bluuebunny/crossref_metadata_2025 huggingface dataset:
Radiotracer Measurement of the Desorption Energy of Silver from Molybdenum and Nickel
Authors: von Goeler E. , Peacock R. N.
Published: January 2005

When Cd107 undergoes decay by electron capture, the radioactive daughter Ag107m is given sufficient energy by neutrino recoil to enable it to escape from adsorbed sites. Sources of Cd107 were made of sufficient strength and cleanliness to enable use of the recoiling Ag107m as a very pure beam of tracer atoms to study surface interactions of silver with thermally cleaned polycrystalline foils of molybdenum and nickel. Constant beams of Ag107m with intensities greater than 106 particles per minute were attained in 1% geometry. The desorption energy of silver on molybdenum was found to be 1.9±0.3 eV, and of silver on nickel, 1.6±0.3 eV. All measurements were made under ultra-high-vacuum conditions, and techniques were developed to permit using a volatile isotope in a baked-out system.
Correlation Energy for Atomic Systems. II. Isoelectronic Series with 11 to 18 Electrons
Authors: Clementi Enrico
Published: January 2005

The correlation energy for the ground-state isoelectronic series of the second-row atoms of the periodic table are estimated. In this estimate the relativistic energies for the closed and the open shells, and the Hartree—Fock energies are taken from calculations we have recently performed. As expected, the second-row correlation energy parallels, in general, the characteristics of the first-row correlation energy. The principal contribution to the correlation energy is due to pairing of electrons in a given orbital. The intershell correlation is smaller than the intrashell correlation (but not negligible) and the 3s—3s electron correlation is linear in Z.
On the Optimum Use of Ionization-Efficiency Data
Authors: Morrison J. D.
Published: January 2005

The electron energy spread causes much fine detail in ionization efficiency curves to be obscured. The reduction of this spread by electron velocity analyzers is experimentally quite difficult. The present paper examines whether it is possible to reduce the effect of the energy spread by any analytical method.

It is found that the problem is very similar to that of the detection of radar signals in noise, and that similar methods can be applied. It is shown that typical ionization efficiency data contain a very much greater amount of information than is generally believed. Methods are developed for obtaining a marked reduction in the scatter in the experimental data and for reducing the effective electron energy spread by a factor of four or five times. The methods do not require an exact knowledge of the form of the electron energy spread, although the better this knowledge, the better the ultimate result.

Tests made on several artificial examples and on two actual cases show that the methods are of some promise. The results of this study also indicate a possible unconventional solution to the problem of achieving even higher resolution in energy in experimental ionization efficiency curves.
Unimolecular Decomposition of Chemically Activated Propyl Radicals. Normal Intermolecular Secondary Kinetic Isotope Effect
Authors: Falconer W. E. , Rabinovitch B. S. , Cvetanović R. J.
Published: January 2005

The vibrationally excited radical pairs n-propyl-d0, n-propyl-d6 and isopropyl-d0, isopropyl-d6 were produced at 25°C by the addition of H atoms to propylene-d0 and propylene-d6. Decomposition of n-propyl is by C–C rupture, whereas C–H rupture appears to be the predominant path for isopropyl decomposition, possibly to the exclusion of C–C rupture. The average rates of decomposition ka were determined relative to collisional stabilization by complete product analysis: for n-propyl-d0 C–C rupture, kan≃108 sec—1; for isopropyl-d0 C–H rupture, kai(—1)≃10—2 kan. For vibrationally excited propane, formed by the addition of H atoms to isopropyl radicals, kapr≃6.6×105 sec—1. The secondary kinetic isotope effect for n-propyl unimolecular decomposition in this nonequilibrium system was found to be ∼5.0 at the low-pressure limit, and ∼4.5 at the high-pressure limit; that found for isopropyl decomposition is ∼6.

The Marcus—Rice specific rate expression was used with a quantum statistical harmonic oscillator model to calculate theoretical rate constants for the decomposition of n-propyl radicals which are in good agreement with the experimental values. A loosened activated complex was assumed, in which all vibrational modes and internal rotations were taken as active. The effect of different treatments of the internal rotations on the distribution function f(E)dE was demonstrated to be small.
Hole Theory of Liquids and Dense Gases. II. Internal Entropy, Energy, and Heat Capacity
Authors: Henderson Douglas
Published: January 2005

The internal entropy, energy, and heat capacity of the inert gases in the liquid and dense gas states are calculated on the basis on the hole theory of liquids under the assumptions that the free volume increases linearly with the number of neighboring holes and that the holes and molecules are randomly distributed. The agreement with experiment is good in the dense gas region but becomes less satisfactory for the liquid state. The various assumptions inherent in this work are discussed and improvements are suggested.
Application of the Second-Order WBK Approximation to Radial Problems
Authors: Beckel Charles L. , Nakhleh Jamil
Published: January 2005

When the WBK approximation is applied to radial problems, difficulties are encountered at the origin. Previous work has led to the conclusion that the difficulties are removed by substitution of (J+½)2 for J(J+1) in the effective potential. The use of (J+½)2 is here shown to be justified for the first-order WBK approximation only. The second-order WBK wavefunction is found to approximate the exact one as r→0, if one substitutes K for J(J+1), where K obeys the equation K+1/(64K)=J(J+1). Moreover, the second-order WBK energy levels can be made to coincide with the exact levels for the hydrogen atom and for the radial harmonic oscillator if the same substitution is made. Implications with regard to the rotating vibrator problem are discussed.
Interaction Energies and Transport Coefficients of Li+H and O+H Gas Mixtures at High Temperatures
Authors: Krupenie Paul H. , Mason Edward A. , Vanderslice Joseph T.
Published: January 2005

Accurate potential energy curves for the X 1Σg+, A 1Σu+, B 1Πu, and C 1Πu states of the Li2 molecule are calculated from observed spectroscopic data by the method of Rydberg—Klein—Rees (RKR), and compared with previous quantum-mechanical calculations, Long-range attractive potentials are estimated by extrapolation of functions fitted to the RKR ground-state curves of Li2, LiH, and OH. From these, the repulsive potentials derivable from interacting ground-state atoms are estimated semiempirically. Collision integrals are computed from the potentials, and transport coefficients of the gaseous systems Li+Li, Li+H, and O+H are calculated for temperatures of 1000° to 10 000°K.

A surprising result is the extraordinarily large values of the collision inregrals for Li+Li (and Li+H) interactions, which result in unexpectedly small values of diffusion coefficient, viscosity, and thermal conductivity. For traces of Li in Li+H mixtures at low temperature, the thermal diffusion factor is very large. Various approximate formulas for viscosity and thermal conductivity of mixtures are seen to give poor agreement with exact calculations for the systems considered.
Vibrational Energy Levels of Ionic Molecules Bound by Classical Forces
Authors: Finn Edward J.
Published: January 2005

Theoretical vibrational energy levels of LiI, NaCl, and InF (chosen as representative diatomic ionic molecules) are computed by means of the first-order WKB approximation. Two classical vibrational potentials are studied for each molecule. The first consists of a Coulombic attraction and an exponential repulsion term, while the second potential adds a polarizability term to the first. Analysis of the data shows that at very low v a power series in (v+½) adequately represents the energy levels, while at very high v the energy levels approach those of a hydrogenlike atom. Further, the first energy difference curves show positive curvature at all v for all cases. Formulas are presented that accurately yield the vibrational energies at all v.
Vibrational Spectra and the Inversion Phenomenon in Cyanamide and Deuterated Cyanamide
Authors: Fletcher William H. , Brown Farrell B.
Published: January 2005

The infrared and Raman spectra of H2NCN and D2NCN have been examined in the liquid state in the region of 2.5 to 35 μ. Polarization data imply a planar configuration, but the experimental data for the region beyond 12 μ are inconsistent with this. The observed product rule ratio for the symmetric N–H stretch, NH2 deformation, N–C and C≡N stretches are also inconsistent with a planar molecule. The observations do fit a nonplanar molecule with an inversion barrier described by a Manning potential. The barrier height is found to be 660 cm—1, with q0 = 0.176 Å. Every distinct feature of the infrared and Raman spectra of the liquid state for both isotopic species may be given a satisfactory assignment with this model.
Neon—Hydrogen Ion—Molecule Reactions
Authors: Moran T. F. , Friedman L.
Published: January 2005

Ion—molecule reactions producing NeH+ in a Ne–H2 mixture subjected to electron bombardment in the ion source of a mass spectrometer have been studied. Ionization-efficiency curves show that NeH+ is primarily formed by reaction of H2+ and Ne. The calculated rate constant is in good agreement with theory when only H2+ ions in the second or higher vibrational levels are considered as reactant. The energetic requirements of reaction appear to be satisfied exclusively by internal energy of H2+. At higher ion-source pressures NeH+ is formed in a third-order process which was found to be first order in hydrogen and second order in neon pressure. The ionization-efficiency curve of the third-order NeH+ closely resembles a Ne* metastable excitation curve. Results suggest a Ne*–H2 interaction producing a highly excited hydrogen molecule which subsequently ionizes to H2+ and then reacts with Ne producing NeH+. The H2+–He ion molecule reaction served as a sensitive probe to show that Ne*–H2 collisions produce H2+ in vibrationally excited states with v≥5. A momentum-transfer cross section calculated for the metastable atom—molecule interaction is in reasonable agreement with the measured cross section.
Preparation and Properties of Monomolecular Films of Chlorophyll a and Pheophytin a
Authors: Bellamy W. D. , Gaines G. L. , Tweet A. G.
Published: January 2005

Monomolecular films of chlorophyll a and pheophytin a on aqueous subphases have been prepared and studied. The preparation and preservation of these pigments in a state of high purity has required procedural refinements which are described. Chemical degradation in solution and in the monolayer can be prevented by appropriate precautions. At surface pressures below 22 dyn/cm for chlorophyll and 10 dyn/cm for pheophytin, the films on pH 8.0 buffer are mechanically stable in the dark at 20°C. At these pressures, there is little difference in the force—area curves of chlorophyll and pheophytin, although the surface potentials and surface dipole moments of the two pigments are markedly different. The visible absorption spectrum of the pigment monolayers on the aqueous subphase is rapidly altered by illumination, although under optimum conditions it shows little change in the dark over periods of several hours. These experiments were performed with a monolayer spectrometer, which permits measurements of the absorption spectra of monolayers in situ. This instrument is briefly described. The unified set of quantitative measurements of this study, together with previous observations in the literature, provide evidence for a monolayer structure in which the pigment molecules, with a folded configuration (both porphyrin plane and phytol sidechain rising above the water surface), are closely packed but randomly oriented in the two-dimensional array. There is no evidence for any marked rearrangement on compression under our conditions. Anomalies in the absorption spectra are observed when pheophytin monolayers are compressed beyond the stable limit.
Dissociative Charge-Exchange Reactions of Rare-Gas Ions with Propane
Authors: Futrell Jean H. , Tiernan Thomas O.
Published: January 2005

Dissociative charge-exchange reactions of rare-gas ions with propane and with partially deuterated propanes have been investigated using a modified commercial mass spectrometer. The experimental results for propane are in good agreement with data previously obtained using much more sophisticated instrumentation. Charge-exchange spectra obtained with 2,2-dideuteropropane and with 1,1,1,3,3,3-hexadeuteropropane permit the determination of details of the fragmentation mechanism. The data suggest that both s-propyl and n-propyl ions are formed by charge exchange, but that the latter is a relatively unimportant process. Ethylene is formed chiefly by 1,3 elimination of methane from the molecule ion, but 1,2 elimination becomes relatively more important with increasing recombination energy of the rare-gas ion. In contrast to observations on the vacuum uv photolysis of deuterated propanes, the present data indicate that elimination of molecular hydrogen as HD is of substantial importance in the over-all ionic decomposition of both compounds.
Vacuum Ultraviolet Photochemistry. VII. Photolysis of n-Butane
Authors: Okabe H. , Becker D. A.
Published: January 2005

The photolysis of n-butane has been carried out at room temperature at the Xe resonance lines. A few photolyses have been done at the Kr resonance lines. The isotopic analyses of products—hydrogen, methane, ethane, and ethylene—produced in the photolysis of mixtures of C4H10+C4D10 and of CH3CD2CD2CH3 were made, in the presence and the absence of 10% NO, to obtain information on the detailed modes of decomposition. From these results, it was concluded that, at the Xe lines: (1) Hydrogen is detached mainly by a molecular process C4H10→H2+C4H8and preferentially from the inside carbon atoms. (2) Methane, amounting to 5% of hydrogen, is produced both from the methyl radical and probably from three different molecular processes. (3) Ethylene is produced chiefly by the molecular process CH3CD2CD2CH3→2CH2CD2+2H.(4) Ethane is produced by molecular elimination as well as the combination of methyl radicals CH3CD2CD2CH3→CH3CD3+CH3CD,2CH3→C2H6.Other unsaturated hydrocarbons are produced largely by molecular processes, whereas saturated hydrocarbons are produced mainly from free-radical processes. Relative probabilities of the primary processes are assessed.
Sulfur and Silicon Isotope Effects in Fluorine Nuclear Magnetic Resonance Spectroscopy
Authors: Gillespie R. J. , Quail J. W.
Published: January 2005

Satellites due to fluorine on S33 have been observed in the F19 NMR spectrum of sulfur hexafluoride. Values of the S33–F coupling constant and of the S33 isotope effect on the fluorine chemical shift have been obtained from the spectrum. We have also observed a S34 isotope effect on the fluorine chemical shift of sulfur hexafluoride and other sulfur—fluorine compounds. A Si29 isotope effect on the fluorine chemical shift has been observed for silicon tetrafluoride.
Dielectric Constant and Interactions of Polar Molecules
Authors: Cole Robert H.
Published: January 2005

The theory of the dielectric constant previously developed by Van Vleck and others for permanent dipoles is extended to third-order interactions with inclusion of induced polarization represented by harmonic oscillators. This is carried out by a high-temperature expansion of the partition function in powers of dipole coupling energy.

Third-order interaction terms are of the triangle and shuttle forms found by Rosenberg and Lax for permanent dipoles, but for induced moment contributions only the triangle interaction sum is involved. For neither type of term can agreement with Onsager's model be secured in any reasonable way.

Kirkwood's treatment of long-range interactions is shown to be consistent with the series expansion results if short-range correlations are properly evaluated, but the results of this evaluation depend on molecular distributions.
Atomic Calculations. II. Polarizabilities and London Force Constants for F—, Ne, and Na+
Authors: Donath Wilm E.
Published: January 2005

Calculations are described for the polarizabilities and London force coefficients for F—, Ne, and Na+. The ground-state wavefunctions are with and without correlation. The perturbing functions are singly and doubly excited configurations, which form a set of pseudostates; the polarizability is then calculated by second-order perturbation theory. The various effects occurring here are considered.
Theory of the Effects of Concentration and Chain Length on Helix—Coil Equilibria in Two-Stranded Nucleic Acids
Authors: Applequist Jon , Damle Vinayak
Published: January 2005

The formalism for treating a dissociating two-stranded helix is developed from the system partition function. The behavior of finite chains is examined according to the model in which only one helical region is allowed in a molecule, and staggering of the paired strands is not allowed. Numerical results for chain lengths in the range of 1 to 300 residues show that the helix—coil transition curve is markedly broadened and shifted as the chain length decreases, and that a decrease in concentration results in a significant decrease in degree of bonding for chain lengths less than about 100. The ultraviolet absorbance transition curves are calculated from the Rich—Tinoco predictions for stack-length dependence of hypochromicity, and are found to be markedly different from the transition curves in terms of degree of bonding for chain lengths less than about 100.
Zero-Field Splittings in Some Triplet-State Aromatic Molecules
Authors: Chiu Ying-Nan
Published: January 2005

Zero-field splitting constants for the lowest triplet states of naphthalene, benzene, triphenylene, and coronene were calculated using configuration-interaction Hückel molecular orbitals. The mixing coefficients for different configurations were used as parameters to fit experimental data. The two-, three-, and four-center dipolar interaction integrals were computed using both the Mullikan—Hameka approximation and the Gaussian wavefunction method. The latter method gave better results. When more and more multiple-center integrals were included, the results essentially converged. It was concluded that inclusion of all two-center Gaussian integrals sufficed in such calculations. First-approximation triplet wavefunctions were formed according to the conventional choice of configurations obtained from two highest filled and two lowest empty orbitals. Where these two orbitals are degenerate as in molecules with threefold symmetry the third highest filled and the third lowest empty orbital were found to be significant. The effect on zero-field splitting due to extended mixing of doubly excited and independently excited configurations was investigated. The introduction of negative spin correlation in triplet state due to configuration interaction was shown. Spin correlation and its positive and negative nature between various pairs of atoms at different interatomic distances were computed. Atom pairs were then grouped under two types (starred and unstarred) which behaved as an entity in a specific manner during a specific configuration interaction.
Molecular Motion and the Moment Analysis of Molecular Spectra in Condensed Phases. I. Dipole-Allowed Spectra
Authors: Gordon R. G.
Published: January 2005

Molecular absorption and emission spectra (of a vibrational transition or of a single vibrational component of an electronic transition) are analyzed in terms of moments of their intensity distributions. The results are valid for an arbirtary intermolecular potential energy. The first-moment formula allows one to identify, in an experimental spectrum, the shifted band origin. The second moment is found to have additive contributions from dynamical terms and from fluctuations in the environmental frequency shift. The dynamical terms depend on the average molecular rotational kinetic energy, the principal moments of inertia of the molecule, and the direction of the transition moment relative to the principal axes of inertia. In the classical limit, the average rotational kinetic energy is determined by the temperature, and the dynamical terms of the second moment are then independent of the intermolecular potential energy. If general, the measurement of a second moment gives an upper limit to the average rotational kinetic energy. If the shift fluctuation effect is small, the second moment measures the rotational kinetic energy. The third and higher moments depend on averages of angular derivatives of the intermolecular potential energy, as well as on the rotational kinetic energy and shift-fluctuation-type terms found in the second moment. For example, one of the contributions to the fourth moment of a linear molecule is the mean squared torque on the molecule.
Optical Spectra of Exchange Coupled Mn++ Ion Pairs in ZnS:MnS
Authors: McClure Donald S.
Published: January 2005

The optical spectra of several ZnS:MnS (1 to 10 mole%) mixed crystals were obtained at temperatures from 4.2° to 300°K. A concentration dependence was found which proved that certain bands were due to pairs of Mn++ ions in nearest-neighbor cation sites. Temperature—dependent absorption bands were found which were interpreted to give an interionic exchange integral in the ground state of —9 cm—1 in the spin—spin Hamiltonian H = —2JS1·S2. This agrees with the value obtained from the analysis of the susceptibility of pure MnS. The narrow bands due to transitions to the 4A1, 4E(G) states were shown to fit an isotropic spin—spin coupling law with J = +6 cm—1 for each state. The inversion of sign from the ground state is not fully understood. The selection rules for the transitions do not follow those for the total spin (ΔS = 0).
P—R Maxima Separations in Unresolved Parallel Bands of Symmetric- and Slightly Asymmetric-Top Molecules
Authors: Goldfarb Theodore D.
Published: January 2005

The formulas derived by Gerhard and Dennison for calculating P and R branch separations in parallel type vibration—rotation bands have been applied to 50 symmetric and slightly asymmetric molecules. If consideration is restricted to those fundamental bands that are not obviously overlapped or perturbed by interaction with other bands the average difference between observed and calculated separations is found to be ±5% with only seven differences exceeding ±10%.
Crystal Structure of Cerium Magnesium Nitrate Hydrate
Authors: Zalkin Allan , Forrester J. D. , Templeton David H.
Published: January 2005

According to single-crystal x-ray diffraction data, crystals of Ce2Mg3(NO3)12·24H2O are rhombohedral, space group R3̄. The hexagonal cell with a = 11.004±0.006, c = 34.592±0.012 Å contains three formula units. Atomic parameters were refined by least squares, and interatomic distances were corrected for thermal motion. The average N–O bond distance in nitrate is 1.26 Å. The Ce atoms, on the threefold axis at z = ±0.2497, are each surrounded by 12 oxygen atoms at an average distance of 2.64 Å. These oxygen atoms, belonging to six nitrate ions, are at the corners of a somewhat irregular icosahedron. The Mg atoms are of two kinds, located, respectively, at the origin and on the threefold axis at z = ±0.4279. Each Mg atom is surrounded by six water molecules with the oxygen atoms at the corners of an octahedron with an average Mg–O distance of 2.07 Å. One-fourth of the water molecules are not coordinated to cations. Evidence for the hydrogen atom positions from the diffraction data indicates that six of the eight independent hydrogen atoms are involved in normal hydrogen bonds.
Antiferromagnetic and Crystal Structure of Lithium Cupric Chloride Dihydrate
Authors: Abrahams S. C. , Williams H. J.
Published: January 2005

A neutron-diffraction study of LiCuCl3·2H2O in the temperature range 1.4°—5.1°K, together with a magnetic susceptibility study in the range 1.4°—300°K, has determined its magnetic and crystal structure. The crystal contains linear Li–Cu–Cu–Li, planar Li2Cu2Cl6 groups. Each cation is at the center of a distorted octahedron, of composition LiCl3O3 and CuCl5O: the four octahedra share Cl–Cl edges. The most important distances in this complex are Cu–Cl at 2.25, 2.34, and 2.96 Å; Cu–O at 2.56 Å; Li–O at 2.04 and 2.18 Å; Li–Cl at 2.44 and 2.97 Å; Li–Cu at 3.34 Å; and Cu–Cu at 3.47 Å. The ``nonbridging'' Cl atoms in the Li2Cu2Cl6 group form OH···Cl bonds of 3.17 and 3.26 Å to other complexes in the crystal. The spins (S = ½) on the Cu2+ within each complex are antiparallel and lie on the 3.47-Å Cu–Cu internuclear line. The spin-density maximum is displaced 0.15 Å from the nearest neighbor Cu2+ of opposite spin. The neutron-scattering data indicates dx2—y2 to be the ground-state orbital. Above a critical field Hc = 9kOe, spin flopping similar to that in CuCl2·2H2O takes place.
On the Hydrogen—Bromine Reaction Rate in a Nonsteady State
Authors: Shin H.
Published: January 2005

The deviations of atom concentrations and over-all rate from steady-state conditions for the H2–Br2 reaction are evaluated as functions of the extent of reaction in a temperature range 1000°—1600°K. Both the concentration and rate deviations are serious at 1400°—1600°K. The major source of the nonsteady state deviation in rate is the reaction k5[H][Br2] and the regenerating cycle proceeds in nonsteady state except at the later stage of the reaction. A previously obtained result that two atom concentration deviations ε1 and ε2 are nearly identical is equivalent to the condition that the rate of change of the H-atom concentration vanishes. At elevated temperatures, analysis of the atom concentration deviations alone does not give sufficient information for the evaluation of the steady-state hypothesis; the over-all rate deviation must be obtained to answer the question of steady-state validity.
Vibration—Rotation Spectra of CH4 and CD4 Impurities in Xenon, Krypton, and Argon Crystals
Authors: Cabana A. , Savitsky G. B. , Hornig D. F.
Published: January 2005

The infrared spectra of CH4 and CD4, present as substitutional impurities in crystals of argon, krypton, and xenon, were studied at temperatures ranging from 5° to 40°K.

Both v3 and v4 of CH4 in xenon showed a simple four line pattern which is consistent with that expected for a slightly hindered rotor. In krypton and argon a fifth line appeared on v3, as expected from King's theoretical calculations for a tetrahedral rotor in an octahedral field. In addition, argon showed absorption due to pairs or higher aggregates of CH4 molecules.

The rotational spectrum of CD4 is much more highly perturbed. Detailed assignments to hindered rotational levels could not be made but the general features are in accord with King's model.

The frequencies of the CH4 and CD4 absorption bands increase steadily in going from xenon to krypton to argon. This can be accounted for by the decrease in the sizes of the cavities occupied, with corresponding larger repulsive interactions between the CH4 or CD4 and the host atoms.
Numerical Calculations by the Hellmann—Feynman Procedure
Authors: Salem L. , Alexander M.
Published: January 2005

Simple calculations of atomic forces and of force constants in homonuclear diatomics confirm the unreliability of the Hellmann—Feynman procedure for calculating molecular forces unless very accurate one-electron densities are used.

Electronic forces are extremely sensitive to polarization and to small density changes near atomic centers, so that in general they cannot be used alone to determine accurately a totally a priori one-electron density. They may, however, be useful in testing the features of the density obtained from a variational wavefunction.
Deuterium Kinetic Isotope Effect in the Hydrogen—Iodine Reaction
Authors: Sullivan John H.
Published: January 2005

Rates of reaction of deuterium with iodine were measured in the range 633°—800°K. The elementary reactions are: I2=2ID2+I2→2DI2DI→D2+I2I+D2→DI+DD+DI→D2+ID+I2→DI+II+DI→I2+D.The three independent constants, k1, k3, k4/k5, in (mole/cc)—1sec—1, are given by log(k1/T½) = 12.50— 40 790/4.575T, log(k3/T½) = 12.41–33 770/4.575T, and k4/k5 = 0.073. From a comparison of these with previously obtained rates in the H2 system, the kinetic isotope effects for Reactions [1] and [3] are: log(Hk1/Dk1)=0.225+150/4.575T,  log(Hk3/Dk3)=0.124+1020/4.575T.The results for [3] were fitted to absolute rate theory including tunneling (unsymmetrical Eckart barriers) to obtain permissible ranges of tunneling factors and vibrational frequencies of the linear IH2 complex. Internuclear distances in triangular IH2 complexes were found to be only slightly greater than re(HI) = 1.60 Å and re(H2) = 0.74 Å. Sato energy surfaces were calculated for a number of Sato parameters; tunneling for these surfaces was found to be negligible when computed from Eckart potentials fitted to the Sato surfaces. Agreement of theory with experiment could not be obtained for both the pre-exponential factor and the activation energy of I+H2 for any value of the Sato parameter.
Electronic Bases of Molecular Vibrations. I. General Theory for Diatomic Molecules
Authors: Phillipson Paul
Published: January 2005

The force constant of a diatomic molecule in a given electronic state is the second derivative with respect to the internuclear distance R of the molecular electronic energy, evaluated at the equilibrium distance Re. In principle it is determined by the electronic-charge distribution ψ*ψ, where ψ is the appropriate solution of the electronic-wave equation. Expressions for the force constant in terms of the electronic-charge distribution are derived which differ depending upon (1) what coordinate representation is used to describe the wavefunction, (2) whether the virial theorem or the Hellmann—Feynman theorem is employed to define the first energy derivative. Correspondingly, if the wavefunction is expressed in confocal elliptic coordinates, two different expressions for the force constant are obtained. These expressions give identical results for exact wavefunctions or for approximate wavefunctions which are constructed to satisfy the virial theorem for all R. If this condition is not satisfied, the two expressions will give, in general, different results. It is shown that if the Hellmann—Feynman theorem is used to define the first energy derivative, then the force constant assumes a particularly simple form which is suggestive of the force constant of a classical harmonic oscillator. The utility of the force constant expressions as probes to explore molecular electronic-charge distributions is discussed and related problems are suggested.
Motion of the H2O Molecule in Barium Chlorate Monohydrate
Authors: McGrath J. W. , Silvidi A. A.
Published: January 2005

When NMR is used for the study of the structures of molecules in solids the effects of molecular motion often must be considered. In the past those persons using proton magnetic resonance to study hydrates have not taken into account possible torsional vibration of the H2O molecule. The Das theory predicts a significant effect upon proton doublet splitting by this motion. This work reports study of the Das effect in Ba(ClO3)2·H2O as functions of crystal orientation and temperature. It was found that there is a change in doublet splitting that has the theoretical orientation dependence and the proper relative temperature dependence. However, the doublet splitting shows a zero-point effect that is much smaller than that predicted. The reduction in splitting is about 1 G when the temperature of the hydrate changes from —79° to 94°C. Possible reasons for the lack of agreement between theory and experiment at very low temperatures are discussed.
Jahn—Teller Effect and Valence-Bond Method
Authors: Birman Joseph L.
Published: January 2005

The static Jahn—Teller effect is examined, in molecules of octahedral and tetrahedral symmetry, in the simplest valence-bond framework. The electronic eigenstate of the molecule is here taken as a basis for a reducible representation of the molecular point group, instead of an irreducible representation as is conventional. Novel results include the appearance of odd modes of instability in Oh, and generally more complexity (independent matrix elements) vis à vis the usual approaches. The general features of these results are pointed out, as are suggestions for further work.
Unitary Operator Formalism of the Eigenvalue Problems
Authors: Chen Joseph C. Y.
Published: January 2005

Utilization of the parameters involved in the system under consideration leads to a unitary operator formalism for dealing with eigenvalue problems. The existence of a unitary linear operator which transfers a known function, being predetermined for a special choice of the parameter, to the general eigenfunction is demonstrated and its properties are discussed. The related hypervirial theorems for variational Hellmann—Feynman wavefunction are discussed. The scaling problem and virial theorem are treated in some detail by means of the unitary operator techniques.
Statistics of Irreversible Termination in Homogeneous Anionic Polymerization
Authors: Coleman Bernard D. , Gornick Fred , Weiss George
Published: January 2005

The effect of irreversible termination on the molecular weight distribution of a polymer prepared by homogeneous anionic polymerization is examined for cases in which the initiator is monofunctional and initiation is instantaneous. A general procedure for the calculation of the chain length distribution, as well as its moments, is presented. The procedure is then illustrated by an exact treatment of an isothermal batch polymerization for which we obtain the ratio rσ(t) of the weight to number average molecular weights as a function of the fraction of monomer consumed, the initial ratio σ of the terminator concentration to that of the initiator, the ratio ρ of the rate constant for termination to the rate constant for propagation, and the average degree of polymerization at time t, 〈n1〉t.

When σ is much less than unity, and the limiting number average D.P. 〈n1〉∞ is very large, rσ(t) approaches the following value as the reaction nears completion: rσ(∞) = 1+σρ(2+ρ)—1.
Smooth Curve Approximation to the Energy-Level Distribution for Quantum Harmonic Oscillators
Authors: Thiele Everett
Published: January 2005

It is pointed out that the distribution of energy levels for a set of quantum oscillators may be expressed exactly as the inverse Laplace transform of a function closely related to the quantum partition function. This observation leads quite easily to a smooth curve approximation for the energy-level distribution which can be expressed in terms of a generalized Bernoulli polynomial. A connection between this approximation and those given by Schlag and Sandsmark and by Whitten and Rabinovitch is established. A detailed comparison with Whitten and Rabinovitch's results is made for the special case of degenerate oscillators.
Analogies between Higher-Order Analytical and Numerical Perturbation—Iteration Methods
Authors: Sack R. A.
Published: January 2005

An analogy is pointed out between Hirschfelder's perturbation—iteration method for the determination of eigenvalues and eigenfunctions of linear differential operators and Roothaan's numerical procedure applicable to finite matrices. An analytical procedure analogous to Ostrowski's third-order matrix method is shown to lead to unmanageable differential equations.
Forces in Molecules. III. Analysis of an Empirical Potential Function
Authors: Clinton William L. , Frattali Sandra D.
Published: January 2005

The oscillating potential function reported in Part II of this series is analyzed in detail for all diatomic molecules for which sufficient experimental data exist. The potential function is calculated and compared to the experimental curve for several internuclear positions on either side of the equilibrium position. Criteria are given for determining the region of usefulness of this function. Some further discussion of the possible physical significance of the oscillating potential is also included.
Hyperfine Electron Spin Resonance Spectrum of the NH2 Free Radical
Authors: Sutcliffe Brian T.
Published: January 2005

The unrestricted Hartree—Fock method in the LCAO—MO approximation is used to calculate the coupling constants for nitrogen and hydrogen in the NH2 free radical. Both Slater and self-consistent field orbitals are used as basis functions. The effect of a spin annihilator after energy minimization, and the effects of ``freezing'' the nitrogen core are examined. The results are compared with those obtained in a recent configuration interaction calculation; and with the experimental results.
Effect of Radio-Frequency Fields on the Electrophoretic Mobility of Some Colloids
Authors: Wilkins David J. , Heller John H.
Published: January 2005

Four sizes of polystyrene latex, starch grains, and gelatin-coated polystyrene showed a voltage-dependent, frequency-specific response to radio-frequency fields as a function of particle size.

This response was a loss of negative surface charge irrespective of whether the initial surface charge was negative or positive.

The charge returned to original values linearly with time over a period of hours, but returned to original values in 1 min if exposed to another frequency.

At high concentrations of colloid (mean interparticle distance greater than 20 diam) no change in surface charge was apparent after exposure to an rf field. But dilution of this concentrated colloid without further exposure to rf reduced the surface charge to the value which it would have had if the diluted material had been exposed to rf.

All these phenomena occurred irrespective of whether the colloids were in distilled water or in 10—3 M NaCl.
Chemical Effects of Isomeric Transitions: Separation of the Isomers of Te127, Te129, and Te121
Authors: Hahn Richard L.
Published: January 2005

The problem of the chemical separation of radioactive tellurium isomers has been reinvestigated. The separation efficiencies obtained with end-window β-particle detectors for Te127 and Te129 are significantly less than unity and are in agreement with the values determined by Williams. It is demonstrated, however, that these values are not proper in that they have not been corrected for differences in detection efficiencies for the different β particles which were observed. Use of γ-ray spectrometry has overcome this difficulty; measurement of the relative rate of growth of an individual γ ray, from a sample in which the equilibrium between metastable- and ground-state isomers has been disturbed by the chemical separation, determines the percent of isomer separation, independent of detection efficiency. The separation efficiencies for Te127 and Te121 were found to 0.984±0.022 and 1.0±∼0.05, respectively. These results also were used in support of the concept that the chemical properties of the unstable Te species formed in internal conversion are essentially independent of the details of the nuclear decay, and are the same for all Te nuclides which decay via highly converted isomeric transitions. Application of these results to the study of the decay of Te129 is then discussed. The apparent separation factors determined for the 0.475-, 1.12-, and 0.027-MeV γ rays in Te129 were, respectively, 0.952±0.007, 0.863±0.020, and 0.254±0.005. These values were used to obtain relative γ-ray transition probabilities in Te129 through an analysis of the dependence of the isomer separation process upon nuclear decay parameters.
Infrared Spectra of HF—DF Mixed Crystals and the Structure of Hydrogen Fluoride
Authors: Sastri M. L. N. , Hornig D. F.
Published: January 2005

The infrared spectra of HF—DF mixed crystals have been studied throughout the composition range. Unlike HF, the spectrum of pure DF shows only the two peaks in the stretching region which are characteristic of the zigzag chain structure found by x-ray studies for HF and spectroscopically for HCl and HBr. The spectrum of pure HF shows the anomalous features previously reported. From the mixed crystal spectra it is clear that there is only one kind of site and one kind of strongly interacting pair in either HF or DF. A resolved peak due to triplets of HF (in DF) and of DF (in HF) has been observed. It is concluded that the extra peaks in pure HF probably arise from lattice combinations; in any case all of the major features of the spectra are accounted for by the zigzag chain structure of symmetry D2h16-Pmnb. It has not yet been possible to interpret the lattice spectrum in detail.
Proton Spin—Spin Coupling Constants from the NMR Spectra of Paramagnetic Molecules
Authors: Eaton D. R. , Josey A. D. , Phillips W. D. , Benson R. E.
Published: January 2005

``Chemical shifts'' for protons in the paramagnetic Ni II aminotroponeimineates are up to 250 times greater than for shifts of analogous protons in the diamagnetic chelates or ligands. These increased shifts are attributed to isotropic hyperfine contact interactions between protons and pπ spin densities transferred from Ni II to aminotroponeimine ligand as the result of pπ—dπ bonding. Widths of the nuclear resonances for these chelates in solution are sufficiently narrow that in many cases spin—spin (I·I) couplings can be resolved. The large separations between the different resonances lead to simple first-order spectra from which the spin—spin coupling constants can be obtained directly. Proton coupling constants for a number of simple conjugated groups obtained in this way are reported and compared with values for analogous diamagnetic compounds. Close agreement is found. Proton coupling constants have also been obtained for the first time for a number of more complex groups which give rise to prohibitively complicated spectra in diamagnetic compounds. For a number of olefinic systems the coupling constants for cis protons are found to correlate with the C=C bond length.
Polarized Absorption Spectra of Purines and Pyrimidines
Authors: Stewart Robert F. , Davidson Norman
Published: January 2005

Polarized absorption spectra in the molecular planes for thin sections (0.1 μ and up) of single crystals of 1-methylthymine, 9-methyladenine, and their 1:1 hydrogen-bonded complex (the AT dimer) have been obtained. For 1-methylthymine, the first absorption band (λmax≈275 mμ) is polarized close to the N1–C4 axis, and the second uv band (λmax<230 mμ) is polarized approximately perpendicular to the first. For 9-methyladenine, the crystal structure is not known but the data for the AT dimer can be interpreted by assuming that the intense long-wavelength band [λmax≈275 is short-axis (C6–C5) polarized]. There is a weak band with λmax≈255 which is then long-axis polarized, and probably the second strong band (λmax<230) is also long-axis polarized. All of the crystal spectra, and especially the AT dimer, are hypochromic with respect to the solution spectra. The 9-methyladenine spectrum is markedly red shifted in the crystals. The intensity changes and spectra shifts probably cannot be explained by a dipole—dipole exciton interaction. The spectrum of the AT dimer perpendicular to the molecular planes sets in at about 300 mμ and is still rising at 230 mμ; it is attributed to n—π* transitions.
Dissociation Energies of Some Metal Sulfides
Authors: Marquart J. R. , Berkowitz J.
Published: January 2005

The dissociation energies (or upper limits to D0) of the following molecules have been deduced from a mass-spectrometric study: D0(CaS)=79.5 kcal/mole, D0(SrS)=80 kcal/mole, D0(FeS)≤77 kcal/mole, D0(ZnS)≤50 kcal/mole, D0(CdS)≤47 kcal/mole, D0(HgS)≤50 kcal/mole.
Monte Carlo Calculations. III. A General Study of Bimolecular Exchange Reactions
Authors: Blais Normand C. , Bunker Don L.
Published: January 2005

About 10 000 planar trajectories were computed for the reaction A+BC→AB+C. Principal variables were the reactant masses, the type of interaction potential, and the exothermicity. The activation energy was assumed negligible. The results consist of distributions of product emission angle and vibrational and rotational energy.

For the simplified interaction potentials used, the following generalizations hold: a normal reaction is one in which AB is most likely to recoil backward along the approach line of A; the energy of reaction is predominantly converted to internal excitation of the product AB; and the final rotation of AB absorbs as large a fraction of the initial orbital angular momentum as is consistent with the reaction energy. If the moment of inertia of AB is too small to allow this fraction to be close to unity, unusual distributions of emission angle and rotational excitation occur. Independently, lowered values of the internal energy of AB are observed if A is much less massive than either B or C, or if the interaction potential is not of the type involving much reactant attraction and little product repulsion.

Tentative mechanical explanations of these phenomena are presented.
Self-Consistent-Field Wavefunctions for the N3— and NO2+ Molecules
Authors: Clementi Enrico , McLean A. D.
Published: January 2005

The self-consistent field (SCF) wavefunctions for the N3— and NO2+ molecules are reported. The basis set of Slater-type orbitals (STO's) includes 3dπ and 3dσ STO's, to account for polarization in the bonds. A gain over a previous computation of about 5 eV was obtained in the total energy despite the limited number of functions in the basis set.
Model for OH-Radical Stabilization in Ice at 77°K under γ Irradiation
Authors: Siegel Seymour
Published: January 2005

An analytical equation is derived for the stabilization of OH radicals at 77°K as a function of total irradiation dosage. The derivation is based on a purely phenomenological model that invokes the concept of a reactive volume in which the H+OH→H2O reaction has a probability greater than zero; outside this volume the probability is identically zero. The theoretical curve and the experimental results agree very well.
Calculation of the Electron Spin Resonance Line Shape of Randomly Oriented Molecules in a Triplet State. I. The Δm=2 Transition with a Constant Linewidth
Authors: Kottis Philémon , Lefebvre Roland
Published: January 2005

The electron spin resonance line shape for the Δm=2 transition of randomly oriented aromatic molecules in a triplet state is analyzed. This is an extension of the treatment of van der Waals and de Groot to molecules having less than ternary symmetry. In the present paper the spectrum of a molecule is approximated by a Gaussian function of constant width and the electron g tensor is assumed to be isotropic. The various stages of the calculation have been fitted into a computer program, using as input data the principal values of the electron spin-spin coupling tensor. The calculations show that a characteristic structure may be present in the spectrum. The experimental spectra of naphthalene and its deuterated homologue present in effect enough of this structure to make it possible to determine the absolute values of the two constants characterizing the electron spin—spin interaction.
Infrared Spectra of Metal Chelate Compounds. IX. A Normal Coordinate Analysis of Dithiocarbamato Complexes
Authors: Nakamoto Kazuo , Fujita Junnosuke , Condrate Robert A. , Morimoto Yukiyoshi
Published: January 2005

The infrared spectra of dithiocarbamato and N-alkyldithiocarbamato complexes with various metals have been obtained in the range between 4000 and 280 cm—1. The spectra of their deuterated forms have also been obtained to confirm the band assignments. A normal-coordinate analysis has been carried out for the 1:1 (metal/ligand) model of the dithiocarbamato PtII complex. The results indicate that the Pt–S stretching bands are at 375 and 288 cm—1 and the corresponding Pt–S stretching force constant is 2.1×105 dyn/cm. The effects of changing the metal and of alkyl substitution on the electronic structure of these compounds have been inferred from the infrared spectra.