bluuebunny/crossref_metadata_2025_split huggingface dataset:
Some Deductions from a Formal Statistical Mechanical Theory of Chemical Kinetics
Authors: Ross John , Mazur Peter 
Published: January 2005

A perturbation solution of an assumed Boltzmann-type equation for bimolecular chemical reactions in a homogeneous gas phase consisting of molecules with or without internal degrees of freedom, leads to the conclusion that the law of mass action as well as the usually assumed phenomenological rate expressions for chemical reactions, is strictly valid only in lowest order of the perturbation. Higher order perturbations introduce an affinity and time dependence in the rate coefficient and the law of mass action becomes inadequate to the extent of the contribution of the effects of the perturbations.
A transition state formation of rate coefficients for bimolecular gas-phase reactions is presented under less restrictive sufficient conditions than reported previously.
Magnetic Susceptibility of Mercuric Oxide at Various Temperatures
Authors: Mikhail H. , Hanafy Z. , Salem T. M. 
Published: January 2005

Mercuric oxide exists in two forms, the red and the yellow oxides. Magnetic susceptibility determinations showed no appreciable difference between the two oxides; the red one has a mass susceptibility of (—0.2217±0.0002)·10—6 emu/g, while the yellow one has a slightly lower mass susceptibility of (—0.2165±0.0002)·10—6 emu/g at room temperature (25°C).
The temperature variation of their mass susceptibility between room temperature (25°C) and about 300°C was also investigated. The general shape of the curve for the two oxides is essentially the same, namely, an increase in diamagnetism with rise in temperature followed by a mild drop and subsequently a sharp rise. The position of the peak occurs at about 50°C for the red oxide and at about 114°C for the yellow oxide. A tentative explanation of their behavior was given, based on impurity ionization.
Molecular Orbitals in Some Boron Compounds
Authors: Moore Emmett B. , Lohr L. L. , Lipscomb William N. 
Published: January 2005

An LCAO treatment of boron framework orbitals in B10H14 yields a charge distribution of +0.05e on atoms 1 and 3, of —0.25e on atoms 2 and 4, of —0.03e on atoms 5, 7, 8, and 10, and of +0.27e on atoms 6 and 9. When a charge of about —0.2e is assigned to each bridge H atom, the order of reactivity agrees with that expected from the chemical behavior (neg 2,4&lt;1,3&lt;5,7,8,10&lt;6,9 pos).
An LCAO investigation of boron orbitals in the B5H5 molecule of D3h symmetry and with nine equal B–B distances indicates expected stability for the B5H5—2 ion, but not for the neutral molecule. A simplified method of accounting for the molecular orbitals in icosahedral B12H12—2 yields some conclusions concerning B11 hydrides and ions.
Collision Mechanics in Crossed Maxwellian Molecular Beams
Authors: Datz Sheldon , Herschbach Dudley R. , Taylor Ellison H. 
Published: January 2005

A general treatment of the mechanics of collision between two Maxwellian molecular beams is described. Expressions are obtained for the distribution in collision energy, for the elastic and reactive collision rates, and for the angular distribution of the center of mass vectors for beams colliding at any angle. The treatment can accommodate any reaction cross section which can be expressed as a step function multiplied by a linear combination of powers of the relative energy.
The recoil momentum which affects the product distribution in the laboratory system is discussed, and the treatment is applied to some experimental data on the reaction of K with HBr.
Studies of Transient Species Formed During Catalytic Reactions of CO2 + D2 and of 1-Butene
Authors: Melton Charles E. 
Published: January 2005

Transient species in a catalyzed reaction have been observed in the gas phase by placing the catalyst in a specially designed mass spectrometer ion source.
The reaction, D2+CO2→ lim PtD2O+CO,was studied over a pressure range 0.1–1 mm Hg and a temperature range 50–1100°C to demonstrate the applicability of the techniques. A free radical, of molecular formula CDO, was shown to be formed by and desorbed from the Pt catalyst during the reaction. In addition, DCOO— ions were observed suggesting the presence of an intermediate DCOOD on the catalyst.
The production of the products CO and D2O was not a monotonic function of catalyst temperature, but instead showed a maximum in the temperature range 400–500°C. The rate increased approximately as the first power of PCO2 and was nearly independent of the partial pressure of D2. The catalytic decomposition of butene-1 was studied in the same way. Free radicals produced by the catalytic decomposition of this compound are compared to those known to occur from thermal decomposition at the same temperature. In the catalytic decomposition, the radicals C4H7 and C3H5 were found to be most abundant; in contrast, CH3 and C3H5 are most abundant in the thermal decomposition.
Theory of the Spin and Charge Distribution in Aromatic Ion Radicals; Application to the Naphthalene Negative Ion
Authors: Schug John C. , Brown Thomas H. , Karplus Martin 
Published: January 2005

The valence-bond method is extended to positive- and negative-ion radicals. General formulas for the required energy, overlap, spin-density, and charge-density matrices are developed and specialized to pielectron systems. An application of the method to the pi electrons of the naphthalene negative ion is given. Included in the calculation are all unexcited structures with the negative charge in each of the ten possible positions. When approximate exchange and transfer integrals are used to determine the coefficients of valence-bond structures, the α to β position spin-density ratio is found to be equal to 2.60, in good agreement with the ``experimental'' value of 2.65. The magnitudes of the calculated spin densities are such that a Q of —26.3 gauss is required to obtain the measured hyperfine splittings.
To test the validity of these valence-bond results, their sensitivity to the molecular integral values is examined. Also, comparisons with a variety of molecular-orbital calculations are given. It is of considerable interest that the charge distributions obtained from the valence-bond theory and the molecular-orbital theory are very different in spite of the similarity of the spin distributions calculated by the two methods.
Heat Capacities and the Residual Entropy of Ta2H
Authors: Saba W. G. , Wallace W. E. , Sandmo H. , Craig R. S. 
Published: January 2005

Heat capacities of Ta2H have been determined over a range of temperature extending from 12° to 555°K. Three very sharp λ points were observed, at 306, 332, and 333.5°K, suggesting that Ta2H exists in four forms—β1 below 306°K, β2 between 306 and 332, β3 at about 333, and α above about 334°K. The heat capacity data for Ta2H are used together with similar data obtained earlier for elemental tantalum and the entropy of formation of Ta2H, evaluated from vapor pressure work by Kofstad, Wallace, and Hyvönen, to compute the residual entropy of β1—Ta2H. This is found to be —0.39±0.30 cal—1 deg—1 mole—1. The data also are used to estimate configurational entropies of the β2 and β3 forms. These are 0.70 and 3.3 cal—1 deg—1 mole—1, respectively. The corresponding quantity for the α form is 4.9.
The λ points are attributed to rearrangements of the hydrogens in the 12-fold more abundant tetrahedral sites. At low temperatures the solute hydrogen atoms are presumed to populate the sites in an orderly fashion. With increasing temperature the ordered arrangement is altered and finally, in the α phase, destroyed. It is inferred from entropy calculations, however, that local order, probably pairing, persists in the α form even to 555°K, the highest temperature studied.
Consideration is given to the possibility that the upper two λ points, which nearly coincide, should really be one, the splitting being due to concentration gradients or strains. Differential thermal analysis of samples containing from 27.5 to 44.0 atomic % hydrogen suggests that the splitting is a true property of Ta2H, but the results are not completely conclusive.
Electron Spin Resonance Study of Radiation Damage in Single Crystals of Urea Compounds
Authors: Jaseja Thadho S. , Anderson Roy S. 
Published: January 2005

Single crystals of urea compounds were examined by 3-cm electron spin resonance techniques after x and γ irradiation. All experiments were conducted at room temperature. No resonances were observed in urea and thiourea. This is interpreted to indicate that the lifetimes of any resulting unstable species must be less than 30 min. at room temperature. However, methylurea and ethylurea showed strong, highly stable spectra centered at g≃2.00. Analyses of these spectra suggest that the trapped radicals[Complex chemical formula]are formed from methylurea and ethylurea, respectively, by the loss of a hydrogen atom.
In both cases all radicals in the unit cell were considered to be magnetically equivalent. Calculated hyperfine intervals agree favorably with those observed. The spin density of the unpaired electron at the adjacent N–H group is believed less than 0.002, since the only apparent effect of this group was a broadening of the hyperfine lines.
In methylurea the ·C–H2 group was found to have an H–C–H angle of 117°. The principal components of the diagonal electron-nuclear coupling dyadic were 10, 22, and 32 gauss. In ethylurea the ·C–H bond was observed to lie along a crystallographic axis. The principal components were 10, 21, and 24 gauss. In this case the isotropic coupling constant was 18 gauss.
Copolymerization Mathematics and the Description of Stereoregular Polymers
Authors: Price Fraser P. 
Published: January 2005

The mathematics of Markoffian processes has been applied to the description of the copolymerization of vinyl monomers and to the characterization of stereoregular polymers. Expressions for polymer compositions for copolymerization of two monomers are given for the cases where the terminal sequence of the growing chain contains one, two, or three units, including the terminal radical. Expressions for polymer compositions are also presented for the case of the copolymerization of three monomers.
The mathematics are extended to cover the characterization of stereoregular polymers formed either from monosubstituted or from α-β-disubstituted vinyl monomers. The mathematical requirements for the experimental characterization of such polymers are discussed.
Activated Complexes of Fast Bimolecular Reactions
Authors: Ree Teresa S. , Ree Taikyue , Eyring Henry , Fueno Takayuki 
Published: January 2005

The specific rates of radical association and ion-molecule reactions (e.g., CH3+CH3→C2H6, H2++H2→H3++H, etc.) were calculated with the use of the absolute reaction-rate theory and were compared with the observed values. Except for some special reactions, the observed rates agree with the theoretical values with a transmission coefficient, 1 to 1/10.
The over-all entropy change of the backward reactions ΔSb were calculated by the usual statistical thermodynamical method, and also the activation entropy of the backward reactions, ΔSb‡, were calculated. The two quantities agree fairly well.
From these results it was concluded that the activated complexes of the fast reactions have loose structures such that the reactant molecules (radicals or ions) rotate freely with the restriction that they cannot move independently in the translational degrees of freedom.
Unimolecular Decomposition of Vibrationally Excited Ethane and Ethyl Radicals
Authors: Heller Carl A. , Gordon Alvin S. 
Published: January 2005

H or D atoms and ethyl radicals were concurrently produced by the mercury sensitized photolysis of mixtures of H2 (or D2) and diethyl ketone. Combination of an ethyl radical with a hydrogen atom produces vibrationally excited ethane molecules. Their rate of dissociation into methyl radicals relative to stabilization to ethane was studied as a function of pressure of ketone for both H and D.
Similar studies were made of the mercury sensitized reactions of mixtures of D2 or H2 and ethylene, which permitted the measurement of the maximum rates of decomposition of excited ethyl radical and of excited ethane both as a function of pressure and of temperature.
Our results show that vibrational energy is not used in overcoming the barrier for alkyl radical addition to an olefin bond.
Organic Liquid Scintillators. III. On the Quantum Yield of Fluorescence and the Quenching of Fluorescence by Oxygen
Authors: Heller Adam 
Published: January 2005

Expressions for the quantum yield of fluorescence of aromatic hydrocarbons in benzene and alkylbenzenes have been derived assuming zero internal quenching. These expressions indicate that the molecular quantum yield of fluorescence increases with (a) the lifetime of the first excited singlet state of the solvent, (b) the transition probabilities from the levels of the solute that correspond to the levels involved in the excitation of the solvent [A. Heller, J. Chem. Phys. 35, 1980 (1961)], and (c) the increase in the degree of degeneracy in the solute levels corresponding to those involved in the excitation of the solvent.
Minimum values of the molecular quantum yield of fluorescence of a group of aromatic hydrocarbons have been computed at different concentrations of the solutes. The compounds with the highest values are p-divinylanthracene, perylene, p-quaterphenyl and p-terphenyl.
The dimensions of the excited aggregates that are formed by the exchange interaction between the molecules in liquid or plastic scintillators are estimated from Basile's data for solutions of PBD in polyvinyltoluene [L. S. Basile, J. Chem. Phys. 27, 803 (1957)]. The number of monomer units per aggregate is about 1.2×103 and the radius of interaction about 18 A.
The quenching of fluorescence by oxygen is explained by the existence of π-electron level pairs of almost similar energy difference in the solvent and the solvent—oxygen complex [H. Tsubormura and R. S. Mulliken, J. Am. Chem. Soc. 82, 5966 (1960)], and by the short lifetime of the complex compared with that of the solvent. The latter results from the lower order of symmetry of the complex in comparison with that of the π-electron system in benzene.
Decomposition of (CH3Xe131)+ Following the Nuclear Decay of CH3I131
Authors: Carlson T. A. , White R. M. 
Published: January 2005

The charged fragments resulting from the decay of CH3I131 have been measured by a specially designed mass spectrometer. In 70% of the decays, the parent ion CH3Xe+ remained intact in direct contrast to the decay of CH3T in which hardly any CH3He+ was found [A. H. Snell and F. Pleasonton, J. Phys. Chem. 62, 1377 (1958)].
More than 20 other ions were also detected including the doubly charged methyl xenon (CH2Xe)+2. Their relative abundances are discussed in terms of excitation resulting from the sudden change in nuclear charge, and from multiple Auger processes in cases where internal conversion accompanies the decay.
Vibrational Spectra of MoF6 and TcF6
Authors: Claassen Howard H. , Selig Henry , Malm John G. 
Published: January 2005

Infrared spectra of gaseous MoF6 and TcF6 from 6–43 μ, the Raman spectrum of MoF6 gas, and an incomplete Raman spectrum of liquid TcF6 are reported. These are interpreted in terms of the octahedral point group 0h. The fundamental frequencies for MoF6 are 741(ν1), 643(ν2), 741(ν3), 264(ν4), 306(ν5), and 190(ν6). For TcF6 they are 705(ν1), 551(ν2), 748(ν3), 265(ν4), 255(ν5) and ν6 has not been determined.
Differences between the spectra of MoF6 and TcF6 are explained as a consequence of orbital degeneracy in the ground state of the latter, in analogy with similar differences in the 5d series.
Open-Shell Calculations of Hyperfine Splitting for the Ground State of Li-Like Ions
Authors: Kerwin J. , Burke E. A. 
Published: January 2005

The hyperfine splitting of the ground state of lithium is calculated using analytic open-shell wavefunctions. The difference in the experimental and calculated value for the Li7 nucleus by this method is 36.468 Mc/sec as compared to a difference of 57.011 Mc/sec using Hartree-Fock wavefunctions.
The nuclear-spin-independent contribution to the hyperfine splitting is computed for the Li-like ions He— to Ne7+ using both open- and closed-shell wavefunctions, and the results are discussed with reference to contributions from the orbital and core electrons.
Rare-Gas Molecule-Ion Formation by Mass Spectrometry. Kinetics of Ar2+, Ne2+, and He2+ Formation by Second- and Third-Order Processes
Authors: Dahler J. S. , Franklin J. L. , Munson M. S. B. , Field F. H. 
Published: January 2005

The ions Ar2+, Ne2+, and He2+ are formed in a mass spectrometer operated at high pressures (up to 300 μ) by the bimolecular excited atom reaction R*+R=R2++e, and Ar2+ and Ne2+ are formed by the termolecular ion-molecule reaction R++2R=R2++R. In helium, while He2+ is formed by a third-order process, there is doubt that an ionic reaction is involved.
Ratios of the rates (cross-sections) for excitation leading to R2+ formation and ionization are found to be 5.5×10—2, 1.0×10—2, and 6.4×10—2 for argon, neon, and helium. The measurements were made at nominal electron voltages (EV) of 15, 20, and 22 v, respectively, which correspond to maximum excitation. Values of 1.4×10—2 and 0.45×10—2 were also obtained at EV=70 v for argon and neon.
The experiments yield only the product of the bimolecular rate constant and the lifetime of the R* reactant atom (krτu), and the values of this product obtained at EV=15, 20, and 22 v are for argon, neon, and helium 3.6×10—16, 11.6×10—16, and 0.58×10—16 cc/molecule. At EV=70 v values of 2.7×10—16 and 1.1×10—16 cc molecule are obtained for argon and neon. Speculations are given concerning the magnitude of the lifetimes of R*, and it is concluded that values of about 10—8 sec must be considered as possible. The corresponding cross sections for the reaction forming R2+ lie in the range 1000–10 000×10—16 cm2.
The rate constants for the formation of Ar2+ and Ne2+ by the three-body process are, respectively, 2.1×10—28 and 2.0×10—29 cc2/molecule2sec. It is recognized that values as large as these are in disagreement with values inferred from pulsed-discharge ion-drift velocity experiments. A possible mode of reconciliation is suggested; namely, at sufficiently high pressures collisional decomposition of R2+ ions formed by the termolecular process occur in the drift-velocity experiments.
High-Temperature Evaporation and Thermodynamic Properties of Zirconium Diboride
Authors: Leitnaker James M. , Bowman Melvin G. , Gilles Paul W. 
Published: January 2005

Vapor pressures of zirconium over zirconium diboride have been measured by the Knudsen technique over the temperature range 2150° to 2475°K. A new type of apparatus was constructed and used successfully in the study.
Zirconium diboride was determined to evaporate congruently at a composition of ZrB1.906(+0.025 or —0.010) by heating solid pressed plugs of both zirconium-rich and boron-rich material to constant composition at 2400°C to 2500°C. The over-all reaction is ZrB1.906(s)=Zr(g)+1.906 B(g)Three series of measurements were made using tungsten crucibles and different orifice sizes. Second-law and third-law treatments of the data did not agree. Thermodynamic calculations were made which indicated that water vapor at low background pressures would produce volatile oxides of both zirconium and boron. This reaction was investigated by adding water vapor to the system and the increased transport of zirconium was clearly demonstrated. Accordingly, each pressure measurement was corrected by a factor β, constant for each series, related to the background pressure.
From the corrected pressures, values of ΔH0o for the reaction were computed by the third-law treatment. From the three series a vaporization coefficient of 0.025±0.010 was computed, leading to an equilibrium ΔH0o of 458.3±6.5 kcal/mole for reaction 1, or a partial pressure of Zr over ZrB1.906 of 2.38×10—10 atm±20% at 2000°K. The variance between this and an expected value of 477.4 kcal/mole is presumed to be related, at least in part, to discrepancies in the heat of vaporization of zirconium.
The results verify the prediction that the Zr–B system exhibits a congruently evaporating phase and suggest that the congruently evaporating composition in many high-temperature systems will occur at nonstoichiometric compositions.
Infrared Spectra of Ammonia Suspended in Solid Nitrogen
Authors: Pimentel George C. , Bulanin Mikhail O. , Van Thiel Mathias 
Published: January 2005

Matrix isolation studies of the infrared spectra of ammonia suspended in solid nitrogen at 20°K are presented. Variation of the mole ratio of nitrogen to ammonia shows that monomeric NH3 in solid nitrogen absorbs at 3440, 3332, 1620–1632, 1143, and 970 cm—1. A large enhancement of ν3, 3440 cm—1, occurs relative to ν1, 3332 cm—1, just as observed for the pure solid. The totally symmetric vibrations ν1 and ν2 are relatively sharp (half-widths are 1 and 1.5 cm—1, respectively). The umbrella mode ν2 shows no evidence of inversion nor of free rotation. The band at 1143 cm—1 is ascribed to ν2 in combination with librational movement about the B axes. The constraints to movement within the nitrogen matrix cage seem to be larger than those reported for inert-gas matrices.
Some results on the hydrogen bonding in dimeric and polymeric ammonia are reported. The dimer absorbs at 3404, 1004.5, 987 cm—1 and possibly as well at 3313, 3246 and 3237 cm—1.
Negative Atomic Ions. II
Authors: Edie J. W. , Rohrlich F. 
Published: January 2005

Electron affinities of negative atomic ions were obtained in a previous paper [H. R. Johnson and F. Rohrlich, J. Chem. Phys. 30, 1608 (1959)] by isoelectronic extrapolation using a four-term approximation formula. Recently, Edlén [B. Edlén, J. Chem. Phys. 33, 98 (1960)] simplified this procedure, using only three terms and improved experimental input data. The theoretical justification of this procedure lies in the assumption that these formulas are the beginning terms of a perturbation series which is at least semiconvergent. Therefore, a four-term formula should give better results than a three-term formula. It is shown here that the experiments indicate that this is not likely to be the case, thereby raising strong doubts about the justification of this method.
An alternative method is therefore suggested. Here, the regularity pattern of the ionization potentials as a function of Z (fixed degree of ionization) is extrapolated. This is therefore an extrapolation of the results of a ``horizontal analysis.'' The method requires one experimental affinity for each p shell as long as sufficiently precise data on ionization potentials of highly ionized atoms (fourth and higher spectrum) are not available. The results agree within experimental error, except for the most recent value of C— which is about 10% too low.
Strong Field Stark Effect
Authors: Howe John A. , Flygare W. H. 
Published: January 2005

The energy levels of a rigid asymmetric rotor containing one or more quadrupolar nuclei and subject to an electric field are discussed for the case in which the Stark effect energies are larger than those arising from quadrupole coupling effects.
The theory is applied to quantitative Stark effect measurements on COCl235 and CH2CCl235. The dipole moments determined by this method are 1.17 and 1.34D, respectively.