bluuebunny/crossref_metadata_2025 huggingface dataset:
Isotope Effects on Vibrational Transition Probabilities. II. Electronic Transitions of Isotopic Nitrogen, Nitric Oxide, and Oxygen Molecules
Authors: Halmann M. , Laulicht I.
Published: January 2005

Franck—Condon factors are given for the major electronic transitions of the normal and stable-isotope-labeled molecules N2, NO, and O2, for vibrational levels up to 10 of the v″=0 and v′=0 progressions and for the (1, 1) transition. Appreciable isotope effects on vibrational transition probabilities are found in the O2 Schumann—Runge and Herzberg bands, in the O2+ second negative bands, in the NO beta and ``M'' bands, and in the N2 Vegard—Kaplan bands. The magnitude of isotope effects on Franck—Condon factors is determined by differences in reduced masses between two isotopic molecules, as well as by differences in equilibrium internuclear distances between the two electronic states involved. The ratio of Franck—Condon factors of the light and heavy molecules decreases in the v″=0 and v′=0 progressions with increasing quantum number. The isotope effect on r centroids is very small.
Mass-Spectrometric Study of Ions at Near-Atmospheric Pressure. II. Ammonium Ions Produced by the Alpha Radiolysis of Ammonia and Their Solvation in the Gas Phase by Ammonia and Water Molecules
Authors: Hogg A. M. , Kebarle P.
Published: January 2005

A new mass-spectrometric method for the study of solvation of ions and of ion complexes is applied to the ammonium ion.

The major ion in the α-particle radiolysis of NH3 is the clustered ammonium ion NH4+·nNH3. A study of the distribution of these clusters is made at room temperature and in the pressure range 0.05 to 200 Torr ammonia. Clusters up to n=20 can be observed. The intensity distribution of the ions shows that the inner solvation shell contains four molecules. Approximate free-energy changes for inner- and outer-shell solvation are obtained.

Studies of competitive solvation of the NH4+ ion by water and ammonia molecules confirm the inner four shell. Ammonia is preferentially taken up in the inner shell and water in the outer shell. The higher stability of the ammoniated inner shell requires a very small effective NH4+ radius. This requirement leads to an examination of the structure of the NH4+·4NH3 ion.
Electron Spin Resonance Spectrum of FCO
Authors: Adrian Frank J. , Cochran Edward L. , Bowers Vernon A.
Published: January 2005

The electron spin resonance spectrum of the fluoroformyl radical (FCO) has been observed at 4.2°K in solid carbon monoxide. The radical was prepared by reaction between the CO matrix and fluorine atoms produced by in situ photolytic dissociation of fluorine oxide (OF2). The fluorine hyperfine splitting of FCO is very large and approximately axially symmetric: A1/h=1437.5, A2/h=708.2, and A3/h=662.0 Mc/sec. The large hyperfine splitting results from spin polarization of an exceptionally weak CF bond, and is consistent with the theory for the proton hyperfine interaction in HCO. This implies that FCO, like HCO, is a sharply bent molecule in which the unpaired electron occupies an in-plane or σ orbital, a conclusion which is in agreement with theoretical predictions.
On the Nature of Stimulated Emission in Rigid Organic Solutions
Authors: McClain W. M. , Albrecht A. C.
Published: January 2005

A dilute solution of an aromatic amine in a saturated hydrocarbon is frozen to a rigid state in liquid nitrogen and irradiated with ultraviolet light in the absorption band of the amine. The amine undergoes a one-electron ionization to give its colored radical cation and an electron trapped in the matrix. Subsequent infrared illumination causes a burst of blue-green luminescence called stimulated emission, which is investigated here. It is found to be a recombination luminescence composed of the fluorescence and phosphorescence bands of the amine, though the phosphorescence appears in much greater proportion than when the amine is excited by ultraviolet light. The kinetics of the two bands are analyzed and it is shown that the phosphorescing state and the fluorescing state are both populated directly by the recombination process, and through the same rate-determining step. The recombination is also observed as a bleaching of the colored cation, which closely follows the kinetics of the stimulated fluorescence. It is shown that the system possesses electron traps of several different depths, ranging from shallow, thermally ionizable levels to depths of more than 3 eV.
Electron Spin Resonance and Optical Absorption in GeO2
Authors: Weeks R. A. , Purcell T.
Published: January 2005

Paramagnetic states of GeO2 in the glass and in the powdered crystalline hexagonal and tetragonal phases have been investigated by the means of electron spin resonance after irradiation with γ rays and electrons. Three of the resonances observed in the glass were identified as intrinsic paramagnetic states on the basis of concentration, g values, and the shapes of the resonances. The g values of these lines were 1.9957, 2.0060, and 2.0080. The g=1.9957 line had a shape which was invariant with temperature (300°, 78°, and 2°K) and with magnetic field. The shape was a characteristic powder pattern for a center with S=½ and an approximately axially symmetric g tensor, where g‖=2.0016 and g⊥=1.9957. This line was characteristic of all glass and hexagonal crystal-phase specimens for all irradiations at temperatures∼300°K. The spin concentration after an irradiation of ∼1017 (1.5 meV) electrons cm−2 was ∼3×1018 cm−3 with no indication of saturation. Tentative correlation of this paramagnetic center with optical absorption in the region of 4.5 eV was established by a series of irradiations and subsequent heat treatments. The data on the g=1.9957 line was sufficient for the proposal of a model in which an electron is trapped at an oxygen vacancy. The g=2.0080 line was observed in all electron-irradiated glass specimens and the g=2.0060 line was found in all γ-ray irradiated glass specimens along with the g=2.0080 line. Other lines were observed at lower g values in β and γ irradiated glass and were tentatively assumed to be due to impurities. Irradiation of the glass with 60Co γ rays at 78°K and measurements without intervening warmup showed only one resonance with g=1.9957 but with a shape quite different from the g=1.9957 line found after irradiation with the same dose of 60Co γ rays at approximately 40°C. This line was assumed to be another intrinsic center. Resonances observed in the tetragonal-phase powder bore no relation to the resonances in the glass and hexagonal-phase powder.
Extended-Hückel-Theory and Lattice-Energy-Theory Investigation of Diboron Tetrachloride, B2Cl4
Authors: Moore Emmett B.
Published: January 2005

An extended-Hückel-theory investigation of the electronic structure of molecular B2Cl4 shows the staggered form to be more stable than the eclipsed form by 1.1 kcal/mole, as compared with the experimental value of 1.7±0.6 kcal/mole. The same method fails to predict intermolecular binding in crystalline B2Cl4, as expected; but lattice-energy theory gives a reasonable binding energy for the known eclipsed crystalline form and shows this form to be more stable than either of two assumed staggered crystalline forms.
Mössbauer Effect in the System BaFeO2.5–3.0
Authors: Gallagher P. K. , MacChesney J. B. , Buchanan D. N. E.
Published: January 2005

Mössbauer spectra were measured at 298°, 78°, and 4°K for a number of samples in the system barium ferrate(III)—barium ferrate(IV). The composition with highest iron(IV) content (BaFeO2.95) has an isomer shift, at 298°K, of =0.29 mm/sec relative to Cu(57Co). At 78°K, the absorption is magnetically split having an isomer shift of =0.31 mm/sec and a hyperfine field of 227 kOe. Barium ferrate(III) is similar to the strontium analog and YIG in that there are equal numbers of octahedral and tetrahedral iron sites. The Mössbauer spectrum at 78°K indicates isomer shifts of 0.29 and 0.10 mm/sec and hyperfine splittings of 536 and 459 kOe for the octahedral and tetrahedral sites, respectively. Spectra of intermediate compositions are more complex. Results of this system are compared with those previously determined for the analogous strontium system.
Polarization of the Fluorescence of Solutions Subjected to an Electric Field
Authors: Weber G.
Published: January 2005

The dipole moments of fluorescent molecules in nonpolar solvents in the lowest singlet excited state has been previously calculated from observations of the increase in fluorescence polarization when the molecules are subjected to an electric field on the assumption that the Langevin distribution prevails at the time of the emission. By the use of Benoit's theory of the rotational diffusion of a dipole placed in an electric field, and under conditions of isotropic depolarization, an equation is obtained which allows the calculation of the excited dipole moment when the equilibrium distribution is not reached during the excited state.
Reactions of Atomic Oxygen with Acetylene. I. Kinetics and Mechanisms
Authors: Arrington C. A. , Brennen W. , Glass G. P. , Michael J. V. , Niki H.
Published: January 2005

The room-temperature reaction of acetylene with atomic oxygen has been studied in a moderately fast flow system. The course of the reaction was followed using both the Bendix T.O.F. mass spectrometer and a photometric method. The major products of the reaction were carbon monoxide and hydrogen. Large amounts of atomic hydrogen were also observed.

The following reaction scheme is consistent with our results: (1)  C2H2+O→[C2H2O*]→CH2+CO,(2)  CH2+O→HCO+H,(3) CH2+O→H2+CO,(4)  HCO+H→H2+CO,(5)  HCO+O→OH+CO,(6)  HCO+O→H+CO2,(7)  OH+O→H+O2.The rate of the over-all reaction is determined by the first initial step in which atomic oxygen adds to acetylene to yield an excited complex which then undergoes unimolecular decomposition to give triplet methylene. The rate constant for this initial reaction was measured, at room temperature, as (8.9±2.8)×10−14 cc molecule−1·sec−1. The activation energy was less than 1 kcal mole−1.

Experiments with acetylene-d2 have established that Reactions (2) and (4) constitute the major pathway by which triplet methylene, produced in Reaction (1), is consumed.
One-Dimensional Model of Polymer Adsorption
Authors: DiMarzio Edmund A. , McCrackin Frank L.
Published: January 2005

A detailed treatment of the conformations of a one-dimensional polymer molecule adsorbed to a surface is given. The average number of contacts of the chain with the surface, the end-to-end length, and the distribution of segments ρ(z) with respect to distance z from the surface are computed as functions of the chain length (N) of the polymer and the attractive energy of the surface. Both theoretical and Monte Carlo calculations are used. A transition is found at an attractive energy of kT ln 2. For attractive energies less than this value, the average number of contacts of the chain with the surface approaches a finite value as N approaches infinity, while the end-to-end length vaires as N½. However, above the transition the number of contacts is proportional to N and the end-to-end length is independent of N. The distribution of segments ρ(z) also shows a marked change as we go through the transition. The one-dimensional model is shown to correspond to the projection of a three-dimensional model on the direction normal to the surface. Therefore, these results are believed to represent the distribution normal to the surface for real systems.
One-Center Perturbation Approach to Molecular Electronic Energies. II. Exact Wavefunctions and Energies for H2+-Like Molecular Puffs
Authors: Hauk Peter , Parr Robert G.
Published: January 2005

The exact solution is given for the problem of the ground state of one electron moving in the potential field V(r) = —Z/r>, produced by an effective nuclear charge Z uniformly spread over a sphere of radius R, with r> the greater of R and the electron's distance r from the sphere center. The lowest eigenvalue and corresponding eigenfunction are tabulated as functions of R and Z.

For the case corresponding to the spherical approximation to H2+ at its equilibrium distance, R = 1, Z = 2, the energy is found to be −1.018502 a.u., in agreement with previous variational calculations of Cohen and Coulson, Howell and Shull, and Houser, Lykos, and Mehler.
Collision Cross-Section Study of CO2
Authors: Lassettre Edwin N. , Shiloff Jerome C.
Published: January 2005

Electron-collision cross-section determinations, as a function of scattering angle, for carbon dioxide are described. A weak transition at 9-V excitation energy is of special interest. The shape of the peak changes markedly with angle. The theory of the effect is discussed in general terms.
Force Constants for MC, CN Interaction in Metal—Cyanide Complexes
Authors: Jones Llewellyn H.
Published: January 2005

Accurate measurements of the Raman-active CN stretching frequency, v1, and the infrared-active CN stretching frequency, v3, have been made for aqueous KAu(CN)2 and the disubstituted 13C and 15N species. The results are 2164.0, 2133.6, and 2115.6 cm−1 for v1 of Au(CN)2−, Au(C15N)2−, and Au(13CN)2−, respectively. The respective values for v3 are 2145.7, 2115.3, and 2099.3 cm−1. From the results it was possible to to calculate the stretch—stretch interaction constants. It is found that for adjacent MC, CN interactions, FMC, CN≈0.3 mdyn/Å while for nonadjacent interaction, FMC, C'N≈0.
One-Center Expansion Wavefunctions for CH3−, CH4, and CH5+
Authors: Rutledge Ronald M. , Saturno Antony F.
Published: January 2005

One-center expansion (OCE) wavefunctions for the species CH3−, CH4, and CH5+ are presented. These wavefunctions are expressed by configuration interaction of the singly excited states of a closed-shell ground state. The basis set consists of STO's through l=4, belonging to the irreducible representations spanned by the σ-bonding representation. In addition the calculations on CH3− and CH5+ were done as a function of nuclear geometry. These calculations indicate that CH3− has a D3h configuration rather than a C3v configuration. The molecular configuration of CH5+ was indicated to be D3h rather than C4v or C3v.

The ground-state energies of CH3−, CH4, and CH5+ were calculated to be −39.236, −39.859, and −40.036 a.u., respectively. The proton affinity of methane is calculated to be approximately 5 eV.
Electron-Diffraction Study of the Structure and Internal Rotation of Cyclopropyl Carboxaldehyde
Authors: Bartell L. S. , Guillory J. P.
Published: January 2005

The structure and conformational behavior of cyclopropyl carboxaldehyde in the gas phase have been investigated by electron diffraction. Rotational isomers did not correspond to the trans and gauche isomers observed in a parallel study of the isopropyl derivative, but rather to s-trans and s-cis. The latter isomers were present in nearly equal concentrations. The rotational barrier appears to be greater than 2.5 kcal/mole. Results are interpreted in terms of Walsh's π-electron picture, and various comparisons of cyclopropyl and vinyl groups are made and discussed.

The diffraction experiment yielded normal values for bond angles and amplitudes of intramolecular vibrations. No tendency was detected for the aldehyde to assume a nonclassical structure of the sort postulated for its analog, the cyclopropyl carbinyl cation.
Electron-Diffraction Study of the Structure and Internal Rotation of Isopropyl Carboxaldehyde
Authors: Guillory J. P. , Bartell L. S.
Published: January 2005

An electron-diffraction study of gaseous isopropyl carboxaldehyde has been carried out for comparison with a parallel study of cyclopropyl carboxaldehyde described in the preceding paper. The isopropyl compound, unlike its cyclic analog, exists in normal trans and gauche rotational isomers. Gauche conformations predominate, accounting for about 90% of the molecules present. Normal values of bond distances and amplitudes of vibration were found and are reported along with other derived molecular parameters. The barrier to rotation was studied and its threefold component was estimated to be in excess of 2 kcal/mole.
Comparison of Some Calculations on H2O and H2S
Authors: Hake R. B. , Banyard K. E.
Published: January 2005

For the H2O and H2S molecules, a comparison is made of the values of the molecular energy, molar diamagnetic susceptibility, coherent x-ray scattering factor, dipole moment, 〈1/r〉 and 〈1/r2〉 as calculated by different approximate treatments. The results of a united-atom (UA) calculation, the LCAO—MO—SCF extended one-center expansion (OCE) approach of Moccia, and the LCAO—MO—SCF minimal multicenter expansion (MCE) treatment of Ellison and Shull are compared for H2O. For H2S, UA and OCE calculations are compared. All theoretical values are compared with experiment where possible, and the relative merits of the different approximate treatments are discussed. We also discuss results which might be obtained for H2S from a minimal LCAO—MO—SCF—MCE calculation.

Also for H2S, we report the results of modifications in our earlier UA approach. Although the conclusions drawn in our earlier work remain unchanged by the modifications, we note a pleasing improvement on our earlier values for the force constant, molar diamagnetic susceptibility, and molecular energy.
On the Molecular Kinetic Theory of Cooperative Relaxation Processes in Dipolar Liquid and Crystalline Phases
Authors: Adam Gerold
Published: January 2005

The correlation-function method is used to describe the dielectric relaxation behavior of liquids and directionally isotropic crystalline phases.

The physical model used is that of a regular mixture of dipole molecules and vacancies on a lattice, i.e., the equivalent of the Bragg—Williams approximation.

To calculate the cooperative transition probabilities, which govern the relaxation correlation function, the effect of vacancies in the neighborhood of the representative dipole is taken into account. The effect of vacancy diffusion is neglected.

The result is a discrete distribution of relaxation times corresponding to cooperative regions with none, one, two, etc., vacancies.

This relaxation spectrum is shown to be narrow in the case of liquids and broad in the case of molecular crystals.

Upon application of the theory to measurements of the dielectric relaxation of crystalline hydrogen and deuterium halides and of liquid bromoalkanes, the fraction of vacancies and an interaction parameter for these substances were obtained.

The values of both quantities were shown to be of the order to be expected from the energy of molecular interactions.
Frequency-Dependent Transport Coefficients in Fluid Mechanics
Authors: Zwanzig Robert
Published: January 2005

Exact time-correlation formulas for frequency-dependent shear viscosity, bulk viscosity, and thermal conductivity are presented. These formulas are evaluated for a fluid composed of molecules with internal degrees of freedom, in the limit of very weak coupling of internal and translational motions. In this limit, the shear viscosity is unaffected by internal modes. The bulk viscosity consists of two parts, one due to translational motions, and the other due to relaxation of the energy contained in internal modes. The thermal conductivity consists of two parts, one due to translational motions, and the other due to diffusion of energy in internal modes (the Eucken correction). The resulting excess sound absorption is in complete agreement with the predictions of the thermodynamic theory of relaxation in fluids.
Infrared Spectra of Difluoroborane and Difluoroborane-d
Authors: Perec M. , Becka L. N.
Published: January 2005

Gaseous H–BF2 and D—BF2 were obtained by a new method of preparation. Analysis of high-resolution ir spectra gave approximate values for the B–F distance (1.30±0.15 Å) and the F–B–F angle (120°±5°). Five of the six fundamentals were observed and assigned unambiguously: ν2 = 2620 and 1962 cm−1, B–H and B—D stretches; ν1 = 1166 and 1128 cm−1, 11B–F symmetric stretches in H–BF2 and D—BF2; ν3 = 545 and 540 cm−1, F–11B–F bending in H–BF2 and D—BF2; and ν4 = 1402, 1392, 1419 cm−1, 11B–F asymmetric stretches in H–BF2 and D—11BF2 and 10B–F stretch in D—10BF2, respectively; ν6 = 944, 924, 810, 790 cm−1, out-of-plane deformation in H–10BF2, H–11BF2, D—10BF2, and D—11BF2, respectively. The H–B–F bending appears to have a frequency ν5 = 1200 cm−1 for H–11BF2 and is estimated at 887 cm−1 for D—11BF2. A force-constant calculation was made, obtaining the following values (in millidynes per angstrom) : fD = 3.66, fd = 6.625, fd′ = 0.725, fDd = 0.37, fr = 0.772.
Mass-Spectrometric Study of the Oxidation of Tungsten
Authors: Schissel P. O. , Trulson O. C.
Published: January 2005

A mass spectrometer has been used to study the kinetics of the oxygen—tungsten reaction over the temperature range 1400° to 3150°K at oxygen pressures as high as 2×10−4 Torr. The main products of chemical reaction are identified as W3O9, W2O6, WO3, and WO2; their intensities are given as a function of surface temperature and oxygen pressure. At high surface temperatures, atomic oxygen is observed in an abundance comparable to the impingement rate of molecular oxygen on the surface. These observations lead to a reaction mechanism involving two types of oxygen on the surface, the first tightly bound with a desorption energy near 144 kcal/mole, the second more loosely bound with a desorption energy near 114 kcal/mole. A detailed kinetic model is proposed to account for the observations.
Separation of Oxygen-17 from Natural Oxygen in Thermal Diffusion Columns
Authors: Narten A. H. , Landau L.
Published: January 2005

Two prototype columns used as the basic unit in a thermal diffusion cascade for the final enrichment of oxygen-17 are described. An analysis of transient data from these two columns is made. Column parameters derived from this analysis are compared with parameters calculated from theory, using the Lennard-Jones (12/6) model. Discrepancies between observed and calculated column performance are discussed.
Variational Approach to Perturbation Theory. I. Application to the Calculation of Atomic Polarizabilities
Authors: Kolker H. J. , Michels H. H.
Published: January 2005

A variational approach to perturbation theory is derived which establishes the relationship between variational and conventional approaches that utilize expansions in terms of atomic or molecular eigenfunctions. This approach is based upon the observation that the variational approach to perturbation theory is formally equivalent to a variational method for constructing a special set of excited-state wavefunctions. A mathematical demonstration of this equivalence has been formulated. With the use of this new approach to perturbation theory, we have calculated both the static and dynamic polarizabilities of the two-electron helium isoelectronic series, H−, He, and Li+ and a four-electron system represented by the beryllium atom. Multiconfiguration open-shell wavefunctions were employed. These flexible wavefunctions permit a quantitative analysis of the near-degenerate s—p orbital mixing in the ground state of the beryllium atom. The inclusion of this orbital degeneracy effect results in a substantial reduction in the calculated polarizability.
On the Collision Mechanism of Bimolecular Reactions. IV. Intramolecular Isotope and Stripping Effects in the Reactions of Ar+ and of N2+ Ions with HD
Authors: Henglein A. , Lacmann K. , Knoll B.
Published: January 2005

The velocity spectra and cross sections for the reactions of Ar+ and of N2+ with HD have been measured at different kinetic energies of the incident ions. The bands of the secondary ions ArH+, ArD+, N2H+, and N2D+ appear at the positions in the velocity spectra predicted by the stripping model. The cross sections for H- and D-atom transfer are half as large as for the corresponding reactions with H2 and D2, respectively. The intensity ratio XH+/XD+ strongly increases at high energies as is expected from the stripping model.
Isotopic Mixing in Nitrogen Chemisorbed on W
Authors: Yates John T. , Madey T. E.
Published: January 2005

The chemisorption of an equimolar mixture of 14N2 and 15N2 on polycrystalline tungsten has been studied. The flash-filament mass-spectrometer technique was used at sample temperatures of 77°K and above, in an ultrahigh-vacuum system. The molecular identity of the low-temperature γ state was confirmed since the γ—N2 desorption spectrum showed no formation of 14N15N. On the other hand, the strongly held β-nitrogen was completely isotopically mixed on desorption. A careful study of β-nitrogen, using 15N2, has revealed two overlapping binding states, β1 and β2, associated with surface heterogeneity in the W substrate. The β1 state shows first-order desorption kinetics, and the more tightly bound β2 state appears to desorb with higher-order kinetics. Under saturation conditions, the coverage of β-nitrogen is essentially constant from 300°—1100°K.
Scaled Particle Theory of Fluid Mixtures
Authors: Lebowitz J. L. , Helfand E. , Praestgaard E.
Published: January 2005

An extension of a previous one-component theory of hard-sphere systems (in three, two, and one dimensions) and the surface tension of real systems is made to mixtures. The theory is based on consideration of an approximate expression for the work of adding an additional hard sphere to a mixture. Comparison between theory and molecular-dynamics calculations of the various contributions to the virial pressure (related to contact distribution functions) of such hard-sphere mixtures is excellent. Comparison of the theory with experimental surface tensions of mixtures of simple liquids is satisfactory.
Theory of Helium Dissolution in Uranium Dioxide. II. Helium Solubility
Authors: Olander Donald R.
Published: January 2005

The solubility of helium in uranium dioxide was calculated directly from atomic properties and compared with experiment. The calculations were based upon a statistical-mechanical formula which assumes dissolved helium to behave as a simple harmonic oscillator in an interstitial site in the UO2 lattice. Knowledge of the interactions between helium and the oxygen and uranium ions of the lattice permits computation of the heat of solution and the vibration frequency, which yield the Henry's law constant. The calculated solubility of 6.6×10−4 cc (STP)/g·atm at 1200°C was in good agreement with the experimental measurements, but the heat of solutions differed appreciably. This discrepancy was attributed to experimental errors, for the very large observed heat of solution (∼−30 kcal/mole) could not arise from purely physical interactions.
Calculation and Interpretation of the 129I Isomer Shifts in the Alkali Iodide Lattices
Authors: Flygare W. H. , Hafemeister D. W.
Published: January 2005

Starting with an ideal alkali halide lattice composed of closed-shell ions, the overlap and electrostatic interactions are computed between the nearest and next-nearest neighbors in the alkali iodide lattices. The electrostatic perturbation on the s electrons is found to be small relative to the overlap deformation of the free-ion wavefunctions. Both effects predict the same correct dependence for the relative isomer shifts, however. The deformed free-ion wavefunctions are used to compute the relative isomer shifts at 129I in the alkali iodide lattices. The value of the nuclear parameter in 129I is ΔR/R=0.5×10−4.
Libration of the OH— Ion in LiOH
Authors: Coogan C. K.
Published: January 2005

Much discussion and controversy has taken place in recent years on libration of the OH− ion in hydroxide crystals. Recent work on the charge distribution in the OH− ion makes it feasible to calculate the librational frequency and amplitude in LiOH arising from thermal agitation. A simplified model of the libration is chosen which corresponds with the Einstein model for this mode. The calculation is based on the change in lattice energy with rotation of a single OH− ion, involving Madelung, van der Waals, and repulsive terms.

The results indicate considerable anisotropy of libration at thermal amplitudes at room temperature. The calculated frequency thus varies with direction so that ν̃a=342 cm−1 while 〈ν̃〉Av=396 cm−1. At room temperature the calculated rms thermal displacements of the hydrogen atom arising from libration agree well with those derived from the results of neutron-diffraction experiments. The apparent success of this simple model in LiOH suggests that it might be extended to similar layer-lattice hydroxide crystals.
Some Triplet States of the Hydrogen Molecule
Authors: Wakefield Charles B. , Davidson Ernest R.
Published: January 2005

The potential curves for the 2s, 3s, 3d 3Σg+ states of H2 have been computed in the Born—Oppenheimer approximation. Some points on the potential curves for the 3d 3Δg, 3d 1Δ, 3s 1Σg+, and 3d 1Σg+ states were also obtained. Vibrational levels have been computed in various approximations. Lambda doubling in the 3s, 3d triplet ΣΠΔ complex is discussed. This doubling is complicated by the near degeneracy of the 3s 3Σg+ and 3d 3Σg+ states at the equilibrium nuclear separation.
van der Waals Forces between Conducting Bodies
Authors: Kattawar G. W. , Eisner M.
Published: January 2005

The van der Waals force of attraction between a perfectly conducting cylinder and a plane, and a sphere and a plane, was calculated. The calculations were made using first-order electromagnetic perturbation theory coupled with the concept of zero-point energy. In each instance the force was found to vary as the inverse fifth power of the distance of separation of the bodies. As in the case of an atom and a plane, the force between the sphere and plane was proportional to the static polarizability of the sphere.
Mercury-Sensitized Photolysis of C2F4
Authors: Cohen Norman , Heicklen Julian
Published: January 2005

Tetrafluoroethylene was decomposed by mercury photosensitization at temperatures from 21° to 224°C. At pressures below 60 mm, the only product was c-C3F6 and its production was linear with the C2F4 pressure and enhanced by raising the temperature. The CF2 radicals produced during photolysis can either recombine or add to the substrate: 2CF2→ lim k6C2F4,CF2+C2F4→ lim k7c−C3F6.The rate constant ratio k7/k6½ was found to be 395 exp (−6700/RT) (liter/mole·sec)½.
Raman Spectrum of Potassium Azide Single Crystals
Authors: Bryant James I. , Brooks Robert L.
Published: January 2005

The Raman spectrum of single crystals of KN3 has been investigated over the frequency range from 30 to 4000 cm−1. The ``unit cell'' method of Bhagavantam and Venkatarayudu was used to classify the normal modes and to derive their selection rules. In addition to making available the Raman shifts for KN3 crystals, this work also provides a check on assignments of much of the fine structure observed previously in the infrared spectrum.
Second Virial Coefficients from Acoustic Isotherms
Authors: Lestz S. S. , Grove R. N.
Published: January 2005

The generalized second virial coefficients are calculated from measured acoustic isotherms and compared with theoretical values. Agreement is poor. The calculated second virial coefficients are very sensitive to slope errors of the experimental acoustic isotherms. For the temperature range of the experimental data, a 1% slope error can yield results for the calculated second virial coefficient that disagrees with the theoretical values by as much as 14%. The difficulty of maintaining small slope errors in experimental data appears to rule out this method as a means of determining the second virial coefficient.
Chemical Kinetics as a Relaxation Process in a Multilevel System. II. General Formulation of the Many-Shot Expansion
Authors: Serauskas R. V. , Schlag E. W.
Published: January 2005

For a complete understanding of rates in chemical kinetics it is necessary to analyze kinetic processes on the molecular level. For such an analysis one must know the change in the distribution of internal energy as the result of a collision process. It is suggested that this information can be obtained from an analysis of weak-collision terms in a reacting system excited to a nonequilibrium distribution from which it relaxes by way of a many-level process.

The relaxation problem in a nonequilibrium multilevel system weakly coupled to a heat bath can be expressed in terms of a Pauli master equation. It has previously been shown that this relaxation problem can be solved in terms of a many-shot expansion, the leading term being the strong-collision result and further terms being due to weak collisions. In this paper it is shown that this many-shot expansion can be derived from a generalized matrix form of the master equation, as well as by the phenomenological approach used previously. Furthermore, a matrix form for a generalized nearest-neighbor model is analyzed and developed in terms of a series which considers the asymptotic contributions of upward transitions in terms of successively less-probable Markov chains. The input for these computations is a complete set of transition probabilities, for which these methods predict the appropriate laboratory observable. Under certain experimental conditions the laboratory observable is particularly sensitive to the weak-collision terms, and it is in this region that one should be able to obtain information about the effect of collisions on the distribution of internal energy.
Excitation of Molecular Nitrogen by Electron Impact
Authors: Winters Harold F.
Published: January 2005

Relative cross sections for excitation of the triplet series of molecular nitrogen have been obtained. The cross sections have a maximum within a few volts of threshold as expected for electron exchange collisions. In particular, the C 3IIu state has a sharp maximum within a few tenths of a volt of threshold and then decays sharply.

The A 3Σu+ state has an increasing slope through the Franck—Condon region and then is a strictly linear function of energy for about 1½ V. It subsequently reaches a maximum and starts to decay. This leads to the postulate that the region of increasing slope is caused by the continual excitation of new vibrational levels and that the excitation function of a given vibrational level may be linear to near threshold. This interpretation is shown to be consistent with the experimental data.
On the Specific Heats of Ferroelectric Crystals
Authors: Grindlay J.
Published: January 2005

A thermodynamic identity relating the specific heat at constant electric field and constant stress to the specific heat at constant displacement and constant strain is derived. The identity is applied to the case of the ferroelectric crystals and it is shown that the free specific heat has a singularity at the transition if, and only if, the clamped specific heat has a singularity.
Hartree—Fock—Roothaan Wavefunctions, Potential Curves, and Charge-Density Contours for the HeH+(X 1Σ+) and NeH+(X 1Σ+) Molecule Ions
Authors: Peyerimhoff Sigrid
Published: January 2005

Hartree—Fock—Roothaan wavefunctions for the ground state of the HeH+ ion and the NeH+ ion are reported. The potential curves for HeH+ and NeH+ are calculated using wavefunctions, which are optimized at the equilibrium distance and also at each internuclear distance, and their relative behavior is discussed. The Hellmann—Feynman forces on the nuclei are studied as a function of the internuclear distance with regard to the size of the basis set and optimization of the wavefunction. Spectroscopic data are calculated in different ways, a dissociation energy of 1.74 eV for HeH+ and 2.03 eV for NeH+ is computed, and calculations made to find the center of negative charge for every internuclear separation. Electron-density maps are plotted for several internuclear distances in HeH+ and for the total wavefunction and the individual molecular orbitals of NeH+ at the equilibrium distance.
Variational Treatment of the HeH+ Ion and the β-Decay in HT
Authors: Wolniewicz L.
Published: January 2005

The nonrelativistic energies of the HeH+ ion have been computed by the variational method for the ground state and for the first excited 1Σ+ state. The wavefunction employed was a 64-term generalized James—Coolidge expansion. The computed binding energy of the ground state amounts to De=16448.3 cm−1 at the equilibrium separation Re=1.46324 a.u. The excited state is found to be repulsive.

The HeH+ wavefunctions are used to compare quantitatively the theory of β-decay in molecules with experiment. It is shown that for the HT molecule, the theory predicts the dissociation in at least 17.8% of the events while the corresponding experimental number is 6.8%±1.9%.
Perturbation Treatment of the Ground State of H2+
Authors: Lyon William D. , Matcha Robert L. , Sanders William A. , Meath William J. , Hirschfelder Joseph O.
Published: January 2005

Rayleigh—Schrödinger perturbation calculations are carried out for the ground state of the H2+ molecular ion. The zeroth-order wavefunction for this problem is chosen to be the Guillemin and Zener variational function ψ=N[exp(−αrA−βrB)+exp(−βrA−αrB)].The energies through third order and the expectation value E(1) of the Hamiltonian calculated with the wavefunction accurate through first order are computed for various choices of the parameters. For the optimum choices of both α and β, we obtain for all separations values of E(1) which agree almost perfectly with the accurate series calculations of Bates, Ledsham, and Stewart. Also the values of the wavefunction accurate through the first order agree almost perfectly at most points in configuration space with Bates et al.
Theory of the Linear Heisenberg Antiferromagnet. Application to Paramagnetic Excitations in Organic Crystals
Authors: Soos Zoltán G.
Published: January 2005

We consider a linear array of tightly bound electrons that are exchange coupled to their neighbors. The Hamiltonian, in the Heisenberg model, is H= ∑ j=112N{J(1+δ)S2j·S2j+1+J(1−δ)S2j·S2j−1−12J},where δ is the alternation parameter and the exchange integral J is positive, corresponding to antiferromagnetic coupling. We investigate the solutions for the one-dimensional antiferromagnet, for any |δ|≤1, by transforming the Hamiltonian first to Fermi creation and annihilation operators and then to pseudospin operators similar to the ones used by Anderson in connection with superconductivity. We thus take into account the coherence between antiparallel electrons in a self-consistent manner. We exploit the similarity between the linear antiferromagnet and superconductivity theory to obtain the ground-state energy and the excitation spectrum for arbitrary δ and temperature. We thus obtain a complete thermodynamic description. In particular, we calculate the paramagnetic susceptibility and compare it with experiment.

At 0°K, the solutions we present agree with or improve upon previous calculations, for either the regular (δ=0) or the alternating (δ≠0) antiferromagnet, of the ground-state energy, the excitation spectrum, and the short-range order. Using the finite temperature extension of the theory, we find good agreement between the calculated and the experimental paramagnetic susceptibilities of organic crystals whose structures, so far as spin properties are concerned, may be approximated by either the regular or the alternating antiferromagnet. The temperature dependence of the excitation energies, a many-body effect describing the decrease of coherence between antiparallel electrons with increasing temperature, agrees with the observed behavior of the singlet—triplet energy gap in paramagnetic exciton systems. Thus, we obtain the extension of exciton theory to arbitrary temperature and alternation. The electron pairs forming triplet excitations are, for any alternation, increasingly separated at high temperatures, where, as expected, the electrons behave like a paramagnetic gas.
Internal Energy of Reaction Products by Velocity Analysis. II. Scattered KBr* from the Crossed Molecular Beam Reaction K+Br2
Authors: Grosser Arthur E. , Bernstein Richard B.
Published: January 2005

The velocity distribution of excited KBr* formed in reactive collision between crossed beams of velocity-selected K and thermal Br2 has been measured at several laboratory scattering angles and initial relative kinetic energies of 1.26, 2.14, and 3.27 kcal/mole. From these observations qualitative information may be inferred regarding the internal energy distribution function and the angular distribution of reactive scattering in the center-of-mass (c.m.) system. It is found that (1) the KBr* internal energy distribution is broad, extending over a range of at least 30 kcal/mole, with most of the 46 kcal/mole exothermicity of the reaction appearing in the form of internal excitation of KBr*, and (2) the angular distribution of reactive scattering in the ``forward'' direction (KBr preferring the direction of the incident K in the c.m. system), is characterized by a cone in the c.m. with an angle of generation of at least 30°.
Shear-Relaxation Processes in Liquids
Authors: Knollman G. C. , Miles D. O. , Hamamoto A. S.
Published: January 2005

Both cooperative behavior, involving breakup and re-formation of molecular aggregates, and environmental dissimilarities, attributed to incompleteness of short-range order, have been proposed earlier by two of the authors as possible mechanisms giving rise to the distribution of shear-relaxation times exhibited by most liquids. Experimental evidence is presented here giving qualitative indication that environmental-dissimilarity effects indeed can be operative in a liquid together with cooperative phenomena. Shear-relaxation characteristics are studied at a number of temperatures for a host liquid, hexachlorobiphenyl, having methanol and toluene in various concentrations as separate impurity liquids. Small amounts of the additive liquids are found to lessen the decay rate of cooperative behavior with increasing temperature, a result attributed to both degraded cooperative behavior and an environmental-dissimilarity mechanism. Although cooperative behavior predominates throughout the temperature and concentration range investigated, in the low-temperature region the impurity additive primarily decomposes aggregates of cooperative molecules, whereas at higher temperatures the impurity markedly enhances environmental dissimilarities and the distribution function widens with increasing (small) concentration. Toluene impurity additive displays greater degradation effect on cooperative behavior as well as greater enhancement of environmental dissimilarities than does methanol. Critical solution temperatures are noted as a matter of interest, and a method is presented for determining analytically the distribution of relaxation times associated with our experimentally determined components of shear modulus.
Microwave Spectrum, Dipole Moment, and Ring-Puckering Vibration of β-Propiolactone
Authors: Boone David W. , Britt Chester O. , Boggs James E.
Published: January 2005

The microwave spectrum of β-propiolactone has been observed in the vibrational ground state and in the first four excited states of the ring-puckering vibrational mode. The variation of the rotational constants with vibrational quantum number and the relative intensities of the observed vibrational satellites indicate that the vibration is essentially harmonic with ν0=160 cm−1 and with no appreciable barrier at the planar configuration. The dipole moment is 4.17±0.03 D, with μa=3.67±0.03 D, μb=1.99±0.02 D, and μc=0 in both the ground and first excited states.
Monte Carlo Equation of State for Hard Spheres in an Attractive Square Well
Authors: Rotenberg A.
Published: January 2005

The equation of state for hard spheres in a short-range attractive square well has been calculated for several values of the well strength by the Monte Carlo method. For shallow wells, it has the same general form but lies everywhere below the equation of state for the simple hard-core potential. As the well strength increases, two van der Waals loops appear, one at a density higher than the density of the order—disorder transition and one at a lower density.
3546-Å System of Formaldehyde
Authors: Henderson J. R. , Muramoto M.
Published: January 2005

Bands of the 1A″↔1A1 system of HCHO have been photographed in absorption at 190°K and in emission at 600°K. Twenty new bands in the absorption system are assigned. The electronic origin is discussed, and an average value of 28 193 cm−1 is reported. The α10 band in emission is shown to consist of two overlapping bands with origins at 27 035 and 27 025 cm−1, and assignments of (0−00)′→(010)″ and (0+00)′→(100)″, respectively, are suggested. Barrier heights in the 1A″ states of HCHO and DCDO are calculated to be 385 and 386 cm−1, implying equilibrium values of 20.7° and 26.4°, respectively, for the out-of-plane bending angles. Some observations about the nature of the electronic transition are made.
Evaluation of Approximations Used in the Calculation of Excitation by Collision. I. Vibrational Excitation of Molecules
Authors: Sharp T. E. , Rapp D.
Published: January 2005

Approximate procedures for calculating transition probabilities for excitation by molecular collision have been examined in terms of a simplified model, vibrational excitation of a harmonic vibrator by collinear collision with an atom. Digital-computer solutions were obtained for the coupled differential equations resulting from time-dependent perturbation theory with an expansion of the total wavefunction in terms of eigenfunctions of the target molecule. Calculations with the expansion truncated at 2, 3, ..., 10 states show that, as the collision velocity is increased, more states must be included to obtain an ``exact'' solution. For single quantum transitions j→j+1 at low velocities, the first-order perturbation approximation results are reliable up to probabilities of about 0.1; at higher velocities, they greatly exceed the ``exact'' results. The two-state approximation always yields drastic underestimates. For multiple quantum transitions at all velocities, the first-order perturbation calculation greatly underestimates the transition probability because it includes only the direct transition j→k and excludes the stepwise transitions during a single collision j→j+1→...→k−1→k. To evaluate this dominant process, a multiple-step perturbation theory was developed. The resulting equation for a harmonic oscillator, P0→n = (P0→1)n/n!, gives excellent predictions in the low velocity range. For higher collision velocities, a computer calculation employing many eigenfunctions is required. The relationship of these results to calculation of other inelastic collision processes is discussed briefly.
Multiphoton Absorption and Optical-Harmonic Generation in Highly Absorbing Molecular Crystals
Authors: Pao Yoh-Han , Rentzepis P. M.
Published: January 2005

In crystals of the appropriate symmetry, it is to be expected that multiphoton absorption is accompanied by optical-harmonic generation. A simple relationship between the cross sections of the two processes has been derived for molecular crystals which are essentially transparent to the incident (laser) frequency but are highly absorbing at the multiphoton frequency. An additional process of interest, namely excitation of the crystal by direct absorption of the optical-harmonic photons is found to be of appreciable magnitude for crystals with the appropriate symmetry. The use of these relationships to provide information concerning the space-group symmetry of the crystal and the nature of the intermediate states is discussed. In the case of two-photon absorption and second-harmonic generation, an order-of-magnitude agreement between theory and experiment has been established.