bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polyhedral Clathrate Hydrates. VII. Structure of the Monoclinic Form of the Tri-n-Butyl Sulfonium Fluoride Hydrate
Authors: Beurskens P. T. , Jeffrey G. A. 
Published: January 2005

The monoclinic form of the clathrate hydrate of (n-C4H9)3S+F— has 23 H2O per guest cation, as determined by a complete three-dimensional crystal-structure analysis.
The water framework consists of sheets of face-sharing pentagonal dodecahedra, separated by layers of hydrogen-bonded water molecules and anions containing large and irregular cavities in which the sulfonium ions are located. These cations are pyramidal in configuration and occupy the large cavities in pairs, with a S+–S+ nearest-neighbor distance of 3.49 Å.
Microwave Spectrum of NO2: Fine Structure and Magnetic Coupling
Authors: Bird George R. , Baird James C. , Jache Albert W. , Hodgeson Jimmie A. , Curl R. F. , Kunkle Albert C. , Bransford James W. , Rastrup-Andersen John , Rosenthal Jack 
Published: January 2005

Some 69 microwave absorption lines from three isotopic modifications of NO2 have been observed and identified. This spectrum has been completely analyzed in terms of moments of inertia, magnetic fine structure, and centrifugal distortion. The early stages of analysis were complicated by the existence of many mathematical solutions satisfying all of the data then available, but special methods have been developed for treating limited data and selecting the one solution giving the true molecular parameters.
The results obtained for 14N16O2 are: Rotational constantsA=239 868.7±11 Mc/secB= 13 000.12±0.6 Mc/secC= 12 303.45±0.6 Mc/secOdd electron expectation values with respect to〈(3r̂a2−1)/2r3〉=−1.73×1024cm−3N−nucleus〈(r̂b−ir̂c)2/r3〉=+3.34×1024cm−3|ψ(0)|2=+3.065×1024cm−3Reduced spin−rotation coupling constantsεaa/A=+0.022563εbb/B=+0.000608εcc/C=−0.007764Force constants from combined microwave−infrared datafd=11.043±0.05  mydn/Åfα= 1.109±0.01fdd=0.481±0.014fdα=2.140±0.05.The magnetic coupling constants are discussed in terms of a simplified electronic structure. The agreement between this structure and the experimental parameters is incomplete, but surprisingly good.
Approximate values for the 14N quadrupole coupling constants are obtained.
Molecular Motion in Solid 1,2-Dichloroethane
Authors: Ragle J. L. , Caron A. P. 
Published: January 2005

35Cl pure quadrupole spin—lattice relaxation has been studied in solid 1,2-dichloroethane over the presently accessible temperature range below 90°K. T1 for 35Cl changes by about three orders of magnitude between 53° and 82°K, and shows the onset of a thermally activated rate process above 63°K. The activation energy for this motion is found to be 3.93 kcal/mole. The temperature dependence of the proton T1 was also examined. At values of H0 for which relaxation is not complicated by the temperature dependent cross relaxation with the chlorine spin system, the activation energy obtained from proton T1 data agrees with that from the pure quadrupole measurements.
An anisotropic least-squares refinement was made using the 133°K. X-ray data of Reed and Lipscomb and amplitudes were assigned to chlorine atom motions. The physical picture that emerges from the combination of these data is that the amplitude of over-all motion is small below the heat capacity anomaly, relaxation being effected by a reorientation between two (or several) close minima 30° to 40° apart and separated by the above barrier. Near the heat capacity anomaly this precursor motion goes over into a large scale motion, still about the Cl–Cl axis, which has been previously described.
Distribution and Relaxation of Vibrationally Excited Oxygen in Flash Photolysis of Ozone
Authors: Fitzsimmons Robert V. , Bair Edward J. 
Published: January 2005

Absolute absorption by a sequence of bands in the Schumann—Runge series arising from oxygen molecules in vibrationally excited levels of the ground state formed by secondary processes of the flash photolysis of ozone was measured as a function of time. Measurements of bands arising from states v″ = 13 through v″ = 19 are analyzed in terms of a continuously generated initial distribution which relaxes to room temperature in single quantum steps.
The vibrational relaxation rate constants are large and are interpreted as an efficient transfer of vibrational energy between ozone and excited oxygen. The relaxation process is consistent with a single quantum step model, and if deviations from this model are real, they are secondary. Vibrationally excited oxygen is formed initially in all of the observed states. The analysis does not give the shape of the initial distribution, but in magnitude it is consistent with a normal distribution of the energy of the reaction in all of the available modes of motion. The absolute concentration of excited oxygen in vibrational states 17 and higher is relatively too small for these molecules to have a major role in the chemistry of ozone photolysis.
Statistical Thermodynamics of the Lattice Model of a Polymer Molecule
Authors: Mazur Jacob 
Published: January 2005

Introduction of a potential energy of interaction between nonbonded neighbors of a lattice-simulated random-walk polymer enables us to study the thermodynamic properties of such a polymer. When the potential energy over a given range of intramolecular separations becomes infinitely large, the free energy and the entropy per unit step can be computed directly either from the attrition data using the Monte Carlo method of generating random walks, or from the exact numerical calculations for short chains. The transition to rodlike molecular configurations and the accompanying change in the free energy per unit step can be followed by gradually extending the range of the infinitely large intersegment interactions.
Instead of using computational methods for estimating the free energy of a polymer with a hard-core potential energy, one can approximate the free energy by limiting the intramolecular interactions to the nearest neighbors only. These interactions are limited to configurations separated by the smallest number of steps needed to bring two polymer segments within a specified range of a hard-core potential energy. The free energy can be calculated analytically, using certain recurrence relations constructed for the number of permissible configurations. A comparison is made of the results obtained on the basis of nearest-neighbor approximation to the more accurate data obtained from the numerical calculations.
Kinetics of Pyrolysis of Alkyl Hydroperoxides and Their O–O Bond Dissociation Energies
Authors: Benson Sidney W. 
Published: January 2005

It is shown that group additivity rules lead to very reliable estimates (±1 kcal) for the ΔHf° of both alkyl peroxides and hydroperoxides. Previously published data for t-BuO2H are unique in showing a discrepancy of 6.3 kcal/mole from the estimated data. From the ΔHf° for the ROOH and the activation energies of pyrolysis of ROOR it is shown that the bond dissociation energies D(RO–OH) are about 42 kcal/mole for alkyl R. On this basis the direct split ROOH→RO+OH is shown to contribute negligibly to the observed kinetics of decomposition of t-BuOOH in solution. Instead the decomposition is shown to be compatible with a chain involving t-BuO2 and t-BuO radicals via the fairly well established reaction: 2 t-BuO2→2 t-BuO+O2.
The rate law for such a chain is shown to lead to 43 power dependence on t-BuO2H in good accord with the kinetic data. Absolute values of the chain rate are also in good accord with the data. It is further shown that very reactive solvents (olefins, etc.) may convert RO2 to RO directly, changing the rate to 32 order with a lower activation energy (∼28 kcal). Published data from studies of tetralin-OOH and cyclohexane-OOH are shown to be in good accord with the proposed mechanism.
Allylic hydroperoxides are discussed briefly and considered from the standpoint of good H-atom donors. The styrene induced decomposition of cyclohexane-OOH is considered in detail and a new, fast initiation step is discussed: 2φCH=CH2+ROOH→φĊH–CH2–CH2–CH2φ+RO2·.
Mechanism of the Photolysis of Ethane at 1470 Å
Authors: Hampson R. F. , McNesby J. R. , Akimoto H. , Tanaka I. 
Published: January 2005

A complete analysis of the products of the photolysis of ethane at 1470 Å has been carried out. Isotopic analyses of products of the photolysis of C2H6+C2D6 and of CH3CD3 have led to the following conclusions.
(1) It is possible to explain the data on the basis that nearly all molecular hydrogen produced in the primary process comes from the end carbon atom. CH3CD3→H2+CHDCD2*,CH3CD3→D2+CH2CHD*.The HD can be accounted for by the decomposition of excited CHDCD2* and CH2CHD*. CH2CHD*→HD+CHCH,CD2CHD*→HD+CDCD.(2) Other primary processes are CH3CD3→CH3+CD3,CH3CD3→H+D+CH2CD2.The importance of the latter, relative to the molecular elimination, is about 15:85.
(3) Propane and butane arise from ethyl radicals formed by addition of H and D atoms to ethylene.
(4) The excited state of ethane has a lifetime smaller than 10—9 sec.
Additional Collision Cross Sections for Helium Especially in the Ionized Continuum
Authors: Silverman S. M. , Lassettre Edwin N. 
Published: January 2005

Additional data on the cross sections for the 1 1S→2 1P transition are reported and compared with extended theoretical calculations. Some additional results on the 1 1S→2 1S transition are also reported.
Collision cross sections and oscillator strengths have been determined for several excitations in the ionized continuum. Oscillator strengths agree well with theory except in the vicinity of the double electron excitations. Two peaks which involve simultaneous excitation of two electrons have been observed. A discontinuity in the ionized continuum on passing through a peak corresponding to a double excitation has been observed.
Calculation of Chemical Shifts. I. General Formulation and the Z Dependence
Authors: Jameson Cynthia Juan , Gutowsky H. S. 
Published: January 2005

Explicit expressions for the paramagnetic contribution σ(2) to the nuclear magnetic shielding are derived in the valence bond and the LCAO—MO framework including d as well as p orbitals on the atom in question. A survey of published experimental data reveals a periodic dependence of the range of chemical shifts on atomic number, which is explained in terms of the paramagnetic contribution to the chemical shift and its dependence on 〈1/r3〉 for the bonding electrons.
A brief discussion is given of related but more complex periodicities in the electron coupling of nuclear spins, using the M—H coupling in Group IV hydrides as an example. It is suggested that the anisotropy in the nuclear shielding and internuclear coupling tensors may combine to give observable linewidth differences in the high-resolution NMR spectra of directly bonded nuclei of large Z.
Quasichemical Approximation and Hole Theory of a One-Dimensional Fluid
Authors: McLellan A. G. 
Published: January 2005

In a one-dimensional lattice whose sites are occupied by a mixture of A molecules and B molecules an exact formula is derived for the number of configurations for which specified numbers of A molecules have 0, 1, or 2 nearest-neighbor A molecules. A hole theory is derived for a one-dimensional fluid, approximate only to the extent that the formula for the free volume per cell may not be exact, and is applied to the case of rigid spheres. Comparison in this case may be made with the exact formulas for the equation of state and the entropy. The solution obtained by using the above exact enumeration of configurations is also com-with that obtained using the approximation of Grindlay.
In deriving the formulas enumerating configurations, it is shown that in one-dimensional lattices, the quasichemical formula is exact, apart from a factor dependent only on the total numbers of A and B molecules.
Role of Thermodynamic Activity in Rate Processes
Authors: Reiss H. 
Published: January 2005

This paper contains an investigation of the relation between rates of diffusion and evaporation and thermodynamic activity. The method of proceeding involves the use of the one-dimensional Ising model for which an exact statistical treatment can be given. The actual system treated may be thought of as an edge dislocation with adsorbed impurity atoms. As a by product, some interesting results concerning the formation of cluster and pinning points along a dislocation are derived. However, the main purpose of this work remains the investigation of the connection between rate and activity.
For the one-dimensional model (for any degree of coupling between molecules) it can be shown exactly that the rate of evaporation is proportional to the thermodynamic activity with constant coefficient and that the rate of diffusion is similarly proportional to the gradient of the thermodynamic activity with constant coefficient. These results, which have been suggested before, therefore receive theoretical justification in terms of this simple model.
Certain not-too-restrictive conditions must be applied, however. The most important of these is the requirement that every subsystem of the system be at equilibrium with respect to all variations save the one which corresponds to the rate process.
Absolute Correlation of Nuclear Spin—Spin Coupling Constants with Atomic Number. II. Couplings JX–C–H and JX—H
Authors: Reeves Leonard W. 
Published: January 2005

A precise correlation of nuclear spin—spin coupling constants JX—Y is presented for molecules where X and Y are bonded or separated by a common atom in a series. If X is a central atom surrounded by equivalent Y atoms with no lone pair electrons and X varies down a group of the periodic table a relationship (JX−Y/γXγY)12=AZX+Bis obeyed where ZX is the atomic number of the element X. A and B are experimental constants to be determined. The constants A and B have been determined from literature values of coupling constants for the series JX—H and JX–C–H where X is a Group IV atom. In future work further series will be investigated. Unknown coupling constants in a symmetrical series can be predicted accurately by use of the equation.
Deviations from the correlation are expressed in terms of a deviation parameter ``D.'' The series (CH3)4Sn, (CH3)3SnH, (CH3)2SnH2, (CH3)SnH3, and SnH4 is investigated in terms of a defined deviation parameter. Positive deviations are shown to be regular in the series for JSn–C–H indicating increased ``s'' character in the Sn–C bond and corresponding negative deviations are noted for JSn–H in this series with decreasing s character in the Sn–H bond. A relative deviation parameter is suggested for a given set of molecules with slightly distorted symmetry which has not yet been investigated fully for a series of molecules.
The correlation fails when JX—H and JX–C–H are considered and X has a low atomic number. The interpretation on the basis of hyperfine splitting constants of the single s electron in the alkali metals suggests that such deviations are expected.
Anharmonic Effects in Unimolecular Rate Theory. Vibrations and Collisions of Simple Polyatomic Systems
Authors: Harter Robert J. , Alterman Elliott B. , Wilson David J. 
Published: January 2005

The equations of motion for the following systems were integrated numerically: (1) a four-atom linear molecule with Morse function bond stretching potentials; (2) a pair of Morse function diatomic molecules undergoing collisional interaction via a Lennard-Jones 6–12 potential; (3) a Morse function linear triatomic molecule interacting with an atom via a 6–12 potential; and (4) a Morse function diatomic molecule colliding with an atom via a 6–12 potential. A commonly used approximate method of solution is also used to analyze Case 4. In all cases the systems are constrained to colinear motion. Results are presented graphically. Our conclusions are as follows:
(1) The behavior of the four-atom anharmonic molecule shows features quite different from those shown by its harmonic counterpart.
(2) Collisional interaction via 6–12 potentials does not lead to efficient transfer of vibrational energy from one molecule to another or to efficient interconversion of translational and vibrational energies.
(3) A commonly used assumption in the calculation of the efficiency of collisional vibrational activation of diatomic molecules breaks down badly at high energies.
Helium Afterglow. I. Atomic Spectrum
Authors: Collins C. B. , Robertson W. W. 
Published: January 2005

Spectroscopic investigation of a flowing helium afterglow revealed the presence of strong lines of neutral helium. An examination of the population distribution of the excited atomic states revealed the presence of a Saha equilibrium between the upper states and the free electrons indicating that the primary process of populating these states was the collisional—radiative recombination of He+. A comparison of the axial variation and pressure dependence of the intensity of the emission with the He2+ and He+ concentrations strengthened this conclusion.
Observations were made at times from 50–250 μsec into the afterglow (flow velocity ≈6×104 cm/sec) in a system having a diffusion half-life for He+ of the order of 100 μ sec, an ion density of 5×1012/cc and a maximum electron temperature corresponding to ≈0.15 eV.
Infrared Spectra of Carbon Monoxide in an Argon Matrix
Authors: Leroi George E. , Ewing George E. , Pimentel George C. 
Published: January 2005

The infrared absorption spectrum of carbon monoxide in an argon matrix shows prominent bands at 2148.8 and 2138.0 cm—1 with half-widths, respectively, 1.5 cm—1 and 3.5 cm—1. The relative intensities of these bands are extremely dependent upon a variety of experimental conditions, including sample concentration, window temperature, and deposition rates. The variability shows that CO isolated in argon absorbs at 2148.8 cm—1 and that it does not rotate. The lower frequency absorption is due to aggregates. The frequency shift of the argon-isolated CO absorption relative to that of gaseous CO shows that carbon monoxide fits tightly in the argon lattice. In contrast, the CO aggregates absorb at lower frequency than gaseous carbon monoxide. Isotopic studies using 13C16O reveal vibrational coupling of 1.1 cm—1 between isotopically identical molecules in an aggregate.
An increase in matrix cavity diameter would be needed if a stationary CO molecule begins to rotate in argon. This ``site expansion,'' which could be as much as 0.4 Å, may be an important factor inhibiting rotation.
Diffusion of Hydrogen, Deuterium, Nitrogen, Argon, Methane, and Carbon Tetrafluoride in Carbon Tetrachloride
Authors: Ross Marvin , Hildebrand Joel H. 
Published: January 2005

The diffusion coefficients of gases in CCl4 have been determined by a steady-state method as follows: first figure in each case is for 0°C, the second for 25°C; 105D in cm2 sec—1: H2—6.28, 9.75; D2—···, 7.80; N2—2.44, 3.42; Ar—2.44, 3.63; CH4—2.05, 2.89; CF4—1.44, 2.04.
The product σ2D, where σ is the molecular diameter, is a constant within the limits of accuracy of the data, including the self-diffusion of CCl4, except in the cases of H2 and D2, where it is considerably larger.
Microwave Absorption and Molecular Structure in Liquids. LVII. Interpretation of the Parameters for the Dielectric Relaxations of 2,6-Dimethylanisole and 3,5-Dimethylanisole and Dipole Moments of 17 Aromatic Compounds
Authors: Fong Francis K. , Smyth Charles P. 
Published: January 2005

The dielectric constants and losses at wavelengths of 1.25, 3.22, 10.02, 24.99 cm, and 575 m have been measured for 2,6-dimethylanisole and 3,5-dimethylanisole in benzene solutions at temperatures from 20° to 60°. Refractive indices were determined for the sodium D line at 34°. The data have been analyzed in terms of two relaxation times, the values of the short relaxation times for 3,5-dimethylanisole being consistent with the intramolecular mechanism involving the methoxy group rotation. The significance of the parameters for dielectric relaxation is discussed.
Dipole moments of seventeen compounds have been calculated for the temperature range 20°—60° from the static dielectric constants and indices of refraction in this and other papers of this series. The temperature dependence of the dipole moments of the 1,4-diacetobenzene molecule gives evidence of the hindered rotations of the acetyl groups. The presence of the two neighboring methyl groups appears to force the methoxy group out of the plane of the 2,6-dimethylanisole molecule, so that the dipole moment of 2,6-dimethylanisole is indistinguishable from that of 3,5-dimethylanisole.
Electron Spin Resonance of Amine Solutions of Alkali Metals
Authors: Bar-Eli Kedma , Tuttle T. R. 
Published: January 2005

Nuclear hyperfine structure has been observed in the electron spin resonance (ESR) absorption spectra of potassium and lithium dissolved in some alkylated amines. The four-line spectrum displayed by the potassium solutions is attributed to 39K-electron contact interaction. This interaction increases with increasing temperature. The spin density at the potassium nucleus in ethylamine solution is 3.37±0.05×1023 cm—3 at —40°C and 1.21±0.05×1024 cm—3 at 50°C. The contact interaction also decreases when methylamine is added to an ethylamine solution. This behavior is interpreted in terms of a modified view of the monomer of the theory of Becker, Lindquist, and Alder. The monomer changes its structure as its environment changes. A statistical model which relates the experimental observations to these changes is constructed.
The differences in the ESR absorption spectra observed for the three systems Na–NH3, K—EtNH2, and Li—EtNH2 are discussed, and in part, attributed to differences among the three systems in the rates of spin exchange, electron exchange, and solvent exchange. Order-of-magnitude calculations relating measured line breadths to the rates of these processes are carried out in certain limiting cases. The results of these calculations lend support to the idea that the monomer includes remote solvent molecules within its structure. The rate constant for spin exchange is shown to increase with decreasing temperature in some potassium—amine solutions.
No evidence for the solvated electron is found in the ESR spectra of K dissolved in ethylamine, or in a range of mixtures of ethylamine with methylamine. An upper limit of 10—4 is placed on the dissociation constant of the monomer. For Li in ethylamine a composite spectrum is observed under some conditions. It consists of a nine-line hyperfine pattern superimposed on a single relatively sharp line with the same g value. This sharp line is attributed to the solvated electron. The nine-line pattern is attributed to hyperfine interaction between the unpaired electron and four equivalent 14N nuclei in the Li monomer. The spin density at each 14N is 1.4±0.1×1023 cm—3, independent of temperature. Similar spectra are observed for Li dissolved in two mixed amine solvents.
The size of the monomer is discussed in terms of an expanded orbital approach. The K monomer is shown to vary between two and three times the size of atomic K. The trend toward lower percent atomic character with decreasing atomic number of the alkali metal is also discussed. Part of this trend may come about because the small atoms undergo a larger expansion in forming a monomer.