bluuebunny/crossref_metadata_2025_split huggingface dataset:
Absorption Spectra of Hydrogen-Halide—Rare Gas Mixtures
Authors: Rank D. H. , Rao B. S. , Wiggins T. A. 
Published: January 2005

The null-gap regions of the 1–0 bands of HCl and HBr have been investigated with a grating spectrograph of very high resolution. The experiments were performed using an absorption tube of 90 cm length and a hydrogen-halide pressure of 25 cm Hg. The hydrogen halide was pressurized with argon, krypton, or xenon of density 2 to 5 amagats. The sensitivity of the apparatus was such that absorption features 10—4 the intensity of the P(1) line of HCl could be observed with ease.
The absorption features observed are complex, relatively sharp, and totally different when argon, krypton, or xenon is used as the pressurizing gas. It is suggested that the hydrogen-halide molecule forms a molecular complex with the rare-gas atoms used as pressurizing agents. The discrete induced absorption features have an intensity considerably less than 10—3 of the intensity of the P(1) line of HCl per amagat density of pressurizing gas. In HBr the ``induced absorption features'' have approximately two to three times the relative intensity observed in HCl.
HCl-Catalyzed Decomposition of Di-Tertiary Butyl Peroxide in the Gas Phase
Authors: Flowers Michael , Batt Leslie , Benson Sidney W. 
Published: January 2005

The homogeneous, gas-phase decomposition of di-tertiary butyl peroxide (dtBP), catalyzed by small amounts (1–16 mole %) of HCl, has been studied in the temperature range 90°—120°C and about 50 mm Hg pressure. Under these conditions, the rate of the uncatalyzed process is negligibly slow. The principal products may be represented by the two stoichiometric equations: dtBP→isobutene oxide+t−BuOH(20%−50%)→isobutene oxide+acetone+CH4(80%−50%).Very small amounts of C3H8, CO, isobutyraldehyde, and C2H6 are also observed. HCl is not consumed. The over-all kinetics may be represented by a simple scheme in which t-BuO and Me radicals abstract H from HCl, and the HCl is regenerated by Cl-atom attack on peroxide. Acetone and isobutene oxide (i-BuOx) act as inhibitors for the Cl-atom chain, yielding the inert CH3COCH2 and Me2CCHO radicals, respectively. The latter is probably responsible for a slow radical isomerization of i-BuOx to the isobutanal. This reaction provides a very fast isomerization path for the conversion of epoxides to aldehydes.
A derived rate law consistent with the data is given by −d(dtBP)dt∼2k1k5(dtBP)2k6(acetone),in which k1 is the rate constant for the splitting of dtBP into two t-BuO radicals, and k5/k6 is the ratio of rate constants for attack of Cl atoms on dtBP or on acetone (and/or i-BuOx), respectively. As predicted, the rate is independent of HCl. The chain length is given by λ=k5(dtBP)/k6(acetone) and is equal to about 25 at 10% decomposition and is almost independent of temperature.
The ratio of yields of acetone to t-BuOH is a direct measure of the kinetics of spontaneous decomposition of the t-BuO radical, and the data show that it is a pressure-dependent process. Unfortunately, the scatter in the data is too great to derive quantitative step constants for the relevant energy-transfer processes.
Studies on the Alternant Molecular Orbital Method. IV. Generalization of the Method to States with Different Multiplicities
Authors: Pauncz Ruben 
Published: January 2005

A general formulation of the alternant molecular orbital method, applicable to states of different multiplicities in systems with an even number of atoms, is presented. The treatment is formulated in such a way that the same integral sums appear in the energy expression for the states belonging to different multiplicities. The resultant energy expressions show a simple dependence on the mixing parameter λ.
Application to cyclic systems shows that the best λ values decrease slowly with increasing multiplicity. Comparison with the configuration interaction treatment reveals that the AMO method corresponds to a restricted CI treatment, but it is capable of yielding a considerable part of the energy improvement obtained by the latter method.
Formation of F18-Labeled Fluoro-Organic Compounds by the F19(n, 2n) Reaction
Authors: Anbar M. , Neta P. 
Published: January 2005

Fluoro-organic compounds were subject to irradiation by fast neutrons produced in a nuclear reactor; fluoroderivatives labeled with F18 were produced and their yield was determined. It was found that labeling yields of fluoro-organic compounds were substantially higher than those of other organic compounds exposed to fluorine 18 produced extramolecularily, either by the O16(H3, n) or by the F19(n, 2n) reactions. The extent of substitution of a hydrogen atom by radiofluorine was found more than 100 times higher than that of a fluorine atom. It was shown that the labeling occurs mainly in the same part of the molecule which carried the original fluorine atom. In some cases it was shown that it is the same atom which is transformed to a radionuclide.
When fluoroorganic compounds were irradiated in solution, a constant molecular labeling yield was observed. This yield which was obtained in dilute solutions in water, acetic acid or ethanol, was found independent of solute concentration; moreover, it was not affected by the presence of scavengers. The labeling yield of the aliphatic solvents was lower when exposed to fluorine 18 produced from an organically bound fluorine than from a fluoride ion.
It is difficult to interpret the experimental results without assuming that a genuine retention of the transformed fluorine 18 in the parent molecule takes place. It is suggested that the (n, 2n) reaction proceeds, in part at least, as a spallation-type reaction, forming an excited F18 nucleus which does not undergo any recoil. The excited F18 is subsequently converted to the ground state following gamma emission; the recoil energy of many of these gammas is not sufficient to cause an irreversible cleavage of the C–F bond.
Solvent Effects in Electron Spin Resonance Spectra
Authors: Gendell Julien , Freed Jack H. , Fraenkel George K. 
Published: January 2005

It has been shown that a simple model can account for the available data on the solvent dependence of the hyperfine splittings in the ESR spectra of organic free radicals. We have assumed that the changes in splittings arise entirely from a redistribution of the pi-electron spin density, and that the spin density is affected only by localized complexes between the solvent and polar substituents or heteroatoms in the radical. This model predicts that the magnitudes of the changes in proton splittings should often be small, although large fractional changes at positions of small spin density can sometimes occur. The large variations found for the nuclei of many electron atoms are shown to arise because their splittings are very critical functions of the spin density.
The effect of the solvent on the proton hyperfine splittings in the semiquinones has been treated by assuming that the solvent alters the electronegativity of the oxygen atoms and by performing molecular-orbital calculations to estimate spin density changes. These calculations reproduce both the directions and magnitudes of the changes in proton splittings with solvent and are in agreement with the very large fractional changes observed at some positions with small splittings.
An analysis of the effects on the ESR spectra of the exchange reactions between the different solvent complexes has shown that the spectra normally observed result from systems undergoing rapid exchange. A simple model for a radical with only one functional group which can interact with the solvent (e.g., the nitrobenzene anion), is shown to account very well for the observed variations in hyperfine splittings as a function of the composition of a binary solvent mixture. The treatment of the exchange reactions by use of the modified Bloch equations is compared with the spectral density method. The contribution to the linewidth from solvent-induced fluctuations in the spin-density distribution is calculated for a simple two-jump case, and other factors affecting the linewidths of radicals subjected to random solvent interactions are discussed.
Study of the Electron Density Distribution in the Simpler Hydrocarbons
Authors: Roux Monique , Cornille Marguerite , Burnelle Louis 
Published: January 2005

The electronic charge distribution is calculated in the molecules of acetylene and ethylene, by making use of a function which characterizes the effect of bond formation on the electronic density. In agreement with earlier results on methane, the effect is found to consist in a charge removal from the vicinity of the nuclei and a build up of electron density in the regions of the bonds.
In acetylene, the calculation of the charge drifts subsequent to the bonding indicates that these are fairly small, as had been found earlier in simpler molecules. It is also observed that the electrons associated with the CC bond tend to accumulate, in ethylene, above and below the molecular plane, and in acetylene, at some distance from the CC axis. This point is in favor of the Pauling picture of bent multiple bonds.
On the Kinetic Theory of Simple Dense Fluids. XI. Experimental and Theoretical Studies of Positive Ion Mobility in Liquid Ar, Kr, and Xe
Authors: Davis H. Ted , Rice Stuart A. , Meyer Lothar 
Published: January 2005

We report in this paper measurements of the mobility of positive ions in liquid Ar, Kr, and Xe at various temperatures and pressures, and an extension of the theory of Rice and Allnatt to the description of ionic motion. It is found that
(a) The magnitude, the pressure dependence, and the temperature dependence of the positive ion mobility in liquid Ar, Kr, and Xe can be quantitatively accounted for by an extension of the theory of Rice and Allnatt [S. A. Rice and A. R. Allnatt, J. Chem. Phys. 34, 2144 (1961)]. As in our previous studies of self-diffusion in these same liquids [J. Naghizadeh and S. A. Rice, J. Chem. Phys. 36, 2709 (1962)], it is found that negative contributions to the momentum autocorrelation function are of dominant importance.
(b) Modification of the simple Nernst—Einstein relationship between the charge mobility and the self-diffusion constant of the parent atom by inclusion of the effects of polarization leads to quantitative agreement between theory and experiment.
(c) The effect of the long-range Coulomb potential is to increase the local density about the ion and thereby to increase the frictional forces arising from the short range interaction potential. The rate of dissipation of energy directly by the long-range Coulomb potential is small compared to the rate of energy dissipation by the short range potential.
(d) The agreement between experiment and theory is very satisfactory if the positive ion is Ar2+, Kr2+, or Xe2+ and it is suggested that this is the ionic species present. Agreement is much poorer if a different ionic species (say Ar+) is postulated.
(e) If the ions are regarded as probes to alter and study the liquid structure it can be deduced that the current theory of liquids seriously miscalculates the change in the equilibrium pair correlation as a function of temperature and pressure. We believe the error to arise from either a premature truncation of a slowly convergent series used in the solution to an integral equation or, at worst, that the assumed series expansion is invalid [T. L. Hill, Statistical Mechanics (McGraw-Hill Book Company, Inc., New York, 1956)].
Spectral Solvent Shift. II. Interactions of Variously Substituted Hydrocarbons with Polynuclear Aromatic Hydrocarbons
Authors: Weigang O. E. , Wild D. D. 
Published: January 2005

Nine electronic transitions in the chromophores naphthalene, azulene, and phenanthrene have been observed in 21 chlorinated hydrocarbons and chlorocarbons. The results support an interpretation of spectral shifts which considers interbond potentials between solvent and chromophore, involving bond polarizabilities and dipole moments. The results are generally in accord with the McRae solvent-shift theory. Exceptional behaviors of some of the transitions in azulene are attributable to changes in the magnitude of static dipole moment on excitation.
The 1La transition of naphthacene has been observed in some 64 substituted hydrocarbons, the substituents ranging over nine groups. The results are also interpreted by a statistical theory using interbond (or intergroup) potentials. They are compared to the McRae theory, especially with respect to variation of the weighted mean wavelength parameter L0 and the quadratic Stark effect. The effect of the latter seems considerable while no effect of the former can be detected.
External Heavy-Atom Spin-Orbital Coupling Effect. I. The Nature of the Interaction
Authors: McGlynn S. P. , Sunseri R. , Christodouleas N. 
Published: January 2005

The effect of external heavy-atom spin-orbital coupling perturbation has been studied in the lowest energy triplet←singlet absorption spectrum of various 1-halonaphthalenes in 1:1 molar 1-halonaphthalene: alkyl halide binary solutions. It is shown that the interaction prerequisite to the charge transfer which must occur in these systems is probably of a donor—acceptor nature, the alkyl halide functioning as the acceptor and the 1-halonaphthalene functioning as the donor. Steric effects are estimated using molar refraction data and are undoubtedly of importance, particularly when the alkyl halide contains more than one halogen atom.
The external heavy-atom effect is spin-orbital coupling in nature as may readily be seen by comparison of the enhancements induced in the T←S absorption of the 1-halonaphthalene by various alkyl halides; the order of enhancement is alkyl iodide&gt;alkyl bromide&gt;alkyl chloride and follows roughly the order of the atomic spin-orbital coupling factors squared. The external heavy-atom effect is greater the larger the internal heavy-atom effect, as is shown both experimentally and theoretically. In fact, an external bromine is more effective than an internal fluorine, while an external iodine is more effective than an internal chlorine, and roughly comparable in enhancement ability to an internal bromine. Simple theoretical considerations enable one to deduce the singlet—triplet mixing coefficients for both the external and internal effects, and to validate the spin-orbital coupling nature of the effect.
Reaction of O(1D) with Nitrogen
Authors: DeMore W. , Raper O. F. 
Published: January 2005

Dilute solutions of O3 in liquid N2 have been photolyzed at several wavelengths in the ultraviolet with light from a monochromator. Nitrous oxide is formed in low quantum yield by reaction of O(1D) with the N2 solvent. Addition of an inert diluent, argon, does not lower the quantum yield, showing that the reaction is not due to ``hot atoms'' and probably has zero activation energy. The effect of added O2 on the N2O quantum yield shows that O2 reacts with O(1D) 4.5 times faster than does N2.
The wavelength dependence of the N2O quantum yield suggests that the O(1D) quantum yield in the primary step of O3 photolysis is constant below about 3000 Å, but has a lower and apparently decreasing value above 3000 Å. In addition, exchange experiments with O236 show that the O(1D) yield is approximately unity at 3000 Å.
The principal reaction of O(1D) with N2 is O(1D)+N2+M→N2+O(3P)+ M, and not O(1D)+N2+M→N2O+M. The low efficiency of N2O formation is due to a feature of the N2O potential energy surfaces which allows decomposition of the excited association complex to N2+O(3P), in the course of stepwise vibrational deactivation.
Molecular and Valence Structures of Complexes of Cyclo-Octatetraene with Iron Tricarbonyl
Authors: Dickens Brian , Lipscomb William N. 
Published: January 2005

Structure determinations by x-ray diffraction methods indicate that Fe(CO)3 units are bonded to a butadiene type of residue in C8H8Fe(CO)3(I), and in (OC)3FeC8H8Fe(CO)3 (II), where the two Fe(CO)3 units are on opposite sides of the C8H8 ring. The dihedral C8H8 ring in (I) and the chair C8H8 ring in (II) are previously unknown and unsuspected geometries for cyclo-octatetraene.
Crystals of (I) have symmetry Pnam, within experimental error, with four molecules in a unit cell defined by the parameters a=6.54, b=13.46, c=11.50 Å. Crystals of (II) are of symmetry P21/n, with four molecules in a unit cell which has parameters a=12.52, b=13.38, c=8.86, and β=111°. Final values of R=Σ | | F0 | — | Fc ‖/Σ | F0 | are 0.09 for (I) and 0.10 for (II) for all observed reflections.
The bonding of Fe to the butadiene-like residues is discussed.
Kinetics of the Reaction of HI with Ethyl Iodide and the Heat of Formation of the Ethyl Radical
Authors: Hartley D. B. , Benson Sidney W. 
Published: January 2005

The kinetics of the reaction between EtI and HI have been studied in the temperature range 263° to 303°C using a spectrophotometric technique for the determination of I2. The mechanism obeyed is the following: I2⇌2I,  KI2I+EtI⇌ lim 21Et+I2,Et+HI⇌ lim 43EtH+I,,which has the rate law (neglecting Step 4): d(I2)dt=k1k3KI212(EtI)(HI)(I2)12k2(I2)+k3(HI).. Decomposition of EtI by unimolecular elimination of HI is negligible.
A differential method was employed to determine the rate constants k1 and the ratio k2/k3. The Arrhenius parameters of these constants were evaluated experimentally and combined with known thermodynamic data to give the parameters of the individual constants k2, k3, k4. As with other I2 molecule systems, the A factors of Reactions (1) and (4) are high, being approximately equal to collision frequencies.
With the assumption E2=0.2 kcal and the experimental activation energy E1, the C–I bond-dissociation energy in EtI is found to be 52.9±1.0 kcal at 25°C. The heat of formation of the ethyl radical as determined here [ΔHf°(Et)=25.3±1.2 kcal] indicates the C–H bond energy in ethane to be 97.7±1.2 kcal. These values agree well with independent estimates.
Magnetic Resonance of Mn2+-Doped LiF Crystals
Authors: Chang T. T. , Tanttila W. H. , Wells J. S. 
Published: January 2005

The electron paramagnetic resonance of Mn2+ in powdered LiF was observed at X-band and room temperatures for various impurity concentrations. The highest concentration was examined at K-band and low temperatures to obtain additional information regarding the distribution of Mn2+ ions which were introduced chemically into the lattice in small amounts. In the highest concentration, the K-band spectra indicate that part of the Mn2+ goes into the powder in the form of clusters of Mn and F which are antiferromagnetic at helium temperatures. NMR linewidth measurements on the lithium nuclei at low temperatures are qualitatively explained by the antiferromagnetism.
The room-temperature data from the more dilute samples exhibit not only the expected hyperfine splitting but also a superhyperfine splitting. The hyperfine interaction of the Mn2+ ion was determined to be A55=90±2×10—4 cm—1, and the isotropic part of the superhyperfine interaction with each of the six fluorine nearest-neighbor nuclei was measured to be As=17.1±0.5×10—4 cm—1.
Comparisons between K-band spectra from chemically prepared powdered samples and single crystals grown from the melt indicate that the melt method is unsuitable for obtaining the solid solution required to examine the superhyperfine spectra.
Vibronic Interactions in the Exciton Theory for Molecular Crystals
Authors: McRae E. G. 
Published: January 2005

The correlation between exciton motion and intramolecular vibrational motions in the electronically excited states of molecular crystals is described in terms of a zone of molecular distortion surrounding the instantaneous site of electronic excitation. It is shown for a model crystal that observable properties of fluorescence spectra and of absorption spectra near the band edge can be related exactly to the distortion zone structure.
An equation governing the distortion zone structure is derived by a variational method in which the exciton energy is minimized with respect to the simultaneous variation of a set of parameters representing the distortion of each molecule in the crystal. It is shown that this equation can be solved by a convergent iterative procedure, regardless of the strength of intermolecular interaction.
An illustrative application to a linear crystal is described. Where appropriate, the theoretical results are compared with those of perturbation theory.
Kinetic Theory of Hot-Atom Reactions. II. Evaluation of Collisional Energy Loss. Application to Reactive Mixtures
Authors: Wolfgang Richard 
Published: January 2005

The kinetic theory of reactions of atoms of high translational energy undergoing moderating collisions is further developed. The nature and validity of the assumptions underlying the treatment and the range of applicability of the final expressions are discussed in detail. It is shown that experimental data on the total probability of reaction in which the hot atom is chemically bound can be used to evaluate two fundamental quantities: (1) the reactivity integral, or reaction probability integrated over energy on a logarithmic scale (I) ; (2) a measure of average energy transfer in collisions of hot atoms with the reactive species (α).
The present treatment involves no variable or arbitrary parameters. As a result sufficient data may be obtained to provide stringent internal consistency tests of the applicability of the model and its assumptions to any given system.
Two types of systems are specifically treated: (1) a single reactant moderated by inert gas; (2) competitive reactions in systems of two reactants. The relative utility of such systems for determination of the basic parameters α and I is discussed. Examples of the use of the expressions developed to calculate average logarithmic collisional energy loss (α) are given. Recent data of Colebourne on interaction of hot F with CF4, and data of Root and Rowland on hot H in mixtures of D2 and CH4 are used. The α's derived indicate that moderating collisions in these media are highly inelastic. Root and Rowland's hypothesis that CH4 is a better moderator than D2 is quantitatively confirmed. The implications of these findings for the mechanism of hot-atom processes are briefly discussed.