bluuebunny/crossref_metadata_2025 huggingface dataset:
Combined Steady and Oscillatory Shearing Flow of Oriented Fluids
Authors: Kaloni P. N. , Sabin G. C. W.
Published: February 2004

The theory of oriented fluids is applied to discuss the behavior of high polymer solutions in time dependent shear flow. Problems of oscillatory shearing flow and of small oscillations superimposed on steady shear flow are studied within the framework of the theory and results are compared with the experimental observations. It is shown that a number of dynamic properties of the non-Newtonian fluids can be satisfactorily described by the theory.
Vibrational Assignment for IF7—a Nonrigid D5h Molecule
Authors: Eysel H. H. , Seppelt K.
Published: February 2004

The observed infrared and Raman frequencies of gaseous IF7 are assigned to the vibrational modes of a D5h model. The assignment is based on infrared band shapes, Coriolis coupling constants, force constants, and vibrational amplitudes. The present study confirms the theory that IF7 undergoes minor dynamic distortions from D5h symmetry. These distortions are observable through violations of the selection rules for the vibrational combination bands but do not cause a breakdown of selection rules for the fundamentals. Force constant calculations reveal that the axial bonds of IF7 are definitely shorter than the equatorial ones.
Calculation of the Infrared Absorption Spectra of the ν3 and ν4 Modes of CD4 in Kr and Xe Matrices
Authors: Nishiyama Ken'ichi
Published: February 2004

Theoretical study is carried out on the rotational motion of deuterated methane embedded in raregas matrices (Kr and Xe), employing the crystalline fields predicted by Yasuda [Progr. Theoret. Phys. 45, 1361 (1971)]. The hindered rotation in the fields is solved in the subspace with J≤ 10, where J is the rotational quantum number. Then the vibration-rotation states are worked out for the threefold degenerate ν3 and ν4 modes, the Coriolis coupling being taken into account. The spacings and relative intensities of the infrared absorption spectra are calculated for CD4 in Kr and Xe matrices and the results are compared with the spectra of the ν3 and ν4 modes in Kr. Good agreement is obtained between theory and experiment.
Intramolecular Charge-Transfer Interactions in Benzyl Derivatives
Authors: Tournon J. , El-Bayoumi M. Ashraf
Published: February 2004

Benzyl derivatives exhibit an enhancement of phosphorescence yields, a quenching of fluorescence intensities, and a shortening in their natural phosphorescence lifetimes relative to toluene. These results reflect an increase in intersystem crossing process, S1→ T with rate constant kisc. Evidence for an intramolecular charge-transfer mechanism which enhances spin-orbit coupling between states of different multiplicities is provided. This mechanism requires some electronic overlap and hence, a spatial approach between the benzene ring and the substituent. Viscosity as well as steric effects that influence such approach are also discussed.
Infrared Spectrum of Matrix Isolated NbF5
Authors: Acquista Nicolo , Abramowitz Stanley
Published: February 2004

The infrared spectra of matrix isolated NbF5 as well as some gas phase spectra have been observed. These spectra have been obtained using double boiler Knudsen cells. An interpretation of the spectra to yield the six infrared active frequencies of a C4v monomeric structure for NbF5 is advanced.
Ab Initio Calculation of Potential Energy Curves for the Ion Molecule Reaction O++N2 → NO+ + N
Authors: Pipano A. , Kaufman Joyce J.
Published: February 2004

Configuration interaction calculations verified an earlier hypothesis that the experimentally observed apparently anomalous behavior of the O++N2 → NO+ + N reaction is due to the symmetry and spin restrictions which prohibit the ground state reactants or products from correlating directly with the ground state intermediate. Complex symmetry adapted functions were used, and all single and double excitations were included for the ground and first excited Πi2 states, the lowest and second 2Σ+ states, the Π4 state and the 4Σ- state of the intermediate NNO+ for two cuts through the potential surface close to the reaction path. The number of configurations included were: Πi2 (123), 2Σ+ (177), 4Π (1349) and 4Σ- (1310). Analyses of the first order CI density matrices at large distances in terms of their ``fragmental'' MO's (or AO's) verified that the 4Σ- NNO+ state was formed from the ground state reactants O+(4Su) + N2(1Σg+) and that it separated into ground state products NO+(1Σ+) + N(4Su). The positions of other electronic states of NNO+ were well substantiated in agreement with photoelectron spectroscopic measurements. The calculated potential energy curves show an even greater wealth of structure than would have been anticipated prior to such a detailed computation. The most significant conclusion of the present research is the unambiguous confirmation of the overriding role that spin and symmetry restrictions play in any type of collisional process.
Raman Spectra of Gaseous CH3ND2, C2H5ND2, and n-C3H7ND2. The Raman and Infrared Spectra of Gaseous CH3NHD
Authors: Wolff H. , Ludwig H.
Published: February 2004

The Raman spectra of gaseous CH3ND2, C2H5ND2, and n-C3H7ND2, as well as the Raman and the infrared spectra of gaseous CH3NHD, have been measured and analyzed with respect to the amino group vibrations. The asymmetric position of the ND stretching vibration of CH3NHD relative to the ND2 stretching vibrations of CH3ND2 is explained by Fermi resonance of the symmetric ND2 stretching vibration with the overtone of the ND2 deformational vibration. A band of CH3NHD found at 878 cm−1 in the infrared spectrum only shows a splitting analogous to that of the band at 688 cm−1 which has been analyzed by Tsuboi et al. in the infrared spectrum and which now also has been found in the Raman spectrum. It is assigned to the higher frequency NHD out of plane bending vibration, formally denoted as NHD twisting vibration, whereas the band at 688 cm−1 belongs to the lower frequency NHD out of plane bending vibration, formally the NHD wagging vibration. Using the sum rule, the twisting vibrations of CH3NH2 and CH3ND2, until now not unequivocally observed, are calculated as approximately 980 and 820 cm−1. The observations for C2H5NH2 and C2H5ND2 and the results of normal coordinate treatments performed by Wu, Zerbi, Califano, and Crawford as well as by Dellepiane and Zerbi are in agreement with such an assignment.
Calculation of the Internal Rotation Barrier and Its Derivatives in BH3NH3
Authors: Palke William E.
Published: February 2004

Self-consistent field calculations using an optimized minimum basis set of Slater orbitals were carried out for BH3NH3 in order to compute the barrier to internal rotation and its derivatives (changes in the barrier caused by variation of the molecular geometry). In principle both the barrier and its derivatives can be determined experimentally. In addition, the change in equilibrium geometry as the molecule internally rotates was predicted, as well as the diagonal force constants and the dipole moment and its derivatives.
Madelung Parameters and Electrostatic Energies for Calcite, Aragonite, and Vaterite and the Charge Distribution on the Carbonate Ion
Authors: Donald H. , Jenkins B. , Waddington T. C.
Published: February 2004

The electrostatic energy changes and Madelung parameters for the process CaCo3(c)→Ca2+(g)+CO32−(g)have been computed assigning various distributed charges to the CO32- ion for the calcite, aragonite, and vaterite forms of calcium carbonate. The results are expressed as quadratic one-parameter functions, A+BQ(O)+CQ(O)2, of the charge Q(O) placed on the oxygen atom of the CO32- ion. A comparison with previous calculations is made and the charge distribution and quadrupole moment of the CO32- ion estimated.
Time-Dependent Solutions for De-excitation Rates of Anharmonic Oscillators
Authors: Hsu C. T. , McMillen L. D.
Published: February 2004

Exact numerical solutions are obtained for level populations of a 45-level anharmonic oscillator model of N2 in an expanding relaxation process with initial Tv=2500°K and T=500°K. Both vibration-vibration and vibration-translation energy transfers are included. An implicit numerical method similar to Lomax's is developed for integrating the stiff master relaxation equations. The de-excitation rate is found to decrease rapidly from an extremely high value at the initial stage to the excitation rate at the corresponding heat bath temperature in the secular adjustment period. Laboratory observations on this de-excitation rate will depend on the instant when it is observed. In the initial stage, the intermediate levels are rapidly overpopulated to form a plateau while the lower-level populations adjust to a Treanor distribution and the upper levels to a Boltzmann distribution of T. This plateau descends gradually to form a ∼ shape and eventually will become a straight line indicating Boltzmann equilibrium. For accurate determination of de-excitation rates in the early stages of relaxation, it is important to include more upper levels in the model. However, these upper levels contribute insignificantly in the later stages of secular adjustments. The first-moment method, with a Treanor distribution for a truncated model, accurately predicts the lower-level populations as well as the de-excitation rates in the secular adjustment period. But this method underestimates the rates in the early stages because of neglect of significant VT transitions from higher levels.
Electronic States and Spectra of p-Benzoquinone
Authors: Trommsdorff H. P.
Published: February 2004

A complete assignment of the electronic transitions involved in the visible and near ultraviolet spectra of p-benzoquinone is given. The following excited states are observed: π-π* 1B2u at 41 330 cm−1 and π-π* 1B1g at 32 800 cm−1 (in the vapor phase); n-π* 1Au at 20 315 cm−1, n-π* 1B2g at 20 060 cm—1, n-π* 3Au at 18 940 cm−1, and n-π* 3B2g at 18 620 cm−1 (in the pure crystal). The π-π* transitions in the near ultraviolet have already been analyzed earlier and the influence of substitution and the solvent effect on these transitions have been studied. The above work is critically reviewed and confronted with the results of recent CNDO calculations which explain qualitatively quite well the experimental data. In the visible spectra only the n-π* 1B2g and n-π* 3Au states had been located unambiguously in earlier work. A compilation of the data on these spectra is given and discussed. New measurements at 4.2°K of the polarized single crystal spectra of p-benzoquinone and its methyl derivatives are presented. They permit us an unambiguous assignment of both n-π* singlet and triplet states. The following splittings of the two n-π* states are obtained: 255 cm−1 for the singlet states and 320 cm−1 for the triplet states. Our results are in contradiction with the most recent views expressed on this subject [W. Hug, J. Kuhn, K. Seibold, H. Labhart, and G. Wagniére, Helv. Chim. Acta 54, 1451 (1971)].
Deuteron Magnetic Resonance of Boron Deuterides
Authors: Witschel John , Fung B. M.
Published: February 2004

Deuterium NMR of several boron deuterides has been studied in the solid state, and deuteron quadrupole coupling constants have been obtained from the powder spectra. Their values (in kilohertz) are: pyridine borane, 100± 2; N-dimethylaminoborane, 111± 2; borazine, 116± 2; tetramethylammonium decaborate, 121 ± 2; decaborane, 180± 4(η=0.16± 0.05) for the terminal deuterons and 211± 4(η=0.30± 0.05) for the bridged deuterons. The relation between the deuteron quadrupole coupling constants and the corresponding B–H stretching frequencies is examined. The occurrence of abnormally high coupling constants in decaborane is explained by the electron deficiency in the compound. In addition, the molecular structure of the N-dimethylaminoborane dimer is discussed.
Visible and Near-Ultraviolet Absorption Spectra of Carbon Subsulfide
Authors: Robertson L. C. , Merritt J. A.
Published: February 2004

The electronic absorption spectra of carbon subsulfide, C3S2, in the vapor phase for λ>2000 Å is presented. Vibrational analyses are given for two observed electronic systems. The first electronic system consists of multiple bands in the 4300–5300 Å region and the second electronic system, of approximately 20 bands, is in the 2200–2550 Å region. Rapid photolysis of the carbon subsulfide by continuum sources precludes studies in the vacuum ultraviolet region.
Zero-Field Splittings of Cm3+ and Am2+ in Fluorite Type Crystals
Authors: Kolbe W. , Edelstein N. , Finch C. B. , Abraham M. M.
Published: February 2004

The Γ6—Γ8 energy level splittings were derived for Cm3+ and Am2+ in several fluorite type crystals from measurements of the anisotropy of the g value of the Γ6 state at 35 GHz. Anisotropy measurements were also made of the g value of the excited Γ7 state for Cm3+ in SrCl2, and the Γ8—Γ7 splitting was obtained.
Molecular Level Anticrossing in the CN Radical
Authors: Levy Donald H.
Published: February 2004

A molecular level anticrossing experiment has been performed on the CN radical. The A2  Π3/2 state is preferentially populated by chemical reaction and various sublevels of this state are crossed with sublevels of the B 2Σ+ state by tuning with a magnetic field. The levels are mixed and anticrossed by application of a perpendicular electric field and the anticrossing resonance is observed by monitoring the emission in the violet bands. A density matrix theory of level crossing and anticrossing has been developed which allows an arbitrary number of molecular states to be included in the computer calculation of the lineshape. This calculation has been carried out for the case of CN in the two and three level limit, and the predicted electric field dependence of the linewidth and intensity agrees with the experimental results.
Positronium Annihilation in Molecular Substances
Authors: Tao S. J.
Published: February 2004

The behavior of the Ps atom in molecular substances, particularly liquids, is investigated. The pickoff rates of o-Ps in various liquid compounds are found to have a simple empirical relationship to the values of the surface tension of the liquids. The relationship is found to have a theoretical foundation. The Ps atom is highly localized in a cavity created by the balance of various molecular forces inside the liquid. From the above relationship, other simple relationships between the pickoff rates of o-Ps and the various properties of the medium, e.g., polarizability, cohesive energy density, etc., and the temperature or pressure changes can be derived and explained. The diffusion of o-Ps is discussed. A similar approach can also be used for molecular solids.
Solvation Shell Relaxation and Ion-Electron Recombination in Strongly Associated Solvents
Authors: Suchard S. N. , Bowers K. W.
Published: February 2004

The relaxation properties of the region in a solution in which there is strong interaction between the solute and solvent molecules (the cybotactic region) were studied with electron paramagnetic resonance spectroscopy used as the detection system. In the system under investigation, perylene radical cation was used as the solute, and either sulfuric acid or fluorosulfonic acid was used as the solvent. The properties studied were the solvent cage reorientation time and the ion-electron recombination time. Modulated light of a known wavelength distribution was used to irradiate the sample and synchronize a lock-in detector, which was used to detect the light-induced effects, to the light modulation frequency. Signal averaging techniques were used so that accurate values of the output as functions of the sample temperature, irradiation light wavelength, and irradiation light modulation frequency were obtained. Two extreme model systems were used to interpret the light-induced signal data, a reversible and an impulse model. A range of times was specified for the solvent cage reorientation and ion-electron recombination as a function of the sample temperature. In sulfuric acid, the cage reorientation time varies from 1176 μsec at 6°C to 99 μsec at 77°C, while the ion-electron recombination time varies from 649 to 42 μsec. The temperature range studied for fluorosulfonic acid was −36–95°C. In this range, the cage reorientation time varied from 857 to 81 μsec and the ion-electron recombination from 815 to 35 μsec. Over the temperature ranges studied, the intermediate coupling constant for the perylene radical cation increased from 13.7 to 224 mG in sulfuric acid and 19.7 to 345 mG in fluorosulfonic acid.
Covalent Bonding in Copper(II) Complexes Having N and S Atoms in a trans Arrangement
Authors: Buluggiu E. , Vera A. , Tomlinson A. A. G.
Published: February 2004

Bonding in the chromophore trans-CuN2S2 has been investigated using ESR and electronic spectra of single crystals of Cu(II) doped (∼2%) trans-bis (thiosemicarbazide) Ni(II) sulfate trihydrate and trans-bis (thiosemicarbazide) Cu(II) nitrate. The unpaired electron is described, in the ``hole'' formalism, in terms of molecular orbitals of D2h symmetry. Crystal polarized spectra of the undiluted nitrate allow a reasonable, if not unambiguous, assignment of d–d bands. Combination of magnetic and optical results gives all bonding parameters, apart from those for the nonmagnetic Ag(d3z2−r2) orbital. All bonds, and particularly Cu–S, are highly covalent in character. The σ Cu–S bond is roughly twice as covalent as σ Cu–N bond. The out-of-plane π bonds, and in-plane σ bonds, show covalence similar to that observed in D4h (CuN4) chromophores and ∼ D4h (more strictly C4v) (CuS4+S). This suggests that bonds between two trans ligands and the copper ion are not influenced by the second pair of bonds in square planar complexes.
EPR Investigations of Er3+, Yb3+, and Gd3+ in Zircon-Structure Silicates
Authors: Reynolds R. W. , Boatner L. A. , Finch C. B. , Chatelain A. , Abraham M. M.
Published: February 2004

The EPR spectra of Er3+, Yb3+, and Gd3+ have been observed in the host single crystals ZrSiO4, HfSiO4, and ThSiO4 which were grown by a flux-gradient technique. For most systems, spectra were observed which exhibited both tetragonal and orthorhombic symmetry. The tetragonal spectra were characterized by a principal axis system which coincided with the principal crystallographic axes. The observed orthorhombic spectra were of two types. For Gd3+ in ZrSiO4 and HfSiO4, orthorhombic spectra due to eight inequivalent sites were observed and had principal axis systems which were not simply related to the host crystallographic axes. All other orthorhombic spectra resulted from four inequivalent sites whose z and x axes lay in {110} planes with equal angles between the crystal tetragonal symmetry axis (c axis) and each z axis. For both types of orthorhombic spectra, the corresponding EPR transitions from the different sites were super-imposed with the applied magnetic field parallel to the c axis. Spin-Hamiltonian parameters have been determined for the observed tetragonal and orthorhombic spectra. Powder pattern analysis was employed for the Gd3+ orthorhombic spectra, due to the complexity which resulted from the large number of inequivalent sites. The implications of these results regarding the nature of the various sites are examined in conjunction with the results obtained previously by others for impurities in zircon-structure and scheelite-structure hosts.
Intermolecular Potentials from Crossed Beam Differential Elastic Scattering Measurements. V. The Attractive Well of He2
Authors: Farrar J. M. , Lee Y. T.
Published: February 2004

The van der Waals well of the helium pair potential has been studied by crossed molecular beam elastic scattering measurements. Low energy helium beams were produced by specially designed beam sources cooled with liquid hydrogen. Only five partial waves were found to contribute significantly to the differential cross section. A multiparameter potential function is used to construct the interatomic potential from experimental results. The potential parameters describing the location and depth of the attractive well are given by ε=11.0± 0.2oK, rm=2.963± 0.01 Å . The potential does not contain a bound state of zero angular momentum. Comparisons with other He2 potentials based on bulk properties and ab initio calculations are presented; the temperature dependence of the second virial coefficient is also discussed for the proposed potential.
15N Spin Lattice Relaxation in Liquid 15NH3 and 15ND3
Authors: Litchman W. M. , Alei M.
Published: February 2004

The spin-lattice relaxation times (T1) for 15N in 15NH3 and 14ND3 have been determined and are presented and discussed. The magnitudes and temperature dependences of T1 for 15NH3 and 15ND3 indicate that spin-rotational and intramolecular dipolar interactions together dominate the 15N relaxation in 15NH3. Since γD≈ 0.15 γH, the dipolar term is small compared with the spin-rotational term in 15ND3 at room temperature. This allows one to separate the spin-rotational and dipolar contributions in 15NH3. Values of τc, τsr, and CN are then derived from the experimental data for 15NH3 and compared with values derived in other work.
Anisotropy of Nuclear Spin-Spin Coupling in Methyl Fluoride
Authors: Ditchfield Robert , Snyder Lawrence C.
Published: February 2004

Equations for indirect nuclear spin coupling tensors are developed within the framework of Hartree-Fock perturbation theory. Calculated values for CF, CH, HF, and HH spin-spin coupling anisotropies (pseudodipolar couplings) in methyl fluoride are compared with the results suggested by recent experimental work. An estimate of the importance of including pseudodipolar coupling in the determination of molecular geometry by NMR in liquid crystals is made.
Absolute Total Scattering Cross Sections of 7Li–Ar
Authors: Ury G. B. , Wharton L.
Published: February 2004

The Li–Ar absolute total scattering cross section was measured to an accuracy of 1%–2% over the relative velocity range 1–4× 105 cm/sec, corresponding to relative energies of 0.03–0.5 eV. The absolute cross section determines the radial scale of the interatomic potential, by reference to the average distance between target molecules. The present study is intended as an exemplary system investigation of inferences that can be drawn from more accurate absolute total cross sections, since currently it is believed that this class of total cross section is known to an absolute accuracy of 5%–10% [R. B. Bernstein and J. T. Muckerman, Advan. Chem. Phys. 12, 414 (1967)]. The primary finding is the value of the interatomic potential with an accuracy of about 5% over a span of the relatively large interatomic distances 6–8 Å. At 7 Å the Li–Ar potential is −1.97 × 10−15 erg± 5%. In this region half of the error arises from the systematic error in the cross section and half from the ambiguity about the proper potential model to apply. The results should be useful for critically testing future model potential calculations and, in conjunction with differential scattering and other data, for giving a more exact and complete understanding of the potential. An apparatus was used that had been previously applied to molecule-atom scattering, where angular resolution corrections were negligible and where absolute pressures were measured with a McLeod gauge modified to physically eliminate trap pumping error. A deconvolution procedure that took into account the effects of target motion upon the glory structure of the total cross section was applied to the data. An economical method for applying nonlinear least squares fitting of model interatomic potentials is described and is applied to the data.
Viscosity of the Binary Gaseous Mixtures He–Ne and Ne–N2 in the Temperature Range 25–700°C
Authors: Kestin J. , Ro S. T. , Wakeham W. A.
Published: February 2004

The paper presents new relative measurements of the viscosity of the binary mixtures He–Ne and Ne–N2, as well as repeated determinations of the viscosity of the pure gases. The experiments were performed using an oscillating-disk viscometer; they were made at atmospheric pressure and in the nominal temperature range 25–700°C. The accuracy of the measurements is one of ± 0.1% at 25°C, deteriorating to ± 0.3% at 700°C. Tables of the thermal conductivity of the monatomic-gas mixture are provided together with values for pure nitrogen. The binary diffusion coefficients for the mixtures have also been computed.
Vibrational Energy Transfer and De-excitation in the HF, DF, HF–CO2, and DF–CO2 Systems
Authors: Stephens Ronald R. , Cool Terrill A.
Published: February 2004

The laser excited fluorescence method has been employed to determine the key rate constants for energy transfer and deactivation processes in the HF, DF, HF–CO2, and DF–CO2 chemical laser systems at a temperature of 350°K. The self-deactivation rates for HF (v=1) and DF(v=1) molecules by ground state molecules were found to be kHF–HF=5.25 ± 0.30 × 104 sec−1 ·   torr−1 and kDF–DF = 2.0 ± 0.2 × 104 sec−1 ·   torr−1, respectively. The measured rates of V → V transfer from HF(v=1) and DF(v=1) to the CO2(0001) state were kHF–CO2 = 3.7 ± 0.3 × 104 sec−1 ·   torr−1 and kDF–CO2 = 17.5 ± 2.5 × 104 sec−1 ·   torr−1. The respective deactivation rates of CO2(0001) by ground state HF and DF were determined to be kCO2–HF = 3.6 ± 0.3 × 104 sec−1 ·   torr−1 and kCO2–DF = 1.9 ± 0.4 × 104 sec−1 ·   torr−1. The large rates for these processes can be attributed to energy transfer to rotation under the influence of a sizable attractive (hydrogen bonded) intermolecular potential well and enhanced repulsion at close range.
Near-Infrared Studies of the Structure of Water. IV. Water in Relatively Nonpolar Solvents
Authors: Choppin G. R. , Downey J. R.
Published: February 2004

The peak positions for the absorption bands of water in CCl4, CS2, CDCl3, and C2H4Cl2 have been measured. The positions agreed closely with values calculated from equations developed for water vapor, indicating the monomeric nature of water in these solutions. In addition, the shifts in frequency maxima from the vapor phase values showed a correlation with the solution dielectric constant. The experimental absorption maxima for liquid water did not agree with the calculated values nor did they fit the correlation with dielectric constant. However, the peak position assigned to water molecules with neither hydrogen involved in hydrogen bonding did agree with the dielectric constant correlation. The absorption maxima for a saturated solution of NaClO4, which was expected to have a large amount of such nonbonded species, were also in satisfactory agreement with the calculated peak positions.
Ab Initio Calculations on the H2 + D2 → 2HD Four-Center Exchange Reaction. II. Orbitals, Contragradience, and the Reaction Surface
Authors: Wilson C. Woodrow , Goddard William A.
Published: February 2004

We discuss the reaction surface for the four-center exchange reactionH2 + D2 → 2HDin terms of the orbitals from spin-coupling optimized GI(SOGI) calculations. The surface is comparable to previously published surfaces determined by configuration interaction. The shape of the surface is discussed in terms of the exchange kinetic energy and contragradience, which have previously been used to discuss the bonding or nonbonding of molecules.
On a Time Dependent Theory of Hot-Atom Reactions
Authors: Keizer Joel
Published: February 2004

A simple time dependent theory of hot-atom reactions in a dilute host gas is developed based on Porter's stochastic theory of hot-atom reactions. Kinetic equations governing the time behavior of the hot-atom probability distribution as well as the concentration of hot atoms are derived. If the frequency of collisions is significantly larger than the reaction rate, it is shown that the probability distribution will relax to a steady state form. The steady state distribution can be used to define hot-atom reaction rate constants and these constants are directly related to product yields. By comparing the time dependent theory to usual kinetic type theories, it is shown that whenever the steady state theory is valid, it gives results identical to those based on the Miller-Dodson formula
Effect of Fluorescence Polarization on Fluorescence Intensity and Decay Measurements
Authors: Shinitzky M.
Published: February 2004

When a fluorescent system is excited with an unpolarized light and its emission is detected without a polarizer, as in the most common fluorescence instruments, the emission intensity displays a typical anisotropic distribution which is directly related to the degree of polarization of the emission. This effect may introduce an error of up to 20% in all steady state and dynamic fluorescence measurements and is discussed in detail for fluorescence intensity and decay measurements. It is shown that when the fluorescence is detected at an angle of 55° or 125° to the direction of excitation the effect of polarization is totally abolished.
Two-Center Two-Electron Spin-Spin and Spin-Orbit Hybrid Integrals
Authors: Matcha Robert L. , Malli Gulzari , Milleur Mac B.
Published: February 2004

General expressions for the two-center hybrid integrals over Slater orbitals occurring in the evaluation of the spin-spin and spin-orbit interactions in diatomic molecules are derived. The final expressions are in the form of one-dimensional integrals over functions which are readily evaluated.
Photodetachment of an Electron from Selenide Ion; the Electron Affinity and Spin-Orbit Coupling Constant for SeH·
Authors: Smyth Kermit C. , Brauman John I.
Published: February 2004

The relative cross section for the gas phase photodetachment of an electron from SeH− has been determined in the wavelength region 428–578 nm (2.90–2.15 eV). 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. The cross section exhibits two sharp thresholds, whose positions remain unchanged for the photodetachment of SeD−. As a result, the electron affinity and the spin-orbit coupling constant have been evaluated: E. A. (SeH·)=2.21± 0.03 eV and A (SeH·)=−1815± 100 cm−1.
Dynamics of the Molecular and Atomic Mechanisms for the Hydrogen-Iodine Exchange Reaction
Authors: Raff L. M. , Thompson D. L. , Sims L. B. , Porter R. N.
Published: February 2004

Theoretical treatment of both the molecular and atomic mechanisms for the hydrogen-iodine exchange reaction (H2+I2→ 2HI) is accomplished by means of extensive classical trajectories calculated on a reasonable potential-energy surface in which the single adjustable parameter is the iodine-core effective charge. The analysis shows the molecular mechanism to be dynamically forbidden, but gives an over-all rate constant for the atomic mechanism in substantial agreement with the experimental values. The formation of a weak H2I complex is predicted to play an important dynamical role if the atomic mechanism is limited to reactions with collision complexes involving no more than two hydrogen atoms and two iodine atoms. Excellent agreement with experiment is obtained for the rate constant for the recombination I+I+H2→ I2+H2 and its negative temperature coefficient. Trajectories for the latter reaction are rich in multiple exchange of internal energy between the molecular species, but the formation of H2I is predicted to be an unimportant process in recombination of iodine atoms with hydrogen molecule as the third body.
Theory of Chemically Induced Dynamic Polarization in Thin Films
Authors: Deutch J. M.
Published: February 2004

An analysis is presented for radical recombination according to a continuous diffusion model for two and three dimensional systems in the context of chemically induced dynamic polarization (CIDNP) experiments. It is argued that diffusional models of molecular motion are most sensitive to changes in dimensionality and that CIDNP or other experiments carried out in thin film, quasi-two dimensional systems, should reveal these effects. The reason for this sensitivity is that according to a diffusion model dynamical quantities of interest will decay more slowly in two dimensions rather than three. We discuss how these conclusions apply to a variety of experiments and two additional examples are cited.
Translational Energy Dependence of the Reaction Cross Section for K+CH3I→ KI+CH3 from 0.1 to 1 eV (c.m.)
Authors: Gersh Michael E. , Bernstein Richard B.
Published: February 2004

A molecular beam study of the reaction K+CH3I→ KI+CH3 over an extended range of collision energy is described. A thermal K beam is crossed with a seeded supersonic nozzle beam of CH3I. The excitation function (energy dependence of the reaction cross section) for this reaction was measured from 0.1 to 1 eV (c.m.). The total flux of the KI reaction product was determined by integration over the laboratory spherical polar coordinates (Θ,  Φ) of the in-plane and out-of-plane angular distributions of KI measured by a two-filament differential surface ionization detector mounted on a goniometer. By seeding the CH3I with a variety of lighter gases, its velocity could be changed from δ ≈ 530–2330  m/sec. The average center of mass collision energy, Ē, was thereby varied from 0.1 to 1 eV. The densities of both beams were monitored during the scattering experiments, so that relative cross sections vs Ē were obtained with a precision of ≈ ± 10%. The supersonic CH3I beam speed distributions were quite narrow (FWHM ≈ 20%). The K speed distribution was essentially Maxwellian. The measured total reaction cross section rises to a maximum at Ē=0.18(± 0.03)  eV, beyond which it decreases continuously. No evidence was found for the occurrence of additional (high energy) processes, such as chemiionization or formation of alternative products.
Vibrational Spectra and Structure of Acetone Oxime and Acetone Oxime-O-d
Authors: Harris W. C. , Bush S. F.
Published: February 2004

The infrared and Raman spectra of acetone oxime have been investigated from 70 to 4000 cm−1. Spectra have been obtained for the gaseous, liquid, and polycrystalline materials, and the data have been interpreted in detail. A suggested vibrational assignment for the molecule is based upon group frequency correlations, relative band intensities, and isotopic and vapor-solid frequency shifts. The interesting methyl torsional vibrations were assigned to a band at 217 cm−1 in the infrared spectrum recorded at liquid nitrogen temperatures. The magnitude of the internal rotational barrier for solid acetone oxime is estimated to be 3.0 kcal/mole. The results of this analysis are considered in conjunction with previous studies on similar molecules.
Nuclear Spin-Lattice and Viscoelastic Relaxation in Selected Hydrocarbon Liquids
Authors: Cutnell J. D. , Stejskal E. O.
Published: February 2004

Spin-lattice relaxation rates of 5,5,11,11-tetramethylhexadecane, squalane, and squalene have been measured as a function of temperature via pulsed NMR techniques. These relaxation rates are discussed in terms of molecular models which yield nonexponential correlation functions. The particular models employed are based on cooperative relaxation mechanisms which have been found useful in viscoelastic and dielectric relaxation studies. It is found that such mechanisms are also pertinent in the nuclear spin relaxation behavior of these compounds. The distribution of correlation times useful in describing shear relaxation data is also found to be useful in describing spin relaxation data.
One and Two Dimensional Lattice Systems of Hard Particles
Authors: Cook Robert , Fixman Marshall
Published: February 2004

The configurational free energies and pressures of single-occupancy systems of hard disks and rods have been evaluated using a coupled oscillator approximation proposed by Fixman. These results compare favorably with computer generated data. The nature of the cell constraint used in the coupled approximation is discussed and arguments are presented to relate the parameter b, which measures the strength of the cell constraint, to the communal entropy of the lattice. Investigation of the 72- and 896-disk cell lattices show that the strong number dependence present in the mean-square displacements at high densities is present in the coupled oscillator approximation as well as in the exact computer results.
On a Vibration-Rotation Hamiltonian for Bimolecular Collisions Analogous to the Wilson-Howard Vibration-Rotation Hamiltonian for Isolated Molecules
Authors: Hougen Jon T.
Published: February 2004

A bimolecular vibration-rotation Hamiltonian is derived which is analogous to the Wilson-Howard vibration-rotation Hamiltonian for isolated molecules. The bimolecular Hamiltonian involves the use of a ``complex-fixed'' axis system, i.e., a system with one of its axes along the line joining the centers of mass of the two interacting molecules. The bimolecular vibration-rotation Hamiltonian shows some similarities to the diatomic-molecule vibration-rotation-electronic Hamiltonian, the role of the two atoms in the diatomic molecule being played by the two interacting molecules, the role of the inter-nuclear axis by the line joining the molecular centers of mass, and the role of electronic orbital and spin angular momenta by the vibration-rotation angular momenta of the two interacting molecules. The application of permutation-inversion molecular symmetry group ideas to a bimolecular complex is described.
ESR Studies of Unsubstituted Cyclic Nitroxides in Solids
Authors: Bodnar John W. , Rowell Charles F.
Published: February 2004

A new photochemical method of producing nitroxides from nitramines is reported. Solutions of un-substituted cyclic nitroxides from nine nitramines were studied in the ESR and splitting constants established. For two cases, single-crystal studies of nitroxides produced in situ by this reaction permitted neighboring hydrogen interactions with the nitroxide electron to be compared with the nitrogen interaction.
Molecular Dynamics of Two-Dimensional Gases and the Formation of Bound States
Authors: Harrison Herman W. , Schieve William C. , Turner Jack S.
Published: February 2004

Molecular-dynamics programs which can solve equations of motion for dilute and moderately dense gases have been developed. In the molecular-dynamics calculation for two-dimensional argon gas, the formation and dissociation of classical bound pairs (dimers) have been observed. The chemical reaction rate constant for this process has been determined and compared with existing classical theoretical models.
On the Symmetry of the Hydrogen Bonds in Ice VII
Authors: Holzapfel W. B.
Published: February 2004

The interaction of the hydrogen atoms with nearest neighbor oxygen atoms in the hydrogen bonds of ice VII are approximated by two equivalent Morse potentials. With the inclusion of a repulsive oxygen—oxygen interaction, the model predicts a transition to symmetric hydrogen bonding in ice VII at a pressure between 350 and 800 kbar.
Determination of Optical Oscillator Strengths by Electron Impact Spectroscopy
Authors: Bonham R. A.
Published: February 2004

An expansion of the square of the momentum transfer times the differential cross section, in powers of the momentum transfer, about the nonphysical point of zero momentum transfer, is carried out through terms of the order of the reciprocal of the square of the incident energy. The results confirm the view that the differential cross section can be regarded as a function of the square of the momentum transfer down to relatively low energies. Simple formulas are presented for calculating corrections to electron impact estimates of the intensity at zero scattering angle in order to obtain accurate optical oscillator strengths. Correction formulas are also presented for obtaining quadrupole transition probabilities from optically forbidden transitions. The case of spin forbidden but exchange allowed transitions is also considered. It is shown that certain second Born exchange corrections exist with the same dependence on the incident energy as that found for the leading term in the first Born approximation for exchange.
SCF and CI Studies of Bonding and Physical Properties of Hydrogen Chloride
Authors: Petke J. D. , Whitten J. L.
Published: February 2004

A detailed self-consistent-field study of bonding effects, geometry, and physical properties of HCl computed from a variety of basis sets is presented. Linear stretch of the molecule is analyzed in terms of variations in physical property data with internuclear distance. The use of optimized d orbitals on chlorine is found to produce well-defined charge shifts in each molecular orbital and a net shift of electron density into the bonding region. This results in a significant lowering of the total energy and improvement in physical property values, compared to treatments in which d orbitals are not employed. Configuration-interaction treatments on the ground state of HCl result in a lowering of the total energy to approximately 0.08 a.u. below the Hartree—Fock value, but only slightly improve the calculated physical properties. Details of the effect of basis set construction on molecular properties are discussed.
Hyperfine Structure of 7Li79,81Br by Molecular-Beam Electric Resonance
Authors: Hilborn R. C. , Gallagher T. F. , Ramsey N. F.
Published: February 2004

The molecular-beam electric-resonance technique has been used to measure the hyperfine interaction constants of the J=1, v=0 state of 7Li79,81Br in the limit of weak external fields. The results for the bromine and lithium nuclear electric quadrupole interaction constants, eqQBr and eqQLi, the spin-rotation constants, cBr and cLi, the ``tensor'' nuclear spin-spin interaction, c3, and the ``scalar'' nuclear spin-spin interaction are (in kilohertz) Li797BrLi817BreqQBr38368.104(36)32050.860(46)eqQLi211.04(10)211.03(13)cBr7.8816(58)8.4740(74)cLi0.859(15)0.815(19)c31.0710(61)1.1789(78)c40.0604(70)0.0711(89)A theory which permits the calculation of the optimum power required to drive the hyperfine transitions is presented and experimentally verified. A possible pseudoquadrupole effect is discussed, and recent calculations of molecular electric field gradients are used to determine the nuclear quadrupole moments.
Coulomb Potential in Ionic Crystals by Direct Summation
Authors: Hajj Fuad Y.
Published: February 2004

A method is proposed to determine the shape and size of the finite crystal piece to be used in the calculations of the Coulomb potential at points in the unit cell of ionic crystals. The Coulomb potential at a point is calculated by direct summation of the potentials of all the ions in this finite crystal piece. A theorem was established which helps to make the resulting series in the calculations converge much faster, thus cutting the computing time by a factor of millions or more, depending on the accuracy desired. With the help of this theorem, it was possible to calculate the Coulomb potential at a grid of points in the unit cells of NaCl and CsCl structures to 10 decimal places. The Madelung constant for NaCl structure was calculated to 25 decimal places as an illustration of the power of this theorem.
Energy Transfer in Monochromatically-Excited Hydrogen (B  1Σ u+). I. Excitation Processes, Electronic Quenching, and Vibrational Energy Transfer
Authors: Fink Ewald H. , Akins Daniel L. , Moore C. Bradley
Published: February 2004

Excitation of HD molecules into specific vibrational and rotational levels of the B  1Σ u+ electronic state by absorption of the 1048 and 1066 Å argon resonance lines has been studied under various experimental conditions by observing the steady-state fluorescence spectra of the (B  1Σ u+→ X 1Σg+) Lyman bands. Strong excitation of the (v′ = 3, J′= 2), (v′ = 5 , J′=2), and (v′ = 6 , J′ = 5) levels was achieved. The HD (B 1Σ u+ → X 1Σg+) electronic fluorescence from v′=3 was found to be quenched by HD, 3He, 4He, and Ne with effective collision cross sections of 79, 8.8, 9.9, and 3.5 Å2 at 297°K. Vibrational energy transfer processes HD(B  1Σ u+ ; v′=3, J′) + M→ HD(B  1Σ u+; v′=2, J′ + Δ J′ ) + M+ Δ Ewere studied for the collision partners 3He, 4He, and Ne. Large effective cross sections of 0.89, 0.76, and 0.81 Å2 were found at 303°K. Rotationally-resolved spectra for Ne show that vibrational energy is transferred into both rotation and translation. All energetically accessible values of ΔJ′ were observed. On the average one-half of the vibrational energy was transferred into rotation.
Tritium Decay Synthesis of Free Radicals. An EPR Study of 2-Naphthyl Radical in Single-Crystal Naphthalene-d8
Authors: Lloyd Roger V. , Wood David E.
Published: February 2004

The 2-naphthyl radical was prepared by allowing naphthalene-2-t to undergo radioactive decay in a single-crystal naphthalene-d8 matrix at 77°K. The resulting, oriented 2-naphthyl radicals were then studied by EPR at 120°K. The parameters in the spin Hamiltonian were determined to be: gT1T3T4x2.004648.136.513.4y2.002465.154.721.8z2.003554.638.918.9, where the hyperfine tensor elements are in megahertz, the x direction is ⊥ to the plane of the radical, the z direction is ∥ to the broken bond (strictly true for g tensor only), and the y direction is in the plane of the radical ⊥ to x and z. These tensor elements are very nearly the same as reported for the 2-naphthyl radical in argon at 4°K with the exception that the g tensor elements are uniformly larger by ∼ 0.0011 in naphthalene-d8. Examination of the g shifts from free spin indicates that the unpaired-electron σ orbital is approximately equally distant from the highest occupied π orbital and the lowest unoccupied π orbital. An INDO calculation based on the x-ray diffraction determined geometry of naphthalene gives the proper relative magnitude of the coupling constants for protons number one and three whereas the ``standard geometry'' gives an inverted result. There are only two magnetically inequivalent sites in the unit cell as a result of reorientation of the 2-naphthyl radical about its long axis.
General Formulas for the Evaluation of the Valence Orbital Ionization Potentials for the K (2) L (8) 3 s23p63dα 4sβ4pγ or the 1s22sm2pn Atoms and Ions
Authors: Anno Tosinobu , Sakai Yoshiko
Published: February 2004

Formulas, with which the 3d, 4s, or the 4p VOIP of any atom in any configuration of the type K (2) L (8) 3 s23p63dα 4sβ4pγ (type I) and the 2s or the 2p VOIP of any atom in any configuration of the type 1s22sm2pn (type II) may be calculated, are obtained. The procedure adopted is a least-squares fitting of all the available data of empirical VOIP's of atoms and ions with these configurations to quadratic functions of α, β, γ, and the atomic number (for the type I atoms) or of m, n, and the atomic number (for the type II atoms) which were derived on both the empirical and the theoretical basis in the previous works by the present authors [Theoret. Chim. Acta 18, 208, 223 (1970)]. The resulting formulas should be useful in predicting VOIP's of those atoms and ions for which direct evaluation is impossible for lack of experimental data. The formulas should thus facilitate the parametrization of the semiempirical molecular orbital theory, both of the extended Hückel and of the Pariser—Parr type.
Application of Faddeev and Watson Techniques to Atomic Composite-Particle Problems
Authors: Chen Joseph C. Y. , Chung Kwong T. , Mizuno Junya
Published: February 2004

The techniques of Faddeev three-body theory and Watson multiple-scattering and final-state interaction theories are applied to atomic problems involving more than three particles. The use of large mass disparity inherent in the atomic and molecular systems permits considerable simplification of the problem. Problems explicitly considered are the three-electron atomic and molecular problems, the collision of three-composite particles, and the problem of electron scattering by polyatomic molecules. Application of the present method to the open-channel resonance problems in electron—molecule systems is investigated in connection with the calculation of the adiabatic complex potential for the constituent atomion interaction by tracing the trajectory of the electronic resonance pole as a function of the internuclear separation.