bluuebunny/crossref_metadata_2025 huggingface dataset:
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.
Bending Motions in the Dihalides of Group II Metals
Authors: Berry R. Stephen
Published: January 2005

A polarizable ion model is used to calculate the force constants for bending in the dihalides of the secondgroup metals. The results indicate that the bending constant is a sensitive function of the polarizability of the metal. The calculated constants are in moderate agreement with the experimental values. Some of the implicit assumptions of the model are discussed together with the implications of the calculated results.
Extension of Sedimentation Velocity Theory to Molecules of Intermediate Sizes
Authors: Fujita Hiroshi , MacCosham V. J.
Published: January 2005

The solutions to the Lamm differential equation of the ultracentrifuge subject to the appropriate initial and boundary conditions constitute the basis from which sedimentation experiments are evaluated. Recently, there has been much interest in the sedimentation behavior of molecules of intermediate sizes. The sedimentation of such molecules is characterized by the fact that the significant change of the concentration distribution occurs close to the meniscus. In such cases an exact mathematical analysis is complex, but we present here an approximate analysis to provide some new information about the sedimentation process. It remains to be seen whether this analysis can be applied in an experimental way to determine the characteristic molecular quantities of such molecules.
Ignition of Combustible Gases
Authors: Rosen Gerald
Published: January 2005

The ignition of a combustible gas is studied by obtaining an approximate solution to the coupled equations of unsteady fluid flow, mass and heat diffusion, and chemical kinetics. At various stages, the theory is contrasted with the ``excess enthalpy hypothesis.'' It is shown that the empirically established minimum ignition energy can be deduced from the well-established laws, without invoking the ad hoc ``excess enthalpy hypothesis.''
Ultrasonic Relaxation in Rotational Isomers
Authors: Chen Joseph H. , Petrauskas A. A.
Published: January 2005

Ultrasonic absorption peaks were observed in liquid 2,3-dimethylbutane, 2-methylpentane, and in 3-methylpentane in the frequency range 3 mc to 35 mc. The mechanism of absorption can be explained in terms of hindered rotation about the middle C–C bond in 2,3-dimethylbutane and about the second and third C–C bond in pentanes. The energy differences between potential minima were found to be about 0.95 kcal/mole in all three liquids. The activation energy of 2-methylpentane was found to be about 3.9 kcal/mole.
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.
Polymers and Theory of Numbers. II. The N-Chain Theory of Degradation
Authors: Pathria R. K. , Nanda V. S.
Published: January 2005

The treatment of the degradation process, developed in analogy with a corresponding problem in the theory of numbers, is extended here to a polymer system in which the distribution of cuts over the member chains is purely random. The problem is solved in two steps and an N-chain theory is thereby developed. Next, in order to determine the various moments and the averages of the distribution, the technique of the ``compound generating function'' is introduced. Further potentialities of the new technique are indicated briefly.
Nuclear Reorientation Spectrum of Li7 in the Gaseous Monomers and Dimers of the Lithium Halides
Authors: Kusch P.
Published: January 2005

The nuclear reorientation spectrum of Li7 has been observed in all of the lithium halides under conditions in which the degree of dimerization of the molecules is first low and then high. In each of the halides the two spectra have a qualitatively different appearance which can only be interpreted under the assumption that at least two different molecular species occur in the beam. An approximate resolution of the spectra into that of the monomer and that of the dimer may be made. Significant differences in both the internal magnetic and the electric quadrupole interactions occur for the monomer and the dimer.
Kinetics of D Atom Reactions with H2, CH4, and D2CO
Authors: Klein Ralph , McNesby James R. , Scheer Milton D. , Schoen Louis J.
Published: January 2005

The activation energies and steric factors of the abstraction reactions D+D2CO→D2+DCO and D+CH4→HD+CH3 have been determined by the technique of competing reactions. Mixtures of formaldehyde-d2 and H2 as well as formaldehyde-d2 and methane were photolyzed over a temperature interval in the region of 350°. Measurements of the HD/D2 product ratios as a function of temperature, initial compositions, and light intensity, give the activation energies and steric factors for D+D2CO→D2+DCO, the values E=4.8±0.6 kcal, P=0.04, and for D+CH4→HD+CH3, the values E=7.8±0.6 kcal, P=0.025. These are based on the values E=5.4 kcal and P=0.11 for the reaction D+H2→HD+H.
Valence-Bond Interpretation of Electron-Coupled Nuclear Spin Interactions; Application to Methane
Authors: Karplus Martin , Anderson D. H.
Published: January 2005

A valence-bond theory, based on the approximate second-order perturbation method of Ramsey, has been developed for the calculation of the electron-coupled nuclear spin interactions in a 1Σ molecule. It has been found possible to derive a general formula which expresses the proton-proton coupling constant in terms of functions that are easily evaluated with the Rumer-Pauling diagrams. The theory is such that, for non-bonded protons, the coupling constant is a sensitive direct measure of deviations from perfect pairing. Application of the theory to methane leads to a numerical value for the coupling constant in agreement with the experimental result. This agreement indicates that contributions of nonperfect-pairing structures to the ground-state wave function of methane are so small that they can have little effect on the energy.
Debye Characteristic Temperature at 0°K of Certain Cubic Crystals. II
Authors: de Launay Jules
Published: January 2005

Numerical tables are given which enable the easy computation of the Debye characteristic temperature at 0°K for certain cubic crystals from a knowledge of the elastic constants. These tables are for the range of elastic constant 0≤c12/c44≤3 and (c11—c12)/2c44⩾1. They include the range of elastic constants usually possessed by the alkali halides. A two-way interpolation formula is also given.
Theory of Solutions. II. Osmotic Pressure Virial Expansion and Light Scattering in Two Component Solutions
Authors: Hill Terrell L.
Published: January 2005

The method of the first paper (I) of this series can be used to provide a rigorous but relatively simple derivation of the McMillan-Mayer osmotic pressure virial expansion and alternative expressions for the virial coefficients Bn. Exact relations are derived relating the Bn to the constant pressure coefficients Cn of Paper I. The initial slope in the usual plot (Hc/τ against c) of light scattering data obtained at constant p is shown to be 2B2—3v̄2°+b11+refrac tive index terms (where b11 is a cluster integral for solvent-solute interaction) and not 2B2, as usually assumed. For hard spheres, this correction is very significant but it is not important if, as is usually the case, the effective solute size for intersolute interactions is large compared with the volume actually occupied by a solute molecule.
Infrared and Raman Spectra of Fluorinated Ethylenes. IX. 1,1-Difluoro-2-chloro-2-bromoethylene
Authors: Theimer Rose , Nielsen J. Rud
Published: January 2005

The infrared absorption spectrum of gaseous CF2:CClBr has been obtained with a Perkin-Elmer Model 112 double-pass spectrometer equipped with LiF, CsBr, and NaCl prisms and a 1-m absorption cell. The Raman spectrum of the compound in the liquid state has been photographed with a 3-prism glass spectrograph of reciprocal linear dispersion 15 A/mm at 4358 A. The 12 vibrational fundamentals have been assigned as follows: species a′: 1731, 1314, 1022, 945, 613, 455, 358, 219, and 166 cm—1; species a″: 566, 324, and ca 155 cm—1. The two lowest a″ fundamentals are rather uncertain. The observed spectra have been interpreted in detail. Thermodynamic properties for the ideal gaseous state at 1 atmos have been calculated for 6 temperatures.
Absorption of Acyclic Oxygen Compounds in the Vacuum Ultraviolet. III. Acetone and Acetaldehyde
Authors: Lake Judith S. , Harrison Anna J.
Published: January 2005

A fluorite prism vacuum spectrograph and hydrogen lamp have been used to determine the 49 000- to 67 000-cm—1 absorption spectra of acetone and acetaldehyde in the vapor phase at 22°C.
Further Considerations of a Previous LCAO-MO Study of the Allylic-Type Transition State in 1,3-Butadiene
Authors: Pilar Frank L.
Published: January 2005

Approximate solutions are obtained for the molecular orbital energies of a perturbed allylic-type transition state involved in the ionic addition reactions of 1,3-butadiene. It is shown that consideration of the perturbation effects on either or both the Coulombic and resonance integrals leads to a correct prediction of chemical reactivity based on the criteria of atom stabilization energies, frontier electron densities, and total electron densities.
Organic Photoconductors. V. A Model for Photoconductivity in Cationic Dyes
Authors: Nelson R. C.
Published: January 2005

It is shown that there is a close relationship between the excited state associated with the lowest optical transition of the molecule in solution and that associated with photoconductivity in the solid dye. The model considers the solid dye as a periodic array of potential wells having discrete bands of allowed energies corresponding to the ground state and excited state of the molecule. In the case of dyes whose conductive properties are strongly temperature-dependent, it is assumed that an excited electron can move in the array by passing over the intermolecular barrier. Extension of this assumption to dyes in which the conductive properties depend only slightly on temperature leads to contradictions, and it is assumed in this case that electrons move through the array by tunneling. It is shown that in such a system the diffusivity will be very large and the mobility very small, and that the Einstein diffusivity-mobility relationship does not hold. The model has properties which are in accord with those observed for the two classes of dyes.
Adsorption of Oxygen on Tungsten
Authors: Eisinger Joseph
Published: January 2005

The adsorption of oxygen on a single crystal tungsten ribbon at room temperature was studied. The maximum coverage was found to be 12.3×1014 atoms cm-2 and the initial sticking probability is 0.24 approximately. The rate of formation of tungsten oxide at the surface of the hot filament was also studied. These results and earlier ones bearing on the adsorption of nitrogen on tungsten are discussed in the light of an idealized atomic model for the tungsten surface.
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.
Free Evaporation of Alkali Halide Crystals
Authors: Rothberg G. M. , Eisenstadt M. , Kusch P.
Published: January 2005

A study has been made of the evaporation of alkali halide crystals directly into vacuum to determine (1) whether or not the velocity distribution of the evaporating molecules is Maxwellian, (2) the chemical composition of the vapor, and (3) the evaporation coefficients and heats of evaporation of the various molecular species. Single crystals of CsBr, CsI, LiF, and NaCl were used. The velocities of the evaporating molecules were analyzed by means of the rotating cylindrical velocity selector used by Miller and Kusch. It was found that within relatively narrow limits of error the velocity distributions were Maxwellian. The vapor of CsI was found to contain only monomers; the others contained polymers in abundances different from those found in the saturated vapors. The heats of evaporation of NaCl monomers and dimers are, respectively, 61.7±4.6 and 67.2±4.6 kcal/mole, which yields heats of activation for evaporation of about 9 kcal/mole. Heats of activation also exist for LiF, but could not be determined from the data. The evaporation coefficients of the CsI and CsBr monomers are about 0.3; the evaporation coefficients of the polymers of NaCl and LiF are temperature dependent and are in the range 0.2 to 1.
Heat Capacities and Thermodynamic Properties of the Pyrrhotites FeS and Fe0.877S from 5 to 350°K
Authors: Grønvold F. , Westrum E. F. , Chou Chien
Published: January 2005

Heat capacities were measured from 5 to 350°K for two pyrrhotites at the iron-rich limit (Fe1.000S) and the sulfur-rich limit (Fe0.877S) of the homogeneity range. The heat-capacity curves follow the normal sigmoid shape with the exception of an upward trend for Fe1.000S above 300°K, and two small, broad humps for Fe0.877S near 8 and 30°K. From these data the entropy and enthalpy functions were calculated. At 298.15°K the values of Cp, S°–S0°, and (H°–H0°)/T are 12.08, 14.415, and 7.496 cal/mole °K, respectively, for Fe1.000S, and 11.92, 14.529, and 7.396 cal/mole °K for Fe0.877S. The values on FeS are lower by approximately 10% over the range 58 to 296°K than those previously reported in the literature.
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.
Elastic and Inelastic Scattering of Low-Velocity Ions: Ne+ in A, A+ in Ne, and A+ in A
Authors: Cramer W. H.
Published: January 2005

Elastic and charge-exchange cross sections have been measured in the energy range 4 to 400 ev for Ne+ in A, A+ in Ne, and A+ in A. Charge exchange was observed only for A+ in A. No evidence was found for the existence of the diatomic ion NeA+. Constants for empirical potential functions have been evaluated and the functions tabulated.
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.
General Approach to the Study of Electrical Conductance and Its Relation to Mass Transport Phenomena
Authors: Laity Richard W.
Published: January 2005

A method of writing phenomenological equations for the description of electrical and mass transport, based on approaches of Onsager and of Klemm, is shown to give rise to a set of coefficients defined in a particularly useful and economical way. Conceptually akin to friction coefficients, these quantities are shown to tie together the results of such very different measurements as electrical conductance, transference numbers, and diffusion coefficients in such a way that a single type of physical concept can be applied in interpreting the results of all three. The characteristics of the phenomenological friction coefficients are examined for three different classes of electrolyte: electrolytic solutions, ionic crystals, and molten salts. Known limiting relations, such as the Nernst-Einstein relation, are shown to follow from the macroscopic treatment in cases where they are experimentally valid. In certain cases it is shown how the macroscopic treatment can be made more consistent with a microscopic model through alternative selection of the entities to be taken as components. Some macroscopic criteria are offered as bases for such selection in cases where more than one possibility seems reasonable.
Curve-Matching Method for Quasi-Unimolecular Reactions
Authors: Powell Richard E.
Published: January 2005

A graphical method is presented for evaluating the high-pressure limiting rate, the low-pressure limiting rate, and the parabolic exponent from data on quasi-unimolecular reactions. A logarithmic plot of k1 against k2, the apparent first-order and second-order rate constants, is matched against a family of theoretical curves. Computations for plotting the theoretical curves are tabulated. The technique is illustrated with data from the literature on cyclopropane and other cyclic molecules, nitrogen pentoxide, and nitrous oxide.
Energetic Species Trapped at 4.2°K from Gaseous Discharges
Authors: Minkoff G. J. , Scherber F. I. , Gallagher J. S.
Published: January 2005

The calorimetric technique developed by Broida and Lutes for estimating the abundance of trapped atoms has been further investigated. A number of difficulties have been recognized, and an apparatus has been constructed which embodies a compromise of the various requirements. The calorimeter is now heated rapidly to 40–50°K by a small heating coil, less heat being required when atoms or radicals are present in the deposit. The concentration is then deduced from the reduction in electric energy needed to raise the calorimeter to some particular temperature. The results for nitrogen, oxygen, argon, and krypton indicate that up to a few percent of the original gas are trapped in an unstable form. The factors affecting the stabilization of energetic species are considered in the light of the results presented.
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.
Color Centers in KI Containing Impurity Electron Acceptors: KI:Tl
Authors: Hersh Herbert N.
Published: January 2005

The optical and chemical properties of KI:Tl after x-raying and subsequent treatments at dry ice temperature or higher, or after coloration by electrolysis or chemical addition, have been investigated. Analysis of the experimental data yields the following conclusions: (1) KI:Tl contains more electron traps than KI; (2) an electron-surplus center (T) is formed when KI:Tl is F-bleached; (3) at concentrations of 10—2 mole percent Tl+, metallic thallium, and not F centers, is produced by additive or electrolytic coloration; (4) KI:Tl, KI, and other alkali halides undergo photochemical changes as a result of x-raying which are related to the production of V centers. Arguments are presented which lead to the following deductions: (1) Tl+ ions act as electron traps; (2) the greater stability of the T center relative to the F center is correlated to the greater electron-accepting nature of the impurity ion (whether it be Tl+ or some other cation) relative to K+, which renders the F, K, R, and M centers unstable; (3) F bleaching at room temperature of x-rayed crystals results in the formation of vacancy aggregates which are stable at room temperature via a transitory stage involving negative-ion vacancies; at low temperatures these aggregates cannot be ``decomposed'' by electrons because of the lack of thermal activation. Similar properties are exhibited by KBr:Tl. Many of the color center properties of KI:Tl should occur with other uni- and polyvalent cationic impurities, since they are most naturally explained on the basis of a greater electron affinity of the impurity ion than of K+.
Determination of the Unreacted Hugoniot for Liquid TNT
Authors: Garn W. B.
Published: January 2005

An optical technique was used to measure the state behind high-explosive induced shock waves in unreacted liquid TNT. Data are reported which determine the unreacted Hugoniot for this material, at an initial temperature of 81°C, over the pressure range from 45 kilobars to 110 kilobars.
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.
Microwave Spectrum and Molecular Structure of Vinyl Fluoride
Authors: Morgan H. W. , Goldstein J. H.
Published: January 2005

The J=0→1 and J=1→2 transitions have been measured in the microwave spectra of the isotopic vinyl fluoride molecules C12H2C12HF, C13H2C12HF, and C12H2C13HF. Parameters obtained from the spectra are b=10636.83, 10295.26, and 10635.02 Mc, and c= 9118.18, 8859.05, and 9082.78 Mc, respectively. Moments were computed for 1134 assumed structures, and used to obtain derivatives of the moments with five structural parameters. Least squares determinations gave the following structure: r2(CC)=1.337±0.002 A, r4(CF)=1.344±0.002 A, ∠CCF=121.0±0.2°, r1(CH)=1.075±0.005 A, and r3(CH)=1.080±0.005 A. Assumed was ∠CCH=120°.
Idealized Theory of the Recombinations of Atoms by Three-Body Collision
Authors: Jepsen Donald W. , Hirschfelder Joseph O.
Published: January 2005

A simple method is given for following the collision dynamics of three potential well molecules restricted to move on a line. The method can be applied to similar simple potentials which involve rigid core repulsion. An expression for the reaction rate for the recombination of atoms is derived in terms of a flux integral over the range of the reaction paths across the Eyring potential surface. The rate is calculated for atoms which interact according to a potential very similar to the potential well model. Finally, the simple reaction A+BC→AB+C is studied by these methods.
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.
Electronic Quenching of OH(2Σ+) in Flames and Its Significance in the Interpretation of Rotational Relaxation
Authors: Carrington Tucker
Published: January 2005

The quenching of fluorescence of electronically excited OH(2Σ+) molecules in the burnt gases above a lean acetylene-oxygen flame burning at a pressure of 3.5 mm Hg has been measured for resolved rotational lines. From these data the lifetime in this flame of the 2Σ+ state with respect to electronic quenching collisions is found to be 0.45×10—7 sec, about one-tenth of the radiative lifetime of the free molecule. Quenching measurements as a function of pressure and composition give cross sections for quenching by O2, CO2, and H2O of 7, 16, and 35 A2. These values exceed by a factor of 10 or more the cross sections to be expected for simple exchange of rotational with translational energy. For argon the quenching cross section is less than 2 A2.

The large cross sections for quenching by the flame gases, and the resultant short lifetime of electronically excited OH molecules in the flame mean that these molecules undergo a radiationless loss of electronic energy in collisions before they have time for either a radiative transition or a collision leading to simple rotational energy transfer. The rotational distribution in the electronic spectrum emitted by OH in flames is thus determined almost exclusively by collision processes involving transfer of electronic energy. Rotational temperatures derived from these distributions bear in general no direct relation to the translational or rotational temperatures which may be associated with the other species in the flame, and are determined principally by specific excitation processes.
Near Ultraviolet Absorption Spectrum of Crystalline 1,3,5-Trichlorobenzene
Authors: Schnepp O.
Published: January 2005

The absorption spectrum of single crystals of 1,3,5-trichlorobenzene in polarized light was investigated at 4.2°K. The spectrum was found to consist of a forbidden molecular part and an allowed crystal field induced system. The two parts of the spectrum are characterized by different polarizations and the polarization behavior of the molecular spectrum leads to conclusions concerning the orientations of the molecular planes in the crystal.
Near Ultraviolet Spectrum of Crystalline Hexachlorobenzene
Authors: Schnepp O. , Kopelman R.
Published: January 2005

The spectrum of single crystals of hexachlorobenzene in polarized light was investigated at liquid nitrogen and liquid helium temperatures, in the 3000 A region. The absorption spectrum consists of a forbidden benzene-type molecular spectrum with transition moment in the molecular plane and an allowed spectrum based on the 0–0 band which is polarized in a direction close to the molecular normals. This spectrum is concluded to be crystal induced. A prominent band at 790 cm—1 from the 0–0 band is assigned as involving the a2g vibrational fundamental and its observation in the b-axis polarized component suggests that the molecule is puckered and has symmetry D3d in the crystal.
Potential Energy Barrier Determinations for Some Alkyl Nitrites by Nuclear Magnetic Resonance
Authors: Piette Lawrence H. , Anderson Weston A.
Published: January 2005

A technique for studying rapid chemical exchange and reorientation reactions by nuclear magnetic resonance techniques is discussed. A treatment for the general case relating the changes in the proton line width with changes in the frequency of rotation about the O–N bond in the alkyl nitrites is developed. Such a treatent gave fairly accurate potential energy barriers to rotation for methyl, ethyl, n-propyl, and isopropyl nitrite. A temperature controlling device for low temperatures applicable to proton resonance techniques is discussed.
Computation of Rigid Asymmetric Rotator Constants from Energy Moments. II
Authors: Parker Paul M. , Brown L. Carlton
Published: January 2005

Further expressions are given which relate the rotational constants of the rigid asymmetric rotator to experimental data through moments of the energy levels. These expressions remove the requirement that all energy levels for given J be known. Instead, the energy levels associated with one symmetry group of the rotational wave functions for given J are required.
Paramagnetic Susceptibilities of the Chromium (III) Halides
Authors: Hansen Wilford N. , Griffel Maurice
Published: January 2005

The paramagnetic susceptibilities of CrF3, CrCl3, CrBr3, and CrI3 have been measured by the Gouy method from room temperature down to a temperature at which the susceptibility is field-dependent. Above approximately 100°K these susceptibilities all obey the Curie-Weiss law with respective constants as follows: θ(°K) = — 124, 31, 51, and 70; Peff (Bohr magnetons) = 3.85, 3.69, 3.94, and 4.03. CrF3 evidently becomes ferrimagnetic below 70°K.
Electrical Properties of Hydrogen Adsorbed on Silicon
Authors: Eisinger Joseph
Published: January 2005

The photoemission from a silicon surface has been studied as a function of the number of hydrogen atoms adsorbed on it. The electric dipole moment of an adsorbed H atom is found to be 0.15×10—18 esu approximately.
Thermodynamic and Spectroscopic Study of Vinylidene Chloride. I. Thermodynamic Properties of the Solid, Liquid, and Ideal Gas
Authors: Hildenbrand D. L. , McDonald R. A. , Kramer W. R. , Stull D. R.
Published: January 2005

The low-temperature heat capacity, heat of vaporization, and vapor pressure of vinylidene chloride have been measured. Data obtained from these measurements are as follows: the heat capacity of the solid from 13 to 150°K; the liquid heat capacity from 150 to 290°K; the heat of fusion, 1557 cal mole—1, at the melting point, 150.59°K; the entropy of the liquid at 298.15°K, 48.17 cal mole—1 deg—1; the heat of vaporization at 298.15°K, 6328 cal mole—1; and the vapor pressure, log10P(mm)=6.98200−1104.29/(t+237.70). The entropy of the ideal gas, evaluated from the calorimetric data, is in agreement with the entropy calculated from spectroscopic and molecular data. Thermodynamic properties of the solid, liquid, and ideal gas have been tabulated at selected temperatures.
Free Energy of a Nonuniform System. II. Thermodynamic Basis
Authors: Cahn John W.
Published: January 2005

The thermodynamic treatment of nonuniform systems of Cahn and Hilliard is shown to be equivalent to the self-consistent thermodynamic formalism of Hart. All parameters of the two treatments have been rigorously related and key equations have been shown to be equivalent.
Osmotic Electric or Magnetic Field
Authors: Hill Terrell L.
Published: January 2005

The usual osmotic pressure method for the determination of molecular weights becomes inaccurate when applied to solutes with high molecular weights because the solvent chemical potential is too sensitive to pressure changes. Since the solvent chemical potential is much less sensitive to changes in electric or magnetic field, the suggestion is made that these variables might be useful in osmotic experiments. A few schematic arrangements and a numerical example are discussed. Any possible advantage of the proposed method, over the conventional osmotic pressure method, rests on the replacement of a measurement of a small pressure difference by the measurement of a sizable electric or magnetic field coupled with a null observation on the pressure difference.
Nitrogen Isotopic Fractionation between Nitric Acid and the Oxides of Nitrogen
Authors: Brown L. L. , Begun G. M.
Published: January 2005

The single-stage nitrogen isotopic separation factor between nitric acid and the oxides of nitrogen has been measured as a function of temperature and nitric acid concentration. Nitric acid molarities were varied from 1.084 to 15.45 and temperatures from 26 to 70°C were used. The separation factor was found to vary from 1.01 to 1.064, with nitrogen-15 concentrating in the nitric acid phase. The experimental data are compared with values calculated from spectroscopic and chemical data.
Microwave Spectrum of Methyl Germane
Authors: Laurie Victor W.
Published: January 2005

The J=0→1 and 1→2 transitions of 28 isotopic species of CH3GeH3 have been measured. From the rotational constants obtained, the following structural parameters have been calculated: rCH=1.083±0.005 A°, rGeH=1.529±0.005 A°, rCGe=1.9453±0.0005 A°, ≰HCH=108°25′±30′, ≰HGeH=109°15′±30′. The K=1 transitions of the asymmetrically deuterated species are split by internal rotation about the C–Ge bond. Withthe assumption of a threefold sinusoidal potential, an internal barrier of 1239±25 cal/mole has been determined from these splittings. Analysis of the Stark effect of several species gives a dipole moment of 0.635±0.006 D. From observed hyperfine structure the nuclear quadrupole coupling constant of Ge73 has been calculated to be +3 Mc.
Infrared Spectra of Alkoxyboranes. II. Chlorodimethoxyborane and Dichloromethoxyborane
Authors: Lehmann Walter J. , Onak Thomas P. , Shapiro I.
Published: January 2005

Infrared spectra of gaseous ClB (OCH3)2 and Cl2BOCH3 in the 2 to 15 μ range are reported, and the observed bands are assigned to the fundamental vibrations of the molecules. The single B–Cl vibration was found to have widely varying frequencies and thus cannot be described by the term ``characteristic.'' Two strong bands, reported by previous investigators at 1376 and 1395 cm—1 in the infrared spectrum of BCl3 have been found to be due to an impurity. By use of a correlation scheme assignments for some skeletal stretching vibrations in FB(OCH3)2 are proposed.
Variable Reaction Rate Theory of Polymer Size Distribution
Authors: Gold Louis
Published: January 2005

The principle of equal reactivity of polymer species in a molecular distribution may be apparent rather than actual owing to relative insensitivity of the size distribution to variations in reaction rate constants. A formalism is developed for polymerization encompassing chain-length-dependent rate constants k(x). For linear and condensation polymers, a perturbation form of solution is outlined based upon the ad hoc assumption k(x) = k/xn, n being a parameter characteristic of the system.
Spectroscopic Evidence for Triatomic Nitrogen in Solids at Very Low Temperature
Authors: Peyron M. , Hörl E. M. , Brown H. W. , Broida H. P.
Published: January 2005

Additional wavelength, intensity, and lifetime measurements of the radiation emitted from solid nitrogen containing trapped atoms have led to the interpretation that a weakly bound triatomic molecule, N2–N, is an emitting species. The three lowest electronic levels of atomic nitrogen 2P, 2D, and 4S are involved in the 8 line groups which have been found. Isotopic substitution has confirmed this model. Evidence also has been found for an N2–O molecule similar to the N2–N.
Deuterium Isotope Effect in the Reaction of Hydrogen Molecules with Chlorine Atoms and the Potential Energy of the H2Cl Transition Complex
Authors: Bigeleisen Jacob , Klein Fritz S. , Weston Ralph E. , Wolfsberg Max
Published: January 2005

The relative rates of reaction of H2 and HD with chlorine atoms have been measured over the temperature range of 243–350°K. In this temperature interval, the ratio of the second-order rate constants, R=kH2/ΣkHD,is equal to (1.24∓0.03) exp (490±6/RT). A search was made for HD after an unequilibrated mixture of H2 and D2 was half converted to hydrogen chloride by photochemical reaction with Cl2. From the failure to detect 0.02% HD in the unreacted hydrogen, a lower limit is set for the ratio of the rate constants of the reactions H+Cl2→ lim k16HCl+Cl and H+HCl→ lim k17H2+Cl.

It is shown that the pre-exponential factors in R for the HD experiments and in the analogous experiments on HT are in quantitative agreement with theoretical calculations for either linear or triangular transition states, subject to the sole restriction that k(HD+Cl→HCl+D) is approximately equal to k(HD+Cl→DCl+H). An intercomparison is made between the experimental difference in activation energies between H2, HD, HT, and D2 for reaction with chlorine atoms and theoretical calculations for linear and triangular transition states. With the most favorable potential function for H2Cl, the maximum deviation between ΔEexp‡ and ΔEtheor‡ is fifteen percent. Inasmuch as there are more experimental data than parameters necessary to construct the potential function of H2Cl, the agreement between theory and experiment constitutes a positive test of the transition state formulation of the effect of isotopic substitution on the rates of chemical reactions.
Determination of Intermolecular Potentials from Thermodynamic Data and the Law of Corresponding States
Authors: Keller Joseph B. , Zumino Bruno
Published: January 2005

It is shown that in classical statistical mechanics the second virial coefficient in the virial expansion of the equation of state of a gas uniquely determines the intermolecular potential provided that the potential is monotonic (i.e., everywhere repulsive or everywhere attractive). This result leads to a partial verification of a conjecture of H. Kammerlingh-Onnes and W. H. Keesom concerning the Law of Corresponding States. An explicit formula for the potential is also obtained. If the potential is not monotonic it is not uniquely determined by the second virial coefficient. All potentials corresponding to a given second virial coefficient are determined explicitly.
Infrared and Raman Spectra of Fluorinated Ethanes. XI. Pentafluorobromoethane
Authors: Klaboe Peter , Nielsen J. Rud
Published: January 2005

The infrared spectrum of gaseous CF3–CF2Br has been obtained with a Perkin-Elmer double-pass spectrometer equipped with CsBr, NaCl, and LiF prisms. The Raman spectrum of the liquid has been photographed with a 3-prism glass spectrograph of reciprocal linear dispersion 15 A/mm at 4358 A. 17 vibrational fundamentals have been assigned as follows: Species a′: 1339, 1240, 1124, 949, 754, 634, 547, 370, 329, ca 297, and ca 167 cm—1; species a″: ca 1240, 1182, 591, 440, ca 297, and ca 152 cm—1. The torsional fundamental, which undoubtedly lies below 150 cm—1, could not be determined. The spectra have been interpreted in detail.