bluuebunny/crossref_metadata_2025 huggingface dataset:
Ab Initio Potential Curve for the X 3Σg− State of O2
Authors: Schaefer Henry F.
Published: February 2004

Using a 4s2p1d set of contracted Slater functions on each atom, configuration interaction (CI) wavefunctions have been calculated at eight points to determine a potential curve for the ground state of O2. The approximate first-order wavefunctions include 128 configurations of three basic types, and convergence to an optimum set of orbitals is attained using the Bender–Davidson iterative natural orbital procedure. Using this approach, the molecule dissociates properly to two oxygen atoms of slightly better than Hartree–Fock accuracy. The ab initio dissociation energy is 4.72 eV, compared to the Hartree–Fock value 1.43 eV and the experimental value 5.21 eV. Other computed spectroscopic constants (with experimental values in parentheses) are also in good agreement with experiment: re = 1.220 Å (1.207), νe = 1614 cm−1 (1580), and Be = 1.417 cm−1 (1.446). Some general conclusions are drawn on the ab initio calculation of bondlengths.
Infrared Spectrum of Solid and Matrix-Isolated H2O2 and D2O2
Authors: Lannon Joseph A. , Verderame Frank D. , Anderson Robert W.
Published: February 2004

The infrared spectrum between 4000 and 200 cm−1 of polycrystalline D2O2 at − 190°C corresponds to that of H2O2 indicating that the crystal structure and spiral chain coupling of excitons for each of the six normal modes are the same in D2O2 as in H2O2. At temperatures near − 100°C the crystal spectra of both H2O2 and D2O2 change with time on CsI and CsBr cold windows. The greatest change observed is that the crystal bands arising from torsion disappear and are replaced by two other bands about 100 cm−1 lower in frequency. Also, the exciton bands in the stretching and bending regions lose their fine structure and shift to lower frequency indicating that the peroxides actually dissolve into the salt windows without decomposition at these low temperatures. The spectra of H2O2 and D2O2 matrix isolated in argon and nitrogen at about 8°K are also reported. The most interesting features of these spectra are the extraordinarily broad bands in the torsional region, ν4, in both nitrogen and argon. The relative intensities of the triplet in argon are observed to change reversibly with temperature. In argon matrices, spectra of the torsional region indicate that the motion of the peroxide in the cavity is similar to that in the gas phase. The techniques of earlier workers for analysis of hindered internal rotation were applied to calculate energy levels for the matrix-isolated molecule. In argon the triplet in the torsion band is explained in terms of combination sum and difference bands of the internal rotation with translational or librational modes. In a nitrogen matrix, the spectra indicate that the internal rotation is much more hindered. The breadth of the band is explained in terms of a coupling between the hindered internal rotation and translation and/or librational motion as well as combination sum and difference bands with these motions.
Luminescence of Transition Metal d6 Chelates
Authors: DeArmond M. Keith , Hillis James E.
Published: February 2004

Emission and absorption spectra have been determined for Rh(III) and Ir(1II) complexes of the nitrogen ligands, ethylenediamine (en) pyridine, 2,2′-dipyridyl (dip), and 1,10-phenanthroline (phen). Emission lifetimes at 77°K in glassy solution and at room temperature have been measured. From lifetime measurements and the energies of emission, luminescence from these heavy metal chelates is assigned as “phosphorescence,” indicating complete intersystem crossing, consistent with the heavy metal spin–orbit mixing of excited singlet and triplet states. Spin–orbit coupling is further manifested in the appearance of room temperature phosphorescence for the bis Ir(III) complexes of dip and phen. The emission can be classified as (1) metal localized (“d–d” emission) or (2) “delocalized molecular” (ligand localized or charge transfer). The metal localized emission appears at low energies, is broad and structureless, and exhibits a large Stokes shift. The delocalized molecular emission appears at higher energies and shows characteristic vibrational structure and a small Stokes shift. The intensity of the delocalized molecular emission is large, indicating a quantum yield approaching one. The “d–d” emission is less intense. Correlation of the relative emission intensities of the “d–d” emitters with the displacement of the emitting state from the ground state determined from the Stokes shifts suggest that recent Jortner and Rice theories of nonradiative transitions rationalizes these relative intensities. The “strong coupling” limit is illustrated by the tris and bis(en) complexes of Ir(III) and is consistent with the low intensity emission of these complexes. The larger emission intensity of the Rh(III) en complexes is consistent with the weaker vibrational coupling predicted for these complexes by the theory.
Medium Effects in NMR. VIII. Temperature and Pressure Dependence of 19F Chemical Shifts in Pure CF4, SiF4, and SF6 Gases and in Gaseous Mixtures
Authors: Mohanty S. , Bernstein H. J.
Published: February 2004

Accurate 19F NMR chemical shift measurements on pure CF4, SiF4, and SF6 gases and their mixtures with other gases have been obtained. These shifts are strictly linear with density like 1H chemical shifts. In mixtures, the second virial screening coefficient has a linear dependence on concentration within experimental errors. The chemical shifts and second virial screening coefficient exhibit a nonlinear temperature dependence. It is shown that these changes in chemical shifts can be adequately described in terms of the London dispersion field and a field due to repulsion.
Experimental Determination of the Excitation Function for the Reaction: H+n-C4D10→HD+C4D9(sec)
Authors: Gann Richard George , Ollison Will Mann , Dubrin J.
Published: February 2004

The excitation function for the formation of HD was determined by means of a nonequilibrium bulb method in the relative energy range of ∼ 0.5–1.7 eV. Hydrogen atoms of various well-known initial kinetic energies, 0.35, 0.48, 0.67, 0.92, 1.15, 1.67, and 2.05 eV, were generated by the photodissociation of HI and HBr in the presence of either n-C4D10 or n-CD3–(CH2)2–CD3. Temperature variation studies performed at the lowest source energy allowed an estimate, 0.35 eV, for the sec-abstraction threshold energy. The excitation function was related to the measured HD yields through an integral equation, derived previously. The cross section rises from threshold to a maximum value (∼ 0.35 Å2) at about 1.2 eV with an energy dependence intermediate between that predicted by the familiar line-of-centers and step function models, and then decreases with increasing energy. The results are compared with other experimental and theoretical studies.
Optical Properties of Six-Member Carbon Ring Organic Liquids in the Vacuum Ultraviolet
Authors: Sowers B. L. , Arakawa E. T. , Birkhoff R. D.
Published: February 2004

Optical data for incident photon energies 2.0–10.6 eV are reported for 1,3-cyclohexadiene, cyclohexene, and cyclohexane in the liquid state. New measurements of the optical constants of liquid benzene over this energy region are included for comparison. An interpretation of the data is made in terms of molecular excitations of π and σ electrons and collective oscillations of the electrons in the liquids.
Explicit Solution for the Wavefunction and Energy in Degenerate Rayleigh–Schrödinger Perturbation Theory
Authors: Silverstone Harris J.
Published: February 2004

The Rayleigh–Schrödinger perturbation series for the energy and wavefunction are derived for the case that the zeroth-order state is degenerate. The solution, embodied in four “rules,” is a generalization of the nondegenerate formulas of Huby and Brueckner. The derivation consists of redefining the unperturbed Hamiltonian and the perturbation (in a particular way) so as to remove the degeneracy, then rearranging the terms in the nondegenerate series in the new perturbation according to the order in the old perturbation. The “choice” of “correct” zeroth-order functions falls out in a natural way, as do the components of the wavefunction in the degenerate unperturbed subspace. The solution given here is not directly related to the degenerate problems solved previously by Kato and by Bloch, in that their solutions do not lead directly to the Rayleigh–Schrödinger series for the energy and wavefunction. The present solution is more related to the one given by Hirschfelder (both being solutions of the same problem), but it differs in not involving the recursively defined operators Qi(n), in being expressed in terms of quantities directly related to the unperturbed Hamiltonian and the perturbation, and in the method of derivation. (An explicit representation of Hirschfelder's Qi(n) is given in Appendix C.)
Vibrational Analysis of the Infrared and Raman Spectra of Oxalyl Bromide in the Crystalline and Fluid States
Authors: Durig J. R. , Hannum S. E. , Baglin F. G.
Published: February 2004

The vibrational spectrum of oxalyl bromide [COBr]2, has been recorded between 4000 and 33 cm−1. The infrared spectra of oxalyl bromide have been examined in the solid, liquid, and gaseous states, and the Raman spectra of the solid and liquid have been observed and qualitative depolarization ratios have been measured. The vibrational spectrum of the crystalline material has been interpreted on the basis of C2h molecular symmetry and C2h5 space group symmetry. Two of the three external lattice modes have been observed in the far-infrared spectrum, and at least four of the six Raman active external lattice modes have also been observed. Six bands appear in the infrared and Raman spectra of the liquid/gaseous states which do not appear in the spectra of the solid. Thus, in the fluid states, molecules with both C2h and C2υ molecular symmetries appear to be present. The enthalpy difference between the two isomers was determined by a variable temperature study to be 2.9 ± 0.1 kcal/mol with the trans isomer being more stable. A rough estimate of the equilibrium mixture at room temperature gives a value of 10% ± 5% for the cis isomer. The barrier restricting the internal rotation around the C–C single bond appears to be governed mainly by V1 and V2 terms of approximately the same order and in the range of 3 kcal/mol.
Dipolar Coupling and Molecular Vibrations in Crystals. IV. Frequency Shifts and Dipole Moment Derivatives
Authors: Frech Roger , Decius J. C.
Published: February 2004

The internal vibrational modes of a dipole coupled crystal are discussed in terms of two models, a “back-ground polarization” model which differs from the transition moment dipole coupled “resonant mode” model in that the additional induced dipolar coupling due to electronic polarization is included. The transverse–longitudinal mode splittings as well as factor group splittings are discussed in terms of these two models. The contribution to the frequency shifts from nonresonant modes is calculated and the effect of dipolar coupling on the overtone frequencies is examined. Dipole moment derivatives and static crystal field frequencies of the ν3 doubly degenerate stretching mode are calculated for a few rhombohedral crystals.
Modified Hamiltonians for Localized Orbitals and for the Removal of Degeneracies
Authors: Amos A. T. , Musher J. I.
Published: February 2004

A single determinant approximate wavefunction ψ0 can be improved by choosing a Hamiltonian of which it is an eigenfunction and applying perturbation theory. If ψ0 is built up of orbitals which are eigenfunctions of a one-electron operator h, an appropriate choice of H0 is Σh(i). This paper discusses two modifications to H0. One consists of adding to H0 an energy-shift operator, and this has several applications the most interesting being the removal of any degeneracies in H0. The second consists of writing the new H0′ as Σh′(i) where h′ is different to h. The h′ can be chosen to have localized orbitals as its eigenfunctions, and this leads to a simple method of performing perturbation theory with localized orbitals. Some numerical examples are given.
Ion–Molecule Reactions by a Photoionization Mass Spectrometer. III. C3H6+n-C4D10 and Cyclo-C3H6+n-C4D10 Mixtures
Authors: Koyano Inosuke , Nakayama Nobuyuki , Tanaka Ikuzo
Published: February 2004

Ion–molecule reactions of the parent ions of propylene and cyclopropane (C3H6+ and cyclo-C3H6+, respectively), with deuterated n-butane (n-C4D10) have been studied by a photoionization mass spectrometer. Ionizing radiation was Lyman alpha (1216 Å) which produced only one primary ionic species (C3H6+ or cyclo-C3H6+) in the mixture of C3H6 and n-C4D10 or of cyclo-C3H6 and n-C4D10. It has been found that, besides the two reactions, D− and D2− transfer, deuterium atom abstraction by C3H6+ (or D atom transfer) takes place in each system. Reaction cross sections for all of these reactions have been determined at a field strength of 4.0 V/cm. These values in angstroms2 unit are: D− transfer 13, D2− transfer 7.1, D transfer 4.8 (C3H6+n-C4D10 system), D− transfer 30, D2− transfer 2.0, D transfer 8.1 (cyclo-C3H6+n-C4D10 system).
Molecular Beam Kinetics: Reactions of H and D Atoms with Diatomic Alkali Molecules
Authors: Lee Y. T. , Gordon R. J. , Herschbach D. R.
Published: February 2004

Crossed-beam studies have been made of the reactions of H and D atoms with K2, Rb2, and Cs2. The hydrogen atoms were generated by thermal dissociation of molecules in a tungsten oven at ∼ 2200–2900°K, the alkali dimers by association of atoms in a supersonic beam expanded from a nozzle at ∼ 900°K. Surface ionization detectors were unable to distinguish among alkali atoms, dimers, and alkali hydrides. However, a kinematic separation of reactive and nonreactive scattering proved to be feasible, owing to the disparity in reactant masses and parity in product masses. The angular distributions of reactive scattering peak at right angles to the initial relative velocity vector. A kinematic analysis indicates that only a small fraction of the available energy appears in product translational motion. This implies that either the vibrational and/or rotational excitation of the product alkali hydride is very high (∼ 30–40 kcal/mole), comparable to or possibly even larger than its dissociation energy, or the product alkali atom is electronically excited. Total reaction cross sections were estimated by normalizing the observed intensity of wide-angle atom–atom elastic scattering to the hard-sphere value. The nominal cross section obtained (no better than a factor of 2) is <̃ 50 Å2 for the H reactions. The D atom reactions show very similar product distributions, with total reaction cross sections larger by a factor of ∼ 2. Variation of the H and D beam temperature indicated the activation energy is negligibly small. The H atoms approach very rapidly compared with the sluggish vibrational and rotational motions of M atoms within M2. From this it is argued that the observed scattering implies an anisotropic reaction probability, favoring configurations with the M2 axis perpendicular to the direction of approach of the H atom. Qualitative comparisons are also made with analogous dissociative electron attachment and photodissociation processes, and with an electron-jump mechanism which involves formation of an intermediate H−+M2+ ion-pair.
Electrical Conductivity in Cholesteric Liquid Crystals
Authors: Shaw David G. , Kauffman John W.
Published: February 2004

The conductivity and activation energies for conduction for three cholesteric liquid crystals in the solid, liquid-crystal, and isotropic-liquid state are presented to describe the transport properties and to observe the effects of varying degrees of order on the transport mechanisms. The conductivities vary from 10−10–10−12 (Ω·cm)−1 between 25 and 125°C according to an Arrhenius temperature dependence with an over-all average of the activation energies of 0.45 eV. The free carrier densities were also found to be exponentially dependent on temperature with an over-all average carrier activation energy of 0.32 eV. These results are discussed in relation to both a band and hopping model of conduction. An unusually small discontinuity in conductivity and activation energy is observed at solid–liquid-crystal and liquid-crystal–isotropic liquid transitions indicating that it is very likely that the same conduction mechanism is present in both the solid and liquid states. These observations agree with the results of I–V measurements. The conductivities calculated from mobilities and carrier densities obtained from I–V curves agree with the conductivities measured directly. The optical absorption spectra is presented between 200 and 1800 mμ.
Ultrasonic Velocity and Attenuation in Liquid Neon
Authors: Larson E. V. , Naugle D. G. , Adair T. W.
Published: February 2004

The velocity and attenuation of 30-MHz sound waves were measured in liquid neon from 25 to 37°K at pressures to 28 kg/cm2. The values of the velocity, extrapolated to the vapor pressure curve, are from 1.5% higher at 25°K to 0.4% higher at 32°K than corresponding values reported for 2-GHz sound waves. This negative dispersion is in agreement with recent predictions by Fleury and Boon. Values of the attenuation exceed the classical values calculated from the Navier–Stokes equation. This excess attenuation is attributed to a volume viscosity of the same magnitude as the shear viscosity. No anomaly in the temperature dependence of either velocity or attenuation was observed near the temperature where an anomaly has been reported for thermal conductivity, shear viscosity, and hypersonic velocity.
Collision Broadening of Rotational Absorption Lines. VI. Pressure Broadening of Microwave Absorption Spectra Involving Oxygen
Authors: Murphy Joseph S. , Boggs James E.
Published: February 2004

The pressure broadening of microwave absorption lines by collisions involving O2 has been investigated using a method presented earlier for analyzing and evaluating microwave linewidth parameters under conditions where impact-theory assumptions are valid. A value of (1.16 ± 0.12) D· Å was obtained for the molecular quadrupole moment of O2 from linewidth data for broadening of NH3 inversion lines by O2. This value is in reasonably good agreement with values determined by other methods, and should constitute an upper limit to the true value since only dipole–quadrupole interaction was considered in the linewidth calculations, This value of the molecular quadrupole moment of O2 was used to calculate linewidth parameters for H2O–O2 broadening, OCS–O2 broadening, N2O–O2 broadening, O2–O2 self-broadening, and the broadening of the 9– line of O2 by various foreign gases. These results are in general smaller than the experimental values, suggesting that the effects of higher-order interactions are important in collisions with O2.
Optical Activity of Transition Metal Compounds. I. Sector Rules for Metal Complexes of the Pseudotetragonal Class
Authors: Richardson F. S.
Published: February 2004

The sector (or symmetry) rules which govern the signs and relative magnitudes of the rotatory strengths associated with ligand-field transitions are examined for metal complexes of the pseudotetragonal class. An independent systems model is adopted in which the complex is partitioned into three separate parts: (a) σ-bond structure of the ML4Z2 cluster, (b) the π-bonding orbitals of the ligating groups, and (c) the nonligating parts of the ligands. Interactions between these three parts of the complex are treated by perturbation theory. Using first-order perturbed wavefunctions, the rotatory strength can be obtained to fourth order. To first order in both the wavefunctions and rotatory strength, the sign and magnitude of the “net” circular dichroism (ellipticity) associated with all ligand-field transitions in a particular complex are determined by a hexadecant rule with respect to the positions of the individual perturber groups. The “relative” signs and magnitudes of the first-order rotatory strengths of the ligand-field transitions cannot be predicted from a single symmetry rule applicable to an entire class of metal complexes. It is shown that the signs and magnitudes of the second- and higher-order contributions to the rotatory strength are determined by “mixed” sector rules in which the positions and charges of two or more perturber groups must be considered simultaneously. These contributions arise from products of pairwise interactions between the chromophoric electron and different perturber groups. In those cases in which the second-, third-, or fourth-order terms are expected to dominate, it is usually possible to pick correctly the appropriate “mixed” sector rule.
Linewidths in High-Resolution NMR Spectra of Coupled Nuclear Systems. Broadening Mechanisms Induced by Molecular Reorientation
Authors: Sýkora Stanislav
Published: February 2004

The perturbation theory of energy-level widths in coupled nuclear systems is applied to the relaxation processes activated by molecular reorientation, i.e., to the dipolar relaxation, the quadrupolar relaxation, the relaxation due to the chemical shift anisotropy, the intermolecular relaxation, and the relaxation due to the spin–rotation interaction. The relaxation processes are divided into two groups with respect to their behavior under rotations of molecular coordinates; the first three are of tensor character while the last two are of vector character. For each of the two groups a theory is developed based on the properties of normed spherical operators. This sheds some new light on the two previously studied cases, i.e., the dipolar relaxation and the intermolecular relaxation, and leads to the solutions of the other cases. The theory of the quadrupolar relaxation is documented by two simple examples. It turns out that in the case of molecules containing quadrupolar nuclei useful information about the molecular structure can be obtained from the linewidth patterns. The same also holds, of course, for the other relaxation processes provided they lead to experimentally accessible effects. Explicit formulas are given for the cross-term contributions due to simultaneous action of two different relaxation mechanisms.
Analysis of the Electron Paramagnetic Resonance Spectrum of Divalent Es in CaF2
Authors: Edelstein N.
Published: February 2004

An analysis of the spin-Hamiltonian parameters of dipositive Es (Es III) in cubic sites in CaF2 has shown that for this ion, the ratio of crystalline field parameters − B6 / B4 < 0.21; the orbital reduction factor (1 − k) = 0.033 ± 0.005; and the value of the nuclear moment of 253Es is μN = (+)3.62 ± 0.5 nm, where the sign is obtained from the consideration of nuclear systematics.
Molecular Beam Electric Resonance Spectra of Reaction Products: Vibrational Energy Distribution in CsF from Cs+SF6
Authors: Freund S. M. , Fisk G. A. , Herschbach D. R. , Klemperer W.
Published: February 2004

Reactively scattered CsF generated at the intersection of crossed molecular beams of Cs and SF6 is analyzed by electric resonance spectroscopy. The observed Stark spectrum arises from transitions between space-quantized components (MJ → MJ′) of particular rotation-vibration (J, υ) states of CsF. The transitions are well resolved for several rotational states (J = 1–4). For each of these states, lines arising from the lowest four or five vibrational levels (υ = 0–4) are identified by comparison with the spectrum of a thermal CsF beam. Intensity ratios for these levels indicate that the reactively scattered CsF has an approximate Boltzmann distribution of vibrational energy. The vibrational temperature is Tυ(CsF) = 1120 ± 90°K with the parent beams at T(Cs) = 580°K and T(SF6) = 230°K; it increases to Tυ(CsF) = 1270 ± 140°K for T(SF6) = 600°K. Concurrent angular distribution, product velocity analysis, and electric-deflection studies show that the reactively scattered CsF is peaked symmetrically forward and backward with respect to the initial relative velocity vector and that its translational and rotational energy is small compared to the reaction exothermicity. The symmetry of the angular distribution indicates that a collision complex is formed which lives for several rotational and many vibrational periods before the products CsF and SF5 emerge. Since the present experiment shows that less than 6% of the approximately 40 kcal/mole exothermicity appears in the mean vibrational energy of the newly formed CsF bond, most of the exothermicity must go into excitation of the SF5 radical. The vibrational temperature of the CsF agrees well with that calculated assuming equipartition of the total available energy into all possible modes of motion of the CsSF6 complex.
Absorption Cross Sections of O2 and CO2 Continua in the Schumann and Far-uv Regions
Authors: Ogawa M.
Published: February 2004

By means of a photoelectrical technique used in conjunction with a 3-m vacuum monochromator, the absorption cross section of the O2 continuum in the region 2350–1814 Å and the absorption cross section of CO2 in the region 2160–1718 Å have been measured. The cross section of the O2 continuum is 3.8 × 10−24 cm2 at 2350 Å; it slowly increases towards shorter wavelengths and reaches 10.7 × 10−24 cm2 at about 1980 Å, then increases very rapidly and reaches 7.1 × 10−22 cm2 at about 1814 Å. In the case of CO2, numerous discrete bands were found overlapping a weak continuum in the wavelength region below 1980 Å. The absorption cross section of the CO2 continuum is about 2 × 10−24 cm2 at 2100 Å; it gradually increases toward the shorter wavelength side, and reaches about 4 × 10−24 cm2 at 2000 Å. The continuum rises rapidly at 2000 Å and its value is 1.19 × 10−20 cm2 at 1718 Å. Origins of the continua of both O2 and CO2 are briefly discussed.
Pyroelectric Ammonium Iodate, a Potential Ferroelastic: Crystal Structure
Authors: Keve E. T. , Abrahams S. C. , Bernstein J. L.
Published: February 2004

Ammonium iodate, NH4IO3, is pyroelectric at room temperature and crystallizes in the orthorhombic system with space group Pc21n and four formulas in the unit cell. The lattice constants at 297°K are a = 6.4115 ± 0.0005, b = 9.1706 ± 0.0005, and c = 6.3740 ± 0.0005 Å. The integrated intensities of 4591 reflections within a hemisphere of reciprocal space of radius (sinθ) / λ = 1.02 Å−1 were measured using PEXRAD. The crystal structure was solved by Patterson and Fourier series and refined by the method of least-squares using 1458 symmetry independent Fmeas. The final agreement factor R is 0.054, based on a model with anisotropic iodine and oxygen and isotropic nitrogen thermal vibrations, and with a spherical distribution of hydrogen around the nitrogen atom. The structure consists of discrete IO3− pyramidal ions arranged to give a highly distorted octahedral environment about the iodine. The IO3− ions and NH4− ions form chains parallel to the polar axis. Three I–O distances are in the range 1.765–1.836 Å and three more are in the range 2.778–2.830 Å. There are four N···O distances under 3 Å, indicative of weak hydrogen bonding. The structure is a highly distorted perovskite, and is potentially ferroelastic. The spontaneous strain at 297°K is 0.00293. The spontaneous polarization, calculated on the basis of point charges on the two ions, is 1.9 × 10−2 C m−2.
Electronic Structures and Potential Energy Curves for the Low-Lying States of the CN Radical
Authors: Schaefer Henry F. , Heil Timothy G.
Published: February 2004

At 11 internuclear separations ab initio calculations have been carried out on those 59 molecular states of CN which dissociate to atomic limits up to DC1 + 2DN. Four electrons are held frozen in carbon and nitrogen 1s Hartree–Fock atomic orbitals, and a full configuration interaction is carried out for the remaining nine electrons using optimized 2s and 2p Slater-type orbitals on each atom. The Π2 calculations, which include 486 configurations, are the most complicated. Eighteen significantly bound states (De ≥ 0.84 eV) were obtained, nine of which have been observed spectroscopically. With the exception of the third Π2 state, the theoretical ordering of states agrees with experiment. Three of the states never observed experimentally (Σ+4, 4Π and Δ4) lie below all but three of the known states of CN. Calculated spectroscopic constants are compared with experiment. The potential curves show many interesting features, including potential maxima in the Σ−4, 2Σ−, J 2Δ, and Π2 IV bound states. By performing natural orbital analyses, dominant molecular orbital configurations have been unambiguously assigned to the lowest 18 bound states. The second, third, and fourth Π2 states experience numerous avoided crossings among themselves, and natural orbitals have been used to follow the changes in electron configuration as a function of internuclear separation. The question of the approximate validity of the quantum numbers g and u is discussed.
Dielectric and Neutron Inelastic Scattering Measurements on Phenanthrene
Authors: Spielberg D. H. , Arndt R. A. , Damask A. C. , Lefkowitz I.
Published: February 2004

The static dielectric constants and the linear coefficients of thermal expansion of high purity single crystals of phenanthrene were measured as a function of temperature in three mutually perpendicular directions and indicate a small increase in the dielectric constant in the a direction at about 72°C. Cold neutron inelastic scattering from polycrystalline phenanthrene was investigated at room temperature, 60, 75, and 85°C, using the Brookhaven Slow Chopper facility. Changes in the density of phonon states above and below 72°C were examined by difference analysis and loss of some low-lying states above 72°C was detected. Some implications of these dielectric measurements and the neutron spectra as well as earlier electrical and heat capacity measurements are discussed. The conclusion is that phenanthrene cannot at present be described as one of the known types of solids. It is suggested that the observed phenomena are not inconsistent with a model in which hindered vibration of the 4, 5 hydrogens above 72°C introduce a new degree of freedom.
N2+ Potential-Energy Curves
Authors: Stallcop James R.
Published: February 2004

A valence-bond method is used to determine a set of relations between the potential energies of those states of N2+ from which dissociation to ground state N and ground state N+ takes place. The potential curves of the sextet and the quartet states are calculated at intermediate internuclear separation distances (2–3.5 Å) from these relations and the experimental curves of the doublet states.
Thermodynamic Functions and Debye–Waller Factor for Adsorbed Particles
Authors: Allen R. E. , Alldredge G. P. , de Wette F. W.
Published: February 2004

A discussion is given of the effect of the particle masses on the thermal properties of an adsorbate–substrate system, with detailed calculations for model systems in which the adsorbate consists of a light or heavy monolayer. These models are more nearly realistic than those used in previous treatments in that there is no disagreement with the condition of rotational invariance. We have examined the dependence of the vibrational contributions to the energy, entropy, free energy, and specific heat upon the temperature, the surface orientation, and the particle masses. The mean-square amplitudes of vibration, which determine the Debye–Waller factor, were also studied. The calculated results for the free energy and the mean-square amplitudes are reproduced exactly at high temperatures and to a good approximation at low temperatures by a very simple model in which, roughly speaking, it is assumed that the vibrational frequencies associated with the adsorbate are proportional to the square root of the adsorbate mass. Arguments are given to show that this result should hold for any adsorbate–substrate system for which the quasiharmonic approximation is valid, regardless of structure or composition. Since the mass dependence can be almost exactly taken into account (in the quasiharmonic approximation), measurements of the temperature dependence of the free energy and Debye–Waller factor should provide direct information on adsorbate–substrate interactions. In particular, the mean-square amplitudes at high temperatures are independent of the masses and are determined solely by the force constants.
Excitation of the CO Fourth Positive Band System by Electron Impact on Carbon Monoxide and Carbon Dioxide
Authors: Mumma M. J. , Stone E. J. , Zipf E. C.
Published: February 2004

Absolute excitation cross sections were measured for five vibrational bands of the CO(A 1Π–X 1Σ+) Fourth Positive band system. The bands were produced by electron impact on CO and CO2 and the cross sections were measured from threshold to 350 eV. Relative intensity measurements on 28 bands were used to determine the dependence of Re on the r centroid, which is Re = 1.9(1.0 − 0.6r̄υ′υ″). Absolute transition probabilities were computed using this functional form for Re and normalizing the total transition probability of the υ′ = 2 level to published experimental results. The total f-value for this transition is then 0.15. Absolute excitation cross sections for the first five vibrational levels (υ′ = 0 → 4) of the A 1Π state were determined for each parent gas using the measured cross sections of specific bands and the absolute transition probabilities. When CO was the parent gas, the relative populations of these vibrational levels were proportional to the Franck–Condon factors, qυ′0. The sum of the cross sections for these levels is 1.87 × 10−17 cm2 ± 15% at 300 eV. This represents 87.4% of the total excitation cross section for the A 1Π state. The relative populations of the first five vibrational levels were also determined for dissociative excitation of CO2 and they differed from the relative populations which resulted from direct excitation of CO. The sum of the cross sections for these five levels is 1.4 × 10−18 cm2 ± 17% at 300 eV.
Gaseous Metal Borides. III. The Dissociation Energy and Heat of Formation of Gold Monoboride
Authors: Gingerich K. A.
Published: February 2004

The AuB molecule has been identified in the vapor phase over an Au–BN–C mixture and an Au–Ce–CeS–BN–C mixture, using a combination of Knudsen effusion and mass spectrometric techniques. Its appearance potential was measured as 8.7 ± 0.5 eV. The enthalpies for the reactions AuB(g)+Au(g)=Au2(g)+B(g), AuB(g)+Ce(g)=CeAu(g)+B(g), and AuB(g)=Au(g)+B(g) were determined by the second and third law method. Combined with published ancillary data these reaction enthalpies yielded the following thermodynamic properties for gaseous AuB: AuB(g)=Au(g)+B(g), D0° = 87.0 ± 2.5 kcal mol−1 or 364 ± 11 kJ mol−1; Au(s)+B(c)=AuB(g), ΔHf,298° = 135.3 ± 3.0 kcal mol−1or 566 ± 13 kJ mol−1.
Pair Correlation Function for Gaseous H2 at Low Density and Temperature
Authors: Poll J. D. , Miller M. S.
Published: February 2004

The results of a quantum mechanical calculation of the density-independent part of the pair distribution function for H2, using a Lennard-Jones potential, are presented. The pair correlation function is written in the form g = gB + gS, where gB is the correlation function for Boltzmann statistics and gS describes the symmetry effects. The major difference from previous calculations of this type, which have been made for 4He, is that for H2 there are contributions from bound states and from a resonance. Numerical results are given for a range of temperatures from 2–80°K.
Emission from Long-Lived States in Ion Beams. New Band Systems of NO+
Authors: Maier William B. , Holland R. F.
Published: February 2004

A method for investigating radiation from long-lived, excited states of ions is described. Emission spectra, apparent lifetimes of the excited states, and electron impact cross sections for producing the radiation can be studied. The spectrum of emission from long-lived states of NO+ in an ion beam has been obtained for wavelengths between 1250 and 2200 Å, but no NO+ emissions have been observed in spectral scans of the 2200–3400-Å region. Some of the spectral features are produced by transitions to the X 1Σ+ state of NO+ from the υ′ = 0 and 1 levels of a single electronic state having an internuclear distance 1.157−0.01+0.02 Å and an apparent lifetime 135 ± 35 μsec. These two vibrational levels are 7.301 ± 0.006 and 7.511 ± 0.01 eV above the ground state of NO+. The other emissions observed can be characterized by two apparent lifetimes, 10.8 ± 2 and 160 ± 50 μsec, and appear to be produced by transitions to the X 1Σ+ state from several upper states. Tentatively, the energies of the upper states are set at 9.639 ± 0.006, 9.437 ± 0.009, and 9.232 ± 0.006 eV above the ground state of NO+. Other radiating levels may be at 9.34, 9.07, and/or 8.79 eV. Some of the observed radiation may be produced by the previously reported A 1π → X 1Σ+ transitions, where the A 1π state would have to be populated by a slow cascade.
Spectroscopic Study of the Phase Transition in Crystalline Adamantane
Authors: Wu Poe-Ju , Hsu L. , Dows David A.
Published: February 2004

The infrared spectrum of crystalline adamantane (tricyclo-3,3,1,1-decane, C10H16) has been studied at temperatures below and above the first-order phase transition at 208°K and as a function of temperature through the transition. Splittings of the vibrational transitions and appearance of gas-phase-forbidden transitions below 208°K are in agreement with theoretical predictions. A hysteresis is observed in the spectroscopic characteristics over a range of a few degrees around the heat-capacity peak occurring at the transition temperature. Calculations of lattice energy, frequency splittings, and barriers to molecular rotation have been carried out using central force functions between nonbonded atoms derived from physical properties of a number of crystals. The splittings, heat of sublimation, transition energy, and crystal structural parameters are in semiquantitative agreement with experiment. The vapor pressure of adamantane in the temperature range 312–366°K has been measured, and the heat of sublimation has been determined.
Intermolecular Forces in Globular Molecules. VIII. Binary Gaseous Mixtures
Authors: Dorsch Robert R. , De Rocco Andrew G.
Published: February 2004

The spherical shell potential is extended to the case where the shells are of differing diameters. From this result, an extension of the geometric-mean mixing rule for the energy is determined which has the form ε12 = (ε11ε22)1/2f(11, 22, 12), where f(11, 22, 12) is a ratio of polynomials arising in the definition of the mixed shells potential. The values of B12 computed on this basis together with those for the case where f(11, 22, 12) = 1 and for 18–6 and 12–6 potentials are compared with experimental values for three mixtures: CH4–(CH3)4C, CH4–SiF6, CH4–Si(CH3)4. A distinct improvement in agreement is noted for these globular mixtures when the extended rule is employed.
Linear Differential Equation for the Radial Distribution Function of Quantum Mechanics
Authors: Kostin M. D.
Published: February 2004

A nonlinear equation for the probability density of quantum theory is obtained from the Schrödinger equation for the case of complex wavefunctions. Motion of a particle in a centrally symmetric field is investigated and it is found that a linear differential equation for the radial distribution function can be derived. The linear equation is used to demonstrate the transition to classical theory and to derive a partial differential equation for the radial distribution function of statistical thermodynamics.
Matrix-Isolation Study of the Vacuum-Ultraviolet Photolysis of Chlorofluoromethane. The Infrared and Ultraviolet Spectra of the Free Radical ClCF
Authors: Smith Clyde E. , Milligan Dolphus E. , Jacox Marilyn E.
Published: February 2004

The vacuum-ultraviolet photolysis of CH2ClF and of CD2ClF isolated in an argon matrix at 14°K leads to the appearance of prominent absorptions at 742 and at 1146 cm−1 which have been assigned to the two stretching fundamentals of ClCF. A weak absorption band system between 3900 and 3400 Å, with a 376 ± 10 cm−1 average band spacing, may be tentatively attributed to ClCF, as may be an emission band system which appears between 4000 and 4900 Å when the sample is excited by 3650-Å radiation. The 379 ± 10 cm−1 average band spacing associated with this emission band system has been tentatively attributed to the bending mode of ground-state ClCF, permitting a normal coordinate analysis for this molecule. The bending and the C–Cl stretching modes are appreciably mixed. Several other groups of absorptions also have been observed in these experiments, but the species responsible for them have not been definitively identified.
Collisional Deactivation of Intermediate C4H8+ Ion in the Photolysis of Ethylene at 1048–1067 Å
Authors: Gill P. S. , Inel Y. , Meisels G. G.
Published: February 2004

The vacuum ultraviolet of photolysis of ethylene with argon resonance radiation leads to ion formation with a quantum yield (ionization efficiency) of 0.218 ± 0.015. Ethylene ion immediately forms an adduct with ethylene with an internal energy of 58 kcal/mole above the most stable 2-butene or methylpropene ion configurations. Neutralization of the C4H8+ ions by charge exchange with toluene, dimethylamine, or trimethylamine yields 2-butene and methylpropene as neutral counterparts to ions assumed to have a similar structure. The relative abundance of the isomers is dependent on the concentrations of charge acceptor and of inert gases. Results are interpreted in terms of an equilibrium between the ionic precursors of 2-butene and methylpropene. A transition state corresponding to a loose methylcylopropane ion structure, with a barrier of about 30 kcal/mole, is postulated for the isomerization. The effects of inert additives and ethylene, which does not react rapidly with C4H8+ ion, are ascribed to successive energy loss by collision and a resultant change in the equilibrium constant. This model is developed quantitatively and it is shown that, within the framework of some limiting assumptions, energy transfer in nonreactive ion–molecule collisions is considerably less than anticipated on the basis of an intimate complex. This is ascribed to inefficient energy loss for ion–molecule collisions at large impact parameters where redissociation occurs rapidly as a result of small increases in over-all angular momentum.
Molecular Beam Study of the K+I2 Reaction: Differential Cross Section and Energy Dependence
Authors: Gillen Keith T. , Rulis Alan M. , Bernstein R. B.
Published: February 2004

A molecular beam study of the reactive and nonreactive scattering of a velocity-selected K beam crossed with a thermal I2 beam is described. Velocity analysis yielded the recoil velocity-angle distribution of product KI flux. The energy dependence of this flux distribution was determined from measurements at several incident K beam velocities, corresponding to a range of collision energies Ē from 1.9 to 3.6 kcal/mole. Computational methods were developed to extract the c.m. differential reactive cross section functions (angular and recoil-energy distributions) from the laboratory data. In accord with previous literature on related systems, the reactive cross section is “forward peaked” and most of the exoergicity (some 40 kcal/mole) goes into internal excitation of the KI product. However, there is also significant KI scattering at wide angles and with large recoil energies. The c.m. angular and recoil-velocity distributions are some-what coupled (i.e., nonfactorizable). An increase in Ē from 1.9 to 3.6 kcal/mole produces only a slight change in the shape of the c.m. differential cross section, accompanied by a small decrease (<̃ 20%) in the magnitude of the reaction cross section. Measurements were also made on the angular and velocity distributions of the nonreactively scattered K over the same energy range.
Photolysis of Formaldehyde at 1470 and 1236 Å
Authors: Glicker S. , Stief L. J.
Published: February 2004

The photolysis of formaldehyde vapor has been examined at 1470 and 1236 Å. Mixed isotope (H2CO+D2CO) and radical scavenger (C2D4) experiments have been utilized in addition to inert gas pressurization and lamp intensity attenuation. The quantum yields for H2 and CO formation are both equal to 2; and both are independent of pressure and lamp intensity at 1470 and 1236 Å. The primary quantum yield for molecular hydrogen elimination (ΦII) was determined from the scavenger results and also from the mixed isotope work. The two values obtained are in reasonably good agreement, viz., ΦII = 0.5. The mechanism most consistent with the experimental observations is as follows: H2CO+hυ→H2+CO, H2CO+hυ→2H+CO, H+H2CO→H2+HCO, 2HCO→H2+2CO, where the quantum yields of primary process (II) and (III) are both equal to 0.5.
Effects of Surface Disorder, Various Surface Structures of Chemisorbed Gases and Carbon on Helium Atomic Beam Scattering from the (100) Surface of Platinum
Authors: West L. A. , Somorjai G. A.
Published: February 2004

Low-energy electron diffraction and helium atomic beam scattering have been combined to investigate on the (100) face of a platinum single crystal the effects of changing surface structure on the gas–solid interaction. The angular distribution of a helium beam scattered from the ordered and disordered crystal face has been monitored. The intensity of the beam scattered at the specular angle increases by nearly an order of magnitude upon atomic ordering of the metal surface. Ordered domains of graphitic carbon also yielded high intensity peaks in the specular direction. The magnitude of the intensity maxima for helium beams scattered from ordered surface structures of various chemisorbed gases (CO, C2H2) was sensitive to surface order but insensitive to the type of surface structure formed. For all the surface structures studied the scattered helium beam distribution was directed with the intensity maximum at the specular angle. The surface temperature dependence of the beam dispersion and intensity scattered at the specular angle was monitored in the temperature range 450–1300°K. Anomalous changes in the beam intensity could be associated with the adsorption of carbon monoxide on the crystal face.
Quantum Corrections to the Second Dielectric Virial Coefficient of Rare-Gas Atoms
Authors: Ely James F. , McQuarrie Donald A.
Published: February 2004

An expression is derived for the first quantum correction to the second dielectric virial coefficient of interacting rare-gas atoms. It is shown that this correction is not large enough to account for the experimently determined negative values of this quantity for helium and neon. Based on this result, along with a previously established argument, it is concluded that the point-dipole approximation is the likely cause of the discrepancy between the theoretical and experimental results.
EPR Studies on Trapped Species Produced in the Gamma Radiolysis of Aqueous Sugar Ices
Authors: Zimbrick J. D. , Myers L. S.
Published: February 2004

The yields, EPR spectral characteristics, and paramagnetic relaxation of trapped electrons (eT−) and sugar radicals were studied in 60Co γ-irradiated monosaccharide ices at 77°K. The eT− yields in the various ices ranged from 0.95 to 1.8 and were strongly dependent on solute molarity and phase of the ice matrix. In most cases the sugar radical yields were the same as the eT− yields. The eT− could be bleached with white light to form dielectrons as previously found for eT− in alkaline ices. The EPR line shapes, linewidths, and line broadening mechanisms of eT− in the sugar ices were similar to the corresponding characteristics of eT− in alkaline ice. Spectral studies on the trapped sugar radicals indicated that two groups of radicals were present. The variation of the eT− and sugar radical relaxation times with radiation dose was studied in H2O and D2O matrices. The results for eT− were interpreted as indicating a spatially nonuniform distribution of this species; the spatial nonuniformity is not as great in the D2O matrix as in the H2O matrix. The results for the sugar radicals suggested that one group was distributed uniformly, whereas the other group was distributed nonuniformly to the same degree as the eT− distribution.