bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Excluded Volume on Polyelectrolytes in Salt Solutions
Authors: Alexandrowicz Z.
Published: January 2005

A recently developed theory of excluded volume, relating α to z ∝ M½βL−3 by means of an integral equation, is applied to polyelectrolytes. The line describing α(M½) is the same for all polymers; the dependence of α on the polyelectrolyte parameters (ionic strength and charge density) requires, however, further elaboration. Thus, the excluded volume β is summarily identified with the high-potential shell coaxially surrounding the charged filament, as treated in a polyelectrolyte theory presented some time ago. Distinction is made between two cases: (a) When the shell radius is smaller than the link length L characterizing the polymer and (b) when the converse holds—so that the length of free hinged links becomes determined by the shell radius. The predicted dependence of α on the molecular weight and on the ionic strength is found to agree satisfactorily with the extensive viscosity data reported by Takahashi and Nagasawa. Additional aspects of investigating α(z) are also discussed.
Shock-Tube Study of the Recombination Rate of Hydrogen Atoms with Oxygen Molecules
Authors: Gutman David , Hardwidge Edward A. , Dougherty Frank A. , Lutz Robert W.
Published: January 2005

Measurements have been made of the rate of chain branching during the induction period of the H2–O2 reaction. Mixtures of H2–O2–CO–Ar were shock heated and the ``blue continuum'' emission from the O+CO→CO2+hv reaction was monitored using an end-on technique for sensitivity. Experiments performed at different densities were analyzed to yield the rate coefficient k4Ar=3.3×109 liters2 mole−2·sec−1 at 1100°K for the reactionH+O2+Ar→k4ArHO2+Ar.This value when combined with other literature values for k4Ar yields the temperature-dependent expressions k4Ar=(2.00±0.25)×109 [exp(870±70 cal/RT)] liter2 mole−2·sec−1 and k4Ar=(1.5±0.7)×1012T−0.88±0.08 liter2 mole−2·sec−1. In addition values of k1 for the reactionH+O2→k1OH+Owere obtained from the data between 975° and 2060°K and combined in the Arrhenius expression k1=9.54×1010 exp(−14.7 kcal/RT) liters mole−1·sec−1 accurate to ±20% over our range. A value for k2=1.98×109 liters mole−1·sec−1 (±40%) at 1500°K was obtained for the reactionO+H2→k2OH+H.The end-on technique is shown to be a useful tool to study recombination reactions involving only one free radical.
New Scaled Atoms-in-Molecules Theory for Predicting Diatomic Potential-Energy Curves. I. General Theory and Application to H2 and He2+ +
Authors: Ellison Frank O. , Wu Ay-ju A.
Published: January 2005

An exact scaled atoms-in-molecules theory for predicting potential-energy curves and other properties of diatomic molecules is developed. The basis consists, in the first place, of linear combinations of antisymmetrized products of atomic substate eigenfunctions. Each such basis function ψn can be modified by introducing variational scaling parameters snA and snB into its component atomic eigenfunctions. Exact equations are developed for determining, by reference to experimental atomic properties, all intra-atomic contributions to the energy matrix elements. All remaining parts of the energy matrix elements are interatomic in nature, and these parts are computed using previously determined approximate atomic eigenfunctions; as the latter are successively made more accurate, results of the diatomic calculation should converge to experiment. A restricted orbital model, which reduces the number of independent nonlinear variational parameters, is also proposed. Initial applications to ground and excited electronic state of H2 and He2+ + are presented. A potentially useful approximate calibration technique is suggested and tested.
Statistical Thermodynamics of Self-Avoiding Random Walks
Authors: Gans Paul J.
Published: January 2005

The statistical thermodynamics of self-avoiding random walks on the diamond lattice with nearest-neighbor interaction energy ε is examined. If the probabilities per step of nearest-neighbor formation are taken as fundamental quantities, it is possible under a reasonable and simple assumption about the form of such probabilities to derive an expression for the canonical partition function. The partition function of a walk of σ+l steps relative to a single walk of length σ is qσ(a,l)=[(3p0+2ap1+a2p2)/(3p0+2p1+p2)]l, where a=exp(—ε/kT) and the pn are suitably defined nearest-neighbor formation probabilities.
Vibronic Coupling in the Exciton States of the Rigid-Lattice Model of Molecular Crystals
Authors: Philpott M. R.
Published: January 2005

The vibrational structure of the Frenkel exciton states of a molecular crystal is investigated by a variational technique using a rigid-lattice-model Hamiltonian. The spirit of the weak coupling formalism is strictly adhered to by constructing crystal wavefunctions from products of isolated molecule wavefunctions so that the only parameters of the theory are Franck—Condon factors and vibrational frequency shifts. The basis set consists of all vibronic, i.e., single particle, states belonging to the same electronic state transforming according to a given wave vector, plus a set of two-particle states in which vibronic and ground vibrational excitation occupy different sites. Interactions between single-particle states are treated in detail, as are interactions between one- and two-particle states. However, part of the interaction between certain two-particle states is neglected and this makes the treatment progressively less accurate for higher vibrational states and stronger coupling. Electron exchange effects, coupling of excitons to photons, higher electronic states, and ion-pair states are not considered.

It is shown how each element of the conventional weak coupling energy matrix is supplemented by terms which account for the interaction between one- and two-particle states as well as interactions among the two-particle states. For a given wave vector each single-particle state is accompanied by a family of two-particle bands which rapidly increases in size for higher vibrational states. In the weak coupling limit the families are widely separated, while intermediate coupling corresponds to two-particle bandwidths comparable with the vibrational spacing. The onset of strong coupling corresponds to overlapping of adjacent families.
Spectroscopy of EDA Complexes at High Pressures. IV. Absorption of Several Haloquinone Complexes in Polymer Matrices
Authors: Offen H. W. , Nakashima T. T.
Published: January 2005

Several haloquinone complexes are subjected to high pressures (0–20 kbar), and the resulting effects are registered in the charge-transfer (CT) absorption spectra. The observed shift in the CT band maxima are discussed in terms of the various interaction terms, including CT forces, which contribute to the displacement of the ground relative to the excited CT state of the EDA complex. The results indicate that the stronger complexes show the smaller red shift or even a blue shift in this pressure range. CT intensities in the 1–20-kbar interval are observed to change by −15% to +40% in this group of related complexes.
Vibrational Spectra and Structure of Four-Membered Ring Molecules. IV. 2-Bromocyclobutanone and 2-Bromo-2,4,4-trideuterocyclobutanone
Authors: Durig J. R. , Morrissey A. C.
Published: January 2005

The infrared and Raman spectra of 2-bromocyclobutanone and 2-bromo-2,4,4-trideuterocyclobutanone in the liquid state have been recorded. The far-infrared spectra of both compounds have also been recorded from 33–300 cm−1 in both the vapor and liquid states. The assignment of the 27 normal vibrations is given. The interesting ring-puckering vibration in 2-bromocyclobutanone has been observed at 153 cm−1 in the Raman spectrum and at 141.5 cm−1 in the infrared spectrum of the vapor. For the deuterium compound the corresponding absorption bands have been observed in the Raman and infrared spectra at 152 and 141 cm−1, respectively. The data indicate that the potential function governing this vibration is only slightly anharmonic. No evidence has been found for the conformers previously reported for this molecule.
Magnetic Optical Rotation and Magnetic Circular Dichroism of Polymers. II. Time-Dependent Hartree Theory
Authors: Harris Robert A.
Published: January 2005

Two different forms of time-dependent Hartree theory are used to obtain the susceptibility which expresses magnetic rotation and magnetic circular dichroism. The two methods are shown to result in the same answer. The susceptibility is origin independent. The possible information that one may obtain is discussed in light of the form of the susceptibility.
Study of the Electronic Structure of Molecules. VIII. All-Electron SCF Wavefunctions for Pyridine Positive Ion, 2A2
Authors: Clementi Enrico
Published: January 2005

The SCF—LCAO—MO wavefunction for the positive ion of pyridine obtained by ionization in the π MO of a2 symmetry is reported. It is shown that the use of orbital energies in predicting ionization potentials yields correct results only in the case of cancellation of terms. The details of the cancellation are analyzed. The π-electron ionization brings about a large charge rearrangement in the σ electrons. The loss of a π charge is balanced by donation of σ electrons from the hydrogen atoms to the ring. The ring atoms are somewhat less negative in the ion than in the neutral molecule; the hydrogen sites are substantially more positive. The over-all electronic rearrangement following the π-electron ionization is about 1.3 σ electrons and 0.2 π electrons. This rearrangement is done at the expense of about 1 eV.
Sigma and Pi Electronic Reorganization in Acetylene
Authors: Griffith Martin G. , Goodman Lionel
Published: January 2005

Accurate SCF—LCAO—MO wavefunctions have been computed for acetylene neutral ground state, singly excited π→π* states, and for the acetylene anion and cation. A limited basis set of Slater orbitals was used, the carbon 2s, 2pπ, and 2pσ orbital exponents were independently optimized for each state, and hydrogen 1s for the ground state. All integrals were computed accurately. For the ground state the C2p±1 optimized orbital (ξ=1.59) is very different from the C2pσ optimized orbital (ξ=2.03) with the result that the Π cloud does not penetrate the Σ cloud as greatly as would be predicted by Slater or best-atom AO. However, the penetration remains sizeable (Fig. 2). The ground-state energy − 76.678 a.u. (1 a.u.=27.2098 eV) is improved by 0.134 a.u. over McLean's best-atom calculations, but is 0.176 a.u. poorer than McLean's Hartree—Fock calculations. Reorganizations of the sigma and pi electronic shells with change in state of the pi system are computed to be large. A gain or loss of a pi electron is accompanied by a sigma energy change of 0.2 a.u. partially due to deformation of the C2s AO and partially due to sigma polarization away from the H atoms in the cation and vice versa in the anion. The large reorganization in the pi distribution is illustrated by the 2pπ exponents: cation 1.68, anion 1.45, ground state 1.59. The total reorganization energy in acetylene (−0.033 a.u. G state→cation; −0.069 a.u. G state→anion) is only 6% of the largest reorganization term: the change in sigma—pi interaction (0.586 and 1.262 a.u., respectively). The success of conventional pi-electron theory then basically depends on cancellation of the sigma and pi reorganization energy terms with the change in the sigma—pi interaction. The Hijcore parameters are found to be nearly independent of pi density providing justification for pi-electron approaches which adjust the pi atomic orbitals according to pi density.
Further Investigations on the Microwave Spectrum of NSF: Evaluation of the Molecular Force Field, Centrifugal Distortion Constants, and the Dipole Moment
Authors: Cook Robert L. , Kirchhoff William H.
Published: January 2005

The measurements of the microwave spectrum of NSF have been extended to include transitions involving J as high as 40 and the centrifugal-distortion effects have been accounted for. By combining the analysis of the vibrational and rotational spectra, the molecular force field for NSF has been calculated and the following quadratic potential constants, in millidynes per angstrom, were obtained: f1=10.703, f2=2.872, Fα/d2=0.411, and f2α/d=0.014. Here 1 refers to the SN bond, 2 to the SF bond, α to the NSF bond angle, and d is the geometric mean of the SN and SF bond distances. It was found that the data were too insensitive to calculate f1α and f12 and these constants were assumed to be zero.

The dipole moment was calculated from the Stark effect of the 51,4→42,3 transition and was found to be 1.902±0.012D, where the uncertainty represents the spread in the value of the dipole moment obtained from different methods of treating the data.
Uniformly Valid Asymptotic Approximation for the Quantized Anharmonic Oscillator
Authors: Handelsman Richard A. , Lew John S.
Published: January 2005

A uniformly valid asymptotic expansion is obtained for the solution of the one-dimensional time-independent Schrödinger equation which describes an anharmonic oscillator. The computational method is suggested by McKelvey's treatment of the two-turning-point problem, but has some practical advantages over his procedure. For turning points which lie close together, the energy levels are expressed as an asymptotic power series in ℏ/ (2m)1/2, with coefficients which depend only on the quantum number n and the derivatives of the potential at its minimum. The leading terms of this series are calculated and found to agree with the JWKB and perturbation results of earlier authors. For turning points which do not lie close together, the application of this method is indicated briefly and pursued up to the recovery of the Bohr—Sommerfeld quantum condition.
Mass-Spectrometric Study of Photoionization. VIII. Dicyanogen and the Cyanogen Halides
Authors: Dibeler Vernon H. , Liston Susan K.
Published: January 2005

Photoionization-yield curves are obtained for the molecule and selected radical ions of C2N2, FCN, ClCN, BrCN, and ICN from threshold to 600 Å. Vibrationally excited states of ions and autoionization of Rydberg levels in the molecules are observed and discussed briefly. The X+ ion thresholds in the heavier cyanogen halides are used to obtain: ΔHf0o (CN) = 101.5 kcal mole−1, ΔHf0o (CN+) = 430.0 kcal mole−1, and I (CN) = 14.2 eV. These are applied to compute ΔHf0o (FCN) = 5.6 kcal mole−1, D (F–CN) = 5.0 eV, I (C2) = 12.15 eV, and other thermodynamic properties. The formation of CN+ from dicyanogen apparently includes about 0.6 eV excess energy near the threshold.
Low-Temperature Heat Capacity of Lithium Tetrammine
Authors: Morgan J. A. , Thompson J. C.
Published: January 2005

The heat capacity of lithium tetrammine—Li (NH3)4—has been measured over the temperature range 2°—4°K using a nonadiabatic, heat-burst technique. The Debye characteristic temperature ΘD was found to be 54.9±0.9°K. Due to the low electron density and to the low ΘD no significant value could be determined for the electronic specific heat. The ``ideal'' electrical resistivity was calculated from the ΘD quoted above and the ρ(ΘD) reported by McDonald and Thompson using the Bloch—Grüneisen theory. Excellent agreement with experiment was found. The specific heat of 99.9% pure cesium metal was also measured from 2.1° to 4.2°K as a test of the apparatus and ΘD found to be 38.5°±1.0°K in agreement with previous work.
Molecular Motion and 19F Relaxation in the Liquid Hexafluorides of Molybdenum, Tungsten, and Uranium
Authors: Rigny Paul , Virlet Joseph
Published: January 2005

In order to study molecular motion in liquid molybdenum, tungsten, and uranium hexafluorides, we have undertaken a 19F relaxation study in these liquids. Measurements of the relaxation times as a function of resonance frequency show that the dominant relaxation mechanism is the modulation of the spin—rotation interaction by the molecular motions. It is shown that the strengths of the spin—rotation interactions, which have not been measured directly, can be deduced very simply from the chemical-shift tensors if some approximations are made. The molecular motion is discussed with the help of a generalized Langevin equation in which it is not required that the particle under consideration be much heavier than the molecules interacting with it. It is thus found that the hexafluoride molecules in the liquid phase can rotate through an angle of about 1 rad at 70°C before their angular velocity changes and that this intermediate degree of rotation is consistent both with the low values of the entropies of fusion, which indicate that the rotations do not occur freely, and with the appearance of rotation—vibration structures in their infrared absorption spectra. The self-diffusion coefficients were also measured as a function of temperature. The relationship between the diffusion coefficients and the longitudinal relaxation times is not in agreement with Hubbard's theory, and this is attributed to the failure of both the Stokes' equation and the rotational diffusion model.
Proton Resonance Study of the Hydrides of S, Se, and Te
Authors: Hindman J. C. , Svirmickas A. , Dixon W. B.
Published: January 2005

Gas-phase shielding values for the protons in the hydrides of S, Se, and Te have been determined. Temperature-dependence measurements have been made on the chemical shifts of the protons of these hydrides in the liquid state. Various aspects of the data indicate that, unlike water, these liquid-phase chemical shifts are primarily the result of dispersion interactions. Problems in relating theoretically derived values for the dispersion contribution to the liquid-phase chemical shift to the experimental data are considered briefly.
Nonbonded Potential Parameters Derived from Crystalline Hydrocarbons
Authors: Williams Donald E.
Published: January 2005

The previously described least-squares derivation of nonbonded potential parameters from crystalline aromatic hydrocarbons was extended to include nonaromatic hydrocarbons. Further evidence was obtained that no specially large energy effects are present in the aromatic crystal structures with their π-electron systems. A better separation of the nonbonded energy into C···C, C···H, and H···H components was obtained when the observational equations for the aromatic and nonaromatic structures were combined. The potentials obtained from the combined observational equations gave better fits to the nonaromatics than to the aromatics. Evidence is presented favoring an H–C–H angle of less than 106° in crystalline n-pentane and n-hexane. The parallel packing of molecular chains in the n-hexane crystal and the nonparallel packing in the n-pentane crystal were reproduced by a steepest descent minimization of the lattice energy using the observed lattice constants.
Potential Function for Phosphorus Trichloride
Authors: Levin Ira W.
Published: January 2005

Separate sets of force constants for phosphorus trichloride were determined using supplemental molecular information to constrain the general force fields compatible with the vibrational frequencies. The Coriolis zeta constant for the ν4 mode, the centrifugal distortion parameters, and the mean vibrational amplitudes provided convenient sources of additional force-field information. The agreement among the three final force fields, particularly, for the E symmetry species, confirms the potential function for this molecule.
Lower Bounds to Eigenvalues of the Schrödinger Equation. III. On the Relationship between the Method of Intermediate Hamiltonians and the Partitioning Technique
Authors: Wilson Timothy M.
Published: January 2005

In this paper it is shown that the eigenvalues of the intermediate Hamiltonians of Bazley and Fox, and of Gay, appear as crossing points of the ε1=ε line in the branches of the corresponding multivalued bracketing function ε1. It is further shown that it is possible, from the properties of ε1, to resolve the problem of determining to which level of H a value, obtained using the procedure due to Gay, is a lower bound. It is then shown that the crossing points of ε1 are independent of the size of the reference manifold φa0. These relationships are illustrated by a calculation of lower bounds to some of the low-lying 3S levels of helium and Li+.
Perturbation Theory and Equation of State for Fluids. II. A Successful Theory of Liquids
Authors: Barker J. A. , Henderson D.
Published: January 2005

The perturbation theory previously shown to give good results for the equation of state of a square-well fluid at liquid densities and temperatures is applied to more realistic potentials with soft repulsion, in particular the 6:12 potential. For an arbitrary potential function a modified potential is defined involving three parameters, namely a hard-sphere diameter, an inverse-steepness parameter for the repulsive region, and a depth parameter for the attractive region. When the latter parameters are zero, the modified potential becomes the hard-sphere potential; when they are one, it becomes the original potential. The configuration integral is expanded in a double-power series in the inverse-steepness and depth parameters, the hard-sphere diameter being chosen so that the first-order term in the inverse-steepness parameter is zero. The first-order term in the depth parameter is evaluated essentially exactly and the second-order term approximately: other second-order terms and all higher-order terms are neglected. The resulting equation of state is in good agreement with molecular dynamics, Monte Carlo results, and experimental data for argon at all temperatures and densities relevant for fluids.
Polarization of Phosphorescence and Symmetry of the Lowest Triplet State in Phenoxide Ion
Authors: Lim E. C. , Chakrabarti S. K.
Published: January 2005

Phosphorescence from rigid-glass solutions of phenoxide ion was subjected to a careful polarization study. The 0, 0 region of the emission is polarized mainly along the short (in-plane) and perpendicular (normal-to-the-plane) axes of the molecule. The presence of a short-axis component in the 0, 0 region of phosphorescence leads directly to a 3A1(3La) assignment for the lowest triplet state of this molecule and, by extrapolation, to a 3B1 u assignment in benzene. The solvent effects on the lifetime and polarization of phosphorescence demonstrate the importance of vibronic spin—orbit coupling in inducing dipole-allowed character into the phosphorescence of the phenoxide ion.
Microwave Spectrum, Barrier to Internal Rotation, 14N Nuclear Quadrupole Interaction, and Normal-Coordinate Analysis in Methylisocyanate, Methylisothiocyanate, and Methylthiocyanate
Authors: Lett R. G. , Flygare W. H.
Published: January 2005

The microwave spectra of methylthiocyanate, methylisocyanate, and methylisothiocyanate have been re-examined under high resolution. The rotational constants of methylthiocyanate are A = 15 703.0±2.0 MHz, B = 4155.59±0.1 MHz, and C = 3354.16±0.1 MHz. The barrier to internal rotation of the methyl group determined from the Q-branch splittings in the v = 0 torsional state is 1600±80 cal/mole. Analysis of the 14N quadrupole splitting yields the following coupling constants: χaa = −3.13±0.05 MHz, χbb = 2.19±0.05 MHz, χcc = 0.94±0.05 MHz. The barrier to internal rotation in methylisocyanate is found to be 83±15 cal/mole from the splitting of the K = 0, m = ±3 lines, and χaa is 2.86±0.03 MHz. The corresponding parameters in methylisothiocyanate are found to be 304±50 cal/mole and 1.90±0.03 MHz. The microwave data are consistent with a CNC angle of 147°—148° in methylisothiocyanate as opposed to 140° in methylisocyanate and indicates C–N bond lengths in these compounds of 1.43–1.45 Å. The observed spectra of methylisocyanate and methylisothiocyanate cannot be fit by the usual semirigid internal-rotation treatment. A reasonable fit of the K = 0 lines is obtained only if a semiempirical nonrigid correction factor of the form CTm2 is used and, in addition, the methyl symmetry axis is tilted ∼3° toward the lone-pair electrons on the nitrogen atom. Calculations based on a model which includes the effects of the CNC bending motion on the over-all and internal rotation failed to improve the fit. It is concluded that an extensive vibration-rotation-interaction treatment is necessary in order to achieve a quantitative fit of the microwave data. A normal-coordinate analysis of the three molecules studied was carried out using a valence force field. The present vibrational assignment in methylthiocyanate is substantiated, and the lowest-frequency mode is found to contain a large contribution from the S–C≡N bend in addition to the CSC bend. The lowest-frequency modes in methylisocyanate and methylisothiocyanate are likewise not pure CNC bends, and the CNC bending frequencies in both molecules must be lower than presently assigned.
Modified Semiempirical Approach to the H3 Potential-Energy Surface
Authors: Pedersen L. , Porter R. N.
Published: January 2005

A modification of the Porter—Karplus potential-energy surface for H3 is formulated in which maximum use is made of diatomic potential-energy functions for both H2 and H2+. In this formulation, the classical barrier height is found to vary by several kilocalories when scaling functions are altered slightly or when three-center integrals are ignored. Results are compared with several other semiempirical surfaces and with presently available a priori calculations.
X-Ray Diffraction Studies of Aqueous Alkali-Metal Halide Solutions
Authors: Lawrence Richard M. , Kruh R. F.
Published: January 2005

Radial distribution functions were calculated for 19 concentrated solutions of eight alkali-metal halides. These are analyzed in terms of the sizes and environments of the aqueous ions. The sizes of the hydrated and associated ions are found to be given by their respective crystal ionic radii. From seven to nine water molecules occupy the first hydration spheres of non-associated halide ions, the numbers being relatively independent of solution concentration but increasing slightly with increasing size of the ion. Second and third hydration spheres are correlated with the halide ions, the region of influence for the anions being larger than for the cations studied. Positive ions are found to lie on the dipolar axes and negative ions on the hydrogen—oxygen bond axes of the primary waters of hydration. In contrast to the lithium and sodium halide solutions, considerable direct contact among ions exists in cesium halide solutions. Increasing association occurs with increasing concentration of the solutions and decreasing size of the halide ion. No preferred spatial arrangement is found for the associated ionic species.
Machine Calculation of Thermodynamic Properties of a Simple Fluid at Supercritical Temperatures
Authors: McDonald I. R. , Singer K.
Published: January 2005

A Monte Carlo method for the evaluation of equilibrium thermodynamic properties of a system of interacting particles is described. The classical configurational partition function at a given density is calculated from the estimated value of the weight function γ(Φ), up to a factor that is independent of temperature; γ(Φ)dΦ is the fraction of all accessible configurations of N particles confined to a fixed volume for which the total potential energy has a value between Φ and Φ+dΦ. The weight function is found to vary approximately as (Φ—Φ0)n, where Φ0 and n are constants; n increases roughly linearly with density. The method is applied to the calculation of thermodynamic properties of gaseous argon at four densities in the temperature range between −100° and 150°C. A Lennard-Jones potential function is used and though the agreement with experiment is good there is evidence of inadequacy in the Leonnard-Jones model. All calculations are made for N=32.
Doppler Line Shape of Atomic Fluorescence of Sodium Iodide
Authors: Hanson Howard G.
Published: January 2005

Measurements on the Doppler profiles of the sodium D line atomic fluorescence of sodium iodide which accompanies dissociation of the molecule in the vapor state by polarized ultraviolet light in the 2100–2500-Å range show no pronounced directional effects. The known hyperfine structure of the sodium states, the response of the measuring instrument, and the experimental uncertainties are taken into account. It is suggested that the upper repulsive state of the dissociating molecule is not necessarily a single state, and that some of these upper states possess minima in which some of the excited molecules are trapped for a short time. The measured Doppler speeds are somewhat less than expected when higher energy ultraviolet photons are used, which may be due to dissociations in which the iodine atom is also excited.
Collisional-Radiative Reaction of O2(1Δg)
Authors: Falick Arnold M. , Mahan Bruce H.
Published: January 2005

The reaction 2 O2(1Δg)→2 O2(3Σg−)+hν(6340 Å)has been studied using EPR detection of O2(1Δg). The light intensity depends on the square of the concentration of O2(1Δg) and is unaffected by total pressure variations and the addition of inert gas. The rate constant for light emission was found to be 5±1×10−23 cm3/molecule·sec. This appears to be consistent with the integrated absorption coefficient of ground-state oxygen.
Geometries and Binding Energies of Hn+
Authors: Poshusta R. D. , Matsen F. A.
Published: January 2005

Ab initio calculations were made for Hn+(n=4, 5, 6), with simple Gaussian orbital wavefunctions. Their geometries were determined by minimizing the total energy with respect to relative proton positions. The stable ions, their geometries, electronic symmetries, and estimated binding energies are: H4+, planar C2v, 2A1, 0.54 eV; and H5+, D2d, 1A1, 0.81 eV: H6+ is unstable. The electron densities and vibration frequencies of H4+ and H5+ were also calculated. A hydrogen-bond model is proposed for the binding of H4+ and H5+ (with extensions to H6+ and H7+). The importance of this model for kinetics of certain ion reactions is discussed.
Effusion. I. Angular Number Distributions of Gaseous CsCl from a Near-Ideal Orifice into Vacuum
Authors: Wang K. C. , Wahlbeck P. G.
Published: January 2005

The angular number distributions of CsCl(g) from a double-oven effusion cell with a near-ideal orifice have been measured as a function of the state of the gas using a surface ionization detector. The orifice was 0.50 mm in diameter with a length of 0.013 mm; L/d equals 0.026. The state of the gas was varied over values of the Knudsen number, K, (ratio of mean-free path to orifice diameter) from 63.38 to 0.16. When K≥8.16, the theoretical angular number distribution given by the cosine law of effusion (slightly corrected for orifice length) was observed to be valid. For runs at K less than 8.16, deviations from the theoretical distributions were observed with increasing probability of effusion in the forward direction. The results are compared with results of previous investigations, and a possible explanation for the observed deviations is suggested.
Pressure-Consistent Integral Equation for Classical Fluids: Hard-Sphere Solutions
Authors: Lado F.
Published: January 2005

An approximate integral equation for the pair correlation function of a classical fluid, proposed previously, has been solved numerically for the hard-sphere potential. The equation contains a parameter which is chosen so as to yield consistency between the virial and compressibility equations of state. The computed thermodynamic quantities are compared with those from the Percus—Yevick (PY) and hypernetted-chain (HNC) integral equations, and with the Ree—Hoover Padé P(3, 3) approximant. Further comparisons are made with a Monte Carlo solution at a density ρσ3=0.8. The pressure-consistent results are found to improve upon the PY and HNC equations.
Optical Birefringence in Alkali Halides
Authors: Squire C. F. , Zamecki E. R.
Published: January 2005

Experiments on a number of alkali halide single crystals of high purity and optical quality have shown evidence of small birefringence properties. These crystals have been found to have a small paramagnetic uniaxial anisotropy when studied with a delicate torsion pendulum technique and the magnetic centers were assigned to dislocations oriented in great number along the 〈100〉 direction. The present optical study suggests that the optical-anisotropy-producing defects also may be aligned with the 〈100〉 direction.
Perturbed Orbital Energies in the Radiolysis of Saturated Hydrocarbons
Authors: So Moon-Tak , Huang Suei-Rong
Published: January 2005

In the combination of two saturated hydrocarbon radicals forming a new bond, a perturbed orbital energy will arise. This energy is equivalent to the energy necessary to decompose the product molecule into the two original radicals. By comparing perturbed orbital energies, it is possible to predict the decomposition products of irradiated molecules. The secular equations derived are solved using the LCBO molecular-orbital approximations. Theoretical predictions of radiolytic decomposition products, based on the calculated perturbed orbital energies, are then compared with experimental G values. The agreement between theory and experiment is satisfactory.
Ground-State Reduced Potential Curve (RPC) and the Anomaly of Cl2
Authors: Jenč F.
Published: January 2005

The study of ground-state reduced potential curves indicates that either there is some error in the analysis of the spectrum and/or in the values of molecular constants of the Cl2 molecule or a nonnegligible perturbation of the ground state of Cl2 exists. In case the analysis of the spectrum and the values of the molecular constants are correct, the RPC method then leads to the following conclusion: The perturbation of the electronic states of halogens, predicted in order to explain the remarkably anomalous intensities of the band spectra, is, in I2, of the type proposed by Van Vleck whereas, for Cl2, the interpretation suggested by Mulliken holds.
Deviations from Pairwise Additivity in Intermolecular Potentials
Authors: Williams D. R. , Schaad L. J. , Murrell J. N.
Published: January 2005

The various contributions to the interaction energy as defined in the theory of intermolecular forces in the region of small orbital overlap [J. N. Murrell, M. Randic, and D. R. Williams, Proc. Roy. Soc. (London) A284, 566 (1965)] are generalized to many-body systems. Each contribution is examined in a qualitative manner for deviations from pairwise additivity. Numerical calculations of the exchange energy for three helium atoms in triangular and linear arrays are made utilizing the available expansions of Slater-type orbitals in terms of a Gaussian set. The nonadditive terms for these energies are then calculated over a range of interacting distances. It is concluded that for weakly interacting nonpolar molecules nonpairwise additive terms in the intermolecular potential are likely to be small.
Strengths, Widths, and Shapes of the Lines of the 3ν CO Band
Authors: Burch Darrell E. , Gryvnak David A.
Published: January 2005

Spectral curves of several CO samples have been used to investigate the 3ν band whose center is near 6350 cm−1. The strength of the band for the common 12C16O isotope has been found to be 0.0130±0.0005 atm−1·cm−1STP·cm−1. An empirical equation, Fm=1+0.011m, has been derived to account for the influence of vibration—rotation on line strengths. The half-widths of the self-broadened lines at 1 atm pressure vary from approximately 0.090 cm−1 at | m | = 1 to 0.062 cm−1 at | m | = 20. The widths of self-broadened lines are 1.08±0.005 times as great as N2-broadened lines at the same pressure. The Lorentz line shape appears to be appropriate for the collision-broadened lines within a few cm−1 of their centers; but the extreme wings of the lines are sub-Lorentzian.
Far-Infrared Spectra of Ring Compounds. II. The Spectrum and Ring-Puckering Potential Function of Cyclopentene
Authors: Laane Jaan , Lord R. C.
Published: January 2005

The infrared spectrum of cyclopentene has been recorded in the range 18–300 cm−1. Two series of thirteen and nine Q branches, respectively, were observed, both of which arise from the strongly anharmonic energy levels of the B1 ring-puckering vibration. The longer, more intense series is assigned to molecules in the ground vibrational state of all the other vibrations, and the shorter, weaker series to molecules in the first excited state of the A2 ring-twisting vibration. Each set of Q branches can be fitted to transitions between the energy levels of a double-minimum potential function of the form V=a(x4—bx2), where x is the B1 ring-puckering coordinate. The height of the barrier opposing planarity is calculated to be 232±5 cm−1, and the equilibrium angle between the two dihedral planes of the puckered ring to be 23.3°±1°.
Magnetic-Field Deflection of XeF6
Authors: Code R. F. , Falconer W. E. , Klemperer W. , Ozier I.
Published: January 2005

The deflection of a molecular beam of XeF6 has been measured in an inhomogeneous magnetic field. From the similarity of the deflection of XeF6 and SF6 and the difference with the deflection of O2 it is concluded that gaseous XeF6 at room temperature does not contain a paramagnetic component greater than ∼1% in abundance. This conclusion is not consistent with Goodman's hypothesis that a low-lying 3Tu state of XeF6 is appreciably populated at room temperature.
Kinetic Theory of Polyatomic Gases
Authors: She Richard S. C. , Sather Norman F.
Published: January 2005

A classical-mechanical kinetic theory of dilute gases is developed for molecules with arbitrary degrees of freedom and interacting according to an arbitrary potential. The Boltzmann equation for the truncated singlet distribution function is derived by application of a general form of the divergence theorem, and the equilibrium solution is obtained from an H theorem for the fluid. The solution of the Boltzmann equation by a procedure of the Chapman—Enskog type is described for the case of molecules having translational and rotational degrees of freedom. Formulas for the transport properties of the gas are obtained in the form of multidimensional integral functionals of the intermolecular potential function.
Near-Infrared Band Progressions of Ring Molecules and Ring-Puckering Motion
Authors: Ueda Toyotoshi , Shimanouchi Takehiko
Published: January 2005

A series of bands found in the 2900–2600-cm−1 region of infrared spectra of 2,5-dihydrofuran, trimethylene oxide, cyclopentene, 2,5-dihydrothiophene, 2,3-dihydrofuran and 2,3-dihydrothiophene are assigned to the ring-puckering difference spectra, of which the reference band is the CH2 symmetrical stretching vibration.

The assignments were confirmed for 2,5-dihydrofuran and trimethylene oxide, for which the pure ring-puckering bands had already been analyzed in detail. From the difference spectra the puckering potential of cyclopentene was determined as V(Z)=0.551×104Z2+0.533×106Z4+0.554×103exp(−100Z2) with the central barrier of 244.6 cm−1, and that of 2,5-dihydrothiophene was V(Z)=0.1396×105Z2+0.6637×106Z4, where V is in cm−1 and Z is in angstroms.

The spectrum showed that 2,3-dihydrofuran has the nonplanar structure with the potential barrier height of about 86.8 cm−1. For 2,3-dihydrothiophene tentative assignments were given and the puckering potential was calculated.
Thermodynamics of the Critical Point: Liquid—Vapor Systems
Authors: Davis Bruce W. , Rice O. K.
Published: January 2005

Two separate Taylor series in pressure are necessary to describe behavior in the G and L single-phase regions of a one-component fluid. It is shown that (∂3P/∂ρ3)c is zero or very nearly so, (∂4P/∂ρ4)c,G=−(∂4P/∂ρ4)c,L and (∂2P/∂ρ∂T)c,G=(∂2P/∂ρ∂T)c,L. Derivations are given for a cubic coexistence curve and the gas branch of the critical isotherm. Higher-order critical coefficients are evaluated and discussed. The theory is consistent with a line of singularities or discontinuities along the critical isochore.
Conjecture Concerning an Asymptotic Modification of the Yvon—Born—Green Equation for Fluids of Rigid Spheres and Disks
Authors: Young David A. , Rice Stuart A.
Published: January 2005

An asymptotic (long-range) modification of the Yvon—Born—Green equation for rigid spheres and disks is made which extends the validity of the equation to pressures above the Kirkwood limit. Modification of the YBG equation with both short-range and long-range terms yields equations of state in good agreement with molecular dynamics experiments up to the fluid—solid phase transitions. The application of this technique to fluids with attractive potentials and to other integral equations is briefly discussed.
Delayed Luminescence of Organic Mixed Crystals. VI. Delayed Excimer Fluorescence of Pyrene in Biphenyl
Authors: Srinivasan B. N. , Kinoshita M. , McGlynn S. P.
Published: January 2005

Phosphorescence, fluorescence, delayed fluorescence, excimer fluorescence, and delayed excimer fluorescence of pyrene have been studied in a host biphenyl system. The delayed fluorescence and delayed excimer fluorescence are biexcitonic, have identical lifetimes at all temperatures and exhibit similar dependency of emission intensity on temperature; therefore, they both originate in identical kinetic events. These events involve thermal depletion of a trap of energy ∼1000 cm−1 less than the lowest energy host exciton triplet band and of lifetime ∼0.2 sec; this trap species may or may not be, but probably is not, a contaminant detected phosphorimetrically in the purified biphenyl material. It appears that trapping of the host triplet exciton occurs more efficiently at monomer pyrene sites than at nascent excimeric pyrene sites (regions, perhaps, of pyrene microcrystallinity). The excimer and delayed excimer fluorescence exhibit vibrational structure under certain circumstances; this structure is analyzable in terms of ag modes of the ground-state monomeric pyrene. Those crystals which possess broad (i.e., unresolved) excimer spectra exhibit a distinct red shift of this spectrum as the temperature is decreased; this behavior is rationalized herein. The guest phosphorescence intensity and lifetime are more or less temperature-independent; this behavior is quite characteristic of materials with large T1H—T1G bandgaps. Excitation spectra for all emissions are presented; it is shown thereby that trap species other than T1G are the reservoir whence thermal excitation to the host exciton band T1H proceeds. The thesis developed is that delayed excimer fluorescence and delayed fluorescence are produced by annihilation of a trap triplet and a guest triplet.
Effect of Pressure on the Lattice Parameters of Manganese Antimonide
Authors: Lynch R. W.
Published: January 2005

The lattice parameters and relative volume of MnSb have been measured as functions of pressure to 100 kbar. The initial compressibilities are (1/a0) (da/dp) = − (4±1)×10−4 kbar−1, (1/c0) (dc/dp) = − (14±3)×10−4 kbar−1, and (1/V0) (dV/dp) = − (22±5)×10−4 kbar−1. It was found that the high-pressure Curie-point data reported by Samara and Giardini and by Hirone et al. do not fit a simple interaction curve defined by the Curie points of MnAs, MnSb, and MnBi. A calculation using an equation proposed by Bean and Rodbell indicates that the thermal demagnetization of MnSb at constant pressure may become a first-order process at a pressure of about 45 kbar. However, no evidence of a first-order transformation could be seen in this work.
Unrestricted Hartree—Fock Calculations on Linear-Atomic-Chain Models Yielding the ``Surface'' (End) States
Authors: Koutecký Jaroslav
Published: January 2005

Restricted and unrestricted Hartree—Fock methods have been applied to the study of the properties of the Tamm and Shockley surface states. Linear polyenic chains were chosen as models and the PPP-type semi-empirical method used. The SPO (spin-polarized orbital) results on Tamm surface states and their physical interpretations are discussed. Further, the radical—or polyradical—character of atomic chains yielding the Shockley surface states was obtained and is discussed. Possible implications for the surfaces of real semiconductor crystals and their geometry are suggested.
Ab Initio Studies of Small Molecules Using 1s Gaussian Basis Functions. II. H3+
Authors: Schwartz Maurice E. , Schaad L. J.
Published: January 2005

Self-consistent-field and CI variational calculations are presented for the ground state of H3+ using a basis of floating 1s Gaussian orbitals. The best SCF calculation, thought to be near the Hartree—Fock limit, gives E=−1.29993 a.u. for Re=1.6405 a.u. in equilateral triangular (D3h) geometry. The CI wavefunction which is the best rigorous variational result presently available for H3+ gives E=−1.33764 a.u. at Re=1.6504 a.u. in D3h geometry. It is estimated to lie 0.004–0.01 a.u. above the exact result. The electronic structure of H3+ is interpreted in terms of three-center bonds since the electron density is found to be higher within the triangle than along its sides. Enthalpy, entropy, and Gibbs free energy are computed, and the thermodynamics of several reactions of H3+ examined. In particular, the standard molar enthalpy of formation is found to have a rigorous upper bound of 270 kcal. Variational studies are also presented for D3h H3+ + which give E=−0.12373 a.u. at R=1.68 a.u.
Significance of the Pariser Approximation on the One-Center Electron Repulsion Integral
Authors: Anno Tosinobu
Published: January 2005

The one-center electron repulsion integral (χpχp | χpχp) as obtained by (χpχp | χpχp)=I−A,where I and A are the ionization potential and the electron affinity of an appropriate valence state, is shown to be the one for the negative ion rather than for the neutral atom. The argument is based on the assumptions that an energy integral for the neutral atom equals the arithmetic mean of the corresponding integral for the positive and the negative ions and that Koopmans' theorem is correct. The validity of the assumptions is discussed. The implication of the present conclusion in the semiempirical MO theory is also discussed.
Nuclear Spin Relaxation in 1,1-Difluoroethylene in Solution
Authors: Kanazawa Yoko
Published: January 2005

An experimental method for the determination of the relative values of τ1 and τ2 by the nuclear Overhauser effect proposed by Kuhlmann and Baldeschwieler is applied to 1,1-difluoroethylene, where τ1 and τ2 are the correlation times for the change in rotational quantum number and for molecular reorientation, respectively. The proton transition probability WH, the fluorine transition probability between the levels belonging to the same symmetry representation WF(A), and the fluorine transition probability between states of different symmetry WF(B) are obtained by NMR and NMDR experiments in solutions of CF2CH2 in various solvents. The temperature dependence of these transition probabilities measured between −40° and 33°C shows that τ1≪τ2. The ratio of diagonal and off-diagonal components of the spin—rotation interaction tensor is (Cxx2+Cyy2+Czz2)/(Cyz2+Czy2)≃40.The change in anisotropic intermolecular interactions obtained by a change of solvent affects τ1 more than τ2.
Anisotropy of Polarizability of n-Alkane and Polymethylene Chains with GG′ Conformations Prohibited
Authors: Smith Richard P.
Published: January 2005

The mean-square anisotropy of the molecular polarizability, 〈γ2〉, is calculated for the finite diamond lattice n-alkane chain with gauche—gauche-prime conformations prohibited, weighting all allowed conformations equally. The result is essentially 〈γ2〉=0.609NΓCC2, where ΓCC is the anisotropy of a CH2 unit and N is the number of units, as compared with 〈γ2〉=0.500NΓCC2 for the unrestricted diamond lattice model. The exact expression for 〈γ2〉 differs significantly from the above approximate expression only for chains having just a few CH2 units.