bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics of Emulsion Polymerization
Authors: Smith Wendell V. , Ewart Roswell H. 
Published: January 2005

As a basis for understanding emulsion polymerization, the kinetics of free radical reactions in isolated loci is discussed subject to the condition that the free radicals are supplied to the loci from an external source. Three cases of interest are considered: that in which the average number of free radicals per locus is small compared with unity, that in which this number approximates one-half, and that in which the number is large. Of these three possibilities, the second, in which the free radicals per locus approximate one-half, is by far the most interesting as it explains in a satisfactory manner the characteristic features of styrene emulsion polymerization. For this case the average rate of reaction per locus is independent of the size of the locus, since this rate is simply one-half the rate of polymerization of a single free radical. Thus the rate of emulsion polymerization, the concentration of monomer in the loci, and the number of loci present provide the information needed for calculating the chain propagation constant for the monomer.
A simplified treatment is given for approximating the number of reaction loci (polymer particles) produced in emulsion polymerization when the rate of polymerization per locus is constant (see case 2 above). The law obtained indicates that the number of particles should increase with the soap concentration (3/5ths power) and with the rate of formation of free radicals (2/5ths power), but should decrease with increasing rate of growth of the free radicals (−2/5ths power).
The Stark Effect for a Rigid Asymmetric Rotor
Authors: Golden S. , Wilson E. Bright 
Published: January 2005

The Stark effect, arising from the interaction of a uniform electric field with a permanent electric dipole that is arbitrarily oriented within a rigid asymmetric rotor, and with a dipole induced in the rotor by the field, has been evaluated by perturbation methods. Tables are given for the perturbation of the energy levels so that, for J≤2, the rotational energies of an asymmetric molecule in an electric field may be readily approximated to terms quadratic in the electric field.
The effect of accidental degeneracy upon the Stark effect and line intensities has been considered. A qualitative discussion of certain features of Stark patterns is given that may be useful in the identification of rotational spectral lines.
Some Studies in Molecular Orbital Theory II. Ionization Constants in Heteroaromatic Amines and Related Compounds
Authors: Longuet-Higgins H. C. 
Published: January 2005

The relative basicities of a series of mono-aza-aromatic amines are calculated by a very simple application of LCAO molecular orbital theory. Rough quantitative agreement between theory and experiment is obtained if the heterocyclic nitrogen atom is supposed to take up the proton; on the other hand, if the amine group is assumed to add the proton in the first ionization, the observed basicities are negatively correlated with theory.
It is also shown how the qualitative differences in reactivity between methyl-aza-hydrocarbons and between heteroaromatic phenols may be understood in similar very simple terms.
The Properties of the Interstitial Compounds of Graphite. I. The Electronic Structure of Graphite Bisulfate
Authors: Hennig Gerhart 
Published: January 2005

1. The electrical resistance, its temperature dependence, and the Hall coefficients of graphite bisulfate compounds have been determined at various oxidation stages. The measurements have indicated that the oxidation removes electrons from a nearly full conduction band.
2. Reduction of the lamellar bisulfate compounds produces residue compounds which retain about a third of the bisulfate ions and half the sulfuric acid originally present in the lamellar compounds. The formula of the residue compounds is approximated by Cn·HSO4·4H2SO4.
3. The model of a hypothetical graphite which has lost electrons from its conduction band, is approximated closely by these residue compounds, since the impurities are distributed in a state of high disorder. The lamellar compounds, on the other hand, may distort the band structure of graphite because they form a superlattice.
Kinetics of CO Formation Studied by Far-uv Flash Photolysis of CO2
Authors: Clerc Michel , Barat Francois 
Published: January 2005

A simple, low-energy (100–200 J), short-duration (3-μsec) flash-photolysis apparatus for the vacuum ultraviolet down to the transparency limit of lithium fluoride (1100 Å) is described.
The photolysis of CO2 has been studied. Recombination rate of CO+O(1D) is 2×109 liters mole−1·sec−1 in the presence of a large excess of nonphotolyzed CO2 which may act as a third body. From kinetic considerations, the average lifetime of O(1D) was estimated to be of the order of 50 μsec under these experimental conditions. The fact that O(1D) plays a role is supported by the observation at 1152±0.5 Å of an absorption which could be attributed to the (2p41D−3s11D°) transition known in emission.
Scattering of High-Velocity Neutral Particles. XIV. He–He Interaction below 1.1 Å
Authors: Jordan J. E. , Amdur I. 
Published: January 2005

Total elastic cross sections have been measured for helium atoms within energies between 300 and 2000 eV which have been scattered by room-temperature helium through an effective laboratory angle greater than about 1×10−2 rad. Special features and procedures used in the experiments include the use of a magnetic field to increase the positive-ion current in the source, acceleration of the positive ions extracted from the source in a region of relatively low pressure with a consequent reduction in their energy spread, production of neutrals by charge transfer in a chamber separated from the scattering chamber, modulation of the neutral beam to produce an ac signal on a compensated thermal detector, and amplification of the detector signal with synchronous rectification, at the modulation frequency, of the amplifier output.
A detailed analysis of the scattering results treats effect on the measured cross sections of the intensity distribution in the beam and of the beam-detector geometry, interpretation of the results in terms of different empirical monotonic potential functions (the exponential, the screened Coulomb, and the point repelling inverse power), and the effects of quantum scattering.
Numerical values for the He–He potential between 0.61 and 1.12 Å for the three assumed potential functions show good internal consistency and agree with the best theoretical values within the combined estimates of the maximum uncertainties in the experimental and theoretical values. The mean potential obtained from the three empirical functions may be represented within about 1.8% by V(r)mean=196 exp(−4.21r) eV; 0.61 Å&lt;r&lt;1.12Å.
Infrared-Emission Studies of Electronic-to-Vibrational Energy Transfer. II. Hg*+CO
Authors: Karl G. , Kruus P. , Polanyi J. C. 
Published: January 2005

In an earlier work (Part I of this series) electronically excited mercury Hg* was formed in a low-pressure flow system by the 2537-Å irradiation of Hg+CO; electronic-to-vibrational energy transfer was studied by recording the infrared emission spectrum of vibrationally excited carbon monoxide (symbolized CO†) in its ground electronic state.
In the present work the earlier experiments have been placed on a more quantitative footing. Absolute concentrations of Hg*1(63P1), Hg*0(63P0) and CO†, v=2–9, have been measured under a variety of experimental conditions. The direct excitation of CO to v≤9 by electronic-to-vibrational transfer has been confirmed. Both Hg*1 and Hg*0 were found to be effective in bringing this about; the efficiency of Hg*1 being, however, about an order-of-magnitude greater than that of Hg*0. Vibrational relaxation was examined by observing the decay of the CO† infrared afterglow down the nonilluminated portion of the reaction tube. A set of rate constants, kv (or cross sections σv2), for electronic-to-vibrational transfer Hg1, 0*+CO→ lim kvHg+COv†were derived from observed sets of steady-state concentrations Nv under various experimental conditions. The best set of kv, expressed relative to kv=9=1.00, was; kv=2=80, kv=3=70, kv=4=60, kv=5=48, kv=6=43, kv=7=35, kv=8=15, kv=9=1.00, kv≥10≈0. These kv and the corresponding σv2 can be converted to approximate absolute units, since the over-all cross section for electronic-to-vibrational transfer in collisions Hg*1 0+CO, symbolized σvib2=(σvib2)1+(σvib2)0=Σv[(σv2)1+(σv2)0], was measured and found to be in the range 0.5–3.0 Å2. The most probable individual values for the total cross sections with Hg*1 and with Hg*0 as the donor atoms were, respectively, (σvib2)1≈1.3 Å2 and (σvib2)0≈0.09 Å2.
Energy matching is of no importance in this transfer, since a ``resonant'' conversion of electronic-to-vibrational energy would require that kv=20=1 and kv2&lt;0=0, in marked contrast to the findings. The results are discussed in terms of a complex HgCO* which undergoes intersystem crossing onto a potential-energy surface which correlates with electronic ground-state Hg(61S0); the electronic potential energy being released into nuclear motion as the system ABC gives A+BC across this lower surface. Two possible types of energy release are distinguished, corresponding to relaxation predominantly along the rAB and the rBC coordinates, respectively.
Microwave Spectrum, Structure, Dipole Moment, and Barrier to Internal Rotation of Phosphorus Trifluoride—Borane
Authors: Kuczkowski R. L. , Lide David R. 
Published: January 2005

The microwave spectrum of several isotopic species of phosphorus trifluoride—borane (F3PBH3) has been measured and the following structural parameters determined: d(BH) = 1.207±0.006 Å; d(PF) = 1.538±0.008 Å; d(PB) = 1.836±0.012 Å; ∠HBH=115°04′±1°; ∠FPF=99°50′±1°. The dipole moment was evaluated from Stark splittings as 1.64±0.02 D.
The vibrational satellite spectrum associated with the excited ν12(E) and ν6(A2) states for F3P11BH3 was found to be strongly perturbed and was fitted to the theory for a first-order Coriolis interaction. The analysis of this perturbation and the measurement of the ν12 fundamental in the infrared spectrum permitted the inactive torsional fundamental ν6 to be determined as 197±5 cm−1. This leads to a potential barrier to internal rotation of 3240±150 cal/mole.
The enthalpy of dissociation for the reaction 2 F3PBH3⇆2 PF3+B2H6 (298°) was determined as 10.99 kcal. The experimental results are compared to those found for other related compounds.
Separation of 1La Excitation Energies of Conjugated Hydrocarbons into Orbital Energy Difference and Two-Electron Term Contributions
Authors: Michl J. , Becker Ralph S. 
Published: January 2005

Working within the framework of the self-consistent-field approximation, an estimate is given for the value of experimental counterparts of the orbital energy difference and the two-electron term contribution to the 1→−1 excitation energy for eight conjugated hydrocarbons. The two-electron term is almost constant for the benzenoid hydrocarbons examined but markedly different in the case of azulene. The orbital energy difference is responsible for the variation of the excitation energy in the benzenoid series, and, in all cases examined, it is simply related to the topology of the molecule.
Semiempirical limited configuration-interaction calculations in the π-electron approximation (Pariser—Parr—Pople) are in qualitative agreement with these findings. The well-known facts that simple Hückel calculations lead to a good correlation with the excitation energies of the benzenoid hydrocarbons if the regression line is not forced to go through the origin and that azulene is far off the regression line are shown to be in accordance with the findings.
Toward a Charge-Density Analysis of the Chemical Bond; The Charge-Density Bond Model
Authors: Ransil Bernard J. , Sinai John J. 
Published: January 2005

Total-charge-density diagrams (ρ diagrams) are presented for the ground states of Li2, N2, F2, HF, and LiF in BMMO (best minimal molecular-orbital) and accurate SCF (self-consistent-field) approximations. On the basis of contour geometry the ρ diagrams are partitioned into regions of localized and delocalized charge density for which approximate average electron populations, called PL and PD, respectively, are computed. The PL are computed as a function of contour value and contour radius and provide a quantitative measure of the degree of charge transfer in the neighborhood of the nuclei attributable to molecule formation. Criteria for binding, nonbinding, and antibinding, following Berlin's treatment of the Hellmann—Feynman electrostatic theorem, are discussed. A positive correlation between the binding energy De and the ratio PD/PL is noted.
An alternate approach to interpreting the ρ diagram is introduced, in which charge-density-difference diagrams (Δρ diagrams) are interpreted as bond maps, i.e., diagrams which define regions of localized charge distributions on the corresponding ρ maps. Binding or antibinding character is then determined for each region of the total-density map using Berlin's forces-on-nuclei criteria. Corresponding electron populations for these regions may be computed by integrating the total density over the regional limits defined by the zero contours. A linear relationship between De and the ratios of these populations is noted. The Δρ maps display distinctly different contour patterns for homonuclear and heteronuclear molecules, which characteristic provides a means of differentiating and classifying binding mechanisms in terms of charge-density sharing and charge-density transfer, compatible with conventional bonding concepts. The possible sources of error in calculation and interpretation of the Δρ maps are enumerated and briefly discussed.
Although interpretable in terms of orbital theory concepts, accurate ρ diagrams and Δρ diagrams provide an opportunity to interpret chemical phenomena strictly in terms of localized nonintegral intra- and intermolecular electron-charge-density distribution and displacement. In this context orbital theories should be regarded as a means to an end, i.e., computation of a total wavefunction. Explanations in terms of orbitals and single or paired electrons are probably best reserved for particle-type phenomena, e.g., ionization potential, spectroscopic data, etc., while phenomena associated with charge interaction, rearrangement, and displacement (i.e., chemical reactions) are perhaps more appropriately studied in terms of spatially localized aggregates of bulk charge and their associated nonintegral electron populations, interpreted from the ρ diagrams and Δρ diagrams.
Electrical Conductivity of γ-Irradiated 3-MP Glass and of Photoionized 3-MP—TMPD during Warming from 4° and 77°K
Authors: Wiseall Barrie , Willard John E. 
Published: January 2005

The electrical conductivity of γ-irradiated 3-methylpentane (3-MP) glass has been studied as a function of γ dose, temperature, applied voltage, post γ illumination, and the nature and concentration of additives. Three distinct populations of charge carriers are found in samples which have been γ irradiated at 77°K. The first, attributed to the combined mobility of weakly trapped electrons and positive charges, decays almost completely in 30 min in the dark at 77°K. It is reduced by 0.01 mole % of the electron scavenger CCl4, but is not affected by 1 mole % of the positive hole trap 2-methylpentene−1 (2-MP−1). The second, attributed to trapped electrons, is revealed by current flow between 83° and 88°K during warmup. It is eliminated by infrared illumination at 77°K before warm up (which causes a burst of current), or by alkyl halides, and is increased by 2-MP−1. The 85°K peak is absent on warmup of γ-irradiated 3-MP containing biphenyl, but appears if electrons are liberated from the biphenylide ion by illumination with 4100-Å light prior to warmup. The third population of charge carriers becomes mobile above about 92°K, giving maximum current at about 102°K. It is not affected by alkyl halide additives, and must be ascribed to migration of positive and negative ions. Additives capable of forming larger ions of lower mobility lower this current peak and produce new peaks. The areas of the peaks at 85° and 102°K are proportional to the applied voltage over the range tested (4×102 to 8×104 V cm−1). They increase linearly with dose below 1×1018 eV g−1 but more slowly at higher doses. Blocking electrodes reduce these peaks. Between about 88° and 92°K the warmup current of γ-irradiated 3-MP becomes negative, suggesting randomization by thermal agitation of radiation-produced charges which have been oriented by the applied electric field at 77°K. The warmup current spectrum of 3-MP following γ irradiation at 4°K shows a peak at about 60°K in addition to the peaks observed for warmup from 77°K.
When tetramethyl-p-phenylenediamine (TMPD) in 3-MP at 77°K is photoionized, the warmup current shows a peak centered at 108°K, which differs from the similar peak produced by γ irradiation in that it is reduced by the presence of alkyl halides. The effect is attributed to complexing of TMPD by the alkyl halide with resultant trapping of the photoionized electrons in close proximity to the positive ion.
NMR Relaxation Mechanisms at Solid—Gas Interfaces. CH3OH, CD3OH, and CH3OD Adsorbed on Porous Glass
Authors: Fiat D. , Reuben J. , Folman M. 
Published: January 2005

Proton relaxation times of CH3OH, CD3OH, and CH3OD adsorbed on porous Vycor glass were studied as a function of the coverage. The shapes of the relaxation rates versus amount adsorbed curves were found to be similar for the three molecules studied, although differences in absolute values and position of extrema were noted.
The longitudinal relaxation time was found to be between one and three orders of magnitude longer than the transverse relaxation time and both were strongly dependent on surface coverage. This is explained by the existence of a distribution of the correlation times characteristic of the molecular motions. Dipolar interactions between the adsorbed molecules and surface OH groups are shown to contribute significantly to the longitudinal relaxation. Other possible interactions and relaxation mechanisms are also discussed.
Triplet—Triplet Transitions in Naphthalene
Authors: de Groot R. L. , Hoytink G. J. 
Published: January 2005

A Pariser—Parr type CI calculation has been made for the triplet—triplet transitions of naphthalene. All configurations singly and doubly excited with respect to the lowest triplet state and with an energy relative to the lowest triplet not exceeding 7.5 eV have been taken into account.
The results have taken away the discrepancy between previous calculations and the experimental observations by Porter and Windsor.
Gas-Phase Photolysis and Radiolysis of Methane. Formation of Hydrogen and Ethylene
Authors: Gorden R. , Ausloos P. 
Published: January 2005

The photolysis of CH4 and of CH4—CD4 mixtures has been investigated at 1236 Å (10.0 eV) and at 1048–67 Å (11.6–11.8 eV). The excited methane molecule dissociates to form H2, H, CH3, CH2, CH, and probably also C. The CH and CH2 radicals insert into methane to form internally excited C2H5* and C2H6* species, respectively. Below one atmosphere, all C2H5 radicals decompose to form C2H4, while the ethane molecules are partially stabilized. The relative quantum yield of CH increases about threefold when the wavelength is reduced from 1236 Å to 1048–67 Å. On the basis of an isotopic analysis of the hydrogen produced in the photolysis of CD4—H2S mixtures, it is concluded that at 1236 Å, D atoms constitute at least 65% of the ``molecular'' deuterium yield.
In the radiolysis, ethylene is largely, although not exclusively formed by the insertion of CH into methane. It is demonstrated that addition of small concentrations of an unsaturated hydrocarbon to methane profoundly affects the ion-molecule reaction mechanism and, therefore, does not lead to a dependable value of the ``initial'' ethylene yield as suggested in earlier studies. Upon application of an electrical field, the production of CH and CH2 is augmented in the saturation current region. The importance of the latter two radicals in the direct and rare-gas-sensitized radiolysis is examined briefly. The formation of hydrogen in the radiolysis will be discussed on the basis of new information derived from CD4—H2S experiments. The production of hydrogen in the radiolysis of Xe–CH4–CD4–NO mixtures has also been re-examined in view of a recent study in which it was asserted that all of the hydrogen in such a mixture is due to the unimolecular decomposition process CH4*→CH2+H2.Our data disagree with this view and actually demonstrate that CH and CH2 play a minor role in the xenon-sensitized radiolysis of methane.
Dielectric Constants of Imperfect Gases. III. Atomic Gases, Hydrogen, and Nitrogen
Authors: Orcutt R. H. , Cole R. H. 
Published: January 2005

A modified cyclic-expansion method has been used to determine dielectric constants as a function of relative density with a precision of less than 1 ppm for He, Ne, Ar, Kr, H2, and N2 at 49°C and pressures below 150 atm, which with data at measured pressures below 7 atm determine the first and second dielectric virial coefficients, and can also be used to determine pressure second virial coefficients.
Dielectric second virial coefficients are for all six gases less than values predicted by present theories of fluctuations and pair polarizabilities, an effect believed to result from overlap interactions at short range. The low-density values of the Clausius—Mossotti function are in good agreement with other recent determinations.
Some Theorems Concerning Symmetry, Angular Momentum, and Completeness of Atomic Geminals with Explicit r12 Dependence
Authors: King Harry F. 
Published: January 2005

Several results are presented which have important implications for the calculation of many-electron wavefunctions. Electron-pair functions are constructed to be eigenfunctions of the two-electron inversion, permutation, and angular-momentum operators with quantum numbers L and M. For a given L and M there exist 2L+1 particular linear combinations of binary products of spherical harmonics called generators. These 2L+1 generators multiplied by members of a complete set of S-type geminals constitute a complete set of geminal basis functions with that angular momentum. This approach establishes a connection between a formulation in terms of Eulerian angles developed by Wigner and others, and analyses based on configuration interaction expansions. One of several possible forms for the complete set of S-type geminals employs only 1s-type orbitals and a correlation factor, R(r12).
Mixing of symmetry may occur when a strongly orthogonal geminal is projected out from a symmetry-adapted one. This problem is easily circumvented. It is shown that any geminal is annihilated by an operator which projects out the component strongly orthogonal to a particular geminal with exponential r12 dependence.
Electronic-Absorption Spectra of Gaseous NiCl2, NiBr2, and NiI2. Axial Ligand Field Calculations Including Spin—Orbit Coupling
Authors: DeKock C. W. , Gruen D. M. 
Published: January 2005

Electronic-absorption spectra of gaseous NiCl2, NiBr2, and NiI2 have been measured in the range 4000–20 000 cm−1. An interpretation of the low-intensity dn←dn transitions is given based on ligand field calculations for a 3d8 configuration in an axial field including spin—orbit coupling.
The main features of the spectra are due to transitions to 3Pπ and 1DΔ,π excited states which are strongly intermixed in the bromide and iodide. An analysis of the nephelauxetic effect in these levels leads to the conclusion that the F2 parameter decreases more rapidly than the F4 parameter in the series NiCl2–NiBr2–NiI2.