bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure of Ammonium Fluoride. IV
Authors: Calvert L. D. , Whalley E.
Published: February 2004

X-ray powder diffraction patterns of ammonium fluoride IV have been obtained at about 450°K and 4 kbar in a pressure vessel made of single-crystal diamond. The unit cell is cubic with a = 5.77 ± 0.04 Å, and has a sodium-chloride-like structure with the space group Fm3m. Since ammonium fluoride IV appears to have a configurational entropy of about 3.8 cal deg−1·mole−1 and the hydrogen atoms of the ammonium ion cannot fit into an ordered sodium-chloride-like structure, the ammonium-ion orientations are probably disordered. The thermodynamic evidence does not favor free rotation. Ammonium fluoride IV is very plastic, in contrast to phases I of ammonium chloride, bromide, and iodide, which have the same structure.
Polarized Single-Crystal Absorption Spectrum of 1-Methyluracil
Authors: Eaton William A. , Lewis Thomas P.
Published: February 2004

The single-crystal absorption spectrum of 1-methyluracil, polarized along three mutually perpendicular axes, is investigated from 3200 to 2400 Å at room temperature. The spectral measurements were made with a microspectrophotometer, and crystal extinction coefficients were obtained from Lambert's law plots. The spectrum polarized normal to the molecular planes uncovers an n → π* transition at 2640 Å. The longest wavelength π → π* absorption band at 2755 Å exhibits well-resolved vibrational structure which broadens considerably on the high-energy side of the band. It is suggested that this broadening results from a perturbation by the underlying n, π* state. The transition moment for the lowest π → π* transition is found to be almost parallel to the N1–C4 molecular direction. The difference of about 23° between the transition moment directions for 1-methyluracil and 1-methylthymine agrees well with π-electron calculations. The exciton splitting of the 0, 0 band for the lowest π → π* transition is in qualitative agreement with dipole–dipole calculations for weakly coupled chromophores. The angular dependence of absorption of plane-polarized light is investigated.
Magnetic Renner Effect: Direct Orbital and Spin Interaction with “Vibrational” Rotation in Linear Triatomic Molecules
Authors: Chang Chen-Fee , Chiu Ying-Nan
Published: February 2004

Detailed and explicit expressions are derived for a new type of vibronic effect that involves the direct magnetic interaction of the electron's orbit and spin motion with “vibrational” rotation; the latter occurs in a linear triatomic molecule executing the doubly degenerate mode of vibration. Such magnetic vibronic interaction (Sec. III) is compared with the corresponding electrostatic vibronic interaction which is the conventional Renner effect (Sec. II). The expansion of the magnetic interaction, which is proportional to an irregular solid spherical harmonic, in terms of electronic and nuclear coordinates is shown in detail (Appendix A). The interaction Hamiltonian is expressed in terms of the eigenvalue, creation, and annihilation operators of the two-dimensional isotropic harmonic oscillator. The Lie algebraic treatment of such a system of operators and the derivation of diagonal as well as off-diagonal matrix elements, which are needed for higher-order perturbations, are shown (Appendix B). Effective Hamiltonian for first-order perturbation and its application in a 2Σ+ molecule, in which the conventional Renner effect is absent, are given (Sec. IV).
Electronic Energies and Electronic Structures of the Fluoromethanes
Authors: Brundle C. R. , Robin M. B. , Basch Harold
Published: February 2004

The high-resolution He i and He ii photoelectron spectra of all fluoromethanes in the series CH4 to CF4 and their deuterated analogs have been recorded and are compared with the Koopmans' theorem results of near-Hartree–Fock calculations performed in a Gaussian basis. The agreement is very good in general and offers an unambiguous assignment of almost all of the bands observed. In particular, repeated correlations are demonstrated between the compositions of the orbitals from which the electrons are ejected and the characters of the resulting photoelectron bands. Identifiable trends throughout the series are stressed and an anomalous feature in the CF4 spectrum is noted. Jahn–Teller effects in CH4 and CH3F are clearly evident, but as expected, they are not observed in CHF3 and CF4. Comparison of the photoelectron spectra excited with He i and He ii radiation shows wide variations in the relative intensities of various bands in certain of the more symmetric molecules, suggesting that relative intensities can be a poor measure of relative orbital degeneracies. Mass-spectrometric appearance-potential data are briefly discussed in the light of the photoelectron results. The carbon and fluorine 1s binding energies as measured with 1254-eV x rays are shown to be electronically adiabatic. The accurate determination of the lower ionization potentials of these molecules leads readily to the assignment of several of their electronic transitions as lower members of ns and np Rydberg series.
Electron Diffraction Study of Rhenium Fluorides. I. Heavy-Atom Corrections and Structure of ReF6
Authors: Jacob E. Jean , Bartell L. S.
Published: February 2004

To date, no theoretical models for electron molecular scattering have been developed which bring calculated scattered intensities from heavy atoms into satisfactory agreement with experiment. Preparatory to an electron diffraction study of ReF7, a molecule with an uncertain and possibly complex structure, an investigation of ReF6 was undertaken. The simplicity of the hexafluoride's geometry (Oh symmetry) allows an empirical characterization of the discrepancy between experimental and calculated intensities, a discrepancy which can be attributed chiefly to the behavior of ReF interference terms rather than to uncertainties in structural parameters. After a structure analysis of ReF6, the observed difference signal (Iobs − Icalc) was used with appropriate scaling to modify ReF7 intensities before structural parameters for the heptafluoride were refined. Parameters determined for ReF6, e.g., rg(ReF) = 1.832 ± 0.004 Å and lg(ReF) = 0.044 Å, are in excellent agreement with those reported from diffraction studies of other 5d transition-metal hexafluorides. Results for ReF7 are reported in Paper II.
Electron Diffraction Study of Rhenium Fluorides. II. Structure, Pseudorotation, and Anharmonic Coupling of Modes in ReF7
Authors: Jacob E. Jean , Bartell L. S.
Published: February 2004

Significant departures from D5h symmetry are indicated by the gas-phase electron diffraction data for ReF7. Observed scattered intensities, corrected for heavy-atom effects as discussed in the preceding paper, are adequately represented by structures with static deformations of either C2 or Cs symmetry of the following character. A puckering of the ring of five fluorines (maximum out-of-plane displacement ≈ 9°) is accompanied by a movement of each axial fluorine from the reference axis of ≈ 8° in the direction which provides maximum avoidance of fluorines on the rhenium coordination sphere. Equally compatible with the data is the much more reasonable dynamic pseudorotation model in which vibrational displacements carry the molecule from C2 to Cs to C2 configurations. The tenfold character of the hindering potential and modest displacements preclude an appreciable barrier. A pronounced skewing of the envelope of axial–equatorial, FaFe, distances reveals a coupling in phase of the e1′ axial bend to the e2″ ring puckering vibration through the S2(e2″) S(e1′) cubic term in the potential-energy function. The skewing, which moves the maximum of the FaFe distribution peak inside the distribution center of gravity, results in an apparent “anharmonic shrinkage” of the nonbonded peak by an amount exceeding the well-known “Bastiansen–Morino” harmonic shrinkage. It is to be noted that the equatorial pseudorotation problem closely resembles that for cyclopentane in reduced mass, in displacement, and therefore, presumably, in frequency. The structure itself may be understood in terms of bond–bond repulsions thrusting the equatorial atoms out of plane; the out-of-plane displacement, in turn, induces an axial bend. The actual structure, however, exhibits too large an axial bend to conform to the simple repelling points-on-a-sphere model of Gillespie and too small a deviation from D5h to correspond to the close packing of hard atoms around the rhenium.
Influence of the Distorted Wave Approximation in Calculations of Chemical Reaction Cross Sections; Ar++HD
Authors: Gelb Alan , Suplinskas Raymond J.
Published: February 2004

Two different approximations to the formal quantum theory of rearrangement collisions are applied to the same reactive system. The comparison enables some conclusions to be drawn concerning the effects of approximations to perturbed translational motion on predicted product energy distributions. In both schemes, the exact wavefunction is approximated by a product of a translational and a molecular wavefunction, where the molecular wavefunction is treated in the perturbed-stationary-state approximation. In one scheme (DWBA PSS) the translational wavefunction is expressed as a WKB solution to the appropriate elastic scattering problem, while in the other (BA PSS), free translational motion is assumed. Calculations are performed for the system Ar++HD using an assumed potential surface. Significant differences are noted in predicted distributions of translational exoergicity and product vibrational and rotational energy. In particular, the behavior of the most probable translational exoergicity with respect to incident energy predicted by the DWBA PSS is in substantial agreement with experiment, whereas the BA PSS consistently overestimates product excitation. Isotope effects predicted by both schemes are in serious disagreement with experiment; it is concluded that the source of this discrepancy lies largely in the neglect of the noncentral nature of the forces in this system.
Collision-Induced Singlet→Triplet Intersystem Crossing of Methylene and Methylene-d2
Authors: Eder Thomas W. , Carr Robert W.
Published: February 2004

The photolysis of ketene or ketene-d2 in the presence of propane, oxygen, and inert gas was studied at 300°K at each of the four wavelengths 2600, 3130, 3340, and 3500 Å. Inert gases used were He, Ar, Xe, N2, and CF4. The inert gases cause the transition of methylene from the first singlet state to the triplet ground state to occur. The observed kinetics of the intersystem crossing process, being first order in methylene and first order in inert gas, are second order. The second-order rate constants, relative to the rate constant for reaction of singlet methylene with propane, are independent of wavelength, and increase in the order He<Ar<CF4≤Xe. The rate-constant ratios for methylene-d2 show the same trend with inert gas but are 2–3 times larger. The results are consistent with a bimolecular intersystem-crossing mechanism where the role of the collision partner is to cause the transition to occur by sufficiently perturbing the singlet methylene stationary states.
Torques in Sheared Nematic Liquid Crystals: A Simple Model in Terms of the Theory of Dense Fluids
Authors: Helfrich W.
Published: February 2004

A fluid of equally and rigidly oriented molecules interacting through a smooth ellipsoidal two-body potential is considered. We derive the ratio of the shear-torque coefficients and the ratio of the shear-viscosity coefficients for two orientations of the unique axis, one parallel to the flow and the other parallel to the velocity gradient. In addition, we confirm the validity of an Onsager relation. Given one of the four coefficients, the other three can be calculated if the axial ratio of the prolate ellipsoids of revolution is known. In accordance with the theory of dense fluids, it is assumed that intermolecular forces rather than molecular motion dominate momentum transfer.
Orientational Freedom of Molecules in Crystals. II. Higher-Order Transition by Progressive Decorrelation of Orientations. A Monte Carlo Calculation
Authors: Brot Claude , Darmon Irène
Published: February 2004

A clear-cut example of a higher-order transition involving orientational disordering in some molecular crystals is presented. In these crystals, which are polar chloromethyl hexasubstituted benzenes, the molecules exhibit a one-axis sixfold disorder at high temperatures. On cooling, the static dielectric constant decreases, indicating the cooperative setting in of orientational order. This is confirmed by x-ray studies which indicate that the superstructure at low temperature is an antiferroelectric arrangement. A quantitative interpretation of the phenomenon is given. The energy which governs the ordering is shown to be essentially electrostatic in origin: Among 288 envisaged ordered arrangements, the electrostatic energy is the lowest for the observed (antiferroelectric) one. These calculations have been made using Coulomb interactions between charges located on the atoms since the point dipole model has been found to be too crude. A Monte Carlo calculation, which is partly dynamic and partly stochastic in nature, has been carried out for the transition region; this yields a semiquantitative agreement for the observed static polarization, and a fairly good reproduction of the shape of the experimental relaxation spectrum at different temperatures.
Investigation of the Quenching of Excited Mercury Atoms by the Alkanes
Authors: Vikis Andreas C. , Moser H. C.
Published: February 2004

The quenching of Hg(63P1), Hg(63P0), and Hg(61P1) by the alkanes was investigated by a theoretical model based on the formation of a relatively long-lived (Hg*HR) complex on a potential energy surface, most likely a polar one, which leads to the quenching of Hg* primarily by C–HHg bond rupture. The decomposition of the (Hg*HR) complex via C–HHg bond scission was treated as a unimolecular decomposition. The potential-energy surfaces associated with the reaction coordinate were defined by thermochemical and spectroscopic data, semiempirical calculations and, whenever not critical, by reasonable estimates. The unimolecular decomposition rate constants were calculated making use of the Rice–Ramsperger–Kassel–Marcus (RRKM) theory. This approach correlates the nature and magnitude of the C–H vs C–D isotope effects and the large variation in quenching efficiencies of the various alkanes satisfactorily with the C–HHg bond strength, zero point energy, and structural effects (vibrational degrees of freedom). Consequently, both the relative increase of the quenching cross section and the relative diminution of the effect of C–H bond strength with increasing excitation energy of the mercury atom is accounted for in terms of the relative increase in the active energies of the (Hg*HR) molecule and its activated complex.
Proton NMR Spectra of Cyclopentadiene, 1,3-Cyclohexadiene, 1,3-Cyclooctadiene, and 1,2-Dihydronaphthalene
Authors: Cooper M. Ashley , Elleman Daniel D. , Pearce Claude D. , Manatt Stanley L.
Published: February 2004

The proton NMR coupling constants between vinyl protons in cyclopentadiene (I), 1,3-cyclohexadiene (II), and 1,3-cyclooctadiene (III) have been obtained by analyses of the spectra of the latter protons when the methylene protons were decoupled. An analysis of the full spectrum of I has also been achieved. Analysis of the spectrum of 1,2-dihydronaphthalene (IV) was undertaken both to obtain a value of JHH3 across the olefinic double bond, and to compare certain of its coupling constants with those from our previous work on indene. The long-range coupling constants between vinyl protons in the planar molecule I and nearly planar II are significantly different from those in the nonplanar III. The differences are discussed in terms of the conformations of these molecules, and the importance of these results for testing theories of long-range coupling constants is pointed out.
Detachment of Electrons from F− Ions in a Shock-Heated Cesium Fluoride–Argon Mixture
Authors: Mandl A. , Kivel B. , Evans E. W.
Published: February 2004

Electron detachment rates from F− have been measured in shock-heated mixtures of cesium fluoride and argon. The detachment rate is found to increase exponentially with temperature, indicating an activation energy comparable to the electron affinity of F−. The rate constants for the reactions F−+Ar→ lim K(Ar)F+Ar+e and F−+Cs+→ lim K(Cs+)F+Cs++e have been found to be 1.2 × 10−11exp(− 40 000 / T) cm3/sec and 2.8 × 10−9exp(− 40 000 / T) cm3/sec, respectively, where T is in degrees Kelvin.
Viscous Liquids and the Glass Transition. II. Secondary Relaxations in Glasses of Rigid Molecules
Authors: Johari Gyan P. , Goldstein Martin
Published: February 2004

The dielectric loss factor and dielectric permittivity of 8–16 mol% solutions of chlorobenzene, o-dichlorobenzene, and 1-chloronaphthalene in cis-decalin; 50–60 mol% mixtures of pyridine with chlorobenzene, bromobenzene, 1-chloronaphthalene, and toluene; 50–60 mol% mixtures of tetrahydrofuran with bromobenzene and 1-chloronaphthalene; the pure liquids cis-decalin, o-terphenyl, iso-propylbenzene, propylene carbonate; and two fused salt systems, 45 mol% Ca(NO3)2–KNO3 mixture and Ca(NO3)2·4H2O have been measured from 50 Hz to 1 × 105 Hz from − 196° in the vitreous state to about 30° above their respective glass transition temperatures. The Tg's of the organic glasses have been measured by DTA. With the exception of propylene carbonate, all glasses show the presence of one secondary relaxation between − 196° and their respective Tg's either as a peak or shoulder in a tanδ–temperature plot at a single frequency, or in the dielectric loss spectrum. Arrhenius plots of the frequency of maximum loss against temperature in the main relaxation region for all systems are nonlinear, with the activation energy at the lowest temperature of our measurements ranging from 55 kcal/mol to 70 kcal/mol. The Arrhenius plots in the secondary relaxation region are linear and have activation energies between 5 and 12 kcal/mol. These glasses, most of which are composed of rigid molecules, show a remarkable similarity in their dielectric behavior to amorphous polymers. The results confirm the prediction made by one of the authors that the occurence of secondary relaxations is an intrinsic property of the glassy state.
Laser-Induced Photolysis of Iodoform. II. Nonlinear Optical Solvent Effect
Authors: Speiser S. , Kimel S.
Published: February 2004

The general theory for the effect of self-focusing on two-photon-induced photolysis is developed. A chemical method of determining the self-focusing length of liquids is described. The method is applied to the case of ruby-laser-induced photolysis of iodoform dissolved in toluene, m-xylene, chlorobenzene, and chloroform. The experimental results are in complete agreement with the theoretical predictions.
Parr–Brown Anharmonic Potential Function Applied to CO2 and CS2
Authors: Smith D. Foss , Overend John
Published: February 2004

An anharmonic potential function proposed by Parr and Brown in a form suited to symmetric linear triatomic molecules has been tested against experimental spectroscopic data for CO2 and CS2. The potential function, with only four or five adjustable parameters, gives a good fit to the spectroscopic data and models fairly well the general quartic force field of CO2, which contains 12 independent force constants.
Theory Concerning the Interaction of an Alkali Atom and a Metallic Surface
Authors: Remy M.
Published: February 2004

The interaction of a metallic surface with an alkali atom causes both a shift and a broadening of the valence level of the atom. We first present the theoretical model which describes the phenomenon and then calculate this shift and broadening by using a perturbation theory. The results are computed for the adsorption of cesium on tungsten and of lithium on rhenium.
Microwave Spectrum, Barrier to Internal Rotation, and Torsion–Vibration Interaction in ortho-Fluoro Toluene
Authors: Susskind Joel
Published: February 2004

The microwave spectrum of ortho-fluoro toluene, C6H4CH3F, was studied in the frequency range 12–38 GHz. Rotational spectra in four torsional states were assigned. Each state could be fit by an effective rotational Hamiltonian quite well. The change in rotational constants from one state to another could not be explained using the standard torsion–rotation coupled Hamiltonian. A simple model is given which helps explain the deviations in the rotational constants in the excited A levels from their expected positions. The true rotational constants for the ground state were calculated to be: A = 3243.08 GHz, B = 2180.44 GHz, C = 1314.36 GHz, κ = − 0.10234. By standard methods the angle between the top axis and the A axis was found to be 32°. The barrier to internal rotation is 649 cal/mol assuming V6 = 0 and Iα = 3.237 amu·Å2. Including the effects of changing average structure, there is evidence of a negative V6 and also that the angle mentioned above is somewhat smaller in the ground state.
Electric Polarizability Anisotropies of Nitrous Oxide, Propyne, and Carbonyl Sulfide by Microwave Spectroscopy
Authors: Scharpen LeRoy H. , Muenter John S. , Laurie Victor W.
Published: February 2004

Very accurate Stark effect measurements were made on rotational transitions of nitrous oxide and propyne-d3. Measurements were made with a microwave spectrometer incorporating a special parallel-plate absorption cell capable of sustaining large magnitude electric fields and of producing very homogeneous fields in the absorption region. Analysis of the data gives an electric polarizability anisotropy of 3.222 ± 0.046 Å3 for nitrous oxide and of 2.7 ± 0.6 Å3 for propyne-d3. The dipole moment of nitrous oxide was determined to be 0.160830 ± 0.000016 D. For propyne-d3, there is evidence for a K dependence of the dipole moment. The determined values for the J = 3 → 4 transition are 0.78780 ± 0.00013 D (K = 0), 0.78765 ± 0.00021 D (K = 2), and 0.78741 ± 0.00014 D (K = 3). Stark effect data reported previously for OCS were reanalyzed using a refined method of statistical analysis and the new molecular beam value for the OCS dipole moment to determine the revised OCS polarizability anisotropy of 4.67 ± 0.16 Å3. In each case, the error limit represents the 95% confidence level calculated in the least-squares analysis, but does not include the uncertainty in the dipole moment value for OCS which was used as a standard in the data reduction.
Photovoltaic Effect in Crystals of Organic Semiconductors as a Function of Wavelength
Authors: Tavares A. Dias
Published: February 2004

Experiments showing photo-emf created by monochromatic light in crystals of bisublimated naphthalene are described. The electrical current caused by monochromatic light is a function of the wavelength. Maxima of such a function have been detected at 750, 600, 550, 500, and 410 nm. We have observed that the current for 750-nm monochromatic light was intensified when previously we illuminated the crystal with 410- or 500-nm monochromatic light. We also have observed an inversion of the current when passing from 750- to 410-nm light.
Microwave Spectrum and Structure of Chlorine Azide
Authors: Cook Robert L. , Gerry M. C. L.
Published: February 2004

The microwave spectra of four isotopic species of chlorine azide, ClN3, have been observed in the frequency range 26–48 GHz. From the measured values of the rotational constants, the molecule has been deduced to be planar with the following internuclear parameters: r(Cl–N(1)) = 1.745 ± 0.005 Å, r(N(1)–N(2)) = 1.252 ± 0.010 Å, r(N(2)–N(3)) = 1.133 ± 0.010 Å, ∠ClN(1)N(2) = 108°40′ ± 30′, ∠N(1)N(2)N(3) = 171°56′ ± 30′, with Cl and N(3) trans. Values for the chlorine quadrupole coupling constants were obtained for all isotopic species, and for the most abundant, 35Cl14N3, were transformed into the principal field gradient axis system. The values obtained are consistent with the deduced structure.
Raman Spectra of AsF5 and VF5 and Force Constants for PF5, AsF5, and VF5
Authors: Selig H. , Holloway J. H. , Tyson J. , Claassen Howard H.
Published: February 2004

Raman spectra are presented for AsF5 and VF5 in which all allowed fundamentals and several overtones are observed. Force constants and normal modes of PF5, AsF5, and VF5 are discussed in terms of the orbital-valency–force-field model. Certain features in the spectra of VF5 and in the force constants are related to rapid intramolecular shifting of the threefold symmetry axis in this molecule.
Cooperative Rotation of Spherical Molecules
Authors: Egelstaff P. A.
Published: February 2004

The rotational diffusion of molecules in the liquid and solid states can be studied by radiation scattering experiments. Both neutron and light scattering data are interpreted, conventionally, on the basis of rotation of single molecules, although in dense systems cooperative rotation is a possibility. It is pointed out that a comparison of incoherent neutron data and depolarized light data allows the cooperative nature of molecular rotational diffusion to be verified. The method is applied to the plastic crystal phase of cyclohexane, and it is shown that individual molecules rotate about 10 times as rapidly as the relaxation rate of the mean orientation of a group of molecules.
High-Pressure Photoionization Mass Spectrometry. Reactions of Alkane and Cycloalkane Molecular Ions with Water Vapor at Thermal Kinetic Energies
Authors: Sieck L. Wayne , Searles Stuart K.
Published: February 2004

The reactions of alkane molecular ions (RH2+) with water vapor were found to proceed via a bimolecular mechanism in both ethane and propane. Parent ions from cyclohexane, cyclopentane, i-butane, n-butane, i-pentane, n-pentane, and n-hexane were observed to react exclusively via a termolecular mechanism involving two water molecules: RH2++2H2O→H+(H2O)2+RH. Thermal rate constants of 1.2 and 1.4 × 10−9 cm3/molecule·sec, respectively, were derived for the bimolecular reactions of C2H6+ and C3H8+ with H2O. The termolecular rate constants found in other RH2+–H2O combinations were quite high, falling in the range 10−25–10−27 cm6/molecule2·sec. The nature of the collision complex is discussed, and new limits are estimated for δHf(H3O+).
Thermal Energy Reactions of C− with O2, N2O, CO, and CO2
Authors: Fehsenfeld F. C. , Ferguson E. E.
Published: February 2004

Thermal energy reaction rate constants for C− ions reacting with O2, CO, CO2, N2O and H2 have been measured using a flowing afterglow technique. The reaction with O2 produces O−, the reactions with CO, CO2, and N2O produce free electrons and neutral products, and H2 is not observed to react.
Grüneisen Parameter from Thermal Conductivity Measurements under Pressure
Authors: Barker R. E. , Chen R. Y. S.
Published: February 2004

A relation is discussed from which a Grüneisen parameter γG can be calculated if the thermal conductivity κ with respect to pressure p and the bulk modulus B are known. The relation, γG(κ) = B (∂ lnκ / ∂p)T − 13, is analogous to the widely known expression, γG(s) = B∂(∂ lns / ∂p)T + 13, which is used to obtain a Grüneisen parameter from measurements of sonic speed s vs p. The first relation can be derived from the second if the Debye equation κ = ρsΛCı / 3 properly relates κ to s, the density ρ, the phonon mean free path Λ, and the heat capacity Cυ. Further assumptions, Λ∝ρ−1/3 and Cυ is constant, are also used. In an alternative derivation, the same form for γG(κ) follows from the assumption that thermal conduction corresponds to the leakage of a fraction of the energy during each vibration, from each localized vibrational mode, i.e., κ = Jν where ν is the frequency and J is a coupling parameter. Estimates of γG(κ) based on data for several polymers, minerals, and inorganic glasses indicate that it is significantly larger (4–20) than values (0.05–5) obtained for γG by certain other techniques. Our experimental techniques, which involve two types (coaxial cylinders and symmetrical sandwiches) of conductivity-pressure cells, are outlined.
Optical Activity of Vibrational Origin. II. Consequences of Polymer Conformation
Authors: Deutsche Craig W. , Moscowitz Albert
Published: February 2004

Calculations of absorption, circular dichroism, and optical rotatory dispersion spectra associated with vibrational transitions of several idealized helical polymers are reported. Although specific assumptions are made regarding the vibrational force field and the charge distribution within the polymer, these assumptions are applied consistently in an investigation of the effects of chain length and helical conformation upon the optical properties. Results obtained for an idealized model of polypropylene indicate that even rather short helical segments (5–10 residues) may have spectra rather similar to those calculated for an infinite helix. Calculations performed for several polypropylene oxide models indicate that the optical rotatory dispersion and circular dichroism spectra may, in some cases, be more sensitive to small changes in the helix geometry than the absorption spectra. Furthermore, in these instances a number of the partial ORD curves exhibit the characteristic triple-extrema shape which may be associated with transitions polarized perpendicularly to the helix axis. The potential usefulness of infrared optical activity measurements in assigning vibrational spectra and in determining polymer conformations is discussed.
Localized Bonds in SCF Wavefunctions for Polyatomic Molecules. III C–H and C–C Bonds
Authors: Newton Marshall D. , Switkes Eugene , Lipscomb William N.
Published: February 2004

Localized molecular orbitals which minimize the exchange energy have been obtained for CH4, C2H6, C2H4, C2H2, CH3CCH, C3H6, HCN, and H2CO. These objectively determined orbitals correspond to the inner shells, lone pairs, and two-center bonds of classical bonding theory. In each case where double or triple bonds occur, the local orbitals correspond to equivalent bent bonds. The hybrids in the C–C bonds of cyclopropane form angles of 28° with the internuclear direction. The local orbitals are analyzed in terms of hybridization, polarity, bond moments, bond directions, and delocalization. Calculation of the curvature of the self-repulsion energy surface provides an indication of the uniqueness of the results. Sigma–pi separability and the sensitivity of the local orbitals to changes in basis set are also discussed.
Correlation Field Coupling of Nondegenerate Nitrate Vibrations
Authors: Brooker M. H.
Published: February 2004

Laser Raman spectra have been recorded for several ionic nitrates. Band multiplicities in the out-of-plane deformation and its first overtone and in the symmetric stretching region are reported and discussed according to the selection rules of the appropriate factor group representation. Evidence exists for mixing between vibrations of the same symmetry species in the first overtone region of the out-of-plane deformation.
Matrix-Isolation Study of the Vacuum-Ultraviolet Photolysis of Methyl Chloride and Methylene Chloride. Infrared and Ultraviolet Spectra of the Free Radicals CCl, H2CCl, and CCl2
Authors: Jacox Marilyn E. , Milligan Dolphus E.
Published: February 2004

Infrared and ultraviolet spectroscopic studies have been conducted on the products of the vacuum-ultraviolet photolysis of normal and isotopically substituted methyl chloride and methylene chloride isolated in argon and nitrogen matrices at 14°K. The cage effect has been found to inhibit halogen detachment processes in these systems. Infrared absorptions attributable to CCl, HCCl, and H2CCl and the 2800-Å ultraviolet absorption of CCl appear in the methyl chloride photolysis studies. Observation of a “negative anharmonicity” for the lowest-frequency infrared absorption of H2CCl can be explained by postulating that the molecule is planar. The C–Cl stretching force constant of H2CCl is exceptionally high. The implications of (p–d)π bonding, which may account for the large C–Cl stretching force constant, are explored. An absorption near 2300 Å behaves appropriately for assignment to a second electronic transition of CCl, providing support for the previous tentative assignment of a group of emission bands to such a transition. Photolysis of methylene chloride in a matrix environment leads principally to the stabilization of CCl2. A revised estimate of the force constants of CCl2 is given.
Correlation Factor in Substitutional Diffusion in Binary Alloys
Authors: Kikuchi Ryoichi , Sato Hiroshi
Published: February 2004

The correlation factor is defined and derived by the path probability method of substitutional atomic diffusion (the vacancy mechanism) in binary alloys. The correlation factor thus defined is shown to be the same as that derived by the traditional random-walk approach in all cases where the latter approach is capable of calculating the factor, namely in self-diffusion, in impurity diffusion, and in randomly disordered alloys (excluding the nonpercolating limit in the last case). The calculation of the correlation factor is further extended by the path probability method to disordered and ordered alloys of arbitrary composition and arbitrary temperature. The relation of the present problem with the percolation problem is also discussed.
Concept of the Long-Range Order in Percolation Problems
Authors: Kikuchi Ryoichi
Published: February 2004

It is proved that the dilute alloy ferromagnet (Ising model) at the absolute zero and the site percolation problem are mathematically identical by introducing the uniqueness theorem (there is only one infinitely extended connected cluster of one atomic species) and the symmetry theorem (the number of clusters of a certain finite shape and size with a plus spin is the same as that with a mimus spin). It is then shown that the long-range order parameter in the site problem is the density of atoms belonging to the infinitely extending cluster. It is suggested that the site percolation problem when atoms interact and the atomic distribution is not random can be treated using the cluster variation method by placing a + or a − tag on the atomic species whose connectively is being sought, with the restriction that no (+ −) connection occurs and by maximizing the entropy (not minimizing the free energy) of the system. These signs are mathematical devices and have no physical meaning. Some results of higher order approximations of the bond and site percolation problems are discussed.
Electronic States of a Disordered Polymer
Authors: Julienne P. S. , Choi Sang-Il
Published: February 2004

A method introduced by Schmidt to give the vibrational frequency spectrum of an isotopic disordered one-dimensional lattice is generalized and applied to an infinite one-dimensional disordered molecular crystal with nearest-neighbor interactions. Such a model is applicable to a polymer having several molecular species arranged randomly along the polymer axis. Equations are derived which may be solved numerically to give the density of states for the following types of polymer: (1) the general disordered polymer having a random arrangement of several molecular species, the coupling constants between two species being determined by the species being coupled; (2) the glassy polymer having only one molecular species but with the coupling constants distributed randomly according to a continuous probability law. A numerical calculation of the density of states is made for the isotopic disordered polymer both with and without positional correlation between the molecular species and for the glassy polymer. When the energies of the two species in the diatomic isotopic disordered polymer differ by more than the nearest-neighbor coupling constant, the density of states is quite structured. Several of the peaks in this structure are associated with clusters of one or two molecules of one species in a lattice of molecules of the other species. Structure also appears in the density of states for the glassy polymer when there is a finite probability of small values for the nearest-neighbor coupling integrals.
Absolute Rates of the Reactions H+C2H4 and H+C2H5
Authors: Kurylo Michael J. , Peterson Norman C. , Braun Walter
Published: February 2004

The hydrogen atom–ethylene system was studied at 298°K employing the methods of resonance fluorescence and absorption by hydrogen atoms of Lyman α radiation at 1216 Å. The contribution of hydrogen atom–radical reactions was evaluated under varying experimental conditions, and the rate of disappearance of H atoms in ethylene was measured under conditions where stoichiometric corrections became significant. Measurements in the literature of reaction rates for H+C2H4 at low total pressure are now in good agreement; however the limiting high-pressure absolute rate constants thus far reported differ depending on the assignment of stoichiometric factors. Our results indicate that stoichiometric factors obtained under low-pressure conditions may not be applicable to high pressure. Furthermore, extrapolations based on plots of inverse rate constant vs inverse pressure may be in error due to significant curvature in such plots. Our high-pressure limiting rate constant for H+C2H4, extrapolated from data at pressures higher than those used by other workers, is free of stoichiometric corrections and is in agreement with our earlier measurements. Absolute rate constants obtained in this work are H+C2H4→k1 = 13.6 ± 1.9 × 10−13 (cm3molecule−1·sec−1) (extrapolated to infinite He pressure), H+C2H5→k4 = 6.0 ± 2.0 × 10−11 (cm3molecule−1·sec−1) (50 torr He). The latter rate has been estimated from the variation of the rate of disappearance of H atoms as a function of initial H atom concentration at 50 torr total pressure.
Combination Rules for van der Waals Force Constants
Authors: Kramer H. L. , Herschbach D. R.
Published: February 2004

A family of combination rules, from which van der Waals coefficients for interactions between unlike molecules may be estimated in terms of those for the corresponding like interactions and the static polariabilities, is tested empirically and related to an approximate parameterization of the frequency-dependent polarizability function. The treatment includes two- and three-body dipole force constants and the higher-multipole terms of the second-order two-body dispersion energy. The rules give agreement within a few percent (about the same accuracy as the input data) when compared with accurate unlike coefficients for systems involving H, He, Ne, Ar, Kr, Xe, Li, Na, K, Rb, Cs, Hg, H2, N2, CH4, He(21S), He(23S), He+, Li+, Na+, K+, Rb+, Cs+. Knowledge of n like coefficients and polarizabilities permits calculation of n(n − 1) / 2 unlike two-body and n(n − 1)(n + 4) / 6 unlike three-body force constants.
Λ
4
Band of 13CH4
Authors: Kyle Thomas G. , Blatherwick Ronald D. , Bonomo Francis S.
Published: February 2004

Absorption spectra of methane enriched to 52% in the 13C isotope were obtained in the 1300-cm−1 region with a 0.45-cm−1 resolution. The theoretical method of Hecht was used to determine the rotational and splitting parameters for the Λ4 band of 13CH4. A line-by-line calculated spectrum, using the calculated line positions, is compared to the observed spectrum.
Gaussian Basis Functions for Use in Molecular Calculations. I. Contraction of (9s5p) Atomic Basis Sets for the First-Row Atoms
Authors: Dunning Thom H.
Published: February 2004

The contraction of Gaussian basis functions for use in molecular calculations is investigated by considering the effects of contraction on the energies and one-electron properties of the water and nitrogen molecules. The emphasis is on obtaining principles which can be used to predict optimal contraction schemes for other systems without the necessity of such exhaustive calculations. Using these principles, contractions are predicted for the first-row atoms.
Hartree–Fock Wavefunctions and Computed Properties for the Ground (2π) States of SF and SeF and Their Positive and Negative Ions. A Comparison of the Theoretical Results with Experiment
Authors: O'Hare P. A. G. , Wahl Arnold C.
Published: February 2004

Self-consistent-field wavefunctions, near the Hartree–Fock limit, have been computed by the Roothaan expansion method for SF(2π) and SeF(2π) at the experimental internuclear separations. The results from the present investigation, coupled with our previous calculations on OF, show that the Hartree–Fock binding energies of OF, SF, and SeF vary nonmonotonically, in harmony with the experimental dissociation enthalpies. Other properties reported herein for SF and SeF include the vertical ionization potentials and vertical electron affinities, and the dipole and quadrupole moments for the neutral and charged species. The computed ionization potential for SF suggests that the experimental appearance potentials for SF+ are too large by approximately 2 eV. Thermodynamic calculations based on the electron affinities predict substantial stabilities for SF− and SeF− at moderate temperatures.
Energy Dissipation Mechanism for Quantum Mechanical Tunneling in Viscoelastic Relaxation
Authors: Reich S. , Eisenberg A.
Published: February 2004

Inelastic tunneling is proposed as a viscoelastic relaxation mechanism at low temperatures for polymers possessing methyl groups capable of rotation. In the process of dynamic mechanical excitation of the sample, the heights of the barriers which restrict the rotation of methyl groups are modulated periodically at the external excitation frequency. The change in the over-all barrier height is accompanied simultaneously by a change in the torsional energy levels of the methyl rotors. If rotational tunneling occurs between the same torsional states but differing slightly in energy (the difference in energy being due solely to the modulation of the barrier height by the stress field), then the difference in energy is given off as a phonon. Since tunneling is a random process, the phonons thus emitted are not coherent with the external excitation, and by interaction with the phonon bath of the sample they are thermalized, i.e., their energy is converted into heat. The concept of inelastic tunneling is reviewed briefly and the coupling of the rotational tunneling process to the phonon field is discussed, as are also the energetics of the process.
Vibrational Relaxation Measurements of Carbon Monoxide in a Shock-Tube Expansion Wave
Authors: McLaren T. Ian , Appleton John P.
Published: February 2004

A novel technique has been developed for use in the study of collisional energy transfer and chemical reaction rates in rapidly cooled gases. The principal feature is that the shock heated test gas sample is stationary during the cooling process so that the temporal behavior of a particular nonequilibrium property may be continuously monitored. The technique has been applied to the measurement of the vibrational de-excitation rate of carbon monoxide in an argon heat bath, using the fundamental infrared emission band of CO to follow its vibrational temperature throughout the expansion. In contrast to some recent investigations which indicate enhanced vibrational de-excitation rates, the present experiments show that when translation–vibration collisions control the relaxation process the characteristic vibrational relaxation time of carbon monoxide diluted in argon is the same no matter whether it is measured in a compression (shock wave) or expansion environment.
Triplet Exciton Trapping by Dislocations in Anthracene
Authors: Arnold S. , Whitten W. B. , Damask A. C.
Published: February 2004

Dislocations have been produced in anthracene crystals by plastic bending. The triplet exciton trapping characteristics have been obtained from a study of the temperature dependence of the triplet decay rate and delayed fluorescence intensity. The results indicate that only one kind of trap with depth 0.3 eV is introduced by the plastic bending. This trap can be removed by annealing the crystal for 1 h at 443°K. The trapping rate constant is three orders of magnitude smaller than expected for diffusion-limited trapping.
Dielectric Relaxation at High Frequencies
Authors: Birnbaum George , Cohen E. Richard
Published: February 2004

A theory of dielectric relaxation is presented which is based on using an interpolation function to represent a classical correlation function which is analytic at the origin and becomes exponential at sufficiently long times. The Fourier transform of this interpolation function is a relatively simple analytical function of frequency which has the Debye character at low frequencies but decreases essentially exponentially in the high-frequency wing. The parameters in the correlation function are discussed in terms of relaxation due to reorientational diffusion. Our model predicts practically the same absorption in the microwave region and somewhat more absorption in the far-infrared region as theories of dielectric relaxation which include the effect of rotational inertia, but in agreement with experiment predicts very much smaller absorption in the infrared region.
Absorption Spectrum of PuCl3
Authors: Carnall W. T. , Fields P. R. , Pappalardo R. G.
Published: February 2004

The absorption spectrum of thin films of PuCl3 was measured at 298, 77, and 4°K in the range 6000–34 000 cm−1. Results were compared to earlier work in LaCl3 :Pu3+, and a number of new assignments were made. Electrostatic, spin–orbit, and configuration-interaction parameters were obtained by direct diagonalization of the energy matrix and a least-squares fitting process to 30 observed levels. The variations in certain energy-level parameters within the actinide series is discussed. Intensity calculations gave only moderate agreement with oscillator strengths of observed bands.
Exact Classical Calculations on Collisional Energy Transfer to Diatomic Molecules with a Rotational and a Vibrational Degree of Freedom
Authors: Kelley J. Daniel , Wolfsberg Max
Published: February 2004

Exact classical calculations are carried out on energy transfer from the translational degree of freedom to the vibrational and rotational degrees of freedom in nonreactive atom–diatomic-molecule collisions. The diatomic molecule is either a harmonic or a Morse oscillator and the interaction potential is exponentially repulsive in the interatomic distances. The exact calculations are used to test the validity of a number of approximations which have been applied in theoretical treatments of this type of system. It is shown that the dynamic interaction between molecular rotational and vibrational motion during collision can introduce important differences between noncolinear and colllinear collisions; as a result, great care must be exercised in drawing conclusions from calculations on collinear systems.
Determination of Autoionization Lifetimes by Ion Cyclotron Reonances Linewidths
Authors: Henis J. M. S. , Mabie C. A.
Published: February 2004

The half-width and half-height for power absorption in the ICR spectrometer is shown to depend upon the time during which an ion absorbs power in the detection region of the instrument. In the case of negative ions, it is shown that autoionization can limit resolution, and conversely that the observed resolution for a given negative ion can be used to determine autoionization lifetimes. The SF6− ion is observed in the ICR spectrometer, and a lifetime of ∼ 500 μsec is calculated for this ion. The C4F8− ion is observed, and a lifetime of ∼ 200 μsec is calculated for that ion. The lifetimes are discussed with respect to other measured and calculated values, which show a wide variation, and it is suggested that the autoionization lifetimes may be strongly dependent on the energy of the impacting electrons. In this study, both ions are shown to be produced by electrons which are trapped in the ICR cell as opposed to being produced by beam electrons.