bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermoluminescent Kinetics of Alpha-Irradiated Alkali Halides
Authors: May C. E. , Partridge J. A.
Published: January 2005

The kinetics of the thermoluminescence of single crystal NaCl, KCl, and KBr irradiated with 40-MeV alpha particles were investigated. Only one glow peak, composed essentially of a single emission band, was obtained for each of the salts investigated. To attempt complete analysis of the kinetics, both glow curve and isothermal annealing experiments were employed. The results from glow curves were shown to be unreliable for calculation of the kinetic order in the case of NaCl and KBr. The isothermal tests indicate the kinetics of the dominant process for NaCl to be first order; for KBr, first order; and for KCl, 32 order. No general statement can be made concerning the order of these processes; thus, at present, the kinetics for each salt investigated must be determined individually. Occasionally, secondary processes occur in specimens of NaCl and KBr, even though essentially only one spectral peak was detected. A simple model for luminescence will explain the kinetics of NaCl and KBr; it involves activation of electrons from traps into the conduction band. To explain the results for KCl, a more complex model is required. Activation energies were also calculated.
Isotope Separation by Thermal Diffusion in Ternary Systems
Authors: Howard A. J. , Watson W. W.
Published: January 2005

The problem of isotope enrichment of the middle component in ternary systems via thermal diffusion is discussed, emphasis being placed on systems where the initial concentration of the middle component is considerably less than that of either end component. The design and operation of a 12-column thermal diffusion apparatus in which 99.99% Ne22, 99.4% Ar36, and 8.0% Ar38 isotopic samples were produced is described. The concentration of the midcomponent as a function of an end concentration is found to be adequately described by the Jones—Furry theory. The experimental results suggest suitable techniques for application in similar isotopic enrichment programs.
Study of Low-Frequency Motions in Polyethylene and the Paraffin Hydrocarbons by Neutron Inelastic Scattering
Authors: Danner H. R. , Safford G. J. , Boutin H. , Berger M.
Published: January 2005

The vibrational spectra between 800 and 30 cm—1, derived from measurements of the time-of-flight distributions of initially ``cold'' neutrons inelastically scattered from thin samples, are presented for highly crystalline polyethylene at sample temperatures below and above both the glass transition and the melting point, and for samples of branched, irradiated, and quenched polyethylene at room temperature. The acoustical torsion mode v9 with a high-frequency limit of 200 cm—1 and the acoustic deformation mode v5 with an estimated high-frequency limit of 550 cm—1 are observed in agreement with recent calculations of the normal modes of an infinite transplanar polyethylene chain. However, the measured spectra indicate that, although intermolecular forces appear to have a negligible influence, the distributions of frequencies associated with these modes are strongly influenced by the presence and by the phase of the disorder in the sample. Similar measurements for a series of n-paraffin hydrocarbons between C6H14 and C32H66 at room temperature indicate that while nearly free internal rotations take place in the liquid phase, these rotations are hindered in the solid phase. As the length of the chain increases, the frequency distribution of the vibrational motions in the solid n-paraffins approaches that observed in polyethylene at room temperature.
Order—Disorder Transitions in Biocolloids
Authors: Peticolas Warner L.
Published: January 2005

The author's theory of order—disorder transitions in associative colloids is tested by comparison with measurements of the viscosity of different colloidal systems as a function of temperature or concentration. The theory predicts that an order—disorder transition from a random array of monomers to a segmented one-dimensional helical rod will occur as the temperature is reduced to the one-dimensional freezing point or the concentration increased to the critical micelle concentration. Under these conditions as enormous increase in the solution viscosity is predicted to occur.

Semiquantitative agreement is obtained between theory and experiment for a variety of associative colloids. Fully quantitative agreement cannot be obtained because the solutions become birefringent upon aggregation of the monomers, due to the large rod lengths which are obtained. This birefringence is well known to be due to the fact that the rods bump into each other and do not have their full freedom of rotation. Although this situation more closely resembles the statistical mechanical theory which neglects rotation of the rods, there is unfortunately no adequate theory of the viscosity of such solutions and the Simha—Kuhn theory which we have used can only be approximate under these conditions.
Transient Species in the Photolysis of Anils
Authors: Wettermark Gunnar , Dogliotti Libera
Published: January 2005

Two photoinduced isomerizations occur in the photolysis of ethanol solutions of the anil, o-hydroxybenzylidene-aniline in the temperature interval 15°—70°C. One isomerization involves the formation of a visible absorption band, λmax 470 mμ, which fades in the dark with a lifetime in the millisecond region. The fading is buffer catalyzed and yields an activation energy of 3.5 kcal/mole for this catalysis. The second isomerization, which is observed as a change in the near ultraviolet spectrum, is about a thousand times more long-lived and not catalyzed by the presence of buffer, activation energy: 15.0 kcal/mole. The two isomerizations are identified as (1) a hydrogen transfer from the ortho hydroxyl group to the nitrogen atom forming an ortho quinoid structure, (2) a cis—trans isomerization around the C–N double bond.
Exponential Correlation Functions for Two-Electron Atoms
Authors: Pritchard H. O.
Published: January 2005

Inclusion of an exponential term in r12 in the correlated orbital treatment of two-electron atoms does not lead to a significant improvement in the calculated energy. However, it does cause the orbital cusp conditions to be satisfied more accurately, and at the same time, it leads to a very considerable reduction in the computing time required.
ESR Study of NO2 and NO3 in Irradiated Lead Nitrate
Authors: Golding R. M. , Henchman Michael
Published: January 2005

Lead nitrate crystals have been irradiated with electrons at room temperature and their electron spin resonance spectra examined at 77°K to reveal three paramagnetic species. One species shows no hyperfine structure and has an isotropic g tensor with a g value at the free spin value: little can be said of its nature. The others are located, by their spectral anisotropy, at nitrate sites in the crystal with the axes of their axially symmetric g tensors parallel to the nitrate triad axes. One of these species is interpreted as NO3: it shows no nitrogen hyperfine structure but a slight interaction with 207Pb. The other is identified as NO2 rotating in the plane of the nitrate site. Theoretical predictions are in accord with these assignments.

Various conclusions are drawn for the radiation chemistry. Other species than the NO2— and O2, revealed by chemical analysis, are significant products. The particular lattice determines the nature of these products, their stability and, in the case of NO2, its mechanism of formation. The annealing kinetics of NO2 and NO3 differ from that of the NO2—: Mechanisms previously postulated for the latter are almost certainly too simple.
Systematic Approach to Explanation of the Rigid Disk Phase Transition
Authors: Stillinger F. H. , DiMarzio E. A. , Kornegay R. L.
Published: January 2005

By classifying particle center positions with a hexagonal grid, evaluation of the two-dimensional rigid sphere partition function is reduced to a special lattice statistics problem, with precisely defined nearest-neighbor effective pair interactions. The hexagonal cell size is chosen to be the maximum consistent with no more than double occupancy. Since the resulting lattice partition function (with three states per site) contains a collectively determined many-cell effective interaction Δ*, as well as nearest-neighbor contributions, it becomes necessary to examine in detail the statistical geometry of available phase space for the original spheres, under varying restraints of nearest-neighbor cell distribution. Accordingly, we obtain for the first time an unambiguous definition of ``random close-packed'' or ``glassy'' arrangements of spheres (which however are not themselves equilibrium states), and to relations between properties of these arrangements, and of Δ*. The key features which subsequently allow description of rigid sphere order—disorder behavior are: (1) the observation that certain nearest-neighbor cell pairs which occur in the glassy state (both unoccupied and both doubly occupied) are geometrically excluded completely in the ordered, close-packed arrangement; (2) Δ* sensitively depends upon these pair distributions. In spite of the fact that Δ* is thereby assigned a specially generalized free-volume form, the theory leads to a proper virial series development at low density.

In addition, we report some preliminary results for the effective cell interactions, for glassy state parameters, and some calculations designed to reveal the structure of Δ*.

Although this analysis does not yet represent a full quantitative theory of the two-dimensional rigid disk system, it does lead to a novel qualitative explanation of how a fluid—solid transition can occur, and suggestions are given for completing the quantification.
Role of Hard-Core Collisions with Large Angle Deflections in the Kinetic Theory of Dense Fluids
Authors: Berne Bruce , Gray Peter
Published: January 2005

The validity of the Fokker—Planck equation is discussed within the framework of Kirkwood's time smoothing formalism. It is shown that the equation is equivalent to the Boltzmann equation for a dilute homogeneous system in which grazing binary collisions predominate. Using this as a mathematical prescription, the Rice—Allnatt equation is modified by replacing the Boltzmann collision integral by a Fokker—Planck operator, but leaving the excluded volume term unchanged. The kinetic and collisional transport coefficients derived from the modified equation are compared with those derived from the Chapman—Enskog equation, the Rice—Allnatt equation, and the Fokker—Planck equation. It is concluded that the role of hard core collisions in the theory is to emphasize the importance of large angle deflections, which are not important in a dilute gas.
Orbital Following in the Methyl Radical
Authors: Schrader D. M. , Karplus M.
Published: January 2005

Incomplete orbital following of the molecular vibrations in the methyl radical is examined through its relationship to the hyperfine splittings observed in the ESR spectrum. A semiempirical nonionic valence-bond theory with different degrees of carbon sigma-orbital following is used to estimate the proton and C13 splitting constants as a function of the nuclear positions that correspond to the out-of-plane bending mode. It is found that a considerable ``lag'' in the orbital motion with respect to that of the nuclei is required to achieve a consistent interpretation of the hyperfine spectrum in the methyl radical and its isotopic analogs. A variety of additional factors (i.e., integral parameter variation, breakdown of Born—Oppenheimer approximation, ionic contributions, other vibrations) are also investigated to determine their effects on the hyperfine splittings. Although some of the factors are found to be significant (particularly the choice of integral parameters), it appears that they cannot serve to explain the hyperfine data in the presence of complete following. Comparisons of the present conclusions with other studies of hyperfine splittings and related investigations of orbital following are presented.
Branched Polymers. III. Dimensions of Chains with Small Excluded Volume
Authors: Berry G. C. , Orofino T. A.
Published: January 2005

Mean-square radii 〈s2〉 for various branched molecules are calculated taking into account the initial effect of segment excluded volume β. Explicit expressions are given for the coefficient of the linear term in the series development of 〈s2〉 in powers of z=(3/2πb2)32n12β, for certain idealized regular star and regular comb structures containing n segments, each of length b. Numerical values of the coefficient, derived primarily through computer calculations, are tabulated as functions of pertinent structural parameters. It is found that at given molecular weight the coil dimensions of star molecules with excluded volume are initially augmented by increase in the number of branches; for comb structures the relationship of size to number of branches and branch-to-backbone length ratio is more complex. For both classes of branched molecules the theoretical quantities evaluated find direct application in analyses of dilute solution data obtained on polymer—solvent systems.
Mass Spectrometric Study of the Systems Boron—Carbon and Boron—Carbon—Silicon
Authors: Verhaegen G. , Stafford F. E. , Drowart J.
Published: January 2005

The vaporization behavior of the systems boron—carbon and boron—carbon—silicon has been studied with a mass spectrometer. In addition to the gaseous species characteristic of graphite, silicon carbide and boron, the molecules BC2, B2C, BCSi, BSi2, BC, and BSi were identified and their atomization energies measured. The values are: 294, 254, 247, 174, 106, and 68 kcal/mole, respectively. The atomization energies of SiC, Si2C, and SiC2 have been redetermined.
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.
Raman Spectra of Ices Ih, Ic, II, III, and V
Authors: Taylor M. J. , Whalley E.
Published: January 2005

The Raman spectra at 77°K of Ices Ih, Ic, II, III, and V made from H2O and D2O have been obtained. The spectra in the O–H and O—D stretching region were obtained both photographically and photoelectrically using Hg 4358 Å as the exciting radiation, and the low-frequency spectra were obtained photographically using Hg 2537 Å as the exciting radiation. In the O–H stretching region, the spectra of ices Ih and Ic are identical, and the spectra of Ices II, III, and V are similar except that the frequencies are higher than in Ice I. Ices II, III, and V appear to be essentially fully hydrogen bonded, as was concluded from the infrared spectra. In the low-frequency spectrum there is one band or sometimes two bands in all the Ices, and they are probably due to translational vibrations of the molecules.
Low-Temperature Emission Spectrum of O2— in Alkali Halides
Authors: Rolfe J.
Published: January 2005

The fluorescence emission spectrum of the O2— molecule-ion has been measured at 4.2°K in the alkali halides NaF, NaCl, NaBr, KCl, RbCl, KBr, RbBr, and KI. The most intense peaks in the emission spectra are shown to be due to transitions to vibrationally excited levels of the ground state of O2—. The vibrational properties of O2— in its ground state can be represented by an anharmonic oscillator with a vibrational constant (ωe) of approximately 1170 cm—1, and an anharmonicity (ωexe) of 8.5 cm—1. The cause of the fine structure which appears around these intense peaks is not known, but the fine structure for the alkali halides NaF, KCl, and RbBr, which have almost equal anion and cation masses, is quite different from the other alkali halides NaCl, NaBr, KBr, and KI.
Thermal Activation Relations
Authors: Macdonald J. Ross
Published: January 2005

A material is considered which has one or more thermally activated linear response functions that obey Boltzmann statistics to good approximation. These response functions may, for example, be mechanical or dielectric relaxation times, diffusion coefficient, viscosity, etc. Neither the entropy change, ΔS, nor the enthalpy change, ΔH, in the activation process need be temperature-independent. An expression for ΔG, the Gibbs free-energy change in the thermally activated process, is considered which applies to a system with a nonzero or zero glass transition temperature, Tg, and allows the product c1gc2g of the WLF polymer equation to be interpreted and its variation with material explained by an activation energy model. Explicit expressions for the resulting temperature-dependent ΔS and ΔH are given which involve the material parameter E; this is the enthalpy and activation energy of the process only when Tg=0 and thus an Arrhenius equation applies. The results pertain to mechanical and dielectric dispersion experiments on amorphous polymers and other glass-forming materials. In addition, they apply to such processes as diffusion by a vacancy mechanism, to viscous flow, and, when Tg=0, to intrinsic semiconduction and many other processes. It is found that the Lawson—Keyes relation, ΔS/ΔH≃4α, should not be applied when Tg≠0 and may be very inaccurate even in the case where Tg=0. An improved relation between ΔS and ΔH which holds for Tg=0 is presented; it furnishes a possible explanation for the negative value of ΔS sometimes found experimentally. An expression for ΔG correct to first order in pressure and temperature is given which applies to all situations where an Arrhenius equation is found. On identifying the semiconductor energy gap for thermal activation as a Gibbs free energy difference, the results are illustrated by analyzing pressure and temperature data pertaining to intrinsic semiconduction in Si and Ge. Experimental dielectric dispersion results for isoamyl bromide (Tg≠0) are also analyzed and compared with results of previous work. Finally, temperature-dependent aspects of the transient and frequency response of a distributed, linear activated system with Tg≠0 are examined when either the pre-exponential factor or the activation parameter E is distributed, or when they are simultaneously distributed and are linearly related.
Chemically Pumped Molecular Lasers
Authors: Young Robert A.
Published: January 2005

The feasibility of efficient conversion of chemical energy to radiation in chemically pumped lasers is discussed. Suitable specific systems are suggested and analyzed.
Statistical Mechanics of Defect-Containing Solids. I. General Formalism
Authors: Allnatt A. R. , Cohen M. H.
Published: January 2005

A formalism is set up for treating the contributions of point defects to the thermodynamic functions of crystalline solids by means of a cluster expansion of the partition function. Similar expansions for the defect distribution functions and potentials of average force are derived. The assumptions involved and the necessary differences between the formalism and the McMillan—Mayer theory of solutions are discussed. Problems arising in the explicit evaluation of the coefficients of the virial expansions are discussed and possible applications of the formalism suggested.
Experimental Determination of the Thermal Conductivity of Molten Lithium from 320° to 830°C
Authors: Cooke J. W.
Published: January 2005

A comparative, axial-heat-flow apparatus with compensating guard heating was developed to determine the thermal conductivity of 99.8+ wt% molten lithium. Contrary to the data for two other alkali metals (sodium and potassium), the conductivity of lithium was found to increase linearly from 0.445 W/cm·°C at 320°C to 0.606 at 830°C. The total uncertainty in the results was conservatively estimated to vary from ±8% to ±15% from the lower to the higher temperatures. Unpublished data from 282° to 521°C by the Naval Research Laboratory average 4% below the present results. The values predicted by two correlations—the equation of Ewing et al. and the Wiedemann—Franz relationship—are uniformly 10% and 6% higher, respectively, than the present data.
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.
Crystal Structure of 9-Methyladenine
Authors: Stewart R. F. , Jensen L. H.
Published: January 2005

The crystal structure of 9-methyladenine has been determined with limited x-ray diffraction data. The final R factor is 0.091 with atomic standard deviations of about 0.006 Å. The x-ray determination confirms the proposed structure based on polarized absorption measurements. We conclude that the first ultraviolet transition for 9-methyladenine is short axis (C4–C5) polarized.
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.
Flows Through Charged Membranes. I. Flip-Flop Current vs Voltage Relation
Authors: Kobatake Yonosuke , Fujita Hiroshi
Published: January 2005

Flow processes in a (porous) charged membrane separating two solutions of different concentration of the same electrolyte are studied theoretically, using a capillary model for the membrane and the Debye—Hückel approximation for the calculation of ion distributions in the double layer formed near fixed charges on the capillary wall. Steady-state solutions to the continuity equations derived are obtained subject to the external conditions that there is the passage of a constant forced electric current I through the membrane, the salt concentrations on both sides of the membrane are held constant, and a constant pressure is imposed on the more concentrated solution. The results yield a characteristic I vs transmembrane potential Δφ relation, which consists of two nearly straight lines of different slopes involving a discontinuous transition between them. This feature well compares to the experimental data obtained recently by Tasaki et al. with sintered glass membranes and thought by them to be significance in relation to the physiology of nerve excitation. It is shown that, in the framework of the theory presented, the occurrence of a discontinuous change in I at a certain particular potential mainly stems from the dependence of the electro-osmotic coefficient on salt concentration. The probable causes for the discrepancies between theory and experiment are discussed briefly.
Free Energy of a Plasma at Infinite Dilution
Authors: Bellemans A.
Published: January 2005

The electrostatic free energy of a finite plasma is expanded in semi-invariants, which are conveniently represented by diagrams corresponding to clusters of interacting particles. At infinite dilution the free energy is related to unbranched linear diagrams as well as to ring diagrams. For a macroscopic system only the contribution of the ring diagrams is significant.
Structures of Mercury Mercaptides. I. X-Ray Structural Analysis of Mercury Methylmercaptide
Authors: Bradley D. C. , Kunchur N. R.
Published: January 2005

The structure of crystalline Hg (SCH3)2 has been determined by x-ray diffraction analysis. The dimensions of the unit cell are: a=19.80 Å; b=7.58 Å; c=7.80 Å. There are eight formula units per unit cell and the space group is D2h15, Pbca. The packing of the simple formula units in the crystal suggests the compound is a coordination polymer involving weak mercaptide bridges. Each mercury has two closest sulfur atoms with Hg–S=2.36 Å and three sulfurs with Hg–S=3.26 Å, comprising an irregular tetragonal pyramidal configuration.
Quantum Isotope Effect in Permeation
Authors: Frisch H. L. , Rogers C. E.
Published: January 2005

A diffusing penetrant of sufficiently light mass (e.g., H2, D2) dispersed in sufficiently small cavities of certain diffusion systems will possess ground-state quantizations of energy, both in the cavity and in the transition state, which are not negligible. Hence even at or above room temperature one expects to observe small, but sometimes measurable, differences of activation energy for diffusion and apparent enthalpies of sorption for two isotopic species of the penetrant diffusing in the same medium, providing the mass ratio of the lighter to the heavier isotope is sufficiently small. The change in the apparent enthalpy of sorption is proportional, roughly, to the inverse square of a length available to free motion of the center of mass of the penetrant in the cavity and can thus be used as a measure of the free volume involved in the diffusion. The ratio of the change in diffusion activation energy to the change in the apparent sorption enthalpy yields a length characteristic of the transition state. Gas transmission of H2, D2, and He through ``synthetic'' natural rubber and polyethylene films was studied from 30° to 60°C. Statistically significant differences in temperature coefficients of permeation, sorption, and diffusion were obtained in these membranes on going from H2 to D2. The implications of these observations are developed.
Zero-Field Splitting, One- and Two-Center Coulomb-Type Integrals
Authors: Geller Murray , Griffith Richard W.
Published: January 2005

One- and two-center Coulomb-type integrals of the form ∫ [N,L,M]a1O1,2[N′,L′,M′]b2dτ1dτ2,where O1 and O2 are the two-particle operators ½r12—5(3z122—r122) and 3r12—5(x122—y12 2), respectively, needed in the evaluation of zero-field splitting, are evaluated in closed analytical form.
Magnetic Shielding of a Nucleus by a Neighboring Atom
Authors: Musher Jeremy I.
Published: January 2005

The Lamb term of the magnetic shielding of a nucleus is calculated for an electron on a neighboring atom in an s or a p state using Slater atomic wavefunctions. This exact calculation is presented in order to illustrate the radial dependence of long-range nuclear magnetic shielding and to point out explicitly for these wavefunctions the distance at which the dipole approximation introduces only a negligible error.
Low-Temperature Infrared Study of Intermediates in the Photolysis of HNCO and DNCO
Authors: Jacox Marilyn E. , Milligan Dolphus E.
Published: January 2005

HNCO and DNCO suspended in Ar and in N2 matrices at 4° and at 20°K are shown to yield upon photolysis the corresponding tautomers, HOCN and DOCN, for which vibrational assignments are proposed. HOCN may be produced by recombination at the O atom of H+NCO produced in a primary photolytic rupture of the N–H bond, as well as by the attack of NH (3Σ—) on the carbon—oxygen bond of CO, giving an unstable cyclic intermediate.
Elementary Derivation of Time-Correlation Formulas for Transport Coefficients
Authors: Zwanzig Robert
Published: January 2005

This article presents an elementary derivation of time-correlation formulas for transport coefficients. The derivation, based on classical statistical mechanics, is modeled on one by Kubo, Yokota, and Nakajima. In agreement with theirs, it makes use of the assumption of regression of fluctuations. It differs, however, in its avoidance of Markoffian assumptions. The decisive point of the derivation is the introduction of a parameter ξ to measure the rate of the transport process. In the limit of a very slow process, i.e., in the limit ξ→0 and time t→∞ with ξt held constant, the results coincide with those obtained by Markoffian assumptions. The relation to other work, and in particular to Kirkwood's friction constant theory, is touched on briefly.
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.
Composition Dependence of Nonequilibrium Effects in Gas-Phase Reactions
Authors: Pyun Chong Wha , Ross John
Published: January 2005

The process of a chemical reaction perturbs the translational and internal distributions of reactants and products. The composition and affinity dependences of the effects of the nonequilibrium distributions are derived for variously defined rate coefficients of reactions occurring in a dilute, homogeneous, and isothermal gas phase by a first-order perturbation solution of appropriate Boltzmann equations for all reactants and products. In general, the ratio of forward-to-reverse rate coefficient differs from the equilibrium constant to the extent of the influence of the nonequilibrium distributions; one exception is the ratio of the apparent forward-to-reverse rate coefficient in the respective limits of infinite affinity for an isomerization or excitation reaction proceeding in large excess of inert gas. Detailed calculations are presented for this and some other simple cases including a bimolecular reaction of hard-sphere molecules and a reaction with components in only two internal states. In the limit of zero product concentrations the nonequilibrium contributions to the rate coefficient differ from those obtained by an analysis entirely neglecting the presence of products in violation of the law of microscopic reversibility. The difference vanishes if one reactant is present in large excess. The analysis is applied to dissociation-recombination reactions of diatomic molecules and is compared with other approaches to the problem of nonequilibrium kinetics, that is, the use of the master equation and the use of the conventional steady-state approximation.
Small-Angle X-Ray Scattering from Sodium—Ammonia Solutions
Authors: Brady George W. , Varimbi J.
Published: January 2005

Some observations on the x-ray scattering from sodium—ammonia solutions are discussed in terms of the cavity model and the cluster model. The data appear to be more consistent with the former than with the latter model.
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.
Microwave Spectrum, Barrier to Internal Rotation, and Quadrupole Coupling Constants of Cis-1-Chloropropylene
Authors: Beaudet Robert A.
Published: January 2005

The microwave spectrum of CH3CH=CH35Cl and CH3CH=CH37Cl was studied in the region from 8–35 kMc/sec. The height of the potential barrier hindering the internal rotation of the methyl top is 620 cal/mole; the Cl quadrupole coupling constants are χaa35Cl= —19.66 Mc/sec and χbb35Cl=31.05. The dipole moments are μa=1.47 D and μb=0.72 D. The even greater lowering of the barrier, trans to cis, for the chlorine compounds as compared with the fluorine analogs supports the hypothesis of a nonbonded interaction between the halogen and the methyl hydrogen atoms.
Determination of the Lennard-Jones Parameters from Total Scattering Cross-Section Measurements
Authors: Lebedeff S. A.
Published: January 2005

Two methods are described that permit the determination of potentials from molecular scattering experiments. The potentials under consideration are of the Lennard-Jones type. Both methods apply to highenergy scattering, where the Born approximation is suitable for determination of the high angular momentum phase shifts. The methods are first checked against the exact calculations of Bernstein and then applied to the determination of the potential parameters of the krypton—lithium system. Finally, a partial analysis of the argon—lithium system is done. It provides an efficiency test for the high-energy approximation method.
Infrared Dispersion of Carbon Tetrafluoride
Authors: Schurin B.
Published: January 2005

The refractive index of carbon tetrafluoride was measured in the 1–20 μ region of the spectrum. The contributions of the molecular vibrations to the index have been calculated and the absolute intensities of the infrared active fundamentals obtained. These are: A3=(1.60±0.01)×1014 cm−1/sec.A4=(1.86±0.13)×1012 cm−1/sec.The results have been interpreted with the aid of a Urey-Bradley type potential to yield alternate solutions for the dipole moment (μ) of the C–F bond in the molecule and the variation of the moment with inter-nuclear distance dμ/dr. The calculated solutions are: dμ/dr=5.99d/A  dμ/dr=3.71d/A,or μ=1.13d  μ=2.98d.The contributions of the infrared bands satisfactorily account for the difference between the static dielectric constant and the square of the refractive index extrapolated to zero frequency from the visible.
Assignment of the Fundamental Vibrational Frequencies and Calculated Thermodynamic Functions for 1,1-Difluoro-2,2-dibromoethylene
Authors: Nielsen J. Rud , Theimer Rose
Published: January 2005

The previous assignment of the fundamental vibrational frequencies of the CF2:CBr2 molecule has been revised in the light of the results of a recent normal coordinate analysis by Mann et al. and other evidence. The revised assignment is as follows: species a1: 1718, 1005, 598, 324, 168; species b1: 1037, 898, 399, 151; species b2: 572, 303; species a2: 151 cm—1. All but the two lowest wave numbers are for the gaseous state. Thermodynamic functions have been recalculated for the ideal gaseous state at 1 atmos pressure for 4 temperatures above the boiling point.
Triatomic Linear Molecules Containing Carbon and Oxygen, Sulfur, Selenium, or Tellurium. II. Potential Constants
Authors: Wentink Tunis
Published: January 2005

The fundamental vibrational frequencies for CO2, CS2, CSe2, OCS, OCSe, SCSe, and SCTe have been used in a uniform analysis based on the valence force field to evaluate the force constants. The extensive literature on CO2, OCS, and CS2 has been reviewed since a choice of frequencies is necessary due to significant divergence of some earlier data. The stretching interaction constants have been used to test the validity of a theoretical expression for calculating such an interaction. A compilation of the best values of the internuclear distances in this family is also presented. The main stretching force constant and the bond distance for a given bond (e.g., C=O) may be transferred from molecule to molecule to a high degree of approximation. The force constants, in 105 dynes/cm, for the bonds C=O, C=S, C=Se, and C=Te are, respectively: 15.96±0.04, 7.62±0.20, 5.79±0.16, and 4.58. The interaction constants, for the molecules in the same order and the same units are 1.262, 0.661, 0.36, 0.97, 0.85, 0.53, and 0.30.
Contact Electron-Spin Coupling of Nuclear Magnetic Moments
Authors: Karplus Martin
Published: January 2005

The valence-bond theory for the contact electron-spin coupling of nuclear magnetic moments is used to calculate the proton-proton, proton-fluorine, and fluorine-fluorine coupling constants in ethanic and ethylenic molecules. A considerable simplification is introduced into the theory by approximations which reduce the problem to one involving only a small number of electrons and canonical structures. The agreement between calculated and experimental values is such as to demonstrate that the mechanism considered is the one of primary importance for the nuclear coupling in the compounds studied. Of particular interest is the theoretical confirmation of the observation that in ethylenic compounds the trans coupling between nuclei (HH, HF, FF) is considerably larger than cis coupling.
Models for Luminescence Degradation in Organic Solids
Authors: Rosenstock Herbert B. , Schulman James H.
Published: January 2005

The damage vs dose relationship for radiation damage in organic solids is computed on the basis of several models, and the results are compared with experimental data reported by various workers. Two models are amenable to analytical treatment: (1) after a hit, all molecules within a given sphere centered about the hit molecule are poisoned, and none outside, and (2) there is a constant probability that excitation of any molecule throughout the crystal will result in quenching independent of its distance from the hit molecule. The fact that experiment agrees with the result of the latter model, but disagrees with the former, implies that the damage mechanism has a very large range. A lower limit of approximately 1000 angstroms, corresponding to 3×104 jumps of the excitation energy among neighboring molecules is found as a requirement for consistency with the latter model.
Thermoelectric Power of AgBr Containing CdBr2
Authors: Christy R. W. , Fukushima E. , Li H. T.
Published: January 2005

The thermoelectric power of AgBr has been measured as a function of temperature between 100° and 400°C. The measurements have been made on pure material, and also on material doped with CdBr2 in concentrations between 0.01 and 1.0 mole%. The results are compared with the theory of Howard and Lidiard. Satisfactory agreement is obtained if it is assumed that the heats of transport are temperature dependent. The values required for the sum of the heats of transport of the interstitial silver ions and vacancies are —0.57 ev at 175° and —0.69 ev at 250°C.
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.
Ultrasonic Absorption Associated with Tertiary Butanol Complex Formation in Dilute Solutions in Cyclohexane
Authors: Musa Raiq S. , Eisner Melvin
Published: January 2005

Ultrasonic absorption measurements have been used as a basis for studying the kinetics of the reaction between tertiary butanol monomers and tetramers, occurring in dilute solutions with cyclohexane. Measurements made at 6, 15, and 27°C over a frequency range of 5 to 53 Mc/sec reveal several concentration dependent relaxation effects. An analysis using thermodynamically determined degree of dissociation leads to the determination of the equilibrium constant, rate constants and the heat of reaction. The excess absorption up to 0.02 mole fraction butanol concentration is reasonably well accounted for by the perturbation of the tetramer-monomer equilibrium.
Magnetic Susceptibilities of Uranium (IV) and Plutonium (IV) Ions in Cubic Fields
Authors: Candela George A. , Hutchison Clyde A. , Lewis W. Burton
Published: January 2005

The magnetic susceptibilities of (a) [(CH3)4N]2PuCl6, (b) [(CH3)4N]2UCl6, (c) Cs2UCl6, of solid solutions of (d) PuO2 in ThO2, and of (e) [(CH3)4N]2PuCl6 in [(CH3)4N]2PtCl6 have been measured at room temperature, the boiling point of liquid N2 and the boiling point of liquid He. The measurements of others on (f) solid solution of UO2 in ThO2 are also considered. It has been found that (a), (e), and (f) show strongly temperature-dependent susceptibilities whereas (b), (c), and (d) have susceptibilities that vary only slightly with temperature over the range investigated. The results are discussed in terms of ground state configurations f2 and f4 perturbed by the crystal fields.