bluuebunny/crossref_metadata_2025 huggingface dataset:
The electrical double layer. III. Modified Gouy−Chapman theory with unequal ion sizes
Authors: Valleau J. P. , Torrie G. M.
Published: February 2003

This article examines the consequence of assigning to the cations and anions different distances of closest approach to the charged surface, within the simple Poisson–Boltzmann theory of the diffuse part of the electrical double layer. This introduces asymmetry into electrocapillary and differential capacitance curves. It also leads to a diffuse double layer with zero charge on the surface, and thus to a concentration-dependent potential of zero charge (pzc). These phenomena are usually discussed in terms of solvent-structure next to the surface and of adsorption isotherms for anions on the surface, but it seems that a contribution to such effects must come from the diffuse layer itself.
The structure of liquid chlorine
Authors: Sullivan J. D. , Egelstaff P. A.
Published: February 2003

A neutron diffraction experiment was carried out to measure the structure factor of liquid chlorine at a series of three temperatures along the saturated vapor curve. The results of these experiments are shown, along with the pair correlation functions g(r) found by Fourier transforming the structure factors. By comparing the experimental pair correlation functions with calculations done using the interaction site approximation and with calculations of the low density limit of g(r), conclusions are drawn on a model potential and on the many-body contributions to g(r).
Time-resolved measurement of the escape of charge carriers from a Coulombic potential well by diffusional motion
Authors: Eichhorn M. , Willig F. , Charlé K. -P. , Bitterling K.
Published: February 2003

The irreversible escape of charge carriers from the bottom of a coulombic potential well over the barrier by diffusional motion has been measured, for the first time, directly as a rise time of 1 ns time-resolved current transients in anthracene single crystals with electrolytic contacts. The observed steep decrease in the characteristic escape time down to 1 ns, with rising electric field up to 1×105 V cm−1, is in excellent agreement with the predictions of a stationary one-dimensional charge carrier injection model with generalized boundary conditions. The electric field dependence of the rate constant for escape cannot be approximated simply by an exponential dependence on the barrier height, as in the familiar Schottky correction for the case of electron emission or in the Poole–Frenkel formula for change carrier escape from a charged trap. As a side result, the hole mobility in the c′ direction of anthracene single crystals has been found constant μ = 0.85±0.05 cm2 V s−1 up to an electric field strength of 5±105 V cm−1 at room temperature.
Applications of multiconfigurational coupled-cluster theory
Authors: Banerjee Ajit , Simons Jack
Published: February 2003

A coupled-cluster method which permits the use of multiconfiguration reference states has recently been developed in this laboratory. In the present work, it is applied to several states of H2 (1Σg+), Li(2S), HeH2(1A1), and CH2(3B1,1A1), which include both open and closed shells. These applications are made within an approximation in which the cluster operator (T) is truncated at T2, T≃T1+T2 and the expansion of e−THeT is truncated at the double-commutator level. For cases where a single configuration function ceases to be a good starting point, it is found that a single configuration based truncated coupled-cluster procedure may exhibit serious difficulties. In such cases we find it possible to choose a multiconfigurational reference state for which our coupled-cluster procedure converges reasonably rapidly. This paper contains several illustrations of such convergence characteristics.
NMR study of the behavior of hydrogen in vanadium hydride. I. Superstructure and diffusion of hydrogen in β-VH0.59
Authors: Hayashi Shigenobu , Hayamizu Kikuko , Yamamoto Osamu
Published: February 2003

The behaviors of hydrogen in β-vanadium hydride VH0.59 were studied by the 1H NMR spectroscopy. Fourier-transformed spectra, spin-spin relaxation times, and spin-lattice relaxation times were measured in the temperature range between 77 and 420 K, and it was found that there are two kinds of hydrogen which occupy different sites over the temperature range studied. The diffusional properties of each component were obtained, and the relation between the components and the superstructures of the hydrogen was discussed.
Chemiluminescence from reaction of group IIIa metals with F2 under crossed-beam conditions
Authors: Schwenz R. W. , Parson J. M.
Published: February 2003

The chemiluminescence from the title reactions has been studied under crossed-beam conditions at energies up to 24 kcal mol−1 by heating and seeding the F2 beam. Relative rates of formation of the product vibronic states have been extracted from several spectra at a range of collision energies to reveal vibrational population inversion as found previously in a beam–gas experiment [R.W. Schwenz, L.C. Geiger, and J.M. Parson, J. Chem. Phys. 74, 1736 (1981)]. Increased reactant translational energy goes preferentially to product translational and rotational energy. The rates of formation of the product electronic states have been determined as functions of collision energy, and indicate the absence of significant potential barriers or wells along the paths followed to excited state formation. All of the observations are consistent with reaction to form electronically excited products proceeding by a direct mechanism with mixed energy release.
Multistate vibronic coupling between the excited 2Π states of the NO molecule
Authors: Gallusser R. , Dressler K.
Published: February 2003

The fine-structure analyses of highly resolved low-temperature absorption spectra of four different isotopes of the NO molecule in the vacuum ultraviolet by Miescher and co-workers have revealed a wealth of detailed information, among other results, on the 2Π states of the npπ Rydberg series leading to the first ionization limit and on their interactions with the vibrational progressions of the excited valence states B 2Π and L 2Π. However, measured spectral lines remain unassigned and spectroscopic results on the higher members of the B and L progressions and on their interactions with the npπ Rydberg series are incomplete. The present work attempts a quantitative representation of the observations in terms of five electronic states with mutual electronic coupling, i.e., a so-called diabatic basis. The electronic states: two valence states B and L, and the lowest three Rydberg states of the npπ series C, K, and Q are defined by RKR potential curves, by spin-orbit coupling constants, by electronic absorption dipole transition moments, and by six R-independent electronic valence-Rydberg interaction energies. The coupling is treated with a vibronic interaction matrix which includes the bound vibrational levels of these five electronic states up to the dissociation limit of the B 2Π state, i.e., a total of 69 vibrational levels in each of the two 2Π spin doublets and in each of three different isotopes. The calculated results include vibronic energies, B values, absorption oscillator strengths, and, for a few selected levels, detailed rotational structures. Assignments of v in the vibrational progression of the B state to observed structures in the spectrum have been extended up to v = 37, i.e., to within 226±30 cm−1 of the dissociation limit. The electronic valence-Rydberg interaction energies are found to decrease along the Rydberg series approximately proportional to n*−3/2. The quantitative relationship between the spectroscopically determined two-state interaction energies and the corresponding calculated matrix elements is clarified. Assignments of observed features to a vibrational progression of a valence state L 2Πi with a large spin-orbit coupling constant are confirmed and the positions of unobserved spin components are predicted.
Effect of the internal rotation of the CHD2 group on the aliphatic CH stretching mode of the toluenes C6H5CHD2 and C6D5CHD2 in solid crystalline phases
Authors: Cavagnat D. , Lascombe J.
Published: February 2003

The infrared and Raman spectra of the toluenes C6H5CHD2 and C6D5CHD2in the aliphatic CH stretching mode range have been recorded in a large temperature range (17 to 165 K) for both crystalline phases α and β. At very low temperature, the β form spectra show three bands; each of them is assigned to the vibration of a CH oscillator localized in a different site. Three groups of bands are also observed in the α phase spectra: a single band at higher frequency and two doublets at lower frequency. This splitting is assigned to the existence of two types of molecules in the unit cell, involving six different CH vibrators. A quantum theory of these spectra is carried out, assuming an anharmonic coupling of the CH stretching mode with the CHD2 torsion. As a consequence of this coupling, in the adiabatic approximation, the vibrational energy depends on the conformation and can be considered as an additional torsional potential. This latter has no ternary symmetry so that the total torsional potential has three principal unequal wells that correspond to three different locations of the CH oscillator. Therefore, no tunneling effect appears, which is in agreement with the classical interpretation. Furthermore, this theory ascribes the temperature dependence of the relative intensities of the νCH bands to the population density of the first torsional levels in the vibrational ground state and suggests that, at very low temperature, the isotopic system gets ordered. At higher temperature, a strong relaxation of the νCH vibration bands is observed. This relaxation is much stronger than that of the aromatic ring modes. Thus the relaxation process is essentially due to the influence of the anharmonic coupling between the CH stretching mode and the τCHD2 mode. Two mechanisms are considered: the first one involves Markovian jumps of the system from an equilibrium position to another one, the second one involves fluctuations of the CH vibration around each of these equilibrium positions. NMR and neutron scattering data have already been analyzed on the basis of the first process. Starting from the residence times so determined, the computations show that this mechanism is an efficient relaxation process, but indicate that it is not sufficient to fit the experimental profiles. This fit is obtained rather by using the second model with parameters of reasonable physical values; thus, the second process is also efficient. A better treatment of the relaxation process would be to elaborate; it would have to include both mechanisms and to take into account motions of the methyl group with different amplitudes.
The study of order, disorder, nucleation, and energy changes at surfaces using a He beam
Authors: Mason B. F. , Caudano R. , Williams B. R.
Published: February 2003

He scattering from Cu(001) and adsorbed layers of Kr, Xe, and CO has been studied. It is shown here how the various components of scattering, namely the one-phonon inelastic, the coherent elastic, and the off-specular incoherent elastic yield information on surface modes of vibration and the mechanism of condensation and nucleation. Changes induced in the surface, such as defects due to ion bombardment and adsorption of a containment layer are shown to influence the various components of scattering.
Vibrational relaxation in ground state p-difluorobenzene: Single level preparation by stimulated emission pumping
Authors: Lawrance Warren D. , Knight Alan E. W.
Published: February 2003

We have measured the cross section for vibrational relaxation from the 52302 level (εvib = 2036 cm−1) of S0 p-difluorobenzene (pDFB) due to pDFB-pDFB collisions. Stimulated emission pumping has been used to selectively populate the 52302 level. Single vibronic level fluorescence from the S1 level 302, generated by exciting the 5023022 transition at a variable delay time after 52302 has been populated, has been used to monitor the population dynamics of 52302. We obtain a value of 4±1×107s−1 Torr−1 for the vibrational relaxation rate coefficient, a value which is 2–3 times the hard sphere value. This large cross section is consistent with the cross sections observed in S1 benzene but is an order of magnitude larger than the cross sections observed previously for a variety of molecules in the ground electronic state. (AIP)
Catalytic intermediates in the Ag–O2 system. Evidence for a nonsymmetric AgO2 molecule
Authors: Tevault D. E. , Smardzewski R. R. , Urban M. W. , Nakamoto K.
Published: February 2003

Matrix isolated infrared spectra of AgO2 in Ar matrices is presented and a normal coordinate analysis of AgO2 is performed. (AIP)
The pure rotational spectrum and hyperfine structure of CF studied by laser magnetic resonance
Authors: Saykally Richard J. , Lubic Karen G. , Scalabrin Artemio , Evenson Kenneth M.
Published: February 2003

Laser magnetic resonance spectra have been measured for four rotational transitions and one spin-changing transition in the 2Π ground state of CF, generated in an intracavity methane–fluorine flame. From a detailed analysis of the Zeeman hyperfine structure of the J = 9/2→11/2 transition in the Ω = 3/2 spin component the hyperfine constants h, b, and d as well as B0 and q0 have been determined. Using these fitted parameters in conjunction with ab initio results, the values of 〈1/r3〉, 〈(3 cos2ϑ−1)/r3〉, ‖ψ2(0)‖, and 〈(sin2ϑ)/r3〉, averaged over the unpaired electron distribution, have been determined. Comparison of these integrals with those of the fluorine atom indicates that the unpaired electron has approximately 18% F character, implying a substantial degree of double bonding.
The electronic structure of CuFeS2, chalcopyrite, from x-ray emission and x-ray photoelectron spectroscopy and Xα calculations
Authors: Tossell J. A. , Urch D. S. , Vaughan D. J. , Wiech G.
Published: February 2003

The x-ray emission spectra (SKβ, SL, CuKβ, CuL, FeKβ, FeL) and x-ray photoelectron spectra of CuFeS2 chalcopyrite are reported and are interpreted using SCF-Xα MO calculations on the polyhedral anions CuS−74 and FeS−54 and discrete variational Xα band structure calculations. The highest energy occupied orbitals are found to be of Cu3d-S3p antibonding character. Substantial Fe3d character is observed across a broad range of binding energies indicating strong mixing of the Fe3d orbitals with both the Cu3d and S3p. Both the Xα cluster calculation on FeS−54 and the Xα band structure calculations overestimate the Fe3d orbital binding energies, although the discrepancy is smaller in the band calculation. Both computational methods predict the lowest energy empty orbitals to be of Fe3d-S3p antibonding character with a small (<2 eV) separation from the highest occupied orbitals. This small energy difference provides a possible explanation for the metallic conductivity observed in CuFeS2 at high pressure, particularly if the CuT–S bond is more compressible than the Feiii–S as is expected from compressibility-formal charge systematics.
State selected ion–molecule reactions by a TESICO technique. IV. Relative importance of the two spin-orbit states of Ar+ in the charge transfer reactions with N2 and CO
Authors: Kato Tatsuhisa , Tanaka Kenichiro , Koyano Inosuke
Published: February 2003

Charge transfer reactions Ar+ (2PJ)+N2→N+2+Ar (1) and Ar+(2PJ)+CO→CO++Ar (2) have been studied for the two spin-orbit states (J = 3/2 and 1/2) separately using the threshold electron-secondary ion coincidence (TESICO) technique. Relative cross sections for the two states σ(3/2) and σ(1/2) have been determined at three collision energies 0.2, 1.4, and 5.8 eV. It has been found that in Reaction (1), σ(3/2) is larger than σ (1/2) with ratio σ(1/2)/σ(3/2) ranging from 0.5 to 0.8 depending on the collision energy, whereas in Reaction (2), σ(1/2) is larger than σ(3/2) with the ratio ranging from 1.2 to 1.6. The implications of these results are discussed with regard to the roles of energy resonance and Franck–Condon factors in charge transfer processes.
Cubic contributions in multiconfigurational self-consistent-field (MCSCF) calculations
Authors: Olsen Jeppe , Jo/rgensen Poul , Yeager Danny L.
Published: February 2003

We discuss implementation of cubic contributions in multiconfigurational self-consistent field (MCSCF) calculations. We explicitly demonstrate that, far from convergence, an iterative cubic technique can often eliminate the need for constraint procedures. Chebyshev (perturbative) and recursive (two-point fixed Hessian) cubic techniques are shown to be useful for local, but not global convergence.
Valence effective Hamiltonian study of the electronic structure of poly(p-phenylene) and poly(p-phenylene sulfide)
Authors: Brédas J. L. , Chance R. R. , Silbey R. , Nicolas G. , Durand Ph.
Published: February 2003

The parametrization of atomic potentials for sulfur is presented in the framework of the valence effective Hamiltonian (VEH) technique for polymers. The VEH method is applied to band structure and density of states calculations on poly(p-phenylene) and poly(p-phenylene sulfide), compounds of interest with regard to the conducting polymers area. The quality of the electronic structure description afforded by the VEH technique is demonstrated via a comparison of experimental XPS spectra for these polymers with spectra predicted theoretically. The ionization potential of poly(p-phenylene sulfide) is predicted to be 0.7 eV higher than poly(p-phenylene) in good agreement with experimental estimates.
Generalization of analytic configuration interaction (CI) gradient techniques for potential energy hypersurfaces, including a solution to the coupled perturbed Hartree–Fock equations for multiconfiguration SCF molecular wave functions
Authors: Osamura Yoshihiro , Yamaguchi Yukio , Schaefer Henry F.
Published: February 2003

Analytic configuration interaction gradient techniques for multiconfiguration self-consistent field (MCSCF) wave functions have been developed by solving the coupled perturbed equations for the generalized Hartree–Fock operator. The method has been implemented in conjunction with the loop-driven graphical unitary group approach for the determination of correlated wave functions. This theoretical approach is in principle applicable to any type of configuration interaction (CI) wave function constructed from orbitals determined from a rigorous SCF or MCSCF procedure. Initial applications have been to CI wave functions involving all single and double excitations relative to an open-shell singlet restricted Hartree–Fock reference function. The specific example chosen was the first excited singlet state (b 1B1) of CH2, for which the equilibrium geometry and harmonic vibrational frequencies have been predicted with a double zeta plus polarization basis set.
Separated pair approximation and electron correlation in linear polyenes
Authors: I’Haya Y. J. , Suzuki Hiroo , Narita Susumu
Published: February 2003

A separated electron pair approximation is reformulated from a variation-perturbation point of view. A new method is proposed for determining optimum pair functions (geminals) under the strong orthogonality condition between occupied and virtual geminals. A simple formula for correlation energies is obtained, which can be easily calculated after solving simultaneous equations built from the zeroth order occupied and virtual geminals. Numerical application is made to linear polyenes within the π electron approximation. It is shown that the geminals built from localized orbitals yield larger correlation energy than those built from canonical orbitals and the former lead to the additivity of correlation energies.
Direct first principles algorithm for the universal electron density functional
Authors: Freed Karl F. , Levy Mel
Published: February 2003

An explicit formula is provided giving a formal derivation of the exact universal electron density functional. This abstract theorem enables the derivaton of a funcional Taylor series expansion of this density functional about a reference density. Although wave funcion methods are used in the derivation, the final quantities may be evaluated by a variety of methods including nonwave fuction many-body methods.
Legendre transforms and Maxwell relations in density functional theory
Authors: Nalewajski Roman F. , Parr Robert G.
Published: February 2003

The Hohenberg–Kohn principle of the minimum ground-state energy density functional E[N,v]=Ev[ρ]≡F[ρ]+ ∫ v(1)ρ(1)dτ1, min{Ev[ρ′]−μN[ρ′]}, is reformulated in forms appropriate to the alternative Legendre transformed representations of the system energy. The quantities ρ and N[ρ] denote the one-electron density and associated number of electrons, while v and μ stand for the external and chemical potentials, respectively. The following natural Legendre transformed functionals are introduced: Q[μ,v]=E−(∂E/∂N)cN=Q[ρ]≡F[ρ]− ∫ [δF/δρ(1)]ρ(1)dτ1,F[N,ρ]=E− ∫ [∂E/∂v(1)]cv(1)dτ1=F[ρ], R(μ,ρ)=E− ∫ [∂E/∂v(1)]cv(1)dτ1−(∂E/∂N)cN=R[ρ], where c implies all variables kept constant except for the one in the derivative. The Maxwell relations for these representations are derived and their physical implications briefly discussed. Corresponding ’’thermodynamic’’ mnemonic square diagrams are introduced to generate the differential expressions and selected Maxwell relations. A typical Maxwell relation is [∂ρ(1)/∂v(2)]N,v≠(2)=[∂ρ(2)/∂v(1)]N,v≠(1). It is shown that, as in classical thermodynamics, the extremum principle for each of these basic functionals of state L[g,l](L=E,Q,F,R; g=N,μ; l=v,ρ) can be formulated as follows: The equilibrium value of any unconstructed internal variable of a system specified by its global g and local l parameters, minimizes the L[g,l] Legendre transform of the system energy, at constant g and ℓ. It is shown that the F[N,ρ] minimum principle is equivalent to the Levy variational principle F[ρ]=min <ψρ‖T̂+V̂ee‖Ψρ≳, which may be interpreted as a process determining the system chemical potential.
Low-lying valence and Rydberg states of nitric oxide NO. Configuration interaction studies
Authors: Grein Friedrich , Kapur Anil
Published: February 2003

Large scale SCF and CI calculations have been performed on the ground and low-lying valence and Rydberg states of nitric oxide. Different basis sets (double zeta, double zeta plus polarization, and double zeta plus polarization plus diffuse functions) have been used, and for each state energies have been obtained over a range of internuclear distances. Spectroscopic constants have been calculated via a fourth-degree polynomial fit. Agreement with experimental values is good. The calculated Te is usually 0.3–0.4 eV below the experimental value for valence states, whereas for Rydberg states it is within 0.1 eV. The largest deviation for dissociation energies is 0.75 eV, for the X 2Π state. A third stable 2Π state, suggested by previous theoretical work, has been confirmed.
The viscosity of supercooled aqueous solutions of ethanol and hydrazine
Authors: Halfpap B. L. , Sorensen C. M.
Published: February 2003

We have measured the shear viscosity of solutions of ethanol and hydrazine in water into the supercooled region. Two techniques were used: Poiseuille flow measurements in the range 75°–17.5 °C and photon correlation spectroscopy of light scattered from diffusing microspheres suspended in the solutions in the range from 20 °C down to nucleation. We have found that addition of hydrazine tends to diminish any anomalous increase in the viscosity of supercooled water, an effect similar to that seen in other types of measurements. Addition to ethanol, on the other hand, enhanced the viscosity. This was interpreted to indicate that the cagelike clathrate structures known to be found in aqueous ethanol solutions are also found in pure water and may be responsible for the anomalous properties of supercooled water which have recently been discussed in the literature.
Ionized impurity induced photocarrier generation in organic energy conversion systems
Authors: Popovic Zoran D.
Published: February 2003

Due to the high density of impurities, Schottky barriers in organic semiconductors usually have quite thin depletion regions, of the order of a few hundred angstroms. For typical built in potentials of few tenths of a volt, the average field in the barrier is of the order of 10 V/μm. In this paper, the influence of the localized nature of the ionized impurities on field dependent carrier generation will be investigated. Assuming the existence of exciton diffusion, it will be shown that carrier generation due to a strong local field of ionized impurities can far exceed the generation efficiency predicted on the basis of the average electric field in the barrier. The concept of exciton drift currents will be introduced, which will lead to a unique light collection mechanism by exciton funnelling to the ionized impurities, thus increasing further the probability of photocarrier generation. Experimental evidence will be presented which indicates that the ionized impurity induced carrier generation is the dominant mechanism of carrier production in x-metal-free phthalocyanine photovoltaic cells. The analogy between the proposed mechanism and photosynthesis will be discussed. It will be suggested that the assumption of a charged ’’special pair’’ could naturally explain the low probability for the back reaction in the chain of primary photosynthetic events.
The effect of the metal atom on the absorption spectra of phthalocyanine films
Authors: Davidson A. T.
Published: February 2003

The visible and near ultraviolet absorption spectra have been measured for thin films of H2Pc [C32H18N8], MgPc, FePc, CoPc, CuPc, and ZnPc. Magnesium and iron phthalocyanine have very different absorption spectra. For most of the phthalocyanines, structure of magnitude 0.21 eV is seen on the visible and Soret bands. A d band is indicated in the region 4.0–4.7 eV. This is the spectral region most sensitive to substitutions of the central metal atom.
On the semiclassical calculation of molecular absorption and fluorescence spectra
Authors: Mukamel Shaul
Published: February 2003

A semiclassical expansion is developed for the direct calculation of molecular electronic (absorption and fluorescence) spectra without having to calculate the molecular vibrational eigenstates. The expansion is based on expressing the necessary dipole correlation functions (which do not have a straightforward classical analog) in terms of a hierarchy of other intramolecular correlation functions which do have a simple semiclassical expansion. To lowest order in h/ the spectra may be calculated by running classical trajectories on a zero-order Hamiltonian Hc. The present semiclassical expansion is not unique and depends on our choice of Hc. This arises since the spectra are not analytic functions of h/. Applications are made to the absorption and to the fluorescence spectra of polyatomic molecules (single- and two-photon processes). The present method may be easily generalized to other multiphoton processes.
N+2(A→X) and N+2(B→X) fluorescence excitation spectra by photon impact
Authors: Tabche-Fouhaile A. , Ito K. , Nenner I. , Fröhlich H. , Guyon P. M.
Published: February 2003

N+2(A 2Πu→X 2Σ+g) and N+2(B 2Σ+u→X 2Σ+g) fluorescence excitation spectra were measured using synchrotron radiation from threshold to 38 eV. Rydberg series converging to N+2 B 2Σ+u is seen to autoionize, with a 85% branching ratio into the A 2Πu continuum. For series converging to B 2Σ+u(v = 1), vibrational autoionization observed into the B(v = 0) continuum, is shown to compete efficiently with electronic autoionization. Above 20 eV, Rydberg series converging to N+2, C 2Σ+u as well as a number of unidentified resonances are shown to be coupled to each or both the A and B ionization continua.
Divalent europium as a paramagnetic probe to study strontium precipitates in monocrystalline sodium chloride
Authors: Murrieta S. H. , López F. J. , García-Solé J. , Aguilar G. M. , Rubio O. J.
Published: February 2003

Precipitation of divalent strontium ions in NaCl has been investigated using Eu2+ as a paramagnetic probe. The results presented in this paper show that the annealing of the quenched samples at 200 °C produces the formation of the precipitated dihalide phase SrCl2 in the NaCl matrix. The EPR data established that the Eu2+ ions are located inside this precipitated structure and that they are substituting the host cation Sr2+ ions. However, the observed EPR spectrum shows a significant difference with respect to that reported for the same impurity ion in SrCl2 single crystals, i.e., the value for the cubic spin-Hamiltonian parameter b40 is larger and its magnitude seems to decrease as the particle size of the precipitate increases. On the other hand, annealing of the quenched samples at room temperature produces another precipitated phase. In this case, the EPR data reveal that the Eu2+ ions also occupy a cubic symmetry site in this precipitated structure. However, the value for the b40 parameter describing this cubic site is considerably smaller than the one measured for Eu2+ in SrCl2. Finally, an EPR spectrum, observed in the fast quenched samples, possessing axial symmetry and probably due to Sr2+–Eu2+-vacancy complexes is presented. Values for the spin-Hamiltonian parameters describing this new spectrum are also reported.
Surface infrared and surface enhanced Raman vibrational spectra of monolayer assemblies in contact with rough metal surfaces
Authors: Knoll Wolfgang , Philpott Michael R. , Golden William G.
Published: February 2003

Surface infrared and surface enhanced Raman spectroscopy have been used to obtain the vibrational spectra of monolayer assemblies of cadmium arachidate in contact with a variety of rough silver surfaces. The assemblies were laid down by the Langmuir–Blodgett monolayer deposition technique. The Raman spectra of these assemblies in contact with silver islands show evidence of conformational disorder, i.e., the alkyl chains are not in the all trans configuration. In contrast, the infrared spectra do not show evidence of similar disorder. These results and others, described in the text, are explained by assuming that the infrared photons sense the majority undistorted molecular species, while the Raman photons come from a distorted minority species located in regions where optical electromagnetic fields are enhanced by shape effects, plasmon resonances, etc., of the rough silver surface.
VUV laser photofragmentations of an acrylonitrile molecular beam: One-, two-, and three-photon processes
Authors: Nishi Nobuyuki , Shinohara Hisanori , Hanazaki Ichiro
Published: February 2003

A laser induced photofragmentation study at 193 nm has been made by detecting the fragments directly through a mass spectrometer and by observing the high resolution emission spectra of fragments from acrylonitrile. Time-of-flight (TOF) signals are observed at mass numbers of 27, 26, 25, 24, and 13. They are assigned to primary photofragments produced via the dissociation C2H3CN+hν→C2H3+CN, and via the molecular elimination C2H3CN+hν→C2H2+HCN, and to the products of secondary fragmentation of the primary photofragments produced in the ionizer. The TOF spectra are analyzed as superpositions of two thermalized components at the characteristic temperatures of 2500 and 6000 K for the dissociation and the molecular elimination processes, respectively. The angular distribution of fragments with respect to the polarization direction of the laser beam is found to be isotropic. None of the TOF signals show a higher order dependence of intensities on the photon flux. Two-photon excitation produces emission due to the CN(A 2Πi→X 2Σ+) transition with a lifetime (τ) of 7.1±0.6 μs and due to the CN(B 2Σ+→X 2Σ+) transition with τ = 65±2 ns. The vibrational distribution in the A 2Πi state is found to be highly nonstatistical with maximum population around the v = 9 level which is close to the origin of the B 2Σ+ state. The vibrational and rotational populations of CN(B 2Σ+) are almost thermalized at characteristic temperatures of 5860±420 and 2830±25 K, respectively. Three-photon excitation produces emission of C2(d3Πg →a3Πu) with a lifetime of 111±5 ns. The vibrational temperature is observed to be 7150±160 K and the rotational one to be 4960±150 K. The third photon also pumps the CN(A 2Πi) radical in its highly excited vibrational states generated by two-photon excitation to the E 2Σ+ and the F 2Δr states. Possible multiphoton fragmentation processes are presented based on the observed internal energies of the fragments.
Laser photofragment study of isomeric C4H6+ cations at 5145 Å
Authors: Preuninger F. N. , Farrar J. M.
Published: February 2003

We present a study of the isomerization of seven isomeric C4H6+ cations using laser photofragment spectroscopy. Parent ions created by electron impact intersect the 5145 Å beam of an argon ion laser and the C3H3+ photofragments, the only fragments observable, are energy-analyzed by an electrostatic analyzer. On the basis of C3H3+ photofragment recoil spectra, we argue that five isomerically distinct neutrals 1,3-butadiene, 1,2-butadiene, cyclobutane, 1-methylcyclopropene, and 3-methylcyclopropene, form parent ions which appear to rearrange to a common precursor prior to fragmentation. Neither 1-butyne nor 2-butyne cations photodissociate at this wavelength. The dienes 1,3-butadiene and 1,2-butadiene show a minor fragmentation channel to a higher energy product, which we hypothesize to be the propargyl cation. The very high kinetic energy release upon fragmentation (most probable values of 100–200 MeV) cannot be rationalized on the basis of a statistical model of vibrational predissociation in the ground electronic state. The results are also inconsistent with PIPECO fragmentation studies of 1,3-butadiene ions at comparable excess energies, in which substantially lower kinetic energy releases, consistent with a statistical theory, were observed [Klots, Mintz, and Baer, J. Chem. Phys. 66, 5100 (1977)]. We argue that the high translational energy release observed here is consistent with excitation to the first excited state of the parent cation on a portion of the potential surface, which is coupled strongly to a repulsive potential whose barrier is preferentially disposed of in product kinetic energy.
Diffusion controlled reactions of gases with surfaces and state dependent reactivity
Authors: Hess Siegfried , Monchick Louis
Published: February 2003

Particles with two internal states are considered where the particles diffuse toward a spherical surface and react with a frequency dependent on the internal state. The steady state reaction rate is seen to be an observable function of the state dependent reactivity and the rate of transitions between the states. Since the transition rate can be either spontaneous or induced, say, by a magnetic field, the possibility exists of disentangling the molecular parameters by a set of experiments suitably designed. Most of the results are unchanged when a distribution of particle surfaces with varying reactivity is considered.
Optically pumped cw molecular bismuth laser
Authors: Drosch S. , Gerber G.
Published: February 2003

Continuous laser oscillation of diatomic bismuth molecules was observed. The gaseous Bi2 was optically pumped on individual vibrational-rotational lines of the A–X band system by several single mode lines of a stabilized Ar+ laser. More than 150 Bi2 laser transitions are observed in the wavelength range between 590 and 790 nm and assigned to the A–X system. Laser power conversion efficiencies of up to 15% for broadband laser emission and up to 2.5% for single frequency laser emission were observed. Maximum Bi2 laser power was 150 and 25 mW, respectively. Low pump thresholds of the order of 40 mW are observed for single mode pumping of the strongest lasing transitions. Gain was determined from maximum output coupling to g≊0.02 cm−1. Using the optically pumped cw Bi2 laser as its own probe we measure the hyperfine structure of the Bi2(A–X) v′ = 17−v\ = 40 P(256) transition.
Theory of extended x-ray absorption fine structure: Single and multiple scattering formalisms
Authors: Boland John J. , Crane Stephen E. , Baldeschwieler John D.
Published: February 2003

A generalized formalism for the EXAFS effect is presented. The full T operator in the Lippmann–Schwinger equation is expanded and the first term and part of the second term are seen to effectively correspond to single scattering EXAFS processes. The latter term includes secondary scattering by the absorber, and within this formalism it is this term that introduces the central atom phase shift. The expression obtained for the single scattering problem is identical with that found by other investigators. A solution to the general EXAFS problem involving an absorbing atom and two neighboring atoms is also presented. The expression differs from that previously reported [B. K. Teo, J. Am. Chem. Soc. 103, 3990 (1981)]. Multiple scattering is seen to contribute increasingly to the EXAFS as the three atoms approach colinearity. Both the amplitude and frequency of the multiple scattering components are functions of the geometry of the system. The model systems studied indicate that, in many cases, multiple scattering effects must be considered in the analysis of non-nearest-neighbor shells. The theory may readily be extended to systems and scattering paths of arbitrary complexity.
Franck–Condon factors with vibration–rotation interaction for Morse oscillators
Authors: Ramjee M. , Rao M. L. P. , Rao D. V. K. , Rao P. T.
Published: February 2003

The effect of vibration–rotation interaction on the Franck–Condon factors for various J values of the A–X system of OH molecule has been studied using the Gauss–Laguerre quadrature method. (AIP)
Existence of solutions to spherical moving boundary problems
Authors: Vrentas J. S. , Vrentas C. M.
Published: February 2003

The exact solutions of Tao for the isothermal growth or dissolution of spherical particles are considered. It is shown that these solutions describe an important class of spherical moving boundary problems if they are appropriately modified. It is also shown that the necessary and sufficient condition derived by Tao for the existence of solutions is equivalent to a simple restriction demanded by the physics of the problem.
Comments on ‘‘A new method of deriving electrical double layer equations from electrolyte theories’’
Authors: Lozada-Cassou Marcelo
Published: February 2003

It is shown that the electroneutrality condition is not necessary to prove the equivalence between the so-called asymtotic and direct methods of deriving electrical double layer equations. Therefore, it is to be expected that this equivalence will hold for nonelectrolyte systems. It is shown that the distribution of ions next to a sheet of charge (with a field on both sides of the sheet) is equal to that of ions next to a conducting wall, provided the electric field produced by the wall is the same in both systems. This result seems to unify electrical double layer theories which, in the past, have been derived for one or the other system. (AIP)
Energetic considerations of the vibrational potential function in the effective nuclear charge model. II
Authors: Ohwada Ken
Published: February 2003

Fundamental properties of the vibrational potential function in the effective nuclear charge (ENC) model previously proposed are investigated in detail on the basis of the quantum mechanical energy formula derived by Wilson. Firstly, our model potential assumed in the ENC model is derived formally from the Wilson’s energy formula. Secondly, the R-independent (R: internuclear distance) term W0 in the model potential is analyzed and its analytic forms are presented. Thirdly, the property of the N(r;R) term, arising from the delocalized electrons, in the model potential are discussed semiquantitatively.
Universal systematic sequence of even-tempered exponential-type functions in electronic structure studies
Authors: Cooper David L. , Wilson Stephen
Published: February 2003

Self-consistent field calculations are reported for some first-row atoms and their ions using a universal systematic sequence of basis sets consisting of exponential-type primitive functions. Extrapolation procedures are employed to obtain estimates of the basis set limit. The convergence properties of the calculations with respect to the size of the basis set are examined and compared with previously reported calculations which employed basis sets of Gaussian primitive functions.
Thermodynamic studies of phase transitions in chloropentamethylbenzene
Authors: Gyoten Hisaaki , Yoshimoto Yoshikazu , Atake Tooru , Chihara Hideaki
Published: February 2003

Heat capacities of solid chloropentamethylbenzene were measured from 3 to 300 K. A first-order phase transition (phase IV to III) at 84.0±0.1 K (ΔHt=0.93±0.01 kJ mol−1, ΔSt=11.1±0.1 J K−1 mol−1), and a transition (III to II) at 153.5±0.1 K (ΔHt= 1.33±0.04 kJ mol−1, ΔSt=8.8±0.3 J K−1 mol−1) were found on the sample cooled from room temperature at a rate of about −5 K min−1. A slow exothermic phenomenon was observed below the transition at 153.5 K, which spontaneously transformed III into III′; III′ showed a transition at 187.2±0.2 K (ΔHt=1.50±0.04 kJ mol−1, ΔSt=8.5±0.3 J K−1 mol−1). The temperature dependence of the exothermic phenomenon was analyzed. Another monotropic transition occurred just above 153.5 K, to give a yet new phase II′, which showed a transition at 180.4±0.2 K (ΔHt=1.33 ±0.04 kJ mol−1, ΔSt=7.7±0.3 J K−1 mol−1). The stability relations among the phases were determined in terms of the Gibbs energies. Raman spectra of phase II showed a gradual change in lattice modes. Nuclear quadrupole resonance (35Cl), measured for phases IV and III as a function of temperature between 78 and 145 K, showed only one resonance line. No resonance was observed in phase II. Phase relations are discussed in connection with crystal structure and molecular motion.
The dynamic behavior of a crystal during defect jumps. I. Molecular dynamics studies using Lennard-Jones potential functions
Authors: Becker K. D. , Hoheisel C.
Published: February 2003

Molecular dynamics calculations were performed to simulate the dynamics of an impurity jump process by means of a vacancy mechanism in an fcc lattice. The system, interacting by Lennard-Jones (12-6) potentials, consisted of 254 lattice atoms, one impurity atom, and one vacancy (T=60 K). The temporal and spatial behavior of the impurity and the nearest neighbors of the split vacancies is analyzed, and discussed in terms of several position-dependent quantities. On its way from the saddle-point to the vacant site the impurity exhibits a ballistic behavior with a time of flight of 1.5×10−12 s. In comparison, the relaxation process of the four gate atoms is considerably longer, 2.5×10−12 s, and is superimposed on their vibrational motion. The other nearest neighbors of the split vacancies are not directly affected by the jumping impurity, but their motion is strongly correlated with that of nearest-neighbor gate atoms.
Chemical and electrochemical isomerization of polyacetylene: In situ optical studies
Authors: Feldblum A. , Heeger A. J. , Chung T.-C. , MacDiarmid A. G.
Published: February 2003

In situ optical studies during electrochemical doping demonstrate that doping cis-(CH)x to a fixed dilute concentration induces partial cis-trans isomerization. ‘‘Undoping’’ back to neutral (CH)x converts that portion of the sample which was doped, back into undoped trans-(CH)x. Subsequent doping to the same level (or to lower levels) redopes only that portion which is already trans. Although doping to a higher level induces additional isomerization, complete isomerization is not achieved until dopant levels are obtained which are characteristic of the metallic state. The results indicate that at dilute doping levels cis-(CH)x consists of isolated segments of doped trans-(CH)x in the predominantly cis-(CH)x chains. Since the dopant uniformity in cis-rich samples is determined by the history of partial isomerization and by the simultaneous isomerization induced during doping, care should be taken in drawing fundamental conclusions from studies of doped cis-(CH)x material at all but the highest doping levels.
Resolution of the velocity autocorrelation function in fluids at various density states
Authors: Endo Homare , Endo Yoshikazu , Ogita Naofumi
Published: February 2003

The purpose of this paper is to study the atomic motions of fluids at various density states by finding out the basic modes which construct the velocity autocorrelation function (VAF). For this purpose the VAF in a soft-core system is calculated for the various density states ranging from a dilute gas to a dense liquid. Then the VAF’s are resolved into the Langevin and damped oscillatory modes by the use of an autoregressive (AR) analysis. The merits of the AR resolution is that the VAF’s can be easily resolved into the modes in an analytically expressed form. According to the respective role played by the Langevin modes and the damped oscillatory modes in the VAF and in its spectrum, three cases can be distinguished: (i) gaslike region which consists of one Langevin mode; (ii) intermediate region which consists of a superposition of one Langevin mode and more than one damped oscillatory modes; (iii) liquidlike region which consists of more than two damped oscillatory modes.
Atomization energies of the gaseous molecules SbLi, Sb2Li, SbLi2, Sb2Li2, and Sb3Li determined by Knudsen effusion mass spectrometry
Authors: Neubert A. , Zmbov K. F. , Gingerich K. A. , Ihle H. R.
Published: February 2003

In the course of a systematic investigation of gaseous lithides, the species in the saturated vapor above condensed phases in the system Sb–Li have been studied. As new molecules, SbLi, Sb2Li, SbLi2, Sb2Li2, and Sb3Li were identified. Enthalpy data derived from the analysis of several gas equilibria led to the following atomization energies: D0°(SbLi)=(169.0±10.0) kJ mol−1; D0°(Sb2Li)=(472.2±6.8) kJ mol−1; D0°(SbLi2)=378.5±10.2) kJ mol−1; D0°(Sb2Li2)=(688.8±12.4) kJ mol−1; D0°(Sb3Li)=(698.2±30.0) kJ mol−1. These experimental atomization energies are appreciably higher than those of the corresponding compounds of lithium with bismuth. The experimental dissociation energy of SbLi is lower than predicted by Pauling’s rule as was also found for BiLi.
Vibrational spectra of atomic adsorbates: Carbon, oxygen, and sulfur on Rh (100)
Authors: Dubois L. H.
Published: February 2003

High resolution electron energy loss spectroscopy (EELS), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES) were used to study the adsorption of ordered carbon, oxygen, and sulfur overlayers on a Rh (100) single crystal surface at 300 K. Each adsorption system was characterized by a single vibrational frequency; νRh–C=535, νRh–O=403, and νRh–S=313 cm−1. The observed high resolution EELS spectra of all of these species is consistent with the bonding of adsorbed atoms in the highest coordination site on the Rh (100) surface. During the course of these experiments, modes corresponding to rhodium surface phonons (181, 272 cm−1) and to adsorbed carbon monoxide (bridged: 358, ∼1920; linear: 428, ∼2030 cm−1), boron oxides (740, 950, 1405 cm−1), and disulfur (585 cm−1) were identified. High resolution EELS is clearly a powerful tool for studying the latter two species since they have not been detected by other spectroscopic techniques.