bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Pressure on the Mössbauer Resonance in Ionic Compounds of Iron
Authors: Champion A. R. , Vaughan R. W. , Drickamer H. G.
Published: January 2005

The effect of pressure to 200 kbar has been measured on the Mössbauer resonance in a number of high-spin ionic ferrous and ferric compounds. The isomer shift and quadrupole splitting characterize the ionic state and spin state of iron. In general, there is a decrease in the iosmer shift with increasing pressure correspinding to an increase of electron density at the iron nucleus. This can amount to 8%—20% of the difference in isomer shift between typical ferrous and ferric compounds. The pressure effect is usually larger in ferrous than in ferric compounds, and is associated with changes in the 3d−3s shielding. The quadrupole splitting usually increases with pressure. A quantitative interpretation depends on knowledge of changes in local symmetry and of spin—orbital coupling factors, as well as local compressibility. For six of the eight ferric compounds, we observed a significant amount of reduction to the ferrous state at high pressure. This phenomenon was definitely reversible. It appears to be associated with a general tendency for the ground state of the ferrous ion to decrease in energy relative to the ligands with increasing compression. Thus, electron transfer is facilitated. Some evidence exists that strong light also reduces iron compounds. These results tend to broaden the analogy previously noted between photochemical and high-pressure reactions.
Kinetic Theory of Radiometric Photophoresis in a Knudsen Gas
Authors: Wu Yau
Published: January 2005

The kinetic theory of a small particle suspended in a Knudsen gas in which the temperature of the surface of both the particle and the boundary of the system obey arbitrary distributions has been established according to the revised law of thermal transpiration developed recently by Wu. The external force acting on the particle is mainly due to the radiometric force caused by the incident and the reflecting molecules in the absence of thermal-creep effect in this limiting regime. Several particle shapes have been considered, such as a small disk, flat plate, sphere, and cube presented in a cylinder with uniform temperature gradient in a thermal transpiration system.
Kinetic Theory of Loaded Spheres. IV. Thermal Diffusion in a Dilute-Gas Mixture of D2 and HT
Authors: Sandler Stanley I. , Dahler John S.
Published: January 2005

The Chapman—Enskog method is used to obtain estimates for the coefficients of diffusion, thermal diffusion, and thermal conductivity for a dilute gas composed of two species of loaded-sphere molecules. Calculations are presented for the case in which the load eccentricity of one of the species is vanishingly small and the mass and size of both species are identical. The results of these calculations are in agreement with the observed thermal-diffusive behavior of the D2—HT system.
Gaseous Ion Recombination Rates. IV
Authors: Fisk George A. , Mahan Bruce H. , Parks Eric K.
Published: January 2005

The rates of the bimolecular and termolecular neutralization reactions of gaseous ions generated from the thallium and lead halides have been measured. The absolute values of the termolecular rate constants are generally consistent with Thomson's theory of ion recombination, although the experimental temperature dependence of the rate constant is somewhat greater than the theory predicts. The bimolecular rate constants are consistent with what is known about the energetics and masses of the systems. A mass spectrometric examination of gaseous ion-neutral complex formation is presented.
Cross Sections for Electron-Impact Fragmentation and Dissociation Energies of the Dimer and Tetramer of Bismuth
Authors: Kohl Fred J. , Uy O. Manuel , Carlson K. Douglas
Published: January 2005

Although molecules of bismuth have been the subject of numerous studies, the investigation reported here represents the first reliable mass-spectrometric study of these molecules. First of all, this article describes a new method for handling the problem of apportionment of ion currents in mass-spectrometric analyses when both direct ionization and electron-impact fragmentation contribute comparable currents to a specific ion species. The study of the molecules Bi and Bi2 provides an experimental test of this apportionment method for the ion current of Bi+. Second, this article describes measurements of the heats of dissociation and atomization of Bi4. The results of these measurements provide the only reliable information now available on this molecule. The experimental heat of atomization of Bi4 at 298°K is found to be 139.7±1.9 kcal mole−1. Other thermodynamic data obtained for the dimer and monomer confirm the results of previous investigators.
One-Center Perturbation Approach to Molecular Electronic Energies. III. One-Electron Systems
Authors: Hauk Peter , Kim Hojing , Parr Robert G. , Hameka Hendrik F.
Published: January 2005

A previously formulated one-center perturbation treatment for electronic wavefunctions and energies is applied to the off-center hydrogen atom, the hydrogen-molecule ion, and the HeH++ ion. Two variants of the method are employed to obtain energies up to the second order. In the first, Scheme A, in order to make use of the identity (−12Δ−ζ/r) exp (−ζr)=(−12ζ2) exp (−ζr) for an arbitrary value of ζ, we take exp (—ζr) as the zero-order function with ζ chosen to minimize the expectation value of the total electronic Hamiltonian. In the second, Scheme B, we adopt as zero-order function an accurate analytical approximation to the eigenfunction of the spherical part of the Hamiltonian. Results are tabulated for several one-electron systems. For the electronic energy of H2+ ion at its equilibrium internuclear separation, we obtain −1.07975 and −1.08999 a.u. by Schemes A and B, the exact value being −1.10263 a.u.
Correlation of Ionization Probabilities with Geometric Charge Cross Sections
Authors: King A. Bruce
Published: January 2005

The previous study of the ionization probabilities has been extended to include additional high molecular weight unsubstituted polynuclear aromatic hydrocarbons. The charge distributions for these ions were calculated using Hückel molecular orbitals. These charge distributions were used to calculate a geometric charge cross section by an impact parameter approach assuming a simple classical collision model. The geometric charge cross sections were found to correlate with the molecular ionization probabilities for the unsubstituted compounds, suggesting that the relative ionization probabilities for these compounds result from purely geometric considerations.

The polymethylbenzene series was studied to determine whether the marked effect of substituent groups is purely geometric or whether additional group effects exist. It was found that a 3.3-fold greater group efficiency of methyl groups relative to the ring carbon atoms was necessary to correlate with these data. A number of nitrogen heterocyclics were also studied. The single-ring heterocyclic series showed a significant reduction of the ionization probability with nitrogen substitution. These results did not agree with the HMO calculations suggesting that ionization of the π-electron system does not play a dominant role in the threshold ionization probability for these compounds. By contrast, the quinolines and phenazine gave agreement with the geometric charge cross section due to their lower π-ionization energies.
Paramagnetic Resonance of Mn2+ in Glasses and Compounds of the Lithium Borate System
Authors: Griscom D. L. , Griscom R. E.
Published: January 2005

The paramagnetic resonance spectra of Mn2+ ions in glasses and compounds of the lithium borate system have been investigated at 9.1 and 35 GHz. The spectrum for the Li2O·4B2O3 compound is found to exhibit six very sharp hyperfine lines centered on g=3.3 when observation is made at X band, while at 35 GHz the center of the principal hyperfine sextet is seen to have shifted to g=2.0. This spectrum is interpreted by assuming a spin Hamiltonian containing crystal-field terms comparable to the Zeeman energy at X band. By means of a computed diagram it is determined that | D | /h=3.7 GHz and | E/D | =0.333. The same diagram is found useful in interpreting the ESR spectra of Mn2+ in lithium borate glasses. It is shown that in the glasses the manganese ions experience wide spreads of crystal fields, giving rise to fine-structure parameters ranging from near zero to 4 GHz or greater, with an apparent constraint favoring | E/D | ratios of approximately ⅓. It is concluded that many of the Mn2+ sites in the glasses are probably distorted versions of the site occupied in the Li2O·4B2O3 compound.
On the Use of Green Functions in Atomic and Molecular Calculations. I. The Green Function of the Hydrogen Atom
Authors: Hameka H. F.
Published: January 2005

It is customary to derive the quantum-mechanical theory of quasifree particles by means of Green-function techniques, making use of the Green function of a free particle. It is pointed out here that similar techniques can be used in atomic and molecular calculations if use is made of the Green function of the hydrogen atom, rather than the Green function of a free particle. The Green function of the hydrogen atom is derived by means of contour integrations in the complex plane, following previous work by Meixner. We also derive a slightly modified Green function which is adapted to perturbation calculations of the ground state. Both of these Green functions are obtained as expansions in terms of spherical harmonics; the radial functions are expressed in terms of confluent hypergeometric functions.
Semiempirical Molecular-Orbital Theory of Molecular Spectra. II. Approximate Open-Shell Theory
Authors: Kroto H. W. , Santry D. P.
Published: January 2005

An approximate open-shell theory, based on the CNDO method, has been developed and applied to the calculation of the excited-state molecular parameters of several small polyatomic molecules. The key feature of this theory is that it optimizes the molecular orbitals for the excited-state electron configuration. A comparison of the results of this theory with those of a virtual-orbital theory [H. W. Kroto and D. P. Santry, J. Chem. Phys. 47, 792, (1967), Paper I], which differs only in the fact that the molecular orbitals are optimized for the ground-state electron configuration, indicates that a definite improvement has been obtained. The differences between these two theories are illustrated by direct comparison of the electron densities calculated by the two theories. As is to be expected, the results show the greatest improvement for excitations between orbitals differing greatly in polarity and that the virtual-orbital theory is adequate in those cases where little change in polarity is involved.
Thermodynamic Properties of Aluminum Hydride
Authors: Sinke G. C. , Walker L. C. , Oetting F. L. , Stull D. R.
Published: January 2005

The enthalpy of formation and absolute entropy of AlH3 at 298.15°K have been measured as −2.73±0.20 kcal/mole and 7.18±0.10 cal/(mole·°K), respectively. The derived Gibbs energy of formation at 298.15°K of 11.11±0.23 kcal/mole indicates AlH3 is unstable with respect to decomposition to the elements.
Reaction of O(1D) with H2 and the Reactions of H and OH with Ozone
Authors: DeMore W. B.
Published: January 2005

The reaction of O(1D) with H2 (and D2) has been studied by photolysis of O3–H2 and O3—D2 mixtures dissolved in liquid argon at 87°K. Quantum yields of O3 decomposition and product yields (as water) based on O3 decomposed were measured both with and without added O2 as a scavenger. O(1D) reacts with H2 with zero Ea and at a rate slightly less than the previously studied O(1D)—CH4 reaction. A major path is O(1D)+H2→H+OH. H atoms from this reaction can be scavenged by added_O2 by the reaction H+O2+M→HO2+M. Neither OH nor HO2 reacts with O3 under the conditions of these experiments. By contrast, H atoms not scavenged by O2 react with O3 in a manner which leads to chain decomposition of at_least 25 O3 molecules per H atom. The proposed chain is H+O3→OH*+O2,OH*+O3→H+2O2.The symbol OH* represents vibrationally excited OH, and therefore the process is an energy chain. If the proposed mechanism is correct, OH* must be produced in the reaction of H with O3 with essentially 100% efficiency in order to account for the observed chain lengths. Also, OH* reacts with O3 at least 103 faster than with H2 under the conditions of these experiments.
Study of CH3− and OH3+ by One-Center Expansion Self-Consistent-Field Method
Authors: Joshi Bhairav D.
Published: January 2005

Single-determinant self-consistent-field wavefunctions calculated by the one-center expansion method are reported for CH3− and OH3+ molecules. The basis functions, symmetry adapted Slater-type orbitals, were all centered at the heavy nucleus. In both cases a total of 25 basis functions were used. Both of these molecules were found to be nonplanar. For CH3−, the equilibrium bond length and bond angle were found to be 2.028 bohr and 109°56′, respectively; for OH3−, these quantities were calculated to be 1.918 bohr and 110°54′. The total energy of these molecules was found to be−39.3367 hartree for CH3−, and −76.2330 hartree for OH3+. A limited basis-set calculation for planar OH3+ using 17 symmetry adapted STO's is also reported. The total energy and bond length for this case are −76.1704 hartree, and 1.826 bohr, respectively. Some other interesting features of these calculations are discussed.
Physical Properties of Aromatic Hydrocarbons. III. A Test of the Adam—Gibbs Relaxation Model for Glass Formers Based on the Heat-Capacity Data of 1,3,5-tri-α-Naphthylbenzene
Authors: Magill J. H.
Published: January 2005

The specific heat of 1,3,5-tri-α-naphthylbenzene (TαNB) was measured from 200° to 560°K with a differential scanning calorimeter. The glassy, liquid, and crystalline phases of this material were studied. The latent heat of fusion was found to be 10.14±0.14 kcal mole−1 and the entropy of fusion, 21.5±0.3 cal mole−1·deg−1. The temperature dependence of the viscosity measured by Plazek and Magill is compared with that predicted from an analysis of the Cp data according to the theory of Adam and Gibbs. The temperature dependences of the calculated and experimental viscosities diverge in the vicinity of the melting temperature where presumably space requirements necessary for molecular motions in the melt are less critical than at the lower temperatures. The viscosity temperature dependence of cooperative relaxation processes (based on configurational entropy considerations) in glass-forming liquids is applicable to TαNB over essentially the same temperature range as the well-known empirical free-volume relationships, although the Adam—Gibbs model more closely represents the data outside this range.
Transport Coefficients in the Gas Critical Region
Authors: Fixman Marshall
Published: January 2005

The free energy of a system with nonuniform density or composition is assumed to depend quadratically on the density or composition gradient. The contributions of these quadratic terms to the equations of motion are then deduced from a mechanical variational principle. The resultant equations of motion are used to discuss time-dependent correlation functions in the critical region, and to calculate the anomalous shear viscosity η′ and thermal conductivity λ′ of a gas in its critical region. For CO2, λ′ (theory) and λ′ (experiment) are in good agreement. However, η′ (theory) is very small for CO2 [38 (T—Tc)−1/2 μP], and comparison with experiment is inconclusive.
General Force Field of NF3, PF3, and AsF3 by the Combined Use of Vibrational Frequencies, Centrifugal Stretching, and Coriolis Coupling Constants
Authors: Mirri Anna M.
Published: January 2005

Possible sources of the discrepancies between zeta parameters and centrifugal distortion constants found in the attempt to determine the general force field of NF3, PF3, and AsF3 have been analyzed. Large anharmonicities on the ν2 bending modes cannot be responsible for the results obtained by other authors; the discrepancies become smaller only by assuming that the ν4 bending modes are considerably anharmonic. On the other hand, for smaller values of the bond angle in the case of PF3 and AsF3 it is possible to obtain consistency between infrared and microwave data. For a bond angle of 98° for PF3, in agreement with recent results of electron diffraction measurements, it is possible to determine a force field which gives zeta parameters and centrifugal distortion constants within their experimental accuracy even by using anharmonic vibrational frequencies. Consistency between infrared and microwave data for AsF3 is obtained for ∠FAsF=99°±1°. In the case of NF3 the structure is very accurately known and a force field consistent with all the experimental data has been determined even by using anharmonic vibrational frequencies.
Dynamic Polarization of Fluorine Nuclei in Solutions of Selected Free Radicals
Authors: Poindexter Edward H. , Stewart James R. , Caplan Philip J.
Published: January 2005

Dynamic polarization of fluorine nuclei has been examined with 14 free radicals dissolved in hexafluorobenzene (C6F6) and 1,1,1-trifluoro-2,2,2-trichloroethane (CF3CCl3). The radicals may be broadly grouped by their tendency to produce either positive or negative fluorine NMR enhancement. A large positive enhancement indicates that Fermi-contact coupling between the nucleus and the radical electron is the dominant nuclear relaxation mechanism; a large negative enhancement indicates that dipolar coupling is dominant. The correlation times for dipolar and contact relaxation components are comparable, and approximately the values expected from molecular diffusion. The intermolecular contact coupling may be transmitted by exchange polarization of bonding electrons on the fluorocarbon, or by charge transfer between radical and fluorocarbon, or by a combination of both mechanisms. Steric shielding appears to weaken the contact interaction in certain cases; but it is not the sole physical influence governing the contact coupling, nor even necessarily the most important one. The highest fluorine NMR enhancements observed at 74 G were −220 for CF3CCl3 with 2,4,6-tritertiary butyl phenoxyl, and +260 for C6F6 with 2,4,6-triphenyl pyrylyl in acetone.
Electronic Spectra and Molecular-Orbital Calculations of Dioxazines
Authors: Chen I. , Lardon M. , Weinberger L.
Published: January 2005

An iterative extended Hückel molecular-orbital calculation for the π-electron system has been carried out to interpret the electronic spectra of dioxazines. The absorption peaks in the visible have been identified as the transitions from the highest occupied orbital to the lowest empty one. It is found that the orbital energy difference contributes only about one-third of the transition energy, the rest coming from the difference in the electronic repulsion energies of the ground and the excited states. The spectra in concentrated sulfuric acid solution can be interpreted as that of a diprotonated molecule. By assuming that the effective core charges of the nitrogen atoms to which the protons are attached are increased from 1 to about 1.5 proton charge, it is possible to account for the observed red shift of the band in the visible region. The calculated transition frequencies in the visible as well as in the uv are in good agreement with the observed ones.
Molecular Beam Time-of-Flight Measurements for the Study of Metastable and Repulsive Electronic States
Authors: Freund Robert S. , Klemperer William
Published: January 2005

The time-of-flight distribution in an electrically neutral molecular beam has been analyzed, and from it the mass of the constituent molecules has been determined to an accuracy of about 5%. These experiments have been carried out on molecules in metastable electronic states, excited by pulsed electron bombardment and detected by an Auger process. Mass measurements, excitation functions, and electric deflection measurements verify that molecular beams of metastable benzene, toluene, and xylene can be formed.

Molecular dissociation of N2O and CO2 due to electron impact was observed by Auger detection of dissociation products with high translational kinetic energy. The products are identified as metastable N2 and CO, respectively.
Visible Spectra of Lithium in Inert-Gas Matrices
Authors: Andrews Lester , Pimentel George C.
Published: January 2005

A careful study of the electronic spectrum of lithium atoms deposited in solid argon, krypton, and xenon showed that isolation of the incident lithium atoms improved with increasing matrix atomic weight, decreasing lithium-atom concentration, and decreasing deposition temperature and that dimerization of the incident atoms proceeds to a major extent except in very dilute samples of xenon deposited at 4°K. The lithium atomic absorptions showed multiplet structure similar to those reported earlier for metal atoms in inert-gas matrices. The multiplet components varied in relative intensity on sample warming. Nonnearest-neighbor metal—metal atom interactions were shown to be likely contributors to the observed spectral features. The present work indicates the importance of thorough study of concentration and sample-temperature dependence before multiplet splittings can be interpreted.
Vacuum-Ultraviolet Absorption Spectrum of α,α,α-Trichlorotoluene
Authors: Kimura Katsumi , Nagakura Saburo
Published: January 2005

The vacuum-ultraviolet absorption spectrum of α,α,α-trichlorotoluene has been measured in the vapor phase by a recording vacuum-ultraviolet spectrophotometer, with which the absorption measurement has been extended down to 1600 Å. The spectrum of this compound was found to show considerably great difference in the vacuum-ultraviolet region from that of benzene in the sense that the A1g→E1u transition band of benzene splits into a doublet and a new band appears in the 1600–1700 Å region. Theoretical treatment was also carried out by calculating configuration interactions, on the assumption that electrons in a pseudo-π-molecular orbital, perpendicular to the benzene ring, formed from three C–Cl, conjugate with the π-electrons in the benzene ring. A good agreement was obtained between the experimental and the calculated results, and all the absorption bands observed in the present work have been interpreted well in terms of π→π* transition involving the intramolecular charge transfer. It has been concluded that the CCl3 group in α,α,α-trichlorotoluene has a strong electron donating character for the benzene ring.
Photoionization of Ethane, Propane, and n-Butane with Mass Analysis
Authors: Chupka William A. , Berkowitz Joseph
Published: January 2005

Relative photoionization cross-section curves have been determined for parent and fragment ions of ethane, propane, and n-butane over the photon-energy range from the ionization potential to 14.0 eV. The data have been treated to give experimental breakdown curves which are in good qualitative and fair quantitative agreement with the predictions of the statistical theory of mass spectra. The results are also compared with data obtained by charge exchange, electron impact, and photoelectron energy analysis by other workers. Heats of formation of some ions have been obtained more accurately and the ionization potential of the C2H5 radical is confirmed to be 8.4 eV. Ion-pair formation of H− is shown to occur at least for ethane and n-butane and very probably for propane.
Extended Hartree—Fock Wavefunctions: General Theory of Optimized-Valence Configurations and Its Application to Diatomic Molecules
Authors: Das G. , Wahl Arnold C.
Published: January 2005

A generalization of the extended Hartree—Fock scheme developed by the authors recently and called the method of optimized valence configurations is presented. This method continuously describes molecular formation and yields realistic potential curves, binding energies, and spectroscopic constants by accounting for the ``bonding correlation'' and relaxing the constraints of the single-determinant picture. Its adequacy for a single sigma bond was illustrated in our previous work; in this paper we present a general theory for correlating multiple shells and develop its application to diatomic molecules. The process and the general computer program developed to evaluate the best possible orbitals and mixing coefficients making up our wavefunctions have several interesting new computational features which are discussed. Results presented recently using this method are summarized.
Application of Electron Spin Resonance in the Study of Triplet States. II. Effect of Triplet—Triplet Reabsorption on Quantitative Phosphorescence Measurements
Authors: Brinen J. S. , Hodgson W. G.
Published: January 2005

Simultaneous ESR and optical measurements have been made on the rise and decay of triplet molecules for phenanthrene-d10, triphenylene, and naphthalene-d8. The effect of reabsorption of phosphorescence by triplet molecules on kinetic processes involving population and depopulation of the lowest triplet state and on φP/φF ratios is discussed.
Experimental Observations in the Potassium—Graphite System
Authors: Salzano F. J. , Aronson S.
Published: January 2005

A gravimetric Knudsen effusion technique has been developed to study the phase equilibria and thermodynamic properties of potassium—graphite lamellar compounds. Using this technique the existence of a C10K phase has been established and phase equilibria in the potassium—graphite, rubidium—graphite, and cesium—graphite systems are shown to be completely analogous. The trends in the heats of reaction of cesium—graphite, rubidium—graphite, and potassium—graphite compounds are discussed.
Internal Field and the Additivity of Bond Polarizabilities
Authors: Rowell Robert L. , Stein Richard S.
Published: January 2005

The effect of internal field on the additivity of bond polarizabilities is investigated using a dipole-interaction model. An application of the theory to the isolated ethane molecule, with the aid of an high-speed computer, has demonstrated a marked dependence of bond polarizability parameters on internal field. It is shown by comparison with experimental data that there is less variation in the average bond polarizability than in the ellipticity of bond polarizability. The results suggest that the bond polarizabilities that best fit present experimental data lie in a region in the b̄CC—b̄CH domain at least as large as b̄CC=0.51±0.03 Å3 by b̄CH=0.66±0.04 Å3 with considerable uncertainty in the ellipticity.
Analysis of the Infrared Spectra of Metal Carbonyls
Authors: Haas H. , Sheline R. K.
Published: January 2005

A simplified normal coordinate treatment of the CO stretching vibrations is applied to metal carbonyls of various complexity. Infrared data to compute force constants directly are available for the following three groups of compounds: cyclopentadienyl manganese tricarbonyl and its derivatives [CpMn(CO)3−xLx, x=0→2], the substituted nickel carbonyls [Ni(CO)4−xLx, x=1→3], and some molybdenum carbonyl derivatives [sym-Mo(CO)3L3 and cis-Mo(CO)2L4]. When there are more force constants than observable frequencies in a molecule, the assumption is made that the effects of ligands on force constants are additive. In this way, many additional frequencies are obtained while only a few new force constants are introduced. This method has been used on two additional groups of compounds: Fe(CO)5−x(PF3)x and Mn2(CO)10—x(PF3)x. Excellent agreement between calculated and experimentally observed frequencies is found in all five groups of compounds. In some cases the effective force constants obtained may be interpreted as arising from dipole—dipole interaction. The force constants are then used to calculate frequencies for 13C isotopically substituted species and good agreement with experiment is found.
Excess Thermodynamic Functions for Binary Mixtures as Calculated from the Percus—Yevick Equation for the Lennard-Jones Potential
Authors: Throop Gerald J. , Bearman Richard J.
Published: January 2005

Using the Percus—Yevick equation and the Lennard-Jones 6–12 potential for the noble gases, we have calculated the thermodynamic functions for a number of binary mixtures for supercritical isotherms and at densities up to twice the critical density. From these thermodynamic functions, we have calculated the excess functions along the isotherms as a function of density for two mixing processes, one at constant pressure and one at constant volume. The results are presented graphically but the numerical data are available from the thesis of Throop.

For the constant pressure process, we have found that the excess energy, volume, and Gibbs free energy are positive at low densities, increase with increasing density to a maximum, and then decrease to small positive or negative values at higher densities.

The excess functions for the constant-volume process, in the density and temperature ranges of our calculations, are much smaller than the constant-pressure functions for the same density and temperature. The excess energy of the constant volume process is always positive at low densities, passes through a maximum, and becomes negative at high densities. The variation with density of the excess Gibbs free energy is more complicated, and it is usually negative and decreasing with density, although at temperatures near a critical temperature, this function is positive at low densities.

For both of these mixing processes, the excess functions are not quite symmetrical functions of mole fraction, with the constant-volume excess functions being more symmetric.
Analysis of Proton NMR of s-Trioxane Dissolved in a Nematic Solvent
Authors: Cocivera Michael
Published: January 2005

The proton NMR spectrum of s-trioxane dissolved in the nematic mesophase of p,p′-di-n-hexyloxyazoxybenzene has been obtained at 80°C. Computer analysis of this spectrum indicates that s-trioxane exists predominantly in the ``chair'' conformation. This analysis also indicates that each methylene group is tilted by about 3°. That is, the OCO plane does not bisect the HCH angle. This tilt is in the direction which increases the distance between the axial protons. In addition according to this analysis, the indirect 13C–H spin—spin coupling constant is positive.
Diffusion of Cd2+ Ions in Single-Crystal Sodium Chloride
Authors: Allen C. A. , Ireland D. T. , Fredericks W. J.
Published: January 2005

The diffusion of Cd+ + in commercial NaCl single crystals has been studied over the temperature range from 275° to 500°C by a radiotracer technique from CdCl2 vapor. From measurement of the concentration dependent diffusion coefficient the association energy was extimated to be 0.38 eV at 525°C and 0.52 eV at 376°C, between 376° and 275°; the entropy indicates more complex behavior than single species of cation—vacancy association. The saturated diffusion coefficient Ds is given by Ds=2.06×10−2 exp (−21 250 cal/RT) over this temperature range.
Analysis of the Nucleation of Silver on Sodium Chloride
Authors: Kenty J. L.
Published: January 2005

The data of Walton, Rhodin, and Rollins for the nucleation rate of silver on sodium chloride is analyzed using classical nucleation theory. The difference between the activation energies for desorption and surface diffusion, ΔGdes—ΔGsd, is found to be 0.3 eV, essentially independent of the value used for γ, the surface free energy of silver. The product γ3f(θ), where f(θ) is the contact angle function, is found to be 1.24×109 erg3/cm6. With γ=1140 erg/cm2, f(θ) is 0.839 and the contact angle, θ, is 119 deg. Using values of 1100 to 1600 erg/cm2 for γ results in contact angles of 133 to 75 deg. Since a Pound plot of the data produces a straight line, it is concluded that Walton's data may be interpreted by the formalism of classical nucleation theory. The radius of the critical sized nucleus, r*, is 2 to 3 Å, typical of other nucleation data analyzed in this manner.
Mass Spectrometry at High Temperatures. XVIII. The Stabilities of the Mono- and Difluorides of Scandium and Yttrium
Authors: Zmbov K. F. , Margrave J. L.
Published: January 2005

Mono-, di-, and trifluorides of Sc and Y have been identified in the vapors over mixtures of the corresponding metals and CaF2 in Ta-Knudsen cells at high temperatures. Equilibria among these molecules and Ca and CaF have been studied by a mass spectrometer and their dissociation energies have been determined.
Internal Rotation in Liquid 1-Fluoro-1,1,2,2-Tetrachloroethane
Authors: Alger T. D. , Gutowsky H. S. , Vold R. L.
Published: January 2005

Fluorine and proton high-resolution NMR lineshapes have been observed at 56.4 and 60 MHz, respectively, for a 50 mole % solution of 1-fluoro-1,1,2,2-tetrachloroethane in carbon disulfide, between −120° and −14°C. Fluorine spin echoes were obtained at 25.27 MHz and proton spin echoes were obtained at 26.8 and 17.7 MHz. An iterative complete-lineshape-fitting computer program was used with the experimental lineshapes to obtain best-fit exchange rates for interconversion of gauche and trans rotamers. A value of 18.9 ppm was found for the fluorine chemical shift from the low-temperature high-resolution spectrum and was used to fit the lineshapes at higher temperatures, as well as to fit the observed dependence of the fluorine relaxation rate on rf pulse spacing in the Carr—Purcell experiments.

Other parameters required in the analysis, i.e., the energy difference between trans and gauche rotamers and the proton-fluorine coupling constants in each rotamer, were obtained from the temperature dependence of the proton spectrum under conditions of complete averaging (−90°−25°C). The values obtained for the coupling constants are in good agreement with an earlier determination by the same method but over a different temperature range. At −120°C the fluorine resonance consisted of a singlet and a doublet, with splittings in satisfactory agreement with the high-temperature results. The proton spin echoes at −112°C are sensitive to the proton-fluorine coupling constants, and can be calculated satisfactorily with coupling constants obtained from the high-temperature proton lineshape.

Because of the large fluorine chemical shift, four orders of magnitude of the exchange rate were measurable. Exchange rates obtained from all four sets of data fall on the same, linear Arrhenius plot, with frequency factor (7.0±0.5)×1011 sec−1 and activation energy 7.85±0.05 kcal mole−1. The frequency factor is low compared with a value computed by assuming immediate deactivation from the eclipsed transition state, but agrees with a value calculated by assuming that the molecules undergo ``free'' internal rotation before deexcitation to any one of the stable rotamers.
Time-of-Flight Investigations of Electron Transport in Some Atomic and Molecular Gases
Authors: Wagner E. B. , Davis F. J. , Hurst G. S.
Published: January 2005

The time-of-flight (TOF) method for the determination of electron-diffusion coefficients D and drift velocities w described earlier could not be used to investigate a number of gases because a Gieger—Müller counter was used for an electron detector. A new experimental apparatus using differential pumping and an electron-multiplier detector was developed to remove this restriction. Using this new apparatus, D and w have been measured for He, Ar, H2, N2, CO, CO2, CH4, and C2H4. Considerable divergence of D values from published values by the Townsend method have been obtained, indicating a fundamental difference in the methods.
Time—Correlation—Function Expressions for Linear and Nonlinear Transport Coefficients
Authors: Andrews Frank C.
Published: January 2005

Construction of a statistical-mechanical ensemble to represent a system known to be out of equilibrium is discussed. The consequences of the temperature, velocity, and chemical potential fields are formal time-correlation-function expressions for both linear- and higher-order transport coefficients. Many different forms of correlation functions are equivalent, which permits choice of the most useful for a given purpose. Onsager-type reciprocal relations appear to exist for only the linear coefficients.
Time-Correlation-Function Expressions for Nonlinear Chemical Rate Constants
Authors: Andrews Frank C.
Published: January 2005

Construction of a statistical mechanical ensemble to represent a homogeneous system not in chemical equilibrium is discussed. The consequences of the chemical driving forces are obtained as formal time-correlation-function expressions for both linear- and higher-order chemical-reaction rate constants. Onsager-type reciprocal relations appear to exist for only the linear coefficients. Implications on the validity of using thermodynamic potentials for nonequilibrium systems are discussed.
Electronic Spectra and Coordination Geometry of Nickel Centers in Liquid Mixtures of Magnesium Chloride and Potassium Chloride
Authors: Brynestad Jorulf , Smith G. Pedro
Published: January 2005

The absorption spectra of nickel centers in MgCl2–KCl mixtures of various compositions were measured from about 5–28 kK at temperatures up to 1060°C. The observed behavior was qualitatively similar to that previously reported for nickel centers in liquid LiCl–KCl mixtures and, in a general way, fits the same model.
Sum Rule for Molecular Frequencies
Authors: King W. T. , Zelano A. J.
Published: January 2005

It is shown that the sum of the squares of the fundamental frequencies of a molecule does not depend explicitly upon molecular geometry. Using this sum it is demonstrated that a set of effective Cartesian force constants which are measures of the potential environment of atoms in a molecule can be calculated with little difficulty.
Iterative Quadratically Convergent Algorithm for Solving the General Hartree—Fock—Roothaan Equations
Authors: Wessel W. Roy
Published: January 2005

A detailed numerical method has been developed for solving the most general case of the Hartree—Fock—Roothaan equations, which arise in the numerical calculation of atomic and molecular wavefunctions. The method is quadratically convergent and has been tested on a number of practical problems, including the calculation of a Hartree—Fock wavefunction for the lithium atom and the CN molecule. The generality and reliability of the method are discussed.
Hard-Sphere Solid: Pair Distribution Functions at High Density
Authors: Larsen Russell D. , Salsburg Zevi W.
Published: January 2005

The high-density form of the molecular pair distribution function for a system of rigid spheres near a face-centered close-packed configuration is calculated by a cell-cluster technique. This technique was previously applied to the estimation of the partition function at high density and to the pair distribution functions for one-dimensional rigid rods and two-dimensional rigid-disk systems. The technique is thought to be applicable as an approximation scheme for a high-density rigid-sphere solid or crystalline system. The primary object of this analysis is to compute the quantity ΩN(ζ), the average number of pairs separated between centers by a distance less than or equal to ζ. For a face-centered cubic lattice of rigid spheres the high-density expansion (V→V0) of Ω(ζ) for ζ→σ takes the form 2Ω/N=6η+bη2+cη3+···;  η≪1η=(ζ−σ)/(a−σ),where a is the distance between lattice sites and σ is the diameter of a sphere. The contributions to the constants b and c from one-, two-, and three-particle cell clusters are calculated. The expansion through third order is b=6−2.0813+1.1811=+5.0997,c=0+1.3704−4.9437=−3.5733.The implications of a net positive value of b to considerations of the stability of long-range crystalline order are indicated.
Infrared Dispersion in Methyl Iodide
Authors: Pratt H. A. , King W. T.
Published: January 2005

The refractive indices of liquid methyl iodide have been measured over the 4000–600-cm−1 range using interferometric methods. From these data the integrated intensities of most of the fundamental bands were determined and are compared with other data in the literature and with gas-phase intensities.
Vibrational Quenching of Glory Undulations in Scattering of Na from Polyatomic Gases
Authors: Kramer H. L. , LeBreton P. R.
Published: January 2005

The velocity dependence of total cross sections has been measured for the molecular-beam scattering of Na atoms from Ar, Kr, and eight polyatomic gases. The glory undulations observed for Ar and Kr agree well with other recent work. The molecular systems studied fall into three categories with regard to the appearance of undulations: (a) strong: CF4, SiF4, C2F6, and BF3; (b) weak: GeH4 and C4F8; and (c) very weak or absent: C(CH3)4 and CF3Cl. It seems plausible that damping of the undulations occurs when the polarizability of the molecule changes appreciably during a relatively slow vibration. A semiempirical quench parameter q is defined for molecules of the form ABn to give a relative measure of the effectiveness of spherically symmetric vibrations in damping the glory undulations. q is proportional to (1) an estimate of the derivative of the polarizability with respect to the symmetric stretching coordinate; (2) a semiclassical measure of the vibration amplitude; and (3) the inverse of the symmetric stretching frequency. The values of q for molecules studied here are in qualitative agreement with our experimental results.
Vibrational Spectra and Force Constants for Nitrosyl Fluoride and 15N and 18O Species
Authors: Jones Llewellyn H. , Asprey Larned B. , Ryan Robert R.
Published: January 2005

From infrared absorption studies in the gaseous phase, the fundamental harmonic vibrational frequencies have been determined for 16O14NF, 16O15NF, 18O14NF, and 18O15NF. Two quite different force constant solutions were obtained in a general quadratic valence force field. With the aid of centrifugal distortion constants and the inertial defect, it was possible to select the true force constant solution: FNO=15.9 mdyn Å−1; FNF=2.3 mdyn Å−1; Fα=1.8 mdyn·Årad−2; FNO,NF=2.5 mdyn Å−1; FNO,α=0.27 mdyn rad−1; FNF,α=0.20 mdyn rad−1. These force constants were converted to those of a modified Urey—Bradley force field and a general quadratic central force field. It is shown that the latter gives unreasonable force constants. Interaction displacement coordinates were calculated and correlated qualitatively with valence-bond theory.
Convective Contribution to Total Conductivity in Fixed-Charge Ionic Systems
Authors: Manning Gerald S.
Published: January 2005

A theory is presented for the contribution of convective (electro-osmotic) flow to the total electric current in fixed-charge ionic systems. Although the approximations used are severe, no assumption is made as to the geometrical structure of the system; in particular, the existence of capillary pores is not assumed. The result shows that convective flow contributes to the retardation effect of the fixed charges on the mobility of the counterions; moreover, the contribution is such as to suggest the possibility of measuring, in isolation from other factors, the dependence of the counterion self-diffusion coefficient on interactions with the fixed charges.
Kinetics of Energy Transfer from the Triplet State in Rigid Solutions
Authors: Kellogg R. E.
Published: January 2005

Assuming the energy transfer is dependent on the inverse nth power of the donor—acceptor distance (1/Rn), Inokuti and Hirayama derived an expression for the observed decay of donor emission, using flash excitation of a random solid solution, I=I0exp[−t/τ−(2/π1/2)Γ(1−3/n)γ(t/τ)3/n], where τ is the measured lifetime in the absence of an acceptor, γ is linear in acceptor concentration, and n is the distance dependence parameter. This reduces to the Förster result for a dipole—dipole interaction where n=6. The extent to which we can determine n experimentally will allow us to measure the ``purity'' of the dipole—dipole interaction presumed to induce the transfer.

To this effect, a detailed kinetic analysis of triplet—singlet energy transfer in rigid solution has been carried out using triphenylene-d12 as the donor and rhodamine B as the acceptor. A computer fit of the decay data to the above expression was carried out with a nonlinear regression routine that determined I0, γ, and n simultaneously using the least-squares criterion. Over the concentration range of γ=0.26 to 2.1, a value n=6.05±0.17 was determined, indicating no measurable derivation from the behavior predicted by Förster.

In principle, this procedure could be used to identify a quadrupole transition in the acceptor, where a value of n=8 would signify a dipole—quadrupole interaction.
Rotational Relaxation in Polar Gases
Authors: Zeleznik Frank J.
Published: January 2005

Rotational collision numbers for pure polar gases have been calculated by classical mechanics. For the purposes of the calculation, a polar molecule was taken to be a point dipole imbedded in a hard core and the interaction between molecules was confined to a plane. A perturbation calculation correct through third order gave the result Zrot(1, T)Zrot(2, T0)=γ1γ2(μ2μ1)4(M1M2)(TT0)3[η2(T0)η1(T)]2h11(2, T0)h11(1, T),where the numbers 1 and 2 label chemical species, γ is the number of rotational degrees of freedom, M the molecular mass, μ the dipole moment, T the absolute temperature, T0 a reference temperature, and η the viscosity. The function θ11 has as its argument (16π/5)(I/M)η(πMkT)−1/2, where I is an average moment of inertia. The theoretical results show that the rotational collision number increases for increasing temperature and decreasing dipole moments and moments of inertia. The dipole moment and moment of inertia dependence is in qualitative agreement with experiment. Since the experimental temperature dependence is somewhat in doubt, no conclusion can be made concerning the correctness of the theoretical temperature dependence.
Single-Configuration Wavefunctions and Potential Curves for the Ground States of He2, Ne2, and Ar2
Authors: Gilbert T. L. , Wahl Arnold C.
Published: January 2005

Potential energy curves are calculated for He2, Ne2, and Ar2 using single-configuration wavefunctions constructed from molecular orbitals. In one set of calculations the molecular orbitals are chosen to be linear combination of Hartree—Fock orbitals of the separated atoms (the LCAO-MO approximation). In another set of calculations SCF molecular orbitals are obtained by the expansion method (the SCF—MO approximation) with basis functions taken from SCF calculations on the separated atoms. SCF—MO's for He2 are also calculated with basis functions which have been ``optimized'' by varying the parameters in the exponents until the total energy is a minimum. Potential curves for these different calculations are compared among themselves and with experiment.
Photoionization of the CF3 Free Radical
Authors: Lifshitz Chava , Chupka William A.
Published: January 2005

The photoionization cross-section curve in the wavelength region 1420–860 Å was obtained for the CF3 radical. The shape of the onset of the ionization efficiency curve shows that the adiabatic ionization potential of the radical is much lower than the vertical one, and hence that the equilibrium configuration of the CF3+ ion is very different from that of the molecule. Autoionization probably accounts for some of the ionization near threshold. The ionization potential obtained was I.P.(CF3)=9.25±0.04 eV. The photoionization efficiency curve for aniline was determined in the process of calibrating a nickel photoelectric detector.