bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Kinetic Theory of Dense Fluids. IX. The Fluid of Rigid Spheres with a Square-Well Attraction
Authors: Davis H. T. , Rice Stuart A. , Sengers J. V.
Published: January 2005

By the use of methods previously introduced, we discuss in this paper the statistical theory of a dense fluid of molecules interacting with a square-well potential. The argument proceeds via the derivation and solution of a modified Boltzmann equation. The theory is used in two ways:(a) to provide a test of the theory proposed by Rice and Allnatt; (b) to estimate the attractive force contribution to the transport of momentum and energy in a real fluid.

The approach of Rice and Allnatt is shown to give a friction coefficient in agreement with experiment for liquid argon.

The presence of the attraction has a marked effect on the transport of momentum and energy and the square-well-model fluid gives a surprisingly accurate representation of the properties of liquid argon. The computed thermal conductance and self-diffusion coefficient are in agreement with experiment: κ(calc) 1.33×102 erg/g−sec−deg,κ(obs) 1.26×102erg/g−sec−deg,D(calc) 1.81×10−5cm2/sec,D(obs) 1.84×10−5 cm2/sec,and the temperature dependence of κ/η is in qualitative agreement with the observed temperature dependence of this ratio.
Note on Hyperfine Interaction Tensors in ESR Spectra
Authors: Schreurs Jan W. H. , Kivelson Daniel
Published: January 2005

A theory of linewidths in the ESR spectra of radicals with several interacting equivalent nuclei is developed for the case in which the total nuclear spin angular momentum for the entire group of interacting nuclei is not a good quantum number.
Delayed Fluorescence of Acriflavine in Rigid Media
Authors: Lim E. C. , Swenson G. W.
Published: January 2005

Fluorescence of extremely long duration has been observed from acriflavine in rigid media. The decay rate of the emission is strongly dependent upon such factors as temperature, duration of excitation, and concentration of the sample. From these observations, as well as others, the delayed fluorescence is interpreted as due to excited singlets formed by recombination of ions and trapped electrons produced initially by photoionization of the dye.
Charge Distributions in Positive Ions and Ionization Energies of Conjugated Hydrocarbons
Authors: Hoyland J. R. , Goodman Lionel
Published: January 2005

The π-electron ionization energies of conjugated hydrocarbons and charge distributions of the resulting positive ions are examined utilizing closed and open shell SCF theory with deformation of σ and π orbitals. Ionization energies: Koopmans' theorem is shown to be invalid for conjugated hydrocarbons to the extent of about 2–4 ev, the major breakdown occurring through the Σ and Π deformation effects and not through reminimization of the ionic configuration. It is shown that the sigma description is not the same for both the ground and ionized states. A first-order correction to the Σ-framework energy of the ion can be obtained by removing a π electron from a single carbon atom. Very good agreement is obtained between the calculated and observed onization potentials (average discrepancy 0.1–0.2 ev). Justification is given for the so-called ``ω technique'' for the calculation of ionization energies by the Hückel procedure in that this method contains deformation corrections which approximate those derived in this work. Charge distributions: Both deformation effects and reminimization of the ionized state are important in consideration of the charge distribution in the ions. It is shown that certain sites of negative charge density are predicted in positive ions by the reminimization procedure, and that this is both a reasonable and necessary consequence due to the form of the ionic Hartree-Fock Hamiltonian. The wave functions, and consequently the charge distribution, calculated by the ω technique, are shown to be poor approximations of the ionized state Hartree-Fock eigenfunctions.
Self-Diffusion of Lead-210 in Single Crystals of Lead Selenide
Authors: Seltzer Martin S. , Wagner J. Bruce
Published: January 2005

Self-diffusion of Pb-210 in lead selenide has been studied in an inert atmosphere as a function of temperature (over the range 400–800°C) and defect concentration introduced by doping. Diffusion measurements were performed on specimens of p-type PbSe containing 1018 holes per cc and on specimens doped with ½ mole % Bi2Se3 to give n-type material with 5×1019 electrons per cc or ½ mole % Ag2Se which resulted in p-type material containing 1019 holes per cc.

Experimental results show that doping with Bi2Se3 decreased diffusivities as compared with undoped PbSe, whereas addition of Ag2Se caused diffusion coefficients to be increased. The diffusion activation energies were 0.83 ev, 1.61 ev, and 0.55 ev for undoped PbSe, bismuth doped PbSe, and silver doped PbSe, respectively.

From a consideration of the possible reactions for establishment of equilibrium between solid PbSe and the gas phase, C. Wagner has derived the following equations: [Pb2+ (interstitial)]∝ pPb/[excess electrons]2,[cation vacancy]∝[excess electrons]2/pPb,where the value of pPb is to be treated as a constant under the conditions of this experiment.

From a consideration of the point defects introduced by doping and an evaluation of diffusion data applied to the above equations, it is concluded that Frenkel defects predominate in lead selenide and that diffusion of lead in this compound occurs predominantly by an interstitial mechanism under these conditions.
Intensity of the v2 Infrared Band of Methane
Authors: Herranz J.
Published: January 2005

An expression for the absolute intensity of the v2 infrared ``forbidden'' fundamental band of methane-type molecules has been obtained and the observed intensity of the methane band has been quantitatively explained. The expression, in principle, allows one to decide on the sign of the ratio of the bond moment of the molecule to its bond moment derivative. For the methane molecule this ratio was found to be negative.
Electron Spin Resonance and Internal Rotation of the Methyl Group in the CH3Ċ(COOH)2 Radical
Authors: Heller Chonon
Published: January 2005

The investigation of an x-irradiated single crystal of methyl malonic acid by means of electron spin resonance (ESR) reveals that the two main species produced by the radiation are the CH3Ċ(COOH)2 and CH3ĊH(COOH) radicals. An analysis of the ESR spectra of CH3Ċ(COOH)2 obtained at room temperature, 77°K, and 4.2°K indicates that: (a) the three methyl protons are equivalent, and the principal values of their hyperfine coupling tensor are 75.4 (along the Ċ–CH3 bond), 68.8 and 68.6 Mc; (b) the isotropic component of the coupling tensor (and, therefore, the spin density on the methyl protons) is positive; (c) the methyl group executes nearly free rotation about the C–C bond at 4.2°K.
Charge Distribution in Negative Ions and the Electron Affinities of Conjugated Hydrocarbons
Authors: Hoyland J. R. , Goodman Lionel
Published: January 2005

It is shown that the analog of Koopmans' theorem for the calculation of electron affinities yields poor results for conjugated hydrocarbons due mainly to neglect of atomic orbital deformation effects. Reminimization of the molecular ionic wave function yields a sizable increase of the electron affinity in several cases. It is further shown that the ground state MO's give a poor description of the charge distribution in the negative ion. In particular, reminimized MO's yield sites of positive charge in some negative ions.
Infrared Spectra and Vibrational Assignments for cis and trans 1,2-Difluoroethylenes: HFC=CFH, HFC=CFD, and DFC=CFD
Authors: Craig Norman C. , Entemann Eric A.
Published: January 2005

Infrared absorption spectra from 4000 to 250 cm-1 are given for the cis and trans 1,2-difluoroethylenes, including the isotopically substituted species, HFC=CFD and DFC=CFD. A complete assignment of the fundamentals for the cis series is obtained including observed bands for all but the A2 modes. In the trans series eight fundamentals are given for HFC=CFD and seven each for HFC=CFH and DFC=CFD. Of these the Bg modes and the lowest-frequency Bu modes are calculated.
Scattering Matrix and Chemical Reaction Rates
Authors: Smith Felix T.
Published: January 2005

The connection between macroscopic bimolecular chemical reaction rate expressions and microscopic collision properties is usually based formally on collision cross sections. An alternative formulation based on spherical waves, or on classical trajectories classified according to the initial angular momentum L of the collision, leads to a direct connection between reaction rates and the scattering matrix, from which the collision cross sections can always be derived. Because of the ease of expressing the scattering matrix for many-body collisions, this formulation can be used for three-body or many-body reactions, as well as for two-body ones. For a gas otherwise in thermodynamic equilibrium, the rate coefficient for a reaction taking n+1 reactant molecules in internal states collectively labeled by i to n′+1 products in internal states j is kij(n+1)=(h22πμkT)3n/2h−1 ∫ 0∞ ∑ γ ∑ γ′|Siγ,jγ′(E)|2exp(−E/kT)dE.Here μ is the common reduced mass, μn ∑ k=1n+1mk= ∏ k=1n+1mk,and γ and γ′ are the 3n—1 or 3n′—1 orbital quantum numbers of ordinary and generalized angular momentum which, together with E, specify the initial and final relative motion of the particles. The close connection between the scattering matrix and the lifetime matrix makes it possible to bring out effects, such as those characterizing unimolecular reactions, depending on the lifetime of a metastable intermediate.
Parent-Ion Recapture in Gases
Authors: ElKomoss S. G. , Magee J. L.
Published: January 2005

Very early measurements of conductivity in irradiated gases demonstrated the importance of preferential recombination of charges, i.e., recombination of positive and negative charges before they escape their mutual field. An important part of preferential recombination is the parent-ion recapture of electrons. No theoretical treatment of this process appears to have been given.

In this paper the mechanism of parent-ion recapture of electrons in gases is considered in some detail. Two models are used: one applicable at low and intermediate pressures and the other applicable at high pressures. It appears from this study that essentially all preferential recombination can be explained satisfactorily in terms of parent-ion recapture of electrons. A brief consideration of solids is also given and it is shown that parent-ion recapture is to be expected in irradiated semi-conductors which have small mobility of charge carriers.
Shock Tube Determination of Dissociation Rates of Hydrogen
Authors: Rink John P.
Published: January 2005

The rate of dissociation of hydrogen was determined in noble gas-H2 mixtures over the temperature range 2800° to 5000°K by density measurements in incident shock waves. An x-ray densitometer was used to measure the density profile produced by the shock wave and the dissociation process. The experimental density profiles were compared with calculated profiles which extended from the shock to the equilibrium region to determine the dissociation rates. The three reactions considered were H2+M⇌ lim krkd2H+M,where M can be Xe, H2, and H. The values and error limits of kr=kd/K for these third bodies in cc2 mole—2 sec—1 are 1.5×1018T—1±30%, 3×1018T—1±50%, and 1×1019T—1±50% respectively. The third body efficiencies of H2 and H relative to Xe are 2 and 7. Kr and Ar were found to have the same efficiency as Xe in the hydrogen dissociation process. The temperature dependence of the recombination coefficient could not be determined in these measurements, so the T—1 was arbitrarily selected for all species. These rate coefficients are approximately a factor of 2 larger than the corresponding numbers for oxygen.
SCF-LCAO-MO Wave Function for the 1Σg+ Ground State of C3
Authors: Clementi Enrico , McLean A. D.
Published: January 2005

The 1Σg+ ground state wave function for the C3 molecule is computed in the SCF-LCAO-MO approximation. Four wave functions derived from different basis sets of Slater type orbitals (STO's) are compared. Subject to the limitations of our available computer program we have investigated the effects of expanding a minimal basis set by adding extra functions which should allow for polarisation effects, and changes in optimum orbital exponents of atomic orbitals in the molecular environment.
Correction of Electron Diffraction Data for Failure of the Born Approximation
Authors: Bonham R. A. , Ukaji T.
Published: January 2005

A simple objective method for correcting electron diffraction data for the effects of the imaginary part of the atomic electron scattering factor is presented. Expressions for the phase shifts of the form: η(s,z)=a(z)+b(z)s+c(z)s2,valid for s up to 50 at 40 kv and z up to 98 are given. This analytical form was chosen since it provides a close fit (less than 2% average deviation) to tabulated values of η(s, z), calculated by Ibers and Hoerni, over the useful range of s and thus makes the inclusion of the cos[η1(s)—η2(s)] term in theoretical molecular intensity curves a routine matter. The Fourier transform of the complete constant coefficient molecular intensity curve including the cosine phase shift term has been obtained and simple analytical expressions for peak splittings and corrections to vibrational amplitudes are presented.
Far Infrared Spectra of Solid Methyl Halides
Authors: Lafferty Walter J. , Robinson Dean W.
Published: January 2005

The infrared spectra of solid CH3Cl, CH3Br, CH3I, CD3Cl, CD3Br, and CD3I have been measured in the spectral region from 130 to 30 cm—1 at 78°K. Two sharp bands were found in the cases of the chloride and bromide, and three in the case of the iodide. These absorptions are interpreted as arising from lattice vibrational modes. The isotopic shifts exclude libration about the symmetry axis as a possible assignment for any of the bands, however, definite assignments to B-axis librations or translational modes cannot be made with confidence.
Electrical Properties of Some Dilute Cubic Sodium Tungsten Bronzes
Authors: McNeill William , Conroy Lawrence E.
Published: January 2005

The preparation and electrical properties are described for cubic NaxWO3 single crystals of the compositions x=0.363, 0.291, and 0.234. Specimens were prepared by diffusing sodium from single crystals of Na0.687WO3. The composition and homogeneity of the crystals were established by x-ray powder and back-reflection Laue photographs.

The electrical resistivity-temperature plots show a more complex electronic behavior than had been expected for dilute NaxWO3 on the basis of earlier work; Na0.291WO3 and Na0.234WO3 exhibit resistivity minima at about 150° and 320°K, respectively, with characteristics similar to that of degenerate semiconductors. A polycrystalline sample of Na0.025WO3, having a room-temperature resistivity of 3×10—3 ohm cm and a Seebeck coefficient of —270 μv/deg, is also described.
Magnetic Susceptibility of Potassium Hexachlororhenate (IV) and Potassium Hexabromorhenate (IV) from 5° to 300°K
Authors: Busey R. H. , Sonder E.
Published: January 2005

The Curie points of K2ReCl6 and K2ReBr6 obtained from magnetic susceptibility measurements are 12.4±0.5° and 15.3±0.5°K, respectively, which confirm that cooperative-type transitions observed in the heat capacities of these compounds with maxima at 11.9±0.1° and 15.2±0.1°K, respectively, represent transitions to the antiferromagnetic state. Evidence is presented that the ratios of the next nearest-neighbor to nearest-neighbor superexchange interactions in the two compounds are approximately equal. An estimate of the spin-orbit coupling constants in the crystals is given and compared with other estimates.
Sound Propagation in the Critical-Temperature Region of Hydrogen Chloride
Authors: Breazeale M. A.
Published: January 2005

The velocity and absorption of ultrasonic waves have been measured in the critical temperature region of hydrogen chloride at frequencies between 1 and 9 Mc. To explain the f2 frequency dependence of the absorption on the basis of scattering by molecular ``clusters,'' one must assume that there is a correlation in the fluctuations in density between adjacent volumes of the fluid.
Theory of Magnetic Rotation Spectra
Authors: Hameka H. F.
Published: January 2005

A general theory is developed for optical and magneto-optical rotation in the case of resonance, that is, if the frequency v of the primary light is equal to an absorption frequency vk of the system. It is concluded that for this case optical and magneto-optical rotatory power are physically meaningless quantities since they cannot be measured; instead the total intensities of the emission lines in optical rotation spectra or magnetic rotation spectra should be considered. General formulas for these intensities are derived from the quantum theory of radiation fields by making use of a perturbation method that was introduced by Heitler and Ma for the description of damping phenomena. An important feature of the method is the introduction of a damping constant which causes our results to remain finite for v=vk; this was not the case in the older theories. The possibility of measuring optical rotation spectra is mentioned: it is predicted that they may be observed in dilute gases of optically active molecules. No applications of the general theory to specific molecules are given.
Shock-Tube Study of the Kinetics of Nitric Oxide at High Temperatures
Authors: Wray Kurt L. , Teare J. Derek
Published: January 2005

A shock-tube program was carried out in which the NO concentration was followed as a function of time behind the shock front by absorption of 1270 A radiation, where ground vibrational state O2 and N2 are essentially transparent. The absorption coefficients of the species NO, O2, and N2 as functions of the respective vibrational temperatures were determined by measuring the absorption by the shock-heated gas at a point in the time history corresponding to complete vibrational relaxation but before the onset of dissociation.

Time history analyses were made on a total of 42 shock-tube runs covering a temperature range of 3000°—8000°K on the following six mixtures: ½% NO, ½% NO+¼% O2, 10% NO, 50% NO, 20% air, and 100% air—the diluent in all cases being argon.

An IBM 704 computer was programmed to integrate the vibrational and chemical rate equations as a function of time behind the shock front, subject to the constraints of the conservation equations. The pertinent rate constants were varied in a systematic trial-and-error manner in order to get the best fit to all the data.
Homogeneous Nucleation in a Miscibility Gap System. A Critical Test of Nucleation Theory
Authors: Sundquist B. E. , Oriani R. A.
Published: January 2005

A critical test of the classical nucleation theory applied to condensed phases has been carried out for the liquid miscibility gap system, methylcyclohexane-perfluoromethylcyclohexane (C7H14–C7F14). The densities of, and the interfacial free energies between the coexisting liquid phases have been measured as a function of temperature. The interfacial free energy is found to vary as the 32 power of the critical temperature Tc, less the experimental temperature, and these data are used to calculate the gradient energy parameter κ in the Cahn-Hilliard theory of nucleation. The magnitudes of the relevant parameters are such that the Cahn-Hilliard theory reduces to the classical theory for the present system.

These data, together with literature data on the thermodynamic properties of the bulk solutions, enable the degree of undercooling for a sensible nucleation rate to be calculated from classical theory. The experimentally determined undercoolings necessary to nucleate the C7H14-rich phase from the solution are found to be much greater than those predicted by the classical theory by factors ranging from 8.5 at 10 deg below Tc to 340 at 0.3 deg below Tc. These very large discrepancies are attributable to the breakdown of the traditional approximation in the classical nucleation theory that the number of molecules involved in the embryo population is a negligible fraction of the number of molecules in the system. When this approximation is avoided, the very complicated expression that results can be evaluated for the present case, leading to reasonable agreement between the predicted and the observed undercoolings. This is believed to constitute a satisfactory verification of the ``corrected'' classical theory of nucleation for condensed systems. The ``embryo population'' factor can be neglected in homogeneous nucleation in solidification and condensation (except near the critical temperature) and in most of the corresponding cases of heterogeneous nucleation. However, it is extremely important for nucleation in miscibility gap systems, or in any system in which the properties of the parent and daughter phases become identical at a critical temperature.
Studies on Mutual Diffusion of Polar-Nonpolar Gas Mixtures
Authors: Srivastava B. N. , Srivastava I. B.
Published: January 2005

The two-bulb technique of Ney and Armistead was employed for the measurement of the diffusion coefficient of binary mixtures of ammonia with argon and krypton in the temperature range —20° to 60°C. Diffusion was allowed to take place through a precision capillary tube connecting the two diffusion bulbs, and a previously calibrated thermal conductivity analyser was used for analyzing the gas samples at different times.

A least-square method was employed for determining the unlike interaction parameters of the Lennard—Jones (12:6) potential from the experimental D12 values at different temperatures. The combination rules for such systems and the force constants of pure components were also used for calculating the unlike interaction parameters. It has been concluded that the combination rules for polar-nonpolar interactions are reasonably satisfactory but not sufficiently precise for accurate work.
On the Reduction of Certain Multiplicative Chemical Equilibrium Systems to Mathematically Equivalent Additive Systems
Authors: Dantzig George B. , DeHaven James C.
Published: January 2005

The vectorial formulation of the chemical equilibrium problem, represented by tableaux, provides a concise method for consolidating a large amount of fact and hypothesis relating to large chemical systems involving reactions and states of complex molecules. This formulation plus the associated techniques for minimizing the free energy of the entire system allows equilibrium states under varying conditions to be calculated in a rapid and efficient manner on electronic computers. In biological systems involving hemoglobin, for example, it is possible to account for and to compute the effects of simultaneous changes in pH, CO2, O2, and metabolite concentrations on the oxygenation of hemoglobin. The effects of changes in temperature and total pressure may also be introduced into the model in a convenient fashion. A subsequent paper will present the results of such numerical calculations using the approach developed in this paper.
Nuclear Magnetic Resonance Spectra of Silicon Hydrides and Derivatives. I. Coupling Constants Involving Hydrogen
Authors: Ebsworth E. A. V. , Turner J. J.
Published: January 2005

Measurements of the H–H, H–Si, H–F and Si–F coupling constants for the halogen-substituted monosilanes, disiloxane, disilyl sulfide and trisilylamine are described. The failure of the simple valence-bond calculation to interpret the H–H coupling constants as a function of the H–Si–H angle is attributed to the d orbitals of silicon. A comparison of the H–H and H–Si coupling constants is also presented.
Infrared Spectra and Structures of the Crystalline Phases of CH4 and CD4
Authors: Savitsky George B. , Hornig D. F.
Published: January 2005

Infrared spectra of CH4 and CD4, in the region of the fundamentals ν3 and ν4, have been obtained in all of their crystalline phases at temperatures ranging from 5° to 40°K. In addition, the spectra of dilute solutions of CH4 and CD4 in one another have been studied through the same temperature range. The spectra of the dilute solutions consist of single sharp lines for both fundamentals, demonstrating that the barriers to molecular rotation are high in all the phases. The fine structure observed in the low-temperature phases of the pure crystals is inconsistent with any of the structural models heretofore proposed but a model for phase II is suggested which is consistent with the spectra and which shows very efficient packing. Phase III of CD4 is probably complex and of low symmetry. Phase I is probably disordered.
Motions of Molecules in Condensed Systems. XII. Infrared Spectrum and Structure of a Single Crystal of Allene
Authors: Blanc Joseph , Brecher Charles , Halford Ralph S.
Published: January 2005

The absorption of polarized infrared radiation by thin single crystals of allene at 95°K, and again at 125°K, has been recorded in the frequency range between 700 and 3500 cm—1. Spectra of liquid and vapor phases were also recorded under equivalent conditions. All absorption bands have been measured and assigned. The frequencies of the primary lattice modes of the molecule in the crystal are inferred from combinations, and show a strong dependence on temperature. The allene crystal is found spectroscopically to be monoclinic or orthorhombic, with the molecules located at sites of trivial symmetry, C1. A molecular arrangement, derived from packing considerations, which belongs to space group P21/n(C2h5), is proposed as the crystal structure.
Infrared-Absorption Spectra of LiOH and LiOD
Authors: Buchanan R. A. , Kinsey E. L. , Caspers H. H.
Published: January 2005

Spectra of films of LiOH and LiOD in the region from 450 cm—1 (22 μ) to 4500 cm—1 (2.2 μ) are presented. Polarized spectra of crystals of LiOH, LiOD, and mixed crystals of LiOH and LiOD at room temperature and at 15°K are also presented. The OH— ion stretching fundamental at 3678 cm—1 (2.7 μ) and the OD— ion stretching fundamental at 2713 cm—1 (3.69 μ) are each bracketed by sidebands in a nearly symmetric manner. The sidebands on the low wave-number side of each fundamental, the difference sidebands, all vanish at 15°K, while the main features of the sidebands on the high wave-number side of each fundamental, the summation sidebands, are preserved at low temperatures. In addition, the increased resolution resulting from reduced bandwidths at low temperatures reveals several new summation sidebands not observed in the room-temperature spectrum. A correlation of the LiOH and LiOD summation sidebands is presented and the deuteration effects discussed. These effects are observed to be in very good agreement with the theory which assumes that the sidebands are the result of binary combinations of low-frequency lattice modes with those modes which involve the hydroxyl ion stretching motions. They are not, however, in agreement with the rotation theory which proposes that the sidebands of LiOH, Mg(OH)2, and Ca(OH)2 are the results of the coupling of localized rotations of the OH— ions with their internal stretching frequency. An analysis of the mixed-crystal spectra reveals the significant role of hydroxide—hydroxide interactions in producing the observed intensities of the sidebands.
Distortion of Atomic Orbitals in Molecular Orbitals. I. Polarization of the Hydrogen Atom in H2+
Authors: Geller M. , Frost A. A. , Lykos P. G.
Published: January 2005

The Finklestein-Horowitz wave function for the ground state of the H2+ molecule ion leads to a potential energy function in qualitative agreement with experiment. The addition of p character into the atomic orbitals comprising the molecular wavefunction introduces polarization and leads to an improved estimate of the energy. The use of off-center orbitals to introduce polarization does not lead to significantly improved results, however. The different ways of allowing for charge shift in the atomic orbitals comprising the molecular orbital for the molecule ion and for the polarizability of the hydrogen atom in the presence of a weak electric field are discussed.
Dynamic Polarization in Asphaltene Solutions
Authors: Poindexter Edward H. , Uebersfeld Jean
Published: January 2005

Dynamic polarization experiments in solutions of asphaltene in xylene have been performed at both low and high magnetic fields. The interpretation of the experiments leads to the conclusion that the EPR line of the asphaltene is inhomogeneously broadened. The characteristics of the spin packet are deduced. In particular, the spin-packet width is found to be constant for many different experimental conditions. Specific information is obtained on the residence time of a xylene molecule on the asphaltene particle.
Kinetic Theory of Dense Fluids. X. Measurement and Interpretation of Self-Diffusion in Liquid Ar, Kr, Xe, and CH4
Authors: Naghizadeh Jamshid , Rice Stuart A.
Published: January 2005

The self-diffusion coefficients of Ar, Kr, Xe, and CH4 have been measured as functions of temperature and pressure and the data used to examine critically the current theories of diffusion. It is found that:

(1) The self-diffusion coefficients of Ar, Kr, and Xe fit one corresponding states relationship, and this relationship differs from that needed to fit the observed diffusion coefficients of CH4. For Ar, Kr, and Xe: logD̃=0.05+0.07p̃−(1/T̃)(1.04+0.1p̃),with D̃, T̃, and p̃ the reduced diffusion coefficient, temperature and pressure.

(2) The free volume theory of diffusion is inadequate to describe our observations.

(3) The volume of activation for CH4 is one third of the molar volume, while for Ar, Kr, and Xe it is one molar volume or larger. This observation is related to the steepness of the intermolecular repulsion, as is the deviation of CH4 from the corresponding states curve determined by Ar, Kr, and Xe.

(4) The dominant temperature dependence of D arises from the correlation between successive increments in momentum. In describing molecular motion it is necessary to include negative portions of the momentum autocorrelation function. A simple fluid continuum model appears to be accurate in describing momentum correlations. Calculations of D and (d lnD/dT) are in good agreement with experiment.

(5) The dense square-well fluid provides a zeroth-order approximation to real fluids. The computed temperature dependence of D is in quantitative agreement with experiment, but the computed values of D are in error by about 30%.
Electron Spin Resonance Study of Radiation Damage in Single Crystals of dl-Aspartic Acid
Authors: Jaseja Thadho S. , Anderson Roy S.
Published: January 2005

Single crystals of dl-aspartic acid were examined by the electron spin resonance method after being damaged at room temperature by x irradiation. Analyses of the resulting spectra suggest that the mechanism of the damage is the removal of the amino group, resulting in the stably trapped radical         H         –HOOC–C–C lim ·–COOH.         –     –        H    HThe three protons nearest to the unpaired electron were nonequivalent. The observed values of the isotropic π-electron—π-proton hyperfine couplings were 115±2 and 18±2 Mc. Two nonequivalent radical sites were detected. The values of the two nonequivalent anisotropic π-electron—σ-proton hyperfine interactions were observed to be 90±3 and 50±3 Mc along one axis. Interpretation of the π-proton couplings indicates that one of the methylene C–H bonds lies parallel to the π orbital of the unpaired electron, whereas the other C–H bond in the methylene group makes an angle of 113° with this direction. Comparison of the spectra from the two nonequivalent radical sites suggests that the angle between these is 60±10°. These conclusions were confirmed by similar studies of single crystals of deuterated dl-aspartic acid.
Optical Spectra of Transition-Metal Ions in Corundum
Authors: McClure Donald S.
Published: January 2005

The polarized optical spectra of the ions Ti3+, V3+, Cr3+, Mn3+, Co3+, and Ni3+ in corundum single crystals have been studied at temperatures from 4.2° to 1200°K. A theory of the band strength based on the point-charge model and p-d mixing has been developed and applied to the data with results in fair agreement with experiment. The effects of temperature show that the vibrational-electronic contribution to band strength is quite small at low temperature but may be appreciable at high temperatures. The crystal-field parameters have been calculated as convergent lattice sums. The observed trigonal-field parameter has the opposite sign from that calculated by the point-charge model if the impurity ion is assumed to occupy an Al3+ ion position in the lattice, but has the same sign as calculated for an ion 0.1 Å displaced along the c3 axis toward the empty octahedral site. Details of the spectra have been interpreted as showing that the surroundings of an ion are distorted in some electronic states.
ESR Spectrum of the 4,4′-Dipyridyl Radical
Authors: Bruin F. , Heineken F. W. , Bruin M. , Zahlan A.
Published: January 2005

The high-resolution ESR spectrum of the radical of 4,4′-dipyridyl (Tony blue) is observed and analyzed. Dipyridyl in alcoholic solution is converted into Tony blue upon irradiation with sunlight. The spectrum consists of 153 lines, each of less than 0.1 gauss width. The measurements were also extended to a partially deuterated compound of Tony blue, and the analysis was found to be in agreement with the former within the limits of observation.
Measurement of the Thermal Conductivity of Singly and Doubly Dissociating Nitrogen Peroxide
Authors: Barua A. K. , Chakraborti P. K.
Published: January 2005

The thermal conductivity of dissociating N2O4 involving both the reactions N2O4⇌2NO2 and 2NO2⇌2NO+O2 has been measured between 100° and 200° at a pressure below 1 atm. The absolute hot-wire method and an all-glass apparatus with a glass diaphragm manometer has been employed. The results are, however, not in good agreement with the values calculated on the assumption of local chemical equilibrium for both the reactions. Reasons for this discrepancy have been discussed.
Electron Distributions in Small Molecules
Authors: Clementi E. , Clementi H.
Published: January 2005

Mulliken's atomic gross charge and overlap populations are computed for the C3, C4, and C2N2 molecules. These populations are then compared with those of related molecules. The comparison is given in terms of s, p, and σ, π-atomic populations and σ, π-intramolecular charge transfer. The σ and π charge transfers are found to reinforce one another (one-way charge transfer) in homonuclear molecules and oppose one another (two-way charge transfer) in heteronuclear molecules. In addition, for the one-way case, the σ, π charge transfer is not as large as for the two-way case. It is pointed out that there are correlations between population analysis and orbital energies. This analysis of the electronic distribution is based on recent computations of simple and preliminary wave functions in the self-consistent field one-electron approximation.
Intermolecular Coupling of Vibrations in Molecular Crystals. III. Intermolecular Potential and Crystal Structure of Ethylene
Authors: Dows David A.
Published: January 2005

Intermolecular force constants and vibrational frequency splittings are calculated for ethylene and deuteroethylene on the assumption of certain types of intermolecular potentials. The results of a calculation based on intermolecular hydrogen repulsions as the mechanism of vibrational coupling are in reasonable agreement with the observed band splittings. To a limited extent electrostatic (dipole) interactions are of importance.

In the calculations detailed consideration of the as yet uncertain crystal structure were necessary, and the results lend support to the P21/n space group for ethylene at 65°K.

The hydrogen repulsion parameter obtained from analysis of the data was found to be consistent with a theoretically obtained result and with values obtained from independent experimental studies. A certain amount of information about the variation of repulsive potential with distance is now available from crystal studies.
Radiationless Transitions: A Semiclassical Model
Authors: Gouterman Martin
Published: January 2005

Radiationless transitions of a solute molecule embedded in a crystalline solvent are treated in close analogy to radiative transitions. A semiclassical interaction Hamiltonian employing empirically determined coupling constants connects solute particles to a force field amplitude set up by the phonons of the solvent. By relating this amplitude to phonon energy density an Einstein B coefficient is derived. Debye's formula for the phonon energy density combined with thermodynamic arguments yield Einstein A coefficients. It is shown that the theory (1) explains the fast rates of radiationless transitions, (2) provides for temperature dependence, (3) has a cutoff frequency for radiationless transition, (4) provides for the Franck—Condon principle, and (5) explains the lack of selection rules. A value is derived for the empirical coupling constants.
Observations on the Pink Nitrogen Afterglow
Authors: Young Robert A.
Published: January 2005

New spectrographic observations in the vacuum-ultraviolet region of the pink nitrogen afterglow are reported. Nitrogen bands representing 13 ev of energy, N I lines of 10.6 ev energy, and, upon the addition of Hg, Hg I lines of 10.1 ev and Hg II lines of 7.5 ev were observed with the 1st positive and 2nd positive N2 bands and 1st negative N2+ bands characteristic of the pink glow. The excitation of the nitrogen bands is discussed. Quenching of the pink glow by an ac electric field is related to the excitation mechanisms producing this glow.
Thermoluminescence from Gamma-Irradiated Biochemicals. Investigation of Emission Spectra
Authors: Weinberg C. J. , Nelson D. R. , Carter J. G. , Augenstine L. G.
Published: January 2005

Crystalline powders of the aromatic amino acids and the enzyme trypsin were exposed at 77°K to Co-60 γ rays, and the spectral distribution (between 3000 and 6500 A) of the thermoluminescence emitted upon subsequent heating was determined using band-pass filters. At a temperature corresponding to a particular peak in a plot of emission intensity vs T, a large fraction of the emission (except from phenylalanine) consisted of one characteristic spectral component. In general, the proportion of emission at the longer wavelengths increased with increasing temperature. The thermal-activation energies of thermoluminescence, estimated from plots of lnIT vs 1/T (about 0.2 ev for the amino acids and 0.1 ev for trypsin), are lower than similar determinations at comparable temperatures for alkali halide crystals. The γ-ray induced thermoluminescence from amino acid crystals is composed of longer wavelengths than the uv-excited fluorescence (at room temperature) or long-lived phosphorescence (at 77°K). The possible limitations within which lattice imperfections might account for these effects are discussed briefly. The spectral results for trypsin provide additional evidence that, in accord with previous predictions, at least some of the electronic rearrangements arising from γ-ray interaction become preferentially localized in only a restricted number of configurations. The metastable species which persist at 77°K likely depend upon the native conformation of the protein, and the available evidence suggests that the decay of an excited triplet state of tryptophan accounts for the majority of the trypsin emission. Even so, the activation energies and spectra indicate that the initial trapping and untrapping does not occur at the aromatic amino acid residues. Accordingly, mechanisms are considered whereby electronic rearrangements at other sites in trypsin could lead to the excitation of an aromatic residue followed by phosphorescence from a tryptophan residue.
Vibrational Spectra of ReF6
Authors: Claassen Howard H. , Malm John G. , Selig Henry
Published: January 2005

The infrared-absorption spectrum from 6–43 μ and the Raman spectrum of ReF6 gas are reported. They are interpreted in terms of the octahedral point group 0h. The six fundamental frequencies are 755(ν1), 596(ν2), 715(ν3), 257(ν4), 246(ν5), and 193(ν6). Thermodynamic functions are calculated for the ideal gaseous state.
Thermodynamic Properties of Hydrogen in Benzene Solutions
Authors: Connolly J. F.
Published: January 2005

Partial molal enthalpies, entropies, and internal energies are reported for hydrogen in liquid-benzene solutions at temperatures up to 250°C, pressures up to 150 atm, and hydrogen concentrations up to 13 mole %. Both the cohesive energy density ratio a12/a11 and the pressure at which the entropy of mixing becomes ideal, turn out to be roughly independent of temperature and hydrocarbon type.
Radiolysis of Ethane-1,1,1-d3
Authors: Stief Louis J. , Ausloos P.
Published: January 2005

The radiolysis of CH3CD3 has been investigated with particular emphasis on the effect of pressure, temperature, and addition of xenon on the molecular hydrogen formation. The hydrogen formed by molecular detachment was determined by irradiating CH3CD3 in the presence of C2H4, NO, O2, or I2. The formation of molecular hydrogen in the unimolecular decomposition of the parent ion and in the decomposition of the neutral excited ethane molecule are considered. Methane formed in the presence of scavengers may be attributed to an ion-molecule reaction or to an intramolecular process similar to that proposed in the direct photolysis of ethane. Evidence is presented for occurrence of a reaction producing ethylene in addition to the one in which molecular hydrogen accompanies the formation of ethylene.
Infrared Study of the Reaction of CH2 with CO2 in the Solid State
Authors: Milligan Dolphus E. , Jacox Marilyn E.
Published: January 2005

The photolysis of CH2N2 and of CD2N2 in CO2 at temperatures near 50°K has been studied using infrared techniques. Evidence has been obtained for the production of one or more intermediates by the reaction of CH2 with CO2. These intermediates are precursors of H2CO+CO. Possible structures for such species are proposed and discussed.
Measurement of the Dissociation Rates of Hydrogen and Deuterium
Authors: Sutton Emmett A.
Published: January 2005

Dissociation rates for hydrogen and deuterium have been found by measuring the density profile behind an incident shock wave as a function of time in mixtures of argon and hydrogen or deuterium. The density ratio was measured using an interferometer and drum camera. Relative efficiencies of argon, the molecule, and the atom in causing dissociation have been found for each isotope by varying the relative concentrations. The dependence of the rates on temperature was measured over the range 2800°-4500°K. Association-rate constants derived from the measured dissociation-rate constants showed a 1/T dependence on the temperature in the case of both isotopes when the third body was the molecule or an argon atom. Derived rate constants for association when the third body is another atom were found to be much larger and to have a more involved temperature dependence.
Energy Levels of Hexagonal ErCl3
Authors: Varsanyi F. , Dieke G. H.
Published: January 2005

The absorption spectrum of Er3+ in LaCl3 was extended in the ultraviolet to 2430 A. New fluorescence data were obtained by monochromatic excitation which yielded all the Stark components of several lowlying levels including the ground state. The crystal-field splittings were calculated for all levels. Comparison with the 28 empirical electronic states gives good agreement. The reason for observed discrepancies is believed to lie in inadequacies in the free-ion wave functions.
Spin Correlation in Ion Radical Salts; The System (Cs+)2(TCNQ)3=
Authors: Chesnut D. B. , Arthur Paul
Published: January 2005

The physical properties of the (Cs+)2(TCNQ)3= ion radical salt as measured by electron paramagnetic resonance are discussed in terms of the preliminary crystal-structure data. The salt is characterized by a thermally accessible triplet state lying 0.16 ev above a singlet ground state; the triplet state is described by a rhombic spin Hamiltonian H=βH·g·S+DSz2+E(Sx2−Sy2),with D/hc=±0.009367 cm—1, E/hc=±0.001513 cm—1, and gx, gy, gz equal to, respectively, 2.0025, 2.0015, and 2.0003.

Some conclusions are drawn regarding the general class of ion radical salts exhibiting triplet state character. The concept of spin delocalization over several TCNQ molecules is strengthened, and, from consideration of the temperature-dependent exchange narrowing effects present in these systems, arguments are presented to the effect that the triplet excitation may be free to propagate as a triplet exciton.
Concentration Dependence of the Frictional Coefficient of Polymers in Solution
Authors: Yamakawa Hiromi
Published: January 2005

The frictional coefficient of chain polymers at finite concentrations is calculated on the basis of the Kirkwood—Riseman approach taking into account the intramolecular and intermolecular hydrodynamic interactions. The intermolecular potential energy of Flory and Krigbaum is employed for the calculation of the perturbation velocity produced in the neighborhood of one molecule by the presence of another. Difficulties arising from an improper integral encountered in the intermolecular treatment of the viscosity to the Stokes approximation do not occur in the present problem. Evaluation is carried out up to the term linear in concentration, and the final expression is rewritten in terms of the molecular parameters familiar in the recent dilute polymer solution theories. The results show that the frictional coefficient is initially independent of concentration at the theta temperature, and that the ratio of the coefficient of the linear term to the intrinsic viscosity takes a value of about 1.7 for good solvent systems. These conclusions are in agreement with the experimental observations. A detailed comparison with experiment is made for several systems.
Gaseous Reaction of Methyl Radicals with Propylene
Authors: Miyoshi Mituji , Brinton R. K.
Published: January 2005

A study of the gaseous pyrolysis of Di-t-butyl peroxide in presence of propylene indicates that methyl radicals add predominately (about 90%) to the terminal carbon atom of propylene. The value of k4a/k3½ for the reactions CH3+C3H6→ lim k4aCH3CH2CHCH3    2CH3→ lim k3C2H6is 2.07×10—7 exp (—8800/RT) molecule—½ cm32 sec—½. Disproportionation—combination ratios for methyl—secbutyl radicals and secbutyl—secbutyl radicals were 0.08 and ≈1.2, respectively, independent of temperature. Addition of secbutyl radicals also occurs to propylene under the experimental conditions with a rate about comparable to the initial CH3 addition.
Chemical Equilibrium in Complex Mixtures
Authors: Levine Howard B.
Published: January 2005

The method of White, Johnson, and Dantzig for solving the equations of chemical equilibrium is modified so as to eliminate one step, and also simplify its mathematical structure. The resulting method is particularly suited to use on high-speed electronic computers.