bluuebunny/crossref_metadata_2025 huggingface dataset:
Solitary waves and solitons in liquid films
Authors: Joosten J. G. H.
Published: July 2002

We consider weakly dispersive and weakly nonlinear surface waves on liquid films in which long-range interaction forces are operative. As a first approximation, disturbances on both interfaces of the film can be described as a superposition of symmetrical and antisymmetrical waves even when considering nonlinearities. For small, but finite amplitudes, the antisymmetrical waves are free of nonlinearities, whereas for the symmetrical ones a Korteweg–de Vries equation can be derived. Depending on the particular thickness dependence of the long-range interaction forces the symmetrical disturbances lead to solitary waves with negative amplitudes (holes) or with positive amplitudes (intumescences). Taking as an example a soap film, with electrical double layer and London–van der Waals forces as interaction phenomenon, it is shown that observable solitons can be expected. It is put forward that the theory, presented here, is a contribution towards framing more sophisticated theories of liquid film (in)stability.
The inelastic neutron scattering spectrum of chromous acid at high energy transfers
Authors: Tomkinson J. , Taylor A. D. , Howard J. , Eckert J. , Goldstone J. A.
Published: July 2002

The inelastic incoherent neutron scattering spectrum of chromous acid, at 77 K, is presented. It is dominated by the intense bending mode at 1254 cm−1 with some modes at lower frequencies showing indications of dispersion. The antisymmetric stretch νas(OHS) {‖1〉-‖2〉} was assigned to a broad band centered at ∼2050 cm−1, significantly displaced for the IR assignment (1650 cm−1). The breadth of the band is due to the dispersion, and kinematic coupling, that is anticipated for this compound. These new data allows us to fit chromous acid more clearly into the general trend of hydrogen bonded compounds. Chromous acid compares very well in its overall INS spectrum with the isomorphous sodium bifluoride, except that the kinematic coupling between νas(OHO) and the symmetric stretch does not occur in this compound.
Internal mode vibrational interaction in plastic crystals: Application to the Raman spectra of strongly IR active modes
Authors: Breyman W. , Pick R. M. , Yvinec M.
Published: July 2002

The systematic development of the harmonic, intermolecular, internal mode interaction energy in terms of symmetry adapted Wigner functions of the molecular orientations is given for a plastic crystal. This development is used for the study of the Raman profile of a mode with a strong induced dipole-induced dipole interaction between the vibrating molecules. An approximate form of the profile is proposed, and compared with measurements made on NF3 by Gilbert and Nectoux.
Solvation thermodynamics of water in aqueous solutions. II. Water–ethanol mixtures
Authors: Ben-Naim A.
Published: July 2002

The solvation thermodynamics of both water and ethanol molecules is studied in mixtures of water and ethanol in the entire range of concentrations. It is found that addition of ethanol tends to make the solvation free energy of water less negative than in pure water. On the other hand, addition of water to pure ethanol, makes the solvation free energy of ethanol slightly more negative than the solvation of ethanol in pure ethanol. The sign of ΔΔG* is reversed for very high concentrations of water.
Reactions of uranium hexafluoride photolysis products
Authors: Lyman John L. , Laguna Glenn , Greiner N. R.
Published: July 2002

This paper confirms that the ultraviolet photolysis reactions of UF6 in the B band spectral region is simple bond cleavage to UF5 and F. The photolysis products may either recombine to UF6 or the UF5 may dimerize, and ultimately polymerize, to solid UF5 particles. We use four methods to set an upper limit for the rate constant for recombination of kr<2.0×10−12cm3 molecule−1 s−1. We measure the rate constant for UF5 dimerization to be kd=(1.0±0.2)×10−11 cm3 molecule−1 s−1. The principal method employed in these studies is the use of diode lasers to monitor, in real time, the changes in density of the species UF6 and UF5 after laser photolysis of the UF6 gas sample.
A cluster approach to the analysis of adsorbate vibrations
Authors: Lloyd Kathryn G. , Hemminger John C.
Published: July 2002

We present a method for the analysis of adsorbate vibrations which utilizes FG matrix techniques applied to finite clusters of substrate atoms. This method easily lends itself to the analysis of the vibrations of molecular adsorbates. Spectral densities are employed to generate calculated spectra. We have examined in detail the effects of cluster size and geometry on these calculations. To address the analysis of the vibrations of ordered overlayers we have applied periodic boundary conditions to the clusters. This results in modes with well defined values of the momentum parallel to the surface (k∥), allowing us to examine the dispersion of the mode frequency as a function of k∥. We apply these methods to the experimentally well studied systems of C(2×2) oxygen structure on Ni(100) and the C(4×2) CO structure on Ni(111).
Iron sulfur and iron molybdenum sulfur compounds: Comparison of molecular orbital calculations and spin-Hamiltonian analysis of Mössbauer spectra
Authors: Trautwein A. X. , Bill E. , Bläs R. , Lauer S. , Winkler H. , Kostikas A.
Published: July 2002

The electronic structures of mononuclear Fe–S complexes with a FeIIS4 core and of binuclear Fe–Mo–S complexes containing the FeS2Mo core have been calculated by a semiempirical molecular orbital method (iterative extended Hückel theory), followed by a spin-orbit coupling calculation on the five highest occupied iron-like molecular orbitals. Fine structure and hyperfine structure tensors and parameters (g, D, E, A, and electric field gradient) have been calculated and compared with data from spin-Hamiltonian analysis of Mössbauer measurements. For the mononuclear complex anions [Fe(SPh)4]2− and [Fe(dts)2]2− it was found that Vẑẑ is negative, D positive, and that the magnetic anisotropy places the preferred direction of the hyperfine magnetic field perpendicular to the Vẑẑ direction in agreement with spin-Hamiltonian results. The similarity of parameters of [Fe(SPh)4]2− and reduced rubredoxin (Rdred) confirms the suggestion that this anion has a ground electronic state practically identical to Rdred. The complex anion [Fe(dts)2]2− shows smaller anisotropy, and due to the fact that the orbital ground state is energetically not well separated from higher states in this case a strong temperature dependence of the quadrupole splitting is observed. For the binuclear complex anions [(SPh)2FeS2MoS2]2−, [S5FeS2MoS2]2−, and [Cl2FeS2MoS2]2− it was found that d is negative and Vẑẑ is positive. A specific feature of these binuclear Fe–Mo–S complexes is that Vẑẑ is directed perpendicular to the Fe–Mo line. (This theoretical result is confirmed by single crystal Mössbauer studies on [Cl2FeS2MoS2]2−; see the following paper in this journal.) The preferred direction of the magnetic hyperfine field is close to the Vẑẑ axis. The correlation of calculated values of ρ(0) and isomer shifts for mononuclear and binuclear compounds confirms the role of MoS2−4 as a charge withdrawing ligand.
Single crystal and magnetic Mössbauer studies on [(C6H5)4P][(C6H5CH2)–(CH3)3N][Cl2FeS2MoS2]
Authors: Winkler H. , Bill E. , Lauer S. , Lauer U. , Trautwein A. X. , Kostikas A. , Papaefthymiou V. , Bögge H. , Müller A. , Gerdau E. , Gonser U.
Published: July 2002

A single crystal of [(C6H5)4P][(C6H5CH2)–(CH3)3N][Cl2FeS2MoS2] has been investigated by Mössbauer spectroscopy with various orientations of the crystal with respect to the γ beam. From this investigation we derive that the main component of the electric field gradient tensor Vẑẑ is positive and oriented perpendicular to the Fe–Mo direction. This result was confirmed by additional single crystal measurements applying an external magnetic field, and by magnetically perturbed spectra of polycrystalline samples. The determination of the orientation of the electric field gradient tensor with respect to the molecular axes is a prerequisite for a decisive check of molecular orbital calculations on this type of binuclear bio-inorganic systems. (See also the preceding paper in this journal.)
Steady state reactive kinetics on surfaces exhibiting defect structures
Authors: Grinstein Fernando F. , Rabitz Herschel , Askar Attila
Published: July 2002

This paper considers the steady state situation of an active surface exposed to two species which may adsorb, diffuse on the surface, desorb, and also react. The surface is assumed to contain defect structures corresponding to either inherent lattice faults or foreign material on the surface. In addition, a simple model taking into account the local temperature and heat transfer into the bulk is also considered. A number of case studies are examined corresponding to different assumptions about the desorption and kinetic characteristics of the defect sites. The species profiles, their fluxes and curvatures, are examined to gain physical insight into the competing surface processes. The net effect of surface defects on chemical production rates was examined by integrating the local production rate over a test region on the surface. The reaction–diffusion equations of these models were solved by the multigrid technique which shows promise of providing an efficient numerical procedure capable of handling practical large scale problems.
Consequences of the balance between the repulsive and attractive forces in dense, nonassociated liquids
Authors: LaViolette Randall A. , Stillinger Frank H.
Published: July 2002

Current theories successfully predict the equilibrium structure of many simple liquids near their triple point from the repulsive molecular forces alone. We present a simple model substance whose liquid structure cannot be predicted adequately with only the repulsions. Furthermore, the model’s crystal structure changes drastically upon the removal of the attractions. This failure for our model to conform to the accepted picture of simple liquids gives us the opportunity to sharpen the boundary between substances which, respectively, may and may not be expected to so conform. We conclude that the structure of the corresponding solid deserves more weight than is conventionally given by modern theories of liquids.
Extended thermodynamic description of diffusion in an inert binary mixture
Authors: Rodríguez R. F. , García-Colín L. S. , López de Haro M.
Published: July 2002

The equilibrium concentration autocorrelation function for an inert binary mixture is calculated by means of extended irreversible thermodynamics. The ensuing generalized transport coefficient is explicitly evaluated and the corresponding k-dependent relaxation time is also obtained. The connection with neutron scattering experiments is suggested and expressions for the dynamic structure factor and the half-width dispersion relation are given.
Spatially resolved matrix isolation action spectrum of chromium carbonyls
Authors: Lang Valerie I. , Winn John S.
Published: July 2002

Spatially resolved matrix isolation spectroscopy, in which each position on a rigid, low temperature matrix is subjected to a different photolysis wavelength, was used to ascertain in a single experiment, the wavelength of dependence of the Cr(CO)5+CO and Cr(CO)4+CO photoassociation reactions in an Ar matrix. Relative quantum yields closely followed the absorption spectra of the individual carbonyl fragments.
The formyl and isoformyl cations. A pulsed electron beam high pressure mass spectrometric study of the energetics of HCO+ and HOC+
Authors: McMahon T. B. , Kebarle P.
Published: July 2002

Gas phase proton transfer equilibria involving compounds in the basicity regime near CO have been examined using pulsed electron beam high pressure mass spectrometric techniques. Using the well established proton affinity of C2H4 of 162.6 kcal mol−1 as a reference standard a new proton affinity for CO of 145.6 kcal mol−1 is established. The disagreement between this value and those obtained by photoionization mass spectrometric appearance potential measurements of HCO+ ions from compounds of the type HCOR is interpreted as being due to an activation energy barrier for the reverse process: HCO++R ̇→HCOR+. This barrier results from the significant geometry change involved in HCO+ formation. Correlations of proton affinity of O1S binding energies have been used to establish the proton affinity of the oxygen site of CO as 109 kcal mol−1. This result implies that HOC+ can be readily formed by reaction of H+3 with CO in interstellar clouds.
Statistical mechanics of the Xe/Ag(111) monolayer
Authors: Phillips James M. , Bruch L. W.
Published: July 2002

Calculations are reported of properties of solid and fluid phases of the Xe/Ag(111) monolayer. The thermal expansion of the solid at its sublimation curve is calculated and the monolayer triple point is estimated. Anharmonic effects in the solid are discussed and mean field approximations to the adsorption dipoles in the dense fluid are introduced. The interaction model reproduces the low temperature properties of the monolayer solid, but there are small departures from the experimental data for the thermal expansion above 60 K. The calculated triple point temperature is significantly lower than the values reported for other monolayer xenon systems.
Semiclassical theory in phase space for molecular processes: Scattering matrix as a special case of phase space distribution function
Authors: Takatsuka Kazuo , Nakamura Hiroki
Published: July 2002

The dynamical characteristic function (DCF) introduced previously as a kind of phase space distribution function is generalized so as to give an overlap integral of two wave packets which are to be propagated on different potential energy hypersurfaces. The development of our new semiclassical theory is motivated by the fact that the scattering (S) matrix is just one of this kind of overlap integrals. In this theory the semiclassical DCF is evolved in time by running a pair of classical trajectories, which are determined by two different Hamiltonians, total scattering Hamiltonian of the system, and unperturbed final channel Hamiltonian. The DCF becomes an overlap integral of two wave packets, if these two trajectories coincide with each other in the exit region at t=∞. The validity of this semiclassical theory is shown to be ensured, if the oscillatory wave packets are employed to construct the DCF. The S matrix in the stationary state scattering theory is given as a superposition of the wave packet DCF’s.
Rate coefficients for the oxidation reactions of zirconium ions with oxygen, nitric oxide, and carbon dioxide
Authors: Dheandhanoo S. , Chatterjee B. K. , Johnsen R.
Published: July 2002

Rate coefficients for the oxidation reactions of zirconium ions with oxygen, nitric oxide, and carbon dioxide have been determined in the near-thermal energy range (0.04 to about 0.4 eV) using a selected-ion drift apparatus. The reactions are found to proceed with large rate coefficients [∼5(−10)cm3/s at 300 K]. At elevated ion energies the reactions with NO and CO2 exhibit smaller rates. The secondary oxidation reactions of ZrO+ ions with the same reactants have rate coefficients about two orders of magnitude smaller than those for the first oxidation steps. The discharge ion source used to produce the zirconium ions in these experiments is described in some detail.
Irreversible thermodynamics of kinetic processes in multiple gas mixtures
Authors: Delale Can F.
Published: July 2002

The generalized H theorem of Boltzmann for a multiple gas mixture is written as the law of increase of entropy for small deviations from equilibrium by largely following a method first introduced by Prigogine. It is shown that the local rate of entropy production for such a mixture is a quadratic form of the generalized forces with the kinetic coefficients satisfying Onsager’s principle and all the pertaining properties. The classical expression for the entropy flux of a multiple gas mixture is also derived by this method.
Macromolecular diffusion constants: A calculational strategy
Authors: Goldstein Robert F.
Published: July 2002

Calculations of diffusion constants for rigid molecules of arbitrary shape are often based on hydrodynamic interactions between freely moving spheres. Molecules can be modeled as collections of spheres, and the interactions are approximated as pairwise additive. Singularities previously associated with nearly linear geometries and with geometries dominated by a large central element can be avoided by including torque-angular velocity and torque-velocity coupling, as well as the usual force-velocity coupling between spheres. I provide explicit formulas for these couplings for both nonoverlapping and overlapping spheres, and also show how to include effects of one sphere on the self-diffusion of another. This formulation is incorporated in an algorithm that involves neither Gauss–Seidel iterations nor direct inversion of a large matrix.
Alternative choices of reference potentials in thermodynamic perturbation theories
Authors: Lago Santiago
Published: July 2002

Several divisions of (m,n) potential are discussed. The different divisions are obtained by Taylor expansion around the minimum of potential. The theory is specifically applied to Lennard-Jones substances and Lennard-Jones mixtures. One of the divisions studied known as φ−3, shows better agreement with simulation results for density at zero pressure, and over a larger range of temperatures than WCA divisions. Mixing volume and excess volume also improve considerably and excess enthalpy appears to do the same. Results for GE are less satisfactory.
1
3C magnetic resonance study of the isotropic and nematic phases of 4-cyano-benzylidene-4′-octyloxyaniline
Authors: Wittebort R. J. , Subramanian R. , Kulshreshtha N. P. , DuPré D. B.
Published: July 2002

1 3C magnetic resonance is used to examine molecular ordering and dynamics in the nematogen 4-cyano-benzylidene-4′-octyloxyaniline (CBOOA). A simple, self-consistent model is proposed for evaluating the nematic phase uniaxial order parameter from the large downfield chemical shifts shown by the aromatic carbons on passing from the isotropic to the nematic phase. These results are an extension of the earlier observations of Pines and Chang on the related nematogen 4-methoxy-benzylidene-4′-butylaniline (MBBA). A series of T1 relaxation measurements are also reported and the relevant nuclear couplings for analyzing these results are identified. The results are interpreted in terms of (a) molecular scale reorientational diffusion with an axially symmetric orientational distribution function and (b) reorientation by collective angular modes.
On the stabilization of Ag in Y zeolites: Electron spin resonance observations
Authors: Narayana M. , Kevan L.
Published: July 2002

New experiments show that silver atoms can be observed by electron spin resonance (ESR) in Y zeolite that has been vaccum dehydrated at various temperatures to 773 K. However, the thermal vacuum dehydration procedure alone does not generate silver atoms observable by ESR; it is necessary to generate them by γ irradiation at 77 K after such thermal treatment. It is concluded that there is an apparent discrepancy between ESR and optical spectroscopic observations and the assignment of the nuclearity of silver species generated by thermal vacuum dehydration in Y zeolites.
A new functional with homogeneous coordinate scaling in density functional theory: F [ ρ,λ]
Authors: Levy Mel , Yang Weitao , Parr Robert G.
Published: July 2002

As previously shown [M. Levy and J. P. Perdew, Phys. Rev. A (in press)], the customary Hohenberg–Kohn density functional, based on the universal functional F[ ρ], does not exhibit naively expected scaling properties. Namely, if ρλ=λ3ρ(λr) is the scaled density corresponding to ρ(r), the expected scaling, not satisfied, is T[ρλ]=λ2T[ρ] and V[ρλ]=λV[ρ], where T and V are the kinetic and potential energy components. By defining a new functional of ρ and λ, F[ ρ, λ], it is now shown how the naive scaling can be preserved. The definition is F[ρ(r), λ]=〈λ3N/2 Φminρλ (λr1... λrN)|T̂(r1...rN) +Vee(r1...rN)| λ3N/2Φminρλ(λr1...λrN)〉, where λ3N/2 Φminρλ(λr1... λrN) is that antisymmetric function Φ which yields ρλ(r)=λ3ρ(λr) and simultaneously minimizes 〈Φ|T̂(r1...rN) +λVee(r1...rN)|Φ〉. The corresponding variational principle is EvG.S.=Infλ, ρ(r){∫  drv(r) ρλ(r)+λ2T[ ρ(r)] +λVee[ ρ(r)]}, where EvG.S. is the ground-state energy for potential v(r). One is thus allowed to satisfy the virial theorem by optimum scaling just as if the naive scaling relations were correct for F[ ρ].
Photoabsorption probabilities of H2 levels lying near the H(1S) + H(n=2) dissociation limit
Authors: Glass-Maujean M. , Breton J. , Guyon P. M.
Published: July 2002

The transition probabilities for Hydrogen B 2pσ1Σ+u (v′=32–35)←X 1Σ+g (v″=0), C 2pπ1Πu (v′=11–13)←X (v″=0), and B′ 3pσ1Σ+u (v′=5–8)←X (v″=0) were measured using synchrotron radiation in order to investigate the variation of the transition probabilities in the region of the dissociation threshold. The experimental data which agree with calculated probabilities indicate that B′ and C state continua may be of comparable intensities.
On the charge compensation effects in Mn(II) doped (NH4)2SbF5: EPR study
Authors: Prasad L. Sreeramachandra , Subramanian S.
Published: July 2002

Electron paramagnetic resonance of Mn(II) ion doped in bis (ammonium) pentafluorostibnate is reported. Local charge compensation is proposed as the reason for the doubling of the expected single site. A ±20° rotation of the MnF3−5 moeity about the crystallographic a axis has been attributed to charge compensation processes. The D tensor is found to have the values Dzz=0.0358 cm−1, Dyy=−0.028 62 cm−1, Dxx=−0.007 26 cm−1; the Mn hyperfine coupling is found to be −0.0095 cm−1. The apical flourine does not give resolved hyperfine coupling, while the four basal flourine atoms give hyperfine couplings in the range amax=0.0018 cm−1, amin=0.0015 cm−1.
A dynamic model for locally stiff straight chain polymers
Authors: Szorek Ryszard
Published: July 2002

The influence of intramolecular interactions of the type: U=U(bn, cn, bṅ cn) on the dynamic properties of a polymer chain in dilute solution was determined by introducing into the ‘‘hopping model’’ described by Jones et al., the dynamic nonequivalence of bonds for a linear homopolymer chain.
Comment on ‘‘Negative ion formation in fluoroethers and fluorosulphides’’
Authors: Spyrou S. M. , Hunter S. R. , Christophorou L. G.
Published: July 2002

The fragmentation of HF−2 into HF and F− is discussed. The electron impact formation of HF−2 from fluoroether CF2HOCF2H is further discussed and the electron affinity of HF2 is given. (AIP).
Inelastic neutron scattering on the tetrameric alkoxo-bridged copper(II) complex [CuCl (OCD2CD2N(C2D5)2)]4
Authors: Astheimer H. , Weitzel H. , Haase W.
Published: July 2002

By means of inelastic neutron scattering experiments, we have determined the excitation energy of the first excited state in the magnetic exchange coupled Cu four-nucleus complex [CuCl (OCD2CD2N (C2D5)2)]4. We found for the transition energy the value 4.3 meV, in good agreement with results of magnetic susceptibility experiments. The magnetic origin of this excitation is demonstrated by its temperature and momentum dependence.
Thermochemical study of the molecule BaC2
Authors: Gingerich K. A. , Choudary U. V. , Krishnan K. , Hilpert K.
Published: July 2002

The enthalpy of the reaction Ba(g)+2C(graph.)=BaC2(g) has been determined by Knudsen effusion mass spectrometry over a barium alloy with noble metals contained in a graphite cell. The value ΔH○0 =252.5± 11.5kJ mol−1 has been obtained from second- and third-law evaluations of the equilibrium vapor in the temperature range 1778–2286 K. This reaction enthalpy has been combined with ancillary literature data to derive the following thermodynamic properties in kJ mol−1 of gaseous BaC2: the atomization energy, ΔatH○0 , 1180.9±12.2; the standard heat of formation, ΔfH○298 , 437.1±14.2; the enthalpy of sublimation of BaC2(s), ΔsubH○298 , 511.2±17.1; and the bond dissociation energy, D○0 (Ba–C2), 581.7±14.8. The results are discussed with regard to their possible significance in reactor technology.
Dynamic correlations and microscopic fluid mechanics of a dense fluid
Authors: Irazoqui Horacio A. , Eckey Doris A. , Dahler John S.
Published: July 2002

A method is developed for generating approximate numerical solutions to the coupled kinetic equations for the singlet distribution functions specific to a test particle and to a particle belonging to the surrounding solvent or background fluid. These kinetic equations are replaced with equivalent equations of motion for two sets of scalar valued quantities, each of which depends on time and a single spatial coordinate or displacement variable. These scalar valued quantities are contractions of tensor valued correlation integrals associated with a particular pair of momentum space basis functions. Formulas are given which relate these quantities to the correlation functions which are most directly connected to the observables generated by scattering experiments and by molecular dynamics computer simulations.
Remarks on the mutual diffusion coefficient of Brownian particles
Authors: Yoshida Nobuo
Published: July 2002

The mutual (or collective) diffusion coefficient of Brownian particles treated in most of previous microscopic theories is regarded as defined on the basis of the dynamic structure factor. It is pointed out for cases where both direct and hydrodynamic pair interactions are present between Brownian particles that this diffusion coefficient does not satisfy the generalized Einstein relation which results from conventional irreversible thermodynamics and which should be obeyed by the diffusion coefficient as would be determined by conventional gradient diffusion experiments. This is ascribed to the fact that the diffusion coefficient based on the dynamic structure factor is generally not identical with the conventional diffusion coefficient, i.e., whereas the latter diffusion coefficient describes the collective diffusion of Brownian particles under conditions of uniform temperature and pressure, the former describes that under conditions of uniform temperature and uniform chemical potential of solvent. A correct expression for the conventional diffusion coefficient is derived by taking this difference into account. Both diffusion coefficients are evaluated for the case of hard spheres.
Theory of phonon inelastic atom–surface scattering. II. Approximate methods and applications to resonance and adsorption
Authors: Choi B. H. , Poe R. T.
Published: July 2002

Approximate theoretical schemes for the calculation of the phonon inelastic scattering were derived from the formulation in the preceding paper. They can be adopted to flexible input potentials and are more realistic compared to the schemes that have been employed so far and at the same time are capable of yielding effective ab initio computation. An iterative coupled integral equation method thus obtained is much more tractable than that of the coupled differential equation when the phonons are taken into account. In this approach, the multiphonon transitions are readily obtained as higher order processes with the potential matrix elements being limited to the dominant one-phonon transitions. The S matrix elements of both elastic reflection and simultaneous diffraction and phonon transitions can also be obtained from the coupled channel transition matrix (CCTM) approach derived from the diffractive wave Green function where the coupling between the reciprocal

lattice points due to the atom–surface interaction are taken into consideration. A unitarization method of CCTM S matrix was also discussed. Employing the diffractive standing wave Green function, we derived the coupled channel reactance matrix (CCRM) method. Some advantages of this scheme over CCTM are that the scattering wave functions needed for the calculation are all real, and the unitarized S matrix can be directly obtained within a truncated basis set. As an application of the present scattering formulation, the bound state resonance scattering method of the atom–surface system was presented within the framework of Feshbach internal excitation approach. Our emphasis here is the role of the phonon transitions in the selective adsorption and desorption. Our method is adoptable again to arbitrary and flexible input potentials and yields ab initio calculational procedures from which the resonance energies, the energy shift and width functions, the line shapes, and the intensities of the simultaneous diffraction and phonon transitions can be obtained. Among other effective calculational schemes, we discussed a method where the bound state resonance scattering amplitude is computed from simplified wave functions which are obtained as products of the spatial wave function generated from the elastic diffraction potential and that of the phonon state. The nonresonant potential scattering amplitude in the method is obtained from CCTM approach within the open channels. Finally, a method of obtaining the quantal adsorption rates and sticking probabilities, which deals with the half-collision processes, was presented as another application of our scattering formulation.
Generation of oscillations in polymerization–depolymerization systems
Authors: Hyver C.
Published: July 2002

The examples given below show that open systems where the only reaction involved are polymerizations and depolymerizations are able to oscillate. The limit cycles obtained are local or global.
Quenching of the 1.0 and 2.3 μm excited electronic states of PuF6 at room temperature by selected rare gases and small polyatomic molecules
Authors: Barefield J. E. , Rice W. W. , Dye B. A.
Published: July 2002

The quenching rate constants kq for the following rare gases and small molecules (He, Ar, Xe, H2, D2, N2, O2, F2, Cl2, HF, CO, CO2, CH4, CHF3, CF4, NO2F, SOF4, SF6, and UF6) are reported in units of cm3 molecule−1 s−1 for both the 1.0 and 2.3 μm excited electronic states of PuF6 (see Table I). The self-quenching rate constants for PuF6 at room temperture are kq(1.0 μm) =1.12±0.01×10−12 and kq(2.3 μm)=5.01±0.11×10−15 cm3 molecule−1 s−1. The magnitude of the quenching rate constants for most all of the gases considered above suggest that the dominant process in the collisional deexcitation of excited state PuF*6 (1.0 or 2.3 μm) molecules at room temperature is physical quenching (i.e., E-T or electronic-to-translational collisional energy transfer). Our data also indicate that E-V (electronic-to-vibrational) energy transfer is responsible for the efficient quenching of electronically excited PuF6 by H2, HF, CH4, and CHF3. There is also evidence from our data that the efficient quenching of the excited states of PuF6 by ground state PuF6 molecules proceeds via resonant energy transfer.
Delay time experienced by a particle undergoing resonant scattering: The case of the 3D square well
Authors: Munoz Raul C.
Published: July 2002

A formalism to calculate the time delay experienced by a particle undergoing scattering is presented. The formalism is a natural extension of Wigner’s delay time to wave packets which do not exhibit a well defined angular momentum. The delay depends only on the partial wave phase shifts characterizing the scattering event. The formalism is tested by applying it to the 3D square well. The results are shown to agree with the known properties of resonant scattering as deduced from a study of the poles of the scattering matrix in the complex energy plane.
A kinetic energy density functional
Authors: Harriman John E.
Published: July 2002

A functional of the electron density is defined which has as its value the minimum possible kinetic energy for a system of n electrons having the given density. Analytic expressions are given for upper and lower bounds on the functional, and algorithms by which it can be evaluated are discussed. Use is made of the set of n-respresentable 1-matrices consistent with the given density and a matrix representation in terms of special equidensity orbitals.
Oxidation and reduction in irradiated binary crystals of resorcinol and progesterone
Authors: Box Harold C. , Budzinski Edwin E.
Published: July 2002

The binary single crystals of resorcinol and progesterone were x-irradiated at 4.2 K. The semiquinone of resorcinol was generated by radiation induced oxidation. The oxidation and reduction products were identified from ESR and ENDOR measurements. (AIP)
EPR and thermoluminescence investigations of Mn2+ in LuPO4, YPO4, and ScPO4
Authors: Boldú O. J. L. , Muñoz P. E. , Abraham M. M. , Boatner L. A.
Published: July 2002

Divalent manganese has been incorporated in both single crystals and powders of the zircon-structure hosts LuPO4, YPO4, and ScPO4. The single-crystal specimens were grown by slowly cooling a Pb2P2O7 flux from 1360 °C, and finely divided powders of these materials were also prepared using a molten urea precipitation technique. Electron paramagnetic resonance studies have shown that tetragonal symmetry Mn2+ sites are present in both single crystals and powders of ScPO4 and LuPO4 but are not present in either YPO4 single crystals or powders. An orthorhombic symmetry spectrum was observed for Mn2+ in single crystals of all three hosts and in YPO4 powders. Orthorhombic spectra were not found in Mn2+ doped powders of ScPO4 and LuPO4. In the case of the orthorhombic-symmetry spectra, four sites were present in these tetragonal zircon-structure hosts. The sites were magnetically inequivalent but were equivalent in terms of the strength and symmetry of the crystalline electric field. The orientations of the orthorhombic-site principal axes relative to the crystallographic axes were determined in each case. The axial spin-Hamiltonian parameter b02 was found to be positive in the case of the tetragonal-symmetry sites and negative for the orthorhombic-symmetry spectra. Thermoluminescent properties of these materials were also investigated.
Fast orientational motional correlation time measurements from ESR spectra of perdeuterated, normal nitroxide radicals with 14N(I=1)
Authors: Shetty Anil , Lee Sook
Published: July 2002

The new method recently formulated for analyzing the fast tumbling motional ESR hyperfine spectra of perdeuterated nitroxide radicals enriched with 15N(I=1/2) TANOLD-15 (4-hydroxy, 2,2,6,6-tetranethylpiperidine-d17-1-oxyl) are applied to perdeuterated, normal nitroxide radicals with 14N (I=1), TANOLD-14, which are widely utilized as spin probes and labels. The fast motional correlation times τ obtained from different pairs of ESR hyperfine lines from TANOLD-14 spin probes in poly(ethylene oxide) (PEO) polymer matrix are not only mutually consistent, but also agree with those obtained from TANOLD-15 spin probes on the same host matrix. The τ values determined with the present method for normal nitroxide radicals containing 14N should be more accurate and reliable than those obtained with other conventional methods.
Mössbauer and susceptibility study of inter-heme spin coupling in [Fe (OEP) (2-MeHIm)]+ dimers
Authors: Gupta G. P. , Lang George , Scheidt W. Robert , Geiger David K. , Reed Christopher A.
Published: July 2002

Mössbauer spectra of polycrystalline [Fe(OEP)(2-MeHIm)]ClO4 ⋅ CHCl3 (OEP=octaethylporphyrinate; 2-meHIm=2-methylimidazole) were recorded over a range of temperatures (1.54 to 195 K) and applied magnetic fields (0–6 T). Magnetic susceptibility was measured at both 0.2 and 1 T in the temperature range 6–300 K. Mössbauer parameters δ=0.40 mm/s and ΔE=1.39 mm/s at 4.2 K, and the high temperature susceptibility Neff=6 at 300 K indicated high spin iron, but no simple spin Hamiltonian would reproduce the rapid decrease of Neff below 50 K. We interpret the data by assuming a zero field splitting D=12 cm−1 and invoking an antiferromagnetic exchange interaction J=−0.8 cm−1 between the five-coordinate iron atoms of closely spaced face-to-face heme pairs in the crystal. Slow spin relaxation at low temperature permits observation of level crossing and confirms the interpretation. It also permits the detection, through low field Mössbauer measurements, of a small rhombic distortion with E=0.024 cm−1. Mössbauer spectra of the same compound but as a dibromomethane solvate, [Fe(OEP)(2-MeHIm)]ClO4 ⋅ CH2Br2, yield generally similar parameter values, but suggest a slightly larger coupling, J=−0.85 cm−1, consistent with the fact that the paired iron atoms are known to be closer in this material.
On the hydrodynamics of a solvent-saturated lipid bilayer. II. Stability criteria
Authors: Bisch P. M. , Wendel H.
Published: July 2002

We investigate the impact of the steric force (modeled in part I) on the linear dynamics of a thin lipid film with plane parallel surfaces at rest. We perform a stability analysis of the hydrodynamic fluctuations of the film, exposed to an external electric field. For long wavelengths, we find the stability of the film against bending to be governed by the total film tension. Stability against periodic thickness fluctuations (squeezing) is determined by the film elasticity. In both cases, sterics counteracts the destabilizing action of the van der Waals and electrostatic forces. We establish a diagram which displays the regimes of film stability as a function of film thickness and electric cross film potential. The film is predicted to be stable against squeezing for film thickness smaller than a critical film thickness (of the order of 60 Å). The latter depends slightly on the applied voltage. Voltages larger than 190 mV trigger bending of low tension films (single interface tension: 0.05 dyn/cm) above and just below the critical squeezing thickness. For these voltages, bending of the film is prevented only by reducing the film thickness.
Charge transfer in polypyrrole
Authors: Buhks Ephraim , Hodge Ian M.
Published: July 2002

Experimental electrical conductivity and optical absorption data are presented for fully oxidized polypyrrole. A charge transfer theory is described which gives an excellent account of the temperature dependence, carrier density dependence, and magnitude of electrical conductivity. The reorganization energy calculated from the temperature dependence of conductivity, 0.23 eV, is in good agreement with the value obtained from the near IR dielectric loss spectrum, ∼0.25 eV. Self-consistent hopping distances of about 5–10 Å are obtained from the reorganization energy, conductivity preexponential factor, and carrier density. Hopping between localized sites associated with the counteranion is indicated.
Chemisorption of laser-generated fluorocarbon free radicals on single crystal silicon
Authors: Roop Bobbi , Joyce Stephen , Schultz Jocelyn C. , Steinfeld Jeffrey I.
Published: July 2002

We have investigated the interaction of fluorocarbon free radicals generated by infrared multiple-photon dissociation of C2F6 with Si(111)7×7 surfaces. X-ray photoelectron spectroscopy of F(1s) and C(1s) core levels is used to monitor the surface reactions. C2F6 does not chemisorb on these surfaces, even when vibrationally excited by CO2 laser pumping. CF3 radicals are strongly chemisorbed and undergo partial dissociation on a clean silicon surface. This chemisorption process is partially blocked by adsorbed adventitious carbon.
Intramolecular dynamics and multiresonant absorption spectroscopy. II. Power broadening and superposition states in double resonant two-photon excitation
Authors: Bigio Laurence , Ezra Gregory S. , Grant Edward R.
Published: July 2002

A simple theoretical model is developed for relative band intensities in multiresonant molecular three-photon ionization. A specific case is considered in which a dissociative system of states exists at the energy of the first photon and a discreet level system at the second. A third photon ionizes the molecule. Experimentally such a system shows non-Franck–Condon transitions with relative intensities that depend on laser power. Model calculations trace this dependence to the coherent preparation of a superposition state over the levels at the energy of the first photon that lie within the power-broadened bandwidth of the laser. For reasonable choice of field and molecule parameters, the model reproduces well the power-dependent band intensities reported in the previous paper for NO2.
On bimolecular kinetics, the Bloch equation and Wigner path integrals
Authors: McLafferty Frank
Published: July 2002

We continue our study of Wigner path integrals. We first define a Wigner path integral for the kernel of the Wigner–Bloch equation, solve it for the free particle and harmonic oscillator cases, discuss the physical interpretation which is new and then we apply it (along with the path integral representation of the Liouville equation) to obtain a path integral representation in phase space of the quantum transition state theory of Miller. We also obtain an expression involving products of Wigner kernels for the correlation function form of the exact bimolecular rate constant.
Picosecond dynamics of barrier crossing in solution: A study of the conformational change of excited state 1,1′-binaphthyl
Authors: Millar David P. , Eisenthal Kenneth B.
Published: July 2002

The rates of optically induced conformational changes of excited state 1,1′-binaphthyl in a series of alcohol solvents were measured by a picosecond laser technique. Excellent agreement with experiment is found for the Kramers model for both the intermediate and high friction regimes using a frequency independent friction coefficient evaluated from classical hydrodynamics. This is the first observation of Kramers behavior in the intermediate friction regime and indicates that deviations from Kramers behavior is not a universal phenomenon in the conformational dynamics of flexible molecules in solution. It also emphasizes the possibility that the observed deviations from the Kramers model can be due to effects other than non-Markovian friction.
Debye–Waller effects in helium diffraction from Ni(115)
Authors: Conrad E. H. , Kaufman D. S. , Allen L. R. , Aten R. M. , Engel T.
Published: July 2002

Debye–Waller effects in helium diffraction from Ni(115) have been analyzed in order to assess corrections required to determine surface corrugation functions from data taken at nonzero temperatures. It can be concluded that effective corrections can be made for all diffraction peaks by measuring the intensity as a function of temperature for the specular peak. Nonlinearities in Debye–Waller plots at high temperatures can be attributed to anharmonic effects but measurements must be carried out at Bragg angles of the three-dimensional lattice to avoid spurious nonlinearities due to the formation of kinks and steps. It can be further concluded that surface corrugation functions can be accurately determined without Debye–Waller corrections in general if the surface temperature is below 300 K and the Debye–Waller factor is not appreciably greater than the value for Ni(115).
Structure of bimetallic clusters. Extended x-ray absorption fine structure (EXAFS) studies of Re–Cu, Ir–Cu, and Pt–Cu clusters
Authors: Meitzner G. , Via G. H. , Lytle F. W. , Sinfelt J. H.
Published: July 2002

The extended x-ray absorption fine structure (EXAFS) associated with the LIII absorption edges of rhenium, iridium, and platinum, and the K absorption edge of copper, has been used to study the structures of silica supported Re–Cu, Ir–Cu, and Pt-Cu, bimetallic clusters. The atomic ratio of copper to the other metal was approximately one in all cases. The systems were chosen to investigate the effect of varying miscibility of the components on the structural features of the bimetallic clusters. At one extreme, platinum and copper are totally miscible in the bulk. At the other extreme, rhenium and copper are completely immiscible. Iridium and copper are only slightly miscible in the bulk. In the bimetallic clusters, atoms of rhenium, iridium, or platinum are all coordinated to copper atoms about as extensively as they are to atoms of their own kind. This result is particularly interesting for the Re–Cu and Ir–Cu clusters, in view of the limited miscibility of either iridium or rhenium with copper in the bulk. The surprisingly good coordination of iridium and rhenium to copper is attributed to a very high state of dispersion of these metal clusters.
Local density approximations to moments of momentum of diatomic molecules with Hartree–Fock–Roothaan quality electron distributions
Authors: Allan Neil L. , Cooper David L. , West Craig G. , Grout Peter J. , March Norman H.
Published: July 2002

By generalizing local density arguments for atoms it is found that the mth moment of momentum for molecules 〈pm〉 is proportional to ∫ρ(r)1+(1/3)mdr, where ρ(r) is the electron density. This relation is tested for m=−1, 1, and 2 using wave functions of Hartree–Fock–Roothaan quality: 〈pm〉 is computed directly and the density integrals are evaluated using ρ(r) generated from these wave functions. Eleven neutral diatomic systems and two singly charged positive ions are considered. Apart from changes in the proportionality constants, the local density approximation is vindicated; for m=−1, 1, and 2 the magnitudes of the changes in the predicted constants are less than ∼10%. Finally, 〈p〉, which is proportional to the Dirac–Slater exchange energy, is compared with the appropriate self-consistent Hartree–Fock–Roothaan energy terms and, again, a linear relationship emerges.
The glass transition in an ionomer: Interpretation of Mössbauer data
Authors: Meagher A. , Smyth G. , McBrierty V. J. , Coey J. M. D. , Pineri M.
Published: July 2002

The glass transition in α,ω-dicarboxylatopolybutadiene (M̄n=4600) neutralized with ferric iron has been studied by quasi-static and high frequency techniques (shear modulus, differential scanning calorimetry, pulsed NMR and Mössbauer spectroscopy). The temperature dependence of the Mössbauer recoilless fraction f begins to deviate from Debye behavior at the quasi-static glass transition at T=190 K due to softening of the long-wavelength vibrational modes. f  becomes unmeasurably small above a higher temperature T0 which is identified as the glass transition on a time scale of 10−7 s.
Optical spectroscopy of PbCl2 particles embedded in a NaCl host matrix
Authors: Zaldo C. , García Solé J. , Diéguez E. , Agulló-López F.
Published: July 2002

The absorption and luminescence data reported in this paper definitely confirm that the precipitates formed during high-temperature aging of Pb-doped NaCl are PbCl2 microcrystals. A detailed comparison of the optical spectra of the precipitates and free PbCl2 is presented. The absorption and luminescence spectra are essentially similar in both cases, although the splitted structure of the prominent exciton band has now been resolved for the first time in the absorption spectrum of the precipitates. The splitting has been interpreted in terms of the noncubic crystal field effect on the 3P1 excited level of Pb+2 which is considered as a cationic exciton. The gap energy Eg and the binding energy εb of the exciton have also been determined (Eg=4.86 eV, εb=0.18 eV). The same UV and blue luminescence bands, as well as a thermally induced interconversion among them, have now been observed for the precipitates as well as for free PbCl2. This luminescence behavior, not previously understood, has been explained in terms of two coexisting AT and Ax minima in the adiabatic energy surface of the 3P1 level of a Pb+2 localized exciton (Fukuda’s model).
X-ray diffraction investigation of Co(II) ions in borosilicate glasses
Authors: Corrias A. , Magini M. , de Moraes M. , Sedda A. F. , Musinu A. , Paschina G. , Piccaluga G.
Published: July 2002

The radial distribution functions of cobalt glasses with 6%, 8% and 14% CoO are compared with those of suitable cobalt-free borosilicate matrices leading to ‘‘difference distribution curves’’ representative of the cobalt structural arrangement. Analysis of the curves indicates that cobalt ions are surrounded by approximately four oxygen neighbors at the distance expected for fourfold coordination.