bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature Dependence of the Absorption Spectrum of Nickel(II)-Doped KMgCl3 and the Crystal Structure of KMgCl3
Authors: Brynestad Jorulf , Yakel Harry L. , Smith G. Pedro
Published: January 2005

Temperature dependence from 80° to 763°K is reported for the intraconfigurational 3d8↔3d8 transitions of octahedrally coordinated [NiCl6]4− in single crystals of K(Mg1−x, Nix)Cl3 with small x. The crystal structure of the host material, KMgCl3, is reported at 298°, 383°, and 448°K. Band energies are treated in terms of the Liehr—Ballhausen model of d2,8 electronic systems with Dq, B, C, and λ used as empirical parameters. At all temperatures the data are satisfactorily represented by B=850 cm−1, C/B=3.986 (free-ion value), and λ=−275 cm−1. Thus, B, C, and λ are all reduced to about 82% of their free-ion values. The parameter λ is estimated from band splittings at 80°K. The parameter Dq varies between −570 cm−1 at 80° and −500 cm−1 at 763°K. Oscillator strengths of the 3A2g→3T1g(F) and 3A2g→3T1g(P) transitions increase by a large factor between 80° and 763°K, while that of 3A2g→3T2g increases by a small factor. The compound KMgCl3 has a cubic perovskite-type structure at 448°K. At lower temperatures it has an orthorhombically distorted perovskite-type structure in which the distortion is small and magnesium retains approximately Oh coordination.
Isotope Exchange Rates. IV. The Homogeneous Reaction Between CH4 and D2
Authors: Watt W. S. , Borrell Peter , Lewis David , Bauer S. H.
Published: January 2005

The rate of exchange of deuterium for hydrogen in the homogeneous gas-phase reaction between D2 and CH4 (highly diluted in argon) was measured behind reflected shocks in a single-pulse shock tube of the ``magic hole'' design. The studies covered the temperature range 1440°—1755°K, at CH4/D2 ratios from 0.1 to 3.0. The exchange rate was found to be approximately first order with respect to deuterium and one-half order with respect to methane and argon. The empirical rate expression and the measured exchange rates cannot be accounted for either by a direct four-center bimolecular exchange process or by a mechanism involving a dissociation followed by a chain of atom displacement steps. However, these results are readily accounted for by a vibrational excitation mechanism in which the exchange rate is limited by the rate of populating a critical vibrational level for D2 (approximately the fifth). The activation energy for exchange is 52.0±2.2 kcal/mole.
Potential-Energy Curve for the B 1Σu+ State of the Hydrogen Molecule
Authors: Kol/os W. , Wolniewicz L.
Published: January 2005

An accurate potential-energy curve for the B 1Σu+ state of H2 has been computed using variational wavefunction in the form of an expansion in elliptic coordinates and depending explicitly on the interelectronic distance. The theoretical clamped-nuclei binding energy (De=28 896.3 cm−1) with diagonal corrections for nuclear motion (ΔD=−46.1 cm−1) gives the adiabatic binding energy De=28 850.2 cm−1 in a good agreement with the experimental value De=28 852.8 cm−1. However, for small and large values of the internuclear distance, the theoretical potential-energy curve very significantly differs from the corresponding RKR curve. The computed wavefunctions are analyzed in terms of some simple functions and it is shown that for 3<R<7 a.u. the B state is predominantly ionic in character.
Cusp Conditions for Molecular Wavefunctions
Authors: Pack Russell T , Brown W. Byers
Published: January 2005

The conditions on the behavior of a wavefunction for a system of charged particles near the coalescence of any two of them are derived. The new features of the derivation are: (a) the fixed-nucleus approximation is not required; (b) the wavefunction is not spherically averaged; (c) the wavefunction can have a node at the singularity; and (d) the consequences of the two particles being identical are examined. In addition to the general treatment, the electron—nucleus cusp conditions for diatomic molecules are discussed in detail.
Faraday Effect of Charge-Transfer Transitions in Fe(CN)63−, MnO4−, and CrO42−
Authors: Schatz P. N. , McCaffery A. J. , Suëtaka W. , Henning G. N. , Ritchie A. B. , Stephens P. J.
Published: January 2005

Measurements of the magneto-optical rotatory dispersion (MORD) and magnetic circular dichroism (MCD) through the accessible charge-transfer bands of Fe(CN)63−, MnO4−, and CrO42− in the visible and ultraviolet are described and interpreted. The apparatus employed combines a superconducting solenoid furnishing maximum fields of 45 000 G with a commercial ORD—CD instrument which covers the range 185–700 mμ. The MCD measurements are found to be more reliable and are much easier to make; they are also more useful for theoretical interpretation. However, Kramers—Kronig transforms of the MORD results agree well with the experimental MCD measurements. Comparison of the theoretically derived Faraday parameters for Fe(CN)63− with those extracted from experiment shows that the 24 000-, 33 000-, and 38 500-cm−1 bands are due, respectively, to 2T2g→2T1u, 2T2u and 2T1u, ligand-to-metal(t2g) charge-transfer transitions. A similar analysis confirms the assignment of the lowest band in MnO4− and CrO42− to a t1(π)→e(π) transition. The observed parameters for higher bands agree well with predictions based on the recent Wolfsberg—Helmholz calculation of Viste and Gray but do not unambiguously confirm their assignments.
Atomization Energies of the Polymers of Germanium, Ge2 to Ge7
Authors: Kant Arthur , Strauss Bernard H.
Published: January 2005

Using information derived from a combination of effusion and mass-spectrometric techniques at high temperature, the atomization energies and free energies for the reactions Gen(gas)=n(Ge gas) (n=2, 3, 4, 5, 6, 7) have been determined. The values of the energy as obtained from the variation of the free energy of atomization with temperature (second law of thermodynamics method) are in kilocalories per mole: they are 65, 149, 238, 321, 407, and 481 for n of 2, 3, 4, 5, 6, 7, respectively. A comparison of these values with the atomization energies as calculated from the third law of thermodynamics (absolute entropy method) assuming that the geometric configuration of the molecules (n>2) is either a linear chain or a cyclic structure indicates that the former structure is to be preferred.

The bond-dissociation energies (process Gen=Gen−1+Ge) as obtained from the second law are 75, 86, 83, 89, 84, and 65 kcal/mole for n of 7, 6, 5, 4, 3, and 2, respectively.
Crystal Structure of Solid Hydrogen and Deuterium, and of Neon—Hydrogen and Neon—Deuterium Mixtures
Authors: Barrett Charles S. , Meyer Lothar , Wasserman Judith
Published: January 2005

Solid hydrogen (normal and para), deuterium, and the systems neon—hydrogen and neon—deuterium were studied by x-ray diffraction at various temperatures with and without prior plastic deformation. Under most conditions D2 freezes from the liquid phase as hexagonal close packed (hcp) and is stable in this form against plastic deformation; similarly H2 usually freezes in the hcp form. When gold foil with a cube texture is present, D2, normal H2 and para-H2 freeze in the face-centered-cubic (fcc) form. Plastic deformation at about 3° and 4.2° causes the addition of fcc reflections to the hcp diffraction pattern with samples of normal H2 that previously had shown only hcp.

It is concluded that normal H2 is metastable in the hcp structure at these temperatures, and that the spontaneous transformation to cubic on cooling may often be incomplete.

It was found that, in concentrations between 0.25% and 99.5% Ne, Ne and the hydrogens are immiscible.
Crystal-Structure Effects in Hot-Atom Chemistry of Copper Phthalocyanine
Authors: Yoshihara K. , Ebihara H.
Published: January 2005

Structure sensitivity of the recoil-atom reactions and thermal annealing reactions in α- and β-copper phthalocyanines were studied in detail. Isothermal annealing curves were analyzed by the method of Vand and Primak. Two groups of activation-energy spectra appeared corresponding to two stages of the annealing reactions. Stage I was more sensitive to the crystal structure than Stage II. Stage I could be explained by the exchange reaction, Cu2+(1+,0)*+CuPn4→Cu*Pn4+Cu2+(1+,0), and Stage II by the synthetic reaction, Cu2+(1+,0)*+4 Pn→Cu*Pn4 (Pn denotes a phthalonitrile molecule). From the analysis of the initial retentions in the α and β crystals, hot and thermal processes in the initial recoil reactions could be estimated.
Vibronic Energy and Dipole Moment of HD
Authors: Kol/os W. , Wolniewicz L.
Published: January 2005

The HD molecule has been treated by perturbation theory using the complete nonrelativistic four-particle Hamiltonian. In the zeroth order the calculations have been carried out with a 147-term variational wavefunction. The resulting energies and expectation values of several operators for the ground state and for the first vibrationally excited state are reported. The computed ground-state dissociation energy, D0, is by 1.9 cm−1 larger than the experimental value. By treating the mass difference of the nuclei as the perturbation parameter, a 103-term correction function was computed which yields the second-order correction to the energy E(2)=−0.04664 cm−1, and the dipole moment of the molecule μ=1.54 10−3 D.
Infrared Band Contours. II. The Influence of Coriolis Coupling on Oblate Symmetric-Top Bands
Authors: Edgell Walter F. , Moynihan Robert E.
Published: January 2005

The influence of first-order Coriolis coupling on the shapes of perpendicular infrared bands of oblate symmetric-top molecules has been treated generally and quantitatively. The results are expressed in a table of band envelopes for various ratios of the moments of inertia and various values of the coupling parameter, ζ. A pronounced dependence of the band envelope on the extent of coupling has been found which makes it possible to evaluate the Coriolis constant ζ with good accuracy by comparing experimental and computed band envelopes. The scale factor required to equate the computed band envelope with the observed one provides a measure of the vibrational transition moment. In many cases this will provide the easiest, and perhaps the most accurate, method of obtaining this quantity.
Matrix-Isolation Study of the Photolysis of Cyanogen Azide. II. The Symmetric Stretching Fundamental of the Free Radical NCN
Authors: Milligan Dolphus E. , Jacox Marilyn E.
Published: January 2005

The photolysis of Ar:N3CN samples at 14°K with the full light of a cadmium arc has been found to permit complete conversion of the cyanogen azide to the free radical NCN, plus molecular nitrogen. At the high concentration of NCN thus achieved, a weak absorption appears at 2672 cm−1. The photolytic behavior of this feature and its shifts upon isotopic substitution support its assignment as the combination band (ν1+ν3) of NCN, permitting deduction of a value of 1197 cm−1 for ν1 of this species. The thermodynamic properties of NCN have been revised in accord with this assignment. The carbon—nitrogen stretching force constant approaches a value characteristic of a doubly bonded species, and the stretching interaction constant is relatively large and positive. Cyanogen azide photolyzes in both its 2750- and its 2200-Å absorption regions to produce NCN+N2. However, NCN itself photolyzes when subjected to radiation near 2500 Å, producing carbon atoms in the 3P state, which, in turn, may react with N2 to form the free radical CNN.
Infrared Spectra of Isotopic Nitrous Acids
Authors: McGraw G. E. , Bernitt D. L. , Hisatsune I. C.
Published: January 2005

The infrared spectra of isotopic cis- and trans-nitrous acid molecules including the 15N and D species have been obtained in the vapor and solid phases. All fundamentals of the normal cis and trans isomers have been identified, and previous assignments of two modes have been revised. From the isotopic frequencies of the torsion fundamental and the temperature dependence of two pairs of fundamentals, the potential-energy minimum of the cis isomer was deduced to be 0.39±1.0 kcal/mole above that of the trans isomer. The torsion barrier above the trans-isomer minimum was calculated to be 11.57±0.2 kcal/mole. Valence force constants for the cis and trans nitrous acids have been derived also. These constants reproduced the experimental 18O frequencies reasonably well.
Atom—Atom Ionization Cross Sections of the Noble Gases—Argon, Krypton, and Xenon
Authors: Kelly Arnold J.
Published: January 2005

An experimental investigation of the initial phase of shock produced ionization in argon, krypton, and xenon has been conducted in order to elucidate the atom—atom ionization reaction and to determine the atom—atom ionization cross sections. A high-purity shock tube was employed to heat these gases to temperatures in the range from 5000° to 9000°K at neutral particle densities of 4.4×1017, 7.0×1017, and 13.3×1017 cm−3, and impurity levels of approximately 10−6. A K-band (24-GHz) microwave system situated so that the microwave-beam propagation direction was normal to the shock tube, monitored the ionization relaxation process occurring immediately after the passage of the shock front. Electron density was calculated from the microwave data using a plane-wave—plane-plasma slab interaction theory corrected for near field effects associated with the coupling of the microwave energy to the plasma. These data, adjusted to compensate for the effects of shock attenuation, verified that the dominant electron-generation process involve a two-step, atom—atom ionization reaction, the first step (excitation to the first excited states) being rate determining. The quadratic dependence on neutral density associated with this reaction was experimentally demonstrated (with an uncertainty of ±15%). The cross section, characterized as having a constant slope from threshold (first excited energy level), represented as the cross-sectional slope constant C, was found to be equal to 1.2×10−19±15% cm2/eV, 1.4×10−19±15% cm2/eV, and 1.8×10−20±15% cm2/eV for argon, krypton, and xenon, respectively. The electron—atom elastic momentum-exchange cross sections derived from the microwave data correlated quite well with Maxwell-averaged beam data, the agreement for the case of argon being ±20%; krypton, ±30%; and xenon, within a factor of 2.
ESR of Free Radicals Trapped in Inert Matrices at Low Temperature: CH3, SiH3, GeH3, and SnH3
Authors: Morehouse Roger L. , Christiansen Jørn J. , Gordy Walter
Published: January 2005

The free radicals CH3, SiH3, GeH3, and SnH3 have been produced in a krypton matrix at 4.2°K by γ irradiation of the matrix containing dilute concentrations of CH4, SiH4, GeH4, and SnH4. The electron spin resonances indicate free or restricted rotation for all the radicals in the matrix. Observed anisotropies in g show that SiH3, GeH3, and SnH3execute restricted rotation about an axis perpendicular to the symmetry axis. From the observed values for the rotating radicals, the axially symmetric principal g values for the static radicals are derived as follows: for SiH3, g∥ = 2.003, g⊥ = 2.007; for GeH3, g∥ = 2.003, g⊥ = 2.017; for SnH3, g∥ = 2.003, g⊥ = 2.025. Hyperfine structure caused by 29Si is observed for SiH3 with isotropic coupling constant Af = 266 G and anisotropic coupling Aμ = 24 G. These couplings reveal 22% scharacter in the orbital of the unpaired electron, which indicates that the radical is nonplanar with bond angles of 110.6°. Probably GeH3 and SnH3 are also nonplanar. The magnitudes of the isotropic proton couplings are: 23, 8.1, 15, and 26 G, respectively, for CH3, SiH3, GeH3, and SnH3. The coupling of SiH3 is probably negative like that for CH3, but that of GeH3 and of SnH3 may be positive.
Valence Levels of Beryllium Oxide
Authors: Verhaegen G. , Richards W. G.
Published: January 2005

The low-lying valence levels of BeO, are calculated by the LCAO MO SCF method in order to ascertain the nature of the ground state of the molecule. Calculations of excited states using virtual orbitals are found to be inconclusive. Better results are found by doing variational calculations on three low-lying configurations for a series of internuclear distances, employing a large basis set and data on differences in molecular correlation energies between the various configurations. The calculations indicate a closed-shell 1Σ+ ground state. Spectroscopic constants are derived for this and other valence states. An unobserved 3Σ+—3Π transition is predicted to lie in the infrared region at about 9000 Å. The lowest-lying excited state is a 3Π. This level is shown to lie sufficiently high with respect to the ground state so as not to require an alteration of the published dissociation energy.
Microwave Spectrum of Propylene. II. Potential Function for the Internal Rotation of the Methyl Group
Authors: Hirota Eizi
Published: January 2005

Rotational spectrum of propylene, the normal as well as some of the deuterated species, were observed in the first and second excited states of methyl torsion, to determine the shape of the potential function precisely. Two terms in the function, V3 and V6, are obtained to be 698.4±0.5 and −13±2 cm−1, respectively, where the moment of inertia of the methyl group about its symmetry axis is assumed to be 3.160 amu·Å2. The symmetry axis is nearly parallel to the CH3–CH bond, thus excluding the tilt of the methyl group in propylene. The theory of internal rotation is satisfactory in explaining the gross feature of the rotational spectra. Possible effects of other vibrations on the internal rotation is discussed briefly.
Transient and Steady-State Overhauser Experiments in the Investigation of Relaxation Processes. Analogies between Chemical Exchange and Relaxation
Authors: Hoffman Ragnar A. , Forsén Sture
Published: January 2005

An exposition is given to demonstrate the close analogies that exist between chemical exchange and relaxation, and it is suggested that relaxation processes may be investigated by a procedure completely analogous to the double-resonance method recently introduced for the study of chemical exchange. A rederivation of the Solomon equations for the time dependence of the longitudinal magnetizations of interacting spins which brings out the dependence of the relaxation times on the relative abundance of the different spins is given. Experimental results on samples of formic acid and acetaldehyde are presented.
Monte Carlo Study of a One-Component Plasma. I
Authors: Brush S. G. , Sahlin H. L. , Teller E.
Published: January 2005

A Monte Carlo study has been made of a plasma of heavy ions immersed in a uniform neutralizing background. Systems containing from 32 to 500 particles, with periodic boundary conditions, were used. The results of the study are presented in terms of a dimensionless parameter Γ= (4πn/3) ⅓[(Ze)2/kT], where n is the ion density (particles per cubic centimeter), T is the temperature (degrees Kelvin), k is the Boltzmann constant, e is the electronic charge, and Z is the atomic number. Thermodynamic properties and pair distribution functions were obtained for values of Γ ranging from 0.05 to 100.0 from the canonical ensemble by the Monte Carlo (MC) method.

Two different methods were used to determine the potential energy of a configuration. The first is the ``minimum-image convention'' employed in many previous MC calculations. Each particle is allowed to interact only with each other particle in the basic cell, or with the nearest periodic image of each other particle if the image is closer. In the second method, the interaction of a particle with all the images of the other particles, and with the uniform background is taken into account by a technique similar to the Ewald procedure used to calculate lattice sums. It is found that both methods of determining the potential energy yield essentially the same results for the pair distribution function g for Γ values of 10 or less. For larger values of Γ the results given by the two methods differ significantly, indicating that the minimum image convention is inadequate for plasma systems at high densities and low temperatures.

Energies and values of the pair distribution function are compared with predictions of various approximate theories for small Γ values. It is found that the nonlinear Debye—Hückel (DH) theory is in agreement with the MC results for values of Γ up to 0.1. At Γ=1.0, significant deviations from the DH theory are observed. For Γ=1.0, g is found to be in close agreement with Carley's calculations based on the Percus—Yevick equation. For values of Γ above 2, g is no longer a monotonic function of the interparticle distance r, but begins to show oscillations characteristic of latticelike structures. For large values of Γ these oscillations are quite pronounced. The system is observed to undergo a fluid—solid phase transition in the vicinity of Γ=125.
Raman and Infrared Spectra and Structures of the Aluminate Ions
Authors: Carreira L. A. , Maroni V. A. , Swaine J. W. , Plumb R. C.
Published: January 2005

The Raman and infrared spectra of the aluminate ions in alkaline solutions have been measured. Two ionic species, one predominant from pH 8 to pH 12 and the other predominant above pH 13, may be identified from the spectra. At intermediate pH's both forms are present. The selection rules and the polarization of the lines of the low-pH species are consistent with either a square-planar Al(OH)4− structure or a polymeric structure in which each metal ion is surrounded by six OH− ions and the perturbations on the Oh symmetry are not great enough to be resolved. The ion does not appear to be tetrahedral Al(OH)4−, as has been previously thought. Pronounced aging effects observed with the low-pH anion support a polymeric structure rather than the square-planar Al(OH)4−. The spectra show that the high-pH species is AlO2− with D∞h symmetry. The observation of two distinct species and measurements of the pH ranges over which they are stable, confirm the results of earlier measurements by some of these authors using Leden's techniques of studying complex-ion formation.

The Raman spectra of deuterated aluminate solutions were measured. The low-pH species shows the expected frequency shifts and the frequency of vibration of the high-pH form is not affected by deuteration, in agreement with the supposition that the aluminate ion contains hydrogen at low pH but does not contain hydrogen at high pH.
Chemisorption of Hydrogen on Tungsten (100)
Authors: Estrup P. J. , Anderson J.
Published: January 2005

The interaction of hydrogen with a single-crystal tungsten (100) surface has been studied, using LEED in conjunction with flash-desorption and surface-potential measurements. As hydrogen is adsorbed at room temperature a sequence of LEED patterns is observed, consisting of the formation of ``extra'' ½ ½ spots, splitting and eventual disappearance of these spots with simultaneous formation of ¼-order spots, and finally, at saturation, the disappearance of all extra diffraction features. The possibility that these LEED patterns are caused by diffraction in the adlayer rather than in a reconstructed tungsten lattice is discussed in some detail.

The initial adsorption is found to occur with a sticking probability of 0.65 and is accompanied by dissociation of the hydrogen molecules. At saturation there are two hydrogen atoms per surface tungsten atom. The surface potential decreases approximately linearly with coverage and at saturation the total change is about −0.9 V.

For coverages above 0.25 the adsorption proceeds with formation of a series of arrangements characterized by large superstructure units with ``out-of-step domains,'' the size of which depends on the density of adatoms. It appears that these structures cannot be explained by existing theories of adsorption and lattice statistics.
Internal-Energy-Transfer Efficiencies in Eu3+ and Tb3+ Chelates Using Excitation to Selected Ion Levels
Authors: Dawson William R. , Kropp John L. , Windsor Maurice W.
Published: January 2005

Fluorescence yields of solutions of several chelates of europium and terbium have been measured: (a) upon excitation in the ligand absorption bands and (b) upon selective excitation to individual upper levels of the rare-earth ion. Yields with upper-ion-level excitation are lower than when the emitting level is excited directly and yields with ligand excitation are lower still. Efficiencies of energy transfer to the emitting level from upper ion levels and from the ligands, for the solutions studied, are calculated from the data.

The fluorescence yield observed when the emitting level is excited directly, together with the fluorescence lifetime, allows both radiative and radiationless rate constants for deactivation of the emitting level to be calculated. The enhanced fluorescence yields of chelates compared to unchelated rare-earth ions are found to be due primarily to the enhancement of the radiative transition by the chelate environment rather than to a protective influence against quenching provided by the ligands.

For terbium chelates the strong temperature dependence of the fluorescence intensity is explained in terms of quenching of the emitting level via thermal excitation to the lowest triplet state of the ligand. This is indicated by the agreement between the activation energy for quenching and the energy difference between the emitting level and the triplet state.
First- and Second-Overtone Intensity Measurements for CO and NO
Authors: Schurin B. , Ellis R. E.
Published: January 2005

The intensities for the first and second overtones of CO and NO have been measured using the Wilson—Wells—Penner—Weber self-broadening technique. The reported values are ACO2,0=2.15±0.10, ACO3,0=0.0127±0.0013, ANO2,0=2.11±0.10, and ANO3,0=0.0458±0.0046 in units of cm−1/cm·atm at 273°K. The results have been interpreted using an anharmonic-oscillator model to obtain alternate sets of dipole-moment coefficients.
Continuum Radiation in an Argon Positive Column
Authors: Prince J. F. , Robertson W. W.
Published: January 2005

A weak continuum with a maximum near 3100 Å is radiated from the positive column of an argon normal-glow discharge. The intensity distribution of this continuum (observed here from 2900 to 7000 Å) does not correspond to that of a free—free, free—bound recombination spectrum. The continuum intensity, the 3P2 metastable population, and the relative populations of more energetic atomic states are examined as functions of pressure (5–30 torr) at constant currents and as functions of current (0.5–5 mA) at constant pressures. It is shown that the continuum is best represented as radiation emitted in transitions from weakly bound molecular states to dissociative molecular states, where the radiating molecular states are populated by electron excitation from metastable molecules formed by three-body conversion of metastable atoms.
Operator for Spin-Forbidden Transitions
Authors: Englman Robert
Published: January 2005

It is shown that the use of the dipole-moment operator to calculate probabilities of transitions with change of spin gives results in many cases correct to within 1% to 1/100%. The matrix element of the operator is between the large components of spinors.
NMR Studies of a Series of Iron (III) Dithiocarbamate Complexes
Authors: Golding R. M. , Tennant W. C. , Kanekar C. R. , Martin R. L. , White A. H.
Published: January 2005

The temperature dependence of the proton NMR spectra of a series of iron (III) dithiocarbamates can be interpreted on a model with an iron atom in an intermediate crystal field of octahedral symmetry. The hyperfine interaction coupling constants for the various protons in the 6A1 state arise from d-electron delocalization through the ligands.
Configurational Entropy of Adsorption of Large Atoms
Authors: Baker B. G.
Published: January 2005

Monte Carlo methods are used to compute the arrangements of atoms large enough to prevent adsorption on neighboring surface sites for square and triangular surface lattices. Results are shown for sequential filling of the surface and for equilibrium after shuffling. The latter values are used to calculate the configurational entropy for localized adsorption and it is shown that the adsorption behavior of such systems could be mistaken for nonlocalized adsorption.
Phase Diagrams of Sodium Nitrite and Potassium Nitrite to 40 kbar
Authors: Rapoport Eliezer
Published: January 2005

The phase diagrams of NaNO2 and KNO2 were determined to 40 kbar. The NaNO2 phase diagram consists of five solid phases and the liquid. The ferroelectric Curie point (the III—II phase transition) and the Néel point (the I—II transition) were detected by differential thermal analysis (DTA) and determined to 40 kbar. The results are in good agreement with the work of Gesi and his co-workers to 10 kbar. Points on the III—IV boundary were determined by the volume-discontinuity method. The transition manifests itself as a break in the slope of the compression curve of NaNO2 and seems to be a second-order transition. The transition pressures are lower than those estimated previously. The melting curve increases with pressure. A new high-pressure solid-phase, NaNO2 V, wad discovered. The I—V phase boundary branches off the melting curve at the liquid—I—V triple point at 9.8 kbar and 343°C.

The KNO2 phase diagram consists of six solid phases and the liquid. The I—II and IV—V phase boundaries, determined by DTA, rise very slowly with pressure. The II—IV, I—IV, and I—V boundaries were determined by the volume-discontinuity method with application of piston rotation. Two new high-pressure phases, KNO2 V and KNO2 VI, were discovered. The melting curve of KNO2 exhibits a maximum at 7.0 kbar and 466°C, meets the I—V boundary at a triple point at 15.2 kbar and 413°C, and then increases steeply with pressure.
Microwave Absorption and Molecular Structure in Liquids. LXVII. The Dielectric Behavior of Mixtures of Two Polar Components
Authors: Kilp H. , Garg S. K. , Smyth C. P.
Published: January 2005

Dielectric constants and losses have been measured at wavelengths of 575 m, 10.1 cm, 3.22 cm, 1.22 cm and 2.2 mm for eight binary mixtures of benzophenone, 2-chloronaphthalene, 4-iodobiphenyl, tetrahydrofuran, chloroform, and pyridine. Three of these mixtures have also been measured in dilute benzene solutions. The dielectric data for each mixture have been analyzed in terms of two superimposed Debye regions. In each case there is evidence of two distinct relaxation times corresponding to the two polar components. The effect of weak hydrogen bonding between benzophenone and chloroform has been found in their binary mixtures, but in ternary mixtures with benzene the relaxation of one polar component is independent of the other. The relaxation times in the binary mixtures are closely related to the relaxation times of the pure components.
Effect of Pressure on Self-Diffusion in Lead
Authors: Nachtrieb Norman H. , Resing Henry A. , Rice Stuart A.
Published: January 2005

Data are presented for the self-diffusion of lead as a function of temperature from 174° to 322° and for pressures from 1–8000 atmos. The decrease in the self-diffusion coefficient with pressure follows a relationship of the form (dlnD)/dζ=−(1/RT0)(Q0−ΔVactdTm/dP),where ζ = Tm/T, T0 and Q0 are the normal melting point and the zero pressure activation energy, respectively, and ΔVact is the activation volume. To first order the derivative is constant, deviations arising at high pressure because of the pressure dependence of dTm/dP. Several relationships are derived from thermodynamic considerations of the activated state, and are shown to be valid experimentally: (1) ΔHact = bRTm, with b = 20.7, and (2) ΔHact = ΔHm·(ΔVact/ΔVm), where ΔHm and ΔVm are the latent heat and volume change on fusion, respectively.
Infrared Spectra of the Frozen Oxides of Nitrogen
Authors: Fateley William G. , Bent Henry A. , Crawford Bryce
Published: January 2005

Infrared studies have been made of several oxides of nitrogen trapped at liquid-helium temperatures in matrices of argon, N2, O2, CO2, H2, and N2O. The novel techniques permitting these studies are described. NO is found as the monomer and two forms of dimer, ``cis'' and ``trans''; the cis is more stable. NO2 is found as the monomer, the known stable dimer of planar structure, and two new dimers; one of these has the ONO–NO2 structure, and the other may be the twisted Vd form of the stable dimer. N2O3 is found in its stable form ON–NO2 and in a second form whose spectrum is consistent with the structure ONONO. Observations on covalent N2O5 are also reported.
Separation of Gas Mixtures in a Supersonic Jet
Authors: Waterman P. C. , Stern S. Alexander
Published: January 2005

In 1954, E. W. Becker and co-workers in Marburg, Germany, discovered that large composition gradients existed in the supersonic jet generated by expanding a gas mixture through a Laval nozzle. Further experimental observations of this effect are presented for the mixtures A–N2, O2–N2, and N2–C2H4, showing characteristics of the phenomenon not previously reported. A quantitative theory based on free-molecule kinetics is suggested, and gives reasonable agreement with the experimental results in several respects.
Thermal Conductivity of Multicomponent Gas Mixtures. II
Authors: Mason E. A. , Saxena S. C.
Published: January 2005

An investigation is made of the accuracies of the two recently derived formulas for the translational thermal conductivity of multicomponent gas mixtures. It is found that neither formula is sufficiently accurate in all cases, but that a slight modification of the Muckenfuss-Curtiss formula makes it as accurate as current experimental measurements. The modification consists of the replacement of first approximations to binary diffusion coefficients by more accurate values.
Free Energy of a Nonuniform System. III. Nucleation in a Two-Component Incompressible Fluid
Authors: Cahn John W. , Hilliard John E.
Published: January 2005

By finding the saddle point in the expression derived in Paper I (see reference 8) for the free energy of a nonuniform system, we have derived the properties of a critical nucleus in a two-component metastable fluid.

At very low supersaturations, we find that the properties of the nucleus approach those predicted by the classical theory that assumes the nucleus to be homogeneous with an interfacial energy that does not vary with curvature. However, with increasing supersaturation, the following changes occur in the properties of the critical nucleus. (a) The work required for its formation becomes progressively less than that given by the classical theory, and approaches continuously to zero at the spinodal. (b) The interface with the exterior phase becomes more diffuse until eventually no part of the nucleus is even approximately homogeneous. (c) The composition at the center of the nucleus approaches that of the exterior phase. (d) The radius and excess concentration in the nucleus at first decrease, then pass through a minimum and become infinite again at the spinodal.

These properties are deduced without resort to any specific solution model. In addition, they are evaluated for a regular solution to permit a quantitative comparison with the predictions of previous treatments.
Vibrational Relaxation of CN in the Shock Tube
Authors: Roth W.
Published: January 2005

The violet system of CN is observed in emission behind shock waves in impure Xe. Electronic transitions originating from high vibrational levels are observed earlier than those originating from lower levels. The time lapse between (1, 1) and (0. 0) transitions is attributed to the v′ = 1→v′ = 0 vibrational transition and this is shown to be in agreement with Bethe-Teller theory.
Energy Distribution Among Reagents and Products of Atomic Reactions
Authors: Polanyi J. C.
Published: January 2005

A simple valence bond resonance description of the activated complex in exothermic reactions A+BC→AB+C, coupled with experimental and theoretical evidence concerning the efficiency of transfer of vibrational energy at a collision, leads to the prediction that almost the entire heat of reaction will be contained in vibration of the bond being formed. The predicted activated complex configuration, which involves extended internuclear separation in the bond being formed, may be connected with increased collision diameters. The high efficiency of association reactions A+A+M→A2+M requires that in these reactions also the product contains almost the entire heat of reaction in vibration of the bond being formed. An attempt is made to account for the hitherto unexplained negative activation energy of these reactions in terms of the collisional redissociation of the highly vibrating product; a value for Eact of the required order of magnitude is obtained. The rate of the endothermic processes which constitute the reverse of the above reactions will be greatest if the molecule under attack is vibrationally excited. This is discussed in relation to the rate equation and is illustrated from experiment. For ``linear'' reaction the argument of the paper can be formulated in terms of potential-energy surfaces; this is done in order to illustrate points of similarity and divergence from earlier theories. Further evidence is adduced for the predicted activated complex configuration by an alternative method of calculation applied to the reaction H+Cl2→HCl+Cl. Twenty-three particular cases of exothermic exchange reactions and association reactions are discussed, in each of which some experimental evidence exists for the presence of more than equilibrium vibrational energy in the bond formed.
Microwave Spectrum and Internal Rotation of Ethyl Cyanide
Authors: Laurie Victor W.
Published: January 2005

The microwave spectrum of ethyl cyanide has been studied in the region from 17–36 kMc. Both parallel and perpendicular transitions have been assigned. Rotational constants (Mc) for the ground vibrational state are a0=27 663.30, b0=4714.14, c0=4235.14, DJ=0.0035, DJK=—0.0496. From Stark effects the dipole moment is calculated to be μa=3.78 D, μb=1.38 D, μ=4.02 D. Hyperfine splittings lead to a value of —3.3 Mc for the quadrupole coupling of the N14 nucleus along the a axis. Rotational transitions of molecules in several excited vibrational states have also been measured. A Coriolis interaction between the torsional mode and the in-plane CCN bend has been found and is discussed. Splittings of transitions of molecules in the first excited torsional state show that the barrier hindering internal rotation of the methyl group is 3.05 kcal/mole.
Electron Impact Studies of Aromatic Hydrocarbons. I. Benzene, Naphthalene, Anthracene, and Phenanthrene
Authors: Wacks Morton E. , Dibeler Vernon H.
Published: January 2005

A systematic survey of ionization-dissociation processes of fused-ring aromatic compounds is initiated. Mass spectra and appearance potentials of the singly and doubly charged molecule ions are reported.

The observed ionization potentials of benzene (9.38 ev), naphthalene (8.26 ev), anthracene (7.55 ev), and phenanthrene (8.03 ev) are compared with available spectroscopic data, with values obtained from molecular orbital calculations, and with other electron impact data. The empirical method of group equivalents is extended to the calculation of the ionization potentials of the fused-ring aromatic compounds.
NMR in Hydrate Crystals: Structural Information from Broadened Fine-Structure Lines
Authors: Pedersen B. , Holcomb D. F.
Published: January 2005

The effects of interpair broadening upon the NMR spectra of proton pairs in hydrate crystals are explored experimentally. The shape of a fine-structure line is generally found to be asymmetric. The importance of using the position of the center of gravity of a fine-structure line rather than the position of maximum absorption in determining structural parameters is emphasized by several experimental illustrations. In a coupled pair framework the former quantity is independent of interpair broadening to first order, the latter only to zero order (isolated pairs), but the position of maximum absorption is the quantity most commonly used in the literature. Data for a crystal not previously investigated with NMR, K2C2O4·H2O, illustrates the importance of the use of centers of gravity for a case in which the interpair interactions are relatively weak. It also demonstrates how the nature of the line asymmetry may be interpreted to give information about relative positions of neighboring water molecules.

The proton spectra of CaSO4·2H2O and Li2SO4·H2O have been remeasured and are reinterpreted. For these crystals short interpair distances suggest large modifications of the zero-order treatment given in the literature. It is demonstrated that in CASO4·2H2O a first-order treatment gives consistent results, with minor changes in the previously derived structural parameters. Second-order effects on the position of the center of gravity of the NMR line are largely suppressed by the relatively large number of interacting pairs.

In Li2SO4·H2O it is concluded that strong interpair couplings along a chain of water molecules cast grave doubts on any interpretation of the spectra based on an analytical treatment using a coupled pair framework.
Dielectric Constant of Hydrogen-Bonded Liquids. I. Cyanoacetylene
Authors: Dannhauser Walter , Flueckinger Arthur F.
Published: January 2005

The dielectric constant of cyanoacetylene has been determined over the normal liquid range: ε (T) = (71 000/T) —170. Analysis of the data in terms of a hydrogen-bonded linear polymer yields: ΔH = —2.80 kcal; ΔS = —15.8 eu per mole of hydrogen bond. The vapor pressure of solid and liquid HCCCN has been measured. Molar enthalpies and entropies of fusion and vaporization are: 3.38 and 6.72 kcal; 12.1 and 21.3 eu, respectively. Hydrogen bonding in this and similar systems is discussed.
Dilute Solution Properties of Linear Polystyrene in Θ-Solvent Media
Authors: Orofino T. A. , Mickey J. W.
Published: January 2005

Dilute solution parameters descriptive of polymer coil size and segment—solvent interaction have been evaluated for each of three polystyrene—solvent systems at various temperatures in the vicinity of the Θ value characteristic of a given pair. The pure solvents selected for these studies were diethyl malonate, cyclohexane, and 1—chloro—n—undecane, which with polystyrene display Θ temperatures of 35.9°, 34.8°, and 32.8°C, respectively, as ascertained from analyses of second virial coefficient—temperature relationships. A single polymer sample of narrow molecular weight distribution was employed in all investigations.

Parameters interpolated for each polystyrene—solvent pair at the Θ temperature of the system are examined from the point of view of the specific influence of the medium on coil characteristics. Differences are observed, for example, among the intrinsic viscosity values. Accurate, relative comparison of such solution properties is facilitated through use of the common polymer sample and intentional selection of pure solvents displaying Θ temperatures in proximity. The complicating effects of variable molecular weight, molecular weight distribution, and temperature per se are thus conveniently eliminated.

Intrinsic viscosity and second virial coefficient data obtained for each pair at various temperatures near Θ are examined in accordance with the formal functional interdependence predicted by certain theoretical treatments, applicable to weakly interacting systems of the kind here investigated.
Vibrational Fluorescence of Carbon Monoxide
Authors: Millikan Roger C.
Published: January 2005

Carbon monoxide gas (1 atm pressure) has been vibrationally excited by absorption of infrared light emitted by rich CH4–O2 flames. The CO issued from a 286°K porous plate with a laminar flow velocity of 10 cm/sec. It was contained in an annular flow of argon of matched velocity. Resonance fluorescence was observed in the fundamental vibration—rotation band of CO at 2143 cm—1 when impurities were reduced below the ppm level. Intensity measurements showed that a vibrational temperature of 993°K had been reached by light absorption. Under the same conditions the rotational temperature remained at 286°K as shown by the intensity distribution of the rotational lines. Trapping of the resonance radiation permitted observation of the vibrational excitation for 0.2 sec after removal of the exciting light. The rate of the quenching reaction CO (v=1)+M→CO (v=0)+M has been determined from Stern—Volmer quenching curves for the collision partners H2, HD, D2, He, Ne, and O2. An extreme dependence of collisional vibrational relaxation time upon collision mass has been observed, as predicted by theory. Oxygen is anomalously efficient as a collision partner by several orders of magnitude.
Photolysis of Nitrogen Dioxide at 3660 and 4047 Å at 25°C
Authors: Ford H. W. , Jaffe S.
Published: January 2005

Nitrogen dioxide was irradiated at 3660 and 4047 Å at various pressures of NO2, with and without CO2, NO, and N2 as added gases. The data indicate a primary dissociation at 3660 Å and shorter wavelengths corresponding to energies greater than the ON–O bond energy. At 4047 Å, the data are explained by an excited-molecule mechanism. Isotopic oxygen scrambling experiments at 4047 Å indicate the probability of reactions to produce oxygen atoms at that wavelength, but photolysis of NO2 at trace concentrations and high inert-gas pressures indicates that these atoms are not derived from the unimolecular decomposition of the photoactivated molecule. The inhibition of the quantum yield by NO addition was pressure-dependent, lending further support to the premise that oxygen atoms are important in the mechanism at 4047 Å. It is postulated that the reaction NO2*+NO2→N2O3+O is the source of atomic oxygen.
Gel Formation in Polymers Resulting from Simultaneous Crosslinking and Scission
Authors: Inokuti Mitio
Published: January 2005

An equation giving the gel fraction of polymers undergoing simultaneous crosslinking and scission is derived for an arbitrary initial molecular-size distribution. Application is made to the case where the initial distribution is the generalized Poisson type. For an initial distribution which is either very broad or very narrow as compared with the Poisson type and for a moderate value of the ratio of the scission rate to the crosslinking rate, considerable deviations from the Charlesby—Pinner relationship (derived for an initial random distribution) occur.
Mean Lives of Positrons in Aqueous Solutions
Authors: Jackson Jerome E. , McGervey John D.
Published: January 2005

By measurement of the time distribution of positron annihilations in aqueous solutions, reaction rates for oxidation of positronium by the ions MnO4—, IO3—, and Hg++ have been determined. In strong oxidizing solutions the mean life of the positrons reaches a lower limit of 4.3×10—10 sec; the short lifetime τ1 in water was measured and found to agree with this value. A Pb(ClO4)2·3H2O solution reduced the intensity I2 with no significant change in the long life τ2, an effect previously observed in nitrate solutions. This may mean that in these two cases oxidation can occur before Ps is thermalized but not afterwards. The decay distributions from a mixture of Hg++ and MnO4— ions in solution and the Hg++ ion in separate solutions with Cl— and ClO4— indicated an association taking place between the negative and positive ions.