bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular-Beam Kinetics. II. Magnetic Deflection Analysis of Reactions of Li with NO2, CH3NO2, SF6, CCl4, and CH3I
Authors: Parrish David D. , Herm Ronald R.
Published: February 2004

Thermal energy crossed-molecular-beam studies have been made of the reactions of Li with NO2, CH3NO2, SF6, CCl4, and CH3I. An inhomogeneous deflecting magnet between the collision zone and detector was used to distinguish elastic scattering of Li from reactive scattering of LiZ. The total reaction cross sections and the reactive attenuations of the wide-angle Li nonreactive scattering for these gases are considerably smaller than are the corresponding features previously reported for the Li+XY(XY is Cl2, Br2, and ClI) reactions. Interesting differences are observed in the LiZ center-of-mass (c.m.) product angular distributions for the five gases studied here. The LiO product of the NO2 reaction is more sharply forward peaked in the direction of the incoming Li atom than are the corresponding LiX products of the Li+XY reactions. The LiNO2 and LiF products of the CH3NO2 and SF6 reactions exhibit very broad, almost isotropic c.m. angular distributions. The LiCl and LiI products of the CCl4 and CH3I reactions are predominantly scattered into the backward hemisphere in the c.m. coordinate system. The features of the NO2 reaction are discussed in terms of the electron transfer mechanism which was originally advanced to account for the features of the reactions of the alkali atoms with the halogen molecules.
Production of H3O+·nH2O from NO+ Precursor in NO–H2O Gas Mixtures
Authors: Puckett L. J. , Teague M. W.
Published: February 2004

Stationary afterglow techniques have been employed to determine reaction rate constants for ions reacting in NO–H2O gas mixtures. Krypton resonance radiation at 123.6 and 116.5 nm is used to ionize only the NO molecules. The NO+ ion is the precursor to a chain of reactions which result in NO+·nNO(n = 1,2), NO+·nH2O(n = 1,2,3), and H3O+·nH2O(n = 2,3,4) being formed. Rate constants and/or equilibrium constants are provided for all forward and all reverse reactions at 296°K.
ESR Studies of Gamma-Irradiated Crystalline 1-Bromobutane
Authors: Bonin Mary L. , Bonin Michael A. , Williams Ffrancon
Published: February 2004

Radiation damage in 1-bromobutane has been studied by ESR spectroscopy. The use of aligned crystals gives well-resolved spectra which can be clearly assigned to the Br2−.. center and the n-butyl radical. Other unidentifiable paramagnetic species are also produced. A quantitative interpretation of the Br2−. spectrum in the parallel orientation gives the magnetic resonance parameters A (81Br) = 472 G and g = 1.992 in satisfactory agreement with previous studies of Br2−. in single crystals of alkali halides. The spectrum of the n-butyl radical shows equal hyperfine interaction with the two β protons and as in other studies this is interpreted in terms of anisotropic internal rotation about the Cα–Cβ bond. The same two paramagnetic species can be identified in the γ-irradiated 1-bromobutane glass, but the ESR spectrum of the n-butyl radical in this case suggests that the internal rotation is frozen out and the radical adopts a nonsymmetrical configuration. Through the positive assignment of the dihalogen anion, the results provide strong confirmation of dissociative electron capture in the radiolysis of this system.
Photoelectron Spectra of the Halogens
Authors: Cornford A. B. , Frost D. C. , McDowell C. A. , Ragle J. L. , Stenhouse I. A.
Published: February 2004

Photoelectron spectra of valence shell electrons in F2, Cl2, Br2, and I2 yield information on the molecular and electronic structure of the lowest several states of the corresponding positive ions, some of which is not available from previous spectroscopic studies. Spin–orbit fine structure is resolved for the ground Π21 states of F2+ and Cl2+; values obtained are ζ = 337 ± 40 and 645 ± 40 cm−1, respectively. The first excited states of the ions are identified as Π2u and approximate values of ζ = 2000–2200 and 6400 cm−1 obtained for Br2+ (A 2Πu) and I2+(A 2Πu), respectively. A state in F2+ reported previously [D. C. Frost, C. A. McDowell, and D. A. Vroom, J. Chem. Phys. 46, 4255 (1967)] to lie at ∼ 17.4 eV is not observed here and is attributed to nitrogen impurity. Vibrational frequencies for F2+ and Cl2+(X 2Πg) are in agreement with spectroscopic work. The corresponding frequencies for Br2+ and I2+ are ωe = 360 ± 40 and ∼ 220 cm−1. A change in bond length to Br2+(2Πg) of Δre ∼ (−)0.095 Å is estimated from the vibrational envelope of the X2Πg state of Br2+.
Deconvolution of Ionization Efficiency Data as a Means of Determining Fragmentation Mechanisms in the Mass Spectrometer
Authors: Flesch G. D. , Svec H. J.
Published: February 2004

A method for deconvoluting fragment ion ionization efficiency data based upon total ionization efficiency data has been developed which makes it possible to discern multiple sources of fragment ions. The method requires observing automatically recorded I.E. curves in the 18-eV energy range immediately above the molecular ionization potential. The method has been tested with the model methanelike compounds CrO2F2 and CrO2Cl2 and has been a successful aid in explaining probable fragmentation reactions and pathways. Ionization efficiency curves convoluted from the deconvolution results produces agreement with experimental data within a few percent in all cases except those involving minor possible contributions to the over-all fragmentation reactions.
Reactions between H+ and D2
Authors: Maier William B.
Published: February 2004

Cross sections have been measured for the production of D2+, HD+, and D+ in reactions between H+ and D2. The initial kinetic energies Ec.m. in the center-of-mass system are between 0.3 and 80 eV. The total cross section σT for these reactions can be represented by σT = 1.54 Ec.m.−0.7 for 8 ≤ Ec.m. ≤ 80 eV, and σT = 2.11 Ec.m.−1.43 for 0.3 ≤ Ec.m. ≤ 2 eV, where σT is in square angstroms, and Ec.m. is in electron volts. Apparent thresholds for the endothermic reactions H++D2→D2++H, H++D2→HD++D are found at Ec.m. = 1.84 ± 0.3 eV. The cross section for H++D2→D++HD drops rapidly with increasing energy. For Ec.m. ≳ 6 eV, D+ appears to be produced mostly by the reaction H++D2→D++D+H. When Ec.m. ≳ 8 eV, the reaction products are primarily D2+ and a smaller amount of D+. There is only fair agreement between these results and those of previous studies.
Infrared Spectrum and Structure of Matrix Isolated Thallous Oxide
Authors: Brom J. M. , Devore T. , Franzen H. F.
Published: February 2004

The infrared absorption spectrum of Tl2O isolated in solid Ar, Kr, and N2 matrices was observed. From the observed spectra and the isotope shifts for Tl216O and Tl218O it is possible to conclude that Tl2O has a bent symmetrical structure and that the Tl–O–Tl angle is near 90°. The Tl–O bond distance is estimated to be 1.86 Å. The Tl–Tl bond distance is estimated to be 2.63 Å, and it is proposed that there is a strong Tl–Tl bond within the molecule. A force constant analysis and a comparison of the calculated and observed entropy of Tl2O support the proposed structure. The three fundamental frequencies for Tl216O in an argon matrix are ν1 = 571 cm−1, [ν2 ≃ 130 cm−1], and ν3 = 643 cm−1.
Chemisorptive Luminescence: Oxygen on Si(111) Surfaces
Authors: Brus L. E. , Comas J.
Published: February 2004

Chemisorptive luminescence, very similar to that seen by McCarroll [J. Chem. Phys. 50, 4758 (1969)] for oxygen on polycrystalline W, has been observed for oxygen on Si(111) surfaces. It is a diffuse gas-phase emission extending 2–3 cm above the crystal surface; the spectrum appears continuous, in low resolution, throughout the visible. About 1 in 107 O2 adsorptions produces a photon; no emission is seen during chemisorption of NO, NO2, CO, CO2, and N2. The luminescence decays with hyperbolic kinetics; a model is proposed relating the hyperbolic dependence to the logarithmic rate of surface oxide growth.
Paramagnetic Defects in TiO2 Produced by Radiation
Authors: Purcell T. , Weeks R. A.
Published: February 2004

Single crystals of TiO2, space group D4h14, reactor irradiated at 140°K and measured at 78°K, without warmup, exhibit intense electron spin resonance spectra. The most intense component of these spectra has an orientation dependence expected of a substitutional site. Two other less intense components of the spectra could be associated with interstitial sites or perturbed substitutional sites. The concentration of each of these was ∼ 0.1, the concentration of the intense component. These three spectral components and a blue–black color were no longer observed after warming to 300°K. An additional radiation with 137Cs gamma rays at 77°K gave a new intense resonance having an orientation dependence expected for an interstitial site. Weak satellite lines observed for one orientation were attributed to hyperfine interaction with 47Ti and 49Ti. Good agreement between the observed orientation dependence and that calculated from a spin Hamiltonian for which S = 12 and for which D4h14 point symmetry is used was found for each species. On the basis of concentration, g values, and hyperfine interactions, the two most intense spectral components are attributed to singly charged oxygen vacancies and interstitial Ti3+ ions.
Exact Classical Harmonic Free Energy of the Triangular Lattice
Authors: Huckaby Dale A.
Published: February 2004

The exact classical Helmholtz free energy per particle for a monatomic triangular lattice with first-neighbor harmonic interactions is shown to be given as F / kT = − 2ln(kT / hν0) + 12ln6 − (9 / π)L(π / 6), where ν0 = (2π)−1(κ / m)1/2, and L is Lobachevskiy's function.
Zeeman Effect Study of the Nuclear Quadrupole Resonance of 81Br in 4,4′-Dibromodiphenylether and 4,4′-Dibromodiphenylthioether
Authors: Ambrosetti R. , Angelone R. , Cecchi P. , Colligiani A.
Published: February 2004

The Zeeman effect of the 81Br NQR line was studied on single crystals of 4,4′-dibromodiphenylether and 4,4′-dibromodiphenylthioether. The relative orientations of the electric-field-gradient tensors acting upon the Br nuclei in the same molecule have been determined. The angle between the two Z-axis directions is 129°0′ ± 5′ in the former compound and 107°15′ ± 4′ in the latter. The angle between the normal to the plane determined by the two Z axes in a molecule and the X axis of each gradient is 33°30′ ± 1° and 37°25′ ± 30′, respectively. These values are in general agreement with known data from x-ray diffraction although the differences are significant. An accurate comparison is not, however, possible since carbon-atom coordinates are not reported in the literature.
Simple Model of Short-Range Interactions. III. Ethane, Propane, and Butane
Authors: Magnasco V. , Musso G. F.
Published: February 2004

With a Hückel-type Hamiltonian it can be shown that in a molecule described by a one-determinant wavefunction of localized nonorthogonal bond orbitals the intramolecular interaction energy turns out to be additive between pairs of different bonds to second order in the intergroup overlap. The possibility of building up the conformational energy of a molecule simply by adding contributions from all pairwise interactions between vicinal bonds has been examined for ethane, propane, and butane. The numerical results obtained within a crude first approximation to the matrix elements of the energy operator are highly encouraging.
Vibrational Energy Transfer in Shock-Heated N2–HI and N2–DI Mixtures
Authors: Breshears W. D. , Bird P. F.
Published: February 2004

The vibrational relaxation of N2–HI mixtures in the temperature range 1000–2700°K and of N2–DI mixtures in the range 1200–2000°K has been studied behind incident shock waves by time-resolved measurement of the postshock density gradient using a laser-beam deflection technique. In both systems the vibrational relaxation of N2 is dominated by vibration–vibration (V–V) energy transfer from the halide gas; contributions due to translation–vibration (T–V) and/or rotation–vibration (R–V) energy transfer are negligible. V–V energy transfer is more efficient in N2–HI than in N2–DI collisions, but the difference is much less than predicted by the SSH theory. Results for the effect of N2 on the relaxation of HI and DI support previous suggestions that R–V energy transfer is the dominant mechanism for vibrational relaxation of the hydrogen halides.
Electronic Spectra of Trapped Electrons in Organic Glasses at 4°K
Authors: Hase Hirotomo , Noda Masato , Higashimura Takenobu
Published: February 2004

The optical absorption spectra of trapped electrons were observed in γ-irradiated ethylene glycol–water, methanol, 10M NaOH, and MTHF at 4°K. The prominent infrared absorption bands were observed in ethylene glycol–water and ethanol glasses, while the bands in methanol, 10M NaOH, and MTHF glasses were similar in shape, slightly red shifted, to the bands for the radiolysis at 77°K. When the glasses were warmed to 77°K, the bands changed irreversibly into those for the radiolysis at 77°K, reducing the absorption intensity. The spectral changes at the intermediate temperatures between 4°K and 77°K were recorded for ethylene glycol–water and methanol cases. The results are interpreted by the molecular reorientation model proposed in the previous paper [T. Higashimura, M. Noda, T. Warashina, and H. Yoshida, J. Chem. Phys. 53, 1152 (1970)].
Kinetics of Diffusion-Controlled Reaction between Chemically Asymmetric Molecules. I. General Theory
Authors: S≅olc K. , Stockmayer W. H.
Published: February 2004

The treatment of diffusion-controlled bimolecular chemical reactions is extended to molecules with axially symmetrical distributions of reactivity on their spherical surfaces. Whereas an explicit solution exists for the time-dependent effective rate constant at small times, the physically more interesting solution at large times can be obtained only approximately (though to any required degree of accuracy) by solving sets of linear equations.
Theory on the Mechanical Properties of Dilute Polymer Solutions
Authors: Ogasa Tatsuo , Imai Satoshi
Published: February 2004

The concentration dependence of mechanical properties of polymer solutions may be attributed to the changes in relaxation spectra due to the hydrodynamic and thermodynamic interactions between molecules in solution. In this work, the changes in intramolecular modes of motion caused by intermolecular interactions are calculated on the random-flight model of polymer chains by using the perturbation method developed by Fixman and the representation of the reciprocal intersegmental distances devised by Imai. The Huggins' constant in the viscosity equation is shown to be a universal constant, 0.842, in theta solvents independent of molecular weight and to be a decreasing function of solvent power. Its behavior in the neighborhood of the theta state can be written as KH = 0.842 − 0.498(α2 − 1), where α is the expansion factor for the intrinsic viscosity. These results are compared with recent experiments. The concentration dependence of dynamic shear moduli is also calculated on the same model. The results can describe, at least qualitatively, the apparent transition of frequency dependence of dynamic shear moduli from Zimm type to Rouse type which occurs with the increase in concentration, observed by Ferry et al., Lamb et al., and others. This transition comes from the superposition of the intramolecular contribution (Zimm type) and the intermolecular contribution.
On the Existence of Minima and Maxima in the Composition Dependence of the Thermal Diffusion Factor and Thermal Conductivity
Authors: Biolsi Louis , Mason E. A.
Published: February 2004

The kinetic theory of nonspherical molecules is shown to be unable to account for sharp dips in the composition dependence of the thermal diffusion factor and thermal conductivity of He–H2 mixtures; at most only shallow minima can be accommodated. No maxima or minima in the thermal diffusion factor of Xe–CO2 can be accounted for. In view of these results and the recent careful measurements on He–H2 by Taylor and Weissman, it is concluded that the anomalies reported previously are probably spurious.
MO Calculations on Sign and Magnitude of the Metal Spin Density in Alkali Radical Ion Pairs
Authors: Canters Gee W. , Corvaja C. , de Boer E.
Published: February 2004

Formulas for the spin density at the metal nucleus in alkali radical ion pairs are derived by means of molecular orbital theory combined with first order perturbation theory. The formulas have been used for computer calculations of the metal spin density in the Na naphthalene (NaNl) ion pair. The results show that the zero- and first-order contributions to the metal spin density are of the same order of magnitude, but have different signs, and that the sign of the total spin density at the Na nucleus varies with the position of the Na ion in the ion pair. The experimentally observed dependence of the sign of the alkali coupling constant upon the atomic number of the metal is related to the difference in polarizing influence exerted by small and large ions on the π MO's of the aromatic ion. The temperature dependence of the metal coupling constant is explained by taking into account the change in the average position or the root-mean-square position of the alkali ion with a change in temperature.
Electric Dipole Moment of Diatomic Molecules by Configuration Interaction. II Fixed-Core Approximation
Authors: Green Sheldon
Published: February 2004

A configuration interaction function was calculated for the ground state of CS starting with the restricted Hartree–Fock function and including single and double excitations from the valence orbitals only. The dipole moment calculated from this function is compared to that from an open-core CI function, which includes single and double excitations from all the occupied Hartree–Fock orbitals, and to the experimental value; the fixed-core approximation is found to be unsatisfactory for calculating dipole moments. A perturbation theory approximation to the eigenvalue and eigenvector of the Hamiltonian matrix is developed for arbitrary order and is used to examine the way that single and double excitations couple to the Hartree–Fock function through second order in the perturbation series.
Molecular Orbital Calculation for Trigonally Distorted Octahedral Complexes
Authors: O'Reilly Thomas J. , Offenbacher Elmer L.
Published: February 2004

A perturbed ligand molecular orbital (PLMO) method is presented for the calculation of magnetic ion properties in diamagnetic cubic lattices at a site having trigonal (C3i) symmetry. Expressions for the anisotropic orbital reduction factors k‖ and k⊥ and spin–orbit coupling constants ζ‖ and ζ⊥ are derived in terms of the coefficients of the molecular orbital. Numerical calculations are reported for the trigonal field υ, cubic field splitting 10Dq, ζ's, and k's for the low-spin 4d5 Ru3+ ion in sixfold O2− coordination as found in the garnets YAlG, LuAlG, YGaG, LuAlG. The PLMO calculation can account for the sign of the trigonal field in the garnets and reasonable values for the effective charge η lead to good agreement with the experimental g values. Analysis of the hyperfine data gives values for the core polarization factor H for 4d electrons in the range of 2.4–2.8.
Correction to the Devonshire Theory of Accommodation Coefficients for Bound-State Transitions in Gas–Surface Interactions
Authors: Goodman Frank O. , Gillerlain Joseph D.
Published: February 2004

A calculation is presented of the bound-state correction to the quantum mechanical theory (that is, the Devonshire theory) of energy accommodation coefficients (a.c.); this correction takes account of transitions of gas atoms into bound states at the solid surface. Using certain simplifications which are easily interpreted physically, bound-state analogs of the Devonshire formula are presented. Although the treatment is one-dimensional throughout, the corrected theory is compared with experimental data on the a.c. of He–W as a function of temperature T. It is concluded that the bound-state correction improves considerably the agreement with experiment obtained by Roach and Harris using their modified Devonshire formula, although there is still some disagreement, at both high and low T. The theoretical a.c., even after correction, vanishes at T = 0, in disagreement with present experimental trends; a plea is made for further experiments to help resolve this point.
Dissociation by Electron Impact of Oxygen into Metastable Quintet and Long-Lived High-Rydberg Atoms
Authors: Freund Robert S.
Published: February 2004

Excitation of O2 by low energy electrons leads to its dissociation with the formation of metastable oxygen atoms. The metastable atoms which have been detected are in the 3s5S0 state at 9.14 eV and in long-lived high-Rydberg states. A molecular beam time-of-flight method is used to measure their translational energy. Electron impact excitation functions are given for the formation of metastable atoms. High-Rydberg atoms result from dissociation of initially formed high-Rydberg molecules. Because a high-Rydberg molecular orbital is nonbonding, dissociation is determined by states of the core O2+ ion. This mechanism is supported by general agreement between the observed kinetic energy distribution of high-Rydberg atoms and the kinetic energy distribution of O+ from dissociative ionization of O2. The fragment kinetic energy distributions are discussed in terms of known and predicted states of O2 and O2+.
Molecular Potential Functions Expressed in Cartesian Coordinates: Application to the Orbital Valency Force Field
Authors: Tyson John , Claassen Howard H. , Kim Hyunyong
Published: February 2004

Potential energy matrices are derived for molecules of the type XYn in terms of the Heath and Linnett orbital valency force field. Cartesian coordinates are used, and a simple calculation procedure is outlined that makes use of generally available computer subroutines for matrix diagonalization, etc. The method makes no use of symmetry coordinates, and is therefore particularly convenient for problems involving isotopic substitutions. Extension to larger molecules is suggested but not carried out in detail. The general method may be useful for other force field models, also.
Raman Spectrum and Polymorphism of Titanium Dioxide at High Pressures
Authors: Nicol Malcolm , Fong Mei Y.
Published: February 2004

Raman spectra of the rutile and high-pressure orthorhombic (TiO2 II) phases of titanium dioxide have been studied at pressures as high as 40 kbar. The frequency of the B1g mode of rutile has an unusual negative pressure dependence, dυ / dp = − 0.3 ± 0.1 cm−1·kbar−1. Onset of the rutile:TiO2 II transition is observed at pressures above 26 kbar at room temperature, although the apparent transition pressure and extent of transformation depend upon shear stresses applied to the sample. Shears applied normal to the optic (tetragonal) axis of rutile are most effective for inducing the transition.
Localized Bonds in SCF Wavefunctions for Polyatomic Molecules. IV. Ethylene, Butadiene, and Benzene
Authors: Newton Marshall D. , Switkes Eugene
Published: February 2004

Ab initio molecular-orbital wavefunctions for ethylene, butadiene, and benzene have been analyzed in terms of the localized orbitals (LMO's) defined by minimizing molecular exchange energy. The effect of conjugation on the LMO's is studied in terms of the delocalization of LMO's and the curvature of the energy surface which determines the LMO's. The degree of preference for bent double-bond LMO's over σ–π double-bond LMO's is also examined. In all cases, the former LMO's represent the correct solutions, while the latter LMO's, obtained by imposing the constraint of σ–π separation, correspond to saddle-point solutions. The double-bond LMO's for ethylene and butadiene are quite similar, whereas in the case of benzene, appreciably greater delocalization is found, and the preference for bent bonds over σ–π bonds is greatly reduced.
Ferroelectric Ferroelastic Paramagnetic Beta-Gd2(MoO4)3 Crystal Structure of the Transition-Metal Molybdates and Tungstates. VI
Authors: Keve E. T. , Abrahams S. C. , Bernstein J. L.
Published: February 2004

Beta-gadolinium molybdate, β-Gd2(MoO4)3, is ferroelectric and ferroelastic with a Curie temperature of about 160°C and is paramagnetic with a moment of 7.98 μB. β-Gd2(MoO4)3 crystallizes in the orthorhombic system with space group Pba2 and four formulas in the unit cell. The lattice constants at 298°K are a = 10.38582 ± 0.00014, b = 10.41861 ± 0.00010, and c = 10.70039 ± 0.00004 Å. The integrated intensities of 14 490 reflections were measured with PEXRAD, within a hemisphere of reciprocal space of radius (sinθ) / λ = 1.02 Å−1. The crystal structure was solved by interpretation of Patterson and Fourier series and refined by the method of least squares, using a total of 2545 symmetry independent Fmeas. The final agreement factor R is 0.089, based on isotropic thermal vibrations for all atoms. X-radiation exposure introduces appreciable nonrandom error in the Fmeas. The structure consists of three crystallographically independent discrete sets of (MoO4)2− tetrahedra; one set is oriented with apex oxygen atoms pointing along + c, a second has apex oxygens pointing along − c, and a third has a pseudo-4̄ axis parallel to c. The Gd ions occupy GdO7 polyhedra. The average Mo–O distance is 1.753 Å, the average Gd–O distance is 2.332 Å. The spontaneous polarization Ps is antiparallel to the sense of the polar crystallographic c axis: The calculated value, assuming point charges of Gd3+ and (MoO4)2−, is − 0.26 × 10−2 Cm−2. The experimental value is about 0.2 × 10−2 cm−2. The interchange of axes in ferroelastic switching and the polarity reversal is due to a single process involving small displacements of all atoms. The crystal belongs to the three-dimensional class of ferroelectrics. The phase transition is represented by: ΠPP(4̄2m)FcFcP(mm2).
Overhauser Studies in Two-Spin Systems
Authors: Kumar Anil , Gordon Sidney L.
Published: February 2004

Expressions have been derived for fractional changes in intensity of double resonance transitions for weak irradiation of two spin systems for random field and dipole–dipole interactions. The relative fractional changes are shown to be independent of the strength and small offsets of the irradiation and the strength of the observing field. The fractional changes are found to be quite sensitive to the relaxation mechanisms, thereby allowing a simple interpretation of the observed fractional changes in terms of the relaxation mechanism operative in the spin system. Overhauser experiments have been performed on the AX spin system of 2,2-dichloroacetaldehyde, studied in different sample conditions and the AB spin system of 1-bromo-1-chloroethylene. All the degassed samples have been shown to have contributions from both random field and dipole–dipole interactions, the magnitudes of which have been obtained in each case. An analysis of sources of errors in these experiments indicates that even for strengths of irradiation much smaller than the observed linewidths in the spectra, splittings of the connected transitions are important for quantitative estimates of the intensities. The diagonal elements of η, the change in density matrix due to the observing field, are shown to be negligible in the present experiments.
Electrochemical Potential as the Sum of Chemical and Electrical Potentials with a Generalization to a Wider Class of Perturbations
Authors: Brews J. R. , Hwang C. J.
Published: February 2004

It is shown that the local relation EF = μ(n, T) + eΦ(x) relating the Fermi level EF, the chemical potential μ, and an electrostatic potential Φ(x), does not predict the correct dependence of the electron density, n, upon position, x, for every choice of Φ(x). As a consequence, the electrochemical potential, μ̄, in the form μ̄ = μ + eΦ(x) cannot be used in formulating the equilibrium conditions of the system for every choice of Φ(x). The restrictions upon Φ(x) are found to be identical with those of the “band-bending” approximation of semiconductor physics. The simplicity of the above form of μ̄ can be extended to more general potentials Φ(x) by using instead the form μ̄ = μ + ΔE(x), where ΔE(x) is that shift in energy of the unperturbed density of states which would give rise to the electron density actually produced in the presence of Φ(x).
Energetics of HeH+ Formed in H2+–He Collisions
Authors: Leventhal J. J.
Published: February 2004

Kinetic-energy distributions of forward-scattered HeH+ ions resulting from H2+–He collisions have been experimentally determined for H2+ laboratory kinetic energies in the range 1.7–12.5 eV. These distributions have two main peaks over most of this primary ion energy range. The lower-energy peak which appears to correspond to completely inelastic collisions is believed to result from enhanced collection efficiency, a conclusion which is supported by energetic considerations. The behavior of the higher-energy peak, which corresponds to ions formed in the forward direction (center of mass), is consistent with theoretical calculations for the HeH+ species.
Correlation Effect in the Rotation Barrier of Ethane
Authors: Levy B. , Moireau M. C.
Published: February 2004

An ab initio calculation of the barrier to internal rotation in ethane using a minimum basis of Slater-type atomic orbitals is reported. Electron correlation is partly taken into account by a second-order perturbation method. It decreases the barrier by 0.13 kcal/mol with respect to the SCF value of Pitzer or 0.17 kcal/mol with respect to another set of bond orbitals. These small lowerings are discussed in terms of localized orbitals.
Dielectric Relaxation of Dihalobenzenes. III. Pure Liquids
Authors: Mansingh Abhai , McLay David B.
Published: February 2004

The real and imaginary components of the complex relative dielectric permittivity have been measured at 100 kHz and at several microwave frequencies for pure liquid ortho- and meta-dihalobenzenes at several temperatures in the range 0–80°C. The data for the difluorobenzenes, for the dichlorobenzenes and for the dibromobenzenes essentially obey the simple Debye theory while the data for the diiodobenzenes lead to the Cole–Cole arc plots. The derived values of the macroscopic relaxation times decrease as the temperature increases in all cases and the value for the ortho isomer is always greater than that for the meta isomer at the same temperature except for diiodobenzene. In addition, the relaxation times increase as the mass of the halogen substituent increases. However, the microscopic relaxation times calculated from the dielectric data are not consistent with the corresponding values calculated from the molecular volumes, temperatures, and viscosities. In all cases, the extrapolated value ε∞ is significantly greater than the square of the index of refraction and the difference is approximately proportional to the square of the electric dipole moment. Use of the Onsager relation allows the calculation of the dipole moment from either ε∞ or nD2. The calculated values increase as the temperature increases but the ratio of the value calculated from nD2 to that calculated from ε∞ varies inappreciably with temperature. Also the ratio of the dipole moment for the meta isomer to that for the corresponding ortho isomer is almost independent of temperature.
Mixtures of Hard Spheres with Nonadditive Diameters: Some Exact Results and Solution of PY Equation
Authors: Lebowitz J. L. , Zomick David
Published: February 2004

We investigate the properties of binary mixtures of hard-sphere fluids with nonadditive diameters: calling Rij the distance of closest approach between particles of species i and j we assume R12 = 12(R11 + R22) + α with α ≠ 0. We find the exact correlation functions as well as the solution of the Percus–Yevick integral equation for this system with 0 ≤ α ≤ 12(R22 − R11), in one dimension. For the three-dimensional case the Percus–Yevick equation is solved partially.
Fourier Transform Study of NMR Spin–Lattice Relaxation by “Progressive Saturation”
Authors: Freeman Ray , Hill H. D. W.
Published: February 2004

When a nuclear spin system is subjected to a repetitive sequence of strong radiofrequency pulses, a steady state is established where there is a dynamic balance between the effect of the pulses and spin relaxation. Under certain readily satisfied pulse conditions, the deviation of the intensity of the free induction signal from its thermal equilibrium value is an exponential function of the pulse interval with time constant equal to the spin–lattice relaxation time. The determination is unaffected by spin–spin relaxation provided that the interval between pulses is long enough to permit all transverse components of magnetization to be eliminated, and provided precautions are taken to inhibit spin-echo formation. Through Fourier transformation of the transient response, high resolution spectra with many component resonances may be studied, and the spin–lattice relaxation times of the individual lines determined. The technique lends itself particularly well to repeated accumulation of the transient signal for the purpose of improving sensitivity. It has been applied to the problem of determining the spin–lattice relaxation rates of the eight different carbon-13 resonances in 3,5-dimethylcyclohex-2-ene-1-one. The results span a range from 2.6 to 39 sec, and are in good agreement with those obtained by applying 180°–t–90° sequences to the same sample.
Mass Spectrometric Determination of the Heats of Atomization of NdO2, NdBO, and NdBO2 and Upper Values for the Dissociation Energies of NdAg and Nd2
Authors: Pupp C. , Gingerich K. A.
Published: February 2004

During evaporation of Nd and Ag from a boron nitride Knudsen cell the new molecules NdO2(g), NdBO(g), and NdBO2(g) were detected by mass spectrometric analysis. The enthalpies of the following reactions were determined by a third-law method: NdO2(g)+Nd(g)→2NdO(g), ΔH0° = − 10.5 ± 1.2 kcal mol−1, NdBO(g)→Nd(g)+BO(g), ΔH0° = 77.4 ± 1.9 kcal mol−1, Nd(g)+NdBO2(g)→NdBO(g)+NdO(g), ΔH0° = 10.5 ± 4. kcal mol−1. From these reaction enthalpies the heats of atomization of NdO2, NdBO, and NdBO2 were calculated: NdO2(g): ΔH0°atom = 323.5 ± 12.5 kcal mol−1; NdBO(g): ΔH0°atom = 268.7 ± 10 kcal mol−1; NdBO2(g): ΔH0°atom = 446.2 ± 13 kcal mol−1. A discussion of the possible geometric arrangement of these molecules on the basis of thermochemical data is given. Upper limits for the bond energies of Nd2(g) and NdAg(g) are given as 39 and 50 kcal mol−1, respectively.
Free Energy Bounds and the Stability of Mixtures
Authors: Rudd W. G. , Frisch H. L.
Published: February 2004

A simple derivation of the so-called Gibbs bound on the Helmholtz free energy is given. Formal lower bounds, analogous to the bounds previously derived by Mansoori et al., allow qualitative comments regarding variational calculations of the equation of state. The theory is applied to binary mixtures, with sufficient conditions for stability of the random mixture relative to that of either of the pure components or to the two-phase mixture of the same composition as the end result. The conditions are used to determine the stabilities of mixtures of hard spheres and hard-core molecules with additional square wells and steps.
Molecular Orbital Study of NH2, NO2, and NF2
Authors: DelBene Janet E.
Published: February 2004

The orthogonality constrained basis set expansion method has been used to determine SCF wavefunctions for ground and lower excited doublet states of NH2, NO2, and NF2. The calculations on NO2 and NF2 were performed using a minimal basis set, while both minimal and extended bases were used in the study of NH2. Geometries and dipole moments of the various states were obtained and found to be in good agreement with available experimental data. Calculated vertical and 0–0 transition energies in these systems were also found to approximate the experimentally determined excitation energies.
Mid- and Far-Infrared Spectra of HF and DF in Rare-Gas Matrices
Authors: Mason M. G. , Von Holle W. G. , Robinson D. W.
Published: February 2004

The “vibration–rotation” and “pure rotation” spectra of HF and DF in rare-gas matrices near 4°K have been studied, and assignments of the features due to the monomeric molecules have been made. The perturbations of the purely vibrational levels have been used to compute Lennard-Jones parameters for the interaction between the polar molecule and its neighboring atoms. The center of action of the dispersion forces has been calculated for HF, and the rotational perturbations have been evaluated. The spectral absorption frequencies are rather well reproduced. It has been found that the experimental frequency shifts are not consistent with a theory of rotational–translational coupling but that they, and other “anomalous” spectral features, are predicted by considerations of the anisotropies in the rotational potential function.
Magnetic Structure of α-Tb2C3
Authors: Atoji Masao
Published: February 2004

Neutron powder diffraction measurements have shown that, in the body-centered cubic α-Tb2C3 below 33 ± 4°K, two out of four body-diagonally linked Tb arrays become antiferromagnetic linear chains but the two remaining Tb arrays exhibit no ordered moment. The nearest Tb atoms between the different ordered spin arrays are related ferromagnetically. Six alternative ways of choosing two body-diagonal antiferromagnetic arrays are mutually equivalent due to the crystal symmetry but not to the multiplet degeneracy in powder diffractometry. The moments are most likely directed along the face diagonal which lies in the plane formed by two body diagonals parallel to the ordered spin arrays. The next probable moment direction lies longitudinally along any one of the two ordered arrays. The saturation moment per magnetically ordered Tb in these collinear spin structures is very insensitive to the selection of the moment direction and approximates closely the free Tb3+ value of 9 μB. An equivalent multiaxial antiferrostructure is obtained by combining two collinear magnetic structures with the mutually orthogonal face-diagonal moments. In this alternative biaxial structure, all Tb atoms possess the same saturation ordered moment of 9 / 2 μB. A sizeable magnetic diffuse scattering having the modulation of an apparently ferromagnetic short-range order was observed in the magnetically long-range ordered region.
Magnetic Structure of α-Ho2C3
Authors: Atoji Masao , Tsunoda Y.
Published: February 2004

The antiferromagnetic structure of α-Ho2C3 as revealed by neutron powder diffraction is stabilized below 19 ± 1°K and is markedly different from the ordered spin structure of the isostructural α-Tb2C3 (the cubic body-centered Pu2C3 type). Two out of four body diagonally linked arrays of Ho atoms become the ferromagnetically ordered chains and the remaining two arrays show one-dimensional antiferromagnetic alignment. Among three nearest Ho–Ho neighbors bridging between the different body-diagonal arrays are two antiferromagnetic pairs and one ferromagnetic pair. The moment direction is most likely parallel to one of the ferromagnetic linear arrays. The maximum spontaneous moment is 7.3 ± 0.2 μB which is considerably smaller than the free He3+ value of 10 μB. The temperature dependency of the spontaneous magnetization is approximated by the Brillouin function with S = 1 ± 12 but departs significantly from the free ion function with J(g − 1) = 2. The magnetically ordered phase exhibits a sizeable magnetic diffuse scattering having the characteristics of a ferromagnetic short-range order and this persists down to near 0°K.
Particle Method for the Numerical Solution of the Time-Dependent Schrödinger Equation
Authors: Weiner J. H. , Askar A.
Published: February 2004

A method for the solution of the time-dependent Schrödinger equation in two dimensions is presented which is based on the hydrodynamic analogy to quantum mechanics. The continuum introduced in that analogy is approximated by a finite number of particles, whose trajectories are computed. The procedure is applied here to the dynamics of a Gaussian wave packet on a two-dimensional quadratic potential surface containing a saddle point. Comparison with the known analytical solution indicates that the method is capable of accurate results with substantially less computer time required than in methods previously employed. This particular check problem was chosen because of its close relationship to the wave-packet dynamics of chemical reaction rates.
Monte Carlo Calculations on Polypeptide Chains. II. A Four-State Hard-Sphere Model for Randomly Coiling Polyglycine
Authors: Knaell Kenneth K. , Scott Roy A.
Published: February 2004

A Monte Carlo study of randomly coiling polyglycine was carried out using the same hard-sphere model applied previously to poly-l-alanine in which the bond lengths and bond angles are held fixed, the peptide bond is fixed in the planar trans configuration, free rotation is assumed about the backbone N–Cα and Cα–C′ single bonds, and the individual atoms or groups of atoms interact pairwise by hard-sphere potential functions. For polyglycine each peptide unit in the chain is restricted to four sterically allowed conformational states, the right- and left-handed α-helical states and the right- and left-handed ribbon structure states. Non-self-intersecting chains of various chain lengths up to 150 amino acid residues were generated by the sample enrichment technique of Wall and Erpenbeck and used to calculate the average chain dimensions. Chains were also generated in which the hard-sphere potentials were neglected and from which the unperturbed average dimensions were calculated. As found previously for poly-l-alanine chains, the point-by-point attrition parameter λ, defined as N−1ln(W0 / WN), was found to be an increasing function of chain length over the entire range included in the calculations, and the data could be fit by an empirical equation of the form λ = λ∞[(N − c) / (N + d)]e, where λ∞ = 0.111070 ± 0.000005 is the best estimate of the traditional attrition constant for the model. The mean-square end-to-end distance and mean-square radius of gyration for both non-self-intersecting and unperturbed chains were found to obey the laws 〈r2〉 = aNb and 〈s2〉 = a′Nb′ for large N with b = 1.201 ± 0.008 and b′ = 1.236 ± 0.041 for non-self-intersecting chains and b = 1.054 ± 0.080 and b′ = 1.047 ± 0.051 for unperturbed chains. A reanalysis of the data for poly-l-alanine chains yielded similar results except that b′ for the non-self-intersecting chains was found to be 1.31–1.33 rather than 1.21–1.23. It was also found for polyglycine as for poly-l-alanine that the ratio 〈r2〉 / 〈s2〉 for both non-self-intersecting and unperturbed chains when plotted vs N passes through a maximum at N ≈ 10 and then, within the statistical reliability of the data, decreases to a value of 6 for the longest generated unperturbed chains and to 6.4–6.6 for the longest generated non-self-intersecting chains.
Evidence of Sixfold Coordination of Nd3+ in Barium Rubidium Silicate Glass
Authors: Robinson Charles C.
Published: February 2004

Recent low-temperature spectroscopy and spectral analysis by Robinson and Fournier have shown that Yb3+ is sixfold coordinated in silicate glass at a site of near octahedral symmetry. A similar analysis is reported for Nd3+-doped barium rubidium silicate glass. The absorption and emission spectra associated with the J multiplets of the I2 term have been examined for the most part at low temperatures. The energies of the five Kramers doublets in the I9/24 multiplet have been fitted to the octahedral crystal field calculations of Lea, Leask, and Wolf, and parameters A4〈r4〉 = 337 and A6〈r6〉 = 25 cm−1 were obtained. These parameters predict the energy separations of the two bands in the I11/24, 4I13/2, andI15/24 multiplets and the energies of the lower Kramers doublets in the I15/24 multiplet thus indicating that the Nd3+ is also in a site whose symmetry approached octahedral.
Lattice Dynamics of Methanol: Hydrogen Bonding and Infrared Absorption
Authors: Dempster Andrew B. , Zerbi Giuseppe
Published: February 2004

Mathematical methods of treating lattice dynamics of solids have been applied to interpret the infrared spectrum of crystalline CH3OH and CH3OD. New spectra were recorded in the near-infrared region for crystalline CH3OH, CH3OD, and of mixed crystals at various concentrations. The far-infrared spectrum is also reported. Attempts were made to find spectral evidence of the two crystalline modifications of CH3OH. A valence force field has been derived by a least squares fitting on the k = 0 modes of both molecules; the assignments of fundamental frequencies are discussed. Based on this derived force field, phonon dispersion curves and one-phonon and two-phonon densities of states have been calculated in the single-chain approximation. These are used in the interpretation of the infrared spectrum. The vibrational spectra of mixed crystals of CH3OH and CH3OD reveal unusual features which suggest that the breadth of absorption bands due to the hydrogen-bonded atoms is not a property of a single hydrogen bond but arises from cooperative effects with similar neighbors in the chain. The broadness seems to be a function of the chain length.
Polarizabilities and Hyperpolarizabilities of Small Polyatomic Molecules in the Uncoupled Hartree–Fock Approximation
Authors: Liebmann S. Peter , Moskowitz Jules W.
Published: February 2004

Near Hartree–Fock LCAO–MO–SCF contracted Gaussian wavefunctions are used to calculate the polarizabilities and hyperpolarizabilities of water, methane, carbon monoxide, and formaldehyde. The polarizabilities are shown to be in good agreement with the experimental data. In the case of water, an attempt was made to use the calculated hyperpolarizabilities to predict the line intensities and the depolarization ratio of a double quantum scattering experiment. Unfortunately, direct comparison with the actual experiment is premature at this time due to ambiguities in the interpretation of the experimental results.
Comparison between Quantum Mechanical and Classical Treatment of a Hard-Sphere Model for Colinear Three-Body Rearrangement Collisions
Authors: Baer Michael
Published: February 2004

The three-dimensional model for exchange reactions previously presented by Baer and Amiel is now treated quantum mechanically in order to study quantum effects. To do this the three interacting particles are restricted to movement along a straight line. It was found that the assumed potential energy surface, in certain cases, yields a potential barrier when the computations are performed quantum mechanically. The characteristics of a potential barrier disappear when the problem is treated classically.
Mössbauer Spectroscopy of Organometallics: Lattice Dynamics and Structure of Butyltin Compounds
Authors: Herber Rolfe H.
Published: February 2004

The Mössbauer parameters of a number of butyltin compounds have been determined in order to elucidate the relationship between molecular structure and spectroscopic properties of such species. The temperature dependence of the resonance effect magnitude (Debye–Waller factor) has been determined in the range 85 < ∼ T < 160°K for (Bu3Sn)2SO4, Bu3SnOAc, Bu3SnF, and Bu2SnF2, and the isomer shifts and quadrupole splittings at 85°K for these compounds, as well as for Bu2Sn(OAc)2, are reported. From these data, as well as from the temperature dependent intensity asymmetry (Gol'danskii–Karyagin effect) which is observed in these compounds, a monomeric, binuclear structure is inferred for (Bu3Sn)2SO4, in consonance with infrared, mass spectrometric, molecular weight, and solubility data. The Debye–Waller factor for the 119Sn resonance in Bu3SnOAc which has been recrystallized from CCl4 is interpreted in terms of a low molecular weight polymeric form for this compound similar to that which has been reported for the “soluble” form of trimethyltin acetate.