bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Diffusion of Helium and of Hydrogen Through Pyrex Chemically Resistant Glass
Authors: Taylor Nelson W. , Rast William 
Published: January 2005

The effects of temperature and of heat treatment on Pyrex chemically resistant glass have been studied by measuring the rate of diffusion of helium and of hydrogen through a tube of about one millimeter wall thickness. Measurements were made with helium between 180°C and 590°C, and with hydrogen at 512°C. The influence of gas pressure was determined and the diffusion rate was found to be directly proportional to the pressure for both helium and hydrogen.
The diffusion data throw light on the processes of molecular rearrangement involved in stabilization of the glass. Below 548°C the rates of diffusion (R) were increased about 10 percent by giving the glass sufficient heat treatment to assure ``stabilization,'' i.e., equilibrium in the processes of dissociation and association. This increase occurred despite the fact that such heat treatment normally increases the density of the glass and therefore points to a chemical theory rather than a simple theory of holes governing the diffusion process.
The data also showed a continuous linear dependence for the stabilized glass of log R on 1/T from 440°C—590°C. This range extends into the region of a true viscous liquid and it follows that the properties of a stabilized glass are continuous with that of a viscous liquid and that there is no need to postulate a separate glassy state. The ``transformation point'' mentioned by some investigators is merely the temperature of rapid strain release of an unannealed sample.
At or near 440°C the log R versus 1/T curve takes a lesser slope (for lower temperatures) and this change is attributed to the loss of rotational or vibrational freedom in the silicate complex, analogous to that frequently found in dielectric studies on solids. Activation energies have been calculated for the two temperature ranges.
At 512°C the rate of helium diffusion is approximately 45 times that of hydrogen, and it is believed that chemical forces delay the progress of the hydrogen molecule through the silicate network.
The general conclusion is drawn that gas diffusion furnishes a highly sensitive method for studying the molecular condition of silicate glasses and similar materials.
Infra-Red and Raman Spectra of Polyatomic Molecules. III. Ethane
Authors: Crawford Bryce L. , Avery William H. , Linnett J. W. 
Published: January 2005

The Raman and infra-red spectra of ethane have been re-examined. The 993, 2900, and 2955 cm—1 Raman lines are polarized; there were indications of very faint lines appearing at 620 and 820 cm—1. The strong infra-red peak at 1480 cm—1 is found to be a single minimum; the weak band at 1740 cm—1 is confirmed.
The available Raman and infra-red data are evaluated, and possible assignments discussed. It is shown that the observed frequencies do not require a 740 cm—1 fundamental, but are consistent with an ``uncertain frequency'' of about 1100 cm—1 and a high restricting potential.
Modifications in the Near Infra-Red Absorption Spectra of Protein and of Light and Heavy Water Molecules When Water is Bound to Gelatin
Authors: Ellis Joseph W. , Bath Jean 
Published: January 2005

Comparisons are made between the near infra-red absorption spectra of protein molecules in oven-dried gelatin and gelatin saturated with light and heavy water vapor respectively. The intensity of the first overtone valence N – H band at 1.50μ is greatly diminished by the addition of H2O molecules, and this band is almost completely destroyed when D2O molecules are taken on. The combination deformation-valence N – H bands at 2.05μ and 2.18μ are only partially destroyed in either instance. These facts suggest that the dipole moment oscillation of the N – H group constituting a part of the inter-molecular hydrogen bridge, C = O≡H – N, is reduced when this bridge is broken and water molecules themselves become bridged to the N – H group; that the transverse dipole moment change is less affected than the parallel change; and that D2O is much more effective than H2O.
The 1.72μ and 2.28μ C – H bands do not change appreciably in intensity. However, at least the former shifts toward higher frequencies when water is taken on, indicating that the C – H groups are in a more vapor-like environment and corroborating the usual assumption that water molecules are attached only to the polar groups of the gelatin molecules.
The destruction of some of the usual absorption on the short and the long wave sides of the 1.44μ (νσ+νπ) and 1.93μ (νσ+νδ)H2O bands indicates the nonexistence, or a reduction in number, of unperturbed vapor-like molecules as well as of the more highly perturbed molecules involving three and four hydrogen bridges. The presence of a sharpened and enhanced 1.79μ (νσ+νδ+νR) band indicates hindered rotation of H2O molecules in a field more homogeneous than that in liquid water but having the same average value. A new weak band appears at 1.35μ and is believed to be (νσ+νπ+νR). Somewhat similar results occur with D2O, requiring for complete interpretation, however, frequency contributions from hindered translation νT.
Molecular Interaction in Mixed Monolayers on Aqueous Subsolutions I. Mixtures of Alcohols, Acids and Amines
Authors: Harkins William D. , Florence Robert T. 
Published: January 2005

Mixed films are of fundamental importance in biological systems, so mixtures of long chain alcohols, acids, and amines on acidic and basic subsolutions have been investigated. The principal effect of mixing is to change the conditions with respect to the pressure, area, and temperature at which one surface phase changes into another.
In general a mixture of two liquid films gives a monolayer of the same type, with the mean molecular area: a liquid expanded film is made more condensed by admixture of a substance which gives a condensed film, and the condensing action increases with the length of the hydrocarbon chain; an alcohol condenses an acid more than the corresponding acid. The interaction, or departure from the mean value may be either positive or negative, and on acid subsolutions is greatest when one of the components is an amine. Only in amine-acid mixtures is there an indication of chemical action. The 1 : 1 mixture of stearyl alcohol and stearic acid ``freezes'' at a much larger area than the film given by either component, so the area of the solid mixed film is abnormally high. The area interaction with an amine present is negative, and the potential interaction has a high value and is positive. Calcium ions in a basic subsolution condense a Type II to a solid Type I monolayer.
An Approach to the Internal Rotation Problem
Authors: Karplus Martin , Parr Robert G. 
Published: January 2005

A method is described for a direct calculation of the barrier to internal rotation in ethane and ethanelike molecules. The approach suggested should identify the physical origin of the barrier, provided a satisfactory account would be forthcoming from exact Hartree—Fock calculations of the energies of the staggered and eclipsed forms in the Born—Oppenheimer approximation.
A simple model is considered in which the electronic distribution is taken to be cylindrically symmetric about the central bond. It is demonstrated that this model predicts energy differences between staggered and eclipsed forms, composed solely of nuclear—nuclear repulsion energy, that are consistently about 5/3 of the experimental energy barriers. A slight expansion of the wavefunction in the eclipsed configuration is shown to be required by the virial theorem, but this does not appreciably change the predicted magnitude of the barrier.
It is proposed that the model can be refined by a calculation of the electronic energies of the actual staggered and eclipsed forms of ethane relative to that for the cylindrical distribution. By means of second-order Hartree—Fock perturbation theory, it is shown that the energy differences are a simple sum of contributions from the nine occupied molecular orbitals. The individual contributions can be calculated by the solution of certain differential equations or their variational equivalent. To simplify the treatment further, an approximate set of uncoupled differential equations is suggested for finding the perturbed functions from estimates for the charge densities of the cylindrical-model molecular orbitals.
Collisional Transition Probabilities for Vibrational Deactivation of Chemically Activated sec-Butyl Radicals. The Rare Gases
Authors: Kohlmaier G. H. , Rabinovitch B. S. 
Published: January 2005

Vibrationally excited sec-butyl radicals, having a narrow range of energies above 40 kcal mole−1, were produced in a heat bath of cis-butene-2-rare-gas mixtures by H addition to cis-butene-2. He, Ne, Ar, and Kr were used. Two competing reactions of the chemically activated radicals, decomposition by C–C rupture with critical energy of 33 kcal mole−1 and collisional stabilization, were studied as a function of pressure. Apparent rate constants for decomposition ka were obtained at three temperatures over a range of bath pressures by analysis of the decomposition and stabilization products. Strong and weak multistep collisional deactivation processes, corresponding to transfer of all or only part of the initial excess vibration energy (≥7 kcal mole−1) of the radicals, were considered. Multistep models of various step sizes (ΔE) give a family of calculated curves of ka as a function of p, each of which turns up from a quasi-constant value at higher pressures to higher values at low pressures. Comparison with the low-pressure experimental ``turnup'' yielded information on ΔE, independent of the assumed collision cross section. Comparison of relative rates in the higher-pressure region gave minimum estimates of ΔE or, alternatively, conventional ``efficiency'' factors, βmin; these conclusions are somewhat dependent on the assumed cross section.
Values of ΔE from the lower-pressure turnup data bunch at 2.5–3.5 kcal mole−1 on an assumed stepladder model of transition probabilities. Such a model corresponds only formally to harmonic oscillator restrictions, and encompasses the characteristics of models in which small steps are less probable than large ones. Values of 〈ΔE〉exp for an exponential weighting of transition probabilities group at 1.2–1.8 kcal mole−1; this distribution describes the characteristics of models in which small steps are more probable than large ones and seems to be the preferred description of the rare-gas behavior here. He and Ne appear to transfer less energy than Kr and Ar. ΔE for cis-butene itself was confirmed to be ≥9 kcal, as derived in a previous study of deactivation of sec-butyl-d1 radicals by Harrington, Rabinovitch, and Hoare; and by contrast, the stepladder model is more appropriate here.
From the higher-pressure data, values of βmin which varied from 0.16 for He at 100°C to 0.62 for Kr at −78°C were found. The efficiencies increase with increasing atomic weight of the rare gas and with decreasing bath temperature.
Energy transfer between rare-gas atoms and butyl radicals is thus surprisingly efficient, with relatively large amounts of energy transferred per collision (〈ΔE〉&gt;kT). The findings provide further detailed evidence concerning the inapplicability of the Landau-Teller theory and related models to polyatomic molecules at high vibrational energies (cf. Herzfeld and Litovitz). The possible role of rotational degrees of freedom is considered.
11B Quadrupole Coupling Tensors in the Hydrated Borates. II. The Pentaborate Polyanion
Authors: Lal K. C. , Petch H. E. 
Published: January 2005

The quadrupolar splitting of the 11B nuclear magnetic resonance signal has been investigated in potassium pentaborate tetrahydrate, KB5O6(OH)4·2H2O, and ulexite, NaCaB5O6(OH)6·5H2O. In the case of the former material, a good single crystal was available, permitting a complete determination of the quadrupole coupling tensors at the single unique tetrahedral site and at the two unique triangular boron sites. A complete determination of the tensors was not possible in the case of ulexite because of the fibrous nature of the material but, by combining single-crystal and powder techniques, it was possible to identify unambiguously three tetrahedral and two triangular boron sites and to set upper and lower limits on the quadrupole coupling constants.
The electric quadrupole coupling constants eqQ/h and asymmetry parameters η of the electric-field gradient tensors at the boron sites were determined to be eqQ/hCoordination of(kc/sec)ηboron sitePotassium pentaborate tetrahydrate234±10.093±0.009Tetrahedral2536±30.212±0.004Triangular2521±30.195±0.005TriangularUlexite50&lt;eqQ/h&lt;600Tetrahedral2530±50TriangularThe orientations of the principal axes of the electric-field gradient tensors have also been determined for potassium pentaborate tetrahydrate.
The NMR results are in complete agreement with the crystal structures of both compounds as to numbers and coordinations of the boron atoms and as to the nature of the boron—oxygen polyanions.
Photolysis of Low-Temperature Glasses. II. Temperature and Oxygen Effects in Ethanol and Ether
Authors: Judeikis Henry S. , Siegel Seymour 
Published: January 2005

The effect of temperature and oxygen on the processes occurring in the aromatic solute-sensitized photodecomposition of ethanol and ether glasses is described. The results are discussed in terms of the proposed sensitization mechanism, and they are shown to be in excellent agreement with predictions. The effect of oxygen diffusion (at ∼100°K) is to remove the aromatic solute triplet-state population, the latter being an intermediate in the sensitization mechanism, and thus decrease the rate of radical formation. Oxygen also reacts with any radicals present to form peroxy radicals which are stable to light with wavelengths greater than ∼2500 Å.
In the absence of oxygen, the triplet-state population and rate of total radical production are virtually independent of temperature over the range 77° to 125°K. However, the composition of the radical concentration exhibits a strong temperature dependence. It is shown that the latter observation results from a competition between secondary photoreactions (temperature independent) involving the radicals produced by the sensitization process and abstraction reactions (temperature dependent) involving the products of the secondary photoreactions.
Motion of Localized Triplet Excitons
Authors: Soos Zoltán G. , McConnell Harden M. 
Published: January 2005

A theory is developed for exciton—phonon interactions in ionic molecular crystals showing triplet-exciton magnetic resonance. By using a simple model for the phonon Hamiltonian it is shown that the triplet excitons tend to be localized, or ``self-trapped,'' and to move in a diffusional manner.
The activation energy for diffusion is found to be essentially ½Λ, where Λ is the ``self-energy'' of the triplet exciton due to exciton—phonon interaction. It is suggested that the anomalous excess activation energy for exciton—exciton spin-exchange line broadening is ½Λ rather than the phonon-coupled exciton—exciton repulsion suggested previously. It is also shown that exciton creation and annihilation with the absorption and emission of phonons has no significant effect on the exciton magnetic resonance linewidths at low temperatures.
Photolysis of Cyclobutane at Photon Energies Below and Above the Ionization Energy
Authors: Doepker R. D. , Ausloos P. 
Published: January 2005

The photolysis of cyclo-C4H8 and of cyclo-C4H8—cyclo-C4D8 mixtures has been investigated at 1470 and 1236 Å in the absence and presence of NO. In addition, a series of experiments carried out in which H2S was used as a free-radical interceptor in the photolysis of cyclo-C4D8 at 1236 Å. Approximately 90% of the observed products can be accounted for by the primary process: C4H8+hv→2C2H4. The extent to which the internally excited ethylene formed in this process will decompose further increases with diminishing pressure and wavelength.
The photolysis of cyclobutane has been investigated at energies above the ionization energy (I.E.=10.3 eV), using the argon resonance lines at 11.54 and 11.72 eV. It is shown that when NO is added to the system, cis-2-butene, trans-2-butene, and 1-butene are major products. These butenes are, however, not produced when NO (I.E.=9.25 eV) is replaced by O2 (I.E.=12.1 eV) and are only formed in trace amounts when no additives are present. It is suggested that the parent ion acquires the olefinic structure and undergoes charge exchange with NO.
Lifetime and Quenching of Anthracene Fluorescence in the Vapor Phase
Authors: Ware William R. , Cunningham Paul T. 
Published: January 2005

The fluorescence lifetime and self-quenching of anthracene vapor has been examined as a function of temperature. The fluorescence lifetime in the absence of quenching is found to be 5.7±0.2 nsec and is independent of temperature over the range 200° to 300°C. This value, together with published Stern—Volmer constants is used to determine the quenching probability for quenchers such as O2 and NO. Probabilities considerably less than unity are obtained.
The second-order rate constant for self-quenching of anthracene vapor is found to have a negative temperature coefficient. The previously reported negative coefficient found in the Stern—Volmer constant for self-quenching can be explained by a temperature effect on the actual quenching process without resort to excimer decomposition.
Vapor-phase absorption and fluorescence spectra are reported. The oscillator strength and the quantum yield calculated from the actual and natural lifetimes are compared with corresponding values for solution.
Pyrolysis and Oxidation of Formaldehyde in Shock Waves
Authors: Gay I. D. , Glass G. P. , Kistiakowsky G. B. , Niki H. 
Published: January 2005

The pyrolysis and oxidation of formaldehyde have been studied in shock waves by mass spectrometry and by ionization measurements over the temperature range 1400° to 2100°K. The pyrolysis shows first-order rate dependence with respect to both formaldehyde and inert gas after a temperature-dependent induction period. Experiments with formaldehyde-d2 show that the pyrolysis proceeds by a radical chain mechanism. The formation of the radical H3CO has been detected. The observed activation energy is 28±2.5 kcal/mole, which is surprisingly low; various mechanisms are suggested to explain this result.
The initial stage of the oxidation consists mainly of an oxygen-induced decomposition of formaldehyde into CO and H2, followed by branching chain oxidation of the H2 thus produced, as well as of remaining formaldehyde, and partial oxidation of the CO. Chemi-ionization is observed in the oxidation reaction, the species H3O+ and H3CO+ being the only ions detected. The total yield of ions is virtually independent of temperature. Very good agreement is obtained between measurements in reflected shock waves with the TOF mass spectrometer and in incident waves with a Langmuir probe. The mechanism of the oxidation reaction and of ion formation is discussed.
Ternary Excess Enthalpies in Simple Reciprocal Fused-Salt Mixtures. II. The Systems Na+–Ag+–Cl−–NO3 and Na+–Ag+–Br−–NO3−
Authors: Meschel S. V. , Kleppa O. J. 
Published: January 2005

Calorimetric measurements in the liquid range of these fused-salt systems at 350° are reported. These results, when compared with data for the binary systems involved, permit an evaluation of the ternary excess enthalpies. These quantities are compared with the predictions of the conformal ionic solution theory of Blander and Yosim and with quasichemical theory.
It is found that to a first approximation the excess enthalpies are in good agreement with quasichemical theory. Thus, the systems considered, for which the enthalpy change associated with the metathetical reactions is of the order of 15–20 kcal/mole, behave in a manner similar to that of the previously investigated system Na+–K+–Cl−–Br−.
Paramagnetic Resonance of Vanadium (II) in Ferroelectric Potassium Ferrocyanide
Authors: O'Reilly D. E. , Schacher G. E. 
Published: January 2005

Electron paramagnetic resonance of ferroelectric potassium ferrocyanide trihydrate doped with divalent vanadium has been investigated in the temperature range −180° to 20°C. Below the ferroelectric Curie temperature (Tc=−26°C) the resonance line positions may be expressed by a spin Hamiltonian for which the fine-structure terms D and E are linearly dependent on the spontaneous polarization. Above Tc the spin Hamiltonian is independent of temperature, D is an order of magnitude smaller than at low temperatures, E=0, and the z principal axis lies in the crystal a—c plane.
An anomaly in the linewidth of the ±32→±12 satellite resonance lines is observed in the vicinity of the ferroelectric Curie temperature. With the applied magnetic field along the z principal axis, the linewidth decreases abruptly by a factor of 2 with increase in temperature through the phase transition.
Dielectric constant and spontaneous polarization data are reported which agree with values previously given by Waku. The temperature dependence of the electron resonance is attributed to noncubic components of the crystal-field potential at an iron site produced by the permanent dipole moments of aligned water molecules. Orientations of water molecules determined by NMR are used to calculate the fine-structure tensor including both quartet and doublet T2g excited states. A mechanism of the anomalous line broadening due to fluctuations of the spontaneous polarization is proposed. Effects of both long-range electrostatic and short-range hydrogen-bond interactions in the ferroelectric transition of KFCT are qualitatively discussed.
Analysis of the Nuclear Overhauser Effect in the Difluoroethylenes
Authors: Kuhlmann Karl F. , Baldeschwieler John D. 
Published: January 2005

Analysis of the nuclear Overhauser effect observed in proton double resonance is used to determine the probability of relaxation between spin states of different symmetry in the three difluoroethylene isomers. The probability of relaxation between states of A and B symmetry is much greater for CH2CF2 than for either cis- or trans-CHFCHF. This indication of an appreciable A to B transition probability in CH2CF2 provides some detailed information on the symmetry properties of the interactions responsible for nuclear relaxation. A qualitative comparison of the Overhauser effects in these three molecules indicates that the fluorine spin—rotation interaction is probably responsible for the A to B relaxation in CH2CF2, but further experiments are suggested to test this hypothesis.
The relaxation equations for these spin systems are solved for steady-state and transient behavior using transition probabilities given by assuming relaxation by randomly varying isotropic local fields. Overhauser effects and the transient recovery of the spin systems from the steady state in the presence of an irradiating rf field to thermal equilibrium are used to estimate quantitative proton, fluorine, and A to B relaxation rates.
On the Dielectric Dispersion of Polyelectrolytes, with Application to DNA
Authors: Pollak M. 
Published: January 2005

It has been reported in the literature that dielectric relaxation times measured in a DNA solution are orders of magnitude too large to be consistent with a Maxwell—Wagner mechanism. It has thus been concluded that the dielectric dispersion is associated with the rotation of molecules. It is shown in this paper that this conclusion is based on the use of an expression for the relaxation time which is not applicable to the case of highly elongated molecules. An expression is given which is appropriate to the case of a Maxwell—Wagner mechanism for highly elongated polyelectrolyte molecules. It yields a value for the relaxation time which compares well with the experimental results reported in literature.
Results of experiments on the anisotropy of the relaxation times in a flowing solution of DNA are reported. These results indicate clearly that the dielectric dispersion is indeed due to a Maxwell—Wagner mechanism.