bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Analytical Mechanics of Chemical Reactions. Quantum Mechanics of Linear Collisions
Authors: Marcus R. A.
Published: January 2005

The analytical quantum mechanics of chemically reactive linear collisions is treated in the vibrationally near-adiabatic approximation. The ``reaction coordinate'' in this approximation is found to be the curve on which the classical local vibrational and internal centrifugal forces balance. Expressions are obtained for the calculation of transmission coefficients for these nonseparable systems. Some implications for tunneling calculations in the literature are noted. Expressions for nonadiabatic corrections are derived, the latter being associated with vibrational transitions undergone by the transmitted and reflected waves. When the system does not have enough energy to react, the last results refer to the vibration—translation energy-transfer problem in linear collisions.

Two novel features are the introduction of an actual coordinate system which passes smoothly from one suited to reactants to one suited to products and the introduction of an adiabatic-separable method, a method which includes curvilinear effects. Extensions to collisions in higher dimensions are given in later papers.
Calculated Heats of Dilute Solid Solution among the Alkali Halides Other Than Cesium Salts
Authors: Douglas Thomas B.
Published: January 2005

Limiting high-temperature heats (energies) of dilute solid solution are calculated for all 96 cases of one NaCl-type alkali halide (except Cs salts) dissolving in another having a common ion. The direct-summation shell treatment used is based on a slightly modified Born—Mayer potential function and on the polarization energy up to terms square in the ion polarizabilities. Preliminary general expansion of the energy in positive powers (up to cubic) of the lattice-relaxation (ion-displacement) parameters of the first eight shells (98 neighbors) facilitated application to specific cases. In the linear solution for the minimum-potential lattice relaxation, one or two iterations for the first two shells sufficed. The convergence of the energy expansions and the sensitivity of the calculated energies to arbitrary variations in the semiempirical parameters were extensively investigated. Comparison is made with calorimetric heats of solution in 16 cases, the agreement (averaging ±10%) lying within the experimental and computative errors.
Line Shapes due to Anisotropic Interactions in Magnetic Resonance Experiments
Authors: Forman Richard A. , Kahn Arnold H.
Published: January 2005

Magnetic resonance line shapes resulting from anisotropic interactions of the form ap(3 cos2θ−1) have been calculated. Typical shapes are displayed. Of particular importance is the presence of a reasonably strong resonance peak occurring in the absorption derivative at the position of the step (θ=0°) in the absorption curve.
Electron Spin Resonance Studies of Photodegradation in Poly(Methylmethacrylate)
Authors: Michel R. E. , Chapman F. W. , Mao T. J.
Published: January 2005

The strength of the ESR spectrum produced in poly(methylmethacrylate), PMMA, by exposure of the polymer to ultraviolet light (2537 Å) has been measured as a function of exposure time. The signal strength initially increases and then saturates under continued exposure. It decays when the light is removed. While the time needed to produce saturation depends inversely upon the light intensity it is only slightly affected by changes up to an order of magnitude in the decay rate. It is also observed that, for similar samples, the maximum ESR signal strength obtained is independent of the light intensity. This dynamic behavior strongly suggests that: (1) the ESR spectrum arises from radicals which are produced by the light from a limited number of centers already present in the polymer, and (2) the saturation mainly occurs due to exhaustion of these centers rather than some dynamic equilibrium between the creation and destruction of radicals. Additional experiments were performed in order to identify these centers. In these investigations it was found that the intensity of the ESR signal following irradiation decreases when the amount of residual monomer is descreased. Furthermore, when the monomer of poly (ethyl-α-chloroacrylate), PEαClA, is added to a sample of PMMA which has been purified to remove its own monomer and this sample irradiated, the resulting ESR signal is the one normally associated with photodegradation in PEαClA. These results indicate that the residual monomer molecules are the centers which are converted by the radiation into the free radicals which produce the ESR signal. While no attempt was made to obtain the exact form of the radicals, these results could be consistent with previous suggestions that the ESR spectrum arises from radicals which have the form of the propagating polymer radical.
Cloud-Chamber Droplet Growth and Evaporation
Authors: Lund L. H. , Rivers J. L.
Published: January 2005

A droplet-growth law used by Fletcher and others to study growth of cloud droplets is modified for cloud-chamber conditions. Growth and evaporation of cloud-chamber droplets are investigated using the Becker—Döring nucleation rate law, following the step-by-step growth of droplets, and correcting nominal supersaturation obtained from the adiabatic process equation for vapor depletion. Drop-count and drop-size results obtained are in reasonable agreement with observations.
Search for Discontinuities in the Temperature Dependence of the Dielectric Constant of Pure Water from −5° to +25°C
Authors: Rusche E. W. , Good W. B.
Published: January 2005

A search for discontinuities in the temperature dependence of the dielectric constant of pure water was made using 43 data points extending from −5° to +25°C. The dielectric constant values were determined by capacitance measurements made at frequencies varying from 500 cps to 50 kc/sec and the temperature controlled to ±0.01°C by a temperature control chamber. The analysis was performed by means of a statistical method of variance and an F test employed to determine the level of significance of any deviation from the least-squares fit of the data. An examination of the data in 1°C intervals from −1° to +21°C revealed no discontinuities between these limits and demonstrated the sensitive character of the variance method to slight errors in the data.
Ion Association of LiI in p-Dioxane—Water Mixtures. I. Conductance Measurements
Authors: Atkinson Gordon , Mori Yoshihiro
Published: January 2005

The conductance of LiI has been measured in p-dioxane—water mixtures at 25° over the composition range 0%—95% dioxane. The data were analyzed using the Fuoss—Onsager theory to give Λ0, aJ, and KA parameters. Although aJ remains constant over the whole composition range, the Walden product decreases monotonically. Both the Stokes radius and the association constant show markedly different behavior in the range over 80% dioxane.
Structure and Properties of Liquid Water
Authors: Orentlicher M. , Vogelhut P. O.
Published: January 2005

The properties of liquid water are shown to be explicable in terms of a short-range tetrahedral structure. Conclusions regarding transport processes in liquid water are of biological importance.
Microwave Spectrum of Nitrosobenzene in Excited Vibrational States
Authors: Hanyu Yoshiaki , Britt Chester O. , Boggs James E.
Published: January 2005

The rotational spectrum of nitrosobenzene in the first four excited states of the torsional vibration has been observed. The vibrational fundamental is at about 100 cm−1. The barrier to rotation around the C–N bond is 3.9±1 kcal/mole, based on relative intensity measurements. Variations in the inertia defect in the excited states are compared with theory. The next-lowest vibrational state is at about 220 cm−1 and is an in-plane vibration.
Orientation Relaxation in Symmetrical-Top Gases and Binary Gas Mixtures
Authors: Frenkel Lothar
Published: January 2005

A phenomenological treatment of dielectric relaxation for symmetric-top gases and binary gas mixtures is developed. It is shown that the orientational Z number is a monotonously increasing function of a collision parameter F=2(IA+IB)/mb02. Long-range attractive forces contribute substantially to the cross sections and give rise to a temperature dependence. A formula is derived which permits the prediction of the cross sections from kinetic-theory data for the molecules. A graphical presentation of the formula illustrates various features of the process. The predictions of the model are shown to be in agreement with dielectric relaxation data for 25 gas mixtures.
Infrared Spectrum of Methyldifluoramine
Authors: Atalla Rajai H. , Craig Alan D. , Gailey Joseph A.
Published: January 2005

The infrared spectra of gaseous CH3NF2 and CD3NF2, and of solid CH3NF2 have been recorded. They are discussed in terms of the symmetry of Point Group Cs. The unsymmetric methyl vibrations, which are degenerate under the local C3v symmetry of the group, were found to undergo splitting of smaller magnitude than in analogous compounds of Cs over-all symmetry. The two nearly degenerate components of each of these motions appear to be coupled through rotation.
Effect of Dielectric Relaxation on the Mobility of Ions in Solutions at Finite Concentrations
Authors: Fernández-Prini R.
Published: January 2005

Boyd's model for the calculation of the friction constant due to dielectric relaxation is extended to deal with solutions of finite concentrations. The first-order effect of concentration on the friction constant is calculated using the Debye—Hückel potential for the moving ion. It is found that the concentration-dependent ionic mobility due to dielectric relaxation contains no terms of order smaller than c32.
Electronic Density Distribution in Lithium Hydride
Authors: Politzer Peter , Brown Richard E.
Published: January 2005

The electronic density distribution in lithium hydride has been studied, and compared to the two hypothetical situations of the free atoms and the free ions (Li+ and H−) at the equilibrium separation. It is found that these two models are very much the same in the case of LiH, because of the natures of the entities which are involved. It is proposed that the molecule can best be viewed as being made up of a lithium ion and a polarized hydrogen atom, with the fourth electron partly concentrated on the outer side of the lithium nucleus and partly spread out in a diffuse manner around and beyond the hydrogen nucleus.
Nonintegral Elliptical Orbital Studies on H2+, H2, and HeH+
Authors: Hoyland James R.
Published: January 2005

Calculations are performed on the 2Σg+ and 2πu bound states of H2+ and the ground states of H2 and HeH+ using a basis set of nonintegral elliptical orbitals. The H2+ calculations are in the form of a single-configuration wavefunction while both self-consistent-field and configuration-interaction studies are carried out on H2 and HeH+.
Temperature Dependence of the Structure and Transport Properties of Liquid Thallium
Authors: Halder N. C. , Wagner C. N. J.
Published: January 2005

Using a theta—theta diffractometer and quartz-crystal monochromatized MoKα radiation, x-ray scattering from liquid thallium has been measured as a function of temperature ranging from 350° to 700°C. The radial distribution functions (RDF) which have been obtained by Fourier inversion of the normalized intensity do not show any unusual feature and indicate a close-packed structure for the liquid thallium. The modulation-free part of the RDF in the region of small r where r is the radial distance suggests a high degree of reliability in the calculated value of atomic scattering factors of thallium and a considerable accuracy in the measured intensity. The interatomic distance r1=3.30 Å of thallium does not change with temperature, and the coordination numbers change very little from 11.5 atoms at 350°C to 10.9 at 700°C. This decrease may be explained with excess- or free-volume theory.

The resistivity and thermoelectric power have been determined using the x-ray interference functions and theoretically calculated values of the pseudopotential elements. The predicted values of the resistivities Rpred are little lower than the measured values Rexpt1 (e.g., Rpred=63 μΩ·cm, Rexpt1=79 μΩ·cm at 500°C). Further, the temperature coefficient of the predicted resistivities is also smaller than that of the measured resistivities. The observed discrepancy has been attributed to the inadequacy in pseudopotential elements.
Exchange and Direct Second Virial Coefficients for Hard Spheres
Authors: Boyd Marjorie E. , Larsen Sigurd Yves , Kilpatrick John E.
Published: January 2005

We have separated the quantum-mechanical second virial coefficient for hard spheres B into two terms. The first represents the contribution of a Boltzmann gas, and the second is an exchange term embodying the effects of quantum statistics. Numerical computation of B to high precision then allows us to analyze the temperature dependence of the exchange term, which is found to decrease exponentially with temperature, and to determine the asymptotic expansion of the Boltzmann term at high temperatures.
Comparison of the Infrared Spectra of the Hydrates and Anhydrous Salts in the Systems UO2(NO3)2 and Th(NO3)4
Authors: Ferraro J. R. , Walker A.
Published: January 2005

The infrared spectra from 4000–80 cm−1 of the hydrates and anhydrous salt of UO2(NO3)2 and Th(NO3)4 have been obtained. The change in symmetry of the nitrate group is followed and discussed, and metal to coordinated nitrate assignments made.
Study of the Water Molecules in CuSO4·5H2O by Nuclear Magnetic Resonance
Authors: El Saffar Z. M.
Published: January 2005

The validity of the NMR technique in studying complex hydrates has been questioned by Pedersen and Holcomb. Fully hydrated copper sulphate has been investigated by NMR, and the results have been used to establish the orientations and proton—proton separations of the water molecules. The experimentally determined proton—proton vectors are in good agreement with the neutron diffraction structure of Bacon and Curry. It appears that the NMR technique remains of value in studying complex hydrates.
Effect of Very High Pressure on the Compressibilities of NH4Cl, TlCl, CdO, and CdS
Authors: Lewis G. K. , Perez-Albuerne E. A. , Drickamer H. G.
Published: January 2005

The effect of pressure to several hundred kilobars has been measured on the compressibilities of NH4Cl, TlCl, CdO, and CdS. NH4Cl and TlCl have the simple cubic (CsCl) structure at all pressures covered by this study. Our results for these compounds agree quite well with Bridgman's data to 98 kbar. The Born—Mayer equation fits NH4Cl very well at all pressures. TlCl shows a lower compressibility than predicted by the B—M equation above about 150 kbar.

CdO has the face-centered-cubic (NaCl) structure at all pressures. The B—M equation fits well up to 160 kbar, above which pressure CdO is less compressible than is predicted. CdS transforms from wurtzite to NaCl structure at 23 kbar. The compressibility of the high-pressure phase is quite small and does not present a good test for ionicity by the B—M equation.
Semiclassical Theory of the Three-Turning-Point Problem
Authors: Livingston P.M.
Published: January 2005

A new theory is presented for phase shifts resulting from scattering by atoms with attractive potentials, i.e., the three-turning-point problem. A simple formula, valid in and below the three-turning-point region is derived η=η0−12Tan−1{cosα sinβ/[(−1)nsinα−cosβ]}+θ[(−1)nsinα−cosβ]12π,where the angle α is related to the Stokes constant for the two outer turning points; β is proportional to twice the action integral minus π times the number of WBKJ wavefunction nodes in the inner region, (n−1); and τ is a unit step function which is zero for negative arguments. The theory predicts virtual energy states for incident energies in the three-turning-point range whose location compares well with numerical quantum calculations. The resonance portion of the phase shifts shows only semiquantitative comparison with the quantum results.
Heat Capacity and Entropy of NiSiF6·6H2O in the Region 0.30°—4.25°K with Magnetic Fields 0–90 kG Parallel to the c Axis
Authors: Hornung E. W. , Brodale G. E. , Fisher R. A. , Giauque W. F.
Published: January 2005

The heat capacity of nickel fluosilicate hexahydrate has been measured over the range 0.30°—4.25°K in stabilized magnetic fields of 0, 0.25, 0.5, 1, 2, 3, 5, 10, 20, 40, 60, 80, and 90 kG. The field was directed along the crystallographic c axis of the 3.5-cm-diam, spherical, single crystal. The variation of temperature with magnetic field has been measured with a carbon thermometer in a calorimetric apparatus at nearly constant entropy. Very minor corrections for entropy leakage and the empty calorimeter have enabled the accurate tabulation of entropy changes in NiSiF6·6H2O with temperature and field over the area 0.30°—4.25°K and 0–90 kG. At the higher fields and lower temperatures it was necessary to consider a small amount of entropy removed by nuclear magnetization of the hydrogen and fluorine atoms. All of the data apply to a sphere in a homogeneous external field uncorrected for the demagnetization effect. The substance gave no indication of magnetic irreversibility. These results will serve as a base for a thermodynamic treatment of later observations in the region below 0.30°K. The total electronic entropy removed to magnetic saturation was Rln3.
Uranium Mononitride: Heat Capacity and Thermodynamic Properties from 5° to 350°K
Authors: Westrum Edgar F. , Barber Carolyn M.
Published: January 2005

The low-temperature heat capacity of UN was determined by adiabatic calorimetry and found to have a normal sigmate temperature dependence, except for the presence of an anomaly near 52°K associated with antiferromagnetic ordering of the electron spins. At 298.15°K the heat capacity (CP), entropy (S°), enthalpy function [(H°—H°0)/T], and Gibbs energy function [—(G°—H°0)/T] are, respectively, 11.43, 14.97, 7.309, and 7.664 cal/(gfm·°K).
Exchange Effects in the 3A2→1E Absorption Transition of the Ni2+ Ion in Fluoride Compounds
Authors: Holloway W. W. , Kestigian M.
Published: January 2005

The effect of the exchange interaction between nickel ions on the structure and position of the 3A2→1E Ni2+ ion absorption transition has been studied experimentally in fluoride compounds. The spectra observed in these materials are found to depend on the concentration of the nickel ion component and the crystal structure.
Vibrational Spectrum of Cesium Azide Crystals
Authors: Bryant James I.
Published: January 2005

The infrared and Raman spectra of CsN3 crystals have been investigated over the frequency region from 30 to 4000 cm−1 by using grating photoelectric recording spectrometers. The selection rules for the k≃0 modes of the crystals, determined by the method of Bhagvantam and Venkatarayudu, were used for the vibrational analysis. By making use of frequencies observed in the infrared and Raman lattice frequency regions, assignments were made by species of numerous absorptions constituting fine structure about the fundamental absorptions in the medium infrared. In most cases, because of the wealth of spectral data, numerical checks were provided for assignments of lattice combinations and for combinations due to internal mixing. Several observations, believed to represent violations of the k≃0 selection rules, are mentioned. A previously reported discrepancy related to the symmetry of N3− in CsN3 crystals is cleared up.
Low-Frequency Motions of H2O Molecules in Crystals. II
Authors: Prask Henry J. , Boutin Henri
Published: January 2005

Translational and librational motions of H2O molecules in a frequency region lying below 1000 cm−1 have been previously examined for various configurations using the inelastic scattering of low-energy neutrons (0.005 eV). In the present work, H2O motions are studied in cases where neither of the lone electron pairs on the oxygen of the H2O molecule is specifically directed (K2C2O4·H2O), where the lone pairs are directed toward two monovalent metal ions (KF·2 H2O), where the H2O molecule has a single orientation [Ba(ClO3)2·H2O] or two distinct, equally probable orientations (Li2SO4·H2O). The neutron spectrum of K2C2O4·H2O typically exhibits torsional peaks at 500, 605, and 700 cm−1 which shift by 1.35 in frequency upon deuteration. They are well separated from a sharp peak at 195 cm−1 which is assigned to the stretching motion of an H2O molecule H bonded to the oxalate ion and does not shift upon deuteration. The neutron spectra are discussed and compared with the results of proton magnetic resonance, Raman, and infrared measurements.
Geometry of Molecules. I. Wavefunctions for Some Six- and Eight-Electron Polyhydrides
Authors: Peyerimhoff Sigrid D. , Buenker Robert J. , Allen Leland C.
Published: January 2005

Potential surfaces have been investigated for BH2+, BH2−, NH2+, BeH2, BH3, CH3+, and BeH3− by means of LC (Hartree—Fock) AO MO SCF wavefunctions. One-electron-energy-versus-angle diagrams were determined for these AH2 and AH3 molecules, and comparison with the widely used empirical diagrams of Walsh demonstrates a quantitative similarity between them. In addition, mathematical inequalities are derived relating changes in the sum of one-electron energies with angle to changes in the total energy with angle. Aided by these expressions, we are able to make direct connection between Walsh's qualitative rules and the physically well-defined ab initio solutions.
Sign of the Nuclear Quadrupole Coupling Constants in Some Ionic Ferrous Compounds
Authors: Grant R. W. , Wiedersich H. , Muir A. H. , Gonser U. , Delgass W. N.
Published: January 2005

Nuclear quadrupole coupling constants have previously been determined for a large number of iron-containing compounds by using the Mössbauer effect. In general, the sign of the coupling constant has not been determined although this parameter can have interesting structural implications. We have used the magnetic perturbation technique to determine the sign of the nuclear quadrupole coupling constants in FeSO4, FeSO4·7H2O, FeCO3, FeCl2·4H2O, and FeSiF6·6H2O. A recent proposal that a correlation exists between the isomer shift and quadrupole coupling in ionic ferrous compounds and that this correlation can be used to infer the sign of the latter is found to be incorrect.
Mössbauer Studies of Divalent and Trivalent 57Fe in CoSO4 and CoSO4·7H2O
Authors: Ingalls R. , Coston C. J. , De Pasquali G. , Drickamer H. G. , Pinajian J. J.
Published: January 2005

We report the results of a Mössbauer study of 57Co(57Fe) in CoSO4 as a function of temperature at atmospheric pressure and as a function of pressure at room temperature. In addition to the expected divalent 57Fe component, one also observes a trivalent component, the relative intensity of which decreases with increasing temperature or pressure. The isomer shifts of both charge states also decrease with increasing temperature or pressure. The behavior of the large quadrupole splittings observed in each charge state is analyzed using the crystal field approximation. We also find similar results in a temperature study of CoSO4·7H2O at atmospheric pressure. The relative intensity of the trivalent 57Fe component is considerably greater in the hydrate and also decreases with increasing temperature.
Effect of Spin—Orbit Interactions on the Zero-Field Splitting of the NH Radical
Authors: McIver James W. , Hameka Hendrik F.
Published: January 2005

We have calculated the spin—orbit contributions to the zero-field splitting of the NH radical and found them to be 0.496 cm−1. As this value is over 25% of the experimental ZFS, we conclude that it is not permissible to neglect spin—orbit contributions when calculating ZFS parameters.
Theoretical Depolymerization Kinetics. II. The Effect of Molecular-Weight Distribution in Degrading Polymers Undergoing End-Group Initiation
Authors: Boyd Richard H. , Lin Tung-Po
Published: January 2005

It is shown that the set of coupled rate equations describing the end-group-initiated degradation of a polymer containing various degrees of polymerization can be transformed into a set of coupled equations describing the rate of change of the moments of the molecular-weight distribution. These moment equations can be used as the basis for approximate but systematic treatments of degradation in systems with arbitrary initial molecular-weight distributions. In particular, in this paper it is shown that if the Schulz—Zimm distribution is assumed to be sufficiently general to represent the molecular-weight distribution through the course of the degradation, the moment equations allow the problem to be reduced to three simultaneous differential equations. These equations have been solved by digital computer and the sample weight, number-average molecular weight, and distribution-width parameter tabulated as functions of time for a wide range of kinetic parameters and initial distributions.
Study of the Reaction of Electronically Excited Oxygen Molecules with Carbon Monoxide
Authors: Fisher Edward R. , McCarty M.
Published: January 2005

The reaction of oxygen in the 1Σg+, 1Δg, and 3Σg− states with CO was investigated at temperatures below the point at which heterogeneous reaction is detectable. The excited oxygen was produced photochemically. In spite of moderate partial pressures of excited oxygen (about 0.25 μ), and an extremely sensitive method of analyzing for the product, no evidence of reaction was found. Upper limits for hypothetical bimolecular and termolecular rate constants are reported.
Polymer Dynamics: Non-Newtonian Intrinsic Viscosity
Authors: Fixman Marshall
Published: January 2005

The operator techniques developed in the preceding paper are here applied to the determination of the intrinsic viscosity as a function of excluded volume and shear rate. The force constants which represent the excluded-volume interaction are determined, at nonvanishing shear rate, by a criterion of self-consistency. Numerical results are given for the intrinsic viscosity and the equilibrium expansion of the mean-square end-to-end distance.
Substituent Effects on Chemical Shifts and Spin—Spin Coupling Constants in Trifluorovinyl Derivatives
Authors: Moreland Charles G. , Brey Wallace S.
Published: January 2005

Examination of the NMR spectra of a variety of trifluorovinyl derivatives of the type CF2=CFY has led to the following correlations between the fluorine NMR parameters and the nature of substituent Y: (1) the chemical shift of the fluorine atom trans to Y and the geminal F–F coupling constant both depend upon the conjugating ability of the group Y, and (2) the chemical shift of the fluorine atom attached to the same carbon as is Y and the cis F–F coupling constant both depend primarily upon the electronegativity of the directly attached atom in substituent Y. The chemical shift of the fluorine cis to Y and the trans coupling constant are not simply related to either of these properties of Y. Although the trans coupling constant is temperature-independent, the cis and gem coupling constants increase with increasing temperature. Long-range coupling in a trifluorovinyl thioether compared with that in trifluorovinyl ethers is consistent with d-orbital participation in bonding of the sulfur atom in the thioether.
Electronic Spectra and Coordination Geometry in Molten Mixtures of CsCl and NiCl2 Containing up to 60 Mole% NiCl2
Authors: Smith G. Pedro , Boston Charles R. , Brynestad Jorulf
Published: January 2005

Optical absorption spectra (5–26 kK) of fused mixtures of CsCl and NiCl2 containing 2–60 mole % NiCl2 were measured at about 860°C and a mixture containing 20 mole % NiCl2 was studied at 560°—862°C. Up to 20 mole % NiCl2 the Bouguer—Beer law was accurately obeyed, and each nickel was tetrahedrally coordinated to four chlorides. At higher NiCl2 contents, nickel coordination was partitioned between tetrahedral and other (unidentified) geometries. The fraction with tetrahedral coordination progressively decreased with increasing NiCl2 content but was still appreciable at 60 mole % NiCl2. The most prominent feature of the spectrum associated with the unidentified geometries was a band between 18 and 19 kK. These results indicate that nickel has very similar coordination geometries in the liquid and crystalline phases of Cs3NiCl5 but very different coordination geometries in crystalline and liquid CsNiCl3.
Gas-Phase Photolysis of Isopentane at Photon Energies below and above the Ionization Energy
Authors: Scala A. A. , Ausloos P.
Published: January 2005

The photolysis of (CH3)2CDCH2CH3, (CH3)2CHCH2CD3, and of equimolar (CH3)2CHCH2CH3−(CD3)2CDCD2CD3 mixtures has been investigated in the presence of NO at 1470 Å (8.4 eV), 1236 Å (10 eV) and at 1048–1067 Å (11.54–11.72 eV). Furthermore, in order to obtain quantitative information concerning the free radicals produced in the fragmentation processes, (CD3)2CDCD2CD3 has been photolyzed at 1236 Å in the presence of various concentrations of H2S.

Fragmentation of the excited isopentane molecule produced at 8.4 or 10 eV, as well as of the superexcited molecule formed at 11.54–11.72 eV, yields mainly olefinic products and the following radicals, in order of decreasing yield: H>CH3>C2H5>C3H7. In addition, on the basis of the various isotopically labeled products, it is concluded that methane, ethane, and propane are split off from the excited isopentane molecule by formation of (a) the corresponding carbene (1,2 elimination), or (b) the corresponding olefin (1,3 elimination). When the energy of the photon is increased from 8.4 to 10.0 eV, the 1,2-elimination processes become more important relative to the 1,3-elimination processes in all cases. At 11.54–11.72 eV, the parent ion decomposes to form methane and ethane mainly by a 1,3-elimination mechanism. It is derived from the results that, in addition to the C4H8+ and C3H6+ ions formed by the latter fragmentation processes, the ions C4H9+ and C3H7+ are produced with ion-pair yields (M/N) of 0.15 and 0.06, respectively. The ion-pair yield of the parent ion is estimated to be 0.35. In contrast to observations derived from an earlier investigation of photoionization of n-butane at 11.54–11.72 eV, an increase in pressure from 0.15 to 15 torr has only a minor effect on the fragmentation of the parent ion.
Microwave Absorption in Compressed CO2
Authors: Ho W. , Kaufman I. A. , Thaddeus P.
Published: January 2005

Induced absorption in carbon dioxide has been studied at a frequency of 9260 Mc/sec over the temperature range 270°—500°K and to pressures as high as 95 atm. Since the dielectric loss ε″ is expected on the basis of the dispersion relations to be proportional to frequency throughout the microwave region the data has been fit with an expansion in the amagat density ρ of the form ε′′/ν̄=Aρ2+Bρ3, where ν̄ is in wavenumbers. It is found that A=2.5(1)×10−8(T/273)−3.0(1), and B/A=−1.05(8)×10−2(T/273)−2.3(3). The molecular quadrupole moment calculated from the first coefficient of the dielectric loss A is then 6.7×10−26 (esu).
``Hydrogen Overvoltage and Electrode Materials.'' Comments
Authors: Liebhafsky H. A. , Cairns E. J.
Published: January 2005

Attention is called to the fact that a claimed quantitative relationship between cathodic hydrogen overvoltage and the (gas-phase) heat of adsorption of atomic hydrogen on the electrode material is not quantitative, and an attempt is made to correct the impression that this relationship is general and well established. An indication is given of the kinds of information necessary before a quantitative test can be made.
Microwave Spectrum, Molecular Structure, Barrier to Internal Rotation, and Dipole Moment of Methylketene
Authors: Bak Børge , Christiansen Jørn J. , Kunstmann Kaj , Nygaard Lise , Rastrup-Andersen John
Published: January 2005

The microwave spectra of the CD3 species and of seven monosubstituted isotopic species of CH3CH=C=O have been examined, and a complete structure of methylketene has been obtained by the substitution method. The structural parameters found are: C=O=1.171, C=C=1.306, C–C=1.518, C–H (vinyl)=1.083, and C–H (methyl)=1.083 or 1.11 Å (see text). The ketene group is linear, and the methyl group is staggered, ∠CCC=122.6°, ∠C(1)C(2)H(2)=113.7°, and ∠HCH=109.9° or 108.8°.

The barrier splittings were used to determine the value of the barrier to hindered rotation and the angle between the methyl-axis and the principal-axis system for each of the monosubstituted species; V3=1177±20 cal/mole. The dipole moment of methylketene was measured on the 21,2→31,3transition, yielding μa=1.755, μb=0.35, μ=1.79 D.
Electronic Specific Heats of Alloys of the MgCu2−xSix System
Authors: Klar Erhard , Mallya R. M. , Craig R. S.
Published: January 2005

Specific-heat measurements were made on a series of alloys of the pseudobinary system MgCu2−xSix between 1.5° and 4°K. The compositions studied ranged from MgCu2 to MgCu1.25Si0.75 and included 12 alloys having the MgCu2 structure, two having the MgZn2 structure and three involving mixtures of phases. The variation of γ with electron concentration shows maxima at 1.44 and 1.58 electron/atom. These are identified as marking contact between the Fermi surface and the 311 and 222 Brillouin zone faces, respectively. The peaks in the curve of γ vs concentration are more pronounced in the MgCu2−xSix alloys than those which were observed in MgCu2−xAlx alloys reported earlier, suggesting that the distortion of the Fermi surface is greater in the alloys containing silicon.
Infrared Spectra and Antiferroelectric Behavior of Cesium Trihydroselenite
Authors: Khanna R. K. , Horak M. , Lippincott E. R.
Published: January 2005

The infrared spectra of CsH3(SeO3)2 in the region 4000–300 cm−1 have been investigated at several temperatures above and below the Curie point (−128°C). The transition from the low-temperature (antiferroelectric) phase to the nonferroelectric phase seems to result due to a statistical disorder in the lattice. The mechanism causing this transition is discussed in terms of the changes in the potential field of the hydrogen bonds. A comparison with the spectra of NaH3(SeO3)2 reported earlier gives some information on the characteristics of the hydrogen-bond vibrations.
ESR Line Shape Due to Anisotropic α-Fluorine Coupling in the Polycrystalline State
Authors: Iwasaki Machio
Published: January 2005

The ESR line shape due to an anisotropic hyperfine coupling was calculated including the nuclear Zeeman term in the spin Hamiltonian. Since it was desirable to see the effect of the nuclear Zeeman term explicitly, the line shape was calculated for the ideal case where the component linewidth is infinitesimally small. In such a case, it was possible to derive the shape function analytically for an axially symmetric hyperfine tensor, and even for an orthorhombic symmetry the numerical integration in the line-shape function was not so difficult. The numerical calculation was executed for the α-fluorine coupling with the tensor elements of 189, −4, and −16 G, and the result was compared with the simpler cases in which the nuclear Zeeman term is neglected.
Bandlike Structure from Continuum—Continuum Emission: The He2 600-Å Bands
Authors: Mies Frederick H. , Smith Allan Laslett
Published: January 2005

The continuous spectrum produced by the radiative de-excitation of metastable atoms by atom impact is an example of molecular continuum—continuum transitions. It is shown that if the upper molecular state has a deep attractive well and the lower state is repulsive, the continuous spectrum will show bandlike structure similar to that obtained in bound—continuum transitions from high vibrational states. The analysis is applied to the radiative de-excitation of He(21S) by He, which gives rise to the ``600-Å bands.'' The structure and temperature dependence of these bands are well explained as bandlike continuum—continuum emission. Bandlike continua observed in other rare gases are briefly discussed in terms of the molecular states involved.
On the Calculation of Autocorrelation Functions of Dynamical Variables
Authors: Berne Bruce J. , Boon Jean Pierre , Rice Stuart A.
Published: January 2005

In this paper we develop a formalism for calculating the autocorrelation function of a dynamical variable in terms of a well-defined memory function. Guided by simple physical arguments, an ansatz is adopted for the functional form of the memory function. This ansatz asserts that the memory of dynamical coherence decays exponentially. It is found that:

(a) Despite the monotonic exponential decay of the memory function, the autocorrelation function deduced can display negative regions in some circumstances and decay monotonically in other circumstances.

(b) The form of the autocorrelation function deduced is identical with that obtained from two other very different analyses, suggesting that the major properties of the function are of general validity.

(c) The computed linear momentum autocorrelation function and power spectrum for liquid Ar are in good agreement with the computer experiments of Rahman.

(d) The computed dipolar autocorrelation function reproduces all the features of the experimentally determined autocorrelation function, though at present insufficient data are available to provide a quantitative test of the theory.

(e) The ansatz used, although obviously not exact, is consistent with the theory of linear regression (Appendix B).
Absorption of Light by Pairs of Exchange-Coupled Manganese and Nickel Ions in Cubic Perovskite Fluorides
Authors: Ferguson J. , Guggenheim H. J. , Tanabe Y.
Published: January 2005

The absorption of light by exchange-coupled pairs of manganese and nickel ions in KZnF3 is reported. Three absorption regions are discussed, of which two (4000 and 3300 Å) are associated with electronic excitation of the manganese and the third (6600 Å) corresponds to electronic excitation of the nickel ion. The lines can be analyzed by means of an exchange interaction of the type JS·S and a value of J = 18 cm−1 for the manganese—nickel pair in its electronic ground state has been obtained. The mechanism of the electronic transitions has been discussed using the theory developed for like pairs in an earlier paper and reasons for the greater intensity of absorption by unlike pairs are considered. Corresponding effects of exchange interaction have also been observed in the spectra of KMnxNi1−xF3 crystals. The energies and intensities of the absorption bands have been measured as a function of x and a theoretical analysis of the main results has been given. The main features of these spectra can be interpreted satisfactorily using our model for a pair of exchange-coupled ions.
Variational Calculation for Bound States in an Electric-Dipole Field
Authors: Fox Kenneth , Turner J. E.
Published: January 2005

The quantum-mechanical problem of an electron moving in the field of a permanent electric dipole has been investigated in an attempt to determine whether negative energy eigenvalues, i.e., bound states, exist for small dipole moments. When the expectation value of the Hamiltonian is minimized in a variational calculation and then set equal to zero, the solution of the resulting equation gives a value of the dipole moment which is sufficient to assure the existence of a bound state. Use of the trial wavefunction ψ=exp (—αrt) (C0Y00+C1Y10) shows that 1.65×10−18 esu·cm is sufficient.
Quantum-Theoretical Study on the Bond Angle for a Single Bond between Carbon Atoms
Authors: Gotoh Haruo , Nagahara Shigeru , Sawai Kisaku
Published: January 2005

Bond energies and bond lengths of the single, double, and triple bonds between carbon atoms were studied with nonempirical calculations by one of the authors with the scheme of the electronic configurations of fictitious diatomic molecules; ≡C–C≡, –C–C–, and –C≡C–, where open bonds of the atoms were treated as suitably hybridized orbitals taking into account all possible spins. This treatment is examined for the bond angle of a single bond between carbon atoms. The result shows that the tetrahedrally hybridized bonding is the most stable.
Lattice Disorder in Some CaF2-Type Crystals
Authors: Barsis E. , Taylor A.
Published: January 2005

The ionic conductivity of BaF2, SrF2, and SrCl2 single crystals doped with monovalent and trivalent cations has been investigated from 300°C to within 100°C of the melting temperature. These measurements correct the intrinsic conductivity of SrF2 and show a consistent trend in the slopes of the Arrenhius plots of the conductivity for these and other fluorides: both the activation energy for conduction and the resistivity decreases with a decrease in the melting temperature of the materials. A Koch—Wagner-type analysis of conductivity isotherms confirms an anion Frenkel thermal-disorder model for the fluorides. The type of disorder for SrCl2 could not be determined unambiguously, however. Values for the energy of formation of the intrinsic defects and their motion energies have been deduced from the slopes of the conductivity curves. Estimates of concentration of the thermal defects were made in each case.
Low-Pressure Study of Heterogeneous Hydrogen—Deuterium Exchange at Steady State
Authors: Bergsnov-Hansen Bjorn , Pasternak R. A.
Published: January 2005

The hydrogen—deuterium exchange reaction on a clean molybdenum filament has been investigated at pressures of 10−8 to 10−5 torr and temperatures of 25° to 800°C; a steady-state approach was employed, and the exchange rates were measured with a mass spectrometer. The adsorption step is found to be rate determining and is characterized by pressure independent total sticking probabilities of about 0.4 at temperatures above 200°C, and declining to 0.2 at 25°C; the sticking probabilities are identical for the three hydrogen species. The net rates of adsorption and the saturation coverages at 25°C measured for hydrogen and for deuterium show also that the surface cannot distinguish between the hydrogen species.

Both the high value and the pressure independence of the sticking probability indicate that at either temperature, exchange occurs in adsorption states of low population. Surface coverage is immeasurably small at high temperatures. However, since at 25°C the total surface coverage is of the magnitude of a monolayer, exchange apparently involves adsorption states of low coverage which may be identified with low-energy states observed previously in flash-filament studies.
Ionization of Molecules at Low Energies
Authors: Berry R. Stephen
Published: January 2005

A general formal theory is developed for the autoionization of molecules at energies within a few electron volts or less of threshold, specifically to include effects of the interaction of an excited Rydberg electron with the rotating, vibrating molecule—ion to which it is bound. The dominant coupling mechanism involves conversion of vibrational energy to electronic energy and is most efficient when the core can undergo a single quantum jump. A number of simplifications and approximations are discussed. Some of these are used in an application of the theory to the autoionization of H2. Autoionization rates are computed for a number of vibronic Rydberg states of this molecule, and are consistent with the available data. Model calculations for heteronuclear diatomics are presented to show how the presence of a vibrating dipole in the molecular core enhances the rates of autoionization, in comparison with the rates in homonuclear diatomics where vibrating quadrupoles stimulate the process. Several experiments are suggested, particularly the measurement of the angular distributions of electrons detached from heteronuclear diatomics.
Vibrational Relaxation in CO—D2 Mixtures
Authors: White Donald R.
Published: January 2005

The vibrational relaxation of 0.1 D2+0.9 CO has been observed in a shock tube by means of optical interferometry and infrared photometry. From 940° to 1600°K deuterium and helium are found to be equally effective collision partners for the vibrational excitation of carbon monoxide. From 1600° to 2800°K the data suggest that vibrational exchange from the more rapidly excited D2 contributes to the excitation of CO.
Atomic Distribution and Electrical Properties of Liquid Mercury—Thallium Alloys
Authors: Halder N. C. , Metzger R. J. , Wagner C. N. J.
Published: January 2005

The x-ray-diffraction patterns of liquid binary Hg–Tl alloys have been measured using a theta—theta diffractometer and quartz crystal monochromatized Mo Kα radiation. Pure mercury and five alloys of 5, 8.5, 16, 28.6, and 40 at. % thallium were studied at room temperature (25°C), whereas pure thallium was studied at 350°C. Since mercury and thallium are next to each other in the periodic table, the contribution of the Laue monotonic scattering to the scattered intensity should be negligible.

The radial distribution functions were refined by an error-analysis program and then the refined interference functions were computed and used to calculate the electron transport properties of the alloys. The general equation for the scattering cross section of the electrons in liquid metals has been used and expressed in terms of the matrix elements of the pseudopotentials and the interference functions of the respective elements. Assuming that the atomic distribution is random, the resistivity and thermoelectric power of the alloys and the pure elements were calculated. There is some disagreement between the calculated or predicted and measured values of the resistivity. The predicted value of resistivity of mercury and thallium are 30 and 60 μΩ·cm, respectively.

The interatomic distances were found to vary linearly from 3.05 for pure Hg to 3.28 Å for Hg−40 Tl alloy. The value for pure Tl is 3.30 Å. This linear variation is not in agreement with previous results. The positive deviation from Vegard's law has been attributed to the electrochemical and valence difference of the two elements. The behavior of the coordination number with concentration, the change being from 10.0 to 11.5 for pure Hg to pure Tl, is similar to that of the interatomic distance with the concentration.
Environmental Effects on the Infrared Frequencies of Polyatomic Molecules. Evaluation of Perturbation-Theory Parameters for HCN and DCN
Authors: Mann Richard H. , Horrocks William DeW.
Published: January 2005

Buckingham's equations describing solvent-induced vibrational frequency shifts for polyatomic solute molecules are applied to experimental solvent-shift data for HCN and DCN. The equations were transformed to internal coordinates such that the expressions for the frequency shifts involve the first (Vi′) and second (Vii″) derivatives of the solute—solvent interaction energy with respect to the internal vibrational coordinates. Numerical values for these energy derivative terms were determined from the experimentally observed shifts of the six fundamentals of HCN—DCN in a series of solvents in a manner such that the problem was overdetermined. (Note that this method fails when applied to diatomic molecules.) It is found that second-derivative terms make significant and often dominant contributions to the observed shifts and that solvent perturbation of a given internal vibration in a molecule materially affects the shifts of other vibrational bands in the molecule. The equations of Huong et al. relating the relative frequency shifts of the stretching vibrations of HCN and DCN are shown to be a consequence of the equations of Buckingham. Expressions are given for the solvent perturbation contribution to 〈Qi〉 and 〈Qi2〉. Quantitative estimates of average bond extensions and mean-square vibrational amplitudes are given for certain cases.
Dielectric Studies. VII. Rate Processes of Saturated Amines
Authors: Tucker S. W. , Walker S.
Published: January 2005

Dielectric absorption studies of pyrrolidine, piperidine, and dicyclohexylamine in cyclohexane and also in 1,4-dioxan solution have been carried out at microwave frequencies, and the static dielectric constant at 1 Mc/sec has also been determined. For pyrrolidine and piperidine in cyclohexane the dielectric data have been analyzed in terms of contributions from two relaxation times, one of which can be identified with reorientation of the molecule. The magnitude of the other relaxation time seems dependent on a rate process connected with the presence of the dimer.