bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydroxyl Radical Kinetics by Kinetic Spectroscopy. V. Reactions with H2 and CO in the Range 300–500°K
Authors: Greiner N. R.
Published: February 2004

The reactions of OH with H2 and CO were studied by the flash-photolysis–kinetic-spectroscopy technique over the temperature range 300–500°K. At both ends of this range it was verified that the reactions are first order in [OH] and [H2] or [CO]. The Arrhenius parameters and their 95% confidence limits, as determined from least-squares fits of the data, follow: For H2+OH→H+H2O, E = 4020 ± 180 cal/mole and logA (cc/mole·sec) = 12.61 ± 0.10; for CO+OH→CO2+H, E = 230 ± 140 and logA = 11.10 ± 0.07.
Model for Correlated Molecular Rotation
Authors: Casey L. M. , Runnels L. K.
Published: February 2004

We report studies of models designed to emphasize the thermodynamic consequences of coupled molecular rotation in condensed phases. The coupling arises from hard molecular cores of nonspherical shape, here represented by flat coplanar squares in a one-dimensional array. Various forms are considered for the orientation-independent part of the interaction, from none to harmonic to delta function (or lattice model); the first and third are shown to represent the high- and low-temperature limits of the second, treated classically. The lattice model gives rise to a particular sort of first-order phase transition, the significance of which is clarified by the temperature dependence of the properties of the harmonic model.
Investigation of the Hylleraas Method for Determining the Potential-Energy Function from the Phase Shift
Authors: O'Brien T. J. P. , Bernstein R. B.
Published: February 2004

The Hylleraas solution of the quantum mechanical inverse problem of scattering theory is discussed. A practical method for deducing the potential from the phase shift by this method and a variant upon it is described. A simple example (a model potential function) is used to illustrate the procedure. For this case, first-order results are obtained analytically, higher-order results by (extensive) numerical computations. The method converges properly if there are no bound states. However, for the model problem under investigation, the procedure converges to yield a phase-equivalent potential when the potential well contains a bound state.
Investigation of the Magnetic Moments of S2, Se2, Te2, Se6, and Se5 by the Stern–Gerlach Magnetic Deflection Method
Authors: Meschi David J. , Searcy Alan W.
Published: February 2004

An apparatus consisting of a Knudsen effusion cell, collimator, inhomogeneous-field magnet, and quadrupole mass spectrometer has been applied to investigation of the fraction of S2, Se2, Te2, Se6, and Se5 molecules that show a magnetic moment. The expected high concentration of paramagnetic S2 molecules was found, but the concentration of paramagnetic Se2 and Te2 molecules at 1000°K was less than the 10% detection limit. The concentration of paramagnetic Se6 and Se5 at 500°K was unmeasurably low. The results indicate that Se6 and Se5 are not diradicals and that the splittings between the 0g+ ground state and the 1g paramagnetic state of Se2 and Te2 exceed 2000 K. The Se2 data support the conclusion that the dissociation energy of Se2 is 78.63 kcal/mole.
Electron Spin Resonance of Two Radicals Formed in X-Irradiated Cyanoacetylurea, Another Sigma-Electron Radical of the RCOṄH Type
Authors: Lau P. W. , Lin W. C.
Published: February 2004

Two radical species were formed when cyanoacetylurea CNCH2CONHCONH2 crystals were irradiated with x ray. One was a π-electron radical, CNĊHCONHCONH2, and the other a σ-electron radical, CNCH2CONHCOṄH. The latter was found to have similar hyperfine coupling tensors as H2NCOCH2CONH which was formed in x-irradiated malonamide, and the former as CNĊHCOOH which was formed in γ-irradiated cyanoacetic acid.
Translational Energy of Fragments of Ion Decomposition and Totality of States Functions
Authors: Spotz Ellen L. , Seitz William A. , Franklin J. L.
Published: February 2004

Translational energies of the fragments of ionic decompositions have been calculated for sets of harmonic oscillators with the totality of states obtained by three methods. Best agreement with experimental values observed by Haney and Franklin was obtained with a direct count of states. Good agreement was also found using the expression of Vestal, Wahrhaftig, and Johnston and the recent modification of it by Tou and Wahrhaftig. Finally, the function derived by Thiele in terms of the generalized Bernoulli polynominals gave lower energies than the observed values. The activated complex was viewed first as having one vibrational degree of freedom transformed into a translational degree of freedom and then as a “loosened” complex in which three degrees are transformed. The excluded modes were determined by a consideration of the reaction and the effect of varying them was examined. In all methods the agreement was improved with the assumption that three degrees of freedom, rather than one, are transformed to translation in the activated complex.
Velocity and Attenuation of Hypersonic Waves in Liquid Nitrogen
Authors: Pine Alan S.
Published: February 2004

High-resolution thermal Brillouin scattering techniques have been used to measure the velocity and damping of sound in liquid nitrogen in the 3–5 GHz range. The measurements were carried out along the saturated vapor line from the triple point to the normal boiling point. No deviation from previous ultrasonic values of velocity or the classical ν2 attenuation is observed at these frequencies. Thus acoustic dispersion due to the 2 GHz relaxation frequency of the internal molecular vibration is completely negligible.
Observations on ESR Linewidths and Concentration Measurements of Gas-Phase Radicals
Authors: Westenberg A. A. , deHaas N.
Published: February 2004

The factors affecting linewidths of gas-phase atoms and free radicals as observed under various conditions with the usual type of ESR spectrometer are reviewed. The significance of the linewidth in the problem of determining relative concentrations of labile species from their ESR signal heights is emphasized, which is a matter of great importance in chemical kinetic applications. For all species (except S-state atoms) in dilute concentration, the true unsaturated linewidth is simply determined by the total pressure, and several experimental examples of this are given. Relative concentrations of such species at constant pressure may thus be easily monitored by their signal heights. For S-state atoms (ground-state H and N being the most important examples) in a nonparamagnetic diluent, the true linewidth depends on the atom concentration via spin-exchange collisions, so that more caution is necessary in monitoring them. The practical considerations for handling this problem are discussed. The H–H spin-exchange cross section was measured to be 18 Å2, which is shown to be in good agreement with the theoretical value as estimated by the method of Wittke and Dicke. The D–D cross section was found to be the same within experimental error. Other cross sections evaluated from linewidth measurements are (in angstroms squared) σO2–O2 = 65, σO2–Ar = 60, σO2–He = 21, σO–O2 = 37, σCl–Ar− = 32. A significant dependence of σCl–Ar on the MJ state of Cl was observed. The factors affecting the spin–lattice relaxation time t1 are also noted, and it is shown that for H atoms the controlling step is probably diffusion to the walls of the flow tube. Values of t1 in the apparatus employed were about 50 × 10−6, and the difference between this and the much longer value reported in the literature for N atoms is discussed.
Paramagnetic Anisotropy and Two-Dimensional Antiferromagnetism in Copper Formate Tetrahydrate
Authors: Gregson A. K. , Mitra S.
Published: February 2004

The paramagnetic anisotropies of the single crystals of copper formate tetrahydrate have been measured between 300 and about 80°K. The distinct layer structure parallel to the (001) plane make this crystal a good example of a two-dimensional antiferromagnetic lattice. While the average moment is lower than the normal value of 1.9μB, the crystal shows in this temperature range a molecular anisotropy which is typical of normal copper compounds. Although the molecular moment in the plane of the layer is only about 1.6μB compared to an almost normal value of 1.87μB normal to it, the temperature variation of the principal molecular susceptibilities show that both K‖ and K⊥ obey a Curie–Weiss law with almost the same Weiss constant, θ‖ = −160°K and θ⊥ = −170°K. This result is in agreement with the theory of a two-dimensional antiferromagnetic lattice, but disproves the earlier belief that the temperature variation of K‖ and K⊥ should be quite different, in this case K‖ obeying a Curie law and K⊥ obeying a Curie–Weiss law with a large Weiss constant. The temperature variation of K‖ and K⊥ within this temperature range is quantitatively explained using the high temperature series expansion solution for a two-dimensional Heisenberg antiferromagnet.
Minima in Generalized Oscillator Strengths: C2H4
Authors: Krauss M. , Mielczarek S. R.
Published: February 2004

A characteristic of electron impact excitation of low-lying Rydberg states is a minimum in the generalized oscillator strength as a function of K, the momentum transfer. This characteristic is used as a probe of the Rydberg character of four transitions in C2H4. Three, the Ag1 → 1B3u(π → 3s + 3s), 1Ag → 1B3u(π → 3pz − 3pz), and Ag1 → 1B3u(π → 4s) transitions, have long been identified as Rydberg and are found to exhibit the characteristic minimum. A fourth transition Ag1 → 1B1u(π → π*) is normally termed a valence excitation, and a theoretical calculation using Hartree–Fock molecular orbitals had predicted no minimum. For an energy loss of 8.0 eV which is identified with the valence transition a definite minimum is observed. Speculation on the source of this anomaly centers on a type of valence–Rydberg configurational mixing which can occur in many molecules. It is suggested that the presence or absence of minima in generalized oscillator strength curves be used to probe this aspect of the character of the excited state.
Isotopic Volume Shifts in the Inert Gas Solids at 0°K
Authors: Brown J. S.
Published: February 2004

Recent perturbative calculations of isotopic shifts in Ne are extended to include these shifts for the other inert gas solids.
Dielectric Relaxation in Nitroalkanes
Authors: Chandra Suresh , Nath Dina
Published: February 2004

Permittivity and dielectric loss (ε′ and ε″) of four nitroalkanes have been measured at five frequencies at 3, 15, 30, 45, and 60°C. The values of ε′ and ε″ have been used to plot Cole–Cole diagrams. The relaxation time and the distribution parameter have been calculated from these arc plots. It has been observed that the relaxation time increases with the increase in the number of carbon atoms and decreases with increase in temperature. The dielectric relaxation and the viscous flow phenomena have been compared using the theory of chemical rate processes.
Dipolar Coupling and Molecular Vibrations in Crystals. III. Polarizabilities of Molecular Anions and the Internal Field in Some Rhombohedral Crystals
Authors: Frech Roger , Decius J. C.
Published: February 2004

Using the formalism and the dipole coupling sums developed in an earlier paper the equations relating the optical refractive indices to ionic polarizabilities are given for certain classes of rhombohedral crystals. Anion polarizabilities are calculated from measured refractive indices and previously calculated cation polarizabilities for several series of crystals. Finally the validity of the widely used Lorentz–Lorenz internal field in these systems is examined.
Photodissociation of O2 and N2 in the Far Vacuum uv and Production of Excited O and N Atoms
Authors: Beyer K. D. , Welge K. H.
Published: February 2004

Photodissociation of O2 and N2 yielding highly excited O and N atoms has been investigated in the region from 1000 to 450 Å by observing the fluorescence of fragments in the region between 1500 and 1100 Å. Fluorescence intensities were measured as a function of the incident wavelength. The following dissociation processes have been identified: O2 → O(3s3S0) + O(3P), → O(3p3P) + O(3P), → O(3s1D0) + O(3P), N2 → N(3s4P) + N(4S0), → N(3s2P) + N(2D0). The threshold wavelengths of these processes coincide closely with the corresponding dissociation energies. The fluorescence intensities of the 1305- and 1200-Å resonance lines of O and N, respectively, were calibrated and absolute cross sections for the production of O(3s3S0) and N(3s4P) have been determined. Depending on the incident wavelength, cross sections of up to 4 × 10−18 and 5 × 10−19 cm2 are found for the O(3s3S0) and N(3s4P) production, respectively.
Host Cation Effects on the Fluorescence Spectrum of Eu3+ in Oxysulfides
Authors: Sovers O. J. , Yoshioka T.
Published: February 2004

Fluorescence spectra of M2O2S:Eu3+ (M = Lu, Y, Gd, La) are investigated in the 4000–9000-Å region. Nearly complete identification of the crystal components of F0–67, 5D0–3 is made, and the results are interpreted by means of intermediate-coupling and crystal-field splitting calculations. A rise of the barycenters of DJ5, as well as a contraction of the over-all crystal splitting of FJ7 and DJ5 with increasing host cation size, accounts for the blue shift of the fluorescence spectrum in the above series. The results can be qualitatively understood as an approach to the free Eu3+ ion, but quantitative interpretation remains obscure.
Effect of Electrode Materials on the Kinetics of Electron Exchange Reactions
Authors: Vojnović M. V. , ̆Sepa D. B.
Published: February 2004

The electrode reaction Fe(CN)63−/Fe(CN)64− is studied at sodium tungsten bronzes of compositions Na0.50WO3, Na0.70WO3, and Na0.90WO3. The average standard exchange current densities of the order 101·cm mole−1 appear to be slightly dependent on the composition of bronzes. Transfer coefficient is found to be 0.5. On the basis of these results and those available in the literature for several redox reactions at various metals, a theory of heterogeneous electron exchange reactions is discussed. The influence of electrode material on the rate of electrode reaction is shown to depend on the density of states of electrons at the Fermi level of metals. The exchange integral, the other parameter where the influence of material should be contained, appears only slightly dependent either on a particular electrode reaction or on electrode material. Standard exchange current densities for some other redox reactions at platinum are predicted.
Electrostatics of Diffuse Anisotropic Interfaces. II. Effects of Long-Range Diffuseness
Authors: Buff Frank P. , Goel Narendra S.
Published: February 2004

Within the framework of macroscopic continuum theory, we formulate the calculation of the electrostatic potential for a charge in the presence of an anisotropic diffuse interface. We present a systematic method for determining the analytical forms of dielectric profiles for which the Fourier–Bessel components of the electrostatic potential can be obtained analytically. We discuss in detail a smooth exponential profile which manifests long-range diffuseness. On the basis of exact and approximate calculations, the image potential for this model is obtained in the main region of interest for applications.
Nucleation of Supersaturated Vapors in Nozzles. I. H2O and NH3
Authors: Jaeger Harry L. , Willson Ernest J. , Hill Philip G. , Russell Kenneth C.
Published: February 2004

Measurements have been made of the results of homogeneous nucleation of NH3 and H2O vapors expanding in steady flow in a supersonic air nozzle. From the effect of the nucleation and growth of liquid from the vapor phase on the nozzle pressure distribution, the point of incidence of condensation is readily detected. Experimental results have been compared with the predictions of the classical nucleation rate equation and with the quantum-statistical treatment of Lothe and Pound. While H2O nucleation rates are in agreement with the classical equation, NH3 nucleation follows the very much higher rates (12 to 18 orders of magnitude) of the Lothe–Pound equation. A mass accommodation coefficient of 0.01 < ξ < 0.1 for H2O was inferred from the experimental data.
Alternating-Current-Field Induced Cholesteric–Nematic Phase Transitions
Authors: Baessler H. , Labes M. M.
Published: February 2004

In order to determine whether interaction between the permanent or the induced molecular dipole moments of a cholesteric liquid crystal and an applied electric field is responsible for inducing a transition to a nematic phase, ac-field measurements were performed. In a mixture of cholesteryl chloride and cholesteryl myristate, phase transitions can be induced by an ac field of a frequency up to a threshold value fpt; fpt is approximately equal to the relaxation frequency for rotation of cholesteryl chloride molecules around a short molecular axis which has recently been determined by dielectric measurements. A relation between the rms field and fpt is derived and experimentally verified. The absence of ferroelectric ordering in the induced and aligned nematic phase is demonstrated.
Phase Diagram and pV Isotherms of Argon
Authors: Henderson M. , Wertheim M. S.
Published: February 2004

A simple model for classical fluids has been applied to argon. The model contains only the excess entropy of hard spheres and the second virial coefficient for the actual intermolecular potential function. Three forms of the potential were used in the computation. Thermodynamic functions in one-phase regions and the location of the gas–liquid transition were calculated. Insensitivity to the potential shape was found over a large region in density and temperature. A simple extension of the model was used to estimate the location of the fluid–solid transition. The agreement with experiment is very good for the phase diagram in the pressure–temperature plane and moderate for the coexisting densities. Calculated and experimental pressures, entropies, and internal energies are compared in the fluid region.
Discrete Structure in the Spectrum of Sodium Iodide Vapor
Authors: Berg Robert A. , Skewes G. W.
Published: February 2004

The fluctuation bands of NaI are shown to be intensity alternations in a resolved band system. The fluctuations, spaced by about 300 cm−1, are associated primarily with the ground-state vibrational spacing; the band structure spacing of 36 cm−1 is probably to be associated with the vibrational frequency of the excited state. The discrete line spectrum occurs without any break from 2945 to 5400 Å. From the low-wavelength limit a dissociation energy for the ground state, D0 = (26 343 ± 232) cm−1, is derived.
Time-Dependent Effects Associated with the 50°K Resistivity Anomaly in the Pd–H and Pd–D Systems
Authors: Ho N. S. , Manchester F. D.
Published: February 2004

The characteristics of the time dependence of the electrical resistivity of Pd–H and Pd–D alloys in the vicinity of the 50°K resistivity anomaly are presented. It is suggested that there is a connection between the time dependence of the resistivity and the exothermic processes observed by others in these alloys at low temperatures, in that both effects are associated with the low-temperature annealing out of lattice damage produced by the transition at 50°K.
Photoionization with Atomic Beams. II. Cadmium Atoms between 8.99 and 83 eV and Zinc Atoms between 27.35 and 65 eV
Authors: Cairns R. B. , Harrison Halstead , Schoen Richard I.
Published: February 2004

The energy dependences of the photoionization cross sections to produce Cd+, Cd2+, and Zn2+ have been measured with modulated atomic beams and pulsed, dispersed vacuum-ultraviolet radiation. Results are presented for cadmium ions at energies between 8.99 and 83 eV and for zinc ions at energies between 27.35 and 65 eV.
Effect of Solvent on Excimer Fluorescence Yields
Authors: Horrocks Donald L.
Published: February 2004

It was observed that certain solvents enhanced the relative amount of fluorescence from the excimer of an excited solute molecule. The ratio of intensity of excimer fluorescence ID to intensity of monomer fluorescence IM for solutions of equal concentration of 2,5-diphenyl-1,3-oxazole, PPO was approximately four times greater in cyclohexane and ethanol than in the aromatic solvents benzene, toluene, p-xylene, and 1,2,4-trimethylbenzene. Also at room temperature 24°C excimer fluorescence of 2-(4-isopropylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole (i-p-PBD) was observed only from concentrated solutions in cyclohexane. The effect of temperature on the intensity of excimer fluorescence indicated the role of the solvent in excimer formation and dissociation.
Carlson's Sum over Points and Local Energy
Authors: Harriss Donald K. , Carlson Charles M.
Published: February 2004

An alternate local-energy derivation is given of Carlson's linear nonsymmetric eigenvalue equations. Relationships between his procedure and other numerical approaches are shown and in one case illustrated with calculations on the hydrogen molecule–ion.
Molecular-Beam Kinetics: Reactions of Na with CH3I, Br2, and ICl
Authors: Birely J. H. , Entemann E. A. , Herm Ronald R. , Wilson K. R.
Published: February 2004

Crossed-beam studies have been made of the reactions of Na with CH3I, Br2, and ICl. An approximate kinematic transformation of the measured laboratory angular distributions to the center-of-mass coordinate system yields distributions of the recoil angle for elastic and reactive scattering and estimates of the product recoil energies and total reaction cross sections, Qr. The results are qualitatively similar to those found in previous beam studies of the reactions of K, Rb, and Cs and are consistent with the early Polanyi flame experiments. As compared with the analogous K systems, the Na reactions exhibit the following properties: (1) smaller values of Qr (approximately 5, 90, and 100 Å2 for CH3I, ICl, and Br2, respectively); (2) most of the reaction exothermicity still appears as product excitation for Br2 and ICl, whereas a considerably larger fraction appears as recoil energy for CH3I; (3) the wide-angle nonreactive scattering falls off less rapidly; and (4) the Br2 and ICl stripping reactions produce more backward scattered product. These features are consistent with the electron-jump model for alkali atom reactions.
Semiclassical Transition Probabilities for Collinear Collisions between an Atom and a Morse Oscillator
Authors: Locker David J. , Endres Paul F.
Published: February 2004

The N-state semiclassical approach is used in the calculation of vibrational transition probabilities for atom–Morse-oscillator collinear collisions. Exact semiclassical calculations for several initial classical phases are compared with rigid-body results. The transition probabilities are found to be strongly dependent upon the initial phase. Two procedures are used for matching the Morse potential to a quadratic potential. The resulting transition probabilities indicate that the potentials should be matched on their repulsive sides rather than at their minima.
Transition Probabilities and Collision Broadening Cross Section of the N2 Lyman–Birge–Hopfield System
Authors: Shemansky D. E.
Published: February 2004

Bands of the N2 Lyman–Birge–Hopfield system (a 1Πg − X 1Σg+) have been observed in absorption in path lengths ranging from 5.6 × 10−3 to 0.5 m·atm. Comparison of theoretical and measured curves of growth and band profiles have allowed the computation of band transition probabilities, lifetimes of the a 1Πg state [τ(0) = 1.4 × 10−4sec], relative probabilities of electric quadrupole and magnetic dipole components, and a measure of the collision self-broadening cross section (σ = 1.6 × 10−14cm2).
Spectroscopy of Na2 Using Laser-Induced Fluorescence
Authors: Demtröder W. , McClintock M. , Zare R. N.
Published: February 2004

The argon-ion laser lines at 4658, 4727, 4765, 4880, 4965, 5017, and 5145 Å are each found to excite one or more resonance fluorescence series of the Na2 (X 1Σg+ − B 1Πu) blue-green band system. Altogether, 19 different fluorescence progressions have been identified and assigned υ, J quantum numbers. The absolute wavenumbers of many of these emission lines have been measured interferometrically using a Fabry–Perot etalon crossed with a Bass–Kessler type spectrograph. A revised set of spectroscopic constants has been determined for both the upper and lower states which reproduce the observed term energies to better than 0.1 cm−1 on the average. Using these improved spectroscopic data, potential curves have been constructed for the B and X states of Na2 by the Rydberg–Klein–Rees method. These potential curves are used in turn to compute Franck–Condon factors for the Na2 B–X band system.
Impurity Pairs in Mixed Molecular Crystals
Authors: Sommer Bat-Sheva , Jortner Joshua
Published: February 2004

In this paper we consider the energy levels and the polarization ratios of an impurity pair in mixed molecular crystals using the one-particle Green's function method. The off-diagonal matrix elements of the weighted density of states function for the first singlet exciton band in crystalline benzene have been obtained and applied for the splitting of the energy levels of an isotopic impurity pair. An extension of Rashba's formula for the polarization ratio of the impurity pair has been derived.
Energy Transfer in Classical Br2–Ar Collisions
Authors: Razner Ronald
Published: February 2004

Computer calculations of three-dimensional classical trajectories for Br2–Ar collisions indicate that vibration-rotation coupling in the Br2 molecule can play a significant role in energy transfer. For Br2 molecules with specified initial internal energies embedded in a heat bath of Ar at 1800°K, probability distributions for internal energy changes and angular momentum transfers were determined. These indicate the possibility of attaining classical Br2 angular momenta large enough so that “vibrational energy” and “rotational energy” for the free molecule are not separable, and that collisions with large angular momentum changes may be responsible for a large part of the over-all Br2–Ar energy transfer. Amplitudes of vibration–rotation coupling are presented for Br2 energies of 0.1 De, 0.5 De, and 0.9 De, through a range of angular momentum found to be pertinent to the problem. Possible implications of the results for Br2–Ar energy transfer in shock-tube studies are discussed.
Laser-Induced Photolysis of Iodoform
Authors: Speiser S. , Kimel S.
Published: February 2004

Iodoform dissolved in various solvents was irradiated with a Q-switched ruby laser. The two-photon photolysis was studied by measuring the concentration of the liberated iodine. Different two-photon absorption cross sections were obtained for iodoform in different solvents. The major solvent effect was found to be due to the self-focusing properties of the medium. After appropriate corrections for this effect, good agreement was obtained between measured and calculated cross sections. It was also found that the self-focusing length of a liquid could be determined “chemically” from the degree of photolysis.
Comparison of the Kingston and Morse-6 Hybrid Potentials Based on Second Virial Coefficients
Authors: Zakheim David S. , Konowalow Daniel D.
Published: February 2004

We show that the Morse-6 hybrid potential, which incorporates the accurate theoretical C6 coefficient of the dispersion interaction, is substantially superior to Kingston's hybrid potential which is based on the Lennard-Jones 12–6 model. We reconfirm Kingston's result that the theoretically calculated C6's are not inconsistent with experimental second virial coefficient data for Ar–Ar, Kr–Kr, and Xe–Xe interactions; we also treat Ar–Kr interactions.
Isotopic Thermal Diffusion Factor for CO2
Authors: Mathur B. P. , Watson W. W.
Published: February 2004

In continuation of our study of thermal diffusion in common, nonpolar, polyatomic gases, we report the values of the isotopic thermal diffusion factor α0 as a function of temperature for carbon dioxide. We have used a 60% 13C16O2–40% 12C16O2 mixture in a 10-tube metal trennschaukel over an average temperature range of 220–500°K. The experimental α0 values can be represented in this temperature range by the equation, obtained by least squares: α0 = −0.422 + 0.00155T. In this linear variation, α0 is −0.075 ± 0.070 at 239.5°K, and 0.343 ± 0.039 at 502.4°K, the highest average temperature of our measurements. The negative values of α0 below about 250°K confirm our earlier observations made in the case of isotopic N2 and O2 gases. As expected, the agreement between Chapman–Enskog theory and these experiments is poor. Also it has not been possible to correlate the present results with the other transport properties of this gas. Besides the inadequacy of the usual potential models, the plausible reasons for this disagreement are: (a) neglect of the inelastic collisions and internal degrees of freedom in the theory, and (b) incipient dimerization at the lowest temperature.
Double Configuration Self-Consistent Field Study of the Πu1, 3Πu, 1Πg and Πg3 States of H2
Authors: Zemke Warren T. , Lykos Peter G. , Wahl Arnold C.
Published: February 2004

Complete potential energy curves for the four lowest-lying Π states of the hydrogen molecule are calculated using an hierarchy of one- and two-configuration model wavefunctions: the Hartree–Fock model, the configuration interaction model, and the optimal double configuration model (a double configuration SCF model). Comparison and evaluation of the three models are given as a function of internuclear separation of the nuclei for the Πu1 state. An extended basis set of 10 Slater-type orbitals on each nucleus is scaled optimally for the Πu1 state; the spectroscopic constants for this state are in excellent agreement with experiment. The basis set used for the Πu1 state is employed in determining the potential energy curves for the Πu3, 1Πg, and Πg3 states; the Πu3 state shows good agreement with experiment, and the essential features for the Πg states are characterized properly.
Ultrasonic and Light-Scattering Studies of Benzene
Authors: Nichols W. H. , Kunsitis-Swyt C. R. , Singal S. P.
Published: February 2004

A detailed examination of ordinary Brillouin light scattering in liquid benzene at 25°C reveals that no single total relaxation of all the vibrational modes can make the ultrasonic absorption data consistent with the light-scattering data. Consistency can be achieved, however, by assigning a viscosity η1 = 0.845P and a relaxation time >τ1″ = 2.98 × 10−10sec(f1″ = 533 MHz) to all the vibrational modes except the lowest; and η2 = 0.07P with τ2″ = 3.6 × 10−11sec(f2″ = 4400 MHz) to the degenerate lowest mode. The volume viscosity ηυ is equated to 43ηs and ηυ + 43ηs is made a relaxing viscosity η3 with τ3″ = 10−12sec.
NMR of Absorbed Systems. I. A Systematic Method of Analyzing NMR Relaxation-Time Data for a Continuous Distribution of Nuclear Correlation Times
Authors: Lynch L. J. , Marsden K. H. , George E. P.
Published: February 2004

Methods are outlined for the systematic analysis of NMR relaxation-time data in terms of the continuous distribution of nuclear-correlation-time theories of Odajima and Resing. It is shown how unique values of the two significant parameters of these theories—the width parameter β and the apparent rigid-lattice second-moment parameter σ02—can be obtained if a minimum occurs in the spin–lattice relaxation-time data. While these parameters are only defined for the temperature where the minimum in the spin–lattice relaxation time occurs, it is possible, by seeking a form of the thermal activation law that enables reproduction of the temperature variations of the experimental data, to define further parameters related to the system—i.e., the thermal activation coefficients. The Resing theory, which takes into account an apparent phase transition effect that can occur in the spin–spin relaxation-time data, is successfully applied by the method described, to NMR relaxation-time data of water absorbed on both hair keratin and charcoal. The Eyring form of the thermal activation law is found to be appropriate in both instances.
NMR of Absorbed Systems. II. A NMR Study of Keratin Hydration
Authors: Lynch L. J. , Marsden K. H.
Published: February 2004

The proton magnetic resonance spin–spin and spin–lattice relaxation times of water absorbed by wool keratin at different levels of water absorption have been measured as a function of the temperature in the range −65 to 50°C. Results are consistent with the absorbed water being described in terms of a continuous distribution of nuclear correlation times. An analysis of this data according to the Odajima–Resing theory for such a system resulted in physically reasonable values being obtained for the analytical parameters involved. It is proposed that the absorbed water exists as small clusters of no more than a few molecules, even near saturation absorption. By assuming an Eyring thermal activation law to govern the temperature dependence of the median nuclear correlation time, it was possible to closely fit the results over the experimental temperature range by this theory at all levels of absorption for which suitable data were obtained. The general application of this activation law enables the absorbed water at a given level of absorption to be defined in terms of a further two parameters−the apparent activation enthalpy and entropy. The analytical results suggest that as the level of absorption is increased, the width of the distribution of the nuclear correlation times of the absorbed water is decreased, but that there is little shift in the median correlation time of the distribution. By comparison with corresponding parameters obtained for ice, it is estimated that the average molecular reorientation time of the absorbed water is about 1000 times shorter than for water molecules in ice at 270°K.
Permeability for the Reaction H + H2 = H2 + H Treated as a Linear Encounter Using Variational Techniques
Authors: Mortensen Earl M. , Gucwa Lois D.
Published: February 2004

Variational calculations for determining the permeability of the Sato potential-energy surface as described by Weston have been made for the reaction H + H2 = H2 + H treated as a linear encounter. The results compare favorably with the corresponding calculations of Mortensen and Pitzer. The variational functions describing the asymptotic regions have a form after that of Kohn.
QM Tunneling as a Viscoelastic Relaxation Mechanism
Authors: Eisenberg A. , Reich S.
Published: February 2004

It is proposed that quantum-mechanical tunneling may be the viscoelastic relaxation mechanism for methyl group containing polymers at low temperatures. This proposal is based on the agreement of the tanδ peaks at given frequencies with the tunneling frequencies for methyl groups of reasonable barrier heights at corresponding temperatures. The proposed mechanism, in conjunction with published frequency–barrier-height correlations, allows the estimation of the barrier heights for a wide range of methyl groups from the knowledge of a single tanδ maximum. The barriers are in general agreement with those obtained by NMR techniques for similar materials.
Field Ionization from Helium Films
Authors: Halpern Bret , Gomer Robert
Published: February 2004

Field ionization from He films has been investigated from 4.2 to 1.6°K on clean and oxygen covered W emitters. At low fields (1.8–2.2 V/Å) electron tunneling from He controls current generation; reasonable values of the He ionization potential are obtained by fitting the i–F data to WKB tunneling or simple perturbation-theory models. At higher fields current becomes supply limited, and it is concluded that the latter occurs by diffusion of He from the shank over distances whose lower limits can be estimated to be ∼10−3 cm. The variation of supply-limited current with pressure is interpreted in terms of such a diffusion model. It is concluded that adsorption of He is stronger on oxygen covered than on clean W.
Vibrational Transition Probabilities for the Morse Oscillator
Authors: Endres Paul F.
Published: February 2004

The method of Shuler and Zwanzig has been used to calculate the vibrational transition probabilities for a Morse oscillator suffering an impulsive, colinear collision with an atom. Results are presented for the system H2 colliding with D.
On the Approximate Treatment of Exchange Symmetry in Second-Order Interaction Energies
Authors: Sanders William A.
Published: February 2004

The second-order energy expression from Hirschfelder–Silbey perturbation theory is rewritten in a form which facilitates a comparison with the conventional Rayleigh–Schrödinger theory. It is shown that the approximate procedure used by McQuarrie and Hirschfelder to evaluate the second-order energy for the 1sσg and 2pσu states of H2+ is equivalent to approximating the first-order Rayleigh–Schrödinger function by a symmetry-projected combination of unsymmetric polarization functions. The addition of a correction term to the values calculated by McQuarrie and Hirschfelder leads to substantial improvement of their results.
Pulse Radiolysis Study of the Formation of Triplet Excited States of Naphthalene, Anthracene, and Biphenyl in Cyclohexane Vapor
Authors: Johnson G. R. A. , Sauer M. C.
Published: February 2004

The first triplet excited state of naphthalene is produced in significant amounts when cyclohexane–naphthalene mixtures are pulse irradiated in the gas phase (120°C). The yield is independent of naphthalene concentration from 0.15 mole % up to at least 3.5 mole %, and can be decreased by about 95% by SF6, CCl4, C6H5CH2Cl, CH3Br, NH3, and H2O. The scavengeable part of the triplet yield is attributed to neutralization of the ion C10H8+ (which is formed by charge transfer from cyclohexane positive ion) by C10H8− which is itself formed by electron capture. The scavengers compete with naphthalene for positive ions or for electrons. The rate-constant ratios at 120°C for the reaction of the positive ions from cyclohexane with naphthalene and NH3, K(RH+ + C10H8) / k(RH+ + NH3) = 0.8 ± 0.2, and for electron capture by naphthalene and benzyl chloride, k(e− + C10H8) / k(e− + BzCl) = 3.0 ± 0.5, are obtained from competition studies. The triplet state of biphenyl observed in cyclohexane–biphenyl (0.2 mole %) is completely eliminated by SF6 (1 mole %). In cyclohexane–naphthalene–anthracene mixtures, energy transfer from triplet naphthalene to anthracene is observed.
Orbital Approximation to Spatial Eigenfunctions of the Many-Electron Hamiltonian
Authors: Hameed Sultan , Hui Shirley Seung , Musher Jeremy I. , Schulman Jerome M.
Published: February 2004

A new procedure is developed for calculating the best wavefunction for an N-electron atom in terms of N one-electron orbitals which are eigenfunctions of l2, lz and sz. This is a special case of a method for calculating the best wavefunction in terms of N orbitals unrestricted in angular momentum but restricted in spin component and is thus a partial generalization of Löwdin's EHF method. We calculate approximate spatial eigenfunctions of H using the function Φ[α,λ] = Dλλ[α] ∑ i = 1k δiPiφ, where φ is a product of N spatial orbitals and where the Pi are the k permutations out of which k linearly independent projections onto the Young tableau [α,λ] can be obtained. The method gives an improvement to each of Goddard's GI solutions in such a way that they all give the same energy when fully minimized, while only involving k−1 additional parameters. For Li atom there is only one additional parameter and calculations are performed using Goddard's GI and GF orbitals, obtaining small improvements in the energy. An energy of −7.4477076 a.u. is obtained.
Vaporization of Antimony and Tellurium in the Vicinity of the Critical Point
Authors: Ban Vladimir S. , Knox Bruce E.
Published: February 2004

Laser-produced vapor of antimony and tellurium was analyzed with a time-of-flight mass spectrometer. Several new vapor species have been observed: Te5 and Sb3 are the most abundant species in the vapor of the respective metals. The conditions of laser–solid interaction are discussed; it is shown that critical temperatures and pressures for Sb and Te can be attained when a sufficiently strong laser interacts with these metals.
Electronic States of Molecules. II. Calculations of the Potential-Energy Curve and Molecular Constants of LiH(X 1Σ+)
Authors: Sahni R. C. , Sawhney B. C. , Hanley M. J.
Published: February 2004

The self-consistent-field molecular-orbital method in the LCAO (linear combination of atomic orbitals) approximation is applied to the ground state of LiH at a number of internuclear distances (R) for the calculation of the potential energy (PE) curve. In this calculation both the LCAO coefficients and the oribital exponents of 1s, 2s, and 2p AO's of Li and H atoms are optimized. The computed wavefunctions are further subjected to a configuration-interaction treatment using 41 configurations at each R to obtain a PE curve. The PE curves, computed with and without configuration-interaction treatment, have been used in the solution of the radial Schrödinger equation to compute the molecular constants ωe, ωexe, Be, αe, Re, and De. The dipole moment computed at Re shows Li+H– polarity. The computed results are compared with the experimental data.
Born–Green Pair Potentials for Liquid Lead
Authors: Gehlen P. C. , Enderby J. E.
Published: February 2004

The k-space form of the Born–Green (BG) equation has been investigated numerically. In particular, the equation has been used to derive the effective interatomic potential φBG from the measured structure factor S(k) for liquid Pb. These potentials are compared with those derived from another theory of liquids, namely, the Percus–Yevick theory (PY). It is found that φBG (like φPY) is very sensitive to the low-angle form of S(k); however, if the same input data are used for both theories, the resulting interatomic potentials are remarkably similar and are not like those derived from the pseudopotential theory of the metallic state.
Knudsen Flow and Chemical Reaction in a Porous Catalyst
Authors: Strieder William
Published: February 2004

Chambré has shown that the diffusion and reaction in a catalyst whose relevant dimensions are much smaller than the molecular mean free path are determined by the Clausing–DeMarcus integral equation for internal free-molecule flow. A rigorous upper bound on the reaction rate for the irreversible reaction A → B occurring on the internal surfaces of such a catalyst is formulated from a variational inequality due to Kourganoff and DeMarcus. The bounds are evaluated for two pore models, a bed of randomly over-lapping solid spheres and a right circular cylinder.
Uranium Diboride: Preparation, Enthalpy of Formation at 298.15°K, Heat Capacity from 1° to 350°K, and Some Derived Thermodynamic Properties
Authors: Flotow H. E. , Osborne D. W. , O'Hare P. A. G. , Settle J. L. , Mrazek F. C. , Hubbard W. N.
Published: February 2004

A sample of uranium diboride was prepared and characterized as UB1.979±0.006 with 0.06 ± 0.03 wt % of identified impurities. The standard enthalpy of combustion in fluorine was determined to be − 1021.2 ± 1.1 kcal mole−1. The heat capacity was measured from 0.84° to 350°K. At 298.15°K the heat capacity CP°, entropy S°, and enthalpy increment H° − H°0 are 13.23 ± 0.03 cal K−1·mole−1, 13.17 ± 0.03 cal °K−1·mole−, and 2108 ± 4 cal mole−1, respectively. The following values were obtained for the standard enthalpy, entropy, and Gibbs energy of formation of UB2 at 298.15°K: ΔHf° = − 39.3 ± 4.0 kcal mole−1, ΔSf° = − 1.54 ± 0.05 cal °K−1·mole−, and ΔGf° = − 38.8 ± 4.0 kcal mole−1. These agree within experimental error with values calculated from high-temperature effusion measurements. The heat-capacity results below 4.2°K follow the equation CP = (9.40 ± 0.01)T + (3.18 ± 0.14) × 10−2T3mJ °K−1·mole−1. The relatively high value for the coefficient of the linear term indicates that uranium diboride is a good electrical conductor. There seems to be an anomaly in the heat capacity between 40° and 100°K, which may be due to a two-level Schottky anomaly with the upper level having a degeneracy twice that of the lower level and a separation of the levels equal to 175° ± 5°K or 122 ± 4 cm−1.
Mössbauer Effect in CsI3 and Tri-iodide Complexes of Benzamide and Amylose
Authors: Ehrlich Benjamin S. , Kaplan Morton
Published: February 2004

Mössbauer resonance experiments have been carried out at 4.2°K on CsI3 and the tri-iodide complexes of benzamide and amylose. The data unambiguously demonstrate the existence of inequivalent iodine atoms in the tri-iodide ions of each species. For all three compounds, the quadrupole couplings of the central iodines are similar and indicate a small positive charge on the atom. The terminal iodine atoms are negatively charged, and in CsI3 are significantly different from those in the benzamide and amylose complexes. The close relationship between the Mössbauer spectra of benzamide–HI3 and amylose–I3 supports a similar configuration of the tri-iodide ions in these helical complexes, as predicted by a previous model of the blue starch–iodine complex.
Quantum Transition Probabilities for Diatomic–Diatomic Molecule Collisions
Authors: Grimaldi John J. , Endres Paul F. , Wilson David J.
Published: February 2004

The method of Shuler and Zwanzig is used to calculate quantum transition probabilities between vibration levels of colliding diatomic molecules. The molecules are assumed to have harmonic bond potentials, the intermolecular interaction is taken to be impulsive, and only collinear configurations are investigated. Vibration–vibration transfer is found to be a quite significant mode of energy transfer, and it is apparently not sensitive to the degree of close matching of the vibration frequencies of the colliding molecules. It is suspected that this insensitivity may be due to the impulsive collision model used.
Vibrational Dependence of the Magnetic Quenching in Iodine
Authors: Degenkolb E. O. , Steinfeld J. I. , Wasserman E. , Klemperer W.
Published: February 2004

The magnetic quenching (field-induced predissociation) of electronically excited I2 vapor has been measured as a function of excitation wavelength and iodine vapor pressure at fields up to 70 kG. Collision-induced self-quenching cross sections and magnetic predissociation efficiencies are quantitatively determined. From the latter data, a portion of the repulsive (0u−) potential-energy curve has been determined in the range 0.5–1.0 eV.
NMR Determination of Deuterium Quadrupole Coupling Constants in Nematic Solutions
Authors: Caspary William J. , Millett Francis , Reichbach Moshe , Dailey Benjamin P.
Published: February 2004

The analysis of the NMR spectra of suitable nematic liquid crystal solutions appears to offer a convenient and desirable method for the determination of small nuclear quadrupole coupling constants for molecules in the liquid state. Nuclear quadrupole coupling constants have been determined for deuterium in the CD3 groups of methyl iodide, methyl bromide, and acetonitrile and for deuterium in fully deuterated benzene. Values of e2qQ / h measured along the molecular symmetry axis were found to be 66.9 ± 1.2 kHz for CD3I, 63.0 ± 1.0 for CD3Br, and 54.5 ± 1.5 for CD3CN. If the assumption is made that the C–D bond has rough axial symmetry then values of e2qQ / h along the bond axis are found to be 180 ± 5 kHz for CD3I, 171 ± 4 for CD3Br, and 165 ± 5 for CD3CN. e2qQ / h along the bond axis was found to have a value of 194 ± 4 for C6D6.
Optical Transitions in 13CC5H6–C6H6 Mixed Crystals in the Region of the Factor-Group Components of Crystalline Benzene
Authors: Hanson David M.
Published: February 2004

High-resolution spectra at 4.2°K show that the shallow impurity 13CC5H6 shifts the C6H6 factor-group components by 2 cm−1 and increases the linewidth by 5 cm−1 in going from 6% to 50% 13CC5H6. The effect is explained qualitatively by an extension of the Frenkel exciton theory to the mixed-crystal system. Although transitions to virtual bound exciton states have been predicted, none was observed.