bluuebunny/crossref_metadata_2025 huggingface dataset:
Carrier Generation and Transport in Anthracene under Electron Bombardment
Authors: Delany J. L. , Hirsch J.
Published: February 2004

Bombardment of anthracene crystals by 10–60-keV electrons produces equal numbers of electrons and holes by an intrinsic process throughout the region penetrated by the beam. Over the range examined, the yield is proportional to the total energy deposited at the rate of 400 eV per carrier pair. In “good” crystals, the yield at room temperature is independent of the applied field (for fields >3 kV cm−1). This is interpreted as saturation of the generation process. The results are compared with those reported for other forms of excitation. The values for the drift mobilities, viz., μe = 0.38 and μh = 0.92 cm2sec−1·V−1, and their temperature coefficients, agree well with other published values.
General Remainder Theorem
Authors: Epstein Saul T.
Published: February 2004

There have appeared in the literature several theorems of the type: Given the wavefunction correct through the nth order, one can calculate the energy correct through the (2n + 1)st order. Here we make explicit the simple general theorem which underlies the various special results.
Separation of Gas Mixtures in Chemical Equilibrium in a Temperature Gradient. II
Authors: Paul R. , de Vries A. E.
Published: February 2004

The theory of separation of gas mixtures in chemical equilibrium has been verified experimentally for the systems: (a) Ar/He/NO2/N2O4 and (b) 2NO2⇄2NO + O2 with a large excess of O2. The separation in the second system was smaller than calculated, which was attributed to the slowness of the chemical reaction. This was tested by experiments with two different concentrations of NO2. The results agree well with a simple model.
Assignments in the Ultraviolet Spectra of Olefins
Authors: Robin M. B. , Basch Harold , Kuebler N. A. , Kaplan B. E. , Meinwald J.
Published: February 2004

Indirect SCF calculations in a Gaussian basis of the lower π→σ* and σ→π* states of ethylene demonstrate that the lower π→σ* excitations are Rydberg and involve 3s and 3p orbitals on carbon, whereas the lower σ→π* excitations are strictly valence shell. Calculations in an identical basis using the virtual-orbital approximation instead lead to excited states which are mixtures of Rydberg and valence-shell configurations. The calculations also show that the oscillator strengths of π↔σ transitions should not exceed 0.1, and that in twisted olefins, the rotational strengths of π→σ* excitations, in general, are smaller than those for σ→π* excitation. The e.ectronic spectrum of tricyclo[3.3.0.02,6]oct-3-ene(TCO) in the gas phase shows that an olefin can have up to four π↔σ transitions preceding the π→π* absorption. Comparison of the spectra of ethylene in high-pressure nitrogen and of TCO in rare-gas matrices show that the lowest transition in the latter is a valence-shell transition, but that the second and third are π→σ* Rydberg transitions. It is concluded that Rydberg π→σ* excitations will be lowest in simple olefins, but in the more complex polycyclic strained olefins, a low-lying valence-shell transition (probably π→σ*) is nearly degenerate with, or falls below, the lowest Rydberg π→σ* transition.
Anomalous Viscosity of Critical Mixtures and Its Dependence on Velocity Gradient
Authors: Sallavanti Robert , Fixman Marshall
Published: February 2004

The anomalous viscosity is calculated from a direct solution of the differential equation for the perturbed radial distribution function. The resultant expression for the anomalous viscosity is a fourfold integral which depends parametrically on the velocity gradient. A series expansion of the viscosity in powers of the velocity gradient is divergent, but numerical integration yields a well-behaved non-Newtonian viscosity.
NMR Evidence of H3O+ Ions in Gallium Sulfate
Authors: Kydon D. W. , Pintar M. , Petch H. E.
Published: February 2004

Hydrated gallium sulfate has been studied over a wide temperature range using both steady-state and transient proton resonance techniques. Second moment and spin–lattice relaxation time data support the suggestion that oxonium H3O+ ions exist in this material and that the structural formula should be written (H3O)Ga3(OH)6(SO4)2. The oxonium ions undergo thermally activated reorientations and translational diffusion. These motions induce dipolar proton spin–lattice relaxations which are most effective at 135° and 300°K, respectively.
Reaction of H2 + D2⇆2HD Catalyzed by Molybdenum and Observed by Mass Spectrometer
Authors: Moore George E. , Unterwald F. C.
Published: February 2004

Papers I, II, and III of this series emphasize chemical reactions of the same designation. I describes H2–D2 exchange, II describes 28N2–30N2 exchange, and III reports some measurements on ammonia synthesis. All reactions were catalyzed by the same Mo ribbon. I and II are simpler than III and their study facilitates understanding III. Publications for I show a trend toward the expected equilibrium, but evaluation of catalytic effectiveness usually involved many sorptions of each reactant molecule with the heated catalyst. Our technique permits evaluation resulting from a single sorption interaction and shows for I that sorbed molecules leave our catalyst S at relative abundances agreeing with the equilibrium constant K of the exchange reaction. This equilibration during a single interaction occurs throughout the experimentally accessible temperature range 335°K to above 1000°K and for covers between 0.05 and approximately a complete monolayer. Contamination by nitrogen and by CO does not affect equilibration. Results imply that the catalyst splits the reactant molecules at least intermittently and may suggest atomic, rather than molecular sorption. However, published experiments warn against complete acceptance of atomic sorption. If exchange reactions involve only the catalyst surface, as generally thought, relative departure rates for H2, D2 and HD molecules would satisfy the usual conservation relation calculated from incidence rates from the gas phase onto the catalyst. This relation is independent of K but, with K, would completely specify relative desorption rates of the three molecular forms of hydrogen. Experimentally, only K is satisfied. Desorption rates are not directly related to incidence rates and are only understood if much of the hydrogen and deuterium participating in exchange comes from a phase dissolved in the catalyst, rather than from an adsorbed layer. This and other results suggest that H2–D2 exchange is related more critically to the volume of the catalyst than to its surface. If such results occur for other catalysts and other reactions, widely accepted models for catalysis must be reconsidered.
Diffusion of Bismuth Ions in Potassium Chloride Crystals
Authors: Reisfeld Renata , Honigbaum Alexander
Published: February 2004

The diffusion of bismuth in single crystals of potassium chloride was measured by a spectrophotometric method. The measurements were carried out in the temperature range 275°–674°C. The Arrhenius plot consists of two straight lines intersecting at about 400°C. The corresponding diffusion coefficients are expressed by D<400°C = 1.7 × 10− 3exp(− 0.63 / kT), D>400°C = 5.6× 10− 3exp(− 0.97 / kT). In the high-temperature region bismuth diffuses in its divalent state. The energy of formation of the diffusing complex Bi2 + and vacancy is found to be 0.57 eV. The low-temperature diffusion is that of trivalent bismuth and is attributed to an interstitial mechanism limited by the jump frequency w1. An interstitial mechanism is also proposed for other polyvalent cations with small radii which are able to exist in tetrahedral coordination.
Quantum-Statistical Ab Initio Calculations on Ionic Crystals
Authors: Olszewski S. , Dubejko M.
Published: February 2004

A model of the ionic crystal is proposed on the basis of the atomic quantum-statistical equation with exchange. The crystal is composed of ionic spheres touching one another. The equilibrium state of the crystal is the result of electrostatic attraction being balanced by repulsion due to the electron gas pressure acting on the surfaces of the ions. Several empirical, or semiempirical, quantities relating to the properties of the crystals could be estimated for the first time by an ab initio calculus. These were the univalent and multivalent radii of crystal ions, the compressibilities and cohesive energies of crystals containing the multivalent ions, and the energies of ultraviolet absorbtion maxima; also several structrual properties could be predicted from purely theoretical considerations. Only compounds whose ionic components had an atomic number not exceeding 40 have been examined.
Electron-Bombardment Desorption: Carbon Monoxide Adsorbed on Tungsten
Authors: Sandstrom D. R. , Leck J. H. , Donaldson E. E.
Published: February 2004

Experiments are described in which the surface properties of an electron-bombarded tungsten (211) surface are studied by the technique of surface mass spectrometry. In most of the work the tungsten ribbon was in a controlled carbon monoxide atmosphere at a pressure between 10−9 and 10−6 torr. Electrons bombarding this surface release an O+ ion current which has two distinctly separate components coming from different molecular sorption states. The smaller of these components has been identified as direct desorption from the α-phase carbon monoxide. The other was observed to depend in a complex manner upon both the sorption of gas on the surface and the prior history of electron bombardment. These results can only be explained fully by assuming that the electron bombardment produces an intermediate adsorbed state having a large cross section for O+ ion desorption under subsequent electron bombardment. This so-called “intermediate” state is stable always building up to the same equilibrium density under prolonged electron bombardment.
Magnetic Structures of TbAu2
Authors: Atoji Masao
Published: February 2004

Neutron-powder-diffraction study has shown that, in the range 55°-42.5°K, TbAu2 (tetragonal, iso-structural to MnAu2) exhibits a linear-transverse-wave spin alignment propagating along the a axis (the face-centered description) and polarized in the c axis direction. The wavelength of this static magnetization wave is incommensurable with the atomic repetition and varies 1.200-1.186 in a spacing units in the range 55°-42.5°K. The rms moment per Tb at 42.6°K is 5.1 Bohr magnetons. At just below 42.5°K, a first-order magnetic transition takes place and the wavelength of the transverse wave abruptly becomes equal to the a spacing. The resulting antiferromagnetic structure persists down to 2°K and the saturation moment is practically identical to the ordered moment of the free Tb3+ ion, 9.0 Bohr magnetons. The crystallographic data in the range 300°-5°K are also presented.
Scattering of High-Velocity Neutral Particles. XV. He–H2 and He–D2
Authors: Amdur I. , Smith Allan Laslett
Published: February 2004

Total collision cross sections have been measured for helium atoms with energies between 500 and 1900 eV scattered by room temperature H2 and D2. Within the experimental precision of ±2% the cross sections of the two systems are identical. The results have been analyzed to obtain the following average potentials: He–H2: V(r) = 12.11r−6.07eV, 1.44 Å < r < 1.76 Å; He–D2: V(r) = 12.27r−6.06eV, 1.45 Å < r < 1.79 Å. The measurements are in good agreement with a calculated He–H2 interaction of Krauss and Mies, suitably averaged over molecular orientation. The effect upon scattering of the anisotropy of the potential is discussed in the light of a classical perturbation theory of small angle scattering developed by Cross.
Intramolecular Radiationless Transitions
Authors: Bixon Mordechai , Jortner Joshua
Published: February 2004

In this paper we consider a theory for intramolecular radiationless transitions in an isolated molecule. The Born–Oppenheimer zero-order excited states are not pure in view of configuration interaction between nearly degenerate zero-order states, leading to the broadening of the excited state, the line shape being Lorentzian. The optically excited state can be described in terms of a superposition of molecular eigenstates, and the resulting wavefunction exhibits an exponential nonradiative decay. The linewidth and the radiationless lifetime are expressed in terms of a single molecular parameter, that is the square of the interaction energy between the zero-order state and the manifold of all vibronic states located within one energy unit around that state. The validity criteria for the occurrence of an unimolecular radiationless transition and for exponential decay in an isolated molecule are derived. Provided that the density of vibrational states is large enough (i.e., exceeds the reciprocal of the interaction matrix element) radiationless transitions are expected to take place. The gross effects of molecular structure on the relevant molecular parameters are discussed.
Physical Properties of Fluid CH4 and CD4: Theory
Authors: Grigor Anthony F. , Steele William A.
Published: February 2004

Experimental data for the differences in the physical properties of CH4 and CD4 are subjected to a theoretical analysis. The theory is presented in a form which represents the total effects as sums of terms which are due to differences in the intermolecular potential functions plus other terms due to quantum effects on the translational, rotational, and (internal) vibrational degrees of freedom of the molecules. It is shown that the differences in liquid molar volumes, isothermal compressibilities, and critical constants are almost entirely accounted for if it is assumed that the CD4 molecule is 0.4% smaller than CH4; that the depth of the intermolecular potential well is 0.9% smaller for CD4 than for CH4 and that other contributions to the net changes in these properties are small. The vapor-pressure differences are due only in part to the differences in potential function; in addition, the various quantum contributions to this property are estimated, and it is concluded that the translational and vibrational effects are important for the CH4–CD4 pair but that the rotational quantum effect can be neglected. It is shown that the experimental vapor pressures and heat of vaporization differences can be accounted for if the vibrational zero-point energy change upon vaporization is chosen to fit the data at one point.
Fluctuation Theory of Light Scattering from Liquids
Authors: Litan Adiel
Published: February 2004

It is shown that, within the frame of the starting assumptions in the conventional fluctuation treatment, Rayleigh scattering from any liquid cannot ever be smaller, and in most cases will in principle be larger, than the value calculated from the final formulas derived by this treatment. This is a result of additional assumptions which are made in deriving the final formulas and which may be especially inadequate in certain multicomponent liquids, where it may be necessary to consider fluctuations in concentrations of molecular species, rather than of thermodynamic components. The study is restricted to liquids whose molecules or ordered molecular aggregates, if any, are small compared to the wavelength of the light used.
Proton Magnetic Relaxation in Polyethylene Oxide Solutions
Authors: Liu Kang-Jen , Ullman Robert
Published: February 2004

Proton magnetic relaxation times have been measured in solutions of polyethylene oxide. Molecular weight, temperature, and solution concentration have been systematically varied. Several low-molecular-weight oligomers have been studied as well as polymers which vary in molecular weight from 4 × 103 to 4 × 106. The results show that in dilute solution both T1 and T1 are independent of molecular weight. T1 decreases with increasing concentration for concentrations greater than 0.2 g per ml of polymer, but is independent of concentration for more dilute solutions. T2 is independent of concentration in the limit of low concentration, but decreases rapidly with increasing concentration. The concentration dependence of T2 is a sensitive function of molecular weight. The relaxation mechanism has been analyzed using a model of rotameric transitions and the molecular geometry calculated from the known crystal structure of the polymer. The most important term is that arising from a conformational change about the C-C bond, in which the oxygen atoms move from a gauche to a gauche′ position. The relaxation times (T1) of water in aqueous polyethylene oxide solutions decrease with increasing polymer concentration, and are independent of the molecular weight of the polymer.
Paramagnetic Resonance of I2− Centers in PH4I Single Crystals
Authors: Marquardt Charles L.
Published: February 2004

The I2− centers have been produced by x irradiation of PH4 crystals at liquid-nitrogen temperature and have been studied by electron paramagnetic resonance. The molecular axes of the centers were inclined 14.4° from the (001) plane, as might be expected from the crystal structure of PH4I. Constants of the spin Hamiltonian of I2− in PH4I have been determined to be G‖ = 1.901, g⊥ = 2.28, A‖ = 364 G, A⊥ = 73 G, and | Q′ | = 68 G. From this data the admixture of Πu2 wavefunction into the Σu+2 ground state of I2− is estimated to be about 15%.
Perturbation Treatment of Large-Angle Elastic Scattering
Authors: Cross R. J.
Published: February 2004

A perturbation treatment, valid for small impact parameters, is developed for the WKB phase shift and the classical deflection angle for a general Lennard-Jones potential. The unperturbed problem is the scattering at zero impact parameter from a repulsive interaction given by Cr−8. The centrifugal term in the effective potential and an attractive term are added as perturbations. The phase shift and deflection angle are obtained as a simple series to third order in both perturbations. A simple expression is obtained for the large-angle differential cross section which may be used to obtain the well depth ε and the power of the repulsive wall s.
Conformal Solution Theory of Certain Molten Salts
Authors: Davis H. Ted , McDonald John
Published: February 2004

The conformal solution theory of molten salts developed by Reiss, Katz, and Kleppa is utilized to obtain formulas for the thermodynamic excess quantities for mixing at constant temperature and pressure. The RKK theory was developed for mixing at constant temperature and volume. For the special case that the anion-cation repulsive potential may be represented as a hard-sphere potential we have simplified the theoretical formulas by eliminating an integral involving a four-particle correlation function. Some of the integrals in the theoretical expressions are related to the thermodynamic properties of a reference system. Number estimates of the heat of mixing, based partially on a pseudo one-component fluid model and partially on a lattice model, compare favorably with experiment. According to the theory, the volume of mixing should vary as the square of the difference in the ionic diameters of the components salts. This is in contradiction to the empirical fit achieved by Powers, Katz, and Kleppa who found that the fourth power of the difference in diameters represented the data. We have shown, however, that the data agrees with our theory as well as it does with the proposed fit of RKK.
Projected Hartree Product Wavefunctions
Authors: Gallup G. A.
Published: February 2004

A method for performing a restricted configuration interaction calculation on atoms or molecules based on the use of Young operators from the symmetric groups is discussed and its relation to some other types of calculations is pointed out. The method in its most general form can be said to be an extension of the independent particle approach which represents the wavefunction in terms of the n best possible one-particle orbitals for the n-particle system. Illustrations are given for the hydrogen molecule, the helium atom, and the allyl radical.
Numerical Solution of the S-Limit Schrödinger Equation
Authors: Winter N. W. , Diestler Dennis , McKoy Vincent
Published: February 2004

Numerical solutions to the S-limit Schrödinger equation have been obtained for He and Li+. Using these the energy and the expectation values 〈Σri〉 and 〈Σri2〉 were calculated and compared to the radial configuration interaction values. The results demonstrate that the direct numerical solution of many partial differential equations in chemical physics can be accomplished in a practical and straightforward manner.
Semiempirical Molecular-Orbital Calculations. VI. Dimers of Benzene
Authors: Srinivasan B. N. , Russell J. V. , McGlynn S. P.
Published: February 2004

Semiempirical charge self-consistent MO calculations have been carried out for a large number of benzene dimers of different geometric conformations (e.g., D6h, C2h, S2, C6, S12, C2υ, etc.). It has been found that the most stable excimer conformation is not the most symmetric (i.e., D6h), but rather one in which the rings are rotated relatively about the D6h axis and/or tilted, one with respect to the other. The lifetime of excimer fluorescence can be satisfactorily explained in two ways: (1) The transition is made vibronically allowed in much the same way as the B2u1→1A1gtransition of benzene; or (2) the excimer possesses C1 or C2υ symmetry, in which case a very small relative tilting of the benzene planes can induce transition moments of proper magnitude without invoking vibronic effects at all. A number of suggestions are made concerning solvent effects, and the presence of underlying continua in discrete absorption spectra, etc. In particular, a concept of contact excimer absorption is broached and rationalized. The results of computation are in excellent agreement with the general run of available experimental data.
ESR Spectrum of the Radical Species Trapped in X-Irradiated Single Crystals of Dimethyl (9-fluorenyl) Sulfonium Bromide
Authors: Lucken E. A. C. , Mazeline C.
Published: February 2004

The electron spin resonance spectrum of single crystals of dimethyl (9-fluorenyl) sulfonium bromide, irradiated with x-rays at room temperature, reveals the presence of three free-radical species. Two of these have been identified with reasonable certainty as (CH3)2SBr (A) and 9-fluorenyl (B). The third radical (C) is probably one in which the unpaired electron is mainly localized on a sulfur atom i.e., RS. The components of the hyperfine coupling and g tensors for these radicals have been determined and the results discussed in terms of the electronic structure of these radicals. For radical A the 79Br and 81Br nuclear quadrupole coupling constants were also determined.
Mössbauer-Effect Studies in 129ICN Molecular Crystals
Authors: Pasternak M. , Sonnino T.
Published: February 2004

The Mössbauer effect in 129I (Er = 27.8 keV) has been used to investigate some properties of ICN crystals at 100°K. From the quadrupole split spectrum the value of e2qQ(127I) was found to be −2640 ± 20 Mc/sec and the isomer shift +0.119 ± 0.002 cm/sec with respect to a ZnTe source. The η parameter was found to be zero. From these values, it was concluded that the iodine promotes 0.27 p electrons (there is no sp hybridization) to the cyanide group. From considerations based on NQR data in BrCN and ICN and from the fact that no anisotropy was detected in the recoilless fraction, it was concluded that intermolecular (covalent) bonding to form a chain structure is negligible. The absolute recoilless fraction at 100°K was found to be 0.012 ± 002 corresponding to a Debye temperature of 61 ± 5°K.
Electron Paramagnetic Resonance of Beef-Heart Ferricytochrome c
Authors: Salmeen Irving , Palmer Graham
Published: February 2004

We have observed an anisotropic EPR spectrum in a frozen solution of the low-spin (S = 12;) hemoprotein ferricytochrome c. These results are interpreted in terms of the theory for the low-spin ferric ion in an octahedral crystal field which is subject to an (axial) distortion along the axis perpendicular to the heme plane and a (rhombic) distortion in the plane of the heme, and a spin-orbit constant which is less than that found in the free ion. This model also leads to calculated values for the effective magnetic moment which agree well with experiment.
Franck–Condon Calculations for Double Ionization of Molecular Hydrogen
Authors: McCulloh K. E.
Published: February 2004

The Franck–Condon radial overlap integral for transition from the ground vibronic state of H2 to a state in the H2++ continuum is expanded as an asymptotic series in powers of a small parameter. The initial semiconvergence of the series is sufficiently rapid to provide a convenient basis for computing the kinetic energy distribution for protons formed by double ionization of H2. The results of these computations are presented. The analysis includes a derivation of the reflection approximation for the particular case of transition to the repulsive Coulomb potential curve. Preliminary results of a more general study indicate that this approximation can be applied to a much larger class of repulsive potentials. Previous forms of the reflection approximation, which have heretofore lacked theoretical foundation, are classified and discussed in relation to the derived approximation.
Ultrasonic Relaxation in Ethanol-Ethyl Halide Mixtures
Authors: Solovyev V. A. , Montrose C. J. , Watkins M. H. , Litovitz T. A.
Published: February 2004

Ultrasonic studies in mixtures of ethanol and various ethyl halides show that maxima exist in the plots of the absorption coefficient versus concentration. These maxima are located at relatively small ethanol concentrations. The measurements made include a detailed investigation of the temperature and frequency dependence of the absorption in the ethanol-ethyl chloride system and somewhat less complete studies of the ethanol-ethyl bromide and ethanol-ethyl iodide systems. In each of the systems the measurements were made as a function of concentration. The results in the ethanol-ethyl chloride mixtures indicate the presence of a single relaxation process occurring in the range of measurement (15-165 MHz). The mechanism for this relaxation process is considered both in terms of a quasichemical association theory and in terms of a fluctuating concentration theory. The suggestion is made that the relaxational behavior may be connected with the existence azeotropic concentrations in these mixtures.
Classical Isotope Effect in Vibrational Relaxation: The Relaxation of H2 and D2
Authors: Kiefer John H.
Published: February 2004

A general classical analysis of the effect of uniform mass scaling on vibrational relaxation is given which shows that the thermal rate of excitation of a system from an initially vibrationless state varies inversely as the square root of the mass ratio. This accurate classical result affords an unambiguous comparison of the augmented classical methods used by Parker and others with measurements of relaxation in H2 and D2. The Parker formulation of the relaxation time alone does not produce the observed isotope effect, but close agreement does result when this method is symmetrized. Consideration of the high-temperature behavior of the ratio τD2 / τH2 shows that the deviations from the Landau-Teller temperature dependence found by Kiefer and Lutz are simply a property of the normal relaxation process, and not a consequence of relaxation-dissociation coupling.
Phosphorescence of Crystalline Pyrazine at 4.2°K
Authors: Moomaw W. R. , El-Sayed M. A.
Published: February 2004

The high-resolution phosphorescence spectrum of pyrazine crystals has been recorded and analyzed. The fact that the crystal structure of pyrazine crystal is known and that the ground-state molecular and lattice vibrations are assigned, made it possible to accurately analyze and assign the observed spectrum. The comparison of the observed spectrum obtained from pyrazine crystals with that obtained from pyrazine in cyclohexane matrix at 4.2°K leaves no doubt that the observed emission from the crystals results from the B3u3←Ag1π*→n transition of the pyrazine molecule. The 0,0,0 band in emission is found to be 102 cm−1 lower in energy than the 0,0,0 band in absorption. This might suggest that the emission centers have slightly different environment and thus lower energy than those absorbing the radiation. This difference in environment also leads to the trapping of triplet excitons by pyrazine molecules located at physical defects. The different types of trapping mechanisms are briefly discussed in the light of the observed spectrum. There is a strong coupling between the electronic motion and the lattice modes of b3g symmetry (the most prominent ones have frequencies of 57 and 82 cm−1). The intensity of the emission of the phononic and phonon-vibronic bands is greater than that of the vibronic bands. This observation suggests that either the lattice parameters are different in the excited triplet state from those in the ground state or else there is a lattice-induced emission resulting from the coupling of the different molecular electronic states of pyrazine with lattice vibrations. These two mechanisms of phonon enhancement of the emission are discussed in terms of the site symmetry of the emitting pyrazine molecules at the trapping sites. Spectral evidence is given showing the coupling between the intramolecular C–H in-plane bending vibrations and the lattice modes. The b3g lattice modes are found to have lower frequencies when coupled to the C–H in-plane bending vibration than when it is coupled to the other vibrations. This observed phonon-vibronic coupling as well as the phonon-electronic coupling is consistent with the form of the force field proposed for the pyrazine crystal which consists of one term representing an intermolecular hydrogen bonding (C–H···:N) and two intermolecular hydrogen-hydrogen repulsion terms. A change in the distribution of the hydrogen atoms (as produced by C–H vibrations) or the lone-pair electron density (as produced in π*→n transition) can give rise to observed effects on lattice parameters and vice versa.
Effective Operators and Spectroscopic Properties
Authors: Wybourne B. G.
Published: February 2004

Perturbation summations that are characteristic of a wide range of spectroscopic problems are shown to be simply expressible in terms of effective operators involving the zero-order states of the preponderant configuration. The methods developed involve the use of generalized unit tensor operators. Detailed applications to configuration-interaction effects in lN configurations and to third-order contributions to spectral intensities of ions in crystal fields are considered.
Reactive State in the Photoreduction of Acridine in Ethanol
Authors: Wilkinson F. , Dubois J. T.
Published: February 2004

Quenching of the fluorescence of acridine in ethanol solution by iodide ions takes place with unit collisional efficiency converting the excited singlet state to the triplet state. The photoreduction of acridine in the presence of iodide ions is descreased by an amount corresponding to the decrease in fluorescence, illustrating that the reactive state is a singlet-state probably (π, π*)1 in nature.
Composition Dependence of the Thermal-Diffusion Factor in the Hydrogen–Helium Gas Mixture
Authors: Ghosh A. K. , Barua A. K.
Published: February 2004

The composition dependence of the thermal-diffusion factor of the H2−He system has been measured at temperatures 155.8° and 241.5°K by a two-bulb apparatus. The measurements show a similar dip in the α vs mole fraction of H2 plot as observed by Ghosh, Batabyal, and Barua earlier. Two peculiarities ha been noticed in these measurements: (1) The percentage of H2 at which the dip occurs shifts with the change of T̄ and (2) the extent of the dip decreases with the decrease of T̄. An attempt has been made to interpret the data from semitheoretical considerations.
Dissociation Energies of Group VIa Gaseous Homonuclear Diatomic Molecules. II. Selenium
Authors: Budininkas P. , Edwards R. K. , Wahlbeck P. G.
Published: February 2004

The dissociation energy of Se2(g) has been determined by the simultaneous Knudsen-torsion effusion method. The equilibrium, Se2(g) ⇋ 2Se(g), has been studied with a double-oven, alumina effusion cell; one oven contained elemental selenium and supplied vapor to the hot oven from which the effusion occurred. The value of D0° found in this study is 75.7 ± 2.5 kcal/mole; this value is in excellent agreement with values determined in mass-spectrometric equilibrium studies and in good agreement with a value from a spectroscopic experiment.
Temperature Dependences of Isotope Effects
Authors: Stern Marvin J. , Spindel W. , Monse E. U.
Published: February 2004

It is shown that the harmonic-vibrational contributions to an isotope effect can by themselves lead to several types of temperature-dependence “anomalies,” including inflections, maxima, minima, and “cross-overs,” in a plot of the logarithm of an isotopic equilibrium-constant or rate-constant ratio vs temperature (or vs logarithm of temperature). In a series of calculations for a large number of 15N and 18O isotope-exchange equilibria among fourteen simple oxynitrogen compounds, such “anomalies” are found in 15 of the 91 15N exchanges considered and in 97 of the 153 18O exchanges considered. The significance of the prevalence of temperature-dependence “anomalies” to equilibrium and kinetic isotope-effect studies is discussed.
Quantum-Mechanical Treatment of Inelastic Collisions. I. General Theory and Application to Nonreactive Collisions
Authors: Diestler Dennis J. , McKoy Vincent
Published: February 2004

A general method for the quantum-mechanical treatment of the inelastic collision of composite particles is presented. The method, which is applicable to both nonreactive and reactive collisions, consists of constructing the total stationary scattering wavefunction describing the collision as a linear combination of linearly independent functions which satisfy the Schödinger equation and also arbitrary boundary conditions specified in the asymptotic region. The formalism is developed for nonreactive collisions using a collinear model to simplify the mathematical treatment. In this paper, it is applied to two examples of impulsive collisions. In one case, for which a comparison is possible, calculated transition probabilities agree well with previously published values.
Far-Infrared Spectra and Hydrogen-Bond Frequencies of Imidazole
Authors: Perchard C. , Novak A.
Published: February 2004

Far-infrared spectra of imidazole, imidazole-d4, 1-methyl imidazole, and 1-methyl-d3 imidazole have been examined in the 300 − 33-cm− 1 range. Six of the nine infrared-active lattice modes of crystalline imidazole have been observed and assigned. A tentative assignment of these frequencies in terms of hydrogen-bond motion is given. Far-infrared spectra of solid and liquid imidazole and its methyl derivatives are compared and discussed. There is no obvious relationship between the hydrogen-bond frequencies and the structure of the νNH absorption band of crystalline imidazole.
Variation–Perturbation Treatment of Electron Correlation in Molecules. I. Bare Nucleus Model for H2
Authors: Kirtman Bernard , Decious Daniel R.
Published: February 2004

A variation–perturbation (VP) calculation of the electronic energy of H2 is carried out using r12− 1 as the perturbation. The first-order wavefunction gives a total energy through third order which is only 0.4 kcal/mole greater than the exact value. It is seen that the VP energies are relatively insensitive to errors in the unperturbed wavefunction and that accurate results can be obtained with limited variational basis sets of only two or three functions. Application of either the bare nucleus or a similar model to more complicated molecules is discussed.
Lattice Dynamics and Specific-Heat Data of CsCl, CsBr, and CsI
Authors: Karo A. M. , Hardy J. R.
Published: February 2004

Detailed calculations are presented for the frequency distributions and dispersion curves of the three cesium chloride-structure alkali halides: cesium chloride, bromide, and iodide. Three distinct models have been used: the rigid ion model, the polarization dipole model, and two variations of the deformation dipole model. In each case combined frequency spectra and dispersion curves are presented and detailed critical-point assignments made. Plots of the effective Debye temperature θD as a function of temperature are shown and compared with experiment. In addition, the moment functions of the frequency distributions ωD(n) = [13 (n + 3) μn] / n, where μn is the nth moment of a given distribution, have been computed, and plots of these results show that they provide a better means of discriminating between the various models than the θD curves, but unfortunately, no experimental data exist.
Exact Calculation of the Partition Function for a Model of Two-Dimensional Polymer Crystallization by Chain Folding
Authors: Zwanzig Robert , Lauritzen John I.
Published: February 2004

A model of two-dimensional polymer crystallization by chain folding is treated by equilibrium statistical mechanics. The Laplace transform of the partition function with respect to the length of the polymer chain is obtained in exact analytical form. The model leads to thermodynamically well-defined chain-folded crystals. Under certain circumstances in the limit of an infinitely long polymer chain, the model shows a second-order phase transition from an “extended-chain” crystal to the chain-folded crystal.
Magnetic Structure of DyC2
Authors: Atoji Masao
Published: February 2004

The compound, DyC2, having the tetragonal body-centered CaC2-type structure has been shown by neutron diffraction to exhibit the magnetic spin alignment of a linear, transverse wave mode below the Néel temperature of 59°K. This static moment wave is propagating along the a axis and is polarized in the c-axis direction. The root-mean-square and maximum saturation moments per Dy are 8.37 and 11.8 Bohr magnetons, respectively, the latter being considerably larger than the ordered moment of the free Dy3 + ion, 10.0 μB. The wavelength of the moment wave is about 1.3 times the a spacing and is practically temperature independent. An additional, coexisting spin alignment with a very small moment appears to take place below 31°K. The crystallographic parameters in the range 300°–5°K are also presented. The thermal-neutron coherent scattering amplitude of Dy is established as (1.70 ± 0.01) × 10− 12 cm.
Kinetic Theory of Nonspherical Molecules
Authors: Bjerre A.
Published: February 2004

Using the kinetic theory of nonspherical molecules of Curtiss et al., a series expansion of the transport coefficients of a model for plane molecules is given. Going to a limiting case, partial equivalence with transport coefficients derived from other classical kinetic theories, and from the semiclassical theory of Wang Chang and Uhlenbeck, could be demonstrated. Numerical calculations are given for models of three planar molecules.
Spectra and Structure of Mixed Organic Crystals
Authors: Hochstrasser Robin M. , Small Gerald J.
Published: February 2004

The multiplet structure in the electronic spectra of phenanthrene in biphenyl is interpreted in terms of there being inequivalent sites available for the guest in the host lattice. The interconversion of these inequivalent sites has been observed at temperatures above 10°K, and such interconversion has been shown to occur for ground states and triplet excited states only. The dispersion shifts for phenanthrene in biphenyl are +4 cm−1 (ground state), 14 cm−1 (lowest-excited singlet state), and −13 cm 1 (lowest triplet state). All of these results are based on interpretations of (i) spectroscopic splittings and (ii) variations of the line intensities with temperature in the range 1.8°–30°K. The results of calculations of one-dimensional potential-energy curves for the motion of guest molecules in host lattices suggest that it is not uncommon for a guest molecule to have a number of energetically similar lattice dispositions. The results of the calculations are supported by the appearance of multiplet structure in a number of other mixed-crystal systems, namely: pyrene in biphenyl, anthracene in biphenyl, phenanthrene in naphthalene. The calculations also suggest that the total repulsive energy for a guest gives an indication of its solubility in a given host. The calculations also suggest that one should not in general expect exact alignment of the principal axes of a guest and host molecule although this seems most likely to occur when the guest molecule is larger than the host molecule.
Chemistry of Detonations. IV. Evaluation of a Simple Predictional Method for Detonation Velocities of C–H–N–O Explosives
Authors: Kamlet Mortimer J. , Hurwitz Harold
Published: February 2004

Measured detonation velocities of a variety of C–H–N–O explosives agree with values predicted from the equation D = 1.01φ1 / 2(1 + 1.30ρ0), where φ = NM1 / 2Q1 / 2, with an average absolute error of ∼1%. The H2O–CO2 arbitrary assumption of detonation product compositions is used in the calculation of N, the number of moles of detonation gases per gram of explosive; M, the average molecular weight of these gases; and Q, the chemical energy of the detonation reaction.
Infrared Spectra of H-Bonded Systems
Authors: Marechal Yves , Witkowski Andrzej
Published: February 2004

For the linear triatomic X–H··· system, the separability of the X–H stretching vibrations from the hydrogen bond vibrations is analyzed in the spirit of the adiabatic approximation. The adiabatic wavefunctions for X–H stretching vibrations are shown to be suitable functions for the evaluation of the principal factors determining the infrared spectral properties of the actual species of carboxylic acid dimers and imidazole crystal. Theoretical infrared spectra in the X–H stretching region of these systems are then obtained and compared with the experimental ones. The quantitative reconstitution of the experimental spectra and, in particular, the predictions for the effect of isotopic substitution of H by D are confirmed. The principal features of the unusual spectral properties of the X–H stretching vibrations in hydrogenbonded systems seem therefore to result from a somewhat peculiar coupling mechanism suggested in the theory.
Complex Refractive Index and a Two-Band Model in the Theory of Hypochromism
Authors: Bullough R. K.
Published: February 2004

A calculation of the complex refractive index of an arbitrary thermally agitated fluid is adumbrated. The theory starts from a 3-space Dyson-type equation comparable with a 4-space equation recently discussed in the literature in the context of the hypochromism of biological materials. It is shown that the refractive index contains a local field “self-energy” term which involves multiple-scattering processes of all orders. Poor convergence close to resonance means that the high-order multiple-scattering processes are important there. It is shown that the complexity of such processes does not necessarily prevent the proof of a sum rule for oscillator strengths. It is shown also that in the one case of a system of rigid macromolecules at infinite dilution the multiple-scattering terms can even be explicitly summed to a single-scattering expression. The implications of this particular expression in the theory of hypochromism (in which it must necessarily have restricted validity) are contrasted with those consequent on the more general multiple-scattering theory; but here, because of complexity, only the first-order (single-scattering) contributions to the general theory can be considered in detail. The contrast is explicitly exhibited in terms of a two-band model. Although qualitative generalizations to an arbitrary number of bands are then easy, the choice of only two bands means that closed-form (non-perturbative) analytical expressions for band shifts, changes of oscillator strength, and other features of their interaction can be given. It is shown that a one-band model considered previously is valid for small enough shifts or large enough band spacings, that a collective mechanism is possible in principle but scarcely compatible with the small shift and large hypochromism observed in DNA, that the band-shifting term and therefore the band shifts can be considerably reduced or even eliminated in the single-scattering model, and that this last contrasts strongly with the consequences of the rigid macromolecule (rodlike) model. It is argued that the single-scattering model can exhibit features of the more correct multiple-scattering theory which are eliminated in the rigid macromolecular model. The reduction of the shifting term may therefore be a significant feature of the small shift exhibited by the 2600-Å band in DNA.
ESR Spectrum of a Trioxide Radical
Authors: Fessenden Richard W.
Published: February 2004

ESR examination of the radical produced by the photolysis in solution at −196°C of CF3OOCF3 in the presence of small amounts of oxygen enriched in 17O shows that the radical so obtained contains two oxygen atoms with 17O hyperfine constants of 23.3 and 14.0 G. An experiment with CF3OOCF3 enriched in 17O and normal oxygen shows the presence of a third oxygen with an 17O hyperfine constant of 3.59 G. These data plus simple chemical arguments point very strongly to CF3OOO· as the structure of this radical. Comparison of the two large 17O coupling constants and the g factor (2.00373) to those of FOO· indicates a very close similarity in the electronic configuration around the two terminal oxygen atoms of these radicals. It is suggested that radicals of the type RO3 (including HO3) may have similar g factors.
Model Atomic Hamiltonians
Authors: Piech Kenneth R. , Wilson Kenneth G.
Published: February 2004

A model Hamiltonian for the n = 1 and n = 2 states of the first- and second-row atoms is developed. The model is easily soluble and represents total and ionization energies reasonably well. The model is constructed on a cubic lattice space and is defined by five postulates. They are: (1) Each electron is confined to seven lattice sites: the origin and its six nearest-neighbor sites; (2) The form of the Hamiltonian is taken from the finite difference approximation to the exact Hamiltonian; (3) The parameters in the Hamiltonian are determined phenomenologically; (4) The parameters scale as simple functions of Z. The fifth postulate allows one to distinguish s states from p states in the spectra of the models. A matrix diagonalization problem results which is easily solved by perturbation expansion. The model is applied to the atoms H to B, together with associated isoelectronic sequences. Ionization energies are given to approximately 25%, and total energies to approximately 2%. The eigenfunctions of the model are of nonproduct form and demonstrate correlation effects. A simple approximation to the ground-state energies of H–Ne is developed, which involves a calculation of the minimum-energy electron configuration on the seven-point lattice, and which is accurate to approximately 3%. The model results are compared to previous semiempirical Z− i expansions of ground-state atomic energies. Implications of the model for the problem of complex molecules are discussed.