bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron Spin Resonance of MnCl42− in Molten Tri-n-butylbenzylphosphonium Halides
Authors: Sundheim Benson R. , Flato Jud , Yarmus Leonard
Published: February 2004

Electron spin resonance measurements are reported for solutions of Mn(II) in molten tributylbenzylphosphonium chloride. By examining the broadening of the hyperfine lines as a function of temperature and composition, it was concluded that the increasing temperature merely produces motional narrowing and that there is no evidence of spin–spin interaction. Comparison with simple pictures of transport in liquids leads to the conclusion that the pair distribution function at contact for MnCl42− is reduced over the random value by a factor of at least 100.
Low-Temperature Viscosities and Intermolecular Forces of Simple Gases
Authors: Clarke A. G. , Smith E. B.
Published: February 2004

The viscosities of nitrogen, helium, neon, and methane have been measured in the temperature range 77–374°K relative to that of nitrogen at 273°K. The nitrogen viscosities are within 0.5% of those obtained in an earlier investigation except at one temperature, 114°K, where a difference of 1.5% is noted. The results for methane are close to those of earlier workers except at the lowest temperatures, but the results for helium and neon are from 1% to 2.5% above previous data below room temperature. The relationship between the low-temperature transport properties of gases and dispersion forces is examined in detail and a comparison is made of the coefficients of r−6 determined experimentally and theoretically. The phenomenon of a maximum or minimum in the ratio of viscosities for two gases is noted, and a test of intermolecular potential functions based on this fact is suggested. The agreement between several potential functions and the recent results of the authors for the viscosity of argon is examined.
Nonequilibrium Statistical Mechanics of Free Electrons in Some Disordered Systems
Authors: Popielawski Jan
Published: February 2004

A functional-integral representation of the quantum-phase-space transformation function is postulated and various expansion representations for this function are generated. The binary-collision expansion is discussed in some details, and it is shown how dynamics of the system can be described in terms of the quantum irreducible cluster operators. The developed formalism is applied to the derivation of the kinetic equations for free electrons in the conduction band of the simple liquids and dense metallic vapors. It is proved that equations postulated on the ground of intuitive arguments can be regained if the multiple electron–neutral-atom scattering and the interference between electron–electron and electron–neutral-atom scattering are neglected. A brief discussion of the relation of presented formalism to Ziman and Edwards theoretical descriptions of disordered systems is also included.
Second-Order Perturbation Treatment of the Ground State of H2+
Authors: Jackson M. , McEachran R. P. , Cohen M.
Published: February 2004

Rayleigh–Schrödinger perturbation theory has been used through second order to obtain an analytic representation for the ground-state wavefunction of H2+. Values of the electronic energy and other molecular properties computed with this approximate wavefunction are compared with the corresponding exact values, and they demonstrate its high accuracy.
Rotational Isomerism in Fluoroacetyl Halides
Authors: Khan A. Y. , Jonathan Neville
Published: February 2004

Infrared and Raman spectra have been recorded for fluoroacetyl fluoride, chloride, and bromide. The data show that each compound exists as an equilibrium mixture of two isomers in the vapor and liquid states. Normal coordinate analysis calculations based on a Urey–Bradley potential function indicate that the two preferred conformations are a trans and a staggered conformation which is close to the cis. In all three compounds the trans isomer is found to be the more stable in both liquid and vapor phases, with its stability being relatively diminished in the vapor state. Approximate, but nearly complete vibrational frequency assignments are made for each isomer. The vapor phase enthalpy difference ΔH° = (H°trans − H°staggered) was measured as − 2.05 ± 0.25 kcal/mole for fluoroacetyl bromide.
Electron Detachment in Collisions of O−, OH−, and O2− Ions with Rare-Gas Atoms
Authors: Wynn M. J. , Martin J. D. , Bailey T. L.
Published: February 2004

Total cross sections for the electron detachment process X− + Y = e− + X + Y have been measured for the collision systems O−–He, O−–Ne, O−–Ar, O2−–He, and OH−–He, in ion-beam gas-scattering experiments which extend from primary ion energies of 400 eV down to several electron volts. Detached electrons were separated from other negative reaction products either by a radio-frequency electron filter, or by electrostatic-retardation analysis. Particular emphasis was placed on the low-energy region near detachment threshold; the data obtained in this region was found to conform fairly well to predictions of theoretical threshold laws. The cross sections obtained at higher energies are, for the most part, in good agreement with previous measurements.
ESR of the CN Radical in Inert Matrices
Authors: Easley Warren C. , Weltner William
Published: February 2004

CN has been trapped as a randomly oriented molecule in argon, krypton, and neon matrices at 4°K. The ESR spectra of 12C14N and 13C14N in their ground Σ+2 states have been determined and yield the following magnetic parameters in solid argon: g‖ = 2.0015(5), g⊥ = 2.0003(5), A‖(14N) = + 18.2(4) MHz, A⊥ (14N) = − 28.0(3) MHz, A‖ (13C) = + 678(1) MHz, A⊥ (13C) = + 543.1(5) MHz. Weak forbidden ΔMI = ± 1 transitions are also observed. Upon slight warming, the sites are irreversibly changed so that CN thereafter exhibits hindered rotation, even at 4°K, and raising the temperature leads to the isotropic ESR spectrum of rotating CN. Variations in linewidths due to motional effects make it possible to confirm the relative signs of the A values. The g⊥ shift is shown to arise from small negative contributions from spin–orbit coupling with both the Πi2 and Πr2 excited states. Approximate spin densities in the molecule are qC(2s) = 0.19, qC(2p) = 0.48, qN(2p) = 0.32, qN(2s) = − 0.008. These values are compared with those obtained from a Hartree–Fock wavefunction provided by Cade.
Ion–Molecule Reactions in Pure Nitrogen and Nitrogen Containing Traces of Water at Total Pressures 0.5–4 torr. Kinetics of Clustering Reactions Forming H+(H2O)n
Authors: Good A. , Durden D. A. , Kebarle P.
Published: February 2004

The ion–molecule reactions in pure nitrogen and nitrogen containing traces of water were studied with a pulsed electron-beam mass spectrometer having a field-free high-pressure source. The reaction N2++2N2 = N4++N2 occurring in pure nitrogen was found to have a third-order rate constant k = 8 × 10−29cc2molecule−2·sec−1 at 300°K and a negative temperature coefficient corresponding to an “activation energy” of − 2 kcal/mole at pressures up to 3.5 torr. The results for the reaction N++N2→N3+, investigated under the same conditions, indicated either third-order dependence with k = 5 × 10−29cc2molecule−2·sec−1 and energy of activation − 1 kcal/mole or second-order dependence with k = 1.3 × 10−12cc molecule−1·sec−1 with no temperature coefficient. The reaction mechanism in nitrogen in the torricelli range containing water vapor in the millitorr range was found to proceed by the following reaction sequence: N2+→N4+→H2O+→H3O+→H+(H2O)2→H+(H2O)n. The rate constants for all reactions were determined. The clustering reactions H+(H2O)n+H2O=H+(H2O)n+1 were found to be third order for n = 1 to n = 4 and all approximately equal to 3 × 10−27 cc2 molecule−2·sec−1. Equilibrium constants for the clustering reactions and the rate constants for the reverse reactions were also obtained.
Mechanism and Rate Constants of Ion–Molecule Reactions Leading to Formation of H+(H2O)n in Moist Oxygen and Air
Authors: Good A. , Durden D. A. , Kebarle P.
Published: February 2004

The formation of H+(H2O)n clusters in moist oxygen is of interest since this process must occur in the troposphere and has been observed to occur in the D region of the ionosphere. The reaction mechanism leading from O2+ to H+(H2O)n was investigated with a pulsed electron-beam high-pressure mass spectrometer. At oxygen pressures in the torr range and for [O2]/[H2O]>102 the major reaction proceeds by the sequence O2+→O4+→O2+·H2O→H3O+·OH→H+(H2O)2→H+(H2O)n. The rate constants for all major steps were determined. Rate constants for parallel reactions which may become important at different conditions were also determined.
Superoperator Direct Method of Calculating Spectra
Authors: Cohen Sheila M.
Published: February 2004

The so-called “direct” method of calculating spectra, developed by Banwell and Primas, yields the transition frequencies directly as eigenvalues of the derivation superoperator belonging to the Hamiltonian. A set of relationships between the elements of the derivation superoperator matrix hD and those appearing in the corresponding energy matrix H is given. The derived rules result in a great simplification of the problem when the method is applied to the calculation of NMR spectra; this is exemplified by treatment of the three-spin systems.
Mass-Spectrometric Study of the Laser-Induced Vaporization of Compounds of Bismuth with the Elements of Group VIa
Authors: Ban Vladimir S. , Knox Bruce E.
Published: February 2004

The laser mass-spectrometer combination has been used to study the vapor species emanating from various binary, ternary, and quarternary compounds of bismuth with the elements of the VIa group. It has been postulated that some of the species present in the laser-produced vapor can be correlated with the short-range-order features of the condensed phase. Molecular configurations of some complex species are discussed.
Mass-Spectrometric Study of the Laser-Induced Vaporization of Compounds of Arsenic and Antimony with the Elements of Group VIa
Authors: Ban Vladimir S. , Knox Bruce E.
Published: February 2004

The laser mass spectrometer has been used to study the vapor composition of various compounds of arsenic and antimony with the elements of Group VIa. It is shown that in some cases there is a direct correlation between the vapor composition and the structure of the condensed phase. The mechanism of the laser-induced vaporization is discussed; it is shown that the critical region (or vicinity) can be reached in laser–solid interactions.
Force Constants in Hartree–Fock Theory
Authors: Freed Karl F.
Published: February 2004

Force constants in Hartree–Fock (HF) theory are examined in view of the fact that they are predicted to be good through first order in the wavefunction, but are usually found to be in error by more than is “typically” found for one-electron operators. It is shown that the evaluation of force constants by the differentiation of HF potential-energy curves is formally equivalent to their calculation at a single internuclear distance by the use of the fully coupled HF-perturbation calculation of the requisite second-order-type expression (the relaxation contribution).
Number of Bound States in Lennard-Jones Potentials
Authors: Mahan G. D.
Published: February 2004

Accurate approximation techniques are derived for evaluating WKBJ integrals for Lennard-Jones potentials. These techniques allow one to evaluate the WKBJ integral at only two energy values: E = 0, which is the dissociation limit, and secondly, the energy at the height of the centrifugal barrier. These two special cases allow one to determine the number of bound and quasibound states of the Lennard-Jones potential: Quasibound states have an energy greater than zero but less than the centrifugal barrier. A simple analytical formula is presented which estimates accurately the number of bound and quasibound states. Numerical results are presented for the interactions of alkali and noble-gas atoms. The chemical equilibrium constant for molecule formation is also estimated for these systems.
Ion–Molecule Reactions in Olefins
Authors: Henis J. M. S.
Published: February 2004

The reactions of parent olefin ions with neutral olefin molecules from ethylene through hexene were studied. Addition reactions giving higher molecular-weight products were most generally observed, and reactivities and product distributions were found to be related to the molecular structure of the reactants. 1-Olefins were the most reactive systems and gave more complicated product distributions than did 2- or 3-olefins. Analysis of the product distributions and reactivities indicates the reactions in isomeric olefins do not proceed through equivalent intermediates and suggests that isomeric parent ions have not rearranged to give equivalent reactant ions prior to reaction. Specific structures are suggested for the intermediates produced in several of the reactions. Experimental conditions were found to be quite important in determining product distributions and correlating the results of studies made under substantially different conditions.
Isotopic Exchange in Olefin Ion–Molecule Reactions
Authors: Henis J. M. S.
Published: February 2004

Isotopic exchange was examined in the products of ion–molecule reactions involving deuterated and undeuterated olefins. The results were used to obtain information regarding the structure of reaction intermediates, and the factors governing H–D exchange. Analysis of product distributions in mixtures of 2-C4D8 with various pentenes and hexenes suggested quite specific structures for the reaction intermediates which were in good agreement with earlier work on undeuterated systems. In addition it was found that different products, which almost certainly arose from the same intermediate, showed significantly different degrees of H–D exchange.
Coherent Elastic X-Ray Scattering by Atoms. Use of an Improved Thomas–Fermi Model
Authors: Csavinszky P.
Published: February 2004

A recently obtained approximate variational solution of the Thomas–Fermi (TF) equation is used for the calculation of the total cross section of coherent elastic scattering of x rays by the noble-gas atoms. It is found that, apart from He and Ne, the calculated cross sections in the 1–1000 keV range agree within a few percent with the quantum-mechanical values.
Gas-Phase Electron Resonance Spectra of BrO and IO
Authors: Carrington Alan , Dyer Paul N. , Levy Donald H.
Published: February 2004

The gas-phase electron resonance spectra of BrO and IO in their π23/2 levels are described. The analysis confirms that both radicals have π23/2 ground electronic states, and values of the fine-structure splitting A and rotational constant B0 are obtained. Nuclear hyperfine structure from 79Br and 81Br in BrO and 127I in IO is observed. Analysis yields values for the axial component of the magnetic hyperfine interaction, and also values for the electric quadrupole coupling constants.
ESR Studies of Heisenberg Spin Exchange. III. An ELDOR Study
Authors: Eastman Michael P. , Bruno Gerald V. , Freed Jack H.
Published: February 2004

We report the first quantitative test of the theory for electron–electron double resonance (ELDOR) of free radicals in solution. The reduction factors R for the ELDOR spectra of aqueous solutions of the peroxylamine disulfonate dianion radical (PADS) were examined and shown to fit the theory given by Hyde, Chien, and Freed in the extrapolated limit of infinite pump power. Some of the experimental and theoretical problems are discussed. The effect of exchange on the saturation properties of PADS was investigated and shown to agree, within experimental error, with the theory discussed in Part I of this series. The implications of these results for the determination of relaxation times in complex systems are briefly discussed.
Metastable Peaks in the Mass Spectra of N2O and NO2. II
Authors: Newton Amos S. , Sciamanna A. F.
Published: February 2004

Metastable peaks arising from the delayed unimolecular dissociation of NO+ to O++N in the mass spectra of both N2O and NO2 and from the dissociation of N2+ to N++N in the mass spectrum of N2O have been investigated. A new metastable dissociation of N2O2+ to NO++N+ was also studied. Further studies were made on the previously known metastable transitions of N2O+ to NO++N and of NO2+ to NO++O. The appearance potential, the kinetic-energy release in fragmentation, and the half-life were determined for each metastable transition. Comparisons were made of the energetic and half-life characteristics of the metastable NO+ ion as produced from the sources NO, N2O, and NO2, and of the metastable N2+ ion from the sources N2 and N2O. The results are consistent with the unimolecular dissociation of these diatomic ions, N2+ and NO+, proceeding by predissociation mechanisms.
Configuration, Energy, and Heat Capacity of Small Spherical Clusters of Atoms
Authors: Burton J. J.
Published: February 2004

The configuration, energy, vibrational frequency distribution, and heat capacity of very small clusters are calculated. The properties of these clusters are not as expected from extrapolation from large crystal surface properties. The surface energy per unit area is not a smooth function of the radius, and the heat capacity per atom is not a monotonic function of the cluster size. The behavior of the heat capacity gives rise to a peak in the entropy for clusters of between 19 and 43 atoms. The presence of this entropy peak affects vapor phase nucleation. It also causes clusters of about 43 atoms to be metastable with respect to the infinite solid at temperatures above the melting temperature of the solid.
Matrix Isolation Studies of Group IV Oxides. II. Infrared Spectra and Structures of GeO, Ge2O2, Ge3O3, and Ge4O4
Authors: Ogden J. S. , Ricks M. J.
Published: February 2004

The vapor-phase germanium oxides GeO, Ge2O2, and Ge3O3 have been isolated in nitrogen and argon matrices. In a nitrogen matrix, infrared absorptions are observed at 973.4 (74Ge16O); 667.0, 599.0 (Ge216O2); 824, and 440 cm−1 (Ge316O3). A fourth species, Ge4O4, is formed on diffusion, and gives infrared absorptions at 553.3, 490.0, 476.0, and 457.5 cm−1. With the aid of 18O substitution, estimates are obtained for the molecular dimensions of these species: Ge2O2 (Vh symmetry), rGe–O = 1.87 Å, ∠OGeO = 83°; Ge3O3 (D3h symmetry), RGe–O = 1 85 Å, ∠OGeO = 100°. The concentration changes occurring on diffusion are investigated.
Depolarization of Resonance Fluorescence from Interacting Atoms
Authors: Chiu Lue-Yung Chow
Published: February 2004

The polarization of the resonance fluorescence of interacting atoms and the transfer of coherence, due to the exchange of excitation, are studied theoretically. The treatment is for the general case where both the excited and the ground states can have arbitrary angular momenta, except that they can be connected to each other by an allowed transition. Electrostatic dipole–dipole interaction and electromagnetic radiative interaction are considered simultaneously as the perturbations on the system. Heitler and Ma's generalized time-dependent perturbation method is used. The system is quantized with respect to the space-fixed z axis and a static magnetic field along the z axis may be present, so that the magnetic sublevels (m, m′, etc., for the excited state J, and α, β, etc., for the ground state J′) are not necessarily degenerate. The intensity of the scattered light of a given polarization, in a given direction, is expressed as a function of kR (where ℏck is the energy of excitation and R is the internuclear distance), and of the orientation of R with respect to z axis. The matrix elements (ℏ / 2)γmβ,αm′ and Vmβ,αm′, which cause resonant transfer of excitation between two atoms through radiative and electrostatic interaction, respectively, are also expressed as a function of kR, and of the orientation of R. For randomly oriented atoms, the polarization after being averaged over the random orientation of R becomes a function of kR. Numerical calculations have been carried out for S01 → 1P1 transition. The coherence is shown to be conserved upon resonant transfer of excitation when R is parallel to the quantization axis.
Study of the Motion of Water Molecules in NaBr·2H2O by the NMR Method
Authors: Sarma J. S. M.
Published: February 2004

The temperature variation of the second moment of the NMR spectrum of a powdered sample of NaBr·2H2O has been studied experimentally and explained on a theoretical basis. Below 126°K the second moment is constant at about 27.4 G2 (the rigid-lattice value); above this temperature it decreases at first slowly to 25.4 G2 at 174°K and then more rapidly until it reaches a value of 11.5 G2 at about 240°K, where it remains practically constant up to the room temperature (295°K). The slow diminution between 126 and 174°K is attributed to the flipping motion of the water molecules. Theoretical formulas are newly developed for the powder spectrum based on the single crystal formulas given by Pederson to explain quantitatively this slow fall. The agreement between the theoretical and experimental value is satisfactory. The large drop in the second moment beyond 174°K is explained partly on the basis of an onset of free rotation of one of the water molecules about one of its O–H axes and partly attributed to the increased rocking and twisting vibrations of the other water molecule which is bound more strongly in the lattice. The estimated value of the potential barrier hindering the rotation of this water molecule is found to be of the expected order of magnitude. The NMR line has no fine structure below 240°K but starts exhibiting it above this temperature. It is characteristic of a three-spin system. This feature is discussed in the light of the rotating water molecule model suggested above. The above results on the second moment confirm the hydrogen-bonding scheme suggested for NaBr·2H2O from an NMR study of the line splittings in single crystals.
Vibrational–Translational Energy Transfer in the Near-Adiabatic Approximation
Authors: Attermeyer Mary , Marcus R. A.
Published: February 2004

Vibrational–translational energy transfer is examined in the near-adiabatic (or perturbed stationary states) approximation. The results are classical, and the method used is related to that of Marcus [J. Chem. Phys. 49, 2617 (1968)]. The results are compared with those of the more usual (“static”) approximation and with the exact results. The PSS results were good at low energies at all mass ratios studied, unlike the static results. For certain mass ratios the static approximation fails badly, even at very low transition probabilities. For other mass ratios, the results are of comparable accuracy except at high energies where the static one is somewhat better. Reasons for the above behavior are discussed, and implications regarding existing infinite-order distorted wave and semiclassical calculations are noted. The relation to a recent correction of the Jackson–Mott calculation is described.
Resonance Raman Effect and Resonance Fluorescence in Halogen Gases
Authors: Holzer W. , Murphy W. F. , Bernstein H. J.
Published: February 2004

The various output frequencies of the argon ion laser at 5145, 5017, 4965, 4880, and 4765 Å lie in the absorption bands of the heavier halogen gases. With the appropriate choice of exciting line, either resonance Raman effect or resonance fluorescence can be observed. The difference between the two types of spectra are discussed in some detail. In the case of a strong resonance Raman effect, overtone sequences up to the 14th harmonic could be observed. Raman frequencies, depolarization ratios, and relative scattering cross sections are given for the fundamentals and overtones of Cl2, Br2, I2, BrCl, ICI, and IBr at 4880 Å excitation.
Airlike Discharges with CO2, NO, NO2, and N2O as Impurities
Authors: Niles F. E.
Published: February 2004

Computer solutions to 24 time-rate-of-change equations have been obtained for airlike discharges attainable in a laboratory facility designed for the study of reactions of ionospheric importance. The manner in which the solutions are affected by initial number densities of CO2, NO, NO2, and N2O corresponding to impurity levels of 0, 0.1, 10, and 1000 ppm is presented. The effects of principal reactions on the number densities of detectable species are discussed. For the conditions specified in the computer program, the initial NO density greatly affects the negative-ion densities, and the initial NO density greatly affects the observable positive-ion densities.
Small Gaussian Expansions of Slater-Type Orbitals
Authors: Stewart Robert F.
Published: February 2004

Small Gaussian expansions of Slater-type orbitals by the method of least squares are presented. Expansion lengths are from one to six. Slater-type orbitals 1s through 5g are included. The least-squares equations were solved by a full-matrix method. Expectation values, r−2, r−1, r, and r2 for the several expansions are tabulated. Orbital products of the small Gaussian expansions have been Fourier analyzed and are satisfactory for x-ray scattering analysis of x-ray diffraction data or of molecular wavefunctions comprised of extended STO basis sets.
Infrared Spectra of Matrix-Isolated Antimony and Arsenic Pentafluorides
Authors: Aljibury A. L. Khidir , Redington R. L.
Published: February 2004

The infrared spectra of SbF5 and AsF5 suspended in argon and neon matrices have been recorded between 4000 and 100 cm−1. The spectra of SbF5 and AsF5 are radically different and show that monomeric SbF5 belongs to symmetry group C4υ rather than to group D3h. The spectral effects induced by forming solid SbF5 from the monomers are understood in terms of associations through Sb–F–Sb fluorine bridge bonds. The behavior is compared with that observed previously for SF4. No evidence for fluorine bridging occurs with AsF5.
Lattice Dynamics of a Linear Chain Model of an Imperfect Molecular Crystal
Authors: Munn R. W.
Published: February 2004

The lattice dynamics are discussed, using the method of Green's functions, for a linear chain of homonuclear diatomic molecules, one of which has a different force constant from the others. The model can represent a molecular crystal in which one molecule is electronically excited. The frequencies of the antisymmetric normal modes can be deduced from the frequencies of the symmetric modes of a chain of alternating masses, in which one of the lighter atoms is replaced by an isotopic impurity, and vice versa. The alternation of symmetry arises because, in the present model, the defect consists of two atoms instead of one. A localized mode in the bandgap or above the optical band is obtained.
Experimental Study of the Higher π → π* Transitions of Benzene in Low-Temperature Matrices
Authors: Katz Benjamin , Brith Malka , Sharf Benjamin , Jortner Joshua
Published: February 2004

In this paper we present the results of an experimental study of the absorption spectrum of benzene and deuterated benzenes in solid Ar, Kr, Xe, and N2 in the spectral region 2800–1700 Å, with special reference to the 2100- and to the 1850-Å transitions. Our main results are:

(a) On the basis of the observed vibrational structure the second excited singlet state of the benzene molecule is assigned to the A1g1 → 1B1u rather than to the A1g1 → 1E2g excitation.

(b) Theoretical calculations of the dynamic electronic–vibrational coupling between the B1u1 and the E1u1 states support the B1u1 assignment of the 2100-Å transition.

(c) The vibrational structure of the 1850-Å A1g1 → 1E1u transition was resolved.

(d) No experimental evidence for Jahn–Teller coupling in the π → π* 1E1u state was observed, in agreement with theoretical analysis.

(e) Information on site splittings for the higher π → π* excitation of benzene in rare-gas solids has accumulated.

(f) Analysis of matrix shifts for the A1g1 → 1B1u and A1g1 → 1E1u transitions indicates that the “solvent effect” is dominated by dispersion interactions.

(g) Information on deuteration effects on the B1u1 and E1u1 energy levels was obtained.

(h) Qualitative information on intramolecular radiationless decay in the two higher π → π* excited states of the benzene molecule has been inferred from the linewidths in the absorption spectrum.
Infrared Spectrum of Matrix-Isolated Cyanate Ion. I. Vibrational Analysis, Bandwidths, and Absolute Intensities in Potassium Halides
Authors: Schettino V. , Hisatsune I. C.
Published: February 2004

Solid solutions of the cyanate ion in KCl, KBr, and KI matrices have been prepared by heating standard infrared pressed disks. The infrared spectra of these disks have been measured from 5000 to 400 cm−1 and analyzed. Our frequency data are in excellent agreement with those obtained from doped single crystals by earlier investigators. Anharmonicity constants, harmonic frequencies, and force constants have been calculated for the isotopic species 16O12C14N−, 16O12C15N−, 16O13C14N−, 16O13C15N−, and 18O12C14−. The anharmonicity constants are essentially independent of the matrix, and only quadratic force-constant changes appear necessary to account for the frequency shifts of the fundamentals as the matrix is varied. The temperature dependence of the bandwidths and peak frequencies of the fundamentals have been studied in the range from 95 to 530°K. The fundamentals in all matrices can be represented well by Lorentz band shapes. The absolute band intensities have also been measured. In addition to bands arising from the internal modes of the cyanate ion, combination bands of the intense cyanate fundamentals with external modes of the cyanate and with lattice modes of the host matrix have been observed.
Variational Approach to the Dielectric Constant of a Polarizable Medium
Authors: Prager Stephen , Kunkin William , Frisch H. L.
Published: February 2004

The Kirkwood theory of the dielectric constant for a nonpolar fluid is shown to imply a negative electrostatic self-energy for certain configurations of point dipoles. It is shown that this unphysical behavior can be eliminated by introducing a hard core of radius larger than or equal to the cube root of the molecular polarizability. The introduction of such a core also permits the derivation of variational upper and lower bounds on the dielectric constant. In particular, the Clausius–Mossotti formula can be shown to give too low a value for the dielectric constant of a polarizable sphere fluid. The relationship of these bounds to those developed elsewhere for the bulk properties of random two-phase media is discussed, as is the effect of dipole fluctuations.
Anisotropies and Absolute Signs of the Indirect Spin–Spin Coupling Constants in 13CH3F
Authors: Krugh T. R. , Bernheim R. A.
Published: February 2004

Proton and 19F magnetic resonance experiments on 13CH3F partially oriented in the liquid crystal solvent p,p′-di-n-hexyloxyazoxybenzene show conclusively that JCH = + 148.8 ± 0.4 Hz, JCF = − 161.9 ± 0.7 Hz, and JHF = + 46.3 ± 0.3 Hz, with the signs absolutely determined. Assuming that there is no change of molecular geometry between the gas phase and the nematic solution, and neglecting solvent effects, isotope effects and corrections due to vibrational averaging, the experimental results suggest unexpectedly large anisotropies of the spin couplings, (J‖ − J⊥)CH = + 1890 Hz, (J‖ − J⊥)CF = + 700 Hz (measured with respect to the molecular symmetry axis), whereas JHF has negligible anisotropy. The anisotropies in Jij are examined with respect to their sensitivities upon the appropriate average molecular geometries used in their determination, and the effects of solvent are also discussed. The accuracy of the above anisotropies cannot be determined without a knowledge of the complete vibrational potential of methylfluoride. However, it can be concluded that indirect spin coupling anisotropies do exist for directly bonded nuclei, and that at least one of them is sizeable, of the order of magnitude of the isotropic Jij.
Rotational Structure of a Novel Raman Effect in Quantized Symmetric- and Spherical-Top Molecules
Authors: Chiu Ying-Nan
Published: February 2004

By angular momentum techniques, the theoretical line intensities of a higher-order odd-parity Raman effect have been derived. This effect may be used as an alternative mechanism to study the silent modes forbidden in the infrared spectra, and in the conventional lower-order Raman effect which is of even parity. It can be compared with the recently discovered (three-photon) hyper-Radman effect which is also of odd parity and contrasted with the recently studied electronic Raman effect using the antisymmetric scattering tensor which is of even parity: It has different selection rules (Secs. IV, V) and angular characteristics (Sec. III and Appendix B). It is Raman scattering in which one photon is in an electric dipole mode, whereas the other photon is in a magnetic dipole (or electric quadrupole) mode. The scattering tensor is of odd parity. The intensities along the perpendicular direction of observation of the scattering by symmetric-top molecules in their transition from the state | J′K′〉 to | JK〉 and by spherical-top molecules in their transition from the state | J〉 to | J′〉 have been derived (Sec. II and Appendix A). Depolarization ratios for linearly polarized and for unpolarized incident light may be computed from these intensities. Similar intensities for scattering of circularly polarized light into forward as well as into arbitrary observation directions were derived (Sec. III and Appendix B). These allow the computation of the reversal coefficients. In the limit when both photons are in the electric dipole mode the results will agree with those for the conventional even-parity Raman effect studied by Placzek and by Teller. The total intensity for the scattering of unpolarized light into an arbitrary direction and the integrated intensity for scattering into all directions have been obtained (Appendix B). Explicit forms of the new scattering tensors, which are bipolar harmonics, in Cartesian coordinates are given (Sec. IV and Appendix C). Their similarity to, as well as difference from, spherical harmonics are shown. Special features are pointed out for the tensors. Their transformation under the C3υ point group, to which a symmetric-top molecule may belong, and under the T point group, to which a spherical-top molecule may belong, have been derived and tabulated (Tables I and II). The scattering tensor may connect different electronic states of opposite parities in an electronic Raman effect, or may give rise to a rotational and vibrational Raman effect with different selection rules (Sec. V) from the conventional Raman effect, and thereby may serve as a supplement for the study of molecular structure.
High-Temperature Evaporation and Thermodynamic Properties of Cm2O3
Authors: Smith P. K. , Peterson D. E.
Published: February 2004

Curium oxide has been shown to vaporize congruently as Cm2O3. Effusion measurements have been carried out, using tungsten and molybdenum cells, over a temperature range from 1800 to 2600°K and a pressure range from 10−9 atm to 0.5 mm. The linear least-squares fit to the total volatility, calculated as Cm2O3, yields the equation logP(atm) = 7.32(± 0.26)− 29 050(± 590)/T(°K). The corresponding ΔH2200°K and ΔS2200°K were computed to be 133.0 ± 2.7 kcal/mole of gas and 33.5 ± 1.2 cal/deg·mole of gas, respectively. The predominant vaporization process is thought to be the formation of CmO(g) and O(g), based on estimates of the heat of formation of Cm2O3(s), comparison of experimental and estimated entropies of vaporization, consistency between second- and third-law heats of vaporization, and trends in the vaporization behavior of lighter actinide oxides. The heat of vaporization at 0°K would then be 429 ± 8 kcal/mole of Cm2O3.
Constrained Variation Method in Molecular Quantum Mechanics. III. The Use of Multiple Constraints and the Hellman–Feynman Theorem
Authors: Loeb Robert J. , Rasiel Yecheskel
Published: February 2004

The result of (a) constraining the forces on the nuclei in the lithium hydride molecule to their theoretical values and (b) satisfying the virial theorem by a constrained variation technique are presented. A method for the imposition of multiple constraints was developed, and criteria for the reliability of wavefunctions with regards to the possibility of satisfying theoretical constraints are discussed.
Interpretation of Diamond and Graphite Compressibility Data Using Molecular Force Constants
Authors: Riter J. R.
Published: February 2004

The diamond and in-plane graphite compressibility data of Lynch and Drickamer are analyzed in terms of simple bond-compression and bond-compression, buckling, and puckering models, respectively, using carbon–carbon stretching and out-of-plane displacement force constants from molecular studies. To the highest experimental pressures of over 300 kbar it is found that the quotient of potential energy of bond compression and macroscopic work of compression, for the same values of the lattice parameter ratio (a/a0), remains essentially constant for diamond at 0.7 indicating that bond compression is the dominant mechanism for storing energy of compression. Similar quotients for graphite at corresponding values of (a/a0) vary from 1.4 at the lowest pressures to 0.6 at the highest for the in-plane bond compression, from 100–4 for the out-of-plane buckling, and from 300–13 for the out-of-plane puckering with the last two modes assuming a fixed C–C in-plane bond distance. It is suggested that in graphite bond compression is the primary mechanism for absorbing intraplanar energy of compression with out-of-plane buckling and puckering much less important until quite high pressures are reached, in contrast to earlier views. This would seem to lead to a partial understanding of the difficulties present in synthesizing diamond from graphite.
New Nuclear Quadrupole Resonance Frequencies at 14N in Saturated Cyclic Amines
Authors: Colligiani A. , Ambrosetti R. , Angelone R.
Published: February 2004

The values of the nuclear quadrupole coupling constants e2Qq of 14N and the asymmetry parameters η in a series of saturated six-, five-, four-, and three-membered cyclic amines and of their N-methyl derivatives have been measured at various temperatures, starting from liquid nitrogen temperature. Several resonance lines which could not be observed at 77°K, were detected at higher temperatures. By applying the Townes and Dailey theory to the experimental results, the electron populations of the atomic orbitals used by the nitrogen atom for the bonds with the carbon and hydrogen atoms have been evaluated. The values of the valence angles of nitrogen in the various kinds of molecules have also been evaluated. A particularly interesting result has been obtained for the four- and three-membered cyclic amines.
Transport Mechanics in Systems of Orientable Particles. II. Kinetic Theory of Orientation Specific Transport for Hard-Core Models
Authors: Henline William D. , Condiff Duane W.
Published: February 2004

The role of orientation and polarization in the transport phenomena of hard-core polyatomic gases is developed in detail from the standpoint of the Boltzmann equation. A rigorous orientation specific Chapman and Enskog scheme is used to establish linear constitutive relations and anisotropic transport coefficients for orientation-specific translational and rotational diffusion and for the orientation-summed fluxes of mass, momentum, and heat. Calculations are reported for the effect of polarization upon the shear viscosity and thermal conductivity tensors of loaded spheres. The anisotropic expressions for rotational and translational thermal diffusion, shear diffusion, and concentration diffusion coefficient tensors are determined for a dilute system of loaded spherocylinders in a bath of rigid spheres. With the use of time reversal invariance, a microscopic reciprocal theorem is established and employed to prove Onsager reciprocal relations among the transport coefficient tensors.
Effect of Internal Viscosity on the Deformation of a Linear Macromolecule in a Sheared Solution
Authors: Booij H. C. , van Wiechen P. H.
Published: February 2004

The deformation of macromolecules in a solution subjected to time-dependent shear flow is described by means of a modified Rouse model. Into every segment of this model an internal viscosity force is introduced which is proportional to the rate at which the end-to-end distance of the segment is changed, and acts in the direction of the tie line between the end points. No a priori assumptions have been made on the motion of the segments themselves. An analytical solution for the distribution function of the segment lengths can now no longer be derived. At low values of the internal viscosity, an approximate solution can be obtained by means of a perturbation calculus. The effect of internal viscosity on the moments of the distribution function and, hence, on the average dimensions of the macromolecules, can be calculated. It appears that with constant shear flow at high rates of shear, as well as with oscillatory shear at high frequencies, an increase of the internal viscosity results in a decrease of the average deformation of the molecules. The flow birefringence at high shear rates decreases as the internal viscosity increases, whereas the optical extinction angle is hardly influenced by it. In the literature there is no unanimity on the relation between the deformation of the molecules and the shear stress; in the present study we use the formula of Kirkwood and Riseman. In the case of constant shear flow, the apparent viscosity of the solution decreases with increasing rates of shear. With oscillatory shear flow the internal viscosity leads to a finite limiting value of the dynamic viscosity at high frequencies, and this value should increase when a constant shear rate is superimposed on the oscillatory shear rate. This theoretical prediction conflicts with experimental data.
Solubility of Condensed Substances in Dense Gases and the Effect on PVT Properties
Authors: Haar Lester , Sengers J. M. H. Levelt
Published: February 2004

An analytic relation is derived in terms of the molecular interactions for the density dependence of the solubility of a liquid or solid in a dense gas using a modified van der Waals equation. It is shown that at high gas densities the solubility is sharply reduced. It is also shown that the effect of the solubility enhancement on high-density PVT measurements is smaller than previously thought. The analysis is applied to the case where the condensed material is liquid mercury. Solubility-vs-density isotherms and the effect of the solubility on PVT measurements are obtained at 50, 150, 250, and 400°C for the following gaseous species: He, H2, Ne, Ar, Kr, Xe, N2, NH3, H2O. The need for accurate experimental data at high gas densities to test further the essential features of the analysis is discussed.
ESR Studies of N32− and N2− Molecular Ions in Anhydrous Barium Azide
Authors: Marinkas Paul L.
Published: February 2004

Crystals of anhydrous barium azide, Ba(N3)2, have been exposed to 2537-Å ultraviolet light at room temperature. This process leads to the production of the N2− molecular ion which has been previously identified by electron spin resonance. Further ESR studies reveal that a second irradiation at low temperatures with light in a broad band of wavelengths centered at 325 nm partially bleaches the N2− and produces a new center which is identified by ESR as an N32− ion in a Type II azide ion site. Light in a second broad band of wavelengths centered at 425 nm accomplishes the reverse reaction. The angular variation of the ESR spectrum of the new center is expressed by the spin Hamiltonian: H = βH·g·S + I1·A1·S + I2·A2·S + I3·A3·S, with S = 12, I1 = I2 = I3 = 1, and A1 = A2. The principal values of g, A1, and A3 are: gx = 2.004 ± 0.001, gy = 1.996 ± 0.001, gz = 2.000 ± 0.001, Ax1 = 7.5 ± 0.5 G, Ay1 = 14.0 ± 0.5 G, Az1 = 6.2 ± 0.5 G, Ax3 = 19.6 ± 0.5 G, Ay3 = 28.0 ± 0.5 G, Az3 = 15.7 ± 0.5 G.
Acrolein: Spectroscopy, Photoisomerization, and Theoretical Considerations
Authors: Becker Ralph S. , Inuzuka Kozo , King Jimmie
Published: February 2004

The quantum yields of fluorescence (φF ∼ 0.007) and phosphorescence (φP ∼ 0.00004) indicate that excitation results in nearly complete internal conversion and/or photochemistry. Theoretical calculations have been made including the potential energy curves resulting from twisting around the central carbon–carbon single bond as well as the terminal carbon–carbon double bond. It appears that photoisomerization cannot occur around the single bond in either the π, π* or n, π* states but could occur around the double bond in the lowest π, π* triplet state. In the latter case, a potential energy minimum exists near 90° and degeneracy occurs with the ground state. Based on the spectroscopic and theoretical considerations herein reported, an analysis is made of the published spectroscopic results of conjugated keto steroids.
Potential Curves of Diatomic Rare-Gas Molecules and Their Ions, with Particular Reference to Xe2
Authors: Mulliken Robert S.
Published: February 2004

The excited and ionized states of the heavier rare-gas molecules are discussed, existing evidence on the dissociation energies of the ions are reviewed, and estimates of these dissociation energies are made. Estimated potential curves for the Xe2+ ion and for the lower excited states of the Xe2 molecule are given. Applications to the interpretation of the observed spectra of the heavier rare gases, especially Xe2, are discussed.
Competitive Unimolecular Decomposition of Alkyl Radicals. Tertiary Butyl Rupture
Authors: Larson C. W. , Rabinovitch B. S.
Published: February 2004

The competitive unimolecular decomposition of vibrationally excited 3,4,4-trimethylpentyl-2·* radical was investigated. Relative and absolute rate of decomposition by tert-butyl (tBu) and methyl (Me) radical rupture were measured. Results were interpreted in terms of the Rice–Ramsperger–Kassel–Marcus (RRKM) unimolecular rate theory and lead to a value for D0°(tBu–H) of 89.0 kcal mole−1. Activation energies at 0°K for tBu and Me radical addition to olefins are discussed; some disproportionation-recombination ratios involving tBu radical were obtained.
Comments on the Coupling between Linear and Angular Momentum of Structured Molecules
Authors: Ailawadi N. , Forster D. , Berne B. J.
Published: February 2004

We consider systems of structured molecules which are capable of translational as well as rotational motion. Using symmetry arguments we show that the linear and the angular momentum of each molecule are statistically independent for systems which possess a center of symmetry. This result applies, in particular, to the case of Brownian rotors, and it implies that the Langevin equations for translational and rotational motion are uncoupled.
Knudsen Diffusion and Chemical Reaction in a Random Bed of Solid Spheres
Authors: Strieder William
Published: February 2004

In a previous publication a variational upper bound on the reaction rate was presented for the irreversible surface reaction A→B within a catalyst in which relevant pore dimensions were small compared to the mean free path of the gas molecules. The bounds were evaluated for two pore models, a cylinder, and a bed of randomly overlapping solid spheres. In this paper the bound for the bed of spheres is improved by introducing into the trial function a term that varies with the local structure of the catalyst pore wall surface.
Energy Disposal in the Photodissociation of Ethanethiol
Authors: White John M. , Johnson R. L. , Bacon D.
Published: February 2004

Ethanethiol has been photolyzed in the presence of D2 at 2537 and 2288 Å. Using data previously obtained for the HBr–D2 system, the energy available for product excitation is shown to reside chiefly in the translational modes of motion rather than the internal modes of the C2H5S radical.
Chemical Bond and Ab Initio Molecular Calculations
Authors: Nelander B. , Re G. Del
Published: February 2004

The problem of finding a mathematical description of a bond or functional group from a series of wave-mechanical calculations on molecules containing the bond or group in question is discussed in the light of the success of these concepts in empirical chemistry. Methods for obtaining mathematical descriptions of common features of different molecules from more or less accurate wavefunctions for these molecules are given for different types of descriptions.