bluuebunny/crossref_metadata_2025 huggingface dataset:
Frequency Counting in Lattice Dynamics
Authors: Hwang Jenn-Lin , Wang Chen-Show
Published: January 2005

A method for determining the frequency distribution of crystal lattices on the basis of Born—von Kárman theory is proposed. This is a full account of the previous work, and a generalization to the case of three-dimensional crystal lattices is described.

The procedure for obtaining the frequency distribution involves the following stages:

(1) One must solve the secular equation for determining the squared circular frequency ω2 along the edges of an appropriate part of the first Brillouin zone in the reciprocal lattice in the same manner as did Houston.

(2) One must find, in addition, a few important contours of constant frequency on the surface of the zone as accurately as possible.

(3) On the basis of (1) and (2), one can calculate or trace the desired contours of constant frequency on the surfaces by the proposed interpolation scheme [Eq. (1) or Eq. (2)].

(4) The contours of constant frequency in the inner planes can be calculated or traced by the proposed interpolation scheme described in Sec. IV.

(5) The volume V(ω2) enclosed by the surface of constant frequency means the number of modes of vibrations whose frequencies are less than ω2, and its magnitude may be computed by the proposed numerical or mechanical mean of integration described in Sec. V.

(6) V(ω2) thus calculated is fitted in an analytical form, and at this time the results of van Hove's analysis for singularities may be taken into account to obtain the actual shape of frequency distribution in the vicinity of singularities. A differentiation of V(ω2) with respect to ω2 yields the frequency distribution.

Applications to the two-dimensional and three-dimensional simple cubic lattices are made, and an excellent agreement with the exact frequency distributions calculated by Montroll and Rosenstock is obtained. The present method is thought to be far easier to handle than the conventional ones.
Field Desorption of Barium from Tungsten
Authors: Utsugi H. , Gomer R.
Published: January 2005

The field desorption of Ba has been studied over a range of fields and coverages in an attempt to determine the mechanism of desorption and the charge of the desorbing species. It was found that adsorption seems to be polar but not ionic and that desorption of Ba++ occurs under our conditions. If this interpretation is correct α≅60 Å3 for the polarizability of adsorbed Ba results, close to the value for the free atom. The accessible field-temperature range is restricted by the onset of field-dependent surface diffusion, which was also investigated. It was found that positive fields have more effect on the activation energy Ed and pre-exponential term of the diffusion coefficient than negative ones. While a ½ αF2 dependence of Ed is compatible with the limited data obtained for negative fields, no simple behavior was found for positive ones, Ed going through a minimum of 0, accompanied by a drastic reduction in pre-exponential term. A tentative explanation in terms of a compensation effect is advanced.

Values for the zero field heat of adsorption were obtained over a wide coverage interval and agree well with those of Moore and Allison where overlap occurs.
Field Desorption of Cesium from Tungsten
Authors: Utsugi H. , Gomer R.
Published: January 2005

The field desorption of Cs from tungsten has been investigated at low coverage. The results can best be explained on the basis of a polar groundstate and suggest that an adiabatic transition is involved in the desorption process. On this basis the polarizability of adsorbed Cs is found to be close to that of the free atom. The results are very similar to those obtained with Ba.
Luminescence Decay Times: Concentration Effects
Authors: Yguerabide Juan , Burton Milton
Published: January 2005

The optical properties (e.g., absorption spectrum, fluorescence spectrum, luminescence decay) of solutions of 2,5-diphenyloxazole (PPO) and p-terphenyl in benzene and cyclohexane are reported as functions of solute concentration. The absorption spectra of the solutions, when plotted as extinction coefficient vs wavelength, are unaffected by scintillator concentration, but the fluorescence spectrum of PPO solutions is affected in both intensity and shape. The luminescence decay of all solutions studied is nonexponential and can be resolved into the sum of two exponential decays. The fluorescence spectra and decay curves are affected by oxygen.

The interactions between excited and unexcited molecules and between unexcited molecules themselves and the effect which these interactions have on the optical properties of luminescent solutions are examined. The experimental results can be adequately explained by a mechanism which involves formation of transient dimers by an interaction between excited and unexcited molecules in addition to excitation of solute domains of unexcited solute molecules. It is shown that cage effects by themselves cannot account for the luminescent properties of the systems studied.
High-Pressure Mass Spectrometric Study of Reactions of Rare Gases with N2 and CO
Authors: Munson M. S. B. , Field F. H. , Franklin J. L.
Published: January 2005

Studies have been made in a mass spectrometer at ionization chamber pressures of about 160 μ on mixtures of rare gases, R=He, Ne, Ar, Kr, and Xe, with N2 or CO. The ions R2+, ArN2+, KrN2+, XeN2+, ArCO+, KrCO+, XeCO+, N4+, and C2O2+ were observed in these mixtures as a result of reactions of excited rare-gas atoms. The addition of Ar to N2 enhances the formation of N4+ by reactions initiated by excited states of Ar; the addition of Ar or Kr to CO promotes the formation of C2O2+ through reactions initiated by excited states of Ar and Kr. Rate constants were determined for the reactionsArN2++N2=N4++Ark=1×−10cc/molecule−secKrCO++CO=C2O2++Krk=3×10−10cc/molecule−secat a repeller field strength of 50 V/cm. Other combinations of rare gases with N2 or CO show no such promotional effect on the formation of N4+ or C2O2+. Ratios of the rate constants for the formation of RN2+ and R2+ in rare-gas-nitrogen mixtures and for the formation of RCO+ and R2+ in rare-gas-carbon monoxide systems were also determined. At high pressures of N2 or CO alone the formation of N4+ or C2O2+ is observed, and the reaction is a bimolecular chemi-ionization involving highly excited N2 or CO. At still higher pressures these ions are formed by termolecular ion—molecule processes.

At sufficiently high electron energies there are formed in binary mixtures of N2 or CO with different rare gases the following ions: RC+, RN+, C2O+, CO2+ and N3+. The N3+ and RN+ ions are formed by the reaction of excited nitrogen molecule ions with R and/or N2, and the relative rates of these reactions were determined.

No compound ions between He or Ne and N2 or CO were observed under any of the conditions of these experiments.
Dissociation and Isomerization of Vibrationally Excited Species. II. Unimolecular Reaction Rate Theory and Its Application
Authors: Wieder Grace M. , Marcus R. A.
Published: January 2005

Data on quasi-unimolecular reactions have usually been compared with theoretical equations based on classical treatments, because the expressions are simpler than those obtained on the basis of a quantum model. The quantum reformulation of the RRK theory in Part I is used to compute the pressure dependence of the rate constants and the limiting low-pressure rates for a variety of unimolecular reactions without employing adjustable parameters. An asymptotic expansion of the integral for the limiting low-pressure second-order rate constant provides a very simple expression for this quantity.

The errors inherent in corresponding classical calculations are estimated by comparing these results with those obtained from the theory in its classical limit. The error is temperature dependent and at low pressures increases from a factor of about three (under typical experimental conditions) for small reactants such as O3 and N2O to 105 or more for large molecules such as cyclopropane, C2H6, and N2O5. In most cases the rates calculated from the quantum form are in reasonable agreement with those obtained experimentally when all of the reactant oscillators are assumed effective in intramolecular energy transfer.
Sedimentation in Chemically Reacting Systems. I. The Isomerization Reaction
Authors: Van Holde K. E.
Published: January 2005

A solution has been obtained for the differential equations describing the changes in concentrations with time and position in an ultracentrifuge cell during the sedimentation of an isomerizing substance. It is assumed that diffusion is negligable, and that the centrifugal field and cell cross section are constant. In addition to the general result, simple approximate solutions are presented for the cases where the chemical reactions are moderately slow and moderately fast, compared to the rate of separation of species by the centrifugal field.
High-Temperature Spectral Absorption of the 4.3-Micron CO2 Band
Authors: Ferriso Carmine C.
Published: January 2005

The absorption coefficients of the ν3, 4.3-μ CO2 band were measured over a temperature range of about 1200° to 2400°K at various pathlengths. The hot CO2 sample was investigated in the exhaust jet of a small supersonic burner, while the jet composition was obtained using a radiation temperature measurement and a simple thermochemical calculation. The present experimental results are compared with existing experimental values and theoretical calculations. The results indicate that above 2000°K a weak line approximation can be used to describe the absorption or emission of the band. The apparent integrated band intensity of the CO2 fundamental as a function of temperature is also reported and discussed in relation to other measurements.
Theory of Electronic Energy Relaxation in the Solid Phase
Authors: Robinson G. W. , Frosch R. P.
Published: January 2005

A theory of electronic energy relaxation in the solid phase is presented. This process is sometimes called internal conversion when applied to states of the same multiplicity, or intersystem crossing when applied to states of different multiplicity. The physical limit where the electronic transition is slow compared with vibrational relaxation is shown to be a well-defined mathematical limit in the theory. In the other limit, where the electronic transition is rapid compared with the vibrational relaxation time, vibrational relaxation plays the dominant role in the over-all relaxation process. The result derived from a continuum model for the final states is justified only in the first limit and only then providing the assumption of a large number of final states is physically justified. Two different models are used to illustrate the source of the mathematical limitations and the range of applicability of the theory. These models remove the ambiguities which arise from the normalization of continuum states in the continuum model. The most important conclusions of the paper are embodied in Eqs. (22), (23), (40), (48), and (50).
Infrared Spectrum of Acetylene-d1
Authors: Lafferty Walter J. , Plyler Earie K. , Tidwell Eugene D.
Published: January 2005

The high-resolution absorption spectrum of C2HD has been studied in the 1900 to 3400 cm—1 region. Several bands at lower frequencies have been examined with medium resolution. Nineteen bands were analyzed for their rotational constants. Combination differences of four transitions from the ground state were averaged and the rotational constants B0=0.99156±0.00004 cm—1 and D0=1.17±0.07×10—6 cm—1 obtained. This B0 value together with those recently obtained for C2H2 and C2D2 have been used to calculate the ground-state and equilibrium bond distances of the acetylene molecule. The l-doubling constants for the degenerate modes were determined to be q4=4.42×10—3 cm—1 and q5=3.6×10—3 cm—1. The frequencies of the bending modes have been calculated by use of difference bands to be ν41=518.38 cm—1 and ν51=677.77 cm—1.
ESR and Optical Spectrum of Potassium Perchromate
Authors: McGarvey B. R.
Published: January 2005

The ESR powder spectra of both pure K3CrO8 and of K3NbO8, containing small amounts of K3CrO8, have been obtained. The spectra have yielded the values: g∥=1.9434, g‖=1.9848, for the two spin Hamiltonian parameters of chromium in the +5 oxidation state. It has been shown that the g factors can only be explained by assuming the ground state to be B1(dxy). Further, the optical spectrum of K3CrO8 in 30% H2O2 has been obtained and the single observed band at 20 000 cm—1, has been assigned to the B1→E transition. Both the ESR and the optical spectra indicate a strong degree of covalent character in the bond between the chromium atom and the peroxide ions.
Scattering of Helium and Argon from the Cleavage Plane of Lithium Fluoride
Authors: Crews J. C.
Published: January 2005

The scattering of helium and argon from the cleavage plane of lithium fluoride has been studied using molecular-beam techniques and under vacuum conditions which were somewhat better than are typical for systems of this type. The helium measurements confirm the diffraction effects reported by O. Stern and co-workers and reveal, in addition, a broad scattered beam approximately symmetrical about the specular position which apparently has not been previously recognized. Measurements with argon beams gave scattering patterns which were quite different from those obtained for helium. The scattered beams were very broad and had an intensity maximum between the specular position and the crystal normal. Analysis of the data showed that this deviation of the maximum from the specular position cannot be obtained by superposition of specular and cosine-law scattering components. Furthermore, the experimental data on the scattering of argon seem to be inconsistent with a diffraction mechanism.
Benzene Ring Distortion by One Substituent. Microwave Determination of the Complete Structure of Benzonitrile
Authors: Bak Børge , Christensen Daniel , Dixon William B. , Hansen-Nygaard Lise , Rastrup-Andersen John
Published: January 2005

Microwave spectra of benzonitrile, C6H5CN, and 9 isotopic species are reported. Moments of inertia of these 10 molecules are combined to give the rs structure of benzonitrile. The final structure is: C(1)C(2) = 1.391 Å, C(2)C(3) = 1.393 Å, C(3)C(4) = 1.400 Å, C(1)C(7) = 1.455 Å, C≡N = 1.159 Å, C(2)H(2) = 1.069 Å, C(3)H(3) = 1.082 Å, C(4)H(4) = 1.081 Å, C(6)C(1)C(2) = 122.5°, C(1)C(2)C(3) = 118.45°, C(2)C(3)C(4) = 120.3°, C(3)C(4)C(5) = 120.0°, C(1)C(2)H(2) = 121.8°, C(4)C(3)H(3) = 119.9°.
Phosphorescence and Stimulated Emission in Organic Molecules
Authors: Morantz D. J. , White B. G. , Wright A. J. C.
Published: January 2005

Stimulated emission of light has been demonstrated using aromatic organic molecules in a rigid glass matrix, e.g., acetophenone, benzaldehyde, benzophenone, α-bromonaphthalene, and pyrazine. This system is compared with the inorganic crystalline light masers. The experimental technique is described. Characteristic properties of the emitted light are given in detail and discussed. The conditions for achieving the stimulated emission threshold are described. The possibility of orienting molecules in a maser cell is proposed.
Origin of the Cotton Effect of Helical Polypeptides
Authors: Schellman John A. , Oriel Patrick
Published: January 2005

A theory of the 225-mμ Cotton effect is presented in which the optical rotation is produced by the static helical electric field with the large quadrupole moment of the nπ transition of the peptide link. As a result of the helical perturbation, a component of electric transition moment is borrowed from the π—π transition moments and from the charge transfer associated with the nπ transition. This component is parallel to the large magnetic moment of the nπ transition and accordingly is associated with an induced rotatory strength as well as enhanced absorption. Both effects disappear in the random chain form. The theory is in sufficiently general form that it may be applied to other nπ transitions. In particular, the theory predicts that the contribution of a perturbing atom to the rotatory strength is proportional to the quantity XY where X and Y are the Cartesian coordinates of the perturbing atom relative to the nucleus of the heteroatom. X and Y are oriented such that X=0 defines the nodal plane of the π system and Y=0 defines the nodal plane of the nonbonding orbital.
Semiclassical Model of Atomic Interactions
Authors: Jefimenko Oleg
Published: January 2005

The possibility of obtaining approximate solutions to atomic interaction problems by using a drastically simplified version of the quantum-mechanical atomic model is discussed. The atom on this simplified model is regarded as a point-charge nucleus enclosed by a thin, spherical, uniformly charged electron shell. The model allows a description of atomic interactions on an essentially classical basis and gives fairly realistic expressions for the dissociation energy of homonuclear diatomic molecules and for certain other interaction parameters. It is concluded that the model provides a tool helpful for discussions of interatomic forces and effects associated with these forces.
Electron Spin Resonance of Gamma-Irradiated Single Crystal of Acetyl-L-Glutamic Acid
Authors: Katayama Mikio
Published: January 2005

The electron spin resonance spectra of gamma-irradiated single crystals of acetyl-L-glutamic acid have been measured at 9 and 23.4 kMc/sec for various orientations of the crystal in the external magnetic field.

From the analysis of the hyperfine interaction constants, the free radical produced immediately after the irradiation of acetyl-L-glutamic acid is thought to be[Complex chemical formula]However, this radical transforms to another more stable one in the half-life of three days. The structure of the stable free radical is inferred from the hyperfine structure of its electron spin resonance.
Photoelectric Phenomena in Hemoglobin and Dyed Gelatin
Authors: Nelson R. C.
Published: January 2005

Hemoglobin shows photoconductivity with a threshold at about 3.9 eV. A similar phenomenon is found in dyed gelatin films. In the latter case, the response arises from light absorbed by the protein rather than by the dye, and it is suggested that the energy is transferred to the dye by a nonradiative resonance process involving the aromatic amino acid residues in the protein, and that the dye functions only as a relatively easily ionizable center in the solid. The same is presumably true of the porphyrin group in hemoglobin. No evidence for the existence of band-model structure in these proteins could be inferred from the data.
Structural and Magnetic Characteristics of TiFe2–ZrFe2 and ZrCo2–ZrFe2 Alloys
Authors: Piegger E. , Craig R. S.
Published: January 2005

Structures and unit-cell dimensions for a number of alloys of TiFe2–ZrFe2 and of ZrCo2–ZrFe2 have been determined at room temperature, and the magnetic properties of alloys of the two systems have been investigated over a range of temperature extending from 4° to 650°K. Results for the TiFe2–ZrFe2 system show two terminal phases separated by a two-phase region extending from 56 to 85 mole % ZrFe2. TiFe2 behaves like a strongly paramagnetic substance with a susceptibility which is practically temperature independent, whereas ZrFe2 is ferromagnetic with a Curie temperature of 355°C. The effective moment per iron atom, obtained from the observed saturation magnetization at 4°K, is 1.62 μB. The reduced moment in both the TiFe2 and ZrFe2 phases compared to that for elemental iron is attributed to a transfer of charge from Ti or Zr to iron.

The ZrCo2–ZrFe2 alloys form a single phase system which approximately obeys Vegard's law. ZrCo2 is found to be fairly strongly paramagnetic at room temperature, while at low temperature it appears to be either very weakly ferromagnetic or paramagnetic with a susceptibility which is field dependent and shows saturation effects. As ZrCo2 is dissolved in ZrFe2, the shapes of the magnetization—temperature curves change in a way which indicates that the destruction of the ferromagnetism occurs over an unusually large temperature interval. This effect is attributed to microscopic variations in the molecular field in the solid solutions. The small values of the observed magnetic moments suggest that in these materials zirconium donates electrons to iron and cobalt. When Fe in ZrFe2 is progressively replaced by Co, the average moment of Co and Fe is observed to decrease initially and to reach a minimum at about 40 mole % ZrFe2.
Spectrum of N3— in Solution
Authors: Burak Itamar , Treinin Avner
Published: January 2005

The electronic absorption spectrum of N3— in solution was investigated. For this purpose environmental effects on this spectrum were studied, and the thermodynamic properties of the I2–N3— complex were determined. In the 190–300-mμ region the spectrum consists of at least three bands, designated by A, B, and C. Their identification is based on the comparison with the spectra of solid alkali azides. Band A which is of moderate intensity (ε∼400 liter mole—1 cm—1) appears at 230 mμ and is assigned to 1Δu←1Σg+ transition. Band B with λmax at about 200 mμ originates from a charge transfer to the solvent (CTTS). For Band C, the peak of which is at the vacuum uv, a 1Σu+ excited state is suggested.

The nature of the CTTS state of N3— is discussed and evidence is provided for the mixing of this state with the 1Δu state. The investigation of the CTTS band leads to a value for the electron-affinity E(N3)=81 kcal. One method for deriving this value is based entirely on solvent effects by means of a method which was recently developed. This method yields also an estimate of the crystallographic radius of the ion: R(N3—)∼1.92 Å.
Adaptation of the Urey—Bradley Force Field to NH3, PH3, SbH3, and AsH3
Authors: Pariseau Marian , Wu Ellen , Overend John
Published: January 2005

It has been pointed out previously that the Urey—Bradley force field (UBFF) is not a satisfactory potential function for ammonia. However, a modification of the basic UBFF, based on consideration of the lone pair of electrons, has been shown to be a useful force field for the Group V hydrides.
Correlation Effects in the Alternant Molecular Orbital Approximation
Authors: Adams William H.
Published: January 2005

Examination of the two-electron density matrix in the alternant molecular orbital approximation for a large system in a singlet state reveals that there are both short- and long-range correlations between the electrons of opposite spin. There is also a long-range correlation between electrons of the same spin. These correlations are not found when the wavefunction for the system is approximated by a single determinant of alternant molecular orbitals.
High-Resolution ESR Spectra of Photochemically Generated Free Radicals: The Viologens
Authors: Johnson C. S. , Gutowsky H. S.
Published: January 2005

High-resolution electron spin resonance spectra have been obtained for free radicals produced from methyl, ethyl, and benzyl viologen and 4–4′-bipyridyl in ethanol—water solutions by irradiation with sunlight. From the analysis of these spectra we find that the hyperfine splittings for the protons ortho and meta to the nitrogen atoms are almost equal. The spin density distributions are discussed in terms of McLachlan's approximate SCF theory and we conclude that |QNHH|≈|QN CH3H|≈25.
Optical Studies of Anisotropic Color Centers in Germanium-Doped Quartz
Authors: Halperin A. , Ralph J. E.
Published: January 2005

The optical absorption induced by x rays in germanium-doped quartz has been investigated using polarized light. The wavelength range was 220–800 mμ, and the behavior of the various bands was examined over the temperature range of 77°—600°K. Absorption bands polarized in parallel to the optical axis were observed at 250, 285, 296, 450, and about 620 mμ, and bands at 260, 272, 290, and 330 mμ were found to be polarized perpendicularly to the optical axis. The experiments also included a study of the optical bleaching of the bands and the effects of exchange of interstitial monovalent ions by electrical diffusion.

The results are discussed and correlated with results of electron paramagnetic resonance measurements carried out on the same specimens by J. H. Mackey.
Vibrational Analysis of the Heitler—London Potential of H2
Authors: Beckel Charles L.
Published: January 2005

The vibrational levels associated with the Heitler—London potential of H2 have been found through use of the first-order WBK approximation. The vibrational energies G as a function of quantum number v are accurately represented by G=—D0(1—Av—Bv2)n, where D0 is the Heitler—London dissociation energy and A, B, and n are parameters. The ΔG curve has negative curvature at all v. At high v the vibrational levels show the rapid convergence characteristic of covalent molecules. The Heitler—London ΔG curve has very nearly the same shape as the experimental curve for H2; horizontally displaced to agree with experiment at low v, the Heitler—London ΔG curve predicts a dissociation energy which is 93% of the experimental value.
Calculation of London—van der Waals Energies
Authors: Musher Jeremy I.
Published: January 2005

A simple expression for the London—van der Waals interaction energies of like molecules, in the absence of retardation effects, is obtained by a perturbation theory calculation using a new approximate method. The approximate method, which is useful for certain second-order p.t. sums when the unperturbed wave-functions can be described as products of determinants, is presented with a discussion of its generally small error. This method enables one to express the London—van der Waals energy (also called ``dispersion energy'') as products of certain expectation values over the unperturbed wavefunctions, involving essentially approximate solutions, to the first-order perturbation Schrödinger equation in its differential form. In particular, the energy in the inverse sixth power of the intermolecular separation R can be expressed as the product of electric dipole polarizabilities and mean-square electric dipole moments. For two interacting 1s hydrogen atoms the energy is very easily computed and found to be EL=−e2a0[6.75(Ra0)−6  (Ra0)−8+819(Ra0)−10+···].The first two terms compare favorably with the results of variational calculations while the third does not. Using the approximate perturbed wavefunction, the expectation values of r2 and 1/r for each electron proportional to R—6 are obtained. These expectation values which contribute to the atomic magnetic susceptibility and to the magnetic shielding of the proton agree well with the variational calculations. Also obtained is the third-order p.t. energy between three like molecules which for three 1s hydrogen atoms is E3=−23.1(R12/a0)−3(R13/a0)−3(R23/a0)−3Ω,where Ω is an angular factor.
Potential and Effective Diffusion Constant in a Polyelectrolyte Solution
Authors: Coriell Sam R. , Jackson Julius L.
Published: January 2005

Numerical computations of the electrostatic potential and the effective diffusion constant of counterions in a periodic polyelectrolyte solution are reported. Some results for the potentials for various polyion charge densities and polyion sizes are presented graphically. The calculated diffusion constants are compared with experimental data on the diffusion of labeled sodium ions in polyacrylic acid-sodium hydroxide solutions as well as with the earlier approximate calculations.
Use of the Nuclear Overhauser Effect in the Analysis of High-Resolution Nuclear Magnetic Resonance Spectra
Authors: Kaiser Reinhold
Published: January 2005

Relative intensity changes may be observed in a high-resolution proton magnetic resonance spectrum when one of the lines is partially saturated by irradiation with a radio-frequency field. This is a manifestation of the general Overhauser effect since the intensity changes result from changes in the populations of the eigenstates of the spin Hamiltonian. A simple theory is based on the approximation that population changes are negligible for energy levels not connected by the irradiated transition. This theory appears to be adequate for applications in the analysis of high-resolution spectra. Examples are given for systems with spin couplings of low or moderate strength to show how the Overhauser effect may be used to determine the relative signs of spin coupling constants, and to assign spectral lines to transitions between energy levels. The experimental techniques are discussed. Previously reported results for trans-crotonaldehyde and m-dinitrobenzene are confirmed, and all coupling constants in m-dinitrobenzene are found to have the same sign.
Theory for Zero-Field Splittings in Aromatic Hydrocarbons. III
Authors: Boorstein Seth Alan , Gouterman Martin
Published: January 2005

The assumptions underlying a calculation of the zero-field splitting parameters D and E are stated in order of increasing severity. Under these assumptions, a number of molecules are calculated and the results compared with experiment. The sensitivity of the calculations to changes in some of the assumptions is examined. The present theory is shown to be in excellent agreement with experiment for the molecules benzene, naphthalene, and anthracene; in fair agreement for phenanthrene; and in poor agreement for triphenylene and coronene.
Satellite Bands in the Spectra of Gaseous Mixtures and the Shape of Potential Curves for Neutral Atoms and Molecules in the State of Collision
Authors: Jefimenko Oleg
Published: January 2005

An analysis of the experimental data on Cs satellite bands in the spectra of gaseous mixtures suggests the existence of auxiliary minima and relative maxima in the excited-state potential curves representing binary interactions between colliding atoms and molecules. The auxiliary minima are indicated for interactions of the radiating atoms with the foreign-gas molecules which produce a red shift of the atomic spectral lines (exhibit the Ramsauer—Townsend effect). The relative maxima are indicated for interactions of the radiating atoms with the foreign-gas molecules which produce a violet shift of the atomic spectral lines (do not exhibit the Ramsauer—Townsend effect). The depth of the auxiliary minima and the height of the relative maxima are determined primarily by the effective cross sections of the foreign-gas molecules for collisions with the valence electrons of the radiating atoms. The assumption of such minima and maxima leads to a plausible explanation of most experimentally determined properties of the alkali—foreign-gas satellite bands.
Infrared Spectra and the Structures and Thermodynamics of Gaseous LiO, Li2O, and Li2O2
Authors: White David , Seshadri K. S. , Dever D. F. , Mann D. E. , Linevsky M. J.
Published: January 2005

The vapor above heated lithium oxide (Li2O) has been investigated mass spectrometrically and by infrared matrix-isolation spectroscopy. The vapor composition and Knudsen effusion rates were measured as functions of temperature, and the matrix spectra of the principal lithium oxide species—Li2O, LiO, Li2O2—identified and analyzed for different isotopic abundances. The predominant vapor species Li72O is probably linear with r(Li–O) = 1.59 Å, and has fundamentals ν1, ν2, ν3 at [760], [140], and 987 cm—1, respectively. Its heat of formation ΔH0°(f) = —43.7±2.5 kcal/mole. The diatomic molecule Li7O has ν = 745 cm—1, an estimated bond length r = 1.62 Å, and ΔH0°(f) = +16.0±5 kcal/mole. The previously undetected molecule Li72O2 is shown to resemble the alkali halide dimers in having a planar rhombic (Vh) structure for which the O–Li–O angle and Li–O bond length are estimated to be 116° and 1.90 Å, respectively. Its B2u and B3u frequencies are found at 324 and 522 cm—1, respectively, in a krypton matrix. The remaining unobserved modes are estimated in cm—1 as follows: ν1(Ag) = 400, ν2(Agt) = 250, ν3(B1g) = 300, ν4(B1u) = 270. Its ΔH0°(f) = +27.5+6 kcal/mole.
Computation of Unique NMR Parameters for ABC Systems with the Aid of C13–H Satellite Spectra
Authors: Hobgood R. T. , Mayo Ralph E. , Goldstein J. H.
Published: January 2005

Theoretical analyses of proton magnetic resonance spectra of ABC systems have on occasion resulted in more than one set of acceptable parameters. It is proposed that such ambiguities can be eliminated by requiring the parameters to satisfactorily predict not only the normal spectral patterns but also those of the C13–H satellite spectra. This procedure has been successfully applied to tetravinylsilane and acrylonitrile.
Ionization Rate Constants of Alkali Metals in CO Flames
Authors: Hollander Tj. , Kalff P. J. , Alkemade C. T. J.
Published: January 2005

The deviation of the alkali ionization from Saha equilibrium outside of the reaction zone is shown, and experimental results are given concerning the rate constants of the ionization and recombination reactions. On the basis of these results conclusions are drawn about the kind of reactions leading to ionization of the alkali metals in CO flames at atmospheric pressure.
Nuclear Magnetic Shielding Constants and X-Ray Atomic Scattering Factors for Two-, Three-, and Four-Electron Systems by Means of Analytic Hartree—Fock Wavefunctions
Authors: Rustgi M. L. , Tiwari P.
Published: January 2005

Nuclear magnetic shielding constants and x-ray atomic scattering factors have been calculated for two-, three-, and four-electron systems using the best analytical self-consistent field functions of Roothaan, Sachs, and Weiss, and where possible, the reported values have been compared with the ones already published. It is pointed out that it may not be possible to extract any reliable information about the angular and radial correlations of electrons in the atoms and ions considered here from the scattering factors.
Viscosity Dependence of the First-Order Decay of the Triplet State of Anthracene and Related Molecules
Authors: Livingston Robert , Ware William R.
Published: January 2005

In fluid (nonviscous) solvents, the first-order term in the rate equation for the decay of the triplet state of an aryl hydrocarbon appears to be the sum of a unimolecular, practically temperature-independent process and a bimolecular quenching reaction involving an adventitious quencher, present in trace amounts. The rate of this bimolecular reaction is diffusionally limited, over a wide range of temperatures and viscosities. In highly viscous media, the temperature dependent components of the first-order reactions have energies of activation ranging from 0.8 to 0.3 of the value which corresponds to the variation of the viscosity of the solvent with temperature.
Conformal Ionic Mixtures
Authors: Blander Milton , Yosim S. J.
Published: January 2005

The excess free energy of mixing of molten reciprocal salt solutions (A+, B+, X—, Y—) has been calculated up to the second order by the perturbation method of Reiss, Katz, and Kleppa. The result is a power series containing integral powers of the ion fractions (concentrations). This demonstrates that mixtures of two salts of the same valence type cannot be considered as a mixture of a salt with a dielectric solvent.

The first term in the series is proportional to the free-energy change for the reaction AX+BY→AY+BX and is the same as the theory of Flood, Fo/rland, and Grjotheim. The results of the symmetric approximation based upon the quasilattice model are consistent with the first term and one of the second-order terms. The remaining second-order terms are related to the excess free energy of mixing in the binary systems AX—AY, BX—BY, AX—BX, AY—BY and are of a form first suggested by Fo/rland. This theory, thus, gives a relatively rigorous justification to aspects of previous theories of reciprocal salt solutions which were based upon restrictive models and assumptions.
Viscosity and Diffusion Coefficients of Gaseous Sulfur Hexafluoride—Carbon Tetrafluoride Mixtures
Authors: Raw C. J. G. , Tang Helen
Published: January 2005

The viscosity coefficients of gaseous mixtures of sulfur hexafluoride and carbon tetrafluoride have been measured in the temperature range 300°—350°K. These experimental results are discussed in terms of the kinetic theory expression for mixture viscosities (using the empirical combining rules for the potential parameters), and the Sutherland—Wassiljewa equation. Diffusion coefficients for the mixtures have been determined from the mixture viscosities using the procedure of Weissman and Mason.
Isotope Bands and the Vibration Assignment of the D 2πg—A 2πu System of N2+
Authors: Namioka T. , Yoshino K. , Tanaka Y.
Published: January 2005

The D 2πg—A 2πu bands of (N215)+ have been studied in the 2050 to 2570-Å region in order to determine the correct vibrational quantum number assignment. The results obtained from the study of the isotope shifts of the band heads show that the quantum number of the previously observed lowest vibration level of the D state is v=3. The potential energy curve of the D state has also been calculated by means of the Rydberg—Klein—Rees method, which has been modified by Vanderslice et al.
Effect of Pressure on the Activation Energy of Electrical Conduction in Aqueous Solution
Authors: Horne R. A. , Myers B. R. , Frysinger G. R.
Published: January 2005

The specific conductances of aqueous KCl, KOH, and HCl solutions have been measured as functions of hydrostatic pressure and temperature over the ranges 5° to 45°C and 1 to 6900 bars. The activation energy for the conductance of KCl solutions varies in roughly the same way with pressure as does the viscosity of the medium. The activation energy for the conductance of HCl solutions does not vary with pressure in the same way as do KCl solutions and the viscosity because the principal contribution to the conductance arises from a Grotthuss-type protonic transfer rather than from simple translational ionic movement. At lower pressures the rotation of water molecules appears to be the rate-controlling step, but above about 1380 bars the proton jump becomes rate determining.
Gas-Phase Complexes in Hydrogen Chloride
Authors: Rank D. H. , Sitaram P. , Glickman W. A. , Wiggins T. A.
Published: January 2005

The null gap region of the fundamental band of HCl has been studied in the case where argon and xenon are used as perturbing gases. The experiments were performed using an absorption cell of 150 cm length. The absorption cell could be varied in temperature from room temperature to 195°K. The complex features previously observed in the spectrum at room temperature were greatly enhanced in intensity at the lowest temperature. The absorption spectrum of pure HCl gas was found to show strong evidence for dimer formation, which feature becomes strikingly evident at the lowest temperature employed. ``Arrhenius'' plots were made of the HCl–Ar, HCl–Xe, and the dimer data. The heats of formation were found to be 1.1, 1.6, and 2.14 kcal/mole, respectively, with a probable error of ±0.2 kcal/mole. The concentration of the dimer is estimated to be 1 part in 50 000 at 195°K at a gas density of 0.36 amagat.
Temperature Dependence of the Pure Quadrupole Resonance Frequency and Spin—Lattice Relaxation Time in NaBrO3 at Low Temperature
Authors: Tipsword R. F. , Moulton W. G.
Published: January 2005

The pure quadrupole resonance frequency of Br79 and Br81 in NaBrO3 has been measured between 4.2° and 77.3°K. The spin—lattice relaxation times have been measured between 4.2° and 16°K. The frequency measurements were compared with the Bayer—Kushida theory. While qualitative agreement with the theory is found over the entire temperature interval investigated, the theory does not fit the data in detail. The spin—lattice relaxation times were compared with the theory developed by Chang for NaClO3. If a linear or parabolic temperature dependence of the Br quadrupole frequency is used, as has been the case in all previous work, the theory can be made to agree with the data by appropriately choosing the Debye temperature. However, if the more nearly correct temperature dependence of the quadrupole frequency given by Bayer is inserted into the theory, it is found that no reasonable adjustment of the Debye temperature gives agreement. Fair agreement with the data can be obtained in this case by adjusting the velocities of the longitudinal and transverse lattice waves. Furthermore, at low temperatures the frequency dependence of Bayer leads to nearly equal contributions to the relaxation of Δm=±1 and Δm=±2 transitions, in contrast to the assumption of a linear or parabolic temperature dependence which leads to negligible contribution by the Δm=±2 transitions.
Temperature Dependences of Nuclear-Transfer and Spin-Relaxation Phenomena of Water Adsorbed on Silica Gel
Authors: Woessner D. E.
Published: January 2005

NMR relaxation-time measurements have been made from 193° to 374°K on the protons in a sample of ¾ statistical monolayer of water adsorbed on silica gel. Protons in two different environmental states were observed. Proton transfers occur between these two environmental states. For the first time, the T2 value for the longer T2 state has been observed without shortening by nuclear transfers. This longer T2 value increases with temperature in accordance with an activation energy of approximately 7 kcal/mole. The weighted average T1 value has a similar temperature dependence in the range 225° to 270°K. The data were analyzed in detail by use of previously developed theory. Near room temperature, the activation energy for proton transfer is 4.9 kcal/mole, and the average lifetime of a proton in a given state is a few milliseconds. The protons in both states experience very rapid motion; one of the states has an additional slow motion.
Valence-Bond Theory of Resonance: Aniline, Phenol, and Fluorobenzene
Authors: Schug John C.
Published: January 2005

A perturbation-type valence-bond theory is developed for the computation of pi-orbital charge distributions in substituted benzenes. Application is made to aniline, phenol, and fluorobenzene, employing for comparison approximate charge distributions derived from proton chemical shift measurements. An important finding is that the previously employed approximation of including only single-electron transfers between adjacent atoms is not valid. The inclusion of second-order transfer interactions permits one to compute charge distributions which agree well with the experimental data. However, one must employ empirical integral parameters which are slightly different from the estimated values. Detracting from the theory is the fact that the computations apparently place too much charge on the carbon atom adjacent to the substituent.
Growth of Anthracene Whiskers by Vapor Deposition
Authors: Sears Gerald W.
Published: January 2005

Anthracene whiskers were observed to grow at low supersaturations consistent with the screw dislocation mechanism of whisker growth. Whiskers were observed to grow coherently from a larger crystal in a few crystallographic directions. The simultaneous growth of whiskers in the habit plane and normal to the habit plane, for example, requires a regenerative axial growth defect. A screw dislocation appears to be the only line defect with the required properties.
Study of Moderately Rapid Chemical Exchange Reactions by Means of Nuclear Magnetic Double Resonance
Authors: Forsén Sture , Hoffman Ragnar A.
Published: January 2005

A nuclear magnetic double-resonance method for the determination of chemical exchange rates has been developed. The method is applicable to systems in which a nuclear spin is reversibly transferred between two nonequivalent sites, A and B. The lifetime (τA) and spin—lattice relaxation time (T1A) in Site A are obtained through the study of the decay to a new equilibrium value of Signal A upon the sudden saturation of Signal B. The converse experiment permits the determination of τB and T1B. A number of data for cross checks are furthermore obtained through the study of the recovery of the signals upon the release of various combinations of saturating rf fields.

A simple theory based on the Bloch equations as modified by McConnell to incorporate the effects of chemical exchange is given. Experimental results on the hydroxyl proton exchange in the system salicylaldehyde and 2-hydroxyacetophenone are well described by this simple theory.

The present method, which can readily be extended to systems with several sites, offers a complement to the Gutowsky—Saika single-resonance method and is particularly suited to the study of exchange rates slower than those accessible by the single-resonance method.
Sound Dispersion in Substituted Methane—Inert Gas Mixtures
Authors: Olson J. R. , Legvold Sam
Published: January 2005

Binary halomethane—noble gas mixtures were examined ultrasonically. The methanes used were CF4, CHF3, and CCl2F2 and the noble gases were Ar, Ne, and He. Results obtained show that the reciprocal relaxation times for these mixtures vary linearly with the concentration. Also, Ar—X collisions are less effective, He—X collisions are much more effective, and Ne—X collisions differ little from X—X collisions in vibrational energy transfer. X represents the dispersive gas. Theoretical values of Z10AB, the mean collision lifetime of an A molecule in an otherwise pure gas of B molecules, were calculated according to the Schwartz, Slawsky, and Herzfeld theory. Intermolecular potentials appropriate for the treatment of the data were examined, and it was found that the Lennard-Jones 6:12 potential was appropriate for the noble gases, and the 7:28 form was appropriate for the halomethanes.
Structure of Molten Oxides. II. A Density Study of Binary Germanates Containing Li2O, Na2O, K2O, and Rb2O
Authors: Riebling E. F.
Published: January 2005

An improved counterbalanced sphere viscometer—densitometer was used to obtain density information between 1050° to 1500°C for a series of binary germanate melts containing as much as 60 mole% Li2O, Na2O, K2O, and Rb2O. Densities and the expansion coefficient of molten GeO2 between 1100° to 1400°C were estimated from the binary data. The molar volume, expansion coefficient, partial molar volume and partial molar expansion deviations suggest a mode of network alteration that differs from that observed for silicate melts. This confirms the previously reported viscosity results for binary alkali germanate melts. It is suggested that a gradual change from tetrahedral to octahedral configuration occurs for GeO2 with the addition of alkali oxide. The maximum stability of octahedrally coordinated germanium at 1300°C appears to occur for melts containing from 15 to 30 mole% M2O. A rapid return to tetrahedral configuration appears to take place for most germanate melts as the alkali oxide content is increased above 30 mole%. These alkali-rich germanate melts possess properties that are similar to those found for their silicate analogs. It is suggested that discrete anions also exist in these alkali rich germanate melts.
Combination of the Lattice Modes with the Internal Modes in a Crystal
Authors: Mitra S. S.
Published: January 2005

The possible origin of the complexity in the near-infrared spectra (around the single factor group allowed hydroxyl stretching fundamental) of some hydroxide crystals has recently been the subject of considerable controversy. The possibility of this structure arising from the combination of the internal mode frequencies with the lattice frequencies at the critical points in the Brillouin zone boundary is examined here in general terms.
Thermodynamic Functions for Nonuniform Systems
Authors: Hart Edward W.
Published: January 2005

The thermodynamics of simple, nonuniform equilibrium systems is formulated in terms of phenomenological variables. A careful investigation of the mechanical properties leads to the deduction of a free-energy density and to the description of its principal characteristics. An integrability condition for the free energy results in a condition that must be satisfied by the principal mechanical tensors of the system. The mechanical tensors are then expressed in terms of microscopic variables, and it is shown that the free energy can be evaluated by application of the virial theorem.