bluuebunny/crossref_metadata_2025_split huggingface dataset:
Infrared Spectra of Ices II, III, and V in the Range 4000 to 350 cm—1
Authors: Bertie J. E. , Whalley E. 
Published: January 2005

The infrared spectra of Ices II, III, and V between 4000 and 350 cm—1 have been obtained. The ices were made at appropriate pressures and temperatures, cooled under pressure to liquid-nitrogen temperature, and removed from the pressure vessel. Mulls were made near liquid-nitrogen temperature using isopentane or perfluoropropane as mulling agents, and the spectra of the mulls at ∼100°K were recorded. The spectra of ices made from H2O, D2O, 5% H2O in D2O, 5% D2O in H2O, and, for Ices II and III, 1% D2O in H2O were obtained. In general features, the spectra of pure H2O and D2O Ices II, III, and V are similar to those of Ice I. For most bands there is a shift of frequency from that in Ice I towards the vapor frequencies, but the shift is small compared with the shift between Ice I and the vapor. Ices II, III, and V are therefore essentially fully hydrogen bonded and are probably four coordinated. This agrees with a proposed structure for Ice III.
In Ices II and III the bands due to the O–H and the O—D stretching vibrations of HDO in dilute solution in D2O and H2O, respectively, show a good deal of fine structure, and are quite narrow, the half-width of the O—D bands being about 5 cm—1. These are by far the sharpest O–H (or O—D) stretching vibrations of hydrogen-bonded O–H———O groups so far observed. Clearly, breadth is not inherent in the O–H stretching bands of O–H———O. There is also a good deal of fine structure in the bands due to rotational vibrations of water molecules in Ices II and III, and much of this fine structure broadens and weakens when a small amount of H2O is added to D2O, and of D2O to H2O. The only simple explanation of this, and of the fine structure of the O–H stretching bands, is that the hydrogen atoms in Ices II and III are ordered. No corresponding fine structure occurs in Ice V, and the hydrogen atoms are probably disordered, as in Ice I.
Monte Carlo Calculations. IV. Further Studies of Unimolecular Dissociation
Authors: Bunker Don L. 
Published: January 2005

Distributions of lifetimes with respect to dissociation were determined vs energy for a variety of rotating anharmonic triatomic molecular models. About 235 000 trajectories were included in the study. Results are in adequate agreement with the Rice—Ramsperger—Kassel—Marcus (RRKM) theory as regards high-pressure dissociation rate vs energy. However, some models (especially those with widely separated vibration frequencies) fail to conform to the necessary RRKM assumption that lifetimes are randomly distributed.
A theory of the lifetime distributions is developed which accounts for the computed results. Application of this theory to actual molecules indicates that intramolecular energy relaxation is complete in about 10—11 sec regardless of molecular complexity. Nonrandom lifetime distributions are likely only for a few triatomic molecules, or under exceptional experimental conditions. The RRKM theory is then endorsed for all reactions to which it has been applied.
Partition of excess energy between product vibration and translation is discussed.
Excess-Kinetic-Energy Ions in Organic Mass Spectra
Authors: Olmsted John , Street K. , Newton Amos S. 
Published: January 2005

The characteristics of excess-kinetic-energy ions in mass spectra have been studied with a Dempster-type mass spectrometer. A method was devised whereby the total initial kinetic energies possessed by such ions could be measured more accurately than has been done previously, and the kinetic energies of methyl ions, both near-thermal and excess-kinetic-energy, from a wide variety of different organic compounds, are presented. Appearance potential curves were obtained for several excess-kinetic-energy methyl ions; these show a second-power dependence of cross section on electron energy in the threshold region with threshold values of the order of 30 eV. Finally, a method of estimating the discrimination factor of the mass spectrometer toward ions possessing excess kinetic energy was utilized to obtain values for the actual abundances of excess-kinetic-energy methyl ions in the fragmentations of several organic compounds. Actual abundances of from 2% to 10% of the total ions in the mass spectrum were found from many compounds.
The values of appearance potentials, kinetic energies, and abundances that have been measured for the complementary excess-kinetic-energy ion pairs from methyl amine (masses 15 and 16) and propane (masses 15 and 27) are consistent with a mechanism for formation in which both ions arise from the same initial state in each respective case. The data support the suggestion that excess-kinetic-energy fragment ions from the organic compounds are formed by breakdown of doubly charged parent ions.
Laser Phenomena in Europium Chelates. II. Kinetics and Optical Pumping in Europium Benzoylacetonate
Authors: Samelson H. , Lempicki A. , Brecher C. 
Published: January 2005

The laser application of europium chelates is considered in some detail by means of an analysis of the steady-state kinetics of the fluorescence and of the optical pumping. An energy-level model of the chelate molecule is proposed and the kinetics analyzed in terms of the various transition probabilities. The solutions for the steady state indicate the effect of the various transition probabilities on the threshold for laser action. It is also pointed out that the triplet state associated with the phosphorescence can function as a trap state.
A consideration of the pumping problem reveals that the intense absorption leads to extremely non-uniform excitation which reduces the width of the effective pump band. The rate of pumping becomes relatively insensitive to concentration but is extremely dependent on the diameter of the cylindrical optical cavity. These considerations are then applied to a comparison of the thresholds for laser action in ruby and EuB.
Spectral Effects of Strong Exciton Coupling in the Lowest Electronic Transition of Perylene
Authors: Hochstrasser Robin M. 
Published: January 2005

Measurements have been made of the absolute intensity of the lowest-energy electronic state of perylene. The intensities of the Au and Bu factor group states have been found to deviate from an oriented gas model to such an extent that the model proves valueless in this case. The perturbation treatment of crystal-induced intensity stealing has been very briefly reviewed to examine the effect of the orientation of molecules on the relative importance of second-order terms. It has been shown that these terms can be responsible for most of the intensity when the active molecular axis is very nearly 90° to the crystal symmetry axis. Numerical values have been obtained for the influence of five higher-energy states on the intensity of the lowest state. The oriented gas polarization ratio is Ia/Ib=344: 1; the observed value is 1:1.76; the calculated value is 1: 2.05. The calculated and experimental values of the absolute a and b polarized intensity are in fair agreement.
The observed splitting (5250 cm—1) between the origin of the b spectrum and the peak of the a spectrum has been considered as a strong coupling Davydov splitting which is calculated to be 5013 cm—1 using a dipole approximation.
Vibrational frequencies of 350 and 1270 cm—1 have been obtained from absorption spectra data with perylene at 4.2°K. The possible role of vibronic coupling and charge resonance on the spectrum, and the nature of the diffuse fluorescence are also discussed.
Adsorption—Desorption of Hydrogen on Tungsten and Molybdenum
Authors: Moore George E. , Unterwald F. C. 
Published: January 2005

Adsorption of hydrogen on tungsten and molybdenum was investigated over the range 300° to 1000°K using a mass spectrometer. These phenomena alone are observed below about 1200°K. A mass spectrometer affords a practical method for studying different adsorbates simultaneously adsorbed. Although the method is less sensitive than those depending on measurements of total pressure, it does not require the dangerous assumptions made tacitly in much published work employing the latter method.
Molecular hydrogen is readily desorbed below 900°K from both W and Mo, although somewhat less so from Mo. The amount remaining is probably not over 10—5 monolayer. Over the experimental range, only one mode of adsorption—desorption is detected. Despite intense effort, CO, H2O, and CH4 were nevere liminated. CO is much more tenaciously bound than hydrogen and thus may have confused earlier measurements for hydrogen. H2O and CH4 do not compete successfully with hydrogen for adsorption sites; they are less tenaciously adsorbed and their abundance was low.
Effect of Unimolecular Decay Kinetics on the Interpretation of Appearance Potentials
Authors: Chupka William A. 
Published: January 2005

The interpretation of appearance potential data on diatomic molecules should take account of possible effects caused by predissociation, emission of light and autoionization. In the case of complex polyatomic molecules, the kinetics of predissociation and the internal thermal energy of the molecules become especially important. The intensities of the parent, fragment, and metastable ions produced by photoionization of n-propylamine, n-propanol, and methyl ethyl ketone are studied as a function of photon energy. The excess kinetic energies of the fragment ions are found to be negligibly small. The data are interpreted in terms of Rosenstock's quasi-equilibrium theory of unimolecular decomposition and indicate that the theory is qualitatively correct for the dissociative processes investigated. However, the theory is shown to be quantitatively inadequate at least in the energy range near threshold. In this region the rate constant for dissociation varies much more rapidly with energy than the theory predicts. Some of the assumptions of the theory are examined and compared to deductions from the data.
The meaning of appearance potential data is examined in the light of these results. The effects of both the kinetics of dissociation and of internal thermal energy on ionization efficiency curves are significant. Most of the methods used to determine appearance potentials tend to minimize these effects and there is probably some cancellation of errors. A new method for the determination of appearance potentials is described. Experimental methods which can yield more detailed information concerning dissociation processes of complex molecular ions are suggested.
Statistical Mechanics of Helix-Coil Transitions in Biological Macromolecules
Authors: Gibbs J. H. , DiMarzio E. A. 
Published: January 2005

The polypeptide backbone, common to the macromolecular chains of proteins, represents a highly co-operative system which is essentially one dimensional and, therefore, tractable theoretically.
The complete partition function for such a system can be evaluated with the aid of either the method of Lagrangian multipliers or the method of steepest descents. When this is done a transition from alpha helix to random coil is obtained as a result.
When the effects of solvation are included, the transition may or may not be inverted depending upon the nature of the solvent. The quantitative theoretical results for dilute solutions are in agreement with the available experimental data on the reversible ``denaturation'' of synthetic polypeptides.
The separation of the two strands of the double-stranded helix of the genetic material, desoxyribonucleic acid, can be treated with the same theoretical method.
Mass Spectrometric Study of Inter-Group IVB Molecules
Authors: Drowart J. , De Maria G. , Boerboom A. J. H. , Inghram M. G. 
Published: January 2005

The systems germanium-graphite and germanium-silicon-carbon have been studied. Several gaseous molecules containing Ge, Si, and/or C were observed and their dissociation energies determined from measured partial pressures. A general picture of the dissociation energies of di-, tri-, and tetraatomic intergroup IVB molecules is deduced from these measurements.
Incidental to this study the vapor pressure of pure Si was determined; the result confirms the heat of sublimation obtained previously.
Theory of Detonations. III. Ignition Temperature Approximation
Authors: Curtiss C. F. , Hirschfelder J. O. , Barnett M. P. 
Published: January 2005

This paper is one of a series in which we discuss the effect of viscosity, diffusion, and heat conductivity on the structure of steady-state plane detonation waves. It is shown that the consideration of these phenomena may lead to considerable overlapping of the reaction and shock zones and also to the existence of detonation limits.
In order to discuss in more detail the topological nature of the solutions and the nature of the detonation limits, the equations are simplified by idealizing the chemical kinetics in the following manner: At temperatures below an ignition temperature, the reaction rates are taken to be zero; at temperatures above this ignition temperature, the reaction rates are taken to be functions of the chemical composition but independent of the temperature. In order to further simplify the equations, the Prandtl number is taken to be ¾ and the Lewis number to be unity. These idealizations lead to an uncoupling of the detonation equations, although the importance of the transport properties remains unchanged. In the high-temperature range, the fractions of the mass rate of flow, Gi, are functions of the chemical composition only. In the low-temperature range, the Gi are constant.
With these simplifications, we consider in detail both flames and detonations involving the unimolecular A→B or the equivalent bimolecular reaction A+X→B+X where X represents either a molecule of A or B. Calculations are made for values of the ignition temperature greater than, equal to, and less than the von Neumann spike temperature. Comparison of these calculations with numerical calculations previously performed, using an Arrhenius type variation of the reaction rate with temperature, gives the best agreement when the ignition temperature is taken to be greater than the von Neumann spike temperature. If the ignition temperature is greater than the von Neumann spike temperature, it is found that the thickness of the detonation wave is of the order of one mean free path. This suggests the conclusion that under the extreme conditions of a detonation the usual concept of chemical equilibrium between activated state and reactant molecules cannot apply. Instead, the molecules gain their energies of activation in successive stages. With this more complicated reaction mechanism, the detonation wave would be much thicker. These conclusions, regardless of the functional form of the rate law, depend upon the existence of a lower limit for the value of the rate constant which can support a steady-state detonation. Such a lower limit was suggested by our previous calculations with the Arrhenius rate law. However, more detailed studies are required to determine under what conditions such a lower limit may exist.
Solutions under Pressure
Authors: Rosen Joseph S. 
Published: January 2005

A method is given which permits the calculation of the volumes of aqueous solutions of salts at higher pressures solely from the volumes of these solutions at atmospheric pressure and the compressibility data of the pure substances involved. The volumes of aqueous solutions of sodium chloride, ammonium nitrate, and potassium sulfate are computed to 10 000 bars pressure and these agree with the observed values to within a fraction of one percent. Tammann's hypothesis, to the effect that water in solution is compressed by an ionized solute, is used; but, the extension of this hypothesis permits the calculation of the volumes of the solute and the water in solution and the effect of pressure on these volumes. The interpolation formulas derived also appear to be applicable to nonaqueous solutions of salts; and some tentative results are also given for mixtures of liquids (ethyl alcohol in water).
An equation is introduced, which like Tait's equation, represents the variation of volumes with pressure. This equation is fundamental to the development of the interpolation equations for solutions which are given in this article. It is found that an analogous equation reproduces refractive index and dielectric constant data for liquids and gases at high pressures. This leads to an equation, previously proposed, which is considered more useful in representing experimental data analytically than the corresponding formulas of Lorenz-Lorentz and Mossotti-Clausius.
Microwave Absorption and Molecular Structure in Liquids. XXV. Measurements of Dielectric Constant and Loss at 3.1-mm Wavelength by an Interferometric Method
Authors: Rampolla R. W. , Miller R. C. , Smyth C. P. 
Published: January 2005

The theory and apparatus for an interferometric method for the measurement of the dielectric constant and loss of a liquid at 3.1-mm wavelength are described. The 3.1-mm wave is obtained as the fourth harmonic from a K-band reflex klystron. The probable error of the dielectric constant measurements is 0.5%, while that of the loss measurements is 2–5% for high loss liquids. For very low losses, only an upper limit can be obtained because of the small amount of harmonic energy obtainable.
Four tetrahalogenated methanes, three substituted benzenes, two methylquinolines, three alcohols, and water have been measured and the results examined in the light of measurements at lower frequencies. All of the liquids but the three alcohols give 3-mm points lying satisfactorily on Cole-Cole arc plots drawn through points previously obtained at lower frequencies. The losses observed at 3 mm are, however, some-what higher than the calculated indicating the probable presence of overlapping absorption regions at still higher frequencies. The apparent optical dielectric constant value 6.0 found for water evidences further absorption at much shorter wavelengths. Methyl, ethyl, and n-octyl alcohols show absorption regions at frequencies too high to be attributable to molecular dipole orientation. The critical or maximum absorption wavelengths found for these additional high-frequency absorption regions are 0.57 cm for ethyl alcohol and 0.50 cm for n-octyl alcohol.
Kinetics of the Thermal Decomposition of Dimethylmercury. II. Carbon-13 Isotope Effect
Authors: Russell Morley E. , Bernstein Richard B. 
Published: January 2005

The C13 kinetic isotope effect in the pyrolysis of gaseous dimethylmercury has been studied in the presence and absence of cyclopentane inhibitor from 290–375°C for the inhibited and 290–350°C for the uninhibited reactions. The isotopic fractionation factor (S) is defined as the ratio of rate constants for the decomposition of Hg(C12H3)2 vs C12H3HgC13H3. S shows a strong dependence upon the degree of inhibition of the methyl radical chain, which, in turn, is a function of the ratio of cyclopentane to dimethylmercury. S is also a function of the total pressure.
The dependence of S upon the degree of inhibition agrees quantitatively with the predictions of the mechanism proposed in I. The pressure effect on the isotope effect is attributed to the unimolecular nature of the rate determining step (Hg–C bond rupture) and is consistent with the over-all kinetics.
The isotope rate factor in the fully inhibited high-pressure limit, α, is 1.034±0.002 (essentially independent of temperature over the range studied), compared to a value of 1.011±0.001 for the uninhibited (chain) decomposition.
Electronic Structure of Nitric Oxide
Authors: Brion H. , Moser C. , Yamazaki M. 
Published: January 2005

The self-consistent field (SCF) molecular orbitals for nitric oxide have been calculated in the linear-combination-of-atomic-orbitals molecular orbital approximation (LCAO-MO) using 1s, 2s, and 2p Slater atomic functions. Three different calculations have been made.
(1) An ``incomplete treatment'' in which mixing between the inner orbitals, which contain only 1s functions, and outer orbitals, which contain orthogonalized 2s and 2p functions, is neglected.
(2) A similar calculation, but here the outer orbitals are forced to be orthogonal to the inner orbitals.
(3) The ``complete treatment'' in which all orbitals are combinations of 1s, 2s, and 2p functions. The single Slater determinant wave function built from the orbitals calculated from the complete treatment gives a negative binding energy, but a limited configuration interaction calculation accounts for 26% of the observed binding energy. The agreement between the calculated and observed first ionization potential is very good. Certain aspects of the uv spectra seem to be reasonably well explained from this calculation. The dipole moment is calculated to be 0.5 D (N-O+) as compared to an observed value of 0.16 D with undetermined sign. Following Mulliken, atomic and overlap populations have been calculated.
Dielectric Absorption in Crystalline Long-Chain Methyl Ethers
Authors: Cook J. S. , Meakins R. J. 
Published: January 2005

The dielectric properties of three long-chain methyl ethers and two methyl ketones have been measured at frequencies between 5 cps and 2.4×1010 cps, and at different temperatures. No dielectric absorption was detected in the ketones.
The ethers were investigated in both the α- and the β-crystalline phases. In the β phase the ethers gave two regions of dielectric absorption, and the energy parameters associated with these absorptions were determined.
In the α phase, the methyl ethers give larger dielectric absorption, which occurs mainly in the microwave region, although two of the compounds also give a smaller peak at very low frequencies. The experimental values of the total absorption are in good agreement with the values calculated from the dipole moment. The results suggest that the molecules all contribute to the dielectric absorption, which is in contrast to the situation in β-phase long-chain compounds where it has been suggested that molecular rotation occurs only at imperfections in the crystal lattice.
Energy Levels of Bound Electrons in Liquid Ammonia
Authors: Jortner Joshua 
Published: January 2005

The properties of infinitely dilute metal ammonia solutions are interpreted on the basis of Landau's model for electron binding by polarization of the dielectric medium. The electrons are bound in cavities of radius 3.2–3.45 A. The energy levels of the trapped electrons are computed by the variation method using one-parameter wave functions. It is possible to obtain theoretical values for the heat of solution of the electron and the energy of the 1s→2p transition in agreement with experimental data.
The susceptibility of the energy of the electronic transition to temperature cannot be interpreted by the temperature dependence of the dielectric constant only, and it is presumed that the electron cavity radius is temperature dependent.
Nature of the Hydrogen Bond
Authors: Paoloni Leonello 
Published: January 2005

Starting from a molecular orbital viewpoint, a general description is given of hydrogen bonds X—H···Y. The case of weak hydrogen bonds, as in associated liquids, is developed in detail, with the O–H···O bond as an example. The new feature in the treatment is the introduction of excited 2s and 2p orbitals of the hydrogen atom (Sec. II), the consequences of which, it is shown, provide a satisfactory account of the effects of hydrogen bonding both on the X—H stretching infrared band and on dipole moments (Sec. IV).
The energy change accompanying hydrogen bond formation is considered as depending on the nature of the hybridization of the atomic orbitals involved (Sec. V). Again it is found that the experimental pattern is reproduced when the 2s and 2p orbitals of hydrogen are included. Moreover the behavior of the energy as a function of the hybridization parameters suggests a way in which the changes in the Xmdash;H bond and in the atom Y can account for the various properties observed in molecular associations due to hydrogen bonding.