bluuebunny/crossref_metadata_2025 huggingface dataset:
Calculation of Neutron Magnetic Form Factors for Rare-Earth Ions
Authors: Lander G. H. , Brun T. O.
Published: February 2004

Certain coefficients that arise in considering the magnetic scattering of neutrons from rare-earth tripositive ions have been calculated, by using the tensor approach of Johnston, Rimmer, and Lovesey. Together with the 〈ji〉 integrals derived from the radial wavefunctions, tabulated, for example, by Blume et al., these coefficients allow the neutron magnetic form factors for the rare-earth ions to be derived. An additional advantage of the tensor approach is illustrated by a discussion of the asymmetry of the magnetization distribution, arising from the coupling of orbital and spin moments.
Electric Deflection of Binary Hexafluorides
Authors: Kaiser E. W. , Muenter J. S. , Klemperer W. , Falconer W. E. , Sunder W. A.
Published: February 2004

The deflections of molecular beams of the binary hexafluorides SF6, SeF6, TeF6, MoF6, WF6, UF6, RuF6, RhF6, ReF6, OsF6, IrF6, and PtF6 in an electric quadrupole field have been studied. In no case was refocusing of the molecular beam observed when an electric field was applied. The reduced or unchanged signals are characteristic of beams of nonpolar molecules and support the assignment of centrosymmetric structures to the hexafluorides. The OsO4 was also found to be nonpolar.
Calculated Dipole-Moment Functions and the Infrared Intensities of HCN and N2O
Authors: Bruns Roy E. , Person Willis B.
Published: February 2004

The dipole moments of HCN and N2O are computed for different geometric configurations of these molecules, using the best available wavefunctions from the “near-Hartree–Fock” calculations of McLean and Yoshimine. From these calculated dipole-moment functions the derivatives with respect to the two stretching coordinates of each molecule are computed and compared with the experimental values obtained from infrared intensity measurements. The absolute magnitudes of the calculated derivatives for both HCN and N2O agree reasonably well with the experimental values. The relative signs of the calculated derivatives, ∂μ / ∂rNN and ∂μ / ∂rNO, appear to be in agreement with experiment for NNO, whereas the relative signs calculated for ∂μ / ∂rNH and ∂μ / ∂rCN are not consistent with the experimental results for HCN. Possible reasons are suggested for this discrepancy, which appears to be more serious than the recent controversy regarding the sign of the CO dipole moment.
Microwave Measurements of the Dipole Moments of CFCl3 and CHCl3 and Their Pressure-Broadened Spectra
Authors: Reinhart P. B. , Williams Quitman , Weatherly T. L.
Published: February 2004

The Stark effect in the J = 2 → 3 transition was analyzed to obtain the values 1.04 ± 0.02 and 0.46 ± 0.02 D for the dipole moments of CHCl3 and CFCl3 respectively. Taking into account Stark and quadrupole interactions and using an approximation to the Van Vleck and Weisskopf pressure-broadening equation, pressure-broadened spectra for the J = 2 → 3 transition were computed for both molecules and compared with measured spectra. The results show the great effect pressure broadening can have on the general appearance of a spectrum.
Theoretical Treatment of Penning Ionization—He(1s2s 1S, 3S) + H(1s 2S)
Authors: Miller William H. , Schaefer Henry F.
Published: February 2004

The potential curves involved in the Penning ionization of the hydrogen atom by helium metastables have been computed by a large-scale configuration interaction. These are the potentials of the He–H system which dissociate to a ground-state H atom and He atom in the four states 1s2s1S,3S,1s2p1p,3p; the ground-state He–H+ potential curve is also required. A simplified description of the ionizing collision is introduced which permits the determination of approximate cross sections (total ionization cross sections, associative ionization cross sections, the energy distribution of the ionized electron, etc.) without knowledge of the autoionization rate; numerical applications to the He* + H system are presented.
Phonon Curves and Frequency Distribution for Hydrogen-Bonded Systems: β Modification of Solid HCOOH, HCOOD, and DCOOH
Authors: Tubino Riccardo , Zerbi Giuseppe
Published: February 2004

Molecular vibrations of the β form of solid formic acid and of its deuterated isotopes are studied throughout the first Brillouin zone with the use of a Urey–Bradley force field. Phonon dispersion curves and related densities of states are calculated. It is shown that low-energy phonons arising from the hydrogen bond are strongly dispersed. The time of flight neutron spectrum reported by others is discussed and interpreted.
Interaction of Sound Wave with Matter Transport across Semipermeable Membrane. I
Authors: Huang Huey-Wen
Published: February 2004

Problems of sound waves propagating in a circular cylindrical tube made of a semipermeable membrane and plane sound waves confronting a semipermeable wall are studied. The formulas obtained can be used to measure the membrane permeabilities and also serve as a basis for our further studies on mechanochemical instability and applications to biophysics experiments.
Magnetic Properties of Tb–Ho Single-Crystal Alloys. II. Neutron Diffraction Studies
Authors: Spedding F. H. , Ito Y. , Jordan R. G.
Published: February 2004

A neutron diffraction study of single-crystal Tb–Ho alloys is reported. Three single-crystal samples, containing 10%, 50%, and 90% Ho, were studied in detail from 5–298°K. We find that all three alloys have similar ordered phases with uniform magnetic structures. Between the Néel temperature and Curie temperature, each alloy exhibits a spiral magnetic structure with the magnetic moments confined to the basal plane of the hcp structure. The temperature dependence of the interplanar turn angle changes gradually from that similar to pure Tb to that of pure Ho as the Ho concentration increases. Below the Curie temperature, all the alloys exhibit a collinearly ferromagnetic structure with the magnetic moments parallel to or closely parallel to the basal plane. The transition temperatures agree well with the corresponding values determined from magnetization measurements. The observed magnetic form factors also show a gradual change in shape as the Ho concentration increases from the shape similar to pure Tb to that of pure Ho. They show little change with temperature (within the accuracy of the present experiment) in the temperature range of the magnetically ordered states for each alloy. Similarities found between the magnetic properties of the 50% alloy and pure Dy are discussed.
Scattering Factors for Atomic Lithium from Correlated and Independent Particle Model Wavefunctions
Authors: Benesch Robert , Smith Vedene H.
Published: February 2004

The natural orbital (NO) expansion of a highly accurate Hylleraas-type wavefunction (99.90% of the correlation energy) is used for the determination of correlated x-ray scattering factors for the S2 ground state of the lithium atom. Correlated electron scattering amplitudes are also obtained within the first Born approximation. For purposes of comparison, scattering factors for this system were computed from various independent particle model (IPM) wavefunctions. Calculations based on the best density (BD) and symmetry-adapted best density (SABD) determinants for Li yielded better approximations to the correlated (NO) scattering factor values than did those based on conventional IPM's. The latter included restricted and spin-polarized Hartree–Fock (RHF and SPHF) functions. The accuracy of x-ray scattering factors and electron scattering amplitudes is seen to depend on the value of the scattering variable μ. Although relative differences between the correlated and various HF values never exceed 1% for any given value of μ, these differences can be attributed almost entirely to “one-electron” rather than to “pure correlation” effects.
Hulthèn Transform Functions of Two-Electron Atomic Systems
Authors: Yue C. P.
Published: February 2004

Hulthèn-type functions are considered as special integral transform functions (Hulthèn transforms) and are used to approximate the ground-state closed-shell and open-shell and also the 21P excited-state wavefunctions of some two-electron atomic systems. The ground-state energies obtained are lower than those obtained with Slater functions. In contrast, for the 21P excited state, Slater functions give energies as good as Hulthèn transform functions. The (radial) Hulthèn transform of the 2p orbital gives a better energy for the 21P state than the 1p function suggested by Parr et al.
Interaction Potential between Li+ and H2. I. Region Appropriate for Rotational Excitation
Authors: Lester William A.
Published: February 2004

A self-consistent-field calculation of the interaction energy between Li+(1S) and H2(X1Σg+) has been computed with the H2 separation fixed at 1.4 a.u. The binding energy, De, of H2 and the total energy of Li+ are determined to within 0.01 eV of the Hartree–Fock limit. An analytical fit to the interaction surface is presented in the form V(r,θ) = υ0(r) + υ2(r)P2(cosθ) + υ4P4(cosθ) to facilitate collision studies. At long range in the nonoverlap region, the ab initio results are found to be in very good accord with perturbation theory estimates.
Intermolecular Potential Function and the Second Virial Coefficients of Simple Polar Gases
Authors: Kong Chang Lyoul
Published: February 2004

A modified form of the Stockmayer potential function is used to represent the pair interactions of axially symmetric polar molecules. The potential function is modified by assuming that the dispersion–repulsion part of the potential energy is the sum of all the pair interactions between constituent atomic groups on adjacent molecules and that the molecules are polarizable. The second virial coefficient is then calculated by treating the directional part of the potential energy as a perturbation on the central force part. With two adjustable potential parameters, this model closely reproduces the experimental second virial coefficients for methyl fluoride and fluoroform.
Hyperfine Structure of Thallium Iodide and an Upper Limit for the Electric Hexadecapole Moment of the Iodine Nucleus
Authors: Stephenson David A. , Dickinson J. Thomas , Zorn Jens C.
Published: February 2004

The hyperfine structure of thallium iodide has been studied in the J = 3 and J = 4 rotational states in an attempt to observe a nuclear electric hexadecapole effect. This study was carried out on a high-resolution molecular-beam electric resonance spectrometer at very weak electric and magnetic fields. The molecule is well described by the usual five hyperfine interaction constants which are (in kilohertz) Tl127205ITl127203IeqQ− 438 916.3 ± 0.5− 438 917.3 ± 1.0c13.05 ± 0.053.09 ± 0.1c234.65 ± 0.1534.36 ± 0.3c3− 2.48 ± 0.1− 2.59 ± 0.2c4− 6.67 ± 0.05− 6.57 ± 0.1. No evidence for a hexadecapole interaction constant as large as 500 Hz was found; this result is interpreted as setting an upper limit of ∼ 10−47 cm4 for the nuclear electric hexadecapole moment of 127I.
Microwave Spectrum of Methylbromodiazirine
Authors: Wollrab James E.
Published: February 2004

Ground-state rotational spectra of CH379BrCN2 and CH381BrCN2 have been assigned, and a set of calculated r0 structural parameters are: r(NN) = 1.240 ± 0.005 Å, r(CBr) = 1.904 ± 0.02 Å, ∢CCBr = 116.5° ± 2.0°, and ∢CCN2 = 124.5 ± 2.0°. The Br quadrupole coupling constants (megahertz) for CH379BrCN2 are χaa = 539.8 ± 8.0, χbb = −279.4 ± 6.0, χcc = −260.4 ± 8.0 and for CH381BrCN2 are χaa = 451.1 ± 8.0, χbb = −232.3 ± 6.0, and χcc = −218.8 ± 8.0. A preliminary value for the barrier to internal rotation is 1.7 kcal mol−1.
Quenching of Glory Undulations for Scattering from Polyatomic Molecules: Clover-Leaf Model for Spherical-Top Molecules
Authors: Helbing Reinhard K. B.
Published: February 2004

A formula is derived which describes the quantum-mechanical analog to Huygens' principle in optics. From this the quantum-mechanical analog to Kirchhoff–Fraunhofer diffraction is formulated and is used to calculate small-angle differential cross sections and total cross sections. Complex scattering phase shifts (optical potentials) are easily accommodated. The method is applied to the case of glory quenching, employing potential models (“breathing sphere,” “clover leaf,” and certain combinations) which can be carried through analytically. As an example, the clover-leaf model was chosen for comparison with experimental data. By applying some suitable approximations the quenching effect can be expressed in simple known terms, both as far as quenched glory amplitudes as well as “misplaced” and “distorted” glory extrema are concerned. For glory scattering from spherical-top molecules (tetrahedral molecules) the clover-leaf model seems to offer a reasonable approximation. It can be used to derive potential parameters and anisotropy parameters.
Reactions in Crystalline Lattices: Chemistry of Lower Valence States of Lanthanides
Authors: Fong Francis K. , Fenn John B. , McCaldin J. O.
Published: February 2004

Reduction of rare-earth (RE) ions to lower valence states in ionic crystals is described in terms of the equilibrium distribution theory for the (alkali halide):RE2+ and (alkaline-earth halide):RE3+ systems. Thermoluminescence glow curves of radiation-reduced CaF2:RE3+ systems reveal that the reoxidation of the divalent ions apparently occurs through thermal excitation of an f electron to the d bands. The additive reduction of RE2+ to the monovalent state in alkali halides yields striking results: While Sm1+ ions in KCl obtained by gamma radiation give rise to broad-band optical spectra which were attributed to 4f66s1 → 4f56s2 transitions, those obtained through high-temperature additive treatment with liquid K give rise to narrow-line spectra that are not easily interpreted. These results illustrate well the major differences between the radiation reduction and additive reduction processes.
Normal Modes of Branched Polymers. I. Simple Ring and Star-Shaped Molecules
Authors: Chompff Alfred J.
Published: February 2004

A molecular theory is developed to calculate the viscoelastic properties of free-draining branched or cyclic macromolecules in concentrated solution or in bulk. The approach taken is that of the normal-coordinate method of Rouse, together with a procedure which involves transformation of crosslinked chains into mechanically equivalent decoupled chains. This method simplifies the calculation of relaxation times. Application of the decoupling procedure to symmetric star-shaped, irregular star-shaped, and cyclic macromolecules permits a rigorous calculation of the viscoelastic properties. Examples of the viscoelastic behavior are given in the form of the steady-state zero shear rate viscosity, the steady-state shear compliance, and the viscoelastic spectra. The excellent agreement between the results obtained presently and those obtained by other methods confirms the validity of the decoupling process for the general case.
Widths of Rotational Lines of an Asymmetric-Top Molecule SO2. III Broadening by Dipolar Gases
Authors:   Krishnaji, Prakash Vinod
Published: February 2004

Widths of six rotational lines of SO2, broadened by OCS, have been measured. The self-broadened widths of 10 lines have also been measured. For the OCS-broadening case, the linewidths have also been calculated theoretically on the basis of the Anderson theory, and the relative importance of different interaction mechanisms has been assessed. The calculated linewidths do not agree with the observed linewidths.
Mechanism of the Reaction H2+D2→2HD. A Simple Molecular Orbital Description
Authors: Gimarc B. M.
Published: February 2004

A bimolecular mechanism is proposed for the exchange reaction H2+D2→2HD based on simple molecular orbital calculations, qualitative molecular orgital pictures, and symmetry arguments. The mechanism assumes a broadside collision of one molecule with another, followed by rearrangement.
Paramagnetic Anisotropy, Electronic Structure, and Ferromagnetism in Spin S = 32 Manganese(II) Phthalocyanine
Authors: Barraclough C. G. , Martin R. L. , Mitra S. , Sherwood R. C.
Published: February 2004

Measurements are reported of magnetization and the average magnetic susceptibility of manganese (II) phthalocyanine in the range 1.7–300°K, which confirm that the Mn(II) atom is in an S = 3 / 2 spin state, and that weak ferromagnetic interactions are present in the crystal, presumably between adjacent molecules. Single crystals of MnPc are moderately anisotropic; the principal magnetic moment μ‖ = 4.0 μB remains constant between 80–300°K while μ⊥ increases from 4.4 μB (300°K) to 5.0 μB (90°K). This magnetic anisotropy is consistent with a A2g4 ground state into which the excited term Eg4 is mixed by spin–orbit coupling. Possible pathways for superexchange are considered.
Infrared Spectra of the dn-Borohydride Ions
Authors: Coker E. Howard , Hofer Douglas E.
Published: February 2004

Solid solutions of the dn-borohydride ions in potassium bromide were prepared by diffusing the borohydride ions into optical grade single crystals. Their infrared spectra at 90°K yielded frequencies for each of the 24 infrared-active fundamental vibrations. Four fundamentals are significantly perturbed by Fermi resonance. The frequencies of the remaining 20 are reproduced to 10 cm−1 or better by the symmetry force constants F1 = 2.99, F2 = 0.316, F3 = 2.79, F4 = 0.317, and F5 = 0.018 mdyn/Å.
Integral Transform Gaussian Wavefunctions for H32+ and H3+
Authors: Somorjai R. L. , Yue C. P.
Published: February 2004

Wavefunctions obtained from a particular integral transformation of 1s Gaussian orbitals were used to calculate the ground state energies of both H32+(D3h) and H3+(D3h) molecular ions. A linear combination of integral transform Gaussian-orbital–molecular-orbital (LCITGO–MO) wavefunction, with basis orbitals kν(qr) placed on the nuclei, gives for H3+ a total energy of − 1.27724 a.u. at the equilibrium internuclear separation Re = 1.62 a.u. The best floating function of this type gives E = − 1.29367 a.u. at the internuclear separation R = 1.66 a.u. This accounts for 99.5% of the Hartree–Fock energy. The same integral transform of a total wavefunction, with the basis functions placed on the nuclei gives E = − 1.21243 a.u. at Re = 1.69 a.u., while letting the orbitals float improves the energy to − 1.22292 a.u. (R = 1.66 a.u.). The best single-center function gives E = − 1.16021 a.u. (99.4% of the s-limit energy) at R = 1.66 a.u., whereas the best single-centre total transformed wavefunction has E = − 1.13836 a.u., also at R = 1.66 a.u. The ground state energy of the H32+(D3h) system is E = − 0.09167 a.u. (R = 1.68 a.u.) with our best non-floating function, and becomes − 0.11708 a.u. (R = 1.68 a.u.) for our floating wavefunction. The latter is 94.6% of the exact energy. The optimum single-center function gives E = − 0.04366 a.u. at R = 1.68 a.u.
Vacuum-Ultraviolet Photolysis of GeCl4, HGeCl3, and H2GeCl2; The Matrix-Isolated Infrared Spectra of GeCl3 and GeCl2
Authors: Guillory William A. , Smith Clyde E.
Published: February 2004

The vacuum-ultraviolet photolysis of HGeCl3 and GeCl4 has resulted in evidence suggesting the stabilization of GeCl3 in argon, nitrogen, and carbon monoxide matrices at 4°K. Dichlorogermane photolysis has led to the stabilization and isolation of GeCl2. Additional evidence has been obtained for H-atom photodetachment resulting in the isolation of a GeCl3 species having two stretching frequencies, and therefore is pyramidal in shape. A normal coordinate calculation using a four-constant valence potential function suggests that the angle between the threefold symmetry axis and any of the GeCl bonds is approximately 73° (Cl–Ge–Cl angle, 111°), slightly greater than the sp3 hybridization angle.
Measurements of the Reflection, Adsorption, and Desorption of Gases from Smooth Metal Surfaces
Authors: Palmer R. L. , Smith Joe N. , Saltsburg Howard , O'Keefe D. R.
Published: February 2004

The scattering of thermal energy beams of 4He, H2, and D2 from the (111) surfaces of epitaxially grown Ni and Ag single crystals has been measured. Also measured were the angular dependences of the desorption of HD resulting from the dissociation–recombination exchange reaction of H2 and D2 on active (111) Ni surfaces. The angular desorption dependence of HD is contrary to the Knudsen law and is describable analytically by cosdθr where 2.5 < d < 4.0 depending on the condition of the particular surface under study. Comparison of these results with the complementary nonreacted scattering distributions, i.e., direct reflection on (111) Ni, indicates that the two measured components, reflection and desorption, combine to yield the total scattered flux from the surface. An artificial synthesis of the total flux distribution expected from the surface assuming an isotropic hydrogen source and the measured reflection and desorption distributions yields a cosine dependence, as expected, at equilibrium. The reflection distributions for the other systems studied are also consistent with this result if a desorption distribution per unit surface area of the form cosdθr is assumed. The results further indicate that adsorption proceeds as cosaθı where a ≈ d − 1.
Dipole Moment and Hyperfine Parameters of H35Cl and D35Cl
Authors: Kaiser E. W.
Published: February 2004

The molecular-beam electric resonance spectra of H 35Cl and D 35Cl have been analyzed. The molecular constants obtained in the observed states are as follows (numbers in parentheses are the errors in the final significant figures): HCl35υ = 0, J = 1υ = 0, J = 2υ = 1, J = 1υ = 2, J = 1eqQCl(kHz)− 67 618.93(47)− 67 638.53(15)− 69 272.89(93)− 70 908.1(24)CH(kHz)− 41.80(25)− 41.68(4)− 41.09(24)− 39.94(94)CCl(kHz)+ 53.851(42)+ 53.887(14)+ 58.597(45)+ 63.68(17)μ(D)1.1085(5)1.1085(5)1.1390(10)1.1685(10)DCl35υ = 0, J = 1υ = 0, J = 2υ = 0, J = 3υ = 1, J = 1eqQD(kHz)+ 187.36(30)+ 187.0(28)+ 184.8(38)eqQCl(kHz)− 67 393.38(9)− 67 403.32(29)− 67 418.00(10)− 68 583.1(10)CD(kHz)− 3.295(46)− 3.308(80)CCl(kHz)+ 27.426(7)+ 27.430(28)+ 29.121(62)μ(D)1.1033(5)1.1033(5)1.1256(10) The above dipole moments were used in conjunction with available absolute infrared intensity measurements of vibrational bands to obtain the dipole moment function of the molecule. The derivatives with respect to the internuclear distance R, evaluated at Re, for H 35Cl are: (dμ / dR)e = + 0.925 ± 0.020 D/Å; (d2μ / dR2)e = + 0.16 ± 0.11 D/Å2; (d3μ / dR3)e = − 3.83 ± 0.90 D/Å3; (d4μ / dR4)e = − 9.3 ± 4.5 D/Å4. In addition, an isotope effect in the dipole moment due to a violation of the Born–Oppenheimer approximation was observed by comparing the relative HCl and DCl dipole moments. The distance derivatives of the field gradient, qCl, at the 35Cl nucleus were also determined: (dqCl / dR)e = (+ 13.52 ± 0.55) × 1015 (esu/cm3)/Å; (d2qCl / dR2)e = (− 23.9 ± 3.3) × 1015 (esu/cm3)/Å2. The rotational magnetic moment of H 35Cl (υ = 0, J = 1) was measured, yielding the molecular g value: gJ = + 0.47 ± 0.03. This parameter, when combined with other available data, allowed a better determination of relative values of Re in H 35Cl and D 35Cl: Re(HCl35) = 1.274700 ± 0.000010 Å; Re(DCl35) = 1.274652 ± 0.000005 Å. The isotope effect on Re is apparent in this determination.
129I Mössbauer Emission Spectrum of (NH4)2129TeCl6
Authors: Jones C. H. W. , Warren J. L.
Published: February 2004

The Mössbauer emission spectra of the labeled compounds (NH4)2129TeCl6 and (NH4)2129mTeCl6 have been studied against the single line absorber Na129I. In both instances a single line was observed with an isomer shift of − 6.49 ± 0.3 mm/sec relative to Na129I. There is no evidence of molecular fragmentation following the isomeric transition in the 129mTe labeled compound. The spectra are interpreted as evidence for the formation of the octhedral ICI6− ion in the decay. This interpretation is based on the isomer shifts of other iodine–chlorine compounds previously reported in the literature. The number of p holes, hp, on the iodine is deduced from the isomer-shift–hp relationships previously derived by other workers.
Fluorescence Efficiencies and Collisional Deactivation Rates for N2 and N2+ Bands Excited by Soft X Rays
Authors: Mitchell Kenneth B.
Published: February 2004

Efficiencies for excitation of the 3914-Å N2+ first negative band and several prominent N2 first positive bands and N2 second positive bands were measured in pure nitrogen and air as a function of gas pressure. These nitrogen bands were excited by the deposition of monochromatic x rays in the energy range 0.9–8.0 keV. The efficiency for the 3914-Å band in air, at pressures where there is no deactivation was determined to be 0.53% ± 0.07%. Efficiency in air was 0.21% ± 0.03% for the 3371-Å N2 second positive band and 0.23% ± 0.08% for the 8912-Å N2 first positive band. The efficiencies of the first negative and second positive bands were invariant for photon energies between 0.9 and 8.0 keV. Quenching of the 3914-Å band in pure nitrogen follows the Stern–Volmer relationship for two-body processes. The quenching constant K was 0.96 torr−1 and the corresponding deactivation rate constant 4.53 × 10−10 cm3/sec. The rate constant for the 3914-Å band, quenched by O2, in air at low pressures, was 7.36 × 10−10 cm3/sec. Three-body processes were evident in air at pressures above 100 torr. The deactivation of the υ′ = 0 vibrational levels in the second positive bands had a rate constant of 1.12 × 10−11 cm3/sec by nitrogen and had a rate constant of 3.12 × 10−10 cm3/sec by oxygen. Quenching constants were measured for seven first positive bands for the sequences υ′ = 1–7. The mean value of K, averaged over all υ′ sequences, was about 3 for nitrogen and 6.5 for air. The deactivation rate constant for the 8912-Å (1, 0) band quenched by N2 was 8.4 × 10−12 cm3/sec.
Spin-Generalized SCF Wavefunctions for H2O, OH, and O
Authors: Guberman Steven L. , Goddard William A.
Published: February 2004

Wavefunctions from spin-generalized SCF calculations using the GF method, are reported for H2O, OH, and O. Three different basis sets are examined for each of these systems. The shapes and angles between the localized GF orbitals are described in some detail. It is shown that the resulting GF orbitals change in a chemically reasonable manner as we proceed from O to OH to H2O. The dipole and quadrupole moments, electric fields, field gradients, densities, and potentials are reported for the GF wavefunctions.
Semiclassical Perturbation Theory of Molecular Collisions. I. First and Second Order
Authors: Rabitz Herschel A. , Gordon Roy G.
Published: February 2004

Explicit formulas are derived for the first- and second-order semiclassical rotationally inelastic transition probability with an electric multipole potential. The symmetry properties of the second-order integrals are discussed, and a method for their evaluation is presented. An expression for the interference terms between first- and second-order perturbation theory is also derived.
Semiclassical Perturbation Theory of Molecular Collisions. II. The Calculation of Collision Cross Sections
Authors: Rabitz Herschel A. , Gordon Roy G.
Published: February 2004

The numerical calculation of semiclassical rotational transition probabilities up to second order is presented. Various electric multipole potentials are considered. The results are used to calculate rotationally inelastic collision cross sections. This is applied to energy and angular momentum transfer in HCN–HCN and ICN–ICN collisions, respectively. Applications to rotational linewidth calculations are also discussed.
Microwave Spectrum, Molecular Structure, and Bromine Nuclear Quadrupole Coupling Tensor of Bromodiborane
Authors: Ferguson Arthur C. , Cornwell C. D.
Published: February 2004

The rotational spectra of eight isotopic species of bromodiborane (11B2H579Br, 11B2H581Br, 10B2H579Br, 10B2H581Br, 10B11BH581Br, 11B10BH581Br, 11B2D579Br, and 11B2D581Br) were studied in the region 10–27 GHz, and analyzed to obtain values for the rotational constants and the complete bromine nuclear quadrupole coupling tensor. Structural parameters found by isotopic substitution are B–B = 1.773 ± 0.003 Å, B–Br = 1.930 ± 0.005 Å, ∢B–B–Br = 121.4 ± 0.3°. The aplanarity, with estimated correction for inertial defect, yields the bridge proton–proton distance, Hb–Hb = 1.992 ± 0.026 Å. Compari on of the structural parameters with those for diborane indicates that the bridge dimensions are affected negligibly by substitution of Br for terminal H. The nonvanishing bromine nuclear quadrupole coupling tensor elements for 79Br in 10B2H5Br are, in megahertz, χaa = 288.87 ± 0.15, χbb = − 150.96 ± 0.30, χcc = − 137.9 ± 0.36, χab = − 198 ± 9. The major principal axis of this tensor makes an angle 1.1 ± 1.0° with the B–Br internuclear line. The significant asymmetry of the tensor about the B–Br bond axis (Γ = − 0.24 ± 0.02) corresponds to an electron defect of 0.08 electron in the bromine pπ orbital normal to the molecular symmetry plane. The electric dipole component μa, determined from Stark splittings for 11B2H5Br, is 1.16 ± 0.03 D.
Determination of the Bond Energies for the Series O2–O2+ through O2–O10+
Authors: Conway D. C. , Janik G. S.
Published: February 2004

Equilibrium constants for the reactions O2 + O2n+ = O2n+2+, n = 1–8, have been determined mass spectrometrically. The fraction of the O4+–O12+ ions which dissociate in the spectrometer is computed theoretically. It is found that a signicant fraction of the O10+ and O12+ ions dissociate in this region. The equilibrium constants are corrected for this and other phenomena. Rotational entropies are computed for the theoretical structures of these complexes. Vibrational entropies are used to estimate weak mode vibrational frequencies. By extrapolation of the enthalpy data to 0°K, the bond energies are found to be D0(O2–O2+ = 10.53 ± 0.10, D0(O2–O4+) = 6.51 ± 0.07, D0(O2–O6+) = 2.56−0.06+0.16, D0(O2–O8+) = 2.43−0.09+0.06, and D0(O2–O10+) = 2.0−0.6+0.4kcal/mole. The De(O2–O2n+) for n = 3–5 obtained by correcting D0(O2–O2n+) for zero-point energy differences are in reasonable agreement with the values computed by a classical electrostatic model. The vibrational entropy of O4+ at 298°K is found to be 9.93 e.u. This is in good agreement with the theoretical value of 10.21 eu obtained from the theoretical (semiempirical SCF MO) potential surface. Various models are used to analyze the equilibrium constant data to determine the model dependence of the derived quantities. The ΔHn°, ΔSn°, and D0(O2–O2n+) values are only weakly dependent on the assumed geometry and weak mode vibrational frequency distribution of the O2n+. On the basis of the De(O2–O2n+) values for O8+–O12+, it is tentatively concluded that the frequencies for the O6+ base cluster in O8+–O12+ are close to those of free O6+. The experimental data are not accurate enough to prove this hypothesis.
Photoconductivity in γ-Irradiated Alkaline Ice
Authors: Eisele Ignatz , Kevan Larry
Published: February 2004

The photoconductivity due to radiation-produced trapped electrons in glassy alkaline ice (10M NaOH) at 77°K has been studied. The temperature dependence of the photocurrent from 4 to 120°K and the coincidence of the wavelength dependence of the photocurrent with the absorption band show that no stable bound excited state exists for the trapped electron. The relation of this result to the importance of short-range interactions in electron binding is discussed. It is also found that radiation-produced shallow traps for electrons are formed. These traps have an average depth of 0.048 eV and appear to be associated with a lattice distortion created by the presence of O−. Both Ohmic and super-Ohmic currents are found under certain conditions. The super-Ohmic current is interpreted as due to a voltage-dependent lifetime of conduction band electrons.
On Stationary State in Irreversible Processes
Authors: Yao Y. L.
Published: February 2004

For linear irreversible processes in an isotropic system, the law of minimum entropy production may be broadened to a mini–maxi law—the relative minima approaching the infinity time monotonically. Both laws are not applicable to linear processes in an anisotropic system, because the rate of entropy production is no longer a homogeneous quadratic function. In the more general case of an “approximately linear” process in one degree of freedom, the stationary state of entropy production may not exist. If it exists, the trajectory of entropy production recedes from the limit cycle to the right as time increases or approaches it from the left as time decreases. While the distinction between past and future and the distinction between right and left do not violate the law of conservation of CPT symmetry, it is difficult to tell whether the extreme is a maximum or a minimum.
Semiclassical Treatment of Vibrationally Inelastic Collisions
Authors: Roberts R. E.
Published: February 2004

A semiclassical theory for inelastic collisions is used to calculate direct and multiple transition probabilities for the collinear collision of an atom with a harmonic oscillator. The method is based upon a single optimal choice of the effective interaction potential for the entrance and exit scattering channels. In light of the simplicity of this approach as well as the agreement with exact quantum-mechanical results for this model problem, extensions of the theory to more complex inelastic processes are possible.
Luminescent Properties of Hexafluoroacetone. III. Vibrational Relaxation and Radiationless Processes in the Gas Phase
Authors: Halpern Arthur M. , Ware William R.
Published: February 2004

Flourescence decay of hexafluoroacetone (HFA) vapor, excited at 2977, 3160, 3370, and 3577 Å, was examined over a pressure range 0.1–700 torr. The single photon technique, which possesses very high sensitivity, was employed. Under isolated conditions, HFA fluorescence followed a single exponential decay, and the lifetime gradually decreased with increasing excitation energy. The radiative lifetime was found to be constant over this wavelength range. From a comparison of the energy dependence of the nonradiative rate constant with that of the dissociation rate predicted from RRKM theory, it is suggested that the radiationless process depleting the excited singlet state at the above wavelengths is intersystem crossing. At intermediate pressures, fluorescence decay was nonexponential, showing the effects of vibrational relaxation. The analysis of these decay curves resulted in the rejection of the hard collision mechanism. By comparing these time-dependent studies with recent steady-state fluorescence data, a four-level model is proposed which combines an intermediate vibronic level with the hard collision mechanism. Approximately one collision in three was calculated to be effective in removing excess vibrational energy. Some discrepancies between these kinetic data and the steady-state results are discussed. The temperature dependence of the fluorescence lifetime was also examined, and an equivalence between optical and thermal excitation was found. HFA was calculated to be in the statistical limit of radiationless transitions.
Field Ion Microscopical Observation of a Transient Stage of Adsorption in the Pt–H2–Ne System
Authors: Nishikawa Osamu
Published: February 2004

A new experimental technique for the direct observation of initial stages of gas–surface interactions using a field ion microscope is described. Experiments with hydrogen on platinum indicate that at 21°K the adsorbate first assumes a metastable state and then a stable adsorption state. The observed transition probabilities from the metastable state to the stable state are 0.15/msec for adsorbed hydrogen around the {134} planes, and 0.28/msec around the {012} planes. Neon adsorbed on platinum at 21°K reduces the platinum–hydrogen interaction.
Nonequilibrium Vibrational Excitation Mechanism for the Reaction H2+D2→2HD
Authors: Poulsen Lise Lotte
Published: February 2004

A reaction mechanism for the four-center exchange reaction H2+D2→2HD is described in detail. The principal idea is that H2 and D2 react with higher probability when the energy present originates in vibrational rather than translational energy. Detailed calculations are presented which show that the mechanism agrees with available results of shock tube experiments, when experimental rate constants are used for the vibrational relaxation. It is shown that the energy necessary for reaction to occur is about 38 kcal, in addition to the vibrational zero-point energy, and that the main part of the experimental HD yield is formed in elementary reactions which involve either D2(3) or H2(2), where the superscripts are the vibrational quantum numbers. The concentrations of these species are depleted below the equilibrium values, and in this way the mechanism explains the surprising experimental dependence of the reaction rate on the concentration of Ar, which constitutes about 90% of the reaction mixture. It is very plausible that the important elementary reactions are D2(3)+H2(1), D2(2)+H2(2), and possibly also D2(1)+H2(2), where in the latter reaction the translational energy must be at least 8 kcal. H2, D2 pairs involving more vibrational energy are too rare to contribute significantly to the reaction. The calculations show that a stationary distribution of the molecules over the vibrational levels should be obtained experimentally within 4% of the time of reaction. The mechanism implies an over-all rate expression of complex form.
Correlation of Molecular Motions from the Point of View of the Cell Model
Authors: Fischer J. , Kohler Friedrich , Weissenböck F.
Published: February 2004

The variational treatment of the single occupancy cell model is extended in order to also include binary correlations of molecular motions within a limited correlation distance. The probability density function of the whole system is written as a product of self-consistent one-particle probability functions and binary correlation terms. Correlation proves to be decisive at low densities and still important at high densities. At high densities, difficulties arise because the one-particle probability function cannot sufficiently account for ternary correlations and does not exclude certain impossible configurations. The results are discussed in comparison to Monte Carlo calculations, to the uncorrelated cell model, and to a cell model where only binary correlation and no independent molecular motion is taken into account.
Absorption Spectrum of the Argon Molecule in the Vacuum-uv Region
Authors: Tanaka Y. , Yoshino K.
Published: February 2004

The absorption spectrum of diatomic argon has been investigated in the 780–1080-Å region with a 6.65-m normal incidence vacuum spectrograph using the helium and argon continua as background sources. Nine discrete band systems are identified. The present analysis shows that the ground state is stable, has a dissociation energy D00 = 76.9 cm−1, and six vibration levels, υ = 0–5. A number of previous calculations of intramolecular potentials agree with these experimental results. Definite dissociation products are assigned for some of the upper states of these systems. State designations, stabilities, and transitions from the ground state are discussed by analogy with an earlier study of the xenon molecule. In some of the upper states, the existence of potential humps (for which no definitive explanation is yet known) is demonstrated by the assignment of transitions to bound molecular states above the dissociation limits and by the onset of diffuseness in band progressions. The origin of the vacuum-uv argon emission continuum and of other emission features is discussed in relation with the observed absorption band systems.
Infrared Spectrum of the ClHCl− Ion Isolated in an Argon Matrix
Authors: Milligan Dolphus E. , Jacox Marilyn E.
Published: February 2004

Upon vacuum-ultraviolet photolysis at 14°K of samples of HCl isolated in an argon matrix at mole ratios favorable for the presence of an appreciable concentration of dimeric HCl, prominent absorptions appear at 696 and 956 cm−1. The positions, contours, and relative intensities of these absorptions correspond within experimental error with those previously attributed to the ClHCl free radical isolated in an argon matrix. Studies of a chlorine-37 enriched sample have confirmed the presence of two chlorine atoms in the molecule. A broad, unstructured absorption at 2870 Å may also be contributed by this ClHCl species. When a small concentration of atomic potassium or cesium is codeposited with the Ar:HCl sample, evidence is obtained for the formation of an alkali-metal-containing complex. Photoionization of the alkalimetal atoms upon exposure of the resulting sample to the radiation of a medium-pressure mercury arc leads to the appearance of very prominent absorptions at 696 and 956 cm−1. It is proposed that these absorptions may more suitably be assigned to the ClHCl− ion, trapped in an inert, essentially nonionic environment. Implications of this reassignment with regard to the nature of the hydrogen bonding of ClHCl− are discussed, and possible mechanisms for the production of ClHCl− under the conditions of these experiments are considered.
Vibrationally Adiabatic Model for the Dynamics of H+H2 Systems
Authors: Tweedale Alan , Laidler Keith J.
Published: February 2004

Dynamical calculations are made for the reactions H+H2, D+D2, D+H2, and H+D2, for linear activated complexes, on the basis of the hypothesis that the zero-point vibrational energy of the reactant molecule passes smoothly into zero-point energy for the stretching vibrations of all of the intermediate complexes. By considering vibrations normal to the minimal reaction path, zero-point energies are calculated at each point along the path. Profiles for P + Z, the sum of the potential and zero-point energies, show single maxima at the activated state. Dynamical calculations for linear systems show that at high impact energies additional energy is required for crossing the P + Z barrier, arising from the centrifugal effect, but that this energy approaches zero as the impact energy is reduced towards the threshold energy. Free-energy profiles are constructed for the H+H2 and D+D2 systems; at higher temperatures these show double maxima, at each side of the potential-energy maximum.
Study of Defect Reactions in Crystals by Means of Anelastic and Dielectric Relaxation
Authors: Nowick A. S.
Published: February 2004

A general theory of anelastic and dielectric relaxation processes has previously been developed for a single defect species which can exist in several crystallographically equivalent orientations. In the present paper, the occurrence of a reaction between different defect species is considered. It is shown that the existence of such a reaction introduces a mode of relaxation, called the “reaction mode”, which involves a net change in the concentration of each species, but no reorientations. This mode gives rise to relaxation of those compliance (or susceptibility) constants associated with stress- (or electric-) field components which are invariant under the symmetry operations of the crystal. A table of these components and the corresponding material constants is presented. The thermodynamic and kinetic theory for such relaxation processes is developed in general, and then considered for important special cases. The few examples in which the reaction mode has been studied are reviewed. Finally, an example (the Al–Na defect in α quartz) is given to demonstrate the value of studying the reaction mode.
Quantum Vibrational Transition Probabilities in Diatomic–Diatomic-Molecule Collisions
Authors: Wilson David J.
Published: February 2004

Collinear collisions of diatomic molecules (harmonic oscillators) are examined by means of the method of Cheung and Wilson, and the dependence of the vibrational transition probabilities on incident relative translational energy, atomic masses, and intermolecular interaction potential is ascertained. Vibration–vibration transfer processes are found to be significant but not necessarily dominant, and the matching of the vibration frequencies of the colliding molecules does not appear to be an important factor in vibration–vibration transfer. Certain mass ratios lead to computational difficulties with this method.
Stochastic Collision Density Calculations for Hot Hydrogen Atoms in Thermal Xe Mediums. I. Application to Photolytic Hot Atom Experiments
Authors: Rebick Charles , Dubrin J.
Published: February 2004

Collision density functions have been stochastically computed for photolytically generated hot hydrogen atoms of known initial energy (∼ 0.5–2 eV) relaxing in a thermally equilibrated Xe medium. The collision density functions together with abstraction yield measurements from Xe moderated alkane systems may be used to determine the H–alkane excitation functions. Calculations were carried out for various assumed H–Xe interatomic potentials; and at energies slightly less than the H–source energy, the stochastic results could be accurately represented by very simple, physically meaningful analytical expressions. The latter are shown to be extremely useful in facilitating the evaluation of the excitation function.
Vibronic Perturbations and Phosphorescence of Phthalazine
Authors: Lim E. C. , Stanislaus J.
Published: February 2004

The phosphorescence and EPR spectra of phthalazine (2,3-diazanaphthalene) were studied in rigid glass solutions at 77°K. It is shown that the perturbation of the zero-point level of the emitting ππ*3 state by the nearly nπ*3 states leads to a number of spectral features which are not expected from a π* → π phosphorescence. Among these are a blue shift of the spectrum in hydroxyl solvents, a positive polarization of the 0, 0 band with respect to π → π* (Lb and Bb) excitations, and a severe modification of the vibrational structure of the emission by halogenated solvents. It is concluded that when the Born–Oppenheimer approximation breaks down, the usual optical criteria for distinguishing nπ* and ππ* triplet states become invalid or at best ambiguous. A strong optical criterion based on the polarized phosphorescence spectrum is presented. The low quantum yield of the phosphorescence and the strong solvent dependence of the emission yield and lifetime were ascribed to the dependence of the radiationless transition on the vibronic coupling between nπ* and ππ* states.
Retarded van der Waals Interactions. I. Simple Atoms
Authors: Getzin Paula Mayer , Karplus M.
Published: February 2004

The effect of retardation on the dipole dispersion interaction between atoms has been determined. By the use of accurate frequency-dependent polarizabilities, quantitative calculations of the retardation correction to the interaction of (H, H), (H, He+), (He+, He+), (H, He), and (He, He), as well as to the three-body system (He, He, He), have been made. The procedure used was to evaluate the Casimir–Polder integral for two atoms and its three-body extension directly so as to obtain results correct for all R. Although the corrections to the limiting behavior (1 / R6 for “small” R, 1 / R7 for large R) are not large, they may be of significance for high accuracy measurements in some cases.
Electron Paramagnetic Resonance in Gamma-Ray-Irradiated Niobium-Doped Calcium Molybdate
Authors: Breslow Richard A. , Owens Frank , Gilliam O. R.
Published: February 2004

Calcium molybdate (CaMoO4) doped with niobium impurity ions was studied by electron paramagnetic resonance (EPR). Single crystals were irradiated with 60Co gamma rays at 77°K which caused three paramagnetic species. One of these is associated with the niobium impurity ion substitutional for molybdenum; the major part of its EPR spectrum showed an S = 12 defect with a 10-line hyperfine structure for each of four equally probable defect sites. Normally forbidden δMI = ± 1 transitions were also observed. The spectra were fit to a rhombic spin Hamiltonian with parameters: gxx = 2.006 ± 0.002, gyy = 2.011 ± 0.002, gzz = 2.053 ± 0.002, | Axx | = 23 ± 2 G, | Ayy | = 30 ± 2 G, and | Azz | = 30 ± 2 G where zz lies approximately along a normal Mo–O bond direction in the lattice. A partially resolved six-line ligand hyperfine structure appeared on the major resonances with the intensity expected for overlapping 95Mo and 97Mo hyperfine interactions. The model proposed for this defect is a hole shared between adjacent niobate and molybdate complexes with a higher probability density on the niobate.