bluuebunny/crossref_metadata_2025 huggingface dataset:
Scattering of High-Velocity Neutral Particles. XIV. He–He Interaction below 1.1 Å
Authors: Jordan J. E. , Amdur I.
Published: January 2005

Total elastic cross sections have been measured for helium atoms within energies between 300 and 2000 eV which have been scattered by room-temperature helium through an effective laboratory angle greater than about 1×10−2 rad. Special features and procedures used in the experiments include the use of a magnetic field to increase the positive-ion current in the source, acceleration of the positive ions extracted from the source in a region of relatively low pressure with a consequent reduction in their energy spread, production of neutrals by charge transfer in a chamber separated from the scattering chamber, modulation of the neutral beam to produce an ac signal on a compensated thermal detector, and amplification of the detector signal with synchronous rectification, at the modulation frequency, of the amplifier output.

A detailed analysis of the scattering results treats effect on the measured cross sections of the intensity distribution in the beam and of the beam-detector geometry, interpretation of the results in terms of different empirical monotonic potential functions (the exponential, the screened Coulomb, and the point repelling inverse power), and the effects of quantum scattering.

Numerical values for the He–He potential between 0.61 and 1.12 Å for the three assumed potential functions show good internal consistency and agree with the best theoretical values within the combined estimates of the maximum uncertainties in the experimental and theoretical values. The mean potential obtained from the three empirical functions may be represented within about 1.8% by V(r)mean=196 exp(−4.21r) eV; 0.61 Å<r<1.12Å.
Molecular-Orbital Treatment of IF7
Authors: Oakland Richard L. , Duffey George H.
Published: January 2005

The naive extended Hückel theory has been employed in determining the stable conformation of IF7. The Slater-type atomic orbitals that form σ bonds were used as basis functions. The D5h bipyramidal structure was found to be lowest in energy.
Infrared-Emission Studies of Electronic-to-Vibrational Energy Transfer. II. Hg*+CO
Authors: Karl G. , Kruus P. , Polanyi J. C.
Published: January 2005

In an earlier work (Part I of this series) electronically excited mercury Hg* was formed in a low-pressure flow system by the 2537-Å irradiation of Hg+CO; electronic-to-vibrational energy transfer was studied by recording the infrared emission spectrum of vibrationally excited carbon monoxide (symbolized CO†) in its ground electronic state.

In the present work the earlier experiments have been placed on a more quantitative footing. Absolute concentrations of Hg*1(63P1), Hg*0(63P0) and CO†, v=2–9, have been measured under a variety of experimental conditions. The direct excitation of CO to v≤9 by electronic-to-vibrational transfer has been confirmed. Both Hg*1 and Hg*0 were found to be effective in bringing this about; the efficiency of Hg*1 being, however, about an order-of-magnitude greater than that of Hg*0. Vibrational relaxation was examined by observing the decay of the CO† infrared afterglow down the nonilluminated portion of the reaction tube. A set of rate constants, kv (or cross sections σv2), for electronic-to-vibrational transfer Hg1, 0*+CO→ lim kvHg+COv†were derived from observed sets of steady-state concentrations Nv under various experimental conditions. The best set of kv, expressed relative to kv=9=1.00, was; kv=2=80, kv=3=70, kv=4=60, kv=5=48, kv=6=43, kv=7=35, kv=8=15, kv=9=1.00, kv≥10≈0. These kv and the corresponding σv2 can be converted to approximate absolute units, since the over-all cross section for electronic-to-vibrational transfer in collisions Hg*1 0+CO, symbolized σvib2=(σvib2)1+(σvib2)0=Σv[(σv2)1+(σv2)0], was measured and found to be in the range 0.5–3.0 Å2. The most probable individual values for the total cross sections with Hg*1 and with Hg*0 as the donor atoms were, respectively, (σvib2)1≈1.3 Å2 and (σvib2)0≈0.09 Å2.

Energy matching is of no importance in this transfer, since a ``resonant'' conversion of electronic-to-vibrational energy would require that kv=20=1 and kv2<0=0, in marked contrast to the findings. The results are discussed in terms of a complex HgCO* which undergoes intersystem crossing onto a potential-energy surface which correlates with electronic ground-state Hg(61S0); the electronic potential energy being released into nuclear motion as the system ABC gives A+BC across this lower surface. Two possible types of energy release are distinguished, corresponding to relaxation predominantly along the rAB and the rBC coordinates, respectively.
Adsorption of Simple Diatomic Gases on Evaporated Boron Films
Authors: McElligott P. E. , Roberts R. W.
Published: January 2005

The adsorption behavior of N2, H2, O2, and CO has been studied on evaporated films of amorphous boron at 300°K. Evidence is presented for believing that H2, O2, and CO chemisorb readily on these films at 300°K. This evidence is derived from several sources: observations of significant reductions in the surface areas of the films after exposure to the gases, the rapid adsorption of large amounts of the gases on the films, and the apparent irreversibility of the gas adsorption. Nitrogen is not observed to chemisorb to any significant extent on the boron films at 300°K.
Vibrational Assignment of Phenanthrene-d10
Authors: Schettino V.
Published: January 2005

A vibrational assignment of phenanthrene-d10 is presented. The infrared spectrum in polarized light of the single crystal and the Raman spectrum of the solution are analyzed with the help of a theoretical prediction of the normal frequencies by using a valence force field derived from anthracene. The results obtained are in complete agreement with the previous assignment of phenanthrene-d0.
Microwave Spectrum, Structure, Dipole Moment, and Barrier to Internal Rotation of Phosphorus Trifluoride—Borane
Authors: Kuczkowski R. L. , Lide David R.
Published: January 2005

The microwave spectrum of several isotopic species of phosphorus trifluoride—borane (F3PBH3) has been measured and the following structural parameters determined: d(BH) = 1.207±0.006 Å; d(PF) = 1.538±0.008 Å; d(PB) = 1.836±0.012 Å; ∠HBH=115°04′±1°; ∠FPF=99°50′±1°. The dipole moment was evaluated from Stark splittings as 1.64±0.02 D.

The vibrational satellite spectrum associated with the excited ν12(E) and ν6(A2) states for F3P11BH3 was found to be strongly perturbed and was fitted to the theory for a first-order Coriolis interaction. The analysis of this perturbation and the measurement of the ν12 fundamental in the infrared spectrum permitted the inactive torsional fundamental ν6 to be determined as 197±5 cm−1. This leads to a potential barrier to internal rotation of 3240±150 cal/mole.

The enthalpy of dissociation for the reaction 2 F3PBH3⇆2 PF3+B2H6 (298°) was determined as 10.99 kcal. The experimental results are compared to those found for other related compounds.
Rotational Relaxation of Homonuclear Diatomic Molecules
Authors: Nyeland Carl
Published: January 2005

Through the use of Wang Chang and Uhlenbeck's theory of polyatomic gases, rotational relaxation times for homonuclear diatomic molecules have been calculated. The model adopted is that of two molecules rotating in the same plane which also serves as the collision plane. The intermolecular potential used is Parker's modification of the Morse potential, where the molecular orientations are taken into account only in the repulsive part. This leads to a relaxation time, for which the ``collision number'' Zrot is essentially independent of temperature. Owing to the lack of any experimental information concerning the temperature dependence of rotational relaxation the discussion has been limited to a few comments about earlier calculations.
On the Separation of the Broadening-Relaxation Time and Molecular Concentration from Pure-Rotational Spectroscopic Intensity Data
Authors: Harrington Howard W.
Published: January 2005

The broadening-relaxation time τ and the molecular concentration N of the absorbing species become separable at the transition frequency if a new intensity coefficient Γ is substituted for the conventional Beer's Law intensity coefficient γ. This investigation reveals that Γ generally can be factored into two measurable terms, η and φ. η is shown to be linear with molecular concentration and independent of relaxation time and φ is a dimensionless function of the broadening-relaxation time. The essence of this separation is that it is possible to fix to a constant value the number of radiation excited transitions each molecule will undergo during the molecular rotational relaxation time. When the number of transitions per molecule is the same for all relaxation times, the amount of radiation absorbed during the relaxation time is proportional to the molecular concentration of the absorbing species. The theory has been subjected to experimental examination. Several of the results are presented and discussed. This intensity coefficient gives rise to a new line shape, which is compared with the conventional line shape.
Crystal Structure of Paramagnetic DyMn2O5 at 298°K
Authors: Abrahams S. C. , Bernstein J. L.
Published: January 2005

Paramagnetic DyMn2O5 crystallizes in the orthorhombic system with lattice constants a=7.2940±0.0008, b=8.5551±0.0008, and c=5.6875±0.0008 Å, in the space group Pbam(D2h9). There are four DyMn2O5 per unit cell. The crystal structure was solved by a combination of three-dimensional Patterson and Fourier series and refined by the method of least squares. The integrated intensities of 5094 reflections were measured by PEXRAD, with 976 symmetry-independent structure factors significantly above background. The final agreement factor between measured and calculated structure factors is 0.0401. There are two independent Mn atoms. One is pentacoordinated, with a slightly distorted tetragonal pyramidal configuration: two basal Mn–O distances are 1.926±0.006 Å, the other two are 1.911±0.005 Å, and the apical Mn–O bond, nearly normal to the basal plane, is 2.020±0.005 Å. The other Mn occupies a slightly compressed octahedron, with four planar Mn–O bonds of 1.940±0.004 Å and two, normal to this plane, of 1.873±0.004 Å. The octahedral Mn environment closely resembles that in β-MnO2. The Dy is surrounded by a somewhat distorted square-antiprismatic polyhedron of oxygen atoms, the Dy–O distance ranging from 2.341±0.005 to 2.469±0.005 Å, the average being 2.390 Å. The thermal vibrations are significantly anisotropic. The room-temperature paramagnetism could mask an antiferromagnetic ordering of the octahedral Mn atoms.
Analytical Treatment of Excluded Volume. II. Quasi Random-Flight Behavior
Authors: Alexandrowicz Z.
Published: January 2005

A ``quasi'' random-flight behavior of real chains of r segments is described by the following: The distribution of long statistical elements in typical chain configurations can be expressed by a product of functions, each describing an element independently of the others. This random property differs from true random flight in three aspects: (a) The elements' length depends on r, being as stretched as the most probable end-to-end distance of the chain. (b) The randomness holds only for elements constituting a large enough fraction of r. Its employment is restricted therefore to describing distances of correspondingly long enough sequences of j segments, or j/r> (j/r)min. (c) The random behavior is characteristic of typical configurations, corresponding to a given mean state of the chain. It will lead therefore to a Gaussian distribution of distances hi only if the specification of various hi's does not vary the shape, and the mean state, of the chain to any appreciable extent. This implies however that j is not too large, or j/r< (j/r)max. This description, it is argued, appears to be self-consistent. For: assuming that the mean density of contacts in the bounded range of (j/r) can be evaluated in terms of the random elements, computing on this basis (as fluctuations) the microscopic variation of the interaction energy, and, from it, the typical variation of the configurational probability, and judging from the results, it is concluded that the mean density of contacts can be indeed evaluated with random elements—as assumed to begin with. The contacts contributing to long-range interactions in 3-dimensional chains fall within the range bounded by (j/r)min to (j/r)max; their evaluation with Gaussian probabilities (Pt. I) will therefore be justified if the above description is correct. Examination of two-dimensional chains shows that (j/r)max is violated; a relatively simple modification of the treatment however suffices, leading to αn2∼n0.434. The behavior of four-, and more-, dimensional chains is also considered.
Separation of 1La Excitation Energies of Conjugated Hydrocarbons into Orbital Energy Difference and Two-Electron Term Contributions
Authors: Michl J. , Becker Ralph S.
Published: January 2005

Working within the framework of the self-consistent-field approximation, an estimate is given for the value of experimental counterparts of the orbital energy difference and the two-electron term contribution to the 1→−1 excitation energy for eight conjugated hydrocarbons. The two-electron term is almost constant for the benzenoid hydrocarbons examined but markedly different in the case of azulene. The orbital energy difference is responsible for the variation of the excitation energy in the benzenoid series, and, in all cases examined, it is simply related to the topology of the molecule.

Semiempirical limited configuration-interaction calculations in the π-electron approximation (Pariser—Parr—Pople) are in qualitative agreement with these findings. The well-known facts that simple Hückel calculations lead to a good correlation with the excitation energies of the benzenoid hydrocarbons if the regression line is not forced to go through the origin and that azulene is far off the regression line are shown to be in accordance with the findings.
On the Internal Rotation Potential in H2O2
Authors: Palke William E. , Pitzer Russell M.
Published: January 2005

Self-consistent-field calculations for the 0°, 60°, 100°, 110°, 120°, 130°, and 180° (dihedral angle) configurations of the H2O2 molecule are presented. A minimum basis set of Slater orbitals with Slater exponents was used in each case. Further calculations for the 0°, 120°, and 180° geometries were made with improved exponents. The energy minimum was obtained at 180° in both sets of calculations; the computed cis—trans energy differences were considerably larger than the experimental value.
Dimerization and the Initial Pressure Dependence of the Viscosity of Polar Gases
Authors: Singh Yashwant , Deb S. K. , Barua A. K.
Published: January 2005

The contributions of bound and metastably bound molecules to the second virial coefficient of polar gases have been calculated by assuming equal probability for all the relative orientations of the interacting dipoles. The results have been utilized to explain the initial pressure dependence of the viscosity of polar gases. The results obtained for steam and ammonia are quite satisfactory.
Consideration on Frictional Coefficient of a Chain Polymer in Solution
Authors: Isihara A. , Guth E.
Published: January 2005

The translational diffusion constant of a long chain molecule is evaluated by taking into consideration of the hydrodynamical interactions between the segments of the molecule in the Oseen approximation. The molecules are assumed to be represented by a Gaussian chain for an explicit result, but the basic theory itself can be applied to more general cases. An integral equation similar yet different from that of Kirkwood and Riseman is proposed. A Fourier transform method is presented to solve this integral equation. As a result the diffusion constant can be related to a characteristic length R0 of a polymer molecule.
Toward a Charge-Density Analysis of the Chemical Bond; The Charge-Density Bond Model
Authors: Ransil Bernard J. , Sinai John J.
Published: January 2005

Total-charge-density diagrams (ρ diagrams) are presented for the ground states of Li2, N2, F2, HF, and LiF in BMMO (best minimal molecular-orbital) and accurate SCF (self-consistent-field) approximations. On the basis of contour geometry the ρ diagrams are partitioned into regions of localized and delocalized charge density for which approximate average electron populations, called PL and PD, respectively, are computed. The PL are computed as a function of contour value and contour radius and provide a quantitative measure of the degree of charge transfer in the neighborhood of the nuclei attributable to molecule formation. Criteria for binding, nonbinding, and antibinding, following Berlin's treatment of the Hellmann—Feynman electrostatic theorem, are discussed. A positive correlation between the binding energy De and the ratio PD/PL is noted.

An alternate approach to interpreting the ρ diagram is introduced, in which charge-density-difference diagrams (Δρ diagrams) are interpreted as bond maps, i.e., diagrams which define regions of localized charge distributions on the corresponding ρ maps. Binding or antibinding character is then determined for each region of the total-density map using Berlin's forces-on-nuclei criteria. Corresponding electron populations for these regions may be computed by integrating the total density over the regional limits defined by the zero contours. A linear relationship between De and the ratios of these populations is noted. The Δρ maps display distinctly different contour patterns for homonuclear and heteronuclear molecules, which characteristic provides a means of differentiating and classifying binding mechanisms in terms of charge-density sharing and charge-density transfer, compatible with conventional bonding concepts. The possible sources of error in calculation and interpretation of the Δρ maps are enumerated and briefly discussed.

Although interpretable in terms of orbital theory concepts, accurate ρ diagrams and Δρ diagrams provide an opportunity to interpret chemical phenomena strictly in terms of localized nonintegral intra- and intermolecular electron-charge-density distribution and displacement. In this context orbital theories should be regarded as a means to an end, i.e., computation of a total wavefunction. Explanations in terms of orbitals and single or paired electrons are probably best reserved for particle-type phenomena, e.g., ionization potential, spectroscopic data, etc., while phenomena associated with charge interaction, rearrangement, and displacement (i.e., chemical reactions) are perhaps more appropriately studied in terms of spatially localized aggregates of bulk charge and their associated nonintegral electron populations, interpreted from the ρ diagrams and Δρ diagrams.
On the Decay of Initial Correlations in Stochastic Processes
Authors: Oppenheim Irwin , Shuler Kurt E. , Weiss George H.
Published: January 2005

We study the relaxation of a noninteracting, initially correlated many-particle system in contact with an infinite reservoir. We use the master equation to study the time development of the r-particle distribution function Pr(n;t) and assume that the relaxation process is Markovian. We study the decay of the correlations by investigating the time development of the r-particle Ursell functions, Ur(n;t). We show that the correlation function Ur(n;t) goes to zero much more rapidly with time than the r-particle distribution function approaches its equilibrium value Pr(n; ∞)=Π lim i=1rP(ni; ∞).The exact forms of the relaxation of Pr(n;t) and Ur(n;t) depend upon the eigenvalue spectrum of the transition rate matrix of the master equation. The general theory is developed and then applied to a number of examples.
Thermogravitational Thermal Diffusion in Liquids. III. Velocities, Gradients, and Fluxes in a Narrow Cylindrical Annulus
Authors: Horne Frederick H. , Bearman Richard J.
Published: January 2005

The velocities, gradients, and fluxes in a binary liquid system in a narrow, cylindrically symmetrical annulus subjected to a horizontal temperature difference are obtained by a self-consistent application of the locally linear macroscopic transport equations. In the case of thermogravitational thermal diffusion, the expression for the vertical composition gradient is identical in form to the expression previously found by the authors [J. Chem. Phys. 37, 2842 (1962)] by a less rigorous procedure. The nine independent partial differential equations are solved for nine independent pointwise steady-state properties. These are, in the order in which they are obtained formally, vertical barycentric velocity, radial barycentric velocity, pressure, composition, radial diffusion flux, vertical diffusion flux, temperature, radial heat flux, and vertical heat flux. Final equations are infinite series which may be truncated according to the experimental system of interest. Formulas are derived for three experimental cases: binary mixture subjected to zero temperature gradient, pure fluid, and binary mixture subjected to nonzero temperature gradient.
Shock Compression of Argon. II. Nonadditive Repulsive Potential
Authors: Ross Marvin , Alder Berni
Published: January 2005

By means of the Monte Carlo method the shock Hugoniots of argon have been analyzed for an effective pair potential. This effective pair potential for the low-density Hugoniots closely agrees with the potential derived from molecular beams indicating the high accuracy of the pair-wise additivity approximation besides confirming the consistency of two complex experiments. For the high-density Hugoniot, however, the effective pair potential is considerably stiffer than the pair-wise potential at high compression. For liquid argon compressed twofold, the nonadditivity effect in the potential is about 30%. The theoretically derived pair-wise potential is only a few percent softer than this nonadditive potential. This theory might be improved further by allowing for distortions of the outer electron shell in a direction away from the contact region of the interacting pair of atoms. At high density the surrounding medium inhibits this distortion which leads to the observed stiffening and to the close agreement with the theory of spherical atoms.
Frenkel and Wannier Spin Excitons in Organic Free-Radical Crystals
Authors: Soos Zoltán G.
Published: January 2005

It is shown that organic molecular crystals containing linear chains of exchange-coupled free radicals fall into two classes which may be characterized by their spin excitations. Two spins forming a Frenkel spin exciton remain adjacent in the crystal, while spins forming a Wannier spin exciton move through the crystal independently. This difference in the structure of the triplet excitations leads to a different temperature and pressure dependence for the width of the exchange-narrowed line observed by spin resonance, to different exciton fine structure, and to different magnetic susceptibility-vs-temperature curves. It is suggested that paramagnetic excitations in organic charge-transfer compounds containing chains of alternately positive and negative ion radicals are Wannier spin excitons.
Overlap as a Criterion for Conduction in the Cubic Tungsten Bronzes
Authors: Gerstein B. C. , Thomas L. D. , Silver D. M.
Published: January 2005

Overlap calculations using Slater orbitals with exponents adjusted to match SCF functions have been performed on eight pairs of orbitals which have been considered to have some pertinence to conduction in the cubic sodium tungsten bronzes. The results support the dπ—pπ model proposed by Sienko and by Good-enough and clearly indicate where the overlap criterion alone breaks down, namely for the case of sodium—sodium pσ—pσ overlap.
Effect on the Lifetime of an Atom Undergoing a Dipole Transition Due to the Presence of a Resonating Atom
Authors: Power Edwin A.
Published: January 2005

The modification of the transition rate from the Einstein A coefficient for an atomic dipole transition due to the presence of a similar atom is obtained without the use of damping theory.
Mean-Square Displacement and Mean-Square Velocity of a Point Mass Defect in NaI
Authors: Jaswal S. S.
Published: January 2005

Following the treatment of Dawber and Elliott for a monatomic system we have derived the expressions for the mean-square displacement (or Debye—Waller factor) and the mean-square velocity (or second-order Doppler shift) of a point mass defect in a diatomic cubic crystal in the harmonic approximation. These quantities are computed as functions of temperature for isotopic impurities substituting for positive and negative ions separately in NaI. The lattice dynamics of the perfect crystal required in these calculations is obtained on the basis of the deformation-dipole model. Finally a brief discussion of the results is given.
Measurement of Excitation and Ionization in an Arc-Heated Supersonic Argon Beam
Authors: Winicur Daniel H. , Knuth Eldon L.
Published: January 2005

Measured values of fractional excitation and fractional ionization are reported for a 1.52-eV argon beam extracted from an arc-heated supersonic free jet. The data indicate that the ions are molecular during at least a portion of the free-jet expansion, that nearly all of the ions are neutralized during this expansion, and that most of the excited particles formed as a consequence of this neutralization are long-lived.
Electrical Conductivity of γ-Irradiated 3-MP Glass and of Photoionized 3-MP—TMPD during Warming from 4° and 77°K
Authors: Wiseall Barrie , Willard John E.
Published: January 2005

The electrical conductivity of γ-irradiated 3-methylpentane (3-MP) glass has been studied as a function of γ dose, temperature, applied voltage, post γ illumination, and the nature and concentration of additives. Three distinct populations of charge carriers are found in samples which have been γ irradiated at 77°K. The first, attributed to the combined mobility of weakly trapped electrons and positive charges, decays almost completely in 30 min in the dark at 77°K. It is reduced by 0.01 mole % of the electron scavenger CCl4, but is not affected by 1 mole % of the positive hole trap 2-methylpentene−1 (2-MP−1). The second, attributed to trapped electrons, is revealed by current flow between 83° and 88°K during warmup. It is eliminated by infrared illumination at 77°K before warm up (which causes a burst of current), or by alkyl halides, and is increased by 2-MP−1. The 85°K peak is absent on warmup of γ-irradiated 3-MP containing biphenyl, but appears if electrons are liberated from the biphenylide ion by illumination with 4100-Å light prior to warmup. The third population of charge carriers becomes mobile above about 92°K, giving maximum current at about 102°K. It is not affected by alkyl halide additives, and must be ascribed to migration of positive and negative ions. Additives capable of forming larger ions of lower mobility lower this current peak and produce new peaks. The areas of the peaks at 85° and 102°K are proportional to the applied voltage over the range tested (4×102 to 8×104 V cm−1). They increase linearly with dose below 1×1018 eV g−1 but more slowly at higher doses. Blocking electrodes reduce these peaks. Between about 88° and 92°K the warmup current of γ-irradiated 3-MP becomes negative, suggesting randomization by thermal agitation of radiation-produced charges which have been oriented by the applied electric field at 77°K. The warmup current spectrum of 3-MP following γ irradiation at 4°K shows a peak at about 60°K in addition to the peaks observed for warmup from 77°K.

When tetramethyl-p-phenylenediamine (TMPD) in 3-MP at 77°K is photoionized, the warmup current shows a peak centered at 108°K, which differs from the similar peak produced by γ irradiation in that it is reduced by the presence of alkyl halides. The effect is attributed to complexing of TMPD by the alkyl halide with resultant trapping of the photoionized electrons in close proximity to the positive ion.
NMR Relaxation Mechanisms at Solid—Gas Interfaces. CH3OH, CD3OH, and CH3OD Adsorbed on Porous Glass
Authors: Fiat D. , Reuben J. , Folman M.
Published: January 2005

Proton relaxation times of CH3OH, CD3OH, and CH3OD adsorbed on porous Vycor glass were studied as a function of the coverage. The shapes of the relaxation rates versus amount adsorbed curves were found to be similar for the three molecules studied, although differences in absolute values and position of extrema were noted.

The longitudinal relaxation time was found to be between one and three orders of magnitude longer than the transverse relaxation time and both were strongly dependent on surface coverage. This is explained by the existence of a distribution of the correlation times characteristic of the molecular motions. Dipolar interactions between the adsorbed molecules and surface OH groups are shown to contribute significantly to the longitudinal relaxation. Other possible interactions and relaxation mechanisms are also discussed.
Effects of High Pressures on the Phosphorescence of Aromatic Hydrocarbons
Authors: Baldwin B. A. , Offen H. W.
Published: January 2005

The phosphorescence spectra, intensities, and lifetimes have been measured for 10 aromatic hydrocarbons, dispersed in polymethylmethacrylate, in the 0–32-kbar pressure range at 298°K. It is observed that the red shift is small (200–450 cm−1 at 32 kbar) and comparable to the red shift observed in fluorescence. The measured phosphorescence lifetime decreases monotonically with increasing pressures over the 0–32-kbar range for nine of the ten aromatics. From dynamic intensity measurements at 0, 10, and 20 kbar pressure it is concluded that the natural lifetime decreases by ≲30% at 20 kbar. Also, the radiationless rate constant must increase by at least the same amount. It is concluded that pressure enhances spin—orbit interaction and the vibrational overlap factors.
Triplet—Triplet Transitions in Naphthalene
Authors: de Groot R. L. , Hoytink G. J.
Published: January 2005

A Pariser—Parr type CI calculation has been made for the triplet—triplet transitions of naphthalene. All configurations singly and doubly excited with respect to the lowest triplet state and with an energy relative to the lowest triplet not exceeding 7.5 eV have been taken into account.

The results have taken away the discrepancy between previous calculations and the experimental observations by Porter and Windsor.
Long-Range First-Order Interaction Energy between Two Excited Hydrogen Atoms in Either 2s or 2p States
Authors: Kim Hojing , Hirschfelder Joseph O.
Published: January 2005

The long-range interactions between two hydrogen atoms in either 2s or 2p states yields the first-order perturbation energy matrix which is still nondiagonal even after the symmetry adaptation of the zero-order degenerate functions. In the diagonalization process of the nondiagonal blocks, it is found that the familiar series expansion of the interaction potential energy in inverse powers of the internuclear separation is not practicable even up to 60 Bohr units.
Thermal Diffusion Factors from the Measurements on a Trennschaukel: Ar–He and Kr–Ne
Authors: Mathur B. P. , Joshi R. K. , Saxena S. C.
Published: January 2005

Measurements of the thermal diffusion factors αT are made on an eight-tube glass trennschaukel with its two ends at about 0° and 100°C. The two systems investigated are Ar–He and Kr–Ne at a composition for which some special interest exists. The αT results are compared with the other available literature values, and the previously observed anomalies are explained on the basis of these new measurements. For the Ar–He mixture containing 81.6% Ar we get an αT value of 0.30 at 318.6°K. Similarly for a Kr–Ne mixture (27.5% Ne) the value is found to be 0.303 at 318.5°K.
Photochromism. I. The Spectroscopy and Energy Levels of Salicylideneaniline
Authors: Ottolenghi Michael , McClure Donald S.
Published: January 2005

As a prerequisite to understanding the photochemistry of salicylideneaniline, its energy levels and their characteristics are deduced from absorption and emission spectra, and by comparison with related molecules. Theoretical calculations are used to help to establish relations between stilbene, benzylideneaniline, azobenzene, and salicylideneaniline (SA). It is concluded that all the ππ* bands observed in SA below 6 eV have analogs in the allowed or forbidden transitions of stilbene. From a study of solvent effects, it is concluded that the internal hydrogen bond of SA causes large changes of band intensity, but relatively small energy changes. The luminescence of SA appears to come from the second triplet rather than the first. This could be understood if the two lowest triplets have quite different geometries. The problem of the triplets is discussed further in the second part of this series.
Theoretical Model for Metal Electrode in Electrolytic Solution. I. Electrical-Double-Layer Structure in Equilibrium
Authors: Hashino T.
Published: January 2005

A model for the potential barrier which arises at the interface as a result of a contact equilibrium between a metal electrode and an electrolytic solution is discussed in an analogy to the electrical junction model of the metal rectifier. Every type of so-called electrode reaction can be represented by a general expression. Involving heterogeneous chemical process in the metal-rectifier model and approaching in terms of the behavior of real charged species from the standpoint of statistical thermodynamics and solid-state physics, the picture of the so-called electrical double layer becomes quite a modified structure compared with that in existing electrochemistry. According to this model it is possible to define unambiguously the so-called preelectrode state and the differential dielectric constant region. This model may be quite useful in problems of electrostatic and kinetic phenomena and also useful in the rate theory of electron-transfer reaction.
Theoretical Model for Metal Electrode in Electrolytic Solution. II. Absolute Rate Theory of Heterogeneous Electron-Transfer Reaction
Authors: Hashino T.
Published: January 2005

A theory of the electron-transfer reaction at the boundary between an electrode and an electrolytic solution is discussed as a heterogeneous process, in analogy with the metal-rectifier theory, according to the contact model proposed in the previous paper. Using the theory of the absolute reaction rate, the rate constant is related to the partition function of the substances participating in this reaction. The relation between the faradaic current and the applied polarization, i.e., the so-called overpotential, can be theoretically derived in a similar form with the familiar expression. Various kinetic parameters, e.g., α value, rate constant etc., may be exactly rearranged as a problem of statistical mechanics and electromagnetism.
Studies of Thermal Annealing of Neutron-Irradiated Tris(dipyridyl)Cobalt (III) Perchlorate. Redistribution of Electrons among the Donors
Authors: Nath Amar , Vaish S. P.
Published: January 2005

Thermally treated and untreated anhydrous samples of tris (dipyridyl) Co(III) perchlorate were ``hydrated'' at 30° in air at a relative humidity of 93%. Some of them were chilled at −78° while others were kept at 30° for a prolonged period before chilling at −78°. The chilled samples were neutron irradiated at −78°. Thermally treated samples chilled immediately after hydration exhibit a much faster rate of thermal annealing as compared to the latter and to the trihydrate. These observations have been interpreted on the basis of the ``variable-depth-electron-donors—isotopic-exchange'' model which postulates an annealing rate proportional to the free-electron density. Evidence is presented for the creation of electron traps and electron—hole ``recombination centers'' during thermal treatment of the anhydrous form and for populating of the electron traps with electrons to form shallow donors during hydration through exo-electron emission. Hence, in the freshly hydrated samples kept at 30° for prolonged periods before chilling and irradiation, a considerable amount of depopulation of the shallow donors takes place resulting in a slower rate of postrecoil thermal annealing. In contrast, the hydrated complex prepared by hydrating the untreated anhydrous sample exhibits a faster rate of annealing on storage at 30° after hydration and prior to irradiation as compared to the samples chilled immediately after hydration. For the trihydrate it has been shown that the electron traps constituted by the crystal imperfections are largely filled up with electrons during crystallization from aqueous solution. However, the process of filling up continues slowly during storage of Co(dipy)3-(ClO4)3·3H2O at 30°C (or at higher temperatures). Consequently, the stored samples show a faster rate of annealing as compared to the freshly prepared ones.
Viscous Flow and Electrical Conductance in Ionic Liquids: Temperature and Composition Dependence in the Light of the Zero Mobility Concept
Authors: Angell C. A.
Published: January 2005

Using the concept of vanishing mobility consequent on the Gibbs—Dimarzio interpretation of the liquid—glass transition, it is shown by a quasiempirical treatment of the data that the isothermal composition dependence of transport at low temperatures may be understood, and expressed analytically, on the basis that the zero mobility temperature T0, is the only composition-dependent parameter in the transport equation. T0 reflects the forces of cohesion in the liquid. Simple equations developed on this basis lead to a description of conductance in uni-divalent nitrate melts, and an account of viscous flow in 0–15N concentrated aqueous solutions which is consistent with the electrical-conductance behavior of the same solutions. The usefulness of the Tobolsky and related parameters in describing deviations from additivity in the conductance of mixed molten univalent nitrates is interpreted in the same terms, providing a rational basis for the parallel between kinetic and thermodynamic behavior in these melts. Attention is drawn to the importance of pre-exponential terms to transport composition dependence at higher temperatures.
Orbit—Orbit Interaction in Many-Electron Atoms
Authors: Fraga Serafin , Malli Gulzari
Published: January 2005

The formulation of Wybourne and Jucys and co-workers has been used for the evaluation of the orbit—orbit interaction (for pn configurations) and the corresponding parameters α, β, and δ (for dn configurations). Values are presented for positive ions, neutral atoms, and negative ions, and for a number of isoelectronic series.
Hydrogen Formation in the Radiolyses of Liquid Butene−1 and trans-Butene−2
Authors: Hatano Yoshihiko , Shida Shoji
Published: January 2005

The effect of temperature and various electron or positive-ion scavengers on hydrogen formation in the radiolyses of liquid butene−1 and trans-butene−2 have been examined. The hydrogen formation is not appreciably affected by temperature and these additives, which indicates that thermal free radicals and ionic species may not play an important role in hydrogen formation from these olefins. The liquid-phase radiolyses of C4H8−1—C4D8−1 and trans-C4H8−2-trans-C4D8−2 mixtures have also been investigated. The data indicate that hydrogen for the most part may be formed by bimolecular processes. The results have led to the conclusion that the mechanism of the hydrogen formation may be interpreted in terms of the hydrogen-atom abstraction reaction of hot hydrogen atoms or the equivalent formed by the direct excitation which may involve ``superexcitation.''
Gas-Phase Photolysis and Radiolysis of Methane. Formation of Hydrogen and Ethylene
Authors: Gorden R. , Ausloos P.
Published: January 2005

The photolysis of CH4 and of CH4—CD4 mixtures has been investigated at 1236 Å (10.0 eV) and at 1048–67 Å (11.6–11.8 eV). The excited methane molecule dissociates to form H2, H, CH3, CH2, CH, and probably also C. The CH and CH2 radicals insert into methane to form internally excited C2H5* and C2H6* species, respectively. Below one atmosphere, all C2H5 radicals decompose to form C2H4, while the ethane molecules are partially stabilized. The relative quantum yield of CH increases about threefold when the wavelength is reduced from 1236 Å to 1048–67 Å. On the basis of an isotopic analysis of the hydrogen produced in the photolysis of CD4—H2S mixtures, it is concluded that at 1236 Å, D atoms constitute at least 65% of the ``molecular'' deuterium yield.

In the radiolysis, ethylene is largely, although not exclusively formed by the insertion of CH into methane. It is demonstrated that addition of small concentrations of an unsaturated hydrocarbon to methane profoundly affects the ion-molecule reaction mechanism and, therefore, does not lead to a dependable value of the ``initial'' ethylene yield as suggested in earlier studies. Upon application of an electrical field, the production of CH and CH2 is augmented in the saturation current region. The importance of the latter two radicals in the direct and rare-gas-sensitized radiolysis is examined briefly. The formation of hydrogen in the radiolysis will be discussed on the basis of new information derived from CD4—H2S experiments. The production of hydrogen in the radiolysis of Xe–CH4–CD4–NO mixtures has also been re-examined in view of a recent study in which it was asserted that all of the hydrogen in such a mixture is due to the unimolecular decomposition process CH4*→CH2+H2.Our data disagree with this view and actually demonstrate that CH and CH2 play a minor role in the xenon-sensitized radiolysis of methane.
Flash Photolysis of Ethylene
Authors: Back R. A. , Griffiths D. W. L.
Published: January 2005

The flash photolysis of ethylene has been studied at pressures from 1 to 20 torr and flash energies from 72 to 1800 J, with light of a broad spectral distribution from about 1550 to 1900 Å. The products were acetylene, hydrogen, ethane, propane, butane, methane, 1-butene, and propylene, in approximately decreasing order of importance. The primary processes are thought to have been C2H4+hν→C2H2+H2  (∼51%)and C2H4+hν→[C2H3*+H]→C2H2+2H  (∼49%)in close agreement with the low-intensity photolysis at 1470 Å. A hydrogen-atom ``cracking'' mechanism followed by radical combination appears to account for the products. The formation of 1-butene and propylene indicates that some of the vibrationally excited vinyl radicals formed in the second primary process were stabilized by collision at the higher pressures and trapped by combination with methyl and ethyl radicals. About 12% of the vinyl radicals were stabilized by the addition of 600 torr of nitrogen.
Structure and Intermolecular Potential of Liquid Carbon Tetrachloride Derived from X-Ray Diffraction Data
Authors: Narten A. H. , Danford M. D. , Levy H. A.
Published: January 2005

The scattering of x rays from the free surface of liquid carbon tetrachloride has been analyzed at 25°C. The diffractometer used was specially designed for the study of liquid structure. The radial distribution function derived from the experiments is in agreement with previously published work on CCl4 showing, however, much higher resolution. Intensity and radial distribution functions have been computed for a model structure and compared to those derived from experiment. The model assumes a perturbed close packing of chlorine atoms, surrounded by a continuous distribution of distances, as an adequate description of the short-range order in liquid carbon tetrachloride. The model intensity and radical distribution functions are in quantitative agreement with those derived from experiment. An intermolecular potential function, derived from the model structure, predicts the heat of vaporization and second virial coefficient in agreement with experiment.
Nuclear Magnetic Resonance Study of V2O5
Authors: Gornostansky S. D. , Stager C. V.
Published: January 2005

The quadrupole-coupling and the chemical-shift tensors of 51V were measured in a single crystal of V2O5 at room temperature. The quadrupole-coupling constant is 805(6) kc/sec and the anisotropy factor η is 0.04(1). The chemical-shift tensor, relative to a solution of Na3VO4, has principal values of −1.8(4)×10−4, +6.5(3)×10−4, and −3.0(3)×10−4. Attempts to calculate the electric-field-gradient tensor at the vanadium nucleus, using a point-charge model, led to results that did not agree with experiment.
Model for Electro-osmosis in Fixed-Charge Systems
Authors: Manning Gerald S.
Published: January 2005

To a fixed-charge lattice model previously employed to investigate ionic mobility in a system with no bulk flow, we have added crude hydrodynamic boundary conditions which make possible a solution of the appropriate Navier—Stokes equation in the presence of an external electric field. The resulting flow, electro-osmosis, is strongly dependent on the concentration of neutral salt present, attaining a maximum in the absence of salts. The gradual transition from Poisseuille parabolic flow to ``plug'' flow as salt concentration or fixed-charge density increases is explicitly demonstrated for the model.
Effect of Hydrogen Bonding on the Electrical Conductivity of Organic Solids
Authors: Gravatt C. C. , Gross Paul M.
Published: January 2005

The bulk electrical conductivities of a series of monocarboxylic and polycarboxylic aromatic acids and some derivatives of these acids have been measured in order to study the effect of hydrogen bonding on conductivity. Electrical measurements were made on carefully purified, polycrystalline samples, compressed to remove voids, using a guarded direct-current method. The measurements were characterized by time-dependent currents which decreased to equilibrium values in times ranging from seconds to hours. The temperature dependence of the conductivity followed the usual exponential law for all the compounds. The activation energy for conduction, Ea, was independent of the polarization effects and sample purity and served as a reliable parameter for comparison among the compounds. A definite relationship existed between Ea and the position and number of carboxyl groups on an aromatic system. This relationship was interpreted in terms of the hydrogen bonding and electron withdrawing properties of the carboxyl groups on the assumption that the aromatic pi electrons were involved in the generation of charge carriers. Those substituents which tended to reduce the electron density of the aromatic system produced a rather substantial increase in the activation energy. Extended intermolecular overlap resulting from the hydrogen bonding of polycarboxylic acids produced a decrease in Ea.
Correlation between Exchanging Electrons
Authors: Alexander M. H. , Salem L.
Published: January 2005

Attempts to introduce overlap and exchange into a purely general study of interatomic or intermolecular long-range forces lead to complicated, physically opaque expressions for the interaction energy. A study is made of a most simple system, two hydrogen atoms at large distances, taking overlap and exchange rigorously into account. This system is especially interesting due to the failure of the Heitler—London wavefunction to describe adequately the lowest-triplet (3Σu+)—lowest-singlet (1Σg+) separation at very large distances. A formal study separates the interaction energy into a ``generalized dispersion'' and ``generalized exchange—correlation'' energy. A many-configuration calculation performed at an internuclear distance of 8 a.u. shows that, whereas certain configurations yield the well-known dispersion energy, other configurations, particularly those of the excited charge-transfer type, correct for the erroneous triplet—singlet separation. This distinction reflects the introduction of two distinct types of correlation effects which are investigated in terms of the two-electron distribution function.