bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of the Homogeneous Exchange Reaction: 14–14N2+15–15N2⇋214— 15N2. Single-Pulse Shock-Tube Studies
Authors: Bar-Nun Akiva , Lifshitz Assa
Published: January 2005

The kinetics of the homogeneous exchange reaction in molecular nitrogen highly diluted in argon was studied in a single-pulse shock tube over a wide range of temperatures, initial pressures, and compositions. The reaction order with respect to the total nitrogen, argon, and the over-all reaction order were determined. A rate law: Rate=kb[Ar][N214]+kb[Ar ][N215], which is a sum of two parallel reactions, was found to be compatible with the experimental results kb=1013.82±0.31 exp[−(116±5)×103/RT) cc mole−1·sec−1. It was shown that the exchange reaction does not proceed via a radical chain. A mechanism based on vibrational excitation of the nitrogen molecule to a critical vibrational level as a rate determining step is proposed. A rate constant, computed from available vibrational relaxation data in nitrogen agrees very well with the observed rate constant.

It was found that slight amounts of oxygen, up to O2/N2∼0.01, had very little effect on the reaction rate. In the presence of higher oxygen concentration, O2/N2∼0.5, the exchange proceeds mainly via an atom displacement mechanism. An approximate rate constant for the reactionN*+N2→ lim k3N+N2*, k3=3×1011 cc mole−1·sec−1at 3400°K was obtained.

The temperature range involved in this study, i.e., 3200°—3800°K, is the highest ever reported in a single-pulse shock-tube study. The gas-dynamic conditions and an innovation in the design of the shock tube are briefly described and discussed.
Microwave Absorption and Molecular Structure in Liquids. LXX. Dipole Moment, Atomic Polarization, and Dielectric Relaxation in Polymethylpolysiloxanes
Authors: Dasgupta S. , Smyth C. P.
Published: January 2005

Dielectric constants and losses have been measured at wavelengths of 0.22, 1.25, 3.22, 10.01, and 57 500 cm at temperatures of 25°, 40°, and 60° for four liquid polymethylpolysiloxanes of the general formula (CH3)3Si[OSi(CH3)2]xOSi(CH3)3, where x=1, 2, 3, and 5. The data have been used to calculate the small dipole moments, very large atomic polarizations, and two rather small dielectric relaxation times for the molecules. The squares of the dipole moments, the atomic polarizations, and the relaxation times are found to be linear functions of the size of the molecule as measured by x, the number of (CH3)2SiO groups. It is concluded that dipole orientation or relaxation occurs by molecular rotation and by intramolecular motion, which includes group rotation around Si–O bonds and, probably, bending of the Si–O–Si bonds. The bending and twisting of these bonds are the principal causes of the large atomic polarizations, as the absorption frequencies associated with them extend into the far infrared.
Four-Center Molecular Integrals in Quantum Chemistry
Authors: Roberts P. J.
Published: January 2005

A new method is presented for the calculation of two-electron interaction integrals for Slater-type orbitals. The method is suitable for any form of interelectronic interaction and applies to orbitals with arbitrary integral quantum numbers, located at arbitrary spatial points with arbitrary relative orientations. Computational work is reduced to a minimum for inverse-power interactions, since the analysis utilizes existing programs for two-center overlap integrals.
Some One-Electron Properties of H2O and NH3
Authors: Harrison James F.
Published: January 2005

Several one-electron properties have been evaluated for H2O and NH3 using ab initio SCF functions. The functions are obtained from the Hartree—Fock—Roothman equations using a minimal Gaussian-lobe basis. The diamagnetic-susceptibility tensor, quadrupole-moment tensor, diamagnetic nuclear shielding tensor at O, N, and H, and the nuclear quadrupole coupling constants for 17O, 14N, and D have been evaluated. These properties have been compared, when possible, with experiment. The total magnetic susceptibility tensor for NH3 and H2O and the diagonal elements (in the principal inertia system) of the absolute nuclear shielding tensor at H and N in NH3 have been estimated by combining the ab initio diamagnetic results with the experimental paramagnetic contributions available from measurements of the rotational magnetic moment and the spin—rotation interaction, respectively.
Statistical Mechanics of Linear Molecules. I. Potential Energy Functions
Authors: Sweet John R. , Steele William A.
Published: January 2005

Intermolecular potential energy functions for a pair of linear symmetric molecules are considered. The orientation- and distance-dependent molecular properties of pairs of such molecules are expressed in a standard series form. The terms in these series consist of orthonormal polynomials dependent upon the angle multiplied by arbitrary functions of distance. A number of the arbitrary functions are computed numerically for two model interaction energies: the linear Kihara core potential, and a model denoted by the term ``Diatomic'' which was obtained by assuming that each molecule consisted of a pair of atomic interaction centers. Changes in the components of the series for the energy are shown for both models as a function of the length of the molecule. Some conclusions are reached concerning the relative importance of the various angle-dependent terms in the potentials for molecules of a given length. The results obtained for the two models with equivalent values for the parameters are compared, and the adequacy of the spherically symmetric approximation which is often invoked for these functions is discussed.
Statistical Mechanics of Linear Molecules. II. Correlation Functions and Second Virial Coefficients
Authors: Sweet John R. , Steele William A.
Published: January 2005

Pair correlation functions for linear molecules are expanded in series in orthogonal functions of the orientation angles of the molecules. In the limit of zero density, the distance-dependent coefficients of some of the terms in the series are computed numerically for two simple models of linear symmetric molecules. The models are identical to those considered in the preceding paper and are the Kihara core potential and a ``Diatomic'' model. Second virial coeficients were calculated from the pair correlation functions and compared with the experimental data for a number of linear or quasilinear molecules. The significance of the molecular parameters obtained by fitting experiment to theory is briefly discussed and the two models are compared. The calculation of other properties from the correlation functions and the potential energies is outlined.
Capture Collisions between Ions and Polar Molecules
Authors: Dugan John V. , Magee John L.
Published: January 2005

The manner in which a permanent dipole in a molecule affects capture collisions of the molecule with ions is investigated. Analytical capture cross sections are considered, and three cases are distinguished. None of these is strictly applicable to real collisions, but they are useful in establishment of the general magnitudes of cross sections. The Langevin cross section is somewhat of a lower limit. A strict upper limit to the cross section is derived; it depends on the magnitude of the dipole moment. A quantum-mechanical treatment at small relative velocity uses the effective potential of interaction determined by the Stark effect; cross sections for this case depend explicitly on the rotational energy of the polar molecule. Molecules which have a first-order Stark effect have a term ε−1 in their cross sections, whereas the second-order Stark effect only leads to the ε−1/2 term of the Langevin theory (ε is the relative translational energy).

Numerical cross sections are obtained by using a computer study of collisions. The classical equations of motion are solved. Spiraling collisions (predicted in the Langevin theory) are not obtained, but it is found to be possible to define ``capture'' adequately and to set up a procedure for calculation of capture cross sections. This procedure involves averaging initial conditions with proper weighting. The real molecule HCl has been used in the calculations, and the results are compared with experiment as far as possible. A hypothetical molecule with the same dipole moment and polarizability of HCl but with a moment of inertia 100 times larger is also considered.
Energy Bands in Cubic Boron Nitride
Authors: Wiff D. R. , Keown R.
Published: January 2005

Results of numerical calculations of the electronic band structure of cubic boron nitride are reported. The calculations have been carried out using the augmented-plane-wave method of Slater. A total of 20 points in the first Brillouin zone have been examined which, by symmetry, determine eigenvalues at 256 different points from which a density-of-states histogram and curve have been plotted. The general shape and configuration of the energy bands resemble those obtained in previous energy-band calculations. It proved necessary to use the average potential between the spheres and the Madelung correction for ionicity as adjustable parameters in order to obtain a satisfactory band picture. The potential used is a modification of the carbon potential of Keown scaled according to a scheme introduced by Herman and Skillman.
Molecular Mechanism of Stimulated Raman Scattering
Authors: Wallace R.
Published: January 2005

The nature of the four-photon molecular scattering process involved in stimulated Raman scattering is considered by means of collision theory. An accurate expression is obtained for the scattering amplitude which explicitly illustrates its partitioning into coupled Stokes and anti-Stokes scattering processes. The dependence of the cross section for stimulated Raman scattering upon the lifetime of the excited vibrational state is derived. Such a dependence was assumed from phenomenological considerations by Bloembergen and Shen and is consistent with the observation that stimulated Raman scattering is observed only for vibrations having narrow linewidths. The lifetime dependence of the cross section is shown to be in agreement with the two-step mechanism of stimulated Raman scattering involving subsequent Stokes and anti-Stokes scattering processes, and contradictory to a single-step mechanism proposed by Buckingham. The single-step mechanism is shown to correspond to a physically unrealizable limit of the two-step process.
Measurement of the Translational Energy of Ions with a Time-of-Flight Mass Spectrometer
Authors: Franklin J. L. , Hierl Peter M. , Whan David A.
Published: January 2005

A mathematical analysis of peak shapes in a Bendix time-of-flight mass spectrometer shows that ions formed with excess translational energy exhibit considerable peak broadening. A method is developed by which this translational energy can be readily determined from the peak width. Experimental results are presented which confirm the validity of the theoretical calculations.
Appearance Potentials and Kinetic Energies of Ions from N2, CO, and NO
Authors: Hierl Peter M. , Franklin J. L.
Published: January 2005

A recently developed method has permitted the measurement of excess translational energy of ions formed in a time-of-flight mass spectrometer. The method, in conjunction with the RPD technique for determining appearance potentials, has been applied to the electron-impact study of nitrogen, carbon monoxide, and nitric oxide. A total of 31 different ionization processes have been observed and identified, several of which had not been previously reported in the literature.
Electronic Spectra and Coordination of Nickel Centers in Liquid Lithium Chloride—Potassium Chloride Mixtures
Authors: Brynestad Jorulf , Boston Charles R. , Smith G. Pedro
Published: January 2005

The electronic absorption spectra (4–28 kK) of dilute solutions of NiCl2 in liquid LiCl–KCl mixtures were measured at representative solvent compositions and temperatures from pure LiCl to pure KCl and and from 363° to 1070°C. Phenomenologically the spectra respond to changes in temperature at high temperature and changes in solvent composition at low temperatures in ways that are quantitatively very regular. At intermediate temperatures the behavior is more intricate. The data agree well with the following model. Nickel is partitioned between two types of centers, labeled T and O, which are in equilibrium. The T/O concentration ratio increases with increasing temperature and KCl content in the solvent. At low temperatures the fraction of each kind of center varies linearly with the mole fraction of KCl. The O-center concentration falls below the detection limit at 900°C in all solvents and in KCl at all temperatures. The coordination geometries of these centers are best described as being distributions about particular averages rather than as sharply defined arrangements. At low temperatures T centers have a distribution of coordination geometries that is narrow, composition invariant, and are clustered about a tetrahedral average. Their outer-shell cations are mostly K+. At high temperatures the distribution broadens and in LiCl-rich melts, Li+ ions invade their outer shells. The O centers are accurately studied only at rather low temperatures where they have a relatively broad coordination-geometry distribution with an average distinctively different from tetrahedral. Their outer shells consist largely of Li+ ions.
Effect of Melting on the Electronic Spectra of Cs3NiCl5 and CsNiCl3
Authors: Boston Charles R. , Brynestad Jorulf , Smith G. Pedro
Published: January 2005

A method is described for measuring the optical absorption spectra of the crystalline and liquid phases of a transition-metal salt close to the melting point. Supercooling the liquid permits measuring both phases at the same temperature. This technique was applied to Cs3NiCl5 (mp 547°C) and CsNiCl3 (mp 758°C). It was shown that when Cs3NiCl5 melts, the approximately tetrahedral arrangement of chlorides about nickel is affected only in minor ways, but when CsNiCl3 melts, the octahedral coordination geometry in the crystal is completely destroyed and replaced by a different distribution of geometries. The spectrum of molten CsNiCl3 and its temperature dependence is closely similar to that of nickel centers in molten KMgCl3 at high temperatures. The latter are believed to consist of a single broad distribution of geometries rather than two distinctly separate distributions. It was previously supposed that there are two distinctly different coordination geometries in molten CsNiCl3.
Microwave and Infrared Measurements on HCN and DCN: Observations on l-Type Resonance Doublets
Authors: Maki Arthur G. , Lide David R.
Published: January 2005

Microwave measurements have been made on the direct doublet splittings (ΔJ=0 transitions) of the 0110, 0220, 0310, and 0330 levels of DCN and the 0110 and 0220 levels of HCN. The sensitivity of the Δ and φ level splittings to certain vibrational and rotational constants enables us to obtain new values for those constants. New infrared measurements are given for ν1, 3ν21, 4ν20—ν21, and 4ν22—ν21 of HCN.
Benzene Vibrational Exciton Spectrum
Authors: Kopelman Raoul
Published: January 2005

A critical discussion of the infrared polarization assignments of Zwerdling and Halford, in view of the now accepted benzene crystal structure, leads to acceptance of their results, though with somewhat reduced credibility. The controversial 707-cm−1 absorption is assigned as the B2 interchange component (b axis polarized) of the a2u fundamental (674-cm−1 gas-phase) exciton band. The resulting, unusually large, static and dynamic exciton interaction terms are tabulated. Recent calculations based on atom—atom interactions are in reasonable agreement with the above results.
Interpretation of the Transition-State Parameter for Adiabatic Electron-Transfer Reactions
Authors: Harris R. , Weir W. D.
Published: January 2005

The consequences of a quantum-mechanical formulation of the adiabatic electron-transfer problem, using a transition-state parameter as defined by Hush, are examined. It is shown that the parameter λ‡ so defined warrants the same geometric interpretation given by Marcus to his parameter —m, subject to restrictions which are discussed. The treatment lends support to Marcus' view that λ‡ refers to a virtual charge density, specifically an equivalent equilibrium distribution.
Capture of Thermal Electrons by Oxygen
Authors: Stockdale J. A. , Christophorou L. G. , Hurst G. S.
Published: January 2005

Permanent capture of thermal electrons by O2 to form O2− ions requires the participation of a third body in the collision process to provide a dynamical channel for stabilization. The effectiveness of H2O and C2H4 as stabilizing agents in three-(C2H4–O2–H2O) and two-(C2H4–O2) component mixtures has been investigated. The results are analyzed through the following three-body reaction scheme: e+O2+O2→ lim k1O2−+O2+energy,e+O2+H2O→ lim k2O2−+H2O+energy,e+O2+C2H4→ lim k3O2−+C2H4+energy,and the rate constants k1, k2, and k3 are equal to 0.20±0.02 [J. L. Pack and A. V. Phelps, J. Chem. Phys. 44, 1870 (1966); 45, 4316 (1966)], 1.4±0.5, and 0.34±0.04×10−29 cm6 sec−1, respectively.
Vibronic Spin—Orbit Interactions in Heteroaromatic Molecules. I. Polycyclic Monoazines
Authors: Lim E. C. , Yu Jack M. H.
Published: January 2005

The phosphorescence of several polycyclic monoazines is more in-plane polarized in hydrocarbon solvents than in hydroxyl solvents outside the 0,0 band. The results are attributed to the solvent effect on the second-order spin—orbit coupling involving vibronic interactions between n, π* and π, π* electronic states. It is suggested that the solvent effect on the vibronic spin—orbit interactions is partly responsible for the solvent dependence of phosphorescence lifetime. The solvent effects on the fluorescence and intersystem crossing of heteroaromatic molecules are examined and discussed in light of these results.
Theory of the Dissociation Kinetics of Diatomic Molecules
Authors: Valance W. G. , Schlag E. W. , Elwood J. P.
Published: January 2005

A general rate constant for the reaction of diatomic molecules is presented. The derivation directly includes nonequilibrium and non-steady-state [W. G. Valance and E. W. Schlag, J. Chem. Phys. 45, 216 (1966)] effects, unless these are explicitly excluded, which can be done readily. Collisional transition probabilities of any general form can be employed in the evaluation of the final rate constant. The specific case of a nearest-neighbor model (one-quantum transitions) is also investigated, since this leads to some great simplifications in the final rate constant. An upper and a lower bound to this rate constant are derived, and are shown to be usually extremely close to one another. The exact solution for this case is given in terms of an iteration of the lower-bound solution. A value can be computed for the upper-bound solution which lies above that computable from any specific transition probability model, and is independent of such models. In using this maximum value for a nearest-neighbor rate constant it is shown that this value usually lies below the experimental values, hence indicating an inherent inadequacy in the nearest-neighbor model for at least these reactions. These results are also compared with those from simple-collisional theory and a non-nearest-neighbor model.
Theory of Reversible Termolecular Reactions in a Multilevel System
Authors: Valance W. G. , Schlag E. W.
Published: January 2005

A general theoretical form of the three-body recombination rate constant for atoms in the presence of a deactivating gas is presented. The starting point is provided by a master equation which includes the reverse dissociation of the diatomic molecules as a possibility. The master equation is written for the energy-transfer mechanism as well as the radical molecule mechanism. The solution is explicitly worked out for the steady-state case. The recombination involves the presence of hot diatomic molecules and hot atommolecule loosely bound species. In the latter case nonequilibrium effects must become severe, and an explicit formulation of these contributions is presented.
Magnetic Resonance Studies of Met-Myoglobin and Myoglobin Azide
Authors: Eisenberger P. , Pershan P. S.
Published: January 2005

The variation of electron spin resonance lineshapes with orientation of single-crystal myoglobins are studied for high-spin (S=52) Fe3+ in met-myoglobin and low-spin (S=½) Fe3+ in myoglobin azide. It is found that for both these crystals random variations of about 2° in the orientation of the symmetry axes contribute significantly to the observed linewidths. For met-myoglobin, these misorientations are sufficient to explain the observed angular dependence of the linewidths. In the case of myoglobin azide, however, there is an additional broadening due to a 3.5% random variation in the rhombic molecular field. Theoretical expressions describing the effects of random distributions of rhombic field parameters on linewidth are derived and fitted to the observed linewidths. Further lineshape changes are interpreted in terms of an anisotropic-exchange interaction between equivalent paramagnetic sites. A brief account of attempts to study the electron nuclear-double resonance (ENDOR) spectrum of the myoglobin is given.
Radiative Lifetimes of Ultraviolet Emission Systems Excited in BF3, CF4, and SiF4
Authors: Hesser James E. , Dressler Kurt
Published: January 2005

Radiative lifetimes in the range 2 to 11 nsec have been measured by the phase-shift method of Lawrence for four extensive near- and vacuum-ultraviolet emission systems excited by 200-V electrons in low-pressure BF3, CF4, and SiF4 gases. With the possible exception of the system excited in BF3, the systems appear continuous under 0.4−Å resolution and all are probably due to polyatomic emitters. Electron excitation spectra of several other gases are briefly described.
ESR Studies of Nitrobenzene,o-Dinitrobenzene, andm-Dinitrobenzene Alkali-Metal Salts
Authors: Ling Chi-yuan , Gendell Julien
Published: January 2005

The hyperfine splittings for the lithium, sodium, potassium, and cesium salts of nitrobenzene and the sodium, potassium, and cesium salts of o-dinitrobenzene over a range of temperature in DME are reported, as well as the splittings for the nitrobenzene and o-dinitrobenzene radicals produced by electrolytic reduction in DME. The sodium salt of nitrobenzene was also studied in a mixture of DME and DMSO. Results for nitrobenzene and o-dinitrobenzene are correlated with those previously reported for m-dinitrobenzene salts. For all three anions it was found that the perturbation of the anion on ion-pair formation increases along the series Cs+ to Li+. Line-broadening effects associated with cation motion from one nitro group to the other in the o- and m-dinitrobenzene salts correlate well with the extent of the perturbation of the anion by the metal cation. On the basis of (1) similar magnitudes and similar variation with temperature of the alkali-metal hyperfine splittings for all three anions, (2) the absence of line-broadening depending on alkali-metal quantum number, and (3) the observations in the mixed solvent system, a model for the ion pairs in DME is proposed in which the cation interacts with a single nitro group at a given instant of time, the cation is tightly bound to the nitro group with a fairly strongly bound cage of DME molecules solvating the nitro group cation complex, and temperature variation of the alkali-metal splitting is attributed to motion of the cation in the vicinity of the nitro group. Simple molecular-orbital calculations were performed in which the electrostatic interaction of the cation with the nitro group was simulated by increasing both the oxygen and nitrogen Coulomb integral parameters and good agreement between calculated and experimental changes of anion hyperfine splittings on going from the nitrobenzene free ion in DME to the sodium salt was obtained.
Theoretical Multiplet Strengths for Mg I, Al II, and Si III
Authors: Weiss A. W.
Published: January 2005

Superposition of configurations wavefunctions have been computed for the ground state and some lower excited states of the first three members of the magnesium isoelectronic sequence. The excited states are all those with configurations involving the low-lying orbitals 3s, 3p, 3d, and 4s. Multiplet strengths were also computed for all the allowed electric dipole transitions among these states. Only excitations of the outer two valence electrons were included in the multiconfiguration expansion, with the virtual orbitals being derived from a pseudonatural orbital transformation. Comparisons are made with predictions of the Z-expansion method.
Evaporation Rates and Lifetimes of Clouds and Sprays in Air. II. The Continuum Model
Authors: Zung Joseph T.
Published: January 2005

An alternate mathematical model is proposed for the prediction of the evaporation rates and lifetimes of clouds and sprays in air. It is based on the continuum approach which considers a droplet system as a uniform spherical source of vapor with a strength equal to the amount of vapor evaporated from the droplets per unit volume. The cloud equations derived from this model are expressed in terms of either the vapor concentration or the droplet mass. Further approximation leads to a linearized cloud equation which can be reduced to a simple diffusion equation to be solved by standard methods. Numerical results show that the continuum model describes the behavior of a saturated droplet system much more satisfactorily than the cellular model which has been recently proposed. For an unsaturated system, however, the cellular model remains adequate. By combining both of these models, a general model is obtained, which should be of general validity for all droplet systems evaporating into a fixed atmosphere.
Longitudinal Acoustical Vibrations of Finite Polymethylene Chains
Authors: Schaufele R. F. , Shimanouchi T.
Published: January 2005

The low-frequency Raman scattering spectra of finite polymethylene chains, observed utilizing laser excitation, show a band progression whose frequencies vary inversely and continuously as a function of chain length. It was established that these transitions arise from the longitudinal acoustical vibration of the chain skeleton and its overtones. These results are related to recent theoretical calculations for crystal vibrations of the infinite chain and are found to be in excellent quantitative agreement. An accurate spectroscopic value is derived for the elastic modulus of polyethylene.
Optical Studies of Electronic Transitions in Hexa- and Tetracoordinated Mn2+ Crystals
Authors: Lawson Katheryn E.
Published: January 2005

The polarized absorption spectra of Mn2+ in (CH3)4NMnCl3 and [(CH3)4N]2MnCl4 have been studied at 298°, 77°, and 2°K. Marked optical anisotropy was observed in both complexes. Details of the spectra indicate that the surroundings of the hexacoordinated Mn2+ ion are trigonally distorted from octahedral symmetry. Unlike the chemically similar alkali metal manganese halides, (CH3)4NMnCl3 undergoes no paramagnetic—antiferromagnetic transition between 298° and ≈4°K. Abnormal intensities in the spectrum appear to be unrelated to exchange mechanisms. The surroundings of the tetracoordinated Mn2+ ion very nearly approximate tetrahedral symmetry. However, the true Cs site symmetry is evident in the very sharp line absorption near 23 000 cm−1. The polarization behavior of the ion in both coordinations is discussed qualitatively in terms of the selection rules for the appropriate double group. The green luminescence of the tetrahedral complex and the pink luminescence of the octahedral complex have also been measured. The emission is shown conclusively to involve the transition 6A1g(6S) ←4T1g(4G) in the (CH3)4NMnCl3 complex.
Infrared Spectrum of the Methyl Radical in Solid Argon
Authors: Andrews Lester , Pimentel George C.
Published: January 2005

Reaction between lithium atoms and methyl halides during condensation in solid argon at 15°K produces absorptions at 730.3 and 1383 cm−1 that can be attributed to the methyl radical CH3. Isotopic substitutions (CH3, CH2D, CHD2, CD3, 13CH3) and behavior on warming, during which ethane absorptions replace the methyl features, furnish convincing evidence for the assignment.

Normal-coordinate analysis shows that the 730-cm−1 band is due to ν2, the out-of-plane bending mode of CH3 with a force constant of 0.25 mdyn/Å. These calculations favor the planar structure and they exclude an equilibrium deviation from planarity in excess of 5°. The absorption at 1383 cm−1 is due to ν4, the in-plane bending mode, with a force constant of 0.34 mdyn/Å. The asymmetric stretching mode, ν3, was not detected.

The out-of-plane bending force constants of D3h molecules can be correlated by separating the force constant into sigma- and pi-bonding parts. This correlation leads to a prediction of the out-of-plane frequency of BH3, 590 ±50 cm−1. Thermodynamic functions for both CH3 and BH3 are presented.
Perturbation Theory for Intermolecular Interactions in the Wave-Operator Formalism
Authors: van der Avoird Ad
Published: January 2005

A Schrödinger-type perturbation theory for intermolecular or interatomic interactions is developed in the wave-operator formalism. To include all exchange effects, wavefunctions are used whose symmetry with respect to permutations of both electronic and nuclear coordinates can be prescribed arbitrarily. This necessitates a modification of the usual perturbation theory. The interaction energy is obtained as a series in ascending powers of the interaction operator. It is proved that every term in this series is real and that the terms of even order are negative definite for perturbation of the ground state. It is verified that up to and including third order the results of this theory, if they are restricted to electron exchange only, agree exactly with those of the Eisenschitz—London theory.
Mechanisms of Energy Transfer Involving Trivalent Er and Tb or Tm in Sodium Rare-Earth Tungstates
Authors: Van Uitert L. G. , Dearborn E. F. , Rubin J. J.
Published: January 2005

Emission is observed from six manifolds of Er in the tungstates at 77°K. Their signatures and intrinsic lifetimes in microseconds are: Er2H9/2, <5; Er4S3/2, 25; Er4F9/2, ∼5; Er4I9/2, ∼13; Er4I11/2, 120; and Er4I13/2, ∼4500. A seventh manifold (Er2H11/2) emits when thermally populated from Er4S3/2 at 295°K. The principal transitions from all of these manifolds are to the ground manifold (Er4I15/2); as a result, radiation reabsorption is strong for each manifold and random migration of excitation between Er4I13/2 manifolds is possible at low Er concentrations. Further, due to the small spacings between the various manifolds of Er, relaxation by internal conversion processes is prevalent. Taking these factors and self-quenching interactions of Tb5D3 and Er into account, the nonradiative transfer of energy from Tb5D3 or Tb5D4 to Er, from Er2H11/2, Er4S3/2, Er4I9/2, Er4I11/2, or Er4I13/2 to Tb, and the equivalent self-quenching interactions of Er are all indicated to be by dipole—dipole in character.
Certain Atomic Integrals for Correlated Wavefunctions
Authors: Roberts P. J.
Published: January 2005

Analytical expressions are given for certain three- and four-electron atomic integrals which contain in their integrands products of Slater-type one-electron functions and inverse first powers of two or three of the interelectronic distances.
Rise of Temperature on Fast Stretching of Butyl Rubber
Authors: Dart S. L. , Guth Eugene
Published: January 2005

The rise of temperature on fast stretching of natural and synthetic rubber stocks was investigated recently by Dart, Anthony, and Guth (D.A.G.). Since then the experimental technique was considerably improved and the taking of data greatly simplified thereby. By D.A.G. emphasis was placed to record temperature rises of up to 15°C for extensions up to 700 percent by a fast galvanometer of moderate sensitivity. In the present work this high heat was investigated. In addition, however, a less fast but more sensitive galvanometer was employed to record changes of temperature as small as 0.001°C for 0–80 percent extension. In accordance with early work by Joule on natural gum (1859) it was found that also Butyl gum stocks show an initial cooling effect. This passes at a thermoelastic inversion point into a heating effect. In agreement with the recent theory by James and Guth the thermoelastic inversion point was found to depend solely upon the thermal expansion coefficient of the unstretched stock. The coefficient of thermal expansion was measured for Butyl stocks in the present work. Butyl tread stocks also show the thermoelastic inversion point. The work of D.A.G. showed that the rise in temperature on extension is a slowly rising function of the extension with a steep upward turn and almost linear continuation after the onset of crystallization. The samples were kept extended for a minute and then the cooling arising on retraction also measured. The negative of the cooling on retraction plotted against extension fall, according to the second law of thermodynamics as it should under the extension curve, but crosses it at the onset of crystallization. For Butyl gum stocks this crossing takes place at rather high (600 percent or more) extensions in agreement with x-ray work. More similarity was found between Butyl and Hevea tread stocks than between the corresponding gum stocks. Loading shifts the onset of crystallization to a range of smaller extensions. In addition to measuring the change of temperature on extension and retraction, the residual rise in temperature after an extension and immediate fast cycle retraction was also observed. This quantity is a measure of internal friction in Butyl rubber and is closely connected with rebound and free vibration tests. Summarizing, the method described has a twofold application for development work: 1. Changes of the temperature on extension and delayed retraction indicate in a simple manner the onset and progress of crystallization. 2. Changes of the temperature in a fast cycle give an estimate for internal friction. Both these applications will facilitate attempts to improve present synthetics.
Molecular Weight Comparisons from Density and X-Ray Data. The Atomic Weights of Calcium and Fluorine
Authors: Hutchison Dwight A.
Published: January 2005

Molecular weights have been compared by combination of the x-ray and density data for the crystals, calcite, diamond, lithium fluoride, sodium chloride, and potassium chloride. By assumption of the chemical atomic weights of carbon, chlorine, potassium, lithium, and sodium, values for the atomic weights of calcium and fluorine have been calculated. The method employed consists of a series of independent calculations from the results of which final weighted average values have been taken for the atomic weights of calcium and fluorine. This has yielded 40.0849±0.0030 and 18.9967±0.0013, respectively. These values are most probably the most precise values for these constants at the present time. From the results of the present work it becomes apparent that the determination of atomic weights from comparison of molecular weights by combination of density and x-ray data is as reliable as other standard atomic weight procedures.
Thermodynamics of Dilute Solutions of High Polymers
Authors: Flory Paul J.
Published: January 2005

Whereas extensive efforts have been directed recently toward improving the mathematical exactness of the statistical mechanical theory of polymer solutions, fundamental limitations set by the nature of the physical approximations have not received adequate attention. A careful comparison between theory and experiment in dilute solutions reveals a large discrepancy between the calculated and the observed departures from the ideal entropy of dilution. The assumption of random occupancy of lattice sites by polymer segments, which is employed in previous treatments, is at fault. In very dilute solutions of high polymers the solution is microscopically discontinuous. Two regions of the volume can be distinguished: one is totally unoccupied by segments of polymer molecules; the other consists of regions encompassed by the irregularly coiled polymer molecules. In the latter the concentration of lattice cells occupied by polymer segments is determined by the configuration of the polymer molecule, being independent of the over-all average concentration.

The above concepts have been employed in the formulation of a new statistical mechanical theory of the thermodynamic properties of very dilute high polymer solutions. The deviation from ideality, e.g., the slope of the osmotic pressure: concentration ratio plotted against concentration, is related to the ``effective volume ratio'' of the irregularly coiled solute molecule. This ratio, or ``swelling factor,'' can be estimated from the intrinsic viscosity of the polymer. Satisfactory agreement between theory and experiment is obtained in this way. The comparatively small deviations from ideality which are observed for protein molecules, not extremely dissymmetric in shape, receive semi-quantitative interpretation under the present theory. The failure, of the van Laar expression to account for heats of mixing in polymer solutions at all concentrations is a necessary consequence of the discontinuities in the dilute region.
Free Volume and Entropy in Condensed Systems III. Entropy in Binary Liquid Mixtures; Partial Molal Entropy in Dilute Solutions; Structure and Thermodynamics in Aqueous Electrolytes
Authors: Frank Henry S. , Evans Marjorie W.
Published: January 2005

The ideas of the first and second papers in this series, which make it possible to interpret entropy data in terms of a physical picture, are applied to binary solutions, and equations are derived relating energy and volume changes when a solution is formed to the entropy change for the process. These equations are tested against data obtained by various authors on mixtures of normal liquids, and on solutions of non-polar gases in normal solvents. Good general agreement is found, and it is concluded that in such solutions the physical picture of molecules moving in a ``normal'' manner in each others' force fields is adequate. As would be expected, permanent gases, when dissolved in normal liquids, loosen the forces on neighboring solvent molecules producing a solvent reaction which increases the partial molal entropy of the solute. Entropies of vaporization from aqueous solutions diverge strikingly from the normal behavior established for non-aqueous solutions. The nature of the deviations found for non-polar solutes in water, together with the large effect of temperature upon them, leads to the idea that the water forms frozen patches or microscopic icebergs around such solute molecules, the extent of the iceberg increasing with the size of the solute molecule. Such icebergs are apparently formed also about the non-polar parts of the molecules of polar substances such as alcohols and amines dissolved in water, in agreement with Butler's observation that the increasing insolubility of large non-polar molecules is an entropy effect. The entropies of hydration of ions are discussed from the same point of view, and the conclusion is reached that ions, to an extent which depends on their sizes and charges, may cause a breaking down of water structure as well as a freezing or saturation of the water nearest them. Various phenomena recorded in the literature are interpreted in these terms. The influence of temperature on certain salting-out coefficients is interpreted in terms of entropy changes. It appears that the salting-out phenomenon is at least partly a structural effect. It is suggested that structural influences modify the distribution of ions in an electrolyte solution, and reasons are given for postulating the existence of a super-lattice structure in solutions of LaCl3 and of EuCl3. An example is given of a possible additional influence of structural factors upon reacting tendencies in aqueous solutions.
Further Studies of the Structure and Stability of Burner Flames
Authors: von Elbe Guenther , Mentser Morris
Published: January 2005

It is shown that, contrary to Mache's model of the progressive extinction of a flame from the burner rim, a combustion zone cannot vanish within a combustible stream. The depth of penetration of the quenching of the explosive reaction by the burner wall is calculated from values of burning velocity and critical boundary velocity gradient for flashback; it is compared with the limiting distance between plane-parallel plates and the limiting tube diameter for flame propagation. The thermal expansion of the gas normal and parallel to the combustion zone is discussed. An experimental analysis and discussion of partial entrance of the combustion zone into the burner tube (tilted flame) and partial attachment to the burner rim are given. New data have been obtained on hydrogen and acetylene flames. For instantaneous flashback, the boundary velocity gradients are independent of tube diameter, as expected; these gradients are not a satisfactory criterion for flame stability because flashback can be readily induced by tilted flames. The limit of the tilted-flame range is represented by the semitheoretical equation g/(1–4Su/gR)12=const.g is the boundary-velocity gradient, Su the burning velocity, and R the tube diameter. The boundary-velocity gradients for blow-off are again found constant over the laminar flow range. The compression of acetylene-oxygen streams by the combustion zone has been measured. The burning velocities calculated from these and additional thermodynamic data agree well with those determined from gas flow and cone surface.
A Method for Obtaining Depolarization Factors of Raman Lines, with Results for Carbon Tetrachloride and Toluene
Authors: Cleveland Forrest F.
Published: January 2005

A method for obtaining depolarization factors of Raman lines is described in which a 90°, split-field Polaroid disk is placed in contact with the window of the Raman tube and is focused upon the slit of the spectrograph by means of a condensing lens. Corrections for real or apparent polarization owing to the spectrograph, reciprocity failure of the plates, and convergence errors are made. The precision of the results was tested by measurements on five different spectrograms of CCl4. The results indicated that the method is equal in precision to the method of Reitz. Intensities were obtained by use of a Gaertner microdensitometer. Depolarization factors for toluene were also obtained. It is shown that, for this method, a reasonable working rule is to regard those Raman lines having observed depolarization factors equal to or greater than 0.78 as depolarized, all others as polarized.
The Measurement of Potentials at the Interface Between Vitreous Silica and Solutions of Potassium Chloride by the Streaming Potential Method
Authors: Jones Grinnell , Wood Lloyd A.
Published: January 2005

Improvements in the technique for the determination of the electric potential at the interface between a non-conducting solid and an aqueous solution of an electrolyte (commonly called the zeta-potential) have been developed and are described in detail. Zeta-potentials of vitreous silica capillaries in contact with three dilute solutions of potassium chloride (10−3, 10−4, 10−5N) have been determined. These data have been used for the interpretation of the surface tension data of Jones and Ray by using Langmuir's theory for the thickness of wetting films as a function of the zeta-potential.
Molecular Theory of the Scattering of Light in Fluids
Authors: Zimm Bruno H.
Published: January 2005

A molecular theory of the scattering of light by fluids of isotropic molecules is developed, utilizing recent advances in the statistical mechanics of condensed phases. The results are shown to be the same in first approximation as those of the continuous theory based on fluctuations originally proposed by Smoluchowski and Einstein. Higher approximations of the molecular theory are especially applicable to the study of critical opalescence and fluids consisting of very large molecules.
Distribution of Chain Lengths and Compositions in Copolymers
Authors: Stockmayer W. H.
Published: January 2005

The instantaneous distribution of chain compositions and chain lengths in vinyl copolymers is obtained in a simple form valid for long chains. The compositions of chains of a given length are normally distributed about the mean value, with a standard deviation which can be calculated from experimentally observable quantities. The distribution of chain lengths intimately resembles that for simple polymers.
The Elastic Scattering and Neutralization of Low Velocity Hydrogen Ions in Ethylene and Propylene
Authors: Simons J. H. , Unger L. G.
Published: January 2005

The low velocity scattering of H+, H2+, and H3+ in both ethylene and propylene has been measured at ion velocities of less than 150 volts. Both elastic scattering and neutralization have been obtained over a velocity range. An effect of gas pressure at constant voltage on the total scattering was experienced. This is briefly discussed as is also the change of the relative amounts of elastic scattering and neutralization with pressure at constant voltage. The amount of neutralization compared to elastic scattering is large in all six cases. The elastic scattering in ethylene is somewhat similar to that in methane whereas that in propylene is somewhat greater.
The Near Ultraviolet Absorption Spectrum of Phenol Vapor
Authors: Matsen F. A. , Ginsburg Nathan , Robertson W. W.
Published: January 2005

The absorption spectrum of phenol as observed with a 3-m grating spectrograph consisted of 330 bands. A tentative analysis is made on the basis of the fundamental ground-state frequencies 245, 397, 527, 811, 824, and 999 and the fundamental excited-state frequencies 208, 374, 476, 562, 783, 935, 975, 1274, and 1565. These agree well with Raman data.
Low Temperature Specific Heats of α-Manganese and γ-Manganese
Authors: Shomate C. Howard
Published: January 2005

The specific heats of α- and γ-manganese were measured in the temperature range 52° to 298°K. The specific heat curve of α-manganese exhibited a small ``hump,'' extending over the temperature range 63°—103°K, with the peak of the ``hump'' occurring about 95°K. No anomaly appeared in the specific heat curve of γ-manganese. The computed heat contents and entropies per gram-atom are as follows: α-manganese, H°298.16—H°0=1193±4 cal., and S°298.16=7.59±0.04 E.U.; γ-manganese, H°298.16—H°0=1221±4 cal., and S°298.16=7.72±0.04 E.U.
Rate-Dependent Chromatographic Adsorption
Authors: Walter John E.
Published: January 2005

The process of chromatographic adsorption is studied from the kinetic viewpoint, assuming a bimolecular reaction between adsorbent and solute. Boundaries characteristic of equilibrium adsorption are obtained only if the time of passage of the solution through the column is greater than the half-life of the reaction by a factor of at least one hundred.
Nonresonant Absorption and Collision Diameters in the Foreign-Gas Broadening of Symmetric Top Molecules
Authors: Birnbaum George , Maryott A. A.
Published: January 2005

The nonresonant microwave absorption spectra of CH3Cl and CHF3 have been determined in a large number of mixtures with another gas, which for the most part has little or no dipole moment. The relaxation times were obtained from these spectra, and from the usual kinetic relation the equivalent hard-sphere diameters were computed. There is very little correlation between these diameters and the kinetic diameters, which are larger or smaller than the nonresonant diameters. Although there appears to be a correlation between the nonresonant collision diameter and the polarizability of the foreign gas, suggesting that these diameters may be interpreted on the basis of a dipole—induced-dipole interaction, the functional relationship between the collision diameter and the polarizability differs from that expected on the basis of this interaction.