bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transport Properties of Polar Gases
Authors: Monchick L. , Mason E. A. 
Published: January 2005

A model is proposed for the calculation of viscosity, diffusion, thermal diffusion, and the translational part of the heat conductivity of dilute polar gases. It is assumed that the molecular-collision trajectories are negligibly distorted by transfer of internal rotational energy, and that the relative orientation of two colliding dipoles remains fixed throughout the significant portion of the collision trajectory around the distance of closest approach. For this model, the Chapman-Enskog theory retains its usual form, but the collision integrals which appear must be averaged over all possible relative orientations occurring in collisions. Collision integrals have been calculated for the Stockmayer (12–6–3) potential, [open phi](r)=4ε0[(σ0/r)12−(σ0/r)6+δ(σ0/r)3],for kT/ε0 from zero to 100 and for δ from —2.5 to +2.5, and averaged over all orientations (assumed equally probable). Sufficient collision integrals are tabulated that the convergence error of the Chapman-Enskog theoretical expressions is not a problem.
Experimental viscosities and dipole moments of a number of polar gases have been used to determine the potential parameters ε0, σ0, and δ, which were then used to calculate other properties for comparison with experiment. The over-all agreement between experiment and this model for polar gases is comparable to that of the Lennard-Jones (12–6) model for nonpolar gases.
Effect of Pressure on the Optical Properties of Organic Phosphors
Authors: Gregg D. W. , Drickamer H. G. 
Published: January 2005

The effect of pressure to 54 kbar has been measured on absorption spectra, emission spectra, and decay rates of four organic phosphors. For fluorescein and dichlorofluorescein the decay rate increases with increasing pressure. The emission spectrum consists of two peaks which approach each other at high pressure. Thus there appears to be an increased mixing of triplet and excited singlet states at high pressure.
For acridine yellow and orange the absorption spectrum shows a dimer and monomer peak. The dimer peak decreases rapidly in intensity with increasing pressure. At high concentrations the component decay rates are largely independent of pressure. At lower concentrations the decay rate becomes slower at higher pressure. Evidently the emission can be associated with the dimer.
An Analysis of the Infrared Absorption Spectrum of Am+3(5f6) in LaCl3
Authors: Gruber John B. 
Published: January 2005

The polarized infrared absorption spectrum of single crystals of Am+3(5f6) in LaCl3 has been studied from 0.79 to 16.0 μ. In almost every instance the spectrum is sharp and completely polarized, and appears in definite groupings. Transitions from the ground level, 7F0, to excited levels of the ground term, 7F1, 7F2, 7F3, 7F4, 7F5, and 7F6 have been observed. For the particular point symmetry C3h that is consistent with experiment, magnetic-dipole transitions are observed from the 7F0 level to the 7F1 level, and forced electric-dipole transitions are observed to levels J = 2, 3, 4, 5, and 6.
A theoretical analysis is presented for the crystal-field split 7FJ levels. Using four parameters—A20〈r2〉=206 cm—1, A40〈r4〉=—94.1 cm—1, A60〈r6〉=—93.8 cm—1, and A66〈r6〉=1100 cm—1—excellent agreement is obtained between theory and experiment.
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.
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.
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.
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.
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.
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%.
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.
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.
Gas-Phase Radiolysis of Propane
Authors: Ausloos P. , Lias S. 
Published: January 2005

The radiolysis of CH3CD2CH3 and of equimolar C3H3—C3D8 mixtures in the presence of radical scavengers has been investigated as a function of pressure from 0.35 to 6000 mm and as a function of temperature from 40° to 220°C.
In the presence of scavengers, hydrogen and methane are mainly produced by molecular elimination. Values for the ratio CH3D/CH4 were found to increase with pressure and with surface to volume ratio of the irradiation vessel. Ethane is mostly formed by a hydrogen transfer reaction such as C2H5++C3H8→C2H6+C3H7+.From the distribution of the isotopic ethanes formed in the radiolysis of CH3CD2CH3, it can be concluded that the hydrogen atoms in the CH3CD2+ ion undergo a rapid randomization prior to reaction with propane.
Ethylene can be accounted for by the occurrence of the following processes: (a) decomposition: C3H8*→CH4+C2H4, (b) ion molecule reactions, (c) decomposition of vibrationally excited propyl and/or ethyl radicals.
From a comparison of the radiolysis results with the mass spectral cracking pattern of propane and recent photochemical studies, it can be deduced that the decomposition of propane ion and of neutral excited propane molecules are responsible for the products. The relative importance of these two modes of decomposition depends on the pressure and the size of the reaction vessel.
Photo-ionization of Alkyl Free Radicals
Authors: Elder Fred A. , Giese Clayton , Steiner Bruce , Inghram Mark 
Published: January 2005

Studies of the photo-ionization of the methyl, ethyl, propyl, and isopropyl radicals are reported. The radicals were prepared by pyrolysis of the appropriate alkyl nitrites, tetra-alkyllead compounds, and the dialkylmercury compounds. Secondary processes occurring in the energy range covered (7.2–11.7 ev) are discussed.
The appearance potentials for the methyl, ethyl, propyl, and isopropyl radicals, as measured by photo-ionization—mass spectrometric techniques are 9.82±0.04, ≤8.4, ≤8.1, and ≤7.5 ev, respectively. The adiabatic transition is accessible for the methyl radical only. Hence, the ionization potential of the ethyl, propyl, and isopropyl radicals cannot be determined by ordinary photon or electron impact experiments.
Reliability of the Hellmann—Feynman Theorem for Approximate Charge Densities
Authors: Salem L. , Wilson E. Bright 
Published: January 2005

A spherical atom in a uniform external field and the long-range interaction of two molecules are examples which illustrate the unreliability of the Hellmann—Feynman theorem when applied to systems described by approximate wave functions or charge densities. However, in the first case a wave function correct to first order in the perturbing field and in the second case a wave function correct to second order in the mutual interaction will yield the correct force.
For spherical atoms in an external field, the contribution of the continuum states to the electronic screening of the field is very large, 54% for hydrogen and about 72% for helium. From this case also one can evolve general considerations concerning the use of effective nuclear charges in electrostatic force calculations.
In the general case it is shown that for a system submitted to a given perturbation the wave function correct to order n, or the corresponding charge density, yields the force correct to order n and to order n only. This result leads to a brief comparison of the Hellmann—Feynman procedure and the variational method.
Theory of Condensation of Liquids of One and Two Components
Authors: Cernuschi Felix , Segre Myriam 
Published: January 2005

Cernuschi and Eyring's theory of condensation has been reconsidered, taking account of Kirkwood's criticisms, by the introduction of vibrations in the model. Variation of Einstein's frequency with temperature has been considered, following some works of Raman. With these modification results according with experiment are obtained, overcoming thus Kirkwood's objections.
The possibility of extending the model to the case of two components is then examined. The resulting formulas do not allow, because of their complexity, an analytic determination of the critical point. The equations can be simplified supposing that only one of the three previous interactions is different from zero. Numerical calculation has been done for the case of interaction between different particles. The critical curve is found by trial and error. The calculations made for three different concentrations of one of the components (parameter in the theory) shows that the exp(ε/kTc)—ε interaction energy decreases with such concentration.
Assignment of Electronic Transitions in Azo Dye Prototypes
Authors: Robin Melvin B. , Simpson William T. 
Published: January 2005

Quantitative calculations of the absorption frequency, transition moment length, and polarization of the first strong absorption band in the series of compounds C6H5N=N(C6H4N=N)xC6H5 have been successfully carried out using a model employing delocalization of electronic excitation energy rather than delocalization of electrons. It is found that the compounds can be treated as azo-perturbed phenyl groups interacting with both an electrostatic force and through conjugation. Because of the electrostatic part of the interaction, there results a demonstrable heat of single bond isomerization in phenylazo-β-naphthalene, its conformational isomers possessing different colorband spectra.
The n—π* transition in the azo dyes is shown to be, in all probability, the low-frequency component of two previously degenerate n—π* bands which have split. The intensity and polarization of the formally forbidden, low-frequency n—π* band can be explained by assuming a mixing of the n—π* band with the strong, low-frequency band responsible for the color in azo dyes.
A high-frequency band found at 44 kk (the symbol kk used throughout this paper stands for kilokayser or 103 cm—1) having a constant intensity throughout the series of dyes investigated has been shown to be isolated within the end phenyl groups.
Vacuum Ultraviolet Photochemistry. II. Photolysis of Ethylene
Authors: Okabe H. , McNesby J. R. 
Published: January 2005

The direct photolyses of CH2CD2 and trans-CHDCHD were carried out at room temperature in the vacuum ultraviolet region. Kr, Xe, and Hg resonance radiations were used for photolyses. Products at the Kr lines were mainly hydrogen, acetylene, ethane, and n-butane. The ratio of acetylene/hydrogen was 2.8±0.2 at 1236 A. The photolysis of CH2CD2 gives 40% H2, 40% HD, and 20% D2. The acetylene was 12% C2H2, 62% C2HD and 26% C2D2. The relative amounts of H2, HD and D2 depend upon whether a hydrogen molecule is eliminated from two (type I process) or one (type II process) carbon atom. The remaining vinylidene rapidly rearranges to acetylene.
The photolysis of trans-CHDCHD gives 17% H2, 73% HD, and 10% D2. This shows that hydrogen is formed from the trans as well as from the cis position and that the isotope effect for the type I process is slightly smaller than that for the type II process. Nearly free rotation of the molecule in its excited state is suggested. The percentages of the hydrogen isotopes produced are almost independent of exciting wavelength in both isotopic ethylenes. A comparison is made with Hg(3P1)-sensitized photolysis.