron, and the hexakaidecahedron—is considered. The fundamental lack of strict regularity is discussed and the extent of possible limited regularity is examined for each in turn.
Vibrational Spectrum and Structure of K3Ir(CN)6, K3Rh(CN)6, and K3Co(CN)6
Authors: Jones Llewellyn H.
Published: January 2005

The infrared spectra of crystalline K3Ir(CN)6 and K3Rh(CN)6 have been recorded. This information is combined with Raman data of other workers to yield a nearly complete assignment of the fundamental vibrational frequencies of the M(CN)63— ions. Force constants have been calculated for these ions and that of Co(CN)63— from previously reported spectra, and it is shown that there is a regular increase in metal—carbon force constant in the order Co<Rh<Ir. The CN stretching force constant is about the same for these ions. The force-constant data along with intensity data indicate an increase in both metal—ligand sigma bonding and pi bonding in the order Co<Rh<Ir.
Conduction—Ionic or Electronic—in BaTiO3
Authors: Glower D. D. , Heckman R. C.
Published: January 2005

Conduction in single crystal and ceramic BaTiO3 has been investigated using a concentration cell and activation analysis. Ionic conduction occurs near 100°C in single crystals containing Fe2O3 while electronic conduction predominates in ``pure'' crystals from 100° to 600°C. Ceramic samples conduct predominately ionically at 100°C and electronically at 500°C. It is found that the iron ion is mobile in single crystals and that the titanium ion is immobile.
Refractive Index of the Hydrogen Molecule
Authors: Karplus M.
Published: January 2005

The variation—perturbation method is employed for the estimation of the frequency-dependent polarizability and the refractive index of the hydrogen molecule. Use of a one-term expression for each component of the perturbation function leads to a simple formula for the frequency dependence. Application of the formula is made to several approximate ground-state wavefunctions for the hydrogen molecule. Comparison of the values computed with different functions shows large differences. Good agreement with the experimental frequency dependence is obtained only from certain molecular orbital wavefunctions. It is suggested that this result may be partly fortuitous and that more refined calculations are needed, particularly for examination of the high-frequency range.
Angular Dependence of Fluorescence from Chlorophyll a in Monolayers
Authors: Tweet A. G. , Gaines G. L. , Bellamy W. D.
Published: January 2005

Angular distribution of fluorescence from monomolecular films containing chlorophyll a spread on water has been determined. The transition moment of the red fluorescence is found to make an angle ≤20° with the water surface, while the transition moment responsible for the blue absorption band is estimated to make an angle of ≃28° with it. Both angles are measured in the porphyrin plane.
Nuclear Magnetic Resonance Relaxation in Associated Liquids
Authors: Favret A. G. , Meister R.
Published: January 2005

NMR spin—lattice and spin—spin relaxation times have been measured in the associated liquids 1,3-butanediol, 2-methyl-2,4-pentanediol, glycerol, and 1,2,6-hexanetriol at resonant frequencies of 10 and 20 Mc/sec and over the temperature range —40° to +40°C using ``spin echo'' techniques. These data were translated into average correlation times using the Kubo—Tomita model of the NMR relaxation process. By using a log Gaussian type of distribution it was possible in all four liquids to reconcile the average correlation times derived from both relaxation times and at both resonant frequencies. The rigid lattice limiting value of T2 and the variation of the distribution width with temperature were also determined.
Hartree—Fock Hamiltonians and Separable Nonlocal Potentials
Authors: Epstein Saul T.
Published: January 2005

It is pointed out that there are many Hamiltonians which have the Hartree—Fock wavefunction as an eigenfunction. These can be used to start perturbation calculations, different choices giving different results. The possible usefulness of separable, nonlocal potentials is outlined.
Spectroscopic Investigation of the Mechanism of the Intramolecular Heavy Atom Effect on the Phosphorescence Process. I. Naphthalene Emission
Authors: Pavlopoulos T. , El-Sayed M. A.
Published: January 2005

The infrared (240–3000 cm—1), Raman (100–3000 cm—1) and phosphorescence spectra of eight naphthalene mono- and dihalogenated derivatives are obtained and the polarization of the phosphorescence spectra is measured and compared. It is found that each phosphorescence spectrum is composed of two subspectra: Subspectrum I, which correlates with that of naphthalene and involves only totally symmetric C–C modes and Subspectrum II, which is caused to appear by an out-of-plane mode. The variation in the appearance of the unpolarized phosphorescence spectra of the different molecules in the series is explained mainly in terms of changes in the relative intensity of the two Subspectra I and II (and not in terms of the Franck—Condon principle). Subspectrum I is polarized perpendicular to the 1La, 1Lb excitation as in the parent hydrocarbon, while Subspectrum II is polarized parallel to the 1La excitation in the α derivatives but almost depolarized in the β compounds. This strongly indicates that the two subspectra originate from two different coupling schemes. The relative intensities of Subspectra II to I in the unpolarized emission spectra of the α-halonaphthalenes (which is also a measure of the relative importance of the corresponding two mechanisms involved) is found to increase as the number of the halogens or their atomic number increases. Since the heavy-atom effect involves orders of magnitude intensification of the phosphorescence emission, and since the intensities of Subspectra I and II are not greatly different in all the different compounds, it is concluded that the halogen enhances the original naphthalene-type mechanism as well as introduces a comparably important new mechanism of its own. A possible coupling scheme for Subspectrum II is (Sπ,π* or Sσ,σ*)↔ lim vib. Sσ,π*↔ lim S.O. Tπ,π*, or (Sπ,π* or Sσ,σ*)↔ lim S.O. Tσ,π*↔ lim vib. Tπ,π*,and that for Subspectrum I is Sσ,π*↔ lim S.O. Tπ,π*;where σ and σ* orbitals involve the carbon—halogen electronic system. The spin—orbit (S.O.) coupling can account for Subspectrum I, whereas the vibronic—S.O. interaction explains Subspectrum II.
Electron Spin Resonance and Molecular Motion of the RCH2ĊHCOOR′ Radicals in X-Irradiated Ester—Urea Inclusion Compounds
Authors: Griffith O. Hayes
Published: January 2005

Single crystals of the inclusion compounds formed between long-chain alkyl esters and urea were x irradiated at room temperature, and the free radicals produced were investigated by electron spin resonance. The 11 esters studied were diethyl adipate and the methyl, ethyl, hexyl, and octyl esters of monocarboxylic acids. The long-lived free radicals observed in all of these compounds are of the type RCH2CHCOOR′. These are π-electron radicals with the unpaired electron largely localized on one carbon 2p orbital. The coupling constants of the alcohol protons (R′) were resolved in the spectra of several radicals and the values ranged from 3 to 6 Mc/sec. The ester radicals undergo motion in the tubular cavities formed by the urea molecules of the crystal, and this affects the magnitudes of the proton coupling constants. The dependence of the α-and β-proton coupling constants on this motion is briefly considered. From the ethyl heptanoate radical ESR data, recorded over the range of 352° to 7°±3°K, and from the room-temperature ESR data of all eleven ester radicals, information is obtained regarding the motions and orientations of the ester radicals. In addition, two carboxylic-acid—urea inclusion compounds were investigated, and the orientations and motions of the well-known radicals produced in these systems (RCH2ĊHCOOH) are compared to those of the ester radicals. Approximate equations are given which relate the observed α-proton coupling constants and spectroscopic splitting factors to the diagonal elements of the α-proton tensors and g tensors of all radicals investigated.
Reaction of Deuterated Polystyrenes with Hydrogen and Deuterium Atoms
Authors: Wall Leo A. , Ingalls Ronald B.
Published: January 2005

Investigation of the electron spin resonance spectra shown by finely divided polystyrene and selectively deuterated polystyrenes, upon exposure either to hydrogen atoms or to deuterium atoms, demonstrates that the predominant reaction is the addition of a hydrogen atom to the phenyl ring, thus producing a cyclohexadienyl-type radical. The specific rate of this reaction at room temperature is estimated to be 4×103 liters mole—1·sec—1; the specific rate at which hydrogen atoms react with the cyclohexadienyl-type radical is estimated to be 106 liters mole—1·sec—1. The rate at which iodine vapor reacts with the cyclohexadienyl radicals is probably about the same value. Qualitatively, the results produce an insight into the mechanism of the radiolysis of polystyrene. It seems evident that although the mechanism is complex, both the evolved hydrogen and the crosslinking seen in the irradiation of polystyrene occur by means of radical precursors.
Mechanism of Proton Transfer in Acid—Base Reactions
Authors: Weiss Joseph J.
Published: January 2005

It is proposed that proton transfer in acid—base reactions goes by a quantum-mechanical tunnel effect. The predominance of the tunnel effect in these reactions is attributed to the recognition that the proton transfer can proceed alonga hydrogen bond between the two reactants and the distance which the proton has to travel is only 0.4 to 0.6 Å. On this basis some calculations have been carried out with a one-dimensional Eckart potential barrier, the (apparent) activation energy of the proton transfer being identified with the endothermicity (Q) of the proton-transfer reaction: AH+B→A+HB−Q. For the primary isotope effect for proton and deuteron transfer, it can be shown that increase of the (apparent) activation energy for the deuteron transfer (due to the difference in the zero-point energies) necessarily also affects the magnitude of the transmission coefficient and that this effect can compensate, to a greater or lesser extent, for the increased mass of the deuteron. The Bro/nsted relation in acid—base catalysis can also be derived, as a first approximation, from such a model and without any further a prioriassumptions between activation energies and free energies.
Crystal Shape Dependence of Exciton States in Molecular Crystals
Authors: Fox David , Hexter Robert M.
Published: January 2005

The transition-dipole—transition-dipole interaction model has been analyzed quantitatively, in application to the prediction of fine structure of spectroscopic transitions in molecular crystals, in the range where the particle size is much greater than the lattice parameter but is much less than the wavelength of the exciting radiation. A definite effect of sample shape on apparent multiplicity of a band is predicted. It is shown that the Hamiltonians for Davydov splitting and for shape splitting are separable. The ``shape Hamiltonian'' does not affect inactive states neither can it contain contributions from interactions shorter in range than r—3. Splitting energies and relative intensities of components have been calculated as functions of a parameter which measures the axial ratio of crystallite particles. The calculations have been carried out for cubic crystals, in which cases they are relatively simple because the results are independent of the sample orientation relative to the crystallographic axes. The symmetry of a dipole lattice is higher than that of the actual crystal; some of the effects of this ``supersymmetry'' on the spectrum predicted in this approximation have been examined. Several comparisons with experiment (primarily in the infrared region) have been made. The model predicts qualitative features of spectra correctly and where the transition is strong, reasonable quantitative results have been obtained. In most cases, when the transition is weak, the dominance of other effects, such as higher multipole interactions, repulsive forces or crystal defects, is indicated.
Partial Pressures in Equilibrium with Group IV Tellurides. III. Germanium Telluride
Authors: Brebrick Robert F.
Published: January 2005

The partial pressures of Te2(g) and GeTe(g) over Ge–Te condensed phases between 1 and 52 at. % Te have been determined between 525° and 940°C by measuring the optical density of the vapor. Partial optical densities due to each species are calculated and converted to partial pressures by assuming Beer's law and published vapor pressures.

Over Te-saturated GeTe(c), pTe2 reaches a maximum value of 2.5±0.2 Torr between 644° and 679°C. In the same temperature interval pTe2 over Ge-saturated GeTe(c) is about 20 times smaller. At the maximum melting point of GeTe(c), 725°C, pTe2 is 0.6±0.3 Torr and pGeTe is 17 Torr. Values of pGeTe and pTe2 over GeTe-saturated Ge(c) reach maximum values of respectively 125 and 2.2 Torr near 890°C. The value of pGeTe is the same over Te- and Ge-saturated GeTe(c) and up to 725°C is given by logp (Torr)= —(10.1±0.2)103/T+8.84. The standard Gibbs free energy of formation of GeTe(c) according to Ge(g)+ ½Te2(g)=GeTe(c) is ΔG°=—(117.8±3)+41.3(10—3)T kcal/mole. The heat of fusion of GeTe(c) is 11.3±2 kcal/mole. For the dissociation of GeTe(g) into Ge(g) and Te2(g), ΔG°=(71.5±2)—(14±1)(10—3)T kcal/mole between 637° and 940°C. This leads to a value of 95±4 kcal/mole for the dissociation energy, D0°, of GeTe(g) at 0°K in close agreement with the spectroscopic value of 95±9 kcal/mole. Our previous data for the standard enthalpies of formation of PbTe(g) and SnTe(g) lead to dissociation energies of PbTe(g) and SnTe(g) at 0°K of 52.7 and 79.3 kcal/mole, respectively.
Kinetics of Capillary Condensation in Wedge-Shaped Pores
Authors: Philip J. R.
Published: January 2005

The kinetics of capillary condensation into an initially dry pore is treated as an unsteady diffusion problem with a moving boundary at which the vapor concentration satisfies the Kelvin equation. The (justifiable) approximation that the phenomenon is radial leads to important simplifications. An exact similarity solution is found which is valid for the early stages of the condensation process. An approximate method of analysis is developed, using the class of similarity solutions of the two-dimensional radial diffusion problem with a constant concentration condition at an appropriately moving boundary. The method has some analogies to the Pohlhausen method in fluid mechanics in that the initial and boundary conditions are satisfied exactly, and the diffusion equation is satisfied in an integral sense. The method depends on numerical methods of integration, but approximate analytical solutions are available when the time is sufficiently large.

Numerical solutions are given for the capillary condensation of water. The characteristic equilibration time is highly sensitive to h0, the relative saturation of the atmosphere to which the dry pore is exposed, varying approximately as (1—h0)—3. The initial condensation rate is a constant, largely independent of h0 when this is close to one. The kinetics of capillary condensation is highly sensitive to temperature, equilibration times for water at 80°C being only 1/233 as great as at 0°C. The major influence of temperature on kinetics is due to the temperature dependence of the saturated vapor density.

A limitation to this approach is that the treatment is essentially macroscopic, although the early stages of condensation may involve relatively few molecules.
Franck—Condon Factors for the Ionization of CO, NO, and O2
Authors: Wacks Morton E.
Published: January 2005

Calculated values of the vibrational overlap integrals for the following transitions are given: (a) CO(X 1Σ+, v′′=0)→CO+(X 2Σ+, v′=0→10); (A 2Πi, v′=0→10); (B 2Σ+, v′=0→10).(b) NO(X 2Π, v′′=0)→NO+(X 1Σ+, v′=0→10); (A 1Π, v′=0→10).(c) O2(X 3Σg−, v′′=0, 1)→O2+(X 2Πg, v′=0→10); (a 4Πu, v′=0→15); (A 2Πu, v′=0→20); (b 4Σg−, v′=0→10).

These probabilities are used to construct theoretical ionization-efficiency curves assuming an energy dependence for the electronic transition integral for both photoionization and ionization by electron impact. Previously published experimental data are discussed in terms of the theoretically calculated Franck—Condon probabilities.
Frictional Coefficient of Polymer Molecules in Solution
Authors: Pyun C. W. , Fixman M.
Published: January 2005

The coefficient ks is calculated in the expression for the frictional coefficient f=f0(1+ksc+···), where f0 is the frictional coefficient at infinite dilution, and c is the concentration. Results are given for hard spheres and for interpenetrable spheres of uniform segment density. Difficulties caused by the long-rangedness of hydrodynamic interactions are removed by taking the translational velocity of the spheres relative to the mean solvent velocity; f is computed after transformation to a laboratory frame. All orders of ``reflections'' are correctly summed within the approximation of slow spatial variation of the velocity perturbation arising from a sphere in the vicinity of another. The derived velocity agrees well with that obtained exactly by others for the special case of the line of centers of the two interacting spheres in the direction of the external force. For hard spheres, a value of 7.157 for ks is found when c is the volume fraction of the spheres in the solution. For soft spheres where ks is smaller, the dependence of ks on the segment—segment interaction constant is obtained with the approximation that the binary clusters of overlapping spheres are treated as prolate ellipsoids of varying axial ratio. A substantial drop in ks, but not quite to zero, at the theta temperature is predicted by this model. Also the dependence of ks at the theta point on the polymer molecular weight is briefly discussed.
Configuration-Interaction Study of the Ground State of the H3+ Molecule
Authors: Christoffersen Ralph E.
Published: January 2005

A configuration-interaction calculation on the ground state of H3+ has been done using Slater-type orbitals of the form 1s, 2s, 2px, 2py, 2pz to form the basis set. The calculation was effected by approximating the exact wavefunction for the system by a linear combination of configurations, each of which is a properly antisymmetrized function constructed from the basis orbitals, and by applying the variation theorem to the approximate wavefunction.

The most stable nuclear geometry for H3+ is an equilateral triangle, since a plot of total energy versus central bond angle shows a deep minimum at a bond angle of 60 deg.

The best energy that was obtained for the equilateral triangle was —1.33264 hartree at R=1.6575 bohr, using 12 basis orbitals and 12 symmetry-adapted configurations. The experimental energy for H3+ is not known, but is estimated to be —1.35 hartree from these calculations.

The first excited singlet state, which is a doubly degenerate 1E′ state, has been examined at many values of R for an equilateral triangle with three basis orbitals, and has been found to give a typical repulsive energy curve.

The fundamental vibrational frequencies for the ground state have been calculated, and it has been found that the symmetric stretch frequency is 3354±60 cm—1, and the doubly degenerate bending frequency is 2790±100 cm—1.
Nuclear Magnetic Resonance Study of Solid Perfluorocyclohexane
Authors: Fratiello A. , Douglass D. C.
Published: January 2005

A nuclear magnetic resonance second-moment study of perfluorocyclohexane over the temperature range +25° to —130°C gave evidence for a rotational transition at about —95°C. This transition was indicated by a sharp decrease in the second moment from a value of 9.6 to 0.5 G2. Theoretical second moments agreed favorably with the experimental rigid-lattice value, if the chair form of the molecule was assumed. In addition, spin—lattice relaxation times were measured as a function of temperature. Again rotational motion in the solid was indicated by a sharp minimum in the T1 vs T curve at about —93°C.
Pulse Radiolysis Studies. IV. The Solvated Electron in the Aliphatic Alcohols
Authors: Taub Irwin A. , Harter Douglas A. , Sauer Myran C. , Dorfman Leon M.
Published: January 2005

Some of the physical and chemical properties of the solvated electron in the aliphatic alcohols have been investigated by means of the pulse radiolysis technique.

In ethanol the optical absorption spectrum exhibits a maximum at 700 mμ. The decadic molar extinction coefficient at 5461 Å is determined to be εe—sol5461=(1.1±0.4)×104 M—1 cm—1. From this the oscillator strength of the band from 270 mμ to about 980 mμ is estimated to be f=0.7. The radiation chemical yield of the solvated electron in ethanol is found to be 1.0±0.3 per 100 eV of absorbed energy.

Absolute rate constants for a number of reactions of the solvated electron in ethanol and methanol have been determined. The diphenylide ion, formed by electron attachment to diphenyl in ethanol, shows a fast first-order decay for which the rate constant has been determined.
Quantum Corrections to the Transport Cross Sections
Authors: Wood Herbert T. , Curtiss C. F.
Published: January 2005

By a method developed earlier, the second quantum correction to the phase shift in a collision between particles with spherically symmetric potentials is obtained. This expression, along with the classical limit and the first quantum correction developed earlier, is used to obtain the classical limit and the first and second quantum corrections to the transport cross sections Q(1) and Q(2). In these expressions the potential function is not restricted to monotonic functions; the results apply to a potential with an attractive minimum.
Infrared Spectrum and Structure of Diimide
Authors: Blau Edmund J. , Hochheimer Bernard F.
Published: January 2005

Diimide has been prepared by decomposition of hydrazine with a microwave discharge, and the infrared spectrum of the solid and gas obtained. The spectrum of the solid at liquid nitrogen temperature agrees with the planar structure predicted for diimide, and the molecule appears to be principally in the cis form. Frequency assignments of the observed bands have been made. The structure of the molecule in the gaseous state cannot be unambiguously determined from the spectrum.
Classical Theory of Fluids and the Square-Well Potential
Authors: McQuarrie Donald A.
Published: January 2005

The term E3, proportional to the cube of the density in an expansion of the internal energy in powers of the density, has been evaluated for the Percus—Yevick, hyperchain, Born—Green—Yvon, Kirkwood, and Meeron equations. The potential used is a square well having a hard-core diameter a and an attractive diameter 2a. A certain thermodynamic requirement of the E3 is investigated and it is found that the hyperchain, Born—Green—Yvon, and Meeron equations give the best result, in contrast to fourth virial coefficient studies, in which the Percus—Yevick equation gives the best result. On the basis of these calculations, it seems that the use of virial expansions are of little use in the elucidation of the relative merits of liquid theories.
Infrared Spectrum of CF2
Authors: Milligan Dolphus E. , Mann David E. , Jacox Marilyn E. , Mitsch Ronald A.
Published: January 2005

A low-temperature infrared study of the photolysis products of CF2N2 in inert matrices has yielded the three vibrational fundamentals of the species CF2, at 668, 1102, and 1222 cm—1. Supplementary ultraviolet observations have confirmed the presence of CF2 in high concentration. Detection of the stretching fundamentals of 13CF2, present in natural abundance, has permitted an estimate of the FCF angle. The thermodynamic properties of CF2 have also been estimated. CF2 appears not to react with CO or with CO2 in a matrix environment.
Normal Vibrations of Polyacrylonitrile and Deuterated Polyacrylonitriles
Authors: Yamadera Reizo , Tadokoro Hiroyuki , Murahashi Shunsuke
Published: January 2005

Polarized infrared spectra of polyacrylonitrile, poly-α-deuteroacrylonitrile, poly-β,β-dideuteroacrylonitrile and poly-α,β,β-trideuteroacylonitrile have been measured in the region from 4000 to 200 cm—1. β,β-dideuteroacrylonitrile was prepared by the hydrogen re-exchange reaction of α,β,β-trideuteroacrylonitrile with H2O in the presence of CaO. The calculations of the normal vibrations of polyacrylonitrile and these three polydeuteroacrylonitriles have been made, assuming a syndiotactic planar zigzag chain as the most simple model for calculation. The calculation was made by the use of the GF-matrix method with the Urey—Bradley force field. The results show fairly good agreement between the observed and calculated frequencies. The assignments of the bands are given and discussed.
Far-Ultraviolet Photolysis of Acetone
Authors: Leiga Algird G. , Taylor H. Austin
Published: January 2005

A survey of the trends in acetone decomposition in the range from the near-ultraviolet photolysis to gamma radiolysis has been made using a xenon discharge (1470 and 1295 Å) and a krypton discharge (1236 and 1165 Å) for room temperature photolysis. The variation of the ratios to CO of products as a function of acetone pressure and wavelength has been noted. Analysis of the mixed products from mixtures of acetone and acetone-d6 presents evidence for methyl radicals in the production of ethane, of hot methyl radicals in the production of methane and of hydrogen atoms in the production of hydrogen. Deviation from the H2—D2 equilibrium indicates molecular hydrogen elimination. The conclusions are confirmed by scavenger studies using propylene, iodine, and oxygen, as well as by the effects of added xenon and neon. The results are consistent with the existence of two excited states of acetone, the higher state eliminating either H or H2; the lower state, methyl. The far-ultraviolet photolysis appears to be closer in over-all behavior to the gamma radiolysis than to the near-ultraviolet photolysis and the trend of the decomposition may be explained by the increase in energy of the radiation.
Theory of Nuclear Magnetic Shielding in Diatomic Molecules
Authors: Kolker H. J. , Karplus M.
Published: January 2005

A variation-perturbation method is employed for the calculation of the magnetic shielding tensor for the nuclei of a series of diatomic molecules (H2, Li2, N2, F2, LiH, HF, LiF). The SCF—LCAO—MO functions of Ransil are used as unperturbed solutions and polynomials are introduced to represent the orbital perturbations. For certain nuclei (e.g., F in HF, N in N2), special perturbation functions are required to account for the pi-orbital nodes. Although no total shielding measurements are available, the paramagnetic contributions can be compared with those calculated from spin—rotational constants. Good agreement is found for H2, H in LiH and HF, Li and F in LiF, but larger errors appear for the other nuclei. Estimates for the shielding anisotropy ΔσN and average shielding 〈σN〉 of some of the nuclei are given that should be accurate to ±10%. Since relative chemical shifts for H, Li, and F in several molecules can be obtained from these results, some experimental tests of the theory by standard NMR measurements are possible.
Theoretical Investigations of Reactive Collisions in Molecular Beams: K +CH3I
Authors: Karplus M. , Raff L. M.
Published: January 2005

The formulation and results of a dynamical quasiclassical calculation of the reactive scattering of K+CH3I to yield KI+CH3 are reported. With a Blais—Bunker interaction potential UB and the approximation that the CH3 group can be treated as a single atom, Hamilton's equations of motion are solved to determine collision trajectories as a function of initial conditions. By appropriate Monte Carlo averaging over certain of the initial variables, the desired attributes of the reactive scattering are evaluated; these include the total reaction cross section Sr, the differential reaction cross section σr(Θ), the partitioning of the exothermicity of the reaction among the degrees of freedom of the products, and the distribution of angular momentum between the products molecule (J′) and relative orbital motion (L′). A detailed examination is made of the relation between the results obtained from two-dimensional (2-D) and from three-dimensional (3-D) trajectories. It is found that, although Sr and the energy partitioning are similar in the 2-D and 3-D cases, the form of σr(Θ) and the angular momentum distribution are different. Comparison with the crossed molecular-beam data available for this system shows that the 3-D calculation with the potential UB yields a reasonable reaction-energy distribution, but total and differential cross sections in disagreement with the experimental information; i.e., Sr equals 400 Å2 instead of the measured value of 7 Å2, and σr(Θ) is independent of angle instead of being strongly peaked in the backward direction. An analysis of the scattering trajectories shows that the erroneous results derive from the neglect in the interaction potential of an attenuation factor that decreases the K, I attraction for an I atom that is part of a CH3I molecule. Introduction of such a three-body term yields cross sections and energy distributions in qualitative agreement with the experimental data. Additional measurements are required to test the theoretical angular momentum distribution.
Mass-Spectrometric Study of the Reactions of O Atoms with NO and NO2
Authors: Klein Fritz S. , Herron John T.
Published: January 2005

The reactions of O atoms with NO and NO2 have been studied using a mass spectrometer to directly measure the O-atom partial pressure. The results obtained are as follows: NO+O+M→NO2+M,  k1(M  is  N2)=(1.44±0.20)×1015exp (1930±100/RT) cc2 mole−2·sec−1;NO2+O→NO+O2,  k2=(1.95±0.61)×1013exp (−1060±200/RT) cc mole−1·sec−1.

These reactions are discussed in terms of the general mechanism O+XO⇌ lim BA[OXO]*+M→ lim CXO2+M→ lim DX+O2→ lim EXO2+hv.

The rates of the elementary reaction steps have been calculated from the over-all rate constants and previous results on the isotopic exchange rates of 18O with O2, NO, and NO2.
Ligand Field Spectra of Some New Laser Chelates
Authors: Nugent L. J. , Bhaumik M. L. , George S. , Lee S. M.
Published: January 2005

The high-resolution emission spectra from microcrystals of three new europium benzoylacetonate chelates, EuB4HP, EuB4HM, and EuB4HD, are presented and discussed in terms of the ligand field symmetries. It is established that the ligand fields about the Eu3+ in these compounds must be of one of the point symmetries C1, C1h, C2, or C2v; however, the exact symmetry in each case cannot be determined from the evidence presented. The emission spectra of EuB4HP and EuB4HM are found to be identical, indicating that the ligand field magnitudes and symmetries are the same for these cases. The emission spectra of EuB4HD, on the other hand, is considerably different, indicating that the magnitude and/or the symmetry of the ligand field in this compound must be different from the other chelates. A vibronic energy level for EuB4HP, probably corresponding to an europium molecular vibrational mode, was determined to be 37 cm—1 above the 5D0 energy level, and 33 cm—1 above the 7F0 energy level. A general tendency is noted in these spectra for the lines terminating on the higher ligand energy levels to be shaded toward longer wavelengths. This may be attributed to the greater number of vibronic states which are closer and more thoroughly mixed with the higher-lying ligand field states.
Two-Dimensional Second Virial Coefficient in Physical Adsorptions
Authors: Krizan John E. , Crowell A. D.
Published: January 2005

Recently Sinanoğlu and Pitzer have shown that a third-order perturbation calculation of the three-body system consisting of two interacting nonpolar molecules and an adsorbent surface leads to a three-body term for the intermolecular interaction in addition to the pairwise interaction. We investigate the effect of this additional force on the thermodynamic properties of the adsorbed phase by calculating the two-dimensional second virial coefficient. The statistical-mechanical model assumed lateral interactions and small oscillations normal to the plane. An expression given by Everett and Barker in terms of the two-dimensional virial coefficient and empirical data is used to calculate the area for the case of argon on carbon black. It is found that the additional term leads to better agreement with values obtained by means of electron-microscope measurements.
Molecular Schrödinger Equation. II. Monte Carlo Evaluation of Integrals
Authors: Conroy Harold
Published: January 2005

A novel method for the evaluation of many-centered, polyelectronic integral matrices of the type which occur in quantum chemical problems is proposed.
Time-Dependent Perturbation Theory of the Hartree—Fock Wavefunction of Atomic and Molecular Systems
Authors: Levine Howard B. , Taylor Howard S.
Published: January 2005

It is shown that time-dependent perturbation theory can be applied exactly to the Hartree—Fock model of closed-shell atoms and molecules by means of integration over the excited-state continuum. The frequency-dependent polarizability of the Be atom is calculated as an example.
Two-Center Wavefunctions for ABHn Systems. Illustrative Calculations on H3+ and H3
Authors: Hoyland James R.
Published: January 2005

Two-center wavefunctions are constructed for linear H3+ and H3 and for triangular (equilateral) H3+ using a basis set of generalized elliptical orbitals. The results are encouraging and possible future applications of the method are discussed.
Isotope Shifts and the Vibrational Structure in Some Weaker Systems of N2
Authors: Mahon-Smith D. , Carroll P. K.
Published: January 2005

The emission spectrum of 15N2 has been studied in the region 2000–9000 Å with a view to investigating the vibrational structure of some of the weaker systems. In the cases of the Herman infrared bands and the Gaydon—Herman green bands, it has been possible to decide between alternative vibrational schemes which have been suggested. Observations have also been made on the Goldstein—Kaplan and the B′→B systems. In the near-ultraviolet spectrum it is shown that the h→a, s′→a, r′→a, m→a, and d→a progression all arise from upper levels with v>0. The possibility that some of these progressions may belong to a single system is discussed. The vibrational schemes for the fifth positive and Kaplan's first and second systems have been confirmed. Some new bands of 15N2 corresponding apparently to hitherto unobserved transitions are reported.
Evaporation Mechanism of CdS Single Crystals. I. Surface Concentration and Temperature Dependence of the Evaporation Rate
Authors: Somorjai G. A. , Jepsen D. W.
Published: January 2005

The vacuum-evaporation rate of CdS single-crystal c face has been measured in the temperature range 600°—860°C. The activation enthalpy and entropy have been derived from the data. The mechanism of the surface dissociation reaction which limits the vaporization, was studied by evaporating CdS in vapor beams of cadmium and sulfur. The rate of impingement of cadmium and sulfur on the CdS surface was varied over more than two orders of magnitude. For high sulfur flux, the RCdS≃RS2—½ dependence was established. The evaporation rate of CdS remained virtually independent of the cadmium impingement rate over the studied range. A detailed evaporation mechanism is presented.
Two-Photon Capture Cross Sections of Pyrene and Benzpyrene from SCF–MO Calculations
Authors: Evleth Earl M. , Peticolas Warner L.
Published: January 2005

The two-photon capture cross sections for pyrene and 3,4-benzpyrene are calculated using SCF–CI pi-electronic wavefunctions and the theory of Goeppert-Mayer. The cross section is shown to be dependent on the product of the photon flux and a constant, δ, which may be calculated from suitable matrix elements and the line shape function. For randomly oriented molecules and polarized light the calculated values of δ for pyrene and 3,4-benzpyrene are, respectively, 260×10—51 and 1500×10—51 cm4·sec atom—1 photon—1. These are to be compared with the experimental values of, respectively, 1×10—51 and 50×10—51 cm4·sec atom—1·photon—1. The effect of molecular symmetry on the two-photon absorption of polarized light is illustrated for molecules of D2h symmetry. For a two-photon transition to a B1g state, the maximum probability is shown to lie approximately 45° between the x and y axes of the molecule which are the axes of maximum probability for one-photon absorption.