bluuebunny/crossref_metadata_2025 huggingface dataset:
Correlation functions of classical fluids. I. The radial distribution functions of mixtures of Kihara molecules in the Percus-Yevick approximation and their thermodynamic functions
Authors: Lee Lloyd L. , Hulburt Hugh M.
Published: February 2004

The Percus-Yevick integral equation is solved for systems of molecules interacting with the Kihara potential. Radial distribution functions for the pure fluid systems of argon, krypton, and xenon, and for the binary mixture argon-nitrogen are obtained. For the one-component system, the use of the Kihara potential yields equivalent results in comparison with previous theoretical and experimental studies. For the case of argon, a numerical potential proposed by Dymond and Alder is also employed and the results show superior agreement with the x-ray diffraction data. The solutions of the two-component case cover a wide range of temperatures, densities, and compositions, including those of the liquid state. The variations of the radial distribution functions with density, temperature, and composition are ascertained. It is found that the main features of the radial distribution functions, such as the peak heights, their relative magnitudes, and the zeros of the total correlation functions, vary under quite complex rules, yet in most part are verifiable by experiments. The macroscopic properties of Ar–N2 mixtures, such as the internal energy and the Helmholtz free energy, are also calculated. Hiroike's formula for the calculation of the free energy is adopted which avoids the usual procedure of integrating a pressure term that has two values, one from the virial theorem and the other from the fluctuation-compressibility derivation. Agreements with values derived from the Strobridge equation of state are close for the internal energy and less satisfactory for the Helmholtz free energy. Their variations with temperature, density, and composition are also demonstrated.
Solvent and pressure dependence of the absorption and fluorescence spectra of anthronitrile
Authors: Nicol Malcolm , Wild Stanley M. , Yancey Janelle
Published: February 2004

Solvent and pressure dependences of the absorption (430–300 nm) and fluorescence spectra of anthronitrile are reported and compared with earlier studies of anthracene. The origins of the solvent dependences are analyzed in terms of dielectric theories developed by McRae and by Baur and Nicol. Satisfactory fits of the experimental data are obtained, which suggest that the dipole moment of the 1La excited singlet state of anthronitrile is 2.5±1.0 times as large as the dipole moment of the ground state. Two absorption bands at 27.4±103 and 28.8× 103 cm−1 (in hexane solutions) are assigned as the 1Lb transition, and the solvent dependences of these bands are interpreted as suggesting that the dipole moment of the molecule is not changed by this transition. Although pressure dependences of the spectra of polymethylmethacrylate and polyacrylonitrile solutions of anthronitrile can be qualitatively interpreted in terms of the solvent dependences, quantitative discrepancies between the anthronitrile and anthracene results indicate that solvent shift theories based upon the dielectric continuum approximation are inadequate to explain the pressure dependences quantitatively.
NMR and EPR studies of the coordination of vanadyl perchlorate in dimethylformamide and dimethylacetamide solutions and the rate of exchange of axially coordinated ligands
Authors: Miller G. A. , McClung R. E. D.
Published: February 2004

The temperature dependence of the NMR linewidths of the solvent resonances in solutions of VO 2+ in dimethylformamide (DMF) and in dimethylacetamide (DMA) indicates that chemical exchange from axial and equatorial coordination sites can control the formyl proton relaxation in DMF, but axial exchange does not produce broadening of the methyl resonances in either DMF or DMA which could be distinguished from outer sphere broadening. The rates at 25 °C and activation parameters for equatorial exchange in DMA are 4.7× 103 sec−1, Δ Heq†= 10.1± 0.5 kcal/mole and Δ Seq†= −7.9± 1.6 eu, and in DMF are 2.0× 102 sec−1, Δ Heq†= 13.1± 0.6 kcal/mole and Δ Seq†= −4.1± 1.8 eu. The rate of axial exchange in DMF is 4.6× 104 sec−1 at 25°C, and the activation parameters are Δ Hax†= 15.3± 2.5 kcal/mole and Δ Sax†= 13.9± 9.0 eu. The rotational tumbling times of the vanadyl complex ions in DMF and in DMA were determined from EPR linewidth studies of VO 2+ in these solvents. The tumbling times were used to show that inner sphere broadening of the formyl proton resonance in DMF and the C-methyl resonance in DMA is dominated by dipole-dipole interactions, while the broadening of the N-methyl resonances is caused primarily by hyperfine interactions.
Reaction of O+ with CO
Authors: Murad Edmond
Published: February 2004

The apparent charge exchange reaction between O+ and CO has been studied for ground state ions in the energy range, Ec.m., from threshold to 0.65 eV. The cross section was found to rise sharply at threshold (∞ 0.4 eV) reaching a plateau at ∞ 0.6 eV. At Ec.m. = 2–3 eV, a further increase in the cross section is observed, and this rise is attributed to a new process, namely, the formation of CO+ in the A 2Π state. The reaction has also been studied using excited O+ and in this case a threshold is not observed; furthermore, the cross section depends on the source of excited O+. Reactions of 18O+ with CO were studied and in both ground state and excited state reactions, electron transfer process was found to predominate. Kinetic energy analysis of the products showed two distinct groups of secondary ions: one at low energy (attributed to electron transfer products) and the other at high energy (attributed to ion-atom interchange). From the measured kinetic energies of the secondary ions, −Q (the amount of kinetic energy tranferred into internal modes) was calculated. These results show that at Ec.m.≥ 8.5 eV the products of both processes decompose. At Ec.m.∞ 15.5–17.7 eV the ion-atom interchange process occurs with ionization (i.e., O++CO→ O++CO++e). −Q was found not to be affected by the excitation of O+. The abundances of excited O+ formed upon bombardment of CO2 and N2O by 50-V electrons are estimated to be 0.05 and 0.25, respectively. The state of excited O+ is discussed and the possibility that it may be 2P is considered. A model for the reaction is briefly discussed.
Study of the potential curves of xenon with other rare gas atoms
Authors: Schneider Barry
Published: February 2004

The model for the forces between closed shell atoms recently developed by Gordon and Kim is applied to the ground state potential energy curves of Xe–Xe, Xe–He, Xe–Ne, Xe–Ar, and Xe–Kr. Agreement between experimentally determined values of the distance between the nuclei at the potential minimum and the depth of the potential well is quite good considering the simplicity of the calculation.
Mössbauer effect and thermal analysis of frozen ferrous perchlorate solutions. II
Authors: Fröhlich K. , Keszthelyi L.
Published: February 2004

During fast freezing to liquid nitrogen temperature, aqueous solutions of Fe(ClO4)2 · 6H2O segregate into two phases: phase I consisting of pure water, and phase II composed of ferrous salt + water. It was established that the number of water molecules ``accompanying'' the ferrous perchlorate molecules, in addition to the six molecules of water of crystallization, is about 12.
Low-temperature (4.2°K) study of the E1u2 ←E2g2 band system in the electronic spectra of various ferricenium compounds
Authors: Hendrickson David N. , Sohn Y. S. , Duggan D. Michael , Gray Harry B.
Published: February 2004

The E1u2 ←E2g2 (16 200 cm−1) band system for the three ferricenium salts [Fe(C5H5)2]PF6, [Fe(C5H5)2]BF4, and [Fe(C5H5)2](CCl3CO2H)2–(CCl3CO2−) has been studied at 4.2°K. Analysis of the observed vibrational structure indicates that the 2E1u excited state is split into two Kramers doublets, with the extent of splitting being a function of the anion. Several ferricenium 2E1u vibrational frequencies have been identified and compared with corresponding values for ground state ferrocene. It appears from these comparisons that the iron 4px and 4py orbitals are minimally involved in the iron-ring bonding.
On the use of radial asymptotic expansions in the calculation of scattering parameters for rotational excitation
Authors: O'Brien T. J. P.
Published: February 2004

A method is presented for determining asymptotic expansions for the solutions of the coupled, radial equations describing the scattering of a particle by a rigid rotor. The expansions are valid for large r for potentials with matrix elements that can be represented (asymptotically) as a series in inverse powers of r. By matching the results of numerical integration of the regular solutions to these expansions, the phase shifts and amplitudes can be accurately determined at values of r for which the potential is still nonzero. Thus the range of r for which numerical integration is required can be reduced significantly for these long-range potentials.
Anharmonic force field of the metaborate ion in alkali halides
Authors: Smith D. Foss
Published: February 2004

The anharmonic force field of metaborate BO2− isolated in KCl and KBr lattices has been calculated using the simplified quartic force field introduced by Smith and Overend. These force fields have been used to calculate approximate force fields of metaborate in other alkali halide lattices.
Optical study of charge exchange collisions between He+ and CO2
Authors: Coplan M. A. , Mentall J. E.
Published: February 2004

The optical emission between 2800 and 5000 Å resulting from collision of He+ with CO2 has been investigated over a range of ion energies from 200 to 1500 eV. The strongest emission was in the CO2+ Ã2 II−X̃2 Σg band system which was found to have a cross section of 4× 10−17 cm2 at [sine wave] 200 eV. An upper limit for the cross section for the production of excited CO+ was determined to be of the order of 8× 10−18 cm2. Two triplet lines of He were also observed with cross sections on the order of 10−19 cm2.
Linewidth parameters for Δ J=1, 0≤ J ≤ 43, rotational transitions of the sulfur dioxide molecule
Authors: Yang W. H. , Roberts J. A. , Tejwani G. D. T.
Published: February 2004

A systematic study was made of the rotational quantum number (J,K) dependence of the linewidth parameters for sulfur dioxide (SO2) at 300 °K. Linewidth parameters were used to calculate effective hard-sphere collision diameters for SO2 over the pressure range 0.001 ≤ P ≤ 0.06 torr. Linewidth parameters were calculated using the Anderson collision theory with appropriate modifications for dominant dipole-dipole interaction between these molecules. These calculations compare favorably with the experimental values obtained. The linewidth parameter trend was explored for transitions Δ J=1, 0≤ J ≤ 43, with all transitions lying within the frequency range of the instrument 4–80 GHz.
Electron-electron double resonance study of trapped electrons in γ-irradiated 2-methyltetrahydrofuran glass: Magnetic energy transfer between two different spin systems
Authors: Yoshida Hiroshi , Feng Da-Fei , Kevan Larry
Published: February 2004

Electron-electron double resonance (ELDOR) of trapped electrons and radicals in γ-irradiated 2-methyltetrahydrofuran (MTHF) glass at 77°K was investigated. Magnetic energy pumped into the radical spin system is transferred to the trapped electron spin system to partially saturate it. The cross saturation mechanism is consistent with dipolar cross relaxation in which a radical spin flips down and an electron spin flips up. Analysis of the rate of spin relaxation shows that the reciprocal ELDOR reduction is linear with pumping microwave power with an intercept which gives the ratio of the cross-relaxation time to the electron spin-lattice relaxation time. The experimental data are found to fit this relationship. This ratio of relaxation times is of the order of 0.5 while the relaxation times themselves are in the 10−4-sec range. The observation of cross relaxation in this system supports the concept that the trapped electron and radical are spatially correlated in γ-irradiated MTHF.
Low frequency sound velocity measurements in xenon in the critical region
Authors: Kline J. L. , Carome E. F.
Published: February 2004

We have measured, using a resonating cavity technique, the low frequency sound velocity in xenon along various isochores in the single phase portion of the critical region. The frequencies employed were of the order of 8 kHz. Using our velocity results and available equation of state data, we calculated values of adiabatic compressibility and specific heat at constant volume. The latter results are shown to be consistent with those obtained by other workers.
Electron impact ionization cross sections of Cu and Au between 40 and 250 eV, and the velocity of evaporated atoms
Authors: Schroeer Juergen M. , Gündüz Dincer H. , Livingston Spencer
Published: February 2004

The total ionization cross sections of Cu and Au were measured with a simple crossed-beam apparatus for bombarding electron energies between 40 and 250 eV. The maximum cross sections were σ (Cu)=(7.6 ± 1.1 × 10−16cm2 at 95 ± 10 eV and σ (Au) =(15.3 ± 2.1) × 10−16cm2 at 100 ± 10 eV. The ratio of the cross sections is σ (Au)/σ (Cu) =2.0 ± 0.2 between 50 and 180 eV. The shape of our cross section curve for Cu compares well with a previous measurement by Crawford. An evaporation model which predicts thermal equilibrium between a liquid and the atoms evaporating into a vacuum is discussed, and the average velocity of atoms evaporated from an evaporation boat is calculated.
Matrix infrared spectrum and bonding in the monoiodomethyl radical
Authors: Smith David W. , Andrews Lester
Published: February 2004

The codeposition of CH2I2 diluted in argon with 6Li, 7Li, Na, or K atoms produces new infrared absorptions attributable to the alkali iodide and the CH2I free radical. The identity of the radical is confirmed by reacting the CHDI2, CD2I2, and CH2IBr precursors with alkali atoms. Absorptions assigned to the symmetric H–C–H bend, the symmetric C–I stretch, and the out-of-plane hydrogen bend are supported by vibrational analysis. The high C–I force constant (2.81±0.04 mdyn/Å) indicates pi bonding in CH2I.
Negative ion reactions with neutral ozone
Authors: Rutherford J. A. , Turner B. R. , Vroom D. A.
Published: February 2004

Charge transfer reactions between O−, O2−, OH−, and NO2− and O3 have been studied to obtain cross sections for information of O3− The charge transfer reaction O3− on NO2 has also been remeasured. The range of ion energies considered extends from 1 to 500 eV. Upper limits have been obtained for the charge transfer cross section of F−, Cl−, and CO3−, with O3. The results show that the electron affinity of O3 must be close to accepted value of approximately 2 eV. The method used to produce a neutral beam of pure O3 is discussed.
The ESR line shape of free radicals in aqueous environments
Authors: Force Gunilla Gillberg-La , La Force Richard Conley
Published: February 2004

We have calculated the line shape to be expected in the electron spin resonance spectra from free radicals in an aqueous environment. We have assumed microwave power to be incident from the left on a planar sample transverse to the waveguide, and that the transmitted power is detected to the right of the sample. We consider two kinds of samples: a solution of free radical of thickness [inverted lazy s] 1 cm, and a thin membrane of thickness [inverted lazy s] 0.1 mm containing free radicals and bathed on each side by a water solution of thickness [inverted lazy s] 0.5 cm. The line shape is markedly affected by the presence of water for each kind of sample. When the unpaired spins are confined to a thin membrane bathed with water, the line shape changes from absorptive to dispersive to absorptive of the opposite phase as a function of the dielectric constant of the sample region. We conclude from the calculation that the presence of thick aqueous regions can be exploited to obtain new information from experiments on spin labeled biological membranes that are sustained in vitro.
Collision-induced ion pair formation of thallium halides: Absolute cross sections
Authors: Parks E. K. , Hansen N. J. , Wexler S.
Published: February 2004

Collision-induced dissociative ion pair formation (polar dissociation) of thallium chloride, bromide, and iodide by aerodynamically accelerated Xe and Kr atoms has been studied by the crossed-beam method. Absolute cross sections for total positive ion formation from both the monomer and the dimer were determined from the threshold to several electron volts relative energy above threshold. The cross sections for the monomer varied over three orders of magnitude, ranging from 0–1.0 × 10−16 cm2 for TlCl, to 0–8 × 10−18 cm2 for TlBr, to 0–1.6 × 10−19 cm2 for TlI when Xe was the collidant. Similar ranges were measured for Kr on TlCl and TlI, but the cross sections were approximately a factor of 10 smaller for TlBr. The observed cross sections for positive ion production from the dimer molecules were in the range of 1 to 20 × 10−16 cm2. Time-of-flight mass spectrometry permitted the determination of partial cross sections for each positive and negative ion channel in the collision. The excitation functions for the reaction A+BC → A+B++C− (direct polar dissociation) exhibited a concave upward curvature in the postthreshold region, while those for A+BC → AB++C− (complex formation) showed a step behavior for TlCl and a concave downward curvature for TlBr. The yield of Tl2X+ was used in calculating the cross section for polar dissociation of the dimer. Only monatomic halogen negative ions were observed. The experimental results are discussed within the framework of a surface crossing model. The model predicts the essential features of the experimental results for both the thallium halide monomers and dimers.
Effects of variations in reaction coordinate eigenvalue and eigenvector on the rate and hydrogen isotope effects of the reaction H+Cl2 → HCl+Cl
Authors: Wei G.-J. , Yankwich Peter E.
Published: February 2004

Effects on the rate constant k, and on the temperature independent and temperature dependent factors of kh/kD, of variations in the eigenvalue (λ1) and eigenvector (L1) associated with the reaction coordinate have been studied by computation for the reaction H+Cl2 → HCl+Cl. A slightly bent transition state was assumed and its diagonal force field maintained invariant at partial bond levels. The properties of the transition state were varied by systematic manipulation of the three off-diagonal force constants. Values of the several temperature dependent quantities calculated were controlled largely by the interaction force constant between the H···Cl stretch and the H···Cl···Cl bend. Curving the potential barrier affects drastically the range of reaction coordinate ``compositions'' which correspond to acceptable transition states, but neither k nor kH/kD is sufficiently sensitive to barrier curvature to allow an estimate of a ``best value'' for λ1 by comparison of calculated and experimental values. Eigenvector variations have similarly modest effects on k, but the sensitivity of kH/kD seems enough greater that it could be used for model refinement if experimental results of moderate precision were available. Both these sensitivities would be enhanced if the transition state diagonal force field were treated as a parameter in concert with L1. The hypothesized general inverse correlation between isotope effects and reaction rates is shown to be limited by temperature.
Nuclear magnetic relaxation under hindered internal rotation
Authors: Versmold H.
Published: February 2004

Time correlation functions for intramolecular reorientation by a jump mechanism about angles of ±2π/3 are computed. Contrary to previous discussions it is found that some of the cross correlation terms, which result from the internal rotation, do not vanish. The influence of the cross terms on the nuclear magnetic relaxation rate is discussed.
Influence of paramagnetic impurities on molecular self-diffusion as seen by nuclear spin-lattice relaxation and dynamic polarization
Authors: Verdun H. , Meerovici B. , Volino F.
Published: February 2004

Measurements, near the melting point, of nuclear spin-lattice relaxation and dynamic polarization in plastic cyclohexane doped with a nitroxyde free radical show deviations from the expected spin-diffusion theory. These deviations are explained by the quenching of the molecular self-diffusion around the radical and interpreted semiquantitatively in terms of a two zone model. It is shown that the quenching extends up to more than four intermolecular distances and the spin-diffusion coefficient in this region is shown to be around 0.3× 10−12 cm2 sec−1. It seems that similar measurements would be of interest in any crystal which exhibits NMR motional narrowing due to fast molecular self-diffusion.
Laser power and vibrational energy transfer in CO2 lasers
Authors: Bulthuis K.
Published: February 2004

The decay of the laser power in the afterglow of a CO2 laser discharge is shown to be exponential when the upper laser level is excited directly by electrons. The decay time is shown to be a function of the rate coefficients describing the relaxation of the lower laser level. From power decay measurements it is found that the deactivation of the lower laser level to the ground state occurs in two steps. The rate coefficient for the transfer of vibrational energy from the 1000 level to the 0110 level of CO2 is found to be 5× 10−13 cm3 sec−1. This is an order of magnitude smaller than a previously reported value. The rate coefficients for the relaxation of the 0110 level of CO2 by H2O and D2O are found to differ by a factor of 1.8. These rate coefficients increase with increasing temperature in agreement with calculated results using the theory of Marriott. The measured dependence of the relaxation time of the lower laser level on the H2O vapor density explains the observed maxima of the laser power and small signal gain in conventional and gas-dynamic CO2 lasers. The power decay for a CO2 laser, when the upper laser level is additionally excited indirectly via the N2 (ν = 1) level, is shown to be described by the sum of two exponential functions. The two time constants depend on the rate coefficients for the relaxation of the lower laser level as well as for the transfer of energy from the N2 (ν = 1) level to the upper laser level. The decay time of the laser power is found to increase with increasing N2 density.
Resolution of motions in the three solid phases of methylammonium chloride (CH3NH3Cl) by NMR
Authors: Albert Shmuel , Ripmeester John A.
Published: February 2004

The α, β, and γ phases of solid methylammonium chloride (CH3NH3Cl) and its partially deuterated analogs (CD3NH3Cl and CH3ND3Cl) were investigated using temperature dependent static and rotating frame proton spin-lattice relaxation times, T1 and T 1ρ, respectively. Broadline proton magnetic resonance studies were performed in the supercooled γ phases of two of the substances. Discontinuities in the spin-lattice relaxation plots were observed at the reported β → γ and γ → a phase transitions for CH3NH3Cl. It was found in our experiments that partial deuteration of this salt causes the β → γ transition temperature to shift to higher temperatures. The motions in the three modifications of these substances were analyzed using the spin-lattice relaxation data and the second moments for the supercooled γ phase. A resolution of the CH3 and NH3+ rotations about the C–N axes was accomplished in the γ and β phases. The onset of CH3 reorientations in the γ and β phases occurs at lower temperatures than those for NH3+, while the frequencies of these motions are quite close to each other in the β forms and further apart in the γ modifications. In the α phases CH3 and NH3+ seem to rotate relatively fast about the C–N axes and more or less as a unit. The various motional parameters were derived from calculated fits to our relaxation time data. The NMR results pertaining to the three phases of these compounds are discussed and related to other studies.
Mechanism of condensation. I. Direct determination of coefficients for condensation of molecular beams of sodium chloride on oriented single crystals of NaCl
Authors: Schoonmaker Richard , Lo Vincent
Published: February 2004

Coefficients for condensation of a composite beam of NaCl(g) and Na2Cl2(g) on the 100 face of oriented single crystals of sodium chloride have been measured over a range of crystal temperature from 185–700°K, over a range of 50 in dislocation density at the crystal surface, as a function of molecular beam flux, as a function of deposition time, and as a function of the angle of impingement between the molecular beam and the crystal surface. In one set of experiments a thin layer of silicone oil was spread over the surface of the crystal prior to molecular beam deposition. Crystal surfaces have been studied by chemical etching and microscopic examination. It is concluded that dislocations at the surface of the oriented crystal serve as intrinsic nucleation sites for molecules in a two dimensional, mobile adsorbed surface state. The density of molecules in the mobile surface state depends on the flux of the molecular beam. At sufficiently low crystal surface temperature, centers of nucleation are generated spontaneously on the surface as a result of formation of molecular clusters in the adsorbed surface state. At low surface temperature with an adequate beam flux, the controlling factor in the condensation of sodium chloride appears to be the spontaneous formation of molecular clusters of a critical size from which nucleation and growth can occur. As the surface temperature increases there is a decrease both in the number of intrinsic nucleation sites (surface dislocations) and in the tendency of mobile molecules on the surface to cluster and form spontaneous centers of nucleation. However, as the temperature increases the rate of diffusion along the surface increases. The results of this work suggest that the rate of surface diffusion is a dominant factor in the mechanism of condensation of sodium chloride at high crystal surface temperatures. In the intermediate range of surface temperature all of the previously mentioned factors are in competition as rate determining steps in a complicated mechanism of condensation.
EPR studies of NH4Br:Cu2+
Authors: Narayana P. A. , Sastry K. V. L. N.
Published: February 2004

Expressions for the spin Hamiltonian parameters g∥, g⊥, A, and B have been derived for Cu2+ in a tetragonal field with the unpaired electron in a predominantly d3z2−r2 orbital, using a LCAO-MO scheme. Overlap integrals have been considered in treating σ bonds. The nondiagonal first order contribution to the hyperfine structure anisotropy is included. The theory has been applied to NH4Br:Cu2+. It is found that the complex exhibits strong out of plane π bonding. The contribution of the nondiagonal elements to the hyperfine structure anisotropy is found to be small.
Diffusion interactions in glasses arising from discontinuities in anion concentration
Authors: Okongwu D. A. , Lu W-K , Hamielec A. E. , Kirkaldy J. S.
Published: February 2004

A multicomponent diffusion formalism based on the Nernst-Planck equation is presented which is capable of generating from tracer diffusion data the discontinuous cation diffusion profiles which arise in diffusion couples when a stationary anion concentration profile contains a step discontinuity. Such couples can be constructed with ion exchange resins, zeolites, and glasses. This formalism introduces the electroneutrality condition through the zero flux (ΣZ1J1=0) condition alone, thus avoiding the mathematical difficulties associated with the application of the discontinuous neutrality condition (ΣZiCi=0) to a set of differential equations. The agreement between the predictions and the experiments for a series of silica glass couples is found to be good.

It is argued that the well-known contradiction between the electroneutrality constraint on the real charge and the nonuniform field predicted within the Nernst-Planck formalism can be removed if the proposition is accepted that a distribution of dipoles, and therefore of dipole charge, is associated with each diffusion profile of such magnitude that solutions of the Poisson equation become exactly consistent with the diffusion-generated electric field.
Magnetic field enhancement of electrochemiluminescence intensity: Effect in an energy sufficient system
Authors: Periasamy N. , Shah S. J. , Santhanam K. S. V.
Published: February 2004

Enhancement of electrochemiluminescence (ECL) intensity in the magnetic field of rubrene, tetracene and phenanthrene anion-cation reactions suggests triplet intermediates in the ECL reaction schemes of these systems. The possible pathways of triplet formation in the energy sufficient ECL of phenanthrene are discussed.
Flash photolysis studies in a time-of-flight mass spectrometer. I. Divinyl ether and reactions of the vinyl and vinoxy radicals
Authors: MacFadden K. O. , Currie C. L.
Published: February 2004

The lower pressure flash photolysis of divinyl ether has been monitored by time-of-flight mass spectrometry. The primary photodecomposition process is restricted essentially to the formation of vinyl and vinoxy radials: C2H3OC2H3→C2H3+C2H3O. The vinyl radical (m/e=27) has been observed directly and its 2nd order decay constant measured. The decay is primarily by disproportionation 2C2H3→C2H4+C2H2 and k10 has an average value of 5.3± 0.5× 10−12cc molecule−1·sec−1 over the pressure range studied (65–200 mtorr). The vinoxy radical has not been observed directly in this work. Our results favor a rapid isomerization, followed by decomposition C2H3O⇄CH3CO→CH3+CO. A mass balance is achieved within 400 μsec of the photolysis flash and a mechanism proposed to account for the major (C2H4, C2H2, CO) and the minor products (CH4, C2H6, 2-butenal, acetaldehyde, and ketene).
Stark effect of BaCl2
Authors: Dagdigian Paul J. , Wharton Lennard
Published: February 2004

Observation of the refocusing in an electric quadrupole state selector of a velocity-selected supersonic BaCl2 beam has yielded directly a lower limit of 1.2 D on the molecular electric dipole moment and a lower limit to the degree of ionic character of the BaCl bond of about 28%. An upper limit of 135° on the BaCl2 bond angle is obtained with the additional assumption that the bond degree of ionic character is less than that of RbCl, 78%. Combined with the lower limit to the degree of ionic character of 28%, this angle sets a lower limit to the molecular dipole moment of 2.2 D. The refocusing spectrum is characterized by a sharp refocusing threshold.
Barriers to linearity in triatomic molecules. II. Comparison of curvilinear and rectilinear models and determination of the barriers in some electronic states of hydrogen sulfide, water, and sulfur dioxide
Authors: Brown Farrell B.
Published: February 2004

The results of the first paper (I) in this series are applied here to ground state hydrogen sulfide, to ground state and excited state water, and to three excited states of sulfur dioxide. For the first three molecular species the bending potential is shown as deduced by both models developed in I and it becomes more apparent how the two models differ. In all cases the curvilinear model demonstrates a potential more nearly invariant to isotopic substitution than does the rectilinear model. For the three excited states of sulfur dioxide, plots are shown only for the potential deduced from the curvilinear model. Finally the computational aspects are described whereby vibration-rotation eigenvalues are found from the truncated infinite determinants developed in I.
Formation spectra and some chemical properties of oxydiodine radicals in aqueous solutions
Authors: Tendler Y. , Faraggi M.
Published: February 2004

The reactions of the hydrated electrons (eaq−) and OH radicals (generated by the interaction of fast electrons with water) with IO3− and IO− have been investigated by the pulse radiolysis technique. Absorption spectra of the transient species producted in the range 250–800 nm, have been obtained. IO2 formed by the reaction: IO3−+eaq−→IO2+2OH−, k1=7.7× 109M−1·sec−1 has a maximum absorption at 490 nm (ε490=1.5× 103M−1·cm−1). No evidence was found for an absorption band at λmax=715 nm as previously claimed for this species. The transient absorbing species at λmax=360 nm (ε360=8.0× 102M−1·cm−1) formed by the reaction of OH radicals and IO3−, is probably (IO3)2−, e.g., IO3−+OH→IO3+OH−, k2=1.7× 107M−1·sec−1, IO3+IO3−⇄(IO3)2−, K3=23M−1. In I−+IO− alkaline solutions two transient absorption bands at 370 and 700 nm are formed which decay at the identical rate (8× 109M−1·sec−1). This and the fact that in I− alkaline solutions the same spectrum was observed indicate that the band at 700 nm is also due to I2−. The decay kinetics of IO2 radicals have been measured. It is a second-order reaction: IO2+IO2→prod, 2k5=9.3× 109M−1·sec−1. The decay of (IO3)2− depends on IO3− concentration. A mechanism for this reaction is proposed.
Analysis of the Barker-Henderson local-compressibility approximation. II. Comparison with other theories of liquids
Authors: Moffat Marshall J. , Kozak John J.
Published: February 2004

In this paper a representation is developed wherein certain features of the Barker-Henderson theory in the local-compressibility approximation can be analyzed. Previous work by the authors has shown that the use of the local-compressibility approximation to estimate higher-order terms in the Zwanzig expansion introduces new classes of diagrams not found in the Zwanzig expansion itself. The representation introduced here, which we call the summed-mean-field (SMF) representation, permits one to analyze these ``extra'' diagrams. A principal result of this study is that there seems to be extensive self cancellations among these ``extra'' diagrams, which in our view lends considerable support to earlier statements on the formal consistency of the Barker-Henderson closure. The Barker-Henderson theory is also compared with two other successful theories of liquids, the Mansoori-Canfield theory and the Weeks-Chandler-Andersen theory, within the framework of the SMF representation. Finally, some comments are made on the SMF representation itself, especially with regard to its possible usefulness.
Implications of ion-molecule reactions observed in silane for recoil silicon atom studies
Authors: Stewart G. W. , Henis J. M. S. , Gaspar P. P.
Published: February 2004

Ion-molecule reaction sequences in silane, producing tertiary product ions, are reported. A mechanism is presented by which trisilane can be producted from Si+ ions in recoil silicon studies. It is also reported that Si+ ions can be efficiently neutralized by charge exchange with triethylamine. Preliminary studies indicate that the addition of triethylamine to recoil silicon experiments results in a decrease in the absolute yield of trisilane without affecting the yields of other products. In addition, information obtained from ion-molecule studies in silane is applied to radiolysis studies of silane. A mechanism is presented by which higher homologues are produced by hydride ion transfer.
One-dimensional shock waves in a chemically reacting mixture of elastic materials
Authors: Nunziato Jace W.
Published: February 2004

We consider the propagation of shock waves in a chemically reacting mixture of elastic materials without diffusion. A differential equation is given for the strain jump across the shock in terms of the strain gradient behind the shock and a ``critical strain gradient'' and the growth and decay behavior of both compressive and expansive waves is discussed. The properties of the critical strain gradient are considered when the reaction behind the shock is exothermic and endothermic. It is found that the qualitative behavior of compressive shocks in mixtures which react exothermically agrees with experimental observations on the solid explosives, PBX-9404 and TNT.
Exchange of iodide ion with triiodide ion studied by nuclear magnetic resonance
Authors: Genser Edward E. , Connick Robert E.
Published: February 2004

Previous studies of NMR line broadening of the iodide resonance in aqueous solutions of triiodide have been interpreted in terms of the rate of dissociation and formation of triiodide, with the result that the derived rate constant appeared to exceed the diffusion limiting value. The present study has resolved this anomaly and shows the exchange to be described instead by the reactions I*−+I3−=I3*−+I− at iodide concentrations greater than 0.05M. Several mechanisms of exchange are considered based on both symmetrical and unsymmetrical forms of triiodide ion, the latter of which is supported by Raman data in the literature. The interpretation makes use of nuclear quadrupole coupling constants reported for solid salts of triiodide. The data are fitted to the exchange modified Bloch equations to obtain a value of the rotational correlation time, τr, for each of the mechanisms; τr is then compared to a theoretical value of τr calculated for triiodide ion. Although the data do not permit a unique mechanism to be established, it appears that at least two of the iodines in triiodide must be involved in exchange. The results are compatible with an attack on an end iodine of triiodide with the formation of the intermediate I42−.
Spatial distribution function of reaction coordinates. II
Authors: Bomberger D. C. , Kostin M. D.
Published: February 2004

Solutions for the quantum and classical spatial distribution functions along reaction coordinates are obtained as a function of temperature. The method used, which is based on a newly derived partial differential equation, gives the temperature-dependent quantum spatial distribution function directly without the necessity of first solving the Schrödinger equation numerically for all the eigenfunctions, which are complex and have numerous oscillations, and then averaging the results over a Boltzmann distribution.
On the metastable dissociation of the CH+ ion produced by electron impact
Authors: Newton Amos S. , Sciamanna A. F.
Published: February 2004

The metastable dissociation of CH+ and CD+ ions has been investigated. CH+(m) from CH4, C2H2, C2H4, CHCl3, CH2Cl2, and CD+(m) from CD4, C2D2, C2D4, and CDF3 were studied. CH+(m) and CD+(m) dissociate with an apparent half-life of 0.4± 0.2 × 10−6 sec and with kinetic energy release in the dissociation of 1.1±0.3 and 1.4±0.3 eV, respectively. Using 70 eV electrons, CD+(m) and CH+(m) are formed with initial kinetic energy, the value being dependent on the compound irradiated. Appearance potential measurements show that when formed from C2H2 and C2D2, the CH+(m) and CD+(m) must dissociate to the lowest dissociation limit of CH+, i.e., C+(2P1/20) and H(2S). It is postulated that the metastability arises from a predissociation of the b 3Σ− state with the repulsive c 3Σ+ state of CH+.
Relative proton affinities of hydrogen sulfide and water
Authors: Hopkins J. M. , Bone Larry I.
Published: February 2004

The difference in proton affinities for H2S and H2O has been measured in a photoionization mass spectrometer by studying the following equilibrium H3S(g)++H2O(g)⇄ H3O(g)++H2S(g). Mixtures of H2S and H2O are photolyzed at 10.63 eV in the source of the mass spectrometer. H2S+, which is the only ion produced, reacts with H2S to produce H3S+. H3S+ reacts with water to produce H3O+ which further hydrates to H(H2O)n+. The equilibrium constant is measured as a function of temperature and a van't Hoff plot produces ΔHo=2.9 kcal/mole ΔSo=5.5 eV. Thus the proton affinity of H2S is 3 kcal/mole greater than the proton affinity of H2O. Species such as H3S(H2S)n+ and H3S(H2O)n+ are not observed while H(H2O)n+ hydrates are highly favored. A possible explanation is offered which involves the weakness of hydrogen bonds to sulfur.
Binary cluster integrals in the theory of dilute polymer solutions
Authors: Yamakawa Hiromi , Fujii Motoharu
Published: February 2004

The binary cluster integral β for polymer segments is evaluated on the basis of the very crude smoothed-potential cell model, regarding it as equivalent to the second virial coefficient for a binary liquid mixture of small molecules. For polystyrene and polyisobutylene in various solvents at various temperatures, it is shown that the model can interpret qualitatively the behavior of β in terms of intermolecular forces. However, the calculated values of β are about one order of magnitude greater than the observed values, which are one order of magnitude smaller than the values expected from second virial coefficients observed for small molecules. This indicates that interactions between polymer segments in dilute solution are different from those between small molecules. It is pointed out that the difference arises from the fact that polymer segments bound in the chain have fewer degrees of freedom, translational and rotational, than free small molecules.
Collision broadening of C2H4O lines. II. Broadened by quadrupolar molecules N2 and H2
Authors: Pandey Prem Chand , Srivastava Shyam Lal
Published: February 2004

A double modulation microwave spectrograph has been used to measure the linewidth parameters (Δ ν/p) of four rotational lines of C2H4O broadened by quadrupolar molecules N2 and H2. Linewidth parameters have been calculated theoretically using the Anderson-Tsao-Curnutte theory as well as the Murphy-Boggs formulation taking the dipole-quadrupole interaction into consideration. By fitting the calculated (Δ ν/p) to the measured (Δ ν/p), molecular quadrupole moments Θ of N2 and H2 have been obtained. Inadequacies in the theory have been pointed out.
Polarization characteristics of Raman scattered radiation as a function of angle between incident and scattered beams
Authors: Sharma R. D. , Levin L. A.
Published: February 2004

The expressions for the angular distribution of the Raman radiation scattered by an isotropic medium (E·k=0) are derived for arbitrary direction of the polarization of the incident and scattered beams. The method of extension of this expression to anisotropic medium is indicated. Polarizabilities which transform as components of spherical tensors are introduced and it is pointed out that the definition commonly used for the anisotropy of polarizability is inadequate for computing Raman spectra for species in which K degeneracy has been removed, e.g., asymmetric rotors. It is shown that angular distribution and polarization characteristics of Raman radiation depend only upon the rank of the scattering tensor and are independent of its components.
Evidence for a t−a(a∼1/2) time dependence of chain fluctuations as observed by NMR on cis-1,4-polybutadiene
Authors: Martin-Borret Y. , Cohen-Addad J. P. , Messa J. P.
Published: February 2004

From a detailed analysis of spin -echo envelopes, the transverse magnetization of protons bound to cis 1–4 polybutadiene chains is found to vary according to M(t)=M0exp(−ξ tα) (5/4≲ α ≲ 3/2). It is shown that this function may be related to a tα−2 time dependence of chain fluctuations. The effects of the partial chain ordering on the fluctuations of the remaining disordered chains, permit the ordering process to be followed by NMR. The ordering rates (k1/2≳ 0.5 min−1) are found to be much higher than those which have been measured on natural rubber. In the presence of good solvents such as CFCl3, C7D8, and CS2 the time constant of the transverse magnetization exhibits an exponential concentration dependence that we have related to the increase of microscopic jump rates, We, which govern chain fluctuations; We∼1012 sec−1.
Nonsteady-state theory of droplet growth
Authors: Nix Norbert , Fukuta Norihiko
Published: February 2004

A general expression for the nonsteady-state growth or evaporation of droplets in gaseous media is obtained by simultaneously considering vapor diffusion and heat conduction. The results are compared with solutions which assume a quasisteady-state. In the nonsteady-state treatment, the growth rate initially exceeds the quasisteady-state rate, but converges to it at longer times. Methods for estimating the deviations from the quasisteady-state results and the range of applicability of the new theory are described. It is pointed out that neglect of variations in the temperature field in nonsteady-state droplet kinetics leads to a serious error in the corresponding vapor field, as well as in the rate of growth or evaporation.
Green's function form for the dynamic paramagnetic susceptibility of a spin-orbit coupled system
Authors: Bogdanovic R. , Whitehead M. A.
Published: February 2004

The frequency dependent susceptibility of a single spin-orbit coupled system has been calculated by means of linear response theory. Instead of truncating the resulting Green's function equation, the relevant Heisenberg equations of motion are solved directly to obtain an exact Green's function for the system. The values of the resonance frequencies of the susceptibility tensor are compared, in a few cases, with the splittings of energy levels calculated by different theories and experimentally observed.
Magnetic circular dichroism studies on d–d transitions of tetrahalogeno manganese(II) complexes
Authors: Katô Hajime
Published: February 2004

The magnetic circular dichroism spectra for spin-forbidden d–d transitions of the complexes MnCl42− and MnBr42− have been measured in solution at room temperature. Theoretical calculations predict that the transitions A16→A24 and A16→T24 show positive MCD and that the transitions A16→E4 and A16→T14 show negative MCD.
Trichloromethyl and other radicals in irradiated single crystals of trichloroacetamide
Authors: Kispert Lowell D. , Rogers Max T.
Published: February 2004

The trichloromethyl radical has been identified in irradiated single crystals of tricholroacetamide. When the magnetic field lies along the a axis of the monoclinic crystal it is also nearly normal to the plane of the three chlorine atoms and the spectrum may be interpreted as the superposition of spectra from the radicals Cl335C·, Cl235ClC37·, and Cl35Cl237C· with the expected abundance ratios 27:27:9. To a good approximation 35Cl and 13C hyperfine splittings in this orientation may be taken as the principal values of the 35Cl and 13C hyperfine splitting tensors, Azz(35Cl)=18.1 G, Azz(13C)=136 G. Although the complexity of the spectra precludes a complete determination of the hyperfine splitting tensors, these data are sufficient to show that the radical is nonplanar and to provide considerable information concerning the electronic structure.
Analysis of ESR spectra of the S-state ion Gd3+
Authors: Darby M. I.
Published: February 2004

A method of Koster and Statz is used to analyze an electron spin resonance spectrum for the S-state Gd3+ ion in CeO2, when the ion occupies a crystalline site of cubic symmetry. It is found that six ``g values'' are required, and the values g1=g2=2.0, g3=5/3, g4=g5=1.0, and g6=2.1 give an approximate fit to the spectrum. It is shown that the method can qualitatively explain the existence of low field resonances which are not easily accounted for using a conventional spin Hamiltonian.
Sum rules for dipole coupled crystals
Authors: Frech Roger
Published: February 2004

In simple dipole coupled anisotropic crystals with infrared active internal optic modes, certain optical properties and spectroscopic quantities of interest such as the indices of refraction, electronic polarizability components, internal mode frequency shifts, and internal mode intensity shifts are necessarily related to each other due to the nature of the predominant intermolecular interactions which occur in these crystals. These relationships can be expressed as a set of sum rules each utilizing the trace of the dipole interaction matrix. The trace of the dipole interaction matrix also suggests a choice for the convergence parameter in the Kornfeld-Ewald method of calculating dipole sums.