bluuebunny/crossref_metadata_2025 huggingface dataset:
Moment Equations for Vibrational Relaxation Coupled with Dissociation
Authors: Heims S. P.
Published: January 2005

Sets of equations for the moments of the vibrational energy distribution for a diatomic species in a gas are derived, considering simultaneous dissociation and vibrational relaxation. In first approximation a set of two coupled equations are obtained, one for the number of diatomic molecules and the other for the vibrational energy per molecule. The latter contains two correction terms to the Bethe—Teller equation, due to the coupling. The next higher approximation gives three coupled equations, in which the second moment (dispersion) of the distribution function is taken into account. In these equations the dissociation rate ``constant'' is a function of both the average vibrational energy and the second moment. The recombination process is described by three constants which define the over-all rate, the average vibrational energy, and the dispersion about the average energy of just recombined molecules. The starting point in the development is a gain—loss equation for occupation numbers of vibrational levels. The assumption of harmonic vibrations is used. In order to close the set of equations in any order of approximation, those terms involving higher moments are determined by application of a general method due to Jaynes which gives the least biased estimate in view of the information contained in the moments considered. Consideration of the steady state in first approximation leads to Onsager reciprocal relations and, in second approximation, to more complicated relations.
Anharmonic Effects in Unimolecular Rate Theory. Dynamics of a Rotating Anharmonic Triatomic Molecule
Authors: Hung Narl Chow , Wilson David J.
Published: January 2005

The motion of a rotating linear symmetrical triatomic molecule is investigated by numerical integration of the equations of motion. Harmonic- and Morse-function bond potentials are used, and vibrations of large amplitude are studied. Contrary to one of the usual approximations of unimolecular rate theory, the coupling between rotational and vibrational energy in the anharmonic system is quite strong when the vibrational energy is large (of the order of the dissociation energy); rotational energy is roughly 50% effective in inducing dissociation.
Nuclear Relaxation of N14 by Quadrupole Interactions in Molecular Liquids
Authors: Moniz W. B. , Gutowsky H. S.
Published: January 2005

Radio-frequency pulse methods have been used to measure the N14 spin-lattice relaxation time in 25 molecular liquids, with the N14 in several types of groups. For eight of the compounds, microwave or pure quadrupole resonance measurements of the N14 quadrupole coupling constant were combined with our T1 results to give values for the correlation time τq describing the molecular reorientations which govern T1. These values for τq at 25°C are about an order of magnitude shorter than reorientational correlation times calculated from the viscosity and molecular radius using the Debye—BPP approach. For the other compounds, τq was estimated and used with the observed T1 for N14 to predict values of the quadrupole coupling constant. The temperature dependence of T1 was observed for nine compounds, leading to activation energies for molecular reorientation of 1.4 to 3.2 kcal/mole and inverse frequency factors τq0 of 2×10—14 to 9×10—14 sec. The temperature dependence of the proton T1 was observed in CH3CN and it is compared with that of N14. It appears that the relaxation of some quadrupolar nuclei affords considerable promise for studying molecular reorientations in liquids and for separating diffusional and rotational processes. These possibilities, as well as that of estimating quadrupole coupling constants not otherwise readily accessible, are discussed.
Theoretical Interpretation of Force Constants
Authors: Salem Lionel
Published: January 2005

The quantum-mechanical definition of the force constant k of a diatomic molecule is given. The three main approaches to the calculation of force constants—the perturbation approach, the virial theorem approach, and the strict Hellmann—Feynman approach—are discussed. Several new expressions for k are derived. In particular the Hellmann—Feynman theorem leads to a general expression for k in terms of the charge density ρ and of the change δρ/δR with internuclear distance R. It is also possible to relate the force constant to the quadrupole coupling constant (eqQ) of either nucleus by the formula k=ZA[qA+43πρ(A)− ∫  (∂ρ/∂XA) (cosθA/rA2) dτ].The experimentally observed relation k≅qH for diatomic hydrides is then interpreted in terms of the properties of the charge density of these molecules.
Magnetic Susceptibility of Diatomic Molecules
Authors: Karplus M. , Kolker H. J.
Published: January 2005

A variation—perturbation method is presented for the calculation of the magnetic susceptibility tensor χ from a single-determinant ground-state wavefunction for a 1Σ molecule. The diamagnetic contribution χd is obtained directly by first-order perturbation theory and the paramagnetic contribution χp is determined by extremizing a functional corresponding to the second-order energy in an external magnetic field. By an appropriate choice of perturbation function and zero-order Hamiltonian, the functional is expressed in a relatively simple form requiring only one-electron matrix elements. The importance of employing Hartree—Fock functions as the zero-order solution is stressed and an analysis given of the order of the errors in the variation—perturbation treatment. Explicit comparisons of the present method with simplified forms of the variational procedure demonstrate that the neglect of electron exchange or use of an ``average'' perturbation function can introduce significant errors in the results.

Calculations are made of the magnetic susceptibility tensor for a series of diatomic molecues. Ransil's minimal basis set functions serve as unperturbed wavefunctions and a four-term polynomial is used to represent orbital perturbations in the second-order treatment. The values obtained for χd, χp, and χ of H2, Li2, N2, F2, LiH, HF, LiF, and CO are presented. Comparisons with the available magnetic data for these molecules demonstrates that the variation—perturbation method is a useful tool for ab initio susceptibility calculations. For the more difficult paramagnetic term χp, criteria for the convergence of the second-order energy are discussed and applied to the molecules considered. The magnetic anisotropy (Δχ=χ⊥—χ∥) is evaluated theoretically for hydrogen and found to be in reasonable agreement with experiment. The inaccuracies arising in Δχ values for more complex species (through differencing in a purely theoretical treatment) are overcome by the inclusion of rotational magnetic moment data to obtain relatively reliable results. To examine the effect of the vibrational state on the susceptibility of a molecule, an exploratory calculation is made for LiH, which demonstrates that small sut significant deviations from the equilibrium-distance value are to be expected. Finally, some indication is given of the additional experimental and theoretical work that is required in this field.
Comprehensive Spectroscopic Investigation of Polynuclear Aromatic Hydrocarbons. I. Absorption Spectra and State Assignments for the Tetracyclic Hydrocarbons and their Alkyl-Substituted Derivatives
Authors: Becker Ralph S. , Singh Indra Sen , Jackson Elizabeth A.
Published: January 2005

The absorption spectra have been investigated and state assignments made for benz (a) anthracene, benzo (c) phenanthrene, chrysene, triphenylene, naphthacene, and pyrene. In addition, these results are compared with existing theoretical and experimental studies. The identification of electronic transitions have been made for all monomethyl drivatives of the above hydrocarbons except for naphthacene. The study extends over the spectral region 16 500–52 500 cm—1. In addition, vibrational analyses are proposed for all cases considered. Certain dimethyl-, alkyl- and fluorosubstituted derivatives have been studied. General spectral characteristics are included.
Thermodynamic Properties of a Monatomic Hydrogen Gas at High Temperatures
Authors: Oppenheim Irwin , Hafemann Dennis R.
Published: January 2005

A study is made of a gas in which the internal and intermolecular degrees of freedom are not separable. Expressions for the partition function and thermodynamic properties are derived for a gas of monatomic hydrogen. The number of bound states of the system is limited by interactions between the hydrogen atoms. The potentials of interaction of hydrogen atoms with protons, electrons, and other hydrogen atoms are estimated, and the partition function is evaluated at a series of densities from 10 to 10—5 amagats. The occupation numbers of bound states and the percent ionization are changed significantly by considering atom—atom and atom—proton interactions, but the value of the partition function is only slightly changed relative to that calculated by considering only the effect of interatomic forces upon the single-atom energies.
Fermion Behavior of One-Dimensional Excitons
Authors: Chesnut D. B. , Suna A.
Published: January 2005

The problem of noninteracting singlet excitons (of the Frenkel variety) in a one-dimensional crystal is investigated using a second-quantization formalism. It is shown that only for the nearest-neighbor approximation in the open linear chain does the many-body solution result in independent quasiparticles exhibiting exact fermion behavior. The choice of coordinates for a general problem is briefly discussed and an expression is given which allows one to expand any (second-quantized) operator in terms of a set of either exact boson or fermion creation and annihilation operators.
On the Theory of Torsional Vibrations of (CH3)3—X Type Molecules
Authors: Möller K. D. , Andresen H. G.
Published: January 2005

Torsional vibrations of (CH3)3—X type molecules having C3v point group symmetry have been analyzed by using a periodic potential function, and by taking into account mutual top—top interaction terms. The energy scheme was calculated by perturbation methods, and the selection rules have been derived. For the high-barrier case, two allowed transitions from the ground state to the first excited state can be predicted.
Absorption Spectrum of Cs in the Presence of Isomeric Hydrocarbons
Authors: Jefimenko Oleg , Exton Reginald J.
Published: January 2005

The satellite bands and the shifts of the Cs lines in the spectra of Cs—hydrocarbon mixtures were studied. The hydrocarbons were isomers of butene (butene-1, butene-2, isobutene), butane (n-butane, isobutane), pentane (n-pentane, isopentane, neopentane), and hexane (n-hexane, 3-methylpentane, 2,3-dimethylbutane, neohexane). Four different types of satellite bands were observed. The shifts of high members of the Cs principal series extrapolated to relative density 1 were 41, 47, 47, 48, 55, 58, and 61 cm—1 for n-pentane, isopentane, n-hexane, 3-methylpentane, 2,3-dimethylbutane, neopentane, and neohexane, respectively. The results of simultaneous measurements of the band positions and shifts of high members of the Cs principal series suggest that the positions of the high-intensity red satellite bands are determined primarily by the effective cross sections of foreign-gas molecules for slow electrons rather than by the mass or polarizability of these molecules as thought previously.
Molecular, Crystal, and Valence Structures of B18H22
Authors: Simpson Paul G. , Lipscomb William N.
Published: January 2005

A three-dimensional x-ray diffraction study of single crystals has yielded the molecular structure of B18H22. The molecule is centrosymmetric, has six bridge H atoms, and has the geometry of two decaborane-14 cages sharing a common B9–B10 edge. The space group is Pccn, and there are four molecules in a unit cell having dimensions a=10.844, b=12.107, and c=10.803 Å.

The valence structure has been studied in the two-center and three-center resonance approximation, which is comparable in its predictions to the Hückel molecular orbital method in the other boron hydrides. The charge distribution in B18H22 has been obtained from an analysis of the 6506 resonance structures.
Investigation of the Bonding of Iron-Group Ions in Fluoride Crystals. II
Authors: Hall T. P. P. , Hayes W. , Stevenson R. W. H. , Wilkens J.
Published: January 2005

This paper describes an ESR investigation of the bonding of iron-group ions with the configurations d6(Fe2+) and d7(Fe+, Co2+, Ni3+) on cubic lattice sites in the crystals LiF, NaF, and KMgF3. To aid the analysis of the bonding of d7 ions, the optical absorption spectrum of Co2+ was measured in LiF and KMgF3. A discussion is given of the effects of lattice dimensions and the charge state of the impurity ion on the bonding parameters.
X-Ray Study of Critical Opalescence in Argon
Authors: Thomas J. E. , Schmidt Paul W.
Published: January 2005

The small-angle x-ray scattering from argon has been investigated at the critical pressure and at four other pressures over a range of temperatures above and below the liquid—vapor transition temperature for each pressure. For three of these pressures the angular distribution of the scattering was analyzed in terms of the Ornstein—Zernike theory of critical opalescence and found to be in good agreement with this theory. Values of the short-range correlation length and relative values of the isothermal compressibility were determined for each condition of pressure and temperature. For the conditions for which compressibilities can be found by numerical differentiation of the isotherms of Michels, Levelt, and De Graff, the compressibility values calculated by numerical differentiation are in good agreement with those obtained from the scattering curves.
Electrostatic Contribution to the Energy of the Hydrogen Bond in Hydrogen Fluoride Dimer. I. Utilizing Approximate Evaluation of Multicenter Integrals
Authors: Howard Bentz B.
Published: January 2005

The electrostatic energy of the hydrogen bond has been calculated for a pair of hydrogen fluoride molecules using the Ballinger wavefunction for the isolated molecules, and the approximations of Mulliken and Löwdin for estimating the overlap population between two centers of charge distributions. The calculations were carried out for variable angle between the axes of the two molecules, keeping the hydrogen bond distance fixed at 3.086 a.u., and taking the bonding hydrogen atom in line between the two fluorine centers. It is concluded that the electrostatic energy terms arising from the penetration of the charge clouds are very important. These terms are dominated by the penetration of the nuclear and electronic charges associated with the fluorine atom into the charge cloud of the hydrogen atom.
Direct Determination of Scattering Phase Shifts from Differential Cross Sections
Authors: Brackett J. W. , Mueller C. R. , Sanders W. A.
Published: January 2005

As the first step in the analysis of molecular beam scattering data, a computational method has been developed for the determination of the asymptotic phase shifts from the differential cross sections. The phase shifts were represented by a linear combination of two Gaussian functions and an exponential function, and the parameters of this empirical function were determined from a least-squares fit of the observed cross sections. The computational time required was less than 10 sec per iterative cycle on the IBM 7090 computer. In order to obtain a unique fit of the positive phase shifts, it was necessary to use data from a range of scattering angles wide enough to include at least the first minimum and second maximum of the differential cross sections.
EPR Spectra of SH, SD, and SO Radicals in the Gaseous State
Authors: McDonald C. C.
Published: January 2005

A 12-line EPR spectrum at a microwave frequency of 8.850 kMc/sec has been observed in the field region from 7400 to 7700 G that is attributed to electric-dipole transitions between Zeeman levels of the J=32 rotational state of gaseous SH(2Π32). Average Λ splittings and proton hyperfine splittings were 190 G and 5.4 G, respectively. The SH radicals were produced in the spectrometer cavity by adding H2S at the cavity entrance to a stream of discharge-dissociated H2O vapor flowing through the cavity. When H2S was added to a stream of dissociated D2O, an additional spectrum attributed to SD(2Π32,J=32) was observed. Another species in these gaseous systems gives rise to a third EPR spectrum that is believed to result from electric-dipole transitions between Zeeman levels of different rotational states of SO(3Σ).
Densities and Molar Volumes of Electrolytes in Mixed Solvents
Authors: Padova J.
Published: January 2005

The densities of Na2SO4, MgSO4, MnCl2, NaOCOCH3, KOCOCH3, Mg(OCOCH3)2, and Ba(OCOCH3)2 have been determined at 25°C in ethanol—water and acetone—water mixtures. All the salts have been shown to follow Root's equation. The apparent molar volumes have been calculated and results interpreted in terms of ion solvent interactions and solvated molar volumes as function of the bulk dielectric constant of the solvent.
Shock-Wave Integrated Intensity Measurements of the 2.7-Micron CO2 Band between 1200° and 3000°K
Authors: Breeze J. C. , Ferriso C. C.
Published: January 2005

A shock-wave technique is described which provides a means of measuring the infrared integrated intensity of molecular bands at elevated temperatures. The total band emission from the high-temperature gas region existing between the end plate of a shock tube and the reflected shock wave was measured using a rapid-response infrared detector. The total emission of the band is obtained as a function of pathlength as the reflected shock wave recedes from the end plate. The initial concentration, shock velocity, and reflected-shock pressure were measured and the final conditions of the test gas were calculated from the normal shock relations.

The method has been used to measure the absolute intensity of the 2.7 μ band of CO2 (ν1+ν3 and 2ν2+ν3) in the temperature region 1200° to 3000°K. The shock-heated samples were produced in a 4% CO2—96% Ar mixture using helium as a driver gas. To ensure adequate pressure broadening at high temperatures for this weak band and yet to remain within the optically thin region, the measurements were made at approximately 2.5-atm total pressure, 0.1-atm CO2 partial pressure, and CO2 optical path lengths up to a maximum of 0.8 cm·atm. The observed integrated band intensity of the 2.7-μ CO2 band increases by a factor of approximately 2.5 in going from 300° to 3000°K. This variation with temperature is discussed in terms of a simple harmonic-oscillator model.
Linear Antiferromagnetism in the Organic Free Radical 1,3-Bisdiphenylene-2-Phenyl Allyl
Authors: Hamilton W. O. , Pake G. E.
Published: January 2005

Specific-heat and electron and nuclear magnetic resonance data have been taken on the free radical 1,3-bisdiphenylene-2-phenyl allyl at temperatures down to 1.3°K. The electron resonance spectrum of a single crystal of this free radical has also been examined. The data indicate magnetic ordering along linear chains below 6°K with a coupling between chains at 1.73°K. Impurities are demonstrated to play a large part in the magnetic behavior. The data are compared with theoretical predictions concerning linear antiferromagnetism.
Generation of Charge Carriers in Organic Molecular Crystals through Multiple Exciton Interactions
Authors: Kearns David R.
Published: January 2005

In this paper we have examined theoretically three possible mechanisms of photoconduction in organic molecular crystals: namely, the production of charge carriers as the result of (i) the interaction of two singlet excitons, (ii) the interaction of two triplet-state excitons, and, (iii) the interaction of a singlet-state exciton with a triplet-state exciton. Depending upon illumination conditions and crystal purity we find that any one of these three may be the dominant mechanism for the generation of free carriers by a multiple exciton process. In general, however, the singlet—triplet mechanism is shown to result in higher steady-state carrier concentrations than either the double—singlet mechanism [S. Choi and S. A. Rice, J. Chem. Phys. 38, 366 (1963)] or the double—triplet mechanism. The Franck—Condon factors have been formally included in the calculation of the generation rates and it is clear that they could greatly reduce the magnitude of the rates calculated using purely electronic wavefunctions. In attempting to relate the theoretical predictions with the experimental measurements, the effect of triplet—triplet annihilation has been included. The effect of impurities which could act as energy traps has been considered. It is concluded that trapping of the excitation energy at impurity sites adversely affects the generation of carriers, and when present will lead to photocurrents which vary exponentially with temperature. Such a temperature dependence would be predicted for any carrier generation mechanism which requires the transport of electronic excitation energy through the crystal.
Some Topics in the Theory of Fluids
Authors: Widom B.
Published: January 2005

It is shown how certain thermodynamic functions, and also the radial distribution function, can be expressed in terms of the potential energy distribution in a fluid. A miscellany of results is derived from this unified point of view. (i) With g(r) the radial distribution function and Φ(r) the pair potential, it is shown that g exp (Φ/kT) may be written as a Fourier integral, or as a power series in r2 the terms of which alternate in sign. (ii) A potential-energy distribution which is independent of the temperature implies an equation of state which is a generalization of a number of well-known approximations. (iii) The grand partition function of the one-dimensional lattice gas is obtained from thermodynamic arguments without evaluating a sum over states. (iv) If in a two-dimensional honeycomb (three-coordinates) lattice gas fr(r=0, 1, 2, 3) is the fraction of all the empty sites which at equilibrium are neighbored by exactly r filled sites, then at the critical density the values of all four of the f's as functions of temperature follow from previously known properties of this system; in particular, at the critical point, f0 = 3/8+5√3/24, f1 = 1/8+√3/24, f2 = 1/8—√3/24, f3 = 3/8–5√3/24.
Field Desorption of Carbon Monoxide from Tungsten
Authors: Swanson Lynwood W. , Gomer Robert
Published: January 2005

The field desorption of CO from tungsten has been investigated at three coverage intervals, corresponding to heats of adsorption of 0.7, 1.90, and 3.30 eV, respectively. Potential-energy curves of adsorption have been obtained for these cases which seem to correspond to different binding states of CO on tungsten. Polarization corrections have relatively little effect on the shape of the curves but do shift them outward by small amounts. General agreement with the theory of field desorption proposed previously seems to hold and could be confirmed, in particular, for the energetics of desorption and for adsorbate tunneling. The discrepancy between the calculated values of the pre-exponential terms of the desorption rate constant and the very low values found experimentally at low temperature in this and other cases seems to have no simple explanation and is blamed on entropy effects. The general reasonableness of the potential curves and that of the CO–W spacings obtained indicates that the ion—metal interaction can be expressed by an image potential to distances of the order of 2 Å.
Morphological Development of Aluminum Oxide Crystals Grown by Vapor Deposition
Authors: Sears G. W. , DeVries R. C.
Published: January 2005

The growth of aluminum oxide crystals by vapor-phase chemical reaction has been studied at an elevated temperature. The growth process was observed microscopically in progress. The results are of particular interest since they pertain to the growth of an anisotropic crystal structure. The course of morphological development was consistent with crystal growth theory.
ESR Study of Free Radicals Produced in Irradiated Cyclopentadiene and Cyclohexene: The Cyclopentadienyl and Cyclohexenyl Radicals
Authors: Ohnishi Shun-ichi , Nitta Isamu
Published: January 2005

The ESR spectra of irradiated cyclopentadiene and cyclohexene were measured at various temperatures. The spectra showed motional narrowing on raising temperature and the free radicals were identified from analysis of the narrowed spectra. Cyclopentadiene showed a well-resolved sextet spectrum of 5.6-G splitting, which was assigned to the cyclopentadienyl radical. Cyclohexene gave a spectrum consisting at least of 26 lines, which can be reasonably attributed to the cyclohexenyl radical by assuming appropriate hyperfine constants.
Structure of Oriented Sodium Metaphosphate Glass Fibers
Authors: Milberg M. E. , Daly M. C.
Published: January 2005

The structure of oriented sodium metaphosphate glass fibers has been investigated employing cylindrical distribution functions obtained from the x-ray scattering pattern. Although this method has rarely been used, it is the only sound one available. The difficulties in interpreting the functions were eased somewhat by the use of difference, rather than complete, cylindrical distribution functions. The former are usually less cluttered with spurious peaks than are the latter.

The results indicate that the NaPO3 fibers are made up of long chains of PO4 tetrahedra, and that the axes of these chains have a strong preference for lying along the fiber axis direction. Both the general appearance of the distribution functions and the results of normal distribution function calculations agree with the existence of a very high degree of orientation in the fibers. The locations of sharp peaks on the functions suggest that the individual PO4 tetrahedra have shapes similar to that found in crystalline RbPO3. In the latter material the average in-chain P–O distance is 1.62 Å and the average out-of-chain distance is 1.46 Å. Best agreement with the experimental distribution functions is obtained with a puckered version of a planar chain, in which each tetrahedron is tilted relative to the chain axis through two mutually perpendicular angles of 20° to 30° and the intratetrahedral angles are near 110°.

The high effective radial resolution obtained in the difference cylindrical distribution functions, as a result of the angular resolution, suggests that the simplified cylindrical distribution function will be a useful way to study the structures of orientated amorphous polymer fibers.
Experimental Oscillator Strength of OH, 2Σ+→2Π, by a Chemical Method
Authors: Golden D. M. , Del Greco F. P. , Kaufman F.
Published: January 2005

The line absorption method is used to determine the oscillator strength of OH, 2Σ—2Π, in a discharge-flow system. OH is made quantitatively by the rapid reaction H+NO2→OH+NO. f values for the unresolved Q1—4 doublet and P1—2 line are calculated from the measured absorption of these lines. On the well-supported assumption of Doppler-shaped emission and absorption lines and on the basis of experimental information on the translational temperature of emitting and absorbing OH molecules, a band oscillator strength, f00, of 7.1±1.1×10—4 is reported for the (0, 0) band. Application of corrections for thermochemistry and for vibration—rotation interaction to reported f values leads to improved agreement and suggests an f00 near 8×10—4.
Isotopic Thermal-Diffusion Factor of Argon
Authors: Paul R. , Howard A. J. , Watson W. W.
Published: January 2005

An extensive investigation of the isotopic thermal-diffusion factor α0 of argon in the mean temperature range 127° to 653°K has been carried out with a four-tube swing separator employed previously in similar work with helium and neon. Because of a linear variation of α0 with T in the low-temperature region, the mean temperature T̄ = (T2—T1)/ln(T2/T1 ) has been used instead of the arithmetic mean of T1 and T2. This temperature assignment has been verified by varying the temperature gradient significantly. The experimentally determined value of α0 increases from 0.068±0.015 at T̄ = 127°K to 0.485±0.035 at T̄ = 653°K, in fair agreement with earlier experiments. Just as for helium and neon, a Lennard-Jones 12:6 potential model fails to account for the observed temperature variation of argon α0 values. The best fit for an exp—six force model occurs for α = 17 and ε/k = 176°K. Using these force parameters, the best fit with experimental viscosity data yields rm = 3.535 Å. These parameters are then used to calculate the diffusion coefficient and second virial coefficient for argon. There is fair agreement with the experimental values of these other transport coefficients.
Transpiration Study of Magnesium Oxide
Authors: Alexander C. A. , Ogden J. S. , Levy A.
Published: January 2005

Vapor densities of magnesium-bearing species over magnesium oxide were determined by the transpiration method. The MgO reacted with water vapor present in the carrier gas to form gaseous Mg(OH)2. The standard free energy of formation in calories per mole is given over the temperature range from 1660° to 2010°K by the equation ΔGf° = —168 600+49.8T cal mole—1. Under conditions where water vapor is minimized, a second vaporization process becomes predominant. It is concluded that this process is the congruent sublimation of MgO. A second-law treatment of these data indicates ΔH298 = 142.5+3.3 kcal mole—1 while a third law treatment yields 145.1±0.1 kcal mole—1 using a 1Σ ground state for MgO. The ground state for gaseous MgO would appear to be Σ and most likely 1Σ. A value of 93 kcal mole—1 was obtained for D0 for MgO based upon the second- and third-law treatment of the data.
Relationship between Spectral Shifts and Solubility for Naphthalene in Compressed Nonpolar Gases
Authors: King A. D. , Robertson W. W.
Published: January 2005

The changes in frequency of the 1Lh and 1Lb absorption bands of naphthalene have been measured as a function of diluent density for naphthalene dissolved in various compressed nonpolar gases. A relationship is shown to exist between a thermodynamic internal energy derived from previously reported solubility measurements and the spectral shifts. This internal energy is also compared to estimates of internal energy based on dispersion force theory.
Sensitivity of Exchange-Reaction Probabilities to the Potential-Energy Surface
Authors: Wall Frederick T. , Porter Richard N.
Published: January 2005

Classical-mechanical calculations were made to study exchange attending collinear collisions of H+H2 using a potential-energy surface proposed earlier by the authors. It was found that the reaction probability is unity for all energies in a certain bounded range, and zero elsewhere. The lower and upper bounds are dependent upon the position of the saddle point of the potential-energy surface and the relative masses of the atoms. No long-lived collision complexes were encountered. The vibrational energies of the final molecules were also found to depend strongly upon the position of the saddle point.
Electron Diffraction Study of the Molecular Structures of Sulfur Tetrafluoride (SF4) and Thionyl Tetrafluoride (SOF4)
Authors: Kimura K. , Bauer S. H.
Published: January 2005

The molecular structures of SF4 and SOF4 in the gaseous state were determined by electron diffraction using sector-microphotometer data. Both molecules were confirmed to have trigonal bipyramidal structures (C2v symmetry), with two nonequivalent sets of F–S bond distances. The bond lengths, in terms of the center of gravity parameter, rg, and the bond angles are as follows: For SF4:rg(equatorial S–F)=1.542±0.005 Å,rg(polar S–F)=1.643±0.005 Å,∠(equatorial F–S–F)=103.8∘±0.6∘,∠(polar F–S–F)=176.8∘±2.5∘.For SOF4:rg(equatorial S–F)=1.539±0.005 Å,rg(polar S–F)=1.602±0.005 Å,rg(S–O)=1.422±0.008 Å,∠(equatorial F–S–F)=122.8∘±1.8∘,∠(polar F–S–F)=182.8∘±0.7∘.

The polar F–S–F angles are measured along an arc which bisects the equatorial FSF angle.
Boltzmann Equation and Inverse Collisions. II. A Model for Association and Dissociation
Authors: O'Toole James T. , Dahler John S.
Published: January 2005

The techniques of classical nonequilibrium statistical mechanics are applied to a gas which exhibits two distinct types of molecular interaction. The first allows chemical bonding to the extent of dimer formation; the second, impulsive in nature, provides a tractable mechanism for three-body energy exchange. Hydrodynamic equations are derived for each of the two quasicomponents. A formal description of the reaction kinetics is developed which leads to a perturbation method for obtaining corrections to a theory based on an assumption of uniformly canonical distributions.
Survey of the Spectra of the Divalent Rare-Earth Ions in Cubic Crystals
Authors: McClure Donald S. , Kiss Zoltan
Published: January 2005

The rare-earth ions may exist in the divalent state in suitable host crystals such as CaF2. All of the trivalent ions from Ce to Yb (and probably also La) are reduced in situ to the divalent state in CaF2 by gamma irradiation. The spectra of most of these ions show that the ground and first few excited states derive from fn configurations, but the weak absorption due to these is masked at higher energies by strong broad bands of the parity-permitted fn→fn—1d transitions. The excitation energy of these spectra have been calculated in a first approximation as the energy difference between the ``Hund rule,'' single-determinant states of the configurations fn—1d and fn. This procedure satisfactorily accounts for the remarkable variations in the excitation energy in passing from one ion to the next in the series with the exception of Gd++, Ce++, and Tb++. Gd++ probably has f7d for its ground configuration, while Ce++ and Tb++ are borderline cases. The spectral structure probably arises chiefly from the crystal-field splitting of the d orbital, since each ion in CaF2 has a similar spectrum, and the spectra change drastically in sites of other than cubic symmetry.
Investigation of Early Ionization Processes in Shocked Xenon
Authors: Hacker D. S. , Bloomberg H.
Published: January 2005

Measurements of ionization rates in noble gases have been of considerable interest, with much of the recent experimental work performed at very high temperatures with shock-tube techniques. As a result, there have been several conflicting theories formulated to trace the history of ionization phenomena. A major difficulty has been the problem of precisely identifying the earliest stage of the ionization process. Since the probability of atom—atom collisions leading to ionization is small, another source of energy sufficient to promote the necessary early stage of the process must be provided. It appears that under conditions of relatively low temperatures, as in weak shock waves, the assumption of a photoexcitation mechanism of the gas is plausible. Biberman and Veklenko have suggested such a mechanism for the production of excited states of rare gases in shock waves. This mechanism has been used to explain the initial shock-front ionization. The nature of the processes responsible for visible emission at the shock front, which has been designated as impurity radiation, appears to be a result of the transfer of energy from the excited rare-gas atoms to the impurity molecule.

Spectral observations of the shock zone in xenon have been made in a carefully outgassed shock tube (10—6 mm Hg). The absorption spectrum is typical of molecular fragments of carbon (C2) which has been shown earlier to be localized in the region of 4500 to 4960 Å. Calcium or sodium, usual alkali impurities, were not observed in any measurement. The emission appeared to be predominantly from the xenon and possible carbon impurities.

Microwave absorption measurements were made normal to the shock front. By use of a plasma model which assumes a linear varying electron density, microwave attenuation in the region of cutoff was measured to determine the rate of ionization and the plasma collision frequency. The observed ionization rate was of second order with respect to xenon pressure for the temperature range of 4000° to 9000°K. The observed activation energy was 1.60 eV±0.2. This was the approximate activation energy for the following reactions in xenon:  Xe*+Xe⇒Xe2++e−or Xe*+C2⇒XeC2++e−}collision of the second kind.The experimentally determined rate expression for ionization is given as ki=3.58×1014T12exp[−1.6±0.2/kT]cm3moles−1sec−1.Radiation at the shock front appears to be best described by the excitation of impurity or by the dissociation of Xe2 as suggested by Tanaka: Xe*+C2 ⇒Xe+C2*,collision of second kind,C2*(A3π) ⇒C2(X3π)+hν,radiative transition,XeC2++e−⇒XeC2*⇒XeC2+hνXe2++e− ⇒Xe2* ⇒Xe2+hν}dissociated recombination (visible emission).
Polyhedral Clathrate Hydrates. V. Structure of the Tetra-n-butyl Ammonium Fluoride Hydrate
Authors: McMullan R. K. , Bonamico M. , Jeffrey G. A.
Published: January 2005

The structure of (n-C4H9)4N+F—·32.8 H2O is tetragonal, of space group P42/m with the unit-cell dimensions a=23.52 Å and c=12.30 Å. The clathrate host structure is similar to that of the (n−C4H9)4N+C6H5−COO−·39.5 H2O and consists of a tetragonal pseudo body-centered arrangement of groups of five face-sharing pentagonal dodecahedra interlinked by tetrakaidecahedra and pentakaidecahedra. Whereas in the benzoate there are four salt molecules per unit cell, in the fluoride there are five. This difference in the number of guests accommodated in essentially the same host structure is possible because the four tetrakaidecahedra occupied by the benzoate groups are available for the four alkyl groups of the additional cation. In the fluoride hydrate, four of the cations have the central N+ atom at the fourfold positions (j) and that of the fifth is disordered over the twofold position (f). Thus the structure has lower symmetry than the benzoate hydrate, which is P42/mnm by reason of the disorder of the four cations over eightfold positions.

The fluoride ions replace water molecules in the host lattice, with F—···O distances of 2.80 to 2.87 Å forming an anionic host lattice. As in the other clathrate hydrate structures of this type, some of the pentagonal dodecahedra which are distorted by the presence of the cations are occupied by a guest species presumed to be additional water molecules.
Polyhedral Clathrate Hydrates. VI. Lattice Type and Ion Distribution in Some New Peralkyl Ammonium, Phosphonium, and Sulfonium Salt Hydrates
Authors: Beurskens Gezina , Jeffrey G. A. , McMullan R. K.
Published: January 2005

The crystal data and preparation are discussed for 22 new peralkylated ammonium, phosphonium, and sulfonium salt hydrate crystals. Although these structures have not been determined in detail, it is possible to classify them according to the host-lattice type and to draw conclusions by analogy with known structures concerning the order and disorder in the distribution of the cations and anions with respect to the water lattice.
Photoconduction in Charge-Transfer Complexes
Authors: Akamatu H. , Kuroda H.
Published: January 2005

The photoconduction in the solid molecular complexes of pyrene with tetracyanoethylene, bromanil, and 1,3,5-trinitrobenzene has been observed. In each case, the intrinsic photoconduction arises with photon energy a little higher than the energy gap for the excitation to the conduction state, while its spectral region does not coincide with the charge-transfer band in the electronic spectrum. It has been suggested that in these ``weak'' charge-transfer solid complexes, the excited state associated with the charge-transfer band cannot contribute to conduction, and an energy diagram for the electronic state in these crystals has been proposed.

A structure-sensitive secondary photoconduction has been observed in the spectral region around the threshold of the charge-transfer band, which is likely due to the interaction between charge-transfer excitons and imperfections in the crystal.
Some Thermodynamic Aspects of the Glass Transition: Free Volume, Entropy, and Enthalpy Theories
Authors: Goldstein Martin
Published: January 2005

The well-known equation of Davies and Jones for the pressure dependence of the glass transition temperature, dTg/dP=Δβ/Δα=TgVΔα/ΔCp, depends on two independently testable hypotheses: that a one-parameter description of the excess thermodynamic functions is adequate, and that the glass transition occurs when some one thermodynamic function reaches a critical value. It is concluded on the basis of experimental data available that dTg/dP<Δβ/Δα and that dTg/dP=TgVΔα/ΔCp, which suggests that a one-parameter description will not do, and that either the entropy or the enthalpy rather than the free volume determines the transition. An examination of specific-heat data leads to the conclusion that the only way to reconcile the above results with the WLF equation is to assume that enthalpy per molecular unit rather than free-volume fraction is the determining variable.
Theory of the Single-Ion Heat of Transport in Nonisothermal Electrolytic Solutions
Authors: Bearman Richard J. , Vaidhyanathan V. S.
Published: January 2005

The single-ion heat of transport is determined formally by considering the Soret effect in dilute electrolytic solutions. Specifically considered is the contribution of ion—ion interactions. That part of the contribution depending on nonequilibrium distribution functions is shown to vanish through order κ by means of a direct determination of the nonequilibrium distribution functions. In determining the distribution functions, the statistical mechanical basis of the classical isothermal limiting laws is first considered. They result from the Liouville equation when a superposition approximation for ion triplets is introduced and ensemble-average ion—solvent forces are treated phenomenologically according to the linear laws of the thermodynamics of irreversible processes. The superposition approximation is equivalent to the usual Debye—Hückel approximation at equilibrium. The nonisothermal case is treated by using the same superposition equation and generalizing the phenomenological ion—solvent force equations. The results agree with those of Helfand and Kirkwood who considered a reciprocal isothermal experiment, and therefore they constitute a direct verification of the heat—matter Onsager reciprocity relation.
Raman Study of Zinc Chloride Solutions
Authors: Irish D. E. , McCarroll Bruce , Young T. F.
Published: January 2005

Raman studies of aqueous solutions of zinc chloride indicate the presence of Zn(H2O)6++, ZnCl(aq)+, linear ZnCl2(aq), and ZnCl4(H2O)2= in aqueous solutions less concentrated than ten molar. Ion concentrations are reported as functions of zinc chloride molarity. The tetrachloro complex dominates for stoichiometric zinc chloride concentrations between ∼0.5 to ∼10M with significant concentrations of ZnCl+ below ∼4M zinc chloride and ZnCl2 above ∼4M. For stoichiometric solutions greater than 10M, the evidence suggests a polymeric species or aggregate with structural characteristics similar to those found in the crystal.
Isotropic Proton Hyperfine Interaction and Properties of the CH Bond
Authors: Higuchi Jiro
Published: January 2005

The proton hyperfine splitting (hfs) of aromatic hydrocarbon radicals or ions was investigated in connection with the properties of the CH bond. The calculation was performed for the CH fragment with the use of the first-order perturbation. The result is in general agreement with observation only if MO's of minimum energy are used, but it is not valid for the homopolar CH bond. The dependence of the hfs on the bond angle is very small. In most molecular species, the value of the semiempirical constant Q defined by McConnell1 is between —20 and —30 G, unless there is large spin density on the carbon atom adjacent to the proton in question.
Magnetic Properties of a New Class of Highly Conductive Organic Solids
Authors: Kepler R. G.
Published: January 2005

Magnetic susceptibility measurements have been carried out on a wide variety of organic salts based on the anion radical of tetracyanoquinodimethan (TCNQ). A correlation between the magnetic and electrical properties has been observed. Salts which exhibit the higher conductivities also exhibit a temperature-independent paramagnetic contribution to their susceptibility, but in the less conductive materials, the odd electrons associated with the TCNQ anion radicals are paired in quasimolecular states consisting of a singlet ground state and a triplet state lying slightly above the ground state. These results are interpreted as indicating that in the higher conductivity salts the odd electrons, which are presumably the charge carriers, are degenerate as in a metal.
Fluorescence of Europium Thenoyltrifluoroacetonate. I. Evaluation of Laser Threshold Parameters
Authors: Winston H. , Marsh O. J. , Suzuki C. K. , Telk C. L.
Published: January 2005

A crystalline form of europium thenoyltrifluoroacetonate (EuTTA) with an mp of 164°—166°C has been prepared. Measurements of absorption and emission spectra, fluorescence lifetime, and relative quantum yield have been made on solutions of EuTTA in acetone, toluene, and ethanol. From these measurements the required laser threshold concentration of excited EuTTA molecules in acetone at room temperature for a laser cavity with an optical loss of 1%/cm is calculated to be 2.3×1017 cm—3.
Equilibrium Composition of Sulfur Vapor
Authors: Berkowitz J. , Marquart J. R.
Published: January 2005

Sulfur vapor, as well as the vapors in equilibrium with solid HgS, CdS, ZnS, FeS, SrS, and CaS have been studied mass-spectrometrically. The results indicate the presence of all possible Sn molecules between S2 and S8 in measurable concentration between room temperature and the boiling point of sulfur. Negligible concentrations of S9 and S10 are also observed. The high-temperature experiments are most concordant with the ``high'' value of D0(S2), about 4.4 eV. For the reactions (n/8)S8→Sn(n=2, 3, 4, 5, 6, 7), the enthalpy changes at ∼400°K are ΔH2=23.5 kcal/mole, ΔH3=22.5 kcal/mole, ΔH4=20.5 kcal/mole, ΔH5=14.3 kcal/mole, ΔH6=6.2 kcal/mole, and ΔH7=5.7 kcal/mole.
Gaseous Metaborates. I. Mass-Spectrometric Study of the Vaporization of Lithium and Sodium Metaborates
Authors: Büchler Alfred , Berkowitz-Mattuck Joan B.
Published: January 2005

The vaporization of lithium and sodium metaborate has been studied mass spectrometrically. The vapors of these compounds consist principally of the monomers LiBO2 and NaBO2, with some dimer and a very small amount of trimer also present. Heats of vaporization of the two metaborates and of boron oxide were determined with an effusion cell designed to give reliable second-law heats. The values obtained are: B2O3(l)=B2O3(g)ΔHv,1300=93.6±3 kcal mole−1LiBO2(c)=LiBO2(g)ΔHs,1060=79±3 kcal mole−1LiBO2(l)=LiBO2(g)ΔHv,1160=70±3 kcal mole−12 LiBO2(g)=Li2(BO2)2(g)ΔH1120=−67±3 kcal mole−1NaBO2(c)=NaBO2(g)ΔHs,1070=73±3 kcal mole−12 NaBO2(g)=Na2(BO2)2(g)ΔH1070=−53±3 kcal mole−1.

The composition and the dimerization energies of the metaborate vapors thus resemble those of the alkali halides, hydroxides, and cyanides.
Gaseous Metaborates. II. Infrared Spectra of Alkali Metaborate Vapors
Authors: Büchler Alfred , Marram Edward P.
Published: January 2005

The infrared spectra of gaseous lithium, sodium, and cesium metaborate have been examined between 2500 and 225 cm—1. Bands were observed at 1935 and 600 cm—1 for LiBO2, Li6BO2, NaBO2, and CsBO2, and at 2000 and 610 cm—1 for LiB10O2, NaB10O2 and CsB10O2. The two frequencies have been assigned to a stretching and bending vibration, respectively, of the metaborate BO2 group. Their similarity to the corresponding frequencies of the ion BO2— suggests a bond structure of the form M+(O—–B+–O—) for the alkali metaborates. The variation of the bonding of the BO2 group in a series of related compounds and the absence of alkali—anion stretching frequencies from the spectra of both alkali metaborates and cyanides are also discussed.