bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics for Free-Radical Conversion Processes in Irradiated d,l-Valine
Authors: Horan Paul Karl , Henriksen Thormod , Snipes Wallace
Published: February 2004

The kinetics for two free-radical conversions in irradiated d,l-valine has been studied by use of electron spin resonance (ESR) spectroscopy. In d,l-valine three different radicals are observed. At 77°K only one of these radicals R(1) is formed, which upon subsequent warming converts into the intermediate radical R(2) with an efficiency of approximately unity. The reaction, studied in the temperature range 110–125°K, was found to be first order with an activation energy of 7.6 ± 0.2 kcal/mole. Upon further warming, a third radical R(3) is formed. This formation consists of two separate processes, each proceeding by first-order kinetics. The activation energies, measured in the temperature range 200–260°K, are 6.6 ± 0.3 kcal/mole and 8.3 ± 0.5 kcal/mole, with the smaller activation energy process occurring at slightly lower temperatures. It was found that the concentration of R(3), as observed after warming to 300°K, was significantly greater than the initial concentration of R(1). This increase in total radical concentration is associated with the production of R(3) by the process having an activation energy of 6.6 kcal/mole. Possible mechanisms for the conversions are discussed in light of the known structures of R(2) and R(3).
Evolution of Reduced Distribution Functions. III. General Truncation and Solution of the Linearized Classical BBGYK Hierarchy
Authors: Mortimer Robert G.
Published: February 2004

A linearized version of the nonequilibrium BBGYK hierarchy applicable to simple fluid systems near equilibrium is derived. A sequence of successive extended dynamical superposition approximations is defined to truncate the hierarchy at any arbitrary level. A formal solution, applicable either to the truncated or the complete hierarchy, is obtained by iteration of the Laplace transformed hierarchy followed by inversion of the transform. For the lowest truncation, which produces a single kinetic equation for the one-body reduced distribution function, the Fourier–Laplace transform of the solution is summed to a closed form.
Raman Spectra and the Phonon Dispersion of Polyglycine
Authors: Small Enoch W. , Fanconi Bruno , Peticolas Warner L.
Published: February 2004

The Raman spectra of the two crystalline modifications of polyglycine, I and II, and of N-deuterated polyglycine II have been recorded. The results of a normal-coordinate analysis of polyglycine II and N-deuterated polyglycine II are presented along with the phonon dispersion curves of polyglycine II. Assignments are made on a number of bands not observed in the infrared. Some previous band assignments are found to be inconsistent with the Raman data.
Far-Infrared Spectrum of the Hydrogen Bond in Acetic Acid Dimers
Authors: Witkowski Andrzej
Published: February 2004

An interpretation is proposed and formulated quantitatively for the explanation of the doublet structure in the far-infrared spectrum of acetic acid dimers. The observed splitting is related to the interaction of the degenerate hydrogen bond vibrations in the dimer. Transition to the second component is allowed by the coupling with the OH stretching vibrations. Observed changes introduced in the spectrum by deuteration in the hydrogen bond confirm the proposed interpretation.
Electron Attachment in the Field of the Ground and Excited Electronic States of the Azulene Molecule
Authors: Chaney E. L. , Christophorou L. G. , Collins P. M. , Carter J. G.
Published: February 2004

Azulene attaches thermal and near-thermal energy electrons forming a long-lived parent negative ion in the field of the ground state with a mean autoionization lifetime of 7 ± 1.5 μsec and a mean thermal attachment cross section of 3.5 × 10−15 cm2. The cross section for the thermal process is sharp. Evidence is presented also for electron attachment in the field of a low-lying excited electronic state (possibly the lowest π-triplet state) of azulene in addition to the thermal (∼0.0-eV) process. Using the present values of the thermal attachment rate and lifetime, the electron affinity of azulene in the ground state is estimated to be ≥ 0.46eV.
Methyl Libration in Propane Measured with Neutron Inelastic Scattering
Authors: Grant David M. , Pugmire Ronald J. , Livingston Robert C. , Strong Kenneth A. , McMurry Henry L. , Brugger Robert M.
Published: February 2004

The A2 and B2 torsional vibrational frequencies in propane gas have been directly measured at 217 ± 8 and 265 ± 8 cm−1, respectively, with inelastically scattered neutrons using the “small κ” method of neutron molecular spectroscopy. The theoretical basis of the scattering experiment is discussed, and factors affecting resolution and intensity are enumerated. Not subject to the same selection rules as optical spectroscopy, neutron molecular spectroscopy is capable of observing vibrational transitions which are otherwise forbidden by molecular symmetry. The vibrational frequencies are interpreted by numerically solving the two-dimensional wave equation giving librational motion with a two-dimensional Fourier expansion. In this approach, the potential energy is conveniently expanded also in Fourier form and we obtain a V3 = 3680 ± 190 cal/mole for individual methyl-group librations and a V33 or V6 = − 280 ± 130 cal/mole term which couples the two methyl tops. Evaluation of additional Fourier constants in the potential-energy expansion must await additional spectroscopic data concerning higher vibrational levels. Intermolecular perturbations of the librational frequencies were observed in both liquid and solid propane. These are sufficiently small, however, that one can conclude, to a first approximation, that the librational motions are not greatly effected in condensed states of propane.
1 / Z
Perturbation Expansion for the Natural Orbitals of Two-Electron Atoms
Authors: Wang P. S. C.
Published: February 2004

A perturbation expansion of the natural orbitals and occupation numbers for two-electron atoms in inverse powers of the nuclear charge has been obtained from the wavefunction of Hylleraas. To second order in 1 / Z, the perturbation expansion gives the following principal occupation numbers: 0.99353 for He, 0.99712 for Li+, 0.99837 for Be++, 0.99959 for O6+; as compared to the results of Davidson for He (0.99200), and those of Marcias for Li+ (0.9967), Be++ (0.9982) and O6+ (0.9996), and also those of Kutzelnigg: 0.99303 for He, 0.99707 for Li+, 0.99838 for Be++, and 0.99962 for O6+.
Potential-Energy Curves for the He2 Molecule
Authors: Ginter Marshall L. , Battino Rubin
Published: February 2004

Potential-energy curves for the stable Rydberg states of He2, constructed using RKR procedures, are presented and discussed. The presentation is essentially complete for all states lying below approximately 0.8 eV of N = 0, υ = 0 of X 2Σu+ (He2+), while the relative positions of the molecular and separated-atom term manifolds are probably within 0.03–0.04 eV. Whenever possible, the RKR results are compared with theoretically computed potential energies.
Perturbation Treatment of the Equation of State of Simple Mixtures
Authors: Weres O. , Rice Stuart A.
Published: February 2004

In this paper a previously presented perturbation method for generating the equation of state of fluids is extended to mixtures. The basis is the recently obtained solution of the Percus–Yevick equation for mixtures of hard spheres. To this a correction term in T−1 is added and the second and third virial coefficient contributions are made exact by the addition of further terms. The results for pure substances are re-examined. A complete test of the method was precluded by the scarcity of experimental data, but the method seems as applicable to mixtures as to pure substances in these cases that appropriate potential functions are available.
Electron Scattering by H2 with and without Vibrational Excitation. III. Experimental and Theoretical Study of Inelastic Scattering
Authors: Trajmar S. , Truhlar D. G. , Rice J. K. , Kuppermann A.
Published: February 2004

The ratios of the differential cross sections (DCS's) for excitation of the first, second, and third vibrational states of H2 in its ground electronic state to the elastic DCS have been measured as a function of scattering angle in the 10°–80° range and impact energy in the 7–81.6-eV range. From these ratios the DCS's corresponding to transitions from the ground to the first two vibrationally excited levels (fundamental and first overtone bands) were obtained by utilizing the elastic cross sections determined in the previous paper (II). In addition, the DCS for excitation of the second overtone band was determined for an impact energy of 10 eV. By angular extrapolation and integration of the DCS's the integral cross sections for the vibrational excitations were also determined. In addition, all these cross sections have been calculated using a quantum-mechanical method based on potential scattering in a plane wave scattering approximation which is described in Part I of this series. The present experimental and theoretical cross sections and previous measurements and calculations are compared. The calculated DCS ratios and the DCS's themselves for the fundamental excitation are in good agreement with experiment at 7 and 10 eV; however, at higher energies the calculated DCS's are generally larger than the experimental ones, at some angles by as much as a factor of 10. The calculated ratio of the DCS for the fundamental excitation to the elastic DCS shows a minimum as a function of angle, in qualitative agreement with the experimental results in the 13.6–81.6-eV energy range. The experimental DCS's for vibrational excitation also show a deep minimum. For excitation of the first overtone vibration, the experimental ratios are an order of magnitude larger than the calculated ones at low energy but in better agreement for the magnitude at higher energy. This discrepancy at low energies is explained in terms of resonance scattering. Our experiments are in good agreement with those of others in the few (low energy) cases where comparison is possible.
Plasma Effects in Annulene Molecules
Authors: Chang David B. , Drummond James E.
Published: February 2004

Some plasma effects of the pi electrons in annulene molecules are studied. The dispersion relation for plasma oscillations, obtained by using Hückel molecular orbitals in the second quantization formalism, is found to describe soundlike waves. The resulting polarization response of the pi electrons causes a spatial modulation of the interaction potential between two pi electrons. The polarization response defines the natural correlation units in annulenes to be quartets in all but the angular momentum l = ± 2n states of 4n-annulenes and zero angular momentum states, where the correlation unit is a pair of electrons. Correlation is discussed by using the modified interaction potential with a Wannier hamiltonian in pair and quartet equations. The effect of band alternation is considered in connection with the variation of induced currents in unsaturated annulenes with temperature.
Entropy and Related Thermodynamic Properties of Tetramethylgermane
Authors: Valerga Antone J. , Kilpatrick John E.
Published: February 2004

The heat capacity from 15 to 300°K, the heat of fusion (ΔH = 1779.9 ± 1.7 cal/mole), the temperature of fusion (184.368 ± 0.010°K), the vapor pressure, and the heat of vaporization at 285°K (ΔH = 6722 ± 10 cal/mole) have been determined experimentally for tetramethylgermane. The resulting entropy of the ideal gas at 285°K and 1 atm is 89.81 ± 0.15 cal/deg·mole. Agreement between calculated and experimental entropies requires that the potential barrier to rotation of the methyl groups be 750 ± 90 cal/mole. This value is surprisingly low considering the trends of the potential barriers in other methyl compounds of the Group IV elements.
Effect of Pressure on the Intramolecular and Intermolecular Contributions to Dipolar Spin Relaxation in Benzene and Chlorobenzene in the Liquid State
Authors: Bull T. E. , Jonas J.
Published: February 2004

The pressure dependence of the proton spin–lattice relaxation times has been measured at 23°C in liquid benzene and its mixtures with benzene-d6 up to 600 bar, and in liquid chlorobenzene and its mixtures with chlorobenzene-d5 up to 2000 bar. The separation of the intramolecular and intermolecular contributions to proton dipolar relaxation allowed us to study the effect of pressure on the reorientational and translational motions of the molecular liquids investigated. As predicted by the Bloembergen–Purcell–Pound (BPP) theory the intermolecular T1 were found to follow the changes in the viscosity with pressure. On the other hand, the experimental pressure dependence of the intramolecular T1 in benzene differs widely from the BPP theoretical prediction due to the relatively free rotation about the C6 axis in benzene. Removal of the C6 axis and introduction of a dipole in chlorobenzene result in agreement between theoretical and experimental intramolecular T1 pressure dependences. As an example of a molecule with internal rotation some of the previous results on acetone were also discussed. The results of this study show that the molecular symmetry plays an important role in determining how well the Debye–BPP model describes the rotational motion. From molecular symmetry one can also infer on the degree of coupling between rotational and translational motions in liquids. Activation volumes for the intramolecular and intermolecular T1 were calculated and compared with corresponding activation energies. (ΔV‡)intra ≪ (ΔV‡)inter in benzene and acetone, whereas (ΔV‡)intra ≅ (ΔV‡)inter in chlorobenzene. The data obtained also indicate that in many cases the activation volumes are pressure dependent.
Reactions of Metal Atoms. III. The Combination of Mercury and Iodine Atoms and the Spectrum of HgI
Authors: Greig G. , Gunning H. E. , Strausz O. P.
Published: February 2004

The combination reaction of mercury atoms with iodine atoms from the direct photolysis of CF3I has been studied. The 2π1/2−2Σ system of the HgI transient was observed by kinetic absorption spectroscopy, and analysis of this system led to the following constants: Te = 32 732 cm−1, ωe′ = 236 cm−1, and ωe″ = 125.5 cm−1. A value of 3538 cm−1 was obtained for the doublet splitting. This value is compared with those found for the other mercury halide diatomics, and the nature of the transition involved is discussed.
Electron Spin Resonance of Trapped PF2 and PF4 Radicals
Authors: Nelson William , Jackel George , Gordy Walter
Published: February 2004

Electron spin resonance has been observed for PF2 and PF4 radicals trapped in solid matrices. For PF2 an isotropic ESR was observed in the xenon matrix at 77°K and an anisotropic ESR in this matrix at 4.2°K. The isotropic constants were found to be: giso = 2.0020, aiso(31P) = 84.6 G, and aiso(19F) = 32.5 G. The anisotropic constants are: g∥ = 2.0027, g⊥ = 2.0016, A∥(31P) = 308.1 G, A⊥(31P) = −27.2 G, A∥(19F) = 125.5 G, and A⊥(19F) = −13.5 G. Analysis of the data indicates that the unpaired electron is in a π orbital with approximately 83% spin density on the P and 8% on each of the F atoms. The PF4 radicals were observed in γ-irradiated solid PF3 at 4.2°K. An anisotropic ESR was observed with two pairs of equally coupling fluorines F(1) and F(2). The coupling constants obtained are: A∥(31P) = 1508 ± 20 G, A⊥(31P) = 1328 ± 20 G, aiso(31P) = 1391 ± 20 G, A∥(19F(1)) = 408 ± 10 G, A⊥(19F(1)) = 366 ± 10 G, and aiso(19F) = 380 ± 10 G. Resolution of the hyperfine structure of the second pair of fluorines F(2) was not possible, but from the linewidths the coupling constants are each estimated to be less than 45 G. From analysis of the coupling data, ∠F(1)PF(1) = 180° and ∠F(2)PF(2) = 102°.
Proof of Energy Transfer and Absence of Electron Injection in Spectral Sensitization of Evaporated AgBr by Oxacarbocyanine
Authors: Szentpály L. v. , Möbius D. , Kuhn H.
Published: February 2004

Spectral sensitization by monomolecular layers of cyanine dyes is observed when the dyes are separated from the surface of evaporated silver bromide layers by monomolecular interlayers. The experimental data of the dependence of spectral sensitization on the distance between the sensitizer layer and the silver bromide surface are interpreted by an energy-transfer model with localized acceptor centers in the silver bromide at about 30 Å below the surface. The sensitization is proportional to [1 + (d / d0)n]−1, where d is the distance between the planes of the sensitizers and the acceptors and n = 3.8 ± 0.3; d0 = 35 ± 3 Å for N,N′-distearyl-oxacarbocyanine, n = 3.9 ± 0.4; d0 = 55 ± 2 Å for N,N′-distearyl-4,4′-carbocyanine. This relation with exponent n = 4 is expected for energy transfer. Using an energy-accepting dye competing with the acceptors in AgBr, the sensitizing action of the oxacarbocyanine dye is diminished and by a quantitative investigation absence of electron injection is demonstrated in the case of direct contact between the sensitizer and the evaporated silver bromide.
Collective Atomic Motions in Liquid Sodium
Authors: Jain S. C. , Saxena N. S. , Bhandari R. C.
Published: February 2004

The self-consistent field method developed by Singwi et al. for the collective modes in classical liquids in the region of high-frequency large-wave-vector transfer has been employed to calculate the spectral function of longitudinal current–current correlations in liquid sodium at the melting point. It is found that in liquid sodium the presence of long-range Coulomb forces results into a particularly strong polarization field. The curves for longitudinal current–current correlations at fixed q's show strong peaks lying at different frequency (ωmax) in each case. From these ωmax(q) values a frequency wave-vector transfer dispersion curve is drawn for liquid sodium similar to the phonon dispersion curve in solid phase. Such a dispersion curve reflects pronounced collective excitations, and thus in liquid sodium the collective aspect plays a significant role in high-frequency large-wave-vector transfer region.
Paramagnetic Relaxation of Silver Species in γ-Irradiated Frozen Aqueous Solutions
Authors: Bales Barney L. , Kevan Larry
Published: February 2004

Paramagnetic relaxation of Ag0 and Ag2+ in γ-irradiated frozen aqueous solutions of AgNO3–KF and of Ag0 in γ-irradiated frozen methanol containing AgF was studied at 77°K. (T1T2)1/2 was measured by slow-passage progressive saturation of the absorption signal, and T1 was measured approximately by fast-passage experiments on the dispersion signal which were extrapolated to adiabatic conditions. The spin-lattice relaxation times T1 were directly related to the isotropic coupling constant of the silver species. This suggests that the spin-lattice interaction involves the extent of spin delocalization onto the matrix molecules. The variation of (T1T2)1 / 2 with radiation dose was investigated and interpreted in terms of the spatial distribution of Ag0 and Ag2+. Some spatial nonuniformity exists, but it is not as great as previously found for the trapped-electron precursors of the silver species in 10M NaOH ice.
Widths of Rotational Lines of an Asymmetric-Top Molecule SO2. II. Broadening by a Quadrupolar Gas
Authors:   Krishnaji, Prakash Vinod
Published: February 2004

The widths of six rotational lines of SO2 broadened by N2 have been measured. The linewidths have also been calculated theoretically on the basis of the Anderson theory and the relative importance of different interaction mechanisms has been assessed. The agreement of the Ji dependence of the calculated linewidths with that of the measured linewidths is not quite satisfactory.
Condensation of a Supersaturated Vapor. I. The Homogeneous Nucleation of the n-Alkanes
Authors: Katz Joseph L.
Published: February 2004

The critical supersaturations required for the homogeneous nucleation of the normal alkanes, n-hexane, n-heptane, n-octane, and n-nonane, from their vapor have been measured in the temperature range 225–330°K using an upward thermal diffusion cloud chamber. The principles of operation of the chamber, its design, and construction are described in detail. The measurements are found to be in remarkably good agreement with the predictions of the classical (Volmer, Becker–Doering) theory. The Reiss–Katz–Cohen theory predictions are 8%–20% too low; the Lothe–Pound theory predictions are 30%–70% too low; for both theories the discrepancy increases with decreasing temperature.
Minimum Basis Wavefunctions for Water
Authors: Pitzer Russell M. , Merrifield Donald P.
Published: February 2004

Molecular-orbital wavefunctions are obtained for the water molecule with a minimum set of Slater orbitals. Earlier calculations by Ellison and Shull and by Bersohn are repeated and corrected. The dissociation energy, equilibrium angle, and deuteron quadrupole coupling constants differ considerably from the earlier results. The orbital exponent values are optimized at a sufficient number of geometries to determine a set of force constants. Good agreement results for the bond stretching constant, but not for the bond bending constant. Calculations are also done with the molecule in a linear geometry.
Mobility of Electrons in Dielectric Liquids
Authors: Schmidt Werner F. , Allen A. O.
Published: February 2004

The drift mobilities of electrons in eight saturated hydrocarbons and in tetramethylsilane were determined from the rise time in the conductivity found with a fast-response circuit when a parallel-plate cell was subjected to a pulse of 2-MeV x rays. Careful purification was required to avoid capture of the electrons by impurity centers. The measured mobilities ranged from 0.09 cm2 V−1·sec−1 in n-hexane to 90 in tetramethylsilane. Drift velocities were linear with the applied field up to velocities above 106 cm/sec. Temperature coefficients of the mobility were found to be positive in n-hexane and neohexane. Speculations are offered about the nature of the processes which determine the mobilities.
Calculation of Transition Probabilities for Collinear Atom–Diatom and Diatom–Diatom Collisions with Lennard-Jones Interaction
Authors: Gutschick Vincent P. , McKoy Vincent , Diestler Dennis J.
Published: February 2004

Numerical integration of the close coupled scattering equations is performed to obtain vibrational transition probabilities for three models of the electronically adiabatic H2–H2 collision. All three models use a Lennard-Jones interaction potential between the nearest atoms in the collision partners. The results are analyzed for some insight into the vibrational excitation process, including the effects of anharmonicities in the molecular vibration and of the internal structure (or lack of it) in one of the molecules. Conclusions are drawn on the value of similar model calculations. Among them is the conclusion that the replacement of earlier and simpler models of the interaction potential by the Lennard-Jones potential adds very little realism for all the complication it introduces.
Linewidths in High-Resolution NMR Spectra. Homogeneous Broadening Due to the Intramolecular Dipolar Relaxation
Authors: Sýkora Stanislav
Published: February 2004

The theory of energy-level widths in coupled nuclear systems is discussed, and a detailed study of the intramolecular dipolar relaxations based on it is presented. The restrictions of the theory and all the approximations made are carefully discussed. The nuclear system coupling structure enters the formulas through relatively simple functionals defined over the unperturbed eigenvectors of the system. On the other hand, the spectral density functions, which appear as coefficients of these functionals, depend only on molecular geometry and motions. Both groups of parameters are thus to a great extent separated. In order to show the effectiveness as well as the limits of the method, the structure and the linewidths of resonance transitions of several simple systems (AB, A2, ABX, A2X, A3, and A3X) are studied in detail.
Dynamically Induced Forbidden Electric-Dipole Transitions of Np4+ in ThO2
Authors: Menzel E. R. , Gruber J. B.
Published: February 2004

Forbidden electronic electric-dipole transitions in the optical spectrum of Np4+ in ThO2 are induced by a dynamic distortion to the Oh symmetry. The resulting dynamic line broadening can be described to a first approximation by an averaged Hamiltonian B2αO20, which predicts linewidths in reasonably good agreement with experiment for B2 = 150 cm−1.
Ionization and Metastable Excitation in Low-Energy Collisions of Ground-State Argon Atoms
Authors: Haugsjaa Paul O. , Amme Robert C.
Published: February 2004

A low-energy beam of argon atoms, formed by nonresonant charge transfer of Ar+ in H2, has been used to explore the near-threshold behavior for ionizing and exciting collisions between argon atoms. For excess center-of-mass energies below 12 eV, the ionization data are consistent with the empirical relationship σ− ≈ 1.8 × 10−21(E − 15.8)1.3, where E is the center-of-mass energy in electron volts. Target-gas mixtures of argon and acetylene were used in an effort to observe metastable atoms formed in atom–atom collisions by Penning ionization. In this case, beam energies were restricted to values less than 30 eV to avoid direct ionization of the acetylene (Penning) gas by the ground-state atom beam. At 14.5 eV c.m. energy, the cross section for metastable production is shown to be (3.6 ± 2.4) × 10−20 cm2, but this value is dependent upon assumed values of the Penning cross section for Ar* + C2H2 collisions.
Adsorption and Decomposition of Ammonia on a Polycrystalline Tungsten Filament
Authors: Matsushita Kun-Ichi , Hansen Robert S.
Published: February 2004

Adsorption and decomposition of ammonia on a polycrystalline tungsten filament with and without preadsorbed nitrogen doses were studied by flash-filament desorption spectroscopy. The hydrogen-desorption spectrum resulting from ammonia decomposition was qualitatively similar to that which would have resulted from a comparable amount of hydrogen dosed onto a clean surface, desorption occurring over much the same temperature range but with a somewhat different spectrum shape. Hydrogen desorption was substantially complete by 900°K under all circumstances. With increasing nitrogen predose, the amount of ammonia taken up in a fixed dosing condition decreased, while total nitrogen left on the surface following the dose increased. Partial decomposition occurred during ammonia adsorption at 300°K resulting in desorption of approximately 1.5 atoms of hydrogen per ammonia molecule absorbed. Prolonged dosage of ammonia on clean tungsten at 300°K left 0.65NH1.5 units on the surface per surface tungsten atom. When total nitrogen on the surface exceeds one-half an atom per surface tungsten atom, a second desorption peak appears in the nitrogen-desorption spectrum beginning at about 870°K, with a peak maximum around 1100°K. The nitrogen in this peak is designated x-nitrogen and can be almost completely resolved from β-nitrogen. Desorption of x-nitrogen is found to be second order in the excess of nitrogen over one-half nitrogen atom per surface tungsten atom, with an activation energy of 46 kcal/mole. When the surface was predosed with one isotope of nitrogen and subsequently dosed with ammonia having a different isotope of nitrogen, extensive mixing of isomers was found in both the x-nitrogen and β-nitrogen peaks but with some bias in the x-nitrogen peak toward the predosed nitrogen isotope. The (β + x)-nitrogen surface structure has approximately one nitrogen adatom per surface tungsten atom. This structure forms and decomposes under equivalent conditions to those leading to the surface complex of Dawson and Hansen for which the structure W2NNH2 was proposed, and to the (1 × 1) structure of Estrup and Anderson for which the structure WNH2 was proposed. It is concluded that both of these latter assignments were incorrect and that the properties observed were those of (β + x)-nitrogen. Furthermore, the average rate of x-nitrogen desorption agreed well with ammonia decomposition rates on tungsten wires available in the literature. The (β + x)-nitrogen structure was synthesized, so far as can be judged from its flash-desorption spectrum, by dosing with pure nitrogen activated by electron bombardment. These results strongly suggest that the catalytic decomposition of ammonia on tungsten has as its limiting step the desorption of x-nitrogen; it is shown that kinetic orders, activation energy, and temperature range for effective catalysis are in good accord with this model.
Study of Some Nd3+ Complexes: Interelectronic Repulsion, Spin–Orbit Interaction, Bonding, and Electronic Energy Levels
Authors: Tandon S. P. , Mehta P. C.
Published: February 2004

The values of Slater–Condon (F2, F4, F6) and Racah (E1, E2, E3) interelectronic repulsion and Landé (ζ4f) spin–orbit interaction parameters have been computed from already observed visible and near infrared absorption spectra of 24 Nd3+ complexes. Using these parameters the energies of 27 energy levels of each complex have been calculated. The agreement between the computed and experimental energy levels is good (average deviation, 32–55 cm−1; rms deviation, 59–117 cm−1). The variation of all the parameters in the complexes from the corresponding Nd3+ “free” ion parameters has been discussed. The average values of F4 / F2 and F6 / F2 for Nd3+ complexes have been found to be ≃ 0.15 and ≃ 0.015, respectively, which are different from those calculated assuming wavefunctions to be hydrogenic or by using Hartee–Fock methods. Using F2 values the nephelauxetic ratio β and bonding parameter b1/2 have been calculated. The complexes have been arranged in increasing order of covalent bonding. For the same ligand the covalency decreases as the atomic number of the rare-earth metal ion increases.
Hall Effect in Lithium–Ammonia Solutions
Authors: Nasby R. D. , Thompson J. C.
Published: February 2004

Measurements of the Hall coefficient and electrical conductivity are reported for solutions of lithium in liquid ammonia. The concentration range is from 1.2 to 14 mol % metal (MPM) and the temperature range is from near 200 to 240°K, except in the miscibility gap. Hall coefficients equal to the values expected from the metal-valence-electron density are found above 9 MPM. Below 9 MPM the measured Hall coefficient Rm increases to about twice the free-electron value R0. The latter result does not agree with that previously reported by Kyser and Thompson. Rm is temperature independent at all concentrations. Data for the electrical conductivity σ show thermal activation of the mobility below 8 MPM. Changes in the concentration dependence of both Rm and σ are observed near 3, 5, and 8 MPM. The solutions behave as liquid metals above 9 MPM. As the concentration is decreased from 9 to 3 MPM, departure from metallic behavior occurs and various criteria for metallic conduction are no longer satisfied. We believe deep traps are present below 9 MPM. At concentrations near 3 MPH the influence of free electrons is no longer seen.
Statistical Analysis of Transition Probability Matrices in the Strong Coupled Rotational Excitation Problem
Authors: Lester William A. , Bernstein R. B.
Published: February 2004

Scattering matrices accurately computed via close-coupling techniques are analyzed and discussed as a function of critical parameters of an atom–diatomic molecule scattering system. The usefulness of the t test for delineating the region of strong coupling and ascertaining the range over which statistical approximations may be appropriate is demonstrated.
Pressure Effects on the Vibrational Modes of K2PtCl4, K2PdCl4, K2PtCl6, and K2PdCl6
Authors: Ferraro John R.
Published: February 2004

Pressure effects on the vibrational modes (internal and lattice) of tetragonal crystals of K2PtCl4 and K2PdCl4 were studied. The most pressure-sensitive external mode for these compounds was the translational mode along the long axis a0, while the least sensitive was the translational mode along the short axis c0. Results with cubic crystals of K2PtCl6 and K2PdCl6 showed that the lattice mode demonstrated higher pressure dependency than the internal modes.
ESR Linewidth and Solution Stability Studies of Dilute Solutions of Cesium in Ethylamine–Ammonia Mixtures
Authors: Nicely Vincent A. , Dye James L.
Published: February 2004

An electron spin resonance (ESR) study of the mI-dependent linewidth of the hyperfine pattern from cesium–amine solutions is reported. The ESR spectrum of the monomer in dilute solutions has Lorentzian-shaped lines. A two-state equilbrium model is sufficient to describe the linewidth dependence upon mI of an isothermal spectrum. Due to persistent problems with solution decomposition, however, data could not be obtained over a sufficient range of temperature and solvent composition to permit a distinction to be made among several possible models. A systematic study was made of the solution decomposition at room temperature. Solutions could be prepared which were stable for periods of weeks to months in the presence of excess metal and after some initial decomposition. However, for freshly prepared dilute solutions without excess metal the decomposition was much faster and depended on the surface-to-volume ratio of the container. Zero-order decay of the optical absorption was observed for a solution in a 2-mm-diam tube.
Correlation Energy in Atomic Systems. VI. Comments on the Radial Correlation Energy
Authors: Clementi E. , Kraemer W. , Salez C.
Published: February 2004

A fraction of the radial correlation energy is computed for the first-row atoms in the ground state as well as selected excited states. The same type of computation is reported for the ions of the isoelectronic series from Ne to A8+. The wavefunction we have used is a linear combination of three determinants: One is the standard Hartree–Fock determinant, and the other two contain orbitals shrunken or expanded relative to those in the Hartree–Fock determinant. In the paper we discuss the technique needed to obtain the determinants and the physical interpretation of the results. The large fraction of correlation energy (over 20% for the Ne atom) obtained with such a small expansion (two determinants added to the Hartree–Fock determinant) is explained as a consequence of rejecting the orthogonality constraints among the orbitals. The results of this work seems to indicate that different techniques should be used in order to solve the different effects which are lumped together under the name of “correlation energy.”
Uniqueness of the Intermolecular Potential Extracted from Differential Cross Section Extrema
Authors: Luoma J. R.
Published: February 2004

A Lennard-Jones (12,6) potential was used to generate differential cross sections over a fourfold velocity range. Using functional iteration, a rigid sphere radius was optimized by a least squares criterion which minimized the squared differences between rigid sphere and Lennard-Jones differential cross sections. It was noted that the rigid sphere intermolecular potential could reproduce these high velocity extrema of the Lennard-Jones potential if a small variation in the rigid sphere radius were tolerable. This serves as a caution for a determination of the intermolecular potential from differential cross section extrema without additional knowledge of the magnitudes of the cross sections or knowledge of the cross sections over a large angular range or a larger velocity range.
Theory of the Vibronic Transitions of Substitutional Impurities in Molecular Crystals
Authors: Philpott Michael R.
Published: February 2004

A theory for the vibronic states of a single guest molecule in the vicinity of bands of single exciton states of the host crystal is presented. It is assumed that the lattice is rigid, and that the wavefunctions of isolated molecules are Born–Oppenheimer separable. Expressions are given for the excitation energies, transition probabilities, and polarization ratios of a general guest which are much simpler and easier to interpret than any given before. It is shown that the guest transitions exhibit anomalous polarization ratios (Rashba effect) near the host bands. The use of guests to locate exciton band edges and find guest–host interactions is discussed.
Investigations of the Raman and Infrared Spectra of Thiophosgene and Polymeric Species
Authors: Frenzel C. A. , Blick K. E. , Bennett C. R. , Niedenzu K.
Published: February 2004

The Raman and infrared spectra of thiophosgene and its dimer have been reinvestigated and assignments based on new data and a normal coordinate analysis of the monomer are presented. The spectra obtained in gas, liquid, and solid phases are compared and two polymeric species and their spectra are discussed. A description of the fundamentals of thiophosgene is presented in terms of atom displacements, potential energy distributions, and Coriolis coupling coefficients. The transferability of the valence force field between thiophosgene and phosgene is demonstrated.
Photoelectron Spectroscopy of NH3 and ND3 Using Molecular Beams
Authors: Weiss M. J. , Lawrence G. M.
Published: February 2004

Ammonia and ammonia-d3 have been examined with high resolution photoelectron spectroscopy using the 584- Å resonance line of helium. The spectra consist of two electronic states which are formed as a result of severe geometrical changes in the ground state molecule. The onset for the first state, consisting of a vibrational envelope of the ν2 out of plane banding mode, was at 10.175 ± 0.010 eV in NH3, 10.180 ± 0.010 eV in ND3. The second electronic state of NH3 and ND3 is complex. Onset was found to be 14.94 ± 0.03 eV for both NH3 and ND3. The band in NH3 apparently consists of two consecutive vibrational series (I and II) having different frequency intervals and are superimposed on a continuum. In ND3 series I is missing, although series II is present with a spacing consistent with an isotope effect of some unknown vibrational mode.
Electronic Spectra of the 5f3 Actinides: U3+, Np4+, Pu5+, and AmO2++. The f3 Intermediate Coupling Diagram
Authors: Varga L. P. , Reisfeld M. J. , Asprey L. B.
Published: February 2004

The absorption spectra of fluoride salts of 5f3Np4+ obtained at room temperature in various environments were compared with the known spectra of f3Nd3+ and U3+. Correlation with known spectra allowed assignment of levels to Np4+, and based on these, the complete 41-level f3 intermediate spin–orbit coupling diagram was constructed. The diagram was used to interpret the absorption spectra and to make spectroscopic assignments to 12 low-lying electronic energy levels for Pu5+. Ten low-lying levels for Am(VI) obtained from published AmO2++ aqueous solution spectra were interpreted also. Spectroscopic parameters obtained from least-squares fits to the observed spectra were: Np4+, F2 = 232.4 cm−1, ζ = 2178 cm−1; Pu5+, F2 = 230.5 cm−1, ζ = 2295 cm−1; AmO2++, F2 = 260.3 cm−1, ζ = 3070 cm−1. Only the lowest-lying energy levels were found to be in substantial agreement with the f3 intermediate coupling diagram.
Vibrational Energy Transfer from Highly Excited Molecules
Authors: Rand S.
Published: February 2004

The rates of energy transfer, between molecules in highly excited vibrational states and thermal distributions of gas atoms, has been studied. It is assumed that the molecule is bound by a Morse potential and that the atom–molecule interaction is also a Morse potential, but with different parameters. The electric dipole–perturbation theory approximation is used, and the atom translational wavefunctions are evaluated in the WKB approximation. Results are plotted in terms of four parameters, which are related, respectively, to the molecule excitation energy, the adiabaticity condition, the energy transfer during a single quantum jump, and the long-range attractive part of the atom–molecule interaction.
Polarization Dependence of the Two-Photon Absorption of Tumbling Molecules with Application to Liquid 1-Chloronaphthalene and Benzene
Authors: Monson P. R. , McClain W. M.
Published: February 2004

The two-photon absorption cross section δ for photons of any polarization (linear, circular, or elliptical) is averaged over all orientations of the absorbing molecule. The result is given by 〈δ〉 = δFF + δGG + δHH, where δF, δG and δH are molecular parameters and F, G, and H are simple functions of the polarization vectors. It is shown how the δ's may be calculated from theory and also how they may be measured by experiment. Experiments using only linearly polarized light are insufficient to determine all three δ's; hence, circularly polarized light will play an essential role in this spectroscopy. For absorption of two linearly polarized photons with angle θ between their polarization vectors, the angular dependence is 〈δ〉 = A + Bcos2θ, where A and B are simple combinations of the δ's. We obtain two exact symmetry rules which permit allowed two-photon transitions of different symmetries to be distinguished. For transitions from totally symmetric ground states the rules are: (1) If the excited state transforms like xy, yz, or zx, then δF = 0. (2) If the excited state transforms like x2, y2, or z2, then δG = δH. In cases of near resonance, when a single intermediate state dominates the formula for the cross section, we show that δF = δH, and that linearly polarized light suffices for a complete investigation. These results are applied to liquid 1-chloronaphthalene. We find two allowed two-photon transitions which are assigned Bb11g (perpendicular nodes) at 37 700 cm−1 and A1g (total symmetry) at 42 600 cm−1. This is in reasonable agreement with theoretical predictions of other authors. We have also examined the region of the second excited singlet of benzene, near 6.2 eV. We were not able to detect any two-photon absorption, setting an upper limit of about 10−51 cm4·sec/photon·molecule on its 〈δ〉. This leads to an unequivocal assignment of B11u for this state according to calculations of Jortner. In an Appendix we examine the effect of “hot spots” in the laser beam on the observed cross sections. We show that the elimination of the hot spots is of some importance, contrary to a statement of other authors.
Surface Ionization. V. Desorption of U Neutrals from W Surfaces
Authors: Smith David H.
Published: February 2004

The mean residence time of U neutrals on hot polycrystalline tungsten surfaces has been determined as a function of surface temperature. The desorption parameters for U° were determined from the relationship 1 / τ = ω0exp(− Ea / kT) and found to be ω0 = (9.5 ± 4.5) × 1011sec−1 and Ea = 5.85 ± 0.10 eV. Oxygen contamination was found to have a profound effect on the W surface, with Ea being a sensitive function of the amount of oxygen present.
Comparative Study of Ellipsoidal Gaussians: H2 and H2++
Authors: Katriel J. , Adam G.
Published: February 2004

A series of calculations is carried out for H2 and He2++ using ellipsoidal Gaussian wavefunctions. Comparison to spherical Gaussians shows that the additional variational freedom results in lower energy expectation values.
93Nb Nuclear Quadrupole Resonance Investigation of LiNbO3
Authors: Schempp Ellory , Peterson G. E. , Carruthers J. R.
Published: February 2004

The temperature dependence of the 93Nb nuclear quadrupole coupling constant in stoichiometric LiNbO3 powder specimens was measured from 21 to 515°K. No phase transitions were observed in this range. Analysis of the data on a simple vibrational model gave an Einstein temperature of 514°K in excellent agreement with that calculated from the measured specific heat. Nonstoichiometric specimens showed a very rapid NQR line broadening with a small departure from stoichiometry, and they could not be studied in detail. The temperature dependence of the niobium coupling constant was found to be linearly correlated with the variation of the birefringence over the range − 80 to 200°C.
Phase Transformations and Melting in KH2PO4 to 40 kbar
Authors: Rapoport Eliezer
Published: February 2004

The phase diagram of KH2PO4 was determined to 40 kbar by differential thermal analysis. New phase transitions were found, and the diagram consists of six solid phases and the liquid. Dehydration of KH2PO4 above 200°C is suppressed by pressure, and the melting curve was successfully determined to the highest pressure.
Gaussian-Type Functions for Polyatomic Systems. IV
Authors: Huzinaga Sigeru , Arnau Catalina
Published: February 2004

A new set of combined Gaussian-type orbitals (CGTO) is presented for Na–Ar for the use in the molecular calculation. The accuracy is roughly comparable to that of the double-zeta Slater-type orbitals.
Intermolecular Potentials and Width of Pressure-Broadened Spectral Lines. II. The Rotational Lines of HCl Perturbed by Monoatomic Gases
Authors: Giraud M. , Robert D. , Galatry L.
Published: February 2004

The systematic calculation of the differential collision cross section developed in a previous paper is used here to compute the half-intensity half-width of the rotational lines of HCl perturbed by helium, neon, argon, krypton, and xenon. The comparison of these results with the available experimental data allows one to discuss the influence of the various terms of the potential and of the presence of cross term contributions in the differential cross section. The consistency of the theoretical results with respect to the experiment is fairly good, expect for He as perturbing gas, when the cutoff procedure, proposed by Anderson for the differential cross section, is introduced in the calculations.
Calculation of Wavefunctions for the Excited States of Polyatomic Molecules
Authors: Segal Gerald A.
Published: February 2004

A new method for the calculation of the wavefunctions of the excited states of polyatomic molecules is presented. The method is independent of the symmetry of the state under consideration. Sample calculations on a number of molecules have been carried out in the INDO approximation, and the results, which represent a considerable improvement over comparable configuration interaction calculations, are presented.
Low-Frequency Modes in Molecular Crystals. IX. Methyl Torsions and Barriers to Internal Rotation of Some Three-Top Molecules
Authors: Durig J. R. , Craven S. M. , Bragin J.
Published: February 2004

The low-frequency vibrational spectra of (CH3)3CCN, (CH3)3CCCH, (CH3)3CH, (CH3)3SiH, (CH3)3SiF, (CH3)3P, and (CH3)3N have been recorded for these molecules in both the gaseous and solid states. Both the degenerate E and nondegenerate A2 torsional modes were observed for the molecules in the solid state. The effects of condensation on the torsional modes have been obtained from the far-infrared spectra of the molecules in the gaseous state. The importance of top–top interaction in the torsional potential energy has been demonstrated. The calculated harmonic barriers are 4.31, 4.10, 3.94, 2.49, 2.25, 3.58, and 4.35 kcal/mole for the (CH3)3CCN, (CH3)3CCCH, (CH3)3CH, (CH3)3SiH, (CH3)3SiF, (CH3)3P, and (CH3)3N molecules, respectively, in the solid state. The top–top interaction values ranged from 0.8 kcal/mole for tertiary butylacetylene to 0.3 kcal/mole for isobutane, with an average value of 0.5 kcal/mole.
Polar Distortions in ReF7 and IF7
Authors: Kaiser E. W. , Muenter J. S. , Klemperer W. , Falconer W. E.
Published: February 2004

The deflection of molecular beams of ReF7 and IF7 by inhomogeneous electric fields has been studied as a function of temperature. Polar components were readily observed in molecular beams of ReF7, and their intensity increased as the temperature was lowered. A similar effect was just observable for IF7 at the lowest temperatures attainable. These observations show that the heptafluorides do not have rigid polar structures, but they are compatible with nonrigid distorted geometries for ReF7 and IF7.