bluuebunny/crossref_metadata_2025 huggingface dataset:
Perturbed-Stationary-State Calculation of Collisions in a Reactive System
Authors: Suplinskas Raymond J. , Ross John
Published: January 2005

Collisions in the reactive system K+HBr are treated quantum mechanically in a perturbed-stationary-state approximation. A potential surface for the system is constructed with Morse potentials for diatomic molecules and switching functions representing three-body effects. The cross section is written in an angular-momentum representation which permits an evaluation of the probability of reaction as a function of the impact parameter in the semiclassical limit. For the perturbed stationary wavefunction we take KBr harmonic-oscillator wavefunctions with the force constant varied so as to conform to the assumed potential surface. Computation of the matrix elements at initial relative kinetic energies of 2, 3.5, and 5 kcal/mole yields total reaction cross sections, probability of reaction vs impact parameter, and rotational- and vibrational-state distributions of products which can be brought to reasonable agreement with experiment upon suitable choice of two adjustable parameters in the switching functions.
Effect of Pressure on the Mössbauer Resonance in Ferrocene and Pyrite
Authors: Vaughan R. W. , Drickamer H. G.
Published: January 2005

The effect of pressure to 200 kbars has been measured on the Mössbauer resonance in ferrocene and pyrite. For both compounds a large increase in s-electron density at the iron nucleus with pressure was observed. For ferrocene, calculations showed that the increase is primarily due to decrease in shielding of the 3s electrons by the 3d. To account for the change quantitatively it would be necessary to consider the change both in the occupation and radial extent (shape) of the 3d orbitals.

The quadrupole splitting in pyrites increased with pressure. Although both qlat and qval are probably important, the results could be accounted for in terms of the former component only.

For ferrocene a decrease in quadrupole splitting with increasing pressure was observed. A Wolfsberg—Helmholz type calculation gave a change in electric field gradient which accounted for the effect. The same calculation accounted for the change of the optical absorption frequency with pressure which was previously observed for the e2g→e2g* transition.
Electron Nuclear Double Resonance in an Organic Molecule in a Triplet State. Spin Densities in Fluorenylidene in Diazofluorene Single Crystals
Authors: Hutchison Clyde A. , Pearson Gerald A.
Published: January 2005

The electron nuclear double resonance spectra of the protons in fluorenylidene molecules in the ground triplet state in a single crystal of diazofluorene have been studied. The directions of the principal axes of the proton hyperfine interaction tensor have been found, and the values of the components of this tensor in its principal axis system and in the principal axis system of the fine structure interaction tensor, are given. Best values of seven distinguishable spin densities have been determined on the basis of several models.
Induced Rotation—Translation Spectra of Solutions of H2, HD, and D2 in Liquid Argon
Authors: Holleman Gerald W. , Ewing George E.
Published: January 2005

Dilute solutions of H2, D2, and HD in liquid argon are studied by examining the 1000–140-cm−1 region of their induced absorption spectra. Since the absorption features overlap extensively, an empirical profile analysis is performed. For H2 and D2 several relatively sharp absorptions (Δν1/2≈30 cm−1), which have a Lorentzian line shape and closely correspond to the expected transitions of the freely rotating solute molecules, are observed. The width of these lines appears to be due to uncertainty broadening which depends on the time the absorbing solute molecule spends in a particular solvent cavity. Other features, with a 150-cm−1 half-width, are fitted with a four-parameter exponential equation and are believed to involve quantized translational energy levels of the solute. The range of translational energy levels, which is determined by the distribution of solvent cavity sizes, is responsible for their increased bandwidths. The HD spectrum is unusual in that the rotational selection rules are relaxed and transitions corresponding to ΔJ = +2, +3, and +4 are observed. Furthermore, all of the rotational absorption features are anomalously broad (Δν1/2≈50 cm−1) and their maxima are shifted from the gas-phase frequencies in an irregular pattern. Because of its asymmetrical mass distribution, rotational motion of HD is accompanied by a translation of the molecule in its solvent cavity. This rotation—translation interaction has been given quantitative form in a perturbation treatment by Friedmann and Kimel, and the results are consistent with the observed selection rules, frequency shifts, and linewidths in the spectrum of HD in liquid argon.
Internal Rotation in Completely Asymmetric Molecules. III. Theory for Molecules with Twofold Potential Barriers
Authors: Quade C. R.
Published: January 2005

The theory of internal rotation in asymmetric—asymmetric molecules is extended to planar molecules with twofold potential barriers. Two approaches utilizing a model with one degree of internal freedom are developed for solution of the problem. A framework-fixed-axis method is found to be best for medium barrier heights, where effects that arise from tunneling are important. The results of an internal-axis method are suitable for application in a high-barrier approximation, in which case simple, explicit functions are obtained for the torsional dependence of the moments of inertia and inertia defect. Finally, the theoretical results are discussed in relation to the experimental data from the microwave rotational spectra of phenol and nitrosobenzene.
Diffusion of Oxygen in Near-Stoichiometric α-Nb2O5
Authors: Chen W. K. , Jackson R. A.
Published: January 2005

Oxygen diffusion coefficients have been determined for near-stoichiometric α-Nb2O5 over the temperature range of 850° to 1200°C and the oxygen pressure range of 10−2 to 1 atm. At a constant temperature, the diffusion coefficient is found to be proportional to pO2−1/4. Temperature dependence of the diffusion coefficient at a constant oxygen pressure is expressed (in square centimeters per second) by D=1.72×10−2× exp[— (49.4±3.3 kcal) / RT]. Results are discussed in terms of an oxygen-vacancy model of nonstoichiometric disorder.
Theory of Radiation Chemistry. VIII. Ionization of Nonpolar Liquids by Radiation in the Absence of External Electric Field
Authors: Mozumder A. , Magee J. L.
Published: January 2005

A theory of separated ion pairs in the x and γ irradiation of nonpolar liquids is presented. In this theory consideration is made of the mechanisms involved in the thermalization of electrons, and it is shown that a very significant portion of the prethermalization electron range occurs while the electron is in the subvibrational energy region (∼0.4 eV to thermal energy). The temperature dependence of the yield of separated charges arises in a perfectly natural manner. ``Thermalization lengths'' turn out to be 80–90 Å. Good agreement with experimental observations is obtained with reasonable values of the three adjustable parameters. The theory is also applied to the special case of 37Ar, where most of the effect is due to 2.4-keV conversion electrons. Calculated results are in reasonable agreement with experiment in this case. A small temperature effect is predicted.
De-excitation Rates of Excited Electronic States in Solids
Authors: Dexter D. L. , Fowler W. Beall
Published: January 2005

The importance of the vibrational state in spontaneous radiative and nonradiative electronic transitions is discussed. It is argued that in most cases vibrational excitation enhances these transition probabilities, and numerical results are presented for a range of parameters for a simple model of radiationless transitions. Special attention is given to the case of very slow vibrational energy transfer to the environment, particularly from complex excited molecules.
Cooperative Phenomena in the Triangular Lattice
Authors: Kikuchi Ryoichi
Published: January 2005

A three-point triangle cluster and a W-shaped five-point cluster are used as the bases of the cluster-variation method in the triangular lattice, and the results are used to predict the properties to be obtained by the rigorous calculation. The following systems are treated using the same mathematical formulations: (a) the lattice-gas—liquid system, (b) the phase-separating binary alloy, and (c) the Ising model. In the pressure-versus-density isotherm of (a), the van der Waals-type loop shrinks as the approximation is improved and shows a tendency to approach the flat coexisting line. The central hump of the excess free energy in (b) lowers as the approximation is improved, and tends toward the flat line connecting the minima of the free-energy curve. The free energy of the Ising model (c) as a function of the long-range order parameter behaves in the same manner. When the binary alloy system (b) is quenched, the central hump remains in the free-energy curve (i.e., it does not become flat) in the rigorous treatment. It is pointed out that this nonequilibrium free energy is the quantity to be used in the treatment of the spinodal decomposition.
Study of Some of the Parameters Affecting Knudsen Effusion. I. Experimental Tests of the Validity of the Cosine Law as a Function of Cell and Sample Geometrics and Materials
Authors: Ward J. W. , Mulford R. N. R. , Kahn Milton
Published: January 2005

Experimental studies of the distributions of particles effusing from a Knudsen cell at high temperatures (1000°—2000°K) reveal marked deviations from the cosine law. It would appear that complete thermodynamic equilibrium is seldom achieved in a high-temperature Knudsen experiment; further, in terms of ordinary kinetic theory, descriptions of the behavior of the ``gas'' inside the cell are oversimplified. The measured distributions show clearly, in a fashion analogous to the formation of an image by a pinhole camera, the effects of geometry and choice of materials for each Knudsen cell. In particular, containment problems which force the use of special cell materials may introduce side effects which can cause serious deviations from theory.
Study of Some of the Parameters Affecting Knudsen Effusion. II. A Monte Carlo Computer Analysis of Parameters Deduced from Experiment
Authors: Ward J. W. , Mulford R. N. R. , Bivins R. L.
Published: January 2005

Results of computer calculations of the spatial distribution of the vapor effusing from a Knudsen cell are presented. The mathematical model used allowed variation in cell and sample geometries and the assignment of probabilities to the events thought actually to occur in a real Knudsen cell. Assignment of reasonable loss probabilities to various surfaces within the cell allowed experimental distributions to be duplicated. Explanation of these distributions is offered in terms of cell and sample geometries and the different fluxes produced by various surfaces within the cell.
Study of the Structure of Nickel in Soda—Boric Oxide Glasses
Authors: Hecht Harry G.
Published: January 2005

The results of an investigation of the structure of Ni+ +, ions in Na2O–B2O3 glasses by optical and EPR techniques are reported. The coordination about the ion sites is found to be octahedral, and a small amount of covalency is inferred. The crystal-field splitting of the d8 levels decreases as the Na2O content of the glass increases. No direct evidence for the boric oxide anomaly was found.
Perturbation Theory and Equation of State for Fluids: The Square-Well Potential
Authors: Barker J. A. , Henderson D.
Published: January 2005

The equation of state for a fluid of molecules interacting according to the square-well potential is evaluated by treating the attractive potential as a perturbation on the hard-sphere potential. This leads to an expansion in inverse powers of the temperature. The first-order term is evaluated exactly (except for the approximation of using the Percus—Yevick expression for the hard-sphere radial distribution function). Two slightly different approximations for the second-order term are given and shown to lead to similar results. With first-and second-order terms included, the calculated equation of state is in excellent agreement with quasiexperimental Monte Carlo and molecular-dynamics results at all temperatures including the lowest temperatures for which such calculations have been made, far below the critical temperature and at liquid densities. The reasons for this good agreement, particularly at high densities, are discussed in terms of a novel formulation of the perturbation theory, and the implications of the results for fluids with more realistic potential functions are considered.
Energy Transfer between Trivalent Rare-Earth Ions in Inorganic Solids
Authors: Nakazawa Eiichiro , Shionoya Shigeo
Published: January 2005

The purpose of the paper is to clarify the mechanism of excitation energy transfer between unlike trivalent rare-earth ions in inorganic solids. We have measured the manner in which the intensities of the luminescences of Tb3+ (5D4→7F5) and Eu3+ (5D0→7F2) are quenched and the decay rates are made faster by the coexistence of other kinds of trivalent rare-earth ions as a result of energy transfer. As the host material, calcium metaphosphate glass was used. The combination of Tb3+ donor and Nd3+ acceptor was studied most in detail. The results are discussed in terms of the resonance theory of energy transfer, and the experimental data are analyzed using the numerical calculations of the theory recently made by Inokuti and Hirayama. The overlap integrals of donor emission spectra with acceptor absorption spectra were estimated from the data of spectral measurements. Among the resonance mechanisms due to various electrostatic multipole interactions, the dipole—quadrupole interaction gave the best fit between theory and experiment. The transfer due to the exchange interaction was inferred not to be operative. It has been finally concluded that the mechanism of the energy transfer between unlike trivalent rare-earth ions in inorganic solids is predominantly governed by the dipole—quadrupole interaction.
Computed Ground-State Properties of FH and CH
Authors: McLean A. D. , Yoshimine M.
Published: January 2005

The accuracy of existing comprehensive calculations of wavefunctions of first- and second-row hydrides in close to the Hartree—Fock approximation is confirmed by performing test calculations, with larger Slater-function basis sets, on FH and ClH.

Dipole moments, quadrupole moments, magnetic susceptibilities, rotational g factors, forces on the nuclei, field gradients at the nuclei, and polarizabilities are then discussed and estimated from either computation alone, or by combining computed expectation values with observed properties. Excellent agreement between computation and observation is demonstrated for the quadrupole coupling constant for 35Cl and 37Cl nuclei in ClH. The following estimates of molecular properties not available elsewhere are made: rotational g factor is −0.033 for 19FH and +0.006 for 35ClH; diamagnetic anisotropy (ξ∥−ξ⊥) is −2.1 × 10−6 erg/G2·mole for FH, and −3.3 × 10−6 erg/G2·mole for ClH; eqQ(2H) = 0.34 Mc/sec in FH and 0.18 Mc/sec in ClH. For FH the axial components of the molecular polarizability tensor are (in atomic units) αzz=5.45, βzzz=−8.6, γzzzz=65, Az:zz=4.05, Bzz:zz=−32, 32Czz:zz=8.2. For ClH they are αzz=15.78, βzzz=−33, γzzzz=260, Az:zz=17.5, Bzz:zz=−125, 32Czz:zz=40.2.
Kinetics of Reversible Isomerization in a Multilevel System
Authors: Valance W. G. , Schlag E. W.
Published: January 2005

The theoretical rate constant for a reversible isomerization in a multilevel system is derived. Both forward and reverse constants are derived. The ratio of rate constants is compared with the equilibrium constant for the system. The reversibility of the system is seen to introduce understandable complications which can only be neglected for the forward reaction if special conditions regarding the probabilities are satisfied, as is usually the case for an exothermic, but not for an endothermic system, not even if only the initial rate for the endothermic system is considered. The rate constants for the forward and reverse reactions include nonequilibrium, many-shot, and recrossing effects but are presented in a steady-state form, with non-steady-state corrections indicated. This steady-state form has a simple phenomenological interpretation as a total flux from cold-reactant to cold-product levels in this scheme, including multiple recrossings of the critical surface due to reversibility.
Electronic Structure of Rare-Earth Sesquisulfide Crystals
Authors: Henderson J. R. , Muramoto M. , Loh E. , Gruber John B.
Published: January 2005

Single crystals of R2S3, R = Dy, Gd, Nd, and Y, have been grown by flame fusion in an argon plasma torch and by the Bridgman technique. The purification of R2O3 starting materials, synthesis and analysis of compound powders R2S3, crystal growth, analysis to determine if single crystals are produced, and measurement of electrical resistivity and thermoelectric power coefficient from 300° to 1300°K and discussed. The electrical measurements indicate highly degenerate semiconductor behavior with ρ and α increasing with temperature in contrast with previous reports for rare-earth tellurides and selenides. The presence of the rare-earth ions in their trivalent state and the absence of divalent ions have been confirmed independently by reflectance spectra from powders, by absorption spectra of single crystals, and by measurement of magnetic susceptibility of single crystals. The materials are unusual because they are semiconductors with the (4f)n levels of the rare-earth ions spanning the bandgap in ladderlike fashion. The free ion energy levels of Dy3+ were obtained by diagonalization of the electrostatic and spin—orbit matrices arising from a perturbation calculation, and least-squares fitting of the calculated levels to experimental values. The Dy2S3 spectra are correlated with DyF3 and Dy2O3 results.
The Thermodynamics of High-Polymer Solutions: I. The Free Energy of Mixing of Solvents and Polymers of Heterogeneous Distribution
Authors: Scott Robert L. , Magat Michael
Published: January 2005

The theories of Flory and Huggins for the free energy of mixing of a homogeneous chain polymer of uniform molecular weight with a single uniform solvent have been extended to the case of a polymer mixture of varying chain lengths with a mixture of solvents. By making the similar assumptions as those of Huggins, and utilizing familiar statistical mechanical methods, the partial molal free energy of mixing of the solvent is found to be ΔF0¯=RT[ln φ0+(1−φ0)(1–1/m̄N)+μ(1−φ0)2],where φ0 is the volume fraction of solvent, m̄N a simple function of the number average molecular weight, and μ a constant characteristic of the polymer-solvent mixture (consisting largely of a heat term, but also including γ, the coordination number of the rubber segments). By assuming that a mixture of two solvents behaves like a new homogeneous liquid a method of calculating μ for such mixtures is developed. Applications of these formulas to solubility and fractionation are shown in a subsequent article.
The Principle of Corresponding States
Authors: Guggenheim E. A.
Published: January 2005

The principle of corresponding states in modern form has been applied to the following properties: the critical state, the virial coefficient, the Boyle point, the densities of coexistent phases, the vapor pressure of the liquid, the entropies of evaporation and of fusion, the coefficient of thermal expansion of the liquid, the triple-point temperature and pressure, the heat capacity of the liquid, and the surface tension of the liquid. It has been shown that argon, krypton, xenon, and with less accuracy neon, follow the principle with respect to all these properties. It has further been shown that nitrogen, oxygen, carbon monoxide, and methane follow the principle with fair accuracy as vapors and as liquids, but not as solids. The relations between surface tension, temperature, and densities have been analyzed empirically. For the ``ideal'' substances under consideration Katayama's modification of Eötvos' relation holds good, but McLeod's relation does not; in the relation γ∝ (ρl—ρc)s, the exponent s is not 4 but much more nearly 3⅔.
Deswelling of Gels by High Polymer Solutions
Authors: Boyer R. F.
Published: January 2005

When a cross-linked polymer initially swelled to its equilibrium volume in pure solvent is transferred to a solution of a high polymer in the same solvent and at the same temperature, the gel deswells. A quantitative treatment of this effect is given in terms of the Flory-Rehner theory of the thermodynamic properties of gels, and the Flory-Huggins theory of thermodynamics of high polymer solutions. The extent of deswelling depends on the molecular weight and concentration of the solute, on the solvent-polymer interactions, and on the degree of cross-linking in the gel. It thus offers in principle a new method for determination of the number average molecular weight of the solute. Various calculations are presented to show the extent of deswelling under given conditions. Finally, some experimental data is offered to demonstrate determinations of molecular weights, using styrene-divinyl-benzene copolymer gels and polystyrene solutions.
Statistical Theory of Kinetic Energy of Fragmentation in Certain Unimolecular Dissociations
Authors: Klots Cornelius E.
Published: January 2005

The quasiequilibrium theory, in both its usual form and with a modification applicable to ``loose'' transition states, is used to calculate the kinetic energies of fragments resulting from unimolecular decompositions. It is found that these statistical methods are capable of encompassing the presently available experimental results, except for two relatively unimportant reactions. An extension to the radiation chemistry of the liquid aliphatics is noted.
Perturbation Theory of the Heats of Mixing of Fused Salts
Authors: Davis H. Ted , Rice Stuart A.
Published: January 2005

A theory of the thermodynamic properties of molten salts including the effects of short-range attractive interactions has been developed. The analysis builds upon the work of Reiss, Katz, and Kleppa who showed that many of the thermodynamic properties of molten salt mixtures could be understood in terms of a model ionic melt consisting of rigid impenetrable ions interacting with a long-range Coulomb potential. The RKK theory is inadequate for the description of recent experimental measurements of the heats of mixing of salts whose short-range attractive interactions are expected to be significant. Most of the molten salt data of Kleppa et al. have been fitted to the following equation for the heats of mixing: ΔHm=x1,x2(a+bx1)δ122+x1x2c,    δ12=(λ2−λ1)/λ1,λ2,with xi the mole fraction of the ith component, a<0, b<0, and c>0. The major contribution to a arises from Coulomb interactions, and is well accounted for by the RKK analysis which, however, does not completely account for b and gives c=0.

Using a perturbation analysis it is shown herein that the term c and part of b arise from short-range interactions between ions; the theoretical relationship deduced reproduces the observed composition dependence of the heat of mixing shown above. The qualitative deductions which can be made from the formal analysis are all in agreement with the available experimental data. It is also shown that there is a short-range potential contribution to the leading term (ax1x2) and explicit relationships for the coefficients a and b are obtained. A method of using the theorem of corresponding states to obtain information about the short-range coupling is suggested.
Effects of Hydrostatic Pressure on Linewidths of Free Radicals in Solution. I. Anisotropic Region
Authors: Edelstein N. , Kwok A. , Maki A. H.
Published: January 2005

We have measured the hyperfine linewidths of solutions of di-t-butyl nitroxide in methylcyclohexane vs hydrostatic pressure in the range 6500 to 10 300 kg/cm2. In this pressure range, the linewidths vs viscosity are compared with the theory developed by Kivelson. The pressure dependence of the solvent viscosity was obtained from the data of Bridgman. The anisotropic parameters of the spin Hamiltonian of the radical were obtained from measurements in a frozen glass. Apparent deviations from Kivelson's theory at high viscosities are readily accounted for by assuming an explicit pressure dependence of the anisotropic part of the 14N hyperfine interaction, which is approximately linear with pressure in the region above 8500 kg/cm2. Deviations at high radical concentration are shown to arise from intermolecular dipole—dipole interactions.
Production of Excitation and Ionization in Helium by Single-Electron Impact
Authors: St. John Robert M. , Lin Chun C.
Published: January 2005

The production of excited He+ ions by single-electron impact collisions with ground-state helium atoms has been observed by the optical method. The absolute value of the cross section for the collision process yielding the n=4→n=3 transitions (4686 Å) in He+ was determined for incident electron energies ranging from 60 to 470 eV. The excitation—ionization cross section exhibited a single broad maximum at 200 eV with an onset at 75 eV. The peak value of the cross section was 4.2×10—21 cm2. Stepwise ionization and excitation was nowhere in evidence. The excitation—ionization function obtained at a number of gas pressures was independent of pressure. Light yield was proportional to the electron beam currents. Comparison with previous experimental work and with theoretical calculations were made.
Studies on the Hydrogen Evolution Reaction Down to —150°C and the Role of Proton Tunneling
Authors: Conway B. E. , Salomon M.
Published: January 2005

An investigation of the hydrogen evolution reaction (h.e.r.) at low temperatures down to —150°C is reported for two metals, Hg and Pt. The purpose of the investigation was to examine the kinetic behavior for evidence of proton tunneling. The H/D isotope effect at mercury at low temperatures and the heat of activation behavior do not support any significant contribution from proton tunneling in the reaction. The situation is not as clear, however, for the case of smooth platinum. On the basis of the observation of a linear Arrhenius relation for the heat of activation down to —150°C, it is concluded that a proton tunneling mechanism cannot be appreciable for the h.e.r. on smooth platinum in ethanolic solutions.
Atomic Radii in Crystals
Authors: Slater J. C.
Published: January 2005

A set of empirical atomic radii has been set up, such that the sum of the radii of two atoms forming a bond in a crystal or molecule gives an approximate value of the internuclear distance. These radii give fair agreement with experiment in over 1200 cases of bonds in all types of crystals and molecules, with an average deviation of about 0.12 Å. The radii are similar to a set suggested by W. L. Bragg in 1920, but refined by consideration of many more crystals. They hold for covalent, metallic, and ionic binding equally well. These radii agree remarkably well with calculated radii of maximum radial charge density in the outermost shells of the atoms, as taken from previously unpublished calculations of D. Liberman, J. T. Waber, and D. T. Cromer, of the Los Alamos Laboratory, by relativistic self-consistent field calculation, using the exchange correction suggested in 1951 by the present author. There is discussion of the probable reason for this agreement, and discussion of the relation of these radii to the ionic radii of Pauling, Zachariasen, and others, and the tetrahedral and metallic radii of Pauling.
Ultraviolet-Induced Isotope Exchanges in Gaseous Mixtures of HCl and D2 and of DCl and H2
Authors: De Vries A. E. , Klein F. S.
Published: January 2005

Mixtures of HCl and D2 and of DCl and H2 were irradiated with an ultraviolet mercury resonance lamp and analyzed mass spectrometrically for the different isotopic species of hydrogen. It was found that at room temperature the reaction H+DCl→HD+Cl is slower than the exchange reaction H+DCl→D+HCl. This is to be expected from a consideration of activation energies, but it is in apparent contradiction to earlier results obtained by Leighton and Cross and by Steiner and Rideal. The reaction between hydrogen atoms and hydrogen molecules was found to be much faster at this temperature than is usually estimated.
On the Kinetic-Energy Distribution of Fragment Ions Produced by Electron Impact in a Mass Spectrometer
Authors: Stanton H. E. , Monahan J. E.
Published: January 2005

Distributions of initial kinetic energies have been measured for fragment ions that are produced in the breakup of the excited ions CO+, H2O+, NH3+, CH4+, and C6H6+. These ions were formed by electron impact. The energy of the ionizing electron beam was 400 eV in the case of benzene and 200 eV for the other target gases. The initial-energy distributions of the fragment ions from H2O and CH4 were measured as a function of electron energy over the interval from 100 to 400 eV. No measurable change in the distributions was observed. Evidence presented indicates that the excess-energy ion pair (masses 15 and 63) are formed simultaneously in the decay of doubly charged benzene ions. Included also in this paper are the details of an analytical method to correct measured energy distributions for kinematic effects and instrumental distortions. In this analysis the distributions of the internal energy converted into kinetic energy of the fragments are characterized by their moments.
Intensity Distribution for the X 1Σ+→A 1Π Transition in Carbon Monoxide Excited by Electron Impact
Authors: Silverman S. M. , Lassettre E. N.
Published: January 2005

The envelope shape for the unresolved X 1Σ+→A 1Π transition in carbon monoxide excited by electron impact has been experimentally determined at an incident electron energy of 508 V. The distribution has been compared with calculations using several published theoretical formulations from which the Franck—Condon factors may be obtained.
Spin Hamiltonian for Cr III Complexes. Calculation from Crystal Field and Molecular Orbital Models and ESR Determination for Some Ethylenediammine Complexes
Authors: McGarvey B. R.
Published: January 2005

The spin Hamiltonians of Cr(en)33+ and trans-CrCl2(en)2+ in single crystals of Co(en)3Cl3·3H2O, Co(en)3Cl3·NaCl·6H2O and trans-[CoCl2(en)2]Cl·HCl·2H2O have been determined from the ESR spectra. In the case of the trans-CrCl2(en)2+, ion it was found that the major axis for the spin—spin interaction lay along the C2 axis which is in the plane of the nitrogen atoms and rotates one ethylenediammine ring into the other. D and E for trans-CrCl2(en)2+ were calculated from both a crystal field model and from the results of an extended Hückel molecular orbital calculation. It was found that both calculations give comparable results and give the best results when the spin—orbit coupling parameter of the free ion is used. In the case of the MO calculation, the results agree with experiment when the N–Cr–N bond angle in the ethylenediammine ring is chosen to be 84°. For trigonal complexes of Cr III, D was also calculated using a crystal field model and again it was found that the best results were obtained when the spin—orbit constant was that of the free ion. These calculations also showed that large changes in D and E can be expected for crystal field symmetries that allow for configuration interaction between the ground state and an excited quartet state. The theory for g in these complexes was also developed. In the case of the near octahedral complexes it has been shown that g can be simply related to the charge on the Cr atom in the eg bonding orbitals.
Dissociation Energies of Diatomic Molecules of the Transition Elements. II. Titanium, Chromium, Manganese, and Cobalt
Authors: Kant Arthur , Strauss Bernard
Published: January 2005

Using information derived from a combination of effusion and mass-spectrometric techniques, the dissociation energy of Co2 has been calculated from the ratio of dimeric and monomeric cobalt in equilibrium with the liquid as D00(Co2)=39±6 kcal. Upper limits to the dissociation energy of Ti2, Cr2, and Mn2 are also estimated as D00(Ti2)<58 kcal, D00(Cr2)<44 kcal, D00(Mn2)<21 kcal. These results are correlated with the energy required to promote the atom to the lowest-lying bonding or valence state of electron configuration 3dn—14s.
Crystal Spectra of Pentahalo Vanadyl and Molybdenyl Anions
Authors: Wentworth R. A. D. , Piper T. S.
Published: January 2005

Crystal spectra of some pentahalo complex ions VOX53— and MoOX52— are reported. Polarized spectra were obtained for VOCl53—. Temperature dependence of the intensity and crystal field arguments are used to establish the assignments and to identify the source of the intensity. These results remove all doubt about the assignment of the 2B2→2B1 transition. It is shown that this transition is primarily vibronically allowed and gives rise to a shoulder in the high-energy portion of the intense electronically allowed band of VOCl53— centered at 15 500 cm—1 and assigned to the 2B2→2E transition. The remaining structure of this band is ascribed to a vibrational progression in the vanadyl stretching frequency. The implications of these results in the interpretation of other vanadyl and molybdenyl spectra are discussed.
Approximate Series Solutions of Nonseparable Schrödinger Equations. I. Mathematical Formulation
Authors: Frost Arthur A.
Published: January 2005

A series solution method is developed that is a generalization of the method used by Pekeris for helium-atom calculations. It is equivalent to the linear variation method but requires few, if any, matrix component integrals to be evaluated. The method is illustrated by an application to the s states of the hydrogen atom.
Mass-Spectrometric Studies at High Temperatures. II. The Dissociation Energies of the Monofluorides and Difluorides of Silicon and Germanium
Authors: Ehlert T. C. , Margrave J. L.
Published: January 2005

Calcium fluoride has been used to fluorinate silicon and germanium in a heated Knudsen cell in a mass spectrometer. Second- and third-law calculations using effusion data for the gaseous monofluoride and difluoride species produced at temperatures up to 1575°K are in good agreement and lead to the following atomization energies: D°298[SiF(g)]=5.61±0.2 eV, ΔH°a,298[SiF2(g)]=12.33±0.2 eV, D°298[GeF(g)]=5.04±0.2 eV, and ΔH°a,298[GeF2(g)]=10.0±0.8 eV.
Microwave Rotation Spectra of Hydrogen-Bonded Molecules
Authors: Costain C. C. , Srivastava G. P.
Published: January 2005

The pure rotation spectra have been observed for the hydrogen-bonded bimolecules CF3COOH–HCOOH, CF3COOH–CH3COOH, and CF3COOH–CH2FCOOH. For CF3COOH–HCOOH, the O···O distance RH was found to be 2.69±0.02 Å. The O···O distance becomes 0.011 Å longer when D is substituted for H in the hydrogen bond, i.e., RD—RH=0.011 Å. The heat of formation was found to be —ΔH=15.8 kcal/mole. Similar values, RH=2.67 Å and RD—RH=0.012 Å, were obtained for CF3COOH–CH3COOH, but in this molecule the spectrum of the singly deuterated species shows that the D atom tunnels between the two partners in the bimolecule at a rate faster than the rotational frequency. For a symmetric double minimum potential function the barrier to tunneling is found to be less than 5000 cm—1. The rapid tunneling also implies that only a sixfold barrier to the internal rotation of the CF3 and CH3 groups can exist, and therefore the nearly free rotation of these groups in the bimolecules and in dimers can be expected. This free rotation would explain the failure to detect the low K lines in the pure rotation spectra. The rapid tunneling of the D (and H) atoms in the hydrogen bond also implies an inversion doubling which would contribute to the width of the v(OH) bands in the carboxylic acid dimer infrared spectra. The difference RD—RH predicts a shortening of the O···O distance of 0.073 Å when the O–H vibration is excited, which provides a mechanism to couple the low hydrogen-bond stretching frequency and the v(OH) frequency to produce the broad dimer bands.
Degree of the Critical Isotherm
Authors: Widom B.
Published: January 2005

An argument is presented which indicates that if g is the degree of the critical isotherm, d the degree of the coexistence curve, and f the power of ∥ Tc—T ∥—1 with which the isothermal compressibility becomes infinite as the critical point is approached, then g=1+fd. The relation of this result to other theoretical and experimental facts is discussed.
Effect of Pressure on Emission and Absorption Spectra of Alkali Halide Phosphors
Authors: Alers P. B. , Shannon P. E. V.
Published: January 2005

Absorption and emission energies of certain alkali halide phosphors under pressure have been measured. The systems involved were KCl:Tl, NaCl:Tl, KCl:Pb, NaCl:Pb, CsI:Tl, and NaI:Tl, and pressures in excess of 40 kbar were employed. Data for NaCl:Tl and the low- and high-pressure forms of KCl:Tl could be fitted by a configuration coordinate model, but the behavior of the other systems could not be described in this way.
Partial Ionization Cross Sections for Noble Gases Bombarded with 0.8–3.75-MeV Protons
Authors: Wexler S.
Published: January 2005

The partial cross sections for the production of noble-gas ions in their various charge states were determined for He, Ne, Ar, and Kr bombarded by protons in the energy range from 0.8 to 3.75 MeV. The slow ions formed in the collisions of the swiftly moving hydrogen ions with the isolated noble-gas atoms were extracted in a direction at right angles to the proton beam. Their charge and intensity were analyzed by means of a portable mass spectrometer with special constructional features. These data were combined with values of the total ionization cross sections determined by Hooper et al. to evaluate the partial cross section for the formation of each species. The cross sections are compared with those previously obtained by others for proton projectiles with energies between 5 and 180 keV.
ESR of the Triplet States of Randomly Oriented Molecules
Authors: Wasserman E. , Snyder L. C. , Yager W. A.
Published: January 2005

The observation of the Δm = 1 transitions of the triplet states of randomly oriented molecules by electron spin resonance (ESR) is discussed. The shape of the absorption curve permits the ready determination of the zero-field parameters from the spectrum. In a derivative presentation, the widths of the lines observed give direct information on environmental and hyperfine broadening. Computer simulations of triplet spectra are presented. Good agreement is found with the observed spectra of phosphorescent and ground-state triplets.
Rate of Destruction of Acetylene in Flame Gases
Authors: Fenimore C. P. , Jones G. W.
Published: January 2005

The burnt gas from fuel-rich acetylene—oxygen flames contains larger than equilibrium amounts of acetylene, but only equilibrium amounts of the species [H]>[OH]≫[O]>[O2], which are listed in order of decreasing concentrations. The decay of acetylene in this environment at 1700° to 2000°K can be represented by −d[C2H2]/dt=2×1012[OH][C2H2] moles cm−3·sec−1but cannot be represented by k[X][C2H2] where [X] is [H], [O], or [O2]. Therefore acetylene may be consumed at the rate of its irreversible reaction with OH; and if so, it reacts five to 10 times slower with OH than with an equal concentration of O in flames, the latter rate having been estimated previously in an environment where [O]>[OH].
Theory of Nuclear Hyperfine Broadening of ESR Lines in Liquids
Authors: Kivelson Daniel
Published: January 2005

The theory of the broadening of ESR spectral lines arising from fluctuations in the isotropic and anisotropic g factors and hyperfine tensors is discussed. Particular attention is paid to the case where the molecule has several equivalent nuclei and the spectrum, therefore, has degenerate lines, i.e., several transitions of the same frequency corresponding to different nuclear states. A mean linewidth T2γ—1 is calculated for each degenerate set, and the significance of this quantity is discussed. Certain special cases where the relaxation matrix is diagonal in a spin-state basis are discussed, and the linewidths for each component line of the degenerate set is obtained. The Redfield and the Kubo and Tomita theories are compared, and the limitations of the latter in dealing with degenerate lines is analyzed.
Nuclear Magnetic Relaxation in Camphor
Authors: Anderson J. E. , Slichter W. P.
Published: January 2005

Solid solutions containing d- and l-camphor have been investigated by nuclear magnetic resonance and x-ray powder diffraction between 77° and 473°K. Striking differences are observed among the various solutions in the vicinity of the second-order phase transition. The transition temperature is found to vary with composition, passing through a minimum at the 3:1 d:l solution. The width of the λ transition, reflected in the NMR second moment, increases going from the pure isomer to the racemic mixture. Methyl group reorientation persists at 100°K, although molecular tumbling has been arrested at this temperature in all samples. The x-ray powder patterns of the pure isomer, the 1:1, and 3:1 mole ratio solids differ at 77°K, but are identical at 298°K. Plots of the NMR spin—lattice relaxation time versus reciprocal absolute temperature yield an activation energy of 2.35 kcal/mole for methyl-group reorientation in d-camphor below the λ point. Above the rotational transition, the x-ray and NMR data are independent of concentration. Activation energies of 2.8 and 14.6 kcal/mole are calculated for the processes of molecular tumbling and self-diffusion, respectively. The T1 data are quantitatively examined in terms of the BPP theory.
Spectral Study of Active Nitrogen Flames Exhibiting CN ``Tail'' Bands
Authors: Brown Robert L. , Broida H. P.
Published: January 2005

Flames of active nitrogen and simple chlorinated hydrocarbons which exhibit several zones defined by differences in intensity and spectra have been examined under a variety of conditions of flow rate, pressure, added impurities, and burner configuration. One of these zones exhibited strong emission arising from the CN ``tail'' bands, i.e., bands originating in high vibrational levels of the B 2Σ state. Qualitative spectral evidence is consistent with the assumption that the chemical processes responsible for the emission from the different zones all produce CN selectively in the A 2Π state but with different vibrational distributions, and that population of B 2Σ occurs through interaction of mutually perturbing rotational levels of A 2Π and B 2Σ and through collision-induced transfer from unperturbed levels in A 2Π. As an incidental aspect of the work it has been found that traces of air in the N2 supply were helpful for production of the ``pink'' nitrogen afterglow.
Application of the Theory of Absorbing Markov Chains to the Statistical Thermodynamics of Polymer Chains in a Lattice
Authors: Mazur Jacob
Published: January 2005

A concept of absorbing Markov processes is employed in order to study the statistical thermodynamics of infinitely long polymer chains, simulated by a random flight on a lattice. These polymer chains interact in the sense that certain chain conformations are associated with intramolecular interactions, defined by short-range, steplike potentials. Various thermodynamic functions are derived from the polymer partition function, which, in turn, is obtained from the largest eigenvalue of the matrix of transition probabilities. The thermodynamic functions of this simplified polymer model are evaluated for some lattice models and for different forms of the interaction potentials. The results thus obtained are then compared with more accurate, but much more lengthy, Monte Carlo or direct-counting computations.
Vanishing First- and Second-Order Intramolecular Heavy-Atom Effects on the (π*→n) Phosphorescence in Carbonyls
Authors: El-Sayed M. A.
Published: January 2005

The coupling schemes and matrix elements resulting from the first-order spin—orbit perturbation of the lowest n,π* triplet state in halogenated carbonyl compounds are examined. Because of the one-electron nature of Hs·o·, only seven of the 24 states resulting from one-electron transitions in X2CO, are found to perturb the 3A2(n,π*) state. Of these seven, only three states give rise to interactions involving the halogen atom: 1B2(n,σ2*) through two-center terms and small contribution of one-center term, 1A1(n,σ1*) through a small contribution of two-center term, and 1B1(σ1,π*) through three-center terms. Qualitative calculation indicates that of these three only the first interaction, when X=iodine, can be an order of magnitude larger than the one-center term on oxygen in H2CO. The absence of one- and two-center terms in the moment of the 1B2(n,σ2*)↔1A1 transition, however, reduces the importance of this state in inducing intramolecular heavy-atom effects.

Because of the one-electron property of the spin—orbit and vibronic operators, only two states, the 1B1(σ1,π*) and 1B2(n,σ2*), can be used for second-order (s.o. and vibronic) intramolecular heavy-atom perturbations. It is found that there are no intermediate states through which these states can couple with the emitting triplet state. These conclusions indicate that intramolecular heavy-atom effects on the π*→n phosphorescence radiative lifetime are expected to be small in X2CO or in any other carbonyl. It is pointed out that the large intramolecular heavy-atom effects observed for the π*→π phosphorescence is a result of the relatively small spin—orbit perturbation present in the parent heavy-atom-free molecule.
Thermal Decomposition of Some Alkyl Halides by a Shock-Tube Method
Authors: Tsang Wing
Published: January 2005

The decomposition of several alkyl halides have been studied by a comparative rate method using a single-pulse shock tube. Rate constants for the elimination of hydrogen halide from the parent molecule are compared with the rate of elimination of hydrogen bromide from isopropyl bromide. The Arrhenius expression for the latter reaction has previously been found to be k(i−C3H7Br)=1013.62exp(−47 800/RT)sec−1. On this basis, the following rate expressions have been obtained:  k(C2H5Br)1013.19exp(−53 700/RT) (sec−1)740∘−940∘K, k(C2H5Cl)=1013.16exp(−56 460/RT) (sec−1)820∘−1000∘K,k(i−C3H7Cl)=1013.64exp(−51 100)/RT) (sec−1)750∘−950∘K, k(i−C3H7I)=1013.67exp(−45 065/RT) (sec−1)680∘−850∘K, k(t−C4H9I)=1013.73exp(−38 080/RT) (sec−1)650∘−760∘K.These results are compared with the results of earlier low-temperature studies. The advantages and reliability of this type of kinetic study are discussed.
Mass-Spectrometric Investigation of the Reactions of O Atoms with H2 and NH3
Authors: Wong E. L. , Potter A. E.
Published: January 2005

The reaction of H2 with O in the absence of O2 was studied in the temperature range 400° to 600°K by using a stirred reactor with a mass spectrometer for analysis. The rate constant for the H2+O→OH+H reaction was found to be 4.3×1013 exp(−10 200/RT) cc/mole·sec. The rate of O consumption was about three to five times smaller in the absence of O2 than in its presence. This difference was quantitatively explained as a result of the reaction sequence H+O2+M→HO2+M;HO2+O→OH+O2.The reaction of NH3 with O in the absence of O2 was also studied for the temperature range 350° to 600°K. The stoichiometry of the reaction could be approximately represented by NH3+4.4O→NO+0.5H2+1.2O2+1.0H2O.In contrast to the H2+O reaction, the rates for consumption of O were not affected by the presence or absence of excess O2 within experimental error. A reaction mechanism was proposed, and using this mechanism the rate constant for the NH3+O→NH2+OH reaction was estimated to be 1×1012 exp(−4800/RT) cc/mole·sec.