bluuebunny/crossref_metadata_2025 huggingface dataset:
Frequency dependence of the magnetoimpedance in amorphous CoP electrodeposited layers
Authors: Sinnecker J. P. , Knobel M. , Pirota K. R. , García J. M. , Asenjo A. , Vázquez M.
Published: July 2002

Magnetic properties and changes of impedance upon external field (MI) are studied in amorphous CoP magnetic layers obtained by galvanostatic electrodeposition over cylindrical Cu substrates. The magnetic layer thickness is controlled by deposition time and varies between 3 and 7 μm. Due to the columnar growth of Co, thicker layers have stronger perpendicular radial anisotropy. The field and frequency dependence of the impedance is measured in the kHz/MHz range. Although it is generally accepted that a radial anisotropy should be unfavorable to the MI effect, an increase of the MI ratio with the thickness of the magnetic layer, and thus with anisotropy, is observed. Results are explained in terms of a model considering the current distribution along the sample thickness with two well-defined regions having different transport and magnetic properties.
Silica glass: A material for photonics
Authors: Ikushima A. J. , Fujiwara T. , Saito K.
Published: July 2002

Recent studies on two aspects of silica glass as a photonic material will be described. Part A of this review will be focused on structural disorder and structural relaxations in silica glass. With regard to the structural disorder, investigations have been made to improve transparency and to shift the optical absorption edge in the ultraviolet towards shorter wavelengths. Remarkable advances have been achieved in the understanding of both light scattering, which is a dominant factor in the optical losses in silica fibers, and the absorption edge. Freezing of the structural disorder was observed, and structural relaxations are found to be important for improving the transparency, whereas for the absorption edge thermal vibration effects seem to be more predominant than the structural disorder. From the results, the present authors have tried to control the structural relaxation for developing silica glass with an ultimate optical transparency, finding that a very tiny amount of the proper impurity species gives rise to structural subrelaxations, which are effective in reducing the Rayleigh scattering. The scattering was reduced by 13% by addition of only 10 wt ppm Na2O, for example. In part B of this review the second-order optical nonlinearity induced in Ge-doped silica glass will be described based on recent experiments carried out by the group of present authors. A large second-order optical nonlinearity has been successfully induced in the glass by simultaneous applications of a high dc electric field and ultraviolet (UV) irradiation, so-called UV poling. The nonlinearity induced by UV poling in bulk and film samples has achieved a magnitude of χ(2), comparable to or even larger than those of LiNbO3 and other crystals. Surprisingly enough, the nonlinearity induced by this method then decays after the UV poling as an exact single-exponential function of time, very much unlike the usual decay processes observed in glasses. Evidence is presented associating the nonlinearity with GeE′ defect centers created from oxygen deficient vacancies through photochemical reactions. The decay or degradation can be made much slower with the addition of proper impurities which work as electron scavengers. In addition, we have found that crystallites are generated in the glass by the UV poling, which leads to an increase in the third-order nonlinearity, χ(3), approximately 15 times larger than before the treatment. As a whole, the evidence strongly suggests that a major origin of the second-order nonlinearity induced in the glass is a combined effect of a large third-order nonlinearity associated with the crystallites and an internal space-charge field, where the charges to build up the field are produced during the formation of GeE′ centers.
Application of action-angle variables to the calculation of the density matrix
Authors: Dawson K. A.
Published: July 2002

Using the analogy of action-angle variables in classical mechanics we introduce the notion of quantum actions in the calculation of the density matrix. The result is an integral representation of the density matrix in its semiclassical limit. This involves only the classical generating functions.
Brownian motion of molecules in pure gases and gas mixtures
Authors: Nanbu K.
Published: July 2002

The Brownian motion of molecules in gases is studied by use of three direct simulation methods. First, the correlation coefficient of velocity between two molecules is examined. The coefficient obtained by use of Nanbu’s method increases with time whereas that obtained by use of Belotserkovskiy and Yanitskiy’s or Bird’s method is null at any time. Next, the time-correlation function of velocity of molecules in pure gases is examined. The molecular model is of inverse power type. The functions from the three methods are essentially the same. When the number of simulated molecules is large, the function shows an exponential decay. The harder the molecular interaction, the greater the decay rate is. The self-diffusion coefficient resulting from the time-correlation function agrees with that of the Chapman–Enskog solution. In addition, the time-correlation function of molecules in gas mixtures is examined. The corresponding diffusion coefficient decreases with increasing the concentration of the heavy species whereas it increases with the concentration of the light species.
Conditional lifetimes in geminate recombination
Authors: Agmon Noam
Published: July 2002

In addition to overall mean lifetimes, with which one is well acquainted in the theory of reactive diffusion processes, mean conditional lifetimes for absorption in a given sink also have physical significance. In the theory of geminate recombination of nonisolated pairs, when one imposes an additional outer absorbing sphere, the conditional lifetime for absorption in the inner sphere is the risetime for the recombination products. In the theory of geminate recombination in an homogeneous scavenger concentration, both overall and conditional lifetimes are physically significant. The first describes reactants’ decay, the second products’ formation. We derive, in the backward equation formalism, equations governing the initial variable dependence of these lifetimes. We give the explicit solution for geminate recombination of neutrals (free diffusion). Experimental measurements of recombination lifetimes would supply new data, independent of the yields typically measured in such experiments.
Molecular motions and phase transitions in diammonium hydrazinium(+2) disulfate
Authors: Harrell J. W.
Published: July 2002

Diammonium hydrazinium(+2) disulfate, (NH4)2N2H6(SO)2, has been studied by proton T1 and T1ρ measurements from 123 up to 491 K. Phase transitions have been detected at 330 and 407 K. In the low-temperature phase the relaxation is determined by two types of reorienting NH+4 groups and one type of –NH3 group. An additional motion is evident in the T1ρ measurements just below the lower phase transition. The lower phase transition is characterized by a discontinuous change in the reorientation rate of the –NH3 groups and by the onset of translational diffusion of NH+4 ions. The upper phase transition is characterized by a rapid increase in the reorientation rate of the –NH3 groups and by a discontinuous increase in the rate of translational diffusion of the NH+4 ions. In the high-temperature phase the relaxation is governed by the reorientation and translational diffusion of NH+4 ions.
Memory function approach to electron thermalization
Authors: Nishigori T. , Sakai K.
Published: July 2002

A linear closed equation of the form ε̇(t)=ωε(t) +∫t0Λ(t−t′) ε (t′)dt′ is proposed to describe the nonlinear relaxation of electron energy ε(t) in the Lorentz gas. Higher-order memory functions associated with Λ(t) decay rapidly, and are easily amenable to approximation. Good numerical results for ε(t) suggest a useful extension of our memory function approach to many nonlinear problems for calculating various integral quantities.
Deuterium spin lattice relaxation studies of chloroform-d1 dissolved in mixtures of two thermotropic liquid crystals of opposite diamagnetic anisotropies
Authors: Jacobsen J. P. , Elmelund P.
Published: July 2002

The spectral density functions J1(ω0) and J2(2ω0) have been determined for CDCl3 dissolved in mixtures of N-(4-ethoxybenzylidene)-4′-n-butylaniline (EBBA) and Merck’s licristal ZLI 1167 of various compositions. The measurements have been performed by use of the Jeener–Broekaert pulse sequence at 9.2 and 46.0 MHz. The nematic director is parallel to the direction of the magnetic field at high content of EBBA in the mixture and perpendicular at low content. The molecular dynamic has been studied at the transition point between these two directions. It has been shown that contributions exclusively from molecular rotational diffusion motions and small angle director fluctuations cannot sufficiently account for all the experimental observations.
Palladium L
i
i
i x-ray absorption-edge structures of K2PdCl6, K2PdCl4, (NH4)2PdCl4, and trans-[Pd(NH3)2Cl2]
Authors: Sugiura Chikara , Muramatsu Shinji
Published: July 2002

The palladium Liii absorption spectra of complex compounds K2PdCl6, K2PdCl4, (NH4)2PdCl4, and trans-[Pd(NH3)2Cl2] have been measured with a 50 cm bent-quartz crystal vacuum spectrograph. A strong ‘‘white line’’ has been found at the absorption threshold and a few weak structures have been observed in the energy range of about 20 eV above the white line. These absorption structures have been interpreted in terms of molecular-orbital (MO) theory. The Pd Liii absorption spectrum of trans-[Pd(NH3)2Cl2] is somewhat different from those of K2PdCl4 and (NH4)2PdCl4 which are quite alike. The white line of K2PdCl6 shifts by 2.0 eV toward higher energies relative to that of K2PdCl4 or (NH4)2PdCl4. This chemical shift is due to the difference of the oxidation states of the palladium ions Pd2+ and Pd4+.
Excitation of Rydberg states of HgCl2 and HgBr2 by electron impact
Authors: Spence David , Wang R.-G. , Dillon Michael A.
Published: July 2002

We have examined the electronic structure of HgCl2 and HgBr2 from 5 to 14 eV by high resolution electron energy loss spectroscopy. Our measurements include the near-UV region which has not been examined by any previous technique and which is found to be rich in Rydberg states. In particular, in each molecule we identify members of two optically allowed Rydberg series and one forbidden series with electronic structues σ2gσ2uπ4uπ3g [npπu, npσu, and ndπg, or (n+1)sσg] which converge to the 2∏g ground ionic state. In addition, other structures which form the dominant energy loss mechanisms in our spectra are identified as arising from optically allowed Rydberg states associated with the excited ionic states 2Πu, 2Σu, and 2Σg. Measurements at energy loss below 9 eV confirm previous valence states observed in photoabsorbtion and suggest the existence of two new valence states in each molecule. Angular measurements facilitate identification of many of the newly observed structures in our electron-energy loss spectra.
A minimally dynamic approach to unimolecular decay: CCH and coupled Morse dynamics
Authors: Hamilton Ian , Brumer Paul
Published: July 2002

A technique for obtaining product distributions from unimolecular decay by doing a minimum amount of dynamics is described and shown to provide excellent results for model collinear systems and for RRKM and non-RRKM cases in the Wolf–Hase models of CCH decomposition. The technique allows for the inclusion of decay via long-lived trajectories without performing the dynamics. The results also provide a suggestive means of determining when RRKM-like theories will be applicable.
Complex Gaussian-type basis functions in the calculation of resonance energies and widths
Authors: Isaacson Alan D.
Published: July 2002

Basis set calculations of the energies and widths of several resonances in electron scattering by a one-dimensional model potential are carried out using real basis sets that are augmented with various choices for a long-range complex Gaussian-type function. The results show that neither the form of the complex basis function nor the behavior of the trial wave function near the origin are important for obtaining accurate results. In fact, excellent results are obtained with a modest basis set of real bound functions augmented with a single complex Gaussian orbital when the complex exponential parameter is chosen by a stationary condition and the calculation is stabilized with respect to the bound function exponential parameter.
A Raman scattering study of the pressure induced phase transition in s-triazine
Authors: Dove Martin T. , Ewen Peter J. S.
Published: July 2002

The pressure induced phase transition in s-triazine has been studied using Raman scattering. Some of the features observed in a previous Raman scattering study of the phase transition at atmospheric pressure have also been observed in the present case, and a preliminary analysis based on an estimated form of the pressure dependence of the order parameter is reported. However, the data presented in the present study can not yet be fully reconciled with the corresponding results at atmospheric pressure. It is suggested that some of the different theoretical ideas concerning the transition developed for atmospheric pressure and variable temperature could be applied in the analysis of the effects of pressure. No additional phases of s-triazine were observed at pressures up to about 30 kbar within the temperature range 15–295 K.
Entropy, Baierlein’s theorem, and spin-polarized hydrogena)
Authors: Lim T. K.
Published: July 2002

At low temperature and density and even if statistics are ignored, bulk gaseous spin-polarized hydrogen is shown to invalidate the conjecture of Baierlein that the Gibbs entropy of an ideal gas when pair-wise, velocity-independent interactions are assumed to be extant.
Piezomodulated Raman spectroscopy of molecular crystals: An experimental method for study of the anharmonic properties of solids
Authors: Luty T. , Eckhardt C. J.
Published: July 2002

Consideration of phonon-phonon coupling induced by strain serves as impetus for developing a theoretical structure for piezomodulated Raman spectroscopy which can be used for experimental realization of the coupling. The direct relation of the coupling constant to generalized stress Gruneisen parameters is shown. These describe the crystal’s anharmonic properties such as the thermal expansivity and the temperature dependence of the phonon energies. Numerical calculations are performed for anthracene crystal which exemplify the use of the stress Gruneisen parameters as sensitive measures of anisotropy of intermolecular interactions. Further development shows how the measurement can be used to determine these parameters and how piezomodulated Raman spectroscopy can be exploited to examine the anharmonicity of the lattice.
The application of the Wigner R-matrix theory to molecular collisions
Authors: Bocchetta C. J. , Gerratt J.
Published: July 2002

The Wigner–Eisenbud R-matrix theory is applied to molecular collisions. Previous attempts required a Buttle correction to accelerate slow convergence. The present theory makes use of radial basis functions which satisfy arbitrary conditions at the R-matrix boundary. At the same time within the boundary, the basis functions are eigenfunctions of a realistic effective radial Hamiltonian. Consequently, the radial basis set is slightly nonorthogonal. It is shown that this is sufficient to afford a rapidly convergent expansion which remains reliable both in the neighborhood of and far from resonances. The Buttle correction is no longer needed. The method is applied to a problem of collinear collisions between an atom and a diatomic molecule. Results are in excellent agreement with previous calculations.
Complete dipole oscillator strength distribution and its moments for N2
Authors: Kosman Warren M. , Wallace Scott
Published: July 2002

The complete dipole oscillator strength distribution for N2 has been calculated using the multiple scattering model. From this, the moments of the distribution S(μ) and L(μ) have been computed for −6≤μ≤2. The results are analyzed by decomposing the total moments according to the contributions from various subshells and also according to the contributions from various spectral ranges, e.g., discrete vs ionizing excitations. Since many physical properties depend on these moments, this analysis can pinpoint the spectral ranges with the greatest influence. Special attention is devoted to the distinctly molecular effects on the dipole oscillator strength distribution and its moments, particularly for those channels affected by shape resonances. The Rydberg series, for example, are significantly affected. This analysis offers an explanation for the weakness of certain dipole allowed Rydberg series and suggests a tentative new assignment for Worley’s third series.
Investigation of gaseous LiBO by Knudsen effusion mass spectrometry
Authors: Neubert A.
Published: July 2002

The reaction Li(g)+BO(g)=LiBO(g) has been studied by Knudsen effusion mass spectrometry. Heats of reaction ΔrH00 =(−332.5±5.0), (−317.4±5.0), and (−251.2±5.0) kJ mol−1 were determined for the linear structures Li–O–B and O–B–Li and for the bent structure (LiBO), respectively. These results are compared with values obtained theoretically.
Triplet-state decay kinetics of hydrated chlorophyll complexes
Authors: Alfano A. J. , Showell M. S. , Fong F. K.
Published: July 2002

The triplet-state lifetimes of Chl a⋅H2O, (Chl a⋅H2O)2, and (Chl a⋅2H2O)n aggregates were investigated by fluorometric techniques. A kinetic model is developed to account for the experimental observations. Evidence for the suitability of a four-level system is provided to include possible two-photon excitations involving an excited triplet state T2. In contrast to the dramatic dependence of the singlet-state lifetime of hydrated Chl a on the aggregate size, the triplet-state lifetimes of monomeric, dimeric, and polymeric Chl a aggregates in nonpolar hydrocarbon solvents are all found to be about 1.0–1.1 ms at temperatures <120 K. The experimental observations support a localized Chl a aggregate triplet-state interpretation for negligibly small triplet exciton interactions. Annihilation effects observed in (Chl a⋅2H2O)n are shown to be accompanied by shortening of the triplet-state lifetime, consistent with a four-level kinetic model.
Momentum eigenfunctions in the complex momentum plane. V. Analytic behavior of the Schrödinger equation in the complex momentum plane. The Yukawa potential
Authors: Lassettre Edwin N.
Published: July 2002

A method for solution of the Schrödinger equation in momentum space is described. If the Schrodinger equation in momentum space is represented by Oχ=0, where O is an integral operator and χ is the momentum function, the method involves two steps: (i) the representation of χ as a rational function of P and (ii) expansion of Oχ in a power series in some appropriately chosen variable t (‖t‖≤1) which is a function of P. Equating to zero the coefficients of the first N powers of t (which determines the eigenvalues) makes Oχ differ from zero by terms of order tN. As N increases the eigenvalues approach the correct limiting values if the method converges. Within its circle of convergence a power series converges for both real and complex values of the variable and hence the Schrödinger equation, an integral equation, is forced to hold for both real and complex values of the variable. This is in contrast to variational methods which involve only real values of the independent variable. To test the method the motion of a particle in the field of a Yukawa potential is studied. Only the lowest energy state is considered. Two extreme cases, involving linear combinations of rational basis sets, are studied. Both basis sets are complete but the power series method converges only for one basis set. For the other set the power series method provides an eigenvalue which oscillates around the correct value without approaching a limit but a variation method using the same basis set converges rapidly to the correct eigenvalue. The variation method succeeds because the function is defined only on the real axis while the power series method fails because, in the complex plane, the basis set can only represent a meromorphic function (one whose only finite singular points are poles) and the momentum eigenfunction cannot be meromorphic. Thus the choice of a wrong basis set in a variation method can completely conceal the true analytic nature of an eigenfunction. It is shown that momentum eigenfunctions are not meromorphic because they possess branch points. This is true not only for the Yukawa potential but for several one-electron models including the Hartree–Fock equations.
Comment on the stability of fcc and hcp hard-sphere solids
Authors: Kratky Karl W.
Published: July 2002

In a recent paper, the free energy difference per particle between fcc and hcp hard-sphere solids was calculated. This difference turned out to be very small in the thermodynamic limit so that no decision could be made as to which of the two phases is the stable one. This result is in apparent contradiction to another paper where it was claimed that the fcc solid is the stable one. Detailed inspection of the two papers shows, however, that the discrepancy can be removed.
Energy surfaces of low-lying states of C3
Authors: Jones R. O.
Published: July 2002

Density functional calculations have been performed for the energy surfaces of the ground state [1Σ+g(1A1)] and low-lying excited states [3Πu(3B1,3A1), 3Πg(3B2,3A2), 1Πu, 1Πg] of the C3 molecule. The experimental geometries and symmetric stretch frequencies of 1A1 and 1Πu states are reproduced well, and there is good agreement with CI calculations for the triplet states. The energy surface of the ground state is described qualitatively better than by CI calculations and does not show the unusual square-well form found in Hartree–Fock calculations. The splitting of the Born–Oppenheimer surfaces in the Π states (Renner–Teller effect) is discussed, and the qualitative features of the bonding presented in terms of the geometry dependence of the one-electron eigenvalues (Walsh diagrams). Together with earlier results for C2, the calculations provide insight into the unique features of the C–C bond.
Dissociation energies of diatomic molecules related to equilibrium bond lengths
Authors: Mucci J. F. , March N. H.
Published: July 2002

The problem of calculating dissociation energies of all but the lightest molecules remains a formidable one in quantum chemistry. However, the calculation of equilibrium internuclear distances is much simpler. Therefore, in this paper, we have explored whether the dissociation energies of diatomic molecules can be directly related to the nuclear–nuclear potential energy Vnn, plus molecular invariants. These latter quantities are the total number of electrons N and the ‘‘approximate’’ invariant, the total kinetic energy of the separated atoms, denoted by T. For chemically similar series, a marked correlation of D with Vnn/T is demonstrated, which for the N2, P2, etc. series can be represented approximately by D/N1/2=[300(Vnn/T)−6] kcal which would mean no binding above a limiting atomic number, lying higher, however, than those that span the Periodic Table. The existence of a minimum value of Vnn/T in groups of chemically stable homonuclear diatomic molecules is then contrasted with the situation in chemically similar series of heteronuclear diatomic molecules. Here, no minimum value of Vnn/T is found, due, it is argued, to the stabilization of these molecules by charge transfer.
A lattice gas model for enantiomeric phase separation
Authors: Huckaby Dale A. , Ausloos Marcel , Clippe Paulette
Published: July 2002

There are two nonsuperimposable mirror images (enantiomers) of a tetrahedral molecule consisting of a central carbon atom attached to four different groups, A, B, G, and H. We consider a lattice gas in which the two enantiomeric forms, d and l, are adsorbed onto a triangular lattice, such that the carbon atom is above a lattice site, the three bonds to A, B, and G are pointing toward neighboring lattice sites, and the bond to H points perpendicular to and away from the plane of the lattice. For a certain range of intermolecular interactions (such as may exist between the zwitterion forms of an amino acid) we prove, for a system which is equimolar in each enantiomer, that enantiomeric phase separation occurs at sufficiently low temperature and sufficiently high chemical potential. The phase diagram and critical point for the system are investigated using a first-order Guggenheim approximation.
Radiation damage in thiophene derivatives: ESR and ENDOR studies of x-irradiated 5-nitrothiophene 3-carboxaldehyde single crystals
Authors: Geoffroy M. , Celalyan-Berthier A. , Reddy M. V. V. S. , Bernardinelli G. , Papadopoulos M.
Published: July 2002

The crystal structure of 5-nitrothiophene 3-carboxaldehyde was determined. X-irradiation of these crystals, at 77 K, leads to the formation of a radical pair (D=−875 MHz, E=49 MHz) which exhibits hyperfine interaction with two protons. By using the structural information of the crystal structure together with the ESR tensors, it is possible to show that this pair is composed of an allyl-type radical and of a σ radical produced by a C–H homolytic scission. This pair disappears at 155 K. At 290 K a new species is created; the ENDOR analysis shows that this new radical results from a radical addition at the carbon bearing the NO2 group.
Fluorescence of benzyl chloride in the vapor phase
Authors: Ichimura Teijiro , Mori Yuji
Published: July 2002

Fluorescence spectra, fluorescence quantum yields, and fluorescence lifetimes of benzyl chloride vapor were measured at various excitation wavelengths. Values of the fluorescence quantum yield have an order of 10−4 and the fluorescence decay has been represented by a combination of two exponential functions.
Electronic properties of the liquid metal surface: Effect of ion profile
Authors: Goodisman J.
Published: July 2002

Self-consistent calculations are carried out for conduction electron wave functions and densities for Hg in the presence of a background of ion cores. From the ionic and electronic profiles we calculate surface potentials and work functions. A variety of ion core profiles are used. Electron densities and surface potentials are quite insensitive to the widths of the monotonic profiles used, except when they exceed several Bohr radii. In this case, however, the work function, which is lower than experiment by about a volt for a step-function profile, begins to decrease further. With one type of oscillatory profile, surface potentials change little, but with an ion profile resembling that suggested by D’Evelyn and Rice, a substantial increase in work function results and produces good agreement of calculated work function with experiment.
The deactivation of HF(v=3) by water
Authors: Bott Jerry F.
Published: July 2002

The deactivation rate of HF(v=3) by H2O has been measured at room temperature. It was found to be faster than the deactivtion rate of HF(v=1) by H2O by a factor of 3.6. On the basis of a previously reported measurement of the HF(v=1)–H2O by H2O is estimated to be 16 (Torr)−1, which is a factor of 3 faster than the hard sphere collision rate. The theoretical implications of this fast rate coefficient are reviewed. (AIP)
Analytic representation of the dipole oscillator-strength distribution. II. The normalization factor for electron continuum states in atomic fields
Authors: Dillon Michael A. , Inokuti Mitio
Published: July 2002

We address ourselves to the question what analytic formula is the most suitable for fitting the dipole oscillator-strength distribution df/dε over a wide range of the kinetic energy ε of an electron ejected from an atom or molecule. A suitable expression will enable one to interpolate or extrapolate data reliably and to use them readily in applications such as the modeling studies in radiation physics. It is useful to distinguish two factors that together constitute df/dε. The first factor is defined in terms of the dipole matrix element with respect to a final-state eigenfunction whose amplitude near the origin is independent of ε. As we showed earlier, this factor is analytic at all finite ε except at a singularity at ε=−I, where I is the ionization threshold energy. The other factor arises from the energy-scale normalization of the final-state eigenfunction, and is the object of the present discussion from several angles. First, we present a survey of numerical data for the s,p, and d states with 0≤ε≤5 a.u. for all atoms with Z≤38, evaluated within the Hartree–Slater potential model. Next, we discuss analytic properties of the normalization factor, which include its relation to the phase shift, and its behavior near a resonance. We also elucidate the connection of the continuum normalization with the bound-state normalization. Finally, we illustrate the significance of our findings in the practical fitting of the df/dε data in the presence of a resonance, taking the valence-shell ionization of Ar as an example.
Quantum ergodicity and a quantum measure algebra
Authors: Stechel E. B.
Published: July 2002

A quantum ergodic theory for finite systems (such as isolated molecules) is developed by introducing the concept of a quantum measure algebra. The basic concept in classical ergodic theory is that of a measure space. A measure space is a set M, together with a specified sigma algebra of subsets in M and a measure defined on that algebra. A sigma algebra is closed under the formation of intersections and symmetric differences. A measure is a nonnegative and countably additive set function. For this to be further classified as a dynamical system, a measurable transformation is introduced. A measurable transformation is a mapping from a measure space into a measure space, such that the inverse image of every measurable set is measurable. In conservative dynamical systems, a measurable transformation is measure preserving, which is to say that the inverse image of every measurable set has the same measure as the original set. Once the measure space and the measurable transformation are defined, ergodic theory can be investigated on three levels—describable as analytic, geometric and algebraic. The analytic level studies linear operators induced by a transformation. The geometric level is concerned directly with transformations on a measure space and the algebraic treatments substitute a measure algebra for the measure space and basically equate sets that differ only by sets of measure zero. It is this latter approach that is most directly paralleled here. A measure algebra for a quantum dynamical system is defined within which stochastic concepts in quantum mechanics can be investigated. The quantum measure algebra differs from a normal measure algebra only in that multiplication is noncommutative and addition is nonassociative. Nonetheless, the quantum measure algebra preserves the essence of a normal measure algebra.
On the ionicity of carbon in Be2C. A theoretical investigation of its electronic structure
Authors: Herzig P. , Redinger J.
Published: July 2002

A self-consistent APW band structure calculation for insulating Be2C is reported. From the APW results local partial densities of states have been obtained showing a considerable beryllium admixture in the carbon 2p band. An LCAO tight binding fit and a subsequent Mulliken analysis of the eigenvectors reveals that the carbon carries a charge of approximately 3.5 e. The electrons remaining on the beryllium atom are predominantly of p character giving rise to a covalent pp interaction which is responsible for pronounced features in the valence bands not present in a completely ionic description. A further analysis of the ionicity is made on the basis of a fit of the structure factors derived from the APW valence electron density using a superposition of atomic or ionic form factors. To obtain an optimum fit the electronic charge on the carbon has to be decreased to approximately 3.0. This reduction of charge, compared with the LCAO fit, is traced back to the fact that the atomic form factors have been calculated from a nonorthogonal basis, whereas an orthogonal one underlies the LCAO fit.
The heavy-atom effect in intramolecular vibrational energy transfera)
Authors: Swamy Kandadai N. , Hase William L.
Published: July 2002

Quasiclassical trajectory calculations were performed to understand intramolecular vibrational energy redistribution in tetraallyl tin and carbon. In these calculations a C=C bond initially contains 50, 75, 100, or 125 kcal/mol excess energy, with the remaining modes containing zero-point energy. For tetraallyl tin the trajectory calculations show rapid intramolecular vibrational energy redistribution within the allyl group containing the excited C=C bond. In contrast, energy transfer beyond the central tin atom is negligible for the initial C=C excitation of 50 kcal/mol. As the excitation is increased, energy transfer past the tin atom is enhanced. However, it is still incomplete within 4 ps for the calculation with a 125 kcal/mol excitation. A ‘‘pure’’ heavy-atom effect for intramolecular vibrational energy transfer is not observed. Simply substituting carbon for tin in the tetraallyl tin Hamiltonian has no detectable effect on the rate of the energy redistribution. However, energy redistribution is nearly complete within a picosecond for a Hamiltonian with a potential energy surface chosen to more accurately model that a tetraallyl carbon. The results of the trajectory calculations are compared with recent chemical activation studies of molecules containing heavy atoms, and other trajectory studies of intramolecular vibrational energy redistribution.
Thermal electron attachment to van der Waals molecules (O2⋅N2)
Authors: Toriumi Minoru , Hatano Yoshihiko
Published: July 2002

Electron attachment to van der Waals (vdW) molecules (O2⋅N2) has been investigated at temperatures from 77 to 373 K and N2 densities from 2.0×1018 to 3.5×1019 molecules/cm3 using a microwave conductivity technique combined with pulse radiolysis. The initial electron attachment rate constants to O2 and (O2⋅N2) are obtained as k1=(4.2+17−3) ×10−6T1.5 exp(−1017/T) cm3/s and k5=(3.4±0.4)×10−4T−1.5 exp[−(232±12)/T] cm3/s, respectively. The resonance energy for the electron attachment to (O2⋅N2) is reduced to 20±1 meV owing to polarization energy between O−2 and N2. The electron attachment rate constant for (O2⋅N2) is about 103 times larger than that for O2. The reason is: (i) the increase of electron density at the resonance energy for attachment; (ii) the increase of attachment cross section with decreasing the resonance energy; and (iii) that by vdW interaction partial-wave electrons with lower angular momentum can attach to vdW molecules. Since the resonance width for the electron attachment to (O2⋅N2) is larger (800±100 μeV), the (O2⋅N2)−* formed is easy to ionize. Experimental results at high pressures have shown collisional detachment of electrons from (O2⋅N2)−*.
Thermodynamic self-consistency for hard spheres at low density
Authors: Siders Paul , Kozak John J.
Published: July 2002

We consider the conditions on the triplet-distribution function g(3), and the pair-distribution g(2), sufficient that thermodynamic quantities calculated from g(2) be state functions. We show that g(3) cannot be, even to first order in density, equivalent to the Kirkwood superposition approximation. We obtain a g(3) that does yield a thermodynamically self-consistent g(2), to second order in density. We show that this g(2) differs little from the exact g(2), at that order. We also examine the low-density behavior of a partially self-consistent closure in which angular correlations appear explicitly. The latter closure is found to describe three-particle correlations well when two of the particles are in contact. A principal conclusion which follows from these studies is that the criterion of thermodynamic self-consistency is useful as a constraint in constructing closures, although it does not in itself determine a closure.
Viscosity effect on nonadiabatic isomerization and electronic relaxation of molecules in liquids
Authors: Villaeys A. A. , Boeglin A. , Lin S. H.
Published: July 2002

It is the aim of the present work to analyze the effect of solvent viscosity on nonadiabatic isomerization or electronic relaxation of molecules in liquids. Only the case with a sizable internal barrier is studied here. A quantum model is proposed to evaluate the rate constant of these processes in the overdamped and underdamped cases. The viscosity is introduced through the correlation function for the degrees of freedom that are coupled to the solvent and the correlation function is evaluated classically by using the phenomenological Langevin equation. In addition, the present approach takes into account the role played by other intramolecular degrees of freedom.
A generalization of the AGP model propagator to a reference state including different geminals
Authors: Sangfelt Erland , Goscinski Osvaldo
Published: July 2002

A geminal product (GP) of two different geminals g′(1,2)g′′(3,4) is compared to other GP’s of type g(1,2)g(3,4) and u(1)u(2)g(3,4) in an application to the ground state of Be. The factorization g′g′′ is remarkable since it gives, within the basis sets employed, the same total energy as a multiconfigurational self consistent field (MCSCF) calculation using the same configurations. A model wave function is chosen as an antisymmetrized product of an independent particle function and a correlated four-electron part. The latter consists of a multiconfigurational expansion restricted to pair substitutions of which the product of different geminals is a special case. We construct excitation operators that satisfy certain vacuum conditions for this reference state. In the case of four electrons this leads to a model propagator which is a direct generalization of a recently reported model propagator based on an antisymmetrized geminal power (AGP) reference state.
Removal of orbital degeneracy of the atomic P state for the matrix isolated metal atoms
Authors: Ruffolo Maria Grazia , Ossicini Stefano , Forstmann Frank
Published: July 2002

A theoretical study is made of the matrix effects on the absorption spectra of the noble metal atoms Cu, Ag, and Au isolated in Ar, Kr, and Xe matrices. The matrix influence which is discussed in terms of level shifts and additional crystal field splittings is calculated by a nonlocal pseudopotential method. In order to get a threefold splitting of the P level, we assume an axial symmetry for the metal atom site which is caused by a distorted neighborhood in a fcc matrix. This is the first theoretical investigation of the matrix cage distortion around the impurity. The results show that only small variations of the nearest neighbor distances between isolated atoms and matrix atoms are necessary to account for the observed matrix perturbations.
Solution of a modified wave equation for diffusion
Authors: Torkington P.
Published: July 2002

It is shown that if the wave velocity in the telegraph equation is made time-dependent simple solutions of the diffusion problem are allowed: c=λ−n/1−α(r/λ)2)m−1 for n dimensions, where λ=λ(t) and m=(α−1−n)/2. The coefficient α is a measure of deviation from classical behavior and determines the position of the boundary; α → 0 gives the usual exponential. Factors determining α are considered. With increasing α there are discontinuous changes leading to ‘‘hard’’ boundaries, which could possibly occur in a system that was sufficiently confined initially. (AIP)
Alkoxy radicals: Delta proton hyperfine couplings
Authors: Budzinski Edwin E. , Box Harold C.
Published: July 2002

Single crystals of rhamnose were x irradiated at 4.2 K and the ESR and ENDOR spectra taken at 1.6 K. A component of the ESR absorption arises from an alkoxy radical exhibiting an unusual delta proton hyperfine coupling. Parallels between the radiation-induced oxidation of certain carbohydrates and that of amino acids are pointed out.
Freezing in krypton monolayers adsorbed on graphite
Authors: Sokolowski Stefan , Steele William A.
Published: July 2002

The freezing of submonolayer krypton adsorbed on graphite is examined within the framework of recently proposed analysis of the nonlinear integral equation that relates the densities of the coexisting nonuniform surface liquid and solid phases. Density changes for freezing of the two-dimensional fluids were evaluated for various temperatures, liquid state densities, and values of the parameter characterizing the magnitude of the periodic part of the gas–solid interaction. It is concluded that the theory gives reasonable results which could be improved if more precise values for the structure factors of the fluid phase were available.
Example of a group action determined phase transition
Authors: Felix J. W. , Hatch D. M.
Published: July 2002

The principles of the group action approach to structural phase transitions are outlined. It is assumed that all properties of the transition are determined by the action of a single physically irreducible represention of the space group of the more symmetric phase. We determine the isotropy groups using the image space of the representation. The free energy minima are determined to fourth order and to all orders using the results of Gufan and then compared. This theory is applied to Calcite (R3̄c) to determine all possible continuous commensurate phase transitions.
A diagrammatic approach to ion neutralization at surfaces: On the validity of first-order perturbation calculations
Authors: Battaglia Franco , George Thomas F.
Published: July 2002

A theoretical investigation of ion neutralization from positive-ion scattering from surfaces is presented. Based on the time-dependent Fano–Anderson potential, a diagrammatic expansion of the reduced density matrix elements of the neutralized atom is given. Strictly speaking, the formalism holds only for systems in which the conduction band is completely empty, i.e., insulators, but conditions are given under which the formalism can be used for ion neutralization at metals. Calculations are performed for the simple case in which the atomic level is not degenerate. The validity of the first-order approximation is analyzed and its contribution to the neutralization probability is found to be dominant provided: (1) the discrete energy level of the atomic projectile is not embedded in the continuum of the valence band of the solid; and (2) the duration of the interaction is sufficiently short, i.e., the collision energy is high enough.
EPR study of acceptor doped p-terphenyl crystals: The oriented radical cation precursor for a conducting polymera)
Authors: Robinson Thomas , Kispert Lowell D. , Joseph Joy
Published: July 2002

Upon reacting gaseous SO3 or AsF5 with single crystals of p-terphenyl, the resulting π-radical cation is displaced from its original molecular position by a rotation of 64° about the rod axis and a tilt of 42° toward the c* crystal axis. Such action causes an eventual destruction of the crystal. This observation suggests that polymerization of p-terphenyl occurs between monomers related by a 21 symmetry axis.
Computation of chemical equilibria
Authors: Heuzé Olivier , Presles Henri-Noël , Bauer Pascal
Published: July 2002

A new method for the determination of the equilibrium composition of gaseous mixtures is described. This method is particularly suited for both manual or computer calculations and leads to fast convergence. The mathematical formulation is detailed and a numerical example shows the calculation procedure.
Qualitative propagator theory of CH3CN, CH3NC, and CH3CCH Auger spectra
Authors: Ortiz J. V.
Published: July 2002

A nonempirical two-electron propagator is employed in the characterization of molecular Auger spectra. Based on the Mulliken approximation for many-center Coulomb integrals, the model Hamiltonian requires three parameters for each valence atomic orbital: an exponent for a Slater function, an orbital energy, and an electron–electron repulsion integral. All of these quantities are taken from results of atomic calculations. Certain adjustments of resonance integrals are made to improve agreement with ab initio calculations of orbital energies. Forms of approximate two-electron propagators are discussed, with an emphasis on qualitative factors that assist in interpreting the results. Important orbital energy differences and electron repulsion integrals that govern final state configuration mixing are identified. Intensities for various final states are separated according to the atoms on which the Auger process is initiated for CH3CN, CH3NC, and CH3CCH. Information about local bonding environments is gathered from the calculations, especially spectral features that correspond to sp3 and sp hybridization schemes. Comparisons to the experimental CH3CN spectra are made; the theory helps to interpret the major spectral features. Regularities in the theoretical results are explained in terms of functional group molecular orbitals and electron repulsions.
Low-lying electronic states of nitrosyl cyanide (NCNO): An a
b i
n
i
t
i
o MCHF study
Authors: Dupuis M. , Lester W. A.
Published: July 2002

A b initio multiconfiguration Hartree–Fock calculations of the electronic structure of several low-lying electronic states of nitrosyl cyanide (NCNO) are reported. The essential features of the electronic structure of these states were analyzed to provide a qualitative correlation diagram for the dissociation process NCNO → NC+NO. It is found that the four lowest-lying states 1,3A′ and 1,3A′ are connected directly to ground state products. Excitation energies and geometrical parameters for these states and for the 2- 1A′ and 2- 1A′ states are presented. Implications of these findings for NCNO photodissociation processes are discussed.
Line shape theory for a Doppler-broadened signal in presence of an infrared pump
Authors: Ghoshal Sharmistha , Ghosh Pradip N.
Published: July 2002

A theory of line shape for a Doppler broadened probe in the presence of a strong infrared pump is presented. The optical analog of Bloch equations has been developed; the T1, T2 relaxations are introduced phenomenologically in these equations. Doppler broadening of both the pump and signal transitions are taken into account to obtain the absorption coefficient for the signal. This leads to a Doppler broadened Gaussian function weighted by a pump induced Lorentzian function whose position and linewidth are controlled by the detuning and power respectively of the pump radiation. The absorption coefficient is further modulated by a Lorentzian function containing the fourth power of the radiation. The off-resonance pumping leads to two symmetrically located ‘‘Lamb dips’’ or ‘‘peaks’’ around the Gaussian pedestal for co- and counter propagating laser radiations. A calculation of the line shape of the central sub-Doppler feature for the on-resonance pumping is in good agreement with the observed variation of linewidth with pressure. Numerical results are presented graphically to demonstrate the pump and signal power dependence of the central hole or peak for the bent and cascade-type double resonances. The results obtained confirm the expected behavior based on level populations.
1
3C NMR chemical shift and electronic structure of an infinite polymer chain as studied by tight-binding theory within the CNDO/2 framework: Polyethylene and c
i
s and t
r
a
n
s polyacetylenes
Authors: Yamanobe Takeshi , Ando Isao
Published: July 2002

Formulas for the calculation of the 13C NMR chemical shift of infinite polymer chains were derived by the tight-binding theory within the CNDO/2 framework incorporated with the sum-over-state method. This formalism was applied to the calculation of the 13C NMR chemical shift tensor of polyethylene and cis and trans polyacetylenes. The calculated results were found to agree with the experimental data.