bluuebunny/crossref_metadata_2025 huggingface dataset:
Self-Consistent Field Theory for the Electronic Structure of Polymers
Authors: André Jean Marie
Published: February 2004

A general SCF–SCAO theory for computations of the electronic structure in polymeric species is presented. The theory is essentially a tight-binding model expressed in a manner close to the self-consistent field–LCAO matrix formalism and restricted to closed-shell cases. Particular care has been taken to ensure a theory which can be easily applied in practical applications. A computer program, polymol, has been programmed and a short description is included at the end of this paper. Throughout the paper reference is given to the (H2) infinite chain, as an example.
Effect of Pressure on Dielectric Relaxation in Isomeric Octanols
Authors: Johari Gyan P. , Dannhauser Walter
Published: February 2004

Dielectric constant and loss have been measured in the frequency range 0.1 − 5 × 106 Hz over a wide range of temperature and pressures to 4 kbar for the following compounds: 2-octanol, 7-methyl-, 6-methyl-, 5-methyl-, and 2-methyl-3-heptanol. For each compound, most of the dispersion is well described by the Debye equation. At high frequencies additional regions of dispersion appear which could be resolved in three of the compounds. Activation parameters are derived for all of the compounds and are functions of pressure, temperature, and the nature of the alcohol's alkyl group. A qualitative model of dielectric relaxation based on ideas of Litovitz and Anderson and Ullman is proposed to explain the results.
Further Analysis of the Vinyl Iodide Microwave Spectrum
Authors: Moloney Michael J.
Published: February 2004

Reanalysis of the published vinyl iodide microwave spectrum produced refined values of previously measured constants, and determined two quantities hitherto not known with precision: χab, the off-diagonal quadrupole coupling constant, and Δ, the interial defect. This value of Δ agrees with one computed from the infrared spectrum by the approximate method of Herschbach and Laurie. The rotational constants are, neglecting centrifugal-distortion effects, A = 53.3 ± 0.4 × 104MHz, B = 3258.72 ± 0.03 MHz, C = 3066.66 ± 0.03 MHz, and Δ = 0.24 ± 0.08 amu·Å2. The quadrupole coupling constants are χaa = − 1654.3 ± 1 MHz, χbb = 768.8 ± 1 MHz, χab = −710 ± 25 MHz. Diagonalization of the χ tensor gives χαα = − 1847 MHz and χββ = 962 MHz. The angle between the a axis and the C–I bond is 15.2° ± 0.7°, assuming the χ tensor diagonal along the C–I bond.
Metastable Species Produced by Electron Excitation of N2, H2, N2O, and CO2
Authors: Clampitt R. , Newton Amos S.
Published: February 2004

A molecular beam is crossed by an electron beam to produce metastable molecules and fragments which are detected by electron ejection from a Cs3Sb cathode in a chamber operating at ultrahigh vacuum. Excitation functions for the production of H2(c3Πu) molecules and of photons from H2 are reported. The time-of-flight distribution of the slow group of H(2S) atoms from H2 has been measured and this differs from a previously reported distribution. Threshold-energy and kinetic-energy measurements have been made on the electronically excited fragments known to be produced in the dissociative excitation of CO2 and N2O. It is postulated that in CO2 the initial products are CO(a3II) and O−. A new excitation curve for the E3Σg+ state of N2 was determined.
Thermal Diffusion in the Nonpolar–Polar System Helium–Methyl Chloride
Authors: Ghosh A. K. , Deb S. K. , Barua A. K.
Published: February 2004

The thermal diffusion factor αT for a 1:1 mixture of He and CH3Cl has been measured by the two-bulb method at different temperatures ranging from 338°–530°K. The composition dependence of αT for this system has also been studied at 362.8°K. For the temperature dependence of αT the agreement between experimental and calculated values is poor even when inelastic collisions are taken into account. For the composition dependence of αT the theoretical and experimental curves run approximately parallel to each other over the whole composition range. This probably means that the inelastic collisions do not play a significant role in the thermal diffusion phenomenon of this system.
Neutron Inelastic Scattering and X-Ray Studies of Aqueous Solutions of Dimethylsulphoxide and Dimethylsulphone
Authors: Safford G. J. , Schaffer P. C. , Leung P. S. , Doebbler G. F. , Brady George W. , Lyden E. F. X.
Published: February 2004

Molecular vibrations in solid and liquid dimethylsulphoxide (DMSO) and dimethylsulphone (DMSO2) have been measured by neutron inelastic scattering between 900–8 cm−1. Neutron spectra of the intermolecular frequencies of water molecules in aqueous solutions of perdeuterated DMSO and DMSO2 have also been measured to determine, as a function of concentration and of temperature, the influence of these compounds on the water structure. In addition, the broadening of the incident energy distribution by diffusive motions of H2O molecules has also been investigated. The similarity of intermolecular frequencies in the spectra of both the liquid and solid phases of the pure compounds shows a high degree of dipole association. In dilute aqueous solutions the DMSO and DMSO2 (hydrogenous and perdeuterated) both cause a similar enhancement and sharpening of the intermolecular frequencies of the water structure associated with a small and cooperative perturbation in the orientation of many H2O molecules. This is consistent with the x-ray radial distribution which shows a corresponding small enhancement of the peaks of pure water out to 8 Å. As the concentration of DMSO is raised, the existing water structure is broken down due to the formation of hydrogen-bonded, thermolabile, DMSO–H2O complexes. The angular and temperature dependences of the diffusively broadened incident energy distribution are both in accord with delayed or jump diffusion. At low concentrations, the residence times and the self-diffusion coefficients of H2O molecules in both DMSO and DMSO2 solutions are similar to those for pure water. At higher concentrations of DMSO, the increased formation of the hydrogen-bonded complexes causes a decrease in the self-diffusion coefficient and an increase in the delay or residence time for water molecules. Both neutron spectra and x-ray data indicate that the dipole interactions and hydrogen bonding of DMSO inhibit the formation of hexagonal ice upon freezing; this may account for the cryoprotective properties of DMSO.
Extension of the Debye–Hückel Theory of Electrolyte Solutions
Authors: Outhwaite C. W.
Published: February 2004

The Debye–Hückel theory of electrolyte solutions is extended to take account of the so-called fluctuation potential. An oscillation in the Debye–Hückel potential for symmetrical electrolytes is predicted at approximately κa = 1.495 and the corresponding oscillation in the mean potential of the double layer pointed out. A simple derivation of the oscillation predicted by Kirkwood and Poirier is also given.
Effect of Neighboring Identical Atoms on Radiative Lifetime: The Case of Three Atoms
Authors: Lurie Joan B.
Published: February 2004

Transition frequencies (inverse radiative lifetime) are evaluated as a function of separation for a system of three identical atoms or molecules one of which is initially excited. The resulting frequencies are increased or decreased relative to the value characteristic of an isolated atom according to whether the wavefunction is symmetric or not. The results depend on the geometrical configuration of the atoms.
Anisotropic Molecular Reorientation in Methyl-d3-acetylene in the Liquid State
Authors: Jonas J. , DiGennaro T. M.
Published: February 2004

The temperature dependence of deuteron and proton spin–lattice relaxation times, T1, has been measured in methyl-d3-acetylene and methylacetylene-d1 using the adiabatic fast passage method. The difference in activation energies obtained from deuteron T1 data for acetylenic deuteron (Ea = 1.7 kcal/mole) and methyl-d3 deuterons (Ea = 1.1 kcal/mole) demonstrates that the reorientation is anisotropic without assumption of any model for reorientation. Assuming the validity of the rotational diffusion equation the deuteron T1's due to quadrupolar interactions were analyzed in terms of rotational diffusion constants D⊥ and D|. At −30°C D⊥ = 1.3 ± 0.15 × 1011sec−1 and D| = 18.3 ± 1.2 × 1011sec−1 in methyl-d3-acetylene. The applicability of the rotational diffusion mechanism for the description of the reorientation about the main symmetry axis is questionable as is shown by a comparison of τ| with the time for the mean period of rotation of a free rotor. At temperatures above the bp the spin–rotation interactions contribute to the relaxation rates of protons, in addition to dipolar interactions which are predominant at lower temperatures. The spin–rotation interaction constants were approximately estimated to be 0.6–4.0 kHz for the acetylenic proton in methyl-d3-acetylene and 6–25 kHz for the methyl group in methylacetylene-d1. The results indicate the importance of inertial effects.
Adsorption of CO on Tungsten: Field Emission from Single Planes
Authors: Engel T. , Gomer R.
Published: February 2004

The work functions and Fowler–Nordheim pre-exponentials on the (110), (100), (211), (111), and (210) regions of a tungsten field emitter have been determined by means of a probe-hole method as function of thermal treatment of full CO layers; as function of coverage in incremental dosing at 100°K; and as functions of readsorption on beta layers. The results shows that virgin, alpha, and beta states are formed on all regions investigated, but that their properties vary with substrate orientation. The results on the close-packed planes (110) and (100) indicate complex behavior of beta layers on heating, and suggest surface reconstruction at T > 700°K. Temperatures for the onset of surface diffusion of CO were also determined, and indicate that diffusion occurs most readily on the zones (211)–(110) (at 275°–300°K). This is interpreted to mean that diffusion over (110)-like regions is rapid, but that trapping at the edges of (110) diffusion steps occurs. Adsorption on (110) is not seen below 800°K, and on its vicinals below 500°K, indicating that diffusion over these regions occurs without trapping below these temperatures. This is considered further evidence for surface reconstruction on (110) at high temperature. Diffusion into the vicinals of (111) occurs at 575°K and into (111) at 700°K. Diffusion into (100) was noted at 750°K.
Dipole Properties of Molecular Hydrogen
Authors: Victor G. A. , Dalgarno A.
Published: February 2004

Experimental data on electron scattering, optical refractivity, and molecular anisotropy are used to construct a model dipole spectrum for molecular hydrogen which is consistent with oscillator-strength sum rules. The model spectrum is used to calculate the parallel and perpendicular dynamic dipole polarizabilities, the refractive index, the Verdet constant, the Rayleigh scattering cross section, the Rayleigh depolarization factor, and the molecular anisotropy as a function of frequency of the incident radiation. The tensor components of the van der Waals coefficient for a pair of interacting hydrogen molecules are also calculated.
Electronic Structure and Quadrupole Splittings of Ferrous Iron in Hemoglobin
Authors: Eicher H. , Trautwein A.
Published: February 2004

Unexplained quadrupole splittings ΔEQ of some Fe porphyrin compounds, deuteroheme (Py)2, mesoheme (Py)2, HbCO, HbO2, and Hb, measured by the Mössbauer effect, gave the impulse to evaluate within the 3d6 configuration, the eigenvalues and eigenvectors of a Hamiltonian, involving the Coulomb repulsion of 3d electrons and the tetragonal point symmetry of the iron cation. From these calculations it was found that the levels A11,E3,B25, and E5 lay lowest in energy. The resulting EFG tensors were compared with experiment in order to get information about the energy term scheme of these low-lying levels. The relatively large value of ΔEQ in deuteroheme (Py)2 results from spin–orbit interaction between the ground-state A11 and the low-lying E3 level (≈ 345 cm−1), which is raised to at least 1000 cm−1 in mesoheme (Py)2 and HbCO. In the case of HbO2, it is supposed that an antiparallel orientation of the oxygen spin (S = 1) and the spin of the E3 level would result in zero net spin. The calculated EFG, caused by the E3 level, agrees with experiment. For all diamagnetic compounds there is evidence for α low-lying high-spin level B25. In the case of ferrous high-spin iron in Hb, spin–orbit interaction was proved to be most important, too. In order to fit the measured ΔEQ(T) values, low-lying levels A11,E3,E5, beside the ground-state B25, have to be included in our calculations.
Dissociation of Carbon Dioxide in the Positive Column of a Glow Discharge
Authors: Corvin K. Kutszegi , Corrigan S. J. B.
Published: February 2004

The dissociation of CO2 by electron impact was investigated in the positive column of a dc glow discharge for gas pressures between 0.3 and 4 mm Hg and a current of 0.6 mA in a tube of radius 1.25 cm. The reaction rate was determined by separating and measuring the noncondensable products formed. The effects of the cathode and anode regions of the discharge were eliminated by varying the interelectrode distance to obtain the axial electric field in the positive column and also the molecular dissociation rate per unit length of column. The number of dissociating collisions αd / p by an electron drifting unit length along the field direction of the positive column was measured for values of E / p between 11 and 32 V cm−1·(mm Hg)−1 showing corresponding values of αd / p of 0.15 and 0.67 at these limits. The measured rate coefficients show that dissociation proceeds via uncharged species. A reaction mechanism CO2+e→ lim collisionCO+O is consistent with the observed phenomena. It is suggested that the dissociative excitation is to a 3Π state of CO2 about 6.1 eV above the ground state. Assuming an onset potential of 6.1 eV, a cross section that rises to a maximum of 3.5 × 10−17 cm2 at 6.9 eV and then rapidly decreases with increasing electron energies, is compatible with the observed dissociation-rate coefficients.
Transport in Molten Salts under Pressure. I. Glass-Forming Nitrate Melts
Authors: Angell C. A. , Pollard L. J. , Strauss W.
Published: February 2004

The electrical conductances of calcium nitrate–potassium nitrate solutions have been measured as a function of temperature to 200°C and pressure to 3000 atm, by imposing oil pressure directly on samples held within an externally heated bomb. Log (conductance) varies linearly with pressure at high temperatures, but curvilinearly at low temperatures, the “activation volume” appearing to increase with increasing pressure. “Activation volumes” increase rapidly with decreasing temperature. The observations may be accounted for if the “ideal glass transition temperature” T0 is taken to be the only pressure-dependent variable in a simple equation previously found to describe temperature and composition-dependent variations in conductance in this, and other, systems. Within uncertainty limits, T0 varies linearly with pressure and mole fraction, thus pressure equivalents of given composition changes can be simply stated. Using a thermodynamic relation applicable at the glass transition, the observed dependence of T0 on pressure is used to predict the change of heat capacity at the glass transition. The value is confirmed within error by direct measurements. Application of the Adam–Gibbs theory of relaxation processes leads to the derivation of approximate “constant (configurational) entropy” parameters, E (Sc), which exhibit qualitatively the properties of “constant volume” parameters, E(V), observed in studies of nonionic liquids.
Hydrazine Decomposition in a Flow Reactor
Authors: Logan F. E. , Marchello J. M.
Published: February 2004

The decomposition of hydrazine prompted by an alternating current-glow discharge in a flow reactor was reported earlier. An important observation was the existance of a threshold level of decomposition. The threshold level and experimental data can be explained with a mechanism consisting of three regimes as discussed herein. The first regime is responsible for threshold phenomena, the second regime for the reformation of hydrazine, and the third for the slow decomposition.
Study of the F Model Using Low-Temperature Series
Authors: Nagle John F.
Published: February 2004

The F model is studied for temperatures below Tc by the series method. Particular attention is paid to the behavior of the model in a staggered field which has not been obtained exactly. The accuracy and reliability of the series method as applied to the F model are discussed. It is concluded that the series method is illuminating in revealing the qualitative behavior of the F model, and the series reliably indicate that accurate quantitative estimates near the critical point are not possible unless longer series are obtained.
Sum Rules for Variational Wavefunctions
Authors: Dalgarno A. , Epstein S. T.
Published: February 2004

It is demonstrated that the finite set of wavefunctions obtained by applying the variational principle to a linear combination of basis functions provides bonds to a number of sum rules and that by appropriate choice of the basis functions certain of the sum rules can be satisfied exactly.
Nuclear Magnetic Shielding in F2
Authors: Hindermann David K. , Williams Lesley L.
Published: February 2004

The 19F chemical shift between gaseous F2 and SiF4 has been measured to be − 596.0 ± 0.2 ppm at 30°C. With a recently established absolute shielding scale for 19F this value yields an absolute shielding in F2 of − 232.6 ppm. Combination of this with the measured spin–rotation constant leads to a separate determination of experimental values for σFd and σFp, with arbitrary choice of gauge origin, which are then compared with available theory. An estimate of the vibrational effects is given.
Viscosity and Density in Molten BeF2–LiF Solutions
Authors: Cantor S. , Ward W. T. , Moynihan C. T.
Published: February 2004

The viscosity of the molten salt system, BeF2–LiF, was determined with a coaxial-cylinder viscometer. The concentration range studied was 36–99 mole % BeF2, each composition being measured over a 200° temperature interval within over-all limits of 376°–967°C. The viscosity isotherms exhibit an exponential decrease in viscosity with increasing LiF concentration; the decreases are attributed to the rupturing of fluoride bridges in the BeF2 network structure. Each composition displayed Arrhenius behavior (Eη, energy of activation for viscous flow, was independent of temperature). Eη decreased with LiF concentration in a way that paralleled the decreases in the analogous systems, SiO2–alkaline-earth oxide. Densities were measured between 50 and 100 mole % BeF2. From these measurements and other density determinations in BeF2–LiF, it was found that the molar volumes were additive. Volume expansivity, however, increases markedly with increasing LiF concentration. The decrease of Eη with LiF content in this system is correlated with an increase in volume expansivity; for the composition range 100–70 mole % BeF2, Eη is linear with the reciprocal of expansivity.
Simple Analytic Expression for General Two-Center Coulomb Integrals
Authors: Flannery M. R. , Levy H.
Published: February 2004

A straightforward derviation of a general analytic expression for two-center Coulomb integrals is presented. The expression displays a simple analytic dependence on the nuclear separation.
Luminescence of Phosphors Based on Host Lattices ABO4 (A is Sc, In; B is P, V, Nb)
Authors: Blasse G. , Bril A.
Published: February 2004

The luminescence of the unactivated and Bi3+- and Eu3+-activated compounds ABO4 (A is Sc, In; B is P, V, Nb) is reported and compared with the luminescence of the corresponding rare-earth and yttrium compounds. The ScNbO4 shows a weak, blue emission, ScVO4 a blue-green, and InVO4 a green emission. The other host lattices show no or only a very weak emission at room temperature. The color of the vanadate emission depends strongly on the choice of A. This was studied by replacing part of the A ions by other ions or a combination of ions. The shift of the vanadate emission is ascribed to two effects, viz., metal–metal interaction (e.g., Bi3+–VO4) and the effect of the size of the metal ions at the A sites (e.g., Sc3+). The Eu3+-activated phosphors show some interesting features. The intensity of the forced electric dipole emission from the Eu3+ ion seems to depend strongly on the position of the lowest strong absorption band. In the zircon structure the D50−7F2 emission is hypersensitive to the surroundings, although no linear crystal-field component can be present. Both (In, Eu) PO4 and (In, Eu) VO4 show an orange (D50−7F1) emission due to the presence of inversion symmetry at the In3+ site.
Excitation of Alkali Atoms by Electron Impact
Authors: Mathur K.C. , Tripathi A. N. , Joshi S. K.
Published: February 2004

Electron-impact excitation cross sections of alkali-metal atoms are calculated in a classical impulse approximation, using a quantal momentum distribution function for the atomic electrons in the ground state. The results are compared with the experimental and other theoretical results.
Measurement of Barium Vapor Density
Authors: Hinnov E. , Ohlendorf W.
Published: February 2004

The density of atomic barium emitted from a small aperture in a uniformly heated stainless-steel oven has been measured by the method of resonance fluorescence. The range of the oven temperature was 730°–1200°K. At lower densities, the resonance transition 6s2S1→6spP1 was used for the density measurements, at higher densities the forbidden transition 6s21S → 6p5d 3P orD3. From the measured spatial distribution of the density above the aperture, the equilibrium vapor pressure in the oven was deduced. The latter can be expressed empirically reasonably well by the formula log10p(torr) = 6.80 − (8800 / T) with the temperature T in degrees Kelvin. At temperatures higher than 1000°K the measured densities were progressively slightly lower than this formula predicts. However, the deviation could be due to certain systematic errors in the measurement which become progressively more serious with increasing density. In addition to the barium density, the measurements yielded some information on the atomic transitions employed, generally confirming previous knowledge in this matter.
Far-Ultraviolet Spectra of Xe and CO Adsorbed on Cooled LiF Films
Authors: Brith Malka , Ron Arza
Published: February 2004

The uv absorption spectra of adsorbed Xe and CO in LiF films were investigated. The P31→S10 and P11→S10 transitions of Xe were observed. These atomic absorption lines are very much broadened (1000–200 cm−1) in the adsorbed state. The bands are shifted relative to the gas phase and the magnitude of the shift is a function of the surface coverage. The shift ranges from several hundred wavenumber units to the blue for low coverages to several hundred wavenumber units to the red for high coverages. Removal of orbital degeneracy, if present, is smaller than the bandwidth. The A 1Π ← X 1Σ+ transition of adsorbed CO was investigated in the wavelength region 1600–1300 Å. The bands are quite narrow compared to the bands of adsorbed Xe. Each vibronic state is split into two components. The magnitude of the splitting is 600–1000 cm−1. This splitting is believed to be due to the removal of the π-orbital degeneracy by the LiF surface field.
Mean First Passage Time in a Linear System with Nearest-Neighbor Interactions. Application to a Theory of Muscle Action
Authors: Hill Terrell L. , White George M.
Published: February 2004

Earlier work (in connection with the theory of muscle action) on a mean-first-passage-time problem in a one-dimensional Ising system with no nearest-neighbor interactions is extended here to a case in which interactions of this sort are taken into account. Because of the complexity of the problem, an “internal-equilibrium” approximation is used. It is found that, in general, interactions do not affect the order of magnitude of earlier results.
Absorption Spectrum of the He2 Molecule in the 510–611-Å Range
Authors: Tanaka Y. , Yoshino K.
Published: February 2004

New vacuum-uv absorption phenomena in helium are reported. The most important of these consist of bands between 600 and 611 Å. Individual bands exhibit diffuse rotational structure and together form a υ′ progression. They are attributed to the transition A 1Σu+←X 1Σg+ of He2. Several rotational constants Bυ for the upper state are noted. The dissociation energy and the term value of the upper state are estimated. A minimum height for the potential “hump” in the upper state is determined to be 0.059 eV. The close connection between the emission and absorption bands of He2 around 600 Å is indicated and discussed. The location of the He-continuum (emission) peak is worked out in relation to the A-state term value and the ground-state potential function. A number of absorption bands were also observed in the range from 510–600 Å. They are attributed to other singlet systems relating to ns and nd orbitals (n > 2).
Luminescence from Aromatic Polymers, Monomers, and Dimers under High-Energy Electron Excitation
Authors: Phillips Donald H. , Schug John C.
Published: February 2004

The luminescence spectra of various polymers and solid-model compounds induced by 1-MeV electrons are reported and interpreted. The presence of enhanced triplet emission and absence of singlet emission from poly(p-xylene), poly(monochloro-p-xylene), and the model compound dibenzyl are interpreted on the basis of a molecular resonance model. Some triplet excimer and other long-wavelength (450–550-mμ) emission were also observed in these spectra. The spectra of the monomers p-xylene and 2-chloro-p-xylene consisted primarily of long-wavelength emission (400–600 mμ), while the spectra of frozen toluene and durene exhibited both neutral molecule singlet and the long-wavelength emission. Benzene exhibited only singlet, singlet excimer, triplet, and triplet excimer emission. The polymers poly(ethylene-2,6-naphthalene-dicarboxylate), poly(ethyleneterephthalate), and polysulfone emitted primarily from singlet and singlet excimer states. The model compounds for these polymers, dimethyl-2,6-naphthalenedicarboxylate, dimethylterephthalate, and methyl-p-toluenesulfonate exhibited varying amounts of singlet, triplet, excimer, and neutral or ionic radical emission.
Hyperfine Structure of HD17O by Beam-Maser Spectroscopy
Authors: Verhoeven J. , Dymanus A. , Bluyssen H.
Published: February 2004

Hyperfine structure of the 22→21 rotational transition of HD17O at 10.374 GHz has been investigated with a beam-maser spectrometer. The best-fit results for the spin–rotation coupling constants CJτ(K) and for the components χij(K) of the quadrupole coupling tensors in their principal coordinate systems are in kHz: C22(H) = − 42.20 ± 0.20; C21(H) = − 42.98 ± 0.20; C22(D) = − 2.04 ± 0.02; C21(D) = − 2.0000 ± 0.0015; C22(O) = − 22.5 ± 0.3; C21(O) = − 22.35 ± 0.20; χxx(O) = 10 175 ± 67; χyy(O) = − 8 891 ± 21; χzz(O) = − 1283 ± 87; χx′x′(D) = 307.90 ± 0.14; χz′z′(D) = − 133.13 ± 0.14; χy′y′(D) = − 174.78 ± 0.29; η(O) = (χzz(O) − χyy(O)) / χxx(O) = 0.75 ± 0.01. These results show good agreement with recent ab initio calculations and remove the discrepancy with the experimental results of Stevenson and Townes (η(O) = 1.83 ± 0.20).
Infrared Spectra and Geometry of SO2 Isotopes in Solid Krypton Matrices
Authors: Allavena M. , Rysnik R. , White David , Calder V. , Mann D. E.
Published: February 2004

The infrared spectra of the 32S, 34S, 16O, 18O isotopic species of SO2 trapped in solid krypton matrices at 20°K are reported. Under conditions of medium resolution (∼0.8 cm−1), single bands are observed in each of the spectral regions which correspond to the three vibrational modes. Analysis of all the matrix data on the basis of a valence force field which includes anharmonic corrections and in which the bond angle is treated as a variable parameter yields force constants very close to those derivable from the available gas-phase data. The SO2 bond angle which leads to the best fit of the experimental matrix data is 119°37′, in excellent agreement with the angle determined from microwave data. The use of measured isotopic shifts for the determination of the bond angles in triatomic molecules both from matrix and gas-phase studies is examined in considerable detail. It is shown that the use of observed frequencies in calculations involving two isotopic species can lead in many cases to reliable upper and lower limits of the bond angle. The quality of these limits depends on the magnitude of the anharmonic corrections and the stretch–bend interaction. The infrared spectra of matrix isolated SO2 and NO2 under conditions of higher resolution (0.3 cm−1) reveal some interesting features in the asymmetric stretching mode ν3. These features are discussed in terms of a hindered rotation in the solid krypton matrix.
Spectral Sensitization, Supersensitization, and the Mechanism(s) of Dye-Sensitized Photoconductivity in AgBr Single Crystals
Authors: Zuckerman Bernard , Mingace Herbert
Published: February 2004

Spectral sensitization of photoconductivity in single crystals of AgBr in the 590–600-nm region has been accomplished using a substituted thiacarbocyanine dye. Relative quantum efficiencies (RQE) in this region, as determined by photoconductivity measurements, are shown to increase as dye-layer coverage decreases. The RQE of the larger dye aggregates is degraded by the presence of iodide on the AgBr surface, resulting in a shift of the RQE maximum to the short aggregate absorption region, particularly that of the dimer and trimer. The same red-absorbing dye was supersensitized with a green-absorbing dye and action spectra and efficiencies of carrier generation compared with the previous experiments. Efficiency maxima are now found in the 590–600-nm region, in agreement with the iodide-treated system. The photo-responses and consequent efficiencies, in these systems, decay with time. The form of the decay curve has been investigated with emphasis on the relative behavior of various absorption regions within the spectrally sensitized band. The RQE of larger aggregates is shown to decay more rapidly and more severely. Dye-sensitized photoconductivity occurs through a mechanism of either electron injection or energy transfer. An estimate of the maximum depth through which energy transfer can take place, if this is the appropriate mechanism, is 40–90 Å. We feel that electron injection is a more likely mechanism and the result of this calculation raises some question of the applicability of the energy-transfer hypothesis to this system.
Photovoltaic Effect at Dye–Photoconductor Interfaces
Authors: Petruzzella N. , Ferrier J. , Schaer M. , Nelson R. C.
Published: February 2004

Photovoltages at the junction of a solid-dye film and a cadmium sulfide film were measured where the dye was charged positively with respect to the cadmium sulfide. For blue pinacyanole the photovoltage is approximately equal to the contact potential difference between the dye and cadmium sulfide and is only weakly affected by illumination. On the other hand, for violet pinacyanole and salts of crystal violet the photovoltage is strongly illumination dependent and is only a measure of the relative density of charge carriers in the cadmium sulfide and the dye. In the latter case, equilibrium exists across the junction in the dark, while for blue pinacyanole the behavior suggests that in the dark no charge carriers are exchanged between the dye and cadmium sulfide. The photovoltaic results are consistent with a localized conduction process in organic dyes and a charge-transfer mechanism of dye sensitization. However, only in the case of blue pinacyanole do the photovoltages have any predictive value for dye sensitization.
Electrical Resistivities of Nonstoichiometric Cerium Hydride Single Crystals
Authors: Libowitz G. G. , Pack J. G.
Published: February 2004

Electrical resistivities as a function of temperature (−130° to 25°C) were determined on single crystals of cerium hydride ranging in composition from CeH1.94–CeH2.85. Measurements were performed in an inert-atmosphere dry box using the four-point probe technique. Cerium hydride exhibited metallic behavior in the range CeH1.9–CeH2.7. However, at a composition of about CeH2.85, a positive temperature coefficient of conductivity indicative of semiconductivity was observed. It is proposed that the semiconductivity of cerium trihydride is due to hydrogen vacancies which act as electron donors in the CeH3 structure. The observed change in slope of the resistivity vs 1 / T curves yielding two apparent activation energies is caused by the presence of substitutional oxygen impurities which act as electron acceptors. On the basis of this model, the donor level is calculated to be 0.30 eV below the conduction band.
Proton Magnetic Resonance Solvation Study of Sc(NO3)3, Y(NO3)3, and Th(NO3)4 in Water–Acetone Mixtures
Authors: Fratiello Anthony , Nishida Vone M. , Lee Robert E. , Schuster Ronald E.
Published: February 2004

Cation coordination measurements of Sc(NO3)3, Y(NO3)3, and Th(NO3)4 in water–acetone mixtures have been made by a proton magnetic resonance method. At low temperatures, solutions of these salts exhibit separate proton resonance signals for bulk water and water molecules in the primary solvation shell of the cation. Integration of these signals provides a direct measure of the number of water molecules coordinated to the cation. Values of 3.9, 2.4, and 2.9 were obtained for Sc(III), Y(III), and Th(IV), respectively, over a range of salt and solvent concentrations. These values may reflect extensive ion pairing in these solutions, particularly in the Y(III) and Th(IV) cases. The PMR spectra of Th(IV) solutions revealed multiple signals for the protons of coordinated water molecules, lending evidence to the postulate of ion pairing in these systems.
ESR Spectrum of the 9-Molybdomanganate(IV) Ion in Dilute Single Crystal
Authors: Rasmussen P. G. , Beem K. M. , Hornyak E. J.
Published: February 2004

The ESR spectrum of a single crystal of (NH4)6[NI(IV)O6Mo9O26]·8H2O containing 1% (NH4)6-[Mn(IV)O6Mo9O26]·8H2O has been investigated. This is the first ESR report on quadrivalent manganese in a chemically well-characterized environment. The site symmetry is D3, and anisotropic g values, hyperfine splittings, and zero-field splitting values were obtained by fitting the spectrum with an axial spin Hamiltonian.
Enthalpy of Sublimation of Zinc and Cadmium; Correlation of ΔH° vs ΔS°; Comparison of Torsional and Knudsen Vapor Pressures
Authors: McCreary J. R. , Thorn R. J.
Published: February 2004

The vapor pressures of solid zinc and cadmium have been determined directly by measurements of the torsional recoil of a suspended effusion cell (p) and indirectly by measurement of mass effusion (π). The results with R in calories/mole·degree and p and π in atmospheres are as follows: For zinc (610°–690°K) the torsional recoil yields lnp = − (30.370 ± 0.070) × 103 (RT)−1 + (27.215 ± 0.107)R−1, at 645°K logp = − 4.3423 ± 0.0011; the mass effusion yields lnπ = − (30.379 ± 0.126) × 103 (RT)−1 + (27.087 ± 0.193)R−1, at 645°K log π = − 4.3733 ± 0.0016; for cadmium (525°–590°K) the torsional recoil yields lnp = − (26.361 ± 0.123) × 103(RT)−1 + (27.135 ± 0.219)R−1, at 555°K logp = − 4.4501 ± 0.0017; the mass effusion yields lnπ = − (26.172 ± 0.139) × 103(RT)−1 + (26.672 ± 0.247)R−1, at 555°K logπ = − 4.4768 ± 0.0019. In these equations the cited errors are standard deviations generated in least-squares analyses. The measured pressures for zinc and cadmium are 1.075(± 0.01) and 1.063(± 0.01), respectively, times the equivalent mass effusion for molecular weight corresponding to monomer. This ratio appears to represent a demonstrable systematic difference between the two procedures. A brief survey of measurements for various material by others reveals that p is generally greater than π probably because the restituted momentum from the surroundings makes the former too high. A procedure based on ΔS°T(ΔH°0) is defined which recognizes systematic errors in lnp vs T−1 and which derives a value for ΔH°0 free of the inconsistencies frequently introduced in averaged values of RT lnp (the so-called third law procedure). For zero error in absolute entropies and for mass effusion, the results are for zinc ΔH°0 = 31.043 ± 0.054 kcal/mole and for cadmium ΔH°0 = 26.754 ± 0.062 kcal/mole.
Classical Theory of Small Energy Accommodation Coefficients. Application to 3He and 4He on W
Authors: Goodman Frank O.
Published: February 2004

Some recent experimental data on the energy accommodation coefficients of the systems 3He–W and 4He–W are compared with the predictions of the classical theories of gas–solid interactions. For reasons which are explained, these data should provide a particularly good test of theory. The classical lattice theory of energy accommodation coefficients is generalized, using results from other theories, to take account of the three-dimensional nature of the gas; this generalization involves, for example, elimination of the assumption of normal, head-on encounters of gas atoms with surface atoms and consideration of the hopping of gas atoms at the surface. The gas–solid interaction potential is the recently proposed modified exponential repulsion, the use of which allows considerable simplification of the analysis. The assumption that accommodation coefficients are independent of solid temperature, allowing use of a lattice model at zero temperature, is retained and discussed at some length. The application to He–W allows the calculations to be simplified by means of a perturbation procedure which is valid only for small accommodation coefficients. Although there are some disappointing features, in view of the approximations still existing in the theory the comparisons made are satisfactory. For example, there are no grounds for concluding, on the basis of these comparisons, that a classical model is inadequate for dealing with the accommodation of He–W.
Absolute Differential Cross Sections of Elastically Scattered Electrons. I. He, N2, and CO at 500 eV
Authors: Bromberg J. Philip
Published: February 2004

An electron spectrometer especially designed for the study of elastic scattering has been constructed and used to measure absolute differential elastic cross sections of 500-eV electrons scattered from He, CO, and N2. Comparison with calculated values for He indicates that the first Born approximation with exchange gives results which agree with experiment to within 2% at angles greater than 18°. At small angles the observed cross sections exceed the calculated by a large factor. The cross sections for N2 and CO change with angle in very similar ways.
Reactive Scattering of K by HBr, DBr in Crossed Molecular Beams: Angular and Velocity Distributions of KBr in Laboratory and c.m. Systems
Authors: Gillen Keith T. , Riley Clyde , Bernstein R. B.
Published: February 2004

Measurements of the velocity and angular distribution of KBr formed in reactive collisions between crossed molecular beams of velocity-selected K and thermal HBr(DBr) at a collision energy of 2.8 kcal/mole are described. The results have been subjected to a computer analysis to extract information about the center-of-mass (c.m.) distributions. For both isotopic systems, the c.m. recoil energy distributions are broad, and are similar in shape. The c.m. angular distributions are also broad; HBr shows relatively greater wide-angle scattering than DBr. The total reactive cross section for K+HBr is 40% larger than that for K+DBr. Measurements of the angular distribution of nonreactively scattered K agree well with the results of Airey et al. in the region of the rainbow angle.
Optical Absorption Spectra of Crystal-Field Transitions in MnO
Authors: Huffman Donald R. , Wild R. L. , Shinmei M.
Published: February 2004

A technique is described for growing single crystals of MnO on MgO substrates by heating in a completely closed chamber of pressed powder MnO. The samples are thin enough that the five lowest-energy crystal-field absorption bands could easily be resolved in the optical absorption spectrum, whereas only three had been previously reported. From the transition energies the crystal-field parameters have been determined to be Dq = 1010 cm−1, B = 601 cm−1, and C = 3540 cm−1.
Vibrational Spectra and Structure of Tetramethyldiarsine in the Crystalline and Fluid States
Authors: Durig J. R. , Casper J. M.
Published: February 2004

The infrared spectra of solid and gaseous tetramethyldiarsine have been recorded from 4000 to 33 cm−1. The Raman spectra of the liquid and the solid have also been recorded. A comparison of the Raman spectra of the liquid and the solid indicates that there are two conformers present in the liquid phase. From a comparison of the infrared and Raman spectra of the solid it is concluded that the mutual exclusion rule is operative and that only the trans conformer is present in the solid. The liquid is believed to be a mixture of trans and gauche conformers, with the trans predominating. A study of the temperature dependence of the intensities of the Raman spectrum of the liquid gives an energy difference of approximately 600 cal/mole between the two conformers. A vibrational assignment is proposed for the trans isomer and discussed in detail.
Effects of Ionizing Radiation on Potassium Hydrogen Malonate
Authors: Box Harold C. , Budzinski Edwin E. , Potter William
Published: February 2004

Electron spin resonance spectroscopy was used to observe the primary effects of x rays on a single crystal of KOOC–CH2–COOH irradiated at 4.2°K. Three effects were observed: (1) Anions are formed by the addition of an electron to the oxygen of the carbonyl group; (2) a unique paramagnetic center results from the loss of a hydrogen atom shared between two molecules; (3) pairs of radicals are created by the removal of a hydrogen atom from the CH2 groups of each of two adjacent molecules. In order to explain the hyperfine pattern associated with the radical pair absorption it is necessary to develop the theory of “forbidden” transitions for the triplet state.
Matrix Shape Approach to Scattering Theory
Authors: Rabitz Herschel A.
Published: February 2004

A nonperturbative method of solving scattering problems is presented. It is based on the shape of the potential matrices involved. The matrices are expanded in a basis set whose arguments are the quantum numbers of the system. The resulting set of simultaneous linear equations is easily solved. A numerical example of collinear collisions of an atom and a diatomic vibrator is considered, and the effect of potential matrix shape on the inelastic transition probabilities is investigated.
Microwave Spectrum of BF
Authors: Lovas Frank J. , Johnson Donald R.
Published: February 2004

Direct rotational transitions have been observed in the ground vibrational state of 10B19F and 11B19F produced in the gas phase by a discharge in flowing BF3. Measurements on the J = 1 ← 0 transitions yield B0(10BF) = 48 022.63 ± 0.08 MHz, eq0Q(10B) = − 9.5 ± 0.8 MHz, B0(11BF) = 45 185.77 ± 0.06 MHz, and eq0Q(11B) = − 4.5 ± 0.4 MHz. New molecular parameters are derived for 11BF including Be = 45 481 MHz, and re = 1.2625 Å. The electric dipole moment of BF is determined to be 0.5 ± 0.2 D.
Trajectory Studies of Atomic Recombination Reactions
Authors: Clarke A. G. , Burns G.
Published: February 2004

The radical molecule complex (RMC) theory for bromine atom recombination in the presence of an inert gas M has been tested by computing 3D classical trajectories for BrM+Br collisions. The dissociation energy of BrM was taken to be of the order of one kcal/mole. Monte Carlo methods were used to select random initial conditions of the BrM molecules with bound and metastable states included. The largest cross sections for the recombination reaction were with deep potential wells and small collision diameters for the Br–M interaction. Heavy third bodies were slightly more effective than light third bodies in promoting the reaction. The velocity averaged cross sections decreased with temperature as T−0.4 for M=Xe, T−0.6 for M=Ar and T−0.9 for M=He. Recombination rate constants, kr, were calculated at 300, 600, 1000, and 1500°K. For argon, with a Br–Ar well depth of 1.0 kcal/mole, the absolute magnitude and temperature dependence of kr agreed with experiment. For helium and xenon agreement of the calculated and experimental kr values at 300°K was obtained with the same well depth, 1.0 kcal/mole. The temperature dependence of kr was reasonable for Xe but for He the calculated value of kr at 1000°K was more than a factor of two smaller than the experimental value. The limitations of the RMC model are discussed in the light of these findings. The energy distributions for the bromine molecules formed in the recombination reaction show that the mean total internal energy is close to the dissociation energy but that there are wide spreads of rotational and vibrational energies; recombination does not take place predominantly into a few vibrational levels near the dissociation limit. The trajectory results are compared with the findings of Blake, Browne, and Burns [J. Chem. Phys. 53, 3320 (1970)] who used a Sutherland potential model for the BrM–Br interaction.
Light Scattering from Ethyl Alcohol Droplets Formed by Homogeneous Nucleation
Authors: Clumpner Joseph A.
Published: February 2004

Detailed features are given of light scattering from liquid ethyl alcohol droplets condensed by homogeneous nucleation in a supersonic flow. The results were obtained by using an argon-ion laser and they show that Rayleigh scattering occurs. The number and the mean radii of the condensed droplets have been measured.
HF Vibrational Relaxation by F Atoms
Authors: Bott J. F. , Cohen N.
Published: February 2004

Vibrational relaxation rates of HF in the presence of F atoms have been measured behind incident shock waves in mixtures of SF6, HF, and Ar. The HF emission at 2.7 μ was monitored to infer the rate of HF relaxation. The F-atom concentration was calculated and correlated with the HF relaxation rate. Within the experimental accuracy, the rate coefficient for F-atom relaxation of HF(1) to HF(0) is 3 × 1013cc/mole · sec corresponding to a relaxation time of 0.0059 μ sec·atm at 2000°K. This is approximately 26.5 times more efficient than self-relaxation by HF at 2000°K.
On the Franck-Condon Factor and Band Strength Calculations with Vibration-Rotation Interaction for Morse Oscillators
Authors: Chakraborty B. , Pan Y. K. , Chang T. Y.
Published: February 2004

The effects of vibration-rotation interaction on the Franck-Condon factors and band strengths for various rotational quantum number J values of the transitions B 3πg−A 3Σu+ for N2 and A 2Σ+−X 2πi for OH have been studied by the asymptotic expansion method.
Millimeter and Submillimeter Wave Rotational Spectrum and Centrifugal Distortion Effects of HDO
Authors: De Lucia Frank C. , Cook Robert L. , Helminger Paul , Gordy Walter
Published: February 2004

The rotational spectrum of HDO in the ground vibrational state has been studied in the millimeter and submillimeter microwave region. Twenty-one previously unreported transitions have been measured and assigned. These data have been combined with previous measurements on HDO for a centrifugal distortion analysis based entirely on microwave measurements. In the analysis distortion effects through P10 are included, although only a partial set of terms in P8 and P10 is found to be necessary. The results for the rotational constants, quartic and sextic distortion constants are (in megacycles per second): =701 931.50 ± 0.22, BA=272 912.60 ± 0.11, C=192 055.25 ± 0.10, ΔJ= 10.8375 ± 0.0058, ΔJK=34.208 ± 0.036, ΔK=377.078 ± 0.026, δJ=3.6471 ± 0.0014, δK=63.087 ± 0.035, HJ=1.128 × 10−3 ± 0.099 × 10−3, HJK=7.344 × 10−2 ± 0.092 × 10−2, HJK=−2.740 × 10−1 ± 0.022 × 10−1, HK=1.4651 × 100 ± 0.0027 × 100, hJ=6.546 × 10−4 ± 0.150 × 10−4, hJK=3.096 × 10−2 ± 0.037 × 10−2, and hK=5.549 × 10−1± 0.053 × 10−1.