bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of the Low-Temperature Phase Transition in Solid Methane by Slow Neutron Inelastic Scattering
Authors: Harker Y. D. , Brugger R. M.
Published: January 2005

Slow neutron scattering measurements have been performed on a sample of solid methane at temperatures of 5°, 9.1°, 18°, and 22.1°K. The objective of these measurements was to try to observe differences in the spectra of neutrons scattered from the three phases of solid CH4 above and below the two transition temperatures at 8° and 20.4°K. Whereas definite differences were not observed above and below the 8°K transition, the spectra of scattered neutrons displayed significant changes above and below the 20.4°K transition. The most dramatic differences are in the elastic scattering peakwidths which are narrow and momentum change independent for the two low-temperature phases, while the widths of these peaks for the 22°K data are broader and broaden with increasing momentum change. A comparison of the 22°K data with ``Griffing's discrete rotation gas model'' discounts the possibility of free rotational motion existing at this temperature.

The inelastic scattering data for all four temperatures were fit with calculated curves generated from adjusted frequency spectra. These spectra do not display such dramatic differences as are observed in the elastic peaks. The spectra for the sets of data at the three lower temperatures do show more structure than the spectrum from the 22°K data with peaks at approximately ℏω=6, 9, and 12 meV.
New Absorption Spectra of Atomic and Molecular Oxygen in the Vacuum Ultraviolet. I. Rydberg Series from O I Ground State and New Excited O2 Bands
Authors: Huffman R. E. , Larrabee J. C. , Tanaka Y.
Published: January 2005

Absorption series of ground-state atomic oxygen (3P2,1,0) and new O2 bands in discharged He–O2 mixtures have been observed in the 600–1000-Å wavelength region. The O I spectrum consists of the nine allowed Rydberg series converging to the three lowest states of O II: 4S3/20, 2D5/2,3/20, and 2P3/2,1/20. The series observed were as follows: 2p3(4S0)ns 3S0; 2p3(4S0)nd 3D0; 2p3(2D0)ns′ 3D0;2p3(2D0)nd′ 3S0; 2p3(2D0)nd′ 3P0; 2p3(2D0)nd′ 3D0;2p3(2P0)ns′′ 3P0; 2p3(2P0)nd′′ 3P0; and 2p3(2P0)nd′′ 3D0.Measurement and classification of these lines are given. Most of the atomic-energy levels involved were not previously known. The new O2 bands are a progression of 10 members in the 835–900-Å region. A definite assignment cannot be made at present, but the lower state is either the a 1Δg or the b 1Σg+ metastable state, with the former regarded as most likely. The spectra were observed both in a flowing microwave discharge and in the region downstream from this discharge.
Study of the Isotopic Disproportionation Reaction between Light and Heavy Water Using a Pulsed-Molecular-Beam Mass Spectrometer
Authors: Pyper J. W. , Newbury R. S. , Barton G. W.
Published: January 2005

Isotopic exchange equilibrium in the disproportionation reaction H2O+D2O=2 HDO was studied at 0° and 25° and over a range of deuterium compositions using a pulsed-molecular-beam mass spectrometer. The equilibrium constant K was found to be 3.75±0.07 at both temperatures. The pulsed-beam mass spectrometer was shown to be effective in minimizing the ``memory effect'' in the mass spectrometer. The experimental K is shown to be consistent with equilibrium constants for similar isotopic disproportionation reactions and with current theory.
Infrared Spectrum of Deuterium Sulfide
Authors: Miller R. E. , Leroi G. E. , Eggers D. F.
Published: January 2005

The bending fundamental (v2) of D2S has been investigated under high resolution. Centrifugal-distortion corrections were applied in the rotational analysis, and transition intensities were computed in both the rigid-rotor approximation and with the inclusion of classical centrifugal distortion. The inertial constants arising from this analysis for the ground state are A=5.484, B=4.508, C=2.444; for the excited state they are A′=5.616, B′=4.585, C′=2.4216 cm−1, and the v2 band center is 855.45 cm−1. These results together with information derived from previous investigations of D2S and H2S have been used to evaluate the constants in the quadratic expression for the vibrational energy levels and to compute some of the constants in the general expressions for the moments of inertia as a function of vibrational quantum numbers. The experimental values of the inertia defect for the ground state and the v1 and v2 excited states are in good agreement with those predicted theoretically.
Ultraviolet Absorption Spectrum of SiF2
Authors: Khanna V. M. , Besenbruch G. , Margrave J. L.
Published: January 2005

The electronic absorption spectrum of SiF2 has been recorded in the region 2325 to 2130 Å. The principal feature of the spectrum is the presence of a long progression in the bending frequency of the upper electronic state suggesting that the bond angle F–Si–F undergoes a considerable change during transition. A number of weak bands, identified as arising from the vibrationally excited levels of the lower electronic state, are also observed. There is no definite evidence for excitation of stretching vibrations. The bending frequencies for the lower and upper electronic states are estimated as about 345 and 252 cm−1, respectively. The vibrationless transition (ν1′=0, ν2′=0, ν3′=0←ν1″=0, ν2″=0, ν3″=0) is shown to lie at about 2266.4 Å (44 109 cm−1) and is probably a 1B1←1A1 transition.
Heavy-Atom and Substituent Effects on S—T Transitions of Halogenated Carbonyl Compounds
Authors: Borkman Raymond F. , Kearns David R.
Published: January 2005

The low-lying S0→S and S0→T transitions in six substituted benzophenones and three carboxylic acid bromides have been investigated by direct absorption, phosphorescence excitation, and phosphorescence emission techniques in rigid media. In several bromine-substituted benzophenones, the oscillator strength of the S0→Tn,π transition was found to be larger by a factor of 2 to 3 than in benzophenone. However, comparison with methyl- and chlorosubstituted benzophenones indicates that this enhancement is probably due to a substituent effect rather than a specific heavy-atom effect. There was no intermolecular heavy-atom enhancement of S0→Tn,π transitions. Similar results were obtained, with acetophenone

The absorption and phosphorescence spectra of benzoyl bromide were measured, and it was concluded that the lowest triplet state of this compound is of (π, π) type.

The weak (ε=1.8) 4300-Å absorption band in oxalyl bromide has been reinvestigated. Studies of solvent effects on the absorption spectrum of oxalyl bromide and of the phosphorescence excitation spectrum of oxalyl bromide in rigid glass solutions containing naphthalene or phenanthrene confirm the assignment of the 4300-Å band as an S0→Tn,π transition. The strength of the transition ε=1.7±0.1 is, however, anomalously high as compared to all other known S0→Tn,π or S→Tπ,π transitions in organic molecules containing bromine as the heaviest atom.
Mathematical Analysis of the Thermal Wave Technique for Square-Law Kinetics
Authors: Sekerka R. F.
Published: January 2005

The thermal wave technique, originated by Kramer and Tiller to measure the relationship between interface undercooling and interface velocity during solidification, is discussed from a theoretical point of view. The different data analyses used by various workers in the field are also discussed. It is concluded that previous conflicting experiments on pure tin are inconclusive on the basis of experimental inadequacies, theoretical deficiencies, and/or scatter in the final results. An approximate theoretical solution to the thermal wave problem is obtained for the case where ν=μ′δT|δT|, where ν is interface velocity, δT is interface undercooling, and μ′ is a kinetic constant. This theory is illustrated for the case of pure tin. It is shown that the above kinetic law (square law) and the linear kinetic law, ν=μδT, lead to similar curves for the transmitted amplitude versus angular frequency of the thermal wave except at high frequencies where the transmitted amplitude is highly damped and hence difficult to measure. It is proposed that the factor Q, defined as the square of the ratio of the transmitted wave amplitude to its value for zero kinetics, be studied versus the input amplitude θω to differentiate between square-law and linear-law kinetics. Q should be independent of θω for linear kinetics but can be made, by a proper choice of experimental conditions, to vary roughly as θω−1 for square-law kinetics. Finally, in an Appendix, the Tiller—Kramer ``correction factor'' approximation is discussed in relation to the present theory.
Electric Field Effect on the Critical Opalescence. II. Relaxation Times of Concentration Fluctuations
Authors: Debye P. , Gravatt C. C. , Ieda M.
Published: January 2005

In an investigation of the effect of electric fields on the critical opalescence, time-dependent phenomena have been observed which are related to theoretical relaxation times of concentration fluctuations for a binary mixture. Rectangular dc pulses of 25 to 60 kV/cm and 10–200-μsec duration have been applied to a critical mixture nitrobenzene and 2,2,4-trimethylpentane at a series of temperatures above the critical solution temperature. Relaxation times associated with the change in the transmitted light intensity were found to be independent of the pulse width and the field strength. The relaxation times are proportional to (T—Tc)−0.9 and have magnitudes comparable with relaxation times determined from the frequency broadening of light scattered from similar binary systems. It has also been possible to extend the agreement between the Debye theory of the electric field effect on critical opalescence and the experimental results to within 0.1°C of the critical temperature.
Vibrational Spectra of PF5 and AsF5: Height of the Barrier to Internal Exchange of Fluorine Nuclei
Authors: Hoskins L. C. , Lord R. C.
Published: January 2005

The infrared spectra of gaseous PF5 and AsF5 have been obtained over the spectral range 30–2000 cm−1, and Raman spectra have been observed for the liquid state. The observed frequencies for both molecules are satisfactorily assigned on the basis of a D3h structure. A normal-coordinate calculation is made with the help of a valence-force system and simplifying assumptions about off-diagonal elements in the potential-energy matrix. An approximate potential diagram for internal exchange of axial and equatorial fluorine nuclei is evaluated from the potential constants of species E′. From the calculated exchange rates it is concluded that it is unlikely that the axial—equatorial chemical shifts in the NMR spectra of PF5 and AsF5 will be resolved at low temperatures.
Impact Broadening of the Oxygen Microwave Spectrum
Authors: Ben-Reuven A. , Lightman A.
Published: January 2005

The impact approximation is applied to the shape of the microwave spectrum of oxygen at elevated gas pressures (up to 70 atm). The absorption spectrum consists of a resonant mode comprising all unresolved resonance lines near 60 GHz, and a nonresonant mode. The appropriate 3×3 relaxation matrix includes four independent parameters related, respectively, to the widths of the two modes, the collapse of the resonant mode, and its mixing with the nonresonant mode. These four parameters, assumed proportional to pressure, are evaluated by fitting to the data of Maryott and Birnbaum.
Determination of the Polarizability Anisotropy of OCS by Microwave Spectroscopy
Authors: Scharpen LeRoy H. , Muenter John S. , Laurie Victor W.
Published: January 2005

A gas-phase microwave parallel-plate absorption cell capable of very accurate Stark effect measurements at high fields has been constructed. With this cell the polarizability anisotropy of OCS has been determined to be αzz—αxx = (5.34±0.06)×10−24 cm3, where z denotes the molecular axis.
Collision Density of Hot Atoms. II
Authors: Chapin D. M. , Kostin M. D.
Published: January 2005

Analytical and stochastic methods are used to investigate hot-atom reactions for relatively low-energy hot atoms such as those produced by photochemical processes. Collision densities for hot atoms are presented for several reactive systems in which the reaction probability and the threshold energy are varied. Solutions for the collision density obtained by analytical methods and independently by stochastic methods were in satisfactory agreement. The results show that even small reaction probabilities can have a marked influence on the collision density distribution, an effect attributed to highly anisotropic scattering collisions. The temperature dependence of hot-atom reaction rates for a system containing two kinds of reactive molecules with different threshold energies was also investigated.
Electron Spin Resonance of X-Irradiated Single Crystals of Hydroxyurea
Authors: Shields Howard W. , Hamrick Phillip J. , Redwine Welby
Published: January 2005

The electron spin resonance of x-irradiated single crystals of hydroxyurea have been observed and analyzed for different orientations of the crystal in the magnetic field. The free radical responsible for the resonance has been identified as NH2CONH, and the measurements indicate that 41% of the unpaired electron is localized in the 2p orbital of the nitrogen atom. Principal values for the hyperfine coupling constants in gauss are −21.2, −13.5, and −1.5 for H, and 22.5, 1.5, and 1.2 for N. On the basis of these measurements the induced isotropic hyperfine constants for an electron entirely localized in a 2p orbital of the nitrogen atom in the R–N–H radical would be 20.2 G for nitrogen and −31 G for hydrogen. The principal g values are 2.0027, 2.0062, and 2.0108. The results indicate that the trapped radical retains the approximate orientation of the parent molecule in the lattice and that the radical is planar.
Concentration Quenching of Eu3+ Fluorescence
Authors: Blasse G.
Published: January 2005

The fluorescence quenching of the two phosphors Ba2Gd1−xEuxMe5+O6 (Me5+=Nb5+ or Ta5+) and Gd1−xEuxAl3B4O12 is reported. The shortest distance between the rare-earth sites in these materials is large and nearly equal, viz., 6.0 and 5.9 Å, respectively. The quenching behavior is different: In the materials Ba2Gd1−xEuxMe5+O6, concentration quenching occurs at x≃02, in the materials Gd1−xEuxAl3B4O12, no quenching was found under uv excitation. These results are discussed in relation to the Van Uitert—Johnson model for concentration quenching of Eu3+ fluorescence.
Atomic Scattering Factors for Electrons as Calculated by the Partial-Waves Method
Authors: Kimura Masao , Konaka Shigehiro , Ogasawara Makoto
Published: January 2005

Complex atomic scattering factors were calculated from the partial-wave scattering theory using the Hartree—Fock atomic potentials for the atoms H to Kr and the Thomas—Fermi—Dirac atomic potential for the atoms Kr to Cm. The partial phase shifts were approximated in terms of modified Bessel functions of the second kind.
Measurement of Lifetimes and Quenching Cross Sections of the B State of I2
Authors: Chutjian Ara , Link John K. , Brewer Leo
Published: January 2005

The phase-shift method was used to measure lifetimes of selected vibrational regions from v′=10 to v′∼100, together with self-quenching collision cross sections, of the B3Π0+u state of I2.

The reliability of the method was confirmed by good agreement with other measurements for the lifetime of the mercury 3P1 state. At high optical densities, the observed increase in lifetime was shown to be due to radiation entrapment.

Reasonable agreement was found between the lifetime values and absorption measurements, but, contrary to expectations, the self-quenching cross sections varied only a factor of 1.3 with vibrational excitation whereas the lifetimes varied by as much as a factor of 8.

The substantial variation of lifetime with v′, which cannot be merely a wavelength effect, indicates either that spontaneous predissociation of the B state of I2 is an important process which has a rate at least as great as that for radiative decay and which varies considerably with v′ or that the transition moment is changing with vibrational stretching.
Electronic Structure of the U Center
Authors: Spector H. N. , Mitra S. S. , Schmeising H. N.
Published: January 2005

Wavefunctions and energy levels for the triplet and higher excited singlet states of the U center are calculated using the point ion model of Gourary. The transition energy and oscillator strengths are computed. The calculations of Gourary for the first singlet transition are extended to include all the alkali halides for which experimental information is available including those having the CsCl structure as well as those having the NaCl structure. The theoretical calculations for the first singlet transition are approximately 15% smaller than the experimental values. The oscillator strengths which we compute for this transition agree with those of Gourary. The theoretical calculations for the first triplet transition predict that it will lie in the visible and near-infrared region of the spectra, i.e., from 0.8 to 1.8 eV. The oscillator strength calculated for this transition is less than for the singlet transition. The theoretical values of the transition energies and oscillator strengths for the second singlet and triplet transitions are also calculated.
Interpretation of the Energy of Hydrogen Bonding; Permanent Multipole Contribution to the Energy of Ice as a Function of the Arrangement of Hydrogens
Authors: Campbell E. S. , Gelernter G. , Heinen H. , Moorti V. R. G.
Published: January 2005

A comprehensive calculation of the permanent multipole lattice energy of ice I, performed as part of a study of the orientational energy of ice and the nature of the hydrogen bond, has led to the following conclusions: (1) The energy for existing quantum-mechanical models can be approximated with simple point-charge models (Sec. VI.E). (2) The effects of several characteristics of the molecular charge distribution have been quantitatively determined (Sec. VI.D). (3) There is a variation of energy with the configuration of the hydrogens (Sec. VI.F). (4) There is little correlation between the energy variations and the polarity of the crystal (Sec. VI.C). (5) In a study of these energy variations, the slow convergence in the sums over both lattice points and multipole orders makes it necessary to include interactions beyond next-nearest neighbors for lower-order multipoles as well as interactions of higher than the quadrupole—quadrupole order (Sec. VI.B).
Energetic Ions from N2 Produced by Electron Impact
Authors: Kieffer L. J. , Van Brunt R. J.
Published: January 2005

Energy distributions, appearance potentials, and angular distributions of N+ ions produced by electron impact on N2 have been observed. The energy distribution and appearance potential of the N+ + ions from electron impact on N2 were also observed. The data are interpreted to give the abundance of the ``zero-energy'' N+ and the N+ + ions. The appearance-potential data for the ``zero-energy'' N+ ions disagree with previous measurements, and a possible interpretation indicates that the conclusion of previous investigators that no excited ions are produced may not be valid.
Proton Tunneling in Acetic Acid Dimers
Authors: Ginn S. G. W. , Wood J. L.
Published: January 2005

The group theory of nonrigid systems is applied to determine the effects of proton tunneling in the vibrational spectrum of the dimer. It is shown that the doublet observed in the far-infrared spectrum of the vapor is unlikely to be due to proton tunneling. This conclusion is confirmed by the observation that the doublet remains in the spectrum of (CH3COOD)2.
Relativistic Effects in Chemical Bonding: The H2+ Molecule
Authors: Pavlik P. I. , Blinder S. M.
Published: January 2005

The behavior of the electron in the ground state of the hydrogen molecular ion is examined using the Dirac theory. Since the resulting set of equations is not readily separable, the variational theorem is applied to obtain approximate eigenfunctions for the ground state. Trial variational functions having the same symmetry properties as the exact solution can be conceptualized as a superposition of functions closely resembling nonrelativistic molecular orbitals. The relativistic correction to the electronic energy is approximately −7×10−6 a.u.
Influence of Electric Fields on the Molecular Alignment in the Liquid-Crystal para-Azoxyanisole
Authors: Twitchell Roger P. , Carr E. F.
Published: January 2005

The molecular alignment in the liquid crystal p-azoxyanisole due to external static magnetic fields and audio-frequency electric fields was studied by measuring the dielectric loss at a microwave frequency. For a 500-Hz electric field the long axes of the molecules preferred a direction parallel to the field which is usually observed but not predicted from theoretical considerations. The degree of alignment in a high 500-Hz electric field was less than in a high magnetic field and depended on the frequency of the electric field. The effectiveness of electric fields in aligning the molecules was compared to that of magnetic fields by applying the fields simultaneously and at right angles to each other. The results provide support for an explanation of the molecular alignment at audio frequencies, which was suggested earlier by one of the authors.
Thermokinetic Steady State and Quantum Yields
Authors: Berlad A. L.
Published: January 2005

Experimentally determined quantum yields depend upon the usual thermokinetic parameters as well as the nature of the absorbed radiation. For a radiative field of both photochemical and thermal significance, the thermokinetic determination of the photochemical steady state is examined. The photochemical steady state is a particular case of the thermokinetic steady state. Application is made to the case of quantum yields for ozone.
Thermal-Energy Ion—Neutral Reaction Rates. VII. Some Hydrogen-Atom Abstraction Reactions
Authors: Fehsenfeld F. C. , Schmeltekopf A. L. , Ferguson E. E.
Published: January 2005

Rate constants for reactions in which the positive ions O+, N+, Ar+, N2+, CO+, CO2+, and N2O+ abstract a hydrogen atom from H2 have been measured at 300°K in a pulsed, flowing-afterglow reaction tube. Several additional reactions are observed which occur as secondary reactions in these experiments.
ESR Study on Irradiated Pyridine: Effect of Iodine Addition
Authors: Tsuji Kozo , Yoshida Hiroshi , Hayashi Koichiro
Published: January 2005

When pyridine was irradiated at −196°C, the main free radical formed was the cation radical.[Complex chemical formula]The G value for the formation of the cation radical was 0.5. The addition of iodine to pyridine caused large increase in G value to as high as 13. The high G value is interpreted as due to the fact that the cation radical is produced through the excited state of the charge-transfer complex of pyridine with iodine.
Electronic Raman Spectra. I. Raman Transitions of Trivalent Ytterbium, Europium, and Neodymium in Yttrium Gallium Garnet
Authors: Koningstein J. A.
Published: January 2005

Electronic Raman spectra have been observed of trivalent rare-earth ions doped in the host-lattice yttrium gallium garnet (YGaG). The transitions terminate on the Stark level of the 2F7/2 manifold of Yb:YGaG, 7F1 levels of Eu:YGaG and the first excited state of Nd:YGaG. From an intensity study it can be concluded that the most important contributions to the Raman transition moment of the electronic Raman lines arise from the matrix elements 〈(4f)n |μ| (4f)n−15d〉.
Spectroscopic Temperature Measurements on Laser-Produced Flames
Authors: Mentall J. E. , Nicholls R. W.
Published: January 2005

Time-integrated spectroscopic intensity measurements have been made on the flame produced by the interaction of a focused ruby laser with powdered solids. Target materials used were Ba(AlO2)2, CaS, C, and Al microspheres.

Excitation temperatures of 24 000° and 9000°K have been inferred from the Ba and Ca spectra. Vibrational and rotational temperatures for AlO, C2, and CN were found to lie in the range of 3600° to 5600°K.

It is probable that excitation of the atomic and molecular spectra result from collisions between the emitting species and free electrons which have been superheated by absorption of a small fraction of the laser-beam energy.
Magnetic Interactions for the Electronic Configuration d5
Authors: Dunn T. M. , Li Wai-Kee
Published: January 2005

Applying Horie's method, the matrix elements of spin—other-orbit interaction for configuration d5 have been calculated. The magnetic interaction energy has also been calculated for Mn++ by means of perturbation theory. It is found that spin—other-orbit interaction plays a very important role for atoms or ions with half-filled-shell configuration. Spin—spin interaction is also significant in certain terms.
Infrared Lattice Vibrational Spectra of AgCl, AgBr, and AgI
Authors: Bottger G. L. , Geddes A. L.
Published: January 2005

The infrared transmission spectra of AgCl, AgBr, and AgI have been measured between 400–30 cm−1 at room temperature and at 143°K. Strong absorptions characteristic of the transverse optic modes were found, together with weak subsidiary absorptions arising from multiphonon combinations. The longitudinal optic modes of silver chloride and silver bromide were obtained from the reflection spectra of thin, silver halide films deposited on a silvered substrate. Capacitance measurements were used to determine the static dielectric constant of AgI; ε0=7.0±0.3. For a series of isomorphous I—VII compounds having large reduced masses, approximately linear relations are found between νt2 and the reciprocal reduced masses. The Szigeti relations for effective charge and compressibility were calculated and their significance is discussed.
Electron Paramagnetic Resonance Spectra of Two Zinc-Doped and Nickel-Doped Copper Chloride Pyridine-N-Oxide Complexes
Authors: Kokoszka Gerald F. , Allen Harry C. , Gordon Gilbert
Published: January 2005

The electron paramagnetic resonance spectra of zinc-doped dichlorobispyridine-N-oxide copper(II) [(C5H5NO)2Cu(Zn)Cl2] and zinc-doped dichloromonoaquopyridine-N-oxide copper(II) [C5H5NOCu(Zn)Cl2·H2O] have been observed at liquid-nitrogen temperature. The data could be fit to the usual S=½ spin Hamiltonian. The g values obtained in this study for the copper—zinc pairs agree with the g values obtained for the copper—copper pairs in the pure material to within experimental uncertainty. Copper hyperfine splittings and chlorine superhyperfine splittings were also observed. The magnetic parameters for (C5H5NO)2Cu(Zn)Cl2 are gz=2.323, gx=2.056, gy=2.080, Az=129×10−4 cm−1, Ax=Ay<10×10−4 cm−1, A′=25×10−4 cm−1, and B′=7×10−4 cm−1, while for C5H5NOCu(Zn)Cl2·H2O gz=2.306, gx=2.056, gy=2.083, Az=139×10−4 cm−1, and Ax=Ay<10×10−4 cm−1 obtain. An analysis of the data with a simple LCAO MO approach suggests relatively strong metal—ligand bonds.

The data obtained from the study of nickel-doped (C5H5NO)2CuCl2 could be fit to an S=½ spin Hamiltonian with the following magnetic parameters: gz=2.14, gx=2.54, gy=2.49, Az=35×10−4 cm−1, and Ax=Ay<7×10−4 cm−1. For nickel-doped C5H5NOCuCl2·H2O. gz=2.15, gx=2.61, gy=2.50, Az=40×10−4 cm−1, and Ax=Ay<7×10−4 cm−1 were observed. These appear to be the first reported magnetic parameters from dimers which contain exchange-coupled dissimilar transition-metal ions.
Adsorption on Niobium (110), Tantalum (110), and Vanadium (110) Surfaces
Authors: Haas T. W. , Jackson A. G. , Hooker M. P.
Published: January 2005

Clean surfaces of Nb (110), Ta (110), and V (110) have been prepared by heating in an ultrahigh-vacuum environment. Low-energy, electron-diffraction measurements indicated that all clean surfaces were the same as an ideal (110) plane in the bulk to within experimental error. Adsorption of CO and O2 on the clean surfaces of these metals led to similar patterns suggesting that the same structures formed on all three metals. The patterns obtained from adsorption of CO followed by warming to about 400°C were the same as those obtained by room-temperature exposure to O2. This suggests decomposition of the adsorbed CO. At least three different structures of O2 on these metals are produced as coverage is increased. Unfortunately, dissolution of the O2 into the bulk prevents accurate determination of surface coverage and this, coupled with the inability to handle intensity-distribution curves effectively, has made complete structure determinations of these oxides impossible.
Coupling between Nuclear and Electronic Motion in Diatomic Molecules
Authors: Laue Hans
Published: January 2005

The paper presents a general theory of the coupling between nuclear and electronic motion in diatomic molecules. Special consideration is given to the case of large nuclear separation. It is shown that, for large separation of the nuclei, the electronic—nuclear coupling terms are of the order of the isotope effect. The physical meaning of an (R−2)-dependent potential, which was found by Dalgarno and McCarroll, is explained as a centrifugal effect associated with a certain rotation of the electrons within the atoms. It is not significant at large separations.
Monte Carlo Simulation of the Effects of Molecular Motion on the EPR Spectrum of Nitroxide Free Radicals
Authors: Itzkowitz Martin S.
Published: January 2005

We are concerned with the electron paramagnetic resonance (EPR) spectra of nitroxide free radicals in various molecular environments. These radicals may be described as a single electron interacting anisotropically with a nitrogen nucleus of spin 1 and an external magnetic field. We use exact and approximate solutions to the Hamiltonian to simulate spectra from oriented samples; we perform the orientation averages to obtain simulated polycrystalline spectra. We consider the effects of molecular motion on the system, and we develop a Monte Carlo scheme to evaluate the spectrum for a variety of tumbling rates. We compare the theoretical spectra so obtained with experimental spectra taken in solutions of varying rotational correlation time; excellent agreement is obtained. We estimate the rotational correlation time from the Monte Carlo parameters.
Vibrational Spectra of SPCl3, SPCl2F, SPClF2, and SPF3
Authors: Durig J. R. , Clark J. W.
Published: January 2005

The infrared spectra of thiophosphoryl trichloride and thiophosphoryl dichlorofluoride in both the liquid and gaseous states, and thiophosphoryl chlorodifluoride and thiophosphoryl trifluoride in only the gaseous state have been recorded from 4000 to 100 cm−1. The Raman spectra have also been recorded for the four thiophosphoryl trihalides in the liquid state and depolarization values measured. Complete vibrational assignments based on band contours, positions, and depolarization values are given. The spectra are interpreted in detail assuming Cs symmetry for thiophosphoryl dichlorofluoride and thiophosphoryl chlorodifluoride, and C3v symmetry for the other two molecules. The vibrational assignment proposed for the SPF3 molecule is in marked contrast to that currently accepted. The P–S stretching vibration is found to decrease in frequency with the increased number of fluoride atoms attached to the phosphorous atom. Possible reasons for the decrease in frequency are discussed.
Spin and Orbital Symmetry in Correlated Many-Electron States
Authors: Paulus K. F. G.
Published: January 2005

A detailed discussion of the requirements of spin and orbital symmetry in the pair-correlation theory of Sinanoğlu is presented. The reasons why the theory of Sinanoğlu does not satisfy these requirements a priori are exposed, and it is shown that if some modifications to it are made then the symmetry properties can be incorporated in his scheme without undue complications. This is illustrated by a number of examples, and the relation to other recent work on this problem is pointed out.
Study of Rotational Isomerism in Fluoroacetyl Fluoride by Microwave Spectroscopy
Authors: Saegebarth Ellen , Wilson E. Bright
Published: January 2005

Fluoroacetyl fluoride has been found to have two distinct sets of pure rotational transitions in the microwave region 8 to 36 kMc/sec, which have been identified as arising from two rotamers, one with the two fluorine atoms trans to one another and the other in which they are in the cis position. These spectra have been analyzed and moments of inertia obtained. The Stark effect gives the dipole-moment components: trans μa=0.456±0.010 D, μb=2.63±0.05 D, μ=2.67±0.05 D; cis μa=1.18±0.03 D, μb=1.68±0.04 D, μ=2.05±0.06 D; μc=0 for both forms. Several sets of satellite lines were observed and assigned to torsionally excited trans molecules, to a skeletal bending mode, and to a combination of these. Relative intensities then gave trans frequencies near 127 cm−1 for the torsion and 265 cm−1 for the bending. Intensities also gave an energy difference, Ecis—Etrans, of 910±100 cal/mole. The available data do not completely define the torsional potential function but suggest that the threefold component may be in the range 1000–1300 cal/mole as in acetyl derivatives. The twofold component must be dominant to produce the cis instead of gauche minimum.
Dielectric Studies. XV. Molecular and Additional Relaxation Process(es) of Some Phenyl-Substituted Compounds
Authors: Hassell W. F. , Jarvie A. , Walker S.
Published: January 2005

The dielectric constants and losses at wavelengths of 0.860, 1.249, 1.850, and 3.220 cm and the static dielectric constant at 149.9 m have been measured for liquid phenyltrimethylsilane and triphenylsilane, triphenylarsine, triphenylphosphine, and triphenylphosphine oxide in nonpolar solvents at 25°C. Phenyltrimethylsilane and triphenylsilane have significantly shorter relaxation times than a rigid molecule of that size and shape and are to be contrasted with triphenylarsine, triphenylphosphine, and triphenylphosphine oxide. The shortening of the relaxation time seems to become apparent in molecules containing the phenyl group when the molecular dipole moment is low (e.g., ∼0.4 D for the alkylbenzenes).
Energy Distribution of Hot Atoms in a Reactive System
Authors: Felder R. M.
Published: January 2005

A binary system of hot and thermal atoms is considered in which interactions are governed by an inverse-power potential, and reactions between interacting atoms occur with a probability equal to a constant between two energies and zero elsewhere. Solutions of the time- and space-independent Boltzmann equation are obtained, and are used to develop criteria for the validity of the expression for the hot-atom collision density assumed by Wolfgang and Estrup in their kinetic theory of hot-atom reactions. It is found that this expression has its greatest validity for relatively isotropic scattering, a low reactivity and a large difference between the masses of the interacting species. Errors in the probability that a hot atom reacts before becoming thermalized which result from the assumed form of the collision density are generally of the order of 1%—10%, but for an interaction potential as soft as the inverse sixth power and equal masses the error may be as high as 25%.
Melting Curve of NaClO3 at High Pressure
Authors: Rapoport Eliezer
Published: January 2005

The melting curve of NaClO3 initially increases with pressure and reaches a maximum at 6 kbar and 285°C. A very slight break in the curve at 8.2 kbar and 282°C may indicate the NaClO3 I—II—liquid triple point and is in reasonable agreement with the extrapolation of Bridgman's I—II boundary. The melting curve further decreases with pressure and meets Bridgman's II—III boundary in a triple point at 31 kbar and 100°C. Bridgman's NaClO3 IV is actually the liquid phase. The freezing of NaClO3 exhibits considerable supercooling at high pressure, and above 20 kbar liquid NaClO3 appears to be very viscous and behaves like a glass.
Molecular Vibrations of the PO43− Ion, Site Symmetry D2d, in YPO4
Authors: Mooney R. W. , Toma S. Z.
Published: January 2005

Molecular vibrations of the PO43− ion at a site having D2d symmetry are treated theoretically. Symmetry coordinates and G-matrix elements are derived. Analytical F-matrix elements corresponding to a generalized valence force field are given. Two of the four observed infrared absorptions are assigned to the B2 and two to the E species and corresponding F matrices calculated. The distribution of potential energy among the internal symmetry coordinates for each infrared-active normal mode is derived. The results indicate a marked increase in the force constant for bending along the S4 axis for the B2 species which is interpreted as evidence for the formation of P–O–Y bonds.
Statistical Theory of Electrostriction and Nonlinear Polarization in Imperfect Gases
Authors: Klauder Louis T.
Published: January 2005

A report is given of derivations of useful formulas for the electrostriction and the nonlinear polarization of a gas of neutral molecules in a static electric field. The derivations begin with the definitions from quantum statistical mechanics for the grand-ensemble averages of the two quantities in question, and the resulting formulas are obtained by means of the linked-diagram method of Kaufman and Watson.
Hydroxyl-Radical Kinetics by Kinetic Spectroscopy. II. Reactions with C2H6, C3H8, and iso-C4H10 at 300°K
Authors: Greiner N. R.
Published: January 2005

Gas-phase, room-temperature reactions of the OH radical with C2H6, C3H8, and iso-C4H10 were studied with the flash-photolysis—kinetic-spectroscopy (KS) technique. Rate constants (in units of cubic centimeters per mole·second) were obtained as follows: C2H6+OH→C2H5+H2O,  k3=1.76±0.23×1011 at 302∘±2∘K,C3H8+OH→C3H7+H2O,  k4=8.2±1.2×1011 at 298∘±1∘K,iso−C4H10+OH→C4H9+H2O,  k5=1.28±0.07×1012 at 297∘±1∘K.It is shown that relative theoretical values for frequency factor ratios and Evans—Polanyi activation energies are inconsistent with the ratios of the observed rate constants for H abstraction by OH from these alkanes.
On the Magnetic Optical Rotation and Magnetic Circular Dichroism of Polymers. I. Time-Dependent Correlation Functions
Authors: Harris Robert A.
Published: January 2005

A response-function theory of the Faraday effect is presented. The response function for a polymer made up of coupled harmonic oscillators is obtained. A criterion for the origin independence of the magnetic circular dichroism and magnetic optical rotation is presented.
Diffusion and Heterogeneous Reaction. VIII. Kinetic Considerations of Surface Reactions
Authors: Ablow C. M. , Wise H.
Published: January 2005

A theoretical analysis is presented of the influence of the kinetic order of a heterogeneous surface reaction on a diffusive mass transport of a reactant through a cylinder with catalytic walls and catalytic end plate. Because of the relevance to experimental studies, two cases are considered: (1) a second-order reaction on the cylinder wall and the first-order reaction on the end plate, and (2) second-order reaction on the wall of a cylinder of infinite length. Examination of experimental data by means of this theoretical analysis demonstrates the prevalence of second-order recombination of hydrogen atoms on quartz under certain conditions. The second-order rate constants for this process are computed at 77° and 773°K.
Pressure Broadening of Rotational Lines: Sudden Perturbation Approximation
Authors: Trindle C. O. , Illinger K. H.
Published: January 2005

A treatment, within the framework of the sudden perturbation approximation of time-dependent perturbation theory, of the pressure broadening of rotational transitions is presented. The Lorentz line-shape expression is derived in the limit of low pressures, and explicit expressions for the frequency-shift and linewidth parameters are given in terms of the intermolecular potential. Detailed comparison to other perturbation theories of line broadening is made.
Ionization of Strong Electrolytes. IX. Proton Magnetic Resonance in the Ternary System HNO3—DNO3—H2O—D2O
Authors: Merbach A.
Published: January 2005

Nuclear magnetic resonance (NMR) was previously established as a reliable method for the determination of the degree of dissociation. The proton magnetic resonance shift has been measured in the full range of the ternary system HNO3—DNO3—H2O—D2O. The two nitric acids are about equally strong at 32°C, but at 0° deuteronitric acid is weaker, at 63° stronger than HNO3.
Energy-Partition Parameters in Radiation Studies Involving Rare Gases
Authors: Klots Cornelius E.
Published: January 2005

Ion yields observed during plutonium alpha irradiation of binary mixtures containing at least one rare gas are reported. An attempt has been made to analyze them in terms of the modes of initial energy deposition. In order to do so, it was necessary to take account of ``negative Jesse effects,'' tentatively ascribed to the quenching of chemi-ionization mechanisms (the so-called Hornbeck—Molnar reactions) occurring in the rare gases. Energy-partition parameters, obtained in this fashion and earlier, are qualitatively justified by semiempirical calculations.
Exciton—Exciton Collision Ionization in Anthracene Crystal
Authors: Sharma Ramesh D.
Published: January 2005

A hopping model for excitons is used to calculate the rate constant for electron—hole production due to exciton—exciton collision annihilation. The value for the rate constant obtained using a more recent value for the conduction-band edge and better orthogonalization scheme is 3.0×10−11 cm3 sec−1. This is an order of magnitude greater than the value 2.5×10−12 cm3 sec−1 obtained by Choi and Rice using the coherent model. The only experimental measurement is by Silver, Olness, Swicord, and Jarnagin which gives 5×10−12 cm3 sec−1 for the rate constant.
Nuclear Magnetic Resonance in Rare-Earth—Aluminum Intermetallic Compounds: RAl3
Authors: van Diepen A. M. , de Wijn H. W. , Buschow K. H. J.
Published: January 2005

The Knight shifts of the 27Al NMR in LaAl3, CeAl3, PrAl3, NdAl3, GdAl3, and TbAl3 have been measured at temperatures from 78° up to 450°K. The effective exchange constants J between the 4f electrons localized at the rare-earth ions and the conduction electrons at the Al nuclei have been derived to be −0.2 eV. Ruderman—Kittle—Yosida periodic oscillations of the conduction electron polarization have been used to relate the results with those obtained for RAl2. Nuclear quadrupole coupling constants have been measured to be |e2qQ|=0.8 Mc/sec. On the basis of the ionic point model e2qQ has been calculated for RAl3 and RAl2.
Resonance Energy Transfer: Influence of Heteroatoms on the Donor's Properties
Authors: Ellis David W. , Solomon Barton S.
Published: January 2005

Measurement has been made of the critical transfer distances for five donor—acceptor systems—fluorene, carbazole, dibenzofuran, dibenzothiophene, and 9-fluorenol as donors and 9-phenylanthracene as the acceptor. The good agreement, between the experimentally measured and theoretically calculated critical transfer distances for the first three systems, indicates the applicability of Förster's dipole mechanism of resonance energy transfer. The measured and calculated critical transfer distances for the last two systems also agree, but the low values obtained make the applicability of Förster's dipole—dipole mechanism questionable. The fluorescence quantum efficiencies and the critical transfer distances show similar trends as the molecular structure is changed. The corrected fluorescence spectra and fluorescence quantum efficiencies of the five donor molecules have also been measured.
Theoretical and Experimental Values for Two-, Three-, and Four-Photon Absorptions
Authors: Pantell R. , Pradere F. , Hanus J. , Schott M. , Puthoff H.
Published: January 2005

Transition probabilities are given for dipole—dipole and dipole—quadrupole multiple-photon processes and these values are compared with the results of two-, three-, and four-photon absorption experiments in anthracene and napthalene.
Mechanisms of Energy Transfer Involving Trivalent Dy and Tb
Authors: Van Uitert L. G. , Dearborn E. F. , Rubin J. J.
Published: January 2005

Energy may readily transfer from the 4F9/2 manifold of Dy to the 5D4 manifold of Tb in the Na0.5(Y, Tb, Dy)0.5WO4 tungstates at 295°, 77°, or 4.2°K. The reverse transfer may occur at 295°K but not at lower temperatures. This is due to the requirement that nonzero levels of the ground manifold of Dy must be thermally populated to permit transfer from Tb to Dy. The net flow of excitation at 295°K is from Dy to Tb for low Dy concentrations and from Tb to Dy for high concentrations. The reversal in direction is due to a rise in Dy self-quenching as concentration increases. The intersections are dipole—dipole for either direction of flow.
Valence Excited States of BeO
Authors: Huo Winifred M. , Freed Karl F. , Klemperer William
Published: January 2005

SCF wavefunctions have been computed for the lowest 3Π and 1Π states of BeO at a number of different internuclear separations. The calculations were carried out with a carefully chosen basis set composed of 24 Slater functions. The calculated 1Π—3Π separation is very small; 923 cm−1. The spectroscopic constants and a number of one electron molecular properties for the two states are found to be very similar. This behavior is explained by the strong lone-pair characteristic of the 5σ orbital in these two states. In matching the perturbations observed in the spectrum of the singlet system, it was found that the above calculated results are consistent with the a 3Π state being one of the states that cause the ``unknown'' perturbations reported by Lagerqvist and co-workers.
Temperature Dependence of Sound Velocity in Ferroelectric Potassium Ferrocyanide
Authors: Schacher Gordon E.
Published: January 2005

Sound velocity has been measured as a function of temperature for three orientations in both shorted and insulated potassium ferrocyanide crystals. The results are qualitatively interpreted by means of ionic binding in the material and a change in ionic-bond strength by hydrogen-bond formation at the ferroelectric transition temperature. Anomalies in the shorted crystals are correlated with phenomenological thermodynamic theory.
Combination Lines in Stimulated Raman Emission from Gas Mixtures
Authors: Duardo J. A. , Nugent L. J. , Johnson F. M.
Published: January 2005

Stimulated Raman emission (SRE) spectra were observed from high-pressure CH4 and H2 in two different experiments. In the first experiment the gases were mixed together in one scattering cell, and a laser pulse excited the mixture; in the second experiment they were isolated from each other in separate cells placed in series so that one laser pulse excited both gases. The spectra observed in both experiments are essentially identical: The well-known SRE lines from each gas were at ν̃0+nν̃1(i), where ν̃0 is the wavenumber associated with the laser excitation, ν̃1(i) is the wavenumber associated with the frequency of a totally symmetric vibration of molecule i, and n≐±1, ±2,···. In addition, strong lines at ν̃0+nν̃1(H2)+mν̃1(CH4) were present in all combinations in all orders wherever the spectrograph was sensitive enough for detection. This is the first report of SRE combination lines from the gas phase. In general two thresholds were observed, the first for the appearance of SRE lines from one gas, the second for the appearance of the SRE lines from the other gas, and the threshold order depended on the particular experimental conditions. In every case, at the second threshold all the combination lines were present, and before the second threshold all the combination lines were absent. These results are examined in the light of the classical theory of SRE including the effects of molecular interactions, a mechanism for the generation of the SRE combination lines is presented, and it is conluded that molecular interactions play only a minor and unessential role in this process in the gas phase.
Thermal Conductivity of Ammonia—Diethyl Ether Mixtures at Different Temperatures
Authors: Srivastava B. N. , Gupta A. Das
Published: January 2005

The thermal conductivity of binary polar gas mixtures NH3–(C2H5)2O has been measured over the temperature range 80°—200°C for various compositions by applying the ``thick-wire variant'' of the hot-wire method. The data obtained have been interpreted qualitatively with the help of Hirschfelder's theory based on local chemical equilibrium assumptions. A better agreement is observed when unlike interaction parameters obtained from binary diffusion data are utilized.