bluuebunny/crossref_metadata_2025 huggingface dataset:
First Ionization Potentials of Th, Np, and Pu by Surface Ionization
Authors: Smith David H. , Hertel G. R.
Published: February 2004

The surface ionization comparison technique was used to measure the first ionization potentials of Th, Np, and Pu relative to U. The differences in ionization potentials (ΔI.P.) obtained were: ΔI.P.(U–Th) = −1.29 ± 0.26 eV; ΔI.P.(U–Np) = 0.03 ± 0.01; and ΔI.P.(U–Pu) = 0.48 ± 0.02. The I.P. of U had previously been determined in this laboratory to be 6.19 ± 0.06 eV. Based on this value, the I.P. of Th is 7.5 ± 0.3 eV; Np, 6.16 ± 0.06; and Pu, 5.71 ± 0.06.
Evaluation of the Lamb Shift for the Hydrogen Molecule–Ion
Authors: Gersten Joel I.
Published: February 2004

The Lamb shift of the hydrogen molecule–ions H2+ and HD+ have been calculated to the lowest order in the radiative corrections. It is found to depend sensitively on internuclear separation and therefore to shift the various vibrational levels by a different amount. Possible experimental tests are considered for the detection of these quantum electrodynamical effects.
Conditionally Convergent Integrals Arising from Electromagnetic Interactions
Authors: Pitzer Russell M.
Published: February 2004

The treatment of conditionally convergent electromagnetic-interaction integrals is described for the coordinate systems usually employed for molecular integrals. The change in the value of an integral due to the exclusion of some infinitesimal volume other than a sphere about one of the particles is evaluated for several choices. These contributions to the integrals can be expressed at delta-function terms necessary in expansions of the interaction operator.
Far-Infrared Spectra of Ring Compounds. V. Ring-Puckering Potential Functions of Some Oxygen-Containing Molecules
Authors: Carreira L. A. , Lord R. C.
Published: February 2004

The infrared absorption spectra of gaseous 2,5-dihydrofuran, 3-oxetanone, 2-methyl-4,5-dihydrofuran, diketene, cyclopentanone, and cyclohexanone have been observed in the range 250–25 cm−1. Under high resolution the spectrum of 2,5-dihydrofuran shows a satellite series of Q branches in addition to those observed by Shimanouchi and Ueda. The satellites arise from transitions between ring-puckering energy levels in an excited ring-twisting state with altered spacing due to higher-order cross terms in the potential energy. The spectrum of 3-oxetanone is that of a planar molecule, and the energy levels of the ring-puckering mode fit a potential function of the form V(x) = ax4 + bx2. The absorption of 2-methyl-4,5-dihydrofuran is complicated by several low-frequency modes, but the spectrum can be fairly well interpreted with a double-minimum potential function of the form V(x) = ax4−bx2 with a barrier height of 98 cm−1. Seven sharp Q branches were observed for cyclopentanone, which were fitted to a hindered pseudorotational potential function of the form V = 12V2(1−cos2φ) + 12V4(1−cos4φ). Although one might also expect diketene and cyclohexanone to have anharmonic out-of-plane ring modes, both compounds gave far-infrared spectra which appear to be essentially harmonic.
Rate and Heat of Vaporization of Graphite above 3000°K
Authors: Clarke J. T. , Fox B. R.
Published: February 2004

The rate of vaporization of graphite filaments has been measured from 2500 to 3400°K in vacuum and in He by pulse heating techniques. At 3400°K, the rate of vaporization was sufficiently high that a direct determination of the heat of vaporization could be obtained. The experimental results have been correlated with thermodynamic data obtained at lower temperatures on graphite and its vapor species; the predominance of C2 in vaporizing graphite is shown to satisfy the experimental results. The specific surface area of the filaments was measured and interpreted.
Limiting Laws and Counterion Condensation in Polyelectrolyte Solutions. III. An Analysis Based on the Mayer Ionic Solution Theory
Authors: Manning Gerald S.
Published: February 2004

The interaction with point ions of a line charge supplemented by a distance of closest approach is studied by means of the Mayer theory of ionic solutions. A number of points involved in a recent theory of polyelectrolyte solutions (Papers I and II of this series) are thereby clarified. It is demonstrated that the counterion condensation phenomenon occurs in the limit of zero concentration, that the Debye–Hückel approximation is applicable to the coions and uncondensed counterions, and that the relevant dielectric constant is that of the pure bulk solvent.
Charge-Carrier Injection and the Pre-exponential Factor in Semiconducting Organic Substances
Authors: Green M. E.
Published: February 2004

A charge-carrier injection model is shown to lead to an approximately linear dependence of the preexponential factor on activation energy for small organic semiconductors, without assuming a linear temperature dependence for the activation energy.
Light Scattering from Polydisperse Rods and Gaussian Coils. I. Integrated Intensities
Authors: Tagami Yukiko , Pecora R.
Published: February 2004

Calculations of the effect of polydispersity on the integrated intensities of the various contributions to the spectral distribution of light scattered from infinitely dilute solutions of rigid-rod and Gaussian-coil macromolecules have been performed using Schulz's molecular size distribution. It is shown that rotational (or in the Gaussian-coil case—intramolecular) contributions become more important at lower scattering parameter values as the molecular size distribution becomes broader. Tables of the integrated intensities are given.
Effect of Pressure on the Oxidation State of Ferrates
Authors: Panyushkin V. N. , De Pasquali G. , Drickamer H. G.
Published: February 2004

The effect of pressure has been studied on the oxidation state of Fe(IV) in SrFeO2.86 and of Fe(VI) in BaFeO4−x. Fe(IV) reduces to Fe(III) with increasing pressure, and Fe(VI) reduces to Fe(IV) with perhaps some production of Fe(III). The first process is reversible but the second is not. In neither case does the simple relationship between concentration and pressure found for the reversible reduction of Fe(III) to Fe(II) hold.
Experiments on Er3+ in SrF2. III. Coupled-Ion Effects
Authors: Brown M. R. , Thomas H. , Williams J. M. , Woodward R. J. , Shand W. A.
Published: February 2004

The pumping intensity and concentration dependences of the fluorescence output from three infrared quantum-counter schemes that involve coupled ions in Er3+-doped SrF2 have been measured at 300 and 77°K. The pumping intensity depended linearly on the numbers of photons absorbed in the schemes. The power of the concentration dependence was found to be noninteger in the range 1%–10%. This has been interpreted as indicating the importance of energy migration between the Er3+ ions as mechanism for populating the energy levels of the coupled ions.
Application of Approximation Methods for the Calculation of the Total Differential Ionization Cross Sections to H
Authors: Tavard C.
Published: February 2004

An attempt to improve the description of the differential ionization cross sections is discussed in the special case of electron impact ionization for the hydrogen atom.
Temperature Dependence of Dissociative Attachment in N2O
Authors: Chantry P. J.
Published: February 2004

The attachment of low-energy electrons (<4 eV) by the reaction e+N2O → O−+N2 has been studied as a function of gas temperature from approximately 160 to 1040°K. The ions produced by a monoenergetic electron beam are detected by total ion collection or by mass analysis. The kinetic energy distributions of the O− ions have also been measured and found to be relatively insensitive to the electron energy when the latter exceeds 1.5 eV, in which case the most probable ion energy is 0.38 eV. The shape and magnitude of the cross section below 2 eV is found to be sensitive to gas temperature throughout the range studied. The differences in shape and threshold observed by previous workers occur below 2 eV and to a large extent may be reconciled in terms of the differing gas temperatures employed. The temperature insensitive portion of the cross section is ascribed to electron capture into the highest-energy N2O− state connected to electronic ground state N2 + O−. The O− kinetic energy distributions arising therefrom are explained in terms of the N2O−* potential energy surface involved. It is argued that the strongly temperature sensitive portion of the cross section is due predominantly to excitation of the bending mode of vibration, and arises from the dependence on bond angle of the separation in energy of the electronic ground states of N2O and N2O−.
Approximations in the One-Electron Theory of Optical Rotation
Authors: Stigter Dirk , Schellman John A.
Published: February 2004

The one-electron theory is applied to l-3-aminopyrrolid-2-one. The rotatory strength of the nπ* transition Rα0 is evaluated with various models of the amide chromophore and of the perturbing amino group. It is found that: (1) Rα0 is very sensitive to the degree of delocalization of the nonbonding orbital of the amide oxygen; (2) in the perturbation treatment the transition charge distribution in the amide group is well represented by point quadrupoles on oxygen and carbon, the next higher, 26-pole, terms making only a small contribution to Rα0; (3) the perturbing electrostatic field, as derived from the ground-state electron density of the amino group, is fairly well represented by partial charges on the nuclei, except at very short distance; (4) the representation of all overlap charges in the amino group by point monopoles, an elaboration of a method introduced by London, gives a perturbing field that is about five times too high.
Modification of the Devonshire Formula for the Thermal Accommodation Coefficient of Helium on Tungsten
Authors: Roach D. Vincent , Harris Robert E.
Published: February 2004

The thermal accommodation coefficients (a.c.) of 3He and of 4He on clean tungsten were calculated using the Devonshire formula for temperatures between 70 and 600°K using “realistic” Morse potential parameters. The calculated a.c. values for 3He and 4He and the calculated ratios of the 4He to 3He values are compared with experimental data. The agreement is satisfactory if allowance is made for the error in the transition probability calculation used in the Devonshire formula.
Raman Scattering from Powdered 9, 10-Anthraquinone
Authors: Stenman Folke
Published: February 2004

The Raman spectrum of powdered 9,10-anthraquinone has been studied in the 200–1700-cm−1 region using He–Ne laser 6328-Å excitation and a double monochromator for analyzing the scattered light. Twenty-one lines are observed in this region. The assignment of the lines is discussed on the basis of Raman and infrared data on anthracene and on infrared data on anthraquinone.
Orbit–Orbit Integrals for Diatomic Molecules
Authors: Matcha R. L. , Kern C. W.
Published: February 2004

The one- and two-center Coulomb, hybrid, and exchange integrals that contribute to the orbit–orbit interaction in diatomic molecules are evaluated for arbitrary combinations of Slater orbitals. The basic formulation and the results are compatible with some previous treatments of interelectronic-repulsion and fine-structure integrals.
Antiferromagnetic Spherical Model and Fisher's Relation
Authors: Theumann W. K.
Published: February 2004

We derive a relationship between the magnetic specific heat CM and the zero-field parallel susceptibility χ‖ for the spherical model of an antiferromagnet, and show that this relationship, which does not depend essentially on the range and the detailed form of the interactions, is a particular case of Fisher's relation CM≃A∂(Tχ‖) / ∂T for a nonspherical model. It is shown that Fisher's derivation applies as well to the spherical model, and our result lends support to the argument that Fisher's relation is rather independent of the details of the interaction. A new relation for the spherical model is shown to be related to the phase boundary in the H–T plane in a similar way as Fisher's relation when A−1 is interpreted as the curvature of the phase boundary at H = 0, according to the work of Griffiths and co-workers.
Radiation Damage Dependence of Positron Lifetimes in Sodium Halide Crystals
Authors: Williams Thomas L. , Ache Hans J.
Published: February 2004

Position lifetime spectra in NaCl and NaF single crystals were measured and analyzed as a function of the crystal defect concentration introduced by proton and gamma irradiation. In the irradiated sodium chloride samples a long-lived component was observed with a lifetime (τB) of 8.2 × 10−10 sec and an intensity (IB) of up to 28%. Thermal annealing of the sample caused a drastic reduction of the intensity of this component (IB) to about 10%. Similar observations were made in the positron lifetime spectra in the NaF system.
Absorption Spectrum of Vaporized Titanium Monofluoride
Authors: Diebner Robert L. , Kay Jack G.
Published: February 2004

The electronic absorption spectrum of TiF(g) has been obtained utilizing the techniques of flash heating and kinetic spectroscopy. No spectroscopic data have previously been reported for this molecule, which is observed in the vapor only during the preparative photoflash. The spectrum may be produced by the flash heating of powdered TiF3 or TiF4. It may also be obtained from the powdered metal flashed in the presence of CF4, SF6, or solid aluminum trifluoride. Three band systems have been observed, the main system occurring in the region 3930–4088 Å. The other two systems are in the regions 3855–3906 Å and 3650–3775 Å. The principal spectroscopic features resemble those of TiCl obtained by flash heating TiCl3(s) or Na2TiCl4(s). A vibrational analysis of the main system of TiF shows it to be a Δυ = 0 sequence for the transition from the Σ−4(δ2σ) ground state to a Π(δ24π or δσπ) excited state. An absorption band attributed to the (1, 0) transition is consistent with ωe″ = 593 cm−1. A number of bands remain unassigned.
Angular Correlation of Positron-Annihilation Radiation from Cerium Hydride
Authors: Chouinard M. P. , Gustafson D. R. , Heckman R. C.
Published: February 2004

The angular correlation of positron-annihilation radiation from cerium hydride was measured for hydrogen concentrations in the range H/Ce = 1.8–2.8. The angular correlations were found to be broader than that from cerium metal and to increase in width with increasing hydrogen concentration in a manner consistent with the screened protonic model of the electronic structure. The anionic model does not provide a satisfactory explanation of the measured angular correlations.
Generalized Approximations in Hirschfelder–Silbey Perturbation Theory
Authors: Sanders William A.
Published: February 2004

A procedure used by McQuarrie and Hirschfelder to obtain approximate solutions of the first-order Hirschfelder–Silbey equations for the special case of H2+ is generalized. The contribution due to exchange is determined by applying the Unsöld approximation to the spectral expansion of the first-order function and then determining the closure parameter variationally. The energy is found to be independent of the closure parameter through second order.
Conduction and Diffusion in Crystals Containing Hydrogen Bonds. II. Ammonium Dihydrogen Phosphate
Authors: Pollock J. M. , Sharan M.
Published: February 2004

Electrolysis measurements on crystals of ammonium dihydrogen phosphate (ADP) have confirmed the results of Murphy, showing that protons are mobile in the solid. The ac conductance of ADP crystals along the c axis over the temperature range 40–150°C has been shown to fit the expression σ = 1.26 × 102 × exp[− (11.08 ± 0.02 kcal mole−1) / RT]Ω−1·cm−1, and the conductance results are discussed in terms of the simultaneous formation and migration of proton defects. The diffusion of tritium along the c axis of ADP crystals has been measured as a function of temperature and the results expressed as D = 6.63 × 10−5 × exp[− (9.3 ± 0.8 kcal mole−1) / RT]cm2sec−1. A comparison of the conductance and diffusion results has shown that the Einstein relation is not obeyed, and the deviations have been interpreted in terms of correlated proton jumps in the crystal. The value of the pre-exponential factor in the diffusion equation suggests that there is a small negative entropy factor in the diffusion process.
Low-Frequency Vibrations in Ammonium Iodide and Ammonium Bromide
Authors: Durig J. R. , Antion D. J.
Published: February 2004

The far-infrared spectra of thin films of ammonium iodide were recorded from − 170°C to room temperature. The results varied with the temperature at which the films were formed thus making the interpretation of the spectra difficult. Laser excited Raman spectra of polycrystalline NH4I, ND4I, NH4Br, and ND4Br were also recorded in the same temperature range and four lattice vibrations of translatory origin were assigned in the spectrum of the tetragonal phase III of each salt. The energies associated with the 1 ← 0 torsional transitions of the ammonium ion in phase III NH4I and NH4Br were 287 and 331 cm−1, respectively; the barriers restricting rotation about fourfold axes perpendicular to the crystallographic C axis were calculated to be 3.1 ± 0.1 and 4.0 ± 0.1 kcal/mole, respectively, assuming a harmonic potential and a body-centered cubic lattice. Comparison of the Raman and infrared spectra of the internal fundamentals revealed a large (∼ 30 cm−1) separation between the in-phase and out-of-phase N–H bending frequencies in phase III NH4I. This result indicates a high degree of coupling between these motions of the two ammonium ions in the unit cell. The Raman spectrum of each ammonium halide in phase II was characterized by a translational mode and a combination band, both of which are forbidden by the rigorous selection rules of the space group. The appearance of these bands has been interpreted in terms of the theory advanced by Whalley and Bertie for optical transitions in orientationally disordered crystals. The rest-strahlen frequency in the ordered phase IV ND4Br has been observed at 141 cm−1 in the Raman spectrum of a polycrystalline sample.
Vibrational Relaxation of Shock-Heated Cl2: Effects of CO, HCl, and DCl
Authors: Breshears W. D. , Bird P. F.
Published: February 2004

The vibrational relaxation of pure Cl2 in the temperature range 400–1400°K, and of binary mixtures of Cl2 with CO, HCl, and DCl in the range 400–1100°K has been studied behind incident shock waves by time-resolved measurement of the postshock density gradient using a laser-beam deflection technique. Results obtained for pure Cl2 are more precise than those previously available at these temperatures, and are in excellent agreement with lower-temperature ultrasonic data. The effect of CO relative to Cl2 is found to be much less than indicated by previous data, and is attributed solely to the lower Cl2–CO reduced collision mass. The effects of HCl and DCl are large, particularly at low temperatures, e.g., HCl is ≈100 times more effective than Cl2 at 400°K. HCl is ≈2–4 times more effective than DCl, depending on the temperature. The relative efficiencies are interpreted as a strong indication of rotational effects.
Theoretical Calculation of the Pressure Dependence of Liquid Hydrocarbon Viscosities
Authors: Jhon Mu Shik , Klotz William L. , Eyring Henry
Published: February 2004

The extension of the significant structure theory of viscosity to the calculation of the viscosities of some selected liquid hydrocarbons such as n-C12, n-C15, and n-C18, etc., has been made. In this derivation, the explicit functional expressions of the molar solidlike volume Vs and the intermolecular potential φ(a) were introduced. The agreement between theory and experiment over a wide temperature (35–135°C) and pressure range (1–3600 bars) is quite satisfactory. The advantage of this treatment is that thermodynamic as well as transport properties are calculated from this same model of the liquid state.
Group Theory and the Molecular Configuration Interaction Problem
Authors: Gabriel J. R.
Published: February 2004

The relation of molecular CI calculations and classical Racah theory is discussed, together with the application of some new methods for reduction of group representations.
Infrared Spectra of Crystalline and Matrix Isolated Pyridine and Pyridine-D5
Authors: Castellucci E. , Sbrana G. , Verderame F. D.
Published: February 2004

Infrared spectra of pyridine-H5 and pyridine-D5 in the solid state were measured between 4000 and 200 cm− 1. Frequencies and polarization of fundamental absorptions were established for oriented thin films of freshly crystallized samples. Behavior of the bands in polarized light aided in clarifying several assignments. The multiplicity of several of the bands was accounted for by close-lying overtones and combinations. Some of the components of ν26 are due to the existence of appreciable amounts of 13C isotope species clearly observable in a nitrogen matrix at 5°K. For pyridine-D5 a phase transition was clearly observable after several hours of annealing of thin films at about − 60°C, but similar transformation could not be induced in normal pyridine. The infrared crystal data are consistent with an orthorombic factor group established by x-ray analysis with no molecule on any symmetry element of the crystal. Raman spectra of liquid and solid pyridines are also reported.
Reduced Spin–Spin Matrix Elements for f4
Authors: Armstrong Lloyd , Taylor Lyle H.
Published: February 2004

Reduced matrix elements for all possible two-body Hermitian operators with spin and orbital rank of two are evaluated for the f4 configuration. Most of the vanishing matrix elements can be explained by simple group-theoretical selection rules and some can be explained by vanishing coupling coefficients. However, 16 zeros still remain to be explained.
Molecular Reorientation and Nuclear-Spin Conversion in the Solid Deuteromethanes at Low Temperatures
Authors: Colwell Jack H.
Published: February 2004

The heat capacities of the solid deuteromethanes have been measured down to 0.3°K, tracing out the low-temperature heat-capacity anomalies which had been detected in the earlier work of Colwell, Gill, and Morrison. The anomalies in CH3D and CHD3 have maxima at 0.43 and 0.48°K, respectively, but the CH2D2 heat capacity is still increasing with decreasing temperature at 0.3°K. A small anomaly was found in CD4 but this is ascribed to chemical and isotopic impurities present in the sample. The heatcapacity anomalies are of the Schottky form and are believed to arise from the reorientation of the molecules on the lattice sites. This results in the removal of the orientational degeneracies of the molecules which give rise to the zero-point entropies of R ln4 for CH3D and CHD3 and R ln6 for CH2D2. In molecules having identical protons, conversion between the different nuclear-spin states also occurs. This is substantiated in the case of CH3D where the measured entropy change in the range of the measurements, 0.3–4.0°K, is ΔS = 1.614R, which exceeds the maximum value of R ln4 (1.386R) for molecular reorientation occurring separately. The occurrence of conversion was also indicated by a thermal relaxation process characterized by relaxation times ranging from 110 to 50 sec in going from 0.3 to 4.0°K. Analysis of the CH2D2 data indicates that nuclear-spin conversion is also taking place in this material but the result is less well established. There is no indication of conversion occurring in CHD3. Reasonably precise values of the energy-level splittings have been derived for each of the partially deuterated methanes.
Far-Infrared Absorption in Liquid Hydrogen
Authors: Jones M. C.
Published: February 2004

The far-infrared spectra of liquid hydrogen at three para concentrations have been recorded in the wavenumber range 20 to 250 cm−1. The observed variation of the absorption coefficient with composition is consistent with the theory of translational absorption of Poll and Van Kranendonk.
Quasilattice Interpretation of the Thermodynamic Properties of Mixing of Binary Alkali-Metal Systems
Authors: Goates J. R. , Ott J. B.
Published: February 2004

Quasilattice theory was applied to heats of mixing in the six systems formed from the binary combinations of Na, K, Rb, and Cs. The alkali-metal systems are particularly well suited for a critical test of the quasi-crystalline assumption since the theoretical model for these systems is relatively simple and the thermodynamic data are fairly complex. Very good fits of the heat-of-mixing data were achieved by assuming that the larger atom in the binary system covered multiple sites on the quasilattice. The values of the empirically determined constants appear to fit the physical significance accorded to them by the quasilattice model. Values for the excess free energies of the Na–K system, calculated from the parameters of heat of mixing data, were in semiquantitative agreement with experimental data.
Magnetic and Crystal Structures of the Trigonal Tb2C
Authors: Atoji Masao
Published: February 2004

Neutron powder-diffraction measurements have shown that Tb2C is isostructural with Y2C, i.e., crystallizes with an anti-CdCl2-type trigonal structure (D3d5 − R3̄m), having the following crystallographic parameters in the hexagonal coordinates: the unit-cell dimensions, a = 3.595 ± 0.006 Å and c = 18.19 ± 0.03 Å at 300°K; three Tb2C formula units per unit cell; zTb = 0.2593 ± 0.0006; and zC = 0. Tb2C becomes ferromagnetic below Tc = 266 ± 2°K. The ordered moments are directed along the trigonal c axis, and the saturation moment is 8.6 ± 0.2 μB per Tb. The temperature variation of the ordered moment in the range 260°K < Tc < 5°K is represented by 8.6[1 − (T / Tc)2] in Bohr magnetons. The ferromagnetic ordering accompanies a small-angle magnetic scattering inferring an additional ordered moment with the modulation repetition of roughly 100 Å. The maximum composite ordered moment is estimated to be about 9 μB, the value expected for the free Tb3+ ion.
Magnetic Structures of DyAu2 and DyAg2
Authors: Atoji Masao
Published: February 2004

Neutron–powder-diffraction study has shown that, upon cooling, DyAu2 (tetragonal, isostructural to MnAu2) exhibits the onset of antiferromagnetism at TN(α) = 33.8°K and a first-order-like magnetic transition at TN(β) = 25.5°K. The moment alignment between TN(α) and TN(β) is represented by a static linear–transverse spin wave propagating along the a axis (the face-centered description) and polarized in the direction of the c axis. The wavelength of this modulation wave is 1.21 times (the a spacing), being incommensurable with the chemical repetition. At TN(β), the modulation wavelength becomes abruptly equal to the a spacing with a discontinuous increase in the rms ordered moment but without change in the moment direction. This commensurated magnetic structure persists down to 1.7°K and the saturation ordered moment is 9.2 μB. The DyAg2 structure is analogous to DyAu2 and characterized by TN(α) = 15.0°K; the incommensurate moment wavelength, 1.17a; TN(β) = 9.5°K; and the saturation ordered moment, 7.4 μB, being much smaller than 10.0 μB of the free Dy3+ ion. The crystallographic data at 300–5°K are also presented.
Stochastic Models for Chromatography
Authors: Oxtoby John C.
Published: February 2004

Column chromatography is treated as a diffusional process, interrupted at random for exponential delay times. General formulas for the elution time and for the longitudinal distributions are obtained and their moments calculated. A general form of the van Deemter equation is found to hold exactly, but the HETP is only asymptotically equal to the rate of increase of the longitudinal variance with respect to the mean. Under certain conditions the HETP also measures the displacement of the longitudinal mean from a point at the moment when the concentration at the point reaches its mean value. The times spent in the mobile and stationary phase are shown to be not independent, and their correlation coefficient is calculated.
Self-Consistent Molecular-Orbital Methods. II. Projection of Diatomic Differential Overlap (PDDO)
Authors: Newton Marshall D.
Published: February 2004

A method is developed for approximating 1- and 2-electron integrals over Slater-type orbitals (STO's) involving 2-center charge distributions. The latter are projected by least-squares, with overlap and dipole constraints, onto STO's with appropriate exponents, located only on the relevant atomic centers. The approach is applicable to any AO basis set, and is illustrated for first-row atom minimal STO basis sets. Error analysis is given for the projection per se, and for the 1- and 2-electron integrals obtained from the projected distributions. For integrals with magnitude > 10−2 a.u., the rms relative error is ∼1%. Integral errors are sytematic, and balance of errors in nuclear attraction and hybrid 2-electron integrals is examined. Comparison is made with earlier results of Boys and Shavitt for 1s orbitals.
Self-Consistent Molecular-Orbital Methods. III. Comparison of Gaussian Expansion and PDDO Methods Using Minimal STO Basis Sets
Authors: Newton Marshall D. , Lathan W. A. , Hehre W. J. , Pople J. A.
Published: February 2004

Self-consistent-field molecular-orbital calculations over a minimal basis set of Slater-type atomic orbitals are presented for a set of organic molecules and positive ions containing up to eight first-row atoms. The necessary molecular integrals are calculated by two previously introduced schemes: the Gaussian expansion (STO–KG) method and the projection of diatomic-differential-overlap (PDDO) method. Atomization energies, electric dipole moments, density matrices, optimum STO ζ exponents, and computation times are compared for the PDDO, STO-3G, and STO-4G methods, the latter of which has previously been shown to closely reproduce the full STO results. Relative to the STO-4G values, the PDDO method leads to errors of up to 0.22 a.u. in the atomization energy, 0.16D for the dipole moment, and 0.05 for the optimum ζ exponents. The corresponding limits for the STO-3G method are 0.06 a.u., 0.07D, and 0.02. Two electron integrals are evaluated at rates of 125–175, 25–140, and 10–70 integrals per second for the PDDO, STO-3G, and STO-4G methods, respectively, on a CDC 1604A computer.
Orientation of the Electric-Field-Gradient Tensor in Crystalline Dirhenium Decacarbonyl
Authors: Mooberry E. S. , Spiess H. W. , Sheline R. K.
Published: February 2004

The orientation of the principal-axis system of the field-gradient tensor in a single crystal of Re2(CO)10 was studied at room temperature. The z and y axes were determined independently from curves of constant frequency for the + 32 ↔ + 52 and − 32 ↔ − 12 transitions at a magnetic field of 2 kG. Two sets of principal axes related by the twofold axis and mirror plane of the monoclinic crystal were found. The rhenium–rhenium bond coincides with the intersection of the two y–z planes and forms an angle of 25° with the z axes. The deviation of the z axes from the Re–Re bond is attributed to distortions of the molecule in the solid due to nearest-neighbor interactions of carbonyl groups. The total field-gradient tensor is described as the sum of an axially symmetric tensor with z axis along the Re–Re bond—dominated by intramolecular contributions—and a second axially symmetric tensor arising from the distortion of the molecule in the lattice with z axis in the y–z plane of the total field-gradient system at an angle of 24° from the Re–Re bond. The two tensors have z components of opposite sign and the same order, giving rise to the large η value observed. The descrease of η with increasing temperature is attributed to a reduction of the distortions of the molecule by the vibration of the CO groups.
Excitation of Nitrogen by Electrons: The Lyman–Birge–Hopfield System of N2
Authors: Holland R. F.
Published: February 2004

The intensity of vacuum ultraviolet emission produced by a beam of electrons in nitrogen has been measured to determine the probability of exciting the Lyman–Birge–Hopfield (LBH) bands of N2. Measurements included spectral scans of the region 1250–2150 Å and scans across the electron beam with a photometer sensitive in the range 1230–1800 Å. Some 60 spectral features were attributed to LBH bands. Emission in these bands persisted in a glowing region outside the electron beam. At low gas pressure (0.1 μ), relative band intensities are in rough agreement with values calculated by assuming the Franck–Condon principle applies in excitation and emission. At higher pressure, the intensity was increased by secondary processes, and bands with lower υ′ were enhanced relative to other bands. Photometer scans at low pressure yielded a profile of the glow around the beam which was fairly consistent with a profile calculated by assuming a radiative lifetime of 80 μsec for the parent state of the LBH. Based on the calculated profile and spectrometer and photometer observations, an apparent cross section of 1.1 ± 0.2 × 10−18 cm2 was obtained for excitation of the LBH system by 900-eV electrons. The dependence on energy of representative bands indicated total LBH cross sections for 100- and 2000-eV electrons of 6.7 × 10−18 and 5.2 × 10−19 cm2, respectively.
Model Approach to Nonadiabatic Reaction Processes
Authors: Fischer S. F. , Hofacker G. L. , Seiler Rudolf
Published: February 2004

A transport theory of reactive flux is developed on the basis of a model potential-energy surface with an unbranched reaction path and many harmonic vibrations perpendicular to this path. Coriolis forces are ignored and the vibrational spectrum is assumed to be slowly varying with the reaction coordinate ξ. An interaction between translational and vibrational motion on the potential-energy surface, similar to the one in the Fröhlich Hamiltonian, is derived. The method of equations of motion is employed to calculate Green's functions. With the assumption of equilibrium for the bound degrees of freedom, Green's functions containing higher correlations can be expressed exactly in terms of Green's functions of lower order. Solutions of the integral equations are given for physically relevant energy regions. Explicit account is taken of the internal linewidth and the effects of reactive resonance scattering. The results are expressed in terms of equilibrium ensemble averages and reaction rates.
Coupling Operator Method in the SCF Theory
Authors: Huzinaga Sigeru
Published: February 2004

The coupling operator method in the general SCF theory is discussed. It is shown that there is an abritrariness in the definition of the general SCF operators. In the course of discussion, several SCF equations useful in practical applications are presented.
Molecular Schrödinger Equation. X. Potential Surfaces for Ground and Excited States of Isosceles H3++ and H3+
Authors: Conroy Harold
Published: February 2004

Accurate potential-energy surfaces are reported for the ground states, and for several excited states, of the isosceles triangular configurations of the molecular ions H32+ and H3+. The ground states are A12 and A11, respectively, of group C2υ, and these include the Σg linear symmetric forms and the A1′ states of the equilateral D3h triangles. The four excited-state surfaces are B12 and B22 for H32+, as well as B11 and B21 for H3+; these include the Πu and Σu states of the linear D∞h ions and the A2″ and E′ states of the D3h ions. These excited states are of possible interest in connection with ultraviolet spectroscopic studies of H3+, long known from mass spectrometry to be a stable species. Each of the six surfaces is given in analytic form, and as an energy contour map. The two-electron wavefunctions used are basically of the configuration type, with an extensive additional treatment of electron correlation. In all cases the required matrices were computed with the new Diophantine integration scheme, which supercedes the now obsolete Monte Carlo method employed in our earlier papers on H3+.
Electron Paramagnetic Resonance Study of Manganese in Strontium Fluoride
Authors: Mier Millard G.
Published: February 2004

The room-temperature, electron paramagnetic resonance spectrum of a dilute (0.01%) substitution of Mn2+ ions in a single crystal of SrF2 has been measured. The parameters of the manganese resonance measured at 9.507 GHz are g = 2.0014 ± 0.0010 and | A | = (94.0 ± 1.9) × 10−4cm−1. The cubic field splitting was not resolved. The magnitude of the nearest neighbor hyperfine interaction with surrounding fluorines is | As | = (8.11 ± 0.70) × 10−4cm−1 and | Ap | = (2.02 ± 0.25) × 10−4cm−1, indicating 0.68% σ character in the manganese-to-fluorine bond. Ap is in agreement with the calculated magnetic dipolar interaction between manganese and fluorine nuclei, assuming no pσ bonding and no lattice distortion. These results are compared with similar data on ZnF2, CaF2, CdF2, KMgF3, CdTe, and BaF2.
Nonadiabatic Translations in Polyatomic Molecules
Authors: Young John H.
Published: February 2004

It is assumed that electronic relaxation is due to the nonadiabatic interactions omitted from the Born–Oppenheimer adiabatic approximation. The first step in the present development is to transform the expression for the rate constant as given by Fermi's golden rule so as to simultaneously evaluate the product of the density of states and the square of the absolute value of the interaction matrix element. By then introducing an approximation based on the physical meaning of nonadiabatic interactions, it is shown that the radiationless rate constant can be expressed in terms of known electronic and vibrational molecular parameters thereby providing a basis for calculating radiationless rate constants. The present theory is distinguished from previous theories of electronic relaxation by its emphasis upon the interaction matrix elements as opposed to the Franck–Condon factors. The present theory also predicts a position dependence for the effect of deuterium substitution on the radiationless rate constant in aromatic hydrocarbons and is in qualitative agreement with the recent results of Watts and Strickler [J. Chem. Phys. 49, 3867 (1968)] on partially deuterated napthalenes.
Matrix-Isolation Study of the Infrared and Ultraviolet Spectra of Several First-Series Transition-Metal Dichlorides
Authors: Jacox Marilyn E. , Milligan Dolphus E.
Published: February 2004

Individual molecules of CrCl2, MnCl2, FeCl2, CoCl2, and NiCl2 have been isolated in an argon matrix at 14°K in sufficient concentration for infrared and ultraviolet spectroscopic study not only by using the conventional effusion cell as a source of the MCl2 species, but also by trapping the products of the reaction of chlorine with the hot transition-metal surface. Studies of the infrared spectra of all of these species in the 250–5500-Å spectral range are consistent with a linear structure. Ultraviolet absorptions in the 2000–5500-Å spectral range are in good agreement with the previously reported gas-phase absorptions. However, the absorption observed for matrix-isolated NiCl2 between 4400 and 5000 Å must be attributed to three different electronic transitions, one of which exhibits extensive band structure. A molecular-orbital treatment involving participation of the 3d nickel electrons in the bonding of the molecule predicts the occurrence of several transitions in this energy range and provides a framework for understanding the appearance of extensive vibrational structure in several of the electronic transitions of NiCl2.
Helium-Atom–Hydrogen-Molecule Potential Surface Employing the LCAO–MO–SCF and CI Methods
Authors: Gordon Michael David , Secrest Don
Published: February 2004

Wavefunctions and interaction energies are calculated for the helium-atom–hydrogen-molecule system at a wide range of internuclear separations. Letting X represent the distance measured along a line drawn from the helium nucleus to the midpoint of the hydrogen molecule, R the H2 bond distance, and θ the angle between X and R, results are reported for 2.8 ≤ X ≤ 7.0 a.u., 1.0 ≤ R ≤ 1.8 a.u. (Re = 1.4 a.u.), and 0° ≤ θ ≤ 90°. The orbital basis set consisted of Slater s and p orbitals, and all integrals are accurately evaluated. The wavefunctions are constructed by each of the two major approaches to molecular bonding; the self-consistent-field molecular-orbital method of Roothaan and the configuration-interaction method. The value of the two methods in atom–diatomic-molecule interactions is compared extensively. For each individual method, the effect of the size of the basis set on the resultant interaction energy is examined. The values for the He–H2 interaction energies obtained by the self-consistent-field and configuration-interaction method are very similar. The self-consistent-field method appears adequate for the calculation of interaction energies for closed-shell noninteracting systems except at large center-of-mass separations. The interaction energies are accurately fit to an analytic expression for the intermolecular potential. Configuration-interaction calculations performed at large center-of-mass separations fail to locate the He–H2 van der Waals minimum.
Dielectric and Pressure Virial Coefficients of Imperfect Gases. I. Polar Halogenated Methanes
Authors: Sutter H. , Cole R. H.
Published: February 2004

Dielectric constants for the polar gases CFH3, CF3H, CClF3, and CCl3H in the range 50–143°C, and for CCl3F at 96.3°C, have been measured as a function of pressure and density in the pair interaction range of densities. Accurate values of dipole moment and polarizability of the first four molecules have been derived from the limiting temperature dependence at zero density, and dielectric and pressure second virial coefficients from the variation with density. The pressure coefficients are in good agreement with other compressibility data. The dielectric coefficients are very large and positive for CF3H, very large and negative for CFH3 and CClH3, and positive with approximately the values predicted for spherical polarizable dipoles in the case of CClF3 and CCl3F. The deviations from simple theory indicate major effects of molecular shape, but they are not satisfactorily explained by Buckingham and Pople's anisotropic short-range pair-potential model.
Dielectric and Pressure Virial Coefficients of Imperfect Gases. II. CO2–Argon Mixtures
Authors: Bose T. K. , Cole R. H.
Published: February 2004

Dielectric and pressure second virial coefficients of five mixtures and the pure gases have been determined at 49.7°C, the values for CO2 at 29.4°C. The pressure coefficients are in reasonably good agreement with values predicted from combining rule Lennard-Jones parameters derived from viscosities of the pure gases. The large effect of quadrupole interaction energy on the dielectric coefficient of pure CO2 has been calculated numerically, and analytical treatments of the smaller effects of reaction fields of induced moments, quadrupole-induced dipole energy, and anisotropy energy have also been made. These result in a calculated molecular quadrupole moment of CO2 of 4.3 × 10−26 esu cm2 from the data for pure CO2. For CO2–Ar pairs, the effects in addition to the direct quadrupole-induced dipole contribution are much smaller, and the value 4.1 × 10−26 esu cm2 for the quadrupole moment of CO2 is derived from the dielectric coefficient. Both values are in good agreement with the Buckingham–Disch result and with other less direct estimates from infrared and microwave absorption and from pressure virial coefficients.
Spectra of Europium in Monoclinic Gadolinium Sesquioxide
Authors: Rice D. K. , DeShazer L. G.
Published: February 2004

The absorption and fluorescence spectra of Eu3+ in Gd2O3 single crystals were investigated at 4.2°K. This study demonstrated that the Eu3+ ion occupies three nonequivalent sites of Cs symmetry in this crystal extending previous crystallographic investigations. Unambiguous polarization of the absorption spectra allowed this determination.
Electron Transfer and Detachment in Collisions of Low-Energy Negative Ions with O2
Authors: Bailey T. L. , Mahadevan P.
Published: February 2004

Total cross sections for the production of slow heavy negative ions and of free electrons in collisions of O2−, O−, OH−, and H− ions with O2 molecules have been measured over the primary-ion KE range from a few electron volts to 350 eV. The experiments are of the ion-beam gas-scattering type and utilize a radio-frequency filter to give separately the currents of detached electrons and slow product negative ions. The cross sections for slow ion formation, σt, were appreciable at all energies studied, for all four collision systems. The dominant contributions to σt could in most cases be attributed to simple charge transfer, although in the H−–O2 and OH−–O2 systems at low energies, the data indicate that ion–molecule reactions also contribute. With exception of the H−–O2 system, the electron detachment cross sections were similar in magnitude and in behavior with collision energy to those which have been measured previously for other systems.
Vacuum-Ultraviolet Absorption Cross Sections of CO, HCl, and ICN between 1050 and 2100 Å
Authors: Myer James A. , Samson James A. R.
Published: February 2004

Absorption cross sections have been measured under intermediate resolution (0.25 Å) for CO, HCl, and ICN in the spectral region from 1050 to 2100 Å. An attempt has been made to analyze the spectra in terms of the reactions responsible for the observed features. A Rydberg series has been identified in the absorption spectrum of ICN with a series limit of 1140.6 ± 0.1 Å.
Exact Semiclassical Transition Probabilities for Collinear Collisions
Authors: Locker David J. , Wilson David J.
Published: February 2004

The N-state semiclassical approach is used in the calculation of transition probabilities for atom–diatomic molecule collinear collisions. The diatomic molecule is allowed to oscillate during the generation of the classical trajectories. Comparisons are made with techniques in which the diatomic molecule is constrained to be nonoscillatory as the classical trajectories are traced out. The semiclassical method is extended to include diatomic–diatomic and atom–triatomic molecule collisions with use of the energy conservation equation.
Effect of Oxygen Octupoles on the Electric Field Gradient at the Al3+ Sites in Corundum (α-Al2O3)
Authors: Hafner Stefan S. , Raymond Michael
Published: February 2004

The effect of the electronic octupole moment of oxygen on the electric field gradient at the Al3+ position has been computed. This, together with the previously studied point-charge, dipolar, and quadrupolar contributions to the field gradient, shows that only the point charge and quadrupolar contributions have the correct sign to interpret the nuclear quadrupole coupling data of 27Al. Unless the Sternheimer factor of Al3+ is about twice as large as the theoretical value, a significant oxygen quadrupolar contribution is needed, regardless of whether the quadrupoles are of an ionic or nonionic origin or both. The field gradient has been self-consistently computed using the ideal ionic model for various sets of dipole, quadrupole, and octupole polarizabilities of the O2− ion.
Irradiation of Isobutene with 8.4-, 10-, and 11.6–11.8-eV Photons. Decomposition of Neutral Excited Isobutene and Reactions of C4H8+
Authors: Herman J. , Herman K. , Ausloos P.
Published: February 2004

Isobutene has been irradiated with 8.4-, 10-, and 11.6–11.8-eV photons in the presence and absence of scavengers such as O2, NO, and H2S. Over the entire energy range, 80% of the neutral excited iso-C4H8 dissociates as follows: iso-C4H8*→C3H4+CH3+H. Minor primary fragmentations include: iso-C4H8*→C3H6+CH2 and iso-C4H8*→CH4+C3H4. Isotopic analysis of the products formed in the photolysis of (CD3)2CCH2 and iso-C4H8–iso-C4D8 mixtures throws some light on the mechanistic details. At 10 and 11.6–11.8 eV, iso-C4H8+ ions are formed, with photoionization quantum yields of 0.26 and 0.31, respectively. Thirty percent of these ions react to yield isobutane as a product. The mechanism seems to involve internally excited ions which take part in a proton-transfer reaction: C4H8++C4H8→C4H9++C4H7. When iso-C4D8 is irradiated in the presence of alkanes (AH2), the following H2-transfer reaction is shown to occur: C4D8++AH2→(CD3)2CHCD2H+A+. Experiments performed with a partially deuterium-labeled isopentane demonstrate that the latter reaction is highly stereospecific.