bluuebunny/crossref_metadata_2025 huggingface dataset:
19F Spin—Rotation and Spin—Spin Interactions, 19F Magnetic Shielding, and Molecular Magnetic Moments for OCF2
Authors: Lo Mei-Kuo , Weiss V. W. , Flygare W. H.
Published: January 2005

The microwave spectrum of OCF2 is examined under high resolution using an L-band waveguide and 1 and 5-kc/sec modulation, where half-widths at half-height of 5–7 kc/sec are obtained. The 19F nuclear-spin-nuclear-spin and the 19F spin—rotation interactions are observed. The experimental 19F spin—rotation constants along the principal inertial axes are Maa = | 19±3 | kc/sec, Mbb = | 13±3 | kc/sec, and Mcc = | 5±3 | kc/sec. The calculated magnitude of the nuclear contribution to the 19F spin—rotation constants show that the signs of the above values are all negative, which then leads to the calculated 19F paramagnetic shielding in OCF2 of σp = −324×10−6.

The 19F chemical shift in OCF2 is measured relative to Cl3CF giving 23×10−6. Relating the 19F shielding back to F2 as a reliable standard gives the total shielding at 19F in OCF2 as 236×10−6. Combining this with the paramagnetic shielding obtained from the 19F spin—rotation constants gives the diamagnetic shielding as σd = 560×10−6, which is larger than the corresponding 19F diamagnetic shielding in F2 of 530×10−6.

The first-order molecular Zeeman effect was also observed in OCF2 using a zigzag cell in a magnetic field up to 11 kG giving the diagonal elements of the g-value tensor along the principal inertial axes of gaa = | 0.074±0.002 |, gbb = | 0.038±0.003 |, and gcc = | 0.028±0.003 |. Arguments are given to suggest that the signs of the g values are all negative, which yields the paramagnetic susceptibility of χp = 127×10−6. The g values are combined with an estimate of the molar susceptibility to yield the average diamagnetic susceptibility in OCF2 giving a most probable value of 〈ψ0 | ∑ iri2 |ψ0〉=47.4×10−16cm2.

A theory is presented which allows an estimation of either the molecular g values or the 19F spin—rotation interaction if one of the two quantities is known. The 19F parameters obtained in this study may be transferable to other systems.

Several low-J transitions in OF2 are examined in a 4-ft liquid-N2 absorption cell, and the magnetic properties of 19F in this molecule are re-examined.
Atomic-Nitrogen Recombination
Authors: Evenson K. M. , Burch D. S.
Published: January 2005

Three-body and wall recombination coefficients of atomic nitrogen were measured using an electron spin resonance spectrometer to determine the atomic nitrogen concentrations. Studies were made of nitrogen gas at pressures from 3 to 35 torr flowing in a cylindrical tube and nonflowing nitrogen gas at pressures from 0.3 to 7 torr. The three-body recombination coefficient k1 with molecular nitrogen as the third body was found to be (2.25±0.2)×10−32 cm6 sec−1. The wall recombination probability, λ, of quartz was found to range from 7×10−6 to 5×10−4, decreasing with increasing oxygen impurity; the variation for Teflon was measured to be from 2×10−7 to 2.5×10−5, increasing with increasing oxygen content. The sum of the two-body radiative recombination and two-body wall recombination was a significant part of the total atom recombination; the sum of these coefficients ranged from 0.35×10−15 cm3 sec−1 to 2.8×10−15 cm3 sec−1.

For intervals up to 2 sec following atomic-nitrogen formation, the data indicate a slower decrease of atom concentration than can be accounted for by the measured mechanisms of recombination. The possible existence of an atom-forming mechanism in the afterglow is discussed.
Simple Correlated Wavefunctions for the Ground State of Heliumlike Atoms
Authors: Bonham R. A. , Kohl D. A.
Published: January 2005

A number of correlated wavefunctions of simple form were investigated for heliumlike atoms. Instead of the usual Hylleraas expansion the wavefunctions considered contained exponential correlation functions with nonlinear variational parameters. Wavefunctions of this type are usually avoided because of the nonlinear parameters. However, this type of function was chosen to try to determine some simple but relatively good wavefunctions for use in computing atomic properties. Results for atomic numbers 1 through 3 are presented.
Comparison of Expressions for Cooperative Properties in Glass-Forming Liquids
Authors: Greet R. J.
Published: January 2005

The results of the Adam and Gibbs statistical-mechanical model for relaxation in glass-forming systems are compared with the Williams, Landel, and Ferry empirical correlations. The emphasis is on determining quantitative expressions for the differences in the relationships for comparison with the available experimental data. It is found that the qualitative differences cannot quantitatively be distinguished from the bulk of the existing data but that the differences become magnified for systems with low glass-transition temperatures.
Exact Finite Method of Lattice Statistics. I. Square and Triangular Lattice Gases of Hard Molecules
Authors: Runnels L. K. , Combs L. L.
Published: January 2005

A general, feasible approach is presented for the evaluation of the statistical thermodynamics of interacting lattice gases. Exact solutions are obtained for lattice systems of infinite length and increasing finite width, using the matrix method which treats all densities on an equivalent basis. Through the application of symmetry reduction and the use of an electronic computer to perform logical as well as arithmetical operations, widths of up to 24 sites for two-dimensional lattices can be handled. For examples studied, rapid convergence is obtained away from transition regions and in the vicinity of phase transitions the behavior appears to be a sufficiently regular function of the width to allow meaningful extrapolation to systems of infinite width. Two problems of two-dimensional lattice gases are solved as illustrations of the technique: the square and triangular lattice gases with infinite repulsive interactions preventing the simultaneous occupancy of adjacent lattice sites (excluded-volume effect). Both systems exhibit phase transitions which are most likely second order at densities of 74.2% (square) and 83.7% (triangular) of the close-packed density. For both lattices the compressibility is infinite at the transition point, becoming infinite linearly with the logarithm of the width of the lattice for the square lattice and perhaps slightly more strongly for the triangular lattice.
Structure and Superconductivity of the High-Pressure Phases of InSb
Authors: McWhan D. B. , Marezio M.
Published: January 2005

The high-pressure phases of InSb can be retained metastably at 1 atm by cooling to 77°K before releasing pressure. The orthorhombic phase is obtained by applying pressures much higher than the ∼30 kbar needed to obtain the β-Sn phase. X-ray powder patterns of the quenched phases are given. X-ray-diffraction studies at high pressures show that the β-Sn phase is only observed when the pressure is raised rapidly through the 23–30-kbar range. The superconducting transition temperature of the orthorhombic phase is ∼3.4°K which is about 1° higher than that of the β-Sn phase.
Liquid Structure and Self-Diffusion
Authors: Rahman Aneesur
Published: January 2005

The method of molecular dynamics has been used to study the structure of a liquid and its relation with the process of self-diffusion.

The particles around a given particle are separated into shells of primary, secondary, etc., neighbors by a precise geometrical procedure. Each shell of neighbors of a particle generates a closed convex polyhedron surrounding the polyhedron of the previous shell. The faces of the polyhedra are the bisector planes of lines joining the particle to its neighbors. The primary polyhedron is the smallest closed convex polyhedron around the particle.

The primary polyhedra of a random system of points, of a liquid, and of a solid are compared; the average number f̄ of faces are found to be 15.67, 14.45, and 14.26, respectively. The average number p̄ of sides to the polygons forming the faces is obtained through the relation p̄=6—(12/f̄).

The pair correlation function g(r) is decomposed into a sum Σig(i)(r), where g(i)(r), arises out of neighbors forming the ith-order polyhedra. The distributions up to i=5 have been calculated. g(1) and g(2) give the first two maxima in g(r). For higher values of i the g(i)(r) do not correspond to maxima in g(r). For the liquid and for the random set of points the average number of faces f̄i of the ith-order polyhedra increases linearly with i; the departure from the linear law is significant only for i=1 and 2 in the case of the liquid.

It is found that the shape of the primary polyhedra is related to the direction of displacement, in time τ, of the central particle; and the correlation is maximum when τ=0.5×10−12 sec.

The positions of the neighbors are analyzed with respect to this displacement direction and expressed as a distribution g(r, μ; τ), which, in addition to the dependence on the distance, contains the angular correlation between the position of a neighbor and the displacement direction in time τ of the central particle. The nearest neighbors are found to be preferably situated in a direction away from the displacement direction. As the distance increases, the forward direction becomes more favorable. In the region of the secondary neighbors the same behavior is repeated but is less in magnitude. This local fluctuation in the distribution of neighbors disappears beyond the secondary neighbors.

The velocity autocorrelation function and its spectrum f(ω) are found to have characteristics related to these local fluctuations. f(ω) is found to have a solidlike part having the same Debye ω as that in the solid before melting. The diffusive part of the velocity autocorrelation function arises out of the particle's taking advantage of the local fluctuation in the configuration of its neighbors to move in the ``easy'' direction afforded to it by the fluctuation.
Three-Parameter Theory of Dilute Polymer Solutions
Authors: Yamakawa Hiromi
Published: January 2005

Three-parameter theories of the expansion factor α and the second virial coefficient A2 for chain polymers are presented to interpret primarily the experimental fact that the dimensionless ratio A2M/[η] is not always a universal function of α, where M is the polymer molecular weight and [η] is the intrinsic viscosity. There are two effects to be considered, which are related to a third new parameter: one is the effect of a ternary-cluster integral, and the other the effect of short-range interactions. First, the Orofino—Flory theory is revised with respect to inclusion of the ternary-cluster integral using the random-flight model, and it is shown that this effect is rather of minor importance, though not completely negligible. As for the second effect, a discrete nature of real polymer chains is considered primarily, and a simple analysis is made on suitable model chains. It is shown that the discrete-chain effect becomes significant when an effective bond of the chain is long compared to the range of average force between segments. Thus the most important third parameter is closely related to a degree of chain stiffness. With this parameter defined well, the theory agrees semiquantitatively with experiment for both flexible and stiff-chain polymers.
On the Theory of Chemical-Reaction Cross Sections. I. A Statistical-Dynamical Model
Authors: Marcus R. A.
Published: January 2005

A statistical-dynamical model is formulated for total chemical-reaction cross sections as a function of the relative velocity and the vibrational and the rotational state of the reactants. It is derived for reactions for which activated-complex configurations can be defined; reactions with or without steric and activation barriers. A quasiequilibrium is postulated between reacting pairs and activated complexes of the same energy and angular momentum. An integral equation is obtained which is solved for the reaction cross section by introduction of a second postulate: The reaction probability is a function of the excess initial energy along the reaction coordinate (in excess of potential energy barrier, centrifugal potential barrier, and vibrational adiabatic requirements). A possible dynamical origin of the postulates is considered in later papers.
Photogeneration of Charge Carriers in Tetracene
Authors: Geacintov Nicholas , Pope Martin , Kallmann Harmut
Published: January 2005

The photocurrent and photovoltage of tetracene single crystals with aqueous electrodes were studied as a function of the excitation wavelength in the 220–560-mμ region. The fluorescence efficiency of these crystals was studied in the same wavelength region. At wavelengths longer than 410 mμ, the photocurrent is due to injection of holes at the illuminated electrode. A bulk-generated (electron) photocurrent is shown to be produced with excitation energies in excess of 3 eV, i.e., at wavelengths less than 410 mμ. The relative fluorescence efficiency Φ(λ) begins to decrease with decreasing wavelengths at 410 mμ. The drop in Φ(λ) at excitation energies greater than 3 eV is attributed to the appearance of a nonradiative competitive process. This process involves mostly the formation of nonconducting and nonfluorescent (or weakly fluorescent) charge-transfer states. Formation of separated charges with low quantum efficiency (φi≲5.10−3) also occurs which gives rise to the observed bulk-generated negative current. Since this current appears only for excitation energies ≳3 eV, we associate this value with the smallest band gap for conductivity in tetracene.

The wavelength dependence of the bulk-generated negative photocurrent is related to varying probabilities of transition from the different excited electronic states of the crystal to ionized states. The positive hole current is mostly due to the diffusion of the lowest-energy singlet excitons to the surface and their dissociation at the electrode. The wavelength dependence of this current can be adequately described by a diffusion equation and an exciton diffusion length of 2000 Å is calculated from the experimental data and this equation. The wavelength dependence of the photovoltage is strongly dependent on the negative charge density and exhibits minima in wavelength regions where this density is highest.
Flash Photolysis of Methane in the Vacuum Ultraviolet. I. End-Product Analysis
Authors: Braun W. , Welge K. H. , McNesby J. R.
Published: January 2005

Methane and mixtures of methane and methane-d4 have been subjected to flash photolysis in the vacuum ultraviolet. Ethylene is the major hydrocarbon product. Isotopic distributions of the hydrogen, ethane, and ethylene fractions as well as complete product analysis suggest that CH plays a dominant role in the photolysis. The CH is formed either by direct dissociation of excited methane or secondary flash photolysis of CH2 in the flash. On the basis that acetylene is formed with unit efficiency by association of CH and ethylene is formed by reaction of CH with methane, the collision yield of the latter reaction is about 1/80.
Separated-Electron-Pair Model: Application to the π-Electronic Structure of the Ground State of Benzene
Authors: Ebbing Darrell D. , Poplawski L. E.
Published: January 2005

The separated-electron-pair (geminal) model appears to be a reasonable way to extend the single-particle picture while maintaining most of the simplicity of that picture. There seems to be no doubt about the utility of the model as applied to ``localized'' systems such as H2O, NH3, CH4, etc., although quantitative information is still needed. The question of how the model will do when applied to a ``delocalized'' system is studied in the present paper by applying the model to a π-electron system—the ground state of benzene. The symmetry of the system allows one to set up without difficulty two different separated-pair wavefunctions. Both of these functions are shown to satisfy the variational equations for an extremal, although the calculated energies are quite different. One function is constructed from geminals which are symmetry adapted; and the complete wavefunction is totally symmetric as it should be. The other separated-pair function is constructed from geminals which are equivalent to one another under threefold rotations; the natural orbitals of the geminals are localized. It happens that there are an infinite number of sets of such localized orbitals; all give identical results. As expected the localized geminal function is energetically superior to the symmetry geminal function. When ``resonance'' is accounted for, about 64% of the correlation energy (by comparison with full configuration interaction) is obtained.
Effect of Zero-Point Motion on the Mössbauer Spectra of K4Fe(CN)6 and K4Fe(CN)6·3H2O
Authors: Hazony Y.
Published: January 2005

A detailed calculation of the second order Doppler (SOD) shift of the Mössbauer line for some molecular solids demonstrates that the magnitude of this effect is significant in comparison with the full scale of the known isomeric shifts in iron compounds. The main purpose of this paper is to emphasize the importance of the SOD shift and, in particular, of the temperature-independent portion, which is due to the zero-point motion of the Mössbauer atom.

A simple model for calculation of the SOD shift for some molecular solids is presented, followed by a detailed analysis of the experimental results for K4Fe(CN)6 and K4Fe(CN)6·3H2O. An SOD contribution of 0.275 and 0.285 mm/sec to the measured shifts for the two compounds at room temperature is suggested on the basis of the analysis; an isomeric shift of +0.345 mm/sec, with respect to a 310 stainless-steel absorber at room temperature, is proposed for both compounds. An extrapolated difference of about 0.02 mm/sec at 0°K in the measured thermal-shift curves of the two compounds is attributed to the change in the zero-point motion due to modifications in the normal mode distributions that are associated with the water of crystallization.

Comparison with results on other compounds shows that differences as high as 0.15 mm/sec may be expected in the contribution of the zero-point motion to the Mössbauer line positions.
Thermal Diffusion and Self-Diffusion in Ammonia
Authors: Paul R. , Watson W. W.
Published: January 2005

The temperature dependence of the isotopic thermal-diffusion factor α0 for ammonia has been investigated with the help of an equimolar mixture of 14NH3 and 15NH3. A 10-tube metal swing-separator as well as a two-bulb glass apparatus were used for these measurements. The value of α0 increases with temperature, its value being 0.00±0.02 at 242°K to 0.09±0.03 at 496°K, in disagreement with the values obtained by Watson and Woernley, who observed a definite inversion in the sign of α0 at temperature ∼290°K. The present set of observed values of α0 also disagrees with the theoretical calculation of Monchick and Mason. Possible causes of this disagreement are: (1) inadequacy of the potential model, (2) neglect of inelastic collisions, and (3) formation of dimers.

The self-diffusion coefficient of ammonia has also been studied in the temperature range of 233° to 353°K with a two-bulb apparatus. There is marked disagreement between observed and calculated values at low temperatures. This is also explained in terms of dimerization.
X-Ray-Diffraction Study of Carbon Tetrafluoride in the Liquid State
Authors: Harris Ronald W. , Clayton Glen T.
Published: January 2005

X-ray diffraction patterns obtained from liquid carbon tetrafluoride in equilibrium with its vapor at temperatures of −177°, −153°, and −122°C were used to calculate the corresponding electronic and molecular radial distribution functions. The electronic distributions all showed peaks at approximately 1.36 and 2.20 Å. The areas associated with these peaks are in good agreement with that expected from a tetrahedral model. The most significant result of this work is the calculation of molecular distributions within the liquid since very little experimental information is available concerning molecular distributions in polyatomic liquids in which all atoms in the molecule have appreciable scattering power. Peaks were observed in the molecular distributions at approximately 3.36, 5.20, and 9.00 Å at all three temperatures. In each of these the peaks decreased in magnitude and increased in width as the temperature increased. The number or molecules associated with each peak decreased as the temperature increased. Ideal peak calculations were carefully applied in the analysis. A study of the effects of data modification was also made.
Energy Levels of Er3+ and Pr3+ in Hexagonal LaBr3
Authors: Kiess N. H. , Dieke G. H.
Published: January 2005

The spectra of Er3+ in LaBr3 are similar to, but not the same as, those of Er3+ in LaCl3. The Stark splittings of the Y and Z groups are used to determine the crystalline-field parameters for LaBr3, which are B20=117, B40=−39.6, B60=−19.2, and B66=212 cm−1. These are significantly different from those of LaCl3. The centers of gravity of the excited Stark groups are higher in LaCl3 than in LaBr3, and this shift increases with increasing wavenumber. Spectra and energy levels of Pr3+ in LaBr3 are also given.
Upper Limits to Electric-Field-Induced Nuclear Magnetic Dipole—Dipole Couplings in Polar Liquids
Authors: Sears R. E. J. , Hahn E. L.
Published: January 2005

The alignment of polar molecules in liquids by an external electric field is investigated by pulsed nuclear magnetic resonance methods. Sensitive rotating-frame techniques are described for the detection of the expected induced nuclear magnetic dipole—dipole coupling. In no case could an induced coupling be detected. The upper experimental limits for the induced couplings disagree with the predictions of the Lorentz localfield model. For nitrobenzene and p-nitrotoluene, disagreement is also obtained with the Onsager local-field model by a reduction of almost an order of magnitude in the expected size of the effect. The negative results for these two compounds are indicative of strong local antiparallel ordering of the molecular electric dipoles. The induced coupling in p-nitrotoluene, reported by Buckingham and McLauchlan using standard NMR methods, is found to be absent in this investigation, which employs a measuring technique more sensitive by at least one order of magnitude.
Shear-Rate Dependence of the Intrinsic Viscosity of Flexible Linear Macromolecules
Authors: Kotaka Tadao , Suzuki Hidematsu , Inagaki Hiroshi
Published: January 2005

Shear-rate dependence of the intrinsic viscosity has been studied on polystyrene in four different solvents by using a Zimm—Crothers rotational viscometer and Ubbelohde viscometers. The former viscometer was employed particularly for measuring zero-shear intrinsic viscosity [η]0. The results are summarized in terms of the [η]/[η]0 versus generalized rate of shear β=([η]0ηsM/RT)G, where ηs is the solvent viscosity, M the solute molecular weight, G the rate of shear, and others have usual significance. It has been found that, (i) at the values of β below 0.1, [η] is practically independent of rate of shear (or shear stress); (ii) the non-Newtonian effect does exist even in θ conditions; and (iii) at the values of β below 2, the [η]/[η]0-vs-β curves of the systems with different molecular weights and in different solvents give a single composite curve, which fairly well resembles to the curve of a prolate ellipsoid with the axial ratio p=3.
13C Spin—Rotation Interaction and Magnetic Shielding at the Carbon and Oxygen Nuclei in Formaldehyde
Authors: Flygare W. H. , Weiss V. W.
Published: January 2005

A large-sized L-band microwave absorbtion cell was used to observe the 13C spin—rotation interaction in formaldehyde. The results yield | 32Maa+34(Mbb+Mcc)|=207.5±2.5 kc/sec. By making sign assumptions, the paramagnetic shielding at 13C is estimated to be σp=−215×10−6 compared to σp=−730×10−6 at the oxygen nucleus.

Hybrid orbitals and the symmetric orthogonalization method are used to compute 10 one-electron properties in formaldehyde to compare with the LCAO SCF results. The hybrid orbitals chosen yield slightly better agreement with experiment than the SCF functions. However, the minimal basis set used here and in the SCF functions does not allow enough flexibility to fit all of the observables within the experimental error. Reasonable values of the carbon and oxygen diamagnetic shielding are chosen on the basis of the calculations and are combined with the 13C spin—rotation constants in this paper and the 17O spin—rotation constants in a previous work to yield the absolute shielding at the carbon and oxygen nuclei in formaldehyde. The values for the total magnetic shielding in formaldehyde are σ(carbon)=125×10−6 and σ(oxygen)=−268×10−6.

The 17O–12C spectrum in the literature is reinterpreted to yield the 17O spin—rotation interaction in that molecule. Our interpretation for 17O–12C yields χaa=4.43±0.10 Mc/sec and Mbb=29±10 kc/sec. The 17O spin—rotation information is combined with a recent calculation of the oxygen diamagnetic shielding in CO to yield the absolute shielding at the oxygen nucleus which is σAv=−14×10−6.
Calculation of One-Electron Properties for the Formaldehyde Molecule with the LCAO MO SCF Function of Foster and Boys
Authors: Flygare W. H. , Pochan J. M. , Kerley G. I. , Caves T. , Karplus M. , Aung S. , Pitzer R. M. , Chan Sunney I.
Published: January 2005

Using the approximate molecular orbital wavefunction of Foster and Boys, we have calculated the expectation values of 12 one-electron operators: diamagnetic susceptibility, dipole moment, proton diamagnetic shielding, electric-field-gradient tensor components at the oxygen and deuteron nuclei, and forces at the oxygen, carbon, and hydrogen nuclei. Several methods for evaluating the molecular integrals for these various one-electron operators were employed. Since the one-electron operators sample the electronic distribution differently in various regions of the molecule, the calculation of these molecular properties should provide a critical test of the accuracy of the predicted charge distribution. Some of the results are in fairly good agreement with experiment, but many are off by a factor of 2 or more.
Growth Rate of Ice Dendrites in Aqueous Solutions
Authors: Lindenmeyer C. S. , Chalmers Bruce
Published: January 2005

The free-growth rate and substrate growth rates of ice dendrites in aqueous solutions as a function of supercooling ΔT and solute concentration are presented. The free-growth rate ν in distilled water was found to be ν=0.228(ΔT)2.39 mm/sec. In distilled water having 2° to 4°C supercooling, growth upon a substrate was as much as an order of magnitude faster. Solutes in a concentration on the order of 0.01 moles/liter produced a slight increase in the free-growth rate, while at greater concentration the growth rate decreased.
Use of Hellmann—Feynman and Hypervirial Theorems to Obtain Anharmonic Vibration—Rotation Expectation Values and Their Application to Gas Diffraction
Authors: Bonham R. A. , Su L. S.
Published: January 2005

A recursion relation for the moments of the probability function for a one-dimensional anharmonic oscillator are derived by using a hypervirial relation. In addition it is shown that the first few moments of the probability function can be easily obtained by use of Hellmann—Feynman, virial, and Ehrenfest's theorems if the vibrational—rotational energy is known as a function of the anharmonic force constants. Expressions for the first four moments of a potential function containing cubic and quartic anharmonic terms are given by use of Dunham's expression for the vibrational energy. The application of anharmonic moments in gas electron diffraction is considered in detail.
Geometry of Molecules. II. Diborane and Ethane
Authors: Buenker Robert J. , Peyerimhoff Sigrid D. , Allen Leland C. , Whitten Jerry L.
Published: January 2005

The diborane molecule has been investigated in its equilibrium D2h geometry, in the D3d (ethane) structure, and three intermediate configurations. Charge-contour diagrams show that the electron distribution between the boron nuclei is considerably less concentrated than in the boron—bridge-hydrogen bonds. Calculations for ethane in both equilibrium and bridged-hydrogen configurations show that the carbon p functions of C2H6 play a much greater role in molecular binding than those of boron in B2H6 and this fact explains their different geometry.
Mass-Spectrometric Study of Ion—Molecule Reactions of Ethanol and Methanol
Authors: Sieck L. Wayne , Abramson Fred P. , Futrell Jean H.
Published: January 2005

The ion—molecule chemistry of variously labeled ethanols has been investigated in a single-stage high-pressure mass spectrometer at various field strengths and ionizing voltages. The results have been correlated with data obtained from a tandem apparatus having a primary-beam mass—energy selection capability. The interactions of selected ions have been investigated at low impacting energies with this instrument. Proton transfer and proton transfer followed by dissociation are the major reaction paths observed. The formation of higher-order aggregates corresponding to solvated proton structures has also been studied at elevated pressures and consectutive ion—molecule chemistry has also been investigated in the tandem instrument. Some related experiments with variously labeled methanols are also reported. A complete analysis of the bimolecular ion—molecule chemistry of ethanol including the stereospecificity of the various reactions is presented.
Near-Infrared Spectra of H2O—D2O Solutions
Authors: Worley John D. , Klotz Irving M.
Published: January 2005

Near-infrared spectra have been obtained for HOD in D2O solutions containing a variety of solutes. A sharp band occurs at 1.416 μ (7062 cm−1) and other bands at 1.525 (6557 cm−1), 1.556 (6427 cm−1), and 1.666 μ (6002 cm−1). The absorbances at 1.416 and 1.556 μ increase and decrease, respectively, with increasing temperature. From this variation, a ΔH° of formation of −2.4 kcal/mole has been estimated for the O–H···O bond in these solutions.

Nineteen electrolytes and one polymer, polyvinylpyrrolidone, have been examined for their effects on the spectra of water in this overtone region. No frequency shifts have been observed with added solute, only changes in absorbance. Sodium perchlorate shows the strongest structure-breaking effect. Tetrabutylammonium bromide and polyvinylpyrrolidone exhibit structure-making character. A definite correlation has been found to exist between the effects of salts on the aqueous solvent and their ability to affect the conformation of a macromolecule.
Collisional Deactivation of Excited Oxygen Atoms in the Photolysis of NO2 at 2288 Å
Authors: Preston K. F. , Cvetanović R. J.
Published: January 2005

The isotopic composition of the oxygen produced from the 2288-Å photolysis at room temperature of NO2 in the presence of C18O2 has been measured as a function of the pressure of various additive gases. A simple reaction mechanism involving reactions of excited oxygen atoms is postulated to explain the results and leads to the following relative rates of electronic deactivation (including chemical reaction, where possible) of the excited atoms: CO2, 1.00; Ar, 0.01; Kr, 0.06; Xe, 0.78; N2, 0.24; N2O, 1.02; NO2, 1.62; C3H8, 4.67; and SF6, close to zero. The close correspondence of these relative rate constants to the values obtained from studies of the photolysis of N2O at 1849 Å suggests that the results for the photolyses of both N2O and NO2 refer to the same species of excited atom, namely O(1D2).
Absorption and Ionization Coefficients of Vinyl Chloride
Authors: Sood S. P. , Watanabe K.
Published: January 2005

Absorption coefficients of vinyl chloride were measured by a photoelectric method at many wavelengths in the region 1075–2000 Å, and photoionization yields were obtained in the region 1075–1240 Å with an ion chamber. Many bands were identified as members and their vibrational companions of four Rydberg series and one other electronic transition. These Rydberg series and the photoionization curve yielded the same ionization potential of 10.00±0.01 eV.
Electron Spin Resonance of the Excited Triplet States of Pyrimidines and Purines
Authors: Shulman R. G. , Rahn R. O.
Published: January 2005

The electron spin resonances of the metastable triplet states of various pyrimidines and purines have been observed in ethylene glycol: H2O glasses at 77°K. Generally the Δm=2 transitions were observed and the parameter of spin—spin interaction determined was (D2+3E2)½. However for orotic acid, guanylic acid, and adenylic acid it was possible to observe the Δm=1 transitions and to determine D and E separately. From the values of D and E and the decay times, which were all >0.2 sec, it was possible to characterize the lowest triplet states as π—π* states in all cases. For thymine, 5-methylcytosine, and orotic acid the values of D (and E) agreed quite well with those calculated approximately for π—π* states from Hückel molecular orbitals.

In addition to resonances attributed to neutral molecules, additional resonances were observed for the ionized states of azathymine, thymine, 5-methylcytosine, and 5-hydroxymethylcytosine. From the pH dependence of azathymine and thymine it was possible to show that one resonance appeared when the molecule lost its first proton (T−) and the second resonance replaced it when the molecules had lost two protons. The T− resonance was also observed in TMP and thymidine at pH values above 9.8 where they each lose the N3 proton. However, these compounds did not show the resonance characteristic of the doubly ionized state, presumably because they contain only one ionizable proton. In 5-methylcytosine and 5-hydroxymethylcytosine, one resonance was observed in the neutral molecules. Above pH 12.4, which corresponded to the pK value for the loss of a proton, a different resonance was observed. In 5-methylcytidine, in which the ionizable proton has been replaced by a ribose, only one resonance, characteristic of the neutral molecule, is observed. It is suggested that these results on the lowest triplet state can all be explained by dominant resonance structures in which double bonds switch from the carbonyl group to the ring.
Observation of the D 1Δ→X 1Σ+ Transition of CO in the Vacuum-Ultraviolet Region
Authors: Simmons J. D. , Tilford S. G.
Published: January 2005

Weak new bands in the vacuum-ultraviolet absorption spectrum of CO have been observed and analyzed as the D 1Δ←X 1Σ+ (1–0) bands for both 12C16O and 13C16O. The observed rotational intensity distribution indicates this transition arises through mixing of the D 1Δ state with neighboring states, principally the A 1II state of the strong electric-dipole-allowed fourth-positive system. A brief correlation of observed electronic states with those arising from various electronic configurations is given.
Lambda-Doubling Effect on Molecular Electric-Field Gradient and Nuclear-Quadrupole Coupling
Authors: Chiu Ying-Nan
Published: January 2005

Physical reasons and mathematical arguments are given to show that for a rotating linear molecule or radical, between the degenerate [open phi]+Ω and [open phi]−Ω electronic states of opposite senses of angular momentum, there exists a ``cross-term'' matrix element connected by a nonaxial field-gradient-tensor operator (∇E)2Ω=T2,2Ω/re5. The resulting effect is that the electric-field gradients eq for the two Λ-doubling components are different, giving rise to an additional nuclear-quadruple contribution to the Λ-doubling energy. When the nuclear spin is quantized with respect to the space z axis as in a molecule belonging to Case aβ (Sec. III), it is shown that because the nuclear quadrupole tensor operator transforms with a rotation matrix of the second rank, such Λ-doubling effect on field gradient vanishes for the 2Π½(a) state. For a Case bβ2Π state and a 2Π state intermediate between Cases a and b, the dependence of this effect on J is derived using wavefunctions with a consistent phase and inversion symmetry not otherwise obtainable from the solution of a secular equation. For states with Ω=0 (Table I) the effect is shown to arise from electron spin and orbital interaction in a stationary molecule. For 3Π1(a) and 1Π states, the relative sizes of the ``nonaxial field gradient'' eq2, and the axial field gradient, eq0, are estimated using open-shell electron configurations constructed from one-electron molecular orbitals. The general selection rule based on Ω, the total spin and orbital angular momentum, for the matrix elements over the spinless, one-electron field-gradient operator is justified for various open-shell electron configurations by invoking electron spin—spin interaction in addition to the customary electron spin—orbit interaction. A general method is devised for obtaining diagonal and off-diagonal spin—spin interaction matrix elements over Slater determinantal wavefunctions. In terms of these interactions the relative importance of these configurations of equivalent as well as nonequivalent electrons is given. When the nuclear spin is quantized with respect to the molecular figure axis as in a molecule belonging to Case aα (Sec. V), the additional nuclear quadrupole splitting of the Λ-doubling levels is shown to be independent of J and to be present in states with ΩF=0 only, when the molecule is rotating.
Adiabatic Dissociation Energies for the Ground States of the H2, HD, and D2 Molecules
Authors: Hunter G.
Published: January 2005

Variational adiabatic potential curves for the ground state X 1Σg of these molecules were constructed from the adiabatic coupling corrections computed by Kol/os and Wolniewicz. Energy eigenvalues of these variational potentials were computed. The derived dissociation energies are still larger than those inferred from the spectra of the molecules. It is suggested that the resolution of this discrepancy is more likely to be found in a reinterpretation of the experimental data than through any refinement of theoretical calculations.
Thermal Diffusion in Polyatomic Gases: A Generalized Stefan—Maxwell Diffusion Equation
Authors: Monchick L. , Munn R. J. , Mason E. A.
Published: January 2005

A study is made of the influence of inelastic processes on thermal diffusion in polyatomic gases, based on the Wang-Chang—Uhlenbeck—deBoer treatment of the Boltzmann equation, in which it is assumed that the distribution function for molecular spins is isotropic. A generalized Stefan—Maxwell diffusion equation is obtained for multicomponent mixtures of polyatomic gases, carried to the second Chapman—Enskog approximation. The external form of this equation is the same as the well-known result for monatomic gases, but contains higher-order corrections for the binary diffusion coefficients (i.e., the composition dependence of these coefficients), and correction terms for the effect of inelastic collisions on the diffusion and thermal-diffusion coefficients. Numerical calculations for several selected systems show that the effects of inelastic collisions on the thermal-diffusion factor are not negligible and must be considered in any attempt to derive information on intermolecular forces from thermal-diffusion measurements. However, inelastic effects are not capable by themselves of explaining the known anomalies in systems such as Ar–HCl and D2—HT.
Semiempirical Treatment of Hindered Rotation. II. Molecules Possessing Double Bonds
Authors: Lowe John P.
Published: January 2005

A method using electrostatic models, presented earlier for ethanelike molecules, is extended to include systems containing double bonds. Models are developed for the prototype molecules acetaldehyde, propylene, and methyl ketene. The principal barrier-producing features in these molecules, exclusive of the hydrogen adjacent to the methyl group, are taken to be, respectively, nonbonding, sp2 hybridized electron pairs on oxygen, the cis C–H bonding electrons, and the pi electrons in the C=O bond. These models are shown to predict reasonably well the barriers in vinyl silane and N-methylmethylenimine, and to be consistent with observed barriers for methyl isocyanate and methyl allene. They also are shown to be capable of rationalizing observed trends in barrier values upon halosubstitution for methine or carbonyl hydrogen in propylene and acetaldehyde when inductive and resonance effects are considered. Implications of the models for molecules with double bonds more removed from the methyl group, such as propionaldehyde, are considered, and conditions for steric repulsion are shown to be present in cases where the models fail. The connection between the models and the detailed shapes of the barriers is discussed, and some values of V6 as computed from the models, are given. Rough predictions are made of barriers for molecules derived from prototypes by halo substitution or by substitution of a methyl group by a silyl group. Problems involved in extending the method to molecules with onefold rotors are considered, and illustrative calculations are made for nitrous acid and formic acid.
Electric Anisotropy of Tridymite as Revealed by Electron Diffraction
Authors: Yamaguchi S.
Published: January 2005

An electron beam served to charge the specimen and simultaneously was diffracted by this specimen. Analysis of the diffraction pattern obtained permits one to see that the easy polarization direction of tridymite lies parallel to the c axis of a hexagonal lattice. This diffraction pattern has been registered with the wavelength fluctuating between 0.0295 and 0.0333 Å. The inner field induced within the specimen was about 0.6 V/Å along the c axis.
Quadrupole-Allowed Transitions in the Electron-Impact Spectrum of N2
Authors: Lassettre Edwin N. , Skerbele Ausma , Meyer Vincent D.
Published: January 2005

The forbidden transitions observed in the nitrogen spectrum below 12.5 V have been studied by electron-impact methods. Since the theory indicates that electric quadrupole transitions are preferred to singlet—triplet in electron-impact spectra at intermediate energies, the observed transitions are probably electric quadrupole allowed. This has been demonstrated for the 12.25-V transition by studying its relative intensity as a function of the scattering angle. The data on the 11.86-V transition are also compatible with an electric quadrupole transition. In addition, new data on the Lyman—Birge—Hopfield bands in the 60–400-V energy range indicate that the intensity distribution among vibrational levels is independent of energy.
Low-Lying Energy Levels of Magnesium Oxide
Authors: Richards W. G. , Verhaegen G. , Moser C. M.
Published: January 2005

The low-lying valence levels of MgO are calculated by the LCAO MO SCF method using an extended basis set, in order to ascertain the nature of the ground state of the molecule. Three configurations were computed ab initio using open-shell variational procedures for the excited states. Term values are obtained from the minima of the computed potential curves together with estimates of correlation energy differences between the configurations. The calculations indicate a closed-shell 1Σ+ ground state but with very low-lying (0.3 eV) 3Π and 3Σ+ levels. The electronic partition function of the molecule is recalculated and hence the published dissociation energy adjusted. D0°(MgO) is lowered by 4.5 kcal mole−1. Possible experimental consequences of the proximity of the triplet states to the ground state are discussed.
Reaction of Methylene with Dichloromethane and Nonequilibrium Unimolecular Elimination Reactions of 1,1-C2H4Cl2 and 1,1,2-C2H3Cl3 Molecules
Authors: Hassler J. C. , Setser D. W.
Published: January 2005

The gas-phase reaction of methylene with dichloromethane proceeds by Cl and H abstraction. The two reactions are competitive, although the ratio of rates depends upon the excess energy carried by the methylene and its electronic state. The total rates of reaction of CH2 with CH2Cl2 and with C2H4 are comparable. The methyl, chloromethyl, and dichloromethyl radicals that are generated by the CH2 abstraction reactions form a good chemical activation system for studying the HCl elimination reactions of C2H5Cl, 1,2-C2H4Cl2, 1,1-C2H4Cl2, and 1,1,2-C2H3Cl3 at energies of ∼90 kcal mole−1. The results for the first two molecules agree with previous work; the rate constants for 1,1-C2H4Cl2 and 1,1,2-C2H3Cl2 are 1.2×1010 and 3.4×108 sec−1, respectively. Unusual ``disproportionation''-type reactions in which chloroethenes and HCl are directly formed seem to occur between dichloromethyl and methyl or chloromethyl radicals.
RRKM Calculated Unimolecular Reaction Rates for Chemically and Thermally Activated C2H5Cl, 1,1-C2H4Cl2, and 1,2-C2H4Cl2
Authors: Hassler J. C. , Setser D. W.
Published: January 2005

The RRKM theory of unimolecular reactions has been applied to the HCl elimination reactions of C2H5Cl, 1,1-C2H4Cl2, and 1,2-C2H4Cl2, in both chemical and thermal activation systems. The experimental data are adequately represented by a model which employs a four-center transition state. For example, the model for C2H5Cl gives a pre-exponential factor of 1.14×1013 compared to the experimental value of 0.97×1013. The calculated and experimental nonequilibrium rate constants for C2H5Cl formed by combination of CH3 and CH2Cl radicals are 1.7×109 and 2.6×109 sec−1, respectively. Various models for the molecule were investigated in an attempt to represent the torsional degree of freedom of the molecule and its interaction with over-all rotation. Also several models for the activated complex were studied. For the present data, the conclusions presented are as follows: (1) RRKM theory with all internal degrees of freedom taken as active, satisfactorily reproduces the observed data for these four-center elimination reactions; (2) the torsional degree of freedom can be adequately represented as a low-frequency vibration and the over-all rotational degree of freedom about the ``figure axis'' need not be considered active. The activated complex models developed in this work are significantly different from the models developed by Benson and Haugen for the empirical calculation of activation energies for the H—X+olefin reactions.
Microwave Spectrum of Acetyl Iodide
Authors: Moloney Michael J. , Krisher Lawrence C.
Published: January 2005

The microwave spectra of CH3COI and CD3COI were investigated in the region 8000 to 27 000 Mc/sec. The effects of internal rotation and quadrupole perturbations were found to be essentially independent. The height of the potential barrier hindering the methyl group internal rotation was determined to be 1301±30 cal/mole from measured CH3COI doublet splittings. Level mixing was found for several pairs of rotational states, analogous to Fermi resonance in vibrational levels. Mixing effects permitted determination of the quadrupole coupling constant χab in both isotopic species. The values for quadrupole coupling constants in CH3COI are χaa=−1563±2, χbb=914±2, and χab=−135.6±2 Mc/sec. In CD3COI the values are χaa=−1541±3, χbb=892±2, and χab=−258.5±10 Mc/sec. Diagonalization of each of the above tensors gives χαα=−1569 and χββ=920 Mc/sec.
Low-Frequency Motions of H2O Molecules in Crystals. III
Authors: Prask Henry J. , Boutin Henri
Published: January 2005

The scattering of low-energy neutrons (0.005 eV) has been used to study translational and librational motions of H2O molecules in various configurations in crystals in a frequency region lying below 1000 cm−1. An attempt is made in this paper to determine the effects of various cations and anions on the frequencies of intermolecular motions of H2O molecules in crystalline salts. The neutron spectra were obtained for a series of hydrates in which the H2O is hydrogen bonded to the same anion, Cl−, but on the sphere of coordination of different cations (Al3+, Cr3+, Sr2+, Ca2+, Fe2+, Mg2+, Co2+, Ni2+) and for Al salts with different anions (NO3−, SO42−, Cl−). This investigation tends to suggest that the vibrational frequencies of the H2O molecules are strongly dependent upon the degree and strength of coordination of the molecule as well as upon the degree and strength of the hydrogen bonds formed with neighboring anions or H2O molecules.