bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationship between Absorption Intensity and Fluorescence Lifetime of Molecules
Authors: Strickler S. J. , Berg Robert A.
Published: January 2005

The equations usually given relating fluorescence lifetime to absorption intensity are strictly applicable only to atomic systems, whose transitions are sharp lines. This paper gives the derivation of a modified formula 1/τ0=2.880×10−9n2〈ν̃f−3〉Av−1(gl/gu) ∫ εdlnν̃,which should be valid for broad molecular bands when the transition is strongly allowed.

Lifetimes calculated by this formula have been compared with measured lifetimes for a number of organic molecules in solution. In most cases the values agree within experimental error, indicating that the formula is valid for such systems. The limitations of the formula and the results expected for weak or forbidden transitions are also discussed.
Effect of an Electric Field on Silicon Oxidation
Authors: Jorgensen Paul J.
Published: January 2005

Modified-marker experiments have shown that silicon oxidation is controlled by the diffusion of oxygen through the silicon dioxide film.

The application of an electric field across the silicon dioxide layer enhances oxidation when the silicon is made positive with respect to the oxide—gas interface, and retards oxidation when the silicon is negative with respect to the oxide—gas interface. Oxidation under a retarding electric field ceases when the voltage developed across the growing oxide is equivalent to the change in free energy of the oxidation reaction.

The dependence of the oxidation rate on an electric field indicates that oxygen ions are the predominant species diffusing through the growing oxide film.
Reflection and Dissociation of H2 on Tungsten
Authors: Smith Joe N. , Fite Wade L.
Published: January 2005

Through the use of modulated atomic beam techniques, the reflection and dissociation of H2 at a tungsten surface above 2500°K has been studied. Two experimental configurations were employed. In the first configuration, a collimated beam of molecular hydrogen was directed at the tungsten surface, and the angular distribution of particles evaporating from the surface was examined mass spectrometrically. In the second configuration, the tungsten test surface was located in the first of three differentially pumped vacuum chambers. H2 was admitted into this chamber, thereby providing an isotropic source of incident particles. Particles evaporating from the surface were collimated and examined mass spectrometrically in the third chamber. From these experiments it is observed that at high temperatures the angular distribution of atomic hydrogen evaporating from the target surface obeys the cosine law. However, the angular distribution of reflected H2 displays a shift toward the specular ray. Above 2500°K the sticking probability of H2 on tungsten approaches a limiting value of 0.3.
Electrostatic Determination of Photo-Ionization Potentials of Solids and Liquids
Authors: Pope Martin
Published: January 2005

The determination of the threshold for photo-ionization of solids and liquids by the Millikan condenser technique can be made more accurate by using two different wavelengths of light, both shorter than the threshold wavelength. Measurements made on graphite and magnesium phthalocyanine are in agreement with values obtained by more usual techniques.
Interaction of Degenerate Configurations
Authors: Pandres Dave , Matsen F. A.
Published: January 2005

We show that when two configurations approach a limit in which they represent the same physical state, the energy obtained from a variational calculation using configuration interaction may approach a lower limit than that which results if either configuration is used alone.
Adsorption of Potassium Beams on Surfaces
Authors: Baker Forrest S. , Brink Gilbert O.
Published: January 2005

The adsorption probabilities have been measured for a thermal potassium beam impacting on 20 different target materials. These measurements when included in the general body of previously published data have permitted the derivation of several empirical relations involving binding energies, adsorption coefficients, and heats of formation. These relations may find application in predicting other coefficients, and binding energies. Thus the tedium of time-consuming experiments usually required in the search for suitable beam-collector materials may be significantly reduced.
Electric Conduction in Liquid Hydrocarbons. I. Benzene
Authors: Forster E. O.
Published: January 2005

A technique has been developed which allows the determination of specific conductance in the bulk of a liquid, independent of electrode materials or electrode separation. By this method, the specific conductance of benzene saturated with air has been determined to be 1.1±0.1×10—14 Ω—1 cm—1 for fields between 50 and 400 V/cm. Measurements of the potential gradients between electrodes show them to be strongly asymmetric. The temperature dependence of the dark current conduction of benzene has been shown to follow the typical relation normally associated with semiconductance. The value of E has been determined to be 0.42±0.4 eV for both liquid and solid benzene. The photoconductance of benzene was found to follow closely its spectroscopic behavior. The experimental results have been interpreted to suggest that conduction in both liquid and solid benzene is based on an electron transfer mechanism. The temperature dependence of this mechanism has been shown to be independent of impurities and to be a property only of the bulk of the liquid.
Structure of Simple Fluids: Tunnel Model
Authors: Barker J. A.
Published: January 2005

The radial distribution function for a liquid composed of molecules interacting according to the Lennard-Jones 12–6 potential is calculated using a ``tunnel'' model of the structure. According to this model the liquid is pictured as being built up of lines of molecules distributed independently and almost one-dimensionally in tunnels or fine capillaries of which the walls are formed by neighboring lines of molecules. The calculated distribution function is compared with the experimental distribution function for liquid argon derived from diffraction measurements. The agreement is excellent with regard to the first peak of the distribution function and qualitatively satisfactory at greater distances. A similar comparison is made for a distribution function based on the cell model of Lennard-Jones and Devonshire. The agreement is much less satisfactory, in accordance with the view derived from thermodynamic evidence that the cell model is properly to be regarded as a model for crystals rather than liquids.
Studies in Molecular Structure. VIII. He2++ in the Single- and Many-Configuration LCAO MO SCF Approximation
Authors: Fraga Serafin , Ransil Bernard J.
Published: January 2005

Single- and many-configuration wave functions and their corresponding molecular energies are reported for the diatomic molecular ion He2++ in the LCAO MO SCF approximation for a wide range of internuclear distances. A potential curve displaying a minimum at 0.71 Å and a maximum at about 1.11 Å is obtained with ωe=3295 cm—1 and De=1.21 eV. Comparison with potential curves and correlation energies computed by the more accurate methods of Kolos, Roothaan, Weiss, Yoshimine, and McLean are made. The results are discussed with reference to stability and occurrence of the ion. Correlation energy is computed as a function of internuclear distance and compared with the isoelectronic analog H2.
Aluminum Ion Diffusion in Aluminum Oxide
Authors: Paladino A. E. , Kingery W. D.
Published: January 2005

The self-diffusion coefficient of aluminum has been determined in polycrystalline aluminum oxide over the range 1670° to 1905°C. Diffusion couples were employed using aluminum-26 in oxide form as a radioactive tracer. In the temperature range studied, experimental data can be represented by D = 28 exp {—[(114 000±15 000)/RT]}.
Exchange of Interacting Nuclear Spins in Nuclear Magnetic Resonance. II. Chemical Exchange
Authors: Alexander S.
Published: January 2005

The study of the effect of exchange on high-resolution nuclear magnetic resonance spectra is extended to chemical exchange. A Boltzmann equation for the nuclear spin density matrix is derived. This equation is nonlinear because two uncorrelated molecules participate in each exchange process. For temperatures high compared to the nuclear Zeeman energy the equations can, however, be linearized. In particular the steady-state (slow-passage) solutions can be obtained from a set of linear algebraic equations for the elements of the density matrix.

Explicit approximation formulas for the slow- and fast-exchange limits are derived.

As an example the spectrum of a molecule with two nonequivalent spin ½ nuclei, one of which is exchanging, is calculated explicitly for arbitrary exchange rates and coupling strengths, and the behavior of the spectrum is discussed in detail.
Factors Controlling the Intensity of Emission of Eu3+ and Tb3+ in Scheelites
Authors: Van Uitert L. G.
Published: January 2005

Measurements have been carried out under broadband long-wave ultraviolet excitation to determine the dependences of the intensity of emission of Eu3+ or Tb3+ upon the host-structure cation valence, radius, and ionization potential in compositions which have the scheelite structure. Brightness can either increase or decrease with the binding energy of the rare-earth ion depending upon the strength of coupling between the ion and its environment. In the case of Tb3+ the former occurs in the tungstates and the latter in the molybdates.
Motion in Polyethylene. I. Temperature and Crystallinity Dependence of the Specific Heat
Authors: Wunderlich Bernhard
Published: January 2005

Data for the specific heat of polyethylene as a function of crystallinity are collected from 1° to 420°K. Specific heats, entropies, and enthalpies of the completely amorphous and crystalline polyethylene are extrapolated. The glass transition is located for the amorphous at 237°K with a ΔCp of 2.1 cal deg—1 (mole CH2)—1. Specific-heat values at constant volume are calculated for the crystalline polyethylene.
Measurement by Cyclotron Resonance of Molecular Cross Sections for Elastic Collisions with 295°K Electrons
Authors: Bayes K. D. , Kivelson D. , Wong S. C.
Published: January 2005

Cyclotron resonance absorption is used to obtain molecular scattering cross sections for electrons at 295°K. The electrons were present in active nitrogen obtained by passing N2 through a microwave discharge, and various gases were introduced into the active nitrogen downstream from the discharge. Very weak rf fields, with electric components parallel to the dc magnetic field, were used in order not to ``heat up'' the electrons. The observed width of the cyclotron resonance line is proportional to the molecular-electronic cross section since electron—electron collisions are not significant in these experiments. But suitable averages over electron velocities must be carried out to account for the observed line shapes and to relate the line widths to the cross sections. The spectral lines are sometimes quite asymmetric and this asymmetry can then be used as a rather sensitive measure of electron concentration. Dipolar gases were observed to have large cross sections which exhibited approximately a 32 power dependence on the dipole moment; theoretical calculations based on a partial wave treatment of dipole scatterers agreed well with experiments. The cross section for N2 is 4.96 Å2; for CO2 302 Å2; and for the dipolar gases N2O, NH3, SO2, HCF3, H2O, HCN, and CH3NO2, the cross sections are 56, 1560, 1840, 1760, 2360, 5280, and 6020 Å2, respectively. The dipolar cross sections are inversely proportional to the energy of the electrons, and both theoretical and experimental values of the cross sections refer to energies of 3k(295°)/2. The large cross section for CO2 probably arises from its large quadrupole moment.
Mass Spectrometric Studies of Atomic Reactions. III. Reactions of Hydrogen Atoms with Nitrogen Dioxide and with Ozone
Authors: Phillips L. F. , Schiff H. I.
Published: January 2005

The reaction of H atoms with excess NO2 results in the production of one NO molecule for every NO2 molecule consumed and the consumption of 1.5±0.1 NO2 molecules per H atom initially present. The secondary reactions are rapid and make the over-all reaction very suitable for H-atom titration. A mechanism is proposed to explain these results. The reaction of H atoms with excess O3 results in the consumption of 3.1±0.2 O3 molecules for each H atom initially present. Addition of H2 and N2O to the system showed that vibrationally excited OH formed in the initial reaction decomposes O3. Other mechanisms for the additional O3 consumption are discussed. The rate constant for the primary step was found to be (4.8±0.5) × 10—11 cm3 molecule—1 sec—1 for the NO2 reaction and (2.6±0.5) × 10—11 cm3 molecule—1 sec—1 for the O3 reaction.
Neutron Magnetic Form Factors and X-Ray Atomic Scattering Factors for Rare-Earth Ions
Authors: Blume M. , Freeman A. J. , Watson R. E.
Published: January 2005

The theory of neutron scattering by paramagnetic rare-earth ions has been given by Trammell and more recently by Odiot and Saint-James. Unlike the case for the iron-series transition metals, for which the orbital angular momentum of the 3d electrons is almost completely quenched, the magnetic scattering of neutrons from the rare earths (except for gadolinium and europium) arises from both the spin and orbital contributions to the magnetization. Using recently determined Hartree—Fock wave functions for some of the trivalent rare-earth ions we have determined the functions 〈jn〉 and 〈gn〉 (for n=0, 2, 4, and 6) which are necessary for the theoretical evaluation of the spin and orbital contributions, respectively, to the magnetic form factor. A comparison of these theoretical results with the experiments of Koehler and Wollan for Nd3+ and Er3+ and of Koehler, Wollan, and Wilkinson for Ho3+ is presented. Large differences are found between Trammell's theory and experiment and some possible reasons for this are discussed. X-ray atomic scattering factors for these ions are also given and found to agree very closely with the results of the Thomas—Fermi—Dirac statistical method.
Shock-Tube Study of the Coupling of the O2–Ar Rates of Dissociation and Vibrational Relaxation
Authors: Wray Kurt L.
Published: January 2005

At low temperatures the vibrational relaxation time τv is much shorter than the dissociation time τd. The O2–Ar results of Camac [J. Chem. Phys. 34, 448 (1961)] and Camac and Vaughan [J. Chem. Phys. 34, 460 (1961)] yield τd/τv=60 at 5000°K and, upon extrapolation, τd/τv=1.4 at 18 000°. According to these extrapolations, dissociation at high temperatures would proceed significantly before vibrational equilibration would occur. The purpose of this investigation was to determine how the dissociation rate will be affected by a lack of vibrational equilibrium. Studies of the dissociation rate of dilute O2–Ar mixtures were made in a 24-in. diam shock tube from 5000°—18 000°K. The O2 concentration was monitored by its absorption of 1470 Å radiation. An Arrhenius plot of the data yielded a straight line from 5000°—11 000°K, the rate constant being given by kd=2.9(±12%)×1014 exp (—D/RT)cc/mole-sec. Above 11 000° the data deviate from the line given by this equation—at 18 000° kd being 0.45 times the calculated value. An incubation time Δt was observed during which dissociation does not proceed to a significant extent. The ratio of this incubation time to the vibrational relaxation time (obtained by extrapolating Camac's low-temperature results) when plotted against translational temperature displays a slight negative temperature dependence. At 18 000° Δt/τv=0.4, at 8000° Δt/τv=1, and at 5500° we estimate that Δt/τv≈2.
Realistic Diatomic Potential Function
Authors: Woolley Harold W.
Published: January 2005

An examination of recently published data for diatomic molecules as obtained by the Rydberg—Klein—Rees method has suggested a useful form for the potential-energy function. This form provides an inverse-power dependence at large distance and an extrapolation to infinity at the extreme of close approach. Relations are given to permit an arbitrarily close fit of observed spectroscopic constants. Theoretical formulas covering seven new Ylj's of the Dunham—Sandeman series for the rotating vibrator are included. Potential curves for H2 and HF are shown as examples, including effects of previously determined higher-order spectroscopic constants. Other applications of the new potential are also discussed.
Vacuum Ultraviolet Photochemistry. IV. Photolysis of Propane
Authors: Okabe H. , McNesby J. R.
Published: January 2005

The direct photolysis of propane has been carried out in the vacuum ultraviolet region, at room temperature. Isotopic analyses lead to the conclusion that hydrogen and methane are formed almost entirely by molecular detachment processes. Among the three observed modes of hydrogen detachment CH3CH2CH3→CH3CCH3+H2,CH3CH2CH3→CHCH2CH3+H2,CH3CH2CH3→CH2CHCH3+H2.Process (1), the detachment from the central carbon atom, is most important when the exciting wavelengths are the Xe resonance lines, whereas process (2) increases in importance with the Kr lines. Two modes of methane detachment were observed, CH3CH2CH3→CH3CH+CH4,CH3CH2CH3→CH2CH2+CH4,in which process (5) is more important at both wavelengths. It has been shown that ethylene is formed almost equally from the molecular detachment process and from the disproportionation of of ethyl radicals. Ethane is formed from the disproportionation of ethyl radicals as well as from the association of methyl radicals, the former being more important.

The processes (1) to (6), along with two additional processes, CH3CH2CH3→H+C3H7,CH3CH2CH3→CH3+C2H5,followed by secondary reactions of radicals, can reasonably account for the formation of the photolytic products.
Theory of Relaxation Phenomena near the Second-Order Phase-Transition Point
Authors: Tanaka Tomoyasu , Meijer Paul H. E. , Barry Jeremiah H.
Published: January 2005

One may expect that the observables connected with nonequilibrium processes will show abrupt changes if a substance undergoes a second-order phase transition, since the equilibrium thermodynamic quantities appear to do so. In order to study these phenomena in a connected way the assumption is made that the long-range order parameter and the short-range order parameter can be treated as fluxes and forces in the sense of Onsager's theory of irreversible thermodynamics. Actual calculations are performed for two cases: an order—disorder system with short- and long-range order and a system with two modes of long-range order (antiferromagnet). The absorption of sound is calculated and its behavior near the critical temperature is analyzed. The function is continuous with a discontinuity in the slope provided the phenomenological constants are smooth functions of the temperature.
Theoretical Vibrational Energy Levels of H2 Associated with Various Combinations of Molecular-Orbital Configurations
Authors: Leies Gerard M.
Published: January 2005

A theoretical examination has been made of the influence of various MO configurations on the spacing of the vibrational levels of H2. Eleven previously determined potential curves for the H2 ground state, based upon LC STO MO wavefunctions with configuration interaction, have been used to calculate vibrational-energy levels and their first differences ΔG. Comparison of the 11 curves of ΔG vs vibrational quantum number ν shows that only when the wavefunction contains the configuration (σu1sσu1s′) does the ΔG curve have a shape similar to that of the experimental ΔG curve. The combination of (σg1sσg1s′) and (σu1sσu1s′) provides left—right correlation or variable ionicity and this ionicity is found to vary in the same manner as the curvature of the ΔG curve. The addition of (σg2sσg2p), which gives in—out correlation, and (πu2pπ̄u2p), which provides angular correlation, to the wavefunction raises the ΔG curve especially at large ν. The use of ΔG curves obtained from simple wavefunctions to estimate dissociation energies is discussed.
Vibrational Energies of the CO2 Molecule
Authors: Stull V. Robert , Wyatt Philip J. , Plass Gilbert N.
Published: January 2005

The vibrational energy levels of the eight most abundant isotopic species of carbon dioxide have been calculated. Over 1800 energy levels are given for each isotope. The calculations included terms to the third order in the vibrational quantum numbers and took account of the Fermi resonance. The matrices were diagonalized by an eigenvalue routine of great accuracy.
Solubility of Naphthalene in Compressed Gases
Authors: King A. D. , Robertson W. W.
Published: January 2005

The influence of hydrostatic pressure upon the equilibrium between solid naphthalene and its vapor in various inert gases has been measured over pressure ranges extending from 1 to 1100 atm and temperature ranges of 20° to 75°C, using spectrophotometric techniques.

The variation of naphthalene vapor concentration with the diluent gas density has been used to evaluate second virial coefficients representing diluent—naphthalene interactions for the following diluent gases: He, H2, Ar, N2, CH4, and C2H4. Although the virial coefficients thus obtained vary from large negative values for the systems involving the hydrocarbon gases to small positive values for the helium—naphthalene system, attractive 6–12 intermolecular potentials may be fitted to all the data.
Monte Carlo Procedures for Generation of Nonintersecting Chains
Authors: Wall F. T. , Windwer Stanley , Gans Paul J.
Published: January 2005

A new method is described for high-speed computer generation of non-self-intersecting random walks for use as models of coiling-type polymer molecules. Previous methods for the unbiased generation of self-avoiding random walks have proved to be statistically inadequate when certain intramolecular interactions are assumed to exist. This situation arises because energetically important configurations may have a very low probability of occurrence in a normal sample. With this problem in mind, a method of generating samples in a biased fashion has been developed. The procedure allows energetically important configurations to be generated in such a way that the actual amount of bias can be calculated and compensated for, and the samples so obtained can be incorporated with those obtained in a normal, unbiased way. Data are presented to show how the attrition attending the generation of samples depends on bias.
Temperature Dependence of Spin—Spin Splitting in the Hindered Rotator CHCl2–CF2Cl
Authors: Fessenden R. W. , Waugh J. S.
Published: January 2005

The effective H1–F19 spin coupling in CHCl2–CClF2 changes from 5.40 cps at —40°C to 5.60 cps at +100°C. This variation has been analyzed to obtain the difference in potential energy between the two energetically distinct staggered rotational isomers. The result is that the isomer possessing a plane of symmetry is either 2.0 kcal/mole more stable or 1.8 kcal/mole less stable than the other pair. The consequences of this result for the theory of spin—spin splitting are briefly discussed.
Raman Spectral Studies of Molten Selenious Acid
Authors: Walrafen G. E.
Published: January 2005

Photoelectric Raman spectra of molten selenious acid, obtained in the temperature range of about 70° to 175°C, provide evidence for the existence of a new species H2Se2O5. Comparisons of Raman bands of molten selenious acid with those of very concentrated aqueous solutions of sodium biselenite indicate common frequencies. In concentrated aqueous solutions, the equilibrium 2HSeO3— = Se2O52—+H2O provides Se2O52— ions in considerable concentrations. Similarly, in molten selenious acid the reaction 2H2SeO3 = H2Se2O5+H2O produces H2Se2O5 molecules in quantity. Raman lines common to the two spectra arise from vibrations which are characteristic of the Se2O5 grouping. Such vibrations are those produced by the bending and stretching motions of the Se′–O–Se′ linkage.

When the stoichiometric composition of the melt is between 50 and 66.67 mole% SeO2 in H2O, (H2SeO3)2 and H2Se2O5 are important species. At the higher compositions, however, one weak band of the melt was observed which is close in frequency to an intense band of solid selenium dioxide. The complexity of the Raman spectrum of that solid suggests considerable polymerization. Accordingly, (SeO2)n may make an increasing contribution as the composition is increased above 66.67 mole% SeO2 in H2O, although the contribution of that species to the Raman spectra of the melt is considered to be small at the lower compositions.
Use of Pressure to Investigate Local Symmetry and Compressibility in Glass
Authors: Tischer R. E. , Drickamer H. G.
Published: January 2005

The effect of pressure to 120 kbar has been studied in several silicate and phosphate glasses. Transition metal ions have been introduced as tracers, and from the effect of pressure on the peak locations and intensities, local symmetry, local compressibility, and local distortions are deduced.

Tetrahedral sites are less compressible than octahedral sites. Both are less compressible than the bulk glass and about as compressible as transition metal oxides. Fe2+ and Ni2+ apparently enter octahedral sites which show nearly the bulk compressibility, and considerable distortion.

With increasing pressure there is a tendency for Co2+ and Ni2+ ions to transfer from tetrahedral to octahedra sites, as is predicted from the direction of change of site preference energy with pressure.

There is an irreversible change in structure of the phosphate glass above 50 kbar.
Mechanism for the Chloride-Catalyzed Thermal Decomposition of Ammonium Nitrate
Authors: Keenan A. G. , Dimitriades B.
Published: January 2005

A kinetic study of the thermal decomposition of NH4NO3 in the presence of NaCl has been carried out using the differential kinetic technique previously described. The rate law for N2 evolution is of the form k1(NH4+)+k2(NH4+) (Cl—)½. A radical mechanism is proposed in which the role of chloride is catalytic, being oxidized by NO2+ to Cl atoms which are reduced back by NH4+ and NH3. These hydrogen abstraction reactions leave NH3+ and NH2, respectively, in reaction cages in which subsequent radical recombinations yield nitramide and nitrosamine as precursors for N2O and N2. Parallel Cl atom recombinations give Cl2, part of which escapes by volatilization, the rest reacting with NH3 to provide a second source of N2.
Spin-Orbit Matrices of the d5 Configuration
Authors: Schroeder Keith A.
Published: January 2005

The spin-orbit matrices of the d5 configuration have been calculated in a strong-cubic-field scheme using the methods of Tanabe and Kamimura. The matrices were checked by comparing their eigenvalues with the spin-orbit matrix elements in a j—j coupling scheme.
Growth Rates of Potassium Crystal from the Vapor Phase
Authors: Parker R. L.
Published: January 2005

Measurements of the growth rate of potassium (110) faces, for low vapor supersaturations σ between 3.1 and 0.11 (the lowest value studied) have given unit condensation coefficients for all supersaturations. This result is in agreement with the theory of Burton, Cabrera, and Frank and gives the values βC0 = 1, σ1≤0.046 for potassium. No evidence of two-dimensional surface nucleation was found. Careful attention to the reduction of impurities, through the use of ultra-high vacuum techniques, was shown to be necessary in studying this system. Results of earlier work by Hock and Neumann on potassium can be well described by an application of the Cabrera—Vermilyea theory of impurity effects, with an effective partial pressure of active gases of 0.8×10—11 mm Hg. In the present experiments this value is less than 1.4×10—13 mm Hg. The unit condensation coefficients are shown to be in disagreement with a theoretical prediction of Hirth and Pound.
Vapor-Phase Growth Kinetics of Potassium Whiskers by Field Emission
Authors: Parker R. L. , Hardy S. C.
Published: January 2005

Using the method originated by Gomer, we have studied the growth kinetics of potassium whiskers, as they grow from the vapor phase in an electron field emission tube. To the best of our knowledge, this represents the first use of an alkali metal as a field emitter.

The results for potassium whiskers show some features similar to those previously found for mercury, and some new features. The former include positive exponential growth, and the attainment of terminal lengths. New features include the absence, usually, of symmetric emission patterns, a very low activation energy for surface self-diffusion, the fact that the whiskers cannot be pulled off but instead appear to shorten gradually if the field is raised, and finally, an interesting sensitivity of the growth processes to illumination of the whiskers with visible light.
Direct-Product Representation of Wavefunctions
Authors: Davidson Ernest R. , Jones Leon L.
Published: January 2005

A direct-product representation for N particle wavefunctions is introduced through a coefficient matrix Cp. Density matrices and the natural p states are redefined in terms of Cp. The projection-operator formalism is used to derive an eigenvalue equation for the natural p states. A generalization of the exact self-consistent field equations is derived from the concept of natural group functions.
Fourth Virial Coefficient for a Square-Mound-Potential Gas
Authors: Cole G. H. A.
Published: January 2005

The fourth virial coefficient D is derived for a gas composed of particles interacting according to the square-mound potential ψ(r) defined by the conditions ψ(r) = ε>0 for 0≤r≤1 and ψ(r) = 0 for r>1, where ε is a constant and the particle diameter is the unit of length. The calculations are based on the Born—Green—Yvon equation and the modified form of the original Kirkwood superposition approximation, viz., g(3)(r, s, t) = g(2(r)g(2)(s)g(2)( t)(1+X1n), where g(3) and g(2) are, respectively, the triplet and pair distributions, n is the particle number density, and (r, s, t) are the triplet particle separation distances. X1 is chosen in order to ensure consistence between the values of D calculated from the virial theorem and from fluctuation theory. If z≡1—exp(—ε/kT), where T is the gas temperature, and the function X1 is assumed to be a function of z alone then it is found that (1+532z)X1(z)=(−68105z+154598960z2−2581926880z3)b,where b is four times a particle volume. This leads to a single consistent value of D, written DM,(1+532z)DM=(−289210z4+15219171680z5−3555586016z6)b3.Numerical values are given, and the formulas are discussed.
Influence of Vibrations on Molecular Structure Determinations. I. General Formulation of Vibration—Rotation Interactions
Authors: Herschbach Dudley R. , Laurie Victor W.
Published: January 2005

The structure of a polyatomic molecule derived from observed spectroscopic moments of inertia differs appreciably from both the equilibrium structure and the zero-point average structure. A perturbation expansion of the moments of inertia is derived here in a form which allows the vibrational displacements to be referred to any fixed configuration of the atoms as origin. A method for evaluating the expansion coefficients is given which proceeds ``atom by atom.'' Linear WXYZ, branched WXYZ, and symmetric WXY3 molecules are treated in detail.

Empirical data show that the anharmonicity of the vibrations gives rise to the most important of the corrections required to obtain the equilibrium structure. Except for a few molecules, the anharmonicity is not accurately known. It is shown, however, that to a practical approximation the anharmonic contributions are completely absorbed in displacing the average configuration from the equilibrium one. Therefore the moments of inertia for the zero-point average configuration of a molecule can be derived from the observed effective moments by applying corrections which depend only upon the harmonic part of the vibrational potential.
Rare-Gas Sensitized Radiolysis of Propane
Authors: Futrell Jean H. , Tiernan Thomas O.
Published: January 2005

The radiolysis of mixtures of C3H8 and nitric oxide containing excess amounts of the rare gases Xe, Kr, Ar, and He, and of equimolar amounts of C3H8–C3D8 in the same mixtures has been investigated. The product yields are compared with those expected assuming that the primary process leading to decomposition of the hydrocarbon is charge exchange with the appropriate noble gas, followed by ion—molecule reactions of the hydride-transfer type. The experiments with deuterated propane demonstrate the formation of ethane and acetylene in bimolecular processes, and the production of methane, ethylene, and propylene chiefly by unimolecular decomposition. If it is assumed that neutralization of propyl ions results in the formation of ethylene and propylene as molecular products, the observations are consistent with the reaction sequence charge transfer, ion—molecule reactions, and neutralization leading to the production of unscavengeable species.
Rate of Spherulitic Crystallization with Chain Folds in Polychlorotrifluoroethylene
Authors: Hoffman John D. , Weeks James J.
Published: January 2005

(I) The requirements for making a critical test of whether two- or three-dimensional surface nucleation controls the radial growth of lamellar spherulites in bulk are discussed. Radial-growth-rate data were obtained on spherulites of polychlorotrifluroethylene (PCTFE) for a wide range of supercooling ΔT, and found to agree with a growth-rate law based on coherent two-dimensional surface nucleation, viz., G=G0 exp(—ΔF*/RT) exp[—Kg/T2(ΔT)]. Approximations for ΔF* are given. (II) Parameters related to the recently proposed ``kinetic'' viewpoint of homogeneous nucleation and growth of lamellar polymer crystals with chain folds are obtained. The nucleation constant Kg is analyzed to obtain σσe=184 erg2/cm4[σ is the lateral surface free energy, σe is the end (chain-folded) surface free energy]. A similar value of σσe is obtained from bulk-crystallization studies. The homogeneous nucleation process was identified at ΔTh=70°C, and a value of σ2σe=950 erg3/cm6 calculated from Kh in I=(NkT/h) exp(—ΔF*)exp[—Kh/T3(ΔT)2]. Combination of σ2σe and σσe gives σ=5.2 erg/cm2 and σe=36 erg/cm2, the latter corresponding to a work on chain folding, q, of 3.8 kcal/mole of folds. A value of σ=5.4 erg/cm2 is obtained independently using an empirical method. Further, an independent estimate of σe∼35 erg/cm2 is obtained for PCTFE from electron-microscope studies of the lamellar thickness, after accounting for the increase of thickness resulting from segmental mobility that occurs subsequent to initial growth using melting-point data. The over-all role of q in homogeneous nucleation and growth in linear polymers is discussed in terms of a reduced variable treatment using PCTFE and polyethylene as examples. The ``kinetic'' chain-fold theory gives a consistent picture of surface free energies, rates of homogeneous nucleation and growth, melting behavior, and the variation of initial step height with temperature. (III) A discussion is given concerning the shape of the bulk-crystallization isotherms associated with spherulitic growth, including stage-1 and stage-2 crystallization, and the presence of amorphous material in the spherulites.
Free Electrons in Active Nitrogen
Authors: Kunkel W. B. , Gardner A. L.
Published: January 2005

The resonance shift in an S-band cavity was used to measure the free-electron density [n] in a continuous flow of rf-excited active nitrogen in the mm Hg pressure range. [n] varied between 107 and 6×109 cm—3 and depended distinctly on the oxygen contamination. The ions formed presumably are NO+. By admixing known small amounts of nitric oxide to the stream it could be demonstrated that the ionization rate indeed varied linearly with the amount of NO added. At high pressures and large [n] the electron removal was by recombination, and at low pressures and small [n] it was governed by ambipolar diffusion. The value of Dp/α was estimated at 109 mm Hg/cm. Since the NO must be practically completely dissociated by the active nitrogen, the required large ionization rate indicates that the mechanism probably involves formation of excited nitrogen molecules as an intermediate step.
Nuclear Moments and Intermediate Coupling
Authors: Wybourne B. G.
Published: January 2005

The effect of intermediate coupling on the calculation of the nuclear moments of the rare earths from analyses of hyperfine structure is examined. It is shown that the observed hyperfine splittings may be satisfactorily interpreted as due to the interaction of the spin and orbital moments of 4f electrons with the nuclear magnetic and electric quadrupole moments. The interaction of the electron-spin moments with the nuclear magnetic moment is shown to be very sensitive to the form of the coupling. The consistency of the measurements of nuclear moments by atomic-beam and paramagnetic resonances is discussed. Instead of using the more usual spin-Hamiltonian formalism, the matrix elements of the interactions are calculated explicitly in terms of the actual quantum numbers of the states involved. Calculations are presented for Pr141 and Ho165.
Derivation of Second-Order Jacobians for Three-Dimensional Systems
Authors: Hoch Robert , Manning Francis S.
Published: January 2005

The relations between second-order derivatives of the thermodynamic properties of three-dimensional systems have been evaluated. The method of Jacobians which was used previously for first-order systems has been extended, and results are presented in tabular form.
Proton Magnetic Resonance Spectra of Tetravinylsilicon, Methyl- and Ethylvinylketone
Authors: Castellano S. , Waugh J. S.
Published: January 2005

NMR spectra of tetravinylsilicon, methyl-, and ethylvinylketone have been analyzed. The parameters found do not agree with those previously reported for the same compounds by other authors, although the source of several experimental data is the same; the coupling constants agree well with values already known for other vinyl compounds and correlate satisfactorily with the electronegativities of the elements bonded to the vinyl group.
Microscopic Basis of Macroscopic Magnetostatic Energy
Authors: Kaufman Allan N. , Soda Toshio
Published: January 2005

A microscopic description of the electromagnetic interactions among a set of charged particles, valid to terms of order c—2, is used to derive a number of well-known expressions for macroscopic electrostatic and magnetostatic ``energy'' and ``work.'' Particular attention is paid to the assumptions required for the validity of these expressions, and to the relations between the various nonequivalent expressions bearing the same name (such as ``magnetic work'').
Energy-Transfer Phenomena and Dissociation Processes in Electronically Excited Molecules
Authors: Lorquet J. C. , ElKomoss S. G. , Magee John L.
Published: January 2005

This paper is an extension of previous work by Magee and Funabashi on the influence of electronic coupling on dissociation mechanisms. The same model (linear chain of diatomic molecules) has again been considered. The use of a dynamical version of the Hellmann—Feynman theorem allows the development of a unified treatment valid for any coupling. An application to an infinite linear chain of hydrogen moleculeions is made, and the following results are found:

(1) In the weak-coupling case, immediate dissociation occurs.

(2) In the intermediate case, the electronic excitation energy is converted into vibrational energy, mainly localized on the molecule initially excited. Redistribution of the vibrational energy then occurs.

(3) In the strong-coupling case, dissociation does not occur. Many molecules vibrate with comparable amplitudes.

Short chains, containing two, three, four, and seven molecules, are also considered. For these it is found that two or more dissociations usually occur regardless of the type of coupling and initial position of the excitation.

Finally, an application to intramolecular energy transfer is attempted. The case of the radiation induced isomerization of cis-polybutadiene into its trans isomer, studied by Golub, is examined. With certain restrictions, our results can be considered as supporting Golub's views.
Orbital Theories of Electronic Structure
Authors: Adams William H.
Published: January 2005

We show that in the Hartree—Fock approximation there exists a uniquely defined Hermitian potential which describes the interaction of a model subgroup of electrons with the rest of the system. This potential can be divided into two parts. The first part is the difference between the Hartree—Fock Hamiltonian for the system and the model Hamiltonian. The second part is a nonlocal potential which cancels (screens) some of the first part. The essential point in the derivation is our choice of definition for model orbitals in the system. The only condition that must be satisfied by the occupied orbitals of the system is that they be linearly independent. It is also shown that there exist equations describing the best orbitals to use in a calculation by a linear combination of atomic orbitals method. They are the best orbitals to use because they give the exact answer. As a concrete example of our ideas we have treated numerically the LiH molecule. In order to link our method with others that have been described we indicate how the pseudopotential form of the orthogonalized plane wave method may be derived.
Use of Weak Perturbing Radio-Frequency Fields in Nuclear Magnetic Double Resonance
Authors: Freeman R. , Anderson W. A.
Published: January 2005

A theory is developed to explain high-resolution nuclear magnetic resonance spectra observed in the presence of a second weak rf field at ω2. When ω2 is set on a nondegenerate transition frequency and the rest of the spectrum recorded by sweeping the frequency of the investigating rf field, any transitions that have an energy level in common with the perturbed transition will be split into doublets. If magnetic field inhomogeneities exceed the natural linewidth, the line profile of the doublets gives information about the ordering of the three energy levels involved. Good agreement with the theory has been obtained in experiments on two-spin and three-spin proton systems where the energy-level diagram is already known. The method has been used to establish the ordering of the energy levels of the ABC system of protons in methyltrivinylsilane and the analysis has been completed by two independent methods. Some of the special effects which arise when double-resonance spectra are recorded by sweeping the magnetic field have been examined and discussed.
Attractive Forces between Long Saturated Chains at Short Distances
Authors: Salem Lionel
Published: January 2005

The assumption of locally additive forces is used to describe the London—van der Waals dispersion attraction between long saturated chains. For two linear chains of length L, opposed and parallel, each built out of N identical units of length λ(Nλ=L), the total dispersion energy is given by W=A4λ2D4ρ(3tan−1ρ+ρ1+ρ2),  ρ=LD, where D is the mutual distance of the two chains; A is the coefficient of the dispersion interaction between two basic units. At distances D much smaller than the molecular length L, the energy becomes proportional to L (or N) and inversely proportional to the fifth power of the intermolecular distance.

The coefficient A is calculated for the interaction between two CH2 units in hydrocarbon chains and the result is used to estimate the sublimation energy at 0°K of paraffin crystals. Sound agreement with experiment is obtained. Finally, the particularities of the attractive forces between long saturated chains are examined in more detail and their great sensitivity to distance is shown by several examples. Various applications to systems of biological interest are also suggested.
Use of Gaussian Functions in the Calculation of Wavefunctions for Small Molecules. I. Preliminary Investigations
Authors: Reeves C. M.
Published: January 2005

The results are reported of calculations on H, H2, He, Be, N, and NH in bases of Gaussian elementary atomic orbital functions. Such functions, though physically less satisfactory than the customary Slater exponential functions, have the advantage that all integrals can be evaluated exactly by closed analytical formulas. Some progress has been made with the problem of choosing the orbital parameters for bases of limited size. Predictions of total energy are understandably poor but the values obtained for bond length and binding energy are encouraging.
Fluorescence and Lifetimes of Eu Chelates
Authors: Samelson H. , Lempicki A.
Published: January 2005

The fluorescent lifetimes of a number of europium chelates were determined in solution and as the solid at a number of temperatures and a range of wavelengths of the fluorescent emission. They are compared with the lifetimes of europium fluorescence in other compounds and it is suggested that the variation in lifetime is a result of the ligand—Eu interaction and that discrepancies in the results of different workers on the same compound is related to the manner of preparation of the chelate.
Crystal-Field Spectra of d3,7 Ions. I. Electronic Absorption Spectrum of CoCl4= in Three Crystalline Environments
Authors: Ferguson J.
Published: January 2005

The electronic absorption spectrum of the CoCl4= complex ion has been studied in crystals of the type R2CoCl4, where R is Cs, N(CH3)4, or quinolinium ion. The measurements have been made with single crystals at various temperatures down to 4.2°K with high resolution in the near infrared, visible, and near ultraviolet regions of the spectrum. The data include transitions from the ground state to states arising from six of the seven terms of the free ion. Analyses of the bands have been made, as well as an attempt to sort out the effects of spin—orbit coupling, the site symmetry, and the vibrations of the excited states. It is concluded that the assumption of cubic symmetry for the crystal field is valid only for the determination of the approximate energies of the electronic states and not for the details of the splitting patterns of orbitally degenerate states. The usefulness of crystal-field theory which includes spin—orbit coupling and two inter-electronic repulsion parameters is discussed.
Entanglement Effects in Concentrated Polymer Solutions from Viscosity Measurements
Authors: Bueche F. , Coven C. J. , Kinzig B. J.
Published: January 2005

The viscosity—molecular weight relation for the system polymethyl methacrylate—diethyl phthalate has been measured. Polymer concentrations of 0.10, 0.15, 0.20, and 0.25 g/cc have been used. No variation in entanglement molecular weight Me in the range 30°—80°C was found. Theoretical predictions for the dependence of Me on concentration have been confirmed. After correcting the data for variation in Tg with molecular weight, the dependence of viscosity on molecular weight predicted by theory is confirmed. Possible reasons are given for the discrepancy between the present conclusions concerning Me and those arrived at from considerations of dynamic data on the same system.
Influence of Hydrodynamic Interaction on the Viscoelastic Behavior of Dilute Polymer Solutions
Authors: Tschoegl N. W.
Published: January 2005

The theory of Zimm for the viscoelastic properties of dilute polymer solutions is expanded into a more general treatment containing both the theories of Rouse and Zimm as limiting cases. This treatment predicts a transition from Zimm-like to Rouse-like behavior with changing hydrodynamic interaction. Values of Flory's Φ as a function of the hydrodynamic interaction parameter h are tabulated.
Heat of Formation and Entropy of (BOCl)3
Authors: Blauer Jay , Farber Milton
Published: January 2005

An experimental study of the equilibrium B2O3(l)+BCl3(g) = (BOCl)3(g) has been made by the method of transpiration in the temperature range of 536°—825°K. The enthalpy and entropy changes of the reaction in this temperature range were found to be 5.0±0.3 kcal/mole and 3.1±0.5 cal/deg/mole, respectively. The data have been interpreted to yield the heat of formation, ΔH°f695°K = 391.5±0.3 kcal/mole, and entropy, S°695°K = 124.2±0.5 cal/deg/mole, of gaseous (BOCl)3. Partial pressure studies indicate that the quantity of the monomer, BOCl, present in the temperature range under consideration is negligible.