bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential Cross Sections for the Electron-Impact Excitation of Vibrational Levels in Molecules
Authors: Bonham R. A. , Geiger J.
Published: February 2004

The angular dependence of scattered electrons which have excited a particular vibrational level of the ground electronic state of a molecule is investigated. General expressions are developed for the differential electron-scattering cross sections for the excitation of vibrational levels in terms of derivatives of the ground-state electron density and derivatives of the total electric dipole and quadrupole moments. Results for the small-angle limit are obtained, and the errors in the theory and their possible effect on the small-angle scattering are discussed. It is shown that contributions to the scattering from overtone and combination frequencies increase in comparison to contributions from the infrared allowed fundamental transitions with increasing scattering angle. The relationship between the electronic contribution to the large-angle scattering and certain vibrational corrections to the vibrationally averaged three-dimensional molecular electron density is pointed out.
Consecutive Metastable Peaks in Mass Spectra
Authors: Hills Lorin P. , Futrell Jean H. , Wahrhaftig Austin L.
Published: February 2004

The observation of consecutive metastable peaks in mass spectra has prompted a calculation for the abundance of these species. Expressions for fractional abundance as a function of primary and secondary rates and residence times are derived for all species of normal and metastable ions. Primary and secondary rates for a toluene consecutive dissociation were calculated using the method of Vestal, Wahrhaftig, and Johnston, and the breakdown curves were determined. By assuming a constant energy-transfer function the normalized areas of the calculated curves are found to compare very favorably with the mass spectrum obtained in this laboratory with a double-focusing mass spectrometer.
Note on the Perturbation Equation of State of Barker and Henderson
Authors: Mansoori G. A. , Provine J. A. , Canfield F. B.
Published: February 2004

Perturbation theory of equation of state due to Barker and Henderson is reformulated. This new formulation makes it possible to calculate the Helmholtz free energy of a fluid system analytically by perturbation relations of Barker and Henderson, without use of any approximation or need of any numerical table for the hard-sphere reference system other than the original Percus–Yevick approximations. The results are compared with the calculation of Barker and Henderson, and it is shown that the two agree with each other at all the temperatures which are compared, while the present method produces compressibilities slightly closer to the experimental and machine-calculated data. The results of the present method, based on average Percus–Yevick hard-sphere compressibilities, are also compared with the result of other theories of equation of state of simple fluids, molecular dynamics, and Monte Carlo calculations.
Crossed-Beam Study of the Reactive Asymmetry of Oriented Methyl Iodide Molecules with Rubidium
Authors: Beuhler Robert J. , Bernstein Richard B.
Published: February 2004

A crossed molecular-beam study of the reactive asymmetry of oriented methyl iodide molecules reacting with rubidium is described. The velocity-selected molecular beam of CH3I is focused by an inhomogeneous electric six-pole field; the CH3I molecules are then oriented with respect to the incoming atomic beam of Rb by means of a homogeneous, weak, electric field. Measurements of the intensity of the RbI product have been made at various laboratory scattering angles as a function of the relative alignment of the CH3I with respect to the incident relative velocity vector. A computer analysis of the data has shown that the differential reactive scattering cross section (in the backward center-of-mass direction) for the “favorable” CH3I alignment exceeds that for the “unfavorable” alignment by a factor of 4 or more. A simple hardsphere model, approximating methyl iodide as a partially reactive sphere, accounts for many of the important features of the observations.
Millimeter-Wave Spectrum of Hydrogen Peroxide
Authors: Oelfke William C. , Gordy Walter
Published: February 2004

Some 50 rotational transitions of HOOH in the ground vibrational state have been measured in the millimeter-wave region from 60 to 300 kMc/sec. Analysis of these transitions provides a complete set of values of the rotational constants and the accurate value of 342 885.0 ± 2.0 Mc/sec for the doublet splitting of the ground-state vibrational levels by internal barrier tunneling. The rotational constants in the Hamiltonian for the semirigid-rotor model with an internal axis of rotation are (in megacycles per second): ν01,201,2 = 276 208.0 ± 2.0, ν03,403,4 = 275 912.7 ± 2.0, β01,201,2 = 25 662.1 ± 2.0, β03,403,4 = 25 673.7 ± 2.0, γ01,201,2 = 542.96 ± 0.5, γ03,403,4 = 476.64 ± 0.5. The dihedral angle of the OH bonds is found to be 120°1′ ± 15′ for the lower level and 116°7′ ± 15′ for the upper level of the ground-state doublet. Some 30 millimeter-wave rotational transitions for DOOD were also measured, but analysis of them is not yet complete.
Interaction of H2 with (100) W. I. Binding States
Authors: Tamm P. W. , Schmidt L. D.
Published: February 2004

Flash desorption mass spectrometry is used to study the structures and kinetics of hydrogen adsorption on the (100) plane of tungsten. It is shown that there are two binding states, β1 and β2, in a saturation ratio of 2:1 which obey first- and second-order kinetics, respectively. The activation energies of desorption are 26.3 and 32.3 kcal mole−1 and both vary with coverage by less than 0.5 kcal monolayer−1. Deuterium isotope effects, exchange, and replacement are also examined. These results combined with recent LEED measurements for this system are used to formulate a structure for the adsorbate which appears to quantitatively explain the presently available data. This structure is shown to be reasonable on the basis of the electronic structure of the substrate which predicts multiple states, a c(2 × 2) structure, and island formation at low coverage as observed.
Nucleation of Supersaturated Vapors in Nozzles. II. C6H6, CHCl3, CCl3F, and C2H5OH
Authors: Dawson Daniel B. , Willson Ernest J. , Hill Philip G. , Russell Kenneth C.
Published: February 2004

Measurements have been made of the results of homogeneous condensation in benzene, chloroform, Freon 11, and ethanol vapors expanding in steady flow in a supersonic air nozzle. Experimental results have been compared with the predictions of the classical nucleation rate equation and with the quantum-statistical treatment of Lothe and Pound. Whereas the results on C2H5OH were inconclusive, nucleation rates in the other three vapors are in good agreement with the Lothe–Pound treatment over substantial temperature ranges. It is noted that generally fluids of polar or rod-shaped molecules follow classical theory, and that fluids of compact molecules without a large permanent dipole follow the Lothe–Pound treatment. Mass accommodation coefficients were also inferred. For CHCl3, ξ ≃ 1; for CCl3F and C6H6, ξ ≃ 0.1.
Polarized Singlet–Triplet Absorption Spectra of Normal and Deuterated Anthracene Crystals
Authors: Durocher G. , Williams Digby F.
Published: February 2004

The singlet–triplet absorption spectra of anthracene-h10 and anthracene-d10 crystals have been measured along the a and b crystal axes for temperatures between 350 and 4°K. The delayed fluorescence intensity was used to monitor the absorption. The Franck–Condon overlap factor was found to change with temperature, and the change is discussed in terms of variations in the C–C bond order. A vibrational analysis of the low temperature spectra is given.
Two-Electron Spin–Other-Orbit Matrix Elements
Authors: Gibbs R. L.
Published: February 2004

The two-electron spin–other-orbit Hamiltonian in tensor operator form is recast into a slightly different form. The advantages of the new form are exhibited by obtaining the matrix elements for a general two-electron state. Correlation effects are included to obtain a Hamiltonian with a general correlation factor coupled to it. The matrix elements for nsn′l are shown explicitly as examples.
Extraction of Reaction Cross Section from Rate Constant Data: D+H2→HD+H
Authors: Melton L. A. , Gordon R. G.
Published: February 2004

Assuming a Boltzmann distribution of reactant velocities, rigorous and optimal bounds to the reaction cross section for the reaction D+H2→HD+H have been calculated from rate data. Neither thermal rate constant data nor rate constant data for reactions of monoenergetic D atoms with thermal H2 determine the reaction cross section. An upper bound to the threshold energy of 0.28 eV has been obtained from the thermal rate constant data. Methods based upon Tschebychev analysis have been developed to test the internal consistency of a set of data points.
Molecular-Beam Kinetics. I. Magnetic Deflection Analysis of Reactions of Li with Cl2, ICl, Br2, SnCl4, and PCl3
Authors: Parrish David D. , Herm Ronald R.
Published: February 2004

Thermal energy crossed-molecular-beam studies have been made of the reactions of Li with Cl2, ICl, Br2, SnCl4, and PCl3. An inhomogeneous deflecting magnet between the collision zone and detector was used to distinguish elastic scattering of Li from reactive scattering of LiX. Approximate transformations of the measured laboratory angular distributions to the center-of-mass (c.m.) coordinate system have determined: (1) the total reaction cross sections QR; (2) the approximate product recoil energies E′; (3) the reactive attenuations of the wide-angle elastic scattering; and (4) the LiX product c.m. angular distributions. A procedure has been developed for the determination of values of QR which corrects for resolution effects introduced by broad parent alkali beam profiles. Values of Qr, E′, and reactive attenuations of wide-angle elastic scattering which are reported here for the Li-atom reactions correlate roughly with trends established in previous studies of the reactions of Na, K, Rb, and Cs. However, the observed LiX c.m. product angular distributions are broader and more complex than projections based on studies with the heavier alkali atoms might have predicted. These observations are interpreted in terms of the electron transfer mechanism, which has been applied in previous studies of reactions of the heavier alkali atoms, with the inclusion of a possible mass effect in the alkali-atom reaction dynamics.
Level-Crossing Studies of Na2 Using Laser-Induced Fluorescence
Authors: McClintock M. , Demtröder W. , Zare R. N.
Published: February 2004

The technique of using laser excitation to study level crossings in molecules has been developed and used to determine the radiative lifetime of an excited state of Na2. Optical detection of level crossing in the υ′ = 10, J′ = 12 level of the B 1Πu electronic state of Na2, excited by the 4765-Å argon-ion laser line, has resulted in a precise measurement of the product gτ = 4.11 ± 0.12 × 10−11sec, corresponding to a magnetic field half-width of 1385 ± 42 G. If the g value is calculated assuming Hund's coupling case (a), the radiative lifetime is determined to be τ = 6.41 ± 0.38 × 10−9sec. The influence of molecular hyperfine structure on this measurement is discussed and is found in general to contribute little uncertainty to the value of the radiative lifetime, provided the rotational angular momentum is much larger than the nuclear spin and/or provided the hyperfine interaction is much smaller than the natural width of the excited state.
Optical Pumping of Molecules
Authors: Drullinger R. E. , Zare R. N.
Published: February 2004

A technique is described for the optical pumping of gas-phase molecules based on the orientation dependence of their absorption cross section. It is shown that when the rate of excitation exceeds the relaxation rate of a ground-state (υ″, J″) level, the magnetic sublevels are preferentially “burned away” and the steady-state M-level population is altered appreciably. An experiment to demonstrate molecular alignment has proved successful using the 4880-Å line of a cw argon-ion laser to cause the transition (υ″ = 3, J″ = 43)→(υ′ = 6, J′ = 43) in the B 1Σu − X 1Σg+ blue-green band system of the Na2 molecule. The establishment of an unequal magnetic sublevel population is detected by monitoring the degree of polarization P of the fluorescence as a function of laser intensity. It is found that P first remains constant then decreases by about 50% as the laser-beam power increases from 0.1 to 150 mW. In addition, the absorption becomes nonlinear with a power threshold corresponding to the onset of the decrease in P. This optical pumping technique is applicable to a wide class of molecules, and both simple classical and quantum mechanical theories of the pumping process have been formulated. These theories relate the degree of polarization to both the pumping rate and the relaxation time of the pumped level. The time-dependent as well as steady-state behavior of P is examined. Under conditions of strong optical pumping it is predicted that the degree of polarization as a function of time will overshoot its steady-state value, and as the pumping rate increases large negative transients in P will appear.
Quasielastic Scattering of Thermal Neutrons by CH3OH and CH3SH
Authors: Sampson Thomas E. , Carpenter John M.
Published: February 2004

We report measurements of the line broadening of thermal neutrons quasielastically scattered from room temperature methyl alcohol and methyl mercaptan in the liquid phase. The linewidths for CH3SH are found to be approximately twice those of CH3OH. This is interpreted to be additional evidence of the relative freedom of molecular motions and lack of hydrogen bonding in CH3SH. The linewidth data are discussed in terms of the simple diffusion model, and for methanol, in terms of a globular diffusion model. For methanol a diffusion constant of 3.25 × 10−5 cm2sec−1 and a diffusing globule mass of ∼3.5 molecules are in agreement with the data. An upper limit of D = 6.5 × 10−5cm2sec−1 is found for the diffusion constant of CH3SH.
Rigorous Bounds for Thermodynamic Properties of Harmonic Solids
Authors: Wheeler J. C. , Gordon R. G.
Published: February 2004

A procedure for obtaining rigorous bounds to thermal properties of harmonic solids from moments of the frequency distribution is presented, and methods for improving these bounds when low-frequency expansion coefficients for the frequency distribution function are known are described. The technique is demonstrated by application to a face-centered-cubic crystal with nearest-neighbor interactions, and extremely precise bounds for the thermal properties are obtained.
Configuration Interaction Studies of Ground and Excited States of Polyatomic Molecules. I. The CI Formulation and Studies of Formaldehyde
Authors: Whitten J. L. , Hackmeyer Melvyn
Published: February 2004

A configuration interaction (CI) procedure which is designed to produce energies and wavefunctions from relatively large scale computations on ground and excited molecular states is presented based on an orthonormal set of molecular orbitals. The method of generating configurations is referenced to the particular state of interest and involves a two-pass procedure: First, the generation of configurations by single and double excitations from selected important configurations (parents), subject to a threshold criterion, followed by diagonalization of the energy to obtain an initial approximation to the wavefunctions of interest; second, the use of these wavefunctions as parents and a repeat of the generation and diagonalization steps to produce the final CI wavefunction. CI studies of the A21,3 (n→π*), 1,3A1 (π→π*, n→3p), 1B1 (σ→π*, π→3s), and B21 (n→3s) states of formaldehyde are reported for several large Gaussian basis sets of near atomic Hartree–Fock quality based on molecular orbitals determined from ground and excited state SCF treatments and from certain elementary virtual orbital transformations. Calculated Franck–Condon transition energies are in excellent agreement with experimental results for those transitions which have been observed; of particular interest is the occurrence of a n→3p transition on oxygen in the region of the spectrum atound 8 eV.
Atomic and Molecular Photoelectron Angular Distributions Measured near Threshold
Authors: McGowan J. William , Vroom D. A. , Comeaux A. R.
Published: February 2004

The differential angular distributions of photoelectrons emitted in the formation of various ionic states have been determined for Ar, Kr, Xe, H2, N2, and O2. Where possible several photon energies have been employed, the 21.21-eV He resonance line and the 16.67- and 16.85-eV Ne resonance doublet. In most cases the angular dependence for the photoelectron emission can be described by a function of the form 1 + βP2(cosΘ). For certain of the rare gases ionized by the Ne resonance doublet large deviations from this prediction were obtained. These deviations are related to the energy of the outgoing electron and the structure of the ionic species formed.
Low-Frequency Vibrations of Molecular Solids. V. Globular Molecules—(CH3)3MCl and (CH3)3MBr
Authors: Durig J. R. , Craven S. M. , Bragin J.
Published: February 2004

The far-infrared and Raman spectra of solid (CH3)3CCl, (CD3)3CCl, (CH33SiCl, (CH3)3GeCl, (CH3)3CBr, (CH3)3SiBr, and (CH3)3GeBr have been obtained over a range of temperatures. For (CH3)3CCl, (CD3)3CCl, (CH3)3SiCl, and (CH3)3CBr torsional vibrations were observed, and from the frequencies, barriers to internal rotation of the methyl groups were calculated. The barrier of 4.51 kcal/mole for tertiary-butyl chloride (4.82 for the d9 compound) is consistent with that reported earlier for the fluoride. The 3.90-kcal/mole barrier calculated for the tertiary-butyl bromide is somewhat lower than expected. A barrier of 2.63 kcal/mole was found for the trimethylchlorosilane molecule. Intermolecular fundamentals were observed for all compounds in the series, and the higher-frequency modes observed in the infrared spectra were assigned as librational fundamentals whereas the lower-frequency Raman lines have been assigned as optical translations. The frequency shifts for these intermolecular fundamentals are discussed in terms of the increased intermolecular forces for the higher molecular weight compounds. Although the “heavy” members of the series are globular in shape, no phase transitions were observed and the lack of more than one crystalline form for these solids is believed to be the result of the relatively large intermolecular forces.
Mössbauer Effect of 57Fe Impurities Bound in Vanadium and Vanadium Hydrides
Authors: Simopoulos A. , Pelah I.
Published: February 2004

An experimental study is made of the Mössbauer effect of 57Fe in vanadium and vanadium hydride matrices. We have measured the recoil-free fraction and second-order Doppler shift over the temperature range 100–700°K. The vanadium results are fitted with simple expressions for the mean-square displacement and velocity of the defect at the high temperature range. Both quantities suggest an increase in force constants in the vicinity of the iron defect. The vanadium hydride samples display a higher recoil-free fraction than the vandium samples. This is attributed to hydrogen nucleation around the iron defect.
Possible O6+ Structures Obtained by a Semiempirical SCF–MO Method
Authors: Conway D. C.
Published: February 2004

A semiempirical SCF–MO method which considers intermolecular differential overlap has been used to compute the total dissociation energy (to 2O2 + O2+) for various planar structures of O6+. The five more stable structures with dissociation energies about two-thirds the experimental value are all possible structures at the potential minimum. It is concluded that the spins of the five “1πg-like” electrons are probably parallel in the O6+ ground state.
SCF MO's and Molecular Properties of Methyl Fluoride
Authors: Arrighini G. P. , Guidotti C. , Maestro M. , Moccia R. , Salvetti O.
Published: February 2004

The SCF MO's of CH3F have been calculated by using bases of up to 47 STO's. The best molecular energy obtained is − 139.0612 a.u. The ground-state wavefunctions have been utilized to compute several observables corresponding to one-electron operators, viz., the electric dipole, quadrupole, and octopole moments, the electric field gradient at the carbon atom and at the proton, and the diamagnetic part of the susceptibility. In addition, by using the coupled HF perturbation theory, the electric polarizability and the paramagnetic part of the susceptibility have been computed.
Spin–Lattice Relaxation Times in Deuterated Ferroelectric Ammonium Sulfate and Fluoroberyllate
Authors: Kydon D. W. , Petch H. E. , Pintar M.
Published: February 2004

The temperature dependences of the deuteron spin–lattice relaxation times (T1) in deuterated ammonium sulfate, (ND4)2SO4, and ammonium fluoroberyllate, (ND4)2BeF4, have been studied by transient methods over the range 85°–475°K, which includes the ferroelectric transition temperatures for both materials. The temperature dependence of T1 in both salts is interpreted in terms of reorientation of the two nonequivalent ND4+ ions. Within certain temperature regions in both materials, the deuterons in each type of ND4+ ion have a T1 smaller than the spin-diffusion time with the result that they relax independently, making it possible to measure T1 for each group. The activation energy changes little if at all at the phase transition, although there is an abrupt change in T1 for the deuterons in both ND4+ ions in ammonium sulfate and in one ND4+ ion in ammonium fluoroberyllate. This latter fact has provoked the suggestion that both ammonium ions are involved in the ferroelectric behavior of ammonium sulfate, whereas only one is involved in the fluoroberyllate.
Lifetimes and Total Transition Probabilities for NH, SiH, and SiD
Authors: Smith Wm. Hayden
Published: February 2004

Radiative lifetimes have been measured for the NH (d 1Σ–c 1Π), (c 1Π–a 1Δ), (c 1Π–b 1Σ), and (A 3Π–X 3Σ) systems, and for the SiD and SiH (A 2Δ–X 2Π) transitions. The phase-shift technique yielded lifetimes ranging from 10 nsec for the NH (d 1Σ–c 1Π) transition to 700 nsec for the SiH (A 2Δ–X 2Π) band. All the lifetimes of upper states measured showed the effects of radiative cascading. In particular, the c 1Π state of NH shows radiative cascading originating at least in part from the observed d 1Σ state. The measured d 1Σ state lifetime is near the nominal lifetime computed for the state cascading into the c 1Π state and is considerably shorter than the c 1Π state lifetime. The NH (A 3Π–X 3Σ) and the SiD and SiH (A 2Δ–X 2Π) transitions showed cascading that arises from states which have not been spectroscopically identified. All the systems studied, with the exception of the NH (d 1Σ–c 1Π) transition, showed cascading in which the cascading state lifetime was shorter than the measured state lifetime. This situation has not been completely discussed previously and is given consideration as to the effect on themeasured phase shifts and calculated radiative lifetimes.
Arrhenius Parameters for the Abstraction Reactions of Methyl Radicals with Silanes
Authors: Strausz O. P. , Jakubowski E. , Sandhu H. S. , Gunning H. E.
Published: February 2004

Arrhenius rate parameters for the abstraction reactions of methyl radicals, produced by the photolysis of azomethane, with SiH4, SiD4, Si2H6, Si2D6 and φSiD3 were determined in competition with recombination. Silanes are more reactive than their hydrocarbon counterparts, and the increased reactivity is due to lower activation energies, the A factors being similar. The experimental values of Ea have been compared to those calculated by the bond-energy–bond-order method using a simple three-mass-point model. Calculated kinetic isotope effects, based on absolute reaction rate theory, have been compared with experimental results.
ESR Study of Line Position and Width in γ-Irradiated Polycrystalline Globular GeCl4. Structure and Motion of the GeCl3 Radical
Authors: Roncin J. , Debuyst R.
Published: February 2004

After γ irradiation of polycrystalline globular GeCl4, an ESR spectrum is obtained consisting of 10 line groups. From this pattern, the line position and width, and with the help of the equations of Kivelson and Wilson, it has been possible to determine the structure and the motion of the GeCl3 radical in a GeCl4 matrix. The results point to a pyramidal configuration with a possible rotational 23π motion around Ge–Cl bonds. Correlation times, an activation energy value for this motion, and g‖ and g⊥ values could be computed.
Hellmann–Feynman Theorem for Multiconfiguration Self-Consistent Field Theory and Correlation Energy
Authors: Tuan Debbie Fu-tai
Published: February 2004

The Hellmann–Feynman theorem for the multiconfiguration self-consistent field (MC SCF) theory is derived. This theorem is general enough to be applied to both open- and closed-shell systems. In conjunction of this result with Sinanoǧlu's many-electron theory of atoms and molecules using the multi-configuration general restricted Hartree–Fock (GRHF) method, an expression for the change of correlation energies is obtained. It is shown that the correlation energies should be nearly constant with respect to the change of any one-electron parameter, which is independent of symmetry and exclusion effects, of the zeroth-order Hamiltonian. This result justifies the following: (1) The dynamical correlation energies of isoelectronic atomic systems are nearly constant. (2) The potential-energy surface of a molecule determined from the GRHF approximation should be parallel to the actual potential-energy surface.
Magnetic Polarizations of Electrons at Dislocations in Alkali Halides
Authors: McClurg G. R. , Squire C. F.
Published: February 2004

A new ferromagnet has been studied in the experiments reported in this paper and the hysteresis properties explored for the first time. The magnetization may arise from electrons trapped on the numerous dislocations in pure, single crystals of alkali halides. The ferromagnetic moment could be caused by some 1014 electrons/cm3 which are trapped on dislocations and whose spins are aligned. New measurements are reported in this paper giving the torque on the magnetometer as a function of applied field strength. Both the behavior of the ferromagnetic component and the induced magnetic moment are brought out clearly in the present work.
Equation of State for Nonattracting Rigid Spheres
Authors: Carnahan Norman F. , Starling Kenneth E.
Published: February 2004

A new equation of state for rigid spheres has been developed from an analysis of the reduced virial series. Comparisons with existing equations show that the new formula possesses superior ability to describe rigid-sphere behavior.
Quenching of Metastable Hydrogen Atoms by Molecular Impact
Authors: Gersten Joel I.
Published: February 2004

A theory for the quenching of metastable hydrogen by molecular gases is presented. It is shown that the rather large cross sections observed experimentally by Fite et al. can be accounted for by assuming the quenching to be due to the dipole–multipole interaction. Comparison with experiment gives fair agreement.
Structure of Molten Nitrates. III. Vibrational Spectra of LiNO3, NaNO3, and AgNO3
Authors: James David W. , Leong W. H.
Published: February 2004

The Raman spectra of the molten nitrates of lithium, sodium, and silver change as the temperature is raised. Close to the melting point well-developed low-frequency modes can be distinguished close to the exciting line while at higher temperature these have become somewhat broader but still quite distinct. There are also changes in the magnitude of the splitting of degenerate modes and in the energy of the other vibrations. The spectra have been interpreted on the basis of a quasicrystalline model in which cubic packing is assumed. Spectral changes from the solid, volume change on fusion, entropy changes, and molten-state radial distribution functions are explained on the basis of the model.
Photoionization and Absorption Coefficients of OCS
Authors: Cook G. R. , Ogawa M.
Published: February 2004

Absolute absorption and photoionization coefficients of OCS gas have been measured in the 600–960-Å region using a 1-m Seya–Namioka-type scanning vacuum ultraviolet monochromator. The Hopfield helium continuum was used as a background source with photoelectric detection of the dispersed light. A number of peaks were observed in both the absorption and photoionization spectra at wavelengths that agree well with those of a high-resolution photographic spectrum. A series of the “apparent emission type” which converged at 17.931 eV had the Fano shape for a preionization process in both the absorption and ionization spectra. The total continuum underlying the band structure had been estimated, as well as that fraction due to ionization and to dissociation. Fluorescence emission was observed for all wavelengths of excitation in the Hopfield continuum. Peaks in the spectrum of the total fluorescence yield coincided in wavelength with absorption bands of Rydberg-type series converging to a limit at 16.04 eV. Maximum of the continuum underlying the fluorescence was at about 810 Å.
SCF Dirac–Slater Calculations of the Translawrencium Elements
Authors: Waber J. T. , Cromer D. T. , Liberman D.
Published: February 2004

Total energies of several configurations of the elements in the range of atomic numbers 104–132 were computed using the Liberman–Waber–Cromer program to determine the probable ground-state configurations. These calculations provide evidence for eka-actinium (s2d) at 121, partial filling of the 6f shell through 124 and beginning of a new superactinide series at element 125, in which the 5g shells fill progressively as the atomic number increases.
Spin Polarization and Spin Delocalization in Unrestricted Hartree–Fock Method
Authors: Yonezawa T. , Nakatsuji H. , Kawamura T. , Kato H.
Published: February 2004

A method to separate the spin density calculated with the unrestricted Hartree–Fock method into components due to spin-polarization and spin-delocalization mechanisms is presented, and applied to some doublet and triplet radicals. The results are examined by means of the UHF natural orbitals and of the open-shell restricted Hartree–Fock orbitals, and the validity of the method is confirmed.
Lifetime of the N2 Vegard–Kaplan System
Authors: Shemansky D. E. , Carleton N. P.
Published: February 2004

The results of an experiment by Carleton and Oldenberg, designed for the measurement of the relative lifetimes of the N2 B 3IIg and A 3Σu+ states, have been reanalyzed. The reanalysis was prompted by the assumption, in the original analysis, that the N2 first positive (1PG) (1, 0) band could be described as a Hund's case (b) transition in the levels contributing significantly to the emission. The B 3IIg state is in fact intermediate in coupling between Hund's cases (a) and (b), with a rather gradual change from case (a) to case (b) as a function of increasing J. The error in the calculation of the population of the A 3Σu+ (υ = 0) level from the measurement of self-absorption in the N2 1PG (1, 0) band, assuming Hund's case (b) coupling, is significant. An additional error due to neglect of a degeneracy factor (Λ-type doubling) resulted in a relative lifetime differing by a factor of about 7 from the recalculated value. The lifetimes of the A 3Σu+ (υ = 0) level, calculated using the B 3IIg (υ = 1) lifetime measured by Jeunehomme, are 1.36 sec for the Σ = 0, substate and 2.7 sec for the Σ = 1, −1 substates, with a probable error of about 20%.
N2 Vegard–Kaplan System in Absorption
Authors: Shemansky D. E.
Published: February 2004

Seven bands (6, 0–12, 0), of the N2 Vegard–Kaplan system have been observed in the absorption spectrum of 12 m·atm of gas. The measuring instrument was a 2-m scanning spectrometer with a resolution of about 30 000. Pulse-counting techniques, coupled with the use of a theoretical model based on a measured collision broadening coefficient, have allowed fairly accurate estimates of the transition probabilities of the observed bands. The electronic transition moment has been calculated from the measured transition probabilities and extrapolated with the aid of emission measurements, in order to determine the lifetimes of the system. It is shown that the system has a double lifetime for each vibrational level. The calculated lifetimes [τi(υ′)] for the A 3Σu+ (υ = 0) state were τ2(0) = 1.27 sec for the Σ = 0 substate levels, and τ1(0) = τ3(0) = 2.5 sec for the Σ = 1, −1 substate levels.
Effects of High Pressure on the Far-Infrared Spectra of Paraelectric KH2PO4 and RbH2PO4
Authors: Blinc R. , Ferraro J. R. , Postmus C.
Published: February 2004

Using an opposed-anvil-type diamond cell, the infrared spectra of KH2PO4, RbH2PO4, and monoclinic RbD2PO4 have been measured in the 100–1400-cm−1 region up to pressures of 60 kbar and at several temperatures. The room-temperature spectrum of RbH2PO4 demonstrates the existence of a new high-pressure phase where the PO4 tetrahedra are distorted and the protons are ordered. This phase does not occur in monoclinic RbD2PO4. The results with KH2PO4 are not as dramatic as RbH2PO4. The effects of high pressure in the 300–600-cm−1 region are similar to those obtained on cooling below the Curie temperature (Tc), and have been interpreted in terms of resonance interference between a multiphonon quasicontinuum and discrete states of the distorted PO4 groups.
Carbonyl Carbon-13 σ–π Polarization Constants
Authors: Broze M. , Luz Z.
Published: February 2004

Carbonyl-13C hyperfine splitting constants (hfs) in a number of radicals are analyzed in terms of a Karplus–Fraenkel-type equation. Spin densities are determined semiempirically from 17O and 1H hfs and from MO calculations. The analysis gives QCOC = 36.0 G and QOCC = −24.3 G. These results are compared with independent theoretical calculations using SCFMO wavefunctions for formaldehyde.
Spectra of Benzil
Authors: Bera Subhas Ch. , Mukherjee Ranajit , Chowdhury Mihir
Published: February 2004

The polarized low-temperature absorption spectrum, emission spectrum, and excitation spectrum of benzil and benzil-doped stilbene crystals have been recorded. It has been found that the 3800 Å (n–π*) band system of benzil is split by the weak interaction between the two halves of the molecule. The excitation spectrum reveals the presence of a S→T transition hidden underneath the S→S transition. The crystal spectrum of benzil-doped stilbene is different from the benzil spectrum. The new sharp band at 4850 Å has been interpreted in terms of a trans–planar configuration of benzil. A weak (π*→n) fluorescence has been detected in this crystal.
Resonant Scattering Theory of Association Reactions and Unimolecular Decomposition. II. Comparison of the Collision Theory and the Absolute Rate Theory
Authors: Mies Frederick H.
Published: February 2004

The rate expressions derived in the preceding paper using a resonant scattering theory (RST) to describe recombination and unimolecular decomposition are compared with the absolute rate theory (ART). A one-to-one correspondence exists between the resonance states in RST and the activated states in ART. The “states of the activated complex” are shown to be the channel states in RST, and using the adiabatic approximation to describe the continuum states it is shown that ART does give a proper upper bound to the rate even when nonadiabatic effects are included in RST, i.e., the mean transmission coefficient κ is equal to or less than one. The collision theory gives explicit expressions for κ(kT,P) which is a function of temperature and includes the dependence on pressure. Specific expressions are given for the “tight complex,” where the “activated complex” occurs at some distorted region in configuration space, and for the “loose complex,” where the activated complex is the rotational barrier in the asymptotic channel states. Particular attention is given to the high-pressure rate constant where the specific transmission coefficient can be simply related to the ratio of the mean widths to the mean spacings of the activated states. Criteria are given for the validity of ART, and it is shown that Light's statistical theory of reaction rates is a special microcanonical version of the ART for the “loose complex.”
Dissociation Energy and Ionization Potential of Silicon Monoxide
Authors: Hildenbrand Donald L. , Murad Edmond
Published: February 2004

The dissociation energy of SiO(g) has been determined mass spectrometrically by studying the isomolecular equilibrium Ge(g) + SiO(g) = GeO(g) + Si(g). Third-law calculations lead to ΔH298 = 26.6 ± 2 kcal/mole for the reaction, which yields D°0(SiO) = 182.8 ± 3 kcal/mole, or 7.93 ± 0.13 eV. The ionization potentials of SiO and GeO were measured and found to be 11.6 ± 0.2 and 11.5 ± 0.5 eV, respectively. Both of these ionization potentials are higher than previously published values. These data yield D°0(SiO+) = 4.5 ± 0.2 eV, in accord with the results of recent ion–neutral reaction studies. The relation of D°0(SiO) to the bonding in SiO is discussed briefly.
Thermodynamic Behavior of Dilute Solutions of Hydrogen and Deuterium in Titanium and Zirconium
Authors: McQuillan A. D. , Wallbank A. D.
Published: February 2004

An investigation has been made of the partial free energy of very dilute solutions of hydrogen and deuterium in the high-temperature, body-centered cubic forms of titanium and zirconium. Anomalous behavior is found which manifests itself as a departure from Sieverts' law. Analysis of the results indicates that there is a strongly marked minimum in the partial enthalpy at hydrogen and deuterium concentrations of about 1 at.% in both metals. This may be associated with a departure from complete randomness in the distribution of interstitial atoms in the solution.
Field Emission in Liquids
Authors: Halpern Bret , Gomer Robert
Published: February 2004

Field emission from tungsten emitters into liquid H2, D2, He, Ar, N2, O2, and C6H6 has been carried out in modified field emission tubes, which permitted switching from ultrahigh vacuum to very pure liquids and back to vacuum. In all cases space-charge-limited behavior was found at >10−9 A, from which the following mobilities (in centimeter2 volt−1·second−1/units) could be estimated: 3 × 10−2 cm2 V−1·sec−1 for H2 at 21°K, 0.9∼10−2 for D2 at 21°K, 4 × 10−2 for He at 4.2°K, 0.36 for He at 1.8°K, 8 × 10−3 for O2, 8 × 10−3 for N2, and 4 × 10−3 for C6H6. In the case of Ar a limiting velocity of 5 × 106 cm/sec rather than a field-dependent mobility was observed. For He and Ar onset of high emission (10−9 A) is abrupt, indicating electron avalanching with concomitant gas-bubble formation at the tip which leads to sputtering. In the case of O2 electrochemical etching occurred even at low currents. For H2 and D2 a true Fowler–Nordheim field emission regime could be observed for i≤10−10 A, from which an energy barrier of 0.1–0.5 eV to the solution of free electrons in H2 was estimated.
Improved Quantum Theory of Many-Electron Systems. V. The Spin-Coupling Optimized GI Method
Authors: Ladner Robert C. , Goddard William A.
Published: February 2004

The previously developed GI methods have an arbitrary aspect since they are based on a particular representation of the symmetric group. Here we remove this arbitrariness by optimizing the representation, that is, optimizing the spin-coupling scheme simultaneously with the optimization of the orbitals. The resulting wavefunctions, called the spin-coupling optimized GI or SOGI wavefunctions, have all of the general properties of GI wavefunctions including the independent particle interpretation and are found as the solutions to a set of coupled differential equations which differ from the GI equations only in that the equations are constructed from a different representation of the symmetric group. We have applied this method to the ground state and some excited states of Li, to the ground states of Be+ and B++ and to the ground state of LiH. In each of these cases, we found that the SOGI wavefunction was only slightly different from the G1 wavefunction and led to very similar energies and other spatial properties. For the spin density at the nucleus, however, SOGI led to much better results. In order to illustrate the effects of spatial symmetry on the SOGI orbitals, we examined the lowest B1g1, A2g3, and Eu3 states of square H4 and the Σu+2 state of linear symmetrical H3. We find that in three of these cases optimization of the spin representation is crucial to providing an adequate description of the state. To investigate how the SOGI method would describe chemical reactions, the SOGI wavefunctions were computed for several other nuclear configurations of the H3 system along the reaction path. These calculations showed that the spin coupling changed significantly during the reaction H2 + H⇆H + H2 and that the variation of the SOGI orbitals provides a clear description of the changes in bonding which occur during this reaction.
Heat of Formation of O2−
Authors: Gaffney Edward S. , Ahrens Thomas J.
Published: February 2004

A series of Born–Mayer-type calculations are used to calculate the lattice energies of simple oxides (MgO, BeO, CaO, and ZnO). Repulsion and other non-Coulombic contributions to the lattice energy are obtained using thermodynamic and recent ultrasonic data for the bulk moduli and the isothermal pressure and temperature derivatives of the elastic constants. Using thermochemical data for the heat of formation of MgO, CaO, and BeO and their cations, the heat of formation of O2−, ΔHf°(O2−), is calculated to be 197 ± 5 kcal/mole. Using the largest value of ΔHf°(O2−), obtained for MgO, presumably the most ionic of the crystals treated, a value of 202.3 kcal/mole is obtained. These values are believed to be more accurate than earlier values given by Morris and by Huggins and Sakamoto who obtained 210 ± 6 and 221 ± 15 kcal/mole. The anomalously low value calculated for ΔHf°(O2−) for ZnO is believed to result from a substantial covalent contribution in the Zn–O bond in this oxide.
Hydrodynamic Properties of a Plane-Polygonal Polymer, According to Kirkwood–Riseman Theory
Authors: Paul E. , Mazo R. M.
Published: February 2004

An exact solution of Kirkwood's formalism of transport processes for dilute polymer solutions has been found for the model of a planar rigid ring. Translational and rotatory diffusion tensors and the perturbation in the stress tensor were calculated. Non-Newtonian behavior was found in the intrinsic viscosity, the intrinsic rigidity, and in the existence of normal stresses. In addition to the elastic response at the principal frequency ω for oscillatory fluid flow, non-Newtonian elastic stresses appear at higher harmonics of ω.
Velocity of Ultrasound in Potassium–Ammonia Solutions: Concentrated Solutions
Authors: Bowen D. E.
Published: February 2004

The velocity of 10-MHz sound waves in potassium–ammounia solutions has been determined using a new apparatus for 35 different metal concentrations between 1.5 and 15.5 MPM (mole percent metal) over the temperature range 200° to 240°K. The adiabatic compressibility of these solutions has been determined by combining this data with the available density data. The concentration dependence of the sound velocity changed abruptly at a concentration of 3.2 MPM. This change is quite similar to the one previously observed in the lithium–ammonia solutions although it occurs at a lower concentration. Comparison of the sound velocities in Li–NH3 solutions and K–NH3 solutions shows that the sound velocity is solute independent for concentrations less than about 4 MPM and that the Mott transition is not solute independent but apparently depends on the radius of the solute ion.
Use of Green Functions in Atomic and Molecular Calculations. VI. The First-Order Perturbation to the Eigenfunction of the Helium-Atom Ground State
Authors: Hameka H. F.
Published: February 2004

We present an analytical expression for the first-order perturbation correction to the eigenfunction of the He-atom ground state. The expression is derived from the previously obtained He-atom Green function and it has the form of a series expansion in terms of Legendre polynomials Pn(cosθ12) where θ12 is the angle between the position vectors of the two electrons. The coefficients of the expansion, which are functions of the electron coordinates (r1, r2), are obtained in the form of integral representations.
Low-Temperature Optical Absorption of Americium Halides
Authors: Pappalardo R. G. , Carnall W. T. , Fields P. R.
Published: February 2004

Absorption spectra at low temperatures are reported for AmCl3, AmBr3, and AmI3. Bathochromic shifts have been generally observed in the series from the chloride to the iodide. These shifts are comparable to those observed in lanthanide halides. Hypersensitive transitions have been observed in AmI3. A number of new assignments of excited levels of Am(III) are proposed on the basis of intensity calculations. Electrostatic, spin–orbit, and configuration-interaction parameters were obtained by direct diagonalization and least-squares fitting to 29 observed levels for AmCl3. The parameter values in cm−1 are: E1 = 3582.8, E2 = 17.276, E3 = 334.30, ξ5f = 2593.3, α = 21.634, β = − 158.48, γ = 1240.4.
Proton Magnetic Resonance and Optical Spectroscopy of [Ni(MeOH)5Cl]+ in Methanol
Authors: Luz Z.
Published: February 2004

A proton magnetic resonance and optical spectroscopy study of the complex formation of Ni2+ with Cl− in methanol is reported. NMR studies were made between − 70° and + 100°C. At low temperatures (below − 20°C) in solutions containing both Ni2+ and Cl− it is possible to detect an NMR signal due to a superposition of the solvation shells of [Ni(MeOH)6]2+ and of [Ni(MeOH)5Cl]+. Between − 15° and + 30°C fast exchange smears out the part of the peak due to the monochloro complex; from the decrease in the intensity of the remaining signal, equilibrium constants as function of temperature are determined. From the variation of the bulk-methanol NMR linewidth and frequency shift with temperature the following kinetic parameters and hyperfine interaction constants for the solvation-shell molecules of [Ni(MeOH)5Cl]+ are found: specific rate of exchange at 25°C, 2.3 × 105sec−1; activation energy for the exchange reaction, 15.8 kcal mole−1; hyperfine interaction constants for the methyl and hydroxyl protons, + 0.51 and + 0.37 Mc/sec, respectively. Optical spectroscopy measurements were made at − 40°, + 23°, and + 50°C. Analysis of these data provided evidence that the nickel–chlorine complex formed is a monochloro pseudo-octahedral complex, i.e. [Ni(MeOH)5Cl]+.
Correlation and Distribution of Segments in a Chain Molecule
Authors: Yeh Robert , Isihara A.
Published: February 2004

The singlet and the pair distribution functions of segments of a chain polymer molecule are evaluated at fixed center of gravity of the molecule, the former to the first order in the excluded volume effects and the latter to the zeroth order. The results are applied to the evaluation of the viscosity and other transport coefficients. The mutual relations of these segment distribution functions are discussed in comparison with the recent self-consistent field approach by Reiss and others to the excluded volume effects. Thus, the product assumptions on higher-order distribution functions are examined.