bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theory of the Anomalous Heat Capacity in Solid Hydrogen and Deuterium at Low o-Hydrogen and p-Deuterium Concentration
Authors: Orttung William H. 
Published: January 2005

The theory of the anomalous heat capacity for low concentrations of ortho hydrogen in the solid state has been extended by a calculation based on the angular potential energy between adjacent molecules. The effects included were (1) the chemical or valence energy, (2) the electrostatic quadrupole-quadrupole energy, and (3) the inverse sixth-power dispersion energy. The expression used for the first type of interaction was derived theoretically by de Boer, while gas-phase experimental parameters were used to evaluate the second two types of interaction in connection with a theoretical estimate of the anisotropy of polarizability of the hydrogen molecule.
It was found that only electrostatic quadrupole-quadrupole interactions had to be considered at one atmosphere, but at higher pressures, the valence forces became important. The case of three ortho hydrogen molecules in a row was also treated in the quadrupole approximation. The heat capacity predicted by this model was somewhat different from that predicted for isolated ortho-ortho pairs. The theory was compared with available one atmosphere data on ortho hydrogen and para deuterium at low concentrations in the solid. The results depend not only on the total ortho concentration but also on the relative concentrations of isolated ortho molecules, isolated pairs of ortho molecules, and more complicated configurations. Nakamura's suggestion (that an additional term in the anomalous heat capacity proportional to the ortho concentration is needed to explain the data) seems to be supported by the analysis, although additional data would be desirable.
Mass Spectrometry of Ions in Glow Discharges. II. Negative Glow in Rare Gases
Authors: Knewstubb P. F. , Tickner A. W. 
Published: January 2005

The ions in the negative glow were examined at pressures of about 0.4 mm and currents of about 0.2 ma. Most of the work was done with argon but some measurements were made with helium and with helium-argon and argon-krypton mixtures. To clarify the role of impurities, some work was done with the addition of 1.25% hydrogen to the argon.
The results confirm that the ions of the principal gas or gases are produced by the impact of ``primary'' electrons. Evidence is obtained that when small amounts of gases having sufficiently low ionization potentials are present, they are ionized by interaction with the metastable atoms of the principal gas.
Ar2+ appears to form in the negative glow mainly by Ar++2Ar→Ar2++Ar,but it is confirmed that in the positive column a process depending mainly on excitation must be dominant.
The formation of ArH+ from impurities is thought to occur principally by the reaction of metastable argon atoms with hydrogen atoms, the latter being produced from various sources by electron impact. In the presence of appreciable quantities of hydrogen, the reactionAr++H2→ArH++Happears to contribute but is only important at the cathode edge of the negative glow.
The extremely persistent formation of H3O+ from traces of water suggests that long-lived excited states of water may exist, and be responsible for this effect.
Relations among Vibrational Frequencies of Isotopically Substituted Molecules and the Determination of Force Constants
Authors: Heicklen Julian 
Published: January 2005

A simple derivation is given for the product, sum, and complete isotope rules. Additional sum rules and their implications are presented. In particular, it is shown that if equivalent atoms of a molecule are isotopically substituted, then one relationship (the product rule) exists between two isotopic species; two more relationships (the first-order sum rules) exist among three isotopic species; two more relationships exist among four isotopic species; and for five or more isotopic species all frequencies are related. If the isotopic substitutions retain the full symmetry of the molecule, the aforementioned relationships exist for each symmetry block. Even if isotopic substitution reduces the symmetry, the number of relationships is not diminished. Furthermore, if equivalent atoms are isotopically substituted, then for the inplane vibrations of planar molecules, all the vibrational frequencies are related among four or more isotopic species; for the out-of-plane vibrations of planar molecules and for linear molecules, all the vibrations are related among three or more isotopic species (the complete isotope rule).
To determine the complete F matrix it is necessary to have frequencies of enough molecules so as to include isotopic substitutions of each of the atoms, but one set of equivalent atoms. If less frequencies are known, then information is obtained which relates to the coupling of the isotopically substituted atoms with the remainder of the molecule.
Photolysis of Mixtures of Cyclobutane and Acetone-d6. Reactions of the Cyclobutyl Radical
Authors: Gordon Alvin S. , Smith S. Ruven , Drew Charles M. 
Published: January 2005

The activation energy for abstraction of hydrogen from cyclobutane by a methyl radical is 10.3±0.15 kcal/mole, with a pre-exponential factor relative to methyl radical abstracting D from acetone-d6 of 1.8. At temperatures of less than 200°, the cyclobutyl radicals disappear almost exclusively by combination with methyl radicals to form methyl cyclobutane. At higher temperatures the cyclobutyl radical (a) opens to form the ĊH2CH2CH=CH2 radical with an Eact of 18.1±0.8 kcal/mole, and (b) splits out a molecule of hydrogen. The latter reaction is considerably slower than the former.
The ĊH2CH2CH=CH2 radical is unusually stable, and does not decompose appreciably even at 325°C. At 425°, the highest temperature which could be reliably studied in this system, the product analysis indicates that the radical decomposes slowly to ethylene and a vinyl radical. By contrast, n-butyl radicals and s-butyl radicals readily decompose at 250°C in a similar reaction media. The main reaction of the ĊH2CH2CH=CH2 radical is the abstraction of H (or D) from the parent mixture. It also combines with a methyl radical to form pentene-1. Evidence is presented to show that the ĊH2CH2CH=CH2 radical isomerizes at temperatures of 350° and above to the resonance stabilized CH3ĊHĊHĊH2 radical, with an energy of activation of 20.0±0.7 kcal/mole.
Electron Spin Resonance Absorption and Other Properties of Some Solid Hydrocarbon-Quinone Complexes
Authors: Eastman John W. , Androes Gaylord M. , Calvin Melvin 
Published: January 2005

Crystalline solids have been prepared from aromatic hydrocarbons and tetrahalogenated benzoquinones. The solids contain one molecule of hydrocarbon for every molecule of quinone. The infrared and optical spectra of the solids, as well as their chemical properties, indicate that the components are bound by electronic donor-acceptor interactions which are weak compared to the intramolecular forces.
Electron spin resonance absorption at 9500 Mc/sec was observed in nearly all the hydrocarbon-quinone solids prepared. However, perylene-quinone solids have been prepared which contain less than 1015 unpaired electron spins per gram. That is, they are practically diamagnetic. When unpaired electrons are present they are located at imperfections in the solid. Imperfections containing unpaired electron spins can be introduced thermally into the complexes. More than 1018 unpaired electrons per gram can be produced by heating perylene-ortho-quinone solids.
The temperature dependences, g values, linewidths and spin-lattice relaxation times of the electron spin resonance absorption by the imperfection in some perylene-quinone solids have been investigated. The structure of the imperfection and the mechanism by which it is produced have been discussed.
Analysis of Paramagnetic Resonance Properties of Pure and Bleached F Centers in Potassium Chloride
Authors: Noble Gordon A. , Markham Jordan J. 
Published: January 2005

The electron paramagnetic resonance of color centers in additively colored KCl crystals is measured carefully to observe the effects of optical bleaching at room temperature. Earlier measurements on the F center are confirmed and the susceptibility is measured at 78° and 300°K over five decades of power, including the very low power region. The width and the saturation properties of the individual multiplets are studied in detail and the technique of making EPR measurements on inhomogeneously broadened lines is discussed. A calculation is presented which shows that a slight departure from a Lorentzian multiplet shape can account for the saturation data.
The bleached crystals show a resonance which has a width of 35 gauss and a different rate of saturation than the F center. This resonance is associated with the B band which appears in the optical absorption.
Interaction of Helium, Neon, Argon, and Krypton with a Clean Platinum Surface
Authors: Chon H. , Fisher R. A. , McCammon R. D. , Aston J. G. 
Published: January 2005

The heats of adsorption of helium, neon, argon, and krypton have been studied on a clean platinum black of high area, prepared using the technique of a thermally indicated titration.
These measured heats are compared with the theoretically calculated attractive part of interaction energy between a nonpolar gas and a metal surface.
The Margenau and Pollard formulas best represents the measured values. Considering the uncertainty involved due to lateral interaction and the neglected repulsive part of the potential function it is reasonable to say that all of the theories are inagreement with the measured values to the degree of their approximation.
Quantum Mechanical Study of the Hydrogen Bimolecular Exchange Reaction
Authors: Ruffa A. R. , Griffing Virginia 
Published: January 2005

A theoretical calculation of the potential-energy curves of several linear four-atom hydrogen complexes has been made in order to study the interaction governing the kinetics of the bimolecular exchange reaction. In particular, an attempt was made to determine for what distance of approach the two diatomic molecules make a transition into the four-atom complex. Hence, the linear H4 complex H—r—H—R—H—r—H was chosen for study as function of r and R. The partial potential energy surface constructed in this manner indicates that two hydrogen molecules approaching on a line experience an increase in interatomic separation with the inner two atoms forming a hydrogen molecule at small separations while the outer two atoms are repelled outward from the center of the system. The minimum occurs for r=R=1.8 and gives an activation energy of 65 kcal for the bimolecular exchange reaction, if one assumes a linear transition state.
An additional calculation was performed on a linear chain of six hydrogen atoms with interatomic separation of two atomic units in order to get additional information regarding the relative stability of the linear hydrogen chain in comparison with other possible configurations. Computation of the total energies in the LCAO MO SCF approximation with 1s functions indicates that the energies of the chains of four or six hydrogen atoms generally lie between the energies of the separated hydrogen molecules and the separated hydrogen atoms.
Heat Conductivity of Polyatomic and Polar Gases
Authors: Mason E. A. , Monchick L. 
Published: January 2005

The formal kinetic theory of Wang Chang and Uhlenbeck and of Taxman has been used to derive explicit expressions for the heat conductivity of polyatomic and polar gases. By systematic inclusion of terms involving inelastic collisions the usual modified Eucken expression is derived as a first approximation, and as a second approximation an expression involving the relaxation times for various internal degrees of freedom (as well as the viscosity, diffusion coefficients, and heat capacity). For polar gases a second effect is often important in that a resonant exchange of rotational energy is possible.
The comparison of experimental results with those calculated using empirical values of relaxation times is generally satisfactory, and most of the previously noted anomalies in the ratio f=λM/ηCv are accounted for quantitatively.
On the Thermodynamics of Solutions. VII. Critical Properties of Mixtures
Authors: Redlich O. , Kister A. T. 
Published: January 2005

The applicability of equations of state has been greatly widened by automatic computation. Algebraic relations, however, particularly strict thermodynamic relations, are apt to simplify the calculations and therefore to extend the applications much further.
Explicit general relations between temperature, pressure and composition at the critical line of a binary mixture would be useful and also theoretically interesting. Although the problem is easily formulated, it appears that a general solution cannot be found. But a partial solution can be derived: The derivatives of the variables of state along the critical line in the limits of the critical points of the pure components can be expressed by partial derivatives in these points.
The volume of a mixture increases on condensation in the range of retrograde condensation. This result may have been suspected on the basis of the principle of Braun and Le Chatelier.
Effects of Helium Buffer Gas Atoms on the Atomic Hydrogen Hyperfine Frequency
Authors: Clarke George A. 
Published: January 2005

Calculations are made for the pressure, mass, and temperature dependence of the atomic hydrogen hyperfine frequency shift arising from the perturbing influence of helium buffer gas atoms. The calculated fractional pressure shift is found to be +1.73×10—9 mm Hg—1 compared with the experimental value of +3.7×10—9 mm Hg—1. From the standpoint of the calculation this discrepency may be related to a failure of the simple wave function employed to adequately characterize the unpaired electron spin density at the hydrogen nucleus. The results of the calculations for the temperature variation and mass dependence indicate that these are very small effects. The form of the mass dependent quantum statistical correction, used to elucidate the mass effect, suggests that the relatively large variations experimentally observed with other buffer gases, due to hydrogen isotope variation, are in error.
Finally, a calculation is made for the pressure shift from a kinetic theory point of view and the result obtained (+1.79×10—9 mm Hg—1) is in fair agreement with the above mentioned quantum statistical calculation.
Ultraviolet Spectra of Stilbene, p-Monohalogen Stilbenes, and Azobenzene and the trans to cis Photoisomerization Process
Authors: Dyck Rudolph H. , McClure Donald S. 
Published: January 2005

In order to improve our understanding of the electronic states and photochemical reactions of stilbene, we have carried out a spectroscopic and photochemical investigation of stilbene, some substituted stilbenes, and azobenzene. High resolution absorption and fluorescence spectra of the singlet—singlet transition in dilute mixed crystal have been analyzed, and from them it is estimated that the potential barrier to trans-cis isomerization in the first excited singlet state is about 40 kcal/mole. The absorption spectrum of the first singlet—triplet transition has been observed by enhancement with a heavy atom solvent and is interpreted as showing that the central bond in the lowest triplet state has a very substantial barrier to rotation. An electronic energy level scheme for stilbene has been constructed by treating the molecule as one ethylene molecule interacting with two toluene molecules. This treatment suggests that as many as four triplet states may be of lower energy than the first excited singlet and would then be possible pathways for photoisomerization.
A study of the deactivation processes of photoexcited stilbene has included the temperature dependences of fluorescence and of isomerization efficiencies. The first showed an activated quenching process with a frequency factor of 1012, which makes it a less forbidden process than is common for singlet—triplet crossings. The second showed that the activated process has the major isomerization yield. In p-bromostilbene an unactivated process has the major isomerization yield, indicating that there is an atomic number effect on the rate of the unactivated process.
Thus the direct isomerization in the first excited singlet or first excited triplet states has been ruled out; two other paths, one with a small activation energy and the other apparently a singlet to excited triplet crossing, have been found.
Electronic Spectrum of Decaborane
Authors: Haaland Arne , Eberhardt W. H. 
Published: January 2005

The near ultraviolet absorption spectrum of decaborane has been studied in the gas from 90° to 140°C, in solution in cyclohexane and acetonitrile at 25°C, and as single crystals at 4.2°K, and evidence found for one electronic transition with origin at 3.86±0.03 ev in the gas, 3.81±0.06 ev in cyclohexane, 4.00±0.06 ev in acetonitrile, and 3.850±0.001 ev in the crystal. The existence of another excited electronic state of slightly higher energy cannot be ruled out since the absorption due to transitions to this state might be concealed by that due to the 3.85 ev transition.
Assuming the absorption is due to one transition only, the transition moment and oscillator strength in cyclohexane are p2=0.21×10—16 cm2 and f=0.10, respectively. The shift of the spectrum towards the blue in the polar solvent acetonitrile relative to that in the nonpolar solvent cyclohexane indicates that the dipole moment of the excited state is less than that of the ground state.
The absorption of the crystal is completely polarized perpendicular to the crystal c axis and the twofold axis of the molecule. This result implies that the excited state of the free molecule is of either B1 or B2 symmetry and the transition is allowed. No structure was observed in the gas or solution spectra, but in the crystal the electronic transition is accompanied by three totally symmetric boron framework vibrations of the excited state with frequencies 425, 390, and 135 cm—1. A detailed discussion of the wave functions and energies of the optically excited crystal states indicates that the Davydov splitting should be too small to be observed under the experimental conditions.
The spectrum is entirely consistent with that expected from existent theories of the nature of electronic bonding in this molecule.
Electron Coupling of Nuclear Spins. VI. Relative Signs of JgemHH, JgHH, and JtHH in (2.2) Metacyclophane
Authors: Gutowsky H. S. , Juan Cynthia 
Published: January 2005

The high-resolution proton magnetic resonance spectrum of the methylene groups in (2.2) metacyclophane has been observed at 60 and 15 Mc. In this compound, the C–CH2–CH2–C groups are fixed in position with the dihedral angle between alkyl C–C–C bonds slightly less than the symmetrical, staggered 60° and with little distortion from tetrahedral of the other bond angles in the group. Therefore, the HCCH coupling constants should be characteristic of ethanic trans and gauche orientations and the CH2 should be comparable with the geminal coupling in methane.
A complete analysis of the A2X2 and A2B2 type spectra, in combination with previous, unambiguous experimental findings that |JgemHH|≅|JtHH|&gt;|JgHH|, leads to the following assignments in (2.2) metacyclophane: JtHH=±12.3,Jg′HH (the coupling of the ``central'' pair of gauche protons) =±3.2,JgemHH=∓12.0,and JgHH=±4.0,all±0.1 cps. The magnitudes of these constants agree well with previous valencebond calculations for CH4 and the ethanic HCCH group. However, the opposite signs found for the large trans and geminal constants disagrees with the theoretical prediction that both are positive. The observed difference in sign can not be attributed to substituent effects, angular distortions, or to motional averaging. It is concluded that one of the two sets of calculations is in error; the implications of this result are discussed.
Analysis of Complex NMR Spectra. An Iterative Method
Authors: Swalen J. D. , Reilly C. A. 
Published: January 2005

A method for analyzing complex NMR spectra, which utilizes an iterative technique on the spin energy levels, is described. We show how the experimental energy levels and their errors are derived from the observed spectrum and the assignment of the various transitions. We discuss several techniques and methods that are helpful in obtaining this assignment. Sum rules for the energy levels and the intensities of the transitions, useful in the analysis, are also pointed out.
With the iterative procedure, which uses the eigenvectors of an approximate Hamiltonian, we then calculate the changes in the chemical shielding constants and the spin—spin coupling constants necessary to adjust the approximate energy levels toward the experimental ones. The probable errors in the derived magnetic parameters are also readily determined.
Radiation-Induced Free Radicals in Sulfur Compounds. ESR Studies in the Polycrystalline State
Authors: Henriksen Thormod 
Published: January 2005

The secondary processes occurring in organic sulfur compounds, irradiated with ionizing radiation in the dry state, have been followed by ESR spectroscopy. Samples were irradiated in vacuum at 77°K and the ESR spectra recorded at this temperature before and after stepwise heat treatment at successively increasing temperatures.
The resonance spectra seem to indicate that after irradiation at 77°K, several kinds of ESR centers are formed. No or very few sulfur radicals seem to be formed at this temperature.
The results show that few secondary processes proceed efficiently in solids in the temperature range from 77° to about 110°K. Depending upon the compound, decay processes seem to dominate in the temperature range varying from about 110°K and up to about 250°K. Upon further heat treatment, secondary reactions take place which lead to the formation of sulfur radicals. The threshold temperature for these reactions is about 170°K for simple thiols and disulfides, 240°K for peptides like glutathione, and about 280°K for proteins. The formation of sulfur radicals is found to coincide with an increase in the total number of observable ESR centers. Thus, in the case of penicillamine, the number of unpaired spins observed after annealing to 295°K exceeds the initial value at 77°K by about 70%.
Evidence is presented that diffusion-controlled intermolecular reactions take place in irradiated solids, and it is suggested that the observed formation of sulfur radicals may in part be explained by such a mechanism.
The resonance pattern due to polyoriented radicals of the type R—CH2–S· (e.g., cysteine, cysteamine, glutathione, proteins) was found to exhibit a temperature dependent hyperfine splitting which is not found for radicals of the type R—CX2—S· (e.g., penicillamine). This observation supports the model for organic sulfur radicals proposed by Kurita and Gordy.