bluuebunny/crossref_metadata_2025 huggingface dataset:
Interchange Theorems for Triple Perturbation Theory
Authors: Tuan Debbie Fu-tai
Published: February 2004

Based on Rayleigh–Schrödinger perturbation theory, eight general expressions of the triple perturbation energy εn,m,t are derived. The relationships among them give several general interchange theorems in a compact fashion. These interchange theorems exchange the integrals involving higher-order perturbed wavefunctions related to a complicated perturbation λV, by integrals involving higher-order perturbed wavefunctions related to the simpler perturbations. From the perturbed wavefunction corrected to the >nth order of λV, (1) in general, the interchange theorems allow us to obtain the perturbation energy to the (n + 1)th order; (2) when H° and λV are Hermitian, the interchange theorems allow us to obtain the perturbation energy to the (2n + 1)th order; (3) when H°, λV, and other perturbations are Hermitian, the interchange theorems will reduce the required total order of wavefunctions related to the Hermitian perturbations to almost half. These interchange theorems can be applied to any triple perturbation problem when the unperturbed state is nondegenerate. They are valid to all orders with respect to the three perturbations. The application of these interchange theorems to calculate special kind of second-order physical properties, F, such as electric shielding factors, chemical shifts, and nuclear spin–spin coupling constants, is discussed. It is shown that if (1) the two perturbations associated with the properties are one-electron operators, and (2) the zeroth-order wavefunction of a closed-shell system is obtained by SCF method, then the first-order correction of F is determined solely by the first-order orbitals, i0,1,0 and i0,0,1, related separately to the two perturbations but does not depend on any “cross” second-order orbitals, i0,1,1. This result will simplify the calculation very much.
Intramolecular and Intermolecular Contributions to the Fusion of Linear Aliphatic Polyesters and Polyamides and Their Effects on the Observed Differences in Polyester and Polyamide Melting Temperatures
Authors: Tonelli Alan E.
Published: February 2004

The inter- and intramolecular contributions to the entropy and energy of fusion are calculated for several linear aliphatic polyesters and polyamides assuming the fusion process consists of two independent contributions: the volume expansion (intermolecular contribution) and the increase in the conformational freedom of each polymer chain on melting (intramolecular contribution). The intramolecular entropy and energy contributions are obtained from the configurational partition function and its temperature coefficient calculated for an isolated, unperturbed polymer chain using the rotational isomeric state approximation. Subtraction of the calculated changes in the conformational entropy and energy upon melting from the measured entropy and enthalpy of fusion, respectively, provides an estimate of the intermolecular contributions to these two quantities if the small volume change accompanying melting is ignored and the enthalpy and energy of fusion are assumed to be nearly identical. Application of this procedure to several aliphatic polyesters and polyamides leads to the following conclusions: (i) The calculated intramolecular contribution to the entropy of fusion is nearly the same for the polyesters and polyamides; (ii) the measured enthalpies of fusion are nearly the same for both classes of polymers; (iii) the entropies of fusion are smaller for the polyamides; and (iv) the lower entropies of fusion of polyamides are probably caused by disorder in the crystal resulting in their higher melting points compared to the polyesters.
Microwave Absorption and Molecular Structure in Liquids. LXXVII. Relaxation Mechanisms in Hexamethyldisiloxane and Hexaphenyldisiloxane
Authors: Dasgupta S. , Smyth C. P.
Published: February 2004

The dielectric relaxation processes in hexamethyldisiloxane have been investigated by measuring the dielectric constant and loss of the pure liquid at 2.1-mm wavelength and − 20°C and combining the results with those of previous measurements. Similar measurements have been made on a dilute solution of hexaphenyldisiloxane in carbon tetrachloride at 24° at wavelengths from 2.1 mm to 6 × 106 cm. The relaxation times calculated from these results confirm the existence of two relaxation processes in hexamethyldisiloxane, which are readily distinguished from each other at 0° and lower, but not at 20° and 40°. The magnitudes of the two relaxation times, together with those previously obtained for hexaethyldisiloxane, indicate that the longer relaxation process involves molecular rotation while the shorter involves bending, probably, amounting to inversion of the Si–O–Si group.
Theory of the Kinetics of Conformational Transitions in Polymers
Authors: Helfand Eugene
Published: February 2004

We develop a theory, valid for large friction, for the rate of conformational (rotational isomeric state) transitions in polymers. Such changes are classified according to the effect which the transformation in a finite portion of the molecule has on the attached polymeric chains. Major consideration is given to type 2* transitions, in which the attached chains are merely translated as the conformational alteration occurs. Study of a simplified model indicates that the rates of 2* transformations are not seriously inhibited by the attached polymer chains.
Potential Constants of the Hexacyanocobaltate Ion
Authors: Jones Llewellyn H. , Memering Melvin N. , Swanson Basil I.
Published: February 2004

The infrared and Raman spectra of Co(12C14N)63−, Co(13C14N)63−, and Co(12C15N)63− have been studied in aqueous solution and in the solid state. Fundamental frequencies have been assigned for all but the F2u vibrations. Force constants and compliance constants have been calculated and compared with isoelectronic Cr(CO)6 and with Au(CN)2−.
Microwave Spectra of 13C- and 18O-Containing Species and the Structure of Vinylene Carbonate
Authors: White William F. , Boggs James E.
Published: February 2004

The microwave spectra of two 13C and two 18O species of vinylene carbonate have been analyzed. The spectra were observed with the isotopes present in natural abundance. An rs structure of the heavy atoms in the molecule shows a short C=O bond length of 1.1908 ± 0.0006 Å with the other bonds being of approximately the expected length. The ring angles are nearly equal with two bonds at the carbon atoms making angles of 108°40′ ± 9′ and 108°40′ ± 40′ and the angle at the oxygen atom being 106°56′ ± 24′.
Heat Capacity of Scandium from 6 to 350°K
Authors: Gerstein B. C. , Taylor W. A. , Schickell W. D. , Spedding F. H.
Published: February 2004

The heat capacity of scandium has been measured from 6 to 350°K. The results differ from previous measurements in this temperature range by more than the accuracies of the measurements. The difference is discussed in terms of impurity effects. The following values are obtained for the thermodynamic functions at 298.15°K: Cp° = 25.51 ± 0.05, S298.15° = 34.78 ± 0.20, (H298.15° − H0°) / T = 17.46 ± 0.10, and − (G298.15° − H0°) / T = 17.31 ± 0.14, all in joules per mole per degree Kelvin.
Light Scattering off Fluctuations of a Biological Conformational Change. I. Simplified Stochastic Model
Authors: Simon Eliot M.
Published: February 2004

The use of light which has been scattered off a chemically reacting fluid, then spectrally decomposed to determine rapid rate processes has been proposed and observed in recent publications in this journal. The present paper is an extension of these principles to a study without undue perturbation of the rapid rate processes occuring in a biological conformational change. A master equation describing the time evolution of the fluctuations is considered. The evolution of the mean, covariance, and autocorrelation function is derived. The space–time Fourier transform of the autocorrelation function is calculated and gives the intensity of the scattered light of the associated fluctuations in dielectric constant. It is found that at zero angle extrapolation of the scattered light the rates of opening and closing of the DNA double helix undergoing fluctuations in conformation can be thereby studied.
Exchange Interactions in Crystalline Aromatic Hydrocarbons
Authors: Williams Denis R. , Shapiro Richard C.
Published: February 2004

Exchange interactions between C–H bonds as situated in aromatic crystalline hydrocarbons are calculated using molecular orbitals constructed using a Slater basis set. The results are compared to those calculated by other authors. It is concluded that the use of the empirical formula Bexp(− CR) with constants defined by Rae and Mason [Proc. Roy. Soc. (London) A304, 487 (1968)] is reasonable for exchange between C–H bonds. The interaction of a C–H bond with π systems is also concluded to be important.
Positive Ion–Molecule Reactions in Perfluoropropane
Authors: Su Timothy , Kevan Larry , Tiernan Thomas O.
Published: February 2004

Positive ion–molecule reactions have been studied in C3F8 by tandem and high-pressure mass spectrometry. Rate constants at a nominal 0.3-eV ion energy and kinetic energy dependences of the reactions are reported. The most common reaction is F− transfer which has a typical rate constant of 5 × 10−11 cm3 molecule−1·sec−1. These rate constants are generally more than an order of magnitude lower than those for analogous H− transfer reactions in alkanes. Other reactions, including F transfer to CF2+ and F2 transfer to CF+ as well as several condensation reactions involving C–C bond formation are also observed. Endothermic collision-induced dissociation (CID) reactions are observed for CF2+, C2F3+, C2F4+, C2F5+, and C3F7+ even at a nominal 0.3-eV ion kinetic energy. The effects of ionizing electron energy and of changing the molecular source of the ionic species show that the fragment ions are formed with considerable internal excitation. For ions formed by 76-eV electrons, the ratio of CID to F− transfer rate constants is 0.06 for CF2+, 1.0 for C2F3+, and 5.5 for C2F5+, while C2F4+ and C3F7+ undergo only CID reactions. CID reactions proceed by simple bond scission except for C2F4+ which must undergo rearrangement processes since the dissociative products are CF3+, CF2+, and CF+ while are formed in the ratio of 4.8/1.4/1.0.
Matrix Reactions of K and Rb Atoms with Oxygen Molecules
Authors: Andrews Lester
Published: February 2004

Deposition of atomic beams of potassium and rubidium with oxygen molecules at high dilution in argon together on a salt window at 15°K produces the KO2 and RbO2 molecules, as identified by infrared spectra. Secondary reaction yields the KO2K and RbO2Rb molecules. Oxygen isotopic mixtures and simultaneous deposition of two different alkali-metal atoms verify the molecular composition. Detailed concentration changes and oxygen isotropic mixtures identify the new molecular species O2KO2 and O2RbO2, the potassium and rubdium disuperoxide molecules which likely have the D2d structure. Force constants for the molecules synthesized here are compared with those reported earlier for LiO2 and NaO2.
Generalized Formula for Light Scattering of Optically Anisotropic Macromolecules
Authors: Tagami Yukiko
Published: February 2004

A general expression for the spectrum of scattered light from monodispersed, infinitely dilute solutions of optically anisotropic molecules is presented. Application is made to the particular cases of rigid-rod macromolecules and long, flexible coils. The calculations involve extensive use of the theory of the rotation group. New results are obtained for the anisotropic part of the Fourier transform of the frequency spectrum of light scattered from optically anisotropic, rigid-rod macromolecules. In the case of the random coil, Pecora's results are extended to more general scattering angles and the full range of molecular weight. Horn's formulas for the total scattering of rods and coils are reobtained.
Intermolecular Coupling of Water Molecules in Copper Chloride Dihydrate
Authors: Fifer R. A. , Schiffer J.
Published: February 2004

Polarized and unpolarized infrared spectra have been obtained for copper chloride dihydrate samples, containing low mole ratios of H2O and D2O. The positions of the absorption bands of these samples are shown to differ from those of samples, containing high percentages of these same molecules. The spectral differences noted are shown to be related to the interactions between water molecules in the solid. Furthermore, a criterion is provided for sensing a variation of hydrogen bond strength with deuteration, and the origin of bands in the ν2 overtone regions of H2O, D2O, and HOD is also considered.
Linear Viscoelasticity in Entangling Polymer Systems
Authors: Graessley William W.
Published: February 2004

Molecular models for polymers, such as the Rouse model, yield steady state shear compliance Je and terminal relaxation time τmax of the forms Je, ∝M / cRT and τmax∝ηM / cRT, in which c is the polymer concentration, M is the molecular weight, and η is the zero shear viscosity. Recent experiments have shown that in entangling systems these forms change, becoming Je∝ / c2RT and τmax∝η / c2RT. It is proposed here that the changes are a consequence of the highly uncorrelated nature of entanglement drag interactions, as opposed to the smoothly varying interactions inherent in the Rouse analysis. A new model is proposed to account for this difference. The resulting predictions are consistent with the experimental forms of G′(ω), G″(ω), and G(t) as well as those of θmax and Je. The molecular weight between entanglement points, Me, was estimated from several different viscoelastic properties of undiluted polystyrene. With the exception of that from Je, similar values of Me were obtained in all cases. Calculations of Je for mixtures of two molecular weights MA and MB were made with and without the assumption of an uniformly effective drage coefficient. The former predicted an unrealistically weak dependence on polydispersity; the latter agreed with experimental results for cases in which MB / MA was in the range of 2, but overestimated the effects of polydispersity when the difference in molecular weights was greater.
Measurement of the Rotational Diffusion Coefficient of Lysozyme by Depolarized Light Scattering: Configuration of Lysozyme in Solution
Authors: Dubin Stuart B. , Clark Noel A. , Benedek George B.
Published: February 2004

We have determined the rotational diffusion coefficient (DR) of lysozyme from the spectrum of the depolarized light scattered by this protein. The sample was illuminated by a single-frequency He–Ne laser and the spectrum of the depolarized scattered light was analyzed using a high-resolution spherical Fabry–Perot interferometer. We have determined D20,wR to be (16.7 ± 0.8) × 106/sec at 15% protein concentration. We have, in addition, measured the translational diffusion coefficient (DT) of lysozyme by employing the now-familiar techniques of optical mixing spectroscopy to observe the spectrum of the polarized light scattered by the protein. We find D20,wT to be (10.6 ± 0.1) × 10−7 cm2/sec, independent of protein concentration between 1% and 15%. Our results for DR and DT, combined with Perrin's expressions for the rotational and translational diffusion coefficients of ellipsoids, indicate that lysozyme in solution is hydrodynamically equivalent to a prolate ellipsoid of revolution with major and minor axes of (55 ± 1) Å and (33 ± 1) Å, respectively. These dimensions are shown to be consistent with an unsolvated molecule of dimensions (48 ± 1) Å by (26 ± 0.8) Å covered with a shell of solvent about 3.5 Å thick. The hydrodynamically equivalent oblate ellipsoid of revolution is shown to be inconsistent with other physical properties of the protein. We have, in addition, determined from our diffusion coefficient results the degree of solvation of lysozyme and find this to be (0.60 ± 0.03) g of solvent per gram of (dry) protein. Finally, we present a novel and unambiguous method for the determination of the depolarization ratio (ρυ) of small molecules and find ρυ = (1.4 ± 0.1) × 10−3 for lysozyme. This value of the depolarization ratio is shown to imply an intrinsic anisotropy in the polarizability of lysozyme.
Vaporization Thermodynamics of the Lanthanum Carbon System. Mass Spectrometric Determination of the Dissociation Energy of LaC2, LaC3, and LaC4
Authors: Stearns Carl A. , Kohl Fred J.
Published: February 2004

The vaporization of the lanthanum dicarbide–carbon system has been studied by Knudsen-effusion mass spectrometry over the temperature range from 2267 to 2600°K. Experimentally determined reaction enthalpies were combined with published thermodynamic data to yield the atomization energies D0.atom°(LaC2) = 1257 ± 8 kJ mole−1, D0.atom°(LaC3) = 1759 ± 31 kJ mole−1, and D0.atom°(LaC4) = 2500 ± 16 kJ mole−1. Ion intensities of the parent molecular ions La+, LaC2+, LaC3+, and LaC4+ were combined with absolute effusion measurements from the literature to obtain vapor pressure equations (1900–2600°K): logPLa = (− 2.606 × 104 / T) + 10.162, logPLaC2 = (− 3.327 × 104 / T) + 12.813, logPLaC3 = (− 4.414 × 104 / T) + 14.557, and log PLaC4 = (− 4.301 × 104 / T) + 15.067, where the units of pressure are newtons per square meter.
Superhyperfine Structure in the EPR Spectrum of CdF2:Eu
Authors: Ensign T. C.
Published: February 2004

The superhyperfine structure (shfs) of Eu2+ in the EPR spectrum of CdF2:Eu has been examined experimentally. The results have been analyzed using the formalism of Ranon and Hyde with the aid of Valentin's recent determination of the overlap contribution to the shfs. This analysis has yielded correctly the number of EPR lines observed, the magnitude of the splitting between them, and their relative intensity. It is shown that the shfs arises primarily from the fluorine nuclear Zeeman interaction, but that the intensities and splittings of the lines are influenced by the overlap between the Eu2+ 4f electrons and the nuclear magnetic moments of the surrounding fluorine ions.
Low-Energy Neutron Scattering from Hydrogen Chloride
Authors: Lurie N. A. , Carpenter J. M.
Published: February 2004

Measured double differential cross sections are reported for low-energy neutron scattering by gaseous hydrogen chloride. Comparison of these data against a calculation based on a quantum mechanical treatment of rotations shows excellent agreement and thus provides the first experimental verification of this theory for the class of molecules with linear symmetry.
Reactions of OH Radicals in the H–NO2 and H–NO2–CO Systems
Authors: Mulcahy M. F. R. , Smith R. H.
Published: February 2004

A mass-spectrometric study has been made of the stoichiometry of the reactions of OH radicals generated by the reaction H+NO2→OH+NO, under conditions similar to those used in some previous studies of the kinetics of the reactions of OH radicals with each other and with CO. Contrary to previous assumptions, when H atoms are initially in excess over NO2, the reactions 2OH→H2O+O, O+OH→O2+H, OH+CO→CO2+H, do not account completely for the decay of OH. An additional reaction occurs which produces water and is probably the first-order heterogeneous reaction recently postulated on purely kinetic evidence by Breen and Glass [J. Chem. Phys. 52, 1082 (1970)]. When NO2 is initially in excess over H, a fast reaction takes place involving OH radicals and NO2 {as first observed by Wilson and O'Donovan [J. Chem. Phys. 47, 5455, (1967)]}. This is probably the reaction OH+NO2→HNO3.
Statistical Phase-Space Model of the Collision-Induced Dissociation of Excited O2+ and NO+ Ions
Authors: Moran T. F. , Fullerton D. C.
Published: February 2004

Cross sections for the collision-induced dissociation of O2+ and NO+ ions have been calculated as a function of reactant-ion kinetic energy. The dissociative cross sections for individual reactant-ion electronic and vibrational states, weighted to account for the internal state distributions of reactant ions produced in electron-impact ionization processes, have been compared with recent measurements. The magnitudes of the cross sections estimated by the statistical model are larger than those observed in the laboratory; however, the variations of the calculated cross sections with both ion internal energy and ion kinetic energy are in good agreement with experiment.
Role of Repulsive Forces in Determining the Equilibrium Structure of Simple Liquids
Authors: Weeks John D. , Chandler David , Andersen Hans C.
Published: February 2004

The different roles the attractive and repulsive forces play in forming the equilibrium structure of a Lennard-Jones liquid are discussed. It is found that the effects of these forces are most easily separated by considering the structure factor (or equivalently, the Fourier transform of the pair-correlation function) rather than the pair-correlation function itself. At intermediate and large wave vectors, the repulsive forces dominate the quantitative behavior of the liquid structure factor. The attractions are manifested primarily in the small wave vector part of the structure factor; but this effect decreases as the density increases and is almost negligible at reduced densities higher than 0.65. These conclusions are established by considering the structure factor of a hypothetical reference system in which the intermolecular forces are entirely repulsive and identical to the repulsive forces in a Lennard-Jones fluid. This reference system structure factor is calculated with the aid of a simple but accurate approximation described herein. The conclusions lead to a very simple prescription for calculating the radial distribution function of dense liquids which is more accurate than that obtained by any previously reported theory. The thermodynamic ramifications of the conclusions are presented in the form of calculations of the free energy, the internal energy (from the energy equation), and the pressure (from the virial equation). The implications of our conclusions to perturbation theories for liquids and to the interpretation of x-ray scattering experiments are discussed.
Charge-Exchange Calculations with Hartree Wavefunctions
Authors: Nebenzahl I.
Published: February 2004

Symmetric resonance charge-exchange cross sections are calculated, in the quasiclassical approximation. Previous calculations of the same type, due to Rapp and Francis, give systematically lower cross sections than the experimental ones. It is suggested that this is a result of the rough form of the atomic wavefunctions used by Rapp and Francis. Here, Hartree–Fock–Slater wavefunctions are used. The necessary integrations are done numerically. On the average, much better agreement with experimental results is achieved. The calculations were performed for He, K, Cs, and Hg.
Raman Spectra of Liquid and Crystalline ClCN and BrCN
Authors: Pézolet M. , Savoie R.
Published: February 2004

Raman spectra of liquid and solid ClCN and BrCN have been recorded at various temperatures down to 77°K. Shoulders on the low-frequency side of the stretching fundamentals in the spectra of the liquids are believed to arise from associated molecules. The spectra of the solids are consistent with the reported crystal structures, and polarization effects in a BrCN single crystal have allowed an unambiguous assignment of all the bands in the Raman spectrum.
Transient Pairs in Gases: Quantum Effects on the Equilibrium Constant for O+H⇆OH* (X 2Πi)
Authors: Jackson James L. , Wyatt Robert E.
Published: February 2004

The statistical mechanical theory of transient pairs in gases, formulated by Smith in 1963, is applied to O+H elastic scattering using the X 2Πi potential curve. The equilibrium constant and internal partition function are calculated by averaging the energy derivatives of the scattering phase shifts over the Boltzmann distribution. The equilibrium constant is partitioned into three components: (1) the resonant contribution produced by quantum mechanical tunneling through the outer maximum in the effective radial potential, (2) the orbit contribution, and (3) the nonresonant component. In the temperature range studied (10° to 2800°K), the resonant component dominates pair formation. This result lends support to recent theories of radical recombination.
Anharmonicity in Crystal Vibrations
Authors: Warshel A.
Published: February 2004

A scheme for the calculation of anharmonicity in crystal vibrations is developed for crystals with one molecule per unit cell. This method is applied to n-hexane crystal. It is found that the contribution from anharmonicity can be very important in lattice vibrations of molecular crystals. Hence, the use of harmonic crystal vibrations for evaluation of nonbonded potentials without an anharmonicity correction can lead to an inconsistent potential.
Intra- and Intermolecular Interactions in and between Water Molecules in Calcium Sulfate Dihydrate
Authors: Kling R. , Schiffer J.
Published: February 2004

A study of the infrared spectra of varyingly deuterated thin films of gypsum has afforded information on the relative importance of intra- and intermolecular interactions in determining the stretching bands of water in the spectrum. This study has indicated that the internal forces in water are different for water in gypsum than they are for water in the vapor. It is further indicated that the water molecule in gypsum is much like the average molecule expected to exist in the liquid state.
Structure and Polymorphism of Crystalline 4,5-Iminophenanthrene
Authors: Ern V. , Guggenberger L. J. , Sloan G. J.
Published: February 2004

4,5-Iminophenanthrene (4H-benzo[def]carbazole, C14H9N) crystallizes in space group I41cd of the tetragonal system with cell dimensions of a = b = 7.428(5) and c = 35.58(3) Å. The molecular packing is reported. Tetragonal crystals can undergo a sluggish transformation to a triclinic form with cell dimensions of a = 12.70(4), b = 12.96(3), c = 11.88(3) Å, α = 90.0(1), β = 99.0(1), γ = 98.3(1)°. The new form exhibits a red-shifted, broad, structureless fluorescence spectrum characteristic of excimer emission. Tetragonal form and monomerlike fluorescence are recovered at a well-defined transition at 73°C. Delayed fluorescence due to triplet–triplet exciton annihilation has been observed in both forms of the material.
Vibrational Spectra of the Crystalline s-Tetrazines
Authors: Sigworth W. D. , Pace E. L.
Published: February 2004

The vibrational spectra of the crystalline s-tetrazines show several infrared and one Raman band which have split into two Davydov components. These results are in agreement with the predictions of the correlation table. However, the magnitude of the splittings cannot be successfully explained by either the dipole–dipole or intermolecular hydrogen repulsion potentials. The intermolecular coupling mechanism is probably due to an interaction between the π cloud of one molecule and the ring atoms of its neighbors.
He and H− 11S and 23S States Computed from Feynman Path Integrals in Imaginary Time
Authors: Lawande S. V. , Jensen C. A. , Sahlin H. L.
Published: February 2004

Feynman path integrals in imaginary time are developed for systems of identical particles exhibiting exchange statistics. The Metropolis–Teller Monte Carlo procedure is applied to the integrals appropriate to H− and He 11S and 23S states.
Shock-Tube Study of the Acetylene–Oxygen Reaction. III. Absolute Rate of Chemi-Ionization during the Induction Period
Authors: Matsuda Shimpei , Gutman David
Published: February 2004

The absolute specific rate of chemi-ionization during the induction period of the C2H2–O2 reaction has been measured using a new end-on shock-tube technique. Ion production was monitored using three gas mixtures with [O2]/[C2H2] ratios of 1.5, 3.0, and 6.0 over the temperature range 1409–2467°K. The data from each experiment was used to calculate differential ion yield at 10% reaction. The differential ion yields (ion pairs formed/C2H2 molecule consumed) were found to be independent of density and mixture composition within experimental error. However, the ion yields were found to depend strongly on temperature varying from near 4 × 10−9 at 1400°K to 2 × 10−6 at 2500°K. The exponential growth constants for electron production during the induction period were found to be a factor of 2 greater than those for CO production in each experiment above 1700°K. This relationship verifies the chemi-ionization process to be second order in reaction intermediates which is consistent with the reaction CH+O→CHO++e and rules out the reaction CH*+C2H2→C3H3++e. A theoretical expression for the differential ion yield is derived using an elementary model mechanism for the induction period of a chain-branching reaction. The data obtained in this study are compared with the predictions of the model mechanism.
Low-Frequency Vibrations of Molecular Solids. XI. Torsional Frequencies and Barriers to Internal Rotation of Some Single Methyl Rotors in the Solid State
Authors: Durig J. R. , Player C. M. , Bragin J.
Published: February 2004

The torsional frequencies of CH3CH2Cl, CH3CH2Br, CD3CD2Br, CH3CH2I, CD3CH2I, CH3CHOCH2, CH3CHSCH2, CH3COCl, CD3COCl, andCH3COBr, have been observed in the solid state and the measured values are: 278, 276, 204, 258, 198, 223, 250, 167, 124, and 168 cm−1, respectively. The torsional ferquencies in the solid state are compared with values obtained by both infrared and microwave techniques for the gaseous molecules. The gas–solid phase shifts of the torsional and skeletal bending frequencies are discussed in terms of the intermolecular forces in the crystals. Pronounced factor-group splitting was observed in the far-infrared spectra of the solid ethyl halides and these splittings are also discussed in terms of the intermolecular potential field. Lattice spectra were recorded for all the molecules studied in the crystalline state, and the frequencies are assigned to librational or translational modes on the basis of isotopic shift factors in the cases for which such data are available.
Low-Frequency Vibrations of Molecular Solids. X. CH3CCl3, CD3CCl3, CH3CCl2H, and CH3CF3
Authors: Durig J. R. , Craven S. M. , Lau K. K. , Bragin J.
Published: February 2004

The far-infrared spectra of solid CH3CCl3 and CD3CCl3 have been investigated from 33 to 400 cm−1. Raman spectra of these solids have also been recorded. The internal torsional mode was observed at 290 and 206 cm−1 in the infrared spectra of solid methylchloroform and methylchloroform-d3, respectively. The threefold periodic barrier to rotation was calculated to be 5.5 kcal/mol. This barrier is compared to those previously reported by other techniques for this molecule and the reported value is much larger than that currently accepted. Four lattice vibrations, 46.9, 53.4, 57.7, and 67.5 cm−1 were observed in the far-infrared spectrum of methylchloroform recorded at − 190°C. Both the effect of temperature variation and deuterium substitution were investigated for these bands. These lattice modes shifted to lower frequency and became quite diffuse as the temperature approached the phase transition at − 68°C. The low-frequency Raman spectrum of methylchloroform at − 165°C showed one line at 38.6 cm−1 which shifted to 37.0 cm−1 with deuteration. The infrared spectra of solid CH3CHCl2 and CH3CF3 have been recorded between 140 and 400 cm−1. The internal torsional mode for 1,1-dichloroethane was observed at 232 and 231 cm−1 for the solid and vapor, respectively. The threefold barrier to rotation was calculated to be 3.50 kcal/mol. The internal torsion for methylfluoroform was observed at 220 cm−1 for the solid, and the barrier was calculated to be 3.29 kcal/mol. Substituent effects on the barrier heights are discussed.
Three-Spin Effect in Dynamic Nuclear Polarization: Quantitative Determination of Internuclear Interactions
Authors: Stewart James R.
Published: February 2004

The three-spin effect in dynamic nuclear polarization has been quantitatively investigated. The effect, arising from internuclear transfer of polarization, is observable only in carefully chosen dilute free-radical solutions. Test samples consisted of DPPH in hexafluorobenzene mixed with either normal or perdeuterated benzene. Theoretical calculations support the experimental result that the three-spin effect adds 24 units to the enhancement for a radical concentration of 0.6 × 1017 spin/cc. The effect has direct relevance in the case of chemically induced dynamic nuclear polarization where the enhancement is small.
High-Temperature Mass Spectrometry, Vaporization, and Thermodynamics of Titanium Monosulfide
Authors: Edwards Jimmie G. , Franzen Hugo F. , Gilles Paul W.
Published: February 2004

A high-temperature mass spectrometric investigation of the vaporization of titanium monosulfide, TiS(s), from 1700–2150°K has shown that the three principal vaporization reactions produce TiS(g), Ti(g) + S(g), andTi(g) + 12S2(g), the second being about four times as important as the first and both more important than the third. The disulfide TiS2(g) comprises less than 1% of the vapor. Thermodynamic results were obtained from five investigations, three with stoichiometric samples, one with excess titanium metal, and one with excess sulfur produced from admixed SrS(s). Equations representing partial pressures as functions of temperature are given. Based on Mann's cross sections for atoms, additivity for molecules, and the assumption of no fragmentation, the third-law enthalpy of vaporization to form TiS(g) is 140.7 ± 1.3 and to form one-half mole each of Ti(g) and S(g) is 121.2 ± 1.1 kcal; the dissociation energy, D298°, of TiS(g) is 101.8 ± 1.8 kcal/mole; the enthalpy of formation at 298°K of TiS(s) is − 62.7 ± 2.5 kcal/mole. Earlier vapor pressure data were corrected for the partial dissociation of the vapor, and thermodynamic data derived from them are in excellent agreement with the new results. Appearance potentials are reported for several ionic species. Effects of ionic fragmentation and ionization cross section errors on the thermodynamic results are discussed, and a method for measuring these effects is described.
Classical Theory of Scattering: Three-Body Problems
Authors: Eu Byung Chan
Published: February 2004

The classical theory of scattering for a two-body problem by Prigogine and Henin, Résibois, and Miles and Dahler is extended to include a three-body system in which exchange reactions are allowed as well as excitations in the internal states. The results obtained are parallel to those in the quantum mechanical three-body theory of Faddeev and given in such a way that an introduction of approximation methods is possible without difficulty.
Unimolecular Decomposition and Intramolecular Energy Relaxation in the Suprahigh-Pressure Region
Authors: Oref I. , Schuetzle D. , Rabinovitch B. S.
Published: February 2004

The unimolecular rate constant ka for decomposition of chemically activated sec-butyl radicals was measured at pressures 55–203 atm of hydrogen. The reaction enters its high-pressure region above 0.01 atm. This study extends the range of earlier work. Butyl radicals were produced by mercury photosensitization of hydrogen: cis-2-butene mixtures. The value of ka was obtained from the ratio of stabilization (S) to decomposition (D) according to the equation ka = βωD / S, where β represents the relative collisional efficiency of hydrogen. The average value of ka was found to be 1.78(± 0.2) × 107 sec−1. No systematic change occurred in the value of ka with increase of pressure; this is taken as support for the continued validity of the random lifetime assumption at average intervals between collision of 2 × 10−13 sec, at least in this case. The disporportionation-recombination ratio of sec-butyl radicals was measured as 0.57 in agreement with earlier values from this laboratory.
Vibrational Spectra of Liquid Crystals. II. The Raman Spectrum of p-Azoxyanisole in Crystal, Nematic, and Isotropic Phases, 10–100-cm−1 Region
Authors: Bulkin Bernard J. , Prochaska Frank T.
Published: February 2004

The Raman spectrum of p-azoxyanisole has been observed in the crystal, nematic, and isotropic phases between 10 and 100 cm−1. The spectrum of an oriented single crystal at − 90°C shows that all 12 predicted lattice modes are found. In the polycrystalline sample, a soft mode is observed as the crystal–nematic transition is approached. The liquid crystal exhibits pseudolattice modes, which disappear in the isotropic melt. Assignments for the observed bands are discussed.
Transport Properties of Helium Using Beck's Potential
Authors: Taylor W. L. , Keller J. M.
Published: February 2004

A complete quantum mechanical phase-shift calculation for the transport properties and second virial coefficient of helium has been carried out using Beck's potential. The results are compared with experimental data and with the theoretical calculations based on the Lennard-Jones (12–6) potential. Beck's potential is found to represent the experimental data quite well from one degree to several thousand degrees Kelvin although the predicted results are a few percent high at high temperatures. We conclude that Beck's potential constitutes a significant improvement over previously investigated potentials for representing the helium interaction and therefore include extensive tables of the transport collision integrals.
NMR Investigation of the Nitrogen Quadrupole Coupling Constant in Liquid Samples
Authors: Jenks G. J.
Published: February 2004

Nitrogen quadrupole coupling constants have been evaluated for liquid samples from nuclear spin–lattice relaxation time measurements on the basis of a new molecular model. The relaxation times have been determined either from estimates of the magnetic resonance linewidth or by modifications of the progressive-saturation technique. Use of this model requires calculation of an “apparent molecular volume,” which is defined as the volume traced out by those molecular motions contributing to quadrupolar relaxation. Most of the quadrupole constants thereby obtained are in satisfactory agreement with measurements available from the techniques of pure quadrupole resonance and gaseous microwave absorption. When the apparent molecular volume cannot be calculated directly, an estimate of the coupling constant can be obtained from a comparison of molecules with similarly shaped apparent volumes.
Statistical Mechanics of Linear Molecules. VI. Solutions of the Percus–Yevick Integral Equation for a Hard-Core Model
Authors: Chen Yi-Der , Steele W. A.
Published: February 2004

The Ornstein–Zernike integral equation relating direct and indirect correlation functions has been generalized to linear molecules and solved numerically for a hard-core diatomic model with the aid of the Percus–Yevick approximation. The generalized PY equation was decomposed into a set of coupled integral equations by expanding the correlation functions in series of spherical harmonics. Iterative solutions of the Fourier-transformed form of these expressions were obtained after truncating the set. Correlation functions were calculated in this way as a function of density for two values of the molecular length and then used to evaluate compressibility factors from both the pressure and compressibility equations. It is found that the pair correlations at moderate densities obtained from the PY equation do not differ greatly from those calculated previously from density series. In addition, the various equations of state for this and similar hard-core nonspherical models do not differ greatly from one another or from the hard-sphere results, when the data are plotted as a function of reduced density using a reducing factor proportional to the molecular volume. A brief discussion is given of the limitations imposed upon these results by the mathematical approximations introduced.
Hydrogen Fluoride Elimination Chemical Laser from N,N-Difluoromethylamine
Authors: Padrick Thomas D. , Pimentel George C.
Published: February 2004

Hydrogen fluoride laser emission has been observed following flash photolysis of mixtures of CH4+N2F4 and CH3I+N2F4. Both N2F4 and NF2 were found to be good sources of fluorine atoms to cause HF laser emission through H-atom abstraction. At temperatures below 268°K and with photolysis occurring in a Vycor laser tube, F-atom production was reduced to the point that no emission was observed in the N2F4+CH4 system. However, emission was still observed in the CH3I+N2F4 system and was attributed to the following reactions: CH3I→ lim hνCH3+I*, CH3+N2F4→CH3NF2†+NF2, CH3NF2†→HCN+2HF†. At 248°K, emission was observed in only two transitions P1→0(5) and P1→0(6). The population ratio N1 / N0 has been found to be in the range 0.33–0.37 for the elimination reaction, the lowest yet recorded for a chemical laser.
Infrared Spectra of Divalent Metal Trifluoromonothioacetylacetonates
Authors: Siimann Olavi , Fresco James
Published: February 2004

The infrared spectra of the metal chelates of trifluoromonothioacetylacetone with nickel (II), zinc (II), palladium (II), cadmium (II), and lead (II) have been recorded over the range 1700–300 cm−1. Frequencies and force constants of in-plane vibrations in these chelates were determined by normal-coordinate analyses. Assignments of the metal–ligand vibrations were supported by the infrared spectrum of the dipyridine adduct of bis (trifluoromonothioacetylacetonato) nickel (II). Out-of-plane, methyl group and trifluoromethyl group normal modes were assigned by reference to structurally similar compounds. The influence of the strongly electron-withdrawing group, –CF3, on the chelate ring is discussed.
Configuration Interaction Effects on the Electric Field Gradient: 14N in Ammonia
Authors: Olympia Pedro L.
Published: February 2004

The 14N electric field gradient in ammonia, computed from a series of one-center expansion wavefunctions including configuration interaction with fixed molecular geometry and orbital parameters, is examined. Some emphasis is placed on major contributors to the field gradient other than the lone pair orbitals, and it is shown how the initial choice of important configurations can be made in relation to the field gradient value. The relation between total energy and field gradient is also examined.
Floating Spherical Gaussian Orbital Model of Molecular Structure. IX. Diatomic Molecules of First-Row and Second-Row Atoms
Authors: Chu San Y. , Frost Arthur A.
Published: February 2004

The FSGO model is applied to a large group of diatomic molecules of first-row and second-row atoms, namely, Li2, Be2, B2, C2, N2, O2, F2, CO, PN, P2, CS, SiO, LiF, LiCl, NaF, NaCl, LiNa, and Na2. Groups of diatomic molecules of similar assumed bond structure—CO and N2; N2, PN, and P2; CO, CS, and SiO; LiF, LiCl, NaF, and NaCl; Li2, LiNa, and Na2—are compared within each group. All the bond lengths of the previous systems are predicted quantitatively with an average deviation of 7%.
Multiple Quantum Transitions in Gas Phase ESR
Authors: Tiedemann P. , Schindler R. N.
Published: February 2004

Multiple quantum transitions were observed in atomic oxygen. Data are presented which show that the measured line intensities can be described theoretically.
Diffraction Pattern and Structure of Liquid Trimethylamine Decahydrate at 5°C
Authors: Folzer Cynthia , Hendricks R. W. , Narten A. H.
Published: February 2004

The scattering of x rays from a solution of trimethylamine in water having the same composition as the solid clathrate hydrate has been measured and analyzed at the melting point of the crystal. Two independent sets of small- and large-angle data were collected and combined into one; the resulting diffraction pattern covers an angular range 0.02 ≤ s ≤ 16 Å−1 not previously reported for any liquid. Correlation functions for the solution and for pure water are very similar in the region of intermolecular distances r > 2.5 Å, and the absence of interference maxima in the small-angle portion of the intensity functions precludes any significant deviation of the pair density from the uniform bulk density beyond approximately 8 Å; in other words, there is no “structure” beyond this distance. The x-ray data provide strong evidence for the existence of a three-dimensional network in the solution. Intensity and radial distribution functions have been calculated for two specific structural models. The average short-range order in the solution is explained equally well by either of the two models.
Fluorescence Lifetimes of Vibronic States of Naphthalene Vapor in the Region of Excitation from 3080–2150 Å
Authors: Laor U. , Ludwig P. K.
Published: February 2004

Fluorescence lifetimes of naphthalene vapor have been measured for narrow band excitation ranging from the first to third excited singlet states. It is found that the inverse lifetimes 1 / τ vary linearly with increasing excitation energy when exciting within the first two bands. For excitation within the third band, the variation is approximately exponential. An attempt is made to interpret the results in terms of theories of radiative and nonradiative transitions.
Localized Orbitals in the Theory of Correlated Wavefunctions
Authors: Steiner Erich
Published: February 2004

The proposition that localized orbitals are the orbitals most suitable for extending the wavefunction to take into account electron correlation is examined in the light of recent calculations of correlation energies. It is found, in agreement with the results of other authors, that the total interorbital correlation energy may be expected to be larger than the intraorbital energy in many systems of chemical interest, and that the ratio of these contributions is probably rather insensitive to a transformation of orbitals. It is also found that the correlation between electrons with like spins can make a considerable contribution to the correlation energy, and that this contribution is invariant with respect to a transformation of orbitals. The concept of nearest-neighbor orbitals is used to propose a new localization criterion which minimizes the interaction between electrons in orbitals localized on different atoms in a molecule. The dependence on the orbitals of the two-particle density function is examined. Orbital correlation factors are introduced which provide information as to the dependence of electron correlation on the distribution of electrons in the orbital approximation.
Diffusion of Ni2+ in High-Purity MgO at High Temperatures
Authors: Wuensch B. J. , Vasilos T.
Published: February 2004

Electron microbeam probe spectroscopy has been used to determine diffusion coefficients for Ni2+ in moderate- and high-purity MgO single crystals in an argon atmosphere over a temperature range of 1900–2460°C. Samples were encapsulated in pressed cylinders of MgO powder for protection against contamination and volatilization of both solute and host crystal. No study of mass transport in MgO had previously been extended to temperatures greater than 0.66 TM. The present measurements extend to 0.88 TM but fail to reveal a change in transport mechanism. An activation energy of 2.10 eV and D0 of 1.80 × 10−5 cm2/sec, previously obtained from measurements between 1000 and 1850°C, adequately describe the present results. No significant difference in transport rates was noted between the two grades of crystals employed despite notably different dislocation densities and impurity contents.
Analytical Distorted Wave Born Series for Vibrational Inelastic Scattering
Authors: Roberts R. E.
Published: February 2004

The distorted wave Born series, as developed by Thiele and Weare, is used to determine a simple second-order correction for the Jackson–Mott theory of vibrational inelastic scattering. The higher-order expression for the transition probability suggests an improved method for carrying out the usual first-order perturbation treatment which gives good agreement with exact results.