bluuebunny/crossref_metadata_2025 huggingface dataset:
``Excimer'' and ``Defect'' Structure for Anthracene and Some Derivatives in Crystals, Thin Films, and Other Rigid Matrices
Authors: Fielding P. E. , Jarnagin R. C.
Published: January 2005

The emission lifetimes of matrix-stabilized dimers of anthracene and its derivatives were observed. The two principal conformations considered were the sandwich excimers and the 55° dimers. The excimer lifetimes may be of use in establishing wavefunctions for these transient states. A comparison of the lifetimes and emission structure from the dimers in rigid solvents with the time and wavelength structure of emission from strained crystals permits identification of a crystal defect in anthracene. The variable structure of anthracene thin films was demonstrated and partially identified.
Spectroscopy of EDA Complexes at High Pressures. III. Absorption and Fluorescence of Several TCPA Complexes in PMMA
Authors: Offen H. W. , Studebaker J. F.
Published: January 2005

The absorption and fluorescence spectra of several aromatic hydrocarbons complexed with tetrachlorophthalic anhydride (TCPA) dispersed in polymethylmethacrylate (PMMA) have been studied in the 0–25-kbar range. The pressure effect on the charge transfer (CT) absorption intensity and band maxima have been compared with low-temperature measurements. The molar extinction coefficient increases ∼100% at 77°K relative to 298°K and increases 100%—400% at 25 kbar relative to atmospheric pressure. The absorption-band maxima are rather insensitive to temperature, but shift red by ∼1500 cm−1 at 25 kbar. The CT fluorescence shows only ∼500 cm−1 red shift at 30 kbar. The difference can be rationalized in terms of potential-energy curves for the ground and excited states characterizing the molecular complex.
Electron Spin Resonance Study of Trapped Electrons in Gamma-Irradiated Triethylamine Glasses
Authors: Tsujikawa Hideo , Fueki Kenji , Kuri Zenichiro
Published: January 2005

A study has been made of trapped electrons produced in γ-irradiated triethylamine glasses at low temperature by electron spin resonance methods. A sharp singlet centered at g=2.003±0.001 was observed, which was readily bleachable with near-infrared light. In the presence of an electron scavenger this singlet spectrum was not observed and it has been attributed to trapped electrons. The G value for the formation of trapped electrons has been estimated to be 0.5 at 77°K. Isothermal decay of trapped electrons at 77°K was found to be a first-order process. Thermal decay measurements of trapped electrons indicated their rapid disappearance in a temperature region 105° to 112°K. A nuclear magnetic resonance study of a triethylamine glass revealed that motional narrowing in a resonance line of solvent protons occurred in about the same temperature region as that in which the rapid decay of trapped electrons was observed. The nature of the electron trap is briefly discussed.
Self-Consistent Calculation of Dynamic Polarizability
Authors: Sengupta S. , Mukherji A.
Published: January 2005

The dynamic polarizability of hydrogen and helium have been calculated by considering the effect of an external electromagnetic radiation on an atom through time-dependent perturbation procedure. Self-consistent solutions have been obtained in the Hartree—Fock scheme. The coupling of the perturbed functions through the self-consistency procedure markedly alters the relative contribution of the different terms to the total polarizability. The method developed is quite general and equally applicable to atoms and molecules. Studies of the variation of polarizability with frequency of the radiation reveals certain limitations of the perturbation treatment and also of Koopman's theorem.
Spectroscopic Study of the Vacuum-Ultraviolet Photolysis of Matrix-Isolated HCN and Halogen Cyanides. Infrared Spectra of the Species CN and XNC
Authors: Milligan Dolphus E. , Jacox Marilyn E.
Published: January 2005

Vacuum-ultraviolet photolysis of HCN isolated in Ar and N2 matrices at 14°K is found to lead to the production of HNC in concentration sufficient for direct infrared observation of all three vibrational fundamentals. The spectrum of this species is found to be appreciably perturbed by the presence of N2. The force constants and thermodynamic properties of HNC have been revised to the values appropriate to this species in an environment free of perturbation by an adjacent N2 molecule. The free radical CN is also produced in these systems in concentration sufficient for direct observation not only of the B(2Σ+)—X(2Σ+) transition but also of the ground-state vibrational fundamental. Isotopic data supporting this identification are presented. Upon vacuum-ultraviolet photolysis of matrix-isolated FCN, two infrared absorptions appear which can be identified with the stretching fundamentals of the species FNC. In analogous experiments on the species ClCN and BrCN, infrared absorptions tentatively assigned to ClNC and BrNC have been observed.
Unipolar Diffusion Charging of Small Aerosol Particles
Authors: Gentry J. , Brock J. R.
Published: January 2005

A theory for unipolar ``diffusion charging'' of small aerosol particles is developed for the free-molecule and transition regions. The free-molecule theory is, of course, exact within the restrictions imposed on the physical system. The theory for the transition region is based on the Knudsen iteration solution of a relaxation model of the Boltzmann equation. Insufficient experimental data are available to permit detailed comparison with the developed theories.
Zone Purification of Potassium Chloride
Authors: Susman Sherman
Published: January 2005

A procedure is presented for the direct purification of untreated, stockbottle KCl by zone refining in a dilute halogen atmosphere. The distribution of Na and Br at parts-per-million concentrations is followed by neutron-activation analyses. Computer-analyzed distributions in refined ingots yield k*Na=0.53±0.03 and k*Br=0.72±0.02.
Near-Visible Absorption Spectra of the CsUO2(NO3) Crystal
Authors: Newman John B.
Published: January 2005

The near-visible absorption spectrum of a single-domain crystal of cesium uranyl nitrate at a temperature of 20°K is interpreted. Selection rules are given for a trigonally coordinated uranyl complex in a crystal having two molecules per unit cell. Lower lying levels, whose excitation gives rise to the fluorescent and magnetic series, are assigned as the A2 and E species of the D3 point group. Given these assignments, absorption between levels exhibiting the strongest fluorescence occurs only by allowed quadrupole transitions; a vibronic interaction is suggested to account for the radiative decay rates. Certain higher levels are assigned alternately, in pairs, to the A2g and A2u species of the D3d point group as a consequence of the intermolecular interaction in the unit cell. Estimates of the strengths of the various interactions considered are required and, as a first step, the singlet—triplet intervals for two uranyl models are calculated and found to be comparable with, or less than, the spin—orbit splitting.
Temperature Dependence of the Nuclear Quadrupole Resonance Frequency of 35Cl in KClO3 between 12° and 90°K
Authors: Utton D. B.
Published: January 2005

A precise measurement of the temperature dependence of the NQR frequency of 35Cl in KClO3 has been made at constant pressure in the range 12°—90°K. Analysis using the Bayer—Kushida theory predicts lattice modes at 60 and 126 cm−1. A comparison is made with the Raman spectrum.
Magnetic Transition of Wurster's Blue Perchlorate. III. The Nature of the Transition
Authors: Pott Gerard T. , van Bruggen Chris F. , Kommandeur Jan
Published: January 2005

The anomalous magnetic susceptibility of the low-temperature phase of Wurster's blue perchlorate can be explained on the model of the inequivalent ion pair. Quantitative agreement between the calculated and experimental susceptibilities, between the calculated and experimental heat of transition, as well as between the calculated and experimental integrated difference in enthalpy content of the high- and low-temperature phase has been obtained. The statistics to be used depend on an assumption about the way in which triplets can be formed in this system. In general, a system in which any pair of ions can form a triplet is favored.
Crystal Structure of Manganese (II) and Cobalt (II) Bromide Dihydrate
Authors: Morosin B.
Published: January 2005

The crystal structures at 298°K of MnBr2·2H2O and CoBr2·2H2O have been refined by full-matrix least-squares methods using three-dimensional MoKα intensity data. In these compounds, polymeric chains of metal and bromine atoms arranged in a near-square planar arrangement with each bromine atom shared by two metal atoms parallel the c axis. The water molecules which fill the remaining octahedral positions about the metal atom provide hydrogen bonds to link adjacent chains.
Experimental and Theoretical Study of Sigma-Bond Electronic Transitions in Alkanes
Authors: Raymonda John W. , Simpson William T.
Published: January 2005

Sigma-bond electronic transitions in alkanes have been investigated both experimentally and theoretically. Vacuum ultraviolet spectra of a large number of alkanes have been recorded in the range 50 to 94 kK and absorption intensities as well as frequencies have been determined. The implications of vapor-phase conformational isomerism are discussed. A qualitative interpretation of the observed spectra has been developed using independent-systems theory in connection with a simple model in which excitations in only C–C bonds are considered. A reasonably good topological matching between theory and experiment is achieved. A quantitative theory in which C–H bond excitations are included has also been developed. With this theory parameters are derived from the spectra of methane and ethane which prove sufficient to describe the higher alkanes without recourse to ``fitting.'' The theoretical procedures used are outlined in the text and described in greater detail in an Appendix.
Thermal Diffusion in Hydrogen—Helium Gas Mixture
Authors: Ghosh A. K. , Batabyal A. K. , Barua A. K.
Published: January 2005

The composition dependence of the thermal-diffusion factor for the hydrogen—helium system has been studied by a trennschaukel. Like thermal conductivity, the thermal-diffusion-vs-composition curve for this particular system shows a pronounced minimum. It has been suggested that probably the effects of inelastic collisions are responsible for the apparently anomalous behavior.
Quantum Mechanics of One-Dimensional Two-Particle Models. Electrons Interacting in an Infinite Square Well
Authors: Diestler Dennis J. , McKoy Vincent
Published: January 2005

Solutions of Schrödinger's equation for the system of two particles bound in a one-dimensional infinite square well and repelling each other with a Coulomb force are obtained by the method of finite differences. For the case of a 4.0-a.u. well, the energy levels are shifted above those of the noninteracting-particle model by as much as a factor of 4 although the excitation energies are only about 50% greater. The analytical form of the solutions is also obtained and it is shown that every eigenstate is doubly degenerate due to the ``pathological'' nature of the one-dimensional Coulomb potential. This degeneracy is verified numerically by the finite-difference method. The properties of the model system are compared with those of the free-electron and hard-sphere models; perturbation and variational treatments are also carried out using the hard-sphere Hamiltonian as a zeroth-order approximation. The lowest several finite-difference eigenvalues converge from below with decreasing mesh size to energies below those of the ``best'' linear variational function consisting of hard-sphere eigenfunctions. The finite-difference solutions in general give expectation values and matrix elements more accurately than do the other approximations.
Mechanisms of Energy Transfer Involving Trivalent Tb and Nd in Sodium Rare-Earth Tungstates
Authors: Van Uitert L. G. , Dearborn E. F. , Rubin J. J.
Published: January 2005

Self-quenching of Nd emission from Nd4F3/2 in the Na0.5(Y, Nd)0.5WO4 tungstates (scheelite structure) and transfer from Nd4F3/2 to Tb or Eu involves dipole—dipole interactions. Self-quenching of Nd is largely by thermally activated interactions at 295°K. However, processes requiring the simultaneous transfer of ∼600 cm−1 to the phonon spectrum are indicated for reduced temperatures. Radiative transfer between Nd ions and excitation migration between exchange coupled Tb ions to Nd sinks are observed also. Transfer from Tb to Nd from either Tb5D3 or Tb5D4 is by dipole—quadrupole interactions. Corrections for self-quenching, internal conversion, and excessive drain time to the excited level of interest are discussed.
Antiferromagnetic and Crystal Structures of Alpha-Oxygen
Authors: Barrett C. S. , Meyer L. , Wasserman J.
Published: January 2005

X-ray diffractometer data from polycrystalline samples of alpha-oxygen frozen from the liquid are accounted for by a monoclinic structure: space group C2/m, b axis unique, a = 5.403±0.005, b = 3.429±0.003, c = 5.086±0.005 Å; β = 132.53±0.04°; volume = 69.44 Å3; calculated density = 1.530 g/cm3. The cell contains two molecules centered at the lattice points 000 and ½½0, which are symmetry centers. The atoms are at positions x, 0, z; x̄, 0, z̄; ½+x, ½, z; ½—x, ½, z̄, with x = 0.089±0.01, z=0.153±0.015. The nearest center-to-center distances between molecules is 3.20 Å and the 0–0 bonds are found to be perpendicular to the ab plane within an experimental accuracy of a few degrees.

The published neutron diffraction data, interpreted on the basis of the structure, imply that the antiferromagnetic structure consists of antiparallel moments at 000 and ½½0.
Thermodynamics with Internal State Variables
Authors: Coleman Bernard D. , Gurtin Morton E.
Published: January 2005

This is a study of the thermodynamics of nonlinear materials with internal state variables whose temporal evolution is governed by ordinary differential equations. After employing a method developed by Coleman and Noll to find the general restrictions which the Clausius—Duhem inequality places on response functions, we analyze various types of dynamical stability that can be exhibited by solutions of the internal evolution equations. We also discuss integral dissipation inequalities, conditions under which temperatures can be associated with internal states, and the forms taken by response functions when the material is a fluid.
Dimethylacetylene: An Analysis of the Theory Required to Interpret Its Vibrational Spectrum
Authors: Bunker Philip R.
Published: January 2005

The extant theory concerning the interpretation of the infrared and Raman spectrum of dimethylacetylene is summarized. This theory is extended and the symmetry group, symmetry coordinates, and the symmetry properties of the normal coordinates are all discussed. The usual G matrix theory and FG matrix method for the determination of force constants and normal coordinates has to be modified and the G matrix most useful for the calculations is derived. Detailed expressions are obtained for the energy levels of the first excited state of each of the normal vibrations; it is shown that the approximate expressions previously derived in the literature by Howard, Mills and Thompson, Kirtman, and Bunker and Longuet-Higgins can be obtained from these more exact expressions. Finally the infrared and Raman selection rules are summarized and band shapes are discussed.
Adsorption of Nitrogen on Single-Crystal Faces of Tungsten
Authors: van Oostrom A.
Published: January 2005

Work functions of the (110), (100), and (111) regions of a thermally annealed tungsten field emitter were measured as a function of nitrogen coverage. The experiments were carried out with the emitter at 79° and 295°K, using the probe—hole technique with a Faraday cage. It is shown that faces deviating even less than 10° from a flat plane often show considerable differences in behavior on nitrogen adsorption. This is concluded from changes in work function as well as in the pre-exponential term of the Fowler—Nordheim equation. A simple model is outlined which is in qualitative agreement with the experimental results. Quantitatively the situation is more complicated, as several quantities are not precisely known and some basic assumptions have to be made. However, in general, there exists quite a reasonable correlation between surface structure on the one hand and changes in work function and pre-exponential term on the other.
Electron Binding Energies for Highly Ionized Fission-Fragment Atoms
Authors: Watson R. L. , Rasmussen J. O.
Published: January 2005

Due to the large velocities attained by fission fragments immediately upon fissioning, they are unable to carry along many of their outer orbital electrons and hence become highly ionized. The state of ionization in turn directly affects the binding energies of the various remaining electrons. We have calculated the K- and L-electron binding energies for the typical fission fragment atoms Sr, Pd, Xe, and Sm in a number of ionic charge states ranging from the neutral state to the single-electron state (ionic charge of Z−1). These calculated binding energies have been used to determine an empirical formula for computing the binding energies of atoms from Z=34 to Z=66 in any state of ionization with an estimated accuracy of ±80 eV. It was found that the K and L binding energies are both increased over the neutral atomic values by approximately 0.9 keV for the most probable ionic charges of the fission fragments (20+ to 26+), and consequently that the K x-ray energies are almost unaffected.
WKB Calculation of the Energy Levels of Anharmonic Oscillators
Authors: Lu Pao
Published: January 2005

The WKB approximations in the calculation of the energy levels of the mixed harmonic—quartic oscillator are presented by using Miller and Good's modified version of this method. The results indicate that very close energy eigenvalues in comparison with the exact calculation results given by Chan, Stelman, and Thompson can be obtained with the exception of the ground state. If the harmonic oscillator is chosen as a base, the Miller and Good method coincides with the ordinary WKB method. If the quartic oscillator is used as a base, their method gives better eigenvalues than the ordinary WKB method does.
Study of Some Trapped Hole Centers in X-Irradiated Alkali Silicate Glasses
Authors: Schreurs J. W. H.
Published: January 2005

A detailed study has been made of the EPR spectra of trapped hole centers formed by x irradiation in alkali silicate glasses. The spectra of the five alkali silicate glasses were studied as a function of composition, microwave power, and bleaching temperature. It was found that the spectra could be decomposed into two separate hole spectra. The intensity ratio of these two spectra depends on the alkali-to-silica ratio. The center more abundant in the low-alkali silicate glasses is called Hole Center 1, HC1; the center more abundant in the high-alkali silicate glasses is called HC2. Helpful in separating the two spectra was a dual cavity technique, which makes it possible to obtain sum and difference spectra. The spectra of both centers are fundamentally the same in all alkali silicate glasses, but differences in detail are shown to be due to a relatively small interaction with neighboring alkali ions. Both centers show a distribution in the thermal stability and associated spectral parameters. The proposed model for HC1 is a hole located on a Si–O tetrahedron with two nonbridging oxygens, and with the hole presumably largely restricted to these nonbridging oxygens. The proposed model for HC2 is quite similar, but the tetrahedron now has three nonbridging oxygens. A comparison of the optical and EPR difference spectrum of two potassium silicate glasses with different (K2O)-to-(SiO2) ratios suggests that the 475-nm optical absorption band may be due to HC1.
Energy Transfer and Collisional Deactivation in the Reactions between D3+ Ions and the Hydrocarbons
Authors: Aquilanti V. , Galli A. , Volpi G. G.
Published: January 2005

D+-transfer reactions from D3+ ions to alkanes and alkenes up to C4 have been studied by mass spectrometry in the deuterium pressure range from 0.1 to 1.0 torr and at field strengths between 1.7 and 42 V/cm. Deuteronated ions can, in general, be formed in different states, and all decompose along exothermic patterns. Collisional deactivation at the highest pressures can prevent the dissociation of states with lifetimes longer than 10−8 sec, while kinetic-to-internal energy transfer may contribute to populate those states which lead to faster dissociations.
Low-Frequency Raman Lines from Liquid Benzene, Benzene Derivatives, and Other Organic Liquids
Authors: Blatz L. A.
Published: January 2005

Recently it has been possible to study some heretofore unobserved low-frequency Raman lines from liquids. This study is concerned with some of these low-frequency lines which occur mainly in the 30- to 85-cm−1 region. The effects on these lines of temperature variations, different solvents, deuterium, and other substitutions, and dissolved salts are given. The depolarization ratios of the low-frequency line from benzene and toluene (also carbon tetrachloride) are given. Approximate half-widths and intensities relative to the benzene 75-cm−1 line are given. Some other newly observed low-frequency Raman lines are reported, including those from liquid and solid polystyrene. Evidence from this work indicates these low-frequency Raman lines probably arise from intermolecular vibrations in liquids. The results can be interpreted on the basis of a somewhat disordered solid (quasicrystalline) structure for liquid benzene, and for some other liquids.
Magnetic Resonance Studies on Copper (II) Complex Ions in Solution. III. NMR and EPR in Concentrated Ethylenediamine Solutions
Authors: Alei Mohammed , Lewis W. Burton , Denison Arthur B. , Morgan L. O.
Published: January 2005

Measurements of the proton and 14N NMR linewidths in ethylenediamine—water solutions of Cu(II) combined with EPR studies of Cu(II) in these media demonstrate that the first sphere relaxation and residence times both make singificant contributions to the over-all relaxation of protons and 14N by Cu(II). Moreover, the results are consistent with the view that protons and 14N both experience the Cu(II) evironment through exchange of the ethylenediamine molecule as a whole between the bulk solvent and the Cu(II) first sphere. From the temperature dependence of the Cu(II) EPR linewidth it is further concluded that the relaxation of the electron spin occurs predominantly via the spin—rotational process at higher temperatures. At lower temperatures the EPR linewidth is broadened both by tumbling of a tetragonally distorted complex with an anisotropic g factor and hyperfine coupling constant and by the same fast chemical exchange process which provides 14N and proton relaxation in ethylenediamine.
Vibrational Spectra and Assignment of Iodine Pentafluoride: Fermi Resonance between a Fundamental and a Ternary Combination
Authors: Gillespie R. J. , Clase H. J.
Published: January 2005

The Raman spectrum of liquid iodine pentafluoride has been redetermined. The partial Raman spectrum of the solid and partial infrared spectra of both condensed phases are reported for the first time. It is shown that the molecule can be assigned on the basis of C4v symmetry only if one of the observed polarized Raman lines is not a fundamental, and it is suggested that the strong polarized doublet at ∼700 cm−1 is caused by Fermi resonance between ν1 and the ternary combination 2ν9+ν3.
Study of the Rydberg States of H2
Authors: Hazi Andrew U. , Rice Stuart A.
Published: January 2005

In this paper we apply a formalism based on an effective one-electron Hamiltonian to the Rydberg states of H2. It is assumed that the core can be represented by the ground-state wavefunction of H2+. The energies of the 3Σg, 3Σu, 1Σu, 3Πu, and 1Πu states have been calculated at RAB=2.0 a.u. The good agreement between theory and experiment obtained for the 3Σg, 3Σu, 3Πu, and 1Πu states indicates that the frozen-core approximation gives an accurate description of these states. We examine the discrepancy between theory and experiment in the case of the 1Σu states and suggest a criterion to determine the applicability of the frozen-core approximation to Rydberg states of diatomic molecules.
Molecular Origin of the Optical Rotatory Dispersion of the Benzil Crystal
Authors: Chaudhuri N. K. , El-Sayed M. A.
Published: January 2005

The absorption spectrum and its relative polarization, the optical-rotatory-dispersion (ORD) spectrum, and the circular-dichroism spectrum (CD) of thin benzil single crystals grown perpendicular to the optic axis, are obtained and compared in the 3000–7000- Å region. The CD spectrum shows two main bands that correspond to the absorption bands with maxima at 3325 and 3850 Å. These two bands result from transitions that are found to have similar signs for the Cotton effect, but opposite to that of the strong optically active transition at 2400 Å and responsible for the plain curve on the longer-wavelength side of the absorption edge. The bands at 3325 and 3850 Å have similar values for the dissymmetry factor g, comparable absorption intensity, and similar relative orientation of their transition moments. From the observed value of the g factor, the two bands seem to result from magnetic-dipole-allowed transitions. These observations suggest the assignment of these two bands to the two split components of the n,π* transitions resulting from the intramolecular interaction between the two carbonyl groups of the benzoyl units in the benzil molecule. The CD spectrum assists in understanding the shape of the ORD spectrum, including the minimum on the longer-wavelength side of the absorption edge, that was previously observed, but not explained. An extremely weak band is observed in the CD spectrum of thick single benzil crystals at above 4250 Å, whose origin is briefly discussed. A comparison is made between predicted polarization characteristics, using an independent-model approach, and the observed properties of the split components of the molecular n, π* transition in the crystal. The disagreement is discussed in terms of mixing between the two molecular n, π* states with each other and with the other molecular (or crystal) states.
Absence of a Volume Change upon Dilution of Dilute Sodium—Ammonia Solutions at −45° and Potassium—Ammonia Solutions at −34°
Authors: Gunn Stuart R.
Published: January 2005

Dilatometric measurements of the volume change upon mixing metal—ammonia solutions at concentrations from 0.01 to 0.06N with an approximately equal quantity of pure ammonia have been performed. The observed changes for both sodium solutions at −45° and potassium solutions at −34° are essentially zero throughout the concentration range, and provide no support for existence of sharp minima in the apparent molar volumes at ∼0.02N which have been reported by other workers.
Deuterium Isotopic Disproportionation Reactions: The Ammonia System as Studied with a Pulsed-Molecular-Beam Mass Spectrometer
Authors: Pyper J. W. , Newbury R. S. , Barton G. W.
Published: January 2005

Deuterium disproportionation equilibria in the ammonia system were studied at 0° and 25° with a pulsed-molecular-beam mass spectrometer. The equilibrium constant for the reaction NH3+ND3=NH2D+NHD2 was found to be 8.29±0.25 at 0° as compared with a statistical value of 9. The experimental results are shown to be consistent with theoretical calculations and similar measurements in the water system.
Photodissociation as Studied by Photolysis Mapping
Authors: Solomon Jack
Published: January 2005

We describe a method, called photolysis mapping, which can determine the orientation of the transition moment for gas-phase photodissociations. This method measures the flux of fragments at the wall of a hemisphere when plane-polarized light photodissociates a molecular gas. If the fragments recoil perpendicular to the transition moment, the angular dependence of the flux at the wall is different than if the fragments recoil parallel to the transition moment. Photolysis-mapping experiments for bromine and iodine photolyzed with visible light indicate that the atoms recoil perpendicular to the transition moment.
Simple AMO Function for the Lithium Molecule
Authors: Rai D. K. , Calais J.-L.
Published: January 2005

An AMO calculation for the ground state of the Li2 molecule is described. The calculations are very simple, but quite satisfactory results are obtained. Connections with other calculations are pointed out and certain interesting problems connected with the Li2 molecule and related molecules for which the AMO method might be useful, are discussed.
Calculation of the Barrier to Internal Rotation in Ethane with Improved Exponential Wavefunctions
Authors: Pitzer Russell M.
Published: January 2005

A minimum set of Slater exponential orbitals is used to construct molecular orbital wavefunctions for staggered and eclipsed ethane. The orbital exponents chosen are those which are optimum for methane, rather than those obtained from Slater's rules, as were used previously. The value of the internal rotation barrier is calculated to be 3.5 kcal/mole. Comparison with other calculations indicates that the barrier is fairly insensitive to choice of basis functions and to the value of the total energy.
Infrared Transmission Spectrum and Lattice Vibration Analysis of Some Perovskite Fluorides
Authors: Nakagawa Ichiro , Tsuchida Atsushi , Shimanouchi Takehiko
Published: January 2005

Infrared absorption spectra of the perovskite fluorides KMF3(M:Ni, Mg, and Zn) and NaNiF3 have been measured in the region 700 to 50 cm−1 at room temperature and liquid-nitrogen temperature. Three absorption bands for KMF3 were observed and these have been assigned to the f1u lattice modes. A normal-coordinate analysis of the crystal as a whole has been performed and the interatomic force constants in the crystal have been obtained. The forms of the normal modes of the lattice vibrations have been fully described on the basis of the normal-coordinate treatment. Vibrational assignments have been supported from the experimental ground (temperature effect) and the theoretical side. The compound NaNiF3 reveals a much more complicated spectrum than those of KMF3, which suggests a structure of an appreciable deformation from the regular cubic perovskite. The analysis of the lattice vibrations for the rutile counterparts has been made based on the normal-coordinate treatment by the use of the force constants transferred from the corresponding perovskite. The result gives another evidence for the lattice vibration assignments of the perovskite fluorides.
Crystal Structure of Ferric Chloride Hexahydrate
Authors: Lind M. D.
Published: January 2005

The crystal structure of ferric chloride hexahydrate has been determined from three-dimensional single-crystal x-ray-diffraction data. In the crystals two chloride ions and four water molecules are arranged around each ferric ion to form octahedral trans-[FeCl2(OH2)4]+ ions with C2h−2/m symmetry. Fe–Cl and Fe–OH2 interatomic distances in the complex ion are 2.30±0.02 Å and 2.07±0.02 Å, respectively. The crystals are monoclinic, space group C2h3—C2/m, with a=11.89±0.02, b=7.05±0.01, c=5.99±0.01 Å, and β=100.5±0.2°. The unit cell contains two [FeCl2(OH2)4]Cl·2H2O units. The arrangement of the [FeCl2(OH2)4]+ ions, chloride ions, and water molecules in the crystals indicates hydrogen bonding in addition to the electrostatic forces between oppositely charged ions.
Atomic Z Expansions and Electronic Structure of Molecules: Second-Order One-Center Calculation of the Hydrogen-Molecule Ground State
Authors: Dvořáček Zbyněk , Horák Zdeněk
Published: January 2005

Double-perturbation theory is applied to calculate the ground state of the hydrogen molecule. In this treatment the unperturbed system is formed by the two noninteracting electrons moving in the field of a virtual nucleus of charge Z located halfway between the two hydrogen nuclei. The rest of the molecular Hamiltonian—electronic repulsion and the part of the electron—nuclear attraction—is treated as a perturbation. We determine the virtual charge Z from the variational principle for the total energy through first order. With this approach the total molecular energy of H2 can be built up from the energy Z expansion of (1s)2 1S, twice the exact electronic energy of 1sσ H2+, and correction terms of second and higher orders. Using the published results for (1s)2 1S and 1sσ H2+ we calculate the second-order corrections to get the equilibrium distance within 4% of the very accurate result obtained by Kol/os and Roothaan; our dissociation energy is 4.207 eV, 11% smaller than their value 4.747 eV.
Polyhedral Clathrate Hydrates. XIV. The Structure of (CH3)3CNH2·9¾H2O
Authors: McMullan R. K. , Jeffrey G. A. , Jordan Truman H.
Published: January 2005

The crystal structure of 16(CH3)3CNH2·156H2O has been determined from three-dimensional x-ray-diffraction data obtained at −30°C. The crystals are cubic, space group I4̄3d, with cell dimensions a=18.81±0.02 Å. The host framework of hydrogen-bonded water molecules consists of face-sharing heptakaidecahedra which have three square, nine pentagonal, two hexagonal and three heptagonal faces. The square and pentagonal faces also form octahedra which complete the space-filling arrangement. The amine molecules occupy the larger polyhedra as nonbonded guests undergoing marked oscillatory motion.
On a Theory of Absolute Reaction Rates
Authors: Coulson C. A. , Levine R. D.
Published: January 2005

The methods of multichannel collision theory are used to introduce a yield operator Y which is an observable that determines the rate and yield of a reaction. When the reactants are characterized by a statistical operator U0, the reaction rate can be written as Tr(U0Y)/Tr(U0). By using Heisenberg's equation of motion it is possible to extend the formalism by introducing a yield operator YA that determines the rate of change of any measurable operator A in a system undergoing reactions. It is suggested to base semiempirical theories on approximations to the yield operator. Towards this aim the Arrhenius parameterization of the rate of thermal bimolecular reactions is discussed, and alternative forms for the yield operator are exhibited.
Perturbation Treatment of the Ground State of the Hydrogen Molecule
Authors: Goodisman Jerry
Published: January 2005

Perturbation theory is used to obtain approximate energies and wavefunctions for the hydrogen molecule ground state. A function of simple form is chosen as zero-order function, the zero-order Hamiltonian is constructed, and the variational equation for the first-order wavefunction is solved approximately by expansion in James—Coolidge basis functions, yielding the second- and third-order energies. All integrals are calculated numerically. The binding energy and equilibrium internuclear distance are fair, but not as good as what one obtains from a comparable variational calculation.
Spin Exchange in Nitroxide Biradicals
Authors: Glarum Sivert H. , Marshall James H.
Published: January 2005

The dependence of the electron spin-exchange energy upon temperature and solvent has been studied for the carbonate, oxalate, and succinate diesters of tetramethyl-piperidinol-oxyl. An analysis is given of exchange effects on ESR line positions, intensities, and widths. For the carbonate diester the exchange energy is constant at low temperatures. As the temperature is raised this energy gradually decreases, passes through a minimum, and then increases exponentially. Interpretation suggests that at low temperatures exchange occurs through an indirect process involving the core of sigma electrons, whereas at high temperatures a direct exchange process is more important.
Seebeck Coefficient of Semiconducting Oxide Glasses
Authors: Allersma T. , Mackenzie J. D.
Published: January 2005

The Seebeck coefficient, α, of semiconducting glasses based on vanadium pentoxide can be calculated from a knowledge of the concentration ratio of the high and low valence ions. The concentration of vanadium ions in the glass and long-range order apparently have no effect on α. Semiconducting glasses based on iron oxide, however, are not amenable to the simple treatment presently developed.
Indirect Spin Saturation via Spin—Spin Interaction. I. AB+C System
Authors: Fung B. M.
Published: January 2005

The effect of nuclear magnetic double resonance on an AB+C system, in which A is in chemical exchange with C, is discussed. A strong irradiation at C causes the spin states of A to saturate, while the splitting of B by A is not influenced. When the chemical shift between A and B (ν0δAB) is comparable to their coupling constant (JAB), the indirect spin saturation of A may in turn cause B to saturate via spin—spin interaction. An expression for the ratio of intensity of the AB system after and before irradiating C is obtained in terms of ν0δAB, JAB, and factors accounting for the rate of exchange and relaxation time.
Some Properties of Semiempirical Hamiltonians
Authors: Koutecký Jaroslav
Published: January 2005

The Hamiltonian used in semiempirical Pariser—Parr—Pople (PPP)-type treatments is put in a form such that (a) the parameters on which correlation effects depend become obvious, and (b) the part of the Hamiltonian responsible for deviations from pairing properties of conjugated heterocycles with alternant topology is isolated. A set of approximate rules based on this analysis is derived. The rules concerning the extent of correlation effects are compared for some conjugated hydrocarbons with computations by full configuration interaction in the π-electron approximation. Generalizations are derived of known conditions under which heterocyclic systems are paired. The character of the two first excited states of heteroanalogs and heteroderivatives of alternant hydrocarbons is discussed, and rules determining deviations from the behavior of parent alternant hydrocarbons are formulated. This makes it possible to predict the polarizations of the first two transitions in these compounds in the PPP approximation with limited configuration interaction. The predictions are compared with some results of calculations on azines and amines.
Metastable Molecules in a Nitrogen Afterglow
Authors: Dugan C. H.
Published: January 2005

The electronic metastable molecules in a nitrogen afterglow were sampled by detecting them in a thermalvelocity neutral beam extracted from the glow. Their variation as a function of time in the afterglow was compared with variations of N2 first positive and N2+ first negative emission from the glow. Variation of the former spectral feature may be interpreted as direct support for the recent suggestions (based on indirect evidence) that the process N2(A 3Σu+)+N→N2(X 1Σ)+N is fast. Variation of light from the ion suggests there is no direct connection between the concentration of metastable molecules and the production of excited ions. In an afterglow at 7 torr pressure, two different methods of determining the concentrations of metastable molecules yield very different results: 4×109 cm−3 as a lower limit and 2×1012 cm−3 as an upper limit. These values are discussed.
Chemical Role of Holes and Electrons in ZnO Photocatalysis
Authors: Morrison S. R. , Freund T.
Published: January 2005

The role of the electronic properties of a semiconductor in heterogeneous catalysis and electrochemistry was experimentally investigated on single-crystal ZnO. It was shown quantitatively that the availability of electrons and holes at the surface is dominant in the mechanism of a heterogeneously catalyzed reaction. Chemical rate measurements as well as in situ solid-state measurements were carried out in an aqueous medium for the reaction: HCOOH+O2→H2O2+CO2, photocatalyzed by ZnO. Two new experimental electrochemical methods for semiconductor surface reactions were developed: ``current doubling'' and measurement of ``unfilled'' electronic surface states by the capacitance. They were devised to characterize reactive sorbed species. The detailed catalytic mechanism was based on studies of individual reaction steps under three solid-state surface conditions: (1) only holes reacting, (2) only electrons reacting, and (3) both holes and electrons reacting. The first two correspond to the ZnO being an electrochemical anode and cathode, respectively; the last corresponds to ordinary catalysis when the hole current is balanced by the electron current so that the net current is zero. It was shown that the over-all catalyzed reaction is not simply the sum of individual oxidation and reduction reactions which occur with only holes or only electrons, respectively, but involves a surface intermediate formed when both holes and electrons are present.
Theory of Zeeman Effect for Rare-Earth Ions in Crystal Field with C3h Symmetry. II
Authors: Murao Tsuyoshi , Haas W. J. , Syme R. W. G. , Spedding F. H. , Good R. H.
Published: January 2005

Rare-earth ions in ethyl sulfate crystals give rise to sharp-line optical absorption spectra. In this paper a part of the theory of the Zeeman effect for these lines is developed. The case when the crystal-field and Zeeman splittings are comparable is treated; this is a frequent experimental situation. Only magnetic fields in the basal plane are considered. There is then an antiunitary symmetry operation which leads to simplifications in the energy-level calculations and to the assignment of a quantum number ξ=±1 to the states. A selection rule for electric-dipole transitions is found that shows that the matrix element is real or pure imaginary, depending on the initial and final ξ numbers. Furthermore, the states are found to be of two kinds: Type A, in which the assignment of ξ number to the state does not depend on the choice of coordinate axes, and Type B, in which it does. The possibility of an effective D3h symmetry applying in the optical absorption problem is analyzed. Then the dependence of absorption intensity on magnetic-field direction for transitions between different types of states is found to be qualitatively different from that for transitions between the same types of states.
Deuteron Magnetic Resonance Study of LiOD
Authors: Chiba Takehiko
Published: January 2005

Deuteron magnetic resonance is measured on a LiOD single crystal, and deuteron quadrupole coupling is determined at various temperatures from 77° to 683°K. The quadrupole coupling constant at 77°K is 327.0 kc/sec. From a point-charge calculation it is concluded that the deuteron quadrupole coupling is almost entirely intraionic in origin. The value appears to represent a quadrupole coupling for a non-hydrogen-bonded O—D bond. The agreement of the field gradient at D with the force constant of the OH stretching vibration of LiOH is excellent. The temperature dependence of the field gradient can be explained by the OD libration of 330 cm−1, which is somewhat higher than the librational frequencies determined by spectroscopy. No appreciable anharmonicity of the librational oscillation is indicated in the temperature range of observations. The rotational motion of OH− in LiOH is unlikely. The 7Li quadrupole coupling is also determined at room temperature and at 683°K. The quadrupole coupling constant at room temperature is 94.5 kc/sec.
Temperature Dependence of the Raman Spectrum of SrTiO3 and KTaO3
Authors: Perry C. H. , Fertel Jeanne H. , McNelly T. F.
Published: January 2005

The temperature dependence of the second-order Raman spectrum of SrTiO3 and KTaO3 has been observed over the temperature range 4°—473°K using the mercury 4358-Å exciting line. From group-theoretical arguments for cubic perovskite lattices the spectra have been interpreted in terms of phonon pairs at critical points in the Brillouin zone using the experimental and theoretical dispersion curves determined by Cowley for SrTiO3. Limited neutron data are available for KTaO3, but the spectrum has been interpreted by analogy with the results for SrTiO3. The energies of the phonon branches at the critical X point in the Brillouin zone have been deduced from the observed Raman spectra.
Pressure Dependence of the Diffusion Thermoeffect in Gases (Dufour Effect)
Authors: Mason E. A. , Miller L. , Spurling T. H.
Published: January 2005

A modified Loschmidt apparatus for the measurement of the diffusion thermoeffect as a function of pressure is described. Measurements are reported for H2–Ar, H2–CO2, and H2–CH4 for pressures between 1 and 20 atm at room temperature. The experimental results have been explained semiquantitatively in terms of the pressure dependence of the relevant transport coefficients and their first composition derivatives. Terms arising because of the nonideality of the gases are also included in the phenomenological description. Relative values of diffusion coefficients for the three systems determined from the measurements are in good agreement with those determined by other methods, and the effect of pressure on the diffusion thermoeffect parallels the pressure dependence of the thermal diffusion factor as determined from gas-unmixing measurements. Suggestions are made for the future use of the method in determining other transport coefficients.
EPR Studies of Mo(CN)5NO3−: Magnetic Parameters and Analysis of the Ligand Hyperfine Structure
Authors: Hayes Robert G.
Published: January 2005

We have observed the EPR spectrum of the ion Mo(CN)5NO3− under various conditions and have satisfied ourselves that the given formulation is correct. Our best set of magnetic parameters, for the ion in K3Co(CN)6, is: g∥=1.9736, g⊥=2.0168, A∥(Mo)=163.2 Mc/sec, A⊥=76.4 Mc/sec. We have observed an extensive ligand hyperfine structure at 77°K, which we have assigned to 14N in the nitrosyl and in the equatorial cyanides. We find the 14NO hyperfine tensor to have axial symmetry about the figure axis of the complex, with principal values A∥=3.81 Mc/sec, A⊥=11.30 Mc/sec. We find the C14N hyperfine tensor to have approximate axial symmetry about an axis perpendicular to both the figure axis of the complex and the Mo–C–N bond axis, with principal values A∥=+6.62 Mc/sec, A⊥=−1 Mc/sec. We thus find the fraction of unpaired electron delocalized onto the nitrogen of each cyanide to be 0.053.
Quantum Mechanics of the H2–H2 Interaction. II. A Full Valence-Bond Calculation
Authors: Magnasco V. , Musso G. F.
Published: January 2005

The valence-bond theory of molecular structure in its rigorous formulation is applied to investigate the orientation dependence of the short-range interaction energy for two H2 molecules in their ground state. The electronic wavefunction is extended to include all the singlet valence-bond (VB) structures arising from the minimal basis set of four 1s Slater orbitals; namely, two covalent, twelve singly polar, and six doubly polar structures having S=0 and MS=0. The occurring three- and four-center molecular integrals have been computed by numerical integration to six significant figures. The resulting intermolecular energy and the electron distribution within the system are compared with those obtained in a preceding paper (Part I) using a wavefunction restricted to nine VB structures drawn from the same set of atomic orbitals after symmetrical orthogonalization. The present unrestricted calculation results not only in a much lower intermolecular energy than that obtained in I, but also in a substantially larger orientation dependence of the interaction. Since no orthogonality restriction is implied in the full valence-bond wavefunction, the forced orthogonalization of the atomic-orbital basis appears to be a rather severe constraint with electronic wavefunctions of a restricted form.