bluuebunny/crossref_metadata_2025 huggingface dataset:
Neutron Diffraction Studies of CaC2, YC2, LaC2, CeC2, TbC2, YbC2, LuC2, and UC2
Authors: Atoji Masao
Published: January 2005

The complete-matrix least-squares analysis on the neutron diffraction intensities of CaC2, YC2, LaC2, CeC2, TbC2, YbC2, LuC2, and UC2 yielded the C–C distances in the C2 groups, 1.191±0.009, 1.275±0.002, 1.303±0.012, 1.283±0.004, 1.293±0.009, 1.287±0.010, 1.276±0.012, and 1.340±0.007 A, respectively. The statistical averages of the neutron scattering amplitudes obtained from the dicarbide data and those reported previously are 0.488±0.007, 0.796±0.009, 0.832±0.014, 0.482±0.006, 0.756±0.020, 1.262±0.012, 0.73±0.02, and 0.851±0.022, all in 10—12 cm with positive sign, for Ca, Y, La, Ce, Tb, Yb, Lu, and U, respectively.

The paramagnetic scattering analyses revealed that all metal atoms in these dicarbides are in their trivalent Hund ground state, except Ca (divalent), Yb (possible valency of 2.8), and U (possible tetravalent). The scattering data also deduced the screening constants for the 4f electrons in Ce, Tb, and Yb as 39, 43, and 43, respectively, which are compared with those obtained by other methods. The bond numbers for the rare-earth dicarbides are briefly discussed.
Neutron-Diffraction Studies of La2C3, Ce2C3, Pr2C3, and Tb2C3
Authors: Atoji Masao , Williams Donald E.
Published: January 2005

The neutron diffraction data of the rare-earth sesquicarbides with the Pu2C3-type structure (D5c type), La2C3, Ce2C3, Pr2C3, and Tb2C3, were analyzed using the complete-matrix least-squares method. These sesquicarbides contain the C2 groups with the C–C distances, 1.236±0.009, 1.276±0.005, 1.239±0.003, and 1.240±0.005 A, respectively, for La2C3, Ce2C3, Pr2C3, and Tb2C3. These values are, except for Ce2C3, significantly longer than the C–C distance in CaC2, 1.191 A, but are shorter than the average C–C distance in the rare-earth dicarbides, 1.278 A.

The paramagnetic scattering analyses show that all metal atoms in these sesquicarbides are in their trivalent Hund ground state, except Ce in Ce2C3, whose possible valency is about 3.4. The screening constants for the 4f hydrogenic radial wave functions of Pr and Tb as determined from the diffuse scattering analyses of their sesquicarbides are 40 and 43, respectively. The valency and metallic bonds in these sesquicarbides are briefly discussed.
Structural Requirements of Organic Liquid Scintillators
Authors: Heller Adam
Published: January 2005

A theory is proposed to explain the relationship between the structure and the scintillation efficiency of organic liquid scintillators.

The requirements for good scintillation properties in given solvent-solute systems are found to be: (a) the existence of pairs of energy levels in the solute which are identical with those involved in the excitation of the solvent and (b) a nonrigid structure in the solute, capable of undergoing conformational changes in the excited state.

It was found that the behavior of liquid scintillators satisfied these requirements. Good scintillation properties were predicted for some hitherto unknown scintillators.
Energy Distribution and Fragmentation Processes Resulting from Electron Impact on Propane and n-Butane
Authors: Chupka William A. , Kaminsky Manfred
Published: January 2005

The internal energy distribution has been determined for propane and n-butane ions produced by electron impact. The method involves the use of differential ionization efficiency curves and depends on the validity of the linear threshold law for simple ionization. The experimental distributions are in fair agreement with theoretical calculations of Lennard-Jones and Hall and indicate that the major fraction of the parent ions are formed by simple removal of a valence electron. Only a minor fraction of the parent ions are apparently formed by removal of one valence electron together with excitation of one or more remaining electrons. Breakdown curves for propane and n-butane have been determined experimentally and, except for the energy scales, are in fair qualitative agreement with the predictions of the statistical theory of mass spectra. The discrepancy between theoretical and experimental energy scales is ascribed at least in part to inadequacy of the theoretical rate equations used in the statistical theory. There is no evidence for gross failure of the assumptions of the theory regarding energy randomization although the number of crossings of potential surfaces of the molecular ion is shown to be very much smaller than originally assumed by Rosenstock et al.
Molecular Weight Distribution and Reaction Sequence in Polymerization Kinetics
Authors: Goodrich F. C.
Published: January 2005

A general technique is presented for the prediction of molecular weight distributions from an assumed reaction sequence in addition polymerizations. Several problems in Szwarc polymerizations are worked as examples.
Unimolecular Rates Due to Multiple Critical Oscillators
Authors: Schlag E. W.
Published: January 2005

In the first part it is shown that Kassel's quantum model differs appreciably from the classical model in the description of the unimolecular pressure falloff behavior. In the second part the quantum model is extended to encompass dissociation by the accumulation of energy in several critical oscillators. The specific rate constant for molecules with energy E is developed along with the limiting high and low pressure rate constants, as well as the concomitant activation energy expressions. The approximations of the classical theory are indicated by comparisons of the relevant quantum and classical formulations.
Molecular Weight Distribution of Polymers from Rheological Measurements in Dilute Solution
Authors: Peticolas Warner L.
Published: January 2005

A method for obtaining the molecular weight distribution of linear polymers from rheological measurements in dilute solution is obtained through the use of the normal-coordinate theory of viscoelasticity as modified by Zimm to include hydrodynamic interactions.

Equations for the frequency-dependence of viscoelastic properties in dilute solutions are shown to the form Φ (ω) = Σpλp-nf(ωλp-m), where Φ(ω) is a measurable, frequency-dependent viscoelastic property. The summation extends over the set of characteristic values λp, which accounts for the relaxation of various normal modes of motion of the molecule as perturbed by hydrodynamic interaction with the solvent; and f(ωλ1-m) is directly related to the molecular weight distribution through an integral equation λ1−nf(ωλ1−m)= ∫ 0∞K(M,ω)W(M)dM,where W(M) is the weight fraction of molecules in range dM at M and K (M, ω) is a kernel dependent upon the quantity measured. Inversion of the above summation has been accomplished for the particular case of characteristic values which obey the inequality, Σpλp-n<2λ1-n, so that f(ωλ1-m) may be obtained directly from the experimentally measured Φ(ω). W(M) is then obtained from f(ωλ1-m) through a solution of the integral equation.
Neutron Diffraction Data for Ta2D and the Probable Arrangement of the Deuteriums in Two of Its Polymorphic Varieties
Authors: Wallace W. E.
Published: January 2005

Neutron diffraction data are presented for Ta2D at 4°K, 78°K, room temperature, and 53°C. The patterns are indexed assuming a pseudocubic unit cell, the cell edge being 6.74 A at the three lowest temperatures and 3.37 A at 53°C. The enlarged unit cell in the low temperature (β1) form is attributed to ordering of the deuteriums in the tetrahedral interstices. Attempts are made to establish the arrangement of the deuteriums (D's) in the β1 and β2 forms. For the latter, the stable form at 53°C, the intensities can be accounted for in three ways—by random distribution over ⅔ (L group), over ⅓ (S group) or over all of the tetrahedral interstices. From general considerations the first of these is thought to represent the actual situation in β2—Ta2D. In this the D's are distributed over the sites at ½ ¼ 0, ½ ¾ 0, ¼ ½ 0, ¾ ½ 0+000 and +½ ½ ½. Analysis of the β1 pattern shows that despite the fact that this form has a vanishing residual entropy there is no unique configuration of the deuteriums. Instead, to account for the observed intensities one must accept a structure in which each deuterium is statistically occupying more than one site. Assuming each D to be distributed over two sites three satisfactory structures are obtained. These, designated A, B, and C, belong to space groups I4, I4̄, and I41, respectively. Structure A seems the most reasonable of the three and hence is accepted as the one which is probably correct. In it the 8 D's are statistically occupying the 16 tetrahedral sites at ⅛ ¼ 0, ¼ ⅞ 0, ⅞ ¾ 0, ¾ ⅛ 0, ⅝ 0 ¼, ⅜ 0 ¼, 0 ⅜ ¼, 0 ⅝ ¼+000, and +½ ½ ½.

There is an apparent conflict between conclusions based on thermodynamic work and those developed from analysis of the diffraction data for the β2 form as well as for the β1 form. The observed configurational entropies of both forms are much less than those expected for the accepted structures. The discrepancies are thought to be due to local order.
Adsorption and Electrical Conduction in Thin Films
Authors: Ehrlich Gert
Published: January 2005

Changes in the electrical resistance of high-area, evaporated metal films after adsorption of gases have been attributed to a long-range effect of the adsorbed material. It is shown that the experimental findings do not demand this interpretation, and that contributions to the observed resistance increases may arise from any of the following: (1) A localized resistance change at necks in the film. (2) Changes in surface stress on adsorption. (3) A decrease in the rate of electron tunneling across gaps in the film with an increase in the work function. The last mechanism appears most likely, and experiments to establish these effects quantitatively are outlined.
Unimolecular Decay of the Triplet State of Anthracene in Fluid and Viscous Media
Authors: Jackson G. , Livingston Robert
Published: January 2005

The rate of decay of the triplet state of anthracene, dissolved in hexane, tetrahydrofuran, and glycerol, has been measured at temperatures ranging from 30 to —70°C. In fluid solvents at ordinary temperatures, the decay appears to be chiefly the result of bimolecular triplet-triplet interaction and of a bimolecular quenching reaction involving an unknown quencher, present in trace amounts even in highly purified solvents. In addition, there appears to be a unimolecular, temperature-independent decay, corresponding to an intrinsic mean life of about 0.01 sec. In glycerol, the first-order rate constant decreases rapidly with decreasing temperature, approaching a limiting half life of about 0.04 sec at —25°C. This limiting rate appears to be the same as has been previously reported for solutions in EPA at liquid nitrogen temperatures. Similar results were obtained with solutions of dibenzanthracene.
Thermodynamic Functions of Several Triatomic Molecules in the Ideal Gas State
Authors: McBride Bonnie J. , Gordon Sanford
Published: January 2005

Recent spectroscopic data were used in calculating the thermodynamic functions of CO2(g), COS(g), CS2(g), ClCN(g), HCN(g), H2O(g), H2S(g), N2O(g), NO2(g), and SO2(g) in the ideal gas state from 100° to 6000°K. For each molecule, corrections were made to the rigid-rotator harmonic-oscillator approximation for anharmonicity and when sufficient data were available, additional corrections were made for vibration-rotation interaction, rotational stretching, and Fermi resonance.
Spin Relaxation Processes in a Two-Proton System Undergoing Anisotropic Reorientation
Authors: Woessner D. E.
Published: January 2005

The spin-lattice relaxation time T1 and the spin-spin relaxation time T2 for two identical spins I=½ have been calculated for anisotropic reorientation in which the spin pair reorients randomly about an axis which, in turn, tumbles randomly. The results are applicable to liquids and solids provided that the correlation time for tumbling of the axis is small compared to T2. Although the two types of motion are independent, their contributions to relaxation are not. For nonviscous liquids, T1=T2. The results are generalized to multispin systems.
Effect of Oxygen upon the Heat Capacity of Gadolinium between 1.3° and 5°K
Authors: Crane L. T.
Published: January 2005

A specimen of gadolinium was oxygenated and the heat capacity measured at three levels of oxygen content. The broad low-temperature anomaly reported by Kurti and Safrata was reproduced by the oxygenation. Entropy calculations show that the reported anomaly results from the magnetic ordering of the spin 7/2 Gd3+ ions of the Gd2O3 molecules.
Theory of the Heats of Mixing of Certain Fused Salts
Authors: Reiss Howard , Katz J. L. , Kleppa O. J.
Published: January 2005

A theory is presented for the heats of mixing of fused salts. This theory is based on an assumption made in earlier work that the short-range potential between ions of like sign can be ignored. The development is essentially a conformal solution treatment modified to apply to the special potentials involved in fused salts. The predicted form for the heat of mixing agrees with that discovered by Kleppa and Hersh in connection with measurements on mixtures of alkali nitrates.
Quadratic Potential Function for Ammonia
Authors: King W. T.
Published: January 2005

It is found that the Urey-Bradley force field does not adequately account for the harmonic frequencies or the quadratic potential function of ammonia. The reason for this is that the Urey-Bradley force field does not account properly for the interactions between the valence-bond stretching and angle bending displacements in the potential function. A simple model containing four adjustable parameters is proposed for the potential function of ammonia that reproduces both the harmonic frequencies and the quadratic potential function quite accurately.
Heat of Sublimation and Dissociation Energy of Gaseous C2
Authors: Brewer Leo , Hicks W. T. , Krikorian O. H.
Published: January 2005

Measurements of the temperature coefficient of the emission intensity of C2 bands in the King furnace yield a ΔH00 of sublimation of 195±5 kcal for the ground state of C2 (1Σg+) and a dissociation energy of 6.25 ev for C2.
Detonation Sensitivity and Failure Diameter in Homogeneous Condensed Materials
Authors: Evans Marjorie W.
Published: January 2005

A model is proposed for steady detonation waves in homogeneous condensed materials. The model is one in which the pressure profile in the direction of the wave motion is square between shock front and Chapman-Jouguet surface. The reaction rate in the steady zone is allowed to vary with the steady detonation wave velocity according to the temperature in the reaction zone. The model refines and makes quantitative an early suggestion by Eyring, Powell, Duffey, and Parlin. The results give a failure diameter, with dual-valued solutions at greater diameters. Predictions of failure diameter, wave velocity at failure diameter, induction time during initiation, and shock sensitivity for given charge dimension are possible. The predicted results for two materials of widely different detonation properties, liquid TNT and ammonium nitrate at theoretical crystalline density, are compared with observations.
Monte Carlo Calculations on the Dynamics of Polymers in Dilute Solution
Authors: Verdier Peter H. , Stockmayer W. H.
Published: January 2005

A method is described for simulating the dynamical behavior of a linear polymer in dilute solution, subject to random collision with solvent molecules. Equilibrium distributions of various chain dimensions may be obtained by periodic inspection of the chain. Relaxation phenomena in such chains may also be studied. Results are given for equilibrium distribution and relaxation behavior of the end-to-end length, for chains of 8, 16, 32, and 64 beads. The equilibrium chain dimensions are in satisfactory accord with the calculations of Wall and his collaborators, while the relaxation times are close to those predicted with the aid of the hydrodynamic theory of Rouse and Zimm.
Spin-Forbidden Transition of NO Observed in Solution Spectra
Authors: Piper T. S. , Drago Russell S.
Published: January 2005

The transition 4Π←X 2Π occurs at 3.5 ev in the ultraviolet spectra of NO dissolved in organic solvents. The observed ωe values range from 1100 cm-1 in CCl4 to 1600 cm-1 in CH3OH. These trends are correlated to the shift of electron density out of the π*-antibonding level upon formation of hydrogen bonds with the solvent.
Proton Magnetic Resonance Spectra of 3-Pyridines: The Unsymmetrical Four-Spin ABXY and ABKL Systems
Authors: Kowalewski Valdemar J. , de Kowalewski Dora G.
Published: January 2005

The high-resolution proton magnetic resonance spectra of four pyridine derivatives of the type[Complex chemical formula](R=Cl, Br, aldehyde and acetyl groups) are studied as ABXY and ABKL systems. Detailed analysis of these methods is made and it is shown that in the 3-pyridines the ABKL treatment gives as good an account of the observed spectra as the ABCD, both methods giving the same values for the molecular parameters vi and Jij.

The analysis of the spectrum of the pyridine-3-carboxaldehyde shows an unexpected coupling of 0.44±0.05 cps between the aldehydic and the beta protons but no interaction with the alpha or gamma protons.
Crystal Structure of Cupric Fluoride Dihydrate at 298°K
Authors: Abrahams S. C. , Prince E.
Published: January 2005

A neutron determination of the crystal structure of cupric fluoride dihydrate at 298°K has been made. The structure consists of puckered sheets of nearly square CuF2O2 groups, linked together by hydrogen bonds of 2.715±6 A, with the sheets connected by longer Cu–F bonds to form distorted octahedra around the Cu2+ ions. Dimensions within the octahedra are, two Cu–O distances of 1.941±5, two Cu–F of 1.898±8 and two Cu–F of 2.465±6 A. The long F–Cu–F axis is inclined at 7½° from the normal to the plane containing the remaining CuF2O2 group of the octahedron. The Cu–O bonds bisect the H–O–H angle of 115.5±0.4°. The O–H bond is 0.980±7 A and the O–H···F angle is 164.9±0.7°. The amplitudes of thermal displacement of the atoms along various directions are given. The nuclear scattering length of fluorine is revised to 0.529±13 (10—12 cm).
Crystal and Magnetic Structure of Cupric Fluoride Dihydrate at 4.2°K
Authors: Abrahams S. C.
Published: January 2005

A neutron diffraction study of CuF2·2H2O below the Néel point has determined the crystal and magnetic structure. As compared with this crystal at 298°K, the long Cu–F axial bonds of the distorted octahedron around the Cu2+ ion are reduced in length from 2.465±6 to 2.391±4 A: the short Cu–F bond of 1.899±6 A and the Cu–O bond of 1.945±4 A are unchanged. The H–O–H angle is reduced from 115.5° at 298°K to 110.1±0.4° at 4.2°K, and the O–H distance from 0.980±7 to 0.959±5 A. The amplitudes of vibrational displacement of the Cu, O, and F atoms at 4.2°K are about one-half that at 298°K: The hydrogen atoms have about the same motion, due to zero-point energy. The magnetic unit cell is identical with the nuclear cell, but the spin on the body-centered copper atom is antiparallel to that at the origin. The spin direction is very nearly along the c axis, although an alternative model with the spin along the long octahedral direction fits the magnetic scattering almost as well. The difference between the Néel temperature of 10.9° and that of 26°K at which the magnetic susceptibility is a maximum is consistent with the observed magnetic structure. The revised nuclear scattering length for fluorine of 0.529×10—12 cm found in the analysis of CuF2·2H2O at 298°K is in excellent agreement with the experimental value of 0.534±12 obtained in the present study.
Symmetry of Configurational Entropy in Lattice Statistics
Authors: Kleiner W. H.
Published: January 2005

An investigation is made of the general conditions under which the configurational entropy of a binary solid solution is symmetrical with respect to composition about the 50–50 composition point. Spin coordinate and occupancy number representations of the configurational energy are discussed. When the sites of the site array are equivalent due to spatial symmetry, the configurational entropy is symmetrical for any pair interaction model. Asymmetry of the configurational entropy implies the presence of some n-site interactions, n=3, 5, 7, .... Application of these results to order-disorder alloy and physical adsorption systems is considered.
Raman Spectral Studies of Aqueous Solutions of Selenious Acid
Authors: Walrafen G. E.
Published: January 2005

Photoelectric Raman spectra of aqueous solutions of selenious acid, obtained at various concentrations, and of dilute strongly alkaline and partially neutralized aqueous mixtures of sodium hydroxide and selenious acid, have yielded vibrational frequencies considered to be those of the species H2SeO3, SeO32—, and HSeO3—, respectively. In aqueous solutions of selenious acid, the intensities of two strong bands were found to increase linearly with (stoichiometric) concentration over a wide range of concentrations. This fact suggests essential completeness in the reaction of SeO2 with water, and negligible dissociation of H2SeO3 into its ions, in the solutions for which linearity is obtained.

Polarization studies of the various Raman bands, comparisons of the observed frequencies with those of molecules of known symmetry, intercomparisons of the frequencies of the species SeO32—, HSeO3—, and H2SeO3, and information gained from reported x-ray studies of solid selenious acid have allowed for provisional vibrational assignments on the assumptions of various symmetries.
Experimental Determination of the Heat of Dissociation of N2O4→2NO2 from the Temperature Dependence of Absolute Infrared Intensities
Authors: Guttman A. , Penner S. S.
Published: January 2005

The heat of dissociation of N2O4 has been determined from measurements of the temperature dependence of the integrated absorption of NO2 and N2O4 vibration-rotation bands. Results have been obtained that are in acceptable accord with the earlier estimate of Giauque and Kemp.
Cubic Lattice Model Chain
Authors: Krigbaum W. R. , Kaneko M.
Published: January 2005

The partition functions for conditions of constant force Zf or fixed displacement length Z̃r are derived for the three-dimensional cubic lattice model chain having two possible positions of different energy for each link. The problem can be set up so that it reduces to a one-dimensional Markov chain, thus Zf can be obtained in closed form. The network treatment of Wang and Guth for non-Gaussian chains is used to obtain the partition function for a network of cubic lattice chains. Qualitative comparison with experiment indicates that most of the deviations from Gaussian behavior which have been observed for cross-linked natural rubber at low relative elongations may be ascribed to intramolecular rotational energy effects.
Pressure Dependence of Fluorescence Spectra. III. Effect of Finite Pulse Length
Authors: Brauner Joseph W. , Wilson David J.
Published: January 2005

The effect of finite lengths of square exciting pulses in vibrational relaxation experiments in gases is investigated theoretically. Taking into account the finite duration of the pulse length does not yield results drastically different from those obtained assuming instantaneous excitation, provided that the exciting pulse has a width not more than about half the mean time between 1-to-0 transitions.
Extrapolation of the Orthorhombic n-Paraffin Melting Properties to Very Long Chain Lengths
Authors: Broadhurst Martin G.
Published: January 2005

An analysis of the equation TM=T0 (n+a) / (n+b) is made in order to determine the convergence temperature T0 of the melting temperatures of the n-paraffins from C44 to C100. A good fit is obtained using T0=414.3°K, a=—1.5, and b=5.0. This value of T0 (414.3°K=141.1°C) has an estimated total uncertainty of ±2.4°K and is proposed as the correct value of the equilibrium melting temperature of polyethylene. It is shown that presently available data do not permit accurate extrapolation of the n-paraffin heats and entropies of fusion to the polymer limit.
Tunneling Model for Electron Transport and Its Temperature Dependence in Crystals of Low Carrier Mobility. Example: Anthracene
Authors: Keller R. A. , Rast H. E.
Published: January 2005

A tunneling model is used to explain electron transport in crystals of low carrier mobility. Temperature is incorporated into the model by allowing the barrier width to vary sinusoidally as a result of lattice vibrations. The maximum amplitude of vibration is proportional to T½. The resulting expression for the mobility exhibits a linear temperature dependence. The model can also be used to estimate the width of the conduction band. The calculated results are compared with experimental results on anthracene, and the agreement is quite good for the mobility but not as good for the temperature dependence.
Spectrum of UCl4
Authors: McLaughlin Ralph
Published: January 2005

The spectrum of thin single crystals of UCl4 was obtained at liquid-helium temperature. Under these conditions it was possible to resolve what usually appear as broad bands into groups of lines. By utilizing polarization spectra, line position, and line appearance, it was possible to assign transitions between crystal field states. Knowing the position of the crystal field states allowed calculation of the position of the field-free ion J levels and 2s+1L terms. Configuration interaction is discussed on the basis of the variation of these terms. Results of this study which might pertain to magnetic susceptibility measurements, covalent bonding considerations, f-orbital formation, and descriptions of 5f eigenfunctions are mentioned.
Mössbauer Spectra of Some Iron Complexes
Authors: Epstein L. M.
Published: January 2005

Mössbauer spectra were obtained for the following coordination compounds: iron phthalocyanine, ferrocene, iron carbonyl, iron III acetylacetonate, and iron II acetylacetonate dipyridine; for the following complex ion salts iron II trisphenanthroline chloride, iron III EDTA (monosodium salt), iron II EDTA, hemin, ferricium picrate, sodium nitroprusside, and some ferro- and ferricyanides.

The isomer shift (relative to stainless steel) for iron II has the value expected for an inorganic ion only for iron II EDTA. In the other complexes the shifts are about 0.4 mm/sec, except ferrocyanide which is near zero. For iron III only hemin and ferricyanide have unusually small isomer shifts. The large negative isomer shift in sodium nitroprusside suggests iron IV.

Except for ferrocyanide quadrupole splittings occurred in iron of valence 0, II, and IV and were observed for both spin-paired and spin-unpaired complexes. Splittings varied widely, however not exceeding those for inorganic ferrous salts. Sodium ferricyanide showed an unexpected quadrupole splitting. Other iron III complexes gave broad and unsymmetrical spectra.
Thermal Bleaching of Cl2— Centers
Authors: Neubert Theodore J. , Reffner John A.
Published: January 2005

The kinetics of thermal bleaching of Cl2— centers in x-irradiated KCl–Pb have been studied by measurement of the rate of disappearance of the 3650 Å optical absorption, at constant temperatures in the range 180° to 210°K. Thermal bleaching is second order in Cl2— concentration. A two-part mechanism is suggested: the first being a diffusion of Cl2— via hopping of the positive hole from point to point through the lattice, the second being the recombination of holes with electrons trapped at lead ions. The activation energy for Cl2— center bleaching in KCl–Pb is 0.53 ev.
Magnetic Properties of Hydrogen Fluoride. II. Susceptibility
Authors: Hurst R. P. , Karplus Martin , Das T. P.
Published: January 2005

A method is outlined for the calculation of the magnetic susceptibility χ from the ground-state wave function of 1Σ molecules. The diamagnetic contribution χd is obtained directly by first-order perturbation theory and the paramagnetic contribution χp is determined by a variational technique based on minimizing the second-order energy in an external magnetic field. When applied to an SCF—LCAO—MO function for hydrogen fluoride, the theoretical result is 〈χ〉Av=—8.74×10—6 erg gauss—2 mole—1, in excellent agreement with the experimental value of —8.6×10—6 erg gauss—2 mole—1. The separate contributions, with respect to the fluorine as origin, are somewhat more in error, with 〈χd〉Av=—9.58×10—6 erg gauss—2 mole—1 (exp: —9.2×10—6 erg gauss—2 mole—1) and 〈χp〉Av=0.855×106 erg gauss—2 mole—1 (exp: 0.609×10—6 erg gauss—2 mole—1, as obtained from the rotational magnetic moment). For the isoelectronic atoms F— and Ne (in which there is only a diamagnetic term), analytic Hartree-Fock functions yield 〈χ〉Av values equal to —12.7×10—6 erg gauss—2 mole—1 (exp: ∼—12×10—6) and —7.48×10—6 erg gauss—2 mole—1 (exp: —6.7 to —7.7×10—6), respectively.

By a comparison of the results obtained with different molecular wave functions for hydrogen fluoride (one-center and two-center approximations), the sensitivity of the magnetic-susceptibility components (especially the paramagnetic terms) to the form of the wave function is clearly demonstrated. This suggests that χ and its components can serve as useful criteria for the accuracy of electron distributions and indicates the need for refinements in the hydrogen fluoride functions. Finally, the availability of a method for the theoretical evaluation of the susceptibility tensor components suggests that additional measurements should be done to improve the experimental values.
Gouy Diffractometry in Thermal Diffusion
Authors: Bierlein James A.
Published: January 2005

Symmetrical wide-aperture illumination of binary liquid systems undergoing thermal diffusion produces well-defined Gouy diffraction patterns, arising from the interference of conjugate rays passing at equal distance above and below the midplane of the diffusion cell. The optical theory of this phenomenon is formulated; the diffraction phenomena are described by incomplete Airy integrals, tabulations of which are given.

The theory forms the basis for a new method of measuring Soret coefficients. Applied to experimental data for typical electrolyte and nonelectrolyte systems, Gouy diffractometry gives results of high precision which agree well with older values determined by other methods. The new technique has the advantage of providing two separate estimates for the Soret coefficient, affording a check on the internal consistency of the experiments; further, the presence and approximate magnitude of convective disturbances are automatically revealed.
Microwave Spectrum of Bromocyclobutane
Authors: Rothschild W. G. , Dailey B. P.
Published: January 2005

Rotational transitions of four isotopic species of bromocyclobutane have been observed. For C4H7Br79,[Complex chemical formula]or[Complex chemical formula]the rotational constants are A = 10 003.4±13 Mc, B = 1629.41±0.03 Mc, C = 1488.48±0.03 Mc; for C4H7Br81, A = 10 002.6±13 Mc, B = 1615.14±0.03 Mc, and C = 1476.50±0.03 Mc. The values for the α-deuterated compound are, for C3H6CDBr79, A = 9534.7±13 Mc, B = 1613.67±0.03 Mc, and C = 1486.24±0.03 Mc; for C3H6CDBr81, A = 9533.4±13 Mc, B = 1599.55±0.03 Mc, and C = 1474.24±0.03 Mc. A set of structural parameters which reproduce these constants within 1.8 Mc were obtained with an electronic computer: bond distances Cα–Cβ = 1.540±0.003 Å, Cβ–Cγ = 1.548±0.003 Å, C–Br = 1.939 Å, C–H = 1.096 Å, and C—D = 1.087 Å; bond angles CβCγCβ = 88° 06′±08′, CβCαCβ = 88°41′±08′, HCγH = 110°44′, HCβH = 108°44′, HCαBr = 111°, angle of CβCαCβ plane with C–Br = 131°00′±08′, and dihedral angle = 29°22′±08′ (the dihedral angle is the angle made by the normals of the CβCαCβ and CβCγCβ planes). The quadrupole-coupling constant of C4H7Br79 along the C–Br bond direction is 512.2±5.0 Mc and the asymmetry parameter ηbond is —0.002±0.014; these figures yield an upper limit of about 1% double-bond character due to conjugation of the Br atom with the C ring and an ionicity of the halogen bonding orbital of 25% assuming 8.6% s character. From frequency and intensity measurements of rotational satellites a low-lying vibrational mode was identified. Its effect is a displacement of all atoms in the molecule (out-of-plane bending). Its first and second excited states are 120±25 and 251±56 cm-1, respectively, above ground level. The three lowest levels of the vibrational mode were shown to be large-amplitude vibrations of the molecule about a dynamical equilibrium dihedral angle of 25° to 29°. Highly excited vibrational states, which cause increasing planarity of the carbon ring, are expected to lead to tunneling through the potential barrier to the less stable ``axial'' isomer of bromocyclobutane. The existence of the axial isomer by direct observation could not be established due to instrumental difficulties.
Thermodynamic Properties of Trifluorophosphine from 12°K to Its Boiling Point. Entropy from Molecular and Spectroscopic Data
Authors: Pace E. L. , Petrella R. V.
Published: January 2005

The heat capacity of trifluorophosphine has been measured from 12° to 170°K for a sxmple of 99.7 mole % purity. Two solid transitions were observed; one at 83.75°K involving a heat of transition of 59.9 cal/mole and the other at 110.56°K involving a heat of transition of 552.3 cal/mole. The heat of fusion at the triple-point temperature 121.85°K was 223.9 cal/mole. The heat of vaporization at the normal boiling point 171.77°K was 3485 cal/mole. The vapor pressure of the liquid to the normal boiling point has been measured, and the data are represented by log10Pmm=−606.1714/T+2.98575log10T−0.26322.The density of the liquid is represented by d(g/cc)=2.332−0.004407T.The entropy of trifluorophosphine gas in the standard state at the normal boiling point, 58.48 cal/(mole°K), has been calculated from the calorimetric data. This value is in excellent agreement with the value of 58.49 cal/(mole°K) calculated from the most reliable spectroscopic and molecular data currently available.
Kronig-Structure Variations in the X-Ray K-Absorption Spectra of a Cu Single Crystal
Authors: Boster T. A. , Edwards J. E.
Published: January 2005

The Kronig structure on the high-frequency side of the x-ray K-absorption edge of a thin single crystal of Cu has been investigated using 82.4% polarized x rays. The Kronig-structure energy positions were observed to shift with 30°, 60°, and 90° rotations of the single-crystal absorber. A similar absorption curve was obtained by using a thin polycrystalline copper absorber. The five absorption curves are compared and tabulated out to 350 ev from the main K edge. The shifts in energy position of the Kronig structure are discussed in relation to the highly polarized x rays.
Ionization Differences Between Coordination States of a Cation. Octahedral—Tetrahedral Equilibrium of Transition-Element Chlorides in Dimethylformamide
Authors: Katzin Leonard I.
Published: January 2005

In a high-dielectric-constant, low-base-strength medium, such as dimethyl formamide, formation of chloride complexes of the first transition elements in the tetrahedral configuration is promoted. The effect is linked with a greater dissociation (weaker anion complexing) of the octahedral configuration, as indicated by the over-all equilibrium expression 2oct(MCl2X4)= oct(MClX5+)· tet(MCl3X)−+2X.The corresponding change in the absorption spectrum has been followed for the chlorides of Mn(II), Fe(II), Fe(III), Co(II), Ni(II), and Cu(II). The spectra with and without added LiCl are described. Some relations to current ligand-field theories concerning the configuration change are pointed out.
Proton Magnetic Resonance Studies on Hexamethylenetetramine—Structure, Molecular Reorientation, and Impurity Diffusion
Authors: Smith George W.
Published: January 2005

Nuclear magnetic resonance measurements on protons in solid hexamethylenetetramine have led to information about the molecular structure and motions and diffusion of impurity water molecules in the solid. The information obtained is consistent with previous work indicating that the solid contains distorted molecules with a C–H distance of 1.13 A in a body-centered cubic crystal structure. From temperature dependences of a linewidth transition at 375°K, and a relaxation time minimum at 550°K, a rotational activation energy of 18 kcal/mole was computed. Sublimation, with a latent heat of 18 kcal/mole, occurs at the same temperatures as the rotation. Intermolecular C–H···N hydrogen bonds are the source of both the stability of the crystal and the barrier to rotation. The energy of these bonds appears to be 1.2 kcal/mole per bond. It was determined that a water impurity was present, in an amount of about 0.1% by weight, and was diffusing in the solid. The diffusion produced an anomalous minimum in T1. Rough analysis of the T1 minimum, using the theories of Bloembergen, Purcell, and Pound and of Torrey, yielded values of the infinite temperature diffusion coefficient D0 for the water of 10—3 to 10—1 cm2/sec and an activation energy of 5 to 7 kcal/mole.
Semiempirical Valence Bond Calculations of Electronic Energies of CH, CH2, CH3, and CH4
Authors: Ellison Frank O.
Published: January 2005

A new energy formula based upon valence bond theory is derived for the ground and some low-lying excited states of CHn molecules. The formula essentially partitions the molecular energy into the following parts: promotional energy, Coulomb energy, bond exchange energy, exchange energy from nonbonded interactions (homogeneous and heterogeneous separately), and resonance energy (involving covalent structures only). Dependencies of all parts on hybridization are taken into account. Experimental energies of atomization of the 2Π and 2Δ states of CH, and of CH4, are used to calibrate the method, and a C–H distance of 1.12 Å is used throughout. The unobserved 4Σ— state of CH is predicted to be 10.4 kcal (0–0 difference) above the ground state. A linear 3B1 ground state of CH2 is obtained; 0–0 transitions to strongly bent (100°) 1A1 and linear 1B1 states are predicted at 12.4 and 25.0 kcal, respectively. The energy of CH3 is minimum when planar. C–H bond dissociation energies (in kcal) are predicted as follows: CH3–H, 89; CH2–H, 106; CH–H, 119. Arguments are presented to show that these values are quite consistent with available spectroscopic ionization potentials and electron impact appearance potentials, although the first predicted value may be some 5 to 10 kcal too low, and the last predicted value correspondingly too high.
Many-Electron Theory of Atoms and Molecules. II
Authors: Sinanoğlu Oktay
Published: January 2005

It was shown in Paper I that to calculate the correlation energy of an N-electron system only the unique pairs of Hartree—Fock electrons need be considered. Methods for obtaining these pair correlations are developed. Each pair satisfies a Schrödinger equation similar to that of, say, He or H2. For π electrons the corresponding equation turns out to be just the ``π-electron Hamiltonian.'' In a closed-shell system, to obtain any of the pair functions one minimizes the energy of just that pair. There is no ``nightmare of inner shells.'' With the procedure given, any well-known two-electron method such as Hylleraas' r12-coordinate, ``open shell'' or even Heitler—London can be used for an Hartree—Fock pair depending on the nature of the pair. This ``exact pair'' theory leads to ``first-order'' pairs and to a Brueckner-type theory for finite systems upon further approximation.
Interpair Nuclear Magnetic Relaxation in Hydrated Crystals
Authors: Holcomb D. F. , Pedersen B.
Published: January 2005

A set of pulsed rf spin-lattice relaxation time measurements has been made on the proton system in CaSO4·2H2O. The measurements were performed at several crystal orientations, and over a temperature range from 160° to 365°K. A more limited set of measurements was performed on the proton and Li7 systems in Li2SO4·H2O powder. In both systems there is a strong relaxation mechanism arising from dipolar motion. It appears that this relaxation arises from 180° flips of the water molecules. The T1 data gives a motional activation energy of 6.2±0.5 kcal/mole in CaSO4·2H2O, a reasonable energy for the two hydrogen bonds which must be broken in the postulated motion. Steady-power absorption line measurements show essentially no narrowing of the proton resonance, in spite of the fact that the characteristic motional frequency reaches the Larmor frequency, 9.0 Mc/sec, at about 230°K. Interpair, rather than intrapair, interactions are responsible for the relaxation. A simplified calculation using only two interacting pairs in CaSO4·2H2O indicates that the observed minimum value of T1 and the lack of appreciable motional narrowing is reasonably accounted for by the proposed mechanism. A similar calculation for the Li7 system in Li2SO4·H2O also yields satisfactory agreement with experiment. The results presented demonstrate the importance of an examination of details of internuclear interactions in a particular crystal in the interpretation of motional effects in magnetic resonance experiments.
Mass Spectrometric Studies of Atom Reactions. II. Vibrationally Excited N2 formed by the Reaction of N Atoms with NO
Authors: Phillips L. F. , Schiff H. I.
Published: January 2005

A mass spectrometric method was used to show that 75±5% of the nitrogen formed by the reaction N+NO→N2*+Ohas more than the 24 kcal/mole of excess energy required to decompose ozone. The rate constant for the reaction N2*+O3→O2+O+N2was found to be (5.4±1.1)×10—13 cm3 molecule—1 sec—1. The rate of collisional deactivation of N2* to vibrational levels below the fourth was found to be 3.5×10—16 cm3 molecule—1 sec—1 with unexcited N2 and 1.3×10—15 cm3 molecule—1 sec—1 with N2O as the collision partners. If loss of vibrational energy occurs mainly by single quantum jumps, the measured deactivation rate constant is less than that for a single quantum jump by the ratio of the number of molecules in the fourth level to those in all levels above the third.
Modified Urey-Bradley Force Field for Condensed Aromatic Rings
Authors: Scherer James R.
Published: January 2005

A modification of the basic Urey—Bradley force field, which has been shown to reproduce the planar vibrational spectra of benzene and substituted benzenes, is extended to naphthalene. An alternate modification based on MO theory is compared with the simpler Kekulé model, and both models are shown to lead to the same conclusions regarding the vibrational spectra.

A zero-order calculation using thirteen force constants transferred from other molecules agrees remarkably well with the recent Scully—Whiffen and Freeman—Ross assignments. In the B2u species, where these authors have serious differences, the modified UBFF favors the Scully—Whiffen assignment.

A 16-parameter UBFF is refined to the H8 and D8 isotopes, and the vibrational frequencies of all deutero isotopes having Vh, C2v, or C2h symmetry are calculated with this potential function.
Criteria for the Construction of Good Self-Consistent-Field Molecular Orbital Wave Functions, and the Significance of LCAO-MO Population Analysis
Authors: Mulliken R. S.
Published: January 2005

Criteria for the optimal choice of finite linear combinations of STO's (Slater-type orbitals) adequate to closely approximate SCF (self-consistent-field) MO's are examined in the light of computations on HF and other molecules. First, however, some aspects of the AO (generalized Heitler—London) method are discussed. The concept of induced configuration mixing is proposed as a helpful way of thinking of the higher-order interactions which carry the wave function from that of a ground-state atom pair over toward an SCF-MO form. The concept of valence polarization is suggested as preferable to and/or more general than that of hybridization. When, in the AO method, a molecule is formed from atoms, the AO's of the latter are valence polarized, and if the molecule is heteropolar, also Coulomb polarized. It is noted that both types of polarization are effected in part by the mixing in of highly shrunken excited AO's.

The same concepts are applicable also in the MO method. In an optimal choice of a finite STO basis set for approximating SCF MO's, the principle of balanced truncation, including balanced polarization, should be used; that is to say, an equally generous (or parsimonious) set of primary and of polarizing STO's should be used for each atom, with due respect to the numbers and kinds of occupied AO's in the free atom. The use of flexibilized and polarized SCF AO's (modified SCF AO's, or MAO's) as equivalents to linear combinations of STO's is discussed. In these connections, problems of interpretation and recording of LCAO-MO population analyses obtained using extended STO basis sets are critically examined.

The inherent limitations on the meaning of charges on atoms in a molecule (or of degree of ionic character, or net ionicity) are discussed. It is shown with examples that unacceptable atomic charges are found from an LCAO-MO population analysis made on SCF-MO wave functions approximated using unbalanced STO sets, while acceptable results are obtained with judiciously balanced and sufficiently complete STO sets. Likewise, unbalanced STO basis sets can given unacceptable results for overlap populations. For example, with certain unbalanced sets, there are large apparent π overlap populations in HF and in LiF, where with well-balanced sets a much smaller, but appreciable and probably genuine, amount of π bonding is indicated, confirming evidence from spectroscopic data in the case of diatomic hydrides.

The effects of insufficiently complete and unbalanced STO sets on the computed dipole moments of SCF-MO wave functions are discussed in terms of examples. These indicate that one may expect fairly accurate though slightly too large computed dipole moments for good SCF-MO wave functions. They also indicate that improvement of the latter by limited configuration interaction may give computed values close to experimental values.
Magnetic Susceptibility of ReF6
Authors: Selig Henry , Cafasso Fred A. , Gruen Dieter M. , Malm John G.
Published: January 2005

The magnetic susceptibility of ReF6 has been measured in the range 4°—296°K using the Faraday method. The susceptibility in the range 14°—296°K can be expressed by means of χReF6M=(78±1)×10−4/T+(0.87±0.03)×10−4,from which one calculates a moment of 0.25 Bohr magnetons. Applying a theory developed for gaseous ReF6 [W. Moffitt, G. L. Goodman, M. Fred, and B. Weinstock, Mol. Phys. 2, 109 (1959)] to the magnetic measurements reported here gives ζ=3160 cm—1 and 10Dq/α=55 000 cm—1, where α is an orbital reduction parameter connecting the dl2g and deg levels. The diamagnetic susceptibility of WF6 has been remeasured and preliminary measurements on TcF6 are reported.
Thermodynamics of Iodine Addition to Ethylene, Propylene, and Cyclopropane
Authors: Benson Sidney W. , Amano Akira
Published: January 2005

The gas-phase equilibrium in the systems C2H4+I2⇌CH2I–CH2I,propylene+I2⇌CH3CHI–CH2I,have been studied in the temperature range 365° to 476°K using a new technique for the determination of di-iodides. In addition, existing data are re-examined for the gas system: cyclopropane+I2⇌CH2ICH2CH2I.Using other available data on the ethylene system which with ours cover a range of 200°K it is possible to obtain for 1,2-C2H4I2: Cp0 = 19.2±2 eu, Sp0 = 83.3±0.5 eu, ΔHf0 = 15.9±0.2 kcal/mole. For 1,2-C3H6I2: Cp0 = 24.1±3 eu, Sp0 = 94.6±1.0 eu, ΔHf0 = 8.6±0.4 kcal/mole. For 1,3-C3H6I2, the values of Cp0 and Sp0 are estimated by additivity rules to be 24.7 eu±1.0 eu and 93.0±1.0 eu, respectively. Based on these estimates and the measured ΔF we find ΔHf0 = 10.6±0.5 kcal/mole. A possibility of slightly lower values for 1,3-diiodopropane is discussed with reference to corrections due to the kinetics of the reaction system as well as the conformations of the molecule.

For use with additivity rules, the following partial contributions are assigned for the C–I bond, C–(I) (H)2(C) group and C–(I) (H) (C)2 group respectively: S0 = 24.9, 42.4, 22.6 eu; and ΔHf0 = 14.1 7.95, 10.7 kcal/mole. The group additivity rule is found to be valid for di-iodides to ±0.5 eu for S0 and to ±0.5 kcal/mole for ΔHf0. On the basis of this rule, thermodynamic values are assigned to a number of alkyl iodides and their C–I bond dissociation energies derived relative to the parent hydrocarbons.