bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of Phase Transitions in Solid Methanes. II. Nuclear Spin Species A and T of Light Methane
Authors: Yamamoto Tsunenobu , Kataoka Yosuke
Published: February 2004

The statistical mechanical properties of the James–Keenan model are studied with the purpose of elucidating the mechanism of phase transitions in the solid light methane. All the calculations are made on the basis of quantum statistical mechanics in the subspace with J ≦ 4, J being the rotational quantum number. The molecular field approximation method is employed. The low and high temperature-ordered phases are assumed to have the same sublattice structure as that which James and Keenan predicted in their classical theory. Under the provisional assumption of no interspecies conversion, nuclear spin species A and T are treated separately. The results of the numerical calculations indicate that the James–Keenan model is quite hopeful as a working model to understand the nature of the phase transitions in the whole family of the isotopic solid methanes.
Angular Distribution of Scattered and Desorbed Atoms from Specular Surfaces
Authors: Comsa George
Published: February 2004

The angular distribution of atoms and molecules leaving a cleaved-crystal surface, on which the conditions for specular reflection are fulfilled, is analyzed. Starting from published experimental data concerning the reflecting power vs glancing-angle dependence (He–LiF system) and from some general considerations, the existence of a deviation from the cosine law of the angular distribution of atoms, leaving a specular surface after an inelastic collision, is pointed out. It is shown that this deviation is correlated with the shape of the reflecting power vs glancing-angle curve, belonging to the atoms which undergo a specular reflection on this surface. A tentative model for the specular reflection of helium on LiF cleaved-crystal surfaces is proposed; it considers, in analogy with the neutron case, the specular reflection of atoms as total reflection on a surface of positive average interaction potential. The proposed model leads to a reflecting power vs glancing-angle curve which fits rather well the experimental data. Moreover, it explains qualitatively the correlation between the shape of the reflecting power vs glancing-angle curve and the characteristics of the deviation from the cosine law of the angular distribution for atoms having undergone an inelastic collision. Experiments for the check-up of the general conclusions, as well as of the tentative model, are proposed.
Heat and Entropy of Sublimation of Nickel Dichloride, Dibromide, and Di-iodide; Dissociation Energies of Gaseous NiCl2 and NiBr2
Authors: McCreary J. R. , Thorn R. J.
Published: February 2004

The vapor pressures of solid anhydrous nickel dichloride, dibromide, and di-iodide have been measured directly by measurement of the torsional recoil of a suspended effusion cell and indirectly by measurement of mass effusion. The results with R in calories/mole·degree and p and π in atmospheres are as follows: NiCl2(550°–608°C): RT lnp = − (53.59 ± 0.41) × 103 + (43.70 ± 0.48)T, at 855°K logp = − 4.1472 ± 0.0020; RT lnπ = − (52.76 ± 0.40) × 103 + (42.63 ± 0.46)T, at 855°K logπ = − 4.1670 ± 0.0019. NiBr2(519°–584°C): RT lnp = − (53.01 ± 0.76) × 103 + (45.11 ± 0.95)T, at 820.16°K logp = − 4.2595 ± 0.0036; RT lnπ = − (51.97 ± 0.27) × 103 + (43.73 ± 0.33)T, at 820.16°K logπ = − 4.2843 ± 0.0014. Nil2(462°–505°C): RT lnp = − (35.58 ± 0.36) × 103 + (32.60 ± 0.52)T; RT lnπ = − (37.39 ± 0.24) × 103 + (34.93 ± 0.34)T. For the chloride and the bromide, the measured pressures are 1.05(± 0.02) times the equivalent mass effusion (π) for a molecular weight corresponding to the monomeric dihalide. This deviation from unity cannot be attributable to lack of information about the gaseous species but probably represents a demonstrable systematic difference between the two procedures. The free energies of bonding derived from the measurements are ΔF°b(NiCl2, g) = − 180 000 + 54.78T and ΔF°b(NiBr2, g) = − 131 000 + 38.22T both in calories/mole. The derived dissociation energies to the gaseous atoms are 7.8 eV for NiCl2(g) at 850°K and 5.7 eV for NiBr2(g) at 820°K. The absolute entropy of gaseous NiCl2 at 850°K is 85.4 eu, a value which yields an estimated 13.3 eu for the vibrational and electronic degrees of freedom. An analysis of the results for nickel di-iodide cannot be accomplished because significant but unknown amounts of gaseous NiI and I2 are present causing transport back and forth between the cell and its surroundings.
Effect of Particle Shape on the Spectral Absorption of Colloidal Silver in Gelatin
Authors: Skillman David C. , Berry Chester R.
Published: February 2004

Small prolate spheroids of silver (between 140 and 400 Å av diam) were produced by photographic development of fine-grain silver bromide embedded in gelatin. The shape and size distributions of the silver particles were determined from electron micrographs of thin sections. The average axial ratios of these spheroids had values for different preparations between 0.3 and 0.9. The optical absorption was measured and a shift of the main absorption peak (near 400 mμ) to shorter wavelengths, and of a secondary peak to longer wavelengths, with elongation of the particles was found to be in good quantitative agreement with the theory of Gans. The position of the main peak can be brought into even better agreement with the theory by taking account of the finite average particle size (by using the Mie theory) and by selecting the most appropriate set of optical constants for chemically prepared silver. Small departures from spherical shape affect the spectral absorption of colloidal silver much more than changes in size or refractive index.
Location of the Fourth, Forbidden Factor Group Component of the 1B2u State of Crystalline Benzene
Authors: Colson Steven D.
Published: February 2004

There have been two different experimental techniques used to locate the position of the fourth, forbidden factor group component of the 1B2u state of crystalline benzene. The method of variation of energy denominators gives rise to a very wide exciton band, placing the forbidden Au component at 37 996 cm− 1. More recently, the density-of-states function for the 1B2u exciton band has been determined and used to predict that the Au component lies between 37 815 and 37 875 cm− 1. As both of these techniques rely upon the use of first-order Frenkel theory, their disagreement might be interpreted to mean that a higher-order theory, perhaps involving ion-pair states, is needed to explain the experiments. In order to shed more light on this problem, the method of variation of energy denominators is re-examined in this paper through improved and more extensive experiments. The variation of energy denominators method, which assumes the spectral shift terms to be independent of isotopic substitution, is found to be inappropriate for the study of the 1B2u state of crystalline benzene. In addition to this finding, evidence based upon vibronic spacings is presented that indicates no strong mixing between the ion-pair states and the 1B2u state of the crystal. In fact, this same evidence is used independently to predict the position of the forbidden Au component to be very close to 37 860 cm− 1, in agreement with the limits set by the experimental density-of-states function. The density function, calculated using first-order Frenkel theory and the assumption that nearest-neighbor interactions dominate, is found to be in excellent agreement with the experimentally observed function. It is therefore concluded that mixing with ion-pair states need not be considered to explain the band structure of the lowest excited singlet state of benzene crystals.
Diffusion and Heterogeneous Reaction. IX. Theoretical Analysis of Nonsteady-State Kinetics
Authors: Rajapakse Y. , Wise H.
Published: February 2004

The theoretical analysis of a transient method is presented for the quantitative study of heterogeneous reaction rates and gaseous, multicomponent diffusion coefficients. From observations of the rate of decay of reactant after its source of supply has been shut off, the kinetics of chemical reaction on the catalytic surface may be obtained. This experimental approach is particularly applicable to the study of the diffusional transport of highly reactive species such as free radicals and atoms.
Vibrational Relaxation in the Tetrachlorides of C, Si, Ge, Sn, and Ti
Authors: Rasmussen R. A.
Published: February 2004

Results of attenuation measurements in CCl4, SiCl4, GeCl4, SnCl4, and TiCl4 indicate that thermal relaxation is responsible for the large attenuations observed in these substances. Comparison of relaxation times in the vapor and liquid phases suggests that the collision efficiencies are considerably smaller in the liquids and decrease through the series in the order of increasing force constants. This result is in general agreement with the suggestion by Madigosky and Litovitz that attractive forces do not enhance the collision efficiency in the liquid owing to close molecular packing. However, the theoretical reduction in collision efficiency suggested by these investigators is markedly different from that observed for SnCl4.
Frequency Spectrum of Hydrogenous Molecular Solids by Inelastic Neutron Scattering. Hexagonal H2O Ice
Authors: Prask Henry , Boutin Henri , Yip Sidney
Published: February 2004

A simple method of relating the scattered neutron energy distribution to the molecular frequency spectrum in hydrogenous solids is given. The method is approximate because of the neglect of translation-rotation couplings, but should be of practical interest for systems where translational and librational frequencies do not appreciably overlap. The approach is applied to cold-neutron-scattering data from hexagonal ice at 150°K. The resulting thermodynamic frequency distribution is used to compute moments, specific heat, and root-mean-square amplitude of vibrations. Comparison is made with optical, thermodynamic, x-ray, and neutron measurements.
Magnetic Structure of TbAg2
Authors: Atoji Masao
Published: February 2004

Neutron-diffraction measurements have revealed that TbAg2 having the tetragonal CaC2-type structure becomes antiferromagnetic below the Néel temperature of 35°K. The ordered magnetic structure consists of the ferromagnetic sheets which are perpendicular to the a axis (face-centered description), and the moment directions of the adjacent ferromagnetic sheets are opposite to one another. All moments are aligned in the direction of the c axis, and the saturation moment per Tb is 8.95 ± 0.05 Bohr magnetons which is essentially equal to the ordered moment of the free Tb3 + ion. This ordered structure is identical to the commensurable magnetic structure of TbAu2 at temperatures below 42.5°K, but the incommensurable transverse-wavelike spin alignment of TbAu2 found in the 42.5°–55°K range was not detectable in TbAg2. Also, no detectable moment is observed for Ag in TbAg2.
ESR Studies of Radiation-Induced Niobium Centers in Nb2O5–Na2O–SiO2 Glasses
Authors: Kim Y. M. , Reardon D. E. , Bray P. J.
Published: February 2004

Electron spin resonance (ESR) studies have been made of gamma-irradiated Nb2O5–Na2O–SiO2 glasses. The samples received a gamma-irradiation dose of 2 × 107 R at liquid-nitrogen temperature, and were investigated at that temperature. A broad spectrum which is characterized by an axially symmetric g tensor and hyperfine interaction with the 93Nb(I = 92) nucleus, is identified as due to an Nb4 + center formed in a niobium–oxygen unit. A separate, narrow spectrum located in approximately the center of the broad spectrum can be separated into three distinct spectra: a sharp central spectrum, an asymmetric spectrum on the high-field side, a 10-line spectrum. The sharp central and asymmetric spectra are identified as due to two different centers formed in silicon–oxygen units. A hole in an NbO6 unit is proposed as a model for the 10-line spectrum.
Configuration-Interaction Study of the H3– System. I. 1s Orbitals
Authors: Macías A.
Published: February 2004

A configuration-interaction (CI) calculation on the ground state of H3– has been carried out using a minimal basis set made up of a 1s Slater-type orbital (STO) centered on each nucleus. The most stable nuclear geometry of H3– is a linear symmetric arrangement of the nuclei with a separation of 2.2098 a.u. and the corresponding value of the energy is −1.581076 a.u. The system is unstable relative to H2 + H–. The energy of the system when the nuclei occupy the corners of an equilateral triangle, and the reaction H2 + H– have also been studied. No experimental data are available for H3– but the equation calculated for the interaction of H2 with H– as a function of distance agrees fairly well with equations derived from scattering experiments.
Natural Occupation Amplitudes of Helium-Atom S-Type Wavefunctions
Authors: Nazaroff George V.
Published: February 2004

A study of several approximate singlet solutions of the S-function Schrödinger equation has revealed that all msns 1S(n≥m) S-type wavefunctions for given m have m positive natural occupation amplitudes. These positive amplitudes are associated with the m lowest-energy natural orbitals. The rest of the amplitudes are negative. It is hypothesized that the natural orbitals are only slightly altered as more configurations are added to a wavefunction. This hypothesis is used to justify the application of the many-configuration self-consistent field formalism to explain the observed behavior of the natural occupation amplitudes.
Fluorescence of Eu3 +-Activated Sodium Lanthanide Titanates (NaLn1–)
Authors: Blasse G. , Bril A.
Published: February 2004

The fluorescence of phosphors NaLn1–xEuxTiO4(Ln = La, Gd, Y, Lu) with ordered Sr2TiO4 structure is reported. The unactivated host lattices show broad-band emission peaking at about 450 nm. The quenching temperature of this fluorescence is below room temperature. The relative intensities of the Eu3 + emission lines depend strongly on the choice of Ln. This variation can be accounted for by a varying linear component of the crystal field. Although the requirements for efficient Eu3 +-activated phosphors are satisfied by the phosphors NaLnTiO4, the efficiencies of the fluorescence are not very high. This is ascribed to the anisotropic nature of the crystal structure.
Adiabatic Rotations in Unimolecular Rate Theory
Authors: Forst W.
Published: February 2004

The term “adiabatic rotations” describes rotations that are constrained to remain in the same quantum state when the activated complex is formed from the active molecule because of restrictions imposed by angular momentum conservation. It is shown that these rotations decrease the activation energy for dissociation and therefore increase the rate; a priori, the effect is likely to be largest at the high-pressure limit of a unimolecular decomposition, and least at the low-pressure limit. The general case is considered of a polyatomic symmetric-top molecule decomposing unimolecularly. Assuming a Boltzmann distribution of rotational energies of the molecules undergoing decomposition, an expression is derived for the factor (f) by which the rate constant is increased due to adiabatic rotations. Two approaches are used: one involving the average moment of inertia of complex (I‡), if known from other information, and the second involving the assumption of inverse sixth-power potential between the two incipient fragments. The former approach is useful in demonstrating the dependence of f on I‡ at high and low pressures. The latter approach permits the calculation of f directly from molecular parameters. These calculations are done for four unimolecular decompositions and they show that I‡ is larger than has been usually estimated, and also that the pressure dependence of f is substantial enough in the case of complex molecules to contribute appreciably to the falloff with pressure of the unimolecular rate constant. The effect of the assumed power law in the potential is briefly discussed.
Magnetothermodynamics of Single-Crystal CuSO4·5H2O. II. Fields ‖ to the α-Magnetic Axis. Thermodynamic Temperature and Heat Capacity without Heat Introduction below 0.4°K. Calorimetric Heat Capacity from 0.4°–4.2°K with Fields of 1 and 3 kG
Authors: Giauque W. F. , Fisher R. A. , Hornung E. W. , Brodale G. E.
Published: February 2004

The heat capacity of a 3.700-cm-diam single crystal of CuSO4·5H2O has been measured by means of heat introduction over the range 0.4°–4.2°K with magnetic fields of 1 and 3 kG parallel to the α magnetic axis. These data supplement the previous observations of Anderson and Giauque (A and G) over the range 0–90 KG. A series of 29 adiabatics has been used to evaluate the temperature, heat capacity, and other magnetothermodynamic properties without heat introduction in the range 0.021°–0.4°K. The magnetic irreversibility study reported by A and G on copper sulfate pentahydrate has been extended and indicates that reversible thermodynamic methods may be used when the electronic entropy is as low as 0.05 gibbs/mole provided the field has not been reduced below 1 kG. When the entropy is about 0.1 gibbs/mole or more the field may be reduced to zero reversibly.
Magnetothermodynamics of Single-Crystal CuSO4·5H2O. III. Properties over the Range of 0.4°–4.2°K with Fields to 90 kG ‖ to the γ Magnetic Axis
Authors: Giauque W. F. , Hornung E. W. , Brodale G. E. , Fisher R. A.
Published: February 2004

The heat capacity and magnetic moment of CuSO4·5H2O have been measured over the range 0.4°–4.2°K in stabilized magnetic fields of 0, 1, 3, 5, 10, 20, 30, 50, 70, and 90 kG. The field was directed along the γ magnetic axis of a 3.70-cm-diam spherical single crystal. A sensitive carbon thermometer was used to measure the change of temperature during demagnetizations at essentially constant entropy to connect the several isoerstedic heat-capacity series. Magnetic saturation, corrected for diamagnetism and an almost trivial temperature-independent paramagnetism, was used to evaluate the gyromagnetic ratio as gγ = 2.269, and as a zero entropy reference. Within the limit of accuracy of the estimated “tail” above 4°K the electronic entropy was found to be Rln2. All observations were uncorrected for the demagnetizing effect of the spherical sample. At 90 kG the heat-capacity observations show that the nuclear spin polarization is in thermal equilibrium down to 0.7°K.
Numerical Experiments on Scattering of Noble Gases from Single-Crystal Silver
Authors: Oman Richard A.
Published: February 2004

Three-dimensional numerical experiments on the scattering of noble-gas atoms from single-crystal surfaces of silver are described. This numerical method can be very useful in determining the relative importance of different variables in the interactions although it cannot be expected to give quantitative agreement with individual cases until a better knowledge of the interatomic binding energies and the surface state is available. Most of the cases are for neon on the fcc (111) surface, but isolated cases of helium and argon on (111) and neon on (100) are included. The energies include those of effusive molecular beams from 300° to 45 000°K equivalent source temperatures (0.06 to 7.8 eV). Several interaction parameters describing mean energy and momentum exchanges and traces of the spatially resolved flux in the incident plane are given for most of the cases. Sample out-of-plane flux data and some typical data on spatially resolved energy are also given, and general trends for the rest of the data are described. The results give trapping probabilities that are much greater than those inferred from laboratory experience, and flux patterns that are significantly broader than those encountered in the experiments for the few cases that can be compared directly. The neon trends with increasing energy are quite similar to those of the Saltsburg and Smith experiments for xenon, with new effects appearing in the present results for energies higher than those of the laboratory experiments. These new effects include multiple peaks, one above and one below specular, and a broadening of the patterns with increasing incident energy. They are attributed to increased resolution of the surface atomic configuration due to deeper penetration of the potential field above the surface. The trends of the Logan, Keck, and Stickney hard-cube theory are shown in the present results at low incident energy, and the expected hard-sphere limit behavior is observed at very high incident energy, in agreement with the recent calculations of Goodman.
Permeabilities and Transmission Coefficients for Various Isotopic Reactions of the Type H + H2=H2 + H
Authors: Mortensen Earl M.
Published: February 2004

Permeabilities for the reaction H + H2=H2 + H and its isotopic substitutions have been obtained for a linear collision by numerically solving the Schrödinger equation. Bending corrections were applied to account for the bending motions of the activated state. Transmission coefficients were calculated from the permeabilities at various temperatures. From the results reported here it appears that the zero-point energy of the activated state for reactions in which a light atom such as hydrogen is transferred cannot be obtained from the usual normal-mode treatment using the curvature of the surface at the saddle point.
Analytical Evaluation of Multicenter Integrals of r12− 1 with Slater-Type Atomic Orbitals. I. (1-2)-Type Three-Center Integrals
Authors: Silverstone Harris J.
Published: February 2004

The three-center integral of r12− 1, with one electron on one center in a Slater-type orbital, the second electron on two centers described by a product of Slater-type orbitals, is evaluated analytically. The result is an infinite sum in which the internuclear angles appear in spherical harmonics and the internuclear distances appear in modified spherical Bessel functions and exponential-type integrals. When one of the internuclear distances goes to zero, the two-center hybrid integral is obtained as a finite sum. The main mathematical techniques used to evaluate the integrals are the Fourier-transform convolution theorem, expansion of a Slater-type orbital on one center about another, coupling properties of spherical harmonics, and contour integration.
Analytical Evaluation of Multicenter Integrals of r12−1 with Slater-Type Atomic Orbitals. II. (2–2)-Type Three-Center Integrals
Authors: Silverstone Harris J.
Published: February 2004

The general three-center one-electron nuclear-attraction integral with integer-n Slater-type orbitals is evaluated analytically by letting the orbital exponent of a 1s orbital in the analytical formula for two-electron three-center electron-repulsion integrals tend to infinity. The result is an infinite sum in which the internuclear angles appear in spherical harmonics, and the internuclear distances appear in modified spherical Bessel functions and exponential-type integrals.
Analytical Evaluation of Multicenter Integrals of r12−1 with Slater-Type Atomic Orbitals. III. (2–2)-Type Three-Center Integrals
Authors: Silverstone Harris J. , Kay Kenneth G.
Published: February 2004

The three-center integral of r12− 1, with each electron described by a two-center product of integer-n Slater-type orbitals, is evaluated analytically. The result, obtained via the Fourier-transform convolution theorem, is an infinite sum involving spherical harmonics for the internuclear angular coordinates and exponential integral and spherical Bessel-type functions for the internuclear distances. The two-center exchange integral is evaluated as a special case. All results given are for general values of the n, l, m, and ζ parameters of the Slater-type orbitals.
Intermediate Bracketing Theorems for Lower Bounds
Authors: Wang P. S. C.
Published: February 2004

A set of intermediate resolvents is formed from the truncated Hamiltonians of Bazley and Fox. On replacing the resolvent operator in Löwdin's bracketing theorem by these intermediate resolvents, one obtains lower-bound expressions suitable for calculations involving molecules. This method is applied to the ground state of H2+ (exact energy E0 = − 1.10263 a.u.). The results are −1.15029 a.u. for a one-term and −1.10438 a.u. for a two-term truncated Hamiltonian.
Vibrational Corrections to the Nuclear-Magnetic Shielding and Spin–Rotation Constants for Hydrogen Fluoride. Shielding Scale for 19F
Authors: Hindermann David K. , Cornwell C. D.
Published: February 2004

The theory of vibrational effects on the nuclear shielding and spin–rotation constants for a diatomic molecule is outlined. Corrections for these effects are calculated theoretically for both 1H and 19F nuclei in the HF molecule. The theoretically calculated isotopic shift for 19F shielding between DF and HF is in good agreement with the zero pressure experimental value, 2.5 ± 0.5 ppm. The shielding for the vibrating molecule at 300°K is computed from the theoretically calculated value for σFd and the experimentally measured spin–rotation constant, as 〈σF(HF)〉 = 410 ± 6 ppm. The measured chemical shift between the HF monomer and SiF4(gas) then provides a practical 19F reference of known shielding, 〈F(SiF4)〉 = 363 ± 6 ppm. Vibrational corrections are applied to the measured proton shielding in HF gas at zero pressure to obtain the shielding constant as σH(HF) = 29.2 ± 0.5 ppm for the nonvibrating molecule at the equilibrium internuclear distance. Combination of this with the measured spin–rotation constant leads to a separate determination of experimental values for σHd and σHp, with arbitrary choice of gauge origin, for the non-vibrating molecule.
Effect of Compression and Compositional Changes on the Nature of Chromium Sites in Simple Glasses
Authors: Tischer R. E.
Published: February 2004

The effects of pressure up to 50 kbar and of compositional changes on the absorption spectra of a number of chromium-containing silicate, phosphate, and borate glasses were observed. The spectra were analyzed into their component bands, and ligand-field theory was used to interpret the results to obtain information about the local symmetry, distortion, and local compressibility of the chromium sites. The absorption properties are explained by assuming that, on the average, the trivalent chromium ions are surrounded by six oxygen ions in an octahedral arrangement. The behavior of the spectra indicates that a random distribution of Cr–O distances about an average Cr–O distance exists and that only small disortions from cubic symmetry occur. The variation of the ligand-field parameters and the compressibilities of the sites depends mainly on the number of oxygen ions per unit volume in the glass, whether the changes are induced by external pressure or by compositional changes. Those glasses with a more open oxygen packing exhibit smaller crystal-field strengths, larger compressibilities, and larger distortions from octahedral symmetry than do the more densely packed glasses. Also, the compressibilities of the chromium sites are much less than the bulk compressibilities of the glasses.
Comparison of Condensed-Pair and Separated-Pair Models: Application to the Ground State of Benzene
Authors: Ebbing Darrell D. , Tanin Ateş
Published: February 2004

A calculation is presented for the π electrons of the ground state of benzene using the condensed-pair model (method of biorbitals). The results are compared with previous calculations using the separated-pair model. It is concluded that the model is inappropriate for many-electron systems that are well represented as separated pairs, but will give moderately good results for systems of delocalized electron pairs.
Spectroscopic Evidence for Pseudorotation. II. The Far-Infrared Spectra of Tetrahydrofuran and 1,3-Dioxolane
Authors: Greenhouse Jeffrey A. , Strauss Herbert L.
Published: February 2004

The absorption spectra of tetrahydrofuran and of 1,3-dioxolane at about 0.3-cm−1 resolution are reported in the region of 20–370 cm−1. It is found that dioxolane pseudorotates, and the earlier evidence for the pseudorotation of tetrahydrofuran is confirmed. Both compounds have barriers to pseudorotation of about 50 cm−1. Pseudorotation constants in both the ground and in the first excited radial states are obtained. The spectra show the effects of a considerable number of complex rotation–vibration interactions, which can be understood qualitatively by comparison with the spectra of four-membered-ring compounds. The band shapes are explained semiquantitatively using a number of Coriolis terms in the effective Hamiltonian.
Permeation, Diffusion, and Solubility of Deuterium in Pyrex Glass
Authors: Laska H. M. , Doremus R. H. , Jorgensen P. J.
Published: February 2004

The permeation of deuterium through thin Pyrex bulbs was measured with a mass spectrometer. The activation energies and absolute values at 200°C for permeation and diffusion were nearly the same as for deuterium in fused silica. The solubility of deuterium in Pyrex was independent of temperature, and about the same as the solubilities of several gases in fused silica. These results are consistent with a free-volume theory of gas solubility in glass and the separation of Pyrex into silica and sodium borosilicate phases.
Magnetic Susceptibilities of Rare-Earth–Indium Compounds: RIn3
Authors: Buschow K. H. J. , de Wijn H. W. , van Diepen A. M.
Published: February 2004

The magnetic properties and the lattice parameters for 13 compounds of the composition RIn3 (Cu3Au structure) are reported. The magnetic measurements have been performed between 4.2° and 500°K with magnetic fields up to 30 kOe. With the exception of compounds with R=La, Sm, Y, and Yb Curie–Weiss behavior is observed in the high-temperature region. At low temperatures the magnetic behavior for compounds in which R=Ce, Nd, Sm, Gd, Tb, Dy, Ho, and Er is ascribed to antiferromagnetic ordering. In the case of PrIn3 magnetic ordering is prevented by crystalline fields. The splitting of the J = 4 state of Pr3+ by cubic crystalline fields has been calculated for various combinations of fourth- and sixth-order potentials. Possible energy diagrams are presented.
Inelastic Transition Probabilities and Their Role in the Quenching of Glory Extrema in Atom–Diatomic Scattering
Authors: Olson R. E. , Bernstein R. B.
Published: February 2004

Rotational inelastic transitions in atom–diatomic collisions have been investigated via several approximation treatments. In the high-velocity limit the restricted distorted-wave approximation (RDWA) yields transition probabilities P)j → j′), in agreement with the first-order sudden approximation at all impact parameters. Calculations of P(j → j′) at the glory impact parameter by the RDWA (further reduced by incorporating the Born approximation) agreed well with computations by the full distorted-wave procedure (over a wide range of energies and anisotropy parameters). In the pure distorted-wave treatment no glory quenching arises due to inelastic effects; however, in higher-order approximations inelastic quenching becomes important. By the use of a renormalized distorted-wave procedure (designed to preserve the unitarity of the S matrix) an improved equation for P(j → j′) is developed, leading to a quenching formula equivalent to that of Cross (based upon the high-velocity limit of his “infinite-order” distorted-wave treatment).
Molecular Orbital Interpretation of X-Ray Absorption Edges
Authors: Seka Wolf , Hanson Harold P.
Published: February 2004

The x-ray K absorption edges of transition metal ions in a number of covalent octahedral and tetrahedral complexes have been measured with a high-resolution double-crystal spectrometer. An analysis of the fine structure within about 20 eV of the edge in terms of molecular orbital theory has been attempted. For octahedral complexes a regular dependence of some features of the edge structures on the type of isomer and other perturbing effects of the ligands has been fairly well established. A correspondence of certain structural features to the ligand bond strengths and thus to the spectrochemical series has been predicted on the basis of MO theory and has been checked experimentally. For the chromates, manganates, and the [CrO3Cl]− radical, reasonably satisfactory agreement of the experimental results with MO theoretical predictions has been obtained.
Line Mixing by Collisions in the Far-Infrared Spectrum of Ammonia
Authors: Lightman A. , Ben-Reuven A.
Published: February 2004

The effect of mixing by collisions on overlapping lines in the far-infrared (rotation) spectrum of gaseous ammonia was studied. A merging of the inversion doublets into single lines, similar to the collapse of the microwave inversion spectrum into a nonresonant spectrum, has been observed. The line shape has been analyzed using an adapted form of Ben-Reuven's theory and values of the damping and cross-relaxation parameters have been obtained for the rotational lines 3 → 4, 4 → 5, and 5 → 6.
Internal Rotation and Vibration in CH2=CCl–CH2D
Authors: Meyer R. , Günthard Hs. H.
Published: February 2004

The infrared spectrum of CH2=CCl–CH2D in the region 4000–160 cm−1 is presented and assigned. From a comparison of the observed vibrational spectrum with normal-coordinate results based on the assumption of rotational isomers the methyl group is found to eclipse the double bond. A torsion–vibration calculation is set up and applied to the same molecule for comparison with the normal-coordinate results. Owing to the relatively high torsional barrier the vibrational fundamentals obtained from the two approaches differ by less than 1 cm−1. The results suggest that for more precise treatments of vibrational spectra the dependence of the kinetic-energy matrix on all internal coordinates should be considered.
Occupation Ratio of Large Atoms under Fermi–Dirac Statistics on Integer Lattices
Authors: Verhagen A. M. W.
Published: February 2004

When the diameters of atoms being adsorbed and readsorbed randomly on an integer lattice just exceed unity, an adsorbed atom prevents or “blocks” further adsorption on the site of adsorption and on the nearest-neighbor sites, thus influencing the adsorption patterns which may arise. It is shown that the statistical equilibrium which arises under these conditions obeys Fermi–Dirac statistics for which all physically possible patterns are equally probable. The configurational entropy of the gas on the lattice is expressible in the occupation ratio defined as the quotient of the total number of blocked sites and the total number of adsorbed atoms, averaged over all physically possible patterns. A reformulation of this quotient for each pattern as a mean of scores allocated to each adsorbed atom, and the invention of stochastic-pattern-generating processes have made it possible to derive and evaluate the occupation ratio as a function of the adsorption density ρ for various finite and infinite lattices in one and two dimensions.
Dark Injection and Radiative Recombination of Electrons and Holes in Naphthalene Crystals
Authors: Lohmann F. , Mehl W.
Published: February 2004

Negative carriers have been injected into naphthalene crystals from a contact consisting of the sodium–potassium eutectic which is liquid at room temperature. The voltage dependence of the space-charge-limited (scl) current is determined by an exponential distribution of traps in energy. Positive carriers were injected into naphthalene crystals from the redox systems Ag2+/Ag+ in 7.5N HNO3 and Ce4+/Ce3+ in 15N H2SO4 leading for the first system to a space-charge-limited current and in the second one to a current–voltage curve which is determined by a field assisted hole injection reaction. Double injection of electrons and holes leads to radiative recombination under emission of the naphthalene fluorescence spectrum.
Dielectric Behavior of NaOH-Doped Ice
Authors: Kelly David J. , Salomon R. E.
Published: February 2004

The dielectric behavior of ice doped with different NaOH concentrations was investigated in the 0° to − 25°C temperature range. In the lower concentration range of 1–4 × 10−6M NaOH, the conductivity behavior was similar to pure ice. At higher concentrations in the range of 7 × 10−6M NaOH, significantly higher conductivities were observed with the low-frequency conductivity being about 5 × 10−8 (Ω·cm)−1 and exhibiting only a slight temperature dependence. At lower temperatures the static dielectric constant was found to decrease with increasing NaOH concentration. The dielectric relaxation times and corresponding activation energies were about the same as for pure ice. The over-all behavior is distinctly different from that of HF, HCl, and NH3-doped ice. The model postulated to explain the observed results involves the interstitial incorporation of Na bonded to an (OH) site in its normal lattice position. It is postulated that this mode of incorporation causes lattice distortion that increases either the concentration or mobility of the OH-ionic defects which in turn accounts for the increased conductivity.
Inequalities for Multipole Dispersion Interactions
Authors: Weinhold Frank
Published: February 2004

Some theoretical relations are obtained for various multipole dispersion force constants and for the total second-order dispersion energy in the long-range interactions between atoms.
Semiempirical Model for Atom–Atom Ionization Rates
Authors: Hollenbach D. J. , Salpeter E. E.
Published: February 2004

Numerical calculations are carried out to help interpret ionization rates for rare-gas atoms (particularly argon) obtained in shock-heating experiments. A simplified semiempirical model with three adjustable parameters is used for electronic transitions induced by atom–atom collisions. The three parameters are a measure of the absolute excitation rate from the ground state to the first excited state and of the ratios of different excitation and ionization rates. Numerical results are presented for the total ionization rate as a function of temperature and time for different values of the parameters. Present experiments determine one of the parameters, limit the other two parameters, and yield a relation between them. The possibility for determining all three parameters uniquely from future experiments is discussed.
Configurational Correlations in Chain Molecules
Authors: Jernigan R. L. , Flory P. J.
Published: February 2004

Although the potentials affecting the rotation about a skeletal bond in a chain molecule such as polymethylene (PM) usually depend only on rotations of immediately adjoining bonds, the interdependence of rotational states may be transmitted over greater distances. In the case of PM or of polyoxymethylene(POM) the effective range of correlation is only four or five bonds. This has been established by calculating a priori probabilities for rotational states of a bond as a function of its location relative to the chain termini and of the total chain length. The range of directional correlations between bonds is much greater owing to the further effects of the geometrical constraints imposed by bond angles and hindrance potentials. The correlation between bond directions is reflected in the average sum of the projection on bond i of all bonds i to n. Convergence of this quantity calculated for PM occurs for sequences exceeding about 25 bonds in length. Effects of chain ends are perceptible only for i < 4. In confirmation of these observations, the characteristic ratio 〈rpq2〉0 / | p − q |l2 of the mean-square distance between chain atoms p and q converges only for sequences | q − p | > 100 bonds, but for | q − p | > 3 it differs inappreciably from the value for a finite chain of length | q − p |, i.e., for p = 0 and q = n.
Pi-Electron Charge Densities and Chemical Shifts in Nitrogen Heterocyclics
Authors: Cobb T. B. , Memory J. D.
Published: February 2004

The relation Δσ = aΔq is examined in some detail, where Δσ is the chemical shift between a proton in an aromatic nitrogen heterocyclic and the corresponding proton in its aromatic polycyclic analog, and Δq is the excess π-electron charge density on the carbon to which the proton is bonded in the heterocyclic. It is found that the relation is quite satisfactory for positions ortho to a nitrogen, as long as only one nitrogen appears in that particular cycle.
Relaxation of the String Oscillator
Authors: Hanson M. P. , Blomme M.
Published: February 2004

The earlier work of Widom on the relaxation of a linear string oscillator interacting impulsively with particles of identical mass incident along its line of oscillation is extended to systems of different mass. The transition probability is derived in detail for the systems with mass ratios satisfying the condition 1 ≤ m1 / m2 ≤ 3, where m1 is the mass of the oscillator and m2 is that of the incident particle. In the extended region 13 ≤ m1 / m2 < ∼, the exact transition probability is quoted. The resulting transition probabilities satisfy the conditions of completeness and detailed balance. The result of this work suggests that the relaxation of a string oscillator generally may be described by a relaxation time, except in the special case m1 / m2 = tan2π / 2n, the exponential relaxation time breaking down in these special cases because of the difficulty of exciting or creating low-energy oscillators.
Electron Affinity of Lithium
Authors: Scheer Milton D. , Fine Joseph
Published: February 2004

The positive and negative surface ionization of a lithium atom beam on a thin, heated, molybdenum ribbon was studied using a specially designed mass spectrometer. At a constant incident beam flux, Li+ yields were determined as a function of surface temperature in the 1400°–2100°K range. Using 5.39 eV for the first lithium ionization potential (I), this data yielded an average positive ion work function (φ̄+) of 4.38 eV with a standard deviation of 0.01 eV. The [Li+/Li−] ratio was then determined at beam intensities and surface temperatures made sufficiently large to give measurable Li− yields. From the above values for I, φ̄+, T, and [Li+/Li−], it was found that A (Li) = φ̄− − (3.35 ± 0.05) eV. The quantity φ̄− is an average negative ion work function. This could not be measured with any precision because of the very small Li− yields. A recent determination of the single-plane work functions of molybdenum shows a variation from 4.0 eV for the (116) plane to 5.0 eV for a (110) surface. Since the negative ion work-function average accentuates the low work-function patches, the maximum uncertainty in φ̄− is given by 4.0 < φ̄− < 4.4 eV. Consequently, the electron affinity of lithium is bounded by the following values: 0.65 < A(Li) < 1.05 eV. From previously reported measurements of the polycrystalline work function of molybdenum, it is concluded that A(Li) is more likely to be near the upper rather than the lower limit of this range of uncertainty.
Mössbauer Effect in Low-Spin (d7) Complex Molecules of Fe
Authors: Oosterhuis W. T. , Lang George
Published: February 2004

Mössbauer spectra of Fe(CN)5NO3− (complex I), Fe(CN)5NOH2− (complex II), and hemoglobin nitric oxide are presented and compared with theoretical predictions. The spectra of complex I show no magnetic hyperfine interaction, while those of complex II and hemoglobin nitric oxide correspond to calculated spectra based on the assumption of unpaired spin in sigma bonds. The iron orbital components of the sigma wavefunctions are about 75% and 50%, respectively. In order to account for the Mössbauer spectra in zero applied field, transferred hyperfine interaction of the unpaired spin with the nitrosyl nitrogen must be taken into account. Results are in general agreement with ESR measurements.
Effect of Pressure and Temperature on the Conductivity and Ionic Dissociation of Water up to 100 kbar and 1000°C
Authors: Holzapfel Wilfried B.
Published: February 2004

The effect of pressure and temperature on the equivalent conductance of water is derived from recent conductivity measurements. The results together with experimental data on the ionic conductivity of water at temperatures up to 1000°C and pressures up to 100 kbar are discussed. The ionic product of water and the corresponding thermodynamic data for water dissociation at high pressures and temperatures are derived.
Spectroscopic Closure Property and Franck–Condon Band Structuring
Authors: Weigang Oscar E. , Ong Edith C.
Published: February 2004

A relationship is derived from evaluating the change in molecular equilibrium size on excitation from a moment analysis of the electronic spectrum. The method is applied to the Lb1←A1 benzene spectrum. The agreement of the calculated bond lengthening with that derived from independent rotational analysis would seem to confirm the adequacy of a spectroscopic closure property for benzene.
CNDO Molecular-Orbital Theory of Molecular Spectra. III. Calculations for the Fluorosulfate Radical
Authors: King G. W. , Santry D. P. , Warren C. H.
Published: February 2004

Calculations are presented for the four lowest doublet states of the fluorosulfate (SO3F) radical. The symmetries of these states were found to be, in order of increasing energy, 2A2, 2A1, 2E, and 2E. These results are consistent with the energies and intensities of the observed spectral absorption systems, especially the C̃2E ← X̃2A2 transition at 2.403 eV (5160 Å).
Evidence for the Formation of Neutral Rare-Gas Molecules by Electron-Beam Pulses
Authors: Arai Shigeyoshi , Firestone Richard F.
Published: February 2004

Intense emission and absorption signals in the visible and near-infrared regions have been induced by submitting Ne, Ar, Kr, and Xe and binary mixtures of these gases to brief intense pulses of 500-keV electrons. Measurements of the intensities of these signals as functions of time have been made with a time resolution of ∼ 40 nsec. The majority of the observed signals are attributed to 1s–2p atomic transitions. The lifetimes of the 2p atoms are shown to have been of the order 10−7–10−6 sec and to decrease with increasing pressure at 200–1500 torr. Absorption signals appearing in the near-infrared region unaccompanied by characteristic atomic emission signals were strongly inhibited by presence of a heavier rare gas and exhibited longer rise times than the atomic signals. These near-infrared absorption signals are tentatively attributed to neutral, probably diatomic, rare-gas molecules.
Distribution of Reaction Products. IV. Reactions Forming an Ionic Bond, M+XC (2d)
Authors: Kuntz P. J. , Nemeth E. M. , Polanyi J. C.
Published: February 2004

Recent discoveries arising from crossed-molecular-beam studies of reactions M+XC→MX+C, in which an alkali-metal atom M reacts with a halogen (XC≡XY) or a halide, have been examined in the light of the electron-jump model; M+XC→M++(XC)−→products. A very simple potential function was used to simulate reaction by the electron-jump mechanism. The properties of this potential-energy hypersurface were determined by the classical trajectory method. In the exploratory work described here, the particles were restricted to motion in two dimensions (2d). The effects were explored of variations in a considerable range of parameters. In the subsequent paper (Part V) the most important of these parameters will be investigated with better statistics, in 3d. From the 2d calculations it was evident that the most important parameters governing product energy distribution and angular distribution in these computations were the electron-jump distance, the repulsive energy release between the particles comprising (XC)−, and the admissibility of charge migration from end to end of (XC)−. The M+XC reactions exemplify mixed energy release (see Part II). A simple model of mixed energy release, termed the S.H. (simple harmonic) model, is presented. The model shows that for a wide range of conditions mixed energy release can play a significant role in channeling product repulsion into vibration.