bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of Saturation and Double-Resonance Effects in ESR Spectra
Authors: Freed Jack H.
Published: January 2005

A theory of saturation in the electron spin resonance spectra of dilute solutions of free radicals has been developed in terms of the general Boltzmann equation for the density matrix given by Bloch and Redfield. It is shown, in contrast to the earlier theories, that, in general, a composite line arising from a set of degenerate nuclear spin states must be described by a generalized (matrix) saturated Lorentzian rather than a single line of over-all saturated Lorentzian shape. The general properties of this solution are discussed in detail for the case when electron—nuclear dipolar interactions are the only important nuclear-spin-dependent relaxation mechanism. A particularly simple situation exists when similar nuclei are completely equivalent. Then each composite line consists of a superposition of saturated Lorentzians, and the linewidths and saturation parameters of each component depend only on the values of the total spin and of the z component of spin of the associated configuration of the completely equivalent nuclei. Thus it would be possible to saturate some components to a greater extent than others. These simple components may become coupled together in a complex fashion when the time-dependent fluctuations of the dipolar interactions for equivalent nuclei are no longer identical, which is often the case for aromatic-ring protons. Further coupling may be expected from the effects of nuclear-quadrupole interactions and from intermolecular-exchange phenomena and are only qualitatively discussed. In the absence of saturation the present theory reduces to the linewidth theory of Freed and Fraenkel.

Detailed expressions are obtained for steady-state electron—nuclear double-resonance (ENDOR) effects on radicals containing completely equivalent sets of nuclei. The saturating fields can lead to coherence and induced-transition effects. It is shown how the latter, under appropriate conditions, can result in enhancement of saturated ESR spectra. It appears necessary for enhancements that lattice-induced nuclear spin transitions should be comparable in magnitude to the lattice-induced electron spin transitions, or else cross transitions involving both nuclear and electron spins must be important in the relaxation process. Coherence effects involving both electron and nuclear spin transitions should be unimportant when the main contribution to the ESR linewidths results from secular processes and is nuclear spin independent. This is also the condition for NMR linewidths to be significantly narrower than ESR linewidths. Complications still arise from the coherence and linewidth coupling effects of the different nuclear transitions being excited. A brief discussion of enhancement by a transient ``heating'' effect is also given.
Matrix Formulation of Copolymerization Statistics. II. Extensions to Multimonomeric Systems
Authors: Peller Leonard
Published: January 2005

A matrix formulation of copolymerization statistics for binary systems presented earlier is modified and generalized to include multicomponent monomeric systems. The results are applied to condensation copolymerizations for which a kinetic description is also developed. This approach serves to systematize rather diverse results for linear condensation polymerizations. A particularly simple form for the distribution statistics of copolymeric systems in thermodynamic equilibrium is obtained. The steady-state approximation, which affords a matrix representation for the distribution of radical chains, is employed to provide a description of the distribution of stable copolymeric species formed by two types of termination processes. A generalization is presented for a binary copolymeric system with a chain memory which includes the penultimate unit. A modification of the present analysis is suggested which may be applicable to the treatment of the configurational sequences in stereoregular homopolymerizations where the statistics of the analogous copolymerizations are not Markoffian.
Effect of Pressure on the Dielectric Properties of Ice I
Authors: Chan R. K. , Davidson D. W. , Whalley E.
Published: January 2005

The effect of pressure up to about 2 kbar on the dielectric properties of Ice I at − 23.4° has been measured. The static dielectric constant increases with increasing pressure by about the amount predicted by the Kirkwood theory. The increase in relaxation time yields a volume of activation for the relaxation process of 2.9±0.2 cm3 mole−1 which supports current views that dielectric relaxation occurs by rotation at orientational defects. The volume of activation given by the rapid rise of dc conductivity with increasing pressure is − 11±∼3 cm3 mole−1 which is consistent with the proton-transfer mechanism.
Dielectric Properties of Ices II, III, V, and VI
Authors: Wilson G. J. , Chan R. K. , Davidson D. W. , Whalley E.
Published: January 2005

The dielectric properties of Ices II, III, V, and VI have been measured up to 300 kc/sec over a range of temperatures and pressures. All except Ice II exhibited well-defined dielectric dispersion and so are orientationally disordered under the experimental conditions. The dispersion loci were slightly broader than Debye curves, which may reflect the presence of nonequivalent crystal sites. As for Ice I, the static dielectric constants correspond to values of about 3 for the Kirkwood orientational correlation factor. This suggests that these forms of ice are four coordinated, in agreement with infrared and (for Ice III) x-ray evidence at low temperatures. The relaxation rates are considerably faster than for Ice I, and the activation energies and entropies somewhat lower. The volumes of activation are all about 4.6 cm3 mole−1. The relaxation mechanism appears to be similar to that in Ice I, i.e., relaxation occurs by diffusion of orientational defects.

X-ray and infrared studies have indicated that Ice II is rotationally ordered near liquid-nitrogen temperature. The absence of orientational polarization in Ice II at temperatures as high as −30° shows it to be ordered throughout its region of stability.
Study of the Properties of an Excess Electron in Liquid Helium. I. The Nature of the Electron—Helium Interactions
Authors: Jortner Joshua , Kestner Neil R. , Rice Stuart A. , Cohen Morrel H.
Published: January 2005

In this paper we present a theoretical study of the free and localized states of an excess electron in liquid helium. Electron—helium interactions are treated by the pseudopotential method, while multiple scattering effects on the properties of a quasifree electron in the dense fluid are treated using the Wigner—Seitz model. It is demonstrated that the plane-wave state is not the lowest energy state for an excess electron in liquid helium and that fluid deformation leads to a localized state of lower energy. The large, repulsive helium-atom pseudopotential coupled with the small helium polarization potential lead to electron localization which may be attributed entirely to short-range repulsions. The following experimental observations are adequately interpreted by these results: (a) The energy barrier of liquid helium for electrons, (b) the density-dependent transition from a delocalized state to a localized state of the excess electron, (c) the mobility of an excess electron in normal 4He and in 3He. Pressure and temperature effects on the electron bubble are also discussed. It is concluded that a pressure-induced transition from the localized to the delocalized state of the excess electron will not occur in the fluid domain even at high pressures. Finally, we present some speculations concerning the optical properties of the excess-electron center.
Molecular Entanglement Theory of Flow Behavior in Amorphous Polymers
Authors: Graessley William W.
Published: January 2005

An approximate molecular theory of steady flow in amorphous polymers has been developed by considering the properties of a deforming entanglement network. The dynamics of entanglement formation between pairs of molecules and its influence on the density of entanglements during steady deformation were examined. From a simple model for these processes, apparent viscosity was calculated as a function of the shear rate. An approximate calculation of the normal-stress differences was also made. The viscosity was found to be dependent on the rate of deformation, and at sufficiently high shear rates it approached proportionality with (shear rate)−¾. The onset of non-Newtonian behavior occurs in the same region of shear rates as that predicted by the coil-distortion theory of steady flow. However, unlike the predictions of the latter theory, dynamic-viscosity frequency curves and apparent-viscosity shear-rate curves should not necessarily superimpose, because the dispersion mechanisms are fundamentally different in the two cases. Comparison with experimental results reported in the literature showed generally satisfactory agreement in both the shape of the viscosity master curves and in the order of magnitude of the normal-stress differences.
ESR Spectra and Structure of the Fluorinated Methyl Radicals
Authors: Fessenden Richard W. , Schuler Robert H.
Published: January 2005

The ESR spectrum of the CF3 radical has been observed during the irradiation of liquid C2F6. The isotropic fluorine hyperfine splitting in this radical has a value of 144.75 G which is considerably larger than other known values for α fluorine atoms. Well-resolved spectra of CF3·, CHF2·, and CH2F·, as well as certain of the lines of the 13C containing radicals, have also been observed in krypton and xenon matrices. The 13CF3 and 13CHF2 radicals have carbon hyperfine constants of 271.6 and 148.8 G showing that the unpaired electron is in an orbital with considerable s character and that these radicals are therefore non-planar. The carbon and fluorine splittings in CF3· are sufficiently large that third-order correction terms are necessary in considering the line positions. As a result it is demonstrable that the carbon and fluorine hyperfine constants are of the same sign.
Calculated Bonding in the Pseudohalide Anions and Their Hydracids
Authors: Wagner E. L.
Published: January 2005

The bond characters and energies of the nitrogen-containing pseudohalide anions, CN−, N3−, NCO−, NCS−, NCSe−, NCTe−, and their common hydracids, as well as some related isoelectronic systems, have been calculated using an internally consistent procedure based on the utilization of ``unsymmetrical group orbitals'' (LCGO method). Coulomb integrals are related to the valence-state electronegativities which are obtained by three different procedures. It is concluded that the results are more sensitive to the rate of change of the Coulomb integral with charge than to the value of the Coulomb integral itself. This LCGO—MO method greatly simplifies the calculations and gives results identical with the longer LCAO procedures which correlate well with the physical and chemical properties of the substances. The calculations account for the relative acid strengths and correlate quantitatively with the experimentally determined C–N stretching-force constants and 14N NMR chemical shifts.
Ultrasonic Absorption in Sodium Metaborate Solution
Authors: Yasunaga Tatsuya , Tatsumoto Nobuhide , Miura Masaji
Published: January 2005

The kinetics of reaction in the dilute aqueous solution of sodium metaborate have been studied by ultrasonic absorption measurements over the frequency range from 50 kc/sec to 75 Mc/sec. Single relaxation frequencies have been observed in 0.05, 0.1, and 0.2M at 25°C and in 0.1M at 35°C, and the absorption mechanism has been assigned to be due to the hydrolysis of metaborate ion. The corresponding forward and backward rate constants calculated for the reaction BO2−+H2O⇌HBO2+OH− are 4.11×103 sec−1 and 2.36×108M−1 sec−1 at 25°C for 0.05M solution, respectively. From the magnitude of the relaxational acoustic absorption per wavelength, the partial molal volume change ΔV° for the process is calculated to be 6.83 cm3/mole at 25°C for the 0.05M solution. The temperature dependence of the relaxation frequency indicates that the energies of activation for the reaction are 12.6 and 1.31 kcal/mole for the forward and backward reactions, respectively.
NMR Study of Complex Ions in the Aqueous ZnO–KOH System
Authors: Newman Gerald H. , Blomgren George E.
Published: January 2005

Proton magnetic resonance measurements of the aqueous ZnO–KOH system have been made. Only a single resonance line is observed, but the position of the line depends on the concentrations of KOH and ZnO. Analysis of the data is consistent with the presence of only one zincate species. A value for the chemical shift of the zincate ion is derived, and also a more precise value for the chemical shift of KOH in water is determined. The significance of the results is discussed.
Behavior of Ion Spurs and Tracks in Irradiated Dipolar Systems
Authors: Schiller Robert
Published: January 2005

The problem of electron moderation and subsequent recapture or escape in irradiated dipolar substances is investigated theoretically. By considering the dielectric relaxation, the electric energy of a spur or track consisting of positive ions and diffusing electrons is evaluated. The moderation being fast as compared with the dielectric relaxation time, the energy content of the spur or track decreases due to an increase in the dielectric constant after the moderation has been completed. At the expense of this energy decrease, some thermalized electrons may diffuse away from the field of the positive ions if they are slow enough not to increase the spur energy faster than it is decreased by dielectric relaxation. The theory is tentatively applied to γ and α-irradiated water and ice and, while a substantial fraction of electrons is found capable of escaping in the liquid state, for the crystalline state complete recapture is predicted.
Vibronic Contribution to the Infrared Intensities of Benzene
Authors: Brown Theodore L.
Published: January 2005

Vibronic contributions from the π-electron system to the intensities of the in-plane normal modes of benzene have been evaluated theoretically in terms of Pariser—Parr—Pople semiempirical π-electron theory. The vibronic terms arise in the benzene intensities because of changes in the two-center electron-repulsion integrals, and in the one-electron one-center core integrals, during the normal coordinate displacements. They are very important in determining the intensities of all three in-plane modes. The results indicate that a model which treats the intensities in terms of localized bond dipoles and bond dipole-moment derivatives is untenable in any molecule where vibronic terms may enter. The vibronic terms do not appear to give rise to unusual intensity changes in the 1033- and 1489-cm−1 bands in condensed media as compared with the gas phase, but there may be a major vibronic term involved in the unusual decrease in the 3080-cm−1 band intensity in solid benzene.
Electronic Specific Heats of Alloys of the MgCu2—xAlx System
Authors: Slick Paul I. , Massena Charles W. , Craig R. S.
Published: January 2005

Specific-heat measurements were made on a series of alloys of the pseudobinary system MgCu2—xAlx between 1.5° and 4.2°K. The compositions studied ranged from MgCu2 to MgCu1·15Al0·85, and included 11 alloys having the MgCu2 structure, two having the MgNi2 structure, and three in the two-phase region. From the measured values of γ, the density of states at the Fermi level N (EF) was calculated.

The variation of γ with composition shows a maximum at 1.44 electron/atom and a shoulder on the curve at 1.60 electron/atom. A rapid decrease in γ occurs just before the two-phase region is reached at 1.72 electron/atom. This is followed by a linear increase in the two-phase region as the phase with the MgNi2 structure is approached. The trend of γ and N (EF) with composition shows close correlation with published magnetic-susceptibility data. The variation of N (EF) with composition in the cubic (MgCu2) phase is discussed in terms of interactions between the Fermi surface and Brillouin zone faces, and a comparison is made between measured values of N (EF) and the results of theoretical calculations by Bode and Schnabl.
Paramagnetic Resonance of Alkyl Radicals from Dissociative Electron Attachment in γ-Irradiated Organic Glass
Authors: Skelly D. W. , Hayes R. G. , Hamill W. H.
Published: January 2005

The radicals CH3·, CH3CH2·, CH3CH2CH2·, (CH3)3C·, (CH3)3CCH2·, and C6H5ĊHCH3 have been identified by EPR in γ-irradiated dilute solutions of the corresponding halides in 3-methylpentane at 77°K. For 0.4 mole % CH3I, G(CH3·)=1.2. Methyl radicals disappear by some first-order rate process for which k=4.6×10−4 sec−1. Other radicals did not decay measurably under similar conditions. The results are consistent with the mechanism of dissociative thermal electron attachment, RX+e−→R·+X−, which is an efficient, selective process whenever the electron affinity of X exceeds the bond dissociation energy of R—X.
Calculation of Energies of Excited States
Authors: Goodisman Jerry
Published: January 2005

Using arguments previously employed for derivation of lower-bound principles, we derive a new method for obtaining an upper bound on the nth eigenvalue of a Schrödinger-type equation. The method requires a knowledge only of the single eigenvalue immediately below that being sought—the corresponding wavefunction is not needed, as trial functions need not be orthogonalized to lower states. We illustrate the method on the 2Σg+ states of H2+, using a two-parameter trial function. For instance, we obtain −0.3265 a.u. as an upper limit on the energy of the first excited level (true value=−0.36086 a.u.) and −0.07 a.u. for the second (true value = −0.24 a.u.).
Carbon Dioxide Dissociation at 6000° to 11 000°K
Authors: Davies William O.
Published: January 2005

The dissociation rate of CO2 has been measured for temperatures from 6000° to 11 000°K. The rate of disappearance of CO2 behind reflected shock waves in a 1%-CO2−99%-Ar gas mixture was monitored by observing infrared radiation from the 2.7-μ CO2 combination bands. The dissociation rates expressed in classical collision theory and an Arrhenius equation are (in cubic centimeters per particle·second), respectively, kAr=(8.95)(10−13)(D/kT)3.21 exp(−D/kT) and kAr=(1.92)(10−13)T12 exp(−2.96 eV/kT) where D=5.5 eV is the CO2 dissociation energy, k is the Boltzmann constant, and T is the absolute temperature. A rate constant was also determined from observations of the CO flame band emission at a wavelength of 3500 Å, which, at equilibrium, is proportional to the product of the CO and O concentrations. The rates determined from these measurements are about a factor of three lower than those obtained from the infrared measurements, and the process has an activation energy of 3.68 eV compared to the 2.96 eV for the infrared measurements. It is suggested that the infrared observations are a measure of the CO2 dissociation, while the flame band emission is controlled by the recombination of CO and O into an excited CO2 electronic energy level and the radiative life time of this CO2 level. A summary is given of CO2 dissociation measurements obtained with both methods over a temperature range from 2600° to 11 000°K.
M Centers in Potassium Bromide. I
Authors: Neubert Theodore J. , Susman Sherman
Published: January 2005

Oriented distributions of M centers have been produced in KBr and the resulting anisotropic spectra measured at −76° and −194°C. Dichroic absorption bands are observed corresponding to transitions from the ground state to a variety of higher excited states. Included in these are previously unreported transitions that lie 0.7–1.1 eV to higher energy than the F band. Some energy-level assignments are made using the F2 model of the M center.

A simplified treatment is presented for the interpretation of dichroic spectra arising from the optical dipole transitions of anisotropic centers in an otherwise isotropic lattice.
Hard-Sphere Lattice Gases. I. Plane-Square Lattice
Authors: Gaunt David S. , Fisher Michael E.
Published: January 2005

A plane-square lattice gas of hard ``squares'' which exclude the occupation of nearest-neighbor sites is studied by deriving 13 terms of the activity and the virial series and nine terms of appropriate high-density expansions. Using the ratio and Padé approximant extrapolation techniques it is found that the gas undergoes a continuous (or ``second-order'') transition to an ordered state at an activity zt=3.80±2 and a density ρt=(0.740±0.008)ρmax. The ordered state is characterized by a difference of the sublattice occupation probabilities, R(z), which vanishes at the |transition as (z—zt)β with β≈⅛. The pressure at the transition is given by pa2/kBT=0.792±5. The compressibility exhibits a maximum at or near the transition point but probably remains finite and continuous through the transition. A suitably defined ``staggered compressibility,'' which measures the tendency towards sublattice ordering, diverges sharply as the transition is approached from either side.

A double expansion which converges at all densities is derived and examined numerically and the exact behavior of finite lattices of N=4, 16, 20, and 24 sites is discussed.
Theoretical Considerations Concerning the Intramolecular Heavy-Atom Effect on the Phosphorescence Process: C2v Symmetric Dihalonaphthalene
Authors: El-Sayed M. A.
Published: January 2005

Interactions leading to the observed intramolecular heavy-atom effect on the phosphorescence process of C2v dihalonaphthalenes have been examined. Using one electron operator, the observed heavy-atom effects in these molecules are found to be due to:

(1) Mixing between the Pπ orbitals of the halogen and the π system of the aromatic hydrocarbon.

(2) First-order spin—orbit interaction between the lowest π, π* triplet state and σ, π* (or π, σ*) singlet states (this explains Subspectrum I).

(3) Second-order spin—orbit—vibronic interaction between the lowest π, π* triplet state and π, π* (or σ, σ*) singlet states (this accounts for the appearance of Subspectrum II). These mechanisms are found to give rise to one-center spin—orbit terms on the halogen atom (as well as halogen—carbon two- and higher-center terms). First-order spin—orbit interaction between singlet and triplet π, π* states is found to have vanishing one- and two-center terms involving the halogen orbitals. Direct spin—orbit interaction between π, π* states in haloaromatics does not give rise to intramolecular heavy-atom effect. Mechanisms involving the first-order spin—vibronic terms of the total Hamiltonian are found to give predictions inconsistent with the observed results and thus seem to be unimportant.

The S.O. matrix elements for the A31(σ,σ* or π,π*)↔3B1(σ,π* or π,σ*) is found to vanish for 1,4- but not for the 2,3-dihalonaphthalene. This result, together with the fact that the 1A1 (σ,σ*)←1A1 transition has zero moment for 1,4-dihalonaphthalene but not for the 2,3 derivative, leads to the conclusion that for the 1,4 compound, only the 1B2 (σ,σ* or σ,σ*) (short axis polarized) is an important perturbing singlet state while both the 1B2 and the 1A1 are perturbing the emitting triplet state in the 2,3 derivative. This is found to be in agreement with the observed fact in glasses at 77°K that in the 1,4 derivative, Subspectrum II is highly polarized and parallel to the 1La←1A1 transition (short axis polarized) whereas in the 2,3 derivative, Subspectrum II is almost depolarized with respect to 1La excitation. Using the proposed mechanism it is shown, in agreement with observation, that the relative importance of Mechanism I (giving rise to Subspectrum I) to that of II is practically independent of the atomic number of the halogen. The fact that Mechanisms I and II are comparably important even though Mechanism I involves a first-order interaction whereas II involves a second-order interaction is shown to result from the great difference in the values of the oscillator strength of the perturbing singlet states involved in the two mechanisms.
Semiclassical Theory of Rotational Excitation of a Diatomic Molecule by an Atom
Authors: Lawley K. P. , Ross John
Published: January 2005

The problem of translation—rotation energy exchange is investigated for systems, like K–HBr, for which the energy exchange ΔE is a sizable fraction of the relative kinetic energy, the matrix elements of the potential of interaction are large, and the period of interaction is of the order of ℏ/ΔE. A representation of the wavefunction is chosen where the rotor functions are separately quantized along the moving interparticle axis. This choice implies a coupling scheme for the angular momenta, which is compared with two other schemes commonly used. The time-independent Schrödinger equations for the three coupling schemes yield identical results for the transition probability if solved exactly, or in the first-order Born approximation, but not if solved in the first-order distorted wave approximation. Intermultiplet transitions are a non-adiabatic effect and independent of the strength of the anisotropic part of potential in the (jμ) scheme, and hence their neglect leads to considerable simplication. The same results are shown to hold for the transition probability obtained from solutions of the time-dependent Schrödinger equation obtained by using basis functions quantized along fixed or moving axes. The connection between the time-dependent and time-independent formulations is made with the choice of a suitable classical trajectory based on a WKB solution of translational motion. The quantum-mechanical, time-dependent differential equations for the coefficients in the (jμ) representation, obtained by the method of variation of constants with the time-dependent potential derived from a classical trajectory, are solved numerically in the following article.
Critical Opalescence of a Fluorocarbon—Hydrocarbon Binary Liquid Mixture: Normal Perfluoroheptane—Iso-octane
Authors: Chu B. , Pallesen M. , Kao W. P. , Andrews D. E. , Schmidt P. W.
Published: January 2005

Critical opalescence of a binary liquid mixture, normal perfluoroheptane and iso-octane has been investigated by light and small-angle x-ray scattering over a broad range of s/λ, where s=2 sin (θ/2), λ is the wavelength in the medium, and θ is the scattering angle. The scattering data show that the critical opalescence observed in this system is essentially the same as has been found in other binary liquid mixtures.
Vibrational States of the Hydrogen Molecular Ion
Authors: Wind H.
Published: January 2005

The energy levels of H2+ are computed for all vibrational quantum numbers and for rotational quantum numbers up to J=8. The accuracy of the energy of the uppermost levels is estimated to be better than 10−7.
Measurement by NMR of the Diffusion Rate of HF in Ice
Authors: Kopp Marcel , Barnaal Dennis E. , Lowe Irving J.
Published: January 2005

An experiment is described by which the diffusion of fluorine in monocrystalline ice cylinders is followed quasicontinuously, using the proton magnetic resonance spin—lattice relaxation time T1 to measure the HF concentration along the sample. The diffusion coefficient DF was evaluated for various temperatures between −30° and −4°C. The results show more scatter than the experimental error can account for. A least-squares fit of our data yields DF (−10°C)=0.8×10−6 cm2/sec for the diffusivity and E=0.58 eV=13.4 kcal/mole for the activation energy, with root-mean-square deviations of 0.5×10−6 cm2/sec and 0.08 eV, respectively. We find that the highest concentration of diffused HF which can be absorbed by monocrystalline ice is about 4×10−5 HF/H2O. A possible explanation is offered for the large value and dispersion of the diffusivity.
Intrinsic and Lattice-Induced Distortion of the Tetrachlorocuprate Ion
Authors: Sharnoff Mark , Reimann Curt W.
Published: January 2005

In an effort to determine how much of the distortion of the tetrahedral complex, CuCl42−, may be ascribed to the Jahn—Teller effect, we have studied the changes in the optical and EPR spectra which occur when this ion is embedded in several different lattices. Although the corresponding lattice constants of the isostructural crystals Cs2CuCl4 and Cs2ZnCl4 differ by only about 3%, gross differences exist between the g tensors of CuCl42− suspended in these lattices. These findings are corroborated by a comparison of the optical spectra of the two complexes. The effects are discussed in terms of an LCAO—MO analysis of the primarily 3d(Cu) wavefunctions of the complex, and it is shown that the changes in ionic properties are connected principally with a change in the amount of ligand character in the e, primarily 3d orbitals. The analysis points towards the conclusion that the low symmetry (point group Cs) of the ion is an intrinsic property and that the dominant mechanism of the tetragonal component of the distortion of the ionic symmetry from Td is the Jahn—Teller effect.
Molecular Rydberg Transitions in Rare-Gas Matrices—Evidence for Interaction Between Impurity States and Crystal States
Authors: Pysh E. S. , Rice Stuart A. , Jortner Joshua
Published: January 2005

As a first step in characterizing molecular Rydberg states in the solid state, the absorption spectra arising from acetylene and benzene impurity states in solid krypton and argon in the far-ultraviolet region have been obtained. The first member of the acetylene Rydberg series, which appears at 8.155 eV in the gas phase, is observed to be shifted to 8.67 eV in a krypton matrix and to 9.01 eV in an argon matrix. These large energy shifts are discussed, particularly with reference to the optical spectra of rare-gas solids and rare-gas alloys, where similar large blue shifts are observed. The far-ultraviolet spectra of benzene trapped in krypton and argon matrices show a qualitatively different phenomenon. The Rydberg states of benzene are observed to interact with conduction-band continuum states to exhibit anomalous Fano-type line shapes. The Rydberg states repulse the neighboring continuum states to produce sharp decreases in the continuum absorption intensity. These results are discussed in connection with other systems which show Fano-type line shapes.
Numerical Calculation of H2 and HeH+ Wavefunctions
Authors: Goodisman Jerry
Published: January 2005

Use of purely numerical techniques to evaluate integrals allows for greater flexibility in the trial functions used for variational calculations. For two-electron problems, we have used crossed Gauss quadratures in four dimensions. Accuracy can be assessed in terms of the effect of increasing the number of integration points. Previously given formulas are modified, for singular integrands, so that results are monotonic with the number of points in any dimension, and the new formulas are tested on H2 and on the HeH+ ground state. The meaning of linear dependence of basis functions in the framework of Gauss integration is discussed. The first excited 1Σg+ state of HeH+ is investigated, and found to be nonbonding. The basis functions used here were James—Coolidge functions modified to include polar character. Another example of the flexibility of the numerical method is the use of correlation functions of simple analytical form. This is illustrated with the Gaussian exp(γr122), while formulas are given for calculation with any correlation function expressible as a power series in r12.
Use of Fock-Petrashen and Hydrogenic Orbitals in Single-Center Wavefunctions
Authors: Bishop David M.
Published: January 2005

The use of Fock—Petrashen, Slater, and hydrogenic orbitals within the single-center method is studied and compared for a single determinantal wavefunction of H2O. The use of Slater orbitals is found to be superior and the reasons for this are given.
Mechanism for Ion—Neutral Association Reactions
Authors: Mahan Bruce H.
Published: January 2005

The formation of diatomic molecular ions from atomic ions in the presence of their parent atoms can take place by a three-body association reaction that involves resonant charge transfer. An approximate rate constant for this process can be formulated simply, and calculated rates are in good agreement with experimental data. This mechanism should be an important loss process for ions moving rapidly in a low-temperature gas.
Vanadyl Bond-Length Variations
Authors: Hon Ping-Kay , Belford R. Linn , Pfluger C. E.
Published: January 2005

Alternate refinements of previously reported x-ray-diffraction data for vanadyl acetylacetonate and vanadyl benzoylacetonate provide evidence that the primary vanadyl linkage is considerably longer in the benzoylacetonate.
Nuclear Magnetic Resonance Study of Metal-Ion Binding to Adenosine Triphosphate. II. Proton Studies
Authors: Sternlicht H. , Shulman R. G. , Anderson E. W.
Published: January 2005

We have studied the high-resolution proton NMR spectrum of adenosine triphosphate (ATP) bound to the paramagnetic metal ions Mn2+, Ni2+, and Co2+ from 0° to 90°C at different concentrations of metal and ATP. In conjunction with our 31P study, we conclude that in the MnATP and NiATP complexes the metal ion is bound to the adenine ring all the time it is bound to the phosphates. At 298°K the average time the metal ion sticks to the adenine was measured to be (5±1)×10−6 and (1±0.15)×10−3 sec for MnATP and NiATP, respectively. The corresponding times measured for the phosphates were (5±1)×10−6 and (7±2)×10−4 sec. The excellent agreement between these sticking times indicates that the bonds to adenine and phosphates are made and broken simultaneously. The metal ion was located at a position in space between the amino group on C6 and N7 in the adenine ring by triangulation from the three protons H8, H2, and H1′. The triangulation was made from measurements of T1 under conditions where 1/T1∝ (μ/r3)2τc. The magnetic moment μ and correlation time τc of the metal ion with respect to the proton were determined independently. Therefore, r, the distances from the H8, H2, and H1′ protons to the metal ion, were determined. In CoATP the distances determined were the same as for the other metal ions. From this and from its similar behavior to CoITP (inosine triphosphate) where chemical evidence favors ring binding, we conclude that in CoATP as well as NiATP and MnATP the metal is bound to the ring.
Partial Wave Calculation of the Diatomic Molecule (HeH)++
Authors: Rabinovich Harris
Published: January 2005

The solutions to the Schrödinger equation for the diatomic molecule (HeH)++ in the Born—Oppenheimer approximation have been expanded in a series of partial waves, and radial equations have been derived. These radial equations have been solved numerically for the first three orders of approximation and the energy eigenvalues and wavefunctions have been obtained for seven different Σ states at various values of the internuclear separation. The numerical wavefunctions have been used to calculate dipole transition integrals and dipole moments.
Matrix Isolation Study of the Photolysis of Cyanogen Azide. The Infrared and Ultraviolet Spectra of the Free Radical NCN
Authors: Milligan Dolphus E. , Jacox Marilyn E. , Bass Arnold M.
Published: January 2005

The infrared and ultraviolet absorption spectra of the free radical NCN have been observed following photolysis at wavelengths longer than 2800 Å of cyanogen azide isolated in argon, nitrogen, carbon monoxide, and carbon dioxide matrices. The infrared-active vibrational fundamentals of NCN appear at 423 and at 1475 cm−1. Isotopic studies are consistent with this identification. The force constants and thermodynamic properties of NCN have been estimated. Two ultraviolet absorption systems are associated with NCN. The first of these, previously reported, lies near 3290 Å. The second system is comprised of a progression of bands spaced at intervals of approximately 1045 cm−1, lying between 3000 and 2400 Å. The nature of this second transition is discussed. At wavelengths longer than 2800 Å both cyanogen azide and NCN have been found to photolyze with the production of carbon atoms. The nature of the new features observed in the infrared and ultraviolet spectral regions after photolysis with short-wavelength radiation is considered.
Nuclear Magnetic Relaxation of Polymer Solutions
Authors: Ullman Robert
Published: January 2005

A theory of nuclear magnetic relaxation of solutions of chain macromolecules is presented. The relaxation takes place because of the relative motion of segments of the polymer chain containing magnetic nuclei. The analysis is based on the Brownian motion of isolated polymer molecules using a model which has been applied previously for dynamic viscoelasticity and dielectric relaxation of polymer solutions.

The relative motion of magnetic nuclei may be considered as arising from three sources: (a) the relative motion of pairs of atoms rigidly attached to a chain segment, (b) the relative motion of chain segments, and (c) the motion of atoms relative to a chain segment to which they are attached. Cases (a) and (b) are treated here.
Infrared Spectra and Intensity Enhancements in Solutions of Hydrogen Halides in Liquid Xenon
Authors: Goldring H. , Kwok J. , Robinson G. W.
Published: January 2005

The intensities and shapes of the vibrational fundamental bands of HCl, HBr, and HI dissolved in liquid xenon at 165°K are examined at the resolution of a Beckman IR-7. While no rotational fine structure was observed, rotational branch maxima were exhibited in all three cases. The spectra of the dissolved molecules are different from those of the gaseous molecule in that they exhibit a strong Q branch and probably also O and S branches. This observation should be compared with spectra of hydrogen halides in dense gases where a Q branch is prominent, and with spectra of such molecules in solid rare gases where ordinarily a strong Q branch is not produced. The extended selection rules in the liquid are probably caused by anisotropic fields which are capable of mixing J states. In this sense, the rotational motions of the hydrogen halides in liquid xenon are not ``free.'' The large intensity enhancements, 2.8 for HCl, 3.1 for HBr, and 44 for HI, are inadequately explained on the basis of dielectric polarization effects. Nuclear distortion effects on the intensity enhancements are shown to be negligible. It is concluded that electronic distortion effects must account for the enhancement. A semiquantitative description based on the lowering of ionic states of the hydrogen halides in the presence of the dielectric medium indicates that for each of the halides studied about one-sixteenth of an electron moves from the proton to the halogen when the molecule is dissolved. This is sufficient electronic distortion to account for the intensity enhancement in all three molecules. This increased ionicity should manifest itself not only in infrared intensity enhancements but also in permanent dipole moment corrections for dissolved polar molecules. The permanent moment corrections may exceed those given by the Onsager dielectric theory.
l-Type Doubling in Energy Levels of Carbon Dioxide Coupled by Fermi Resonance
Authors: de Heer J. , Nielsen Harald H.
Published: January 2005

In this paper we discuss the l-type doubling in levels of linear molecules which are coupled by Fermi resonance; in particular we consider here a triad of such levels in carbon dioxide. In principle, it becomes necessary to consider simultaneously the perturbations related to both anharmonic resonance interaction and l-type doubling. A further analysis reveals, however, that we are justified in carrying out an approximate solution, in which we first consider the resonance interaction as if l-type doubling did not occur and subsequently find the energy levels associated with +l and —l as a result of small perturbations on the two-fold degenerate levels involved. It appears that the applicability of the well-known formula Δν=qJ(J+1), in which q is the l-type doubling constant, is inherent to this approximation. The agreement between q values computed by our method and those obtained experimentally is very satisfactory indeed.
The Catalytic Conversion of Parahydrogen by Paramagnetic Complex Ions in Aqueous Solution
Authors: Wilmarth W. K. , Baes C. F.
Published: January 2005

Rates of conversion of parahydrogen by paramagnetic complex ions of copper (II) and chromium (III) in aqueous solution have been measured at 25°C. The results are discussed in terms of the Wigner theory, which predicts the effects of magnetic moment and collision distance. Owing to the planar configuration of the copper (II) complexes, only a qualitative test of theoretical predictions is possible. The rate effects produced by various symmetrical octahedral complexes of chromium (III) can be explained in terms of the theory if one evaluates the various collision distances for H2 from a detailed examination of the complex structure in each case.
Nonisotropic Propagation of Combustion Waves in Explosive Gas Mixtures and the Development of Cellular Flames
Authors: Manton John , von Elbe Guenther , Lewis Bernard
Published: January 2005

The phenomenon of nonisotropic propagation consists in the spontaneous development of blisters or cells on the surface of a combustion wave. The present experiments on spherical flames and the experiments of Markstein on flames in wide tubes show that the phenomenon is characteristic of nonstoichiometric explosive mixtures in which the deficient reactant constituent is also the constituent of largest diffusivity. This suggests that the phenomenon is primarily caused by the effect of diffusion processes on the burning velocity. It is proposed that in curved areas of the wave that are convex with respect to the burned gas, the burning velocity is reduced because the lines of diffusion diverge, and hence the concentration of the faster diffusing constituent decreases; whereas in concave areas the lines of diffusion converge, and hence the concentration of the faster diffusing constituent increases. In rich mixtures of hydrocarbon and oxygen, additional evidence for the effect is furnished by the emergence of carbon streamers and by characteristic changes of light emission from convex wave areas, showing that the oxygen concentration, and probably therefore the burning velocity, is decreased in these areas below the average for the mixture.
Electrical Conductivity of Silver Sulfide
Authors: Hebb Malcolm H.
Published: January 2005

Mixed electronic and ionic conduction in silver sulfide is examined. The importance of terminal conditions which may affect the ratio of ionic to electronic currents in experimental measurements is emphasized. In particular, either the electronic or ionic components can be completely suppressed. This is the basis of a new method of measuring the ionic and electronic conductivities independently, as functions of the chemical potential ζ of the silver component. The electronic conductivity is found to vary as expBζ both above and below the transition at 177°C. However, the coefficient B changes abruptly from e/kT below the transition to e/2kT above. This result can be understood theoretically in terms of the following picture: Excess silver is present mainly as dissolved atoms below the transition and as dissociated ions and electrons above. In the former case, only the electrons contribute to ζ, whereas in the latter there is a contribution both from the electrons and the ions.
Decomposition of Di-t-butyl Peroxide and Kinetics of the Gas Phase Reaction of t-butoxy Radicals in the Presence of Ethylenimine
Authors: Brinton Robert K. , Volman David H.
Published: January 2005

The reaction of di-t-butyl peroxide with ethylenimine has been studied between 129° and 154°C. The t-butoxy radicals formed by the rupture of the O–O bond of the peroxide, (CH3)3COOC(CH3)3→ lim k12(CH3)3CO,are postulated to enter into the following reactions: (CH3)3CO→ lim k2CH3COCH3+CH32CH3→ lim k3C2H6CH3+(CH2)2NH→ lim k4(CH2)2N+CH4(CH3)3CO+(CH2)2NH→ lim k5(CH2)2N+(CH3)3COH.The rate constant for the unimolecular decomposition of the peroxide into t-butoxy radicals is found to be in the range k1=6×1014e−36,000/RT to k1=6×1016e−40,000/RT sec−1. The activation energies E4—E3/2=4.8 kcal/mole and E2—E5=12 kcal/mole are calculated from the kinetic data. The complete rate expression for the capture of imine H atom by CH3 radical, k4=4.5×1010e−4800/RT (moles/cc)−1 sec−1,is obtained by using Gomer and Kistiakowsky's values for k3=4.5×1013 (moles/cc)−1 sec−1 and E3=0. The activation energy for the thermal decomposition of t-butoxy radical is about 17 kcal/mole if E4 and E5 of similar type H capture mechanisms are assumed equal.
Bond Orbitals and Bond Energy in Elementary Phosphorus
Authors: Pauling Linus , Simonetta Massimo
Published: January 2005

A discussion of the relative stability of the P4 molecule and black phosphorus is carried out, with use of hybrid spd bond orbitals. The amount of strain in the P4 molecule, in which the bond angles are 60°, is calculated to be 22.8 kcal mole−1. This value is shown to be compatible with thermochemical data; it corresponds to the value 51.3 kcal mole−1 for the bond energy of the normal P–P bond. A structure is proposed for red phosphorus and other allotropic forms of the element, and some of their properties are discussed in relation to their structure.
Application of the Cell Method to the Statistical Thermodynamics of Solutions
Authors: Prigogine I. , Mathot V.
Published: January 2005

The cell method for pure liquids in the form used by Lennard-Jones and Devonshire is extended to solutions. It is assumed that (a) the constituents are spherical in shape, with an isotropic field of force, (b) the distance of the maximum interaction for AA, BB, and AB pairs is about the same, and (c) there is random mixing.

For the mean field in the ``cage,'' the complete 6–12 law, the harmonic oscillator, and the smoothed potential model have been studied. The smoothed potential model (potential curve with vertical walls and flat bottom, both depth and width depending on concentration) fits the liquid state best. For this model, one obtains important corrections on both the heat of mixing and the excess entropy to the classical, strictly regular solutions. These corrections are related to the volume changes on mixing resulting from the changes of interactions.

According to the value of εAB*, the excess properties such as volume, entropy, heat of mixing, and free energy present a large variety of shapes, including dissymmetry and inversions which correspond rather nicely to experimental evidence.

This model permits discussion of the severe limitations of Longuet-Higgins's recent theory of conformal solutions.
Diffusion through an Interface—Binary System
Authors: Tung L. H. , Drickamer H. G.
Published: January 2005

Diffusion measurements have been made between saturated layers in the system SO2—n-heptane, using S35 tagged SO2 as a radioactive tracer. The results are evaluated in terms of the interfacial transfer coefficient α introduced in a previous paper. The resistance in the interface is significant compared with the resistance to ordinary diffusion, even within 4°C of the critical solution temperature.
The Entropy of Solution of Nonelectrolytes
Authors: Hildebrand J. H. , Scott R. L.
Published: January 2005

The linear relation between the logarithm of the solubility of a solid nonelectrolyte and the logarithm of the absolute temperature, recently set forth by one of us, makes possible a rather accurate calculation of the partial molal entropy of transfer of the solute from solid to saturated solution. By subtracting from this the calculated entropy of fusion of the solid, one obtains the entropy of transfer from pure liquid to solution. This is several entropy units in excess of the ideal entropy in the case of solutions with high activity coefficients, but this difference is satisfactorily accounted for by the entropy involved in the expansion which accompanies the formation of such solutions under constant pressure. The entropy of mixing at constant volume seems to conform closely to the ideal (or Flory-Huggins) entropy.