bluuebunny/crossref_metadata_2025 huggingface dataset:
Nuclear Magnetic Relaxation and Dielectric Relaxation in Isoamyl Bromide
Authors: Roeder S. B. W. , Stejskal E. O. , Vaughan W. E.
Published: January 2005

Nuclear magnetic spin—lattice relaxation times have been measured for supercooled isoamyl bromide at 20 and 60 Mc/sec over the temperature range 113° to 300°K. A distributed correlation function is introduced in order to explain the data. An expression for T1 which fits the data within the experimental error is obtained by using the Cole—Davidson distribution function to distribute the Kubo and Tomita expression for T1. Both the cutoff correlation time of the distribution function and the width parameter are allowed to vary with temperature. These parameters are compared with those reported in the literature from an analysis of the dielectric relaxation of supercooled isoamyl bromide using the Cole—Davidson distribution function. Similarities in the distribution function cutoff times and differences in the width parameters are observed. The distribution function parameters are related to molecular and liquid structure. Measurements of spin—spin relaxation times at 20 Mc/sec are discussed briefly.
Calculation of Rydberg Levels in the Nitrogen Molecule
Authors: Lefebvre-Brion H. , Moser C. M.
Published: January 2005

The energy levels of the lowest members of Rydberg series in N2 have been calculated using LCAO—MO—SCF functions. We have found only one 1Σu+ level around 104 000 cm−1 and this is the first member of a Rydberg series which converges to the X 2Σg+ ground state of N2+. This level can be identified with the p′ 1Σu+ state. Our calculations suggest that, if the Worley—Jenkins Rydberg states have 1Σu+ symmetry (which is not yet absolutely definite) then, no Rydberg series of the type (npπu) 1IIu←X1Σg+ have yet been observed.

Our calculations confirm the configurations previously suggested for the upper states of Worley's third and Hopfield's Rydberg series. The states D 3Σu+, E 3Σg+, z 1Δg, x 1Σg−, and y 1IIg are shown to be the first members of Rydberg series.
Dissociation Energy of Boron Monofluoride from Mass-Spectrometric Studies
Authors: Hildenbrand Donald L. , Murad Edmond
Published: January 2005

Gaseous equilibria involving BF, BF3, Ca, CaF, and CaF2 were studied by mass spectrometry in the range 1583° to 1734°K. The vapor species were produced in a graphite Knudsen cell containing a mixture of elemental boron and calcium fluoride, and they were identified from their characteristic mass spectra and ionization-efficiency curves. From ion-intensity measurements made at ionizing energies a few volts above threshold, the equilibrium constants and heats of several reactions involving BF (g) were evaluated. These results yield the standard heat of formation −27.5±3 kcal/mole for BF (g) and the dissociation energy, D0°, of 7.85±0.15 eV. The thermochemical dissociation energy of BF is significantly larger than a spectroscopic value obtained from linear extrapolation of the ground-state vibrational levels, but it agrees well with a value taken from a short extrapolation of the vibrational levels in the excited 1π state.
Electrical Conductivity of Molten Bi–BiCl3 and Bi–BiBr3 Solutions
Authors: Grantham L. F.
Published: January 2005

The electrical conductivities of molten Bi–BiBr3 solutions were measured as a function of temperature over the entire composition range; the conductivities of Bi–BiCl3 solutions were measured from pure salt to 30 mole % metal. In general, these two systems are very similar. Above 400°C, they resemble the Bi–BiI3 system in which conductivity increases monotonically with metal content; but below 300°C in salt-rich solutions, the conductivities of these two systems decrease with increasing metal content. Between 10 and 80 mole % Bi in the Bi–BiBr3 system and between 10–30 mole % Bi in the Bi–BiCl3 system, positive temperature coefficients were found at all temperatures. Above 500°C, the three predominating conductivity mechanisms are believed to be ionic at less than 10% metal, semiconducting between 20% and 60% metal, and metallic above 80% metal.
Charge-Transfer-Controlled Vaporization of Cadmium Sulfide Single Crystals. I. Effect of Light on the Evaporation Rate of the (0001) Face
Authors: Somorjai G. A. , Lester J. E.
Published: January 2005

Light of greater-than-band-gap energy was found to change markedly the vacuum evaporation rate of the (0001) face of cadmium sulfide single crystals. Evaporation temperatures of 680°—740°C and light intensities of 5.0×103−2.0×105 μW/cm2 were used. The results were interpreted assuming that charge transfer is the rate-determining step in the sequence of vaporization surface reactions. An evaporation mechanism in terms of charge transfer has been proposed. Light (1) changes the free-carrier concentrations at the vaporizing surface, and (2) under proper conditions, changes the composition of the crystals. High-resistivity crystals showed a fivefold increase of their evaporation rate under illumination due to the increase by light of both electron and hole concentrations. In low-resistivity crystals, in which illumination can only significantly increase the minority free-carrier concentration above the dark equilibrium value, effects, which are due to the change of the crystal composition, dominated.
Isotope Effects on Vibrational Transition Probabilities. III. Ionization of Isotopic H2, N2, O2, NO, CO, and HCl Molecules
Authors: Halmann M. , Laulicht I.
Published: January 2005

Franck—Condon factors are given for the normal and stable isotope-labeled molecules for transitions to spectroscopically known ionic states. Appreciable isotope effects on Franck—Condon factors are found in several transitions, and are related both to the differences in internuclear separation associated with different levels and to differences in reduced masses. Isotopic substitution by a heavier element results in a shift in the transition probability towards higher vibrational levels. Therefore an inversion in the ratio of ionization efficiencies of light and heavy molecules is predicted.
Potential-Energy Curves for CO and CO+
Authors: Krupenie Paul H. , Weissman Stanley
Published: January 2005

Potential-energy curves for the X 1Σ+, A 1Π, I 1Σ−, a 3Π, a′ 3Σ+, d 3Δi, and e 3Σ− electronic states of CO and the X 2Σ+, A 2Πi, and B 2Σ+ electronic states of CO+ have been calculated using a modification of the Rydberg—Klein—Rees method. The curves for the a 3Π, d 3Δi, and A 2Πi states, which are intermediate between Hund's Cases (a) and (b), represent fictitious rotationless states calculated using the true Bv. Benesch and co-workers have shown theoretically that this representation is correct for such intermediate cases. The numerical results for the A 2Πi state presented here confirm their conclusions.
Intensity Relations for Determining Gas-Phase OH, Cl, Br, I, and Free-Electron Concentrations by Quantitative ESR
Authors: Westenberg A. A.
Published: January 2005

The theoretical intensities for the absorption lines of gas phase OH and NO as observed with an ESR spectrometer are discussed. Since both species have transitions of the electric-dipole type, it is shown how the absolute concentration of OH may be determined by comparing its integrated intensity with that of the stable NO used as a reference gas. A similar procedure for determining the concentration of free electrons from their electric-dipole cyclotron resonance absorption signal is also outlined. Finally, the intensity relations useful for determining all of the halogen atoms (except fluorine) using O2 as the reference gas are derived.
Quantitative ESR Measurements of Gas-Phase H and OH Concentrations in the H–NO2 Reaction
Authors: Westenberg A. A. , De Haas N.
Published: January 2005

An application of the intensity relations derived previously for determining absolute concentrations of H atoms and OH radicals in the gas phase by ESR spectroscopy is described. Magnetic-dipole transitions in O2 and electric-dipole transitions in NO are used as calibration standards for determining H and OH, respectively. The construction of a cylindrical TE011 cavity suitable for observing both types of transitions in a fast flow system is described. Results of measurements of H and OH concentrations during the ``titration'' reaction H+NO2→NO+OH are presented. The internal consistency of the theoretical OH intensity relations is demonstrated by experimental measurements on J=32 and J=52 OH lines. At reaction times of a few milliseconds, the H titration curve is shown to have an initial linear portion which extrapolates to an NO2/H ratio of unity. It then becomes curved as expected by the generation of an additional H from OH+OH→ lim k2H2O+O  and  OH+O→O2+H.The OH titration curves yield k2=1.2±0.3×1012 cm3 mole−1·sec−1 at 300°K in good agreement with the only other reported value. Finally, some qualitative observations on a striking generation of free electrons associated with the main H–NO2 reaction are noted.
Doppler Shifts in Light Scattering. II. Flexible Polymer Molecules
Authors: Pecora R.
Published: January 2005

The light-scattering spectrum for the bead-and-spring model of flexible polymers is computed. The spectrum is shown to consist of a sum of Lorentzians centered about the incident frequency each with a half-width proportional to the relaxation time of a given normal mode. The contribution of each normal mode to the spectrum is proportional to the ratio of the equilibrium mean-squared length of a mode to the square of the incident-light wavelength.
Radiolysis of Binary Paraffin—Olefin Solutions. II. Effects of Deuterium Isotopic Substitutions
Authors: Yang John Y. , Marcus Inge
Published: January 2005

The effects of deuterium isotopic substitutions on product distributions in the radiolysis of paraffin—olefin solutions have been studied. The total hydrogen yield is apparently not affected by deuterium substitution in the olefin. However, the isotopic compositions of hydrogen from mixtures containing deuterated components are typically those expected by hydrogen abstraction involving large isotope effects. Product distributions of dimers from irradiations of cyclohexane—cyclohexene, cyclohexane—cyclohexene-d10, cyclohexane-d12—cyclohexene, cyclohexane-d12—cyclohexene-d10, cyclopentane—cyclohexene, and cyclopentane—cyclohexene-d10 solutions are found to be highly affected by deuterium substitutions in the olefin but scarcely changed by similar substitutions in the paraffin. Such observations are rationalized by the proposal that physical interactions may take place by positive charge transfer from saturated hydrocarbon ions to the olefin, but that the resulting dimer product distributions are governed primarily by subsequent radical scavenging and abstraction reactions. Differences in dimer product yields observed in the various deuterated-vs-nondeuterated mixtures are thus explained by changes in the relative importance of two different reaction sequences each initiated by the olefin positive ion.
Conformation of an Isolated Polymer Molecule at an Interface. II. Dependence on Molecular Weight
Authors: Roe Ryong-Joon
Published: January 2005

The average conformation of polymer molecules adsorbed from very dilute solution is derived from the partition function Zn pertaining to an isolated molecule with at least one of its segments adsorbed. It is an extension of the treatment in the previous paper in which the generating function Γ (ζ) = ΣZnζn was derived, and from it the partition function Zn, in the limit of very large n, was obtained by the method due to Lifson. In the present paper Zn for finite n is obtained from Γ (ζ) by the use of Cauchy's theorem, the contour integration being evaluated by the steepest-descent method. The numerical result thus obtained agrees well, even for n=5, with the exact results evaluated by direct power series expansion of Γ (ζ) by a computer.

The results show that the conformation of adsorbed polymers can be classified into three distinct types according to the values of the segmental adsorption constant s. When s is large, the molecules lie flat on the surface and various intensive quantities are independent of the chain length n. When s is near the critical point sc, the fraction of adsorbed segments is proportional to n−½, in agreement with the earlier result by Simha, Frisch, and Eirich, but most of the desorbed segments are in the long-chain ends rather than in the internal loops. For very small s, the number of adsorbed segments becomes independent of n, and all the remaining segments are in the free-chain ends, with a negligible probability of loop formation.

The present results apply to the helix—coil transition of DNA with some modifications.
Generalization of Activated-Complex Theory. III. Vibrational Adiabaticity, Separation of Variables, and a Connection with Analytical Mechanics
Authors: Marcus R. A.
Published: January 2005

In Part I, activated-complex theory was extended by including the possibility of a curvilinear reaction coordinate. A separation-of-variables approximation was made in the neighborhood of the activated-complex region of configuration space. In the present paper a more general yet simpler derivation of the final equation is given. It permits subsequent introduction of analytical mechanics in the above neighborhood in a variety of ways such as separation of variables, vibrational adiabaticity, or a method combining certain features of both, the separable—adiabatic approximation. The relationship of these methods is discussed.

Some numerical quantum- and classical-mechanical results obtained for transmission coefficients of nonrotating atom-transfer reactions (linear complexes), using computers, are interpreted in terms of an adiabatic approximation with reasonable agreement. Attention is also called to a modified WBK expression for the transmission coefficient, which generalizes the usual WBK formula in a simple way.
Angular-Momentum Conditions for a Correlated Wavefunction
Authors: McKoy Vincent
Published: January 2005

We obtain the conditions under which a correlation wavefunction containing pair correlation functions for the 2pn electrons of C(3P, 1D, 1S), N(4S), O(3P), and Ne will be an eigenfunction of the orbital and spin angular-momentum operators. These pair functions contain quite general powers of electronic and interelectronic coordinates along with their variational parameters and should avoid the convergence difficulties of configuration interaction. In all these cases, except carbon which has just one pair of 2p electrons, one cannot obtain such a pair function, ûij(1), just by minimizing its pair energy, ε̃ij(1), alone; i.e., minimizing the variational parameters of a ûij(1). Minimization of one pair at a time corresponds to working with just a part of the correlation wavefunction which by itself cannot converge to the right symmetry state. One must minimize sums of pair energies by taking a correlation wavefunction containing enough pair functions so as to have the right symmetry. The sets of variational parameters in these different ûij's are not independent but are coupled. These symmetry requirements now make the determination of pair correlation functions quite a bit more difficult. In carbon (3P), these conditions do not apply, but the ûij(1) of the 2p2 electrons of the 1D multiplet must be made orthogonal to the unoccupied orbitals of the open shell if it is to contain general powers of the interelectronic coordinate. This is in addition to the required orthogonality to occupied orbitals. We also obtain a form of the correlation wavefunction for 2p2(1S), a nonsingle-determinant Hartree—Fock (HF) state. This has not been previously known. We do this by applying the angular momentum stepdown operator to the correlation wavefunctions of multiplet states with single Slater determinant HF states and studying the resulting forms of the correlation wavefunction which, in turn, belong to some nonsingle-determinant states of these multiplets.
Analysis of Ternary Diffusion: Solutions of Diffusion Equations and Calculated Concentration Distribution
Authors: Oishi Y.
Published: January 2005

Solutions have been given in closed form to the simultaneous differential equations for ternary diffusion where the coefficient terms are described in terms of three intrinsic diffusion coefficients. Concentration distributions for various combinations of the three intrinsic diffusion coefficients are calculated here with the solutions for semi-infinite diffusion coupling, and behavior of the respective species is discussed together with the resultant concentration distributions. Numerical solution by the finite-difference approximations has been carried out separately for the same diffusion equations, and the resultant concentration distributions are compared with those obtained by the closed-form solutions. A parameter has been derived for description of the characteristics of the ternary diffusion profile.
Absorption Spectra of H2 in the Vacuum-Ultraviolet Region. III. Potential-Energy Curves for the B 1Σu+, C 1Πu, B′ 1Σu+, and D 1Πu States
Authors: Namioka Takeshi
Published: January 2005

The potential-energy curves for the B, C, B′, and D states of the H2 molecule have been calculated from experimental spectroscopic data with the use of the Rydberg—Klein—Rees (R—K—R) method. The theoretical curve for the C state given by Kolos and Wolniewicz shows excellent agreement with the R—K—R curve over the whole range of internuclear distances. From these two curves and experimental evidence, it is now evident that the C state does have a potential hump at about 100 cm−1 above its dissociation limit at the internuclear distance of about 4.76 Å. Although some difficulties have been encountered in constructing the potential-energy curve for the B′ state in the vicinity of the dissociation limit, there is an indication that the right limb of the R—K—R curve could provide a limiting curve of the form required to explain the observed limiting curve for the dissociation continuum. Through these studies it was also found that the last vibrational levels of the states B and B′ are most probably v=36 and v=8, respectively. In Part II, the predissociation occurring in the D state was classified as the case b0. However, the R—K—R curves for the B′ and D states cross over at about the v=3 level of the B′ state; indicating that the predissociation should be classified as the case b−.
Pentacoordinated Molecules. VII. The Atomic Polarization and Dielectric Properties of PCl4F, PCl3F2, and PCl2F3 in Solution and in the Pure Liquid State
Authors: Holmes Robert R. , Carter Richard P.
Published: January 2005

From measurements of the molecules PCl4F, PCl3F2 and PCl2F3 in cyclohexane solution, molar polarizations and refractions are calculated. The atomic polarizations for PCl3F2 (6.6 cc) and PCl2F3 (6.0 cc) approximate that found for PF5 (6.2 cc) and represent from 20%—40% of the induced polarization. The low-frequency bending vibrations of these trigonal bipyramids are shown to be the principal source of the high atomic polarization values. A value of 4.5 cc is estimated for PCl4F.

The temperature dependence of the dielectric constants and densities of the molecules in the pure liquid state also were measured. Application of the Onsager—Kirkwood theory gives dipole moments in good agreement with precise gas-phase values. A similar comparison is made for the moments from the solution study for this series of low dipole halides.
Time-Resolved Spectroscopy of Europium Chelates
Authors: Bhaumik M. L. , Nugent L. J.
Published: January 2005

Time-resolved fluorescence spectra of several europium chelates have been measured using the stroboscopic time-resolution technique. For each of the β-diketone chelates, where the ligand triplet levels are in general above the 5D1 level of Eu3+, the spectra provide evidence that the Eu3+5D0 state is populated by nonradiative energy transfer from the higher-lying 5D1 state. The relaxation time for energy decay from the 5D1 state is measured both in the microcrystals and in solution to be of the order of a few microseconds. Since this is shorter than the corresponding relaxation time of Eu3+ in systems where there are no vibrational frequencies near 1760 cm−1, the 5D1—5D0 energy separation, it is suggested that the ligand[Complex chemical formula]stretching vibrations and the bending vibration of coordinated water molecules make important contributions to the relaxation process. On the other hand, complete nonradiative degradation to the molecular environment from the 5D0 and the 5D1 energy levels appears to be more strongly influenced by higher-energy molecular vibrations such as the C–H and O–H stretches. Variations with temperature in the relaxation time from the 5D1 energy level are mainly accounted for by the temperature dependence of the rate of energy degradation from the 5D1 level to the environment, and it is suggested that the [Complex chemical formula] relaxation process is temperature insensitive between 300° and 77°K. In general, the nonradiative energy-transfer processes in Eu3+ appear to be dominated by interactions with molecular vibrations, and to a smaller extent by crystal lattice modes, rather than by other possible relaxation mechanisms.
Exchange and Relativistic Effects on Pi Bonding in the Uranyl Ion
Authors: Newman John B.
Published: January 2005

Overlap integrals for the uranyl ion were calculated using Hartree—Fock—Slater and Hartree relativistic U5+ 5f and 6d wavefunctions. Earlier primary overlap calculations by Belford and Belford, using solutions which are approximately Hartree functions, gave π larger than σ overlaps. Exchange effects tend to equalize the σ and π overlaps, and a case was found where the σ overlaps exceed the π values. The relativistic effects are indirect and more pronounced for the 5f orbital. They tend to equalize the σd and πf overlaps, and to increase the πd value which nevertheless remains the largest. These results are indicative of a uranyl structure having strong πd, and weak σf primary bonds, and having at most weak 5f orbital involvement in the secondary bonding. Thus, the overlap results obtained using exchange and relativistically corrected uranium wavefunctions support the view of uranyl complex structures as proposed by Belford and Belford and by Coulson and Lester.
High-Resolution Emission Vegard—Kaplan Bands of Nitrogen
Authors: Miller R. E.
Published: January 2005

A laboratory light source was developed which emits the forbidden Vegard—Kaplan bands of nitrogen with sufficient intensity for a high-resolution spectrograph. The triplet splitting of the A 3Σu+ state was well resolved and shown to be in very good agreement with theoretical calculations. Very precise band origins and molecular constants were determined from three of the Vegard—Kaplan bands. An effective source temperature was obtained from the intensity distribution.
Radiative and Nonradiative Transitions in the Fluorescence Decay of Eu3+ in SrTiO3
Authors: Weber M. J. , Schaufele R. F.
Published: January 2005

The fluorescence excitation and decay properties of Eu3+ in SrTiO3 have been studied using steady-state and pulse techniques. The transient fluorescence response following pulsed selective excitation was used to establish the modes of energy decay. The probabilities for spontaneous magnetic-dipole emission were calculated for several states. These results combined with relative fluorescence intensity measurements are compared with the observed fluorescence lifetimes to determine the probabilities for radiative and nonradiative decay. Whereas the decay of the 5D0 state is radiative, consisting of both zero-phonon and phonon-assisted transitions, the 5D1 decay is composed of radiative transitions to states of 7F and nonradiative transitions to 5D0, the latter being dominant. The 5D0 and 5D1 fluorescence lifetimes exhibit different temperature dependences which are discussed in terms of the contributions from phonon-assisted and multiphonon nonradiative transitions. The change in the 5D0 lifetime as the temperature is varied through the 110°K phase transition of SrTiO3 is ≲ 10%.
Quantum Effects of Methyl-Group Rotations in Magnetic Resonance: ESR Splittings and Linewidths
Authors: Freed Jack H.
Published: January 2005

The effects of internal rotations of methyl groups on ESR hyperfine lines are analyzed in terms of a quantum-mechanical description of the motion. The classical description of rotational averaging is replaced by (1) spin—rotational coupling from a hyperfine operator, and (2) rotational relaxation by thermal collisions. In the absence of collisions, the effects of (1) lead to a static set of splittings whose values depend upon the relative magnitudes of the hyperfine-versus-tunneling frequencies. In the presence of frequent collisions, represented by a strong-collision model, the effects of (1) lead to line broadening, the detailed nature of which also depends on the hyperfine-versus-tunneling frequencies. In general, results predicted from a classical treatment of the motion are obtained when the hyperfine frequency is significantly greater, while quantum effects become important for relatively larger tunneling frequencies. The results are illustrated by application to relevant experimental observations. In the Appendix, the strong-collision relaxation theory is generalized to apply to the present case where the spin—rotational coupling connects states of different nuclear spin symmetry.
Many-Electron-Theory ab Initio Calculation for the Be Atom
Authors: Geller Murray , Taylor Howard S. , Levine Howard B.
Published: January 2005

The details and results of an ab initio calculation of the energy of the Be atom using the Sinanoğlu many-electron theory are presented. Comparisons are made with earlier calculations on the Be atom by this technique and by other techniques. Finally, the pitfalls and shortcomings of the many-electron theory on extension to larger systems are discussed.
Interatomic Forces and Crystal Energy of Alkali Hydrides
Authors: Dass Lachhman , Saxena S. C.
Published: January 2005

The approriateness of a large number of interatomic potentials is investigated to represent the behavior of alkali hydride crystals. The lack of crystal data does not permit a direct determination of the potential according to the conventional procedure. A method suggested earlier by Kachhava and Saxena has therefore been employed. Crystal energies have been computed on all the potentials and compared with the generated experimental values obtained on the basis of up-to-date thermal data. This study established a definite preference and superiority for the Born—Mayer and Hellmann potentials. These are almost equally adequate and we suggest their use for computing the other crystal properties of alkali hydrides.
Structure of Sodium Aluminogermanate Melts with Na2O/Al2O3 Ratio Greater Than Unity
Authors: Riebling E. F.
Published: January 2005

The viscosities and densities of several series of ternary sodium aluminogermanate melts with Na2O/Al2O3 ratios greater than unity have been determined for temperatures between 1050° and 1450°C. The viscosity data suggest that aluminum (III) takes part in network formation in the form of AlO4 tetrahedra for all compositions studied.

The molar-volume data for the 40-mole % Na2O melts and the 53- and 62-mole % GeO2 melts can best be interpreted in terms of a model that involves GeO4 tetrahedra, AlO4 tetrahedra, and v̄Na2O increases that are related to the Al2O3 contents. Molar volumes for 75-mole % GeO2 melts are interpreted in terms of a model that involves GeO6 octahedra. Similar data for the 25-mole % Na2O melts suggest the sudden elimination of GeO2 octahedra and a v̄Na2O minimum with increase of Al2O3 content. This is supported by the expansion coefficient and viscosity results. It is concluded that GeO6 octahedra are stable at 1300°C only within a 10-mole % Na2O semicircular ternary sweep of the 23-mole % Na2O binary point.
Unimolecular Fragmentation of the Toluene Molecule Ion
Authors: Meyer F. , Harrison A. G.
Published: January 2005

Using a pulsed ion source in which the time between ion formation and ion withdrawal for analysis can be varied, the unimolecular fragmentation of the toluene molecule ion C7H8+→C7H7++Hhas been studied. The results indicate that the major part of the fragmentation occurs from a state or states with a half-life of 0.1 μsec or less. However, a significant fraction of the toluene ions decompose from a state with a half-life of approximately 5 μsec. Studies with deuterium-labeled toluenes indicate extensive scrambling of the ring and methyl hydrogens in both the ``fast'' and ``slow'' reactions. The isotope effect in the ``fast'' reaction is quite small, however, for the ``slow'' reaction kH/kD=3.6.
Photoionization and Absorption Cross Sections and Fluorescence of CF4
Authors: Cook G. R. , Ching B. K.
Published: January 2005

Absorption and photoionization cross sections for CF4 were measured in the 600-to-1000-Å region using a 1-m Seya-type scanning ultraviolet monochromator with a resolution of 0.7 Å. The Hopfield continuum of He2 was used as the light source. The cross sections obtained show that from 600 to 1000 Å the absorption is continuous with broad maxima at 910 Å, 780 Å, and 660 Å, and broad minima at 830 Å and 760 Å. The appearance potential of ions was located at 15.56±0.01 eV (796.7 Å). Photoionization efficiencies were computed and the results indicate that processes other than ionization, such as dissociation or excitation to higher electronic states, are appreciable. Maximum fluorescent emission from the irradiated gas was observed to occur when the wavelength of the incident radiation was 905 Å.
ENDOR of Free Radicals in Solution
Authors: Hyde James S.
Published: January 2005

Electron nuclear double resonance has been performed on six free radicals in solution. Polar and nonpolar solvents were employed, and both neutral and ionic radicals investigated. The instrumentation is described in detail. Features of the instrument include: pulsed nuclear radio-frequency magnetic fields, rf fields as high as 40 G in the rotating frame, and provision to observe changes in the EPR spectrum caused by nuclear resonance with the ordinary EPR spectrum subtracted (ENDOR-induced EPR). ENDOR mechanisms and adjustment of experimental conditions to achieve optimum signal intensity are discussed. It is established that successful ENDOR experiments can be performed on a large number of free radicals in solution, resulting in improved resolution, simplification of spectra and more accurate hyperfine splittings.
Theory of Phenomenological Coefficients in Solid-State Diffusion. I. General Expressions
Authors: Allnatt A. R.
Published: January 2005

General expressions for the phenomenological coefficients in terms of jump probabilities have been derived for isothermal solid-state diffusion using linear response theory of the Kubo type. The assumptions required are: (a) the system evolves according to the master equation of a Markoff process, (b) a weak assumption about the general form of the perturbation to the transition probabilities in an applied field, (c) the detailed-balance principle as applied to a Markoff process for a system at equilibrium. The Onsager relations are obeyed.

The advantages of using these results as a starting point for detailed calculations compared with conventional methods are briefly discussed and further developments noted.

An appendix discusses the application of the same method to thermal diffusion.
Inelastic Neutron Spectra and the Vibrational Modes of the Hydrogen Layer in Alkali and Alkaline-Earth Hydroxides
Authors: Pelah I. , Krebs K. , Imry Y.
Published: January 2005

Inelastic neutron scattering spectra of pure and deuterated lithium hydroxides and of Ca(OH)2, Ca(OD)2, and Mg(OH)2 are presented. These spectra are explained by the interaction of neutrons with lattice vibrations in the scatterers. Special emphasis is given to the part of the spectra which is predominantly influenced by vibrations of the hydrogen layer atoms.
Structure and Partition Function of Liquid Water. II. Examination of the Results of Buijs and Choppin
Authors: Senior W. A. , Vand V.
Published: January 2005

It is shown that the experimental results of Buijs and Choppin are not consistent with any thermodynamic model of liquid water based on three species of molecules, each with a sharp level of positive energy.
Structure and Partition Function of Liquid Water. III. Development of the Partition Function for a Band Model of Water
Authors: Vand V. , Senior W. A.
Published: January 2005

A partition function for liquid water is developed, based on the three types of water molecules postulated by Buijs and Choppin. The main feature of this approach is that the concept of discrete energy levels (corresponding to zero, one, and two hydrogen bonds) is abandoned and replaced by the idea of energy bands. The parameters of the partition function are evaluated from the thermodynamic data at 50°C, the results of Buijs and Choppin, and the assumption of dipole—dipole forces within the liquid. These parameters are then used to calculate the thermodynamic functions over the range 0° to 100°C. The calculated results are in very good agreement with the experimental observations, the agreement with Cv being generally better than 0.2%. The experimental results of Buijs and Choppin and our band model of water are therefore consistent with each other and also with thermodynamic data on water.
Charge Dependence in Ionic Solvation
Authors: Golden Sidney , Guttman Charles
Published: January 2005

Systems consisting of a single electrically neutral or ionic species in interaction with a large number of solvent molecules are treated in general quantum-statistical-mechanical terms. Such systems are assumed to have Hamiltonians, for each electronic state, which exhibit a parametric dependence upon charge not exceeding quadratic. Changes in the Helmholtz free-energy, energy, and entropy functions are determined formally for the process of ionic solvation due to Born. On the basis of a general argument that an electrically neutral species acquires a nonzero potential upon solvation, the changes in the cited thermodynamic functions are shown to be capable of taking on positive values for a range of values of the charge parameter. This behavior is in direct contrast with expectations from the Born expression for such changes. Semiempirical treatment of data available for solvation free energies of aqueous ions permits an estimate, of 1 V, to be made of this potential. A possible experimental test of this result is described.
Phase Shifts and the Quantum-Mechanical Hamilton—Jacobi Equation
Authors: Kouri Donald J. , Curtiss C. F.
Published: January 2005

A method of obtaining absolute phase shifts by integration of the quantum-mechanical Hamilton—Jacobi equation is developed and applied to the example of particles interacting through a Lennard-Jones potential. A new expression for the absolute phase shift is obtained in terms of an irregular solution of the Schrödinger equation.
Theory of Hypochromism
Authors: Bullough R. K.
Published: January 2005

A unified theory of complex refractive index in fluids is described. The theory shows that hypo- (or hyper-) chromism is an inevitable consequence of significant anisotropic relative correlation. Formulas are quoted which contain, among other significant terms, the more general form of those given by Tinoco and others. Factors of dispersive refractive index and multiple-scattering terms neglected in the previous treatments are shown to be important. Three alternative reasons why pronounced hypochromism may be accompanied by small frequency shifts in the dipole approximation are indicated: in general, hypochromism is accompanied by changes of band or line shapes as well as shifts of absorption maxima. A proof of a sum rule for integrated absorption in small isolated polymers is adumbrated: under less stringent conditions the sum rule appears to fail. The arguments are developed in much greater detail elsewhere.
Inelastic Electron Scattering from Atoms at Medium Energies. II. Polarization Effects
Authors: Bonham R. A.
Published: January 2005

The effect of inelastic electron scattering on the elastic, total, and discrete inelastic differential scattering cross sections is investigated in the second Born approximation. It is shown that in this approximation the polarization corrections can be written as a function of the Coulomb phase shift and other auxiliary functions to within an additive constant in the Coulomb phase. This constant is chosen by imposing the physically reasonable condition that the polarization correction must tend to zero with increasing scattering angle. The results of the calculation of polarization effects on the elastic scattering amplitudes for Ar and U are given for an incident electron energy of 40 kV.
Nuclear Quadrupole Resonance and Bonding in Crystalline Ammonia
Authors: Lehrer S. S. , O'Konski C. T.
Published: January 2005

Nuclear quadrupole coupling constants (eQq) of 14N have been determined as a function of temperature for each of the isotopic species NH3, NH2D, NHD2, and ND3 in the crystalline state. The temperature dependences are explained, following a theory proposed by Bayer, in terms of an averaging of the electric field gradient (q) by torsional lattice motions. Frequencies and moments of inertia known from other spectroscopic studies of NH3 and ND3 were employed in the calculations, which also led to values for the quadrupole coupling constants without zero-point vibrations. These values turned out to be the same (−3.47 Mc/sec) within 1% for NH3 and ND3, showing that the different field gradients for the various isotopic species in the crystalline solid are well explained in terms of lattice motions.

Comparison of the vibrationless, or ``quasistatic'' values, with the coupling constants of the gaseous molecules (−4.08 Mc/sec) then gave the shift produced by the crystalline field, here called the quasistatic shift. This is large relative to the changes produced by isotopic substitution in the gaseous molecule. Calculations of the electric field and the field gradient produced at a given 14N nucleus by surrounding molecules in the known crystal structure were made to explain the quasistatic shift. Molecules containing the nearest hydrogens were treated as a distribution of four point charges, and the others, to a total of about 100, were taken as point dipoles. Both models were consistent with a crystalline dipole moment evaluated from the gaseous value and the known molecular polarizability, taking into account the reaction field of the lattice. The quasistatic shift was orders of magnitude too large to be accounted for by the direct field gradient of surrounding neighbors; it is better described in terms of a redistribution of electrons in the nitrogen p orbitals by polarization of the molecule in the crystal field.
Cell-Cluster Method for Hard Squares
Authors: David C. W.
Published: January 2005

The partition function of four hard squares at high densities is calculated, and all the cell-cluster integrals associated with this partition function are evaluated. The use of higher cell-cluster integrals in this formalism does not ensure monatonic approach to the true partition function.
Electron Paramagnetic Resonance Spectra of the Ground-State Triplet Diphenylmethylene and Fluorenylidene Molecules in Single Crystals
Authors: Brandon R. W. , Closs G. L. , Davoust C. E. , Hutchison C. A. , Kohler B. E. , Silbey R.
Published: January 2005

The paramagnetic resonance spectra of the triplet ground states of diphenylmethylene and fluorenylidene molecules, oriented in single crystals, have been investigated. The fine structures and 13C hyperfine structures of these spectra have been studied and the parameters for best fit by a spin Hamiltonian have been determined. The implications of these results with respect to electron spin distribution and molecular structures have been examined.
Mobilities of Cesium and Rubidium Ions in Their Parent Vapors
Authors: Lee Yuan-tseh , Mahan Bruce H.
Published: January 2005

The mobilities of Rb+ and Rb2+ in rubidium vapor, and of Cs+ and Cs2+ in cesium vapor have been measured. The mobilities of the molecular ions agree well with values calculated from the Langevin theory in its polarization limit. The mobilities of the atomic ions are consistent with the predictions of simple resonant charge transfer theory. Rate constants for the reactions of the atomic ions with diatomic molecules to give diatomic molecular ions have been obtained.
SF4 and SOF2: Infrared Evidence for Dimer Formation at Low Temperatures
Authors: Redington R. L. , Berney C. V.
Published: January 2005

The infrared spectrum of SF4 trapped in an argon matrix at ∼4°K shows characteristic changes when the sample is warmed to allow diffusion and recooled. These changes are discussed in terms of association of the SF4 molecules, and their simplicity and stability suggest a simple model for the dimer and more highly associated species. Weak bonding appears to exist between the pair of equatorial F atoms on one SF4 molecule and the sulfur lone pair of electrons on an adjacent SF4 molecule. The spectrum of SOF2, present as an impurity, shows changes suggestive of the formation of an SF4–SOF2 complex. The observations, together with the NMR data of Muetterties and Phillips indicate that the mechanism for the rapid exchange of axial and equatorial fluorines in liquid SF4 at room temperature is not intermolecular. A low barrier for the inversion of isolated SF4 is also ruled out by the apparent absence of inversion effects in the microwave spectrum of the vapor, studied by Tolles and Gwinn. The conclusion is drawn that there are two possible paths for the dimerization or association reactions, and that one of these paths involves inversion of the SF4 molecule. The activation energy of the latter reaction corresponds closely to the inversion energy of SF4, which must be markedly smaller in this dimeric transition state than in an isolated SF4 molecule.
Infrared and Microwave Spectra of ClCN
Authors: Lafferty Walter J. , Lide David R. , Toth Robert A.
Published: January 2005

The microwave spectra of 35Cl12C14N and 37Cl12C14N have been obtained for molecules in the vibrational states ν1, 2ν20, and 2ν22. In addition, high-resolution infrared spectra have been obtained for the bands ν3, ν21+ν3, ν1+ν3, and 2ν20+ν3. Estimates for the frequencies of ν1 and ν21 have been made, and equilibrium and average bond distances have been calculated.
Comparison of Theories of the Helix—Coil Transition in Polypeptides
Authors: Poland Douglas C. , Scheraga Harold A.
Published: January 2005

Using Lifson's recent formalism of sequence-generating functions, several theories of the helix—coil transition in polypeptides are compared. The general helix—coil model, say as treated by Lifson and Roig, gives rise to a cubic secular equation. The largest root of this equation can be approximated closely by a quadratic equation, similar to the procedure of Zimm and Bragg, if isolated single helical states are assigned hydrogen bonds of positive (unfavorable) energy of formation. Equations are given to evaluate the effect of this artifice on the entropy of the random coil. It is pointed out that Peller's combinatorial theory, in its present form, significantly underestimates the combinatorial entropy due to the artifice of introducing a triplet of three amino acid residues (the span of a hydrogen bond) to define a unit. If the use of triplets as units is replaced by the use of amino acid residues, and if a positive energy of formation of a hydrogen bond is assigned to single helical states, then Peller's result is identical to the quadratic approximation.
Raman Intensities of HDO and Structure in Liquid Water
Authors: Wall Theodore T. , Hornig Donald F.
Published: January 2005

Photoelectric Raman spectra of HDO in 5-mole % isotopically substituted water show single, broad, slightly asymmetric bands in both of the regions containing the uncoupled fundamental stretching motions. An empirical correlation between O–H or O—D stretching frequency and O···O hydrogen-bonded distance has been used to map the frequency coordinate of the spectra onto an intermolecular distance scale, and the Raman bands are replotted on this abscissa. The resulting intermolecular distribution functions for liquid water agree with x-ray results and support the suggestion that the breadth of the HDO uncoupled stretching bands reflects the variation of intermolecular distance. Moreover, it is noted that the corresponding infrared and Raman bands are almost superposable, and that this indicates little hydrogen-bond breakage in liquid water. The distribution of intermolecular distances represented by the spectra is compared to that incorporated in some of the structural models for liquid water. It appears that a successful model should incorporate the homogeneity, isotropy, coherence, and disorder of the liquid in its local structure.
Magnetic Characteristics of Lanthanide—Bismuth Compounds
Authors: Tsuchida T. , Wallace W. E.
Published: January 2005

The magnetic behavior of the series of lanthanide—bismuth compounds having the formula LnBi was investigated over a range of temperature extending from 4° to 300°K and at field strengths ranging from 5 to 21 kOe. Ln represents Ce, Pr, Nd, Sm, Gd, Tb, Dy, and Er. Curie—Weiss behavior was observed in the upper portion of the temperature range covered for all except SmBi. Effective moments were obtained which were in close agreement with that expected from theory for the free tripositive ions. The behavior for SmBi resembles that of elemental Sm and other Sm intermetallics and is attributed to contribution of the first excited multiplet (J=7/2). Antiferromagnetic ordering was observed for all compounds except the Pr and Sm. A Néel point for the latter probably exists but below 4°K. PrBi exhibits only Van Vleck paramagnetism to the lowest temperatures studied. This is ascribed to crystal field splitting which produces a singlet (nonmagnetic) ground state. From the limiting susceptibility an over-all splitting by the crystal field of 140 cm−1 is estimated. CeBi exhibits metamagnetism with a critical field of about 10 kOe. Its behavior as a metamagnet is atypical and is generally complex in the region where magnetic ordering occurs.
Electrokinetic Energy Conversion in Ultrafine Capillaries
Authors: Morrison F. A. , Osterle J. F.
Published: January 2005

Energy conversion utilizing the electrokinetic effect associated with the flow of an electrolyte through ultrafine capillary tubes is investigated analytically. This represents an extension of previous work by one of the authors to capillaries of fineness such that the Debye length is an appreciable fraction of the radius. In addition to this extension, a model for surface conductivity, not considered in the earlier work but important for ultrafine capillaries, is proposed and its effect on conversion efficiency considered. By numerical integration of the Poisson—Boltzmann equation governing the radial potential distribution in the tubes for the case of pure water in glass capillaries, results are obtained for the surface conductivity and maximum conversion efficiency as a function of capillary radius.
Statistical Thermodynamic Theory for Helix—Coil Transitions Involving Poly- and Oligonucleotides. II. The Case of Partial Binding
Authors: Magee William S. , Gibbs Julian H. , Newell Gordon F.
Published: January 2005

Statistical thermodynamic properties of order—disorder transitions in one-dimensional lattices can be derived from partition functions formulated by means of the matrix method. Direct application is made here to systems comprised of doubly stranded molecular complexes analogous to that proposed for deoxyribonucleic acid (DNA). In the present treatment one strand (the lattice) is taken to be a polynucleotide to which oligonucleotides are attached through complementary hydrogen bonding. The oligonucleotides may be partially bound. Both the case that the species are homopolymeric and the case that they are copolymeric are investigated. Exact numerical and asymptotic results are presented which display the functional dependence of the transition temperature upon the degree of polymerization (D. P.) of the various species.