bluuebunny/crossref_metadata_2025 huggingface dataset:
Bilinear Orbital Expansion of Geminal-Product Correlated Wavefunctions
Authors: Silver David M.
Published: February 2004

Bilinear orbital expansions of geminals are proposed for use in forming a total electronic wavefunction from a single antisymmetrized product of geminals. This gives rise to a more general analytical form for the wavefunction than that represented by the previously discussed interacting, separated, or identical geminal models. Variational determinations of the geminals are enhanced by this more general scheme although additional algebraic complexities arise as well. Explicit expressions are given for the geminal expansions, density matrices, energy, and variational equations in the case of two singlet pairs of electrons.
Kinetics of the Homogeneous Exchange Reaction: NH3 +D2→NH2D +HD. Single-Pulse Shock-Tube Studies
Authors: Schechner Pinhas , Burcat Alexander , Lifshitz Assa
Published: February 2004

The homogeneous exchange reaction between ammonia and deuterium was studied in a single-pulse shock tube over a wide range of compositions and initial pressures within the 1150–1450°K temperature range. The rate of production of HD in the early stages of the reaction, in the composition range 0.67–4% NH3 and 0.67–4% D2 in argon is given by d[HD]/dt = kb[Ar]0.38[NH3]0.61[D2]1.01, where kb = 1013.0 ± 0.3exp[−(37.2 ± 1.0) × 103/RT]cc mole−1·sec−1. The contribution of a chain mechanism to the exchange process was ruled out. A mechanism based on vibrational excitation of the deuterium molecule to a critical vibration level as a slow step prior to the atom switching step is proposed.
Reaction Kinetics of Uranium and Deuterium
Authors: Alire R. M. , Mueller B. A. , Peterson Charles L. , Mosley John R.
Published: February 2004

A uniform and adherent layer of β-UD3 was formed on uranium when uranium reacted with deuterium in the temperature range 175–350°C and pressure range 100–10 270 torr. The rate of reaction was controlled by diffusion of deuterium across this product layer. Reproducible results were obtained only with D2 of very high purity because low-level impurities had a profound effect on the rate of reaction. It was concluded that molecular diffusion with sorption was the predominant method of mass transport, but atomic diffusion may also be occurring. The activation energy for molecular diffusion with Langmuir sorption of D2 on UD3 was determined to be 9.8 ± 0.5 kcal/mole D2. The activation energy for atomic diffusion was determined to be 4.4 ± 0.3 kcal/g-atom of D.
Light Scattering by Solutions of Flexible Macromolecules Subjected to Flow
Authors: Champion J. V. , Davis I. D.
Published: February 2004

A coaxial-cylinder flow assembly is described in which the changes of the intensity of light scattered by solutions of a flexible polymer (polystyrene in cyclohexanone) with flow have been determined over a range of angles and up to velocity gradients of 10 000 sec−1. The results show that flow scattering is concentration dependent and that at low concentrations the theory of Peterlin and Reinhold is approximate description.
Transport of Quasilocalized Excitons in Molecular Crystals
Authors: Munn R. W. , Siebrand W.
Published: February 2004

A model is presented for electron–phonon coupling in molecular crystals and its effect on transport of excitons and charge carriers in aromatic hydrocarbon crystals. The model differs from the usual ones in that the coupling is taken quadratic instead of linear in the vibrational coordinates. It is shown that this coupling dominates in aromatic hydrocarbons, leading to large frequency shifts in out-of-plane molecular vibrations on electronic excitation or ionization. The present study is limited to weak intermolecular electronic coupling, implying quasilocalized excitons (or electrons). There are then two limiting modes of diffusion, governed by the rate either of exciton transfer between molecules or of phonon transfer. In either limit, at high temperatures, transport occurs by incoherent jumps between adjacent molecules (hopping) and increases or decreases gently with temperature, while at low temperatures, coherent transport decreasing rapidly with increasing temperature occurs. The diffusion coefficient is larger for normal than for deuterated aromatic hydrocarbons except for hopping transport in the slow-exciton limit. The observed temperature dependence and deuterium effect of triplet exciton diffusion in the c′ direction of anthracene are reproduced by the model in this case. The transition from hopping to coherent diffusion is not readily observable for anthracene, but may be observable for naphthalene or benzene. Preliminary results indicate that the model also accounts satisfactorily for the magnitude and temperature dependence of charge-carrier mobilities in anthracene.
Molecular Beams of Macroions. II
Authors: Mack L. L. , Kralik P. , Rheude A. , Dole M.
Published: February 2004

Using the electrospray technique and nozzle–skimmer system previously described, the influence of polystyrene concentration in the sprayed solution on the magnitude and substructure of the macroion current in the molecular beam has been investigated. Other variables studied include polarity of the beam, needle–nozzle and nozzle–skimmer distances, shape of spray, etc. Attempts to produce isolated macroions in the beam by carrier gas atomization were not successful; operation at reduced pressures and elevated temperatures was not found to be advantageous. In the case of positive macroions the current–repeller-voltage curves had less substructure than in the case of negative beams, and the first stopping potential was more dependent upon the solution concentration, especially when using a relatively large nozzle–skimmer distance. For molecular weights of the polystyrene from 600 to 97 200 the relative macroion positive charge was roughly proportional to the surface area of the macroions, assuming the latter to be spheres and as calculated from the first measured stopping potential. In the case of negative beams the current at zero repeller voltage and at a solution concentration of 2.2 × 10−6 Mw was proportional to the third power of the molecular weight at the lower solute molecular weights, as is predicted for a diffusional charging process.
Exciton Wave Packet Localization on an Impurity
Authors: Bierman Arthur
Published: February 2004

The time-dependent localization of an exciton wave packet on a single impurity is calculated exactly for an infinite one-dimensional crystal with nearest-neighbor coupling. The problem is solved by a new algebraic operator method, and the resultant expression evaluated by computer. The dependence of the localization probability on the impurity strength a and the distance l of the initial absorption site from the impurity is discussed.
Self-Consistent Molecular Orbital Methods. VI. Energy Optimized Gaussian Atomic Orbitals
Authors: Ditchfield R. , Hehre W. J. , Pople J. A.
Published: February 2004

Minimal basis atomic orbitals expressed as sums of N Gaussian functions are presented for hydrogen and for the first row atoms boron to fluorine. The expansion coefficients and Gaussian exponents are determined by minimizing the total calculated energy of the atomic ground state. For expansion lengths of up to six Gaussians, two sets of atomic orbitals are reported. In the first set, which we describe as unconstrained, different Gaussian exponents are used for the 2s and 2p atomic orbitals. In the second set, the 2s and 2p atomic orbitals are constrained to share the same Gaussian exponents. It is shown that this constraint, which produces a significant gain in computational speed in molecular calculations, does not seriously reduce the quality of the atomic orbitals for given N. A comparison of the contracted sets presented here with previous studies on uncontracted basis sets for the first row atoms, shows that the uncontracted Gaussian exponents are a poor approximation to those of the contracted functions.
Construction of Tetrahedral Harmonics
Authors: Fox Kenneth , Ozier Irving
Published: February 2004

Explicit, detailed, and convenient algorithms have been developed for constructing tetrahedral harmonics for arbitrary J. These functions are expressed as linear combinations of spherical harmonics and also of symmetric top functions. A projection-operator technique was used to produce projected functions which transform according to the rows of the irreducible matrix representations of Td. In general the set of projected functions so constructed may be linearly dependent. The idempotence of the projection operators was invoked to show that all the required orthonormal tetrahedral harmonics can be produced by the diagonalization of the projection-operator matrices. The elements of these matrices are given explicitly for arbitrary J. In an Appendix, alternative procedures, including the Gram–Schmidt method, for the orthogonalization of the projected functions are treated briefly, with special emphasis on the use of these matrix elements. The “symmetry-adapted functions” involve the dK′KJ(π / 2), and a recursion relation is presented which facilitates an accurate and rapid calculation of these constants. An important new sum rule useful in calculations of integrated intensities is derived using the idempotence property. Various physical applications are discussed.
Theory of the Hydrogen Bond: Ab Initio Calculations on Hydrogen Fluoride Dimer and the Mixed Water–Hydrogen Fluoride Dimer
Authors: Kollman Peter A. , Allen Leland C.
Published: February 2004

High-accuracy molecular orbital calculations have been carried out on different geometries of the hydrogen fluoride dimer and the mixed water–hydrogen fluoride dimer. A zigzag (near linear) structure is predicted for the hydrogen fluoride dimer with a dimerization energy in reasonable agreement with experiment. One geometry of the mixed water–hydrogen fluoride dimer has a very large stabilization energy (10 kcal/mole), and a microwave experiment is proposed to determine its exact structure. Changes in molecular properties and charge distribution upon dimer formation are calculated and a dimer rotational barrier determined.
Reactions of He2+, Ne2+, Ar2+, and Rare-Gas Hydride Ions with Hydrogen at 200°K
Authors: Adams N. G. , Bohme D. K. , Ferguson E. E.
Published: February 2004

The flowing afterglow technique has been used to measure rate coefficients for the reactions of the rare-gas molecular ions X2+, XH+, XH2+, and X2H+ (where X = He, Ne, and Ar) with hydrogen at 200°K. An attempt was made to establish the product channels for these processes.
Flash Photolysis of Ketene and Diazomethane: The Production and Reaction Kinetics of Triplet and Singlet Methylene
Authors: Braun W. , Bass Arnold M. , Pilling M.
Published: February 2004

Ketene and diazomethane have been flash photolyzed in their strongest absorption continua in the vacuum ultraviolet and far ultraviolet. Triplet methylene was monitored by kinetic spectroscopy at 141.5 nm. Singlet methylene was not observed directly, but the growth of the triplet absorption as a function of inert-gas pressure indicates that singlet methylene was the major primary product in both the ketene and diazomethane systems. Various inert additives quantitatively quenched the singlet to the triplet state, while reactive additives were able to intercept the singlet before quenching occurred. A number of reactions and deactivations involving singlet methylene (1CH2) and triplet methylene (3CH2) have been investigated at 298°k, and their rate constants are listed below (cm3 molecule·−1 second−1):CH23+3CH2→C2H2+H2 (5.3 ± 1.5) × 10−11 CH21+H2→CH4*→CH3+H (7.0 ± 1.5rparl × 10−12 CH21+H2→3CH2+H2 < 1.5 × 10−12 CH21+CH4→C2H6*→CH3+CH3 (1.9 ± 0.5) × 10−12 CH21+CH4→3CH2+CH4 (1.6 ± 0.5) × 10−12 CH21+He→3CH2+He (3.0 ± 0.7) × 10−13 CH21+Ar→3CH2+Ar (6.7 ± 1.3) × 10−13 CH21+N2→3CH2+N2 (9.0 ± 2.0) × 10−13 CH23+H2→CH3+H < 5 × 10−14 CH23+CH4→CH3+CH3 < 5 × 10−14. The absolute reaction rates for the singlet are apparently independent of the source (i.e., ketene or diazomethane), suggesting that the reactions occur via vibrationally cold singlet methylene. No evidence was found for deactivation of the triplet to the singlet, indicating that the energy difference between the two states is greater than kT (T = 298°K).
3100-Å Electronic Absorption of Dicyanodiacetylene
Authors: McSwiney H. D. , Merritt James A.
Published: February 2004

The diffuse absorption spectrum of dicyanodiacetylene (D∞h) in the gas phase has been measured and analyzed between 3100 and 2300 Å. The main features of the transition can be explained on the basis of a linear Σg+1 ground state and a linear excited state Σg+1, Σg−1, or Δg1 electronic symmetry. The electronic origin is not seen; vibronic origins involving a πu vibration, ν11, and a σu+ vibration, ν7, are seen. The extensiveness of the system results from the ν1′ frequency of 2157 cm−1 (ν1″ = 2235 cm−1) being built on the vibronic origins (ν11)01 and (ν7)01.ν11 has been found to undergo the unusual change from 489 cm−1 in the ground state to 152 cm−1 in the excited state.
Pressure-Scanned Fermi Resonance in the Spectrum of NH4+ Isolated in CsBr
Authors: Sherman W. F. , Smulovitch P. P.
Published: February 2004

By using sample pressures up to 50 kbar at a temperature of 100°K, two energy levels of the same symmetry in the NH4+ in CsBr vibrational system have been scanned through the region of maximum Fermi resonance, (i.e., the “cross-over” region). This experiment shows unambiguously the observed results of continuously varying the coupling between the two resonating levels. Not only do these results afford an improved insight into the phenomenon of Fermi resonance itself, but they also illustrate the value of pressure scanning as a means of resolving detailed interpretational difficulties.
Refined Impulse Approximation for the Collisional Excitation of the Classical Anharmonic Oscillator
Authors: Mahan Bruce H.
Published: February 2004

A modification of the conventional classical theory of vibrational–translational energy exchange is made which leads to an expression of increased accuracy and which has the proper behavior at high energy. It is pointed out that the refined impulse approximation can be used to calculate the energy transferred to an anharmonic oscillator in configurations where the potential energy curve has positive curvature. The case in which the oscillator potential has negative curvature is analyzed and is shown to lead to energy exchanges which exceed the predictions of the impulse approximation. Expressions are given for the energy transferred in grazing collisions which can be used to estimate total inelastic cross sections.
Enhanced Multiple Resonance by Overhauser Effect in Paramagnetic Crystals
Authors: Sukheeja B. D. , Narchal M. L.
Published: February 2004

The Overhauser effect in paramagnetic ions is studied theoretically for arbitrary values of electron and nuclear spins. The nuclear magnetic resonance enhancement and the degree of nuclear polarization are computed in the high-temperature approximation. The results show the possibility of obtaining simultaneous and enhanced NMR at more than one characteristic detection frequency when the hyperfine interaction is dominating. The NMR enhancement and nuclear polarization are found to be independent of the electron spin, indicating the suitability of samples with S > 12 for dynamic nuclear orientation.
Error of Expectation Values from the MC SCF Theory
Authors: Tuan Debbie Fu-tai
Published: February 2004

It is proved that the expectation values of one-electron operators calculated from multiconfiguration self-consistent field (MC SCF) wavefunctions are correct to the order of λ2, when the accuracy of the wavefunctions is correct to the order of λ. By using the formalism of Sinanoğlu's many-electron theory of atoms and molecules, it is further shown that only when the MC SCF wavefunctions include all the nondynamical correlation energies, then the errors of the expectation values for one-electron operators are independent of the specific characters of the operators. This result, in combination with our previous studies of correlation energy of MC SCF theory, suggests a criterion for defining the “best” one-electron model of many-electron atomic and molecular systems.
Molecular SCF Calculations for the Ground State of Some Three-Membered Ring Molecules: (CH2)3, (CH2)2NH, (CH2)2NH2+, (CH2)2O, (CH2)2S, (CH)2CH2, and N2CH2
Authors: Bonaccorsi Rosanna , Scrocco Eolo , Tomasi Jacopo
Published: February 2004

LCAO SCF MO calculations with minimum basis sets of Slater-type orbitals are performed for some three-membered ring compounds. A reinterpretation of the resulting wavefunctions in terms of localized (exclusive) orbitals is presented and discussed: The bent bonds in the rings are closely evidenced. The electrostatic potentials produced in the neighboring space by the nuclear and electronic charge distributions are evaluated and employed to evidence the molecular sites more likely subject to electrophilic attacks.
Reaction of C+ with CH4 in the 2–200-eV Energy Range
Authors: Wilson Patricia Sullivan , Rozett R. W. , Koski W. S.
Published: February 2004

The reaction of C+(2P) with CH4 has been investigated in the 2–200-eV energy region using a tandem mass spectrometer. All possible ions containing one or two carbon atoms were observed except C2H4+. The behavior of the cross sections as a function of the kinetic energy of the incident ion was used to infer reaction mechanism. Evidence was obtained for the presence of a complex, stripping and binary collision mechanisms.
Natural-Orbital Valence-Shell CI Studies of Diatomic Molecules. I. Potential-Energy Curves and Spectra of Imidogen
Authors: Kouba Joseph , Öhrn Yngve
Published: February 2004

A method of CI calculations for ground and excited electronic states using a limited natural-orbital basis is described. Applications to full potential-energy curves for NH in the clamped nuclei approximation yield good splittings and spectral parameters. Two new excited states are predicted to be weakly bound.
Study of Some Pr(III) Complexes: Interelectronic Repulsion, Spin–Orbit Interaction, and Bonding
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) parameters have been computed from the already observed visible and near-infrared absorption spectra of nineteen Pr(III) complexes. The decrease in F2 values of the complexes as compared to the free ion is greatest among all the parameters and has been explained. The bonding parameter b1/2 = [12(1 − β)]1/2 has also been computed calculating a β value for each complex using the relation β = Fkc / Fkf, where Fkc and Fkf refer to the complex and the free ion, respectively. The relative variation of covalent bonding in the complexes has been discussed.
Dielectric Behavior of Cubic and Hexagonal Ices at Low Temperatures
Authors: Gough S. R. , Davidson D. W.
Published: February 2004

Cubic ice Ic and hexagonal ice Ih were prepared in pressurizable dielectric cells at temperatures near − 110°C from the high-pressure ices II and IX. No differences were found between the dielectric properties of Ic and Ih. Freshly prepared samples exhibited longer relaxation times at low temperatures than those commonly found for samples of Ih prepared directly by freezing purified water. These long relaxation times became appreciably shorter with sample aging. These results are attributed to precipitation of impurities from ices II and IX, followed by their gradual reincorporation in the ice I lattice. At temperatures as high as − 50°C the isothermal sequence of transformations I→II→I is capable of producing a substantial degree of purification of ice I in terms of its dielectric relaxation time.
14NH3 Hyperfine Structure and Quadrupole Coupling
Authors: Kukolich S. G. , Wofsy S. C.
Published: February 2004

Hyperfine structure on the inversion transition for rotational states J–K = 2–1, 3–1, 4–2, 4–4, and 5–5 was measured with a high-resolution beam maser spectrometer. Variations of nitrogen quadrupole coupling strength were observed for different rotational states. Derivatives of quadrupole coupling strength with respect to molecular coordinates are given. Additional spin–spin and spin–rotational terms are present for K = 1 states. These terms are compared for J–K = 1–1, 2–1, and 3–1 states. A more complete specification of the nitrogen and hydrogen spin–rotation tensors is obtained with the new data.
New Adsorption Isotherm for Heterogeneous Surfaces
Authors: Misra Dwarika Nath
Published: February 2004

A general method is proposed to obtain adsorption isotherms for heterogeneous surfaces from the arbitrary energy distribution functions if the Langmuir isotherm represents the individual homotattic sites. The method is limited to the temperature dependent distribution functions only. It is observed that the number of distribution functions, yielding physically meaningful isotherms, is extremely restricted on mathematical grounds. The method yields only one adsorption isotherm that is new and simple; the corresponding distribution function, however, seems to be more characteristic of homogeneous surfaces having a strictly limited energy distribution rather than that of heterogeneous surfaces with a wide variation of distributive energies.
Asymptotic Relations between the Thomas–Fermi–Dirac and Thomas–Fermi Atom Models. II. Extension of the Case of Low Atomic Number
Authors: Hartle R. E. , Gilvarry J. J.
Published: February 2004

The asymptotic relation between the pressure with exchange in the Thomas–Fermi–Dirac atom model and the corresponding pressure without exchange in the Thomas–Fermi model for the case of low atomic number considered in the first paper of this series is generalized by including a correction corresponding to the first-order Coulomb contribution to the energy of the atom, in addition to the kinetic energy of the electrons alone. Comparison is made with numerical results obtained by direct solution of the Thomas–Fermi–Dirac equation.
Molecular Motions in Several Solids Studied by Nuclear Magnetic Relaxation in the Rotating Frame
Authors: Roeder Stephen B. W. , Douglass D. C.
Published: February 2004

Rotating frame nuclear magnetic relaxation times have been measured as a function of temperature from 117 to 290°K for perfluorocyclohexane, cyclohexane, 2,2-dichloropropane, neopentane, and tetramethylammonium iodide. The data are interpreted in terms of molecular rotation and diffusion in the solid state.
Induction Forces. An Exact Treatment of Charge Overlap Effects through Third Order
Authors: Singh T. R. , Kreek H. , Meath William J.
Published: February 2004

The interaction of a ground-state atom or ion, consisting of a nucleus and a single electron, with a charge is considered in detail as a model for discussing induction forces through third order in the interaction potential. Expressions for all the angular components of the first-order wavefunction and for all the individual nonexpanded second-order induction energies are given in closed form. Exact numerical values for the total third-order induction energy and its individual nonexpanded components, through terms varying as R−11 at long range, are given in tabular form for the H–H+ interaction. The results are discussed with emphasis on the effects of charge overlap on induction forces through third order and on the complicated structure of the third-order energy in terms of its individual nonexpanded induction energies. In the Appendix the Green function approach to the problem is discussed with the relevant Green functions being obtained as solutions of differential equations rather than by direct summation of their spectral expansions.
Effect of Ion Pairing on the g Value of the Naphthalene Anion Radical
Authors: Williams W. Gavin , Pritchett Roger J. , Fraenkel George K.
Published: February 2004

Measurements have been made of the g values of the naphthalene radical anion associated with several alkali-metal cations at a series of temperatures and in different solvents. It has been suggested previously that the temperature dependences of the g factors of spectra exhibiting alkali-metal splittings can be explained either in terms of equilibrium changes between two paired species (Hirota model) or in terms of changes in the populations of the vibrational energy levels of a paired species of fixed electronic structure (Atherton–Weissman model). Evidence is presented to show that the Hirota model adequately accounts for the g-factor variations of the sodium naphthalenide ion pair in tetrahydrofuran, but not for the cesium naphthalenide ion pair in 1,2-dimethoxyethane. It is argued that the latter ion pair is probably a tight ion pair which does not incorporate solvent molecules, and that the variations of the spectral parameters of such complexes are best described by the Atherton–Weissman model.
Dipole Moment of the First Excited π* ← π State of Fluorobenzene
Authors: Huang Kwo-Tsair , Lombardi John R.
Published: February 2004

A Stark effect is observed in the rotational fine structure of the 0–0 band of the lowest-lying singlet π* ← π state of fluorobenzene. Splittings are found in both P and R branches. This enables us to determine the excited-state dipole moment to be μ′ = 1.96 ± 0.07 D. This result is discussed in relation to previous measurements on substituted benzenes, and it is shown that the previously observed correlation between structure and dipole moment for excited states also extends to fluorobenzene.
Molecular Zeeman Effect of Trimethylene Oxide and Trimethylene Sulfide
Authors: Benson R. C. , Tigelaar H. L. , Rock S. L. , Flygare W. H.
Published: February 2004

The rotational Zeeman effect has been observed in trimethylene oxide and trimethylene sulfide. The molecular g values, magnetic susceptibility anisotropies, and molecular quadrupole moments were obtained for both molecules. The a and b axes are in the molecular plane and the a axis bisects the COC or CSC angle. The magnetic susceptibility values are given below in units of 10−6 erg/G2·mole, and the molecular quadrupole moments are in units of 10−26 esu·cm2. The results for trimethylene oxide are: gaa = − 0.0073 ± 0.0005, gbb = − 0.0429 ± 0.0007, and gcc = − 0.0747 ± 0.0005; 2χaa − χbb − χcc = − 20.1 ± 0.5 and − χaa + 2χbb − χcc = − 13.5 ± 0.8; Qaa = − 4.9 ± 0.5, Qbb = + 2.3 ± 0.7, and Qcc = + 2.6 ± 1.0. A reliable value of the average magnetic susceptibility in ethylene oxide is also given. The results for trimethylene sulfide are: gaa = − 0.0148 ± 0.0010, gbb = − 0.0169 ± 0.0006, gcc = − 0.0554 ± 0.0005; 2χaa − χbb − χcc = − 20.9 ± 1.0 and − χaa + 2χbb − χcc = − 24.6 ± 1.0; Qaa = − 2.7 ± 1.0, Qbb = + 3.2 ± 1.0, and Qcc = − 0.5 ± 1.6. Due to the large vibration–rotation interaction in trimethylene sulfide, it was found that consistent g values could be obtained only when this interaction was included in the analysis. The results are compared with previously measured oxygen- and sulfur-containing molecules.
ESR Studies of Phosphorescent Corannulene; Evidence for Pseudorotation
Authors: Bramwell Fitzgerald B. , Gendell Julien
Published: February 2004

Electron spin resonance (ESR) spectra have been recorded for the lowest triplet state of corannulene. The experiments were performed by ultraviolet irradiation of the molecule in rigid glass solutions at 77 and 15°K. In the high-field (Δm = 1) region the line shape and line positions of the absorptions associated with the X and Y magnetic axes were strongly temperature dependent. From an analysis of the spectra the following conclusions were drawn: Corannulene in its first triplet state has a configuration of lowest energy which is not fivefold symmetric; at 15°K corannulene gives in the high-field region the spectrum of a molecule “frozen” in conformations of less than threefold symmetry; tunneling between equivalent conformations at 77°K is believed to occur at a rate of about 109 Hz.
Effects of Anisotropy in the Potential on Molecular Scattering
Authors: Cross R. J.
Published: February 2004

Semiclassical differential scattering cross sections are calculated for anisotropic potentials and averaged over molecular orientation. Both the high-frequency and the low-frequency quantum undulations in the differential cross section are quenched and shifted in phase by the anisotropy. The degree of quenching is comparable for the two types of undulations. The anisotropy has little effect on the classical differential cross section (excluding the undulations). The primary rainbow is broadened by the anisotropy, and the maximum is decreased and shifted slightly to smaller angles. Several novel features of the scattering from anisotropic potentials are discussed.
Vibration Spectra of Carboxylic Acids by Neutron Spectroscopy
Authors: Collins M. F. , Haywood B. C.
Published: February 2004

Neutron energy-loss spectra in the range 400–1400 cm−1 are reported for formic, acetic, propionic, chloroacetic, trichloroacetic, trifluoroacetic, pentafluoropropionic, oxalic, malonic, succinic, maleic, and tartaric acids. The measurements were taken in the solid state and are used to throw light on the hydrogen-bonding process. Much of the data follow the expected pattern for carboxylic acids, but there are indications from the γ(OH) wavenumbers that the chloro and fluoro acids form weaker hydrogen bonds than the corresponding hydrogeneous acids, a fact that is unexpected in view of the chemical evidence that these are strong acids.
Raman Band Contours. I. Spherical Top Molecules
Authors: Masri Frederick N. , Fletcher William H.
Published: February 2004

The general theory of Raman band contours of spherical tops is discussed, and a computer program for calculation of band envelopes of triply degenerate bands is described. Effects of Coriolis coupling on band contours from ζ = − 1.0 to + 1.0 and a method for determination of Coriolis coefficients from observed bands were investigated. Applications to presently available data are given.
Halogen Atom Reactions. IV. Recombination into Electronically Excited States
Authors: Browne R. J. , Ogryzlo E. A.
Published: February 2004

Absolute emission intensities of the luminescence resulting from the recombination of ground-state chlorine and bromine atoms have been measured in an effort to determine the proportion of the recombination occurring through electronically excited states. The emitting states [Cl2(3Π0+u), Br2(3Π1u), andBr2(3Π0+u)] are found to be efficiently quenched by the corresponding atomic species and the efficiency is found to be dependent on the total pressure. Direct quenching by ground-state molecules is found to be at least 103 times less efficient. Rate constants for recombination via electronically excited states of Cl2 and Br2 are found to be ≥ 1014 and ≥ 1015 cc 1mole−1·sec−1, respectively. Luminescence is also reported from the recombination of ground-state iodine atoms and assigned to the transition I2(3Π1u → 1Σg+).
Statistical Theory of Four-Body Bimolecular Resonant Ion–Molecule Reactions
Authors: Wolf F. A. , Haller J. L.
Published: February 2004

A four-body phase space theory of ion–molecule reactions of the type A2+ + A2 ⇆ (A4+) → A3+ + A is presented. A modified definition of strong coupling is introduced by including the asymptotic resonance or chemical bonding potential in the reactant channel. It is shown that: (a) this leads to a larger cross section for the backward reaction than would be predicted using only the ion–induced dipole (polarization) potential, and (b) leads to cross sections for both the forward and backward reactions using hydrogen which are in better agreement with experiment than previously predicted. A computer program has also been developed following Nikitin's presentation of the four-body phase-space theory. Cross sections are presented as functions of the barycentric kinetic energy E in the range 0.01 ≤ E ≤ 10 eV, and comparison is made between the statistical theories using the resonance potential and the polarization potential. Calculations with vibrationally excited reactants were also performed. Inclusion of the resonance potential shows a larger dependence of the cross section in the forward direction on the reactant vibrational energy than is predicted using the induced-dipole potential only. These results also tend to give better agreement with existing experiments and yield predictions that may be tested by future experimentation.
Electronic Loge Localized Functions for Be
Authors: Ludeña Eduardo V. , Amzel Viviana
Published: February 2004

A model of complete loge localization is employed in the description of the electronic ground state wavefunction of the beryllium atom. The formal construction of loge localized functions by means of projection operators is discussed. The integrals over loge localized orbitals are approximated by integrals over Hartree–Fock (SCF) and Edmiston–Ruedenberg orbitals where the limits of integration have been modified to those of the loge boundaries. The loge localized function used here corresponds to a projected single Slater determinant. The corresponding value for the energy is found to be lower than the Hartree–Fock energy. This fact seems to indicate that the model employed in the present work, besides introducing considerable simplifications, is in addition, physically plausible.
Nuclear Quadrupole Coupling Tensors of 27Al in Andalusite (Al2SiO5)
Authors: Hafner S. S. , Raymond M. , Ghose Subrata
Published: February 2004

The nuclear quadrupole coupling tensors of 27Al at the two crystallographically nonequivalent Al3+ sites in andalusite, Al2SiO5, have been determined from nuclear magnetic resonance measurements. For this, the Hamiltonian matrix for the mixed magnetic and electrostatic interaction was diagonalized and a minimization technique based on the least-squares principle was used. The quadrupole coupling constants and asymmetry parameters are: Site Al1 eQVzz = 15.6 MHz, η = 0.08 (octahedral); Site Al2 eQVzz = 5.9 MHz, η = 0.70 (5-coordinated). The site assignment which cannot be made from NMR data alone is based on point charge calculations (point multipole model). Previous assignments concluded from EPR data of Fe3+ and Cr3+ impurities at the Al3+ sites are confirmed. The principal axes of the magnetic Fe3+ and Cr3+ tensors deviate from the 27Al tensor axes by 1°–10°.
Electron Injection into Quinone Crystals
Authors: Soma Mitsuyuki
Published: February 2004

Photostimulated electron injection from an ethanol or water electrode into single crystals of tetrahalo-substituted p-benzoquinones was observed. The electron transfer processes involve the excited quinone molecules. By the addition of appropriate electron donor molecules such as p-phenylenediamine to the electrode, electron injection in the dark could be observed. Excited chlorophyll molecules also caused electron injection to be enhanced.
Magnetic Susceptibility of IrO2 and RuO2
Authors: Ryden W. D. , Lawson A. W.
Published: February 2004

We have measured the magnetic susceptibility of IrO2 and RuO2 in the temperature range 4.2–300°K using the Faraday technique. We find for RuO2 at 300°K χa = 1.09 × 10−6cm3/g and χa / χc = 0.80, and for IrO2 at 300°K χa = 0.92 × 10−6cm3/g and χa / χc = 1.19. Our results are discussed and compared with the behavior of the susceptibility of some of the transition metals. The temperature dependence of χm in RuO2 is quite similar to that for some transition metals. The temperature dependence of χm in IrO2 below 30°K is quite different possibly owing to trace impurities.
Vibrational Spectra and Structure of Small Ring Molecules. XVI. Vibrational Analysis and Ring-Puckering Vibration of 1-Pyrazoline
Authors: Durig J. R. , Karriker J. M. , Harris W. C.
Published: February 2004

The infrared spectrum of gaseous 1-pyrazoline has been measured from 33 to 4000 cm−1. The infrared and Raman spectra of the corresponding liquid sample have also been recorded. A vibrational assignment of the fundamentals is proposed which is consistent with the Cs equilibrium configuration. The assignment is based on the gas-phase band contours, the depolarization values, and group frequency correlations. A series of 13 pronounced Q branches was observed in the far-infrared spectral region, and they have been attributed to the strongly anharmonic ring-puckering vibration. Although the far-infrared frequencies could be reproduced by two different potential functions, a double minimum potential of the form V = 23.40(z4 − 4.40z2) where z is the reduced ring-puckering coordinate provides the most satisfactory interpretation of all the spectral data. The height of the inversion barrier is calculated to be 113 cm−1, and the equilibrium angle between the two dihedral planes of the puckered ring is 19.7° ± 1.0°. The results are compared with those obtained on cyclopentene.
Ozone Ultraviolet Photolysis. I. The Effect of Molecular Oxygen
Authors: Biedenkapp D. , Bair Edward J.
Published: February 2004

To clarify the role of molecular oxygen in the photolytic decomposition of ozone, measurements of mixtures of ozone with helium, nitrogen, or oxygen were analyzed by the intermediate quantum yield method which separates effects due to fast and slow reactions by measuring the fast components shortly after flash photolysis. Analysis of the results gives the following rate constants (in liters/mole·second): O2 + O(1D) → O2(1Σg+) + O(3P), k4b = 1.5 ± 0.8 × 1011; O2(1Σg+) + O3 → 2O2 + O(3P), k3b = 4.0 ± 0.5 × 109. The efficiency of (4d) for forming O2(1Σg+) is found to lie in the range 1.0 ≥ α > 0.6. As a consequence of the high value of (k4b), which was previously neglected, rate constants reported previously should be revised as follows: O(1D) + O3 → 2O2, k2a = 4 ± 2 × 1010; O(1D) + N2 → O(3P) + N2, k4a = 2 ± 1 × 1010; O(1D) + Xe → O(3P) + Xe, k4c = 5 ± 2 × 1010. The quoted error limits are those which represent the fit of the data to the assumed mechanism with appropriate allowances for uncertainties due to minority processes.
Self-Diffusion and Radical Recombination in Imidazole Single Crystal
Authors: McGhie A. R. , Blum H. , Labes M. M.
Published: February 2004

Self-diffusion measurements in imidazole single crystal in the a crystallographic direction were performed with either Cl4 or tritium bound to nitrogen as tracers. Radical recombination studies were also performed as an independent method of assessing diffusive motion in the crystal. From both of these studies, it is concluded that, in the temperature range 80–90°C, self-diffusion and radical recombination occur by a vacancy-controlled bulk diffusion process. There is no indication that cooperative transport of protons through the crystal, which dominates the conduction process in the c direction, and appears as a component of the conduction process in the a direction, is at all operative in the diffusion process.
Optical Absorption Properties of Vanadate Glasses
Authors: Anderson Gordon Wood , Compton W. Dale
Published: February 2004

The optical absorption of vanadate glasses based on the system V2O5–P2O5 was measured in the range 20 cm−1 to 25 000 cm−1 at room and liquid-nitrogen temperatures. The samples were blown films of thickness about 1–2 μ and of composition 70.0, 80.0, and 87.5 mole % V2O5. Vibrational absorption peaks were observed at about 360, 420, 680, 1010, and 1100 cm−1 with additional structure likely at about 900 cm−1 in the 70.0 mole% V2O5 films. Peaks were observed at about 330, 435, 635, 810, 1007, and 1085 cm−1 in the 87.5 mole % films. Absorption tails were observed extending from the lowest-energy peaks to 20 and 33 cm−1 in the 70.0 and 87.5 mole % V2O5 samples, respectively. No noticeable temperature effects on spectra shape and peak positions were observed. Absorption peaks were also observed at 1038 and 1277 cm−1 in crystalline V2O5 at room temperature and at 915, 1040, and 1274 cm−1 and possibly at 1256 cm−1 at liquid-nitrogen temperature. The peaks at about 1010 cm−1 in the glasses are thought to be the V–O stretching vibrations, and the peaks at about 1090 cm−1 are assigned to a phosphorous–oxygen vibration. Other peaks are unassigned. A broad absorption tail which is responsible for the dark black color of bulk samples was observed between the apparent fundamental absorption edge of the glasses in the short-wavelength region of the visible and about 4000 cm−1. The cause of this absorption is not definitely ascertained, though V4+ ions may contribute. The absorption edge of both the 70.0 and 87.5 mole % V2O5 glasses fits the condition for direct forbidden transitions as does the edge of crystalline V2O5. Eg values were determined to be 2.38 and 2.41 eV for 87.5 mole % V2O5 films at room and liquid-nitrogen temperatures, respectively, and 2.47 and 2.51 eV for the 70.0 mole % V2O5 films at room and liquid-nitrogen temperatures, respectively.
Determination of Effective Atomic Charges from the Chemical Shifts of X-Ray Emission Lines
Authors: Leonhardt G. , Meisel A.
Published: February 2004

The x-ray line shifts obtainable as differences of level shifts from various quantum mechanical calculations using the free-ion model provided values which were in good agreement with each other at least for the Kα shifts. This justifies the determination of effective atomic charges from experimental x-ray line shifts. The formation of inner holes can be taken into account by using the values of Z + 1 for the charge determination of compounds of the element Z. With the 3d elements the Kβ shift must be considered besides the Kα one due to the opposite effects of missing 3d and 4s electrons. The charges determined for the first time only x-ray spectroscopically—generally between 0.8 and 1.5—as well as the 3d and 4s orbital populations change in the same manner as the values obtained from MO calculations. In contrast to the situation with the main group elements where the effective charge increases with increasing formal charge, the former decreases for formal charges above 2 with the 3d elements.
Relaxation Behavior of Aliphatic Alcohols in n-Heptane Solution
Authors: Crossley John , Glasser Leslie , Smyth Charles P.
Published: February 2004

The results of dielectric constant and loss measurements over a frequency range 1 MHz–140 GHz are reported for n-hexanol and 2-methyl-3-heptanol, each at several concentrations, in n-heptane solution at 25°C.
Electron Spin Resonance of Pd(I). I. γ-Irradiated Bis(acetylacetonato)palladium(II)
Authors: Fujiwara Shizuo , Nakamura Michihiro
Published: February 2004

A paramagnetic complex produced in γ-irradiated bis(acetylacetonato)palladium(II) [Pd(II) (acac)2] has been studied by means of the electron spin resonance technique. It is found that the same complex is produced by the uv irradiation of the frozen solution of Pd(II) (acac)2 and N,N,N′,N′-tetramethyl-paraphenylenediamine(TMPD) in ethanol. In this case, it is most probable that Pd(II) (acac)2 has been reduced by the electrons photoejected from TMPD. The g tensor for the paramagnetic complex produced in the γ-irradiated single crystals exhibits axial symmetry with the g‖ direction coincident with that for Cu(II) (acac)2 which is diluted in Pd(II) (acac)2. In view of these results it is concluded that [Pd(I) (acac)2]− has been produced by the above procedures. The ESR parameters for this complex are interpreted in terms of the molecular-orbital theory developed by Maki and McGarvey, and the covalent character of the metal–ligand bond is compared with that for Cu(II) (acac)2.
EPR of CO2− Defects in Calcite: Motional and Nonsecular Contributions
Authors: Hughes Robert C. , Soos Zoltan G.
Published: February 2004

The electron paramagnetic resonance (EPR) of substitutional defect CO2− radicals in single-crystal calcite has been observed between 150 and 500°K. Thermally activated CO2− hindered rotations among three equilibrium positions related by rotations of ±2π / 3 about the calcite trigonal axis average the g-tensor splittings, which are well resolved at low temperature. The EPR spectra up to 380°K, where a single, motionally narrowed line is observed at X band, are reproduced quantitatively by the modified Bloch equations if 2ωe, the CO2− reorientation rate, is given by ωe = 7 × 1010exp (−2500 / T) Hz. Above 380° nonsecular broadening due primarily to motional modulation of the g tensors was observed and identified through its angular behavior. Defect CO2− radicals in calcite provide, both experimentally and theoretically, an ideal system for analyzing the effects of molecular motions on magnetic resonance spectra.
Proton Spin–Lattice Relaxation in Paramagnetic Solid UO2·xH2O
Authors: Sharp A. R. , Pintar M. M. , Komac M.
Published: February 2004

Proton spin–lattice relaxation times of four UO2·xH2O hydrates–hydroxides have been measured at 23 Mc/sec in the temperature range from + 50 to − 140°C. The observed relaxation rate is explained as being due to reorienting water molecules and to Sz (U4+)I+ (H) coupling.
Low-Energy Electron Diffraction Studies of Surface Melting and Freezing of Lead, Bismuth, and Tin Single-Crystal Surfaces
Authors: Goodman R. M. , Somorjai G. A.
Published: February 2004

The surface structures of the (111), (100), and (110) faces of lead, the (0001), (011̄2) faces of bismuth, and the (110) face of tin single crystals were monitored up to the melting temperatures and during melting by low-energy electron diffraction. Measurements of the surface Debye–Waller factor from the different lead and bismuth surfaces indicated mean-square displacements of surface atoms perpendicular to the surface plane, 〈u⊥2〉surf, which were much larger than the bulk mean-square displacements at the melting points as predicted by the Lindemann melting model. However, the diffraction features have persisted in all of the crystal faces up to the bulk melting points of these solids. These results indicate that the surfaces remain ordered up to the bulk melting point and that the crystal surface plays an all important role in nucleating or initiating melting. Several experimental melting studies and pertinent melting models have also been discussed. The surface orientation of lead and bismuth crystals were monitored during freezing and growth from the melts. The dominant surface structures which formed upon freezing were dependent on the cooling rate. Slow rates (≤0.5°C/sec) favored the formation of the Pb(111) and Bi(011̄2) surfaces while during rapid cooling (>0.5°C/sec) the Pb(100) and Bi(0001) crystal faces have predominated.
Low-Energy Electron Diffraction Studies of Liquid Lead, Bismuth, and Tin Surfaces
Authors: Goodman R. M. , Somorjai G. A.
Published: February 2004

The intensities of elastically scattered low-energy electrons from liquid lead, bismuth, and tin surfaces were measured as a function of scattering angle and electron energy. Contour maps were constructed which display all three variables simultaneously. The intensity distribution appears to be due to uncorrelated atom scattering and thus gives directly the low-energy electron–atomic scattering factor. Intensity fluctuations due to the radial distribution function in the liquid surface could not be detected. Several scattering processes are discussed which could all increase the over-all background intensity and would render the intensity changes which are due to the liquid structure undetectable.