bluuebunny/crossref_metadata_2025 huggingface dataset:
Infrared Spectrum of Cyanogen-15N2 and Intermolecular Coupling in the Crystal
Authors: Nixon Eugene R. , Verderame Frank D.
Published: January 2005

The infrared spectrum of cyanogen-15N2 is reported for the gas at room temperature and for the polycrystalline film at 80°K over the range 500–4000 cm—1. Davydov splittings in the ν3 fundamental are discussed in terms of 6–12 intermolecular potentials and also in terms of the intermolecular coupling of mutually polarizable dipoles. Calculated splittings and intensities are given for various assumed crystallite sizes and shapes.
Lifetime Measurements of Some Excited States of Nitrogen, Nitric Oxide, and Formaldehyde
Authors: Jeunehomme Michel , Duncan A. B. F.
Published: January 2005

An experimental method for measurement of short decay times of fluorescence (10—8—10—5 sec) from excited states of molecules is described. The method is applied to the transitions C3IIu—B3IIg (second positive) and B3IIg—A3Σu+ (first positive) of nitrogen and to the transitions A2Σ+—X2II (γ system) and B2II—X2II (β system) of NO. Direct measurement of the lifetime of the lowest singlet excited state of formaldehyde is reported. In some of the transitions, the dependence of lifetime on vibrational quantum number in the initial upper state were studied. The pressure dependence of the lifetimes was also investigated.
Infrared Spectrum of Methylsilyl-d3-Acetylene
Authors: Reeves R. Bruce , Robinson Dean W.
Published: January 2005

The near- and far-infrared spectra are reported for the molecule D3SiC≡CCH3 and the far-infrared spectrum for H3SiC≡CCH3, supplementing earlier work. All of the infrared-active vibrations have been found and assigned to normal modes. The Q branches of most of the perpendicular bands have been resolved and rotationally assigned. Coriolis coupling constants have been calculated.
Electrically Induced Perturbations of Halogen Nuclear Quadrupole Interactions in Polycrystalline Compounds. I. Phenomenological Theory and Experimental Results
Authors: Dixon R. W. , Bloembergen N.
Published: January 2005

When a nucleus in a dielectric solid occupies a lattice site which lacks inversion symmetry, the application of an external electric field causes a change in the electric field gradient at this nucleus. The magnitude of the change is proportional to the applied field. When the nucleus has spin greater than one-half and possesses a nonzero quadrupole moment, the quadrupole interaction energy is, therefore, a linear function of the applied field. This field gradient perturbation is discussed phenomenologically through the use of a third rank tensor R which relates the electric field and the electric field gradient via the equation eΔq=R·E. Changes in the quadrupole interaction energy, observed as broadenings of nuclear quadrupole resonance lines in zero magnetic field, have been obtained for 35Cl, 81Br, and 127I nuclei in halogenated polycrystalline compounds including several halogenated methanes and benzenes, the solid halogens, and iodic acid. Broadened line shapes, local electric field corrections, and restrictions imposed by nuclear site symmetries are discussed. All observations are consistent with the phenomenological theory.
Nuclear Magnetic Resonance and Optical Spectroscopy of [Co(MeOH)5Cl]+ in Methanol and the Kinetics of Methanol Exchange of the Solvation Shell
Authors: Luz Z.
Published: January 2005

A study of the complex formation of Co+ + ions with Cl— ions in methanol at temperatures between —60° and —80°C is reported. The tools used are nuclear magnetic resonance and optical spectroscopy. It is shown that at these low temperatures the dominant cobalt—chlorine complex is an octahedral monochloro complex, [Co(MeOH)5Cl]+. The NMR spectra give the following values for the hyperfine interaction constants between methanol protons and Co+ +: 0.49, 0.33, and 2.4 Mc/sec for, respectively, the methyl protons of methanol cis to the chlorine, the methyl protons of methanol trans to the chlorine, and the hydroxyl proton in methanol cis to the chlorine. At temperatures above —75°C exchange of methanol between the coordination sphere and the bulk solvent contributes to the width of the NMR peaks. The results suggest that the dominant exchange process follows an SN1 mechanism, involving the dissociation of a cis methanol molecule in the complex as the rate-determining step. The rate constant of this process is found to be 510 sec—1 at —63°C, and the activation energy 14.5 kcal/mole.

Optical absorption spectra of the monochloro complex in the visible range are reported. The spectrum of this complex is similar to that of [Co(MeOH)6]+ +, but the maximum absorption is slightly shifted to longer wavelength (from 507 to 527 mμ at —80°C), and the extinction coefficient is 2.7 times that of [Co(MeOH)6]+ +.
Optical Emission from Argon Excited by Alpha Particles: Quenching Studies
Authors: Strickler T. D. , Arakawa E. T.
Published: January 2005

Optical emission from argon gas excited with alpha particles has been studied to determine if electronic states of long lifetimes are excited by swiftly moving charged particles as has been observed in studies of ionization. The spectrum from argon showed a continuum which could be separated into three distinct bands with maxima at 1300, 1800, and 2000 Å. The light intensity of the 2200-Å band was readily quenched with the addition of about 2% of CH4, CO2, O2, and Kr. The 1800-Å band was quenched more slowly than the 2200-Å band by the impurity gases. The results support the notion that alpha-particle excitation of argon at high pressures leaves the argon in long-lived states of about 11.5 or 14.5 eV. The observed continua appear to arise mainly from Franck—Condon transitions between two excited states and the ground repulsive state of the argon dimer which forms as a consequence of the long lifetimes of the excited atoms.
Intramolecular Isotope Effects in the HD—Rare Gas Ion—Molecule Reactions
Authors: Klein Fritz S. , Friedman Lewis
Published: January 2005

The ion—molecule reactions of HD+—He, HD+—Ne, Ar+–HD, and Kr+–HD have been studied and the intramolecular isotope effects determined over a range of kinetic energies of the reactant ion. The intramolecular isotope effects were found to vary with ion kinetic energy, indicating energy transfer to internal degrees of freedom in the reaction products. Three types of isotope effects are proposed to account for experimental data. An atom or ion transfer mechanism which gives rise to a higher probability of formation of XH+ over XD+ is the dominant factor at high ion kinetic energies. At low energies the unimolecular decomposition of a triatomic intermediate is assumed to form preferentially XD+. For the HD+—He and HD+—Ne reactions evidence is obtained indicating dissociation of the ionic product with an associated isotope effect favoring the XH+.
Observation of Rotational De-Excitation of D2 Using Crossed Molecular Beams
Authors: Blythe Anthony R. , Grosser Arthur E. , Bernstein Richard B.
Published: January 2005

The collision-induced transition j=2→0 in ortho-D2 has been observed using a direct kinematic technique. A velocity-selected atomic beam of K was crossed with a cooled, modulated beam of o-D2 molecules. Velocity analysis of the K beam scattered through known center-of-mass angles (near 110°) gave direct evidence of recoil arising from inelastic collisions in which the rotational de-excitation j=2→0 had occurred.
Electron Paramagnetic Resonance of Some Sulfur and Selenium Compounds
Authors: Windle J. J. , Wiersema A. K. , Tappel A. L.
Published: January 2005

A number of organic compounds containing sulfur or selenium are known to be useful as antioxidants or radio-protective agents because of their reactivity with free radicals. We have studied the electron paramagnetic resonance (EPR) of some aliphatic and aromatic sulfide and disulfide compounds and their selenium analogs uv-irradiated at λ=2537 Å in order to characterize and compare the free radicals produced. The irradiation and the EPR measurements were carried out at liquid nitrogen temperature. The EPR spectra obtained for these compounds fall into four categories characteristic of the four types of radical species found—alkyl radicals, benzyl-type radicals, sulfur radicals, and selenium radicals. The selenium radical, which has not been previously observed, exhibits an asymmetric spectrum having an axially symmetric g factor, with g⊥=2.08 and g∥=2.12.
Dielectric Properties of a Binary Mixture of Polar Liquids Having a Critical Solution Temperature
Authors: Quinn R. G. , Smyth C. P.
Published: January 2005

The dielectric dispersion of a mixture of nitromethane and n-heptanol which has an upper critical solution temperature has been measured over a range of 40° to the temperature of phase separation, and a frequency range from 0.5 Mc/sec to 23.8 kMc/sec. The frequency dependence of the complex dielectric constant can be adequately characterized by the superposition of two single relaxation times which may be associated with the two components. The temperature dependence of these two relaxation times has been investigated. The dependence is in general affected by the type of components present, their respective concentrations, and the temperature. It has also been found that the dielectric dispersion process is affected at temperatures as much as 3 deg above the critical solution temperature. On the basis of the data, a number of conjectures concerning the character of the relaxation process of other types of solutions have been made.
Anisotropic Rotational Diffusion and Electron Spin Resonance Linewidths
Authors: Freed Jack H.
Published: January 2005

The recent general theory of ESR linewidths for dilute solutions of free radicals developed by Freed and Fraenkel is extended to cover the possibility that the rotational motions of the free radicals are anisotropic. The analysis is greatly simplified by expressing the solution of the rotational-diffusion equation as an expansion in Wigner rotation matrices. Only the spectral-density functions in the linewidth expressions given by Freed and Fraenkel are changed by the inclusion of anisotropic rotational diffusion. These spectral-density functions are found to depend upon five different relaxation times which are expressible in terms of the three principal values of the diffusion tensor ${ \germ{ R \germ} $}. It is shown how an analysis of the ESR linewidth effects, which vary from one hyperfine component to another, may be used in conjunction with calculations of the anisotropic electron—nuclear dipolar interactions to estimate the principal values of ${ \germ{ R \germ} $}. The experimental linewidth study on the para-dinitrobenzene anion radical is reanalyzed, and it is shown that an anisotropic rotational-diffusion mechanism cannot by itself explain the anomalous absence of any significant quadratic linewidth dependence on the total Z component of spin of the ring protons. While an order of magnitude estimate of ${ \germ{ R \germ} $} was made, further information permitting a quantitative understanding of the anomalous result (presumably due to fluctuations in isotropic hyperfine interactions) would be necessary to obtain a meaningful estimate of the principal values of ${ \germ{ R \germ} $} for this radical. The physical significance of ${ \germ{ R \germ} $} in the approximation of a Brownian particle as well as in terms of intermolecular potentials is discussed.
NMR Spectra of ClF3 and ClF: Gaseous Spectra and Gas-to-Liquid Shifts
Authors: Alexakos Louis G. , Cornwell C. D.
Published: January 2005

Gas-phase 19F NMR spectra at 56.4 Mc/sec are presented for ClF3 over a range of partial pressures (300–1300 mm) extending to sufficiently low values that the shielding and spin—spin coupling constants found can be regarded as true molecular quantities. These are, for the AB2-type spectrum, (σA−σB)/(1−σB)=125.88×10−6,  |J|=441±8 cps.Small systematic relaxation effects in the multiplet splittings were identified and eliminated by graphical procedures.

NMR data are also given for ClF3 as a liquid and as a solute in CCl4 and CCl3F. While these spectra are similar enough to that of the gas to indicate that the T structure persists in all these phases, there are clear trends in σB and J for the sequence: gas, liquid solutions, pure liquid. These trends may result from the existence in the condensed phases of local structure similar to that found in the crystal.

Other chemical shifts (σ—σr) / (1—σr) measured for gases at low densities relative to SiF4(g) at 27°C are, in parts per million: ClF, 273.73; BF3, —36.11; CF4, —104.19; CCl3F, —167.60; ClF3(A), —187.32; ClF3(B), —313.24; ClO2F(?), —499.87; all with an experimental uncertainty of about ±0.10.
Denominator Correction to the Van Vleck Transformation: Internal Rotation Problem
Authors: Stelman David
Published: January 2005

A method is given for obtaining the exact denominator correction to the Van Vleck transformation whether or not the zero-order energy is known in closed form. The denominator correction can be expressed in terms of a commutator involving the perturbation and the zero-order Hamiltonian. The denominator correction is given for a general case, and the correct denominator correction is given for the separation of internal and over-all rotation. The effect of the denominator correction on the structure of acetaldehyde and its implications with regard to asymmetric methyl groups is discussed.
Isotropic Proton Resonance Shifts of Some Bis-(triarylphosphine) Complexes of Cobalt(II) and Nickel(II) Dihalides
Authors: La Mar Gerd N. , Horrocks William DeW. , Allen Leland C.
Published: January 2005

Isotropic proton resonance shifts have been observed for some bis-(triarylphosphine) complexes of cobalt(II) and nickel(II) dihalides. The equations for the pseudocontact shifts were extended to include these complexes which possess g tensors with C2v symmetry. The isotropic shifts for the nickel complexes are interpreted as arising solely from a contact interaction with unpaired spin in the π orbital of the ligand. Based on the postulate that unpaired spin will distribute itself in the same way in a given ligand whether attached to cobalt or nickel, the shifts for the cobalt complexes are separated into contact and pseudocontact contributions. The relative magnitudes of the pseudocontact shifts correspond well with the expected relative strength of the C2v distortion of the tetrahedral ligand field of the cobalt complexes. The evaluation of the proportionality constant, QCH3, between the unpaired spin density and the hyperfine interaction constant for the methyl-substituted complexes demonstrates the consistency of the interpretation of the shifts. The difference in the unpaired spin densities on the cobalt and nickel complexes is explained by slightly greater interelectronic respulsion in the t orbitals of the nickel complexes.
Infrared Spectra of Ammonium Carbamate and Deuteroammonium Carbamate
Authors: Frasco David L.
Published: January 2005

Infrared spectra of thin solid films formed by the condensation of gaseous mixtures of NH3 or ND3 and CO2 at low temperatures were obtained in the region from 4000 to 400 cm—1 at —25°, —78°, and —190°C. Two types of spectra were obtained, depending upon the temperature of formation of the solid. Type I, formed at —78°C, was assumed to be a supercooled glassy solid, but the possibility of a molecular complex exists and is discussed briefly. Type II solid spectra were satisfactorily interpreted on the basis of ammonium and carbamate ions being present in the crystal. Vibrational assignments are made for the carbamate ion assuming over-all symmetry of Cs for the ion. The heavy atom skeletal vibrations of the carbamate ion are discussed in terms of a plane symmetric XY3 model distorted to C2v symmetry. Approximate force constants are calculated for the two ends of the ion assuming the NH2 group behaves as a triatomic molecule and the NCO2 skeleton vibrates as a ZXY2 molecule with C2v symmetry. To aid in the assignments of the carbamate ion the Teller—Redlich product ratios are calculated. A complete vibrational assignment for the ammonium ion is not attempted, but the position and number of bands associated with this species indicate the possibility of several strong hydrogen bonds of different strength existing in the solid. The instability of ammonium carbamate is attributed to a low potential barrier for the transfer of a proton from the NH4+ to the NH2CO2— ion, rather than a weak bond in either species.
Absorption Spectra of H2 in the Vacuum Ultraviolet Region. II. The B′—X, B″—X, D—X, and D′—X Bands
Authors: Namioka T.
Published: January 2005

The absorption spectrum of the H2 molecule has been studied in the wavelength region 840 to 930 Å with a 6.8 m grazing incidence vacuum spectrograph in combination with the helium continuum. All the possible levels, which lie below the dissociation limit H(12Sg)+H(22Sg,22Pu), of the odd singlet states have been identified in the present investigation. There are strong heterogeneous perturbations between the B′ and the D states, weak heterogeneous perturbations between the B′ and D′ states and a medium strength homogeneous perturbation between the B′ and the B″ states. The perturbation parameters have been estimated in each case. In the present paper, the results of the rotational and vibrational analyses are given for the B′—X, B″—X, D—X, and D′—X bands. The experimental evidence found in the present study suggests that the predissociation in the levels with v≥3 of the D state is of the type b0, according to Mulliken's classification.
Calculation of the Field Gradient at the Deuteron in Formaldehyde
Authors: Lowe J. T. , Flygare W. H.
Published: January 2005

The best available approximate Hartree—Fock electronic wavefunctions are used to compute the field gradient at the deuteron in formaldehyde. The calculated values of the principal field-gradient tensor elements are (all in units of esu cm—3)qαα(C–H bond axis) = 8.769×1014, qββ=—4.783×1014, and qγγ(perpendicular to molecular plane) = —3.986×1014. The calculated values of the principal field-gradient tensor elements all lie within the experimental error of the measured quantities.
Kinetic Theory Analysis of the Reaction of Hot Hydrogen Atoms with Propane, Butane, and Butene-1
Authors: Rosenberg Allan H. , Wolfgang Richard
Published: January 2005

The kinetic theory of hot reaction has been applied to results on the reaction of hot hydrogen atoms with propane, with butane, and with butene-1. Recoil tritium, generated by the 3He(n, p)T process served as the source of hot hydrogen. Yields of hot abstraction, displacement, and addition processes were measured by radio gas chromatography. Scavengers were used to suppress interfering thermal processes. Runs were made covering a wide range of moderation of the hot hydrogen by helium.

A complete analysis of the data and the use of appropriate internal consistency checks, shows that within experimental error the kinetic theory provides a satisfactory description of the system. Its application serves to express the data in terms of ``reactivity integrals'', I, and collisional energy loss parameters α. In accordance with previous expectations, the magnitudes of these quantities indicate that hot atom collisions are highly inelastic and have a high probability of leading to reaction.
Pulse Radiolysis Studies. VI. The Lifetimes of Aromatic Anions in the Aliphatic Alcohols
Authors: Arai Shigeyoshi , Dorfman Leon M.
Published: January 2005

The formation and the lifetimes of several aromatic anions in irradiated solutions of arenes in the aliphatic alcohols have been investigated by the pulse radiolysis technique. The aromatic anions show a fast decay which follows a first-order rate law. The absolute rate constants for this decay, suggested to be a proton transfer from the alcohol, arene−+ROH=arene H·+RO−,have been determined for four alcohols and three aromatic anions. The rate constants, which are found to be in the order CH3OH>C2H5OH≅C3H7OH>(CH3)2CHOH, show a close correlation with other measurements of the acidity of the alcohols.

The absolute rate constants have also been determined for the reaction of several aromatic anions with hydrogen ion, arene−+ROH2+=arene H·+ROH,and for the attachment reaction of the solvated electron in ethanol, esol−+arene=arene−.
Luminescence Phenomena in Gamma-Irradiated Pure 3-Methylpentane Glass: Implications for Radiation Chemistry
Authors: Burton Milton , Dillon Michael , Rein Robert
Published: January 2005

Gamma irradiation of 3-methylpentane glass at 77°K causes prolonged luminescence at that temperature with a decay law resolvable into three first-order decays with specific rates of the order of 10—3 sec—1. Activation energies for the release of this ``isothermal'' luminescence are tightly grouped around a value near 0.1 eV. Additional luminescence produced in a ``warmup'' region corresponds to activation energies broadly grouped near 0.25 eV. Absorption of infrared light causes rapid release of ``isothermal'' luminescence but has no observable effect on ``warmup'' luminescence. Added quenchers affect both parts. The spectrum of the luminescence seems to be unaffected by the temperature or other treatment of the sample. Results are interpreted in terms of release of weakly trapped electrons and their interaction with positive holes to yield emitting states. The results suggest that in the radiation chemistry of condensed systems at room temperature some of the electron-neutralization processes require >10—11 sec for their completion. During this time the positive holes involved can react chemically with their environs.
Crystal Structure of (NH4)2CuCl4
Authors: Willett Roger D.
Published: January 2005

The crystal structure of the yellow compound (NH4)2CuCl4 has been determined by x-ray diffraction studies. The compound crystallizes in the orthorhombic space group Cmca with a=15.46 Å, b=7.20 Å, and c=7.20 Å. The structure contains discrete, planar CuCl4= ions with Cu–Cl distances of 2.30 and 2.33 Å. These ions are then bonded together by longer Cu–Cl bonds of 2.79 Å to form infinite two-dimensional sheets. The yellow compounds (CH3NH3)2CuCl4 and (C2H5NH3)2CuCl4 probably have closely related structures.
Mass Spectrometric Studies at High Temperatures. III. Dissociation Energies of the Alkaline Earth Monofluorides
Authors: Ehlert T. C. , Blue G. D. , Green J. W. , Margrave J. L.
Published: January 2005

By heating the difluorides of magnesium, strontium, and barium under reducing conditions, one obtains significant amounts of the respective monofluorides. Mass spectrometric studies of equilibria involving these monofluorides have yielded the dissociation energies (D°298) 4.62±0.1 eV, 5.43±0.1 eV, and 5.83±0.1 eV for gaseous MgF, SrF, and BaF, respectively. These results support an ionic model for these molecules and are considerably higher than those previously accepted.
Vibronic Coupling. II. Spectra of Dimers
Authors: Fulton Robert L. , Gouterman Martin
Published: January 2005

We consider a model dimer composed of units with one allowed excited state and one symmetric vibration. The vibrational mode has the same force constant in the ground and excited states, but the excited state is assumed to have its equilibrium position shifted by an amount measured by λ. The dimer possesses a symmetry operation that exchanges the units and has an exciton coupling ε. Spectra for various λ and ε values are derived by computer. It is shown that the absorption intensity of the two polarizations rigorously satisfies two theorems: the center of gravity is at ±ε for all λ; the bandwidth is | λ | for all ε.
Kinetics of Hydrogen—Oxygen Reaction in Shock Waves
Authors: Miyama Hajime , Takeyama Tetsu
Published: January 2005

The hydrogen—oxygen reaction in reflected shock waves has been studied in the range of conditions 890°≤T≤1350°K, 4.5≤P≤5.6 atm, 1.3≤O2≤13×10—3 moles/liter, and 0.5≤[H2]/[O2]≤2. Measurements of both the induction period of OH absorption and that of pressure increase suggest that the reaction H+O2→OH+O is the rate-determining step of OH formation in this temperature range and has an activation energy of 18.9±0.9 kcal/mole, but that the rate-determining step of over-all reaction is HO2+H2→H2O2+H below 1100°K, while H+O2→OH+O is rate determining above 1100°K. Also, the mechanism of the hydrogen—oxygen reaction below 1100°K is discussed in some detail.
Lattice Constants and Thermal Expansivities of Silicon and of Calcium Fluoride between 6° and 322°K
Authors: Batchelder D. N. , Simmons R. O.
Published: January 2005

An x-ray back-reflection, rotating-camera technique has been used to obtain lattice constants and thermal expansivities of single-crystal silicon and calcium fluoride. Absolute expansivity was obtained over a broad range with an error less than 3 ppm. For silicon, this absolute method discriminates between earlier experiments showing some disagreement, and establishes with improved precision the temperature variation of the Grüneisen parameter γ in the region of particular interest (γ<0). For calcium fluoride the present x-ray measurements test a prediction of Ganesan and Srinivasan that γ should rise sharply below about 80°K. The prediction is not confirmed.
Hermiticity and Gaussian Quadrature
Authors: Goodisman Jerry
Published: January 2005

It is often convenient to use Gaussian quadrature techniques to calculate integrals for variational calculations. A basis set may be constructed which is orthonormal under the summations used to approximate the integrals. For this set, the Hamiltonian matrix is Hermitian, in spite of the matrix elements not being calculated exactly.
Monte Carlo Calculations. V. Three-Dimensional Study of a General Bimolecular Interaction Potential
Authors: Bunker Don L. , Blais Normand C.
Published: January 2005

About 7500 computed trajectories were employed in a Monte Carlo study of a general interaction potential for the reactions A + BC → AB + C without activation energy. Some of the trajectories were constrained to be planar; others were determined in three dimensions.

The most prominent effects on the results (product energy and emission angle distributions) were obtained when the relative proportion of reaction energy released during reactant approach and product departure was changed, or by a change in the shape of the intermediate aggregate ABC. Of lesser importance were the sharpness of the ``corner in the reaction path,'' the rapidity (vs distance) of the kinetic energy release, and the amount of solid angle about B accessible to A.

The dimensionality of the calculation has a relatively unimportant effect on the product energy distributions, but an important one on the product emission angles. Three-dimensional emission-angle distributions are peaked near (but not symmetrically about) the angle of 90° with respect to the relative velocity vector. It is observed that the direction of the orbital angular-momentum vector is not preserved during the course of the reaction.
Configurational Statistics of Highly Branched Polymer Systems
Authors: Dobson G. R. , Gordon M.
Published: January 2005

Applications of the theory of branching processes to polymer systems can be so formulated, that all statistical parameters emerge automatically in a form which applies to the soluble part of the system, i.e., to the whole system up to the gel point, and to the sol fraction beyond. In a self-contained presentation, previous work along these lines is here extended to computing configurational statistics of systems arising most directly by condensation processes. These statistics are the mean-square radii of the molecules in such systems, averaged in various ways and useful for theories of light scattering and viscosity. Numerical calculations for random f-functional polycondensation are presented as plots of configurational parameters against conversion for f=3, 4, and 6. The general equations given extend beyond the random case to condensations with ``first-shell'' substitution effect, i.e., in which the rates of making or breaking a given bond between two repeat units depends on how many other bonds these two units carry (to further units). In terms of current theories, the intrinsic viscosity of a system at its gel point is shown to be finite. The spatial averaging of molecular size is based on random flight statistics. The well-known theorem by Kramers used in this connection is rederived on a simple topological basis, and generalized to deal with copolymerization of units of different sizes.
Gyromagnetic Factors and Spin—Orbit Coupling in Ligand Field Theory
Authors: Misetich Antonio A. , Buch Tomas
Published: January 2005

It has been customary to compute the effect of spin—orbit coupling on the magnetic properties of transition metal ions in crystals with the expression taken over from atomic spectroscopy, although this expression is valid only in a spherically symmetric field.

In the present work, we show how the use of a spin—orbit interaction Hamiltonian derived from the Bethe—Salpeter approximation to the relativistic Breit equation for a partly covalent complex leads to a dependence of the gyromagnetic factor on the spin—orbit coupling parameter of the ligand atoms. We develop an expression of g for a d8-ion in a cubic field and apply it to the case of KNiF3. The calculated g values agree very well with experimental results.

Other differences between our expression and those found by other authors are discussed.
Analytic Self-Consistent Field Wavefunctions and Computed Properties for Homonuclear Diatomic Molecules
Authors: Wahl Arnold C.
Published: January 2005

The analytic and computational framework for Hartree—Fock—Roothaan calculations on homonuclear diatomic molecules is presented. Several approaches to calculating the wavefunction are sketched as well as methods of computing molecular properties from the wavefunction. Emphasis is given to the efficient organization of these calculations for existing digital computers. Typical results obtained through the application of the programs and techniques developed are presented for the fluorine molecule.
Calculation of London Energies. II. An Iteration Procedure
Authors: Musher Jeremy I.
Published: January 2005

The iteration of a previously discussed procedure for the approximate solution of the two-particle partial differential equations of perturbation theory is presented. This iterative procedure is useful when the perturbation can be written as a finite sum of separable terms. The solution obtained is probably an asymptotic expansion of which the leading terms provide a good approximation to the exact solution. The two-particle and nonadditive three-particle London energies for interacting hydrogen atoms are calculated using the second and first iterations, respectively; the third and second iterations, respectively, of these energies diverge. The semiconvergence of the series is demonstrated and discussed, and further applications are mentioned.
Infrared Study of the Crystalline Monohydrates of Nitric, Perchloric, and Sulfuric Acids
Authors: Savoie Rodrigue , Giguère Paul A.
Published: January 2005

The infrared spectra of the solid monohydrates of three strong acids nitric, perchloric, and sulfuric were measured down to 50 cm—1. The last two are completely ionic, viz., H3O+ClO4— and H3O+HSO4—, but the first one always seems to retain a trace of covalent structure, HNO3·H2O. In the three hydrogen-bonded lattices the H3O+ ions have libration frequencies of the order of 700 cm—1 and translation frequencies lying between 120 and 400 cm—1. The frequencies of these lattice modes increase with the strengths of the hydrogen bonds. The deuterated hydrate of sulfuric acid gave only vitreous spectra because of supercooling. Likewise the room-temperature phase of perchloric acid monohydrate showed broad, diffuse absorption bands due to the disordered orientation of the hydronium ions. The pyramidal configuration of the H3O+ ion is confirmed definitely.
Structure in Ionization-Efficiency Curves near Threshold from Alkanes and Alkyl Halides
Authors: Tsuda Satoru , Hamill William H.
Published: January 2005

Appearance potentials have been measured by the retarding potential difference method on a time-of-flight mass spectrometer for: CH2+ from CH4, CH3Cl, CH3Br, and CH3I; CH2X+ from CH3F, CH3Cl, CH3Br and CH3I; C2H6+ and CH3+ from C2H6; C2H5+ and C2H5X+ from C2H5X and C3H7+; and C3H7X+ from C3H7X where X is Cl, Br, or I. Substantially all of the structure in the ionization-efficiency curves of fragment hydrocarbon ions can be accounted for by excitation potentials which are the same for all source molecules or by differences of appearance potentials between ion-pair and ion—neutral processes which match known electron affinities. In all instances the appearance potential of a fragment ion at onset corresponded to an ion-pairing process.
Selenium Isotope Effects in Fluorine Nuclear Magnetic Resonance Spectroscopy
Authors: Birchall T. , Crossley S. L. , Gillespie R. J.
Published: January 2005

A selenium isotope effect on the fluorine chemical shift has been observed in several selenium—fluorine compounds for all of the naturally occurring selenium isotopes except 74Se. Values for some 77Se–19F coupling constants are reported.
Adsorption of Gases Activated by Electron Impact
Authors: Winters H. F. , Horne D. E. , Donaldson E. E.
Published: January 2005

Adsorption of nitrogen which has been activated by electron impact is shown to result from dissociation of the nitrogen molecule and from the interaction of energetic ions with a nickel surface. Excitation of N2 to states at about 10.3, 12.2, and 14.0 eV causes dissociation. Dissociative ionization at 24.5 eV also leads to additional pumping. Energetic N2+ ions have an adsorption probability of approximately 0.85 when they collide with a nickel surface. It is shown that the ion adsorption probability is practically independent of energy between 30 and 100 eV. It is also shown that thermal energy ions have a very low adsorption probability. These results lead to the postulate that the N2+ ions dissociate in impact and that the atomic nitrogen is subsequently adsorbed. Results have also been obtained which indicate that the adsorption probability of Ar+ is strongly dependent on surface structure. Annealing of the surface greatly reduces the adsorption probability.
Anharmonic Forces and the Vapor-Pressure Ratio of Monatomic Isotopic Solids. II
Authors: Klein M. L. , Reissland J. A.
Published: January 2005

The anharmonic contribution to the vapor-pressure ratio of 36Ar and 40Ar has been calculated using a Mie—Lennard—Jones 6, n potential with n=10 and 12. The contribution of the vibrational anharmonicity was found to be large and tended to cancel the effect of thermal expansion. Numerical calculations for the 6, 10 potential were found to agree well with experimental measurements of the isotope separation factor. A brief discussion is given of vapor pressure ratio data for 20Ne and 22Ne.
Zero-Field Splittings. IV. Gaussian Approximation of Integrals
Authors: Boorstein Seth Alan , Gouterman Martin
Published: January 2005

Zero-field splitting integrals over Slater 2pz atomic orbitals are evaluated by substituting for each orbital an approximating linear combination of Gaussians differing in their orbital exponents. Each linear combination is derived a priori for maximum overlap with the Slater orbital. The accuracy of the method for successively higher orders of approximation is assayed by direct comparison with exact Slater values. It is found that a three-term expansion is sufficient to give molecular Slater integrals needed in triplet calculations to 0.1% accuracy.
Mass-Spectrometric Investigation of the Yttrium—Chlorine Surface Reaction
Authors: McKinley John D.
Published: January 2005

Volatile products of the surface reaction between chlorine at room temperature and heated polycrystalline yttrium were identified and their formation rates were measured mass spectrometrically. At surface temperatures between 300° and 1700°K (yttrium melting point 1750°K) and chlorine pressures between 10—5 and 5×10—4 Torr, Cl, YCl2, and Cl2 were observed. No gaseous YCl or YCl3, was detected. The results are consistent with the presence of a strongly chemisorbed layer of chlorine atoms, stable over the entire temperature range, on which Cl2 adsorbs as Cl atoms. These either evaporate or react with YCl to form volatile YCl2. An activation energy of 55 kcal/mole for YCl2 evaporation is apparently associated with dissociative adsorption of chlorine on the chemisorbed Cl layer.
Temperature Dependence of the Pure Quadrupole Frequency and Spin—Lattice Relaxation Time of p-Dibromobenzene
Authors: Tipsword R. F. , Wilkinson E. L. , Moulton W. G.
Published: January 2005

The dependence of the 79Br and 81Br pure quadrupole resonance frequencies on temperature in p-dibromobenzene have been measured over the temperature range 4.2° to 77°K. The results are compared with the Bayer theory, using values for the torsional frequencies obtained from the Raman data for p-dibromobenzene. Good agreement with the theory is obtained if both the low-frequency and high-frequency modes are included in the calculation. The spin—lattice relaxation time of the resonance has been measured in the range 4.2° to 7.5°K and the relaxation time was found to be proportional to T9 in this limited temperature region. The experimental results are compared with the Bayer theory.
``Temperature Effect'' on Triplet State Lifetimes in Solid Solutions
Authors: Kellogg R. E. , Schwenker R. P.
Published: January 2005

The phosphorescence lifetimes of several aromatic hydrocarbons and their deuterated counterparts have been measured in plastic matrices as a function of temperature.

The onset of a dark process at higher temperatures is generally observed and is believed to be a property associated with the aromatic molecule, rather than with some ``unknown'' quencher. Phonon involvement is suggested by the data.

An apparatus for accurately measuring phosphorescence decay over seven half-lives with minimal noise is also described.
Ion-Pair Exciton States and the Optical Spectrum of Crystalline Neon
Authors: Webber Stephen , Rice Stuart A. , Jortner Joshua
Published: January 2005

The energy of the first electronic transition in crystalline neon has been calculated in the Heitler—London scheme. The calculation differs from previous work in that the effects of ionized exciton states are formulated as charge transfer states in which the excited electron resides on neighboring neons while the (1s)2(2s)2(2p5) hole remains on the central neon. Only the Γ(k=0) point in k space is considered, and spin—orbit coupling is neglected.

When correction is made for the nonstationary character of an exciton in solids, the predicted blue shift of 0.25 eV seems to be in reasonable agreement with the trend of spectral shifts of other rare-gas solids.
Halogen-Atom Reactions. II. Luminescence from the Recombination of Chlorine Atoms
Authors: Bader L. W. , Ogryzlo E. A.
Published: January 2005

A spectroscopic study of an orange-red glow from the products of electrical discharge in chlorine has resulted in an identification of the emitter as Cl2(A3II0u+). A kinetic study has provided evidence for the formation of excited molecules in this state by the preassociation of 2P3/2 chlorine atoms. Several detailed mechanisms for the reaction are discussed.
Davydov Splittings in Anthracene
Authors: Mahan G. D.
Published: January 2005

The Davydov splittings are calculated for the 3800-Å state in anthracene. A point-dipole model is used which represents each excited molecular state by a classical dipole. This allows the vibrational sublevels and depolarization forces of an excited state to be included self-consistently in the dielectric function. The numerical splittings are in reasonable agreement with experiment.
Oxygen Stoichiometry in the Barium Ferrates; Its Effect on Magnetization and Resistivity
Authors: MacChesney J. B. , Potter J. F. , Sherwood R. C. , Williams H. J.
Published: January 2005

The barium ferrates comprise a series of compositions exhibiting a wide range of oxygen deficiency. Members of this series are isostructural with the high-temperature polymorph of barium titanate which is hexagonal with space group C63/mmc. Polycrystalline specimens with varying oxygen contents, i.e., Fe4+ concentrations, were prepared by equilibration at oxygen pressures ranging from 0.2 to 2400 atm. The highest oxygen content achieved was BeFeO2.95 which had lattice parameters: a=5.674 Å, c=13.645 Å. This specimen exhibited unusual magnetic properties marked by an abrupt change in magnetization at 164°K. Above this temperature the material appeared to be ferrimagnetic. The peak value of the magnetization per gram, σg, is 13.8 emu at 164°K. At lower temperatures the compound is antiferromagnetic but exhibits a small residual moment. The transition appears to be first order with a thermal hysteresis of approximately 4°C between heating and cooling curves, and is accompanied by a discontinuity in the plot of resistivity vs reciprocal temperature. X-ray diffraction patterns showed no distortion from hexagonal symmetry at temperatures below the transition.

Specimens exhibiting greater oxygen deficiency had larger lattice parameters. In general, these showed a less abrupt magnetic transition which occurred at progressively lower temperatures.
Diatomic Forces and Force Constants. II. Variation—Perturbation Method
Authors: Benston Margaret Lowe , Kirtman Bernard
Published: January 2005

According to Rayleigh—Schrödinger perturbation theory the quadratic (k2) and cubic (k3) force constants of a diatomic molecule are completely determined by the unperturbed and first-order wavefunctions, ψ0 and ψ1. We approximate ψ1 using the Hylleraas variation technique which optimizes a trial function, ψ̃1, by minimizing an expression for k2. Calculations were carried out on H2 with the virial form of the Hellmann—Feynman theorem. Several approximate ψ0's, all of the scaled variety, were tested along with two ψ̃1's containing one and two variation parameters, respectively. Although it is not required by the theory the best results for both k2 and k3 were obtained with the more flexible trial function. Furthermore, with this ψ̃1 we found that improving ψ0 (in the sense of lower E0) had a salutary effect in all but one case. The major error in the better calculations arises not from the ψ1 terms but from evaluating 〈ψ0 | ∂2H/∂R2 | ψ0〉 and 〈ψ0 | ∂3H/∂R3 | ψ0〉. But the latter are readily available experimental quantities since they depend only on the total electronic energy and equilibrium internuclear distance. A semiempirical method for determining force constants is thus suggested. The results are excellent. For example, with the Weinbaum function as ψ0, k2=0.362 and k3=−1.43 (in atomic units) as compared to the experimental values of 0.368 and −1.30.
Multicomponent Polyelectrolyte Solutions. Part IV. Second Virial Coefficient in Mixed Polyvinylsulfonate KCl Systems Near the Θ Temperature
Authors: Eisenberg Henryk
Published: January 2005

The dependence of the second virial coefficient on temperature and degree of polymerization has been studied by light scattering in mixed solutions of potassium polyvinylsulfonate and KCl. Radii of gyration of the macromolecules have been estimated from the angular dependence of the scattered light. The results are discussed in terms of intermolecular and intramolecular excluded-volume theory.
Long-Range Nonbonded Interactions and Rotational Isomerism in Acyl Halides
Authors: Katon J. E. , Feairheller W. R.
Published: January 2005

The infrared spectra of the liquid acyl halides possess a number of carbon—halogen stretching vibrations that are due to the existence of discrete rotational isomers in the liquid state. The only satisfactory explanation for the number of these vibrations is that rotational isomers formed by internal rotation about both the alpha and beta carbon—carbon bonds possess different carbon-halogen stretching frequencies. This implies that alkyl substituents on the beta carbon interact with the halogen atom and provides the first spectroscopic evidence of nonbonded forces operating over so great a chain distance. An assignment of carbon—halogen stretching frequencies to the possible rotational isomers is proposed and the implications of the results concerning the nature of nonbonded forces in this class of compounds is discussed.
ESR Linewidths in Solution. II. Analysis of Spin—Rotational Relaxation Data
Authors: Atkins P. W. , Kivelson Daniel
Published: January 2005

In Part I of this series the residual linewidths for vanadyl acetylacetonate in toluene were found to be proportional to (T/η), where η is the viscosity, and independent of applied field. Since the solutions are dilute, spin exchange is not important. The residual linewidth is attributed to a spin—rotational relaxation mechanism, and calculations based on a perturbation theory of spin—rotational interactions and Hubbard's theory of spin—rotational relaxation yield results in reasonably good agreement with experiment. This relaxation mechanism is probably significant for many dilute S = ½ systems in liquids. For systems with weak anisotropic intermolecular interactions, e.g. ClO2 in CCl4, the correlation time τω for angular momentum and the spin—rotational contribution to the linewidth appear to be larger than those predicted by Hubbard's theory.
Theoretical Studies of Transannular Interactions. I. Benzene Excimer Fluorescence and the Singlet States of the Paracyclophanes
Authors: Vala Martin T. , Hillier Ian H. , Rice Stuart A. , Jortner Joshua
Published: January 2005

The changes in the electronic transition energies of benzene which occur on dimerization have been calculated. It is shown that the energy-level splittings due to the interactions between neutral-excitation states are too small to explain the observed anomalous emission from concentrated benzene solutions and the absorption spectra of the paracyclophanes. To extend the theory, the eight-electron problem is treated for configurationally interacting neutral-excitation and charge-resonance states. Intermolecular overlap is included in a way consistent with the use of a core potential in the Goeppert-Mayer—Sklar representation. Use is also made of Hückel LCAO molecular orbital wavefunctions and a linear combination of four Slater carbon-atom 2pπ wavefunctions fit to an SCF function. The anomalous emission from benzene solutions can now be understood to arise from transitions from the lowest excimer state of α-level parentage for benzene molecules ∼3 or ∼3.3 Å apart when ground-state repulsion is taken into account. The solution absorption spectra of the paracyclophanes are interpreted within this framework of neutral-excitation—charge-resonance configuration interaction. Finally, dimer symmetries different from D6h, have been invesigated in an attempt to understand the absorption spectra of single crystals of [2.2] paracyclophane.
Fluorescent Efficiency of Energetic Electrons in the 3914-Å Band
Authors: Frankenthal S. , Manley O. P. , Treve Y. M.
Published: January 2005

This paper presents a computation of the efficiency of excitation of the state B 2Σu+ in N2+, which is responsible for radiation in the 3914-Å band, by energetic electrons which are slowing down in a thick target. The computed efficiency includes corrections for the Auger effect. In addition, the corresponding fluorescent efficiency of soft x rays is estimated. The calculations appear to be in good agreement with the limited experimental data available. The method of computation is applicable to the treatment of other energy-exchange phenomena associated with the stopping of electrons in thick targets.