bluuebunny/crossref_metadata_2025 huggingface dataset:
Radiation Chemistry of Polyethylene. VIII. Kinetics of Growth and Decay of Polyene and Polyenyl Free Radical Groups
Authors: Bodily David M. , Dole Malcolm
Published: January 2005

Free radicals produced as intermediates during the radiolysis of polyethylene have been most frequently studied by ESR techniques. We have now used ultraviolet absorption spectroscopy because the uv absorption bands of the allyl, dienyl, and trienyl conjugated free radicals are well separated on the wavelength scale and do not overlap as do the ESR signals from these intermediates. Stable polyenes are also produced by the radiolysis and these groups can also be studied quantitatively by ultraviolet spectroscopy. In contrast to the diene groups whose concentration grows linearly with the dose, the allyl and dienyl free radicals as well as conjugated trienes grow with increasing rates as the irradiation proceeds. In fact, a statistical calculation of the triene growth reaction rate constant in terms of the diene concentration and a probability factor based on the vinylene growth rate has been quite successful. From this result and others it is concluded that trienes and allyl, dienyl, and trienyl free radicals are not primary products of the irradiation. The effect of ultraviolet light on the allyl and dienyl free radicals has also been studied. In agreement with others we find that uv light decreases the allyl free radical concentration; however, the dienyl and trienyl concentrations increase. On standing after the uv irradiation the allyl groups recover practically their initial abundance—but the dienyl and trienyl free radical concentrations continue to grow. Various mechanisms are discussed.
Occurrence of a Phase Transition in Nucleic Acid Models
Authors: Poland Douglas , Scheraga Harold A.
Published: January 2005

The double-stranded helix found in nucleic acids suggests a model where order is represented by specific, one-to-one bonding between two infinite chains and where disorder arises from the formation of large loops. The statistical weight per unit in an unordered sequence (i.e., a loop) is given by (1/i) lnui=a—(1/i) (b+clni). This quantity becomes large, as i is increased, slower than 1/i because of the c lni term. From the previous paper, this suggests that a first-order phase transition may take place. It is found that this happens if c>2, in which case both U(x) (the sequence generating function for loops) and ∂U(x)/∂x converge at the point where x1 (the unit partition function) equals u2 (the statistical weight per unit of an infinite loop, i.e., a free chain). If 2>c>1, then U(x) converges at x1=u2 but ∂U(x)/∂x does not. For a loop in three dimensions, c would be about 32 (½ for each dimension); hence, there is no discontinuity in θ, the fraction of ordered states, for a real system. However, θ does behave nonanalytically at x1=u2, giving a continuous or higher-order transition. Specifically, θ does go exactly to zero in the transition region. This is a qualitative difference from infinite polypeptides where the sigmoidal transition curve goes asymptotically to 1 and 0 at the extremes of temperature. Explicit calculations are given for various values of c to illustrate the behavior of the model.
Electron Spin Resonance of Copper (II) Citrate Chelates
Authors: Dunhill R. H. , Pilbrow J. R. , Smith T. D.
Published: January 2005

Electron spin resonance (ESR), paramagnetic susceptibility, and polarographic measurements have been made of copper (II) citrate chelates over a wide range of pH. The signal observed at pH 4 is typical of that found for copper (II) in a distorted octahedral environment. With increasing pH the signal becomes less intense and is replaced by a much broader spin resonance observable at relatively high concentrations of copper (II) and in frozen solutions. At pH's of about 11, a third signal is observed. The broad signal has been interpreted in terms of dipole—dipole coupling of copper (II) ions arising from dimer formation. Measurements show that the paramagnetic susceptibility is independent of pH. Solution of the spin Hamiltonian including the dipole—dipole interaction has made possible calculation of the line shape for the dimer signal. The calculations have led to a value of 3.1 Å as the distance between the copper (II) dipoles and to the conclusion that each copper (II) ion is in a | 3z2—r2〉 ground state rather than | x2—y2〉. The ESR data provides very strong evidence for the formation of a dimer in solution and allows reinterpretation of the data found in the literature. The signal observed beyond pH 11, with its partly resolved hyperfine structure at room temperature, is attributed to a monomer formed as a result of replacement of the hydrogen from the hydroxy group of the citrate anion by copper (II).
Photo- and Radiation-Induced cis—trans Isomerization of Several 2-Olefins
Authors: Golub M. A. , Stephens C. L. , Brash J. L.
Published: January 2005

Benzene photo- and radiation-sensitized cis-trans isomerization of 2-pentene, 2-hexene, 2-heptene, and 2-octene all yield the same photo- and radiostationary trans/cis ratio, viz., 1.0. The G value for benzene triplet formation is estimated at 5.0. G values for the radiation-induced unsensitized isomerization of the above olefins are 2.50, 2.13, 1.85, and 1.67, respectively.
NMR Studies of 7Li in Polycrystalline Lithium Nitride
Authors: Bishop S. G. , Ring P. J. , Bray P. J.
Published: January 2005

The 7Li NMR spectrum for polycrystalline lithium nitride has been examined as a function of both temperature and magnetic field. Two central m=½ to m=—½ transitions and two pairs of m=±32 to m=±½ satellite transitions have been observed; these results are consistent with the presence of the two nonequivalent lithium sites in the known crystal structure of Li3N. The quadrupole coupling constants for the two lithium sites, as determined from the frequency separation of the satellite transitions, are 288±4 and 584±6 kc/sec at room temperature. These values are in good agreement with those determined from the field dependence of the second-order quadrupolar widths of the two m=½ to m=—½ transitions. The central transitions have been examined as a function of temperature at a resonant frequency of 16 Mc/sec, where the linewidth is determined primarily by dipolar effects. As the temperature is increased from 77°K, the linewidths remain relatively constant at low temperatures but narrow abruptly between roughly −75°C and room temperature. The observed narrowing is attributed to the diffusion of lithium ions.
Electronic Structure of the First Excited State of CO. I. SCF Wavefunction Calculated in the Restricted Hartree—Fock Formalism
Authors: Huo Winifred M.
Published: January 2005

An SCF wavefunction calculated in the restricted Hartree—Fock formalism is reported for the lowest excited state (a 3II) of CO. The expansion method is used and exponents are optimized. Even though the calculated energy and Hellmann—Feynman forces are reasonable, there is a large discrepancy between the calculated and experimental dipole moment. The discrepancy is caused by the fact that the restricted Hartree—Fock function for open-shell systems does not satisfy Brillouin's theorem and first-order corrections come in. In particular, it is found that the charge-transfer states have a large first-order effect on the dipole moment. Some preliminary results on the isoconfigurational A 1II state are reported. They indicate that the charge distributions of the two isoconfigurational states are quite different.
Thermodynamic Properties of Condensed CO
Authors: Gill E. K. , Morrison J. A.
Published: January 2005

Thermodynamic properties (heat capacities; vapor pressures; heats of transition, fusion, and vaporization) of condensed CO containing 2.6±0.4% N2 have been measured between 2.5° and 78°K. No anomalies nor unusual thermal behavior were observed at the lowest temperatures. The dielectric constant of the pure solid has been measured between 6°K and the melting point and found to be close to unity over the entire temperature range. The residual entropy of CO is discussed in the light of these results.

The N2 impurity displaces the melting and solid transition regions to lower temperatures but does not appear to alter their forms. Analyses of the vapor-pressure data show that the liquid solution of N2 in CO is nearly an ideal one. Deviations from ideality occur in the solid phases, particularly in the α phase that exists in the region T<61°K.

A simple argument, based on the temperature dependence of the equivalent characteristic temperature for the entropy of the α phase, supports the view that CO molecules librate in the crystal and places an upper limit of 85 cm−1 on the librational frequency. This is to be compared with an average value of 70 cm−1 estimated from the optical spectrum of the crystal.
Molecular Collisions and the Depolarization of Fluorescence in Gases
Authors: Gordon R. G.
Published: January 2005

The polarization of fluorescence is expressed in general as the Laplace transform of a correlation function for molecular reorientation. In a dilute gas of linear molecules, the polarization is shown to be determined by the reorientation angle α through which the molecular angular momentum is rotated by collisions. This reorientation angle appears through a collision cross section proportional to sin2α, integrated over all collision impact parameters. The predicted density dependence of the polarization of total fluorescence is in good agreement with previous measurements of iodine fluorescence. If the fluorescence emission is also resolved into rotation—vibration lines, then polarization measurements allow detailed study of the reorientation by collisions which also produce specific changes in the rotational and vibrational quantum numbers.
Determination of Intermolecular-Potential Parameters from Induced Infrared Spectra: The Complex H2–Ar
Authors: Cashion J. K.
Published: January 2005

A Lennard-Jones 12–6 potential has been used to calculate the induced infrared absorption spectrum for the interaction of argon with molecular hydrogen. The results confirm the conclusion of Kudian, Welsh, and Watanabe that the observed spectrum is due in part to bound H2–Ar complexes. However, the calculations show that some changes are necessary in the tentative assignments which they made on empirical grounds. It is shown that the potential minimum Rm can be determined much more accurately from the spectrum than can the well depth ε. For H2–Ar, the combining rule, σ=½(σ1+σ2), is accurate to within at least 2%. The combining rule for well depth, ε=(ε1ε2)½, holds to within at least 10%.
Deuteron Quadrupole Coupling Constant in CH3D
Authors: Caves T. , Karplus M.
Published: January 2005

The deuteron electric-field gradient qD and quadrupole coupling constant (eqQ/h)D for CH3D have been calculated from extended basis-set LCAO-MO-SCF wavefunctions determined by Woznick for this system. Comparison of the results for different wavefunctions and different distances suggest that a reasonable theoretical estimate is (eqQ/h)D=210±30 kc/sec. Since this disagrees significantly with the present experimental estimate [(eqQ/h)D=100±50 kc/sec], a more refined measurement would be desirable.

Simplified schemes are examined for calculating (eqQ/h)D with neglect of three-center integrals or introduction of a two-center model; errors of 5% to 20% result.
Mass-Spectrometric Investigation of the Nickel—Fluorine Surface Reaction
Authors: McKinley John D.
Published: January 2005

Mass-spectrometric measurements have been made of the reaction of polycrystalline nickel at temperatures between 900° and 1600°K with fluorine at pressures between 10−7 and 10−4 torr. Gaseous NiF, NiF2, and F are the major products, and are formed rapidly on the surface at rates linear with fluorine pressure. NiF is present on the surface over the entire temperature range and desorbs above 1100°C; the desorption step involves rupture of a Ni (substrate)—NiF bond and has an activation energy of 28 kcal mole−1. NiF2 formation and desorption are important between 900° and 1600°K with a maximum rate at 1250°—1300°K. The rate-limiting step in the formation of NiF2 has an activation energy of 39 kcal mole−1 and is probably dissociation of fluorine on the surface.
Microwave Spectra of Some Isotopically Substituted Phenols
Authors: Forest Harvey , Dailey B. P.
Published: January 2005

The rotational spectra of C6H518OH, C6D5OH, and C6D5OD were successfully analyzed to obtain their respective rotational constants in the region from 20 000 to 31 000 Mc/sec. The splitting of the rotational transitions due to the hindered internal rotation of the hydroxyl group was noted in C6H518OH and C6D5OH while the spectrum of the C6D5OD isotope was unsplit. As is the case in C6H516OH, the high barrier to internal rotation produced a doublet spectrum, where the splittings were effectively independent of the J transition and correspond to 115 and 103 Mc/sec for the C6D5OH and C6H518OH isotopes, respectively. The experimental rotational constants are: IsotopeA(Mc/sec)B(Mc/sec)C(Mc/sec)C6D516OH4682.677±0.0062422.815±0.0041596.930±0.004C6D516OD4654.378±0.0052342.102±0.0041558.383±0.004C6H518OH5650.076±0.0082487.321±0.0051727.232±0.005.

It was found that the structure of the C–O–H fragment could not be uniquely determined from the rotational constants. Two structures were found which were essentially the same except for C–O–H configuration relative to the internal rotation axis. Both structures fit the experimental spectra equally well and have standard deviations of 3.2 Mc/sec. The parameters for Structures (I) and (II) are, respectively: C–C, 1.3956±0.0002 and 1.3954±0.0002 Å; C–H, 1.081±0.001 and 1.082±0.001 Å; O–H, 0.985±0.01 and 0.944±0.009 Å; C–O, 1.370±0.001 and 1.379±0.001 Å; COH, 111.87±0.35 and 105.04±0.35 deg; α (off angle from rotation axis), 6.34±0.60 and −11.17±0.50 deg.

In Structure (I) the oxygen and hydrogen are on the same side of the internal rotation axis while in Structure (II) they straddle it. Structure (II) is believed to be the more reasonable.

Neither C–O–H structure could correlate the splitting data to one value of the barrier height, but good agreement was obtained if the moment of inertia of the hydroxyl group was based on CH3OH. The barrier height obtained was 1150 cm−1.
Comparison of Dielectric and Mechanical Relaxation Processes in Glycerol—n-Propanol Mixtures
Authors: Kono R. , Litovitz T. A. , McDuffie G. E.
Published: January 2005

Dielectric and shear mechanical relaxation data are reported for mixtures of glycerol and n-propanol. Measurements of the dielectric permittivity were made at −60° over a frequency range from 50 cps to 600 kc/sec and indicate a distribution of dielectric relaxation times of the Davidson—Cole form. This distribution was observed to narrow with increasing n-propanol content. Shear mechanical measurements in the temperature range +10° to −150°C and frequency range 10 to 130 Mc/sec indicate a broad distribution of times which is essentially independent of the relative concentration of the two components of the mixture.

The width of the dielectric distribution is shown to be a function of the ratio of the average dielectric to shear relaxation times, τ̄D/τ̄S, becoming narrow as this ratio becomes large. These results are in accord with the concepts of McDuffie and Litovitz who proposed that the origin of the distribution of dielectric relaxation times is related to a cooperative breakup of the liquid structure and that the effects of this structural breakup on the dielectric process are lessened when the dielectric reorientation process takes a much longer time than the structural breakup.

In pure n-propanol it is found that τ̄D/τ̄S is temperature dependent in contrast to a temperature-independent ratio in glycerol. In order to explain these results, it is suggested that the local free volume in n-propanol needed for dielectric orientation is larger than that needed for the shear process. Using the free-volume theory of Macedo and Litovitz it is estimated that in pure n-propanol the critical local free volume for dielectric orientation is 40% larger than the critical local free volume for shear flow.
Electron Spin Resonance Spectrum of ClO4 Trapped in Irradiated KClO4
Authors: Morton J. R.
Published: January 2005

Two paramagnetic centers have been detected in KClO4 crystals γ irradiated at 77°K. After consideration of the various possibilities it is concluded that the centers may be described as ClO4 radicals trapped in magnetically distinct sites.
Remarks on the Use of Approximate Wavefunctions for the Second-Order Perturbation Energy
Authors: Dougherty T. J. , Vladimiroff T. , Epstein S. T.
Published: January 2005

The use of approximate ground-state wavefunctions in the calculation of interaction energies by second-order perturbation theory (e.g., calculation of spin—spin coupling constants in nuclear magnetic resonance) has been investigated. It has been found that the approximate zero-order ground-state wavefunction must satisfy a stringent condition if reliable results are to be obtained. The condition is that the approximate ground-state energy must lie below the true energy of the first excited state. This condition is rarely met for molecules more complicated than hydrogen, and hence reasonable results can be obtained only by a fortuitous cancellation of errors.
Transition Moment of the First Positive Band System of Nitrogen
Authors: Jeunehomme M.
Published: January 2005

The light decay after interruption of a pulsed rf discharge was analyzed in the nitrogen first positive system as a function of nitrogen pressure and wavelength.

Values for the natural lifetime of a number of vibronic levels of the B 3IIg state were deduced. The variation of the electronic transition moment over internuclear separation was investigated. The results were found to be dependent on the potential model assumed in the calculations of the Franck—Condon factors. A value of about 2×10−3 is proposed for the oscillator strength f0,0.
Molecular Distributions at Equilibrium. V. Statistical-Mechanical Treatment of Ring—Chain Equilibria
Authors: Levy Richard M. , Van Wazer John R.
Published: January 2005

Partition functions are set up for chain—chain and ring—chain equilibria of the type found in families of compounds in which unbranched molecules exchange parts. It is shown that all of the terms, except the partition function for nonbonded interactions within the molecule, cancel in the case of the chain—chain equilibrium constant, but the constants for equilibrium between the chain population and variously sized rings is considerably more complicated, with torsional freedom being the dominant factor. The terms making up the ring—chain constant are discussed and the ideas resulting therefrom are applied to the available experimental data.
Absolute Infrared Intensities of Some Linear Triatomic Molecules in the Gas Phase
Authors: Yamada Haruka , Person Willis B.
Published: January 2005

Infrared intensities for the low-frequency bending vibrations ν3 have been measured by the curve-of-growth method for N2O, COS, and CS2 in the gas phase. The intensity of ν3 for gaseous COS has been measured by the same method. These results help to determine which of the values reported previously are to be preferred. These preferred values are listed for the intensities of all the fundamental vibrations.
Irreducible Cluster Integrals of Hard-Sphere Gases. II
Authors: Kilpatrick J. E. , Katsura Shigetoshi
Published: January 2005

It is shown that a class of irreducible clusters of hard-sphere gases can be evaluated by a multiple-series method by changing the integration variable from position vectors to bond vectors and from bond vectors to face vectors using bond—face transformation. The class includes graphs which were intractable so far, for example, Nos. 9 and 10 clusters of the fifth virial coefficient. The value of the fifth virial coefficient E of the hard-sphere gases is recalculated and is found to be 0.11040±0.00006, which has maximum accuracy among values so far obtained.
Electronic Structure of Sulfate, Thiosulfate, and Related Ions. I. Calculation of Molecular Orbital Energy Levels
Authors: Bishop David M. , Randič M. , Morton J. R.
Published: January 2005

The results of a semiempirical molecular orbital calculation on the ions SO4−, SO42−, S2O3−, S2O32−, S2O33− are reported and discussed.
Electronic Structure of Sulfate, Thiosulfate, and Related Ions. II. ESR Spectra of SO4− and S2O3−
Authors: Morton J. R. , Bishop David M. , Randič M.
Published: January 2005

The radical ions SO4− and S2O3−, trapped in γ-irradiated K2SO4 and Na2S2O3·5H2O crystals, respectively, have been identified by their ESR spectra. In the preceding paper molecular orbital calculations were described the results of which predict a ···1t163t262a1, 2A1 (symmetry Td) configuration for SO4− and a ···5e45a1, 2A1 (symmetry C3v) configuration for S2O3−. The ESR data show that in the K2SO4 crystal the symmetry of SO4− is no higher than C2v and so correlation with the predicted configuration was inconclusive. In the case of S2O3−, however, the spectral parameters possessed axial symmetry, the ···e4a1, 2A1 configuration being confirmed by the nature of the hyperfine and g tensors.
Wannier Excitons in Anthracene
Authors: Gerhold George A.
Published: January 2005

The high-resolution absorption spectrum of crystalline anthracene is presented. It contains a series of 10 weak bands on the shoulder of the first electronic transition polarized in the b direction. The series can be reproduced via a Rydberg formula which is characteristic of Wannier exciton levels. The effect of impurities and the relation of this Wannier exciton series to the photoconductivity are discussed briefly.
NMR Spectra of Some Nitroxide Radicals
Authors: Kreilick Robert W.
Published: January 2005

We have studied the NMR and ESR spectra of t-butyl−2,6-dimethoxyphenylnitroxide and di-t-butyl-nitroxide. Isotropic coupling constants were calculated from the shifts of the nuclear resonance lines. The calculated coupling constants agree with the ESR spectra.
Ion—Molecule Reactions of Methane
Authors: Abramson Fred P. , Futrell Jean H.
Published: January 2005

The ionic reactions of gaseous methane have been investigated in a tandem mass spectrometer. The reactions of each primary ion, CH4+, CH3+, CH2+, CH+, C+, have been observed at 0.3 eV and several secondary-ion reactions have also been studied. An investigation of the effects of translational energy on many of these reactions demonstrated the efficient conversion of translational energy into internal energy. Evidence for randomization of the intermediate [C2HxD7−x+] ion in the methyl-ion—methane reaction is presented. Isotope effects in hydrogen-transfer reactions have also been investigated as a function of kinetic energy. The results are interpreted in terms of a transition from a complex model of reaction to a stripping model at higher energies.
Resolution of Fine Structure in Ionization-Efficiency Curves
Authors: Winters Robert E. , Collins Jerome H. , Courchene William L.
Published: January 2005

An energy-distribution difference method for determining ionization potentials and for detecting fine structure, i.e., breaks, in ionization-efficiency curves is described which eliminates the difficulties arising from the thermal-energy spread of the ionizing electrons. Although the technique gives essentially the same results as monoenergetic methods, it is much easier experimentally. Ionization-efficiency curves are given for the inert-gas ions Ar+, Kr+, and Xe+ as well as the molecular ions CO+, N2+, and O2+. The ``breaks'' in the efficiency curves are presented and the results are compared to previously reported monoenergetic electron-impact data.
Intermolecular Potential Function for Periodic Linear Arrays
Authors: McCullough R. L. , Hermans J. J.
Published: January 2005

An expression is developed for the interaction energy between rows of periodic force centers. In contrast to previously reported functions, this expression explicitly exhibits the periodicity of the array. Consequently, the activation energy for rigid row ``slip'' is defined in fundamental parameters. The expression was developed from a Mie potential for point-pair interactions by the assumption of pair wise additivity. Constructions are suggested which reduce complicated systems to the simple geometry of the row model.
Paramagnetic Resonance Study of Liquids during Photolysis. II. Acetone and Solutions Containing Acetone
Authors: Zeldes Henry , Livingston Ralph
Published: January 2005

Paramagnetic resonance spectra in liquid acetone and acetone solutions were studied during the course of intense irradiation with ultraviolet light. In the presence of RH, an alcohol or ether, which served as a good hydrogen donor, both radicals of the reaction CH3COCH3+RH→(CH3)2ĊOH+Rwere seen. The abstracted H atom was taken from the carbon alpha to the O atom of the alcohol or ether. When pure liquid acetone was photolyzed, both radicals of the reaction CH3COCH3+CH3COCH3→(CH3)2ĊOH+ĊH2COCH3were seen. In addition some ĊH3 was seen. Higher concentrations of ĊH2COCH3 and ĊH3 were produced by photolyzing acetone containing 1% H2O2. In the latter case, it is believed that the radical OH was produced from the H2O2. The OH radical then abstracted an H atom from acetone to give ĊH2COCH3. It is thought that ĊH3 resulted from the reaction CH2COCH3→H2C=C=O+ĊH3.Accurate measurements were made of the g values and hyperfine parameters for (CH3)2ĊOH, ĊH2OH, and CH3ĊHOH in both water-rich and acetone-rich solutions at room temperature; for CH3CHOCH2CH3 in acetone solution at room temperature; for CH3 in acetone at −53°C; for ĊH2COCH3 in acetone at room temperature and at −49.5°C; and for the radical resulting from the loss of one of the H atoms of dioxane in acetone solution at room temperature. It was found that the OH-proton hyperfine coupling of CH3ĊHOH in aqueous solution could be carried through the value zero by changing the temperature. Effects due to acid-catalyzed proton exchange of the OH proton of CH2OH and of (CH3)2COH with solvent protons were studied in aqueous solutions. These studies gave values for the mean lifetime of a radical between exchanges.
Wide-Line NMR Study of Molecular Motion in [Me3SiNSiMe2]2
Authors: Levy Hiram , Grizzle William E.
Published: January 2005

Wide-line NMR and powder x-ray measurements were made on tetramethyl-N–N-bis(trimethylsilylcyclodisilizane) (Me3SiNSiMe2)2, over the temperature range 77°—300°K. Linewidths and second moments were calculated from the experimental NMR spectra. Theoretical second moments and line shapes were calculated for various motions, and then were compared with experimental results in order to determine the motions present. It was found that at 77°K the molecule is rigid except for rotation of the methyl groups about their C–Si bonds. At room temperature it was found that the molecule is rotating about a molecular axis, the Me3Si groups are rotating about their Si–N bonds, and the methyl groups are rotating about their C–Si bonds. All these motions were uncorrelated and of frequencies>106 cps. At intermediate temperatures various torsional oscillations were observed. The barriers to these motions were calculated and the relationships between the NMR results and the x-ray crystallographic data were discussed.
Kinetic Theory of Dense Fluid Mixtures. I. Square-Well Model
Authors: McLaughlin Ian L. , Davis H. Ted
Published: January 2005

The transport properties are described of a two-component dense fluid mixture of particles interacting with a square-well potential. The Chapman—Enskog method of solution is used to obtain the coefficients of thermal conduction, thermal diffusion, mutual diffusion, self-diffusion, and viscosity. The forms of these coefficients are found to be very similar to those obtained by Thorne for a dense mixture of rigid spheres. Onsager's relation is found to be satisfied for the Dufour and Soret effects.
Microwave Spectrum and Force Constants of SiF2: Centrifugal Distortion
Authors: Rao V. M. , Curl R. F.
Published: January 2005

Over 70 rotational transitions of SiF2 ranging up to J=37 have been measured and assigned in the region 8–40 Gc/sec. The microwave spectrum of the v2=1 state of 28SiF2, and the ground vibrational states of 29SiF2 and 30SiF2 have been assigned. A centrifugal-distortion analysis of the spectrum of ground state 28SiF2 has been carried out. It was found that force constants are not determined by the centrifugal-distortion effect alone. Graphical solutions utilizing centrifugal-distortion data expressing the force constants in terms of the harmonic frequencies ω1 and ω3 are presented.
Kinetics of the Helix—Coil Transition in Polyamino Acids
Authors: Poland Douglas , Scheraga Harold A.
Published: January 2005

The matrix theory of the helix—coil transition in polyamino acids is extended to give the initial rate of change of helical content when the system is suddenly perturbed from equilibrium. Using the matrix to treat chains of arbitrary length, it is possible to assign not only the equilibrium statistical weights for the initial probability of occurrence of each species but also the rate constants for all possible initial reactions involving the formation and breakdown of helical states. It is shown that all the rate constants can be related to the equilibrium statistical weights and to only one rate constant. It is found that reactions at helical ends dominate the initial rate, even though there are many more interior sites than there are ends. As a result, the initial rate of change of helical content goes through a maximum at the transition temperature. With the aid of some approximate expressions for the number of helical ends, it is possible to discuss the initial rate for all ranges of chain length. The technique used to compute the initial rate can also be applied to calculate the moments of the equilibrium distribution of lengths of helical sequences; this calculation is given in the Appendix.
Monte Carlo Studies of Lattice-Model Polymer Chains. II. End-to-End Length
Authors: Verdier Peter H.
Published: January 2005

The relaxation and the equilibrium behavior of lattice-model polymer chains are studied by simulation on a digital computer. Results are presented for the behavior of the square of end-to-end length l2 for chains of 8, 16, 32, and 64 beads, with and without excluded volume restrictions. It is found that the relaxation of the lattice-model chains without excluded volume is remarkably similar to that of statistical-bead models. The introduction of excluded volume restrictions causes drastic qualitative changes in the relaxation behavior of the longer chains, and lengthens the time required for their relaxation by factors of up to 15. While the distribution in l2 for the longer chains with excluded volume departs noticeably from Gaussian form at quite small and quite large values of l2, it appears close to Gaussian in a range from one-third to three times the mean-square value of l2.
Theoretical Calculations of Mass Spectra: Fragmentation of C6–C8 Alkane Ions
Authors: Tou James C. , Hills Lorin P. , Wahrhaftig Austin L.
Published: January 2005

An improved statistical theory of mass spectra is here applied to the fragmentation of five alkanes: n-hexane, 2-methylpentane, 3-methylpentane, n-heptane, and n-octane. The calculated breakdown curves are compared with the experimental curves obtained from photoionization studies by Steiner, Geise, and Inghram. The major fragmentations, the metastable ions, and the ``missing metastable'' ions are computed for gas temperatures of 0° and 300°K. The improved quasiequilibrium theory yields satisfactory breakdown curves for the above molecules using physically reasonable activated complexes and activation energies, and without requiring introduction of artificial parameters such as an ``effective number of oscillators.''
Chemical-Reaction Cross Sections, Quasiequilibrium, and Generalized Activated Complexes
Authors: Marcus R. A.
Published: January 2005

A quasiequilibrium expression is given relating sums over reaction cross sections to properties of activated complexes. When applied to recent classical-mechanical computer data on the H+H2 reaction to test the quasiequilibrium assumption, reasonable agreement is found over the range considered. Suggestions are made with respect to extending the range and to presenting the computer data in a modified form. The latter would permit testing a stronger statement of the hypothesis. The equations are used elsewhere to formulate a statistical-dynamical theory for chemical-reaction cross sections.
Stochastic Models for Second-Order Chemical Reaction Kinetics. The Equilibrium State
Authors: Darvey I. G. , Ninham B. W. , Staff P. J.
Published: January 2005

Stochastic models for a number of reversible chemical reactions involving one or two second-order steps are examined and exact solutions which involve standard orthogonal polynomials are found for the equilibrium states. The expected values and variances of the numbers of molecules present in the systems at equilibrium are expressed in terms of these polynomials. Comparison of the stochastic mean value and the classical deterministic expression, shows that they are equivalent for most systems of physical interest, that is when large numbers of molecules are present. The relative fluctuation is found to be O (N−½), where N is of the order of the number of molecules present in the system, in agreement with the results of equilibrium statistical mechanics.
Alternate-Gradient Focusing of Molecular Beams
Authors: Auerbach Daniel , Bromberg Edward E. A. , Wharton Lennard
Published: January 2005

Space focusing of molecular beams is an established technique achieved by multipole fields for molecules in states that gain energy with applied field. Very often, however, one wants to focus molecules in states that lose energy with applied field. This latter problem is discussed here, and it is shown that the technique called ``strong'' or ``alternate-gradient,'' AG, focusing is of quite general applicability. The dipole, ``two-wire'' field is shown to be the neutral beam analog of the magnetic or electric quadrupole used for AG focusing of charged beams. Exploitation of circular motion or large energy change to achieve focusing is discussed, although these methods do not seem to be as widely applicable as AG focusing. Some specific field configurations and applications are considered: (1) focusing in a molecular-beam accelerator, (2) ``flop-in'' state selection for positive polarizability or effective moment, (3) beam storage, (4) novel spectroscopy for measuring dipole moments and polarizabilities to high accuracy, that has further applications for high-purity state selection, (5) velocity selection.
Chlorine Nuclear Quadrupole Resonance Study of HgCl2
Authors: Dinesh  , Narasimhan P. T.
Published: January 2005

The Zeeman effect of the nuclear quadrupole resonance of 35Cl in crystalline powder of HgCl2 has been studied. The asymmetry parameters (η) of the electric-field gradient for the two physically nonequivalent chlorine sites have been obtained. For the higher-frequency line the η value is 0.30±0.01 and for the lower-frequency line η=0.28±0.01. The variation of the nuclear quadrupole resonance frequency with temperature for both the sites has also been studied from room temperature to liquid-nitrogen temperature. The temperature dependence, when explained in terms of molecular oscillations and crystal lattice vibrations, predicts a new lattice frequency of 35 cm−1 in addition to the frequencies 73, 95, and 124 cm−1 which have been obtained earlier.
Stability of Phases in the Cesium—Graphite System
Authors: Salzano F. J. , Aronson S.
Published: January 2005

The thermodynamic properties of cesium—graphite lamellar compounds prepared from natural graphite flakes have been studied at 400° to 800°C. The factors which contribute to the thermodynamic properties of the compounds are discussed. The stability and structure of the stages below C10Cs can be understood on the basis of a semiempirical reaction mechanism in which it is assumed that the cesium is fully ionized. The reaction mechanism considers the following parameters: the energy required to separate the carbon layers upon formation of the compounds; the density of cesium in the filled layers; the electrostatic interactions between cesium-filled layers; and the bonding energy of cesium in the filled layers. Deviations in the heats of formation from those predicted by the model occur in the case of C8Cs and C10Cs. These deviations are attributed to the unique structure of C8Cs and C10Cs in which each carbon layer is sandwiched between two layers of cesium.
Experimental and Theoretical Considerations for Ionization of Simple Hydrocarbons, H2, D2, O2, H2O, and the Rare Gases by 2.2-MeV α Particles and by Electrons in a Mass Spectrometer
Authors: Rudolph P. S. , Melton Charles E.
Published: January 2005

The measurement of ionization cross sections and mass spectra produced by 2.2-MeV α particles is briefly discussed with emphasis on experimental details which lead to results which are more accurate than those of the previous study. Experimental techniques and apparatus have been developed and applied to these measurements for H2, D2, O2, H2O, CH4, C2H2, C2H4, C2H6, and the rare gases. The experimental results for H2 and He are compared with detailed calculations in the Börn—Bethe approximation and for Ar in the classical approximation. The ionization cross sections for the removal of one electron conform rather well to the predictions although the experimental results tend to be somewhat lower, than the theoretical values. Experimental values for He, Ar, H2, and N2 are in good agreement with extrapolated data of McDaniel and co-workers.

The mass spectra produced by 2.2-MeV α particles show the same fragments as those produced by electrons with the same velocity, but the abundance of some fragment ions differ by a factor of four. Mass spectra produced by 75-eV electrons (the usual energy employed in conventional mass spectrometry) also show significantly more dissociative ionization than those produced by 2.2-MeV α particles.
Line Strength, Linewidth, and Dipole-Moment Measurements on Perchlorofluoride at 4.2 cm−1
Authors: Frenkel L. , Smith W. , Gallagher J. J.
Published: January 2005

The dipole moment of FClO3 has been determined by measuring the absolute-absorption maximum and linewidth parameters due to the J11–12 transition in a resonant cavity at ∼126 196.000 MHz. The linewidth parameter was 3.37 MHz/mm Hg and the dipole moment was found to be 0.025±0.003 D, in close agreement with the value of 0.023±0.003 D found by a dielectric-relaxation method.
Theoretical Studies of Hot-Atom Reactions. I. General Formulation
Authors: Porter R. N.
Published: January 2005

A general treatment of hot-atom reactions is developed to facilitate correlation with molecular-beam and theoretical studies of collision dynamics. Effects of the velocity distributions of the gases in the reaction mixture, inelastic processes, collisional isotope effects, and the temperature dependence of the integral-reaction probability are included in the formalism. The basic integral equation may be solved by iteration for the integral reaction probability (relative yield) as a function of hot-atom energy. Since there is no restriction on the range of energies over which the equation is valid, the theory is equally applicable to photochemically induced and nuclear-recoil-induced hot-atom reactions. The relationship of the treatment to earlier formulations is discussed.
Measures of Covalency in Transition-Metal Chlorides
Authors: Bersohn R. , Shulman R. G.
Published: January 2005

The bonding between transition-metal ions and chlorine is largely ionic. It has been known that the small degree of covalency in transition-metal chloride crystals could be measured by transferred magnetic hyperfine interactions with the chlorine nuclei. Here we show that the Townes and Dailey theory allows one to derive the degree of covalency from the chlorine nuclear quadrupole coupling in these crystals. In the few cases where both magnetic hyperfine interactions and electric quadrupole interactions have been measured at the same nucleus, the degree of covalency calculated by the two methods agrees rather well. Both kinds of experiment indicate the importance of π bonding with the d orbitals as well as σ bonding.
Paramagnetic Resonance of Copper in Amorphous and Polycrystalline GeO2
Authors: Siegel I. , Lorenc J. A.
Published: January 2005

The X-band electron paramagnetic resonance spectra of Cu+ + ions doped into amorphous, tetragonal, and hexagonal GeO2 have been observed at 295°K. Optical absorption and reflection data for, respectively, the doped glass and polycrystalline samples were also obtained. From the experimental results, the symmetry of the cupric complexes and some characteristics of the metal ion's bonding are deduced. In amorphous and tetragonal GeO2, the Cu+ + ions are basically in sixfold coordination. Because these cupric complexes exhibit a significant axial distortion (elongation), however, they have been treated as having square planar symmetry. Since the host cations in amorphous GeO2 are tetrahedrally coordinated, the presence of square planar Cu+ + complexes suggests that, to a significant extent, the cupric ions determine their immediate environment in the glassy host. The Cu+ + ions in hexagonal GeO2 appear to be located within the system of oxygen channels (tunnels) which are present in this crystal.
On the Eu3+ Fluorescence of Mixed Metal Oxides. IV. The Photoluminescent Efficiency of Eu3+-Activated Oxides
Authors: Blasse G.
Published: January 2005

Four rules are proposed to explain the photoluminescent efficiency of Eu3+-activated oxides: (a) uv absorbing groups in the host lattice should be nearest neighbors in the crystal structure to have sufficient wavefunction overlap; (b) the emission spectrum of the absorbing group should overlap the absorption spectrum of the group; (c) the configuration consisting of the center of the absorbing group, the intermediary O2− ion, and the Eu3+ ion should be as collinear as possible; (d) O2− ions surrounding the Eu3+ ion must feel a high potential field.

If all these rules are satisfied, highly efficient Eu3+ phosphors can be expected; if one or more of the rules are violated, phosphors with low efficiency must be expected.

These ideas are applied to a large number of Eu3+-activated oxides. There is a very good agreement between experimental results and predictions from the rules.

As far as possible the physical background of the rules is discussed.
Isenthalpic Solidification and the Specific Heat of Supercooled Liquid Phosphorus
Authors: Glicksman M. E. , Schaefer R. J.
Published: January 2005

Isenthalpic solidification of a unary (one-component) supercooled liquid results in either two-phase invariant equilibrium or in single-phase univariant equilibrium, depending on the degree of supercooling prior to solidification.

When postsolidification univariant equilibrium obtains, a determination of the specific heat at constant pressure, Cpl, of the supercooled phase relative to the stable, solid phase can be made by measuring the adiabatic temperature rise during recalescence.

Values of Cpl for highly supercooled phosphorus over the temperature range −1° to +18°C have been determined with this method. No evidence for the changes in molecular association deduced from earlier viscosity data on supercooled phosphorus was found in the temperature variation of the specific-heat function. The enthalpy and specific-heat values determined for supercooled liquid phosphorus agree with published values for the stable liquid above the normal melting point, Te=44°C.
Magnetic Properties of the BH Molecule
Authors: Hegstrom Roger A. , Lipscomb William N.
Published: January 2005

The unusual magnetic properties of the 1Σ+ BH molecule calculated earlier from perturbed (coupled) Hartree—Fock theory have been confirmed, and rendered more nearly gauge invariant. Predictions of the spin—rotation constant for hydrogen are CH=−14.9 kc/sec with B as origin, and CH=−18.2 kc/sec with H as origin, as compared with the earlier values of −8.5 and −25.3 kc/sec, respectively. Also, the shielding at H is σH=24.46 ppm with B as origin and σH=25.44 ppm with H as origin, as compared with our previous values of 22.55 and 27.62 ppm, respectively. In addition, we present an interpretation of the molecular paramagnetism, the antishielding at B, and the large spin—rotation constant of B, in terms of orbital current densities. It is found that these extreme properties calculated for BH result from a paramagnetic current due to excitations of the lone-pair electrons on the boron atom to an unoccupied pπ orbital on this atom.
Spectral Study of Flames of Carbon Vapor at Low Pressure
Authors: Savadatti M. I. , Broida H. P.
Published: January 2005

Gas-phase reactions of carbon vapor near room temperature with simple gases and their discharge products have been spectrally observed for the first time. Experimental arrangements for obtaining carbon vapor and mixing it with discharge products or gases in a low-pressure flow system are presented. Spectra of the carbon vapor flames with oxygen, atomic oxygen, and atomic nitrogen have been obtained over the range 2200 to 7000 Å. Molecular-oxygen flames emit the C2 Swan and CO triplet and third positive bands. Flames with atomic oxygen are much more intense than flames with molecular oxygen and emit the C3 4050 Å group in addition to C2 and CO bands. Bands from ν=2 in the C2 Swan system are found to be enhanced in atomic- and molecular-oxygen flames. On addition of molecular or atomic hydrogen to the atomic-oxygen flame, CH 4315- and 3900- Å and OH 3064- Å bands appear. Atomic-nitrogen flames emit the CN red and violet systems with considerable intensity in bands from high vibrational levels. Spectra of these flames have been studied as a function of pressure, flow rates, carrier gas, and methods of obtaining carbon vapor. Mechanisms for formation and excitation of the emitters of the various bands are suggested.
Cluster Probabilities for Simple Lattices Containing Two Impurities
Authors: Kreitman Marshall M. , Hamaker Frances
Published: January 2005

Concentration-dependent probabilities for flnding one of two kinds of impurities in a single, pair, or triple cluster within a simple cubic, body-centered-cubic, face-centered-cubic, or hexagonal-close-packed lattice are given as polynomials for which tabulated values are readily available. Both nearest-neighbor interactions and next-nearest-neighbor interactions between foreign impurities in random distribution within the lattice are each separately treated. Graphical comparisons of the results indicate that the effect of introducing an additional impurity is similar to that of including next-nearest-neighbor interactions. In both cases cluster probabilities are decreased.
Temperature-Dependent Quenching of Fluorescence of Europic-Ion Solutions
Authors: Kropp John L. , Dawson William R.
Published: January 2005

The fluorescence lifetime of Eu(NO3)3 in CH3OH, CH3OD, and CD3OD and of EuCl3 in D2O has been determined as a function of temperature. The temperature-dependent quenching of fluorescence from the 5D0 level is attributed to radiationless deactivation through the 5D1 level. From these and other results it is concluded that the 5D0 level of Eu3+ does not possess a mechanism for radiationless conversion to the ground level that does not involve the upper levels or solvent vibrations.