bluuebunny/crossref_metadata_2025_split huggingface dataset:
Formulas and Numerical Tables for Overlap Integrals
Authors: Mulliken R. S. , Rieke C. A. , Orloff D. , Orloff H. 
Published: January 2005

Explicit formulas and numerical tables for the overlap integral S between AO's (atomic orbitals) of two overlapping atoms a and b are given. These cover all the most important combinations of AO pairs involving ns, npσ, and npπ AO's. They are based on approximate AO's of the Slater type, each containing two parameters μ [equal to Z/(n—δ)], and n—δ, where n—δ is an effective principal quantum number. The S formulas are given as functions of two parameters p and t, where p=½(μa+μb)R/aH , R being the interatomic distance, and t=(μa—μb)/(μa+μb). Master tables of computed values of S are given over wide ranges of p and t values corresponding to actual molecules, and also including the case p=0 (intra-atomic overlap integrals). In addition, tables of computed S values are given for several cases involving 2-quantum s, p hybrid AO's.
Hybrid S values for any desired type of hybrid can be obtained very easily from the tables as simple linear combinations of non-hybrid S values. It is shown how S values corresponding to orthogonalized Slater AO's and approximate S values for SCF (self-consistent-field) AO's can also be obtained as linear combinations of the Slater-AO S values. S values for carbon-carbon 2pσ- and 2pπ-bonds using SCF carbon AO's have been computed (see Table in Section Vb); they correspond to stronger overlap than for Slater AO's. Non-localized MO group-orbital S values are also discussed, and are illustrated by an application to H2O. The use of the tables to obtain dipole moments for electronic transitions in certain cases is also mentioned. The use of the tables to obtain S values for various specific atom-pairs and bond-types, and resulting conclusions, will be discussed in another paper.
Measurements of Normal Burning Velocities and Flame Temperatures of Bunsen Flames
Authors: Andersen J. W. , Fein R. S. 
Published: January 2005

Stroboscopically illuminated particle tracks are used to accurately measure normal burning velocities of laminar flames. The precision of the measurements is increased by the use of a constant-velocity profile nozzle which gives a straight-sided Bunsen cone. Normal burning velocity data are presented for 3.7 to 5.3 percent propane-air mixtures. The value for the stoichiometric flame was determined to be 44.8 cm/sec.
From stroboscopic and streak photographs of particle tracks it is possible to obtain the maximum flame temperature and temperature distribution in the flame front. Measurements from the two types of photographs are combined with the equation of continuity and the equation of state to obtain the flame temperature. The flame temperature for a stoichiometric propane-air flame was determined to be 2220°K. An extension of this method is used to obtain an approximation of the temperature distribution in the flame front.
Internal Rotation I A Product Rule for Cis- and Trans-Isomers
Authors: Bernstein H. J. 
Published: January 2005

The assumption of equal force constants in the potential functions of cis- and trans-forms leads to a product rule for the planar vibrations of rotational isomers.
The rotational isomers of symmetrical dichloro- and dibromoethane are trans- and ``gauche.''
Internal Rotation II The Energy Difference between the Rotational Isomers of 1,2-Dichloroethane
Authors: Bernstein H. J. 
Published: January 2005

From the variation of the intensities of infra-red bands with temperature the value of ΔH0 for the reaction C2h dichloroethane →C2 dichloroethane is found to be 1250±50 cals. per mole. The probable energy difference between the isomers is 1100±50 cal. per mole. A tentative assignment of all the fundamentals has been made.
Peak intensities and integrated intensities yield the same results within the limits of the experimental error. The ratio of the number of C2 molecules to the number of C2h molecules at room temperature is 0.29.
The Kinetics of the Rapid Gas Reaction between Ozone and Nitrogen Dioxide
Authors: Johnston Harold S. , Yost Don M. 
Published: January 2005

An apparatus has been designed and constructed which will rapidly mix two gaseous reactants, isolate them in a reaction cell, and, by means of light absorption, follow the course of the reaction photoelectrically in one-tenth of a second or less. The output of the photoelectric tube is recorded by a time-exposure photograph of the screen of an oscilloscope.
The kinetics of the fast reaction between ozone and nitrogen dioxide was studied over a tenfold range of concentration of each reactant. The rate law was found to be −d(O3)/dt=k(NO2)(O3)over the entire course of the reaction. From the temperature coefficient of the rate of reaction the energy of activation was found to be 7.0±0.6 kilo-calories per mole. A mechanism is proposed to account for the observations.
Zinc Sulfide Phosphor Constitution and Its Effect on Electron Traps
Authors: Garlick G. F. J. , Wells A. F. , Wilkins M. H. F. 
Published: January 2005

The phosphorescence and thermoluminescence of zinc sulfide phosphors are governed by the mechanism of electron trapping in the phosphor crystal lattice. Experiments have been carried out to find the effect of phosphor constitution and method of preparation on the numbers and the energy distribution of electron traps. In order to investigate the traps, use has been made of the thermoluminescence vs. temperature characteristics of the phosphors.
These experiments show that pure zinc sulfide and zinc sulfide activated by silver and manganese possess similar ``shallow'' electron trap configurations after preparation and that these configurations are not markedly dependent on the particular activator. However, the introduction of copper impurity to zinc sulfide causes a marked change in the number and distribution of electron traps and is responsible for the long afterglow of these phosphors. Investigations of the effect of firing temperature and crystal form on the electron traps show that below the blende-wurtzite transition temperature (1020°C) the proportion of deep traps increases with firing temperature but that above this temperature the trap distribution is independent of the firing temperature or of fluxes and excess of sulfur. Experiments attempting to show that these traps were due to stoichiometric excess of zinc gave inconclusive results, but it is clear that the deep electron traps which produce the long afterglow characteristics of zinc sulfide are due both to the presence of copper impurity and to some change produced in the zinc sulfide lattice at high temperature without copper being present.
Other studies have been made of the effect of the mixed crystal proportions in the ZnS–CdS–Cu phosphor system on the electron traps. At high CdS contents some relatively deep electron traps are produced. Measurements of the fluorescence vs. temperature characteristics of the above phosphors show how the phosphor constitution and firing temperature affect the temperature at which the thermal quenching of fluorescence becomes appreciable.
The C–C Bond Energy in Ethylbenzene
Authors: Szwarc M. 
Published: January 2005

The pyrolysis of ethylbenzene in the presence of excess of toluene has been shown to be a unimolecular process, the rate-determining step being C6H5·CH2·CH3→C6H5·CH2·+CH3·.The methyl radicals were removed by a reaction with toluene, yielding CH4 and benzyl radicals, and the quantity of methane obtained was a measure of the extent of the decomposition of ethylbenzene. The energy of activation and the frequency factor were estimated experimentally at 63.2 kcal./mole and 1.0·1013 sec.−1, respectively. Taking the D(C–C)C6H5·C2H5 at 63.2 kcal./mole and using this value in conjunction with the value reported previously for D(C–H)C6H5·CH3 and the relevant thermochemical data, we calculated the D(C–H)CH4 at 102.9 kcal./mole.
The results of the thermal decomposition of ethylbenzene in the absence of toluene have been investigated, but it has been found unsuitable for kinetics studies because of a complicating chain process.
A short discussion on the frequency factors of these unimolecular reactions is given.
The Mechanism of the Photo-Chemical Decomposition of Diethyl Ketone
Authors: Dorfman Leon M. , Sheldon Zachary D. 
Published: January 2005

The photo-chemical decomposition of gaseous diethyl ketone in light of 3130A has been investigated at 56°C and 120°C over a wide range of absorbed intensities. The quantum yield of butane was found to increase with increasing intensity, while the quantum yield of total C2 hydrocarbons was found to decrease with increasing intensity. On the basis of a kinetic analysis of these data, the proposed free radical mechanism for the decomposition of this ketone is adequately substantiated.
Assuming zero activation energy for the recombination of ethyl radicals to form butane, the activation energy for the disproportionation of ethyl radicals has been determined as E=4.8 kcal./mole, and that for the reaction of an ethyl radical with a diethyl ketone molecule to form ethane has been found to be E=4.1 kcal./mole.
Statistical Mechanics of Adsorption. V. Thermodynamics and Heat of Adsorption
Authors: Hill Terrell L. 
Published: January 2005

The thermodynamics of an adsorbate on an inert adsorbent is discussed in some detail. Heats of adsorption are given particular attention in an attempt to clarify and extend the available methods in this field. It is found that the true equilibrium ΔH=TΔS of adsorption for adsorbate molecules is given by (∂ lnp/∂T)[open phi]=−ΔH/RT2,where [open phi] is the two-dimensional spreading pressure.
The relation of the work of Rowley and Innes to the present paper is considered.
The Quantum Mechanics of Chemical Kinetics of Homogeneous Gas Phase Reactions II. Approximations for Displacement Reaction between an Atom and a Diatomic Molecule
Authors: Golden S. , Peiser A. M. 
Published: January 2005

The quantum mechanics of a displacement reaction: AB+C→A+BC, has been considered and the results have been applied to the reaction: H2+Br→H+HBr at 500°K. The potential energy of the reacting system is based upon the London approximation as modified by Eyring and Polanyi. The absolute rate has been found to be a sensitive function of the coulombic energy fraction; when this fraction is taken to be 30 percent, the absolute rate is in essential agreement with the observed value. This agreement can only be regarded as fortuitous, however.
Several results have been derived which are not sensitive to the fraction of coulombic energy and furnish, therefore, a more stringent test of the present formulation. It has been found that the variation of the absolute rate with temperature, as calculated at 500°K, compares favorably with the observed variation. Approximately 95 percent of the rate comes from hydrogen molecules in the first excited vibrational state. The contribution from hydrogen molecules in various rotational states is given. The distribution of the initially formed hydrogen bromide molecules has been found to be representable by a pseudo-canonical distribution function of the rotational quantum number, in which the ``rotational temperature'' is approximately one-half the initial temperature.
Electron Deficient Compounds. II. Relative Energies of ``Half-Bonds''
Authors: Rundle R. E. 
Published: January 2005

It is suggested that the tendency to make use of all low energy orbitals is the underlying principle of electron-deficient bonding. Simple theoretical arguments, limited to the special case of two electrons and three orbitals, are given to show that this principle is a direct consequence of quantum-mechanical theories of valence.
Two half-bonds are shown to be of lower energy than a single bond plus an unused low energy orbital in most cases. The tendency to form half-bonds should be most important in symmetrical cases, and particularly where the electronegativities of all atoms involved are equal, e.g., the boron hydrides and H3+.
Certain consequences of the proposal to the fields of organo-metallic compounds, catalysis, and molecular rearrangements are pointed out. It is suggested that at low temperatures complexes may exist between molecules with excess orbitals and molecules with no unshared pairs.
The Heats of Vaporization of Uranium Hexafluoride
Authors: Masi Joseph F. 
Published: January 2005

Vaporizations of uranium hexafluoride were carried out in a heavy-wall, nickel-plated calorimeter. Measurements of the heat of vaporization of the solid were made at seven temperatures and of the liquid at four temperatures, covering the range from 4° to 90°C. The apparatus was tested before beginning the measurements by obtaining the heats of vaporization of water at three temperatures.
The scattering of the data on UF6 is about one percent. The measured heats of vaporization have been used to obtain a consistent correlation of the vapor pressures, heat of fusion, and triple point given in the literature. The results are expressed as vapor pressure equations and an equation of state for the saturated vapor. From these equations and the National Bureau of Standards values for the thermodynamic properties of the solid and liquid, the entropies of the ideal gas are calculated and compared with those given in the literature from spectroscopic data and molecular structure.
Diffusional Boundary Value Problems Involving Moving Boundaries, Connected with the Growth of Colloidal Particles
Authors: Reiss Howard , La Mer Victor K. 
Published: January 2005

A method is suggested for treating problems of diffusion which involve moving boundaries. This method is applicable when the flux of material through any surface in the diffusion field is considerably greater than the rate of change of concentration on that surface. The method is applied to two problems dealing with the growth of monodispersed aerosols and hydrosols.
The solution of the first of these problems indicates that, in a naphthalene-like aerosol system growing by means of the diffusion of vapor toward sinks (nuclei) which cannot support supersaturation, spontaneous nucleation will not occur if the number density of nuclei exceeds 100/cc.
The solution of the second problem permits the reproduction from theory of several curves due to Zaiser and La Mer which depict the rate of growth of sulfur hydrosols, therefore lending support to the idea that the particles grow by means of a simple diffusion mechanism rather than by a surface catalyzed deposition. The critical supersaturation concentration for sulfur in aqueous solution is c0=4.7×10−6 g/atom/liter,and the diffusion coefficient of S8 is D=2×10−6 cm2/sec.These values are in reasonable agreement with those estimated by independent means, although the diffusion coefficient seems to have about one-half the expected value. This indicates that a unit larger than S8 may be diffusing, e.g., a polythionate.
The Structure of Uranium Hexafluoride as Determined by the Diffraction of Electrons on the Vapor
Authors: Bauer S. H. 
Published: January 2005

The structure of uranium hexafluoride has been redetermined by electron diffraction. Special precautions were taken to eliminate sample contamination; both sector and non-sector photographs were analyzed. Even casual inspection of the photographs and microphotometer traces shows that insofar as this type of measurement is concerned, the structure of UF6 is not a regular octahedron. The model which is in best agreement with the data is a distorted octahedron with three short (1.87A) and three long bonds (2.17A). However, a model with a center of inversion, possessing two short (1.87A), two medium (2.12A), and two long bonds (2.22A) cannot be eliminated.
The disagreement between the structures deduced from various technics is discussed, as are also possible experiments which might be done to resolve these differences.
Ultrasonic Velocities of Sound in Some Metallic Liquids. Adiabatic and Isothermal Compressibilities of Liquid Metals at Their Melting Points
Authors: Kleppa O. J. 
Published: January 2005

The ultrasonic velocities of sound at 12 mc in 12 pure liquid metals at their melting points under atmospheric pressure and in 4 equi-atomic liquid metallic mixtures have been determined by the use of the electronic pulse-circuit technique.
For the pure metals the adiabatic and isothermal compressibilities have been computed. The compressibilities were generally found to be somewhat larger than for the corresponding solids at room temperatures. A calculation of Grüneisen's γ for the liquid metals shows that this quantity, in the case of normal metals, does not change appreciably on going from the solid state at room temperature to the liquid at moderately elevated temperature. These facts support the familiar view that the liquid metals at temperatures not far above their melting points are in a ``solid like'' state, and that equations of state for the solid state may be applicable to such liquids.
Light Scattering by Concentrated Polymer Solutions
Authors: Debye P. , Bueche A. M. 
Published: January 2005

The light scattered by benzene solutions of polystyrene up to a volume fraction of polymer of 0.62 has been measured. The results are compared with what was to be expected on the basis of recent thermodynamic theories for polymer solutions.
This comparison has led to the recognition of a new and rapid method for estimating molecular weights. The method also seems to be a convenient one for obtaining thermodynamic information.
Rotation-Vibration Spectra of Diatomic and Simple Polyatomic Molecules with Long Absorbing Paths VI. The Spectrum of Nitrous Oxide (N2O) below 1.2μ
Authors: Herzberg G. , Herzberg L. 
Published: January 2005

The photographic infra-red spectrum of N2O has been investigated with absorbing paths up to 4500 m atmos. Thirty-four absorption bands have been found of which twenty-three have been measured and analyzed in detail. Improved vibrational constants ωi0 and Xik have been determined which give a fair representation of all the bands. The remaining deviations which are outside the present limits of error are due to the effect of Fermi resonance between ν1 and 2ν2.
Precise values of the rotational constants Bv1v2v3 have been determined for almost all vibrational levels involved in the observed bands. For the lowest vibrational level the six most accurately measured bands yield B000=0.419125 cm−1. In this case also the rotational constant D000 representing the influence of centrifugal stretching has been determined: D000=0.193×10−6 cm−1. The value of B000 is larger by 0.000091 than that derived from microwave data. From the Bv1v2v3 values the following values for the rotational constants αi have been obtained, α1=0.00170  α2=−0.00022  α3=0.00339.These values allow the determination of the rotational constant in the equilibrium position Be=0.42145 cm−1 from which the moment of inertia in the equilibrium position is found to be Ie=66.397×10−40 g cm2. The deviations of the individual Bv1v2v3 values from those obtained from the formula Bν1ν2ν3=Be−α1(ν1+12)−α2(ν2+1)−α3(ν3+12) are appreciably larger than would correspond to the errors of measurements and must be ascribed to the effect of the Fermi resonance.
Kinetics of the Isotopic Exchange Reaction between Carbon Monoxide and Carbon Dioxide
Authors: Norris T. H. , Ruben S. 
Published: January 2005

The rate of the exchange reaction between carbon monoxide and carbon dioxide has been studied, using C14 as a tracer. The reaction, whose velocity in a quartz vessel is convenient for study between 800 and 900°C appears to follow the rate law: Rate = k(pCO)0.73(pCO2)0.85. The apparent activation energy is 77 kcal. The reaction is accelerated by added nitrogen but not argon. Packing increases the rate only slightly, giving no indication of a primarily heterogeneous reaction. However, this observation is considered questionable.
The present conclusions differ somewhat from those derived by Brandner and Urey from a similar investigation. Re-examination of these authors' data seems to resolve the apparent inconsistencies. It is concluded that their proposed reaction mechanism is invalid; however, their conclusion of heterogeneity seems more acceptable.
A probable mechanism appears to be a bimolecular exchange between the two reactants adsorbed on the catalytic surface. The acceleration by nitrogen or, as observed by Brandner and Urey, by hydrogen or water is then possibly to be ascribed to ``promotion'' of the catalyst by surface adsorption of these substances.
The Infra-Red Spectra of N15N14O16 and N14N15O16. Some Thermodynamic Properties of the Isotopic N2O Molecules
Authors: Bigeleisen Jacob , Friedman Lewis 
Published: January 2005

The three fundamental frequencies of N15N14O16 have been studied in the infra-red. One stretching frequency and the bending frequency in N14N15O16 have similarly been investigated. The bending frequencies in N15N14O16 and N14N15O16 are found to be in good agreement with calculations from the product rule. Some slight changes are made in the force constants for the stretching vibrations in N2O. The stretching frequency ω3 in N14N15O16 provides a good independent check on the force constants.
The partition function ratios for isotopic exchange reactions involving nitrogen and oxygen in N2O are calculated. The isomerization equilibrium N15N14O16=N14N15O16 has been calculated over the temperature range 273.16°—1000°K. A correlation is drawn between the structures of the isotopic isomers, N15N14O16 and N14N15O16, and the isomerization equilibrium.
The Multiplicity Forbidden Absorption Bands in the Spectrum of Pyridine
Authors: Reid C. 
Published: January 2005

The two singlet-triplet transitions of pyridine have been studied using very long optical paths. The first of these, a π-electron transition, which was previously observed in the liquid phase only as a region of continuous weak absorption at the long wave end of the main absorption system, has been observed in the gas phase as a well-defined band system between 3000 and 3300A with a maximum molar absorption coefficient, ε=0.10.
The sixty observed bands have been fitted into a vibrational scheme which suggests that the transition responsible for them is allowed by symmetry.
The second transition which involves the non-bonding pair of electrons on the nitrogen atom was observed previously as a low temperature phosphorescence emission. Attempts to observe this transition in absorption using very long paths in the gas phase were unsuccessful, but it has been observed weakly using an optical path of 45 cm of liquid pyridine.
Size Effect in Low Temperature Heat Capacities
Authors: Montroll Elliott W. 
Published: January 2005

It has been shown by Bolt and Maa that the distribution of normal modes of vibration of an elastic continuum is given by Aν2+B(S/V)ν+0(1) where A and B are numerical constants and S/V is the ratio of the surface area to the volume of the continuum. When this result is applied to the theory of the vibrational heat capacity of a solid at low temperatures, the Aν2-term yields the well-known T3 law and the B(S/V)ν-term leads to a contribution proportional to T2. About 0.5 to 10 percent of the heat capacity of non-metallic powders and materials with a domain structure can be attributed to the T2 term at 1°K. The importance of the surface term increases with decreasing temperature.
It is well known that at low temperatures the electronic contribution to the heat capacity of a metal is proportional to the temperature. In a system of very small metallic particles, the proportionality constant is increased by a quantity proportional to (S/V⅔)n−⅓ where n is the number of conduction electrons in the metal.
Kinetics of Heterogeneous Nucleation
Authors: Turnbull D. 
Published: January 2005

Consider a phase transition α⇄β. Stable β-embryos can be retained in the temperature range of α-stability in cavities of suitable extraneous solids present in the system. Retained β-embryos may nucleate the α→β-transformation in the range of β-stability.
Using these concepts a theory for the effect of thermal history upon the kinetics of phase transformations is proposed. The kinetics of heterogeneous nucleation in the absence of retained embryos is discussed.