bluuebunny/crossref_metadata_2025 huggingface dataset:
A study of the ‘‘rotator’’ phase of 16-hydroxy–lithium–hexadecanoate
Authors: Busico Vincenzo , Ferraro Angelo , Vacatello Michele
Published: July 2002

The high temperature crystalline modification of CH2OH(CH2)14COOLi was investigated by differential scanning colorimetry (DSC), x-ray diffraction, and IR spectroscopy. The results can be explained assuming that the all-trans chains undergo rotations around their long axes coupled with (small) deformations of torsion angles within the potential well of the trans state. No clear evidence of conformational disorder was found, at variance with what was observed for the rotator phases of the n-alkanes. This would support the view that, in such phases, the generation of conformational defects is associated with the translation of part of the chains in the long axis direction, unfeasible for the system under study since too costly for electrostatic reasons.
On estimates of the quantum recurrence time
Authors: Bhattacharyya Kamal , Mukherjee Debashis
Published: July 2002

Based on the survival probability, improved estimates of the quantum recurrence time are obtained which desirably respect the scale invariance of the Hamiltonian and reveal roughly an inverse energy-spread dependence. The cases considered correspond to uniform distribution, nonuniform distribution with one dominant term, and the distribution determined perturbatively.
A
b i
n
i
t
i
o calculations of spin-orbit coupling in the Group 13 and 17 atoms
Authors: Ross R. B. , Ermler W. C. , Christiansen P. A.
Published: July 2002

Spin-orbit splitting energies are presented for the lowest doublet states of the atoms in Groups 13 and 17 of the Periodic Table. The splittings are computed in procedures involving the use of spin-orbit operators derived from relativistic effective core potentials (REP) and from separate calculations of the individual states in j–j coupling using REP’s. Comparison with experiment and with results due to all electron numerical Dirac–Fock calculations show that using the spin-orbit operator as a first-order perturbation to calculations carried out in LS coupling leads to an error of up to 7% in comparison to Dirac–Fock results. The indirect effect on the results due to orbital relaxation in the presence of the spin-orbit operator recovers about one-half of this error. The REP-based spin-orbit operator is shown to be quite accurate both for light and for heavy atoms. This is contrasted to the use of the spin-orbit operator comprised of one- and two-electron terms due to the Breit–Pauli approximation and Hartree–Fock wave functions, where the results degrade severely as the atomic mass increases. The nature of the spin-orbit interaction in fluorine is discussed.
Ferromagnetic insulating Fe[S2CN(C2H5)2]2Cl: Critical exponents, scaling, and magnetic equation of state
Authors: DeFotis Gary C. , Laughlin John R.
Published: July 2002

Magnetization isotherms for the title system become coincident above Tc when the scaled magnetic field is plotted against the scaled magnetization. The associated critical exponents are β=0.24±0.01 and δ=5.65±0.15, with independently determined Tc =2.458±0.002 K. A separate measurement of the initial susceptibility is analyzed to yield γ=1.165±0.005. Both γ and β agree well with earlier determinations. δ, previously unknown, is consistent with γ and β in light of the scaling relation δ=γ/ β+1. Yet each exponent differs significantly from its theoretical value in the three-dimensional Ising or any other familiar model. The magnetic equation of state is also determined, as an expansion about the critical isochore and as an expansion about the critical isotherm. Coefficients in each power series differ significantly from those available for any familiar theoretical model. Various explanations for the unusual observed behavior are discussed, including the possibility that this system may be an experimental realization of the three-dimensional Ashkin–Teller or related model.
An ESR-ENDOR study of the disulfide anion in x-irradiated L-cystine dihydrobromide dihydrate
Authors: Colaneri Michael J. , Box Harold C.
Published: July 2002

The disulfide anion radical produced by x irradiation in single crystals of L-cystine dihydrobromide dihydrate was characterized from ESR and ENDOR measurements. The g tensor of the absorption and the hyperfine coupling tensors of four β protons were determined. The hyperfine and quadrupole coupling tensors of a weakly interacting bromine nucleus were also deduced from ENDOR measurements. The distribution of spin density as inferred from anisotropic parts of the proton hyperfine couplings is discussed.
Self-consistent calculation of the Fermi level and the electron density in a thin metal film
Authors: Mola E. E. , Vicente J. L.
Published: July 2002

Fermi levels, electron densities, electrostatic potential, and exchange and correlation potentials are self-consistently calculated. A jellium model is used for the positive charge. The thin metal film of thickness L is put between infinitely high potential walls at a distance D of each other. Periodic boundary conditions are used parallel to the surfaces. In order to keep down the number of basis functions used, self-consistent Fermi levels are determined as a function of D and then are extrapolated. In spite of the strong nonlocal character of the electrostatic potential self-consistent results are achieved treating this potential in a direct way, this fact allows to watch the role of this potential in connection with other variables of physical interest. Therefore this model seems to be suitable to be used within more general problems, such as those trying to describe metal–electrolyte interfaces.
Spectra, lifetimes, and kinetics of matrix-isolated NI b 1Σ+ and a 1Δ
Authors: Becker A. C. , Langen Jürgen , Oberhoffer H. M. , Schurath Ulrich
Published: July 2002

NI in argon and in argon/10% N2 matrices has been excited into b 1Σ+, v′=0–4 with a pulsed tunable dye laser. The regular line structure in the fluorescence excitation and emission spectra in pure argon matrices is attributed to a local phonon progression of 15 cm−1, both in the X 3Σ− and b 1Σ+ states. ‘‘Hot’’ local phonon lines, which originate in the thermally populated levels n′=1 and 2 of the local phonon mode at elevated temperatures, have been identified. The matrix lifetime of the vibrationally relaxed b state, which does not relax via the a state in pure argon, extrapolates to a radiative lifetime of 15 μs in vacuo, in satisfactory agreement with a recent gas phase determination. The a state of NI, which emits at 1185 and 1173 nm, could be populated via the b state only in mixed matrices of argon and N2. The lifetime in these matrices is 20.5±2 ms, which extrapolates to a gas phase radiative lifetime of approximately 38 ms. The b state of NI is completely quenched in pure nitrogen matrices, but emission from the a state is still detected with a lifetime of 4.6±0.5 ms. On the basis of these results recently reported a-state lifetimes of NCl and NBr in the ms to sub-ms range appear unreasonably low.
Resonant charge exchange as a means of selective state excitation in the photodissociation spectroscopy of SO+2
Authors: Goss S. P. , Morrison J. D.
Published: July 2002

Differences in the photodissociation spectrum obtained from pure SO+2 formed by electron impact, and that obtained from SO+2 formed in a mixture with a 20-fold excess of xenon, indicates that the populations of the excited states of SO+2 are modified. By spectrum stripping, the contribution due to resonant charge exchange ionization is isolated and spectral complexity significantly reduced.
Polarization sensitive resonance CARS spectroscopy
Authors: Brakel R. , Mudogo V. , Schneider F. W.
Published: July 2002

Polarization CARS spectroscopy is known to considerably enhance the CARS sensitivity of weak Raman resonances by background suppression in transparent media. Experimental control of the spectral line shape through polarization enables the determination of molecular parameters by line shape analysis. We demonstrate that polarization CARS can also be applied to absorbing substances, i.e., under electronic resonance conditions, for the case of pseudoisocyanine chloride. The spectra, recorded in the multiplex mode, are interpreted theoretically and the parameters involved in the third order susceptibility are determined from experiment. Multiplex performance of polarization CARS spectroscopy is also demonstrated for solutions of pyridine in water and benzene in carbon tetrachloride as transparent systems.
Critical effects in the infrared spectrum of hydrogen
Authors: Clouter M. J. , McKellar A. R. W.
Published: July 2002

Measurements of absorption in the fundamental (4000 to 5000 cm−1) vibrational band of H2 have revealed new features in the collision-induced spectrum which attain their maximum intensity under near-critical conditions (Tc=32.98 K for para-H2). The new features are relatively sharp ‘‘spikes’’ (FWHM≊5 cm−1) which occur at the frequencies of the Q1(0) and/or Q1(1) transitions, and the effect is most prominent in pure para-H2. The behavior of these features as a function of temperature and of ortho-/para-H2 ratio has been investigated, they have also been detected in the spectrum of D2 near the critical point. An interpretation is proposed on the basis that long-lived spatial fluctuations in density give rise to a spoiling of the normally active mechanism of destructive intercollisional interference.
Rotationally cold spectrum of the B̃ 2Π–X̃ 2Π system of ClCN+
Authors: Grieman Fred J. , McIlroy Andrew , Perkins Jonathan
Published: July 2002

The rotationally cold spectrum of the B̃ 2Π–X̃ 2Π system of ClCN+ has been obtained by the crossed free jet-electron beam method. The narrowing of vibrational bands has allowed the assignment of many of the major features in the spectrum. The (Cl–C) stretching vibrational frequencies have been determined to be 823 and 526 cm−1 for the ground and excited electronic states, respectively, and the (C 3/4 N) stretching vibrational frequency for the ground electronic state has been determined to be 1915 cm−1. The difference in spin-orbit coupling constants for these two electronic states was also measured in the spectrum to be 87 cm−1. The difference in vibrational frequencies and the difference in spin-orbit coupling constants for these electronic states, in comparison with similar values for the isoelectronic molecules ClC2H+ and SCN, allow a fairly complete picture of the π bonding in these molecules to be formed.
Kinetic energy spectrum of NO+ photofragments from the photopredissociation of the Ã 2Σ+ state of N2O+
Authors: Lermé J. , Abed S. , Larzillière M. , Holt R. A. , Carré M.
Published: July 2002

We have employed an electrostatic energy analyzer to measure the kinetic energy of the NO+ fragment from the photopredissociation of the ion N2O+ (Ã 2Σ+). The collinear FIBLAS technique has enabled us to selectively populate predissociated rovibrational levels. For all levels studied, we obtain a narrow energy distribution, corresponding to preferential population of the v=4 vibrational level of NO+ (1Σ+), with a broad distribution over the rotational levels of this fragment. We have been able to observe the dependence of the kinetic energy liberated in the center-of-mass frame as a function of the initial rotational excitation of the (100) 2Σ+ level. The dissociation channel O+(4S)+N2(X 1Σ+g) has also been observed, but this mode of deexcitation has a small probability for the low-lying predissociated levels studied.
Classical limit analysis of the semiclassical spectral quantization method
Authors: De Leon N.
Published: July 2002

We examine the classical limit (ℏ→0) of the semiclassical spectral quantization method (SQ) proposed in an earlier publication. Using the classical limit analysis, equations are derived which should improve the accuracy of SQ for finite ℏ. Our analysis is focused on problems involving coupled and uncoupled oscillator systems. Special attention is given to the situation when the unperturbed oscillators are anharmonic. Application to cases where classical resonances are present are also discussed.
A photoabsorption method of measuring molecular diffusion coefficients in liquid mixtures
Authors: Mathad R. D. , Umakantha N.
Published: July 2002

A photoabsorption technique employing Fick’s law and Beer’s law is described for determining diffusion coefficients of molecules in liquid mixtures. The values for diffusion of toluene, at 323 K, in 1:9 mixtures of toluene–cyclohexane and of toluene–paraffin are found, respectively, to be 1.3 and 0.43×10−5 cm2 s−1. These values are observed to differ significantly from those based on the macroviscosity of the mixtures. Some advantages and limitations of the technique are also considered briefly.
A comparison of the dynamical behavior of closed ring and chain macromolecules in dilute solution
Authors: Allegra Giuseppe , Ganazzoli Fabio , Ullman Robert
Published: July 2002

The normal Fourier modes of a closed ring polymer chain constitute a complete basis for decoupling the hydrodynamic equations. In this Fourier space, the hydrodynamic interaction terms are converted to a frequency-dependent friction constant. The method is exact for ring polymers, and is approximately correct for linear polymer chains. In this paper, the strengths and weaknesses of the approximation are explored. The approximation is satisfactory except (a) at low frequencies and (b) for motion of the chain ends.
The lower Rydberg states of c
i
s-hexatriene
Authors: Sabljić A. , McDiarmid Ruth
Published: July 2002

The one photon (optical), and two and three photon resonant multiphoton ionization spectra of cis-hexatriene have been recorded and analyzed. Transitions to the 3s(B2), 3p(A1), 3p(A2), 3d(A2), 3d(?) and 4s(B2) Rydberg states have been observed. Three a1, three b2, and one unidentified vibrations have been observed in the assorted Rydberg states. The assignments of the electronic states and vibrational modes are discussed.
Influence of phonons on optically detected magnetic resonances of aromatic molecules in amorphous hosts
Authors: Gradl G. , Friedrich J. , Kohler B. E.
Published: July 2002

We present phosphorescence wavelength selected optically detected magnetic resonance (ODMR) experiments on some aromatic molecules in organic glasses. The change of the ODMR frequency and width as a function of phosphorescence wavelength is interpreted in terms of a spinless stochastic Hamiltonian which describes the interaction between the probe molecule and the solvent. It is shown that the phonons in the optical spectra have a significant influence on the parameters of the ODMR profile.
Free energy difference calculations comparing fcc and hcp structures using molecular dynamics computer simulations
Authors: Moody Michael C. , Ray John R. , Rahman Aneesur
Published: July 2002

Molecular dynamic computer simulation methods have been employed to calculate the free energy difference between the fcc and hcp structures using a Morse potential parametrized to model Ni. The calculation is carried out for a temperature (∼1000 K) where anharmonic effects are important and also for a range of interactions about each particle. In addition, at the same temperature, another calculation using only nearest neighbor interactions was performed. Using lattice sums the potential energy for the two static lattices was calculated. For the Morse potential used, static lattice sums give a lower potential for the hcp structure. With only nearest neighbor interactions, the fcc–hcp free energy difference is determined only by the entropy difference. In this case the fcc structure has the lower free energy. When both anharmonic effects and longer range interactions are considered we find, at the temperature and density investigated, that the hcp structure is more stable.
Computer simulation of adsorption equilibrium for a gas on a solid surface using the potential distribution theory
Authors: Knight J. F. , Monson P. A.
Published: July 2002

Monte Carlo computer simulations of monolayer adsorption of a gas on a solid surface are described in which the potential distribution method was used to directly calculate the adsorption isotherms. The systems studied were the two-dimensional, Lennard-Jones fluid and such a fluid in external potentials chosen to represent the interactions of the adsorbate molecules with exposed faces of an inert fcc crystal. The adsorption isotherms for the structured surfaces show a substantial influence of the surface corrugation upon the adsorption equilibria. The results demonstrate that the potential distribution method is a useful approach to studying adsorption equilibria.
Spectroscopic and dynamical differences between exciplex and electronically excited EDA complex
Authors: Lim B. T. , Okajima S. , Lim E. C.
Published: July 2002

We demonstrate here that the electronically excited electron donor–acceptor (EDA) complex can be different from the corresponding exciplex even in the absence of viscosity constraints that prevent the attainment of preferred donor–acceptor orientation.
Extended model potential calculations on I2 and HI molecules
Authors: Barandiarán Zoila , Seijo Luis
Published: July 2002

An extension of Huzinaga’s model potential method is applied to the study of the equilibrium geometry of the ground electronic state of I2 and HI. In the extended model potential method (EMP) the exchange interactions between the core and valence shells are handled more efficiently than in the standard MP method; furthermore, the long range behavior of the model potential does not depend on the reduction of the valence basis set. Consequently, the results of the EMP molecular calculations are very close to the reference all-electron calculations, with errors of 0.04–0.02 Å (equilibrium distance), 3%–2% (vibrational frequency), 0.4 eV (binding energy), and 10−3 a.u. (molecular orbital energies). The present results show that in molecules with large core–valence interactions the EMP method, which explicitly involves only the valence electrons and uses the theoretical core projection parameters, offers the same accuracy as the standard MP method enhanced by the promotion of the outermost core orbital to the valence space and by using adjustable (soft) core projection parameters.
Accurate coefficient of the Axilrod–Teller triple-dipole term for three hydrogen atoms
Authors: Koga Toshikatsu
Published: July 2002

Using the very accurate first order perturbation wave function reported recently for the van der Waals interaction between two ground-state hydrogen atoms, we derive an accurate coefficient of the Axilrod–Teller triple-dipole term for three ground-state hydrogen atoms, which is an important leading term of the nonadditive three-body long-range force.
Resonances by the complex coordinate method with Hermitian Hamiltonian. IV. The linear correlation procedure
Authors: Engdahl E. , Moiseyev N.
Published: July 2002

On the basis of the Hermitian representation of the complex coordinate method presented in paper I we suggest here a simple procedure to get a good estimate of both the position and width of a resonance for a given Hamiltonian. The complex energy E, which is associated with the resonance is obtained by solving the equation system λ1/‖E−Ē1‖=λ2/‖E−Ē2‖= λ3/‖E−Ē3‖, where {λn, n=1,2,3} are the lowest eigenvalues of a Hermitian Hamiltonian (Ĥθ−Ēn)*(Ĥθ−Ē n), Ĥθ is the complex rotated Hamiltonian, and Ē1,2,3 can be obtained, e.g., from conventional stabilization calculations where Im(Ē1,2,3)=0.
A simple analytic model of the diffusion controlled reaction rates of asymmetric molecules
Authors: Hess S. , Monchick L.
Published: July 2002

A simple model is devised for the diffusion mediated reaction of an asymmetric molecule with ambient reactants. For the particular model in which the surface reactivity is assumed to vary as 1+β cos θ, where θ is the polar angle and 0≤β≤1, an analytic solution in the form of an infinite continued fraction was obtained for the steady state reaction rate. This fills a gap in the theory of reaction rates of asymmetric molecules which generally have been investigated by numerical computation. In agreement with previous studies on other models with smoothly varying reactivity, it is found that the steady state reaction rate depends primarily on the surface averaged reactivity. The effect due to asymmetry is only of secondary importance for such models and even this tends to get washed out as the rotational diffusion coefficient increases.
Photodissociation of the energy selected nitrobenzene ion
Authors: Bunn Thomas L. , Richard Ann M. , Baer Tomas
Published: July 2002

Nitrobenzene ions, energy selected by photoelectron–photoion coincidence (PEPICO), are photodissociated by a pulsed dye laser. The time-delayed laser pulse is triggered by the detection of a zero energy electron indicating the formation of an ion of known internal energy. A detailed description of the experimental requirements is presented. This first report of the combination of PEPICO with ion photodissociation includes the determination of the nitrobenzene ion photodissociation cross section of (6±2)×10−19 cm2, and the study of kinetic energy released in that dissociation. Applications for other uses are discussed.
Hydrogen contribution to the heat capacity of single phase, face centered cubic scandium deuteride
Authors: Moss Marvin , Richards Peter M. , Venturini Eugene L. , Gieske John H. , Graeber Edward J.
Published: July 2002

The heat capacity at constant pressure, Cp, of single-phase, face-centered cubic ScDx (x=1.75, 1.83, 1.91, and 1.99) was measured from room temperature to 950 K, and analyzed in terms of various contributions of the deuterium and metal constituents. Values ranged from approximately 40 to 80 J mol−1 K−1 with increasing temperature. The heat capacity at constant volume was assumed to be composed of lattice contributions from an acoustic vibrational mode, Cl(a)v, and an optical vibrational mode, Cl(o)v, plus an electronic contribution, Cev. The acoustic part, Cl(a)v, was evaluated as a Debye term with characteristic Debye temperatures calculated from measured values of temperature-dependent acoustic velocities and lattice constants. An isotope-adjusted Einstein temperature, derived from inelastic neutron scattering measurements on ScH2, was used to find Cl(o)v. The Cev term was evaluated from a published value of the electronic heat capacity constant for ScH2 (assumed to be the same for ScD2). Particular attention was paid to the dilation term, Cd=Cp−Cv, by evaluating it explicitly from the temperature-dependent volume expansion and elastic modulus. It was found that Cv=Cl(a)v+Cl(o) v+Cev+ΔC, the last term being an excess heat capacity of approximately the same magnitude as Cd. ΔC is attributed to anharmonic deuteron vibrations and deuteron–deuteron interactions, and is calculated for a specific model in reasonable agreement with the data.
Nuclear spin-lattice relaxation in the sodium anion, Na−
Authors: Holton Dolores M. , Ellaboudy Ahmed , Pyper Nicholas C. , Edwards Peter P.
Published: July 2002

We report direct measurements of nuclear spin-lattice relaxation times (T1n) for the sodium anion, Na−, in solutions containing both sodium and a heavier alkali metal in 1,4,7,10-tetraoxacyclododecane (12-crown-4, 12C4). Nuclear spin-lattice relaxation in Na− is found to be essentially independent of the alkali counterion and to depend only weakly upon the concentration of sodide ion in solution. The temperature dependence of T1n for Na− was used to determine an activation energy for the processes responsible for spin relaxation. The results are consistent with a dominant, but very inefficient, quadrupolar relaxation mechanism which involves the modulation of the electric field gradient at Na− via the reorientation and/or translational motion of surrounding 12C4 molecules in the liquid. Furthermore, we find that solvation of Na− in 12C4 as well described by a model in which there is neither preferential orientation of 12C4 molecules nor a clearly identifiable first solvation shell around the sodide ion. Consistent with this description, the activation energies for the processes responsible for spin-lattice relaxation in Na− are close to those observed for the processes causing 1H and 13C relaxation in the neat liquid crown. We outline two methods, which take into account electron–electron correlation effects, for determining the Sternheimer antishielding factor β2 for the sodium anion. The most realistic estimate for β2 (−14.98) is used to calculate the NMR linewidth for Na− when it is associated with an uncomplexed (unsolvated) sodium cation and also in the contact and solvent-separated Na+–Na− ion pairs. A rms value of 0.03 MHz for the quadrupole coupling constant (e2qQ/ℏ) of Na− in 12C4 solutions is deduced. We conclude that Na− in these solutions suffers only minor perturbations on its gas-phase electronic structure; neither does it exist as part of a contact or solvent-separated ion pair. It appears that the sodide ion represents the closest realization of a gas-like ionic moiety in solution.
Theoretical studies of vibrational excitation in collisions of O(3P) with H2O(1A1)
Authors: Redmon Michael J. , Schatz George C. , Garrett Bruce C.
Published: July 2002

The quasiclassical trajectory method is used to calculate cross sections for vibrational excitation in O(3P)+H2O(000) collisions. The potential surface is a Sorbie–Murrell fit to the ab initio MBPT calculation of Bartlett and Purvis. State-to-state transition probabilities are evaluated using the histogram method to discretize the H2O good action variables obtained from a classical perturbative treatment of the molecular Hamilton–Jacobi equation. Integral cross sections are presented for all one-quantum excitations [(010), (100), and (001)] plus some multiquantum excitations. Rotational distributions for each final vibrational state indicate that significant rotational excitation accompanies vibrational excitation. The angular distributions for vibrationally excited final states indicate sidewards peaking. The resulting (001) cross section is in reasonable agreement with experimental shock tube results. The analogous (010) excitation cross section is larger than the corresponding experimental value. Although the experimental error is large, at least part of the difference between theory and experiment is associated with a small time dependence in the computed actions for this very floppy mode.
Trajectory investigations of charge transfer reactions of rare gas ions with geometric isomers of dichloroethylene and difluorobenzene
Authors: Su Timothy , Hu Selina
Published: July 2002

A trajectory calculation is used in conjunction with experimental results to estimate the charge transfer probability functions for the reactions of rare gas ions with dichloroethylene and difluorobenzene isomers. The probability functions are assumed to be exponential functions. It is shown that charge transfer in these systems occurs to a significant extent outside the capture limit.
Electron density studies of porphyrins and phthalocyanines. IV. Electron density distribution in crystals of (meso-tetraphenylporphinato) iron(II)
Authors: Tanaka K. , Elkaim E. , Li Liang , Jue Zhu Nai , Coppens P. , Landrum J.
Published: July 2002

The electron density distribution in crystals of (meso-tetraphenylporphinato)iron(II) has been analyzed using accurate x-ray diffraction data collected at 120 K. The structural results are in agreement with those of the room temperature study. Theoretical calculations predict several different ground states for the complex and in particular support the 3A2g and the 3EgA states. The experimental electron density distribution shows large peaks above and below the iron atom which would not be present for a 3EgA ground state. Comparison with Mössbauer quadrupole splittings and the result of the aspherical atom refinement indicate that the axial peaks may be systematically too high in this acentric crystal structure. Nevertheless, it is concluded that their presence indicates a relatively small contribution of the 3EgA state to the ground state of the complex. This implies that the ground state of FeTPP is different from that of iron(II)phthalocyanine in the crystal. A significant population of electrons is found in the dx2−y2 orbital which is mainly attributed to σ donation of electrons from the porphyrin ligand.
Spatial correlations in diluted gases from the viewpoint of the metric of the thermodynamic state space
Authors: Diósi L. , Lukács B.
Published: July 2002

Assuming the existences of two different correlation scales in a diluted gas, the second one leads to pressure and energy corrections, which are of van der Waals type in the simplest case. The direct connection between the correlation scales and the metric of the thermodynamic state space is discussed here.
Interfacial equilibrium during a first-order phase transformation in solids
Authors: Voorhees P. W. , Johnson William C.
Published: July 2002

A continuum thermodynamic treatment of the local equilibrium concentration at a two-phase interface during a first-order diffusional phase transition in crystalline solids is presented. It is assumed that the second-phase domain has a spherical morphology, is coherent with the matrix, and possesses different elastic constants than the matrix. It is shown that the equilibrium concentration at the solid–solid interface is strongly coupled to the stress states of the matrix, precipitate, and interface as well as the interfacial curvature. This coupling gives rise to many new phenomena, such as the dependence of the equilibrium interfacial concentrations on the magnitude of the supersaturation in the parent phase, the misfit between the precipitate and matrix and the difference in the partial molar volumes of the diffusing species. Capillarity is also strongly influenced by the crystallinity through the surface stress and deformation, supersaturation of the parent phase, and the degree of elastic inhomogeneity. It is concluded that approximating the equilibrium interfacial conditions during phase transformations in solids using thermodynamics which is valid only for fluids may be erroneous in many cases.
Crystal structure and charge transfer energies of complexes of the donor biphenylene with the acceptors TCNB and PMDA
Authors: Stezowski John J. , Stigler Rolf-Dietrich , Karl Norbert
Published: July 2002

Biphenylene:tetracyanobenzene (BPN:TCNB), C12H8:C10H2N4, crystallizes in a monoclinic lattice, space group P21/a, Z=2, with a=15.215(2) Å, b=7.260(1) Å, c=7.573(1) Å, β=90.05(1)° at 296 K. The BPN donor and TCNB acceptor molecules form two symmetry-related mixed linear [001] stacks with the donor and acceptor molecular planes tilted to each other (within the individual stacks) at an angle of Φ=7.6°. Biphenylene:pyromellitic-dianhydride (BPN:PMDA), C12H8:C10H2O6, crystallizes in two different monoclinic modifications, both space group P21/a, Z=2, one red, and the other black. The red form (stable above ∼400 K) with a=9.280(1) Å, b=11.869(2) Å, c=7.293(1) Å, β=98.68(2)° at ∼120 K, exhibits mixed linear stacks (Φ=4.1°). The lattice parameters of the black form (stable below ∼400 K) are a=13.368(1) Å, b=5.809(1) Å, c=10.443(1) Å, β=102.30(1)° at ∼120 K, and a=13.450(2) Å, b=5.917(1) Å, c=10.464(2) Å, β=101.82(2)° at 296 K. Its structure also can be viewed as a mixed linear stacking (Φ=9.9°), but it displays exceptionally little intrastack molecular overlap. Instead, considerable two dimensional interactions among the donors and among the acceptors can be concluded. Single crystals of all three complexes, obtained by the plate sublimation technique, were optically characterized by their charge transfer absorption edges. These are analyzed in terms of the molecular parameters electron affinity and ionization energy. For BPN:TCNB an intrastack and an interstack CT-absorption edge can be distinguished.
Photoionization and photocyanation of 9-phenylanthracene
Authors: Konuk Rengin , Cornelisse J. , McGlynn S. P.
Published: July 2002

The photoinization of 9-phenylanthracene (PhA) and the role of the radical cation in the photocyanation reaction is reported. Radical cations are produced by two processes: (a) biphotonic unimolecular ionization under high intensity laser excitation and (b) a monophotonic bimolecular electron-transfer process in the presence of dicyanobenzene (DCB). In both cases, the singlet excited state is the precursor to the radical cation.
Correlated calculation of the interaction in the nitromethane dimer
Authors: Cole Samuel J. , Szalewicz Krzysztof , Purvis George D. , Bartlett Rodney J.
Published: July 2002

The interaction energy of the nitromethane dimer at several separations between the monomers was calculated using fourth-order many-body perturbation theory (MBPT), with single, double, and quadruple (SDQ) excitations included. The self-consistent field (SCF) counterpoise (CP) correction, and second-order dispersion energy were also computed. A double-zeta plus polarization basis was used. The monomers were oriented so that a hydrogen atom on each monomer could form a hydrogen bond with an oxygen on the other monomer. An interaction energy of 3.57 and 5.04 kcal/mol was found at the SCF and SDQ-MBPT(4) levels of theory, respectively. The CP-corrected SCF energy added to the second-order dispersion energy gives an interaction energy of 5.62 kcal/mol.
Second-harmonic spectra of Fe3+ in borosilicate Pyrex glasses
Authors: Ciccarello I. , Guccione M. , Li Vigni M.
Published: July 2002

The second-harmonic spectra of borosilicate Pyrex glasses containing Fe3+ impurities have been investigated at the fundamental frequency ν=2.9 GHz. The spectra are interpreted by assuming a spin-Hamiltonian containing crystal-field terms yielding an energy not too large in comparison to the Zeeman energy at S band. It is found that the g=4.3 second-harmonic line does originate from the resonance of a Kramers doublet while both the g=6 line and the background signal do not. It is shown that second-harmonic investigations allow discrimination as to whether or not a signal can be ascribed to the resonance of two spin states of the same Kramers doublet.
The nearly elastic scattering of Ne and Ar from LiF(100)
Authors: LeGrand A. D. , Greene E. F.
Published: July 2002

Beams of Ne and Ar of energy 63 meV are diffracted by LiF(100) at 294 K and then passed through a velocity selector (resolution 3%) set to transmit only the nearly elastic scattering. This amounts to fractions 0.13 and 0.054, respectively, of the total scattering reaching the detector when the selector is removed. The clearly resolved structure in the angular distributions of these relatively heavy atoms scattered from the surface may provide useful information about the potential for these systems. A simplified analysis yields an estimate for the corrugation parameter for Ar+LiF(100).
Evaluation of dielectric relaxation spectrum of phospholipids in solution by time domain reflectometry
Authors: Imamatsu Kazuya , Nozaki Ryusuke , Yagihara Shin , Mashimo Satoru , Hashimoto Masao
Published: July 2002

Time domain reflectometry (TDR) was applied to dielectric relaxation measurements and relaxation spectra of four kinds of phospholipids (dipalmitoyl phosphatidylcholine, egg lecithin, phosphatidyl ethanolamine, and sphingomyelin) and were evaluated in chloroform solutions. Fast measurements covering a wide frequency range from 1 MHz to 10 GHz could be done easily for materials having multiple relaxations and dc conductivity. A procedure of extracting individual spectra from the complicated complex permittivity has been presented. Reasonable assignment of molecular motion could be given to each spectrum. The first spectrum observed at about 1.5 ns is caused by an overall rotation of the whole molecule in the solution. The second spectrum at 0.2–0.4 ns is related to a motion of the zwitterionic head group. The third spectrum observed in lecithin at 50–80 ps is mainly caused by internal motions of the ester groups. It is concluded that the TDR method is quite suitable for the investigation of molecular dynamics of biomaterials.
Time domain dielectric measurements of conducting glasses
Authors: Turcotte David E. , Chryssikos Georgios D. , Perl Jeffery P. , Winsor Paul , Cole Robert H. , Risen William M.
Published: July 2002

Dielectric measurements of ionically conducting glasses in the family 0.2Li2O ⋅ yLiF ⋅ B2O3 with y=0,0.1,0.2,0.3,0.4,0.5,0.6, and 0.7, have been made in the 107–1010 Hz region by time domain reflectometry (TDR) at six temperatures in the 25–375 °C range. The presence of a plateau in Ε′ in the ∼107–109 Hz region below an absorptive process near 109 Hz constitutes a static permittivity, Εs, whose temperature coefficient leads to the result that (∂S/∂E2)T is positive and, thus, that the system becomes more disordered upon application of the electric field.
Reply to the ‘‘Comment on ‘Remarks on the mutual diffusion coefficient of Brownian particles’ ’’
Authors: Yoshida Nobuo
Published: July 2002

Phillies’ criticism concerning the present author’s previous contention is accepted, but part of his arguments are questioned.
The structural determination of fluorite-type oxygen excess uranium oxides using EXAFS spectroscopy
Authors: Jones Deborah J. , Roziere Jacques , Allen Geoffrey C. , Tempest Paul A.
Published: July 2002

Extended x-ray absorption fine structure (EXAFS) spectroscopy has been carried out at 77 K at the uranium LIII edge for UO2, β-U3O7, and U4O9 with the aim of determining the structure of these highly defective (oxygen excess) uranium oxide phases, which are of industrial importance. Use has been made of a difference Fourier technique for U3O7, in which the EXAFS of a perfect lattice model is subtracted. U–O bond lengths calculated from the remaining EXAFS signal, assumed to result only from interstitial oxygens, have been used to determine the atomic coordinates of these interstitials. The analysis of EXAFS data in terms of coordination number has allowed an insight into the defect aggregate arrangement of oxygens in U3O7 and U4O9. Furthermore, EXAFS data indicate that the uranium sublattice is perturbed by the incorporation of additional oxygen atoms.
Reaction kinetics on a lattice
Authors: Keller Joseph B.
Published: July 2002

The kinetics of an irreversible reaction on a lattice is analyzed when the reaction rate at a site depends upon the number of its unreacted nearest neighbors.
Near-infrared luminescence from Ti2+ in MgCl2
Authors: Jacobsen Stuart M. , Smith W. Ewen , Reber Christian , Güdel Hans U.
Published: July 2002

The first Ti2+ luminescence from an insulating lattice is reported. In a crystal of Mg0.999Ti0.001Cl2 six electronic origins of the 1Eg→3T1g transition were identified and analyzed.
The action of product tensor operators within and between pure and mixed configurations
Authors: Tuszyński J. A.
Published: July 2002

Atomic and nuclear shell Hamiltonians can be represented in terms of one- and two-body product tensor operators which act both in spin and orbital spaces. In this paper, equivalence conditions for the matrix elements of these operators are used to find their normalization constant. The results obtained for one-body operators are tabulated for all pure and mixed shells with l≤3. The normalization constants for two-body operators are proved to be products of two one-body normalization constants with the corresponding ranks. Subsequently, expressions for the matrix elements of one- and two-body double tensor operators within all pure configurations are found for arbitrary ranks. Since these generalized product tensor operators may include polar components, they are allowed to participate in configuration mixing. Therefore, reduced matrix elements for these operators have also been calculated both within mixed configurations and between all possible combinations of mixed and pure configurations. These formulas have been used in a computer program and selected numerical results have been provided in this paper.
Molecular dynamics studies of complexing in binary molten salts. II. Molten M3AX6 and MA3X1
Authors: Blander Milton , Saboungi Marie-Louise , Rahman Aneesur
Published: July 2002

Molecular dynamics calculations were performed on two liquid ionic solutions, M3AX6 and MA3X10, containing a total of about 500 ions. Four different sets of radii for the M+, A3+, and X− ions were considered in a simplified Tosi–Fumi potential; the cation–anion distances were kept constant but the cation–anion radius ratios varied. These sets generated configurations in which the coordination of A3+ by X− ranged from octahedral to tetrahedral. Our goal was to investigate typical complexing molten salt solutions such as fluoroyttriates and chloroaluminates. In all the melts studied, A3+ tended to have preferential even coordination numbers, 4 or 6, and to form independent AX3−nn moieties in very dilute solutions. As the concentration of AX3 increased, these moieties became interconnected by close to linear A–X–A bridges to form larger species. In the octahedrally coordinated melts, this led to a three-dimensional network with intermediate range order and to the formation of bridged species containing A3+ equilateral triplets, even in M3AX6. In the tetrahedrally coordinated M3AX6 melts, the value for the equilibrium constant of 2AX−4 ⇄A2X−7 +X− was found to be 4×10−2 which is close to the value obtained previously for MAX4. Consequently, the A–X–A bridges were most stable in the octahedrally coordinated melts. For three of the four sets of ionic radii investigated, a composition dependent distribution of the coordination numbers of A3+ cations by X− was observed.
Heats of transport from the diffusion thermoeffect in binary liquid mixtures of toluene, chlorobenzene, and bromobenzene
Authors: Rowley R. L. , Hall M. D.
Published: July 2002

Measurements of heats of transport in binary liquid mixtures of toluene, chlorobenzene, and bromobenzene utilizing the diffusion thermoeffect, or Dufour effect, are reported at 298 and 308 K. The corresponding heat-mass Onsager coefficients are also reported, from which thermal diffusion ratios have been calculated based on Onsager reciprocity. The resultant binary thermal diffusion ratios have been correlated as a function of composition in an attempt to study the relationship between values in binary and ternary mixtures. It was found that the single independent binary values can be used to estimate the two independent thermal diffusion ratios previously reported in toluene+chlorobenzene+bromobenzene ternary mixtures.
The effect of deuteration on the multiphoton dissociation of benzene chromium tricarbonyl
Authors: Samoriski Brian , Hossenlopp Jeanne M. , Rooney Dan , Chaiken J.
Published: July 2002

We have measured one color multiphoton dissociation ionization (MPD/MPI) spectra for h6-benzene chromium tricarbonyl (h6-BCT) and d6-benzene chromium tricarbonyl (d6-BCT). These spectra reveal that the vibrational properties of the ligands determine the distribution of metal atom states formed by MPD of organometallic molecules. Pressure studies demonstrate that the observed effects manifest isolated molecule dynamics and that excited triplet states are probably not involved in those dynamics. Laser power dependence studies show that the observed branching between MPD production of ground state chromium atoms vs excited state atoms is a function of multiphoton excitation rate. It seems likely that photodissociation on potential surfaces corresponding to excited electronic states can occur before intramolecular energy redistribution is complete. Two mechanisms consistent with our results are suggested. One is very unique for MPD/MPI experiments in that ladder crossing based on dissociation is not the source of the branching between observed products.
Sphericalization of the potential of interaction of anisotropic molecules with spherical particles
Authors: Fernández-Prini R. , Japas María L.
Published: July 2002

The possibility of employing sphericalized intermolecular potentials to describe the interactions between nonpolar anisotropic molecules (CCl4 and benzene) with spherical nonpolar molecules (Ar, Xe, and CH4) has been tested for binary systems having liquid- and gas-like densities. Median and RAM sphericalization procedures have been used and their capacity to account for the experimental values of cross second virial coefficients and Henry’s constants are compared. It is shown that the median sphericalized potentials, which are temperature and density independent, give a fairly good description of the data which is better than that provided by RAM potentials. The possibility of accounting correctly for the change of properties when the relative size of the interacting partners changes (e.g., conformal systems) is noteworthy.
The theory of electron scattering from multipolar vibrations of adsorbates
Authors: Lenac Zdravko , Šunjić Marijan
Published: July 2002

The electronic vibrational scattering from a molecule adsorbed on a flat surface is analyzed. In the energy region where the long-range Coulomb interaction is the main scattering mechanism the molecule is described as a point multipole. The cross sections are derived for both the screened and the unscreened multipoles, which enables us to obtain the ‘‘surface multipole selection rule’’ in a rather general form. We compare the multipole with the dipole scattering, and we discuss in detail the scattering from the quadrupole, which can give effects at least comparable with the impact scattering. The molecular vibrations perpendicular and parallel to the surface are analyzed in detail and the resulting angular and energy dependent cross sections are given for parameters corresponding to the electron scattering from H adsorbed on W(100). The comparison shows that the multipole scattering can play an important role in that case.
Double differential cross sections for alkali–Hg collisions in the 100 eV range. I. Time-of-flight measurements
Authors: Düren R. , Gersing E. , Kita S. , Kracht W. , Pauly H. , Schädlich E. , Vonderschen M.
Published: July 2002

Differential cross sections with energy analysis have been measured for Na, K, and Cs atoms scattered from Hg for collision energies between 36 and 200 eV. The energy analysis is performed with standard time-of-flight technique yielding the cross sections for elastic scattering and scattering with excitation of the lowest alkali P state. The cross sections for all other excited states are found to be smaller by several orders of magnitude. A new semiempirical potential model is described which has been used to interpret the experimental results. Parameters for the best fit to our results are given in this two-state model for K and Cs. For Na we can only give a coarse estimate. Some serious failures of the semiclassical theory have been discovered, which have lead us to the use of quantum mechanical calculations.
g̃-tensor calculation for FeIII triads: Application to the 3Fe clusters in iron–sulfur proteins
Authors: Guigliarelli B. , More C. , Bertrand P. , Gayda J. P.
Published: July 2002

The g̃ tensor of a triad of high spin FeIII ions coupled by antiferromagnetic exchange interactions, is calculated in the case where the fine structure terms are not negligible compared to the exchange parameters. Using some simplifying assumptions concerning the relative orientations of the magnetic axes, we obtain the expressions of the g components in closed form. A simple ‘‘g strain’’ model based on these expressions is used to simulate the EPR spectra given by the 3Fe clusters of four different iron sulfur proteins. In each case, a good simulation is only observed if the three exchange parameters are nearly equal, and of the order of −20 cm−1. These conclusions are in good agreement with our earlier estimations which were obtained by an independent method [J. P. Gayda, P. Bertrand, F-X. Theodule, and J. J. G. Moura, J. Chem. Phys. 77, 3387 (1982)].
Optical Hartmann–Hahn resonance and the spatial correlation of inhomogeneous broadening in molecular solids
Authors: Cina Jeffrey A. , Silbey Robert
Published: July 2002

We propose the use of optical Hartmann–Hahn resonance between guest molecules in a solid in order to study the extent of spatial correlation of site energies in the inhomogeneous distribution. The correlation length and the form of the interaction which mediates the resonance between guest molecules can be determined from the time development of fluorescence.