bluuebunny/crossref_metadata_2025 huggingface dataset:
Approximate Self-Consistent Molecular-Orbital Theory. VI. INDO Calculated Equilibrium Geometries
Authors: Gordon M. S. , Pople J. A.
Published: February 2004

The INDO (intermediate neglect of differential overlap) self-consistent theory has been used to calculate equilibrium geometries for a series of small polyatomic molecules with one or two polyvalent atoms (carbon, nitrogen, or oxygen). The results are compared with experimental data where available.
Proton and Deuteron NMR of Ice Polymorphs
Authors: Rabideau S. W. , Finch E. D. , Denison A. B.
Published: February 2004

Proton and deuteron nuclear magnetic resonances in the H2O and D2O ice polymorphs have been recorded at 60 MHz and at 8 MHz, respectively. Proton rigid-lattice second moments have been obtained at 75°K for ices Ih, Ic, II, V, VI, and IX. The modulation-corrected experimental values of the second moments ranged from 32.2 G2 in ice Ic to 37.9 G2 in ice VI. Theoretical inter- and intramolecular contributions to the second moments of these ices have been made, with corrections applied to the latter for librational and vibrational motions after the manner of Pederson. These theoretical results when compared with experimental values strongly support the bent hydrogen-bond model with an H–O–H angle near 104°, in agreement with conclusions reached from our recent neutron-diffraction pattern analyses of ices Ic, II, and IX. Deuteron quadrupole coupling constants for ices Ic, II, V, and IX have been estimated from derivative of dispersion traces by comparison with the ice Ih signal obtained under similar experimental conditions. Because of saturation effects, it was not possible to record deuteron resonances at the temperature of liquid nitrogen; however, signals were recorded at temperatures slightly below the respective phase-transition temperatures for these ice polymorphs. From the relatively constant values of e2qQ / h observed for these ices, it appears that the O–D bond distance is essentially unchanged in the different ice forms. This generalization is also supported by the results of neutron-diffraction studies.
Statistical Mechanics of Crosslink Orientation in a Rubber Network
Authors: Gordon M. , Love J. A. , Pugh D.
Published: February 2004

Existing theories of the origin of the Mooney–Rivlin C2 term in rubber elasticity theory are briefly reviewed. The James–Guth model for the deformation of a rubber network is generalized in a consistent manner to allow for the statistical mechanism of the re-orientation of cross links. An explicit expression for the angular probability distribution of cross links is obtained for a somewhat simplified James–Guth model. The contribution of the re-orientation of cross links to the elastic modulus is calculated and found to be insignificant.
Vaporization of Aluminum Phosphide
Authors: Maria G. De , Gingerich K. A. , Piacente V.
Published: February 2004

The vaporization of aluminium phosphide was investigated over the temperature range of 1270°–1800°K using the Knudsen effusion method in combination with mass spectrometry. Aluminium phosphide decomposes according to the reaction 2AlP(s) → 2Al(g) + P2(g). The enthalpy for Reaction (1), ΔH°298, as calculated by the second- and third-law method is 261.7 ± 5.9 and 254.8 ± 2.1 kcal/mole, respectively. The second- and third-law enthalpies ΔH°298 for the reaction 4Al(g) + Al2O3(s) → 3Al2O(g) have been determined as − 10.7 ± 2.0 and − 10.5 ± 0.5 kcal/mole, respectively. The error terms given represent the standard deviation. On the basis of a selected value of 255.0 ± 6.0 kcal/mole for the enthalpy of Reaction (1) and of pertinent literature data, the standard heat of aluminium phosphide formation, ΔH°f,298 = − 28.2 ± 3.2 kcal/mole is obtained.
ENDOR Study of Irradiated l-Glutamic Acid Deuterochloride
Authors: Whelan D. J.
Published: February 2004

X irradiation of l-glutamic acid·DCl yields the free radical DO2C–CH–CH2–CH(ND3+)(CO2D). The hyperfine splitting tensors were calculated from endor data, and from the subsequent analysis of these data, the structure of this radical was defined. This result was verified from an analysis of the ESR (electron spin resonance) spectra of x-irradiated 2,3,3-trideutero-l-glutamic acid·HCl.
High-Temperature Thermodynamic Properties of Oxygen-Deficient Urania
Authors: Tetenbaum M. , Hunt P. D.
Published: February 2004

Measurements of oxygen partial pressures over oxygen-deficient urania compositions, including the difficult region very close to stoichiometry, have been made in the temperature range 2080–°2705°K. The transpiration method was used with flowing H2–H2O mixtures in order to fix the oxygen potential of the carrier gases. The shape of the isotherms are qualitatively in accord with expectations based on defect theory. At the lower temperatures (2080°–2390°K), the isotherms exhibit a sharp increase in oxygen partial pressure near the stoichiometric composition. At the higher temperatures (2495°–2705°K), large deviations from the stoichiometric composition are accompanied by relatively small changes in oxygen partial pressures. Relative partial molar free energies, entropies, and enthalpies of solution were calculated and discussed in relation to defect theory.
Vacuum-Ultraviolet Photolysis of N2O. I. Metastable Species Produced at 1470 Å
Authors: Young R. A. , Black Graham , Slanger T. G.
Published: February 2004

Various photometric techniques have been used to obtain information about the reactions and quantum yields of the metastable species formed in N2O photolysis at 1470 Å. The total quantum yield of atoms is 1.0; O(1S) is produced with a quantum yield of 0.5; O(1D) has a measured quantum yield of 0.55, although this value may include electronically quenched O(1S); the N2(A3Σ) quantum yield is 0.08, which, from spin considerations, must also be equal to the O(3P) yield. N(2D) is produced, and reacts with N2O, apparently quite inefficiently, to give NO(B2Π).
Infrared Spectrum and Structure of Lithium Hexafluoroacetylacetonate–Tetramethylethylenediamine Adduct
Authors: Shobatake Kosuke , Nakamoto Kazuo
Published: February 2004

The infrared spectra of monomeric 7Li hexafluoroacetylacetonate–tetramethylethylenediamine adduct and its 6Li analog have been obtained from 4000–90 cm−1 in benzene solution. Normal-coordinate analysis has been carried out to estimate the Li–O stretching force constant as well as to assign the Li–O stretching modes. The results indicate that two bands at 544 and 527 cm−1 of the 7Li adduct are due to the Li–O stretching modes. The corresponding Li–O stretching force constant is estimated to be 0.52 mdyn/Å.
Vibrational Spectra of the Polymorphic Solids of Methylene Iodide
Authors: Brown C. W. , Obremski R. J. , Allkins J. R. , Lippincott E. R.
Published: February 2004

Polarized infrared spectra of single crystals of methylene iodide solid I and the laser–Raman spectra of polycrystalline solid I at 90°K have been measured. The absence of the a2 fundamental in the infrared spectrum and the lack of crystal-field splitting in both the infrared and Raman spectra suggest that the site group for the solid I phase is C2υ. The infrared polarization results confirm this assignment of the site group and further indicate that solid I belongs to the orthorhombic crystal system with either C2υ or D2h factor group symmetry. The laser–Raman spectrum of a polycrystalline film of methylene iodide solid II has also been recorded. The observed correlation splittings give new spectroscopic evidence for the previous assignment of the crystal structure as monoclinic C2h.
Hydrogen-Atom Polarizability as a Hartree–Fock Perturbation Expansion: A Geometric Approximation to Atomic Polarizabilities
Authors: Schulman J. M. , Musher J. I.
Published: February 2004

The hydrogen-atom dipole polarizability α is obtained by a double perturbation expansion based on a Hartree–Fock H0. The expansion α = α0 + λα1 + λ2α2 + ···, where λ is the continuous parameter for the Hartree–Fock perturbing potential, is found to be extremely close to a geometric series with αi+1 / αi = 0.433 ± 0.002. Computation of α as α0[1 − (α1 / α0)]−1 gives 4.499a03 in excellent agreement with the exact value 92a03. The origin of this geometric character is examined and its applicability to some many-electron polarizabilities is demonstrated empirically.
Rayleigh–Schrödinger Perturbation Theory in Truncated Basis Sets
Authors: Salzman W. R.
Published: February 2004

Procedures are presented for the computation to arbitrary order of Rayleigh–Schrödinger perturbation theory corrections in finite basis sets of functions. The basis set need be neither eigenfunctions of the zero-order Hamiltonian nor orthonormal. A formula due to Blinder for second-order perturbation theory in nonorthonormal basis sets is rederived and extended to arbitrary order.
Nonempirical Molecular-Orbital Calculations for Protonated Formaldehyde, Acetaldehyde, and Formic Acid
Authors: Ros P.
Published: February 2004

Nonempirical molecular-orbital calculations based on the Roothaan scheme are reported for protonated species of formaldehyde, acetaldehyde, and formic acid. In these calculations a small Gaussian basis is used, which is obtained from optimized atomic orbitals. The results are interpreted with the help of a Mulliken-type population analysis. A number of structural parameters was obtained by minimization of the total energy. Values found for the C–O distances are: 1.23 Å in formaldehyde, 1.27 Å in protonated formaldehyde, 1.31 Å in protonated formic acid. In all protonated molecules the C–O–H angle was close to 120°. For protonated acetaldehyde the stability of the configuration [Complex Equation] was found to be greater than that of [Complex Equation] by 1.4 kcal/mole. For protonated formic acid the stablest system was found to be [Complex Equation] followed by [Complex Equation] which is 1.5 kcal/mole higher in energy. The other possible structure [Complex Equation] was found to be another 6.0 kcal/mole higher in energy. The mechanism of the intramolecular interconversion that transforms one configuration of the protonated system into another depends on the strength of the C– bond. In protonated aldehydes a rotation around the C–O bond is rather difficult and has an energy barrier of 25–30 kcal/mole. A motion in the plane, however, requires only 17–18 kcal/mole, so that it is likely that in aldehyde systems this motion causes the interconversion. In protonated formic acid the C–O bond is not as strong as in aldehydes, and a rotation around the C–O bond requires only 15 kcal/mole, while the motion in the plane still requires 17 kcal/mole.
Triplet State of the Nitrite Molecule–Ion
Authors: Maria H. J. , Wahlborg A. , McGlynn S. P.
Published: February 2004

The absorption spectra of aqueous solutions of a number of nitrite complexes exhibit a common absorption band at ∼ 23 kK. This absorption band is responsible for the color of those metal nitrites in which the cation is colorless. This band is assigned as the T1 ← S0 transition of the nitrite molecule–ion. The intensification of the T1 ← S0 transition in the heavier-metal nitrites is a spin–orbit enhancement brought about by the heavy-metal cation. Equilibrium constants for Cd(II), Pb(II), and Tl(I) nitrite complexes- and extinction coefficients for the 23-kK band have been elicited. The 23-kK band is the reverse absorption to the phosphorescence emission; the T1 → S0 radiative lifetimes correlate with those calculated from oscillator strengths of the 23-kK absorption band.
Electronic Structure of Ionized Molecules. VII. Ethylene
Authors: Lorquet A. J. , Lorquet J. C.
Published: February 2004

The potential-energy surfaces of the neutral C2H4 molecule and its positive ion have been studied, and parts of them have been calculated point by point by a semiempirical self-consistent method (SCF CNDO/2 with slight modifications). The calculations show that (1) the equilibrium configuration of the C2H4+ ion is twisted (D2 symmetry group). The potential function corresponding to the twisting motion has a double minimum and is remarkably flat. The vibrational structure observed in the different Rydberg states of C2H4 and C2D4 can be fitted to such a potential function. Values for the angle of twist and the potential barriers have been proposed. (2) The exchange phenomenon occurring among hydrogen atoms (scrambling) in the ion takes place through the asymetrical configuration CH3CH+.
Excitation by Electron Impact of Vibrational Transitions in Water and Carbon Dioxide at Kinetic Energies between 30 and 60 eV
Authors: Skerbele Ausma , Dillon Michael A. , Lassettre Edwin N.
Published: February 2004

Vibrational excitation by electron impact, in the kinetic-energy range 30–60 eV, has been studied for water vapor and carbon dioxide. Intensities relative to elastic scattering have been determined at scattering angles to 15°. Fundamental vibrations are excited with much greater intensity than either overtones or combination bands, although the latter appear (weakly) in the spectra. Weak scattering in the energy-loss region 4.5–7.0 eV and its interpretation is discussed.
Flash Vacuum Pyrolysis. III. Formation and Ionization of Cyclopentadienyl, Cyclopentadienyl Nickel, and Dihydrofulvalene (Dicyclopentadienyl) Derived from Nickelocene
Authors: Schissel Paul , McAdoo D. J. , Hedaya E. , McNeil D. W.
Published: February 2004

The pyrolysis of nickelocene has been investigated over a wide temperature range (300°–1400°K), at low pressures (∼ 10−3–10−4 torr), and short contact times (∼ 1 msec) in a quartz reactor coupled directly to the ionization source of a mass spectrometer. The cyclopentadienyl and cyclopentadienyl nickel radicals were detected and characterized by their ionization potentials, shutterability, and reactivity with allyl and methyl radicals. The cyclopentadienyl nickel radical, which is produced in relatively low yields, was found to react only with allyl radicals at our conditions while cyclopentadienyl undergoes reactions with both allyl and methyl. Also the cyclopentadienyl radical dimer was detected and its ionization potential measured. Appearance potentials for nickel, cyclopentadienyl, and cyclopentadienyl nickel ions generated from nickelocene on electron impact were obtained. These, in combination with the corresponding ionization potentials, lead to estimates of the dissociation energies of nickelocene to cyclopentadienyl nickel and cyclopentadienyl radicals or to nickel and cyclopentadienyl radicals. The results imply that thermal fragmentation of nickelocene occurs on the reactor walls. A value for the heat of formation of the cyclopentadienyl radical is derived and discussed.
Ionization of Hydrogen, Hydrogen Deuteride, and Deuterium on Impact of Metastable Helium Atoms
Authors: Penton J. R. , Muschlitz E. E.
Published: February 2004

Relative cross sections for the ionization of H2, HD, and D2 have been measured using a thermal-energy beam of 2 3S1 and 2 1S0 helium atoms. The cross sections for the production of H2+, HD+, and D2+ increase in this order. The ions are observed to have average kinetic energies of at least 0.08 eV and perhaps as much as 0.3 eV. The isotope effect is explained in terms of the initial formation of a preionizing state which may then either dissociate or ionize.
Photodetachment of Electrons from SH−
Authors: Steiner Bruce
Published: February 2004

The cross section for photodetechment of electrons from SH− for the first 0.75 eV above threshold (λ = 534.7 to 403.0 nm) has been measured in a crossed-beam experiment. The cross section rises rapidly in the first 0.15 eV (Δλ = 35 nm) to the value 1.9 × 10−17 cm2 determined with a total uncertainty of ± 0.4 × 10−17 cm2 given by the square root of the sum of the squares of the maximum observed deviation and the allowances for various systematic factors; over the rest of the observed range it is constant. The detailed shape of the cross section vs λ curve has been employed to derive the SH− structural parameters (and their upper limits of uncertainty), which are indistinguishable from those of the neutral free radical: R = 0.135 ± 0.002 nm, ωe = 2700 ± 300 cm−1, and Be = 9.46 ± 0.32 cm−1. The electron affinity is identified with the observed photodetechment threshold, 2.319 ± 0.010 eV. These results are in general agreement with the recent calculations of Cade. Evidence is presented for the importance of inclusion of long-range forces in dealing with the threshold behavior of photodetechment from heteronuclear diatomic negative ions.
Study of Some of the Parameters Affecting Knudsen Effusion. V. Free-Path Considerations in Small Knudsen Cells
Authors: Ward John W.
Published: February 2004

Monte Carlo methods have been used to calculate distributions describing the behavior of particles in a typical, small Kundsen cell. For pressure conditions corresponding to free-molecule flow, three distributions were obtained: (1) the wall collisions per particle, (2) the path lengths of the particles between collisions, and (3) the total path lengths of the particles. Knowledge of these distributions provides considerable insight into the behavior of particles at the beginning of the transition region. In particular, the relationship between gaseous collisions and the Knudsen number is clarified. Also, it is shown that the population of free paths depends on the geometry of the cell but is independent of the condensation coefficient αc. The lifetime of a given particle, however, is strongly dependent on αc. The analysis, which can be applied to any vapor species, is described for gold.
Natural Orbitals for H2
Authors: Konowalow Daniel D. , Barker William H. , Mandel Richard
Published: February 2004

Natural-orbital (norb) expansion coefficients are presented for the LCAO–MO–SCF–CI wavefunction of Fraga and Ransil for separations between 1.0 and 12.0 bohrs. These results are compared in detail with those obtained by Shull and Prosser for the He2++ system. Judged at the two-norb level, the norb expansion converges faster for He2++ than for H2 at all internuclear separations. Otherwise, the norb coefficients for the two systems have quite similar dependence on scaled separations. The occurrence of more than one positive norb coefficient is found to be an intrinsic property of the approximate wavefunction.
Matrix-Isolation Spectra of Discharge “Sputtered” Metals
Authors: Shirk James S. , Bass Arnold M.
Published: February 2004

Atomic Cu, Ag, Cd, and Fe are produced by bombarding the appropriate metal with positive ions from a microwave discharge. The process is similar to sputtering. The metal atoms are trapped in an inert-gas matrix on a cold window and their uv spectra observed. This is a new method for isolating high-melting materials in a matrix for spectroscopic study.
Quadrupole Resonance Study of Molecular Motion in Solid Hydrazine
Authors: Zussman A. , Alexander S.
Published: February 2004

Linewidths and spin–lattice relaxation times of the six nuclear quadrupole resonance lines of 14N in hydrazine were measured from 200° to 260°K using pulse technique. Cross-relaxation (Overhauser) experiments between corresponding transitions at the two sites were also performed. It is shown that in this temperature range the dominant relaxation mechanism is a molecular motion which interchanges nuclei between the two inequivalent crystallographic sites. A detailed analysis of the cross-relaxation experiment and of the anisotropies in spin–lattice relaxation leads to a determination of the relative orientation of the principal axes system of the field-gradient tensors at the two sites. The molecular motion has an activation energy of 14.3 ± 0.4 kcal/mole and a rate ∼ 2500 sec−1 at 250°K.
Electron Spin Relaxation in Gases. I. Bis(perfluoromethyl) Nitroxide
Authors: Schaafsma Tjeerd J. , Kivelson Daniel
Published: February 2004

The ESR spectra of the relatively large bis (perfluoromethyl) nitroxide (BFMN) radical has been studied in the gas phase. At low pressures, i.e., below 0.1 atm, the spectrum consists of a 480-G-wide Gaussian line which presumably arises from the unresolved nuclear hyperfine and spin–rotational lines. (The rootmean-square spin–rotational coupling constant is about 3.7 G.) As the pressure is increased by adding more radical or a diluant diamagnetic gas, the line narrows and becomes more Lorentzian. At total pressures, of radical plus diluant, above 10 atm the lines are Lorentzian and their widths vary as the inverse total pressure. This behavior can be explained semiquantitatively by assuming that the angular momentum, and hence the spin–rotational interaction, is relaxed by intermolecular collisions which can be understood in terms of a simple kinetic model. The cross sections for the relaxation of the angular momentum of the BFMN radical have been measured and the ratios, eJ, of these cross sections to the kinetic or van der Waals cross sections were determined. Approximate values of eJ are 0.28, 0.45, 0.70, and 0.84 for BFMN with N2, CF4, CF3H, and BFMN, respectively. As expected, eJ increases as the size and polarity of the colliding molecule increases. At high total pressures and low radical partial pressures the spin–rotational interactions are quenched and the nuclear hyperfine splitting is observed. At high total pressure and relatively high radical partial pressures (above 0.25 atm) the hyperfine splitting is coalesced into a single-exchange narrowed line. The cross section for spin exchange between BFMN radicals is about 0.04 of the kinetic cross section; the amount of exchange is, of course, proportional to the BFMN partial pressure.
Ultrasonics and Water Structure in Urea Solutions
Authors: Beauregard Donald V. , Barrett Robert E.
Published: February 2004

Ultrasonic absorption and velocity in aqueous urea solutions have been measured for concentrations up to 15m and at temperatures down to − 10°C. The velocity itself was measured at pressures up to 2000 lbs/in.2. The structural part of the absorption decreases with increasing concentration of urea, until a limiting value is reached. The slope of the velocity-vs-pressure curve as a function of temperature shows that urea solutions look like water at high temperatures. These data suggest that the net effect of dissolving urea is to cause the clusters in water to be broken up.
Matrix-Isolation Study of the Vacuum-Ultraviolet Photolysis of Trifluorosilane. The Infrared Spectrum of the Free Radical SiF3
Authors: Milligan Dolphus E. , Jacox Marilyn E. , Guillory William A.
Published: February 2004

In studies of the vacuum-ultraviolet photolysis of SiHF3 suspended in argon, nitrogen, and carbon monoxide matrices at 14°K, evidence has been obtained indicating that H-atom detachment occurs and that the SiF3 free radical is stabilized. All of the vibrational fundamentals of SiF3 have been observed in these experiments. The appearance of two stretching fundamentals requires that the molecule be non-planar. A more detailed consideration of the pattern of vibrational absorptions indicates that the angle between each Si–F bond and the threefold symmetry axis of the molecule is approximately 71°, close to the value characteristic of sp3 hybridization of the valence electrons about the central atom. Force constants have been estimated using a four-constant valence-force potential, and the thermodynamic properties of SiF3 have been calculated.
Temperature Dependence of Kinetic Isotope Effects in Gas-Phase Reactions. I. Theory of the High-Temperature Limit
Authors: Tschuikow-Roux E. , Macdonald Digby D.
Published: February 2004

The theory of the high-temperature limit of the temperature dependence of the kinetic isotope effect in gas-phase reactions is discussed in detail and the resulting high-temperature limit is interpreted in terms of contributions from the initial states and activated complexes.
Anharmonicity in Polyatomic Molecules. The CH-Stretching Overtone Spectrum of Benzene
Authors: Henry Bryan R. , Siebrand Willem
Published: February 2004

A long series of CH-stretching overtones in the infrared and visible spectrum of benzene can be analyzed using a single anharmonicity constant (− 57.5 cm−1). This anharmonicity is associated with an independently vibrating local CH oscillator and the spectrum is interpreted in terms of such a local-mode representation. A transformation is made to normal modes which leads to five different normal-mode anharmonicity constants, which are representative of the 13 different CH-stretching anharmonicity constants that characterize benzene. The CH-overtone spectrum of benzene is described in terms of its normal-mode components. A method of assigning relative intensities to these components is developed, and, along with the calculated normal-mode anharmonicity constants, is used to construct the overtone spectrum as a superposition of Lorentzian bands calculated for each individual component. The maxima of these bands compare favorably with the observed band maxima. By adjusting the local-mode anharmonicity constant from − 57.5 to − 55.2 cm−1, the agreement can be made perfect so that the latter value appears to be the appropriate local-mode CH-stretching anharmonicity constant in benzene. This number is relevant to the theory of radiationless transitions in aromatic hydrocarbons. The effect of introducing anharmonic coupling between local modes is investigated and found to be unimportant.
Ab Initio SCF MO and CI Studies of the Electronic States of Butadiene
Authors: Buenker Robert J. , Whitten J. L.
Published: February 2004

Ab initio SCF MO calculations carried out for the ground electronic states of cis- and trans-butadiene show the trans configuration to be more stable by approximately 5 kcal, total energy − 154.7103 hartrees. The set of SCF MO's resulting from these calculations is subsequently employed as a basis for a series of configuration–interaction (CI) treatments investigating the electronic spectrum of butadiene. Results of CI treatments which consider only π → π* single excitation configurations bear a definite resemblance to previous semiempirical studies and give rise to the excited state ordering Bu3, 3Ag, 1Bu, andAg1, in agreement with the current experimental assignment although the singlets are calculated relatively high in energy. Extension of the CI treatment to include multiple excitation configurations and σ → π* excitation decidely alters the spectrum by lowering the Ag1 to 2.5 eV below the Bu1, and also by introducing Bu3andAu3 states lower than the Bu1: a σ → π*1Au state is also calculated to lie close to the Bu1. The relevance of these ab initio results to basic assumptions of the semiempirical model and to the current experimental interpretation of the butadiene spectrum is discussed.
Quantitative Correlations between Rotational and Vibrational Spectroscopic Constants in Diatomic Molecules
Authors: Calder G. V. , Ruedenberg Klaus
Published: February 2004

The rotational constants Be, the vibrational frequencies ωe, the vibration–rotation interaction constants αe, and the anharmonic constants xe of 160 diatomic molecules are examined in order to determine whether or not there exist consistent relationships between them. Basing the investigation on the Dunham analysis the following correlations are found to be valid within about 5%: (1) The Dunham constants a1 and a2 are identical for almost all the molecules examined. (2) For diatomics formed from atoms belonging to the ith and jth columns of the periodic table the following monotonic relations exist: Be / ωe = Kijωe1 / 2 + Lij, αe/Be = Kij′ωe1 / 2 + Lij′, xe = Kij″ωe1 / 2 + Lij″. These equations are shown to be interrelated by virtue of the constancy of a1 and a2. The scope and limitations of the correlations are discussed and several examples are given pertaining to their use for the resolution of incorrect or ambiguous spectroscopic information.
Isotope Effects in the Photoionization Yields and the Absorption Cross Sections for Ethylene and n-Butane
Authors: Person James C. , Nicole Paul P.
Published: February 2004

The absorption cross section σ and the photoionization yield η (the probability that photon absorption produces ionization), are reported for C2H4 and C2D4 at 44 photon energies between 10.44 and 11.78 eV, and they are reported for n-butane and n-butane-d10 at 37 photon energies between 10.56 and 11.78 eV. For ethylene, the nature of the isotope effects on η, σ, and the photoionization cross sections, σı(σı = ησ), indicates that the increase in η upon deuteration is not the result of a simple competition between pre-ionization processes and atomic-rearrangement processes in the superexcited states. The isotope effects for n-butane and the implications of the results for radiation chemistry are also discussed.
Infrared Spectrum in Polarized Light of CH2Br2 and CD2Br2. Determination of the Crystal Structure
Authors: Marzocchi M. P. , Manzelli P. , Schettino V. , Califano S.
Published: February 2004

The infrared spectra of crystalline CH2Br2 and CD2Br2 were measured at liquid-nitrogen temperature, between 4000 and 200 cm−1. Splitting of the normal modes was observed for several fundamentals. These data, together with polarization measurements on polycrystalline oriented films, were used to study the crystal structure of CH2Br2. The technique of mixed crystals was used to prove the nature of the observed crystal splittings. The data accumulated on this molecule are consistent with a monoclinic C2h5(P21 / c) unit cell or with a triclinic Cg1(p̄) cell with two sets of sites. The differences are discussed in terms of close packing.
Vapor Pressure of the Isotopic Ethylenes. IV. Liquid Ethylene-d3 and -d
4
Authors: Ishida Takanobu , Bigeleisen Jacob
Published: February 2004

The purification of ethylene gas samples (200–400 cc NTP) to a chemical purity of 99.9997% is described. The vapor pressures of liquid ethylene-d3 and ethylene-d4 have been measured and compared with that of C2H4 in the temperature range 115°–180°K. The reduced partition function ratios of liquid C2HD3/C2H4 and C2D4/C2H4 compared to the ideal-gas reference state are derived from the vapor-pressure measurements. The experimental reduced partition function ratios of the liquid are in satisfactory agreement with cell model calculations of Stern, Van Hook, and Wolfsberg. The latter calculations have been extended to include interaction force constants between the internal and external modes as well as the external modes among themselves. The experimental partition function ratios show significant curvature in a plot of T lnfe / fgvs 1 / T in contrast to the almost linear behavior inherent in the harmonic oscillator model. Analysis of the curvature shows that the mean square intermolecular force in liquid ethylene decreases by a factor of 2 in the temperature range from 104°–180°K. Correlations of the liquid partition function ratio with the liquid density are consistent with a short-range intermolecular force.
H and F Bands in Alkaline-Earth Fluorides
Authors: Tanton G. A. , Shatas R. A. , Williams J. E. , Mukerji Ambuj
Published: February 2004

Spectral positions of the F-band peaks induced in CaF2, SrF2, and BaF2 by irradiating at LHe temperatures with 50-kV x rays were determined to be at 377, 442, and 611 nm, respectively, and fit an Ivey–Mollwo relation having an exponent of 4. The absorption spectrum of each of the three alkaline-earth fluorides consists of the F band and a band at a shorter wavelength. Both appear to be composite bands. A simultaneous decrease of both bands was obtained by dark bleaching and also by illuminating with F-band light. It is suggested that the bands at shorter wavelength are analogous to the near-uv bands seen in x-ray-irradiated alkali halides. Spectral positions of the peaks assigned to be due primarily to H centers are at 314, 325, and 364 nm in CaF2, SrF2, and BaF2, respectively, and fit an Ivey–Mollwo relation with the exponent 1.5.
Calculation of the Mean-Square-Displacement Function for the Slow Motion of Long-Chain Molecules and Its Application to Neutron Diffusion
Authors: Jannink G. , Saint-James D.
Published: February 2004

We calculate the mean-square-displacement function for the motion of a polymer chain in solution. The motion is described by means of coupled Langevin equations. The peculiar behavior in square root of time obtained by de Gennes is rederived here. It is shown, however, that it is restricted to a certain time interval which depends on the number of beads and rank of the beads at which the mean-square displacement is computed. Implications for a neutron-scattering experiment are discussed. It is also seen that for infinite polymers the influence of inertial effects is entirely negligible, thus showing that the Bueche and Rouse models are equivalent in this respect.
Ground States of Conjugated Molecules. X. 19F NMR Chemical Shifts in Aryl Fluorides
Authors: Dewar Michael J. S. , Kelemen Jozsef
Published: February 2004

The procedures developed in previous papers of this series have been extended to aromatic fluorides, using 19F NMR chemical shifts as a guide to the selection of parameters for fluorine. Attempts to correlate chemical shifts with the local π-electron density on fluorine proved unsatisfactory, the correlation depending on the number of atoms ortho to fluorine that carry p or π electrons. Similar results followed for charge densities calculated by a recently developed semiempirical SCF MO treatment in which all the valence electrons are included. Analysis of the Karplus–Das–Prosser–Goodman treatment of chemical shifts suggested that this “ortho effect” arose from neglected long-range interactions. A treatment including these was developed and shown to account well for the 19F chemical shifts of nearly 100 aryl fluorides.
Electronic Structure and Electronic Spectrum of Nitrogen Dioxide: Study by the Nonempirical Self-Consistent Field Method
Authors: Burnelle L. , May A. M. , Gangi R. A.
Published: February 2004

The nonempirical self-consistent field method, in its form devised by McWeeny, has been applied to the ground state and to a series of excited states of nitrogen dioxide, using as basis functions Gaussians centered on the various atoms of the molecule. Potential-energy curves have been obtained by varying the bond angle; the resulting equilibrium bond angle for the ground state compares favorably well with the experimental value. It is found that five transitions fall into the range covered by the long-wavelength spectrum, which explains the complexity of the latter. From the correlations between the electronic states of the bent molecule and those of the linear system, an attempt is made to obtain indications concerning the potential-energy surfaces of the NO+O system. Finally, the significance of the potential-energy diagram obtained is discussed in relation with two problems: the mechanism of the photolysis of the compound, and the anomalously long radiative lifetime of its first doublet excited state resulting from fluorescence decay.
Ultrasonic and Infrared Studies of the Lambda Transition in NaNo3
Authors: Craft W. L. , Slutsky L. J.
Published: February 2004

The velocity and attenuation of longitudinal and transverse acoustic waves propagating along the three-fold axis of NaNO3 have been measured from room temperature to 300°C. Strong frequency-dependent ultrasonic attenuation is observed at temperatures immediately above and below the λ point. From the attenuation a relaxation time for the equilibration of the long-range order at constant entropy of 4.3 × 10−10 sec is estimated. The totally symmetric stretching mode of the nitrate ion, inactive in the ordered NaNO3 structure, is possibly active in the high-temperature disordered phase. A weak infrared absorption is found at an elevated temperature at the anticipated frequency of ν1 in NaNO3. The temperature variation of the absorption through the transition is consistent with the notion that there is no abrupt change in short-range order at the λ point.
Molecular Association in TiCl4: Laser Raman Spectroscopy and Chlorine Isotope Effects
Authors: Griffiths James E.
Published: February 2004

Evidence for molecular association of liquid TiCl4 is presented. The chlorine isotope structure in the totally symmetric fundamental cannot have originated from a simple tetrahedral molecule belonging to the Td point group. High-resolution measurements, which indicate an associated complex of lower symmetry, possibly D2h, C2h, or C2υ, are interpreted in terms of a chlorine-bridged dimer structure. Additional support for an associative phenomenon rests upon some Raman data obtained for TiCl4 diluted with CCl4. The depolarization ratio (ρs) for the ν1 fundamental is 0.008, substantially greater than for ν1 of CCl4(0.004), but more than an order of magnitude smaller than previously reported (0.12). The ratio drops to 0.007 for a 25 mole % solution of TiCl4 in CCl4, but depolarized fundamentals have constant values of ρs = 0.75 as expected. Earlier results are reviewed and reinterpreted in terms of the new dimer model for liquid TiCl4.
Monte Carlo Studies of Configurational and Thermodynamic Properties of Self-Interacting Linear Polymer Chains
Authors: Mazur Jacob , McCrackin Frank L.
Published: February 2004

Non-self-intersecting walks on the simple cubic and face-centered cubic lattices are used as a model for the linear polymer chain with excluded volume and nearest-neighbor interactions between the chain elements. The statistical properties of this model are investigated using the modified Monte Carlo technique for inversely restricted sampling. The following properties are investigated: the limiting distribution function of chain dimensions, the dependence of mean square length of the chain on the number of chain elements, and the thermodynamic properties of the chain. The results of these investigations are presented by a set of parametric representations. Each of these representations includes a parameter which is descriptive of long-range interactions in the polymer chain. These parameters are investigated for their dependence on the nearest-neighbor interaction parameter. A particular value for the nearest-neighbor interaction parameter is found, in which long-range interaction parameters reduce to the values they would attain were the chain simulated by an equivalent Markovian chain model. Thus, the conditions are found which uniquely define the Flory's theta point of the single chain. It is also found that an infinitely long single chain undergoes a phase transition which is associated with abrupt changes in the thermodynamic properties of the chain at a critical range of the nearest-neighbor interaction parameter.
Far-Infrared and Raman Spectra of Phosphonium Iodide and Phosphonium Iodide-d
Authors: Durig J. R. , Antion D. J. , Baglin F. G.
Published: February 2004

The infrared spectra of polycrystalline PH4I and PD4I have been recorded from 33 to 550 cm−1 at −170°C. Only three bands were manifest in this region; two of them are translatory motions and the other is a librational mode. The Raman spectra of polycrystalline PH4I and PD4I have been recorded at 23°C. Two librations and four translations have been assigned both compounds. Seven internal fundamentals were observed in the Raman spectrum of PH4I and five internal fundamentals were observed in the Raman spectrum of PD4I. Many of the other bands found in the Raman spectra were attributed to overtones and combinations involving external and internal fundamentals. The barrier to reorientation of phosphonium ions in the lattice was calculated from observed librational frequencies, and the barrier height for PH4 ions is 6.4 kcal/mole and for PD4 ions is 6.2 kcal/mole. The barrier height and orientation for the NH4 ions were compared to those for the PH4 ions (in isomorphous phase III NH4Br); the differences can be rationalized on the basis of a simple electrostatic interaction and steric hindrance.
Hot-Atom Reaction Yield and Energy Distribution
Authors: Thomsen P. V.
Published: February 2004

A general integral equation for the reaction probability of energetic ions slowing down in an arbitrary system is formulated. The equation is found to be equivalent to the Boltzmann equation for the energy distribution of incoming particles. An approximate solution corresponding to continuous slowing down is derived, expressing, e.g., the energy distribution through the flux distribution of incoming particles, the stopping power of the system, and the reaction cross sections. The approximate solution for the energy distribution is better the softer the potential, and is found to be accurate if stopping is dominated by target atoms with mass widely different from the mass of the incoming particles. In case of equal masses, the discrepancy is of the order of 50% for a nonreactive system and realistic interactions.
Specific-Heat Anomaly in Solidified Gases due to O2 Impurity
Authors: Burford J. C. , Graham G. M.
Published: February 2004

A specific-heat anomaly of Schottky type has been observed in the heat capacities of both solid CO and N2, which is due to O2 impurity. For both host lattices the peak of the anomaly is at T ∼ 1.95°K, and the shape corresponds to a two-level system with a splitting of 5.14°K and a weight of 2 for the upper level. It is believed to be due to the spin splitting of the molecular oxygen ground state.
Structure of the Alkali Hydroxides. II. The Infrared Spectra of Matrix-Isolated CsOH and CsOD
Authors: Acquista N. , Abramowitz S. , Lide D. R.
Published: February 2004

The infrared spectra of matrix isolated CsOH and CsOD have been observed. Both the CsO stretching and the bending mode have been assigned for each species. The Cs–O stretching mode ν2 is observed at 335.6 and 330.5 cm−1 for CsOH and CsOD, respectively; the bending mode ν2 is observed at 306 and 226 cm−1, respectively. Combination of the infrared results with previous microwave measurements indicates that the equilibrium configuration of CsOH probably does not deviate significantly from linearity. The assumption of a linear model with a harmonic bending potential leads to a bending force constant of 0.047 mdyn· Å.
Nuclear Magnetic Resonance Study of Li3Sb, Na3Sb, and Na3As Powders
Authors: Ossman G. W. , McGrath J. W.
Published: February 2004

NMR spectra showing quadrupole splittings were obtained for 7Li and 23Na in some I–V intermetallic compounds. All are hexagonal and are reputed to be semiconductors. The Li (Na) atoms lie in two sites: planes containing the Sb (As) atoms (site 1) and parallel planes containing only the Li (Na) atoms (site 2). Coupling constants for sites 1 and 2 are, respectively: 75.2 and 17.6 kc/sec in Li3Sb; 1.49 and 0.44 Mc/sec in Na3Sb; 1.70 and 0.53 Mc/sec in Na3As. Asymmetry parameters are zero. Small magnetic shifts appeared in Na3Sb and Na3As. Measured coupling constants are not consistent with an ionic model. Covalent bonding must exist. Suchet's model, of form Na(2)2[Na(1)2−As2+], suggests sp2 hybrid bonds in the Na–As plane consistent with its structure. However, contrary to Suchet, the Na(2) atoms may not exist as Na2 molecules but as atoms with zero charge. Such models do not correlate well with the semiconductivity property. Another model, of the form Na(2)21+[Na(1)1−As1−], was considered. Its bounding in the Na–As plane is via sp and p2 hybrids and this is consistent with the semiconductivity.
Nuclear Magnetic Resonance Study of Hindered Rotations in Some Methylbenzenes
Authors: Allen P. S. , Cowking A.
Published: February 2004

The hindered rotations of methyl groups have been investigated in the solid state of a series of methyl-benzenes. The materials studied were the three tetramethylbenzenes and pentamethylbenzene. Their proton spin-lattice relaxation times T1 and second moments M2 were measured from helium temperatures to the melting points of the respective samples. The reorientation of the methyl groups is found to persist down to 2°K, and in the three tetramethylbenzenes this is the only motion which is well established in the solid state at a rate greater than about 30 kc/sec. However, the T1 results from the low-temperature phase of each hydrocarbon do not always exhibit a single minimum. Furthermore, there exists a correlation between the number of nonequivalent methyl sites in these compounds and the number of minima displayed in their T1 data. The identification of a particular site with a particular minimum is not unambiguous and only tentative suggestions can be made of the relative magnitude of the constraints on the various sites. Activation energies, calculated from the T1 results, for the methyl group motion around each of the minima are shown in Table II. As the temperature is reduced to ∼1°K the NMR data can no longer be accounted for in terms of the theory which was applicable at high temperatures, and a qualitative explanation of T1 and M2 is given in terms of the tunneling splitting of the torsional ground state. In 1,2,3,4-tetramethylbenzene discontinuities in T1 and M2 at 257°K indicate a phase transition not previously reported.
Hydration of Negative Ions in the Gas Phase
Authors: Kebarle P. , Arshadi M. , Scarborough J.
Published: February 2004

The attachment of water molecules to the ions F−, Cl−, Br−, I−, O2−, and NO2− was observed in the gas phase at water pressures from 0.1 to 1.5 torr and 292°K with an alpha-particle ion source attached to a mass spectrometer. The negative ions were produced by adding a suitable compound RX to an 8-torr oxygen carrier gas. The reaction involved was: RX+O2−=X−+R+O2. Equilibrium constants for a number of clustering reactions (n − 1, n): X−(H2O)n−1+H2O=X−(H2O)n were determined. The hydration of the ions falls off with increase of ionic size. Comparison of the free energies ΔG°2,3 and ΔG°3,4 of the halogen and alkali ions with the Pauling radii shows that negative ions solvate more strongly than positive ions. Comparison with the Latimer, Pitzer, and Slanski radii shows that these radii predict stronger (2,3) and (3, 4) hydration for positive ions. The radii based on x-ray measurements predict equal (2, 3) and (3, 4) hydration energies for positive and negative ions. The present data suggest that the single ion hydration energies derived by Latimer et al. and Verwey are either incorrect or due to stronger solvation by negative ions not in the inner hydration shell but in the subsequent hydration interactions.
Stochastic Model of Molecular Relaxation
Authors: Ullman Robert
Published: February 2004

A simple stochastic model is used to show that the time autocorrelation function which determines dynamic susceptibility is generally nonexponential. The nonexponential character is caused by environmental fluctuations which arise in ordinary Brownian motion. Some computations of dynamic susceptibility are presented which indicate the kind of experimental results anticipated for substances which conform to this model.
Far-Infrared Spectrum of Al2O3:V4+
Authors: Wong J. Y. , Berggren M. J. , Schawlow A. L.
Published: February 2004

Two far-infrared lines, 28.1 and 52.8 cm−1, were observed in three different vanadium corundum samples. These lines are interpreted as transitions from the ground state to the first two excited states of Al2O3:V4+. Oxidation and x-ray irradiation data support this assignment. As with the isoelectronic Ti3+ ion in Al2O3, the number of levels is as predicted by crystal-field theory, but their spacing is much less. The far-infrared spectrum of Al2O3:V4+ reported here is in substantial agreement with the results of a recent calculation of 3d1 impurity ions in Al2O3:V4+ in which crystal-field theory is extended by including the dynamic Jahn–Teller effect. It also is consistent with the observation of a new spin resonance spectrum at 4.2°K in vanadium corundum attributed to Al2O3:V4+. The widths of these lines have been measured as a function of temperature and explained satisfactorily on the basis of lifetime broadening due to direct phonon processes. The frequency shifts of these lines as a function of temperature have also been measured, but the data are still not well understood at the present time.
Interpretation of Elastic Scattering in Reactive Systems
Authors: Nyeland Carl , Ross John
Published: February 2004

Semiclassical approximations are applied to the optical model to derive and discuss an equation used in the interpretation of measurements of elastic scattering in reactive systems.