bluuebunny/crossref_metadata_2025 huggingface dataset:
Rotational Relaxation in Polar Gases. II
Authors: Zeleznik Frank J. , Svehla Roger A.
Published: February 2004

A classical calculation of polar gas rotational relaxation times is carried out based on the volume viscosity definition of the relaxation time. The calculation demonstrates that the volume viscosity relaxation time agrees with the relaxation time based on an energy relaxation equation through third order in perturbation. An examination of thermal conductivity data shows that the extraction of rotational collision numbers from such measurements is highly suspect. On the other hand, it might be possible to determine internal diffusion coefficients from thermal conductivity measurements when rotational collision numbers can be obtained from other sources.
Thermal and Recombination Emission of NO2
Authors: Paulsen D. E. , Sheridan W. F. , Huffman R. E.
Published: February 2004

The visible emission from electronically excited NO2 has been studied both with thermal excitation in an electric oven and with recombination excitation from the nitric oxide–atomic oxygen reaction. In both cases the emission is continuous with weaker, diffuse bands superimposed. The correlation of these bands with NO2 absorption bands has been extended. The thermal emission continuum begins near 3300 Å and increases in intensity to the end of our range at 8600 Å. The recombination emission continuum begins near 3800 Å and has a broad maximum at 6200 Å, in general agreement with previous workers. The absolute intensity of the thermal emission has been obtained at 100-Å intervals between 4600 and 8600 Å for temperatures between 972 and 1335°K. Excitation energies, which are obtained from the variation of intensity with temperature, range from 66 kcal at 4600 Å to a minimum of 44 ± 1 kcal near 8300 Å. This latter value is E0, the minimum energy of the emitting state of NO2. Radiative lifetimes are obtained for thermal emission which range from 100 to 1 μsec depending on emission wavelength and which approximately agree with fluorescent lifetimes for comparable excitation energies. The results are compared with shock tube measurements and are discussed in relation to air emissivity and opacity problems.
Remark on Phase-Space Distributions in Quantum Theory
Authors: Pechukas Philip
Published: February 2004

If the choice is limited to quadratic forms, it is impossible to find representations of quantum states by positive distributions on phase space, either in the ordinary or in an extended “coarse-grained” sense.
Strong Quenching of Tb3+ Emission by Tb–V Interaction in YPO4–YVO4
Authors: DeLosh R. G. , Tien T. Y. , Gibbons E. F. , Zacmanidis P. J. , Stadler H. L.
Published: February 2004

Solid solutions in the system YPO4–YVO4, with and without 2 mol% of Tb3, were studied to determine the reason for the total inactivity of Tb in YVO4. The comparison of the diffuse reflectivity of Tb-containing solutions with that of Tb-free ones shows a uv absorption at energies below the absorption edge of YVO4 in materials containing both terbium and vanadium. Selective excitation directly into Tb3+ in these wavelength regions produced reduced Tb3+ emission when there was vanadium present. The band emission of the VO43+ groups, and the Tb3+ emission under electron beam excitation, were strongly quenched whenever terbium and vanadium were both present. Emission of Dy3+, present as a 10-ppm impurity in all samples, was also quenched by the presence of both terbium and vanadium, but not by either alone. All these observations imply energy loss by Tb–V interaction. A particular loss mechanism—the well-known intervalence transfer of charge from Tb to V resulting in an abrupt change of bond strength leading to a transfer of electronic excitation into lattice vibrations—is supported by measurements of Tb activity as a function of V concentration. The intensity of Tb emission is proportionate to the probability that none of four metal ion sites about a Tb is occupied by a V. This suggests the intervalence transfer absorption mechanism because only four of the nearest six metal ion sites have Tb–O–M bond angles (about 150°) consistent with good charge transfer from Tb to V; the remaining two sites have a Tb–O–M near 90° and should be relatively inactive in charge transfer.
Opacity Analysis of Inelastic Molecular Collisions. IV. Statistical Aspects of Rotational Excitation Theory
Authors: Levine R. D. , Bernstein R. B.
Published: February 2004

Cross sections for specified rotational transitions of diatomic molecules are expressed in terms of opacity functions in the dominant-coupling regime and in the limited-coupling domain (where only first-order-allowed transitions occur). The statistical approximation is used to evaluate the opacity functions in the dominant coupling (the “inner”) region. The “outer” zone of limited coupling includes the large angular momenta where the Born (or distorted wave) approximation is satisfactory, as well as the region of somewhat lower J requiring numerical treatment (at least the solution of a limited set of coupled equations). The use of the statistical approximation for direct transitions is discussed in terms of a limited energy average of the S matrix. The vanishing of the average of the diagonal S matrix elements is sufficient for a simple statistical estimate of the total cross section; however, a much more stringent requirement must be met (vanishing of the averaged S matrix itself) for statistical prediction of specific inelastic transition probabilities.
Mobilities of Negative Ions in SF6
Authors: Patterson P. L.
Published: February 2004

Mass identified mobilities were measured at 300°K for negative ions formed by a pulsed spark discharge in SF6. Zero field mobilities of the four ion species, SF5−, SF6−, SF6−(SF6), and SF6−(SF6)2, were found to be 0.595 ± 0.007, 0.542 ± 0.007, 0.470 ± 0.010, and 0.420 ± 0.010 cm2 V−1·sec−1, respectively. The SF6−(SF6)2 ion was observed to be collisionally destroyed at E / n values greater than 100 × 10−17 V·cm2. The present data indicate that the zero field mobility of 0.570 cm2 V−1·sec−1 previously reported by McAfee and Edelson and by McDaniel and McDowell may have referred to the unresolved SF5−1 and SF6− ions. All four mobilities measured in this experiment are significantly below the predictions of the Langevin mobility theory in its polarization limit.
Electronic Structure of NO2 Studied by Photoelectron and Vacuum-uv Spectroscopy and Gaussian Orbital Calculations
Authors: Brundle C. R. , Neumann D. , Price W. C. , Evans D. , Potts A. W. , Streets D. G.
Published: February 2004

The ionization potentials of NO2 up to 28 eV have been measured using He i and He ii high-resolution photoelectron spectroscopy. The assignment of the ionized levels below 16 eV is straightforward, including the singlet–triplet splittings, and allows us to assign Rydberg series in the vacuum uv leading to the first five ionization potentials. Above 16 eV the spectrum is complicated by the absence of obvious singlet–triplet splittings. The assignments we propose fit in with a coherent scheme for the molecular-orbital energy levels of 16-, 17-, and 18-electron triatomic molecules. The SCF calculations have been performed on several states of NO2 and NO2+ (both open shell and closed shell) and the results are in quite good agreement with the experimental ionization potentials.
Gaseous Metal Borides. II. Mass-Spectrometric Evidence for the Molecules UB2, UB, and CeB and Predicted Stability of Gaseous Diborides of Electropositive Transition Metals
Authors: Gingerich Karl A.
Published: February 2004

A combination of Knudsen effusion and mass-spectrometric techniques has been used for the investigation of the reactions (1) UB2(g) + 2C(g) = UC2(g) + 2B(g), (2) UB(g) + C(g) = UC(g) + B(g), and (3) CeB(g) = Ce(g) + B(g). The experimental third-law enthalpies have been combined with appropriate literature data to obtain the following dissociation energies or heats of atomization, D0°, in kilocalories/mole: UB, 76 ± 8; CeB, 72 ± 5; and UB2, 227 ± 10. The Pauling model of a strongly polar M–B2 bond has been used to estimate the heats of atomization of gaseous diborides of selected electropositive transition metals.
Perturbed Angular Correlation Study of the Environment of 111Cd Nuclei in Ice
Authors: Barrett J. S. , Cameron J. A. , Gardner P. R. , Keszthelyi L. , Prestwich W. V. , Kaplan Morton
Published: February 2004

A perturbed angular correlation study of 111Cd ions in frozen aqueous solutions of InCl3 and In(NO3)3 has demonstrated the variation in behavior of these systems with temperature from − 140 to − 20°C. At the lowest temperature a strong static quadrupole interaction (ωQ = 1.6 × 107rad/sec) was observed. Above − 80°C, a time-dependent perturbation was found, and the temperature dependence of the correlation time was measured.
Quantum Dynamics of Anharmonic Oscillators by Numerical Integration
Authors: Park Young R. Lee , Tahk C. Tay , Wilson David J.
Published: February 2004

Numerical integration techniques are used to investigate the quantum dynamical behavior of the Morse, Fues, and truncated square-well oscillators. These procedures, unlike the methods involving expansion in terms of a finite basis set of functions, readily permit the study of dissociating systems. Stability problems arise when the time-dependent Schrödinger equation is solved by difference equation methods; an extension of a difference equation scheme reported by Mazur and Rubin is found to yield a conditionally stable system. A method based on the approximation of the time evolution operator by a finite symmetric matrix is found to yield a simple, rapid, and quite accurate algorithm for integrating the time-dependent Schrödinger equation; this method is also applicable to other partial differential equations of physical interest. The agreement between the results of numerical integration methods and those of expansion in a basis set of functions is found to be excellent for systems in which bound states only are of importance. Numerical integration results for dissociating systems are presented and discussed. Application to the vibrations of linear harmonic triatomic molecules is discussed.
NMR Studies of the Rotational Diffusion of Symmetric Top Molecules in Liquids
Authors: Gillen Kenneth T. , Noggle Joseph H.
Published: February 2004

Temperature-dependent nuclear magnetic resonance relaxation times of quadrupolar nuclei in several symmetric top molecules (as neat liquids) are reported. These include 51V and 35Cl in VOCl3, 11B and 35Cl in BCl3, and 14N and 35Cl in CCl3CN; sufficient in each case to calculate the molecule's complete rotational diffusion tensor as a function of temperature. These results, along with previously reported results for other symmetric top molecules, are discussed. It is found that for small molecules in the liquid phase rotational motions which reorient an electric dipole invariably proceed by small-step Brownian diffusion and that the rates of such reorientations can be calculated with good accuracy by hydrodynamic (microviscosity) theory. The success of the hydrodynamic calculation, the agreement with all available reorientational rates determined by dielectric relaxation, and the semiquantitative “χ test” are used to confirm that these motions are indeed in the diffusion limit. On the other hand, strong inertial effects are usually found in the parallel motions which do not reorient the dipole and in both motions of the nonpolar BCl3. In these cases, the rates of reorientation are faster than predicted hydrodynamically, especially when the relevant moment of inertia is small.
Stability Conditions for the Solutions of the Hartree–Fock Equations for Atomic and Molecular Systems. III. Rules for the Singlet Stability of Hartree–Fock Solutions of π-Electronic Systems
Authors: Čížek J. , Paldus J.
Published: February 2004

The singlet stability conditions for closed-shell electronic systems, which ensure that the Hartree–Fock (HF) determinant with doubly occupied orbitals minimizes the energy expectation value, are applied to the symmetry adapted HF solutions of linear polyacenes, using the Pariser–Parr–Pople-type semi-empirical Hamiltonian. It is found that the symmetry adapted HF solutions for linear polyacenes containing an even number of benzene rings are always singlet stable, while the HF solutions for linear polyacenes having an odd number of benzene rings may exhibit singlet instability if the coupling constant is large enough. For cases where singlet instability was found, we have also calculated new HF solutions having lower energy than the symmetry adapted HF solutions. These new HF solutions violate the space symmetry conservation laws as usual. Furthermore, the qualitative rules for the existence of singlet stability of the symmetry adapted HF solution of π-electronic systems with conjugated double bonds are derived. These rules are formulated through the simple symmetry properties of possible Kekulé structures of the studied system. These rules are used to explain the results of stability calculations for linear polyacenes as well as further illustrated on other examples.
Virial Expansion for Hard Nonspherical Molecules
Authors: Rigby M.
Published: February 2004

The third and fourth virial coefficients for two types of axially symmetrical hard molecules have been calculated using a Monte Carlo method, and the results compared with values obtained from the scaled particle theory and from calculations based on expansions in terms of spherical harmonics. The scaled particle theory is found to give very satisfactory results, and the extension to molecules with attractive intermolecular forces is briefly considered in relation to the extended principle of corresponding states.
Heat Capacity and Magnetization of Polycrystalline MnBr2·4H2O as a Function of Temperature at Magnetic Fields up to 30 000 G in the Liquid-Helium Region
Authors: Stein R. L. , Butera R. A.
Published: February 2004

The heat capacity and magnetization of a spherical crystalline powder sample of MnBr2·4H2O has been determined as a function of temperature in applied magnetic fields up to 30 000 G. The H−T diagram for the magnetic transformations has been obtained from the loci of the points inflection in the derived values of the rate of change of the entropy and magnetization with temperature at constant applied magnetic field. The loci of these points of inflection exhibit an abrupt change in slope, indicative of a transition occuring in the portion of the sample having the spin axis aligned parallel with the applied field. The observed phenomena are in agreement with the data reported for optical and microwave absorption.
Dielectric Function for Insulating Crystals
Authors: Lipari Nunzio O.
Published: February 2004

A calculation for the wavenumber-dependent dielectric function has been made using a model originally proposed by Fry, without any further simplification. We have compared our numerical results with the ones obtained by Fry for KCl and argon and the agreement is very good. Comparison is also made with the results obtained using different models. In this case, the agreement is not as good as in the previous case.
Molecular Density Matrices from One-Center Wavefunctions
Authors: Olympia Pedro L. , Fung B. M.
Published: February 2004

The 1- and 2-matrices of the 10-electron polyhydrides, methide ion, ammonia, and oxonium ion, computed from one-center expansion wavefunctions with configuration interaction, are examined. The results are discussed in relation to the utility and limitations of one-center expansion wavefunctions. An explanation of Rutledge and Saturno's result, that methide ion and ammonia are planar, is proposed.
Ionic Interactions in Crystals: Infrared and Raman Spectra of Powdered Ca(NO3)2, Sr(NO3)2, Ba(NO3)2, and Pb(NO3)2
Authors: Brooker M. H. , Irish D. E. , Boyd G. E.
Published: February 2004

Infrared and Raman spectra have been recorded for room-temperature phase powdered samples of Ca(NO3)2, Sr(NO3)2, Ba(NO3)2, and Pb(NO3)2. The spectra are interpreted in terms of a factor group analysis. Considerable multiplet band structure is reported for the first time.
Approximate Velocity Dependence of the Total Cross Section
Authors: Reck G. P. , Hood R. J.
Published: February 2004

The approximate velocity dependence of the forward scattering amplitude obtained by application of the Landau–Lifshitz procedure to an LJ (6–12) potential is compared to other work and discussed.
Theory of Optical Activity of Crystalline Benzil
Authors: Deutsche Craig W.
Published: February 2004

Within the limits of a tight-binding (Frenkel) exciton model, formulas are derived for the optical rotatory dispersion (ORD) of crystals possessing a screw axis of symmetry. It is seen that transitions having a large electric moment may exhibit ORD with a frequency dependence proportional to [ω02 − ω2]−2 and having intensity proportional to the derivative of exciton energy with respect to wave vector. On the other hand, transitions with a weak electric transition moment but possessing larger magnetic dipole transition moments will show ORD spectra with the more familiar frequency dependence proportional to [ω00 − ω2]−2. It is shown how the rotational strengths of these latter transitions may sometimes arise from purely molecular origins or may sometimes be attributed to configuration interaction among the simple exciton states. The application of the formulas is demonstrated for crystalline benzil, C6H5COCOC6H5. Pi-electron wavefunctions are obtained for this molecule within the Pariser–Paar–Pople set of approximations. Exciton wavefunctions and energies are calculated using both dipole–dipole interactions between molecules and also using more complete expressions for the intermolecular interactions. These functions are then used to predict rotational strengths of the various transitions of the crystal. The calculated results are in qualitative agreement with experiment and tentative conclusions are drawn about the mechanism by which the transitions acquire rotational strength. The difficulty in obtaining good wavefunctions for the molecular nπ* excited states seems to be the source of the quantitative discrepancy between theory and experiment in this particular case.
Proton NMDR in a Liquid-Crystal Solution
Authors: Fung B. M. , Gerace Michael J.
Published: February 2004

The proton resonance and double resonance of isoxazole in a liquid-crystal solution are reported. The three-spin system in isoxazole is chosen to illustrate how the “spin tickling” technique is applied to analyze a complicated spectrum in a liquid-crystal solution. Due to the presence of superimposed signals (either accidental or exact), multiple splittings of peaks are observed during the irradiation. This phenomenon is usually not observed in liquid spectra, and it is very useful in the identification of hidden transitions. The dipole–dipole coupling constants for isoxazole in the liquid-crystal solution studied are found to be D35 = − 64 ± 2 Hz, D45 = − 300 ± 2 Hz, and D34 = − 487 ± 2 Hz.
Excess Electrons in Polar Solvents
Authors: Copeland David A. , Kestner Neil R. , Jortner Joshua
Published: February 2004

In this paper we consider a structural model for localized excess electron states in polar solvents with particular reference to dilute metal ammonia solutions and to the hydrated electron. The over-all energetic stability of these species was assessed by considering simultaneously the electronic energy and the medium rearrangement energy. The present model consists of a finite number of loosely packed molecules on the surface of the cavity which are subjected to thermal fluctuations and a polarizable continuum beyond. The electronic energy was computed utilizing an electrostatic microscopic short-range attraction potential, a Landau-type potential for long-range interactions, and a Wigner-Seitz potential for short-range repulsive interactions. The medium rearrangement energy includes the surface tension work, the dipole–dipole repulsion in the first solvation layer, and most importantly the short-range repulsive interactions between the hydrogen atoms of the molecules oriented by the enclosed charge. The gross features of localized electron states in different solvents can be rationalized in terms of different contributions to the medium rearrangement terms. The energetic stability of the localized state of excess electrons in polar solvents was established and the cavity size in the ground state of the solvated electron could be uniquely determined. Experimental energetic and structural data such as volume expansion, coordination numbers, heats of solution, and spectroscopic properties are in qualitative agreement with the predictions of the present model. Optical line shape data calculated from the theoretical model do not agree with experiment; this discrepancy suggests that more data are required in regard to the excited states of the solvated electron.
Intrinsic Viscosity of Short Chains. II. Comparison with Experimental Results
Authors: Rossi C. , Perico A.
Published: February 2004

In Paper I we extended the Kirkwood–Riseman theory to low molecular weights. We now show that this extension supports the available experimental evidence of the validity of Flory's equation down to this region, once dimensions of the monomeric unit are taken into account in calculating average coil dimensions.
Molecular Structure of Dicyclopentadienylnickel (C5H5)2Ni
Authors: Hedberg Lise , Hedberg Kenneth
Published: February 2004

The structure of gaseous nickelocene has been determined at 110°C by electron diffraction using two independent sets of data. The molecule has the familiar ferrocenelike sandwich shape, but it differs from ferrocene in having weaker metal–carbon bonds and greater amplitudes of vibration for all distances affected by motion of the cyclopentadienyl rings as units. The simplest interpretation of the large inter-ring amplitudes leads to the conclusion that the rings are rotating much more freely than in ferrocene. There is some slight evidence that the Ni–C bonds may not all be equivalent, corresponding to a structure that is not strictly symmetric (D2h or D2d), or alternatively that the molecular motions affecting the Ni–C bonds are unusual in a way which does not give rise to the expected essentially harmonic Ni–C amplitudes, either of which suggests the faint possibility of a Jahn–Teller effect. Based upon a symmetric sandwich conformation with freely rotating rings the principal distance (ra) and mean amplitude (la) values are (values in parentheses are 2σ): rNi–C = 2.196 Å (0.008), rC–C = 1.430 Å (0.003), rC–H = 1.083 Å (0.019), ∠C5,H (angle between the plane of the C5 ring and the C–H bond) = 0.28° (2.90), lNi–C = 0.0842 Å (0.0056), lC–C = 0.0440 Å (0.0031), lC–H = 0.0786 Å (0.0229), lNi···H = 0.1469 Å (0.0346).
Calculation of the Diamagnetic Susceptibility of the Water Molecule
Authors: Pan Yen-chi , Hameka Hendrik F.
Published: February 2004

The diamagnetic susceptibility and its anisotropy are calculated by making use of gauge invariant atomic orbitals. Three calculations are performed, using slightly different approximations. The results are: χ = 11.59, χxx = 8.850, χyy = 11.289, χzz = 14.633 in the first calculation; χ = 12.21, χxx = 11.121, χyy = 13.081, χzz = 12.437 in the second calculation; and χ = 12.84, χxx = 12.150, χyy = 13.696, χzz = 12.674 in the third calculation (in terms of − 10−6 cgs units). The agreement with the experimental values χ = 13.1, χxx = 12.1, χyy = 13.5, χzz = 13.7 is satisfactory.
Reaction of C+(2P) with CH3F
Authors: Wilson Patricia Sullivan , Rozett R. W. , Koski W. S.
Published: February 2004

The ion–molecule reaction C+(2P)+CH3F has been investigated in the 2–200-eV energy region using a tandem mass spectrometer. All possible ions containing one and two carbon atoms were observed except C2H3F+. The behavior of cross section as a function of the kinetic energy of the incident ion was used to infer reaction mechanism. Hydride ion, fluoride ion, and fluorine atom pickup were the dominant reactions at low energies.
Infrared Spectra in Polarized Light of Crystalline Benzene and Benzene-d6
Authors: Marzocchi M. P. , Bonadeo H. , Taddei G.
Published: February 2004

The high-resolution spectra in polarized light of oriented polycrystalline films of C6H6 and C6D6 at 85°K have been obtained. The observation of two different crystal faces allowed the classification of the Davydov components, according to their polarization character, into three different sets, which correspond to the three infrared-active factor-group symmetry species. The complications which arise from the presence of isotopic impurities (13C12C5H6 in 12C6H6, 13C12C5D6 and 12C6D5H in 12C6D6) are removed thanks to the use of polarized light, the aid of the correlation between C6H6 and C6D6 spectra, and solid solution information. Therefore, a complete assignment of all the observed peaks has been possible. The experimental results have been compared with exciton splittings and crystal shifts calculated by other authors.
Matrix Isolation Studies of Group IV Oxides. III. Infrared Spectra and Structures of SnO, Sn2O2, Sn3O3, and Sn4O4
Authors: Ogden J. S. , Ricks M. J.
Published: February 2004

The matrix isolation of vapor phase tin oxides leads to the identification of at least four distinct species: SnO, Sn2O2, Sn3O3, and Sn4O4. Infrared bands for these molecules are observed at 816.1 cm−1 (SnO), 612.6 and 523.2 cm−1 (Sn2O2), 761 cm−1 (Sn3O3), and 516.5 and 416.3 cm−1 (Sn4O4). The spectra of Sn2O2 and Sn3O3 are consistent with molecular symmetries Vh and D3h, respectively, while Sn4O4 may have either D4h or Td symmetry. With the aid of 18O substitution, and normal coordinate analyses, estimates are given for the molecular dimensions of these species. The concentration changes occurring on diffusion are investigated.
Franck–Condon Factors for the Ã←X̃ Transition of Ammonia with Anharmonic Potential Functions for the Ground and Excited States
Authors: Harshbarger William R.
Published: February 2004

The Franck–Condon factors for the Ã←X̃ transition in NH3 have been calculated and compared with the observed relative intensities of electron impact spectra. Calculations were made in which the symmetric bending mode was fitted as an anharmonic oscillator. In addition, the Franck–Condon factors were calculated for the case in which all vibrations were approximated as harmonic. The former calculations best fit the observed intensity distribution. The Ã←X̃ transition consists of overlapping bands in which the symmetric stretching and bending vibrations of the Ã state are excited. The symmetric stretching frequency of the ã state is estimated to be 2900 ± 50 cm−1.
Statistical Mechanics of Single-Occupancy Systems of Spheres, Disks, and Rods
Authors: Ree Francis H.
Published: February 2004

An independent oscillator approximation proposed recently by Fixman has been numerically examined by using single-occupancy systems of hard spheres, disks, and rods over the entire density range. Numerical data on pressure, entropy and the singlet distribution function are compared with existing exact data to elucidate the theory's dependence on dimensionality. A considerable simplification which results after truncating the effective potential appearing in Fixman's theory by its first two nonvanishing terms in the Taylor expansion allows proof of the existence of high-density expansion in a parameter that characterizes available free volume for pressure and entropy, and the second moment of the singlet distribution function. Analytic expressions are given for the first one or two coefficients in the expansion for these quantities. However, complete calculations without the truncation procedure show significantly different high-density behaviors for pressure and entropy. In addition to this pressure and entropy, calculations for spheres from the second approach show the existence of two distinct branches: a “fluidlike” branch, which would be unstable without the cell wall, extending up to 75% of the close-packed density (ρ0), and a “solidlike” branch, which is stable even without the cell wall, starting from 0.73ρ0 and extending to the close-packed density. For the single-occupancy system of hard disks, a similar but continuous van der Waals-like transition is observed in the vicinity of the melting density of normal disks without the cell restriction. Finally, a Monte Carlo method is employed to obtain data for the singlet distribution and its mean-square width for single-occupancy systems of 72, 896, and 1400 hard disks. The resulting data are compared with those derived under the independent oscillator approximation.
Self-Consistent Molecular-Orbital Methods. VIII. Molecular Studies with Least Energy Minimal Atomic Orbitals
Authors: Hehre W. J. , Ditchfield R. , Pople J. A.
Published: February 2004

A minimal set of energy-optimized contracted Gaussian orbitals is used for single-determinant molecular-orbital studies of a set of small polyatomic molecules. Optimized scale factors for valence atomic orbitals are determined by energy variation and are found to be significantly greater than unity for hydrogen and carbon. The convergence of calculated properties with increasing size of Gaussian expansion is studied and found to be less rapid than in corresponding studies using a Slater-type minimal basis. Theoretical equilibrium geometries are determined. The agreement with experimental geometries is resonable but somewhat less satisfactory than with a Slater-type set.
Configuration Interaction Wavefunctions for Small Pi Systems. III. Spatial Wavefunctions for Butadiene
Authors: Amos A. T. , Burrows B. L.
Published: February 2004

The full set of spatial eigenfunctions of the pi-electron Hamiltonian of butadiene has been calculated and, using the properties of the permutation group, divided into the physically real and physically unallowed states. Variational and perturbation calculations of the spatial functions corresponding to the lowest ground state have been made.
Radio-Frequency Spectra of NaCl by the Molecular-Beam Electric Resonance Method
Authors: de Leeuw F. H. , van Wachem R. , Dymanus A.
Published: February 2004

The molecular-beam electric resonance method served to measure the radio-frequency spectra of NaCl and to determine the hyperfine constants and the dipole moments for the υ = 0, 1, 2, and 3 vibrational levels of Na35Cl, and for the υ = 0 and 1 vibrational levels of Na37Cl.
Orientation-Dependent van der Waals Coefficients for Various Species in Molecular Hydrogen
Authors: Victor G. A. , Dalgarno A.
Published: February 2004

Accurate semiempirical values are presented of the anisotropy in the long-range van der Waals interaction for several species interacting with molecular hydrogen.
Test of Transition-State Theory Using the Experimentally Determined Rate Constant Ratio for the Reactions H+H2 and H+D2
Authors: Quickert K. A. , Le Roy D. J.
Published: February 2004

The rate constant ratio k1 / k4 for the hydrogen-exchange reactions H+H2→H2+H and H+D2→HD+D has been measured in the temperature range 290 to 690°K. Reactions [1] and [4] were carried out simultaneously, and k1 / k4 was determined directly using only concentration ratios of stable molecules. The precision of the results was ± 10% or better and it is believed that this also represents the accuracy. The experimental results were compared with the theoretical values of k1 / k4 given by transition-state theory with quantum-mechanical tunneling, using the most recent ab initio potential surface of Shavitt, Stevens, Minn, and Karplus. The one-dimensional tunneling correction was calculated numerically using the minimum energy path on the surface. Good agreement between experiment and theory was found only when tunneling was included; scaling of the one-dimensional barrier, as suggested by the correlation work of Shavitt, improved the agreement. It is concluded that transition-state theory, as applied, leads to results for the hydrogen-exchange reactions which are not inconsistent with experiment.
Determination of Molecular Properties by the Method of Moments
Authors: Handy N. C. , Epstein S. T.
Published: February 2004

In spite of the loss of variational characteristics, many workers have recently found it advantageous to work with the method of moments for the determination of wavefunctions, in preference to the Ritz variational equations. In this paper, a brief review of these methods is given, and it is then shown how first-and second-order properties should be calculated from such determined wavefunctions. A theoretical discussion of the error of the calculated properties is also given.
Paramagnetic Resonance Study of Liquids during Photolysis. VIII. An Emission Spectrum from Solutions of Tartaric Acid
Authors: Livingston Ralph , Zeldes Henry
Published: February 2004

Paramagnetic resonance spectra of several free radicals were observed during photolysis of concentrated aqueous solutions of tartaric acid. Radical A, identified as HOOCCH(OH)CH(OH), gives a spectrum of eight hyperfine lines all of which are in emission. This radical is converted by a pinacollike rearrangement to HOOCĊHCHO, the spectrum of which was also observed. The chemical lifetime and relaxation time of radical A are discussed. By progressively increasing the pH of the solution, the chemical lifetime is lengthened and the emission spectrum is progressively transformed to an absorption spectrum. At intermediate stages, intensity anomalies are seen and discussed. Other radicals seen in this system are also discussed.
Angular Dependence of Differential Cross Sections for Electron Excitation of Singlet→Triplet Transitions
Authors: Steelhammer J. C. , Lipsky Sanford
Published: February 2004

The failure of previous calculations to predict the correct “forward-peaking” angular dependence of the electron-impact differential cross section for the helium 11S → 23S transition is shown to be due to the neglect of the core contribution. Even a simple approximation to the full Born–Oppenheimer transition amplitude based on an expansion in inverse powers of the incident electron momentum predicts the correct angular dependence of this transition for electron energies to within 40 eV of threshold. For electron-impact excitation of the lowest singlet→triplet transition in molecular hydrogen, the peaking of the differential cross section away from zero scattering angle is due mainly to a molecular diffraction effect, and the success of Ochkur's approximation in predicting this dependence is shown to be merely a consequence of the relatively small contribution made by the core terms for this particular transition and cannot be generalized. For higher singlet→triplet transitions in H2, the angular dependence of the differential cross section and the magnitude of the core contribution are shown to depend importantly on the separated atom state with which the molecular wavefunction correlates at infinite separation.
Multipole Polarizabilities and London Dispersion Forces of He and Li+ Using Double Perturbation Theory
Authors: Broussard J. T. , Kestner Neil R.
Published: February 2004

Following the double perturbation-theory method used by Deal, Kestner, and Young, dipole, quadrupole, and octopole polarizabilities with and without correlation have been calculated for He and Li+ at imaginary frequencies. Also calculated are the C6, C8, and C10 coefficients for He–He and Li+–Li+ interactions with and without correlation for several Hartree–Fock-type wavefunctions.
Dielectric Second Virial Coefficients of Simple Polar Gases
Authors: Kong Chang Lyoul
Published: February 2004

A modified Stockmayer potential function with the “heteronuclear diatomic moleculelike” shape factor has been applied for the interpretation of the dielectric second virial coefficients of simple polar gases. Numerical results are presented for methyl fluoride and fluoroform. The effects of moledular shape, polarizability, and the higher multipole moments on the ordinary and dielectric second virial coefficient are discussed.
Hard-Square Solids at High Densities
Authors: Beyerlein A. L. , Rudd W. G. , Salsburg Z. W. , Buynoski M.
Published: February 2004

An asymptotic expansion for the Helmholtz free energy FN of a system of N hard squares of side σ is obtained, with the result FN / NkBT ≃ lim r→1 2 ln(λ / σ) − 2 ln(τ − 1) + C + D(τ − 1) + E(τ − 1)2 + ···, where kB is Boltzmann's constant, λ is the mean thermal de Broglie wavelength, and τ is the ratio of the system area to the close-packed area. A formal expression is derived for the constant C, while D, E, ··· are the coefficients in the expansion of 2 ln(τ1/2 + 1) in powers of (τ − 1). The modified cell-cluster technique is used to evaluate C, with the result C = − 0.26042240.
Glory Scattering of Lithium by a Series of Molecules. III. Spherical-Top Molecules
Authors: Rothe Erhard W. , Helbing Reinhard K. B.
Published: February 2004

The velocity dependence of the total cross section has been measured for the scattering of lithium-7 by 10 spherical-top molecules. The experiments were similar to those described in two previous papers in which the scattering was from 13 diatomics and from 29 polyatomics containing carbon, hydrogen, and fluorine. Potential parameters are derived. The quenching of the normal glory patterns is measured. Anisotropy parameters are obtained, using a “clover-leaf” potential.
Nonadditivity Correction to the Radial Distribution Function
Authors: Chen Chimin Tang , Present R. D.
Published: February 2004

Two derivations of the three-body nonadditivity correction to the radial distribution function of a fluid are given. The first employs only the properties of n-particle correlation functions, and the second is based on statistical mechanical formulas relating to the equation of state. We obtain a new formula for the effective pair potential in the low-density limit, valid through terms in the square of the density, assuming only that the nonadditive three-body interaction is small. An extension of this formula to higher densities is obtained by replacing the exact triplet correlation function for low densities by the superposition approximation. Our results provide no grounds for supposing that the effective pair potential is linear in the density for either gases or liquids.
Molecular Beam Study of the Scattering of Rare Gases from the (110) Face of a Tungsten Crystal
Authors: Yamamoto S. , Stickney R. E.
Published: February 2004

The scattering of He, Ne, Ar, and Kr from a (110) tungsten surface has been investigated for surface temperatures, Ts, in the range 300°–2100°K and for angles of incidence, θi, of 40, 50, and 60 deg. The apparatus consists of a nozzle-type molecular beam modulated at 2650 Hz so that lock-in detection may be used to determine both the mean speed and density patterns of the scattered gas. The majority of the data are for Ts = 2100°K since thermal desorption of contaminants should be sufficiently rapid at this temperature to insure that the surface is essentially clean. (For Ts < 1000°K, the surface became contaminated by residual gases (primarily CO) before measurements could be obtained.) At Ts = 2100°K, the maxima of the density patterns for θi = 40, 50, and 60 deg are at the specular angles for He, whereas they are increasingly subspecular for Ne, Ar, and Kr. Both the mean speed and density patterns are compared with the theoretical predictions of the hard-cube and soft-cube models.
Interpretation of Open-Shell SCF Calculations on the T and V States of Ethylene
Authors: Basch Harold , McKoy Vincent
Published: February 2004

Self-consistent field calculations are reported on (planar and perpendicular geometric conformers of) the lowest energy triplet and singlet (π, π*) orbital configurations of ethylene, which are usually identified with the spectroscopic T and V states, respectively. For the planar conformation the calculation predicts a V state with the characteristics of a Rydberg state, but a T state of expected valence-shell character. The π* orbital is much too large and the internuclear distance too small for the calculated V state, but are as expected for the T state. It is concluded that the calculated result for the supposed V state in the planar conformation is spurious due to the inadequacy of the Hartree–Fock single-configuration theory. The supposed V state here calculated may be identified with a Rydberg state which has been observed spectroscopically at ∼ 1.4 eV higher energy than the V state in the optical spectrum. For the perpendicular conformation, the calculations yield resonable results for both the T and V states. Calculations also have been carried out on a singlet (σ, π*) state for planar ethylene; here the size of the π* orbital is reasonable.
Paramagnetic Anisotropy, Low Temperature Magnetization, and Electronic Structure of Iron(II) Phthalocyanine
Authors: Barraclough C. G. , Martin R. L. , Mitra S. , Sherwood R. C.
Published: February 2004

Magnetic anisotropy, magnetization, and average magnetic susceptibility have been measured for iron (II) phthalocyanine. The anisotropy was measured from the room temperature to about 90°K, the average susceptibility from 296 to 1.57°K, and the magnetization was measured at 1.57°K for field strengths between 1100 and 15 000 Oe. The results are interpreted in terms of a B2g3 ground state with a zero-field splitting parameter D = 64 cm−1, and g‖ = g⊥ = 2.74. Iron (II) phthalocyanine is an unusual example in which a large magnetic anisotropy arises entirely from the zero-field splitting. The danger inherent in the existing method of evaluation of ligand-field parameters from the average magnetic susceptibility data has been highlighted, and the advantages of magnetic anisotropy studies in deducing the ligand-field parameters and the electronic structures are discussed. A change of about 70° of the “setting angle” between 290 and 90°K is observed in this crystal when measured with b axis vertical. It is shown that this change is not indicative of a change in the ligand-field parameters with temperature, as generally assumed previously, but depends on the temperature dependence of the ratio of principal susceptibilities.
Shock Compression of Solid Argon
Authors: Dick R. D. , Warnes R. H. , Skalyo J.
Published: February 2004

The Hugoniot of solid argon (initially at 75°K and approximately 1 bar) has been determined using standard shock-wave techniques. Sample pressures ranged 18–645 kbar with associated densities of 1.39–2.18 times the initial density of 1.65 g/cc. Utilizing an exp-6 interatomic potential, a computed fit was obtained which was in excellent agreement with the data up to 300 kbar. The deviation between theoretical and experimental Hugoniot above 300 kbar is interpreted as either due to melting or to an inadequate model and potential form.
Analysis of Nonlinear Initial-Boundary-Value Problems in Recombination and Diffusion Kinetics
Authors: Wilhelm H. E.
Published: February 2004

The time-dependent diffusion and convection equation with a recombination reaction is reduced by means of a transformation to a differential equation, in which the nonlinear term represents a small perturbation. The general procedure of solution for the nonlinear differential equation is then established by means of the method of successive approximations. As concrete illustrations, some typical initial-boundary-value problems which are of interest in radiation chemistry (recombination in clusters) and plasma chemistry (plasma decay experiments) are treated analytically.
ESR Investigation of Some o-Phenylenebis(dimethylarsine) Complexes of Cobalt and Nickel
Authors: Manoharan P. T. , Rogers Max T.
Published: February 2004

The ESR spectra have been obtained for six complexes with the general formulas [Ni(diars)2X2] X and [Co(diars)2X2]0, where X is Cl, Br, and NCS and diars is o-phenylenebis(dimethylarsine), using pure polycrystalline solids and, in the case of the nickel complexes, solutions, and frozen solutions. Ligand hyperfine interactions with 75As, 35,37Cl, 79,81Br, and 14N have been observed and discussed. The data suggest that a model based on d7 Ni(III) with a Ag2 ground state may be adequate for these complexes.
Sonoluminescence from Stable Cavitation
Authors: Saksena T. K. , Nyborg W. L.
Published: February 2004

Arrays of gas bubbles of uniform size are generated in a liquid and subjected to sound at a frequency of 30 kHz. In a viscous mixture of glycerine and water, sonoluminescence is produced in the absence of cavitation noise or streamer activity. Under relatively low amplitude conditions the light occurs in flashes with the same frequency as the sound field, and with duration less than one-tenth that of the sonic period. The phenomenon is believed to be associated with volume pulsations of the bubbles and, specifically, with dissociation of H2O into the radicals OH and H during the compression phase of each cycle when the temperature is relatively high. Photons are emitted as the radicals recombine. Calculations suggest that about 108 photons/sec might be expected from a single 0.2-mm-diam bubble by this mechanism when the bubble temperature reaches 1800°K. Bremsstrahlung (from accelerated charges) is negligible under these same conditions.
X-Ray Photoelectron Spectroscopy of Carbon Monoxide
Authors: Thomas T. Darrah
Published: February 2004

The ionization potentials for all of the electrons on carbon monoxide have been measured by x-ray photoelectron spectroscopy. The values found (in electron volts) are 1Σ (oxygen 1s) 542.3, 2Σ (carbon 1s) 296.2, 3Σ − 38.9, 4Σ − 19.8, 1π − 17.2, and 5Σ − 14.0. The 1Σ ionization potential is 1.2 eV less than the 1s ionization potential for molecular oxygen; the 2Σ ionization potential is 5.4 eV greater than the 1s ionization potential in methane. These results indicate a positive charge on the carbon of carbon monoxide and a negative charge on the oxygen, in agreement with the relative electronegativities, but opposite to what might be expected from the dipole moment of carbon monoxide. The ionization potentials for the three least bound electrons are in agreement with those found by other techniques, provided that allowance is made for the fact that these values represent vertical (rather than adiabatic) ionization potentials. Although the relative intensities of the photoelectrons reflect the atomic photoelectric cross sections and the molecular orbital composition in a qualitative way, there is not quantitative agreement between the measured intensities and theoretical cross sections.
Some Reactions of Ground-State (3P) and Electronically Excited (1D) Sulfur Atoms
Authors: Breckenridge W. H. , Taube Henry
Published: February 2004

Reactions of S(3P) and S(1D) have been studied by utilizing carbonyl sulfide photolysis as a source of both species. It has been shown that 46% ± 4% of the sulfur atoms generated in the photolysis of OCS in the 2250–2650-Å spectral region can react as S(3P), but that substantial portion of the S(3P) is likely produced by deactivating collisions of OCS molecules with S(1D). Both S(1D) and S(3P) react with CS2. The rate constant ratios for these reactions relative to the reactions with OCS have been determined as ∼ 1.9 and ∼ 2.4 × 102, respectively. Efficient isotopic exchange of S(3P) with CS2 is proposed to occur by means of CS3 formation in a reaction independent of pressure above 50 torr. The reaction of S(1D) with N2O yields N2, but kinetic complexities suggest the intermediate formation of a species such as N2OS. Measurement of the quenching of the N2 yield has led to the determination of the relative rates of collisional deactivation of S(1D) for several gases.