bluuebunny/crossref_metadata_2025 huggingface dataset:
Constitution and Magnetic Susceptibilities of Vanadium-Hydrogen Alloys
Authors: Zanowick R. L. , Wallace W. E.
Published: January 2005

A series of vanadium-hydrogen alloys ranging in composition from 0 to 42 at.% has been examined using powder diffraction techniques. At room temperature the following was found: (1) terminal solubility (bcc phase) to about 2 at.% H, (2) a body-centered tetragonal phase with an axial ratio of about 1.10 in the vicinity of V2H, and (3) a two-phase region extending from about 2 to 30 at.% H. Experiments at elevated temperatures showed that the two-phase region vanished in the vicinity of 150°C. The axial ratio of a β-phase alloy showed a strong dependence on temperature, falling from 1.1 at room temperature to unity at 205°C. Susceptibility measurements revealed (1) a temperature independent susceptibility for the hydrogenated material and (2) a fall in susceptibility with increasing H content. The results are consistent with the notion that (1) H in V ionizes with its electron joining the delocalized electrons in the metal and (2) the interstitial hydrogen tends to order at high concentrations and/or low temperatures.
Study of the Adsorption of Hydrogen, Ethane, Ethylene, and Acetylene on Iridium by Field Emission Microscopy
Authors: Arthur John R. , Hansen Robert S.
Published: January 2005

A field emission microscope permitting precise control of iridium emitter temperature from 4 to 1700°K was used to study changes in emission patterns and work functions resulting from time and temperature dependent surface reactions in the adsorption of hydrogen, ethane, ethylene and acetylene on iridium.

The qualitative character of the emission patterns indicates a rather uniform covering of the high index faces of iridium by all species studies in the temperature range 70–300°K. Hydrocarbon species, once chemisorbed, are substantially immobile at temperatures below 700°K; above 700°K an intensification of emission pattern, probably due to carbonization, occurs around the edges of the 111 planes.

Iridium surfaces containing adsorbed species were flashed for controlled periods of time to controlled temperatures; characteristic changes in work function resulted which were both time and temperature dependent. These experiments indicate that hydrogen is readily desorbed by iridium above 400°K, and that a large portion of adsorbed ethane is readily desorbed at 100°K, but a residue from adsorbed ethane is not desorbed below 1000°K. For a given flash time, curves representing work function as a function of flash temperature for adsorbed ethylene and acetylene show characteristic differences below 450°K but are very similar above 450°K. Results are interpreted as indicating chemisorption of ethylene, dehydrogenation of chemisorbed ethylene to form chemisorbed acetylene and chemisorbed hydrogen, desorption of chemisorbed hydrogen, dehydrogenation of chemisorbed acetylene and finally crystallization of carbon residue.
Reconsiderations of Nucleation Theory
Authors: Lothe Jens , Pound G. M.
Published: January 2005

There are quantum statistical contributions to the free energy of formation of embryos and critical nuclei in transformations to condensed phases. They arise from consideration of the absolute entropy of the embryos or nuclei. In the case of homogeneous nucleation of water droplets from vapor the factor of increase in equilibrium concentration of critical nuclei is about 1017, resulting in a discrepancy of corresponding magnitude between the Becker-Doering equation and the critical supersaturation measurements of Wilson and Powell. It is suggested that some of this disagreement may be removed by treating the problem as a transient rather than a steady-state situation and considering non-accommodation in the smaller size classes. Also there is an appreciable quantum statistical effect in homogeneous nucleation of crystals from the supercooled liquid and a related effect in nucleation from the vapor of crystals on substrates.
On the Applicability of the Temkin-Pyzhev Equation for the Determination of Activation Energies of Ammonia Synthesis at One Atmosphere Pressure
Authors: Brill R. , Tauster S.
Published: January 2005

It is shown that for measurements at 1 atm pressure, rate constants calculated by means of the Temkin-Pyzhev equation cannot be used for the determination of activation energies in the usual way.

Our experimental values lead to activation energies of about 17 kcal/mole for a doubly promoted catalyst which are in reasonable agreement with those given by Ozaki, Taylor, and Boudart if either the rate equation for low yields of these authors or a simple extrapolation process to very low yields is used to define a rate constant.
Mass Spectrometric Study of the Reactions of BF3(g) with BCl3(g), B(OH)3(g), and B2O3(1)
Authors: Porter Richard F. , Bidinosti Dino R. , Watterson K. F.
Published: January 2005

Exchange reactions of halogen and hydroxyl with BX3(g) have been studied mass spectrometrically. The major product produced by the reaction of BF3(g) with boric acid at 25°C and pressures of the order of 10—6 atm is B(OH)F2(g). The species B(OH)2F(g) is also formed at higher temperatures when B(OH)3(g) is observable. Equilibria involving the reactions13BF3(g)+23BCl3(g)=BFCl2(g),23BF3(g)+13BCl3(g)=BF2Cl(g),13BF3(g)+23B(OH)3(g)=B(OH)2F(g),and 23BF3(g)+13B(OH)3(g)=B(OH)F2(g),have been studied as a function of temperature. Heats of formation at 298°K for BFCl2(g), BF2Cl(g), B(OH)2F(g), and B(OH)F2(g) are found to be —154.1±1.0, —211.9±2.0, —249.8±2.5, and —260.2±2.5 kcal/mole, respectively.

Reactions of BF3(g) with B2O3(l) have also been studied at pressures between 10—6 and 10—3 atm and temperatures between 400 and 1000°K. Results are consistent with published data from studies with BF3 at pressures near 1 atm and show that (BOF)3(g) is the primary product at both pressure extremities. For the reactionBF3(g)+B2O3(l)=(BOF)3(g),we obtain ΔHT°=3.46±0.30 kcal/mole.
Optical Spectra of Ni2+, Co2+, and Cu2+ in Tetrahedral Sites in Crystals
Authors: Weakliem Herbert A.
Published: January 2005

The polarized absorption spectra of Ni2+ and Co2+ in crystals of ZnO, ZnS, and CdS; Ni2+ in crystals of Cs2ZnCl4 and Cs2ZnBr4; and Cu2+ in ZnO have been measured at 4°K, 77°K, and room temperature. The spectra have been interpreted by the use of crystal field theory for the states of the (3d)n configuration acted on by a potential of predominately Td symmetry. Certain details of the spectra are accounted for by smaller contributions from fields of lower symmetry, notably a C3v potential contribution for the transition metal ions in ZnO. Crystal field, electrostatic repulsion, and spin-orbit parameters have been obtained for all these cases. An empirical correlation between the electrostatic repulsion parameter, B, for the ions in the crystals and the ligand polarizibility has been obtained. Although the configuration mixing between the states of the configurations (3d)n and (3d)n—1 (4p) has been found to give a negligible contribution to the calculated relative energies of the levels, it does partially explain the large values of the observed intensities of the transitions. The relative intensities of transitions between the spin-orbit components have been calculated by using models for both p—d mixing and σ bonding with the ligands. Neither model gives a quantitatively good account of the observed relative intensities and there is evidence, at least for the Ni2+ spectra, that the observed low energy, intense charge transfer absorptions play a predominant role in the intensity mechanisms of the d—d transitions.
Dielectric Saturation in Aliphatic Alcohols
Authors: Malecki J.
Published: January 2005

The dielectric saturation in solutions of butanol-1, pentanol-1, and hexanol-1 in benzene and hexane was measured. The values of the permittivity variations as measured in solutions of alcohols point to the presence of a new type of dielectric saturation effect, which is shared in common by all the systems investigated. Because of the considerable electric conductivity of the liquids investigated, the pulse method was applied.
Thermal Decomposition of Nitryl Chloride in Shock Waves
Authors: Hiraoka Hiroyuki , Hardwick R.
Published: January 2005

The thermal decomposition of NO2Cl in Ar and in O2 as well as that of pure NO2Cl has been studied from 600° to 1000°K at concentrations of ∼10—3 to ∼10—2 moles/liter using a shock-wave technique. In general the results are compatible with earlier, low-temperature measurements. The activation energy for pure NO2Cl decomposition is about 2.5 kcal/mole less than that for NO2Cl+Ar or NO2Cl+O2. This is compared to the drop in activation energy calculated from the differences in energy transfer efficiency assuming deactivation on every collision.
Reactions of Sodium with Active Hydrogen
Authors: Polanyi J. C. , Sadowski C. M.
Published: January 2005

The chemiluminescent flame produced when sodium vapor diffuses into hydrogen coming from a discharge has been photographed and the ``intensity profile'' has been analyzed in detail according to productemitter flame theory. The analysis shows that sodium is being consumed. Attempts to account for this consumption on the basis of ternary reactions, lead to rate constants 104—105 times larger than those reported in the literature for reactions of this type. It appears that sodium is being consumed by a binary reaction with some species formed in or by the discharge. Since reaction with electronically excited metastable H2* can be excluded, it is proposed that the binary reaction is Na+H2† (v≥6)→NaH+H, where H2† is vibrationally excited hydrogen in its ground electronic state.
Nuclear Relaxation in Adulterated Hydrogen
Authors: Johnson C. S. , Waugh J. S.
Published: January 2005

The proton spin-lattice relaxation time T1 has been measured in normal hydrogen and in mixtures with 12 other gases as a function of density and composition at room temperature. Cross sections for mJ transitions of the H2 molecule deduced from the Bloembergen—Schwinger formula are interpreted qualitatively on the basis of electric multipole moments as measures of the anisotropy of the intermolecular forces, using the transient approximation. This approximation is justified in the case of H2–CO2 mixtures on the basis of the temperature dependence of T1. The assumptions of the Bloemberger—Schwinger formula are discussed, and an experiment is proposed to determine the connection between two correlation times which appear in the theory.
Structure of fn Configurations. II. f5 and f9 Configurations
Authors: Wybourne B. G.
Published: January 2005

The complete energy matrices of the f5 configuration have been calculated using the methods of Racah. Energy level schemes have been constructed for the trivalent samarium, dysprosium, and plutonium ions. A preliminary analysis of the observed spectra of these ions is made.
Potential Energy Curves for C2
Authors: Read Shirley M. , Vanderslice Joseph T.
Published: January 2005

Potential energy curves for the a 1Σg+, X 3IIu, 3Σg—, b 1IIu, A 3IIg, c 1IIg, B 3IIg, d 1Σu+, and e 1Σg+ states of C2 have been calculated by the Rydberg—Klein—Rees method. These curves have been compared with some of the recent quantum calculations of Clementi and Pitzer on this same system. The recent identification of the ground state as the a 1Σg+ by Ballik and Ramsay and the determination of the dissociation energy by Brewer, Hicks, and Krikorian have been used to calculate tentative values for the dissociation energies of all of the observed excited electronic states.
Preferential Adsorption by Polymers Dissolved in Solvent Mixture
Authors: Yoshino Tsuneo , Tanzawa Hiroshi
Published: January 2005

A straightforward method was proposed to measure the magnitude of preferential adsorption by polymers dissolved in solvent mixtures, and was experimentally checked for toluene—isobutanol—polystyrene and benzene—cyclohexane—polystyrene systems. This method can be applied even to concentrated solutions in contrast to the light-scattering method, and is more accurate than the latter. Preferential adsorption of toluene or benzene by polystyrene was clearly observed, and excess toluene around polymer molecules was found to be independent of concentration and molecular weight of the solute, and also of solvent composition.
Atomic Distribution in Liquid Argon Near the Triple Point
Authors: Gingrich N. S. , Tompson C. W.
Published: January 2005

The x-ray diffraction pattern of liquid argon at 84.25°K (triple point 83.99°K) was observed with five peaks out to (sinθ)/λ=0.86. From this pattern the atomic distribution curve was computed, essentially confirming earlier x-ray work. The first maximum in this curve is at 3.78 A and the area under the first maximum represents about 10.5 atoms.
Electrofluorescence of Rare-Earth-Activated Al2O3
Authors: Adams I. , Mellichamp J. W.
Published: January 2005

We have activated α Al2O3 with Sm2+, Sm3+, Eu3+, Gd3+, Tb3+, and Dy3+ by mixing powders of the rare-earth oxide with γ Al2O3 and firing in an N2 and then in a Cl2 atmosphere at 800°—1000°C. When these activated powders are placed between a metal base plate and a conducting glass plate and about 500 v dc is applied, electrofluorescence is observed. The emitted spectra are characteristic of the fluorescence of the rare-earth ion in the corundum structure. A mechanism for excitation is discussed.
Charge Injection into Organic Crystals: Influence of Electrodes on Dark- and Photoconductivity
Authors: Pope Martin , Kallmann Hartmut P. , Chen Augustine , Gordon Peter
Published: January 2005

Studies have been made of dark and photoconductivity in thin anthracene single crystals using a Ce4+ solution as one electrode and a 1MNaCl solution as the other electrode. It was found that the Ce4+ electrode was capable of injecting holes into anthracene in the dark, the saturation current at 15 000 v/cm being about 1 μa/cm2. This current was observed when the Ce4+ electrode was at a positive potential. With the same polarity, it was found that there was practically no increase in the saturation current upon illumination of the crystal with 3650 or 4300 A light; at low voltages there was a distinct photoeffect which was attributed to the emptying of polarization producing traps, thus increasing the internal field. The saturation current was proportional to the sixtenths power of the Ce4+ concentration. At low voltages, the current was very small until a certain voltage, referred to as the onset voltage, was reached, after which the current increased rapidly. The onset voltage was larger for the dark current than for the photocurrent. The efficiency of carrier production by the Ce4+ ion was about 10—10 based on a simple collision hypothesis. Possible explanations for this low efficiency were advanced but no definite mechanism was chosen. The use of Ce3+ ion was without effect in increasing either the dark or photocurrent.

Using a positive electrode of I2 in glacial acetic acid, it was found that there was practically no hole injection, in contrast with the marked hole injecting characteristics of the aqueous I2–I— electrode. Furthermore, the Ce4+ and I2–I— electrodes were ineffective with naphthalene. These results are explained by reference to a criterion for hole injection IA—WE—Ex<0, where WE is the work function of the electrode, IA is the ionization energy of anthracene in the solid, and Ex is the externally supplied energy (optical, thermal, electric field).
Resonant Gamma-Ray Absorption in Potassium Ferrate
Authors: Wertheim G. K. , Herber R. H.
Published: January 2005

The Mössbauer spectrum in a potassium ferrate absorber has been determined at 78° and 298°K using a source of Co57 in stainless steel. A single resonance line is observed with a full width at half-maximum of 0.43 mm sec—1. This linewidth is known to arise mainly in the stainless-steel source, which indicates that the quadrupole splitting of the resonance peak is less than 1 Mc sec—1. The isomer shift is —0.69 mm sec—1 at 78°K and —0.79 mm sec—1 at 298°K. This shift is smaller than that predicted for a 3d2 electron configuration, presumably because the 3d electron density is augmented by d3s hybridization in the tetrahedral ferrate ion.
Infrared Spectra of the Group II Halides: Zinc Halides and the Ionic Model
Authors: Büchler Alfred , Klemperer William , Emslie Alfred G.
Published: January 2005

The bending vibrations of gaseous ZnCl2 and ZnBr2 have been observed in the cesium iodide region at 295 and 225 cm—1, respectively. It is shown that a molecular model based on polarizable ions cannot account for the observed bending frequencies of the Group II dihalides.
Kinetics of Cs+ Desorption from Tungsten
Authors: Scheer Milton D. , Fine Joseph
Published: January 2005

The mean adsorption lifetime τ3 of Cs+ on tungsten has been measured in the 1000°—1200°K temperature range, using a pulsed beam technique. Under conditions of low surface coverage and with either Cs or CsI as beam materials τ3=(1.0±0.5)×10−12exp[(23 600±500)/T]secwas obtained. The heat of desorption can be calculated as the energy required to remove an isolated Cs+ ion from the surface of an electrical conductor. The presence of an adsorbed contaminating layer, arising from residual vacuum gases, decreased the Cs+—W binding energy by 0.5 eV and increased the pre-exponential factor by about two orders of magnitude. Anomalous results were obtained when CsCl was used for a beam material, suggesting a reaction between the surface tungsten atoms and atomic chlorine.
Solubility of Helium in Liquid Hydrogen
Authors: Roellig Leonard O. , Giese Clayton
Published: January 2005

The solubility of helium in liquid hydrogen has been measured as a function of temperature and pressure. It was found the solubility varied from 0.59 mole % for T=26.8°K and 1.98 atm partial pressure of helium to 11.1 mole % for T=19.8°K and 7.0 atm partial pressure of helium.
Absorption Spectrum of Ytterbium in Single Crystal of Calcium Fluoride
Authors: Low W.
Published: January 2005

High-resolution spectrum of Yb3+ in the cubic field of CaF2 is reported. The striking features of the spectrum are two strong sharp lines at 10 384.759 and 10 377.039 cm—1 at 4.2°K. The position of the two lines and their separation was measured as a function of the temperature. The line shape is Lorentzian. The possible position of the various Stark levels of the ground state is discussed.
Linear Variation of Proton Magnetic Shielding with Electric Field
Authors: Musher Jeremy I.
Published: January 2005

The linear variation of nuclear magnetic shielding with electric field is calculated semiquantitatively by a variation method and by a perturbation method. The effect is sufficiently large to be significant for protons in molecules containing polar groups or in ions, as these protons experience intramolecular electric fields of ∼106 statV/cm. The effect on protons in solids for laboratory electric fields would only be a fraction of the (magnetic) dipolar linewidth and is therefore not observable. The calculation gives good agreement with the several experimental values from the literature. The intramolecular (electric) dipolar field is then used to explain the low-field shift in resonance frequency of the methylene protons in in ethyl alcohol—an important example of the chemical ``inductive effect.''
Use of Spin Inversion Operators to Describe Properties of Nuclear Magnetic Double-Resonance Spectra
Authors: Anderson Jay Martin , Baldeschwieler John D.
Published: January 2005

For general spin systems of the type AmAm',…MnMn',…XpXp',…,, it is shown that nuclear magnetic double-resonance spectra recorded by sweeping magnetic field are mirror images if the frequency of the strong radio-frequency field is set at equal intervals Δ above and below the resonance frequency of one type of nucleus. It is further proven that the double resonance spectrum is symmetric for Δ=O when field is swept, and for all values of Δ when frequency is swept. Finally, it is shown that the relative signs of all the coupling constants between nonequivalent or magnetically nonequivalent nuclei in a spin system can, in principle, be obtained in a double resonance experiment.
Molecular-Orbital Theory of Diamagnetism. I. An Approximate LCAO Scheme
Authors: Pople J. A.
Published: January 2005

An independent-electron molecular-orbital theory is developed for the diamagnetic behavior of electrons in the presence of an applied magnetic field. The molecular orbitals are written as linear combinations of gauge-invariant atomic orbitals, the dependence of the (complex) coefficients on the magnetic field being studied by perturbation theory. By making a systematic set of approximations involving the neglect of some interatomic terms, a general expression is derived for the diamagnetic susceptibility tensor as a sum of atomic contributions. Each atomic contribution is made up of two parts, the first being a diamagnetic (Langevin-type) term and the second being a paramagnetic contribution involving the details of the electronic excited states. At a lower level of approximation, this second term can be expressed in terms of atomic charge densities and bond orders together with a mean electronic excitation energy.

It is pointed out that the theory provides a convenient basis for detailed interpretation of the Pascal constants used for empirical calculations of diamagnetic susceptibilities of large molecules. In addition, a similar treatment of the theory of nuclear magnetic screening leads to an expression for the shielding constant involving a set of localized contributions closely related to corresponding contributions for the susceptibility.
Molecular-Orbital Theory of Diamagnetism. II. Calculation of Pascal Constants for Some Noncyclic Molecules
Authors: Pople J. A.
Published: January 2005

The general formulas for atomic contributions to diamagnetic susceptibilities derived in part I are used to calculate Pascal-type constants for some simple molecules containing hydrogen, carbon, nitrogen, oxygen, and fluorine. For noncyclic saturated molecules, the theory reproduces the relative values of empirical atomic contributions fairly satisfactorily, although absolute numerical agreement is poor. For unsaturated groups, the theory provides an interpretation of the constitutive corrections required in the Pascal scheme. Considerable positive corrections are calculated for the carbon—carbon double bond and the carbonyl group, but not for the carbon—carbon triple bond. This is in agreement with the empirical rules. The theory also makes a number of predictions about diamagnetic anisotropies.
Electrical Properties of Heavily Doped Niobium Pentoxide
Authors: Valletta R.
Published: January 2005

An analysis of the resistivity and thermoelectric power of heavily doped Nb2O5 [over-all composition (Nb1−xWx)2O5 where x varies from 0.0025 to 0.15] shows that mixed valence semiconduction has been observed. The major factor determining the value of the thermoelectric power at high temperatures appears to be an entropy of mixing term. In samples with x>0.10, it is concluded that the electrons can be trapped on tungsten ions as well as niobium ions. The low-temperature resistivity data indicate that the conduction mechanism is not simply described at temperatures where the tungsten impurity ions are incompletely ionized.
Studies of Metastable Ion Transitions with a 180° Mass Spectrometer
Authors: Coggeshall Norman D.
Published: January 2005

The decay of metastable ions through transitions giving an ionized fragment and a neutral radical has been investigated with a 180° mass spectrometer. Four aspects of the main problem have been studied. These are: (a) the decay of metastable ions within the ion source to produce a continuous distribution of ``metastable ions''; (b) an examination of the mathematical conditions relating dissociation beyond the ion-source exit slit to the formation of a ``metastable'' peak, to the shape of such a peak, to the cutoff imposed by the analyzer walls and to the length of travel during which detectable dissociation may occur; (c) an examination of the conditions for determining lifetimes with a 180° instrument; and (d) a consideration of the elements leading to the broadness of metastable peaks.

The distribution function resulting from dissociation within the slit drops very rapidly and is ordinarily hidden within the peak due to the daughter ion. The formation of a metastable peak in a 180° instrument results from a low-order dependence of where the ion fragment resulting from dissociation hits the focal plane on the position of dissociation beyond the exit slit. The cutoff mass due to ions striking the walls of the analyzer tube may be readily calculated. In a CEC model 21–103 instrument there is adequate distance of free travel beyond the exit slit to allow the instrument to be used for lifetime measurements. Using repeller voltages up to 120 V, shorter lifetimes than those previously reported have been observed. For the m*=31.9 metastable peak from n-butane, for example, there is evidence that the metastable ions are created in at least three classes, each with its own lifetime. The shortest lifetime observed was of the order of 9×10—8 sec. Evidence has been obtained to indicate that the broadness of the observed metastable peaks is probably the result of the perturbation of focusing conditions by the increased angular spread in the ion beam.
NMR Splittings Due to Molecular Asymmetry
Authors: Gutowsky H. S.
Published: January 2005

An algebraic analysis is given of the relative effects of molecular asymmetry and differences in conformational populations in causing nuclei to be magnetically nonequivalent. Primary importance is attached to the nature of the molecular asymmetry. The temperature dependence of the chemical shift observed between Fa and Fb, in CFaFbBrCFBrCl, is compatable with a small splitting, an ``asymmetry effect,'' which persists when the three rotamers have the same population.
Theory of Singlet—Triplet Transitions in Magnetic Rotation Spectra
Authors: Hameka H. F.
Published: January 2005

The theory of the resonance fluorescence of degenerate or near-degenerate states is derived and it is applied to a description of magnetic rotation spectra of triplet—singlet transitions. The transition probability is obtained as a quotient of two determinants, each containing the matrix of the damping constants between the different states. The mathematical formalism becomes reasonably simple only if the energy differences between the states are large with respect to the absolute values of the off-diagonal damping constants. Therefore our results for the magnetic rotation spectra of triplet—singlet transitions are restricted to the case of large magnetic fields so that the splittings of the triplet levels are large compared to the natural line breadths of their absorption lines. It is found that the relative intensities of singlet—triplet transitions in magnetic rotation spectra are compatible with or even larger than the intensities of singlet—singlet transitions. The possible importance of spin—spin interactions is mentioned.
Infrared Spectroscopic Study of the Photolysis of HN3 in Solid CO2
Authors: Milligan Dolphus E. , Jacox Marilyn E. , Charles Stuart W. , Pimentel George C.
Published: January 2005

Infrared studies have been carried out on the photolysis of HN3 and DN3 in CO2 matrices at 20° and 53°K. HNO and DNO have been identified as products of the reaction of NH and ND with CO2. The presence of HNO has been confirmed by the detection of absorptions at 7400, 7100, and 6850 Å in the visible spectral region. Evidence has also been obtained for the production of a 1:1 compound between NH (ND) and CO2. Several possible structures for this species are discussed.
Rate of Sublimation of Ammonium Halides
Authors: Chaiken R. F. , Sibbett D. J. , Sutherland J. E. , Van de Mark D. K. , Wheeler A.
Published: January 2005

The rates of sublimation of ammonium chloride, bromide, iodide, and fluoride have been determined by two different experimental techniques over the temperature range of 100° to 600°C, corresponding to an increase in sublimation rate of 104. The two experimental methods employed were the isothermal rate of weight loss using a quartz spring balance, and the hot-plate linear pyrolysis method. The low activation energy (about one-third the heat of sublimation) found for ammonium chloride by earlier investigators has been verified and found to extend to the other halides. The frequency factor is also abnormally low for the ammonium halides, by a factor of roughly 104, with the exception of the fluoride, for which the factor is only about 500. These results are in fair agreement with the Schultz—Dekker mechanism for ammonium halide sublimation.
Order—Disorder Theory for Linear Colloids
Authors: Peticolas Warner L.
Published: January 2005

A theory for the order-disorder transitions found in associative linear colloids has been developed from a one-dimensional lattice model using the matrix method of statistical mechanics. Our theory bears exactly the same relationship to the helix-coil theory of single-chain helices as the lattice theory for separation of binary liquid mixtures or condensation of a lattice gas bears to the Ising theory of ferromagnetism. In this paper we show that the condensation of a one-dimensional lattice gas (or the separation of a one-dimensional immiscible phase) involving only finite (nearest) neighbor interactions, can be arbitrarily sharp as the statistical weights assigned to the various occupied sites tend to certain values, but that the one-dimensional condensed phase must always exist in segments. These linear segments of condensed phase are, in fact, the colloid particles or micelles. The critical volume fraction for micelle formation is given as the product of two parameters, σ2 and ζ, while the sharpness of the transition and the resulting degree of aggregation is dependent on the ratio σ2/ζ. In general, the weight-average degree of association increase much faster above the critical point than the number average. The distribution of molecular weights of a linear associative colloid has been calculated and a method for the determination of the molecular weight distribution has been suggested.
Temperature Dependence and Decay Times of Eu3+ Emission Lines in Eu Dibenzoylmethane
Authors: Nardi Eran , Yatsiv Shaul
Published: January 2005

The temperature dependence and the decay times of the Eu3+ fluorescence in DBM provide an unequivocal assignment for the emitting states. The decay times of emissions from the two excited states are due to different depleting mechanisms. The role of the particular J values of the two emitting states in Eu3+ is discussed.
Carbon and Oxygen Isotope Exchange between CO and Ni(CO)4
Authors: Monse E. U. , Spindel W.
Published: January 2005

The single stage factor α of the carbon and oxygen isotope exchanges between liquid Ni(CO)4 and gaseous CO, according to the reactions Ni(C12O)4+C13O⇌Ni(C12O)3C13O+C12Oand Ni(CO16)4+CO18⇌Ni(CO16)3CO18+CO18,respectively, has been determined: For the carbon exchange,α=1.020±0.002 at−10∘ and α=1.010±0.002 at+10∘.For the oxygen exchange,α=1.005±0.002 at−10∘ and α=1.000±0.002 at +10∘.These data are in good agreement with values calculated from spectroscopic data for Ni(CO)4 and CO.

From the isotope fractionation measured in a packed countercurrent column, the activation energy E for the exchange was estimated. The value of E=12 kcal/mole agrees with the results obtained from kinetic data for the thermal decomposition of Ni(CO)4 and the exchange of Ni(CO)4 with labeled CO. The rate of the thermal decomposition of Ni(CO)4 is assumed to be the rate determining step in the exchange.
Anomalous Polymer-Penetrant Permeation
Authors: Frisch H. L.
Published: January 2005

We review briefly and classify the so called ``non-Fickian anomalies'' associated with one-dimensional permeation (or sorption) of a penetrant through a polymer film of thickness l. We point out that ``Fickian'' diffusion controlled permeation can be readily distinguished from anomalous permeation by the l dependence of the experimental flux through the film for the former process, which satisfies a simple scaling law with respect to film thickness. Furthermore, we show that by varying the film thickness one can separate the time lag for ``non-Fickian'' diffusion into a purely ``Fickian,'' l-dependent contribution and an l-independent term due wholly to the anomalies. The latter can serve as a convenient figure of merit for the anomalous behavior, being essentially a mean relaxation time for the explicitly time-dependent process responsible for deviation from the simpler, ``Fickian'' behavior.
Polarization of the Luminescence of Phenanthrene
Authors: Azumi T. , McGlynn S. P.
Published: January 2005

The polarization of the luminescence emitted when a randomly oriented array of phenanthrene molecules is excited with polarized light is discussed. Considerable attention is devoted to various correction methods in an effort to establish a correct zero-polarization base line.

The polarization of the fluorescence excitation spectrum, the fluorescence spectrum and the phosphorescence spectrum of phenanthrene have been determined. The polarization of the fluorescence spectrum validates Platt's assignment of the first four singlet electronic states of phenanthrene as 1Lb, 1La, 1Bb, and 1Cb in order of increasing energy. The possible occurrence of one or two other electronic states in the same energy interval, as suggested by Zimmermann and Joop, is discussed. The phosphorescence emission is primarily polarized out of plane. The results further suggest that either two perturbing singlet states are mixed into the lowest triplet state, or that two perturbing triplet states are mixed into the singlet ground state by spin-orbital coupling; the Platt assignment of 3La for the lowest triplet state is supported. It has been found that polarization measurements are of considerable help in vibrational analysis, and may in certain cases uniquely determine vibrational types. A vibrational analysis of the fluorescence spectrum, phosphorescence spectrum and 1Lb absorption band is presented.
Determination of the Equilibrium Constant for the Gas-Phase Dissociation of Nitrogen Tetroxide by Infrared Absorption Techniques
Authors: Dunn Michael G. , Wark Kenneth , Agnew John T.
Published: January 2005

The gas-phase equilibrium constants (Kp) for the dissociation of nitrogen tetroxide, N2O4⇋2NO2, have been calculated from experimental data based on infrared absorption techniques. The quantitative analysis of NO2 in the mixture was made at varying pressures and temperatures by observation of the 3.425-μ nitrogen dioxide absorption band. Values of the equilibrium constant are given in the temperature range from 300 to 370°K. It was also ascertained that the 3.21-μ band previously assigned to NO2 should be assigned to N2O4.
ESR Studies of Free Radical Decay in Irradiated Polyethylene
Authors: Cracco Francis , Arvia A. J. , Dole Malcolm
Published: January 2005

A study has been made of the temperature and rates at which molecular hydrogen is evolved and free radical decay occurs when semicrystalline polyethylene, irradiated at liquid-nitrogen temperature, is warmed to room temperature. Hydrogen evolution and free radical decay roughly parallel each other. The temperature of half reaction is the same as the temperature of the gamma-maximum in the mechanical dispersion temperature curve. At constant temperature over the temperature range —71° to 41°C, the free radical decay is first order and the free radical concentration seems to decrease to a limiting value at each temperature. The first-order decay constants are approximately constant with temperature. The data are interpreted in terms of free radicals decaying in spurs. If a constant activation energy of 15 kcal mole—1 is assumed, the frequency factors decrease with rise of temperature. This decrease is interpreted on the basis of a decreasing probability of reaction for those free radicals that escape reaction at low temperatures, but react at higher and higher temperatures. An alternative model based upon the release of free radicals from traps as the temperature is raised is also discussed.

The reaction rate constant for free radical decay calculated from D—H exchange experiments agrees with that deduced from the ESR measurements. It is also concluded that the persistent free radical in polyethylene irradiated to moderate doses is the allyl free radical.
Conversion of Solvated Electrons into Hydrogen Atoms in the Photo- and Radiation Chemistry of Aqueous Solutions
Authors: Jortner Joshua , Ottolenghi Michael , Rabani Joseph , Stein Gabriel
Published: January 2005

Radiation chemical and photochemical experiments are reported which show that the conversion of solvated electrons to H atoms is not specific to the H3O+ ion. Proton donors in general may react in the conversion eaq—→H. The relative reaction rates correlate with the pK values of these acids as implied by Brønsted general acid catalysis law. The implications of this result for the nature of the solvated electron in water are briefly considered.
Rate of Dissociation of N2O4 by Ultrasonic Absorption Measurements
Authors: Cher Mark
Published: January 2005

Sound-absorption measurements as a function of the sound frequency in the range of 78 to 394 kc/sec have been made in gaseous mixtures of nitrogen tetroxide, nitrogen dioxide, and a third inert gas. Inert gases studied were nitrogen, argon, and carbon dioxide. The absorption coefficient per wavelength varies with frequency in the typical bell-shape manner associated with a relaxation mechanism. The frequency of maximum absorption increases with increasing concentration of N2O4, is nearly independent of the total pressure, and varies only slightly with temperature in the range 25° to 40°C. The sound absorption is ascribed to the perturbation of the equilibrium reaction N2O4=2NO2. The (equilibrium) rate of dissociation of N2O4 is calculated using an extension of the theory developed by Freedman. It is concluded that the dissociation of N2O4 proceeds according to a Lindemann unimolecular mechanism; specific rate constants for the limiting low-concentration and high-concentration regions at 25°C are 4.5×106 liter mole—1 sec—1 and 1.7×105 sec—1, respectively. The relative efficiencies of the various molecules for energizing N2O4 are: N2O4, 1.0; NO2, 1.0; N2, 0.50; Ar, 0.30; CO2, 1.0. Measured absolute values of the absorption coefficients are in good agreement with calculated values. The effects of viscosity, heat conduction, and vibrational heat capacity relaxation on the observed magnitude of the absorption are considered negligible.
Low-Energy Collision Cross Sections of H— and OH— Ions in Oxygen
Authors: Baker C. E. , McGuire J. M. , Muschlitz E. E.
Published: January 2005

Elastic and inelastic collision cross sections have been measured for collisions of H— and OH— ions in oxygen gas in the energy range 4–350 eV. An improved collision chamber was used for the measurements. The majority of the inelastic collisions in the case of OH— are apparently due to electron detachment, but in the case of H—, charge exchange or an ion—molecule reaction or both predominate, particularly at the low energies. In the range 4–26 eV the interaction potential derived from the elastic scattering of OH— in O2 is V (eV) = —18.4/r5.34(r in Å). The large amount of inelastic scattering observed for H— in O2 precluded an accurate determination of the interaction potential in this case. The electrons produced in electron-detachment collisions of negative ions are shown to have energies considerably in excess of thermal energy.
Proton Magnetic Resonance Spectra of 2-Pyridines. The Strong-Coupled AA′KL System
Authors: Kowalewski Valdemar J. , de Kowalewski Dora G.
Published: January 2005

The 60-Mc/sec spectra of 2-chloro, 2-cyano, 2-bromo, and 2-acetyl pyridines are studied and analyzed as ABKL and AA′KL systems. The results are compared with the exact ABCD solution given by a computer. It is shown that if one of the coupling constants is greater than the corresponding chemical shift, the AA′KL approximation can give a good account of the frequencies of the lines of the experimental spectrum, but not so good for the intensities. The molecular parameters calculated with both approximate methods differ only some hundredths of a cycle per second from the values given by the computer.

An iterative method based on the use of average group frequencies and average splittings and improved by the use of the principle of least squares is fully described.
Mass Spectra Resulting from High-Energy Electron Impact on Some Hydrocarbon Molecules
Authors: Monahan J. E. , Stanton H. E.
Published: January 2005

The mass spectra of five representative hydrocarbon molecules (acetylene, ethylene, benzene, neopentane, and normal heptane) have been measured as a function of electron bombarding energy in the range from 200 to 2400 eV. In addition the distribution of the kinetic energy of formation of most of the fragment ions has been determined. These results are discussed in terms of current theories of the ionization—dissociation process for polyatomic molecules. In particular, the data are shown to be consistent with the assumption that the accessible electronic states in the reactant molecular ion separate into at least two noninteracting groups which lead to experimentally distinguishable fragmentation processes.
Thermoelectric Study of Liquid Semiconductor Solutions of Tellurium and Selenium
Authors: Cutler M. , Mallon C. E.
Published: January 2005

The thermoelectric properties of liquid tellurium have been studied at temperatures ranging between 400° and 500°C both for pure tellurium and for solutions containing up to 20% (by weight) of selenium. This included measurements of the electrical conductivity σ, the Seebeck coefficient α, and the dimensionless figure of merit γ(=α2σT/κ) and from these the thermal conductivity κ was derived. The measurements were made entirely by electronic methods in a sealed Pyrex tube containing platinum and platinum—rhodium leads. The figure of merit was obtained by the small area contact method devised by one of the authors. For liquid tellurium, our results for α, σ, and κ agreed with values which have been obtained previously by other investigators. The unusually large value of κ observed in liquid tellurium is found to decrease upon addition of selenium. This, and the behavior of α and σ indicate that selenium tends to reduce the concentration of electrons in comparison to that of the holes. At higher concentrations of selenium, phenomena are observed which seem to be related to the motion of ions.
Occurrence of H3+ in the Field Ionization of Hydrogen
Authors: Clements T. C. , Müller E. W.
Published: January 2005

Mass-spectroscopical analysis of the ions produced at a point emitter with dynamic supply of hydrogen at room temperature or in modified field ion microscopes at 78° and 20°K showed the abundant occurrence of H3+ besides H+ and H2+ observed earlier by Inghram and Gomer. The triatomic molecule ion is formed only in the narrow range of field strength near best image conditions. The mechanism of H3+ formation under the extreme field conditions is uncertain. Field ion-microscopic observation shows H3+ only over single protruding surface atoms, which might act as sites for deactivation of an intermediate state, or simply provide a region of locally enhanced field to allow quick field ionization of short-lived H3.
Molecular Parameters of Ethane
Authors: Lafferty Walter J. , Plyler Earle K.
Published: January 2005

The combination band ν2+ν6 of ethane at 2754 cm—1 has been studied under high resolution. The value of B0 has been found to be 0.66310±0.00007 cm—1. When this value is combined with values of A0 of C2H6 and B0 for C2D6 determined in other studies, the following parameters are obtained: r0(C–C) = 1.536 Å, r0(C–H) = 1.108 Å, and ∠C–C–H = 110.1°.
Relation between the Compressibility and the Coexistence Curve near the Critical Point
Authors: Widom B.
Published: January 2005

It is known that if a fluid at its critical density is cooled toward its critical temperature, then its compressibility becomes infinite proportionally to (T—Tc)—f, where T and Tc are the temperature and critical temperature, and where the exponent f depends only on the dimensionality of the system. It is also known that along the coexistence curve in the temperature—volume plane, Tc—T becomes proportional to | V—Vc |d near the critical point, where V and Vc are the volume and the critical volume, and where the exponent d, like f, depends only on the dimensionality of the system. If it is conjectured that two features of classical (i.e., infinite-dimensional) systems are in fact independent of dimensionality, it then follows that f=2(1–1/d). The pair f=1, d=2 and the pair f=7/4, d=8 are well known for classical and for two-dimensional systems, respectively. For three-dimensional systems it has often been conjectured that f=5/4, from which it would follow that d=8/3, while it has also often been conjectured that d=3, from which it would follow that f=4/3.
Chemisorption of Hydrogen on Cobalt
Authors: Abeledo Carlos R. , Selwood P. W.
Published: January 2005

The change in saturation magnetization of small particles of cobalt upon adsorption of hydrogen has been measured. It has been found that the average hydrogen atom chemisorbed decreases the magnetization by about 0.5 Bohr magnetons. This result, together with previous results on the effect of hydrogen chemisorbed on nickel, suggests the existence of surface states associated with the adsorbed atoms and the surface metal atoms.

Simultaneous measurement of the magnetization of cobalt and adsorption of hydrogen in a low-field ac permeameter have shown that hydrogen chemisorbs on, and changes the magnetization of, cobalt at temperatures up to 500°C.
Monte Carlo Calculations. II. The Reactions of Alkali Atoms with Methyl Iodide
Authors: Blais Normand C. , Bunker Don L.
Published: January 2005

A large number of trajectories for the reactions of alkali metal atoms with methyl iodide were calculated with a very fast digital computer, and the results compared with those of molecular-beam experiments on the same reactions. Agreement was found to be very good. The calculations also show the relative influence of various collision parameters on the distributions of product internal energy and angle of emission, and the effect of certain general features of the assumed potential energy surface. The calculated distributions of product rotational energy indicate that approximately all the initial angular momentum appears as product rotation.
Dipole Moment of Formic Acid, HCOOH and HCOOD
Authors: Kim Hyunyong , Keller R. , Gwinn William D.
Published: January 2005

The magnitude and the direction of the dipole moment of formic acid were determined through the Stark effect of rotational transitions. The dipole moments of HCOOH and HCOOD are 1.415±0.01 D and 1.39±0.01 D, respectively. The direction of the dipole moment lies between C–H and C=O bonds making an angle of 42.4°±2° with the C=O bond.
Motion of F Centers in KCl and KI
Authors: Gravitt J. C. , Gross G. E. , Benson D. K. , Scott A. B.
Published: January 2005

The drift velocity of F centers in KCl and KI as a function of temperature is determined. The electric field producing this motion in the colored portion of the crystal is measured directly. The electric field in the uncolored region is found to be appreciably higher than the field in the colored portion.

The thermal ionization energy for F centers is found to be 2.4 eV for KCl and about 2.0 eV for KI.