bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectroscopic evidence for higher symmetry effects in monoclinic Tm2(SO4)3 · 8H2O
Authors: Stöhr Joachim , Seidel Ernst R. , Gruber John B.
Published: February 2004

From the relative intensities and distribution of CEF split Stark levels observed in the absorption spectrum of single crystal Tm2(SO4)3 · 8H2O, it is possible to deduce evidence for higher symmetry effects surrounding the Tm3+ ion. Higher symmetry effects have also been reconsidered from further examination of the absorption spectrum of single crystal TmCl3 · 6H2O. The higher symmetry axis is found to be D6 and C6V for the hydrated chloride and sulfate crystals, respectively. The hexagonal symmetry axes predict a CEF splitting and CEF wavefunctions that describe the observed optical and magnetic properties of Tm3+ in these two different hydrated crystals very well.
Photodetachment of electrons from Group IVa binary hydride anions: The electron affinities of the SiH3 and GeH3 radicals
Authors: Reed Kenneth J. , Brauman John I.
Published: February 2004

Relative photodetachment cross sections have been determined for the silyl and germyl anions (SiH3−, GeH3−) in the wavelength ranges 400.0–870.0 nm (3.10–1.43 eV) and 400.0–720.0 nm (3.10–1.72 eV), respectively. An ion cyclotron resonance spectrometer was used to generate, trap, and detect the negative ions, and a 1000 W xenon arc lamp with a grating monochromator was employed as the light source. Both ions exhibited cross sections behaving sigmoidally over the wavelength ranges studied. These experiments afford the following electron affinities: E.A. (SiH3·) ≤1.44±0.03 eV and E.A. (GeH3·) ≤ 1.74±0.04 eV. From estimates of proton transfer equilibrium constants, bond energies are approximated for silane and germane.
Investigation of the planar H + H2 reaction near threshold
Authors: Walker R. B. , Wyatt R. E.
Published: February 2004

We report a study of the quantum dynamics of the hydrogen exchange reaction for collisions in which the nuclei move in a single plane throughout the reaction. Our efforts are concentrated at the reaction threshold, for it is here that classical dynamics is least accurate, and yet it is also this region that contributes most heavily to thermal rate constants. Because transition amplitudes in the threshold region are uniformly small, the distorted wave approximation should provide an adequate description of the dynamics. Assuming the ground vibrational state for all molecules, we compute elements of the scattering (S) matrix for several rotational transitions. From the S-matrix elements, we compute reaction probabilities, angular distributions of products (the differential cross section), and the total reaction cross section. The reaction probabilities indicate that reaction is most likely to occur at small impact parameters. The differential cross sections are strongly back peaked, implying that the product molecule recedes in the direction from which the incoming atom approached. Contrary to an earlier study of this reaction, we observe no forward peaking in the differential cross sections.
Evaluation of relations among stress-wave parameters and cohesive energy of condensed materials
Authors: Rodean Howard C.
Published: February 2004

The shock-wave velocity U and the particle velocity u for many condensed materials are linearly related by the equation U =a + b u along one or more sections of the Hugoniot. Departures from linearity can usually be attributed to porosity, elastic-wave precursors, or phase changes. If there are no such effects to cause nonlinearity, a is approximately equal to the adiabatic, bulk, or hydrodynamic sound velocity ak. Two equations involving the cohesive energy Ec are compared for 56 metals and 13 simple compounds (12 alkali metal halides and MgO): Ec = −(1/2)(a/b)2 and |Ec|=aμ2, where aμ is the shear wave velocity. It is shown that the experimental data are such that the energy of sublimation Es ≈ (1/2)(a/b)2 for the metals and compounds considered, Es≈ aμ2 for the metals, but Es≈ 0.4 aμ2 for the compounds. It is concluded that the shock-wave parameter equation, |Ec| = Es = (1/2)(a/b)2 is preferred because it applies without coefficient adjustments to both metals and simple compounds, and it may be applied to liquids as well as solids if the energy of vaporization Ev is substituted for Es. This equation is also applied to four polymers with |Ec| equated to the initial activation energy of failure Ea, which is equal to the energy of thermal decomposition. Despite the unsatisfactory nature of some shock-wave date (i.e., a ≠ ak), it appears the Ea ≈ (1/2)(a/b)2 although the fit is not as good as for the other materials considered. Therefore, the equations U = a + b u and Ec = −(1/2)(a/b)2 help provide information about the relations between macroscopic and microscopic properties of condensed materials.
Relationship between isotopic scrambling and mechanism in labeled ion molecule reactions: The reaction of CH3+ with CH4
Authors: Henis J. M. S. , Tripodi M. K.
Published: February 2004

The isotopically mixed products of the reaction of CH3+ with CD4 and CD3+ with CH4 are analyzed in terms of the reaction mechanism. It is concluded that the products are not randomly distributed, and that three separate and distinguishable reaction channels may be operative with H2 elimination from the initial ionic carbon the most likely channel. No intermediate is invoked to explain the observed results, and it is shown that significant H–D scrambling during the reaction is not necessary to account for the isotopically mixed products observed.
Absolute rate parameters for the reaction of ground state atomic oxygen with carbonyl sulfide
Authors: Klemm R. Bruce , Stief Louis J.
Published: February 2004

The rate parameters for the reaction of O(3P) with carbonyl sulfide, O(3P) + OCS → CO + SO, (1) have been determined directly by monitoring O(3P) using the flash photolysis-resonance fluorescence technique. The value for k1 was measured over a temperature range of 263–502°K and the data were fitted to an Arrhenius expression with good linearity, k1 = (1.65±0.13)×10−11 exp(−4305±55/R T) cm3 molecule−1·sec−1. A comparison of the present results with those from previous studies of Reaction (1) is also presented.
Specific heat of single crystal NiO from 3.2 to 18.75 K
Authors: White H. W.
Published: February 2004

The specific heat of single crystal NiO has been measured from 3.2 to 18.75 K. The Debye temperature was found to be 595±20 K.
Dynamics of stiff chains. II. Freely jointed chain
Authors: Fixman M. , Kovac J.
Published: February 2004

The equations developed in the preceding paper are applied here to the freely jointed chain. The complex modulus G agrees quite well with Zimm's results for the Gaussian model at low frequencies, even for chains of 5 or 10 bonds, but major differences appear at high frequencies for the imaginary part G″ as a result of the nonvanishing high frequency viscosity of a freely jointed chain.
Molecular dynamics study of liquid water under high compression
Authors: Stillinger Frank H. , Rahman Aneesur
Published: February 2004

The technique of computer simulation by molecular dynamics has been used to investigate highly compressed water at mass density 1.346 g/cm3. The calculations involve 216 rigid molecules, subject to an additive interaction (the ``ST2 potential'') whose strong anisotropic character has been shown to describe the hydrogen bond phenomenon. In the light of previous calculations on the same model at ordinary pressures, substantial restructuring of the liquid in response to compression is obvious. No evidence arises to support description of the liquid in terms of crystal structures of ices VI and VII, the solid forms that might be expected to be relevant at the chosen density. The calculations indicate that the initial effect of pressure increase (at 1 atm) leads to increased fluidity, as is known to be the case for real water.
Cluster expansions for hydrogen bonded fluids. II. Dense liquids
Authors: Andersen Hans C.
Published: February 2004

The cluster expansion theory of Mayer is formulated in a way that makes it useful for application to dense hydrogen bonded fluids, or, in general, to fluids with very strong attractive intermolecular potentials that are very dependent upon the relative orientations of the molecules. In the resulting diagrammatic series, the hydrogen bond appears only in a renormalized form that is much weaker than the Mayer f function for the original unrenormalized hydrogen bond potential. The diagram series for the pair correlation function is divided into various parts according to the topological structure and physical interpretation of the diagrams, and exact relationships among these parts are derived. These exact relationships can become the starting point for approximate calculations of the pair correlation function for hydrogen bonded liquids such as water.
Microwave spectrum, quadrupole coupling, and barrier to internal rotation of 1-chloro-1-fluoroethane
Authors: Thomas Clarence H. , Nisbet Kenneth D. , Graner Georges
Published: February 2004

The microwave spectra of the ground state of the 35Cl and 37Cl isotopic species of 1-chloro-1-fluoroethane have been investigated in the K-band region. An analysis of the 35Cl quadrupole splittings shows that the χ tensor is asymmetric, presumably owing to the partial double bond character of the C–C1 bond. A satellite spectrum of the 35Cl isotope has been assigned to the first excited state of the torsion. The relative intensity of the satellite spectrum leads to a value of the barrier hindering internal torsion of 4300±300 cal/mole.
Vibration-rotation inelasticity in He–H2
Authors: Rabitz Herschel , Zarur George
Published: February 2004

Vibration-rotation inelasticity in He–H2 is studied up to total energy 1.5 eV. This extends the previous lower energy pure rotational studies with the effective potential method. Comparison is made with breathing sphere calculations, and the corresponding vibration-rotation differential and total cross sections are similar. However, it is shown that there are many other nonbreathing sphere type vibration-rotation cross sections of comparable magnitude. The competitive roles of coupling and energetic resonance effects are quite apparent in the cross sections. The differential and total cross sections are examined for general characteristic behavior. An analysis is presented of the energy dependence of the cross sections. Finally, comments on general effective Hamiltonian methods are included.
Theory of distorted-wave Born approximation for reactive scattering of an atom and a diatomic molecule
Authors: Choi B. H. , Tang K. T.
Published: February 2004

Theoretical analysis was made on the transition matrix of the distorted-wave Born approximation for reactive collisions of an atom and a diatomic molecule. Using an ordinary representation in which projections of the angular momentum of the initial and the final molecule are referred to the same fixed space axis, we separate out the angular variables describing the rigid rotation of the three-particle system and thus reduce the five-dimensional integral in the transition matrix to a three-dimensional integral. The significance of the present formulation is illustrated by actual calculations of the reactive scattering of the (H, H2) system. For 0 → 0 rotational transition, early results are reproduced with less than 1% of the computer time previously used. For 0 → 1 rotational transition, present results which are also readily obtained are compared with those of close-coupling calculation. The reliability of the adiabatic distorted-wave model for reactive scattering and possible impacts of the present formulation on kinetics are discussed.
Absolute rates of collisional deactivation of Hg(6p 3P2) by nitrogen and carbon monoxide
Authors: Burnham R. , Djeu N.
Published: February 2004

The total rates of collisional deactivation of the 6p 3P2 state of mercury by nitrogen and carbon monoxide have been measured. The experimental technique involved the use of a narrow-band cw dye laser to probe the absorption at the center of the 5461 Å line of mercury in an optically pumped cell as a function of the pressure of the deactivating gases. The measured rates at 325°K were 3.0×106 and 6.2×106 sec−1·Torr−1 for deactivation by N2 and CO, respectively. Also measured were the rates of collisional deactivation from the 7s 3S1 level into the 6p 3P2 level. These partial quenching rates were found to be less than 7×105 sec−1·Torr−1 for N2, and equal to 4.4×106 sec−1·Torr−1 for CO.
Configuration interaction studies of HeH+ molecular ion. II Dipole and radial coupling matrix elements for the singlet sigma states
Authors: Green T. A. , Browne J. C. , Michels H. H. , Madsen M. M.
Published: February 2004

Configuration interaction calculations of the dipole, gradient, and radial coupling matrix elements among the lowest 10–12 1Σ states of HeH+ are reported for internuclear separations in the range 0≤R≤50 a.u. The forms 〈n|∂/∂R|m〉 and (Em − En)−1 〈n|∂V/∂R|m〉 of the radial coupling element are compared. The results are compared with those of other investigators. The accurate evaluation of these matrix elements in the present work demonstrates the feasibility of a quantitative ab initio treatment of low-energy collisions between light atoms.
Flow tube studies of the deactivation of HF(v) by selected polyatomic molecules
Authors: Kwok M. A. , Cohen N.
Published: February 2004

A large diameter, medium pressure flow tube has been used to study deactivation processes by selected polyatomic molecules potentially relevant in chemical laser systems. Effective vibrational deactivation rate constants for HF(v = 1,2,3) relaxed by H2S, CO2, N2O, CH4, CF4, and SF6 have been determined. Rate constants for chaperones H2S, CO2, and CH4 are found to be about 102−103 times larger than for the CF4 and SF6. The fast rates are order 1012 cm3/mol−1·sec−1. The N2O rates are intermediate. The rates for a given chaperone increase with ascending v. The agreement with results for HF(1) + M reported from laser-induced fluorescence experiments is generally good. The role of HF rotational energy in absorbing a vibrational energy defect is examined. An empirical correlation with adjusted vibrational energy defect is suggested.
Polarized infrared spectrum of crystalline acetone
Authors: Krause P. F. , Glagola B. G. , Katon J. E.
Published: February 2004

Through the use of oriented polycrystals, the polarized infrared spectrum of crystalline acetone has been investigated. The results have been satisfactorily used to deduce both site and possible factor group symmetries. In addition, the oriented gas model has been used as a means of classifying vibrations according to the various molecular symmetry species, thereby clarifying the vibrational assignments of three low frequency modes. This has been accomplished through the use of experimentally determined cosine-squared ratios of the pertinent symmetry species.
Changes of the electronic states of a mixed-valence compound at high pressures-insoluble Prussian blue, Fe4[Fe(CN)6]3
Authors: Hara Yoji , Minomura Shigeru
Published: February 2004

The effect of pressure has been measured on the abosrption spectra, x-ray diffraction, and electrical resistance in the mixed-valence compound ferric ferrocyanide or insoluble Prussian blue (ISPB). In the optical measurements, the charge transfer band from Fe(II) to Fe(III) showed a blue shift and decrease in intensity with pressure. The x-ray diffraction measurements up to 90 kbar showed that Fe(II)–Fe(III) distance decreased continuously. The electrical resistance was found to decrease by a factor of 10−2 up to 130 kbar at 297°K, but was found to have a resistance minimum at 333°K. The ξp2 value which indicates the delocalization of an electron between Fe(II) and Fe(III) was introduced. By using the results from the optical and the x-ray diffraction measurements at high pressures, this ξp2 value was estimated as a function of pressure.
Vibrational multiplet structure of internal optic modes in crystals
Authors: Frech Roger
Published: February 2004

Vibrational multiplet structure in Brillouin zone center internal optic modes can be classed as originating from site group effects, multiple site effects, and correlation field or factor group effects. In many systems where these may occur simultaneously, the separate contributions of each of these effects can be calculated in terms of a molecular dipole model. An example of site group/factor group splitting in orthorhombic KNO3 is analyzed and discussed.
Quantized vortices around wavefunction nodes. II
Authors: Hirschfelder Joseph O. , Goebel Charles J. , Bruch Ludwig W.
Published: February 2004

Quantized vortices can occur around nodes of wavefunctions. This fact, discovered by Dirac (1931) but little noted since, is rederived here and examples are discussed. The derivation depends only on the wavefunction being single valued and continuous. Since the derivation does not depend upon the dynamical equations, the quantized vortices are expected to occur for many types of waves (i.e., electromagnetic, acoustic, etc.). Such vortices have appeared in the calculations (McCullough and Wyatt, Kuppermann) of the H + H2 molecular collisions and play a role in the chemical kinetics. In a companion paper, it is shown that quantized vortices occur when optical waves are internally reflected from the face of a prism or particle beams are reflected from potential energy barriers.
Scaled particle theory of hard spherocylindrical fluids
Authors: Timling Kaj M.
Published: February 2004

For a system of spherocylindrical particles, an integral equation in the singlet angular distribution function is obtained. The integral equation is solved analytically by an expansion in the reduced density. Two nontrivial solutions appear, one corresponding to a nematic phase where the long axes of the molecules tend to align parallel, and one corresponding to a nonstable pseudonematic phase where the short axes tend to align parallel. The transition from the isotropic to the nematic phase is first order, whereas the transition to the pseudonematic phase is second order. None of the ordered phases can exist for reduced densities below a certain value, which is found as a simple function of the length to width ratio of the molecules.
Reactions of recoil 13N atoms in the gas phase
Authors: Stewart G. W. , Dymerski P. P. , Hower C. O.
Published: February 2004

Recoil reactions of 13N atoms in CO2, N2, O2, N2O, and NO were studied. Recoil nitrogen atoms were generated by the 12C(d, n)13N reaction using CO2 as the target molecule. The only products observed were 13NN and 13NNO. Other products sought but not detected were NO, NO2, and CN radicals. The 13NN formation with added N2 is attributed to an exchange reaction involving translationally excited nitrogen atoms with nitrogen molecules. The 13NNO yield is independent of CO2 concentration; however, it increases rapidly with the addition of O2. This increase, along with an equal decrease in the 13NN yield, is explained by the reaction of excited nitrogen molecules (13NN*) with O2. It is concluded that recoil 13N atoms do not react directly with CO2.
Alignment of molecules in gaseous transport: Alkali dimers in supersonic nozzle beams
Authors: Sinha M. P. , Caldwell C. D. , Zare R. N.
Published: February 2004

From measurements of the degree of polarization of the molecular fluorescence, it is shown that one can determine the coefficients of the first three even-ordered Legendre polynomials in the expansion of the spatial distribution of J vectors (MJ population), n(θ)=1 + a2P2(cosθ) + a4P4(cosθ), where θ is the angle between the angular momentum vector J of the molecule and the beam direction. This method is applied to determine the alignment of Na2 molecules in a supersonic nozzle beam generated by expansion of sodium vapor through a converging nozzle (throat diameter = 0.375 mm and channel length = 0.750 mm) with stagnation temperature (oven temperature) up to ∼1015°K, corresponding to stagnation pressures (oven pressures) up to ∼155 torr. The 4880 Å line of a cw argon-ion laser is used to excite the transition (ν″=3, J″=43 → ν′=6, J′=43) in the B 1Πu−X 1Σg+ band system of Na2 molecules and the degree of polarization of a single line of the resulting fluorescence series (Q series) is measured as a function of (1) stagnation pressure p0 and (2) the angle θ0 between the electric vector of the exciting laser light and the molecular beam direction. A decrease in the degree of polarization from its isotropic value of 0.50 for θ0=0 to a value of 0.44 at a stagnation pressure of 155 torr is found, showing increasing alignment of dimer molecules with their angular momenta preferentially pointing perpendicular to the beam direction. At the stagnation pressure of 155 torr the coefficients of the Legendre polynomials are found to be a2=−0.203±0.006 and a4=−0.14±0.03. For this distribution the ratio of molecules with angular momentum J parallel and perpendicular to the beam axis is ∼2:3. Classical models involving the nonreactive collisions between hard spheres (atoms) and ellipsoids of revolution (molecules) and the chemical exchange between atoms and dimers predict the production of alignment in qualitative agreement with experiment.
Theoretical equations for photoionization cross sections of polyatomic molecules in plane-wave and orthogonalized plane-wave approximations
Authors: Ellison Frank O.
Published: February 2004

The general polyatomic molecule in a closed-shell electronic state with nuclei fixed according to the Born-Oppenheimer approximation is photoionized to form a final singlet state in which one electron is excited into the continuum. All bound orbitals are assumed identical in the initial and final states. The unbound orbital is approximated either by a plane-wave or by a plane-wave orthogonalized to all occupied bound orbitals. Formulations are given for cases in which bound orbitals are expressed as linear combinations of Slater-type orbitals, orthogonalized Slater-type orbitals, Cartesian Gaussian-type orbitals, or Gaussian-lobe functions. General equations are derived for the photoionization cross section of randomly oriented polyatomic molecules as a function of angle between the polarization vector of the photon beam and the propagation vector of photoejected electrons. Also derived is the photoionization cross section of the same sample as a function of angle between an unpolarized photon beam and the propagation vector of photoejected electrons.
Hydrates in supersaturated binary sulfuric acid-water vapor
Authors: Heist R. H. , Reiss H.
Published: February 2004

Portions of the free energy surface giving the reversible work W required to form a droplet containing n1 molecules of H2O and n2 molecules of H2SO4 from an initially homogeneous vapor have been calculated for a variety of relative humidities and H2SO4 vapor concentrations. These surfaces are displayed as three dimensional perspective plots. The surfaces predict the existence of stable H2SO4 hydrates in the vapor phase, and the number of hydrates, Nh, with h molecules of H2O per hydrate has been calculated for three different values of the relative humidity. The results of these calculations indicate that virtually all the H2SO4 present, especially for relative humidities greater than 100%, exists in hydrate form. As the relative humidity is increased (i.e., greater than 200%), the distribution of hydrate sized agrees well with that found by Giauque et al. for solid H2O–H2SO4 mixtures. Hydrate formation can exert an appreciable effect on the process of vapor phase nucleation in H2O–H2SO4 mixtures, and must be considered in any theory of nucleation rate.
Kinetic theory approach to simultaneous gas and surface diffusion in capillaries
Authors: Bell Weldon K. , Brown Lee F.
Published: February 2004

Momentum balances are derived for the isothermal, isobaric counterdiffusion of two gases within a capillary, with one of the gases adsorbed in a mobile phase on the surface of the capillary. Interactions between the gases and the mobile adsorbed phase result in equations for describing the gaseous diffusion behavior which are significantly different from the equations derived when these interactions are ignored. Simplification of these equations for low surface coverage by the adsorbate is possible; the simplification eliminates the need for adsorption isotherms in the low-coverage situation. The momentum balances derived here are applied to data from two systems which had earlier defied satisfactory description of the diffusion behavior. The diffusion behavior of helium, from nitrogen and helium counterdiffusing through pelleted Graphon, is described satisfactorily by an equation resulting from manipulation of the low-surface-coverage momentum balances. However, the diffusion behavior of helium from propane and helium counterdiffusing through pelleted Graphon is not described satisfactorily by an equation resulting from the general momentum balances. It is suspected that the principal cause for failure in the latter case is an overly naive model for the gas-adsorbate interactions. The momentum balances derived here can be used to calculate surface fluxes within the adsorbed phase. Values calculated for the nitrogen and propane surface fluxes in the above systems can be drastically different from those calculated when the gas-mobile surface phase interactions are ignored.
ESR of Cu2+ (H2O)6. I. The oxygen-17 superhyperfine tensors in 63Cu2+ doped zinc Tutton's salt at 20 °K
Authors: Getz Daphne , Silver Brian L.
Published: February 2004

The X-band ESR spectrum of 63Cu2+ doped zinc Tutton's salt enriched to 16 at.% in oxygen-17 isotope was studied in a completely deuterated single crystal at 20°K. Satellites from both singly and doubly labelled molecules were observed and the oxygen-17 superhyperfine tensors were found to differ for the two trans pairs of equatorial oxygens. The two tensors are −21.0, −11.9, and −10.9×104 cm−1 and −16.1, −9.9, and −8.8×104 cm−1, where the largest principal value in each case is directed along the copper-oxygen bond and the tensors are associated, respectively, with the shorter and longer of the equatorial copper-oxygen bonds. The tensors, after correction for a distant dipolar contribution from the metal, were shown to imply a value of 1/6 for the ratio 2s0/2p0 in the molecular orbital containing the unpaired electron. This result is discussed in terms of the known geometry of the Cu2+(H2O)6 complex in Tutton's salts.
ESR of Cu2+(H2O)6. II. A quantitative study of the dynamic Jahn-Teller effect in copper-doped zinc Tutton's salt
Authors: Silver Brian L. , Getz Daphne
Published: February 2004

The X-band ESR spectra of 63Cu2+ doped zinc Tutton's salt enriched to 16 at.% in 17O isotope was studied in a single crystal at 20, 77, and 290°K. The powder spectrum of the same material was studied over the temperature range 10–350°K at X band and 120–290°K at Q band. The observed values of the g tensor and 63Cu and 17O hyperfine tensors were found to be strongly temperature dependent except when the magnetic field was parallel to g3, one of the principal axes of the g tensor. The directions of the principal axes of the g tensor and 63Cu hyperfine tensor were shown to be temperature independent, in opposition to the findings of other workers. In the single crystal, marked mI dependent linewidth variations in the 63Cu hyperfine components were observed in the temperature range 14–80°K, except when the external field was parallel to g3. The experimental data are explicable in terms of a dynamic Jahn-Teller effect, in contrast to the previously held assumption that dilute copper Tutton's salt is a static Jahn-Teller system. The energy splittings between the three inequivalent valleys were determined directly from the experimental results and found to be δ1,2 = 75 cm−1, δ1,3 ≃ 450 cm−1. The splittings are discussed in terms of published crystallographic data on Tutton's salts, and a crystal field calculation gave a value of δ1,2/δ1,3 = 1/5 in good agreement with experiment. The rate of intervalley jumping between the lowest two valleys was determined from linewidth measurements and found to be characteristic of an Orbach process, following the law τ = τ0 exp(120/k T). The value of 120 cm−1 is identified with the height of the ``warping'' barrier between valleys 1 and 2. Phonon-assisted tunneling makes no significant contribution to the jumping rate.
Mass-spectrometric study of ionic species present during the oxidation of CO and the decomposition of CO2 in a rf discharge
Authors: Brown Lloyd C. , Bell Alexis T.
Published: February 2004

A mass spectrometric investigation has been performed of the ionic species present during the oxidation of CO and the decomposition of CO2 in a rf discharge. The relative ion current for each species is found to depend upon the discharge power and the gas pressure. A feature of particular interest is the observation that C+ is one of the dominant ions present. An analysis of the mechanisms for the formation of this species suggests that it is formed by the reaction CO+ + CO → C+ + CO2 which occurs in the sheath separating the plasma and the sampling orifice.
Molecular dynamics study of dimer formation in three dimensions
Authors: Schieve William C. , Harrison Herman W.
Published: February 2004

Molecular dynamics is used to study a classical model of dimer formation by three-body collisions in three dimensions. The mole fractions for both stable and metastable dimers are obtained for T*=0.85, 1.1, and 2.2 and compare well with the equilibrium statistical mechanics results. The dimer internal energy and vibrational and rotational energy distributions are obtained and appear to be qualitatively consistent with equilibrium internal distributions. The temperature dependence of K, the reaction rate, varies approximately as T*−=5/8. From this it is concluded that the steric factor P for the formation of stable dimers lies in the range 0.05–0.1 and is even smaller than the previous two-dimensional results.
Monte Carlo quasiclassical trajectory study of Br + HBr and H + HBr: Effect of reactant vibration and rotation on reaction rates and energy transfer
Authors: White John M. , Thompson Donald L.
Published: February 2004

A quasiclassical trajectory study of reactive and nonreactive processes in the H+HBr and Br+HBr systems is reported in which attention is focused on the role of initial internal energy on reaction rate coefficients and on angular scattering distributions and the contribution of atom-exchange reactions to vibrational energy transfer. For both systems the atom-exchange mechanism is a significant contributor to the vibrational relaxation of HBr. Initial internal excitation, either vibrational or rotational, leads to an increase in the reaction rate coefficient. In the Br+HBr case the atom-exchange product molecule is scattered in the forward direction, the distribution is insensitive to initial internal energy changes, and the trajectories are complex. On the other hand, the H+HBr reactions, abstraction and atom exchange, both proceed in a direct, uncomplicated fashion and in the case of abstraction the H2 product is scattered backward. Where possible the results are compared with other work, principally Cl+HCl.
Determination of the anisotropic part of the adsorption potential, on a surface, by nuclear magnetic resonance of adsorbed hydrogen at low temperature
Authors: Dubault André , Legrand André P.
Published: February 2004

Nuclear magnetic resonance spectra of an orthohydrogen molecule, physically adsorbed at low temperature, can give information on the anisotropic part of the adsorption potential which characterizes the surface and the molecule. From this point of view, the molecule can be considered as a probe which is sensitive to the electric field or gradient. By this way it is possible to have an estimation of these quantities, which can be compared to calculated ones of a model of a more or less ionic structure of the adsorbant.
ENDOR study of long-range spin interactions in molecular crystals. I. 1-methyl uracil
Authors: Herak J. N. , McDowell C. A.
Published: February 2004

ENDOR spectroscopy has been used for the precise measurements of the proton couplings in two different radicals derived from 1-methyl uracil by gamma ray irradiation. Couplings of the protons located in as many as seven molecules in the host crystal around the free radical have been identified. The intermolecular spin interaction is predominantly of dipolar character. For the remote protons it is well described by the point-dipole approximation. Intramolecular proton couplings are more complex because of the significant isotropic component and delocalization of the unpaired electron.
Rotational invariance and molecular collisions
Authors: Hunter L. W. , Snider R. F.
Published: February 2004

Direct relations are presented between the transition operator and the three reduced transition matrices defined in the collision theory of Curtiss and his co-workers. It is shown that the existence of each reduced transition matrix may be separately derived from the rotational invariance property of the transition operator.
Theory of the dynamical viscosity of polymer solutions
Authors: Edwards S. F. , Freed Karl F.
Published: February 2004

A dynamical theory of polymer viscosity in dilute polymer solutions is presented. This theory includes the internal chain dynamics and the full dynamics of the hydrodynamic interactions within a polymer chain. The formulation considers the full dynamical coupled equations describing the internal motions of the polymer, the hydrodynamic behavior of the fluid, the polymer-fluid coupling, and the random forces which are responsible for the Brownian motion of the chain. Thus, the theory would reduce to the generalized Kirkwood theory if the dynamics of the hydrodynamics were ignored and the explicit treatment of the polymer dynamics and the random forces were dropped in favor of the thermodynamic force of the Kirkwood theory. As illustrative examples, only the simplest hopping-type models for the polymer dynamics are considered; the nature of the random forces is elucidated by the use of the fluctuation dissipation theorem; and the preaveraged dynamical hydrodynamic interactions are incorporated (with a phenomenological description of excluded volume effects). When the internal dynamics of the chain is ignored along with the dynamics of the fluid, the standard Kirkwood-Riseman result for the intrinsic viscosity is recovered. But in the general case, the dynamics alters the relaxation spectrum. The internal chain dynamics (hopping of individual chain ``beads'') gives rise to the finite high frequency intrisic viscosity and its different molecular weight dependence than the low frequency case.
Computer simulation of multiple chain systems—the effect of density on the average chain dimensions
Authors: Curro John G.
Published: February 2004

In this investigation, a Monte Carlo method was developed for the determination of equilibrium, configuration-dependent properties by the computer simulation of (short chains) multiple chain polymer systems. This method was demonstrated on a system of oligimers of fifteen and twenty units in which the effect of density on the average configuration was studied. Two distinct density regions were observed. In the dilute range, the mean square end-to-end distance was found to be independent of concentration. At higher concentrations, where overlap of chain domains occur, the mean square end-to-end distance decreases rapidly to the random flight result. At these densities, the chains act in effect as a theta solvent for themselves. The results were compared with previous analytical calculations.
Electron spin resonance of Co(CN)53− in x-irradiated single crystals of K3Co(12CN)6 and K3Co(13CN)6
Authors: Booth R. J. , Lin W. C.
Published: February 2004

An ESR study of x-irradiated single crystals of K3Co(12CN)6 showed that any of the three perpendicular bonds of Co(CN)63− may be cleaved in the formation of the Co(CN)53− ion. The delocalization of spin was studied through the 13C splittings in x-irradiated single crystals of K3Co(13CN)6. The spin density distribution was calculated to be Co(3dz2) 0.79,Co(4s) 0.05, C(2s) 0.032, C(2p) 0.068.
Symmetric stretching internal vibrations, and N3− group asymmetry in Ba(N3)2 crystal
Authors: Iqbal Zafar
Published: February 2004

Single crystal Raman and infrared spectra of barium azide, Ba(N3)2, for all polarization orientations, were measured in the N3− symmetric stretching (ν1) spectral region between 1200 and 1400 cm−1. An interesting intensity anisotropy of the Raman and infrared peak at 1347 cm−1 has been observed with respect to polarization along the c direction. This has been related to the localization of one set of ν1 factor group component eigenvectors on asymmetric azide ions aligned closely parallel to the c axis.
Assignments in the electronic spectrum of water
Authors: Yeager Danny , McKoy Vincent , Segal G. A.
Published: February 2004

To explain the inelastic feature at 4.5 eV in the spectrum of water and to study its spectrum in some detail, we have carried out several calculations on the excited states of water using the equations-of-motion method. We conclude that the calculated vertical excitation energy of 6.9 eV for the 3B1 state corresponds to the strong feature at 7.2 eV observed in low-energy electron scattering spectrum. The 4.5 eV inelastic process almost certainly does not correspond to a vertical excitation of water at the ground state geometry. The other excitation energies and oscillator strengths agree well with experiment.
Spin-other-orbit and spin-spin interactions in the metastable, c 3Πu(1s,2p) state of H2
Authors: Jette A. Norman
Published: February 2004

An ab initio calculation of the spin-other-orbit and spin-spin interactions in the c 3Πu(1s,2p) state of molecular hydrogen has been made. This calculation utilized the wavefunction obtained with the optimal double configuration model by Zemke, Lykos, and Wahl. The coupling constants are in good agreement with those calculated by Lombardi using the 45–50 configuration elliptic coordinate wavefunction of Rothenberg and Davidson.
Electron nuclear double resonance of photoexcited phenanthrene-d10 molecules in their lowest triplet state in diphenyl single crystals
Authors: Hutchison Clyde A. , McCann Valda H.
Published: February 2004

Electron deuteron double resonance spectra have been obtained for phenanthrene-d10 molecules in their triplet electronic state of lowest energy, when they are dilutely substituted in a diphenyl host crystal. Four discretely different orientations of phenanthrene-d10 molecules at the same set of translationally equivalent substitution sites of the diphenyl host, have been observed. Values of hyperfine interaction tensor components and of spin densities for these different phenanthrene-d10 molecules have been determined. The distortions of these various molecules from an ideal symmetry and the importance of these different distortions, as well as of the different orientations, for the interpretation of the intensities and polarizations of optical spectra, are discussed in light of the present measurements.
Interactions of hyperthermal atomic beams with solid surfaces
Authors: Liu S. M. , Rodgers W. E. , Knuth E. L.
Published: February 2004

Interactions of high-energy supersonic atomic beams with solid surfaces and surface contaminants have been studied experimentally. In situ Auger electron spectroscopy indicates that hydrocarbons from the oil diffusion pump are the major contaminants. The hypothesis that a threshold energy exists for sputtering of these surface contaminants by an incident beam has been further tested. The dependence of the threshold energy on the incident-beam angle has been examined for three different incident-beam angles, namely 50°, 60°, and 70° from the surface normal. A simple correlating expression for Eth(μ,Θi) has been derived.
Cross section and isotope effect in the reaction of F+ with molecular hydrogen
Authors: Lin Kuo-chin , Cotter R. J. , Koski W. S.
Published: February 2004

The ion-molecule reactions of F+(3P) and F+(1D) with molecular hydrogen and its stable isotopic variants were studied using a tandem mass spectrometer. The cross section behavior and isotope effects were similar to corresponding reactions involving Ar+. In the higher energy regions the reaction appears to proceed by direct mechanisms. No unambiguous conclusions could be drawn about the reaction mechanism in the region below 1 eV relative energy.
Perturbation theory for a mixture of hard spheres and square-well molecules
Authors: Henderson Douglas
Published: February 2004

Perturbation theory is applied to a mixture of hard spheres and square-well molecules. If the higher order perturbation terms are adequately accounted for, excellent agreement with machine simulation results is obtained. In particular, good values for the heat capacity are obtained. This is in contradiction with Alder's conjecture that the hard-sphere reference fluid is unable to deal with concentration fluctuations. In addition, an approximation to the higher order terms in perturbation theory which appears useful at low densities is suggested. Finally, the theory of random mixtures (RM) and the van der Waals (vdW) theory of mixtures, which are identical for this system, are considered. The estimates of the higher order perturbation terms given by the RM and vdW theories are seriously in error for this system.
Absolute differential cross sections of electrons elastically scattered by the rare gases. I. Small angle scattering between 200 and 700 eV
Authors: Bromberg J. Philip
Published: February 2004

Absolute differential cross sections of electrons scattered by the rare gases He, Ne, Ar, Kr, and Xe were measured between 2° and 30° at 200, 300, 400, 500, and 700 eV. The results for He are compared with experimental and theoretical results from other laboratories, and serious discrepancies are found to exist between the data reported by various laboratories.
Ground and excited states of the diatoms CN and AlO
Authors: Das G. , Janis T. , Wahl Arnold C.
Published: February 2004

Multiconfiguration self-consistent field (MCSCF) wavefunctions are obtained for the ground and some low-lying valence excited states of the same symmetry for the diatomic systems CN and AlO. The spectroscopic constants of these states as well as their dipole moments as a function of the internuclear separation are also calculated and compared with previous theoretical and experimental results.
Molecular structure of pyridine-N-oxide
Authors: Chiang Joseph F.
Published: February 2004

The molecular structure of pyridine-N-oxide has been determined by gas phase electron diffraction. The internuclear distances and bond angles were obtained by applying a least squares analysis on the experimental molecular intensity. The bond distances (rg) and angles (ra) were N1–C2=1.384±0.011 Å; C2–C3=1.381±0.009 Å; C3–C4=1.393±0.008 Å; N1–O7=1.290±0.015 Å; C–H=1.070 Å; ∠C2N1C6=120.9± 1.8°; ∠C3C4C5=114.1± 2.5°. The calculated moments of inertia agree with the microwave spectroscopic values.
Vibrational spectrum, torsional potential, and bonding of gaseous N2O4
Authors: Bibart Charles H. , Ewing George E.
Published: February 2004

The infrared spectrum of gaseous N2O4 was obtained under conditions which allowed study of both strongly and weakly absorbing features. These spectral features were assigned with the aid of vibration-rotation band shape theory. Weakly absorbing sequence bands were identified which contain torsional vibrations. The rocking frequency of the NO2 group, the only mode which has not been observed directly, was estimated from a Third Law entropy calculation. The frequencies obtained from this research together with previous Raman work provide, for the first time, a reliable determination of all the vibrational frequencies of N2O4. The observation of the torsional mode frequencies has allowed an internal rotation potential function to be estimated which has a barrier height of 2 to 3 kcal/mole. From this potential function a picture of the bonding in N2O4 and other nitrogen oxides is presented. It is suggested that in addition to the N–N bond, weak σ bonds form between the cis oxygens which stabilize the eclipsed oxygen configurations and tend to lock the N2O4 molecule into a planar configuration. The planarity of N2O3 and the stability of cis (NO)2 can also be explained by these weak oxygen σ bonds.
Vibrational spectrum of gaseous N2O3
Authors: Bibart Charles H. , Ewing George E.
Published: February 2004

Gaseous N2O3 was produced by the equilibrium reaction of NO with NO2. By careful selection of the temperature and pressure the relative concentration of N2O3 was high and its infrared spectrum was obtained without interference from other nitrogen oxide absorptions. The spectrum reveals new features previously unreported including sequence bands containing torsional vibrations. This work, together with other far infrared studies, provides an assignment of all the N2O3 vibrational frequencies. An estimate of the internal rotation potential function indicates a barrier height of the order of 1 kcal/mole.
Laser photodetachment of NO2−
Authors: Herbst E. , Patterson T. A. , Lineberger W. C.
Published: February 2004

An absolute apparent cross section for the photodetachment of nitrite (NO2−) ions has been measured in the region (2.0–2.7) eV utilizing a tunable dye laser as the light source. The electron affinity of nitrogen dioxide (NO2) has been determined to be (2.36±0.10) eV. Photodetachment of an ion thought to be a peroxy isomer of NO2− has also been observed.
Phonon density of states and the vibronic spectra of impurities in K2PtCl6-type single crystals
Authors: Durocher Donald , Dorain Paul B.
Published: February 2004

Single crystals of the K2PtCl6 type at 4°K with impurities of Re+4, Os+4, and Ir+4 show optical absorption with extended phonon structure. To understand the details of this, a phonon density of states was calculated using the model of O'Leary and Wheeler for K2ReCl6 and the method of Gilat and Raubenheimer. The results are compared with the optical spectra of Re+4 and Os+4 in K2PtCl6 that provide strong evidence that the previously used k = 0 phonon analysis is incorrect and that all the lattice vibrations must be used. The implications in the calculation of phonon assisted transition selection rules are discussed.
Kinetic theory of axially elastic spherocylinder molecules
Authors: Pai T. G. , Ramachandra S. M.
Published: February 2004

An axially elastic spherocylinder molecular model has been proposed for a vibrationally relaxing diatomic gas molecule. Binary collision between two such particles is studied first. A Boltzmann equation is given for a gas consisting of elastic spherocylinder particles, and an equilibrium solution is obtained for the same through an H theorem. Three conservation equations are written down as particular cases of the Maxwell transfer equation.
Excimer formation in vinyl polymers. II. Rigid solutions of poly(2-vinylnaphthalene) and polystyrene
Authors: Frank Curtis W. , Harrah Larry A.
Published: February 2004

Excimer formation has been examined in solid films of poly(2-vinylnaphthalene) (P2VN) and polystyrene (PS) as a function of sample temperature from 373 to 4.2°K and film preparation temperature between 373 and 295°K. The concentration of suitable excimer forming sites in the solid state is fixed by the temperature at which the film is cast. A statistical model based on the rotational isomeric state approximation is used to formulate an expression for the fraction of excimer forming sites in the solid systems. This model makes use of the excimer site conformation energy, found to be 2500 cal for P2VN. Excimer sampling in solid solution is shown to be consistent with an activated exciton migration to preformed excimer sites. The mechanism for this process is attributed to a modulation of interchromophore separation resulting from longitudinal acoustical vibrations of the polymer chain. A semianalytical expression for the enhancement of the excitation migration is developed which has the same general form as the experimental results. The effective vibrational frequency is found to be 157 cm−1 for PS and 84 cm−1 for P2VN.