bluuebunny/crossref_metadata_2025 huggingface dataset:
Bounds for the long-range behavior of electronic wavefunctions
Authors: Ahlrichs Reinhart , Hoffmann-Ostenhof Maria , Hoffmann-Ostenhof Thomas
Published: February 2003

Upper bounds to expectation values of many-electron operators for atomic wavefunctions are given. These estimates, which incorporate the ionization potentials of the atom, lead to detailed information about the asymptotic behavior of subcontinuum wavefunctions if more than one electron–nucleus distance tends to infinity. They compare favorably with results given in the literature.
Dynamics of vibrational motion of chemisorbed atoms or molecules; the infrared line shape
Authors: Metiu Horia
Published: February 2003

We present a theory which relates the line shape of infrared absorbtion by chemisorbed atoms or diatomics to the dynamics of lattice vibration. We start from the relationship between the line shape and the thermodynamic Green’s function and use Dyson’s equation to compute the latter with the aid of many-body perturbation theory. The derivation includes local modes and surface states as well as anharmonic interactions. Illustrative calculations show that a variety of line shapes are possible and we identify their dynamical origin.
’’Phase transitions’’ between dense monolayers of atoms and simple molecules on the cleavage face of graphite, with particular emphasis on the transition of nitrogen from a fluid to a registered monolayer
Authors: Larher Y.
Published: February 2003

Adsorption isotherms of N2 on graphite have been studied in great detail in a coverage range corresponding to the transition between the fluid and the registered monolayer. This transition is first order up to a temperature of about 82 K. An adsorption isotherm at 84.69 K shows that the methane monolayer also changes from fluid to registered monolayer through a first order transition. A few adsorption isotherms of Kr and Ar are shown at coverages where a transition of a ’’higher order’’ occurs.
Isotope separation by cw infrared laser enhanced reaction
Authors: Manuccia T. J. , Clark M. D. , Lory E. R.
Published: February 2003

In laser isotope separation it is widely assumed that the rate of the chemical reaction which involves the laser excited reagents must exceed the interisotope energy transfer rate. This is shown to be an unnecessary constraint on the selection of reactions and experimental conditions. Using deactivation processes to compete with energy transfer between the isotopes, it is shown that isotope selectivity can be preserved even under the difficult conditions of cw single infrared photon excitation. The principle is demonstrated by showing bromine isotope selectivity in the radical chain chlorination of methyl bromide in a low pressure discharge–flow reactor intracavity to a CO2 laser. Thermal, VV, and chemical scrambling effects are shown to be unimportant with proper experimental design. Bromine isotope enrichment is limited to ≲5% by the small vibrational rate enhancement of the near-thermoneutral hydrogen abstraction. The temperature dependence of the enrichment is studied and the difficulty in assigning the increased reactivity to a particular vibrational mode is discussed. The energy cost for this particular isotopic enrichment is calculated (6 keV/product molecule) to demonstrate that although energy is wasted by the deactivation process, the flexibility this technique offers in terms of permitting the use of cw (large throughput) ir (efficient) lasers outweighs the above effect. The use of cw techniques allows changes in reactivity of less than 1% to be readily observed.
Properties of the zero-phonon lines in the optical spectra of molecular crystals
Authors: Sapozhnikov M. N.
Published: February 2003

A theoretical interpretation is made of the temperature dependences of the relative integrated intensity, width, and shift of the zero-phonon lines in the luminescence spectra of 1,12-benzperylene and perylene in normal alkane matrices. Temperature properties of the zero-phonon lines in spectra of some other impurity n-alkane crystals are analyzed as well. It is shown that the temperature properties of the intensity, width, and shift are well described by the theory of the electron–phonon interaction if one takes into account the interaction both with acoustic and local vibrations. The zero-phonon line shifts are also essentially determined by the lattice thermal expansion due to the anharmonicity of the crystal vibrations.
Electron transport over barriers of fluctuating height
Authors: Tachiya M.
Published: February 2003

Electron transport over barriers of fluctuating height is theoretically studied. We have obtained an expression for the field-dependent mobility, which is essentially the same as the one obtained in the case of constant barrier height.
Atomic coreless Hartree–Fock pseudopotentials for atoms K through Zn
Authors: Topiol Sid , Moskowitz Jules W. , Melius Carl F.
Published: February 2003

Using the coreless Hartree–Fock (CHF) pseudopotential approach we have generated pseudopotentials for the atoms K through Zn. Atomic calculations indicate that excitation energies and orbital energies using these pseudopotentials are in excellent agreement with ab initio Hartree–Fock calculations. Optimized small basis sets for use with these pseudopotentials are presented along with tests for these basis sets. When used in molecular calculations these coreless Hartree–Fock pseudopotentials should provide ab initio quality energies and wavefunctions while reducing the computational effort.
Photofragment spectroscopy and potential curves of Kr2+
Authors: Abouaf R. , Huber B. A. , Cosby P. C. , Saxon R. P. , Moseley J. T.
Published: February 2003

Photofragment energy distributions have been measured for the process Kr2+[1(1/2)u]+hν→Kr++Kr using a 3 keV ion beam and CW lasers, both coaxial and crossed with the ion beam, at 11 wavelengths between 4680 and 7993 Å. Transitions to the dissociative states 1(1/2)g and 2(1/2)g are observed. The experimental results are used to adjust recent theoretical calculations to provide potential curves for the Kr2+ states 1(1/2)u, 1(1/2)g, and 2(1/2)g with an uncertainty of ±20 meV at internuclear distances near the ground state potential minimum.
Ionization of alkali-metal atoms by He+ impact
Authors: Tiwary S. N. , Rai D. K.
Published: February 2003

The total single ionization cross sections of alkali-metal atoms (Li, Na, K, Rb, and Cs) have been calculated in the binary-encounter approximation (BEA) using the Hartree–Fock velocity distribution function for the bound electron. The calculated cross sections are compared with the experimental data. The BEA results agree with the observations to within a factor of 2–3.
Theory of exciton transport with quadratic exciton–phonon coupling
Authors: Munn R. W. , Silbey R.
Published: February 2003

The coupling of excitons with phonons is an important process determining the mechanism of exciton transport in molecular crystals. Although linear exciton–phonon coupling has been extensively treated before, there has been little work on quadratic coupling. In this paper the theory of exciton transport is extended to take weak quadratic coupling into account, and the diffusion constant computed for a simple model. The results are qualitatively similar to those obtained from other treatments of linear and quadratic coupling, and may show a rather weak temperature dependence.
Photodissociation of molecular beams of arsenic tri-iodide
Authors: Kawasaki M. , Bersohn R.
Published: February 2003

A molecular beam of AsI3 was photodissociated at 280 and 300 nm and the time of flight distribution of the AsI2 fragments was measured. From the broad distributions observed, average total fragment kinetic energies of 13.5 and 10.5 kcal/mole were calculated. If the iodine atom dissociates along the As–I bond direction, the rotational energy of the AsI2 fragment is shown to be nearly equal to the total translational energy. Arguments are given to show that there is little vibrational excitation of the AsI2 fragment and that the iodine atom leaves in the 2P1/2 state. The bond energy D0(AsI2–I) is 55.9±3.0 kcal/mole.
Collisional ionization between fast alkali atoms and selected hexafluoride molecules
Authors: Compton R. N. , Reinhardt P. W. , Cooper C. D.
Published: February 2003

Negative ion products resulting from collisions between orthogonal, crossed beams of alkali metal atoms (Na, K, Cs), and the octahedral hexafluorides MF6 (M=S, Se, Te, Mo, W, Re, Ir, and Pt) have been examined in the energy range from ∼0 to 40 eV (lab). Studies of the dependence of the reaction thresholds upon the temperature of the target molecules SF6, SeF6, and TeF6 have provided electron affinities for these molecules; E.A.(SF6) =0.46±0.2, E.A.(SeF6) =2.9±0.2, and E.A.(TeF6) =3.3±0.2 eV. Energy loss measurements of the alkali, A, in the reaction A+MF6→A++MF−6 at small scattering angles are consistent with these values. Measurements for SF4 together with temperature dependent thresholds for the formation of SF−5 from SF6 and SF−3 from SF4 combined with known bond dissociation energies for D (SF5–F) and D (SF3–F) yield electron affinity values for the SFn series; E.A.(SF6) =0.46±0.2, E.A.(SF5) =2.71±0.2, E.A.(SF4) =0.78±0.2, and E.A.(SF3) =3.07±0.2 eV. Lower limits of ∼5 eV for the electron affinities of MoF6, WF6, ReF6, IrF6, and PtF6 are implied by the detection of MF−6 ions when only the thermal (T∼100 to 300 °C) alkali beam (atoms plus dimers) is incident on MF6. The cross sections for charge transfer A+MF6→A++MF−6 are large at low energies which raises a question as to the mechanism of charge transfer since the zeroth order ground state covalent and ionic curves can never cross.
Molecular dynamics studies of Lennard-Jones liquid mixtures. IV. Further calculation on the behavior of one different particle as a model of real fluid systems
Authors: Nakanishi Koichiro , Toukubo Kazuo , Watanabe Nobuatsu
Published: February 2003

Molecular dynamics calculation has been made on Lennard-Jones liquid mixtures containing 107 solvents and one solute, the attractive term, size, and mass of which are all different from those of solvent for the purpose of simulating real fluid system. The results were compared with those of our previous studies to discuss which factor is effective in determining static and dynamic properties. It was found that, although the position of the first peak of the solvent–solute radial distribution function g12 is primarily dependent on the size of the solute, its height is much influenced by the strength of the attractive term. The attractive term and mass have also a small but nonnegligible effect on the velocity autocorrelation function and diffusion coefficient. A comparison of the present results with the diffusivity in real fluid systems has also been made.
Cluster expansion of the wavefunction. Symmetry-adapted-cluster expansion, its variational determination, and extension of open-shell orbital theory
Authors: Nakatsuji H. , Hirao K.
Published: February 2003

The symmetry-adapted-cluster (SAC) expansion of an exact wavefunction is given. It is constructed from the generators of the symmetry-adapted excited configurations having the symmetry under consideration, and includes their higher-order effect and self-consistency effect. It is different from the conventional cluster expansions in several important points, and is suitable for applications to open-shell systems as well as closed-shell systems. The variational equation for the SAC wavefunction has a form similar to the generalized Brillouin theorem in accordance with the inclusion of the higher-order effect and the self-consistency effect. We have expressed some existing open-shell orbital theories equivalently in the conventional cluster expansion formulas, and on this basis, we have given the pseudo-orbital theory which is an extension of open-shell orbital theory in the SAC expansion formula.
Intensities of binary overtones and combinations in the infrared spectrum of CF4
Authors: Golden W. G. , Marcott Curtis , Overend John
Published: February 2003

The intensities of the binary overtone and combination bands in the infrared spectrum of CF4 have been measured. The dipole strengths of the allowed two-quantum transitions have been determined from the measured intensities and have been compared with the dipole strengths calculated from the anharmonic terms in the intramolecular potential-energy function. The discrepancies between the observed and calculated dipole strengths have been used to estimate the second derivatives of the molecular dipole moment with respect to the dimensionless normal coordinates.
Correlated hopping conductivity in a general two sublattice structure
Authors: Richards Peter M.
Published: February 2003

We show for a general ordered two sublattice model with inequivalent A and B sites that the classical hopping conductivity is anomalously low at stoichiometry (total number of mobile ions equal to total number of A sites). The activation energy increases from its value VA for a mobile ion concentration well off stoichiometry to VA+1/2(VA−VB) at stoichiometry, where VA and VB (VA≳VB) are depths of the potential wells at A sites and B sites. This is a generalization to arbitrary dimensions and coordination number of similar results obtained by Sato and Kikuchi for the two dimensional β-alumina structure and by the author for a linear chain. As an example, the relevance of recent experiments on the alkali zirconium phosphates is discussed.
Raman phonon spectra of partially-deuterated crystalline ethylenes
Authors: Whitfield R. G. , Leroi G. E.
Published: February 2003

The Raman phonon spectra of C2H3D, cis-C2H2D2, trans-C2H2D2, 1,1-C2H2D2, and C2HD3 have been obtained, and various sets of atom–atom interaction potentials were used to calculate the lattice frequencies of the C2H4 crystal using recent single crystal x-ray data. The ’’best’’ interaction potential was used to calculate the librational frequencies of the partially-deuterated ethylenes, assuming that the crystal structure and symmetry is unchanged by deuteration. From a comparison of the observed and calculated frequencies, it was determined that the lattice modes of these crystals are amalgamated, and can be described in the virtual crystal limit. Consistent with the virtual crystal theory, mutual exclusion was retained for the lattice modes of these disordered solids, illustrating the ’’effective’’ Ci site symmetry. Slight changes in the relative intensities of the observed librations were noted, and the experimentally determined perturbation strengths were found to be in agreement with those calculated using the virtual crystal approximation. An attempt to observe the ’’missing’’ optically active translation of C2H4 in the far infrared is described; it is suggested to be at ∼35 cm−1.
Clusters of alkali halide molecules
Authors: Welch D. O. , Lazareth O. W. , Dienes G. J. , Hatcher R. D.
Published: February 2003

The equilibrium geometry and formation energy of clusters (MX)n with n=1 to 44 and the vibrational spectrum of clusters with n=1 to 6 for a variety of alkali halides have been calculated using a simple shell model for the interionic forces. As n increases, the deviation of the binding energy and atomic volume from that of bulk crystals approaches that given by the macroscopic surface energy and tension. The rate of convergence to this asymptotic limit will be discussed. Although the vibrational spectrum converges slowly, the first moment of the spectrum converges rapidly to the bulk crystal value. Approximate analytical formulas have been derived which aid in understanding the competing roles of electrostatic, repulsive, and polarization interactions in determining the equilibriuim surface energy and distortions in ionic clusters and microcrystals.
Elastic scattering of electrons by molecular hydrogen for incident energies 100–2000 eV
Authors: Gupta Prabha , Khare S. P.
Published: February 2003

Energy dependent as well as energy independent polarization potentials along with the most accurate single center wavefunction of Hayes are employed to calculate the average differential cross sections and the total cross sections for the elastic scattering of electrons by molecular hydrogen in the plane wave approximation for incident energies E=100–2000 eV. The agreement with recent experimental result is good throughout the energy range.
Second virial coefficient of helium from 0 to 500°C by the two-temperature gas-expansion method
Authors: Kell G. S. , McLaurin G. E. , Whalley E.
Published: February 2003

Values of the second virial coefficient of helium have been obtained from 0 to 500°C as a by-product of the determination of the thermal expansion of stainless steel vessels used for measurements of the density of water. The Burnett method was used, usually with the two vessels at different temperatures. Gas expansions were made both from the low-temperature vessel to the high and from the high to the low. Truncation problems limit the precision of B2 for one set of measurements but the temperature dependence has been found accurately. The other measurements appear free of significant systematic error.
The hyper-Raman effect: A new approach to vibrational mode classification and assignment of spectral lines
Authors: Andrews D. L. , Thirunamachandran T.
Published: February 2003

The theory of vibrational hyper-Raman scattering (inelastic second harmonic light scattering) is developed within the framework of quantum electrodynamics. The dynamical system comprises the molecule and the radiation field, coupled by multipolar interactions. In the present work, the electric dipole approximation is employed and the results involve the hyperpolarizability tensor. In contrast to previous work, full index symmetry of this tensor is not assumed. The tensor is decomposed into irreducible weights forming the basis for a new vibrational mode classification scheme. A set of five experiments is specified which allows unambiguous assignment of an active mode to one of six classes. The scheme has been applied to several molecules and compared with some experimental results. Explicit expressions for scattering intensities for a wide variety of experimental configurations are given; results for depolarization ratios are also presented.
The effects of ’’post-collision interactions’’ on near-threshold measurements of autoionizing states in Ne from scattered electron spectra
Authors: Spence D.
Published: February 2003

The autoionizing states in Ne have been studied by measuring the yield of scattered sections of chosen fixed final enegies between 20 ev and 3 ev in steps of 0.01 eV. (AIP)
Autoionization structure of nitric oxide (NO) at the first ionization limit
Authors: Miescher E. , Lee Y. T. , Gürtler P.
Published: February 2003

A new and more detailed interpretation is given to the fine structure in the photoionization curve of cold NO observed by Ng, Mahan, and Lee. Resonances are assigned to autoionizing np and ndδ Rydberg levels which give prominent diffuse absorption bands in a spectrum recorded with the synchrotron radiation continuum. Δν<−1 transitions in the vibrational autoionization process are substantiated.
Mechanism of thermal electron attachment in N2O and N2O–hydrocarbon mixtures in the gas phase
Authors: Shimamori Hiroshi , Fessenden Richard W.
Published: February 2003

The attachment of thermal electrons to nitrous oxide at room temperature has been studied, following pulse radiolysis, by a microwave conductivity technique. For pure N2O at pressures from 10 to 300 torr, the results are explained by a combination of two-body attachment followed by reactions leading to partial electron detachment, a two step three-body process, and a process giving overall four-body behavior. The results for mixtures of N2O with alkanes (C2H6, C3H8, n-C4H10, iso-C4H10, n-C5H12, and neo-C5H12) and butenes (1-, 2-cis-, 2-trans-, and iso) are also explained in the same way, but with no electron detachment. Common values of 5×10−15 cm3/molecule sec for the two-body rate constant and 4.6×10−33 cm6/molecule2 sec for the three-body rate constant (with N2O as the third body) explain the data. The three-body rate constants increase with molecular complexity (6×10−34 cm6/molecule2 sec for C2H6 to 1.55×10−31 cm6/molecule2 sec for neo-C5H12). The four-body rate constants range from ∼10−53 to ∼10−51 cm9/molecule3 sec. The branched compounds such as neopentane and isobutene have higher three-body rate constants than the linear isomers. The attachment rates of mixtures of those compounds with the higher three-body rate constants appear to saturate as pressures increase. From the results for N2O-neo-C5H12 mixtures a value of (5.8±0.6) ×10−13 cm3/molecule sec has been determined for the rate constant of the initial two-body electron capture by N2O to form a short-lived N2O−. The autoionization lifetime of N2O− is estimated to be 1.8×10−10 sec or greater. The problem of excess nitrogen in N2O–hydrocarbon radiolysis is discussed in relation to these results.
SCF potential curves for AlH and AlH+ in the attractive and repulsive regions
Authors: Sabelli Nora H. , Kantor Mel , Benedek Roy , Gilbert T. L.
Published: February 2003

Self-consistent-field calculations have been carried out for the systems AlH and AlH+ in their ground and excited states. Distances considered range from separated atoms and ions to 0.1 bohr, or ΔE ?2700 eV. Additional calculations were performed to determine the effect of core and valence electrons at small internuclear separations. A comparison was made of the ab initio potential curve obtained for the 1Σ+ state with results obtained from the Thomas–Fermi statistical model.
The photoionization and photodissociation of CH in the vicinity of the ionization threshold
Authors: Barsuhn J. , Nesbet R. K.
Published: February 2003

The Stieltjes-imaging method is applied to the spectrum of CH which is computed by SCF–MO–CI calculations on single excitation series. The calculations use basis sets of up to 50 Slater atomic orbitals. The continuum cross sections obtained are lower than the previous results of Walker and Kelly who used a perturbation theoretical approach. Our computations indicate strong Rydberg series converging to the ground state and the excited states 3Π and 1Π of CH+. If these Rydberg states were predissociated then the dissociation rate of interstellar CH would be an order of magnitude higher than anticipated. We tentatively derive oscillator strengths for the individual states of the Rydberg series converging to 1Σ+ observed by Herzberg and Johns.
Explicit integration method for the time-dependent Schrodinger equation for collision problems
Authors: Askar A. , Cakmak A. S.
Published: February 2003

To date, only the implicit (Crank–Nicholson) integration method has ben used for numerical integration of the Schrodinger equation for collision processes. The standard explicit methods are known to be unstable and a high price is paid for the implicit method due to the inversion of the large matrices involved. Furthermore, the method is prohibitive in more than two dimensions due to restrictions on memory and large computation times. An explicit method (i.e., a method which doesn’t require the solution of simultaneous equations) is presented, and is shown to be stable in n dimensions to the same order of accuracy as the implicit method with the unitarity being secured to two orders higher accuracy than that for the wave function.
Characterization of molecular defects in crystals by polarization analysis of resonance Raman scattering: Metastable O2* in γ-irradiated NaClO3
Authors: Engstrom Herbert
Published: February 2003

Accurate measurements of the polarization of resonance Raman scattered light from a molecular defect have been made using a combination of polarization modulation and photon counting techniques. A systematic method of least squares analysis of data so obtained is presented. The method is applied to the metastable O2* molecule in γ-irradiated sodium chlorate. The results have permitted the determination of the directions of maximum polarizability and absorption of the defect.
Pretransition in ethanol–water mixtures
Authors: Yamaoka Toshihiko , Kono Ryusuke
Published: February 2003

Ultrasonic velocity data are reported for the ethanol–water mixture of 23 mole% at frequencies between 1 and 5 MHz in the temperature range from −80° to +20° C. Velocities in a crystalline state are far lower than that of ice. The mixtures in the concentration ranging from 9.4 to 23 mole% ethanol indicate a maximum density in a saturated liquid state. The 23 mole% ethanol mixture, among others, grows into a layered hexagonal crystalline structure. Temperature dependency of limiting shear modulus is found to obey the Hirai–Eyring equation, deviating down at high temperatures. The deviation is interpreted in terms of the structural decay process due to the decomposition of the cluster containing 10–15 molecules.
Variation of chemical shielding with intermolecular interactions and rovibrational motion. II. 15N and 13C nuclei in NNO and CO2
Authors: Jameson Cynthia J. , Jameson A. Keith , Parker Harriet , Cohen Sheila M. , Lee Chun-Luan
Published: February 2003

In the gas phase, the chemical shielding of a nucleus in terms of temperature and density can be written in a virial expansion, σ (T,ρ) =σ0(T)+σ1(T) ρ+σ2(T) ρ2+⋅⋅⋅. σ0(T) and σ1(T) functions have been determined for 13C in CO2 and both 15N nuclei in NNO. As expected, the terminal 15N has the largest chemical shift. The results are compared with data for other systems such as 1H, 19F, 31P, and 129Xe.
Variation of chemical shielding with intermolecular interactions and rovibrational motion. IV. 11B and 13C nuclei in BF3 and CH4
Authors: Jameson A. Keith , Moyer James W. , Jameson Cynthia J.
Published: February 2003

The temperature dependence of chemical shielding of 11B and 13C in an isolated BF3 or CH4 molecule is found to be negligibly small. It mat be generally true that the chemical shielding of a nucleus located at the center of symmetry of a molecule changes very little with vibration and rotation. The second virial coefficients σ1 are reported for these systems, as well as the dependence of the 11B–19F coupling constant on temperature and density.
Monte Carlo determination of eigenvalues associated with self-avoiding random walks of large finite order
Authors: Wall Frederick T. , Cheung Agnes S. , Chan Albert
Published: February 2003

Certain eigenvalues of exceedingly large matrices can be obtained by Monte Carlo methods. The procedures, which have quite general validity, are carried out for illustrative purposes in connection with self-avoiding random walks which are used to simulate flexible macromolecules. Lower limits to the statistical dimensions of polymer chains can be expressed in terms of the eigenvalues of transition matrices associated with self-avoiding random walks of finite order. In particular, the largest symmetric and antisymmetric eigenvalues determine how the mean square end-to-end separation, 〈r2〉n, depends upon n, the number of links in the chain. Such eigenvalues have been obtained by Monte Carlo methods for chains on the square and triangular two-dimensional lattices. It is found that, as the order of the walks becomes infinite, the largest antisymmetric eigenvalue approaches the value of the largest symmetric one. This conclusion provides further verification of the generally accepted concept that 〈r2〉/n increases without limit as n becomes infinite.
Power law frequency dependent dielectric function and nonanalyticity properties
Authors: Giaquinta P. V. , March N. H. , Tosi M. P.
Published: February 2003

Experiment yields for many materials a dielectric loss function χ″ (ω) having the behavior χ″ (ω) ∝ωn−1(n<1) over a substantial range of frequencies. Writing the conductivity σ (ω) =ωχ″ (ω) in the form σ (ω) ∝ℱ0∞ω2/1+(ω2/ν2)] g (ν) dν, where g (ν) is the relaxation frequency spectrum, we consider two examples in detail: (a) a relaxing center, at which relaxation is assisted by arrival of defects by diffusion; (b) hopping electronic conduction, with variable range, and thermally assisted. Example (a) is characterized (and dominated) at high frequencies by g (ν) ∝ν−5/2, and for ν≳νD, a characteristic Debye relaxation frequency, σ (ω) ∝ω1/2 results. Example (b) is dominated by low frequency modes, and for ν<νD the behavior is like ω0.8 over a limited frequency range. If one allows in more detail for a distribution of activation energies, then it is argued that σ∝ωn where n<0.8. Some specific experimental results are briefly referred to.
Relativistic scattered-wave theory. II. Normalization and symmetrization
Authors: Yang Cary Y.
Published: February 2003

Formalisms for normalization and symmetrization of one-electron Dirac scattered-wave wavefunctions are presented. The normalization integral consists of one-dimensional radial integrals for the spherical regions and an analytic expression for the intersphere region. Symmetrization drastically reduces the size of the secular matrix to be solved. Examples for planar Pb2Se2 and tetrahedral Pd4 are discussed.
Infrared spectral moments and mean squared torques of OCS mixed with noble gases
Authors: Dreyfus C. , Berreby L. , Dayan E. , Vincent-Geisse J.
Published: February 2003

The spectral moments of OCS mixed with rare gases are measured for the ν1 and ν2 vibrations at various pressures in the 5–300 bar range. Hot bands, isotopic bands, and rotation–vibration interaction are taken into account for the two vibrations. The corrected experimental values of the second moments are in excellent agreement with the theoretical ones. The mean squared torques are therefore deduced, and an estimation of the experimental error is made. We obtain the same values of the mean squared torques from the ν1 and ν2 vibrations and they are found to be a linear function of density. An interpretation in terms of the intermolecular potential is given.
Polarized photochromism in solid solutions
Authors: Pasternak C. , Slifkin M. A. , Shinitzky M.
Published: February 2003

Reversible photochromic transitions are in principle analogous to fluorescence. By this analogy reversible photochromic processes in a rigid transparent medium should display a characteristic anisotropy spectrum with respect to the polarization of the excitation and the monitoring lights. The polarized photochromism spectrum can help to elucidate the chemical structure of the phototransient and to assign the orientation of its transition dipoles. The following report presents and discusses polarization spectra of physical and chemical photochromic processes, measured by a novel steady-state method.
The adiabatic correction for nonlinear triatomic molecules: Techniques and calculations
Authors: Bardo Richard D. , Wolfsberg Max
Published: February 2003

In the Born–Oppenheimer (BO) approximation the isotopic-mass-independent BO electronic energy is the potential energy surface for nuclear motion. The first correction to the BO approximation is obtained by adding the isotopic-mass-dependent adiabatic correction C to this potential energy surface. The adiabatic correction for a nonlinear triatomic molecule in a nondegenerate electronic state is expressed in terms of one-electron integrals over atomic basis functions. Both single determinant molecular orbital BO electronic wavefunctions and configuration interaction wavefunctions are discussed. The adiabatic correction is calculated for H2O and H+3 and their isotopic variants at the respective equilibrium internuclear geometries. Theses adiabatic corrections are combined with those previously calculated for diatomic molecules to obtain correction factors to equilibrium constants for H/D isotopic exchange reactions calculated within the framework of the BO approximation.
Symmetry restricted multiconfiguration annihilation of single excitations. II. Applications: Electronic states of methylnitrene
Authors: Lucchese Robert R. , Yarkony David R.
Published: February 2003

The symmetry restricted multiconfiguration annihilation of single excitations (SRMCASE) procedure is used to obtain multiconfiguration (MC) self-consistent-field wavefunctions for the 3A2, 1E, and 1A1 states of CH3N. The MC description of these states is seen to represent a significant improvement over the single configuration approximation. In particular, a more reasonable value for the 1E–1A1 separation is obtained. The convergence properties of the SRMCASE algorithm are considered and shown to be quite satisfactory.
High-field 23Na magnetic resonance studies in beta-alumina
Authors: West L. C. , Cole Terry , Vaughan R. W.
Published: February 2003

A study of the 23Na magnetic resonance spectrum (1/2– −1/2 transition) at high magnetic field, 63.4 kG, in a single crystal of beta-alumina is reported. A comparison of the high-field rotation spectra obtained at room temperature with previous results obtained in lower magnetic fields allows the extraction of the 23Na chemical shift tensor, the first such tensor measured for an alkali atom. The three principal values for the sodium chemical shift tensor were equal within the experimental error of ±3 or 4 ppm. Linewidth measurements at the high field confirm the suggestions of lifetime broadening of room temperature lines and indicate that by 150 °K second-order quadrupole broadening controls the linewidth. Measurements at low temperatures produce complex spectra which are interpreted to indicate that motional averaging of the sodium environments is still taking place at 77 °K.
Angular momentum distributions in collision processes and the location of the transition state in ion–molecule reactions
Authors: Verboom G. M. L. , Meisels G. G.
Published: February 2003

The relative contributions of angular momentum arising from rotation of reactants and from the orbital motion associated with the collision process are analyzed for spherical species undergoing ion–molecule or neutral–neutral reactions by deriving distribution functions of angular momenta. Under most conditions, angular momenta arising from the molecular rotation are comparable to those arising from neutral–neutral collision, and smaller but not negligible in comparison with the collisional angular momentum in ion–molecule reactions. A measure for the goodness of the neglect of molecular rotation is developed, and it is shown that the approximation is worst at high temperatures and for molecules with low polarizability, small reduced mass, and small rotational constants. In the case of ion–molecule reactions, it is shown that retention of the assumption that orbital angular momentum is conserved separately leads to a distribution function of locations of the transition state in the reaction coordinate. This distribution supports the notion that the transition state is generally loose.
Radiation damage studies by x-ray photoelectron spectroscopy. I. Electron irradiated LiNO3 and Li2SO4
Authors: Sasaki T. , Williams R. S. , Wong J. S. , Shirley D. A.
Published: February 2003

X-ray photoelectron spectroscopy (XPS) was applied to the study of radiation damage on the surfaces of LiNO3 and Li2SO4 single crystals which were free of carbon contamination. Irradiations were done in situ at room temperature with 0.3–1.6 keV electrons. The products, assigned from chemical shifts in the binding energies of core levels, were: LiNO2 and Li2O from irradiated LiNO3 and Li2SO3, elemental sulfur, Li2S, Li2O, and adsorbed oxygen species from irradiated Li2SO4, respectively. There was no indication in either sample of the metallic lithium formation reported previously. Heavy irradiations of the Li2SO4 sample showed that the final products of the radiation decomposition are Li2O and Li2S. The G values (the number of molecules produced or decomposed per 100 eV of radiation absorbed) of the radiation decomposition and product formation for 1.4 keV incident electrons were estimated from differential energy loss to be approximately 10−3–10−4.
Polarization propagator calculations of frequency-dependent polarizabilities, Verdet constants, and energy weighted sum rules
Authors: Jo/rgensen Poul , Oddershede Jens , Beebe Nelson H. F.
Published: February 2003

Expressions for the frequency-dependent polarizability, the Verdet constant, and the energy sum rules have been derived consistent through third order in the electronic repulsion using an analytical polarization propagator method. In this approach, the second order optical properties are obtained directly from the propagator without calculating the individual excitation energies and transition moments which appear in the sum-over-states procedures.
Frequency-dependent polarizabilities and Verdet constants for He, Be, CO, and FH
Authors: Jo/rgensen Poul , Oddershede Jens , Albertsen Preben , Beebe Nelson H. F.
Published: February 2003

Frequency dependent polarizabilities and Verdet constants for He, Be, CO, and FH have been calculated within a first (coupled Hartree–Fock) and second order polarization propagator approach. Except for regions close to excitation thresholds, small differences are found between frequency-dependent polarizabilities calculated in the two orders. The improvements in the polarizability near an excitation threshold are caused by the better description of the excitation spectrum in the second order theory. The trends in the Verdet constants are similar to those found for the polarizability except that the improvements in the second order approach are substantial also away from an excitation threshold (up to 60% of the difference between the coupled Hartree–Fock and the experimental result).
An intermolecular potential for (NH3)2
Authors: Duquette G. , Ellis T. H. , Scoles G. , Watts R. O. , Klein M. L.
Published: February 2003

Model interatomic potential energy functions are presented for the ammonia dimer (NH3)2 which have the correct Coulombic and dispersion interactions for asymptotically large intermolecular separations. Existing data for the second virial coefficient of the gas together with the known structure and binding energy of the solid are used to constrain the parameters of the short range interatomic interactions. Finally, new experimental results for the differential collision cross section of NH3+NH3 are used to test the proposed potential energy functions.
Calculation of dynamically induced electronic transitions of matrix-isolated atomic nitrogen
Authors: Kunsch P. L. , Dressler K.
Published: February 2003

The parity-forbidden transitions 2P→2D and 2D→4S within the ground configuration (2p)3 of atomic nitrogen have been observed as phonon- and vibron-induced emission bands in luminescence spectra of solid nitrogen and have been attributed to dipole radiation induced by dynamic crystal fields of odd parity with respect to the substitutionally trapped atom in the N2 lattice. We confirm this interpretation by an a priori calculation of the absolute transition probabilities and band shapes, using known atomic, molecular, and crystal properties of nitrogen and no adjustable parameters. The induced dipole moments are calculated from the vibrationally modulated quadrupole fields of the host molecules at the site of the polarizable guest atom. The dynamics of the doped lattice are treated by a normal-coordinate analysis of the ’’supermolecule’’ consisting of the atom and its 18 nearest radially relaxed N2 neighbors suspended in the unperturbed surrounding N2 lattice. The calculated dipole-weighted densities of phonon states and the resulting total transition probabilities agree well with observations. The corresponding emissions in rare-gas matrices are represented via superpositions of empirical pair overlap dipole moments.
Reactions of N+4 with O2, CO2, H2, and D2 and mobilities of N+4 in nitrogen
Authors: Lindinger W. , Dotan I. , Albritton D. L. , Fehsenfeld F. C.
Published: February 2003

The rate constants for the reaction of N+4 with O2, CO2, H2, and D2 have been studied as a function of mean relative kinetic energy in a flow-drift tube using a nitrogen buffer gas. The N+2/N+4 equilibrium, which would otherwise deleteriously effect such a study, was suppressed by adding a trace of H2 as a purge gas that preferentially reacted with N+2. The reaction rates of N+4 with CO2 and O2 are found to be fast and independent of energy from 0.04 to 0.16 eV. The reactions of N+4 with H2 and D2, however, have very small rates at room temperature, but the rates increase dramatically with increasing energy, an effect that is attributed to a sensitivity of the reactions to N+4 vibrational excitation. The reaction of N+4 with H2 was studied as a function of temperature and an activation energy obtained. The mobility of N+4 in N2 was extended to higher E/N values than could be done in earlier studies since the effects of the N+2/N+4 equilibrium were suppressed in the present investigation.
The intensity of light scattered by liquid CS2
Authors: Ladanyi Branka M. , Keyes T.
Published: February 2003

We apply our recent theory of light scattering from fluids of optically anisotropic molecules to the case of liquid carbon disulfide. We focus our attention on δ2, the experimentally measured ratio of depolarized to polarized light scattering intensities. With the pair distribution function obtained from the RISM equation, we calculate δ2 using two models for the optical response of the fluid. In the first one (PPA) a point anisotropic polarizability is assigned to each molecule: in the second one (PAPA), each atom is given a point isotropic polarizability. We find that the more realistic PAPA model results in reasonable agreement with measurements of Burnham, Alms, and Flygare.
Modified quantum theory of electronic dielectric constant of III–V semiconductors
Authors: Sarkar K. K. , Goyal S. C.
Published: February 2003

The relationship between the electronic dielectric constant ε and the interionic separation R for III–V semiconductors has been suitably modified by taking into account the d-core effect. This relation gives excellent agreement between the calculated and observed values of the strain derivatives of ε for GaP and GaAs. The variation of d-core effect with R has also been pointed out.
On the theory of unimolecular reactions: Application of mean first passage time to reaction rates
Authors: Procaccia Itamar , Mukamel Shaul , Ross John
Published: February 2003

We apply the theory of first passage times to the process of collision free unimolecular decomposition of large molecules at a given total energy. The theory is intermediate between the dynamical and statistical theories. We find that the rate of decomposition is given in terms of a series, the leading term of which has the form used in the RRKM theory. We analyze the conditions for which this term is dominant, and find that when the molecule is large or the total energy is low or the rate of decomposition is small, our expression coincides with the phase space approach. We show that the separation of time scales (energy redistribution vs decomposition) is large when the same conditions are met. Our analysis reduces to the Montroll–Shuler model for the decomposition of a diatomic molecule in a bath of inert atoms, in the appropriate limits.
Carbon-13 vapor pressure isotope effect in CHF3
Authors: Borodinsky Lester , Wieck Henry J. , Mayfield Darrell , Ishida Takanobu
Published: February 2003

The vapor pressure difference between 12CHF3 and 13CHF3 has been measured by means of a cryogenic distillation under total reflux at 11 temperatures between 161.2 and 204.6 °K. A second-order extension of Cohen’s column kinetics has been tested. The reduced partition function ratio obtained from the distillation data has led to a plot of T ln(fc/fg) vs 1/T, which displays a steep negative slope and points to a crossover at a temperature above those of the present experiment. The steep negative slope is due to strong external–internal interactions in liquid fluoroform, and the predicted crossover is a consequence of a blue shift in the C–H stretching frequency upon condensation of fluoroform.
Time resolved fluorescence of the A 2Σ+ state of GeF
Authors: Anderson R. A. , Hanko L. , Davis S. J.
Published: February 2003

The radiative lifetime and quenching rates for the A 2Σ+ state of GeF have been measured in the flame of GeH4+F2 by pulsed laser induced fluorescence. In addition, the radiative lifetime of the ν′=0 level of the A 2Σ+ state of SiF has been measured in the flame of SiH4+F2. Quenching rates for He, N2, and SF6 on GeF A 2Σ and He on SiF A 2Σ have also been determined. The average zero pressure lifetime of ν′=0, 1, and 2 levels of A 2Σ GeF is 990±100 nsec. The zero pressure lifetime of the A 2Σ state of SiF is 205±20 nsec. The average quenching rates for He, N2, and SF6 on GeF A 2Σ are 1.6×105, 6.4×106, and 8×105 sec−1 Torr−1, respectively. The quenching rate of He on A 2Σ (ν′=0) SiF is 6.5×104 sec−1 Torr−1.
Long and short range correlations in the Brownian motion of charged particles
Authors: Fulton Robert L.
Published: February 2003

Long range electrical forces are shown to produce a long range correlation of the dipolar type between the Brownian motion of charged particles in a conducting solution. A modification of the short range correlation of the displacement of the particles is shown to be associated with the long range correlation.
A perturbation theory calculation on the 1ππ* state of formamide
Authors: Nitzsche Larry E. , Davidson Ernest R.
Published: February 2003

A hybrid orbital basis and a partitioning perturbation theory procedure were developed to calculate the 1ππ* state of formamide. The calculated energies for the 1ππ* state are uncertain by about 1 eV with the predicted energies ranging from 6.96 to 8.21 eV. The 1ππ* state is extensively mixed with several Rydberg states. To calculate the true 1ππ* state this interaction must be properly accounted for and the calculations cannot be biased in favor of any one state. It is also shown that the common practice of using ground state or triplet ππ* orbitals to describe the 1ππ* state of amides is qualitatively incorrect and can lead to completely wrong conclusions.
Solid-state reaction kinetics in single-phase polymerizations
Authors: Baughman R. H.
Published: February 2003

The kinetics of single-phase solid-state polymerization reactions are evaluated using two different approximations for the effect of structural changes at intermediate conversions. Conversion curves are calculated for monomer phases which undergo large dimensional changes in the reaction direction (crystal strain approximation) and for monomer phases which are essentially dimensionally invariant during reaction (nearest neighbor approximation). Using the crystal strain approximation and experimentally derived elastic constants, the different autocatalytic reaction curves observed for thermal and radiation-induced polymerization of a diacetylenic monomer are successfully predicted. The dramatic autocatalytic effect for thermal polymerization can be explained quantitatively by a strain-dependent rate of chain initiation and chain propagation, while the weaker autocatalytic effect for γ-ray induced polymerization suggests that radiation-induced chain initiation is relatively insensitive to crystal strain. Chain propagation lengths as a function of conversion and the effects of external stress and impurities on reaction kinetics are also predicted using the model.
ESR investigations of VO2+ doped ferroelectric tris sarcosine calcium chloride
Authors: Sathyanarayan S. G. , Narayana M. , Sastry G. S.
Published: February 2003

ESR studies of vanadyl ions doped in ferroelectric tris sarcosine calcium chloride single crystals are carried out. The room temperature spectra indicate four magnetically inequivalent complexes which become equivalent along the crystallographic axes. The z axes of two of these correspond to two Ca–O bond directions, suggesting substitutional sites for the paramagnetic ion. The molecular orbital coefficients are estimated from the ESR and optical absorption data which indicate the complex to be ionic except for the extremely low value for e*π2. A new band is observed in the optical absorption spectrum which might be due to the b2↔a transition. The equivalency at room temperature is lost at liquid nitrogen temperature.