bluuebunny/crossref_metadata_2025 huggingface dataset:
Diffusion Coefficients of T2−H2 and T2−D2: The Nonequivalence of the H2 and D2 Cross Sections
Authors: Mason E. A. , Annis B. K. , Islam M.
Published: January 2005

Measurements of diffusion in T2−H2 and T2−D2 in three apparatuses of the two-bulb type are reported at 295.0°K. The ratios of the diffusion cross sections are 1.024±0.014, 1.018±0.011, and 1.015±0.011 in the three apparatuses. This confirms, within mutual experimental error, the observations of Amdur and Beatty (preceding paper). The average diffusion coefficients at 1 atm, corrected to a reduced mass equivalent to H2–H2 diffusion, are 1.441 cm2/sec from the T2−H2 measurements and 1.469 cm2/sec from the T2−D2 measurements.
Inorganic Radicals Trapped in Glasses at Room Temperature. II. Cd+ and Ni+ in Metaphosphate Glass
Authors: Feldmann T. , Treinin A. , Volterra V.
Published: January 2005

The effects of uv and x-ray radiations on sodium metaphosphate glass doped with either CdSO4 or NiO, were studied. The optical and ESR absorptions of the glass were measured. The formation of Cd+ and Ni+ was demonstrated. A new interpretation is given to the color centers induced by irradiation in the pure base glass.
Adsorption of Inorganic Anions on a Mercury Electrode from Solutions in Formamide. I. Adsorption of Iodide Ions
Authors: Payne Richard
Published: January 2005

The adsorption of the iodide ion on a mercury electrode from solutions of potassium iodide in formamide has been studied by measuring the double-layer capacity and the interfacial tension as a function of potential and concentration at 25°C. The adsorption can be described by a modified Langmuir (Frumkin) isotherm with a large lateral repulsive interaction energy, but examination of the inner-layer capacity suggests that the adsorbed layer behaves more like a two-dimensional imperfect gas than an array of particles on localized sites implied by the Langmuir model. The amounts adsorbed are calculated and the capacity resolved into its component parts with the aid of the isotherm and diffuse-layer theory. The capacity of the inner region of the double layer measured at constant amount adsorbed is almost independent of the amount adsorbed and approximates to the inner-layer capacity for a nonadsorbed electrolyte, i.e., potassium fluoride. The relative distances from the interface of the inner and outer Helmholtz planes are calculated from the components of the capacity and compared with similar values for aqueous potassium iodide. Methods devised by Grahame and Parsons for determining the potential at an anion site and the Stern specific adsorption potential Φ are compared and discussed in relation to the form of the isotherm, and values of Φ are calculated. [The symbol Φ is also used elsewhere to denote surface pressure because of established usage. It is obvious from the context which parameter Φ refers to wherever it occurs.] The results are shown to be consistent with both the ideal (Henry's law) and Langmuir forms of the chemical part of the electrochemical free energy of the adsorbed ions. The discreteness of charge effect and the Esin and Markov coefficient are compared for the formamide and aqueous solutions. The absence of any appreciable specific adsorption of potassium ions is demonstrated by comparison of the cation surface excesses with the predictions of diffuse layer theory.
Electron Paramagnetic Resonance and the Primarily 3d Wavefunctions of the Tetrachlorocuprate Ion
Authors: Sharnoff Mark
Published: January 2005

Electron paramagnetic resonance studies of the tetrahedral CuCl4= ion in single crystals of Cs2CuCl4 and Cs2ZnCl4 yield the spectroscopic parameters g1=2.083±0.001, g2=2.103±0.003, g3=2.384±0.006 (Cs2CuCl4) or 2.446±0.002 (Cs2ZnCl4), and | A1 | = (5.1±0.5)×10−3 cm−1, | A2 | = (4.6±0.5)×10−3 cm−1, and | A3 | = (2.5±0.5)×10−3 cm−1. The indicated errors are estimated from the slight asymmetries in the line shapes and from the lack of full resolution of the hyperfine components. The resonances show no resolved superhyperfine structure. It is demonstrated that the linewidths of 2.2×10−3T observed between inflections at low temperatures arise from unresolved superhyperfine interaction and are consistent with the presence of an unpaired electron which spends 1.3% of its time occupying 3s orbitals of the Cl ions of the complex. Comparison with the superhyperfine structure observed in octahedral CuCl64— suggests that this electron also spends 16.7% of its time occupying Cl ion 3p orbitals. Insertion of these numbers into an LCAO—MO analysis of the g values in terms of the known energies of the d—d transitions shows that the unpaired electron spends 12% of its time in a 4p(Cu) orbital and 70% of its time in the 3d(Cu) state. These numbers are consistent with the EPR hyperfine splitting and the polarization ratios and extinction coefficients of the d—d bands. Further considerations demonstrate that the wavefunction of the unpaired electron is a nonbonding orbital.
Fluorine NMR Spectra and Conformational Isomerization of 1,1-Difluorocyclohexane
Authors: Jonáš J. , Allerhand Adam , Gutowsky H. S.
Published: January 2005

The 19F high-resolution spectrum of 1,1-difluorocyclohexane has been observed at temperatures from −93° to +40°C. The rate of conformational isomerization was determined by a complete line-shape analysis method for temperatures from −71° to +6°C. Activation parameters ΔH‡ and ΔGcc‡ in kilocalories/mole and ΔScc‡ in entropy units were 9.0, 9.8, −3.3 and 8.6, 9.8, −5.0 for 1:1 vol/vol solutions in CS2 and CFCl3, respectively, at the coalescence temperature of 228°K. In the low-temperature spectra of the CS2 solution, the resonance of the equatorial fluorine is shifted 15.64 ppm downfield from the axial and JFF is 235.3 cps; also J (Hax–Fax) the axial-axial vicinal H–F coupling constant is 34.3 cps and J (Heq–Fax) is 11.5 cps. At temperatures above −10°C, neglect of the H–F coupling in the line-shape analysis produces systematic errors in the apparent exchange rate.
Relaxation of the Vibrational, Electronic, and Rotational Degrees of Freedom of the NO Molecule
Authors: Bauer H.-J. , Sahm K. F.
Published: January 2005

Relaxation times and collisional de-excitation probabilities of the vibrational, electronic, and rotational degrees of freedom of the NO molecule were determined by acoustic measurements at 296°K (τ0pT vib=4.0×10−7 sec, P10 vib=1/2700; τ0pT el=1.0×10−8 sec, P10 el=1/110; τ0pT rot=1.2×10−10 sec). In fact, these measurements were the first acoustic determination of electronic relaxation in any gas. In comparison to O2 and N2 the vibrational and rotational relaxation times are shorter than expected. This may be attributed to the dipole moment of the NO molecule.
Absorption, Fluorescence, and Zeeman Effect in Emerald
Authors: Wood D. L.
Published: January 2005

The absorption and fluorescence spectra of emerald are characteristic of Cr3+ in the slightly distorted octahedral site of beryl [Be3Al2(SiO3)6]. Details of the spectra, such as dichroism and fine structure, are analyzed successfully in terms of a D3 site symmetry. The large trigonal field parameter values v=−1550 cm−1, v′=+1380 cm−1 arise from polarization of oxygen ligands by next-nearest neighbors. The Zeeman effect for the red 2E lines is analyzed on the basis of the D3 site symmetry, and data are given for the Paschen—Back effect for both emerald and ruby.
Quantum Cell Model. II. A Corresponding-States Approach to an Equation of State at High Densities
Authors: Hillier Ian H. , Jenkins W. Ieuan , Walkley John
Published: January 2005

The equation of state of a system of light molecules is regarded as the sum of a classical term and a quantum correction term. Experimental data for argon are used as the classical contribution and the quantum term is evaluated both for a 12–6 Lennard-Jones cell model and for a uniform potential approximation of this model. The former is seen to give a quantum correction term far too small in magnitude, while the latter approximation produces theoretical isotherms in good agreement with experimental data for both hydrogen and deuterium. Experimental hydrogen—deuterium data are then used to construct high-temperature classical corresponding-states isotherms.
Generalized Oscillator Strengths and Electronic Collision Cross Sections for Nitrogen at Excitation Energies Above 10 eV
Authors: Silverman S. M. , Lassettre Edwin N.
Published: January 2005

Collision cross sections and generalized oscillator strengths have been determined for each of 13 transitions in nitrogen whose excitation energies lie in the interval 10 to 83 eV. Only the generalized oscillator strengths have been reported since the collision cross sections can be calculated from these. Incident kinetic energy was approximately 500 V in each case.
Determination of Molecular Excitation Potentials by Electron Impact. An Anomaly in the N2 Spectrum
Authors: Lassettre Edwin N. , Glaser Frederic M. , Meyer Vincent D. , Skerbele Ausma
Published: January 2005

An improved monochromator is described which provides an electron beam sufficiently homogeneous in energy so that peak widths range from 0.28 V at 400-V kinetic energy to 0.13 V at 150-V kinetic energy. Using this device excitation potentials have been determined for CO2 and N2. The highest peak in the spectrum of N2 occurs at an excitation potential of 12.93 V while the most intense transition in the ultraviolet absorption spectrum, according to Huffman, Tanaka, and Larrabee, occurs at 12.74 V. This discrepancy exceeds the experimental error in the determination and indicates a failure of the Born approximation.
Oscillator Strengths of Several Peaks in the Electron-Impact Spectrum of Carbon Dioxide. Spin—Orbit Coupling
Authors: Meyer Vincent D. , Lassettre Edwin N.
Published: January 2005

Electron-impact spectra of CO2 have been obtained at incident kinetic energies of 150, 200, 300, and 400 V. Oscillator strengths of four transitions are calculated from the spectra and compared with other deminations. Assignment of term symbols is discussed.
Transport Properties of Polyatomic Fluids, a Dilute Gas of Perfectly Rough Spheres
Authors: Condiff Duane W. , Lu Wei-Kao , Dahler John S.
Published: January 2005

A detailed account is given of the kinetic theory for a fluid composed of perfectly rough spheres. When one applies the method of Chapman and Enskog to a dilute gas of these spheres he finds that the nonequilibrium distribution function satisfies a nonself-adjoint integral equation. The solution of this equation is not an isotropic function of the molecular spin velocity. A study has been made of the bearing of this spin anisotropy upon the calculated values for the gas transport coefficients.
Energy-Transfer Processes in Monochromatically Excited Iodine Molecules. I. Experimental Results
Authors: Steinfeld Jeffrey I. , Klemperer William
Published: January 2005

The fluorescence excited in iodine by the green emission line of mercury, in the presence of foreign gases, has been examined by high-resolution photoelectric photometry. Cross sections for quenching, vibrational, and rotational energy transfer for the v′ = 25, J′ = 34 level of the B 3Π0u+ state of iodine have been obtained, for collisions with 3He, 4He, Ne, Ar, Kr, Xe, H2, O2, CO2, SO2, CH3Cl, and NH3. Emission bands have been rotationally analyzed to yield partial total cross sections for the inelastic processes. These have been corrected for multiple scattering by a computer simulation procedure.

The correlation of quenching efficiency with the mass and polarizability of the collision partner, found by Brown for the quenching of the v′ = 15 level of iodine, holds for the v′ = 25 level as well. There is no contribution to quenching efficiency from a permanent electric dipole moment. The data suggest that a complex set of interactions, including electrostatic polarization, spin—orbit forces, and specific chemical effects, are responsible for quenching, indicating a multiplicity of repulsive states contributing to the induced predissociation process. The vibrational energy-transfer efficiency is maximum when the mean collision time equals the period of oscillation of the molecule, which corresponds to a collision reduced mass ≃40 for T = 370°K, v′ = 25 of I2; vibrational transfer is largely independent of the internal structure of the collision partner. The efficiency of pure rotational energy transfer (Δv′ = 0) shows a similar smooth dependence on reduced mass of the collision system, with the exception of the molecules SO2, CO2, and CH3Cl, which are more efficient. Quantitative measurements have been made on partial components of total inelastic cross sections for ΔJ′ up to ±20 angular momentum units, with evidence for a total spread of ΔJ′ up to 30 or 40. The width of the distribution of partial cross section components decreases in the order Δv′=+2>−2≳+1>−1≫0; also, the ΔJ′ distribution is broader for collisions with heavier particles.
Kinetics of Glass Transformation by Thermal Analysis. I. Glycerol
Authors: McMillan J. A.
Published: January 2005

Thermal analysis of the glass transformation permits the determination of the temperature at which the transformation occurs at a maximum rate. It is found that this temperature depends on the experiment's rate of warmup. Appropriate handling of kinetic equations and experimental data permits the evaluation of the thermodynamic functions that characterize the activation barrier. Experimental results on glycerol are comparable to results extrapolated from dielectric relaxation studies.
Direct Observation of the Decomposition of Multiply Charged Ions into Singly Charged Fragments
Authors: McCulloh K. E. , Sharp T. E. , Rosenstock H. M.
Published: January 2005

A new technique has been developed for the direct observation of the decomposition of multiply charged polyatomic ions. Positive ions or ion pairs and ejected electrons, formed in a uniform electrostatic field by a 1-keV electron beam, are accelerated in opposite directions to multiplier detectors. The masses of the positive ions are determined by measuring the time interval between electron and ion pulses by delayed coincidence. The formation of positive ion pairs is demonstrated and their masses determined by electron—ion—ion delayed coincidence techniques. The effects of initial kinetic energy on mass-spectrum peak shapes and travel time correlations between members of an ion pair are discussed. Both of these effects are experimentally observed. The technique has been applied to the study of ionization and fragmentation of CO2, CF4, CH4, and C3H6. Numerous decompositions leading to the formation of positive ion pairs are observed. Significant fractions of particular high-kinetic-energy fragment ions are formed by these processes.
Mass-Spectral Fragmentation of Phenyl-n-Alkanes
Authors: King A. Bruce
Published: January 2005

The fragmentation mechanisms for the 1-phenyl and 2-phenyl alkanes were found to differ from those having substituted two or more carbon atoms from the terminal carbon atom. The latter series of compounds have two competing primary fragmentation reactions involving loss of either alkyl group. The loss of the smaller alkyl group has the lower appearance potential, but the competing reaction to lose the larger alkyl group increases in yield more rapidly at the higher electron energies, and it has greater intensity at 70 eV. The ratio of intensities of these two ions correlates with the relative position of the phenyl group from the center of the chain for phenyl alkanes of different carbon numbers. Subsequent decomposition of these primary ions is by successive loss of olefins of C3 through C6.

The 2-phenyl compounds differ in that subsequent skeletal decomposition of the CH3C+HC6H5 is less probable, thus making this ion the major ion instead of C7H7+. The 1-phenyl alkanes decompose directly to C7H7+ for the lower-carbon-number compounds, while the larger molecules form toluene ion followed by hydrogen-atom loss to C7H7+ and other fragmentation reactions. Partial isomerization to the 4-phenyl compounds is suggested.

Attempts to explain the higher yield of the higher-energy primary path for the internally substituted compounds within the framework of current theoretical models were unsuccessful. It is suggested that the usual method of applying the quasiequilibrium assumption is not valid for molecules of this size and degree of localization of charge and energy.
Normalization of Diffraction Data from Liquids
Authors: Rahman Aneesur
Published: January 2005

In any system, the effective exclusion of an atom from the immediate neighborhood of another atom can be used to derive a necessary (but not sufficient) condition which the diffraction pattern of the system has to satisfy. This condition provides a new method of scaling the observed diffraction data from liquids. The currently available x-ray and neutron-diffraction data on liquid argon at 84°K are found to differ in a systematic manner, and this discrepancy appears to be beyond the experimental uncertainties of the data. It is demonstrated that the above-mentioned condition can be used as a reliability criterion as well. Using this criterion, it is found that the neutron-diffraction data are much more reliable.
Infrared Spectra of Isotopic Bicarbonate Monomer Ions
Authors: Bernitt D. L. , Hartman K. O. , Hisatsune I. C.
Published: January 2005

The infrared spectra of monomeric bicarbonate ions with hydrogen, deuterium, carbon-12, and carbon-13 isotopes have been measured. The ions were isolated in potassium halide matrices as thermal decomposition products of the normal, polymeric potassium or sodium bicarbonate salts. A normal coordinate analysis was carried out and a set of modified valence force constants was obtained which fit the observed isotopic frequencies with an average error of 0.8%. The barrier to rotation of the hydroxyl group was estimated to be 15.8 kcal/mole and a value of −35 cal/deg·mole was calculated for the entropy of hydration of the ion at 25°C.
On the Equation of State of the Rigid-Sphere Fluid
Authors: Rice Stuart A. , Lekner John
Published: January 2005

A well-known integrodifferential equation due to Yvon, Born and Green, Kirkwood, and Bogolubov (YBGKB) connects the pair and triplet distribution functions g(2) and g(3) of a classical fluid. An expression for g(3) is needed in order that the equation may be solved for g(2). An exact formal expression is known: g(3)(123)=gs(3)(123) exp[ ∑ n+1∞ρnδn+3(123)],where gs(3) is the superposition of the pair distribution functions, and the terms δn+3(123) in the exponent evaluate the correlations between particles fixed at 1, 2, and 3 and n other particles in the fluid. The first term δ4 is known for hard spheres, and we have numerically evaluated δ5 for three special configurations in order to approximate the entire series by the simplest Padé approximant, i.e., ρδ4/ (1—ρδ5/δ4). The YBGKB equation was solved using this approximation for g(3), and the pressure obtained from the contact value of g(2) is in almost perfect agreement with the molecular-dynamics data of Alder and Wainwright up to p/ρkT=6.80, which is the Kirkwood upper limit for stability of a fluid of hard spheres. The results obtained with the use of only δ4 in the expression for the triplet distribution function are also presented. The Kirkwood theory of the fluid—solid transition is briefly discussed with reference to the hard-sphere system.
Electronic Spectra of Ferrimyoglobin Hydroxide and other Hemoprotein Derivatives
Authors: Offenhartz Peter O'D.
Published: January 2005

Using the fact that ferrimyoglobin hydroxide is a mixture of high- and low-spin forms, values for some of the energy differences among d orbitals on the metal are derived. The remaining energy differences among d orbitals are obtained by interpreting electron spin resonance data on ferrimyoglobin hydroxide and related complexes. Using these energy differences, the spectrum of the hydroxide is discussed; it is shown that the red and infrared peaks of the high-spin fraction are due to charge transfer from the porphyrin ring to the metal. The positions of other charge-transfer peaks are predicted. The spectra of other hemoproteins are also discussed, and it is shown that charge transfer to or from the porphyrin ring system is probably not important in the spectra of ferrohemoproteins, although charge transfer from ligands on the fifth and sixth coordination positions and d—d transitions may both be responsible for the weak red and infrared bands in the ferrohemoproteins.
Adsorption of Potassium on Tungsten
Authors: Schmidt Lanny , Gomer Robert
Published: January 2005

The adsorption of potassium on thermally annealed and field-evaporated tungsten surfaces was studied by field emission. The φ̄- vs-θ̄ curve has a minimum of 1.78 eV at θ̄=0.83, n̄=3.2×1014 atom/cm2 (which coincides with the minimum of φ110), and approaches φK at θ̄=2–3. Distinct minima also occur for other close-packed planes, like 211. At θ̄=1, n̄=3.9×1014 atom/cm2, φ̄=1.95 eV the emission pattern is indistinguishable from that of clean tungsten. The average charge per K atom, q̄, varies from 0.27 at low θ to 0.2 electron charges at θ̄=0.8. The value of q on the close-packed W planes at low coverage may be considerably higher.

The activation energy of neutral desorption varied from 2.67 to 2.4 eV over the interval 0<θ̄<0.4 and fell rapidly at higher coverage, approaching the heat of sublimation of K, 1.0 eV, at θ̄=1.0. The activation energy of ionic desorption was measured over the interval 0<θ̄≤0.07, and indicates that ionic desorption occurs on regions of φ=5.3 eV. dφ/dθ̄ on these regions is very high, suggesting that the K-atom density there exceeds the average by a factor of 3 or more, and that adsorption on these regions may be nearly ionic at low θ̄.

The activation energy of surface diffusion was measured quasidifferentially as a function of θ̄. Ediff and the pre-exponential term of the diffusion coefficient increased with θ̄ in the range 0<θ̄≤0.6–0.7, Ediff rising from 0.3 eV at θ̄=0 to 0.8 eV at θ̄=0.6. This is tentatively explained in terms of activated hopping into the almost empty second layer, followed by rapid diffusion, terminated by recombination of the excited atom with a hole in the first layer. At θ̄=0.8–1.0, Ediff falls sharply, corresponding to diffusion in the second layer.

It is suggested that K adsorption sites are relatively weakly structure dependent, so that a displacement of atoms from the initially occupied, optimal sites occurs at θ>∼0.4 in order to accommodate more adsorbate in some direct contact with the substrate. The experimental results are shown to be consistent with a model based on delocalized bonding, i.e., metallic adsorption.
Effect of External Magnetic Field on the Rate of Exchange of Magnetic Dipoles
Authors: Shimizu Hiroshi
Published: January 2005

It is shown theoretically that the quantum-mechanical exchange rate of magnetic dipoles such as electrons or protons is decreased by applying an external magnetic field, provided that the zero-field rate constant in frequency units (ωe) is comparable with the ``chemical shift'' (ωs) in the magnetic resonance spectrum of the system subjected to the external field. The decrease of the rate constant depends on the ratio ωe/ωs, and the maximum reduction from ωe to ωe/2 is obtained when the ratio vanishes. The effects of magnetic and electric fields on the rate of transfer of excitons in molecular crystals are also discussed.
Spin Relaxation and Differential Saturation of ESR Multiple Lines
Authors: Shimizu H.
Published: January 2005

The effect of various spin-relaxation mechanisms on the differential saturation of ESR spectra in the solid state is discussed by taking a two-spin system as an example. It is shown that the spin—orbit interaction, the spin—local-field interaction, and the intermolecular dipole—dipole interaction give similar values for the differential saturation. But they depend in complex manner on the angles between the molecular and the laboratory frame differently. In the weak mixing limit where the intensities of the satellite lines are much weaker than those of the main lines the saturation factors for the main and satellite lines are not very different from each other. The relative intensities of these lines change only by a factor of two even in the limit of H1→∞. Therefore, these mechanisms cannot explain the anomalous saturation of the ESR spectrum observed by Kurita and Ohigashi. On the other hand, if the relaxation occurs through the intramolecular dipolar interaction modulated by the torsional oscillation of the molecule, the saturation factors for the main lines are much larger than those for the satellite lines and the anomalous saturation could be produced.
Electronic States of Molecules. I. Self-Consistent Field Calculations of the Ground, Ionized, and Excited States of N2 and O2
Authors: Sahni R. C. , De Lorenzo E. J.
Published: January 2005

A number of electronic states of N2 and O2 have been computed using the self-consistent-field—molecular orbital (SCF–MO) method. The calculated ionization, excitation, and total energies are compared with the available experimental data, as well as with those reported by other workers.
Ab Initio Calculation of the E 1Σg and a 3Σg+ States of the Hydrogen Molecule
Authors: Gerhauser John , Taylor Howard S.
Published: January 2005

Molecular orbital calculations have been made of the potential function for the E 1Σg+ and a 3Σg+ excited state of the hydrogen molecule. Minimum energies of −0.71643 and −0.72730 a.u. were obtained, respectively. It was found that states separate into two hydrogen atoms—that is, one electron is associated with each nucleus. The potential curve for a 3Σg+ is a normal stable species curve, but the E 1Σg+ curve has an unusual hump in agreement with the results of Davidson.
Some Remarks on the Use of the Variational Principle for the Second-Order Energy
Authors: Epstein Jean H. , Epstein Saul T.
Published: January 2005

It is shown that the second-order energy correction calculated by means of the Hylleraas variation principle with an approximate zero-order function need bear no special relationship to the true value. In particular, there may be considerable deviation from the true value even if the approximate zero-order wavefunction is nearly exact, unless one requires that the trial function be orthogonal to the approximate zero-order function.
3p Orbitals, Bent Bonds, and the Electronic Spectrum of the P4 Molecule
Authors: Hart Robert R. , Robin M. B. , Kuebler N. A.
Published: January 2005

The electronic spectrum of P4 has been calculated in the SCF–CI approximation using a 3p atomic orbital (AO) basis. The calculated spectrum is in semiquantitative agreement with that observed in the region 4–9 eV, and this agreement is taken to support the original premise of a 3p AO basis. Earlier work by others suggested that a 3p basis necessarily leads to bent bonds and a bent-bond strain energy. Our calculation predicts that strong pi bonds are present in the molecule, and their presence leads to a resonance which, in turn, vitiates the concepts of ``bend bonds'' and ``strain energy'' in P4. An electron density map is also derived for the valence-shell electrons, and it shows that the regions of highest density are situated symmetrically above each of the triangular faces of the tetrahedral P4 molecule, and, that although arcs of charge are present in the molecule, they do not connect the phosphorus nuclei, as might be expected for bent bonds.
Thermal Decomposition of Fluoroform in a Single-Pulse Shock Tube. II. Pressure Dependence of the Rate
Authors: Tschuikow-Roux E.
Published: January 2005

The thermal decomposition of CF3H has been studied in a single-pulse shock tube between 1200° and 1600°K using dilute CF3H–Ar mixtures at total pressures of about 18.7 and 0.90 atm. The results, together with earlier work at about 4 atm indicate that the observed rate constants for the rate of disappearance of CF3H are those of a second-order energy-transfer process, where collisional activation is rate determining. Kassel's model of unimolecular reaction-rate theory is used to show that the observed pressure dependence of the rate constants is not unreasonable. From the classical Kassel theory for such processes it is calculated that the mean lifetime of a critically energized CF3H* at 1400°K is 1.2×10−11 sec with five effective oscillators.
Complex Formation between Carbon Tetrachloride and Aromatic Hydrocarbons
Authors: Weimer R. F. , Prausnitz J. M.
Published: January 2005

The spectroscopically determined equilibrium constant for complex formation between carbon tetrachloride and hexamethylbenzene is 0.64±0.12 mole/liter at 25°C. This value is about six times as large as the corresponding constant for the carbon tetrachloride—mesitylene complex; therefore, carbon tetrachloride is acting as the electron acceptor. The solubility of solid hexamethylbenzene in carbon tetrachloride at 25°C is 7.7 mole %. When referred to pure subcooled hexamethylbenzene, the activity coefficient of the solute is less than unity giving the unusual result that this solution of nonpolar components exhibits negative deviations from Raoult's law.
Surface Ionization of Niobium
Authors: Scheer Milton D. , Fine Joseph
Published: January 2005

By measuring the temperature dependence of Nb+ emission from a niobium surface heated between 1990° and 2175°K; a value of 10.39±0.15 eV was obtained for the heat of ion vaporization. The work function for the niobium surface was found to be 3.90±0.05 eV in the 1850°-to-2025°K temperature range. The method used for this determination consisted of a mass-spectrometric measurement of the ratio of positive to negative ions formed when a constant-intensity beam of alkali halide molecules impinged upon the niobium surface. These quantities, together with the ionization potential of niobium are sufficient to derive a value of 7.45 eV for the heat of niobium sublimation at absolute zero. This is in excellent agreement with previous direct determinations of this quantity.
Split-Shell Molecular Orbitals for Sigma-Bonded Systems: Hydrogen Halides
Authors: Harris Frank E. , Pohl Herbert A.
Published: January 2005

A split-shell molecular orbital calculation has been made for the pair of bonding electrons in the molecules HF, HCl, HBr, HI. The results compare favorably with an earlier closed-shell calculation by Pohl, Rein, and Appel, and in particular cause the interatomic potential to have the correct limiting behavior at large distances. It is shown that, even using real atomic orbitals, the coefficients in the optimum split-shell molecular orbitals may be complex, in which case the two split-shell orbitals are complex conjugates, describing the same spatial distribution but with different relative phases.
Relations between Raman Spectroscopy and Nuclear Spin Relaxation
Authors: Gordon R. G.
Published: January 2005

Raman spectra and nuclear spin relaxation experiments are both affected by molecular rotation. The information about molecular reorientation furnished by these experiments is shown to be related under certain assumptions, most important of which are the following: (1) The substance is a molecular liquid or gas. (2) The molecules have either linear, symmetric-top, or spherical-top symmetry. (3) The spin relaxation is controlled by the intramolecular electric-quadrupole interaction or intramolecular nuclear magnetic dipole interactions. The relations are independent of the usual crude dynamical models for molecular reorientation, and hold for both classical and quantum systems. For liquid nitrogen, the Raman and spin relaxation experiments are shown to be in satisfactory agreement.

Raman experiments should be of value in interpreting spin relaxation experiments in simple molecules, since Fourier transformation of a Raman spectrum furnishes the detailed time dependence of a rotational correlation function, whereas spin experiments observe only the area under such a correlation function.
Perturbed Hartree—Fock Calculations. V. Magnetic Properties of the BH Molecule
Authors: Stevens Richard M. , Lipscomb William N.
Published: January 2005

The 11B1H molecule of Σ+ symmetry is predicted, on the basis of perturbed Hartree—Fock calculations in which the origin is chosen at the B nucleus, to have a magnetic susceptibility of 18.16 ppm (paramagnetic!), a rotational magnetic moment of −8.17 μN, shielding constants at B of −264 ppm and at H of 22.6 ppm, and spin rotation constants of CB=496 kc/sec and CH=−8.5 kc/sec. When the origin is shifted to H, only the values of H shielding (17.6 ppm) and the spin-rotation constant CH=−25.3 kc/sec are substantially different. Abbreviation of the ground-state wavefunction to the minimum basis set is shown to produce errors as high as 50% in the calculated magnetic properties.
Paramagnetic Resonance Absorption of Copper Ions in Porous Crystals
Authors: Nicula A. , Stamires D. , Turkevich J.
Published: January 2005

The EPR absorption of Cu II ions in porous crystals was studied. The effect of Cu concentration, adsorbed phases, and structure of the crystal on the EPR of Cu+ + ions is discussed in detail.

For small Cu II concentrations, the EPR spectrum obtained is in accord with the theory of Sands for polycrystalline Cu-containing solids. Further, by choosing the appropriate crystal type and physical state it was possible to resolve the hyperfine structure due to the Cu nuclear moment, both in the g∥ and g⊥ bands, and thus obtain values for A and B. Our data fit the following Hamiltonian: H=β0[g‖HzSz+g⊥(HxSx+HySy)]+A SzIz+B(SxIx+SyIy).Using the analysis of Maki and McGarvey, we obtained values of α, β1, β and ``K'' which characterized the type of bonding of Cu II ions in the crystal lattice.

From the variation of A, g, β, and ``K0'' parameters, the mechanism and process of adsorption of water on these crystals were ascertained. Some results obtained on Cu II containing hydrated crystals are compared to some Cu II ions in different solutions.
Madelung Energy of Perovskite Structures. II. The Tetragonal Case
Authors: Saltzman M. N. , Schor R.
Published: January 2005

The Madelung constants for the 4–4, 3–5, 2–6, and 1–7 tetragonal perovskite structures have been calculated for axial ratios α=c/a varying from 0.90 to 1.10. Least-squares fits expressing the Madelung constant as a function of (1—α) are reported.
Quantum-Mechanical Studies of Several Helium—Lithium Interaction Potentials
Authors: Schneiderman S. B. , Michels H. H.
Published: January 2005

The total energies for a number of states of HeLi were computed using a method of molecular orbital calculation in which the total wavefunction is taken as a linear combination of spatial configurations, each a properly antisymmetrized product of flexible one-electron functions in an elliptic coordinate system. Calculations were performed for the 2Σ ground state and a number of excited 2Σ, 2Π, 4Σ, and 4Π states of HeLi. The 1Σ ground state of the molecular ion HeLi+ was also examined to facilitate an evaluation of the neutral excited states. The lowest 2Π and 4Π states as well as two highly excited 2Σ states were found to be weakly bonding with dissociation energies of less than 1 eV. The importance of configuration interaction upon the accuracy of the calculations was examined and a method of obtaining approximate energies for highly excited states was developed. On the basis of these calculations, it is concluded that the weak bonding evidenced by some of the states of this system is due largely to the effects of orbital geometry and nuclear screening at large internuclear distances.
Gas-Phase Photolysis of Cyclohexane in the Far Ultraviolet: Modes of Decomposition of the Neutral Excited Cyclohexane Molecule and Reactions of the Parent Cyclohexane Ion
Authors: Doepker R. D. , Ausloos P.
Published: January 2005

The photolysis of cyclohexane—cyclohexane-d12 (1:1) mixtures and of cyclohexane-1,1,2,2,3,3-d6 was investigated using xenon (8.4 eV) and krypton (10, 10.6 eV) resonance radiation. It is demonstrated that the formation of hydrogen by molecular detachment is the major primary process cyclo−C6H12*→C6H10+H2. In this process, the hydrogen is mainly eliminated from a single carbon atom. The resulting C6H10 diradical rearranges mainly to cyclohexene, a fraction of which decomposes to form 1,3-butadiene and ethylene. It is shown that, because of collisional deactivation, the probability of the latter mode of decomposition decreases with an increase in pressure or an increase in wavelength. Other primary processes such as cyclo−C6H12*→3C2H4 and, to a lesser extent, cyclo−C6H12*→2C3H6 as well as processes leading to the formation of H atoms and CH3 radicals are also shown to occur.

In the photolysis at 1236 and 1165 Å, C6H12+ ions are formed which undergo H2-transfer reactions such as C6H12++CD3CDCD2→C6H10++CD3CDHCD2HC6H12++(CD2)3→C6H10++CD2HCD2CD2H. The efficiency of these ion—molecule reactions does not depend on the concentration of C3D6 or oxygen, but is reduced by NO because of the occurrence of a charge transfer from the cyclohexane ion to NO. The same processes have been reported to occur in the gas-phase photolysis of similar hydrocarbon mixtures.
Systematic Deviations from the Principle of Corresponding States
Authors: Guggenheim E. A. , Wormald C. J.
Published: January 2005

As surmised by Riedel and by Pitzer, many substances which do not conform to the principle of corresponding states have reduced properties whose deviations from this principle can be expressed in terms of a single parameter. It is shown that a simple and useful parameter for a given substance is the number of carbon atoms in the normal alkane which most closely resembles the given substance.
Linewidths of Inhomogeneously Broadened Electron Spin Resonance
Authors: Kaplan Jerome I.
Published: January 2005

It is shown that corrections to inhomogeneously broadened electron spin resonance linewidths arising from cross-relaxation effects can be calculated exactly using the moment formalism. Corrections of about 10% to the total width arising from ``cross-relaxation corrections'' are found for inhomogeneous broadening which is three times the ``spin-packet'' width.
Spectral Intensities of the Trivalent Lanthanides and Actinides in Solution. I. Pr3+, Nd3+, Er3+, Tm3+, and Yb3+
Authors: Carnall W. T. , Fields P. R. , Wybourne B. G.
Published: January 2005

We have correlated the experimentally measured intensities of the solution absorption spectra of Pr3+, Nd3+, Er3+, Tm3+, and Yb3+ in three different solvents with a theoretical expression derived by Judd. The expression, P=Σ lim λTλσ(fNψJ‖∪(λ)‖fNψJ′′)2λ=2,4,6is derived from a theory in which the ligand-field interactions with the central 3+ ion cause a mixing of higher configurations of opposite parity into the fN configuration and gives rise to induced electric-dipole transitions. A prerequisite for the intensity calculations is the computation of complete intermediate coupling eigenvectors for the energy levels investigated. Other possible mechanisms such as magnetic-dipole and electric-quadrupole transitions are considered. The oscillator strengths of important magnetic-dipole transitions are tabulated.

The results give the first experimental verification of the ability of the theory to account for large changes in certain bands of the same lanthanide observed in different solvents. Conclusions are drawn respecting the Tλ's obtained in a given medium for all the lanthanides studied, and also for those obtained for a given lanthanide in different media. The J dependence of the Tλ's is removed to facilitate their intercomparison, and the resulting parameters are tabulated. The Tλ's for Yb3+ are obtained by an extrapolation of the values computed for Tm3+ and Er3+. The nature of the model required by the theory is discussed.
Heat of Fusion of Solid Parahydrogen
Authors: Dwyer Robert F. , Cook Gerhard A. , Shields Bruce M. , Stellrecht Donald H.
Published: January 2005

The heat of fusion of solid parahydrogen has been measured for the first time at pressures above that of the triple point. The measurements were carried out up to a pressure of 338 atm. The heat of fusion was found to be a linear function of the pressure, and its values are well reproduced by the equation ΔHf = 0.04415 P+28.04, in which ΔHf is the heat of fusion in calories per gram mole and P the pressure in atmospheres. The value given by this equation for the triple point of hydrogen is 28.04, which compares with literature values of 28.03, 28.08, and 28.3 cal/mole. A few independent measurements were also made of temperatures corresponding to various pressures along the melting line for parahydrogen; most of the measured temperatures agree within 0.1°K of those previously reported in the literature.
Deuteron Magnetic Resonance in Deuterated Polycrystalline Ammonium Chloride and Sulfate
Authors: Rabideau Sherman W. , Waldstein Peter
Published: January 2005

Values of the quadrupole coupling constants |eQq|/h obtained at the temperature of liquid nitrogen for powdered specimens of deuterated ammonium sulfate and ammonium chloride have been found to be 161.9±0.3 and 175.7±0.7 kc/sec, respectively. Absolute values of the asymmetry parameter were estimated to be less than 0.2 from the powder spectra of the two salts. To obtain the deuteron quadrupole split spectrum of ND4Cl at liquid-nitrogen temperature, it was found necessary to use very low rf field levels and also to irradiate the sample with a 60Co source to reduce the spin—lattice relaxation time. Second-moment measurements were made on the single-line spectrum of ND4Cl between room temperature and −83°C, from which an activation energy for rotational motion of the ND4+ ion was calculated to be 5.0±0.5 kcal/mole. At the temperature of the ferroelectric phase transition in (ND4)2SO4, a significant alteration of the electric field gradient was revealed by the change in the separation of the peaks in the five-line deuteron magnetic resonance spectrum.
Conjecture on the Rate of Vibrational Relaxation of a Diatomic Molecule in a Monatomic Lattice
Authors: Sun H.-Y. , Rice Stuart A.
Published: January 2005

In this paper we use a simple model—a substitutional diatomic molecule in a linear monatomic chain—to examine the problem of intermolecular vibrational relaxation in the solid phase. A binary collision theory of vibrational deactivation is proposed for the relaxation process, with the motion of the collision partners governed by the normal modes of the lattice. The collision frequency is calculated by using an analysis similar to that of the Slater theory of unimolecular reactions. The model calculations predict the relaxation time to be very long compared with the vibrational period of the diatomic molecule. We thus conclude that, in a molecular crystal composed of polyatomic molecules, the excitation energy will be removed by the surrounding medium, not by the transformation of internal energy into lattice modes, but rather by other processes such as the formation of vibration excitons etc.
Dynamics of Polymer Chains
Authors: Fixman Marshall
Published: January 2005

A general formalism is presented to serve as a basis for the calculation of dynamic properties of chain-polymer solutions. The polymer model which is adopted restricts the applicability of the formalism to dilute or moderately concentrated solutions.
Mass-Spectrometric Study of the Bimolecular Formation of Diatomic Argon Ion
Authors: Becker Philip M. , Lampe F. W.
Published: January 2005

Pulsed mass-spectrometric studies of the bimolecular formation of Ar2+ show that the reaction proceeds via three excited states of argon which have excitation functions that peak at 18, 28, and 65 eV. In kinetic studies, effective radiative lifetimes and specific reaction rates have been determined at these electron energies. The rather large rate constants observed (1.3–2.0×10−9 cm3 molecule−1·sec−1) yield collision diameters in good agreement with those predicted by simple theoretical considerations of the radii of argon atoms in the 3p5 4d and 3p5 5p configurations, such configurations being of the lowest energy compatible with the smallest reported appearance potential of 14.7 eV for Ar2+.
Kinetics of the Reaction H+p-H2=o-H2+H
Authors: Schulz W. R. , Le Roy D. J.
Published: January 2005

The homogeneous gas-phase reaction H+p-H2=o-H2+H has been studied in the temperature range 300° to 444°K. Within this range the results fitted the equation log10k1 = 15.454 − 3.490×103/T+3.836×105/T2 cm3 mole−1 sec−1. The results were interpreted in terms of activated-complex theory with quantum-mechanical tunneling. From the information about the tunneling factors provided by the curvature of the Arrhenius plot it was possible to calculate the imaginary frequency of the asymmetric vibration of the complex corresponding to its coordinate of decomposition on the assumption of a truncated parabolic barrier. The value obtained was 1213i cm−1. For the same model ΔE0° was found to be 9.7 kcal mole−1. The almost exponential dependence of the tunneling factor on 1/T for Eckart barriers made it impossible to interpret the curvature in terms of such a barrier except for considerably larger values of barrier height and/or imaginary frequency than have been found in recent theoretical calculations.
Limits on the Lifetime of Nonequilibrium Fe3+ Ions in Some Ionic Solids from the Mössbauer Effect
Authors: Wertheim G. K. , Guggenheim H. J.
Published: January 2005

The lifetime of higher valence states produced by Auger effect can be obtained from the Mössbauer effect in the case of some favorable isotopes. It is shown that valence states higher than Fe2+ which are produced following the electron capture decay of divalent 57Co in ZnF2 have lifetimes less than 10−8 sec. A similar limit is obtained for the lifetimes of higher charge states of iron produced by divalent cobalt diffused into NaF with the aid of charge-compensating sodium vacancies. Trivalent iron has lifetimes greater than 3×10−8 sec in NaF, if charge compensation is accomplished by oxygen. The lifetime in hydrated ferrous ammonium sulfate is 5×10−8 sec. The short lifetimes even of Fe3+ in some divalent lattices indicate that the lifetimes of higher valences will generally be too short to be observed with the present technique. It also suggests that valence states which do not occur in stable compounds will generally have short lifetimes and be difficult to detect.
Theory of Slow Atomic Collisions. I. H2+
Authors: Thorson Walter R.
Published: January 2005

A theory of zero-order elastic and first-order inelastic scattering for slow atomic collisions in the system H2+ is presented. The method of stationary states and partial wave analysis is used and is the first such treatment which meets the formal requirement of scattering theory that the zero-order eigenfunctions become correct eigenfunctions at R→∞; the ``perturbed-stationary-states'' method, for example, fails to meet this criterion. The method is applicable only to electronic states which are ``tightly bound'' (≳0.25 eV below the ionization limit); no treatment of scattering to ``continuum'' states of the electron is given. The use of partial wave analysis makes possible the elimination of practical difficulties which appear in the time-dependent treatments due to nonorthogonality of the electronic basis functions. The zero-order eigenfunctions may properly be termed ``adiabatic'' solutions, since they are physically the logical extension of the Born—Oppenheimer concept to unbound states, and for many problems zero-order elastic scattering is indeed just potential scattering by the Born—Oppenheimer potential. First-order inelastic scattering cross sections can be computed from electronic transition matrix elements which differ in significant respects from those of the ``perturbed stationary states'' method.
Intermolecular Potential-Energy Functions for Pairs of Simple Polyatomic Molecules
Authors: McKinley M. D. , Reed T. M.
Published: January 2005

Intermolecular potential-energy functions for pairs of simple polyatomic molecules are calculated by assuming that the total interaction is the sum of all the interactions between atom pairs on the two molecules. The interaction parameters for the constituent atoms are evaluated from noble-gas and diatomic-gas data. The calculated potential-energy functions are tested by calculating second virial coefficients and comparing with experimental data. It is generally found that the calculated potential-energy functions are good approximations for the molecules considered.