bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic Properties of Tb–Ho Single-Crystal Alloys. I. Magnetization Measurements
Authors: Spedding F. H. , Jordan R. G. , Williams R. W.
Published: February 2004

We have investigated the magnetic properties of three single crystals of the Tb–Ho alloy system containing 10%, 50%, and 90% Ho from 4.2°–300°K in applied fields up to 28 kOe. Magnetic-moment measurements were made along the a 〈112̄0〉, b 〈101̄0〉, and c 〈0001〉 directions of the close-packed hexagonal structures. Within the limitations of such measurements we find that the Tb–Ho alloys exhibit similar characteristics to the pure metals. The trend upon increasing the concentration of Ho in Tb is to enhance and widen the antiferromagnetic region at the expense of the ferromagnetic region. The Néel temperatures and polycrystalline paramagnetic Curie temperatures decrease approximately linearly with Ho content to the pure Ho values. The absolute saturation moments in the basal plane and effective number of Bohr magnetons in the paramagnetic region increase linearly with Ho content. Anisotropy between the a and b directions is observed at low temperatures in all the alloys, with the b preferred. The c direction is the hard direction in all cases, although there is some evidence for a small amount of ordering along the c direction in the alloy containing 90% Ho.
Experimental and Theoretical Study of Triplet–Triplet Absorption in the Phenylnaphthalenes
Authors: Brinen J. S. , Orloff M. K.
Published: February 2004

The triplet–triplet absorption spectra of several phenylnaphthalenes are measured and the absolute extinction coefficients are evaluated using the simultaneous ESR–optical approach. The results of self-consistent-field molecular-orbital calculations are compared with experiment and good agreement is found for the energies, oscillator strengths, and vibrational envelopes of the triplet–triplet transitions. In addition, the angles of polarization of the triplet–triplet transitions are predicted, and their significance in the interpretation of triplet-state structures is discussed.
Electron Paramagnetic Resonance and X-Ray Studies in Doped Silver Carbonate
Authors: Ashford Nicholas A. , Snelson Alan
Published: February 2004

For Y(III)- or Gd(III)-doped silver carbonate with the ratio of dopant to Ag, n ≥ 0.005, a new orthorhombic crystal structure is reported with a = 13.94 Å, b = 5.97 Å, and c = 5.30 Å, determined from x-ray studies. Electron paramagnetic resonance investigations on γ-irradiated Y(III)-doped silver carbonate also indicate the presence of a new crystal structure. The same new crystal structure is thermally attained in undoped carbonate at ∼150°C under 3 atm of CO2.
Monte Carlo of Chains with Excluded Volume: a Way to Evade Sample Attrition
Authors: Alexandrowicz Z.
Published: February 2004

A new method for the generation of long self-avoiding walks on lattice is described: Short self-avoiding walks—say of length N = 50—are generated by direct Monte Carlo method, then linked in pairs to form “dimers.” Each dimer is tested for intersections between its two halves—those passing the test giving a sample of self-avoiding walks N = 100, which is dimerized in turn, etc. In this manner the repeated checking for intersections formed with only a few steps (short loops) is substantially avoided, while precisely such intersections are responsible for the heavy attrition with the direct Monte Carlo method. Thus the attrition accompanying the dimerization is quite insignificant even for very large N. With the help of this method walks N = 50 × 27 = 6400 were generated on the 4-choice cubic lattice, for which the expansion coefficient of the end to end distance is α = 2.2. (The limit reached by others is N ≃ 2000 on the tetrahedral lattice, corresponding to only α ≃ 1.6, while α = 2.2 would require a length of about N = 50 000.)
Ionic Collision Processes in Gaseous Nitrogen
Authors: Ryan K. R.
Published: February 2004

Those collision processes in nitrogen leading to the production of N3+, N2+ and N+ are examined. For N3+ production the specific reaction rate as well as the lifetime of the metastable precursor ion are evaluated. Cross-section measurements for N+ production indicate that under the experimental conditions employed collisional dissociation of the molecular ion is the predominant mechanism. The shape of the symmetrical charge-transfer cross-section curve obtained here agrees well with that derived from calculations based on the impact parameter treatment for N2+ impact energies above 20 eV. Differences between the experimental and theoretical curves below 20 eV are probably caused by experimental effects.
Collision Reactions of Electronically Excited Hydrogen Molecules
Authors: Hotop H. , Lampe F. W. , Niehaus A.
Published: February 2004

Relative abundances of ions produced in collisions of metastable H2, HD, and D2 molecules with various ground-state molecules (M, RH2) are reported. It is found that, in addition to Penning ionization and fragmentation of the target ion, deuteron addition reactions D2*+M→MD++D, exchange reactions D2*+RH2→(RD2++H2), (RHD++HD), and addition reactions with exchange D2*+RH2→(RH2D++D), (RD2H++H) occur. In the case of acetylene, propyne, and the 1-alkenes C2H4, C2H6, C4H8, C6H12, the reactions are explained in terms of an intermediate ion complex RH2D2+ which decomposes within 10−6 sec. In the case of NH3 and H2O only deuteron addition without exchange occurs. This is explained in terms of a stripping mechanism. From the occurance of deuteron addition reactions in collisions with O2, H2O, HCl, CO2, and CO, a lower bound for the proton affinity of these molecules of PA ≧ 6.2 was derived.
Extended Hartree–Fock Calculations for Li and Li-like Ions
Authors: Hardcastle D. L. , Keown R.
Published: February 2004

An extended Hartree–Fock (EHF) calculation is performed for the 1s22s ground state of Li and Li-like ions for z values from 2 through 9. The EHF wavefunction is a two determinant eigenfunction of S2 and Sz. The single-particle orbitals are found by solving the coupled integro-differential equations by an iterative numerical integration technique. The results should be the best for the approximate wavefunction used, since the single-particle orbitals do not rely on a choice of basis functions. The total energy, ionization energy, and hyperfine splitting are calculated and the results are compared with similar previous calculations.
Dynamic Polarization of 31P Nuclei: Some Evidence for Stereospecific Hyperfine Interactions in Liquids
Authors: Poindexter Edward H. , Dwek Raymond A. , Potenza Joseph A.
Published: February 2004

Dynamic nuclear polarization parameters were compared for all combinations of three free radicals and eight representative phosphorus compounds. The chemical nature of the phosphorus compound is shown to be much more significant than that of the radical in determining the degree of scalar coupling. This contrasts sharply with fluorine, where the radical was equally important, and reflects the more complex geometry and bonding associated with phosphorus compounds. The degree of scalar coupling can be correlated with stereospecific interactions between phosphorus substituents and sites of high spin density on the radical, suggesting the formation of virtual transient bonds.
Electronic Transition Moment for the N2 Vegard–Kaplan Bands
Authors: Broadfoot A. L. , Maran S. P.
Published: February 2004

Measurements of relative band intensities for the N2 Vegard–Kaplan bands with υ′ = 0 are used to find a curve that represents the smooth variation of the electronic transition moment with internuclear separation. The Vegard–Kaplan bands were observed in the discharge afterglow without appreciable contamination from other N2 systems. Although the intensity measurements are more accurate than previously reported, the reduced electronic transition moment curve is essentially the same.
Ab Initio Calculations on the H2+D2=2HD Four-Center Exchange Reaction. I. Elements of the Reaction Surface
Authors: Wilson C. Woodrow , Goddard William A.
Published: February 2004

We present the results of ab initio calculations on some interesting regions of the reaction surface for the four-center exchange reaction H2 + D2 = 2HD. These calculations, which use a minimum basis set of Slater orbitals, indicate that for all geometries appropriate to the transition state of the reaction, a barrier height of at least 148 kcal/mole is present. This is far greater than the energy required to produce free radicals and more than three times the experimental energy of activation, 42 kcal/mole. Considering the sources and magnitudes for errors due to correlation and basis set restrictions, we estimate the barrier height for this exchange reaction to be 132 ± 20 kcal/mole exclusive of zero-point energies. In this paper we discuss the surface as determined by configuration interaction techniques. We find that the most favorable geometries for the exchange reactions are the square, rhombus, and kite configurations. However, all of these states are unstable with respect to H2 + 2H. In addition we find no evidence of collision complexes for any of the likely transition state geometries. In the following paper we will examine the G1 wavefunctions for this system in order to obtain an understanding of the factors responsible for the shape of the surface.
Semiempirical and Theoretical Derivation of the Oxygen-17 σ–π Interaction Constants in Carbonyl-Containing Anion Radicals
Authors: Broze M. , Luz Z.
Published: February 2004

Oxygen-17 hyperfine splitting constants aO are determined in ̄a number of carbonyl radicals including simple and substituted semiquinones, semidiones, and ketyls. The values for aO range between 7.5 and 10.4 G. The results are analyzed in terms of the π spin-density distribution in the radicals: Neglecting overlap spin densities the analysis shows that the most important contribution to aO comes from spin density on the oxygen itself and a semiempirical relation of the type aO = QOCOρO where QOCO = 45 ± 5 G accounts satisfactorily for the observed aO's. The over-all range of 17O hfs and the accuracy of the spin densities are not sufficient for a semiempirical determination of the effect of overlap spin density. The semiempirical results are compared with an independent calculation of the σ–π interaction constants of the carbonyl oxygen using the theory of McLachlan, Dearman, and Lefebvre and the approximate Hartree–Fock wavefunctions for formaldehyde calculated by Newton and Palke. These calculations give the following theoretical expression for aO : aO = 48.70ρO − 0.46ρC − 6.03ρCO (where ρCO is the overlap spin density in the C–O bond), in good agreement with the results of the semiempirical analysis. The origin of the oxygen σ–π interaction constants is discussed and it is shown that they result mainly from spin polarization of the lone-pair 2sO electrons, but there is also a small (negative) contribution from the inner-shell 1sO orbital.
Formation of Excited Singlet States in the Nanosecond Pulse Radiolysis and Nanosecond Flash Photolysis of Aromatic Molecules in Liquid and Solid Solutions
Authors: Thomas J. K.
Published: February 2004

The absorption spectra of the excited singlet states of naphthalene and 1:2 benzanthracene have been observed in the nanosecond pulse radiolysis and flash photolysis of these solutes in cyclohexane, benzene, and polystyrene. The effect of xenon, piperylene, and excimer formation on the absorption spectra provides evidence for the assignment of these spectra to excited singlet states. The spectra are very similar both in shape and intensity to the triplet spectra; hence, little growth of the triplet state is observed as the excited singlet state decays. An extinction coefficient at 560 mμ for the 1:2 benzanthracene excited singlet is measured as ε560 = 9700M−1·cm−1. Using the photolysis data it is shown that approximately equal yields of excited singlet and triplet states are initially formed in the radiolysis of these systems. Large yields of ions are also formed in the pulse radiolysis of 1:2 benzanthracene in polystyrene and polymethyl-methacrylate.
Resonant Scattering Theory of Association Reactions and Unimolecular Decomposition. I. A United Theory of Radiative and Collisional Recombination
Authors: Mies Frederick H.
Published: February 2004

A complete quantum-mechanical theory of unimolecular kinetics and of predissociation is developed using a generalized version of Fano's theory of resonant scattering. An important feature of the theory is that it treats the irreversible couplings between the activated molecules and either the photon field (predissociation) or the inelastic collisions with bath molecules (unimolecular decomposition) by means of an optical potential, and leads to very concise and, certainly in the case of predissociation, exact results. The final form of the rate expressions resembles the Eyring Absolute Rate Theory (ART), with the important result that explicit theoretical expressions are given for the `transmission coefficients' as a function of temperature and pressure, which in principle allows us to calculate the rates.
Electron Paramagnetic Resonance Studies of VO2+ Ion Doped in Methyl Ammonium Gallium Alum Single Crystals
Authors: Rao K. V. S. , Sastry M. Dattatreya , Venkateswarlu Putcha
Published: February 2004

The electron paramagnetic resonance of the VO2+ ion in methyl ammonium gallium alum single crystals has been studied. It is observed that the VO+2 ion substitutes for the Ga3+ ion and forms a [VO(H2O)5]2+ complex, a distorted octahedron with a H2O vacancy along VO bond direction. The octahedron cubic axes are found to be displaced from crystallographic 〈001〉 axes by 9° in [110] plane. The EPR results suggest that the host alum probably belongs to β type in which the presence of VO2+ twists the octahedron cubic axes by about 9° from the crystallographic 〈100〉 axes. Optical absorption studies confirm the formation of [VO(H2O)5]2+. By correlating the EPR and optical absorption data, the covalency rates of σ bonding between the vanadium atom and equatorial ligands and of the π bonding between vanadium atom and the vanadyl oxygen have been estimated.
Asymmetry Parameters and the Temperature Dependence of the PQR Frequencies of 127I in SnI4
Authors: Ward R. W. , Williams C. D. , Tipsword R. F.
Published: February 2004

The pure quadrupole resonance spectrum of 127I in solid SnI4 has been measured from 4.2°–300°K at atmospheric pressure. The data have been fitted with a form of Bayer–Kushida theory which incorporates temperature effects due to field-gradient asymmetry. The adjustable parameters were determined for a given temperature range by a procedure designed to yield as nearly as possible both the best fits to the data and the same value for a given parameter for both the high- and low-frequency curves at a given lattice site. This procedure was largely successful and resulted in values for the asymmetry parameter, viz., 0.012 and zero for the two inequivalent iodine sites, which appear almost independent of the temperature range selected. The results for the average normal-mode lattice frequency may be taken to indicate that several of the low-frequency vibrational modes of the SnI4 molecule contribute importantly to the temperature dependence of the quadrupole resonance frequency in the solid.
Viscosity of Binary Polar-Gas Mixtures
Authors: Pal Arun K. , Bhattacharyya P. K.
Published: February 2004

Viscosity of the binary polar-gas mixtures ammonia–diethyl ether and hydrogen sulfide–diethyl ether has been measured as a function of composition and temperature by a precision oscillating-disk method. The experimental results have been interpreted in terms of the Chapman–Enskog theory by using the 12–6–3 potential with a set of combination rules for polar–polar interaction. The viscosity data have been used to obtain the interdiffusion coefficients for these systems.
Hiroike's Test of Compatibility and the HNC Approximation
Authors: Caligaris R. E. , Rodríguez A. E. , Silbert M.
Published: February 2004

It is shown that the HNC approximation is self-consistent in all its virial coefficients with regard to the Hiroike's test. The close relationship between Hiroike's test and the variational principle satisfied by the HNC approximation is stressed.
ESR Spectrum and Structure of HNO2− in KCl
Authors: Adrian Frank J. , Cochran Edward L. , Bowers Vernon A.
Published: February 2004

If a KCl melt containing traces of OH− and CN− is subjected to controlled oxygenation, then ultraviolet photolysis of crystals grown from this melt produces the HNO2− radical anion as a substitutional impurity. The radical is also produced by photolysis of KCl:OH−:NO2− crystals. Formation of this radical is attributed to reaction of H atoms, produced by photolytic decomposition of OH−, with NO2− ions, which in the former case are produced by oxidation of CN−. At 77°K the electron spin resonance (ESR) spectrum of this radical is an isotropic nitrogen hyperfine structure (hfs) triplet. At 4°K, however, the spectrum is anisotropic and contains both nitrogen and hydrogen hfs. The magnetic constants of HNO2− are: g1 = 2.0020, g2 = g3 = 2.0074; A1(N) = 39.2, A2(N) = A3(N) = 12.0 Oe; and A1(H) = − 5.0, A2(H) = − 12.5, A3(H) = 13.0 Oe. Axis 2 is perpendicular to the only symmetry plane of the slightly nonplanar molecule. Axes 1 and 3 are, respectively, approximately perpendicular and parallel to the NH bond. Axes 1 and 2 lie in the same {110} crystal plane, and axis 1 makes a 26.6° angle with the (100) crystal axis contained in this plane. At roughly 25°K a spectrum of (111) symmetry is observed which is the result of motional averaging about that (111) crystal axis which makes the smallest angle with molecular axis 2. It can be shown from the nitrogen and proton hfs constants that the deviation of the molecule from planarity is roughly 10°, and that the unpaired electron density on the nitrogen atom is 0.57.
Field Ionization in Liquids
Authors: Halpern Bret , Gomer Robert
Published: February 2004

Field ionization in liquid H2, Ar, He, N2, and O2 has been studied and approximate mobilities obtained for the respective positive ions. In the case of He, field ionization leads to charge multiplication because of sufficient ion acceleration in the high-field region near the emitter. In the case of H2 and Ar linear lni or lni / V vs 1 / V plots could be obtained at low currents, indicating that current generation was controlled by tunneling. Simple models for tunneling from the valence band and from noninteracting molecules are derived and applied to these systems. For the experimental data applied to Ar the band model yielded a bandgap of 13 eV, in excellent agreement with theoretical and optical measurements. For H2 the noninteracting molecule and the band model give equally reasonable results.
Analysis of the Linear Viscoelastic Relaxation of a Liquid Hydrocarbon
Authors: Hutton J. F. , Phillips M. C.
Published: February 2004

Measurements have been made of the real part of the shear impedance of pure 2,2,4,4,6,8,8-heptamethylnonane at frequencies of 6, 18, 30, and 78 MHz at temperatures between − 132° and − 79°C. The viscosity at zero rate of shear, ρ(0), was also measured down to − 95°C and extrapolated to the lower temperatures. Analysis of the results depends critically on having values of ρ(0) and the limiting shear compliance at infinite frequency, J(∞). New extrapolation techniques are introduced for obtaining J(∞) in the relaxation region. As a result it is found that J(∞) does not vary linearly over the whole of the temperature range. The Barlow, Erginsav, and Lamb model of viscoelasticity fits the measurements well at high frequencies, but there is a small deviation at low frequencies.
Experimental Study of Reaction Kinetics by Light Scattering. I. The Polarized Rayleigh Component
Authors: Yeh Yin , Keeler R. N.
Published: February 2004

Spectral studies of scattered laser light have been conducted in multicomponent solutions where spontaneous fluctuations of the various molecular species occur about the chemical equilibrium. The spectral line broadening observed in these systems reflects the rate of return to equilibrium of these spontaneous fluctuations, and is characteristic of the reaction rates of chemical reactions occurring about the equilibrium. The reaction (Me2+(H2O)SO42−)Aq ⇆ (MeSO4)Aq has been singled out for investigation. Results of the studies on solutions of ZnSO4 and MnSO4 by the scanning Fabry–Perot interferometer and photon counting technique are in reasonable agreement with the data obtained by ultrasonic relaxation spectroscopy. The enthalpies of activation calculated for the process are: ZnSO4, ΔHb‡ = 3.72 kcal/mole; and MnSO4, ΔHb‡ = 6.15 kcal/mole.
Thermodynamics of Lithium Isotope Exchange Reactions. I. Electrochemical Investigations in Diglyme and Propylene Carbonate
Authors: Hall John C. , Murray Richard C. , Rock Peter A.
Published: February 2004

A direct experimental determination of the equilibrium constant for the isotope exchange reaction Li7(s) + 6LiBr(soln) = 6Li(s) + 7LiBr(soln) has been made using an electrochemical cell without liquid junction. The value obtained is K = 1.037 ± 0.004 at 23°C in diglyme as solvent. The value obtained has been compared with values calculated from statistical thermodynamic theory.
Luminescent Reactions of H(2P)
Authors: Wauchop T. S. , Phillips L. F.
Published: February 2004

Hydrogen atoms were excited to the P2 level by absorption of Lyman-α radiation. Relative intensities were measured for emission bands arising from primary reactions of H(2P) with O2, N2, NO, N2O, CO, CO2, and SO2. The emitting species were all diatomic hydrides. The emission intensities observed with different reactants were all very similar, which suggests that the probability of obtaining an electronically excited hydride molecule from a reaction of H(2P) is near unity. Some emission due to secondary reactions was also observed.
Study of Some Excited Singlet and Triplet Electronic States of Fluorene
Authors: Bree A. , Zwarich R.
Published: February 2004

The absolute intensity of absorption parallel to the a and b axis of a fluorene crystal has been measured from 3000 to 2300 Å and allowed the following interpretation to be placed on the solution spectrum: The 3000-Å system of medium intensity and the stronger 2600-Å system are long-axis polarized, and a rather weak band at about 2730 Å is short-axis polarized. The onset of a stronger short-axis polarized transition above 2400 Å was observed. This analysis shows that fluorene has quite different electronic properties from phenanthrene and carbazole. The low-temperature absorption and fluorescence was entirely consistent with these electronic assignments. Vibrational analyses of the absorption and fluorescence spectra of fluorene in a polycrystalline n-heptane matrix at about 15°K are presented; intervals that formed overtones were tentatively assigned as totally symmetric fundamentals. Crystalline fluorene did not measurably phosphoresce when pure, but intense, blue phosphorescence of fluorene could be induced at about 6°K by the deliberate addition of dibenzthiophene as an impurity. A vibrational analysis of this phosphorescence revealed intervals identical with those in the fluorescence and phosphorescence of fluorene in n-heptane.
Limiting Laws and Counterion Condensation in Polyelectrolyte Solutions I. Colligative Properties
Authors: Manning Gerald S.
Published: February 2004

Formulas are derived for the osmotic coefficient, the Donnan salt-exclusion factor, and the mobile-ion activity coefficients in a polyelectrolyte solution with or without added sample salt. The formulas, which contain no adjustable parameters, are based on the (theoretical) observation by several workers that counterions will “condense” on the polyion until the charge density on the polyion is reduced below a certain critical value. The uncondensed mobile ions are treated in the Debye–Hückel approximation. In a restricted sense, the formulas are “limiting laws,” and this aspect is discussed at length. Detailed comparison with experimental data in the literature is given; agreement of the theory with experiment is usually found to be quantitative.
Analytical Evaluation of Multicenter Integrals of r12−1 with Slater-Type Atomic Orbitals IV. Four-Center Integrals by Taylor Series Method
Authors: Kay Kenneth G. , Silverstone Harris J.
Published: February 2004

The four-center integral of r12−1 with Slater-type atomic orbitals is evaluated analytically. The result, obtained after expanding r12−1 in a Taylor series, is for general values of the n, l, m, and ζ parameters of the Slater-type orbitals and of the internuclear distance vectors, R1, R2, and R.
Symmetry-Adapted Second-Order Energy. Some Comments and Results for H2+
Authors: Brändas E. , Goscinski O.
Published: February 2004

Interrelationships between rigorous upper and lower bounds to the second-order energy in several schemes are discussed. The validity of a formula of the type E ≤ E0 + ε1 + λ̄ε2 is further extended to the approximate, symmetry-adapted case. Results for H2+ show that the linear series E0 + ε1 + ε2 obtained in the AV scheme actually crosses the exact energy, being above it at larger distances.
Vibronic Theory of Circular Dichroism
Authors: Caldwell Dennis J.
Published: February 2004

The effect of molecular vibrations on optically active absorption bands is treated by assuming a total wavefunction of the form ψ(Q) χn(Q − Q̄), where ψ(Q) is the electronic wavefunction with the normal coordinates as parameters and χn(Q − Q̄) is a harmonic oscillator function in the nuclear coordinates. The electric and magnetic dipole moments of a transition G → A are determined as functions of Q, μGA(Q), MAG(Q). The rotational strength for the 0–n vibrational mode, 〈χ0(QG) | μGA(Q) | χn(QA)〉· 〈χn(QA) |  MAG(Q) | χ0(QG)〉, is evaluated by expanding μGA(Q) and MAG(Q) as a power series in Q about the conformation of zero rotation. Formulas are obtained which indicate the possibility of several sign changes within a nondegenerate absorption band. The theory shows that these sign changes are possible not only for multiply excited vibrational modes but for those of a single symmetry as well.
Infrared Spectrum of Anthracene-d10
Authors: Bree A. , Kydd R. A.
Published: February 2004

The infrared spectrum of anthracene-d10 is reported with the electric vector of the plane-polarized incident light parallel to all three crystal axes; thus the c-polarized spectrum is recorded for the first time. The measurements extend from 2000 to ∼ 50 cm−1; the single-crystal samples used were too thick to transmit radiation in the strongly absorbing region near 2260 cm−1 so that little new data are available concerning the CD stretching fundamentals. However, a fairly complete assignment of the molecular fundamentals at lower energy is presented, based on the criteria of line strength and polarization, and the product rule. A comparison with calculated frequencies and some earlier experimental assignments is given.
Gaussian-Orbital Basis Sets for the First-Row Transition-Metal Atoms
Authors: Basch Harold , Hornback C. J. , Moskowitz J. W.
Published: February 2004

Contracted Gaussian-type function basis sets have been produced for the first-row transition-metal atoms Sc through Cu for use in molecular SCF calculations. The basis functions consist of 15 s-type, eight p-type, and five d-type Gaussian primitives contracted to a four s-type, two p-type, and one d-type basis set and are exponent and coefficient optimized after contraction. It is shown that this basis set is of single-zeta quality for the core functions and of double-zeta quality for the valence-electron functions. Relaxation of the degree of contraction results in a significant lowering of the total energy.
Raman Spectra of Solid CO2, N2O, N2, and CO
Authors: Cahill J. E. , Leroi G. E.
Published: February 2004

The Raman spectra of solid CO2, N2O, N2, and CO have been observed. Each spectrum can be analyzed by assuming an approximately ordered structure isomorphous with that of CO2. The lattice mode intensities have been calculated on the basis of the oriented gas model; they are in good agreement with the measured values and lead to confident assignments of the observed bands. The frequencies of the Eg and two Tg librations are 73.5, 91.5, and 132 cm−1, respectively, for CO2(15°K) and 68, 82, and 124.5 cm−1, respectively, for N2O (15°K). In α-N2 at 16°K two sharp bands are observed at 33.5 cm−1 (Eg) and 37.5 cm−1 (Tg). The other Tg mode may coincide with the Eg. Only one broad, asymmetric lattice band is observed for α-CO, which is located at 47.5 cm−1 at 12°K. The peak frequencies of these bands decrease an average of ∼ 15% on warming from 15°K to the phase transition, and there is a considerable concommitant increase in their widths.
Study of the Linewidths of the Electron Spin Resonance Spectra of Some Aromatic Hydrocarbon Radical Ions
Authors: Segal Bernice G. , Reymond Axel , Fraenkel George K.
Published: February 2004

Linewidths of the ESR spectra of the naphthalene, anthracene, and tetracene radical anions, and the tetracene cation in dilute solution at low temperatures have been carefully investigated. It was expected that for these systems the linewidth variations would be determined primarily by the anisotropic g tensor and electron–nuclear magnetic dipole interactions. A comparison of the experimental linewidth parameters with calculated values based on this assumption shows that although theoretical expressions can account qualitatively for the observed linewidths, quantitative agreement is not satisfactory. It is shown that the discrepancies between the calculated values and the experimental results cannot be accounted for by errors in the calculations resulting from our ignorance of the exact spin density distribution in the radicals or of the detailed form of the atomic-orbital wavefunction used for the unpaired electron. The relative insensitivity of the calculated ratios of linewidth parameters to changes in spin densities indicates that even if agreement between theory and experiment were excellent, it would not be possible to perform an indirect analysis of the experimental results to obtain reliable values for the spin densities. Both anisotropic rotational motions and fluctuations in the isotropic hyperfine splittings are found to affect the calculated linewidth parameters, and while neither of these factors alone is sufficient to explain the observed values, the calculations indicate that both of them may make significant contributions to the linewidths.
Thermal Conductivity of Mixtures in the Dense Gaseous State: The Methane–Carbon Dioxide System
Authors: Rosenbaum Barry M. , Thodos George
Published: February 2004

Experimental thermal conductivities were established for the methane–carbon dioxide system using a coaxial cylindrical cell. These measurements were carried out on pure methane, carbon dioxide, and three binary mixtures containing 0.755, 0.464, and 0.243 mole fraction of methane. The temperatures of this study ranged from approximately 60° to 160°C and pressures extended up to 10 000 psi. The resulting thermal conductivities k for the dense gaseous state and the corresponding thermal conductivities of the dilute gas at atmospheric pressure, k*, for this binary system were used to produce the unique relationship for this system, (k − k*)λzc5 = 3.075 × 10−8[exp(1.203ρR) − exp(− 4.359ρR2)], where the thermal conductivity parameter, λ = M1/2Tc1/6 / Pc2/3. For the mixtures of this system, pseudocritical constants were used. This relationship was applied for the calculation of thermal conductivities which, when compared with corresponding experimental values, produced an average deviation of 2.24% for 220 experimental points considered.
Effect of Electron Scavengers on the Positive Ion Reactions in the Radiolysis of Cyclopropane Solutions
Authors: Rzad Stefan J. , Schuler Robert H. , Hummel Andries
Published: February 2004

Electron scavengers such as CCl4, SF6, N2O and CH3Br are found to increase the yield of the secondary positive ion reactions which occur in the radiolysis of cyclopropane solutions in cyclohexane. The observed increase can be understood in terms of an increase in the lifetime of the ion pairs which results when the electron initially formed is converted to a less mobile negative ion. The quantitative aspects can be treated in terms of the change in the mutual diffusion coefficient of the ion pair if one includes in the model the concentration dependence for ion scavenging found when only one solute is present. In the present study electron capture by CCl4 is found to result in a decrease in the diffusion coefficient of the ions by a factor of 17. From this and available experimental information on the diffusion coefficients of positive and massive negative ions the diffusion coefficient of the negative entity initially produced by the radiation in cyclohexane is estimated as 2.6 × 10−4 cm2sec−1. This diffusion coefficient is considerably higher than those for the massive negative ions so that there seems to be little question but that the electron is involved in a more or less free state. The absolute rate constant for the electron scavenging process is estimated to be of the order of magnitude of 1011M−1·sec−1 and that for the positive ion reactions of cyclopropane a factor of 30 smaller.
Raman Spectrum of Crystalline Lithium Nitrate
Authors: Miller R. E. , Getty R. R. , Treuil K. L. , Leroi G. E.
Published: February 2004

Polarized Raman spectra of an anhydrous single crystal of LiNO3 have been obtained under optimum experimental conditions. The internal vibrations of the nitrate ion are observed as follows: ν4(Eg) = 735.4, ν1(A1g) = 1071.0, and ν3(Eg) = 1384.6cm−1; these frequencies are essentially independent of the cation in the host lattice. The two Raman-active (Eg) lattice modes have been located and assigned to primarily translational (124.4-cm−1) and librational (237.2-cm−1) motions. No indication of coupling between these vibrations is observed. The frequencies of the external vibrations relative to those of NaNO3 demonstrate that they are dependent on the volume of the crystalline unit cell. Except for small intensity contributions in some orientations which are ascribable to depolarization effects in the birefringent crystal, the polarizability activities of both the internal and external modes follow the expected symmetry selection rules.
Lower Bound for the Dissociation Energy of the Hydrogen Molecule
Authors: Kolos W. , Wolniewicz L.
Published: February 2004

An asymptotic formula for the diagonal nuclear motion corrections is derived for the hydrogen molecule, and a discussion is given of the errors which arise in the adiabatic dissociation energies from the failure of the adiabatic approximation to yield the exact energy of the dissociation products.
Electron Spin Resonance of Paramagnetic Colloidal Particles Exhibiting the Brownian Movement
Authors: Trapp Charles , Smith David , Wasson John R.
Published: February 2004

Electron spin resonance absorption in paramagnetic colloidal suspensions has been investigated both theoretically and experimentally. The nature and shape of the spectra are determined by the Brownian rotation of the particles. A magnetic field tends to align magnetically anisotropic particles so that the direction of maximum magnetic susceptibility in the particles is along the field. The alignment is resisted by the Brownian rotation of the particles. The temperature dependence of the angular distribution function, which is determined from simple statistical resaoning, has been confirmed experimentally in a quantitiative manner. From a comparison of computed and experimental spectra it is possible to determine a mass average mass of the particles. The equivalent of single-crystal spectra can be obtained by freezing a suspension in a strong magnetic field. Angular variation studies of the spectra can then be carried out as with any single crystal. Consequently, accurate values of A⊥ and | gx − gy | can be determined, which is not usually possible from powder spectra.
Electric Field Gradient for 14N in Ammonia from One-Center Wavefunctions
Authors: Eletr S. , Ha Tae-Kyu , O'Konski C. T.
Published: February 2004

The electric field gradient has been computed for 14N in ammonia, employing the one-center SCF wavefunctions of Moccia, Joshi, and Rutledge and Saturno. It is found that the calculated values are comparable to that of a multicenter SCF wavefunction. Influence of configuration interaction on the electric-field-gradient calculation also is discussed.
Diffusion and Heterogeneous Reaction. XI. Diffusion Coefficient Measurements for Gas Mixture of Atomic and Molecular Hydrogen
Authors: Sancier K. M. , Wise H.
Published: February 2004

The multicomponent diffusion coefficient DH, H2 has been evaluated from measurements of the relative atom density in a semi-infinite catalytic cylinder as a function of (a) distance from the atom source under steady-state conditions, and (b) time during the transient condition associated with removal of the atom source after attainment of steady state. An electron spin resonance spectrometer was employed for atom-density measurements and a radio-frequency discharge for atom production in the total gas-pressure range from 0.85 to 2.6 torr. The value for the diffusion coefficient was found to be DH, H2 = 1.8 ± 0.13 cm2sec−1 at 1 atm and 293° ± 3°K. Experimental data for the variation of DH, H2 as a function of temperature (293° to 719°K) are analyzed in terms of different interaction potentials for the atom–molecule collision.
Location of Energy Barriers. I. Effect on the Dynamics of Reactions A + BC
Authors: Polanyi J. C. , Wong W. H.
Published: February 2004

The dynamics of exchange reactions A+BC→AB+C have been examined on two types of potential-energy hypersurfaces that differed in the location of the energy barrier along the reaction coordinate. On “surface I” the barrier was in the entry valley of the energy surface, along the approach coordinate. On “surface II” the barrier was in the exit valley of the energy surface, along the retreat coordinate. The classical barrier height was Ec = 7.0 kcal mole−1 on both surfaces, and was displaced from the corner of the energy surface by the same amount; on surface I, r1‡ = 1.20 Å, r2‡ = 0.80 Å; on surface II, r1‡ = 0.80 Å, r2‡ = 1.20 Å (r1 ≡ rAB, r2 ≡ rBC, and the superscript ‡ refers to the location of the crest of the barrier). Three-dimensional (3D) classical trajectory calculations were performed for the mass combination mA = mB = mC at several reagent energies. The reagent energy took the form of translation, vibration or an equilibrium distribution of the two. The main findings were that translation was markedly more effective than vibration in promoting reaction on surface I, and vibration markedly more effective than translation in promoting reaction on surface II. The total reactive cross section with the entire reagent energy vested in translation was symbolized ST, with the reagent energy (but for 1.5 kcal) in vibration, SV, and with an equilibrium distribution over reagent translation and vibration, Seq. On surface I ST ≫ SV: on surface II SV ≫ ST. Close to the threshold for ST on surface I, ST / Seq ∼ 10; close to the threshold for SV, on surface II, SV / Seq ∼ 10. At high reagent energies (2 × threshold) on surface I ST / Seq fell to 2, whereas on surface II SV / Seq increased to extremely large values. Product energy and angular distributions were recorded for two reagent energies. On surface I with low translational energy in the reagents a major part of the available energy appeared as vibration in the molecular product. At higher collision energy this fraction decreased. On surface II with low vibrational energy in the reagents only a small part of the available energy appeared as vibration in the product. At higher vibrational energy this fraction increased. The product angular distribution at low reagent translational energy on surfaces I and II corresponded to backward-peaked scattering of the molecular product. At increased reagent energy on both surfaces the distribution shifted forward (this is a novel phenomenon in the case of increased reagent vibration; surface II).
Gas-Phase Raman Spectra of Carbon Suboxide
Authors: Smith William Hayden , Barrett Joseph J.
Published: February 2004

The vibration–rotation gas-phase Raman spectrum of carbon suboxide has been obtained for the first time. The spectrum of C3O2 can be discussed in terms of a quasilinear molecule with little or no barrier at the linear configuration and possible barriers away from the linear configuration. Using these concepts, most of the problems of the vibrational spectrum can be satisfactorily solved, especially as to the origin of the infrared and, now, Raman bands, which show great intensity losses when carbon suboxide is condensed.
Magnetic Properties of DyPt3 and DyIn3
Authors: Arnold G. , Nereson N.
Published: February 2004

Neutron-diffraction measurements made on powder samples of the intermetallic compounds, DyPt3 and DyIn3, show that these compounds exhibit antiferromagnetic ordering below Néel temperatures of 13.2° ± 0.3°K and 24° ± 0.5°K, respectively. The magnetic reflections from DyPt3 can be indexed on a doubled chemical cell of cubic symmetry. A suitable magnetic model consists of an arrangement where the Dy moments are aligned in opposite directions in adjacent (111) magnetic planes. For DyIn3, the magnetic reflections can be indexed on the doubled chemical cell of tetragonal symmetry. An appropriate magnetic model is one in which the Dy moments are aligned oppositely in adjacent (110) magnetic planes. The moment direction makes an angle of 27° ± 5° with the unique axis of the tetragonal magnetic cell. The saturated ordered moment is 9.0 ± 0.3 μB per Dy atom for DyPt3 and 8.8 ± 0.3 μB per Dy atom for DyIn3. The magnetic ordering process as a function of temperature closely follows a Brillouin function for DyPt3; the DyIn3 ordering shows a deviation from the customary behavior. The magnetic form factor data from the coherent magnetic reflections agree well between the two compounds but decrease faster with increasing scattering angle than theoretical predictions.
Taxonomy of F-Aggregate Centers in NaF
Authors: Chandra Ashoka , Holcomb D. F.
Published: February 2004

Results of a study of broad and narrow optical absorption bands of F-aggregate color centers in NaF are given in terms of correspondence between optical absorption band and defect model. Comparison is given to previous work. New results or results which modify previous conclusions are reported for F2+, F3+, M′, M, and N centers, as well as for an impurity center which gives rise to a prominent optical absorption band at 312 mμ (300°K). It is proposed that this center consists of an oxygen-impurity–F-center complex. A number of identifications were made possible through use of OH− and O−− dopings, which favor centers with net positive and net negative charges, respectively.
Computation of Antisymmetric Wavefunctions for Molecules
Authors: Gabriel J. R.
Published: February 2004

New methods for reduction of group representations are discussed, and their application to the construction of antisymmetric molecular wavefunctions outlined. The methods are being programmed in pl / 1 for IBM S / 360 because of the combination of list processing and linear algebra involved. It is expected that it will take about 2 man-years to produce a complete program. The methods are suitable for implementation on a large parallel computer.
Dielectric Properties of Ice I
Authors: Wörz O. , Cole R. H.
Published: February 2004

The dielectric properties of ice have been measured from 0° to − 80°C using samples prepared from redistilled water which were further purified by zone refining. The resulting conductivities were low enough that dielectric and electrode space-charge effects could be resolved in three terminal ac measurements to frequencies extended to 0.1 Hz. The relaxation times of the Debye behavior obey an Arrhenius rate equation only above − 50°C, smaller values being found at lower temperatures, the temperature dependence of static dielectric constant gives a Curie temperature of 38°K, and the dc conductance is 4 × 10−11 mho cm−1 at − 10°C for the best sample with an apparent activation energy which is much larger than for less pure ice but somewhat uncertain. The significance of these data for estimates of defect concentrations and other parameters is discussed.
Self-Consistent-Field Molecular Orbital Theory of the Chemical Bond. II. The Carbon–Hydrogen Bond of Methane
Authors: Peters David
Published: February 2004

The theory of the preceding paper is applied to the carbon–hydrogen bond of the methane molecule as a first test case. Many of the features of the theory can be displayed with this example. The resulting theoretical predictions about the carbon–hydrogen bond are set out in detail.
Product Energy Distribution for an Endothermic Reaction: A + B→AB+ + e
Authors: Myers G. H. , Young H. W.
Published: February 2004

The product energy distribution for the reaction A + B→AB+ + e (where A and B are atoms) is considered on a theoretical basis. Due to the large mass ratio of the products, conservation of energy and momentum largely determine the product energy distribution without requiring a detailed knowledge of the mechanics of the collision complex. Assuming a hard-sphere line-of-center model, it is shown that AB+ would be produced with thermal translational and rotational energies. The sum of the average AB+ vibration and electron translation energies is kT. Detailed balancing is used to estimate the partitioning of this kT energy between the AB+ vibration and electron kinetic degrees of freedom. Calculations are presented showing the dependence of electron energy on reaction temperature and the AB+ vibrational frequency. The electron must always be produced at less than thermal energies. For the reaction N + O→NO+ + e at 6500°K it is estimated the electron would be produced at 1800°K.
Nonexponential Relaxation of Three-Spin Systems in Nonspherical Molecules
Authors: Hubbard Paul S.
Published: February 2004

The longitudinal and transverse nuclear magnetic relaxation of a system of three identical spin-12 nuclei in equivalent positions at the corners of an equilateral triangle fixed perpendicular to the axis of a symmetric-top molecule is calculated on the assumptions that :(1) The relaxation is due to the dipole–dipole interactions between the three spins, including the effects of cross correlations, (2) the motion of the molecule can be treated as anisotropic rotational Brownian motion, and (3) the correlation time is short. The relaxation is found to be the sum of two decaying exponentials. The deviation from a simple exponential decay is greatest when the rotational diffusion about the symmetry axis is rapid compared to the rotational diffusion about an axis perpendicular to the symmetry axis.
Sharpness of Some Rare-Gas Resonance Lines
Authors: Yoshida Masakazu , Tanaka Ikuzo
Published: February 2004

An investigation on the nature of krypton and argon resonance lines emitted from a low-pressure lamp has been made applying the sensitized photoionization technique and represented in terms of “sharpness.” Cowan and Dieke's self-absorption theory has given a good interpretation of the dependence of the nature of resonance lines on the rare-gas pressure. The approximate expressions for the total line intensity and the sharpness were obtained from their theory. The experimental results on the effect of neon acting as a foreign gas suggested that the broadening of resonance lines arised from the interaction between neon and rare-gas atoms, and this interaction was larger in the case of the argon resonance line.