bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiple Trapping Sites for Hydrogen Atoms in Rare Gas Matrices
Authors: Foner S. N. , Cochran E. L. , Bowers V. A. , Jen C. K.
Published: January 2005

Hydrogen atoms have been stabilized in nonequivalent lattice sites in matrices of the rare gases at liquid helium temperature. Electron spin resonance spectra of H atoms in argon, krypton, and xenon show that at least two trapping sites are involved in each case. In a neon matrix, H atoms have been stabilized in only one site. Attainability of the various trapping sites apparently depends on the initial energy of the H atom, a simple doublet spectrum being obtained when the atoms are deposited from the gas phase, while multiple trapping spectra are obtained when the atoms are produced by photolysis in the solid.

The hyperfine coupling contants and the electronic g factors for H atoms trapped in the various matrix sites have been determined. The deviation of the hyperfine coupling constant from the free-state value is positive in some cases and negative in others. The experimental results are in good agreement with theoretical predictions. A complex multicomponent H atom spectrum was obtained by photolysis of HI in xenon. The subsplitting in the spectrum is attributed to magnetic hyperfine interactions with matrix nuclei (Xe129 and Xe131). The nature of the trapping sites in rare gas matrices is discussed. Evidence for trapping in substitutional sites and octahedral sites is presented.
Thermodynamic Study of Al2O3 Using a Mass Spectrometer
Authors: Drowart J. , DeMaria G. , Burns R. P. , Inghram M. G.
Published: January 2005

The evaporation of alumina under nearly neutral conditions in tungsten and molybdenum Knudsen cells has been investigated by mass spectrometric methods. The atomization energies of the gaseous molecules are D0o(AlO) = 115±5 kcal/mole; D0o(Al2O) = 245±7 kcal/mole; D0o(Al2O2) = 365±7 kcal/mole.
Mass Spectrometric Study of Gaseous Molybdenum, Tungsten, and Uranium Oxides
Authors: DeMaria G. , Burns R. P. , Drowart J. , Inghram M. G.
Published: January 2005

Partial pressures of the gaseous oxides MoO, MoO2, MoO3, WO, WO2, WO3, UO, UO2, and UO3 in the systems Mo–Al2O3 and U–Al2O3 have been measured by mass spectrometric methods. The vapor pressure of uranium has also been determined. The reaction enthalpies derived from these measurements are: Reaction         ΔH0ο kcal/moleMoO(g)→Mo(g)+O(g)         116±15MoO2(g)→Mo(g)+2O(g)         262±10MoO3(g)→Mo(g)+3O(g)         411±7WO(g)→W(g)+O(g)         154±10WO2(g)→W(g)+2O(g)         296±7WO3(g)→W(g)+3O(g)         443±7UO(g)→U(g)+O(g)         179±7UO2(g)→U(g)+2O(g)         340±7UO3(g)→U(g)+3O(g)         493±7U(s)→U(g)         126±5.
Refractive Index and Dispersion of the Benzene-Methanol System
Authors: Wood Scott E. , Langer Sidney , Battino Rubin
Published: January 2005

The refractive indices of the benzene—methanol system have been measured at 25° at seven wavelengths in the visible region. The electronic polarizability of benzene, methanol, and carbon tetrachloride have been calculated from the refractive indices of this system and those of the benzene-carbon tetrachloride system by use of the Böttcher equation. The data are then used to calculate the molar electronic polarizations of the carbon tetrachloride-methanol system which are found to be in good agreement with experimentally determined values. These results show that, within the experimental error, the electronic polarizabilities of the three components are independent of the composition and hence of the environment. The electronic polarizabilities of the three substances are found to follow a dispersion equation with only one term.
Application of Least-Squares Method to Density-Intensity Calibration in Electron Diffraction Studies
Authors: Kimura Katsumi , Kimura Masao
Published: January 2005

A new method based on the principle of least squares is proposed for the calibration of the characteristics of photographic emulsion employed in electron diffraction studies. The calibration procedure consists of two steps. First, a function having three parameters was found which represents the relation between the optical density and exposure. Secondly, the most probable values of the parameters and their standard errors were determined in a straightforward way by the method of least squares. An application of this method to the diffraction patterns of benzene is described. The standard errors of final relative intensities were evaluated over the entire observed range of optical densities.
Simple Configuration-Interaction Wave Functions. II. Two-Electron Ions: An Analytic Study
Authors: Scherr Charles W. , Silverman Jeremiah N.
Published: January 2005

An analytical study of the 1S ground state of helium-like ions employing the open-shell function (1s1s′) and the angularly correlated configuration-interaction function (1s1s′)+λ(2p)2 has been made. Expressions for the wave function parameters, energy values, and certain other expectation values in terms of the nuclear charge Z have been obtained. These are asymptotic expressions for large Z, but they reproduce numerically obtained results for small Z with sufficient accuracy to be useful for many purposes.
Triplet-Singlet Emission Spectra of Xylenes in Crystalline State at 4.2° and 77°K, and in EPA at 77°K
Authors: Blackwell Lawrence A. , Kanda Yoshiya , Sponer H.
Published: January 2005

The triplet-singlet emission spectra of xylenes in the crystalline state at 4.2° and 77°K and in a rigid glass at 77°K have been photographed and analyzed. The samples were obtained from the National Bureau of Standards. They were kept sealed under an oxygen-free atmosphere of helium gas throughout the experiments. Large well-formed crystals were grown from the vapor on a surface cooled by liquid nitrogen, and some were grown from the melt. At 4.2°K o-xylene produced two sharp spectra similar in structure and separated by 370 cm-1 from each other. These spectra are ascribed to two distinct crystalline phases. At 77°K o-xylene did not produce a significant phosphorescence. The spectrum of m-xylene at 4.2°K consisted of a strong diffuse spectrum and a weak sharp spectrum toward shorter wavelengths. The diffuse spectrum appeared to be associated with the amorphous phase. At 77°K a broad spectrum appeared which was found to be characteristic of an aldehyde. At 4.2°K p-xylene showed a sharp spectrum beginning at 25 254 cm-1. It differs in vibrational structure from the spectrum of this compound in a rigid glass. A vibrational analysis indicated that the carrier of this spectrum is p-methylbenzaldehyde. With crystals of the p-xylene grown from the melt the genuine spectrum due to p-xylene was observed between 28 246 and 25 416 cm-1, over-lapped by the spectrum of p-methylbenzaldehyde in the longer wavelength region. These results suggest a temperature-activated sensitization which had been first observed in toluene.
Thermal Decomposition of Niobium and Tantalum Monocarbides
Authors: Kempter Charles P. , Nadler M. R.
Published: January 2005

The thermal decomposition of polycrystalline NbC was investigated from 2000° to 3200°C, and TaC from 1890° to 3320°C in the presence of one atmosphere of helium. It was found that both compounds lose carbon preferentially, and that the final carbon/metal molar ratio obtained may be represented by an equation of the form C/M=A—B exp(λt), where t is the maximum temperature of heating for a constant time (30 min in both cases). Similarly the resultant lattice constant may be expressed as a0=A′—B′ exp(λ′t), where a0 is in A at 25°C. For a maximum temperature of 3000°C and heating times of 30 min to 12 hr, a0=4.459084+0.0093071 exp(—0.18916 τ) for NbC, where τ is the time in hours. It was found that a0=4.414712+0.056862 (C/Nb) for the C/Nb range 0.885 to 0.981 and that a0=4.385779+0.070204 (C/Ta) for the C/Ta range 0.906 to 0.996. By extrapolation, the lattice constants of stoichiometric NbC and TaC should be 4.47157±0.00012 A at 25°C and 4.45598±0.00038 A at 25°C, respectively.
Raman Spectra of Metal Carbonyl Compounds. II. Raman Spectra, Structure, and Force Constants of Cobalt and Iron Tetracarbonylate Anions
Authors: Stammreich H. , Kawai K. , Tavares Yara , Krumholz P. , Behmoiras J. , Bril S.
Published: January 2005

The Raman spectra of the ions Co(CO)4—, Fe(CO)42—, and HFe(CO)4— have been studied in aqueous solutions of the corresponding sodium salts. The spectra of Co(CO)4— and Fe(CO)42—, excited by the helium radiations 5875.6 and 6678.1 A are in full agreement with the expected Td symmetry of these ions; all observed frequencies were assigned to fundamental vibrational modes. A normal coordinate treatment was carried out under the assumption of a simplified valence force field model making use of only two interaction constants. The values of the fundamental frequencies of the tetrahedral ions, calculated by means of the potential constants of this model, were found to be in satisfactory agreement with the observed Raman shifts.

The Raman spectrum of HFe(CO)4—, put in correlation with that of Fe(CO)42—, points strongly to a C3v symmetry of the former ion.
Electronic States of p-Benzoquinone. V. Vibrational Analysis of the Vapor Absorption Spectrum around 4500-A Region
Authors: Anno Tosinobu , Sadô Akira
Published: January 2005

The absorption spectrum of p-benzoquinone vapor in the region between 4080 and 5100 A was photographed and measured. Although the theoretical calculation as well as the experimental crystal spectrum indicate that two singlet-singlet electronic transitions exist in this region, prominent vibrational structure of the vapor spectrum can be interpreted as caused by a single forbidden electronic transition. If we assume that the hydrogen vibrations are not effective as perturbing vibrations which make the forbidden electronic transitions allowed through the vibrational-electronic interaction, this fact suggests the following two sets of assignments for the symmetries of the forbidden transition and the perturbing allowed transition: (1) the spectrum is a superposition of 1Au, 1B2u←1Ag transitions perturbed by a 1B2u←1Ag transition, (2) the spectrum is caused by a single 1B1g←1Ag transition being allowed through vibrational-electronic interaction with the allowed 1B1u←1Ag transition. Vibrational structure alone cannot exclude the second possibility, but a discussion supporting the first assignment is given. This assignment (1) is in agreement with the theoretical calculation of the energy levels. Most prominent bands are assigned to particular vibronic transitions. Fundamental frequencies in the excited electronic state 436, 796, 1109, and 1220 cm—1 are obtained corresponding probably to the ground-state values of 444, 770, 1144, and 1667 cm—1.
Perturbation Treatment of the Characteristic Vibrations of Polypeptide Chains in Various Configurations
Authors: Miyazawa Tatsuo
Published: January 2005

A perturbation treatment has been made of localized group vibrations of helical polymer chains. The amide I and II frequencies were derived in terms of adjacent group interactions as well as interchain and intrachain hydrogen bonding interactions. Frequency shifts caused by these interactions depend upon the configuration of polypeptide chains and also upon the chain packing in the crystalline region. Each characteristic vibration of the amide group gives rise to parallel and perpendicular bands. The parallel bands of the α helix of poly-γ-benzyl-L-glutamate were observed at 1650 cm—1 (amide I) and 1516 cm—1 (amide II) whereas the perpendicular bands were observed at 1652 cm—1 (amide I) and 1546 cm—1 (amide II). Both the parallel-chain and antiparallel-chain pleated sheets exhibit the perpendicular amide I band at ca 1630 cm—1. A characteristic band of β configurations at ca 1690 cm—1 was assigned to the parallel amide I band of the antiparallel-chain pleated sheet.
Nuclear Magnetic Shielding in Molecules: Hydrogen Molecule
Authors: Sinha S. K. , Mukherji A.
Published: January 2005

A method for calculating the nuclear magnetic shielding in molecules has been developed using valencebond or LCAO type molecular orbitals. The perturbation of the molecular wave function due to a steady magnetic field is derived by solving the first-order perturbation equation. The method has been applied to the calculation of proton shielding in hydrogen molecule with the Wang function. The value of σp=—0.55× 10—5 is in good agreement with the value of —0.56×10—5 derived by Ramsey from the experimental value of the spin-rotational coupling constant in hydrogen molecule.
Relaxation of an Isolated Ensemble of Harmonic Oscillators
Authors: Shuler Kurt E.
Published: January 2005

The collisional relaxation of an isolated ensemble of harmonic oscillators (at constant volume and energy) from initial nonequilibrium distributions is discussed in this paper. The ``transport equation'' for the relaxation process is derived and it is shown that it can be linearized even though the relaxation takes place via binary oscillator collisions. The final, stationary distribution is found to be a Boltzmann one with a temperature uniquely defined by the mean energy of the ensemble. The Boltzmann H function is obtained for this system of relaxing oscillators and it is shown that dH/dt<0 for all t. The time rate of change of the mean-square deviation of the energy during the relaxation process is computed and is shown to be closely related to the time variation of the mean energy in the relaxation of an ensemble of harmonic oscillators in contact with a thermal reservoir.
Electronic Structure and Spectrum of Acetanilide
Authors: Baba Hiroaki , Suzuki Satoshi
Published: January 2005

A molecular orbital calculation has been made for the π electronic structure of acetanilide and related compounds. The simple LCAO procedure, on which the calculation is based, was somewhat modified to allow for electron repulsion. The electronic behaviors of the acetanilide molecule are examined from the viewpoint of the interaction of the phenyl and acetyl groups through the nitrogen atom. From the calculated excitation energies, oscillator strengths, and charge distributions, the features of the observed ultraviolet absorption and other electronic phenomena can be satisfactorily explained. It is shown that the changes of the longer-wavelength bands in passing from aniline to acetanilide may be interpreted in terms of two electronic effects: (1) a decrease in the tendency of the nonbonding electrons at the nitrogen atom to migrate into the benzene ring; (2) an extension of conjugation. The electronic properties in the ground state are shown to be explicable by taking account of the former effect.
Experimental Oscillator Strengths of CH and NH
Authors: Bennett R. G. , Dalby F. W.
Published: January 2005

The radiative lifetimes of the A 2Δ and B 2Σ states of CH and the A 2II state of NH have been measured to be (5.6±0.6) 10—7, (1.0±0.4) 10—6, and (4.25±0.6) 10—7 sec, respectively. The oscillator strengths of the respective ground-state transitions were then calculated to be (4.9±0.5) 10—3, (1.2±0.4) 10—3, and (8.0±1.1) 10—3.
Effect of Pressure on Color Centers in Ag+-Doped Alkali Halides
Authors: Eppler R. A. , Drickamer H. G.
Published: January 2005

The effect of pressure on various color centers in silver-doped alkali halides has been studied. The crystals include NaCl (two concentrations), KCl, and KBr. The resulting shifts are used to confirm the assignments of some peaks, and, in certain cases, to decide among conflicting interpretations.
Brownian Motion in Liquids
Authors: Mandel Gerald , Collins Frank C.
Published: January 2005

The time derivative of the frictional force acting on a single molecule derived by Collins and Raffel was ambiguous with respect to a sign which left uncertain whether the calculated ensemble average velocity would decay exponentially in time or be initially sinusoidal in behavior. This point is now resolved and the exponential decay of the velocity is obtained for a molecule relaxing for an initial steady state. The frictional coefficient is also obtained by an alternative method involving an expansion of the conditional second-order phase density in powers of the distance that the representative molecule travels before its ensemble average velocity decays to zero. The alternative derivation enables the velocity dependence of the frictional coefficient to be examined. An approximate evaluation of the corrected velocity-dependent frictional coefficient for liquid argon averaged over all velocities is in improved agreement with the value calculated from the self-diffusion measurements of Corbett and Wang.
Transport in Dilute Gases and Chemical Forces
Authors: Osborn Richard K.
Published: January 2005

It is shown that the theory of transport phenomena in gases may be so formulated that the potentials characterizing the cross sections, which account for intractions between molecules in the binary collision limit, are the same as those conventionally employed in investigations of molecular structure. Thus it is indicated that at least some of the essential features of chemical forces may be conveniently introduced into the description of such phenomena.
Ionization of Cu, Ag, and Au by Electron Impact
Authors: Blais Normand C. , Mann Joseph B.
Published: January 2005

The relative ionization probabilities of copper, silver, and gold by electron impact have been studied near threshold. Nearly monoenergetic electrons, obtained by means of the retarding potential difference method, were employed. Narrow peaks were found superimposed on the ion yield that arises from transition to the ion ground state. It was possible to correlate these peaks with groups of energy levels, many of which are known to autoionize. The ionization probability curve for formation of doubly ionized gold was also obtained and found to be a sum of linear functions of the electron excess energy. The onset of each linear section indicated the presence of an excited state of Au III. Three energy levels were located at 2.26, 3.92, and 7.81 ev above the ground state.
Vibronic Calculations in Benzene
Authors: Albrecht Andreas C.
Published: January 2005

A group-theoretical reduction incorporating normal-coordinate parameters is applied to obtain expressions for the oscillator strengths of forbidden B2u, B1u, and E2g transitions in benzene in terms of the minimum number of electronic integrals. The simplification obtained encourages the testing of wave functions within the Herzberg-Teller framework as well as empirical evaluation of the theory. An investigation is made of the possible effect of isotopic substitution on forbidden intensities. The group-theoretical reduction is carried out for 1,4 dideuterobenzene, sym-benzene-d3, 2,3,5,6-tetradeuterobenzene, benzene-d6, and a hypothetical molecule p-di-X-benzene (where (X) = 20 and C—X = 1.40 A). It is observed that the B2u and B1u transitions are very insensitive to mass effects independent of the nature of the electronic functions. On the other hand, E2g transitions may or may not show a significant sensitivity depending on the details of the wave functions. By way of illustration, oscillator strengths are calculated for all compounds for B2u, B1u, and two E2g transitions using conventional benzene ASMO functions and published integrals. The distribution of oscillator strengths among all active normal modes is given for benzene, benzene-d6, and p-di-X-benzene. It is found that especially for the E2g transitions the distribution among normal modes is considerably more sensitive to mass effects than is the total oscillator strength.

A general expression is given for the temperature dependence of ``forbidden'' transition probabilities.
Electronic Transitions of Rare Earth Ions in the Infrared Region
Authors: Mandel G. , Bauman R. P. , Banks E.
Published: January 2005

The 2F7/2←2F5/2 transition of the cerous ion has been observed in solid solutions of cerium(III) fluoride in cadmium fluoride. The band center is at about 2250 cm—1, in good agreement with the free-ion value of 2253.0 cm—1. The crystal field splitting of the band appears to be enhanced by the effect of the interstitial fluoride ions which compensate for the excess positive charge of Ce3+ in Cd2+ positions. Addition of NaF, which eliminates the interstitial fluoride ions, decreases the splitting. Praseodymium and neodymium ions in CdF2 also showed absorption bands.
Structure of the Complex Ion in Aqueous Solutions of Zirconyl and Hafnyl Oxyhalides
Authors: Muha George M. , Vaughan Philip A.
Published: January 2005

X-ray scattering by aqueous solutions of MOX2·8H2O (M=Zr and Hf, X=Cl and Br) can be explained if one assumes the existence of a complex [M4(OH)8 (H2O)16]X8. The metal atoms in this complex are arranged in a square and are held together by double OH bridges along each edge. In addition, each metal atom is bound to four additional water molecules in such a manner that the configuration about the metal is a square Archimedes antiprism. The halogen ions are not bound directly to the metal. They do, however occupy definite positions in the complex, and are presumably held in place by electrostatic forces. The structure is very similar to that which has been found in the crystalline oxyhalides.
Note on Secondary Isotope Effects in Reaction Rates
Authors: Wolfsberg Max
Published: January 2005

It is shown that secondary kinetic isotope effects, for all isotopes with the possible exception of hydrogen isotopes, are expected to be small unless the force constants involving the isotopically substituted positions are considerably different in the transition state from those in the reactant. Cases involving secondary hydrogen isotope effects are investigated in detail for certain model reactions. It is concluded that hydrogen isotope effects do not constitute an exception to the above rule.
Conduction Electrons in Sodium Tungsten Bronze
Authors: Keller Joseph M.
Published: January 2005

The vanishing of the Knight shift of Na23 in sodium tungsten bronze is interpreted in terms of an inverted conduction band.
Infrared Studies of Crystal Benzene. IV. Absolute Intensities
Authors: Person Willis B. , Swenson Charles A.
Published: January 2005

The intensity of the absorption due to v20 at 1036 cm—1 in solid benzene at —170°C has been measured relative to the intensity of this band measured with the same benzene film in the liquid phase at 25°C. From this ratio and from the value for the absolute intensity of v20 in liquid benzene reported by Hisatsune and Jayadevappa, a value of 670±90 darks for the absolute intensity of v20 in solid benzene has been obtained. Using the relative intensity measurements reported earlier, the absolute intensities of all the gasphase-allowed fundamentals have been estimated. All the intensities in the crystal are lower than the values in the liquid phase, but the behavior of the bands at 1036 and 1480 cm—1 is not too abnormal. However, the intensities of the fundamentals at 687 and 3060 cm—1 decrease markedly from the gas-phase values, the former by a factor greater than two, the latter by a factor of seven. Thus, it is concluded that the interactions in the solid which cause the intensity to change are quite specifically limited to these two normal modes. Analysis of the data using the isotope intensity sum rules modified for use with crystals reveals that the intensity changes observed are much greater than those expected due to simple distortion of the norma coordinates by the crystal field.
Effect of Pressure on the M Center in Alkali Halide Crystals
Authors: Minomura S. , Drickamer H. G.
Published: January 2005

The effect of pressure to 52 800 atm has been measured on the M band in NaCl, KCl, KBr, and KI, and on the R2 and N bands in KCl. In general, the band peak shifts to higher frequency with increasing pressure for all bands. At the phase transition from fcc to sc there is a blue shift in KCl, but a red shift in KBr and KI. It is suggested that the shift corresponds to a balance between contraction and polarizability effects. From an Ivey-type relation, it would seem that the M center is somewhat less compressible than the F center.

There is a marked increase in intensity of the M center in the potassium halides in going through the phase transition from the fcc to the sc lattice.
Thermodynamic Properties of Unipositive Gaseous Elemental Ions
Authors: Green John W. , Poland Duncan E. , Margrave John L.
Published: January 2005

Thermodynamic properties of unipositive gaseous elemental ions were calculated from available energy level data for a range of temperatures from 100° to 50 000°K.
Radiolysis of Cyclohexane. I. Pure Liquid Cyclohexane and Cyclohexane-Benzene Solutions
Authors: Freeman G. R.
Published: January 2005

The radiation chemistry of pure liquid cyclohexane and of cyclohexane-benzene solutions has been investigated. The cyclohexane radiolysis system appears to contain at least two distinct activated species, one of which (c-C6H12″) is subject to ``protection'' by benzene while the other (c-C6H12′) is not. The approximate yields of these two species, determined by kinetic analysis, are G(c-C6H12″) = 3.0±0.4 and G(c-C6H12′) = 2.5∓0.4. In addition to the usual products, cyclohexylcyclohexadiene and dicyclohexadiene have been measured in the cyclohexane-benzene system. A mechanism has been proposed to explain the formation of the major products and the variation of their yields with benzene concentration.

A limiting case calculation for the upper limit of the rate constant for energy transfer between molecules in the present system (1013—1014 liters mole/sec) agrees well with a similar calculation, recorded in the literature, for energy transfer in organic solution scintillators. Another limiting case calculation shows that the rate constant for energy transfer might also be considerably smaller than the above value.
Entropy Production in Chemical Reactions
Authors: Rastogi R. P. , Srivastava R. C.
Published: January 2005

The generalization of Prigogine and Glansdroff which states that the rate of entropy production is negative in the nonstationary state and zero in the stationary state is verified for reversible isomerization of ammonium thiocyanate and the isomerization of Δα-pentenoic acid involving a monomolecular triangular reaction.
Vibrational Transitions and the Intermolecular Potential
Authors: Amme Robert C. , Legvold Sam
Published: January 2005

Temperature-dependence studies of vibrational collision lifetimes by the authors have indicated that the application of the Schwartz, Slawsky, and Herzfeld theory to substituted methane molecules with heavy surface atoms results in repulsive ranges which are shorter than those expected from a Lennard-Jones 6:12-type interaction. We have shown that the 28:7 potential suggested by Hamann and Lambert for quasi-spherical molecules gives ranges which are in better agreement with experiment. Also, experimental relaxation times of CHClF2-argon and CHClF2-helium mixtures have been used to obtain the collision lifetimes for the CHClF2 molecule undergoing either argon or helium collisions. The results can be explained using the SSH theory, if the 6:12 ranges for helium and argon are averaged with the shorter experimental range for CHClF2.
Shapes and Breadths of Some Molecular Rotation-Vibration Band Lines Perturbed by Rare Gases
Authors: Rank D. H. , Eastman D. P. , Birtley W. B. , Wiggins T. A.
Published: January 2005

The shape of absorption lines of HCl and C2H2 broadened with krypton and xenon as foreign gases is shown to be that due to collision broadening. Corrections for instrumental width are made in the manner described by Pigott and Rank to determine the half-intensity width. These widths show a small J dependence with low-J lines being the broadest. No difference between the widths of P and R lines of the same J could be detected. For high J's the quotient of the shift of the line and the width of the line is approximately constant for krypton and xenon. The breadth of HCl and C2H2 lines are not markedly different in spite of the difference in dipole moment. No asymmetry of lines perturbed by these foreign gases was observed.
Utilization of Order-Disorder Theory in Physical Adsorption. I. Fundamental Equations
Authors: Bumble S. , Honig J. M.
Published: January 2005

The order-disorder theory of Hijmans and de Boer is adapted to a description of equilibrium between a gas and a phase forming a localized submonolayer on an energetically uniform surface. Isotherm equations are derived for adsorption in the absence of lateral interactions, and in the presence of nearest- and next-nearest-neighbor interactions. The Langmuir and Fowler-Guggenheim equations result as special cases of the present treatment. The general theory is then applied to adsorption processes on sites in hexagonal configurations. A discussion of the resulting isotherm equations is presented.
On the Dissociation of Polyatomic Molecules
Authors: Rubin Robert J. , Shuler Kurt E.
Published: January 2005

The dissociation of a simple model of a linear four-atomic molecule is treated classically by considering the motion of configuration points in the configuration space of the molecule. The usual configurational criterion for dissociation, i.e., the crossing of a critical surface in configuration space, is used. The specific problem studied here is the effect of the recrossing of a critical surface by a configuration point corresponding to the ``healing'' of a ``dissociated'' bond. It is shown that, for the model considered here, the above effect results in a greater probability of breaking of the exterior bonds as compared to the interior one.
Application of Ehrenfest Equations to Liquid-Vapor and Liquid-Solid Mixtures of He4
Authors: Lounasmaa O. V.
Published: January 2005

Ehrenfest equations for the constant-volume phase transitions from the mixed liquid-vapor or liquid-solid system to pure liquid or vapor have been derived and applied in the case of He4. Such processes serve as a model of second-order phase transitions. The reasonably good agreement found indicates that these equations may be used to check experimental data at the boundaries of two-phase regions and to determine unknown quantities entering into them.
Distribution Functions of a Fluid in an External Potential Field: Application to Physical Adsorption
Authors: Steele William A. , Ross Marvin
Published: January 2005

The thermodynamic properties of a fluid in an external potential field are expressed in terms of the spatial distribution functions appropriate to the fluid. Several methods of computing these distribution functions are given: integro-differential equations analogous to the Born-Green-Yvon equations; integral equations analogous to the Kirkwood-Salsburg equations; and two approximate methods of computation based on a perturbation approach. The applicability of these methods of calculation to various aspects of the problem of physical adsorption is discussed.
Self-Diffusion of Oxygen in Single Crystal and Polycrystalline Aluminum Oxide
Authors: Oishi Y. , Kingery W. D.
Published: January 2005

The self-diffusion coefficient of oxygen has been determined as a function of temperature in single crystal and polycrystalline aluminum oxide at temperatures up to 1780°C. The rate of exchange between a gas phase and solid particles was measured, utilizing the stable isotope, O18. In single crystals of aluminum oxide intrinsic diffusion occurs in a high temperature region, depending on temperature as D=1.9×103 exp (—152 000/RT). At temperatures below about 1600°C variable results were obtained depending on impurity content and previous heat treatment. For one set of samples experimental results could be represented as D=6.3×10—8 exp (—57 600/RT). The diffusion coefficient of oxygen in polycrystalline samples is about two orders of magnitude larger than that found for the single crystals, and has a somewhat smaller activation energy. With the polycrystalline oxide, variable results were also observed at lower temperatures.
Paramagnetic-Resonance Study of Hyperfine Interactions in Single Crystals Containing α,α-Diphenyl-β-Picrylhydrazyl
Authors: Holmberg Robert W. , Livingston Ralph , Smith William T.
Published: January 2005

α,α-Diphenyl-β-picrylhydrazyl, with and without N15, contained in single crystals of the corresponding hydrazine has been studied by the paramagnetic-resonance method. All resolved hyperfine effects arise from the two hydrazyl nitrogen atoms. The tensors describing the hyperfine interaction for each nitrogen and the principal-axes directions have been deduced. The tensors have been interpreted on the basis of an s-p model with the following electron densities: for the α nitrogen as2=0.011 and ap2=0.263 with the two parts having the same sign of spin density; for the β nitrogen as2=0.024 and ap2=0.396 or as2=0.010 and ap2=0.605. The two choices for the β nitrogen arise from an ambiguity in interpreting the hyperfine tensor, but with either choice the two parts have the same sign of spin density.
Proton-Transfer Studies by Nuclear Magnetic Resonance. II. Rate Constants and Mechanism for the Reaction CH3NH3++OH2+NH2CH3 in Aqueous Acid
Authors: Grunwald Ernest , Karabatsos Photios J. , Kromhout Robert A. , Purlee E. Lee
Published: January 2005

Rate constants were measured by precise nuclear-magnetic-resonance techniques for the reactions CH3N lim −H3++NH2CH3−→ lim k6CH3N lim −H2+HN lim +H2CH3,CH3N lim −H lim +3+OH2+NH2CH3−→ lim k7CH3N lim −H2+HOH+HN lim +H2CH3,in aqueous acid at 25°. The ratio k6/k7 remained virtually constant between 1.7 and 8.1M concentration of CH3NH3Cl. The rate constants were inversely proportional to the viscosity of the solution, and were extrapolated on this basis to infinite dilution to yield the values k60=4.0×108 sec—1 M—1 and k70=5.3×108 sec—1 M—1 at 25°. Acid dissociation constants, densities, and viscosities for 1.7 to 9M solutions of CH3NH3Cl in water were measured also. Measurements of the water activity of these solutions showed that the mean ionic molal activity coefficients of CH3NH3Cl were virtually constant over the entire range. The magnitude of k7, as well as the constancy of k7/k6, indicated that the most probable rate-determining step for the reaction with rate constant k7 is proton transfer from a water molecule in the solvation shell of CH3NH3+ to a molecule of CH3NH2, to produce the triple ion, CH3NH lim +3·OH lim −·HNH2+CH3..
Nucleation and Growth of Mercury Crystals at Low Supersaturation
Authors: Sears G. W.
Published: January 2005

In the present paper it is shown that mercury crystals can be nucleated on a cold glass surface at a much lower supersaturation than has been previously reported. The role of ambient temperature in the growth process is described. It is established that the growth habit is intrinsic to the pure mercury and is not characteristic of a growth modification by foreign gases.
Total Collision Cross Sections for the Interaction of Molecular Beams of Cesium Chloride with Gases. Influence of the Dipole-Dipole Force upon the Scattering
Authors: Schumacher Hugo , Bernstein Richard B. , Rothe Erhard W.
Published: January 2005

Total cross sections (Q) for the interaction of beams of CsCl with a number of molecules were measured using an apparatus of ca 4′ angular resolution in which the temperature of the scattering gas could be varied from 200°—735°K. The temperature dependence of Q was studied for Ar, CH4, CH2F2, CHF3, CF4, NO, H2S, NH3, and for cis- and trans-CHCl=CHCl. Relative values of Q at 300°K were measured for eight additional gases.

The data were correlated using the Massey-Mohr theory, assuming an intermolecular potential V(r) = —C/r6, so that Q=b(C/vr)2/5, where vr is the relative velocity and b a known constant; the potential constant C was estimated from formulas for the dispersion, dipole-induced dipole, and dipole-dipole forces.

For the nonpolar gases the observed small temperature dependence of Q agrees within experimental error (±3%) with that expected from the temperature dependence of vr. The theoretical values of Q differ by a nearly constant factor from the experimental results; thus relative cross sections (Q*) are predicted with fair accuracy.

For the polar gases the Q's are large, decreasing significantly with increasing temperature. Because of the large dipole-dipole interaction, the approximate theoretical treatment (based on the limiting temperature-dependent dipole-dipole contribution to C) accounts only semiquantitatively for the observations.
Diffusion in a Linear Lattice
Authors: Plesner Igor W.
Published: January 2005

Diffusion in crystals by a vacancy mechanism is described by a model consisting of an isotope and a vacancy imbedded in a linear lattice of harmonic oscillators. Assuming a 6–12 potential between defects and lattice atoms, the anharmonic interaction is explicitly calculated. The usual approximation of assuming this interaction to depend linearly on the frequency is shown to be valid as long as the Debye approximation for the frequency spectrum is applicable.

The lattice with defects is analyzed using the formalism developed by Brout and Prigogine. In order to solve the equations, the concept of localized modes is introduced. The localized mode is approximated by the oscillation of the defect (isotope) in the lattice. The justification for this is investigated by a method due to Montroll and Potts.

The diffusion constant is calculated and shown to depend on the fourth power of the defect frequency. This is in agreement with an earlier result by Klemens, but deviates appreciably from the usual first power dependence.
Activity Coefficients of Electrons and Holes at High Concentrations
Authors: Rosenberg Arthur J.
Published: January 2005

The use of the mass-action law in connection with solid-state equilibria involving conduction electrons or holes assumes that the chemical potential of the species is related to its concentration by μ=μ0(T)+kT lnn. This approximation can fail at concentrations which are still very small by ordinary chemical standards. The formalism may be preserved in principle by introducing a suitable activity coefficient γ. It is shown theoretically, however, that γ increases almost exponentially with increasing n when n/λ≳0.1, where λ is the partition function in the quasi-free-particle approximation. As a consequence, the proper exponent of n in mass-action equations becomes much larger than expected from stoichiometry considerations alone. The use of such equations becomes difficult, therefore, when n/λ≳0.5, and entirely unjustified when n/λ≳10. The determination of λ, which lies between 1016 and 1021 cm—3 for most semiconductors is discussed from an experimental viewpoint.
Crystal Structure of β-Ga2O3
Authors: Geller S.
Published: January 2005

The crystal structure of β-Ga2O3 has been determined from single-crystal three-dimensional x-ray diffraction data. The monoclinic crystal has cell dimensions a=12.23±0.02, b=3.04±0.01, c=5.80±0.01 A and β=103.7±0.3° as originally reported by Kohn, Katz, and Broder [Am. Mineral. 42, 398 (1957)]. There are 4 Ga2O3 in the unit cell. The most probable space group to which the crystal belongs is C2h3—C2/m; the atoms are in five sets of special positions 4i: (000, ½½0)±(x0z). There are two kinds of coordination for Ga3+ ions in this structure, namely tetrahedral and octahedral. Average interionic distances are: tetrahedral Ga–O, 1.83 A; octahedral Ga–O, 2.00 A; tetrahedron edge O–O, 3.02 A; and octahedron edge O–O, 2.84 A. Because of the reduced coordination of half of the metal ions, the density of β-Ga2O3 is lower than that of α-Ga2O3 which has the α-corundum structure. Also the closest approach of two Ga3+ ions in β-Ga2O3 is 3.04 A which is considerably larger than the closest approach of metal ions in the sesquioxides with the α-corundum-type structure and, in agreement with the results of thermodynamic measurements, the β phase appears to be the structurally more stable one.

The average Ga–O distances in the structure seem to account for the fact that although the Ga3+ ion is substantially larger than the Al3+ ion its quantitative preference for tetrahedrally coordinated sites when substituted for Fe3+ ion in the iron garnets is very nearly the same as that of the Al3+ ion.

The structure accounts for a recent result obtained by Peter and Schawlow from paramagnetic-resonance measurements on Cr3+-ion-doped β-Ga2O3, namely that the Cr3+ ion substitutes for the Ga3+ ions in a single set of equivalent octahedral sites.

The magnetic aspects of the β-Ga2O3 structure are discussed and it is shown that a possible Fe2O3 isomorph could be expected to be at least antiferromagnetic with a Néel temperature of about 700°K Furthermore, a knowledge of the β-Ga2O3 structure and of the nature of site preferences of the Ga3+ and Fe3+ ions in the garnets lead to a prediction regarding the structure of the ferrimagnetic crystals of formula Ga2—xFexO3 recently discovered by Remeika.
Nitric Oxide-Fluorine Dilute Diffusion Flame
Authors: Rapp Donald , Johnston Harold S.
Published: January 2005

The dilute diffusion flame method for measuring the rates of fast gas reactions has been used to study the reaction 2NO+F2=2ONF. The reaction proceeds with the emission of visible light, and photographic methods were used to obtain concentration profiles in space. The results were interpreted in terms of the mechanism[Complex chemical formula]The interpretation of results is somewhat ambiguous. The observed rate may be that for the first step, in which case the rate constant has a pre-exponential factor of 6×1011 cc/mole-sec and an activation energy of 1.5±1.0 kcal between room temperature and dry ice temperature. Alternatively the observed rate may be a composite of at least four of the elementary steps given above. With a reasonable assignment of rate constants for the succeeding steps, the first alternative is favored, although the margin of safety is not great.
Kinetics of the Alpha Radiolysis of Carbon Monoxide
Authors: Rudolph P. S. , Lind S. C.
Published: January 2005

The radiolytic decomposition of CO induced by alpha particles appears to be initiated by two reactive species, CO+ and CO*. The products of the reaction are CO2 and the solids (C3O2)x and graphite. Carbon dioxide formed during the reaction depletes the CO+ by charge transfer. Thus, when CO2 pressure becomes sufficiently high, CO* only initiates reaction. The reaction mechanism suggested is consistent with previous ionization and photochemical studies in the CO system.
Force Constants for NH4+ and ND4+
Authors: Sundaram S.
Published: January 2005

Normal coordinate analysis, for XY4-type molecules of Td symmetry, has been carried out by the Wilson FG-matrix method. Following Dennison, using the spectral data on NH4+ and ND4+, the anharmonicity factors have been calculated. The constants of the most general quadratic potential-energy function have been obtained for the ammonium ion.
Out-of-Plane CH Vibrations in Some Polynuclear Aromatic Hydrocarbons
Authors: Randić Milan
Published: January 2005

The out-of-plane CH bands in a number of polynuclear aromatic molecules are analyzed. The CH bonds are considered as coupled oscillators. With each group of n neighboring CH bonds an n×n subdeterminant and a single vibrational frequency was associated. The method is applied to the methyl-1,2-benzanthracenes. Observed spectra agree with calculated frequencies well, and thus support the idea that observed CH bands are caused by splitting of n identical coupled oscillators. The spectra of some other polynuclear aromatic hydrocarbons are discussed as well.
Nuclear Magnetic Resonance Spectra of Systems of the A3B2C Type: Proton Magnetic Resonance Spectra and the Absolute Signs of the Proton-Proton Spin Coupling Constants in Ethyl Acetylene and Ethyl Mercaptan
Authors: Narasimhan P. T. , Rogers Max T.
Published: January 2005

The high-resolution proton magnetic resonance spectra of ethyl acetylene and ethyl mercaptan have been studied at both 40 Mc and 60 Mc. Theoretical analysis of these spectra as systems of the A3B2C type enables one to determine the relative signs of the proton-proton spin coupling constants in these molecules. It is thus shown that the spin coupling constants JCH3–CH2 and JCH2–CH are of opposite sign in ethyl acetylene, while JCH3–CH2 and JCH2–SH in ethyl mercaptan are of the same sign. Making use of the results of the valence bond theory regarding the absolute sign of JCH3–CH2 the present analysis has made possible determinations of the absolute sign of JCH2–CH and JCH2–SH in ethyl acetylene and ethyl mercaptan, respectively.
Concise Method for Forming Two-Center Integrals of Operators
Authors: Robinson J. M.
Published: January 2005

Two-center integrals of operators for Slater-type atomic orbitals are concisely expressed in terms of O functions which arise directly from the integral representation in spherical polar coordinates. The O functions are expressible in terms of A and B functions which lend themselves nicely to machine programs. Their greatest asset is their convenient correlation of A and B functions with Slater-type atomic orbitals and operators expressed in spherical polar coordinates. Examples are given for dipole-moment and quadrupole-moment operators.
Orientation Dependence of Magnetic Hyperfine Structure in Free Radicals
Authors: Blinder S. M.
Published: January 2005

The anisotropic part (B term) of the spin Hamiltonian for a free radical is averaged to zero when there is rapid molecular tumbling. Otherwise, it combines with the isotropic part (A term) to produce orientation-dependent hyperfine splittings in ESR spectra. In the high-field case, the electron is strongly coupled to the external field. The nucleus, however, is effectively coupled to the electron's tensor field. Consequently, the two spins have, in general, different axes of quantization. Applying first-order perturbation theory, expressions are derived for the orientation dependence of the resonance in a single crystal and for the line shape in a powder.
Effects of Pressure on Dielectric Relaxation in a Chlorinated Diphenyl
Authors: Perls Thomas A. , Wilner L. Bruce
Published: January 2005

Data are presented on the dielectric properties of a commercial chlorinated diphenyl, Aroclor 1260, over a wide range of frequencies and temperatures, and also over a range of pressures up to 200 kg/cm2 at four fixed temperatures from 17 to 51°C. The data are compared with acoustical-relaxation data previously obtained, and with viscosity-temperature data for the same material. Similar data, from the literature, are evaluated for glycerol. The ratio η/τD is calculated over a range of temperatures for Aroclor 1260 and over a range of pressures for glycerol. The Aroclor 1260 data provide strong evidence against the applicability to this material of Debye's simple hydrodynamic model of a spherical dipole in a viscous medium. A distribution of relaxation times is observed, and it is pointed out that, while this may be due, in part, to the variety of molecules in the Aroclor, it may also be ascribed to the variety of configurations in the vicinity of each molecule, including various degrees of association. Several additional lines of research are suggested. The term ``piezopermittivity'' is proposed for the property of certain materials, such as the Aroclors, which results in large changes in permittivity with pressure. Possible applications of piezopermittivity are discussed.
Activator Center in Magnesium Fluorogermanate Phosphors
Authors: Kemeny G. , Haake C. H.
Published: January 2005

The Mn4+ center in mainly octahedral symmetry has been studied in magnesium fluorogermanate phosphors. Emission and absorption spectra and the temperature dependence of various parameters have been evaluated. Absorption takes place from the 4A2 ground state into the 4F2, 4F1, and higher excited states whereas both emission bands, which lie in the red region of the spectrum, correspond to transitions from the split 4F2 state to the ground state. Electrons in 4F1 and higher quartet states decay nonradiatively into the 4F2 state. The crystal field parameters Dq for the absorption and emission are 2400 and 1600 cm—1, respectively. The electronic and vibrational structure, the temperature dependence and kinetics of emission can be explained by a configurational (normal) coordinate diagram. This coordinate is associated with the distortions from octahedral symmetry and is thus different from that associated with the octahedral crystal field parameter Dq.