bluuebunny/crossref_metadata_2025 huggingface dataset:
Viscosity of He–Ar and He–Kr Binary Gaseous Mixtures in the Temperature Range 25–720°C
Authors: Kalelkar A. S. , Kestin J.
Published: February 2004

Measurements were made of the viscosity of helium, argon, krypton, and the mixture pairs helium–argon and helium–krypton to elevated temperature. The viscosity of the pure gases was measured to a temperature of about 850°C, whereas that of the mixtures was measured to 720°C. The instrument used was that of an oscillating-disk type, and absolute measurements were obtained. The data on the pure gases showed good agreement with previous work on oscillating viscometers but did not agree well with the older capillary-flow measurements. It is contended that the present results enjoy a higher confidence level. The pure-gas results were used to find optimum force parameters for the interaction potential. It was found that argon and krypton are best represented by the conventional Lennard-Jones (6–12) potential, but helium is best represented by a (6–9.5) potential model. Due to the extremely shallow depth of the potential well for helium, the present viscosity data are inadequate to yield meaningful values for the force parameters for it. Consequently, force parameters derived from measured binary diffusion coefficients were used to test proposed combination rules. The combination rules were found to be moderately successful. The viscosity data were then used to calculate diffusion coefficients of the mixtures. These values were in good agreement with reliable correlations referred to in the paper. The viscosity of the pure components as well as that of the mixtures was used to generate skeleton tables for thermal conductivity; the interpolation scheme for them is described in the paper. In cases when these values can be compared with direct measurements, the agreement is good.
Ion–Polar-Molecule Reactions: Energy Dependency of Hydrogen Atom and Ion Transfer in the Methanol–Acetaldehyde System
Authors: Leger L. J. , Meisels G. G. , Tiernan T. O.
Published: February 2004

A tandem mass spectrometer has been employed to investigate hydrogen atom, hydrogen ion, and charge transfer in collisions involving specifically deuterium-labeled methanol and acetaldehyde and their molecular ions at energies between 1 and 7 eV (laboratory system). At the lowest incident ion energies, hydrium transfer is preferred from the electronegative group, while randomness is approached at higher energies. Ion transfer is the most important process at all energies, and transfer of the hydrogen ion from the electronegative group is always favored. The nonrandomization of equivalent atoms in a possible complex suggests that the ion retains its identity in the reaction. Both the atom and the ion transfer show a marked isotope effect. These results are interpreted by charge localization in the reactant ion and a direct mechanism in which long-range forces are important.
Evolution of Reduced Distribution Functions. IV. Momentum Moments of the One-Body Function
Authors: Holmes Curtis F. , Mortimer Robert G.
Published: February 2004

The solution to a Fourier–Laplace transformed kinetic equation is applied numerically to the study of the relaxation to equilibrium of a system of hard spheres. Two different initial distribution functions are considered, and their evolution is studied by computing the time dependence of the first few momentum moments, using a numerical Laplace transform inversion procedure. Physically meaningful results are obtained in for densities less than about 15% of closest packing, where a fast induction period and a slower exponential relaxation are found.
Evolution of Reduced Distribution Functions. V. Binary Diffusion in a Hard-Sphere Fluid
Authors: Holmes Curtis F. , Mortimer Robert G.
Published: February 2004

The solution to a kinetic equation obtained by truncating a linearized BBGKY hierarchy at the lowest level is applied to diffusion in a two-component hard-sphere fluid. Laplace transforms of the force and flux expressions are numerically inverted and compared to yield the binary diffusion constant. The analysis is restricted to low densities, where the expressions predict essentially correct macroscopic behavior, although the calculated diffusion constants are uniformly about 25% of the Enskog values.
Light Scattering from Optically Active Fluids
Authors: Blum L. , Frisch H. L.
Published: February 2004

A rigorous theory for the light scattered from a solution of an optically active species is presented. The theory is based on the quantum-mechanical time displaced correlation function for the suceptibility tensors. This formalism leads to the correct form of the Kronig–Kramers relations. Otherwise, the procedure follows the usual theory of light scattered from inactive solutions. The result shows that the parameters usually associated with the optical rotatory power and the ellipticity are linear combinations of two rotational invariants of the fourth-rank tensor formed by the direct product of the dielectric polarizability tensor and the pseudotensor that gives the optical activity. Only for isotropic molecules do we recover the classical result. The depolarization of the light (or ellipticity) is due both to the dielectric polarizability and to the optical activity pseudotensor. If the scattering experiment is done at an angle different from zero, then information about the anisotropy of the molecular susceptibility tensor be obtained. Also, when the system is opalescent, it could be more convenient to look at the scattered light instead of the “transmitted” one.
Level Crossing and Double Resonance on the A 1π State of CS
Authors: Silvers Stuart J. , Bergeman Thomas H. , Klemperer William
Published: February 2004

Using the coincident atomic spectral line MnII 2576.1 to pump the R(7) transition of the 0–0 band, level crossing and double resonance are observed in the 1Π state of carbon monosulfide. From the Hanle effect a lifetime value of 2.0 ± 0.4 × 10−7 sec is obtained. The analogous Stark level crossing effect and the Stark–Zeeman recrossing effect give estimates of the dipole moment μ and lambda doubling δ. With an rf search aided by these estimates, optical-rf double resonance provides more accurate values: μ8 = 0.68 ± 0.01 D; δ8 = 1099.4 ± 0.3 MHz for the J = 8 level. Considering the effect of nearby perturbing states, it is estimated that μΠ = μ8 ± 0.08 D. A derivation of signal intensity for the double resonance experiment is used to obtain the rf power requirements and criteria for selecting the optimum polarization.
Viscosities of Solutions of Potassium in Liquid Ammonia and Deuteroammonia
Authors: Hutchison Clyde A. , O'Reilly Donald E.
Published: February 2004

The viscosities of solutions of potassium in liquid ammonia and deuteroammonia have been measured with an Ostwald viscosimeter at − 33.6, 0.0, and + 20.0°C over a concentration range from zero to approximately 1.5 mole liter−1. The methods of measurement and the experimental results are given. The viscosities η of the pure liquids, measured in centipoise, are least-squares fitted by the relations logeη = −4.677 +1.577/RT for ammonia and logeη=−4.676+1.670/RT for deuteroammonia, in which R is the gas constant and T is the Kelvin temperature. (The standard deviations are given in parentheses.) The viscosities of the solutions have been discussed previously.
Electron Excitation Cross Sections for Some NV Multiplets
Authors: Davis J. , Morin S.
Published: February 2004

We present calculations of the electron excitation cross sections for multiplets 2, 3, 4, and 5 of NV over the energy range 4–100 eV. The cross sections were estimated by utilizing a weak coupling semiclassical impact theory.
Dioxygen Difluoride: Infrared Spectrum, Vibrational Potential Function, and Bonding
Authors: Loos K. R. , Goetschel C. T. , Campanile V. A.
Published: February 2004

The infrared spectrum of solid O2F2, produced by radiolysis of a mixture of liquid O2 and F2, has been obtained at 77°K. With the help of isotopic labeling, all fundamental vibrations have been located and a normal coordinate calculation carried out to aid in their assignment. These results, together with extended Hückel molecular orbital calculations, show that the O–O bond in O2F2 has considerable double bond character, resembling O2 more than it does H2O2, and having a significant barrier to internal rotation. Evidence indicating the existence of considerable delocalization of electronic density has been noted; the bonding, although similar to the O2F radical in some respects, is more complex with considerably more participation of the fluorine p electrons in the bonding orbitals.
Infrared Intensities of the Lattice Modes of Solid Carbon Dioxide
Authors: Brown Kenneth G. , King W. T.
Published: February 2004

The integrated infrared intensities of the two translational lattice modes of solid CO2 at 114 and 68 cm−1 were measured using the Beer–Lambert law and found to be 40 ± 3 and 26 ± 4 darks, respectively. Calculated intensities, determined by considering quadrupole–induced dipole transitions, have been reported and are compared with these results. It is found that even though the calculated intensities differ significantly from their experimental values, their sum is in good agreement with the sum of the intensities measured here.
Pulse Radiolysis Studies. XVII. Reaction Kinetics of Molecular Cations of Aromatic Compounds in Dichloroethane Solution
Authors: Shank Norman E. , Dorfman Leon M.
Published: February 2004

Fast reaction studies of the kinetics of molecular cations of aromatic molecules, formed by irradiation of the aromatic compounds in 1,2-dichloroethane solution, have provided quantitative information about the modes of formation and of decay of these molecule ions. Specific reaction rates have been determined for the electron transfer from a neutral aromatic molecule to an aromatic cation for three donor–acceptor pairs. The rate of formation of the aromatic cation, thought to be a charge transfer from the aromatic molecule to the solvent cation, is so high as to suggest that migration of the solvent cation is not a process of molecular diffusion, but involves an electron jump process in the solvent. The decay of the aromatic cation appears to be due largely to recombination with the counterion. Absolute rate constants for electron transfer between the aromatic pairs studied are at or near diffusion controlled, with values ranging from 5.1 × 109 to 9.9 × 109M−1·sec−1 at 25°C.
Cohesive Energy and Compressibility of Body-Centered Cubic Sodium
Authors: Brown J. S.
Published: February 2004

The cohesive energy and compressibility of metallic sodium in the body-centered cubic phase are calculated using a Hellmann-type model potential for the ion–electron interaction. The calculation is similar to one recently proposed by Saxena et al. but differs in the determination of the equilibrium spacing by minimizing the total energy per electron. The resulting compressibility and cohesive energy are compared against the results of Saxena et al.
Electron Scattering by H2 with and without Vibrational Excitation. I. Quantum-Mechanical Theory
Authors: Truhlar D. G. , Rice J. K.
Published: February 2004

A quantum-mechanical model of elastic and inelastic electron scattering by a homonuclear diatomic molecule in its electronic ground state is presented. The model should be especially useful in the intermediate energy range (about 10–100 eV). It is applied to the calculation of differential and integral cross sections for elastic scattering and for excitation of the first, second, and third vibrational states of molecular hydrogen for impact energies in the 1–912-eV range. The theory assumes plane waves for the scattering electron wavefunctions; it includes electron exchange effects by use of the Born–Ochkur–Rudge approximation, and it incorporates an electron–H2 interaction potential containing a semiempirical polarization potential and a static potential which includes a semiempirical quadrupole interaction. These potentials are adjusted to agree with available ab initio calculations of these potentials. The effects on the cross sections of electron exchange and the scattering by the various potential terms are examined to elucidate which aspects are important for a detailed mechanism and for contrast with previous incomplete treatments. In particular, calculations using only the long-range interactions give results too small by a factor of 2 or more (when compared to the full calculation) for υ′ = 1 at E > 13 eV and for υ′ > 1 at all energies (υ′ is the vibrational quantum number of the molecule after the collision). The calculations of elastic scattering are compared with high-energy experimental differential cross sections and with theoretical and experimental low-energy cross sections. A formalism which treats the s and p scattering partial waves in the restricted distorted wave approximation while retaining the plane wave scattering approximation for all higher partial waves is also presented.
Electron Scattering by H2 with and without Vibrational Excitation. II. Experimental and Theoretical Study of Elastic Scattering
Authors: Trajmar S. , Truhlar D. G. , Rice J. K.
Published: February 2004

Elastic scattering of electrons by the hydrogen molecule has been studied. The differential elastic cross sections have been determined experimentally from 10° to 80° at seven impact energies ranging from 7 to 81.6 eV. The experimental methods for measuring the relative elastic scattering intensities, the transformation of these intensities into relative cross sections, and their normalization to the absolute scale are presented. The elastic differential and integral cross sections have also been calculated in this energy range by the quantum-mechanical method described in a previous article (I). A comparison is made between the experimental and the calculated cross sections and, whenever possible, with the results of other investigators. It is found that in the energy and angular ranges investigated here our polarized Born and polarized Born–Ochkur–Rudge approximations using the theoretically most justified potential gives better agreement with experiment than any previous calculation and that the inclusion of polarization is necessary to obtain accurate cross sections at low scattering angles.
Evaluation of Data on Cryoscopic and Ebullioscopic Measurements of Dissociation Constants of 1:1 Electrolytes
Authors: Rodgers R. S. , Mukherjee L. M.
Published: February 2004

Applicability of cryoscopic (and ebullioscopic) measurements of the dissociation constants of 1:1 electrolytes has been examined with a view to ascertaining the errors that may arise from the neglect of ionic activity coefficients. In the calculations presented, a finite uncertainly of 10−5 °C has been assumed for the temperature measurements. The smallest pK values determinable by freezing point depression (and boiling point elevation) technique, for which the activity correction amounts to less than 0.05 and 0.10 pK units, are tabulated for four solvents, viz., water, nitrobenzene, ethylenediamine, and acetic acid.
Ornstein–Zernike Relation and Percus–Yevick Approximation for Fluid Mixtures
Authors: Baxter R. J.
Published: February 2004

A transformation of the Ornstein–Zernike relation for fluid mixtures is derived which involves the direct and indirect correlation functions only over the ranges within which the former are nonzero. Also, two closed expressions for the compressibility pressure in the Percus–Yevick (PY) approximation for mixtures are presented. The analytic solution of the PY approximation for mixtures of hard spheres follows immediately, and it is expected that the results should be of use in numerical calculations for systems with short-range forces, where the direct correlation functions normally tend rapidly to zero with increasing particle separation.
Covalency Parameters in MnSe and MnSe2
Authors: Jacobson A. J. , Fender B. E. F.
Published: February 2004

Covalency parameters have been deduced from neutron diffraction measurements on MnSe, Mg0.1Mn0.9Se, and MnSe2. The cubic phase of MnSe is contaminated at low temperatures with a hexagonal phase, and this leads to deduced covalency parameters for Mn2+(Aσ2 + 2Aπ2 + As2 = 6.2 ± 1.9%) of relatively low accuracy. More accurate values (Aσ2 + 2Aπ2 + As2 = 7.5 ± 0.3%) have been obtained from the magnesium-doped compound which remains cubic down to 4.2°K. The measured covalency parameter sum for MnSe2 is 7.8 ± 1.1% indicating that the Se–Se bond has little effect on the total covalency. Covalency in the manganese selenides is seen to be similar to that in α-MnS(Aσ2 + 2Aπ2 + As2 = 7.0%).
Pressure Broadening of the Ammonia Inversion Lines and of the OCS Rotational Lines
Authors: Cattani M.
Published: February 2004

We improve Anderson, Tsao, and Curnutte's theory of pressure broadening by taking the thermal average of the molecular velocities. Widths of rotational lines of the OCS and of inversion lines of the ammonia are calculated with the original and with the improved theory. The improvement of the theory turns out to be quite important in both cases.
Molecular Dynamics of Photodissociation: Quasidiatomic Model for ICN
Authors: Holdy Kalman E. , Klotz Lynn C. , Wilson Kent R.
Published: February 2004

A model for the photodissociation of ICN in its lowest continuum is developed and is used to predict the partitioning of available energy between translational, rotational, and vibrational energies of the recoiling fragments. The model is based on three major assumptions: (i) that only one upper electronic state is involved, (ii) that light absorption affects only the breaking C–I bond, thus allowing the upper-state potential surface to be calculated quasidiatomically from spectral and thermodynamic data, and (iii) that the mechanics of the “half-collision” of the recoiling fragments on this potential surface may be treated as classical to predict the average partitioning between translational, rotational, and vibrational energies, and by a classical-energy forced quantum oscillator approximation to predict the partitioning between vibrational states. The model predicts that most of the available energy will go into translation, which is consistent with flash photolysis studies and with crude measurements of the photofragment spectrum.
Effects of N-Atom Concentration, Pressure, and Carrier Composition on Some First Positive Band Intensities in the Yellow Nitrogen Afterglow
Authors: Brown Robert L.
Published: February 2004

Absolute intensities of seven N2 1st positive bands with υ′ = 6–12 were measured as a function of carrier pressure, carrier composition, and N-atom concentration in the range 4.5–0.06 torr. For an Ar carrier large pressure-dependent shifts in the B 3Πg vibrational distribution to higher levels were observed below 4 torr; similar but much smaller shifts were also found for N2 and He carriers. With Ar, reducing the N-atom concentration shifted the vibrational distribution to lower levels. Changes in carrier composition produced large pressure dependent changes in the absolute and relative band intensities. An attempt was made to fit the results to a model involving vibrational relaxation and electronic quenching in B 3Π. While qualitatively successful, this model could not account quantitatively for the observed relative intensity changes over the whole pressure range for which data are available and, in addition, implied physically unreasonable vibrational relaxation rates. It is suggested that the observed changes in the B 3Πg vibrational distribution below 4 torr may arise from vibrational relaxation in some precursor state.
Triplet State EPR of Substituted Naphthalenes
Authors: Rodgers Edward G. , Vincent James S.
Published: February 2004

Paramagnetic resonance absorption has been observed in single-crystal solid solutions of durene and 2-fluoronaphthalene and 2-methylnaphthalene when irradiated at 80°K with uv light. The fine structure observed at 35 GHz is very similar to that of naphthalene except that the in-plane x and y axes are rotated by 7.3° ± 0.5° and 8° ± 1° for 2-fluoronaphthalene and 2-methylnaphthalene, respectively. Analysis of the hyperfine spectra suggests that the molecules may not be oriented exactly along the durene axes but rotated slightly in the plane of the molecules.
Exchange Reaction of 18O Atoms with CO2 and with SO2 in Shock Waves
Authors: Clark T. C. , Garnett S. H. , Kistiakowsky G. B.
Published: February 2004

A shock tube coupled to a time-of-flight mass spectrometer has been used to study the reactions 18O+S16O2→S16O18O+16O (1600°K < T < 2100°K) and 18O+C16O2→C16O18O+16O (2900°K < T < 3425°K) in reflected shocks of mixtures of 18O2, N2O, SO2, and of 18O2 and CO2, highly diluted with neon. The best values of the rate coefficients were k1 = 3.1 ± 2.1 × 10−12cm3/particle·sec at 2000°K, and k2 = 2.3 ± 1.2 × 10−12cm3/particle·sec at 3000°K. These rate coefficients, and also those deduced in an earlier study in this laboratory for the reactions 18O+C16O→C18O+16O and 18O+16O2→16O18O+16O, are combined with the corresponding low-temperature data of other workers to yield rate parameters which describe each reaction over a wide temperature range.
Calculation of Ground State Vibrational Structure and Phonons of the Isotopic Benzene Crystals
Authors: Bernstein Elliot R.
Published: February 2004

Using the “giant molecule” technique and existing intermolecular potentials, the normal modes, phonon and exciton structure, site shifts, site splitting, and orientational effect for the isotopic benzene crystals are calculated. The agreement between the calculations and the experimental observations is good for an H–H, C–H, and C–C potential set independently obtained by Williams from thermodynamic and structural properties of aromatic crystals. The calculation presented here serves to unify not only the thermodynamic and spectral properties, but also the diverse spectral properties themselves. This calculation emphasizes that all atom–atom interactions, not just H–H interactions, must be considered for best agreement between calculated and observed spectral data. This conclusion was also reached by Williams with respect to the thermodynamic and structural data. A discussion of the potentials, their form, and their relation to standard exciton theory integrals is presented. Future improvements in such calculations must be directed, not toward more extensive parametric data fitting of the atom–atom pair potential, but toward more general potential functions that include anharmonicities and multicenter terms. The use of actual site force constants rather than free molecule force constants is also indicated.
Semiempirical Calculations of Some 2H and 14N Nuclear Quadrupole Coupling Constants
Authors: White W. D. , Drago Russell S.
Published: February 2004

A parameterized LCAO method for the calculation of nuclear field gradients is described. The principal difference between this and other theories concerns the treatment of the two-center contribution to the field gradient. In our method, the two-center terms are included as parameters proportional to their respective nuclear terms. Only three parameters are necessary, one for triple and double bonds, one for single bonds, and one for a bond to hydrogen. The method developed herein not only successfully reproduces 14N field gradients, but also 2H field gradients, heretofore not possible with other semiempirical methods.
Calculation of the Intramolecular Contribution to the Entropy of Fusion in Crystalline Polymers
Authors: Tonelli Alan E.
Published: February 2004

The intramolecular contribution to the entropy of fusion of crystalline polymers is treated through calculation of the change in configurational entropy on melting of a single isolated polymer chain. Perfect backbone conformational order is assumed in the crystalline polymer chain, and the configurational entropy of the molten amorphous polymer chain is obtained through calculations based on the rotational isomeric state model of polymers. Comparison of the calculated change in intramolecular configurational entropy on melting with experimental results is achieved by assuming the entropy of fusion consists of two independent contributions: the entropy of fusion due to volume expansion (intermolecular contribution), and the entropy of fusion at constant volume, which is identified as the change in intramolecular configurational entropy. Several linear polymers are treated in the above fashion. The agreement between the calculated and experimentally determined intramolecular contribution to the entropy of fusion is generally satisfactory, and several conclusions are drawn based on this agreement.
Correlation Effects on ππ* Transition Energies in the Series of Linear Polyenes. I. π Correlation Effects in the Minimal Basis Set
Authors: Denis Armelle , Malrieu J. P.
Published: February 2004

The effect of configuration interaction on the transition energies is developed according to the Rayleigh–Schrödinger perturbation theory. The second-order correction to the ππ* transition energies is separable into three parts: (a) a pure π effect, (b) a σπ effect—both in a fixed minimal basis set, and (c) effects which include the change and the extension of the minimal basis set (mainly dynamical correlation effects). Here the pure π effects are studied as functions of the dimension of the conjugated system. The effect of the di- and triexcited configurations is as important as the effect of the singly excited configurations. The highest singly excited configurations do not play a significant role. The di- and triexcited configurations have a rather small influence on the spacing between the two lowest singlet excited states, while they change significantly the singlet–triplet splitting. The results of various methods for the calculation of transition energies are compared for different sets of parameters. The use of CI limited to singly excited states is especially discussed.
Correlation Effects on ππ* Transition Energies in the Series of Linear Polyenes. II. σπ Correlation Effects in the Minimal Basis Set
Authors: Denis Armelle , Malrieu J. P.
Published: February 2004

The σπ interaction effect on the ππ* transition energies is calculated in a second-order perturbation expansion of transition energies, using π delocalized and σ localized orbitals. The effect of the σσ* monoexcited configurations decreases when the dimension increases, but the effect of higher excitations increases simultaneously, and the final σπ second-order effect is almost constant for the first band of the series of linear polyenes. The σπ interaction changes the spacing between the ππ* singlet excited states in small systems. Three π parametrizations are compared: The σπ interaction is not sufficient to give a reasonable transition energy when one uses the classical atomic orbitals with ζ = 1.625, but when one starts from the atomic orbitals optimized by Silverstone and Joy, the total second-order effect in the minimal basis set gives a final transition energy only 1 eV above the experimental one.
Interaction Potential between Li and HF
Authors: Lester W. A. , Krauss M.
Published: February 2004

The interaction potential between Li and HF has been determined in the Hartree–Fock approximation. An expression for the interaction potential has been determined in the case of fixed internuclear distance of HF in a form suitable for scattering calculations. The results are tabulated as radial coefficients for the intermolecular potential expressed as V(r, θ) = Σlυl(r)Pl(cosθ). At long range, the Hartree–Fock calculation determines the induction energy of a spherical atom Li interacting with a dipolar molecule HF. For the approach of the Li atom toward the F atom, there is a minimum in the energy for a Li to HF center-of-mass distance of 4 a.u. Most of the hemisphere on the F side of the surface ultimately leads to reaction. On the other hand, the spherically symmetric component of the intermolecular potential, υ0(r), has a minimum at about 9 a.u. which is related to the potential well deduced from glory scatter data.
Ab Initio SCF MO Study of the Interaction of Lithium with Ammonia
Authors: Nicely Vincent A. , Dye James L.
Published: February 2004

An ab initio molecular orbital study of the stability and electronic structure of lithium–ammonia complexes was made. A complex of lithium with one ammonia molecule is predicted to be stable by 20 kcal/mole relative to a free lithium atom and a free ammonia molecule. The bonding in the complex is primarily through sharing of the lone pair of electrons on ammonia between the ammonia molecule and the lithium atom. The unpaired electron orbital is rearranged upon formation of the complex so that it has very low density in the region of the ammonia with the exception of a sharp peak in density near the nitrogen nucleus. The complex with two ammonia molecules is nearly isoenergetic with the one ammonia complex plus an ammonia molecule. Addition of a second ammonia causes an increase in the preferred lithium–nitrogen distance and an increase in the occupancy of the nitrogen orbitals by the unpaired electron. Ammonia appears repulsive to the unpaired electron in the diammonia complex, also. The implications of these results for models of the monomer in metal–ammonia solutions are discussed.
Refinement of a Valence Force Field for Polytetrafluoroethylene by a Damped Least-Squares Method
Authors: Boerio F. J. , Koenig J. L.
Published: February 2004

Band assignments in polytetrafluoroethylene (PTFE) are revised based on new spectral results. The method of damped least squares is used to calculate a 19-parameter valence force field for PTFE. Comparisons between calculated and observed optically active fundamentals are made and potential-energy distributions are presented. Dispersion curves and frequency distributions are also presented and compared to those derived from inelastic neutron scattering results.
Molecular Collisions. XII. Generalized Phase Shifts
Authors: Curtiss C. F.
Published: February 2004

The previous development of the theory of rotational excitation in collisions of diatomic molecules is transformed to obtain equations for a set of generalized phase shifts. The resulting equations are in a form which may be interpreted in terms of trajectories and interference effects. Approximate equations valid in the semiclassical limit are obtained. A further approximation leads to the previously developed sudden approximation.
Ratio of Disproportionation to Combination of N2H3 Radicals
Authors: Stief L. J.
Published: February 2004

The hydrazyl radical (N2H3) has been generated in the absence of direct decomposition of hydrazine by the reaction H+H2H4→N2+H2H3. Photolysis of CH3SH at 2537 Å was used as a source of atomic hydrogen. Using various mixtures of 28N2H4 and 30N2H4, the distribution of isotopic nitrogens formed in this system leads to (29N2)2 / (28N2)(30N2) = 1.3 × 10−2. Identifying radomization of isotopic nitrogen with combination N2H3 and nonradomization with disproportionation of N2H3, the ratio of disproportionation to combination is approximately 4. This is an unexpectedly large value, being nearly 30 times larger than that for the analogous hydrocarbon radical C2H5.
Self-Consistent Field Electron Distributions in Molecules with Second-Row Elements
Authors: Boyd Donald B.
Published: February 2004

Electron density maps are obtained for PN, P2, MgO, PO, PO−, PO2−, SO, SiH4, PH3, and H2S using SCF–LCAO–MO wavefunctions. Difference maps are employed to compare the molecular charge distributions with the constituent atomic densities. Quantitative dissimilarities are found to exist between near-minimum basis set SCF and near-Hartree–Fock total densities, but difference maps are similar provided the atomic wavefunctions employed are of the same accuracy as the molecular functions. Covalent and ionic charge distributions are contrasted; trends among the oxides and hydrides are noted. Addition of the heavy-atom 3d orbitals to minimum basis sets increases the electron density in the bonding regions. The optimum size of the 3d orbitals is discussed.
Vibrational Spectrum of Barium Azide Single Crystals
Authors: Iqbal Zafar , Brown Chris W. , Mitra S. S.
Published: February 2004

The infrared spectra of BaN6 single crystals have been measured from 33 to 4000 cm−1 and its laserexcited Raman spectrum from 30 to 2500 cm−1. The optic modes and the numerous side band structure on the fundamental absorptions have been assigned by factor group analysis. The spectral results confirm the presence of an asymmetric azide ion in the unit cell.
Classical Aspects of Energy Transfer in Molecular Systems
Authors: Kuhn Hans
Published: February 2004

The decay time of the luminescence of a molecule S in front of a metal mirror depends markedly on its distance from the mirror. This phenomenon is quantitatively explained by considering the radiation field of this dipole, given by Hertz classical equation. This field arrives at the molecule, after being reflected at the mirror, with a retardation of the order of 10−15 sec. The decay time of the luminescence depends on the phase shift produced by this retardation, and thus on the ratio of the distance of the oscillator from the mirror, and the wavelength of the emitted light. By measuring the distance dependence of the decay time of the luminescence this retardation effect can be studied. In quantum-mechanical terms the phenomenon can be described as being due to a stimulation or inhibition of the emission of the light quantum. In contrast to the known cases of stimulated emission, the stimulating field is the radiation field of the emitter quantum itself. The energy transfer from an excited molecule S to an acceptor A can be treated in a similar manner by considering the phenomenon as a retardation effect. In classical terms the field of S induces A to oscillate, and the induced field of A arriving at S slows down this oscillator. Simple equations are given for the energy transfer from an excited dipole or quadrupole, and for a row of many dipoles, oscillating in phase, to a weakly absorbing acceptor layer. The latter case is considered as a model for a J-aggregating dye and by comparison with experimental data conclusions concerning the size of a J aggregate are drawn.
Metastable Dissociation of the Doubly Charged Carbon Monoxide Ion
Authors: Newton Amos S. , Sciamanna A. F.
Published: February 2004

The metastable dissociation of CO2+ ions has been studied. The appearance potentials of CO2+ (M / q = 14) and the O+ and C+ daughter products were found equal at 41.5 ± 0.4 eV. The kinetic-energy release was found to be 5.75 ± 0.2 eV. The half-life was 20 + 10 or − 5 μsec, and no CO2+ ions of half-life longer than this were observed. It is concluded that the metastable dissociation of CO2+ proceeds via a tunneling mechanism consistent with previous suggestions in this regard.
Interaction of Atomic Oxygen with Various Surfaces
Authors: Riley James A. , Giese Clayton F.
Published: February 2004

A pulsed atomic-oxygen beam is used to investigate the interaction of atomic oxygen with various surfaces at a pressure of 10−7 torr. The probability that an atom after striking a surface will return to the gas phase as an atom is measured for Pyrex, stainless steel, Teflon, gold, and titanium and is found to lie between 45% and 60% for all of these materials at room temperature. This reflection probability β is strongly temperature dependent for metals, dropping below 10% at 450°C, but less so for Pyrex, dropping only to 33% at the same temperature. The atoms which are not reflected apparently stick to the surfaces. In particular there is no evidence that at 10−7 torr they recombine to form O2 or are emitted as parts of oxygen-containing molecules such as CO2 or N2O. Qualitative experiments indicate that recombination does take place at pressures near 1 torr.
Interpretation of Hydrogen Solutions in bcc Early Transition Metals
Authors: McQuillan A. D.
Published: February 2004

Marked departures from ideal thermodynamic behavior have been observed in dilute solutions of hydrogen in niobium and have been attributed to clustering of hydrogen atoms in the solutions. An attempt has been made in this paper to formulate a general physical picture of hydrogen solutions in the early transition metals and to show how this could give rise to the observed behavior in the niobium–hydrogen and other related hydrogen systems. Factors which are important in these systems are the very large number of interstices available to hydrogen in the body-centered cubic metal structure and the particular electronic structure of the early transition metals. A distinction has been drawn between dilute solutions in which dissolved hydrogen atoms may interact with each other by means of scattering of conduction electrons and more concentrated solutions in which the electronic structure of the metal is completely altered by the presence of a high concentration of hydrogen atoms in the metal. The transition from one type of behavior to the other would appear to occur in range 2–10 at.% hydrogen. The paper is largely concerned with effects in dilute solutions and with the conditions governing the possible existence of pairs of associated hydrogen atoms in them. A complete analysis of this problem in terms of many-body theory would appear, at the moment, to present considerable theoretical difficulty, and, therefore, a less rigorous model has been used.
Valence-Shell Ionization Potentials of Halomethanes by Photoelectron Spectroscopy. I CH3Cl, CH3Br, CH3I. Vibrational Frequencies and Vibronic Interaction in CH3Br+ and CH3Cl+
Authors: Ragle J. L. , Stenhouse I. A. , Frost D. C. , McDowell C. A.
Published: February 2004

Photoelectron spectra of methyl chloride, methyl bromide, and methyl iodide obtained with 584-Å radiation yield in each case four of the five valence-shell ionization potentials. Values of 11.29, 10.53, and 9.50 eV are obtained for the first ionization potentials, respectively, corresponding to ionization from halogen “lone-pair” orbitals. Resolved vibrational structure allows determination of frequencies of the corresponding normal vibrations of the positive ions in several cases. Relative intensities of vibrational components in the first ionization potential are dictated by vibronic interaction. Approximate values of the Jahn–Teller parameters D for ν4, ν5, ν6 in CH3Br+ may be obtained from these intensities. Small values of D (D ≤ 0.1) suffice to produce sizeable modifications of intensity for the intermediate spin–orbit splittings observed in these ions.
Shear Viscosity Measurements of Liquid Carbon Dioxide
Authors: Herreman W. , Grevendonk W. , De Bock A.
Published: February 2004

Measurements on the viscosity of liquid carbon dioxide as a function of temperature, pressure, and density are reported and discussed. The measurements are carried out over the entire liquid range at pressures up to 200 kgf/cm2. The viscosity coefficients have been evaluated by measuring the electrical characteristics of a torsionally vibrating quartz crystal immersed in the liquid. The obtained results have been used to test the Arrhenius equation lnη = A + B / T, the Doolittle free volume equation lnη = A′ + B′ρ / (ρ0 − ρ), and the Batschinski equation ηρ−1 = Cη + D.
Electronic Wavefunctions for Atoms. III. Partition of Degenerate Spaces and Ground State of C
Authors: Bunge Annik
Published: February 2004

The atomic configuration-interaction (CI) expansion is expressed in terms of constituents which are invariant under linear transformations of the radial one-electron basis. For open-shell states, the degenerate LS spaces are partitioned into maximal Hartree–Fock (HF) noninteracting spaces and minimal HF interacting spaces. This particular partition is shown to improve considerably the convergence of the atomic CI expansion, and it may be applied to molecular CI expansions in terms of symmetry orbitals. An exhaustive calculation of the ground state of C is carried out. A well-defined linear transformation of the radial one-electron basis is made in order to improve further the convergence of the CI series. The final 234-term CI expansion (formed from a determinantal space of dimension 4836) obtained with an optimized 7s6p4d3f basis, gives an energy E = −37.83378 a.u. (C), accounting for more than 93% of the correlation energy. The C wavefunction is believed to be expressed in its most rapidly convergent form. The advantages of the present approach to atomic CI calculations are discussed.
Valence Structure from X-Ray Diffraction Data: An L-Shell Projection Method
Authors: Stewart Robert F.
Published: February 2004

Generalized x-ray scattering factors, in a simplified form, have been applied to several organic molecular crystals. Atomic charge parameters for L-shell scattering factors have been determined from x-ray structure factors by the method of least squares. L-shell scattering factors have been computed for products of SCF AO's and of standard molecular STO's (Slater-type orbitals). Standard STO's are more satisfactory for point-charge analysis than are SCF AO's. Bias from several sets of thermal parameters is rather small and does not alter general conclusions on valence structure. The experimental x-ray charges are compared with Mulliken gross atomic populations from INDO and STO-3G calculations. Agreement with theory is good for the molecular crystals of s-triazine, cyanuric acid, and uracil. Within the point-charge approximation, the experimental x-ray dipole moment for uracil is 4.0 ± 1.3 D. The direction is at an angle 71° ± 12° from the N(1)–C(4) interatomic vector towards atom N(3).
Self-Consistent Group Calculations on Polyatomic Molecules. IV. Substituted Methanes
Authors: Klessinger Martin
Published: February 2004

The SCGF calculations are reported for the ground state of ethane, methylamine, methanol, and methyl fluoride. A minimal basis of contracted Gaussians was used and optimum hybridization was determined for each of the molecules by systematic variation of the hybridization parameters until the total electronic energy was a minimum. The failure of the SCGF calculations to reproduce rotational barrier heights and the dependence of the properties of the methyl group on the molecular environment are discussed in some detail.
Electronic Structure of Thymine
Authors: Snyder Lawrence C. , Shulman R. G. , Neumann David B.
Published: February 2004

The electronic structures of the ground and low-lying excited states of thymine and the anions 1-HT− and 3-HT−, derived by removing a proton from nitrogen atom N3 and N1, respectively, have been described by all-electron all-integral LCAO–SCF calculations using Gaussian basis functions. In accord with experiment, we find the carbonyl bonds weakened in the anions relative to thymine because of a decrease in their overlap charge densities. On the other hand, our calculations and interpretation of the observed optical and ESR spectra suggest that both for T and 1-HT− the lowest singlet and triplet π → π* states are very similar and localized in the region of the ethylenic bond of thymine.
Vibrational Relaxation and Its Competition with Radiationless Transitions in the B12u State of Benzene
Authors: Kemper H. F. , Stockburger M.
Published: February 2004

Vibrational relaxation in the B12u state of benzene has been studied. The molecules were excited by the mercury 2537-Å radiation or by electron impact in a low-pressure discharge. All information about vibrational relaxation was obtained from the vibrational structure of the optical emission spectra as a function of the vapor pressure or the pressure of a foreign gas. A model is suggested describing the entire relaxation mechanism by transitions between three vibronic levels of the B12u state. These levels have different vibrational properties. Radiationless transitions are assumed to occur at different rates from the three levels. This model is applied to intersystem crossing and a photochemical process, both competing with vibrational relaxation in the B12u state of benzene.
Optical Absorption of Co2+ in Zinc Acetate Dihydrate Single Crystal
Authors: Narayana P. A. , Venkateswarlu Putcha
Published: February 2004

The optical absorption spectrum of Co2+ doped in a single crystal of zinc acetate dihydrate has been studied under polarization. Some of the bands obtained have been found to show up in σ polarization only, while others show up in both σ and π polarizations. An analysis of the results obtained shows that the site symmetry of Co2+ in the crystal is trigonal (C3, C3v, or D3) and that the ground state of Co2+ is 4E. The cubic levels of Co2+ corresponding to octahedral coordination have been observed to be split in the expected manner under the lower site symmetry. The transitions of Co2+ in zinc acetate dihydrate have been found to be in general on the low-energy side compared to those in cobalt acetate tetrahydrate.
Long-Lived Collision Complexes in Molecular Beam Scattering Experiments
Authors: Ham David O. , Kinsey James L.
Published: February 2004

Evidence is reported for long-lived complexes formed in nonreactive collisions in crossed molecular beams of alkali metals and a number of compounds, most of them containing oxygen atoms. Experimental details and a description of the reduction of data into center-of-mass quantities are given. Differential scattering cross sections and distributions of final relative kinetic energy are deduced. A calculation using a statistical theory for one of the systems studied, K + SO2, is compared with the experimental results.
Raman Spectra of MoF6, TcF6, ReF6, UF6, SF6, SeF6, and TeF6 in the Vapor State
Authors: Claassen Howard H. , Goodman Gordon L. , Holloway John H. , Selig Henry
Published: February 2004

Raman spectra of MoF6, TcF6, ReF6, UF6, SF6, SeF6, and TeF6 have been observed for the gaseous state using laser excitation. Some assignments of fundamental frequencies have had to be revised from previously accepted values. The overtone 2ν6 was observed for all these gaseous hexafluorides and several other overtones were observed for some of the molecules. Considerable broadening of the eg and f2g fundamentals was observed for TcF6 and for ReF6. This broadening is attributed to dynamic Jahn–Teller coupling. The best currently available measured values of fundamental frequencies for all 15 hexafluoride molecules of known Oh symmetry are tabulated.
Vibrational Spectra and Potential Functions of Cyclohexane and Related Oxanes
Authors: Pickett Herbert M. , Strauss Herbert L.
Published: February 2004

The vibrational spectra of cyclohexane, s-trioxane, p-dioxane, m-dioxane, and tetrahydropyran and a number of their deuterated derivatives are re-examined. Particular attention is paid to the low-frequency modes. A number of low-frequency difference bands and some hot bands are observed and assigned. Complete normal-coordinate analyses are carried out for all the molecules. It is concluded that the six ring bending modes contain little contribution from other valence coordinates. A potential function for ring bending is then developed using the vibrational frequencies and the available information on molecular geometries. A onefold term in the torsional part of the potential is found to be necessary. The final potential function gives an excellent fit to the frequencies of the lowest-frequency modes and to the geometries of the molecules considered. This potential function should be useful in conformational analysis.
Upper and Lower Bounds for the Ground State of H32+ by the Boundary Condition Method
Authors: Rosenthal C. M. , Wilson E. Bright
Published: February 2004

Upper and lower bounds for the ground-state energy of linear symmetric H32+ are calculated at several nuclear separations as an example of the boundary condition method; it is verified that this form is not stable with respect to dissociation.