bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Surface Tension on Multilayer Gas Adsorption at Moderate Pressures
Authors: Bakri M. M.
Published: January 2005

Taking into account the variation in the particle density and the normal component of stress in the surface layer inside the adsorption layer of a dilute real gas near the plane boundary of the adsorbent, the amount of adsorption, the spreading pressure, and the two-dimensional second virial coefficient are calculated. The corrections due to the surface layer are found to be proportional to the surface-tension coefficient of the gas, and are of the second degree in the pressure. It is also shown that the same expressions can be derived thermodynamically, if the partition function is defined appropriately to include the effect of the surface layer. Simplified approximate expressions are obtained in the cases of monolayer and multilayer adsorption. The correction in the amount of adsorption is evaluated numerically for neon and xenon on graphitized carbon blacks for a wide range of temperatures, and is found to be of the order of one-tenth of the deviations of the amount of adsorption from the corresponding values for the ideal gas.
Anisotropy of Polarizability of Polymeric Chains
Authors: Smith Richard P.
Published: January 2005

A general formula is given for γ2, the square anisotropy of the polarizability of a molecule, in terms of bond polarizabilities and angles between bonds. Expressions are derived for 〈γ2〉, the average over configurations, for a chain of N axially symmetric units. This is done for the freely jointed model and for the diamond-lattice model. The formulas are valid for small N as well as for large N. For both models 〈γ2〉 increases linearly with N for large N.
Direct Radiative Exciton—Exciton Annihilation
Authors: Knox R. S. , Swenberg C. E.
Published: January 2005

Several experiments on organic crystals have demonstrated the existence of triplet—triplet exciton annihilation in terms of fluoresence from the resulting singlet-exciton state. We point out the possibility of direct emission of a photon from a pair of excitons and estimate the corresponding lifetime and bimolecular rate constant. While this decay channel for triplet—triplet collisions is very weak compared with decay into a singlet exciton in a crystal such as anthracene, the process is observable in principle as a characteristic emission with a transition probability of ≲ 105 sec−1 at an energy equal to that of two interacting excitons. Its rate depends strongly on the relative energies of all the molecular states involved. Conditions for observation of this emission band are discussed.
Transport in Dense Square-Well Fluid Mixtures
Authors: Valleau J. P.
Published: January 2005

A simple kinetic theory of transport in a dense fluid of square-well molecules, due to Longuet-Higgins and Valleau, is here extended to mixtures. A minor extension of the original set of postulates is required. The ratio, κ/η=5/3, of the bulk and shear viscosities is again obtained and the purely diffusive Onsager relations are obeyed. In the case of a two-component ``isotopic'' mixture, it is possible to show that the Onsager relation linking the Soret and Dufour effects is also obeyed. In this and other respects the results differ from some others recently published on the same problem and some reasons for this are discussed.
Absorption and Emission Spectra of the Perylene Dimer
Authors: Ferguson J.
Published: January 2005

A method for obtaining perylene dimers is given and their absorption and emission spectra are reported. In absorption the long-axis-polarized band near 4200 Å and the short-axis-polarized band near 2500 Å have been measured and the effects of vibronic coupling discussed for the former. The resonance splittings of the two excited states corresponding to these bands have been estimated and the dipole—dipole term of the point multipole expansion has been shown to be grossly in error. Both excited dimer and excimer emission from the perylene dimer have been found with a very small interconversion barrier to the latter and the results prove that in the excimer state the intermolecular distance is smaller than in the ground state. The absorption spectrum of the dimer has been compared with the crystal spectrum and it has been shown that the neglect of molecular vibrations in the simple Davydov theory leads to misleading assignments of the crystal spectrum.
Reactions of Carbon Atoms with N2, H2, and D2 at 4.2°K
Authors: Moll Norman G. , Thompson Warren E.
Published: January 2005

Photochemical decomposition of matrix-isolated carbon suboxide at 4.2°K with 1470-Å light produces highly reactive carbon atoms, presumably from an observed CCO intermediate. Reactions of carbon atoms with nitrogen lead to the observation of the infrared absorptions of the NCN and CNN radicals. Attempts to form methylene in spectroscopically observable amounts by the reaction of carbon atoms with H2 or D2 in an argon matrix were unsuccessful, although its existence was inferred by the observed production of methane and ketene.
EPR Spectra of Gd3+-Doped LaBr3 and La2(SO4)3·9H2O
Authors: Johnston D. R. , Wong E. Y. , Stafsudd O. M.
Published: January 2005

The EPR spectra of Gd3+-doped LaBr3 and La2(SO4)3·9H2O were measured with X band at room, liquid-nitrogen, and liquid-helium temperatures. The zero-field splitting of the gadolinium ion is shown to have no obvious relation with the crystal-field parameters of the 4f configuration.
Ba(B0.5Ta0.5)O3 Ordered Perovskite-Type Compounds, Possible New Laser Host Materials
Authors: Galasso F. S. , Layden G. K. , Flinchbaugh D. E.
Published: January 2005

The trivalent ions of Nd, Sm, and Yb were incorporated into powders of ordered perovskite-type compounds having the general formula Ba(B0.5Ta0.5)O3, where B is a trivalent rare-earth cation, In3+, Y3+, or Sc3+. Fluorescent lifetimes measured employing these materials indicate that the lifetimes for Nd3+ fluorescence are not as dependent on crystalline field as those for Cr3+ fluorescence. Of the Nd3+-doped phases studied, Ba(Gd0.48Nd0.02Ta0.5)O3 and Ba(Lu0.48Nd0.02Ta0.5)O3 were found to exhibit the longest lifetimes (800 and 850 μsec, respectively, at 77°K).

Preliminary studies show that single crystals of Ba(Y0.5Ta0.5)O3 can be grown from a B2O3 flux by slow cooling or by a modified Czochralski technique. Developing crystals of suitable quality for laser studies, however, requires further research.
Crystal Spectra in Polarized Light, Vibrational Assignment, and Force-Constant Calculations of Phenanthrene
Authors: Schettino V. , Neto N. , Califano S.
Published: January 2005

A complete vibrational assignment of phenanthrene C14H10 is presented. The assignment of the fundamental vibrations of this molecule is based on the following data: (i) a priori calculation of the normal frequencies using a force field including 27 force constants, (ii) infrared spectrum in polarized light of single crystal between 4000 and 80 cm−1, (iii) Raman and fluorescence spectra of single crystals. The force field used in the present calculation was obtained from an ``overlay'' refinement of benzene, benzene-d6, naphthalene, naphthalene-d8, anthracene, and anthracene-d10. The interpretation of the crystal spectrum in polarized light was based on the use of the oriented gas model. It was found however that in some cases large deviations occur between the experimental and the theoretical dichroism. A discussion of the intermode mixing mechanism is included.
Neutron-Scattering Study of Hindered Rotational Motions and Phase Transitions in Hexamethylbenzene
Authors: Rush J. J. , Taylor T. I.
Published: January 2005

The low-frequency motions of solid hexamethylbenzene (HMB) have been investigated above and below its λ transition near 110°K by the energy-gain scattering of cold neutrons. Measurements were also obtained above and below the high-temperature phase transition near 383°K. At temperatures below the λ point the neutron spectra exhibit a band peaked at 137±5 cm−1, which is assigned to the 1→0 transitions of the torsional oscillations of the methyl groups. Above the transition this band is broadened considerably and its maximum is shifted down to 120±5 cm−1. These results show that the λ transition is associated with a small change in the forces hindering rotation of the methyl groups. Assuming a simple threefold cosine potential for the methyl groups, the torsional peaks are used to calculate ``average'' barriers to rotation above and below the λ transition of 1.07±0.09 and 1.35±0.10 kcal/mole, respectively. These barriers are considerably lower than a recent estimate of 3–8 kcal/mole from thermodynamic results. Moreover, the torsional bands and calculated barriers are also significantly lower than those obtained recently by the neutron technique for the methyl groups in o-xylene and durene (vtors≃170 cm−1, V3≃2 kcal/mole). This indicates a considerable difference between the potential experienced by a methyl group surrounded by two other methyl groups on the benzene ring and that experienced by two adjacent groups.

A second band with a maximum around 60 cm−1, which shows little change at the λ transition, is also observed in the low-temperature spectra and is attributed primarily to the over all librational motions of the HMB molecules. The spectra above and below the high-temperature transition show only small changes with the change in phase.
Shear Relaxation Times of Simple Fluids
Authors: Mountain Raymond D. , Zwanzig Robert
Published: January 2005

This article presents a calculation of shear relaxation times of monatomic fluids covering both the liquid and dense-gas phases. The times, which are not experimentally accessible at present, are calculated using low-frequency viscosity data and theoretical estimates of the high-frequency elastic moduli which were produced earlier by the authors. Numerical values of the relaxation times at various temperatures and densities are presented graphically. Except at very low densities, the times are on the order of 10−13 sec.
Calculated Elastic Scattering Cross Sections for the H+–He System
Authors: Weber Gunter G. , Gordon Nahida H. , Bernstein R. B.
Published: January 2005

The ab initio computations by Michels and Harris, and Peyerimhoff, of the ground (1Σ+) state of HeH+ provide a reliable interaction potential V(r) to serve as a basis for prediction of proton—helium elastic scattering. This report summarizes calculations of total elastic cross sections Q(E) for low collision energies (E in the range 0.3–200 eV) where Q is sensitive primarily to the attractive part of V(r). Superimposed upon the monotonic E−⅓ dependence (arising from the long-range r−4 ``tail'' of the potential) are a number of broad extrema in Q(E), characteristic of a potential well with the capacity for several (≥7) bound (vibrational) states.
Nuclear Spin—Lattice Relaxation in Liquid Hydrogen
Authors: Lipsicas M. , Hartland A.
Published: January 2005

Measurements are reported of the nuclear spin—lattice relaxation time T1 in pressurized samples of liquid hydrogen. T1 has been measured as a function of density, temperature, and orthohydrogen concentration in the temperature range 20.7° to 31.2°K. The data are compared with some theoretical calculations of Deutch, based on the Bloom—Oppenheim theory of nuclear spin—lattice relaxation. The density dependence of (T1) ortho—para is found to be opposite to that of (T1) ortho—ortho at constant temperature. This inverted density dependence is discussed and compared with an inverted ``temperature'' dependence reported by other workers.
Study of the DMSO—TCNE Charge-Transfer Complex and Its Kinetics
Authors: Stewart Frank E. , Eisner Melvin , Carper W. R.
Published: January 2005

DMSO and TCNE form a strong 1:1 charge-transfer complex (K25°C=95.4) with an absorption band located at λ=3720 Å. The high enthalpy of complex formation (−11.3 kcal/mole) leads to an appreciably populated triplet state during complex formation. The EPR signal of the TCNE anion arises, reaches a maximum, and then follows second-order decay kinetics. The initial intensity of the EPR signal is proportional to the original TCNE concentration in DMSO. A molecular mechanism for the equilibrium reaction between TCNE and DMSO is proposed.
Concentration Broadening and Oscillator Strengths in Pr:LaCl3
Authors: Dorman E.
Published: January 2005

The absorption and fluorescence spectra of Pr3+ in LaCl3 have been examined for molar concentrations of 0.26%, 2%, 15%, 50%, 85%, and 100%, and have been used to determine the effect of concentration on the energy levels and transitions of the ion. A model is advanced to explain the concentration broadening of spectral lines in crystals as due to heterogeneity of the lattice and resonance interaction between the spectroscopically active ions. Oscillator strengths were measured for the dilute crystal and the ratio of the strength of the ion-pair absorption 3P0+3F2(μ=2) to that of 3P0, in PrCl3, was found to be 1.3×10−5.
Spin—Rotation Contribution to the Relaxation Time of the Fluorine Nuclei in Benzotrifluoride
Authors: Faulk R. H. , Eisner M.
Published: January 2005

The relaxation time of the fluorine nuclei in benzotrifluoride has been measured and is found to be an only slightly varying function of temperature, ranging from 3.2 sec at −20°C to 2.4 sec at +50°C. The contributions to the relaxation time from the dipole—dipole and spin—rotation interactions have been separately calculated, and the effective spin—rotation coupling constant is calculated to be 25±2 kc/sec. This coupling constant has been used to calculate the paramagnetic contribution to the chemical shift of the fluorine in C7H5F3 relative to F2, and yields the value, 453 ppm, which is within 10% of the observed value or 493.3 ppm for the chemical shift.
Absorption, Photoionization, and Fluorescence of CO2
Authors: Cook G. R. , Metzger P. H. , Ogawa M.
Published: January 2005

Absorption and photoionization coefficients of CO2 have been measured in the regions of strong band and continuous absorption in the spectral range between 1000 and 600 Å. The total continuum underlying the band structure has been estimated as well as that fraction due to ionization and dissociation. A strong fluorescent edge was observed at 715.7 Å and was found to contain vibrational structure.
Electrical Conductivity and Structure of Aqueous MgSO4 Solutions in the −2°-to- +12°C Range
Authors: Horne R. A. , Johnson D. S.
Published: January 2005

The electrical conduction of aqueous 0.001, 0.01, and 0.1M MgSO4 solutions has been measured over the range −2° to +12°C. The activation energy of electrical conduction of aqueous MgSO4 solutions, unlike those of solutions of ``normal'' strong 1:1 electrolytes, does not exhibit a maximum near the temperature of maximum density. The local water structure near MgSO4 is so strong and extensive that structural changes in the more remote bulk water have little effect on transport processes involving MgSO4. The mechanism of this process apparently resembles that of viscous flow in water rather than ``normal'' ionic electrical conduction.
Adsorption of Thermally Activated Nitrogen
Authors: Nornes Sherman B. , Donaldson E. E.
Published: January 2005

The interaction of nitrogen with a hot tungsten filament has been investigated. At pressures between 10−6 and 10−3 torr and for filament temperatures in the range 2050° to 2300°K, the nitrogen disappears at a rate proportional to the square root of the pressure with an apparent activation energy of 4.8 eV, half the dissociation energy of nitrogen. The experimental results have been compared with rates derived for various mechanisms of adsorption using absolute reaction-rate theory. It is shown that molecular nitrogen dissociates on the hot tungsten filament. The atoms are evaporated from a dilute surface layer and adsorb on the glass walls of the surrounding tube.
Hornbeck—Molnar Cross Sections for the n=3 States of Helium
Authors: Teter M. P. , Niles F. E. , Robertson W. W.
Published: January 2005

Analysis of the atomic light originating from energy levels of principal quantum number n=3 in the helium positive column shows that a pressure-dependent loss process exists for states other than the S states. The loss mechanism is identified as the Hornbeck—Molnar process, He*+He→He2++e−,by observing the effects of varying the atomic populations when the positive column is irradiated with intense atomic light. Comparison of the pressure-dependent loss rate with the radiation loss rate from a particular state yields the Hornbeck—Molnar cross section. An independent measurement relating the molecular-ion concentration to the 33D population yields a separate value for the 33D cross section, which agrees quite well with that measured by the previous method.
Direct Analysis and Improvement of Electron Densities and Wavefunctions by a Perturbation—Variation Method
Authors: Somorjai R. L.
Published: January 2005

In this paper we introduce a perturbation—variation method for the direct analysis and improvement of electron densities and wavefunctions. The method consists of constructing operators whose expectation values provide the required information (D operators, based on δ functions), and using Dalgarno's ``interchange theorem'' to calculate corrections to these expectation values (D-operator method). The illustrative calculation of an improved charge density for H2 indicates some of the computational advantages of the method. Further applications and extensions are also outlined.
Correlation Energy in Atomic Systems. IV. Degeneracy Effects
Authors: Clementi E. , Veillard A.
Published: January 2005

The degeneracy effects in the isoelectronic series of the first-row atoms are analyzed. The near-degenerate configurations 1s22s22p2 and 1s22s02pn+2 are computed within the framework of a two-configuration SCF technique. The newly obtained correlation energy diagram indicates a remarkable simplicity in its structure.
Theory of the Width and Shift of Molecular Spectral Lines in Gases
Authors: Gordon R. G.
Published: January 2005

A theory is developed for linewidths and line shifts in molecular spectra of gases. A semiclassical method is used, which does not make the approximations of perturbation theory and a straight-line trajectory upon which previous work has been based. General formulas are given for linewidths and line shifts in microwave, infrared and Raman spectra of linear molecules. Numerical application of the results is made to the widths of a number of spectra, and the results are in good agreement with both the magnitude and J dependence of the experimental values.
Electronic Structure of the MnO4−, CrO42—, and VO43— Ions from the Metal K X-Ray Spectra
Authors: Best P. E.
Published: January 2005

New measurements of the K x-ray emission spectra from the metal atoms in MnO4−, CrO42—, and VO43— ions are presented and discussed in terms of dipole transitions from occupied orbitals to the 1a1, i.e., the metal 1s vacancy. Observed emission lines are attributed to transitions from the 3t2 (metal 3p), the 4t2 (oxygen 2s), and the valence 6t2 (predominantly oxygen 2pσ) orbitals. Simple theory accounts semiquantitatively for the relative intensities and energy positions of the lines. The K-absorption spectra of the metal atoms in these ions are considered in conjunction with the emission data. The most prominent absorption peak in each spectrum is attributed to transitions to the 7t2 orbitals, which apparently consist mainly of metal 4p wavefunctions. Also identified in each spectrum is the absorption edge associated with the onset of photoionization of the K shell. The energy differences between the emission lines and the K-absorption edge are taken to be the molecular orbital ionization potentials. There is not good agreement between the present deductions from the x-ray spectra and the results of recent semiempirical calculations of the electronic structure of the MnO4− ion.
Variational Methods and Degenerate Perturbation Theory
Authors: Epstein Saul T.
Published: January 2005

Variational methods related to degenerate perturbation theory are discussed in a general way through second order in the energy and first order in the wavefunction.
Raman Spectra of Liquid MgCl2 and Liquid MgCl2–KCl System
Authors: Balasubrahmanyam K.
Published: January 2005

Raman spectra of molten MgCl2, MgCl2–KCl, and MgCl2–2KCl were recorded, at 730°, 525°, and 475°C, respectively, using a Cary 81 Raman spectrophotometer. Liquid MgCl2 exhibits three Raman lines with frequencies 269, 214, and 142 cm−1, which are explainable on the basis of the presence of MgCl64— ions with octahedral configuration. Liquid MgCl2–KCl exhibits four Raman lines with frequencies 451, 250, 208, and 158 cm−1; and their polarization characteristics indicate the existence of MgCl3− ions with pyramidal configuration C3v. The Raman spectrum of liquid MgCl2–2KCl is almost similar to that of liquid MgCl2–KCl. Force constants for the various Mg–Cl ionic species were calculated using generalized valence forces.
Excitation of Nitrogen Gas by Alpha Particles and Fission Fragments
Authors: Axtmann Robert C. , Sears John T.
Published: January 2005

Excitation of the SPG (second positive group: C 3πu→B 3πg) by fission fragments and by 6.1-MeV alpha particles was studied with a pulse technique. Both types of particles exhibit nearly the same efficiency for excitation from which it was concluded that in either case secondary electrons are responsible for the production of the triplet states.
Luminescence of Rare-Earth-Activated Cadmium Sulfide
Authors: Anderson W. W.
Published: January 2005

The narrow emission lines of Nd3+, Er3+, and Yb3+ have been observed from rare-earth doped CdS. These activators formed the principal radiative recombination centers in selected crystals. Decay-time measurements gave fluorescent lifetimes of ∼100 μsec for CdS:Yb, ∼300 μsec for CdS:Nd and ∼3000 μsec for CdS:Er. Both the emission spectra and lifetime measurements showed that the rare-earth ions occupied more than one type of site in the CdS lattice. No emission was observed from a rare-earth ion metastable level greater than 1.53 eV above the ground state, even though the CdS band gap was 2.43 to 2.52 eV in the temperature range of the experiments. This is taken as evidence for rare-earth-ion-acceptor-type defect pairing.
Ultrasonic Dispersion Observed by Optical Diffraction. II. Ammonia
Authors: Strauch J. G. , Decius J. C.
Published: January 2005

The velocity of sound in NH3 at 300°K has been measured at a frequency of about 1 MHz over the pressure range from 6 atm down to ½ atm, employing the optical diffraction method. All measured velocities were lower than the low-frequency ideal-gas limit of 436 m sec−1. Interpreting this result as evidence of nonideality and not dispersion, we fitted the data to the formula V2=Vi2(1+sp) and obtained Vi2=(19.122±0.034)×104 m2 sec−2 and s=(−13.9±0.05)×10−3 atm−1. The ideal velocity squared, Vi2, agrees with the spectroscopic value to within 0.05% and shows that no loss of vibrational heat capacity occurs up to f/p=2.1 MHz atm−1.

The nonideality correction term s is used to recalculate nonideality corrections to the data of previous workers, and it is suggested that the vibrational relaxation time in NH3 may be of the order of 6 nsec at 300°K.
Photolysis of Liquid Water at 1849 Å
Authors: Sokolov Uriel , Stein Gabriel
Published: January 2005

The photolysis of pure water and of aqueous solutions of alcohols (methanol, ethanol, and isopropanol) at 1849 Å, when the light is absorbed by the water, proceeds according to[Complex chemical formula]The quantum yield for the formation of the geminate pair (H+OH) is φ=0.45 at room temperature. Scavengers compete with the recombination of the geminate pair according to diffusive inhomogeneous kinetics. A value of 3.9×10−6 sec½ is obtained for the Noyes parameter a, in agreement with theory. The results exclude direct interaction between scavenger and excited water molecules and also exclude molecular processes in the formation of H2. Solvated-electron formation has a quantum yield of ≤0.045. Isotope experiments support the conclusions.

In the reaction with the alcohols, that of the OH radicals determines the competition with secondary geminate recombination. From the results a value of k(dim)/k(dis)=6.6 is obtained for the ratio of dimerization to disproportionation of CH2OH radicals.
Solvent Stark Effect and Spectral Shifts
Authors: Baur Mario E. , Nicol Malcolm
Published: January 2005

A theory is developed for the solvent shift in the electronic absorption spectrum of a nonpolar solute in a polar solvent. The shift is regarded as composed of two components, one of which arises from the same mechanism as the London forces and is taken successfully into account by the McRae theory. The second component, the solvent Stark effect, is treated in detail here by considering polarization fluctuations in a dipolar medium surrounding a cavity. A simple result for the contribution of this component in terms of the macroscopic dielectric properties of the solution is given. The model predicts in particular that the Stark contribution to the solvent shift becomes linear in the solution dielectric constant for large values of the latter. The theoretical expression obtained here is compared with the experimental data of Weigang and Wild for the 1La transition of naphthacene, and a satisfactory fit is obtained.
Cooperative Exciton States in Molecular Crystals
Authors: Jortner Joshua , Rice Stuart A.
Published: January 2005

In this paper we calculate the transition probability for excitation of double-exciton states in absorption and emission processes in molecular crystals. The formalism is based on the tight-binding approximation, treating the intermolecular electrostatic and exchange interactions and the interaction with the radiation field by perturbation theory. It is found that:

(1) A major contribution to the transition probability for cooperative excitation to electronic states arises from intermolecular Coulomb interactions, while the contribution of intermolecular electron-exchange interactions is relatively small.

(2) Contributions to the transition probability from high-order-transition multipole interactions are of considerable importance.

(3) Approximate selection rules for cooperative electronic excitation imply that for one component the initial and final states are of the same parity, while for the second component the transition is symmetry allowed.

(4) Theoretical evidence is obtained for the appearance of double-excitation bands in the infrared spectra of solids in the overtone region.

(5) A major contribution to the intensity of the double-vibrational-exciton states arises from an intermolecular Fermi resonance effect.

(6) The direct detection of the radiative annihilation of a double-exciton state is not likely to be experimentally feasible.
Mass-Spectrometer and uv Absorption Study of CHF3 Decomposition behind Shock Waves
Authors: Modica A. P. , LaGraff J. E.
Published: January 2005

The thermal decomposition of CHF3 has been studied in excess argon behind incident and reflected shock waves over a temperature range from 1600° to 2200°K at six total pressures between 0.29±0.03 and 28.2±1.6 atm. Direct mass-spectrometer analysis of the reaction mixture showed HF and CF2 to be the major decomposition products. Kinetics for the reactionCHF3→ lim ArCF2+HFwere determined spectrophotometrically by observing the rate of formation of CF2 in absorption at 2536 Å. The decomposition reaction was first order in CHF3 concentration and dependent on total concentration. The high-pressure limiting rate constant is given by k∞Ar=(7.03±0.70)1011exp[(−58 400±2200)/RT]sec−1,where 58.4±2.2 kcal/mole is considered to be the minimum energy E0 for dissociation. For the lowest pressure 0.29 atm, the reaction is interpreted by a second-order mechanism, d[CF2]/dt=k2[CHF3][Ar], with the rate constant expressed as k2Ar=(2.05±0.14)1035T−5.75±0.23exp[(−58 400±2200)/RT]  cc mole−1·sec−1,indicating in terms of the classical Kassel theory the participation of 7.25 effective oscillators for the dissociation of a critically energized CHF3 molecule. Taking E0=58.4±2.2 kcal/mole as the heat of reaction at 0°K, the heat of formation of the CF2 radical is −40.2±4.0 kcal/mole.
Out-of-Plane Bending Frequencies in Trimethylene Sulfide from Microwave Intensity Measurements
Authors: Harrington Howard W.
Published: January 2005

The first four out-of-plane ring-bending energy separations in trimethylene sulfide[Complex chemical formula]have been determined from microwave intensity measurements on the 000−101, 634−633, and 423−422 rotational transitions in X band.

These separations are 0, 141, 15, and 85 cm−1 for the 0–1, 1–2, 2–3, and 3–4 transitions, respectively, indicating a bent configuration for the ring.

The uncertainty in these numbers is about ±3 cm−1.
Optical Study of Copper Diffusion in Cadmium Sulfide Single Crystals
Authors: Szeto Whalun , Somorjai G. A.
Published: January 2005

The diffusion of copper in cadmium sulfide single crystals has been studied by optical transmission in the temperature range 500°—700°C. Diffusion was made parallel to the c axis. The intensity of the monochromatic light beam (λ=5230–20 Å) transmitted through a small section of the sample was monitored along the diffusion profile. The relationship between the light transmission T and the penetration distance x has been derived and applied to the geometry employed in the experiments. From the slope of the plot lnln (1/T) vs x2, the diffusion coefficient has been determined and the activation energy for the copper diffusion along the c axis has been calculated (ΔE=13.4 kcal/mole).

Light absorption by the doped crystals is primarily due to the copper acceptor centers and defects which are generated by the copper diffusion via the self-compensation mechanism. Scattering of light by copper precipitate aggregates has also been considered. The results of the several diffusion studies may be explained assuming that copper diffuses interstitially in the cadmium sulfide lattice and there is an equilibrium between interstitial and substitutional copper during the diffusion. The solubility of substitutional copper which occupies cadmium sites must be greater than the solubility of copper interstitials. The results of the optical studies of copper diffusion compare favorably with diffusion studies using radiotracer techniques. Since it is a nondestructive method, under certain conditions it should be more useful than other types of diffusion analysis.
Second and Third Ordinary and Dielectric Virial Coefficients for Nonpolar Axial Molecules
Authors: Levine Howard B. , McQuarrie Donald A.
Published: January 2005

In a previous publication, expressions for the second and third dielectric and ordinary virial coefficients of nonpolar axial molecules possessing permanent quadrupole moments and anisotropic polarizabilities were derived. The results are given in terms of several single and triple integrals which depend only upon the ``nonelectrical'' part of the intermolecular potential, e.g., the dispersion-force attraction plus the short-range overlap-force repulsion. These integrals have been evaluated numerically and tabulated for the Lennard-Jones (6–9), (6–12), and (6–15) potentials, and analytic values have been obtained for the hard-sphere potential. Comparisons with experiments will be made in succeeding publications.
United-Atom Approximation Applied to Argonlike Molecules. III. HCl and SiH4
Authors: Hake R. B. , Banyard K. E.
Published: January 2005

The united-atom approximation has been used to obtain molecular wavefunctions for HCl and SiH4 in the gaseous state. Theoretical values were determined, in each instance, for the molecular energy, bond length, force constant, molar diamagnetic susceptibility, and the coherent x-ray scattering factor. Where possible, the results were compared with the corresponding experimental data.

For SiH4, a comparison of the present results was made with the earlier work of Carter and also of Albasiny and Cooper. These workers used, respectively, a numerical Hartree self-consistent-field approach and a numerical Hartree—Fock scheme, the latter study being performed within a spherical and a nonspherical approximation. For the HCl molecule, some comparison is made with the two-center SCF—LCAO—MO calculation performed by Nesbet.

In each case, the united-atom treatment gave a molecular energy which was 98.9% of the experimental value. Other physical properties for HCl and SiH4 derived from the present model compare favorably with similar quantities obtained from the more elaborate calculations and also with the corresponding available experimental data.
Proton Transfer from H3+ to Unsaturated Hydrocarbons and to Cyclopropane
Authors: Aquilanti V. , Volpi G. G.
Published: January 2005

The ion—molecule reactions which H3+ and D3+ ions undergo with acetylene, methylacetylene, ethylene, propylene, and cyclopropane have been investigated by high-pressure mass spectrometry, and the rate constants have been measured. In all cases, proton (or deuteron) transfer from H3+ (or D3+) to the hydrocarbons occurs, and leads to the formation of excited ions which may either be stabilized by collision or decompose in smaller fragments when energy requirements are satisfied. Several kinetic parameters are assessed. Reactivity data for some ions with hydrogen, deuterium, and hydrocarbons are also reported.
Nuclear Hyperfine Coupling Constants of Diphenyl Picryl Hydrazyl
Authors: Kim Y. W. , Chalmers J. S.
Published: January 2005

Two groups of single crystals of diphenyl picryl hydrazine (DPPH2) have been grown from organic solvents. The samples of one group contain large concentrations of residual solvent molecules and those of the other group, practically negligible concentrations of solvent molecules. Diphenyl picryl hydrazyl (DPPH) molecules have been produced in the samples by irradiating with thermal neutrons. The anisotropy of the observed electron paramagnetic resonance (EPR) spectra of DPPH in the samples of the first group has been found to be different from EPR spectra of DPPH in the samples of the second group. However, satisfactory interpretations of the anisotropies have been obtained in terms of the principal values of the hyperfine tensors of DPPH determined previously by Holmberg et al. It appears that different species of molecules neighboring DPPH molecules and varying concentration of residual solvent molecules in the host crystals do not affect noticeably the principal values of the tensors.
Kinetic Isotope Effects in the Reaction between Atomic Chlorine and Molecular Hydrogen. Tunnel Coefficients of the Hydrogen Atom through an Asymmetric Potential Barrier
Authors: Persky Avigdor , Klein Fritz S.
Published: January 2005

Kinetic isotope effects for the reactions between atomic chlorine and molecular hydrogen have been measured in the range of −30° to +70°C. The following expressions were obtained: RH2/HT=(1.27±0.03) exp[(797±14)/RT],RH2/D2=(1.44±0.06)exp[(1128±17)/RT],RH2/DT=1.534exp(1422/RT),RH2/T2=1.545exp(1693/RT).

The isotope effect of HD, RH2/HD=(1.24±0.03) exp[(490±6)/RT],has been redetermined and found to agree with previous measurements.

Theoretical calculations of these isotope effects, using (1) a Sato model, (2) a generalized Sato model, and (3) the Johnston—Parr method, were made to compare the calculated effects with experimental results.

Tunnel corrections were applied using (1) an asymmetric Eckart barrier, or (2) the Johnston—Rapp method with an asymmetric barrier. Best agreement (within 15%) of calculated values with experiment was obtained for a generalized Sato model including Johnston—Rapp tunnel corrections. Empirical sets of four force constants describing the transition state H–H–Cl are also given. These are used to calculate isotope effects which are in excellent agreement with experimental values.
Study of the H3+ Molecule Using Self-Consistent-Field One-Center Expansion Approximation
Authors: Joshi Bhairav D.
Published: January 2005

One-center self-consistent-field calculations have been carried out for the H3+ molecule using symmetry-adapted Slater-type basis functions centered at the center of the molecule. The best computed values of the distance of a hydrogen from the center of H3+ triangle, ROH(H3)+, and the total energy (E) are 0.937 bohr and −1.2863 hartree, respectively. It is estimated that the present result differs from the Hartree—Fock result by about 0.023 hartree in (0.63 eV) E. The orbital density of the 1a1′ orbital is plotted as a function of ROH(H3+) for various basis sets used, and the results are discussed.
Thermodynamic Limitations on the Conversion of Radiant Energy into Work
Authors: Ross Robert T.
Published: January 2005

The fraction of radiant energy incident on an absorber which may appear as work is limited by the radiation entropy and entropy gained in irreversible transfer from the radiation field to an absorber. Irreversibility may result from directionality of the radiation field, and some irreversibility is necessary to cause a net flow of energy from a radiation absorber into work or free-energy storage. Impedance in the conversion apparatus may further limit the efficiency. Maximization of power storage under these constraints is discussed, and the general arguments are then applied to photoelectrical and photochemical systems; in these systems nonresonant decay of the excited state represents a major source of inefficiency, which may be minimized by appropriate choices for the Boltzmann temperature and optical density of the absorber. The relationships are developed for narrow-band absorption, and application to broad-band systems is discussed only briefly.
Electric Dipole Polarizability of Atoms by the Hartree—Fock Method. III. The Isoelectronic 10-Electron Series
Authors: Cohen Howard D.
Published: January 2005

Results are presented for the electric dipole polarizabilities of the neon isoelectronic series in the presence of a finite electric field. The calculations were done analytically, but sufficient numbers of carefully chosen and optimized basis functions were used in order to assure a good fit to the exact solution for the Hartree—Fock equations. Shell polarizabilities are given, and these exhibit some interesting relationships. Approximate hyperpolarizabilities are given.
Microwave Spectrum and Molecular Structure of trans-Acrolein
Authors: Cherniak E. A. , Costain C. C.
Published: January 2005

The rs structure of trans-acrolein has been determined from the microwave spectra of eleven isotopic species: CH2=CH–CHO, 13CH2=CH–CHO, CH2=13CH–CHO, CH2=CH–13CHO, CH2=CH–CH18O, CHD=CH–CHO, CDH=CH–CHO, CH2=CD=CHO, CH2=CH–CDO, CHD=CD-CHO, and CDH-CD-CHO. In the structural parameters listed below the subscripts t and c on the H atoms of the CH2 group designate the trans and cis positions, respectively, with respect to the aldehyde group. rs(CHt) = 1.086±0.005, rs(CHc) = 1.086±0.005, rs(CH) = 1.084±0.003, rs(CHald) = 1.108±0.003, rs(C=C) = 1.345±0.003, rs(C–C) = 1.470±0.003, rs(C=O) = 1.219±0.005 Å, ≰CCHt = 121°27′±10′, ≰CCHc = 119°58′±10′, ≰C=CH = 122°50′±10′, ≰CCC = 119°50′±10′, ≰CCHald = 115°6′±10′, ≰CCO = 123°16′±20′. For the normal species, transitions were observed in torsional vibrational levels up to v = 9, but no spectrum was observed for the cis (or gauche) conformer.
Viscosity and Binary Diffusion Coefficient of Neon—Carbon Dioxide Mixtures at 20° and 30°C
Authors: Breetveld J. D. , DiPippo R. , Kestin J.
Published: January 2005

This paper reports relative measurements of the viscosity of Ne–CO2 mixtures which do not seem to have been studied before. Measurements were made at 20° and 30°C at pressures from 1 to 25 atm.
Anion—Cation Interactions in Molten Inorganic Nitrates: Vibrational Analysis
Authors: Wait S. C. , Ward A. T. , Janz G. J.
Published: January 2005

An assessment of the spectral data (solid state, solutions, and molten state) for LiNO3, NaNO3, KNO3, RbNO3, CsNO3, AgNO3, and TlNO3 reveals significant features not in harmony with the selection rules for NO3− ions of D3h point-group symmetry. Correlations with lower symmetries show that the selection rules for the Point Groups C2v and Cs are adequate for the observed spectra. A ``contact'' ion-pair model is advanced for nearest-neighbor pairwise association in which the metal ion interacts with the oxygen at a unidentate site in the ion pair. Force constants are reported, calculated from a normal-coordinate vibrational analysis for this model, and the Urey—Bradley force-field assumptions. Metal-ion—oxygen vibrational frequencies are predicted in the region of 100 to 350 cm−1; the magnitudes of the force constants for this mode imply definite ionic association interactions, in which the residence time is long compared to the time of a molecular vibration. The results are examined relative to spectroscopically based operational criteria for ion-pair formation for nitrates in solutions and as molten salts.
Spin-Exchange Interactions of MnCl2 in LiCl/KCl Eutectic at High Temperatures
Authors: Swanson Terry B.
Published: January 2005

Spin-exchange interactions of MnCl2 in molten LiCl/KCl eutectic over the temperature range 700°—1200°K have been studied by the method of electron magnetic resonance spectroscopy. The resonance linewidths are determined by the exchange-narrowing process under the experimental conditions used in the present investigation. p, the probability that a paramagnetic ion—paramagnetic ion encounter will result in exchange, is found to be given by the expression pT≈1—exp(—Cη/T), where C is a constant, η is the solvent viscosity, and T is the absolute temperature.
Shifts in the ESR Spectral Parameters of Atomic Hydrogen and Deuterium in Frozen Acids
Authors: Marshall S. A. , Gabriel J. R. , Serway R. A.
Published: January 2005

The ESR spectra of atomic hydrogen and deuterium trapped in frozen acids has been reinvestigated in an effort to determine whether systematic shifts in the spectral parameters exist for this neutral S-state atom. Following the example of Livingston, Zeldes, and Taylor, partially deuterated perchloric, phosphoric, and sulfuric acids were studied after γ irradiation at 77°K. Breit—Rabi expressions which take account of the nuclear quadrupole coupling energy were used in treating the data. This study discloses g-value shifts of −0.00019, −0.00016, and −0.00012 and relative A-value shifts of −0.94%, −0.61%, and −0.38% from the free-gas values for the three acids, respectively. For perchloric and sulfuric acids, nuclear quadrupole coupling energies of 0.18 and 0.13 Mc/sec, respectively, were obtained. The possibility of 1s and 3dz2 mixing in the hydrogen-atom ground term due to crystalline electric fields is discussed.
Intermolecular-Potential-Energy Curves—Theory and Calculations on the Helium—Helium Potential
Authors: Kestner Neil R. , Sinanoğlu Oktay
Published: January 2005

Calculation of intermolecular-potential-energy curves by the application of the many-electron theory of atoms and molecules is outlined. The interaction is split into a Hartree—Fock and a correlation part. Both parts are given both in localized and in MO descriptions. Most of the interaction is calculated directly, not by difference of total energies. The correlation part involves only two-electron variational equations. These results are then used to obtain the many-electron contributions. To examine the method and estimate the magnitude of the various contributions, the helium—helium interaction is calculated for distances over 4.5 a.u. (experimental minimum about 5.5 a.u.) using a very simple localized molecular wavefunction based on single Slater atomic orbitals. The correlation-energy contribution is calculated with the Hirschfelder-Linnett pair function previously used for hydrogen interactions. Many-electron and distortion effects contribute 29% of the correlation part at the potential minimum (Re) and 23% at large distances. Like and unlike spin pairs differ in energy by about 6% at Re. A serious correction for R < Re is the change in atomic correlation due to distortion. The total potential obtained has the correct behavior [minimum of 4.32°K at 3.04 A. (5.75 a.u.) with a long-range behavior of −0.853R−6 in atomic units]. At short distances (R < Re) the molecular orbital (MO) form of the theory becomes more convenient since the interorbital MO pair correlations are large and have some intra-atomic correlation character. The MO pair correlations approach ε(1σg2)=ε(1σu2)=ε(1σgα1σuβ)=12ε(He)=−0.57 eV as R → ∞. The LO description is used for R ≳ Re.
Arrhenius Activation Energy of Electrical Conductance of Aqueous Lithium and Cesium Chloride Solutions in the −2°-+12°C Range
Authors: Horne R. A. , Johnson D. S.
Published: January 2005

The electrical conductivities of aqueous 0.001, 0.01, 0.1, 1.0, and 3.0M LiCl and of 0.001, 0.01, 0.1, and 1.0M CsCl solutions have been measured at 1 atm over the temperature range −2°-+12°C. Although LiCl is a water structure maker and CsCl a structure breaker the Arrhenius activation energies of electrical conduction both show maxima near the temperature of maximum density.
Spectroscopy of EDA Complexes at High Pressures. II. Absorption of Several TCNE Complexes in Polymer Matrices
Authors: Offen H. W. , Kadhim A. H.
Published: January 2005

The charge-transfer absorption of 12 aromatic-hydrocarbon—TCNE molecular complexes in polymer matrices has been studied in the 0–25-kbar range. The observations for these solid solutions are compared with the results for compressed liquid solutions obtained by Gott and Maisch. The spectral shifts in the charge-transfer-band maxima range between +540 and −1700 cm−1 at 25 kbar for the complexes containing the various donors. A 1.1–3.5-fold increase in intensity at 25 kbar can be related directly to electronic transition strengths without applying corrections for complexation equilibria as required in liquid solutions. The bandwidths of the charge-transfer bands appear insensitive to compression. A comparison of the pressure influence on the spectral characteristics of molecular complexes and of the free donors suggests that for complexes the effects from solvent interactions are overshadowed by strong charge-transfer forces which are highly specific in nature.
Optical Study of X-Ray Irradiation Effect on the Phase Transition in Triglycine Sulfate and Diglycine Nitrate
Authors: Sato Yoshiki
Published: January 2005

Infrared spectra are measured at various temperatures on ferroelectric triglycine sulfate (Tc=48°C) and diglycine nitrate (Tc=−67°C) and nonferroelectric diglycine hydrochloride, each of which includes a short hydrogen bond connecting two glycine molecules. Almost all of the spectra of these substances are only slightly changed as the temperature passes through the respective Curie points. In contrast, a band at 575 cm−1 in triglycine sulfate is very characteristically changed, and its behavior is strongly influenced by x-ray irradiation. Further, a detailed inspection of the spectra shows that above and below the respective Curie points one of the two glycine molecules is in zwitterion form in diglycine nitrate and not in triglycine sulfate, and that the potential for the proton is of symmetrical single-minimum type in the latter and of asymmetrical double-minimum type in the former. Based on these facts, it is suggested that the origin of the phase transition, in triglycine sulfate, is not attributable to the hydrogen bond but to the remarkable intensity behavior of the 575-cm−1 band. On the other hand, in diglycine nitrate it is ascribed to a collective motion leading to the interchanging of the hydrogens between two possible equilibrium positions on the hydrogen bonds.