bluuebunny/crossref_metadata_2025_split huggingface dataset:
Monte Carlo Calculations. V. Three-Dimensional Study of a General Bimolecular Interaction Potential
Authors: Bunker Don L. , Blais Normand C. 
Published: January 2005

About 7500 computed trajectories were employed in a Monte Carlo study of a general interaction potential for the reactions A + BC → AB + C without activation energy. Some of the trajectories were constrained to be planar; others were determined in three dimensions.
The most prominent effects on the results (product energy and emission angle distributions) were obtained when the relative proportion of reaction energy released during reactant approach and product departure was changed, or by a change in the shape of the intermediate aggregate ABC. Of lesser importance were the sharpness of the ``corner in the reaction path,'' the rapidity (vs distance) of the kinetic energy release, and the amount of solid angle about B accessible to A.
The dimensionality of the calculation has a relatively unimportant effect on the product energy distributions, but an important one on the product emission angles. Three-dimensional emission-angle distributions are peaked near (but not symmetrically about) the angle of 90° with respect to the relative velocity vector. It is observed that the direction of the orbital angular-momentum vector is not preserved during the course of the reaction.
Gyromagnetic Factors and Spin—Orbit Coupling in Ligand Field Theory
Authors: Misetich Antonio A. , Buch Tomas 
Published: January 2005

It has been customary to compute the effect of spin—orbit coupling on the magnetic properties of transition metal ions in crystals with the expression taken over from atomic spectroscopy, although this expression is valid only in a spherically symmetric field.
In the present work, we show how the use of a spin—orbit interaction Hamiltonian derived from the Bethe—Salpeter approximation to the relativistic Breit equation for a partly covalent complex leads to a dependence of the gyromagnetic factor on the spin—orbit coupling parameter of the ligand atoms. We develop an expression of g for a d8-ion in a cubic field and apply it to the case of KNiF3. The calculated g values agree very well with experimental results.
Other differences between our expression and those found by other authors are discussed.
``Temperature Effect'' on Triplet State Lifetimes in Solid Solutions
Authors: Kellogg R. E. , Schwenker R. P. 
Published: January 2005

The phosphorescence lifetimes of several aromatic hydrocarbons and their deuterated counterparts have been measured in plastic matrices as a function of temperature.
The onset of a dark process at higher temperatures is generally observed and is believed to be a property associated with the aromatic molecule, rather than with some ``unknown'' quencher. Phonon involvement is suggested by the data.
An apparatus for accurately measuring phosphorescence decay over seven half-lives with minimal noise is also described.
Ion-Pair Exciton States and the Optical Spectrum of Crystalline Neon
Authors: Webber Stephen , Rice Stuart A. , Jortner Joshua 
Published: January 2005

The energy of the first electronic transition in crystalline neon has been calculated in the Heitler—London scheme. The calculation differs from previous work in that the effects of ionized exciton states are formulated as charge transfer states in which the excited electron resides on neighboring neons while the (1s)2(2s)2(2p5) hole remains on the central neon. Only the Γ(k=0) point in k space is considered, and spin—orbit coupling is neglected.
When correction is made for the nonstationary character of an exciton in solids, the predicted blue shift of 0.25 eV seems to be in reasonable agreement with the trend of spectral shifts of other rare-gas solids.
Oxygen Stoichiometry in the Barium Ferrates; Its Effect on Magnetization and Resistivity
Authors: MacChesney J. B. , Potter J. F. , Sherwood R. C. , Williams H. J. 
Published: January 2005

The barium ferrates comprise a series of compositions exhibiting a wide range of oxygen deficiency. Members of this series are isostructural with the high-temperature polymorph of barium titanate which is hexagonal with space group C63/mmc. Polycrystalline specimens with varying oxygen contents, i.e., Fe4+ concentrations, were prepared by equilibration at oxygen pressures ranging from 0.2 to 2400 atm. The highest oxygen content achieved was BeFeO2.95 which had lattice parameters: a=5.674 Å, c=13.645 Å. This specimen exhibited unusual magnetic properties marked by an abrupt change in magnetization at 164°K. Above this temperature the material appeared to be ferrimagnetic. The peak value of the magnetization per gram, σg, is 13.8 emu at 164°K. At lower temperatures the compound is antiferromagnetic but exhibits a small residual moment. The transition appears to be first order with a thermal hysteresis of approximately 4°C between heating and cooling curves, and is accompanied by a discontinuity in the plot of resistivity vs reciprocal temperature. X-ray diffraction patterns showed no distortion from hexagonal symmetry at temperatures below the transition.
Specimens exhibiting greater oxygen deficiency had larger lattice parameters. In general, these showed a less abrupt magnetic transition which occurred at progressively lower temperatures.
Electronic Structure of C2
Authors: Fougere P. F. , Nesbet R. K. 
Published: January 2005

The electronic structure of the C2 molecule has been studied over the range R = 1.5a0 to 8.0a0 using three different Slater-type-orbital basis sets and two different levels of configuration interaction. Analytic potential curves and computed spectroscopic constants are given for all states studied. The behavior of all eigenvalues of each CI matrix was studied extensively with excellent agreement between molecular results and those obtained by independent calculations on a pair of separated carbon atoms. The Wigner—Witmer rules were obeyed in every case.
Observed and computed spectroscopic constants were highly correlated statistically; linear relationships were determined which allow semiempirical prediction of spectroscopic constants for those states not yet observed. Using the predictions for Te, an electronic spectrum has been derived.
Scintillations and Energy Transfer in Argon—Nitrogen Mixtures
Authors: Schultz Harvey A. 
Published: January 2005

Pulse-height measurements have been made on scintillations produced by the complete stopping of alpha particles in gaseous argon, nitrogen, and argon—nitrogen mixtures. The results are correlated with the published results of spectrographic studies to derive information about energy transfer in collisions among Ar and N2 molecules.
The optical system responds to light within the spectral range 2200–6000 Å. Total pressures varied from 3.5 to 6 atm. It was observed that the pulse height is greatest for pure argon. As nitrogen is added, the pulse height decreases, then increases, and finally decreases again. From this behavior and the effect of total pressure, it is concluded that the detectable light consists of three components: (1) that emitted by argon excited directly; (2) that emitted by a nitrogen state, probably C 3Πu, excited by energy transfer from an argon state that does not emit in the detection range, apparently the lower metastable state, (3) that emitted by nitrogen excited directly. The states that emit Components (1) and (2) are quenched by nitrogen in the ground state. For three pairs of competing processes, one pair associated with (1) and two with (2), values of the product (lifetime)×(cross section)×(relative velocity) have been obtained by fitting kinetic equations to the pulse-height data. The breakdown of the products into individual factors is discussed.
Absolute Gross Ionization Cross Sections for Electrons (0.6–12 keV) in Hydrocarbons
Authors: Schram B. L. , van der Wiel M. J. , de Heer F. J. , Moustafa H. R. 
Published: January 2005

Measurements have been made of absolute gross ionization cross sections for 0.6–12 keV electrons in the following hydrocarbons: the series of alkanes from methane to hexane, a number of alkenes, butadiene, and benzene. A description of the experimental technique is given, the results are compared with those of other authors and the additivity of the cross sections is discussed.
In all cases the energy dependence of the cross sections is in agreement with the theoretical relation: the cross section σ is proportional to MI2Ee1−1 lnEe1, which gives a possibility of comparing with photoionization cross sections.
Non-Gaussian Corrections to Van Hove's Gs(r, t) for a Monatomic Gas
Authors: Desai Rashmi C. 
Published: January 2005

Non-Gaussian corrections to Van Hove's self-correlation function, Gs(r, t), are studied for real monatomic gases. Gs(r, t) is identified with the motion of a tagged atom in a dilute gas, where the motion is determined entirely by free streaming and random binary collisions with the untagged atoms. In this description, Gs(r, t) is the velocity integral of a distribution function f(r, v, t) which is initially Maxwellian, localized at the origin, and which satisfies a linearized Boltzmann equation. Spatial moments of Gs(r, t) are calculated using the Lennard-Jones (12–6) potential and the modified Buckingham exp (14–6) potential as interatomic potentials. Results are compared with those using a rigid-sphere potential and with those of Rahman from a high-density molecular-dynamics calculation. It is found that (i) the behavior of non-Gaussian corrections is qualitatively similar in all the cases, (ii) the corrections are larger for higher densities, and (iii) at low densities, the corrections increase almost by a factor of 2 when attractive forces are included.
It is also shown that the moments approach (through space-dependent BE) and the velocity correlation-function approach (through velocity—space BE) in calculating the non-Gaussian corrections are equivalent.
Mass-Spectral Studies of Kinetics behind Shock Waves. III. Thermal Dissociation of Fluorine
Authors: Diesen R. W. 
Published: January 2005

The thermal dissociation of molecular fluorine in an inert gas was investigated over the temperature range 1650°—2700°K in a shock tube coupled to a time-of-flight mass spectrometer. Rate constants were determined from both fluorine molecule and atom analysis in mixtures containing 1% F2 or less. The results are compared with the results for other diatomic molecules and the variations discussed.
A simple correlation between the orifice flow parameters and the experimental spectra is presented along with some information concerning the rather elusive boundary layer.
Fundamental Frequency Assignment of Thionyl Fluoride (SOF2)
Authors: Pace E. L. , Samuelson H. V. 
Published: January 2005

The fundamental frequency assignment of thionyl fluoride has been made from Raman spectra of the liquid at −100°C and the gas at 2.5 atm and the infrared spectrum of the gas. The sample used has a purity of greater than 99.9 mole %. The fundamental frequency assignment with the following frequency values taken from the infrared spectrum is ν1(a′), 1329.9, 1339.3 cm−1 (Fermi resonance doublet); ν2(a′), 808.2 cm−1; ν3(a′), 530.4 cm−1; ν4(a′), 377.8 cm−1; ν5(a′), 747.0 cm−1; ν6(a″), 392.5 cm−1.
The symmetric and asymmetric SF2 bending modes, ν4 and ν6, have been definitely identified in all the spectra and their symmetry characterized by polarization measurements from the Raman spectrum of the liquid.
Negative Fragment Ions from Resonance Capture Processes
Authors: Dorman F. H. 
Published: January 2005

An examination of negative fragment ions formed by resonance capture processes has been made using a mass spectrometer. It has been found in some cases that the various fragments for a particular molecule arise at the same ionizing energy, possibly by competing decomposition paths from the same state of the negative molecular ion. Other cases where the fragments do not arise at exactly the same energy may be explained by close upper energy states of the negative molecular ion.
In general the observed ionization energies are greater than those calculated from the energies of bonds broken and electron affinities. Kinetic energy measurements on some of the more abundant fragments, i.e., Cl− (CCl4, CH3·CH2Cl·CO), O− (SO2, CO2, N2O, NO), show that this excess energy is not translational.
Correlated EPR—Optical Spectra of Potassium in Ethylamine—Ammonia Mixtures
Authors: Dalton L. R. , Rynbrandt J. D. , Hansen E. M. , Dye J. L. 
Published: January 2005

Extensive electron paramagnetic resonance (EPR) studies of potassium in ethylamine—ammonia mixtures were made over a temperature range of −180° to +100°C and at varying ammonia concentrations up to 68 mole %. Hyperfine splittings, g values, linewidths, and spin concentrations were measured. Optical spectra were measured from −65° to +35°C for a number of the solutions.
Correlation of optical and EPR results rules out the assignment of the visible absorption to the monomeric species responsible for hyperfine splitting. The unusual temperature dependence of the EPR spectra cannot be explained in the light of current models, nor can the ammonia dependence be quantitatively interpreted. A model involving equilibrium between atoms and monomers quantitatively describes the temperature dependence. To explain the dependence upon ammonia concentration, it is necessary to consider two monomeric species, one fully solvated by ethylamine and the other involving replacement of ethylamine by one molecule of ammonia.
Above about 8 mole % ammonia, computer analysis of the EPR spectra showed the building-in of an extra absorption consisting of a single broad line. The intensity of this absorption relative to the four-line pattern continued to increase until the lines merged at about 25 mole % ammonia.
Under varying conditions, the optical spectra showed the three peaks characteristic of metal—amine solutions. Relative intensities were very sensitive to temperature and ammonia concentrations. At low ammonia concentrations only the visible absorption was obtained while the intermediate and infrared absorptions occurred at higher concentrations. The latter two peaks were favored by high temperature, while the visible absorption was more pronounced at lower temperatures. These spectra are discussed in the light of current models for metal—amine solutions.
Oxygen−17 Nuclear Magnetic Resonance Study of the Hydration Shell of Nickelous Ion
Authors: Connick Robert E. , Fiat Daniel 
Published: January 2005

The solvation shell of nickelous ion in aqueous solution at room temperature was observed using 17O nuclear magnetic resonance. The hyperfine interaction A between the unpaired electrons of the nickelous ion and the 17O nucleus was found to be 3.0×107 cps. The relaxation time of the electron, assuming T1e=T2e, was found to be 4.3×10−12 sec. Calculations show that the relaxation of the 17O nucleus occurs through the scalar coupling with the unpaired electrons, whereas the relaxation of the protons occurs through the dipolar coupling. Consequently, in the latter case the calculated electron relaxation time is very sensitive to the Ni–H distance, whereas in the former it is independent of the Ni–O distance, but governed by the independently determined hyperfine coupling constant. It is also pointed out that in the expression for the dipoledipole interaction between the nuclei and the unpaired electrons it is necessary to distinguish between the longitudinal and transverse relaxation times of the electrons.
The rate constant at 298°K for the exchange of water between the hydration shell and the bulk was found to be (3.0±0.3)×104 sec−1, and the enthalpy of activation 10.8±0.5 kcal/mole.
Formulation of Resonance Conditions
Authors: Coope J. A. R. 
Published: January 2005

A resonance condition is a condition on the variables of a system (external field, orientation, etc.) such that two energy levels differ by a fixed energy δ. This paper discusses the formulation of exact theoretical resonance conditions by methods which do not require knowledge of the energy levels themselves. An exact resonance condition for an n-level system can be written as an algebraic equation of degree ½n(n−1) in δ2. The determination of this equation from the characteristic equation for the energies is an old algebraic problem discussed by Lagrange and by Cayley, the formulation of the equation of differences. Relevant properties are reviewed, and polynomial and determinantal formulas are given. Application is made to a particle of spin S≦52, with a second-order tensor zero-field term, in a uniform external magnetic field.
A second approach is to construct an operator F={(K1×12−11×K2)2}, in a ½n(n−1)-dimensional space of antisymmetric two-particle states, whose eigenvalues are the squares of the differences of the eigenvalues of the Hamiltonian K. The resonance condition is then det |F−δ2I|=0. A feature of this approach is that transition intensities can be calculated directly from the appropriate eigenvector of F, without knowledge of the individual eigenvectors of K.
For a system of many levels the exact resonance condition may be very complicated, and knowledge of the resonance condition is by no means equivalent to knowledge of the resonance fields.
ESR Linewidths in Solution. III. Experimental Study of the Solvent Dependence of Anisotropic and Spin—Rotational Effects
Authors: Wilson Raymond , Kivelson Daniel 
Published: January 2005

The ESR linewidths of vanadyl acetylacetonate in diphenylmethane have been studied as a function of temperature. The results confirm the analysis made previously for the linewidths of vanadyl acetylacetonate in toluene. The major contributions arise from anisotropic g and hyperfine interactions and from spin—rotational effects. The parameter λ⅓=r/3.045 Å, where r, the hydrodynamic spherical radius of the radical, is introduced as an adjustable parameter. This one parameter is sufficient to enable the theory to explain the linewidth results in a number of solvents, but a slightly different value of λ is required for each solvent. This variation may be due to solvation effects.
Studies of deuterated vanadyl acetylacetonate in carbon disulfide indicate that neither intermolecular dipolar interactions nor unresolved proton extrahyperfine splittings contribute appreciably to the linewidth.
Studies of Zero-Field Splittings in Aromatic Molecules
Authors: Godfrey M. , Kern C. W. , Karplus M. 
Published: January 2005

The zero-field splitting parameters corresponding to exponential-orbital wavefunctions for benzene and naphthalene have been evaluated by the Gaussian transform technique. Comparison of the results obtained with and without multicenter integrals shows significant differences; in particular, an erroneous value for E in naphthalene is found if only two-center integrals are included. For the lowest triplet in benzene, the use of accurate integrals with the wavefunction of van der Waals and de Groot for the quinoid structure improves the agreement with the experimental D* value. In naphthalene, Pariser's wavefunction and accurate integrals give a D that is close to the measured result; however, the E determined from the same wavefunction is considerably too small in magnitude.
A qualitative examination of the effect of D on substitution in benzene and naphthalene is made. For benzene it is found that most substituents should decrease D or D*; only if a weak mesomeric interaction is involved (e.g., CH3) is an increase in D* expected. In naphthalene, the effect of substituents is expected to be considerably smaller than in benzene. Comparisons with the limited available data show agreement with these conclusions.
Charge-Transfer Complexes of Carbonyl Cyanide in Gas and Condensed Phases
Authors: Prochorow J. , Tramer A. 
Published: January 2005

Absorption spectra of carbonyl cyanide charge-transfer complexes with common donors were studied in gas phase and in solutions, their fluorescence spectra in n-hexane solutions at 77°K.
The general form of the absorption band is the same in the gas and liquid phases, but the gas-phase spectra show a blue shift of 2000–3500 cm−1, an intensity decrease, and a strong increase in the equilibrium constant of complex formation. The reasons of the frequency shift, the splitting of absorption bands, and the influence of complex formation on the electronic spectrum of carbonyl cyanide are discussed.
On the Melting of Copolymeric DNA
Authors: Reiss H. , McQuarrie D. A. , McTague J. P. , Cohen E. R. 
Published: January 2005

A model for DNA molecules is introduced and treated by the methods of statistical mechanics. This model takes into account the difference in bonding free energy between adenine—thymine and guanine—cytosine base pairs.
The model used is an extension of the Zimm—Bragg model for polypeptides. The partition function for a certain class (which probably corresponds to most DNA sequences) of molecules is evaluated numerically and the linear dependence of the temperature of half-denaturation on base composition is obtained, in agreement with the experimental work of Marmur and Doty. A further, previously unnoted, result is that the breadth of the transition is a function of the base composition. Comparison of the predicted broadening with available experimental data is excellent for DNA from simple organisms which probably possess only one kind of DNA molecule each. However, for complex organisms, which are known to have compositionally heterogeneous DNA, the relationship is not obeyed. This suggests the possibility of using transition breadth as a simple and rapid test for compositional heterogeneity of DNA's.
Reaction between Atomic Oxygen and Nitrous Oxide
Authors: Fishburne E. Stokes , Edse R. 
Published: January 2005

A shock tube has been employed to study the reaction between atomic oxygen and nitrous oxide in an excess of molecular oxygen. The temperature was varied from 1700° to 2300°K. The total gas concentrations ranged from 0.085 to 1.42×10−5 moles/cc. The atomic oxygen was generated by the thermal decomposition of ozone. The rate constant for the reaction between atomic oxygen and nitrous oxide is shown to be k2′+k2″ = (2.3±0.4)×1013 exp(−25 000±800/RT) cc/mole sec.
It is shown that the best fit to the experimental data is obtained when the extrapolation of the low-temperature rate constant for the reactionO+NO+M⇌NO2+M,is employed rather than the rate constant obtained through the reverse reaction and the equilibrium constant. The former rate constant is a factor of 6 greater than the latter rate constant.