bluuebunny/crossref_metadata_2025 huggingface dataset:
The spin-dependent force model of molecular liquids: Solution of the mean spherical approximation (MSA)
Authors: Juanós i Timoneda J. , Haymet A. D. J.
Published: July 2002

The Ornstein–Zernike equation is solved in the mean spherical approximation (MSA) for a model liquid with an internal degree of freedom. The spatial variation of the potential outside the hard core is given by a combination of Yukawa potentials. We compute the equations of state from analytic expressions derived in this work, and also the spin-dependent pair correlation function and its value averaged over the internal degrees of freedom. The model system displays an increase of the pressure over the hard-sphere system, and the pair correlation function that depends on the internal degrees of freedom shows a structure consistent with the effect of such degrees of freedom on interparticle interactions. The usual strengths and inconsistencies of the MSA are observed in this work. These calculations provide a starting point, other than computer simulations, for treatment of liquid models with many internal degrees of freedom, for the study of polar liquids and chemical reactions in solution.
Dynamics of the reactions of C+ with C2H6
Authors: Curtis R. A. , Farrar J. M.
Published: July 2002

We present a crossed beam study of the major reactive channels of C++C2H6 in the collision energy range between 0.8 and 1.6 eV. We find that C2H+5 formation proceeds as a direct hydride abstraction reaction with the accompanying CH product scattered in the forward hemisphere. The product recoil energy distribution shows a distinct Gaussian shape that we correlate with the nature of the potential energy surface for transfer of the light hydride ion between two heavy species. C2H+3 formation occurs through two pathways: the first and most important route is direct interaction of C+ with C2H6 to form a new C–C bond with the ejection of CH3 in a collinear interaction that leads to backward scattering of the ionic product. A second, and much less probable pathway involves formation of this product through a transient collision complex living a significant fraction of a rotational period. The condensation product C3H+3 is by far the most abundant C3 product observed in this collision energy range. The sideways-peaked angular distribution for its formation is consistent with a mechanism where the initially formed C3H+6 complex decays in a step in which a molecule of H2 is ejected in a direction perpendicular to the plane of rotation defined by the three carbon atoms. The kinetic energy distribution for this channel is significantly broader than the predictions of statistical phase space theory and underscores the importance of potential energy exit channel barriers in determining product recoil in such elimination processes. We discuss these results in the context of a schematic potential energy surface incorporating thermochemical data and results of ab initio calculations.
Photoabsorption of molecules at corrugated thin metal films
Authors: Leung P. T. , Kim Young Sik , George Thomas F.
Published: July 2002

A phenomenological study has been carried out for the photoabsorption of molecules in the vicinity of a corrugated thin metal film. In particular, perturbative results for a grating silver film have been obtained to first order in the corrugation parameter, where the effect of the incident field coupled with the long-range surface plasmon is observed. Based on the different coupling nature between the radiations from the incident plane wave and from the molecular dipole to the substate film, it is proposed that, through control of the various parameters of the film, enhanced selective photoabsorption may be achieved.
Collisional line shape for the rotational spectrum of methylcyanide: Experiments and theory
Authors: Buffa G. , Giulietti D. , Lucchesi M. , Martinelli M. , Tarrini O.
Published: July 2002

A collisional line-shape study specialized in the rotational spectrum of CH3CN is presented. This system provides a test for pressure broadening and shift theories which has until now been hindered by inadequate theory and by experimental results at variance. New accurate measurements are presented which allow an explanation of the problem related to the reliability of experimental data. The thorough comparison made between measurements and an improved theory—obtained inside the frame of the Anderson–Tsao–Curnutte approximation—demonstrates the ripeness of the study of such rotational spectrum from both the experimental and theoretical points of view.
A surface enhanced Raman study of carbon dioxide coadsorption with oxygen and alkali metals on silver surfaces
Authors: Maynard Kevin J. , Moskovits Martin
Published: July 2002

The adsorption of CO2 on clean silver films, oxygen treated silver films and alkali metal predosed silver films has been studied with surface enhanced Raman spectroscopy (SERS) and work function measurements. At 50 K, CO2 was observed to adsorb on vapor deposited silver films with downward vibrational frequency shifts of ≈15 cm−1 from the corresponding gas phase values. On oxygen pretreated films, CO2 reacts to form a surface carbonate. Isotope studies with C18 O2 show that the carbonate is formed from the reaction of CO2 with oxygen, and not from the disproportionation of CO2 . Based on the observed intensities of the vibrational bands, an orientation of the carbonate is suggested in which the molecule’s plane is perpendicular to the surface. On silver films dosed with submonolayer amounts of potassium, CO2 reacts to form the C2v isomer of a K+CO−2 surface complex. Bands at 755 and 1220 cm-1 observed with potassium dosed surfaces were assigned to the νs and δ vibrational modes of CO−2. The orientation of the CO−2. ion is likely with its molecular plane perpendicular to the surface and bonded to the alkali metal through the O atoms. Experiments on lithium and cesium dosed silver surfaces led to similar conclusions. The similarity of these vibrational spectra to those reported in our recent study of CO adsorption on potassium predosed silver in which we proposed that a KOC surface complex was formed [K.J. Maynard and M. Moskovits, Chem. Phys. Lett. 142, 298 (1987)] lead us to the conclusion that K+CO−2 was formed, in that case also, from the reaction of CO with residual oxygen. The SERS band intensities associated with CO−2 showed an amonotonic dependence on CO2 exposure. This has been ascribed to depolarization by the induced dipole fields of the adsorbate molecules upon one another. Experiments with varying potassium coverage imply that the K+CO−2 ion pairs are not randomly distributed on the surface but are aggregated into islands. A Monte Carlo simulation confirmed the conclusion that only island formation could adequately account for the observed results.
Position moments linearly averaged over the wave function. II
Authors: Koga Toshikatsu
Published: July 2002

Based on the Fourier transform of the position–space Schrödinger equation in a finite domain, a set of relations is derived among position moments linearly averaged over the wave function in that domain. The present results add nontrivial information for the structure of the Schrödinger equation, including the known relations for an infinite domain. A special case provides a regional form of the zero momentum energy expression, which measures the accuracy of wave functions in some specific region.
Longitudinal and transverse waves in a viscoelastic fluid
Authors: Miles Danny G. , Le Nhat , Kivelson Daniel
Published: July 2002

We have studied both the vertical–vertical and vertical–horizontal dynamic light scattering spectra of triphenylphosphite over a wide range of viscosities, temperatures, densities, and pressures. In particular, we have focused on the propagating modes, both the longitudinal (Brillouin) and the transverse (shear) modes. We find that the linewidths of the associated spectral side peaks can be described over the entire range, from low viscosity hydrodynamic to high viscosity viscoelastic behavior, as a function solely of viscosity. The same is true for the frequency shifts of the shear waves but not for those of the longitudinal waves. We give an interpretation of these results. We also find that at a given temperature the shifts are unexpectedly linear in pressure over the entire range; this, we believe, is not a consequence of the pressure dependence of the adiabatic sound speed, but rather of a frequency-dependent viscosity with a broad distribution of relaxation frequencies. Our analysis suggests that the low-frequency longitudinal and shear viscosities are rather similar.
Interactions of CO and surface K: Negligible CO adsorption on K/Ag(111)
Authors: Roop B. , Blass P. M. , Zhou X.-L. , White J. M.
Published: July 2002

Unlike transition metals which are active for chemisorption of CO, Ag(111) shows no tendency to adsorb CO at 100 K even when various amounts of K are added. This observation supports the proposal of Solymosi and Berko (Ref. 1) that bonding of CO with the host metal plays an important role in the interactions of K and CO on transition metals.
Diffusion-controlled reactions of ions in fluctuating ionic atmospheres
Authors: Sridharan S. , McCammon J. A. , Hubbard J. B.
Published: July 2002

The effects of co- and counterion dynamics on the rates of diffusion controlled reactions are investigated. A model system consisting of univalent soft spheres in a uniform dielectric medium is simulated by the Brownian dynamics method. This system is used to study the effects of ionic atmosphere dynamics on the rate of recombination of an ion pair. The results show a small (2%) increase in the rate compared to the traditional Debye–Hückel description. A parallel calculation where the atmospheric ions are frozen in equilibrium configurations around the target (unperturbed by the incoming reactant) yields results which are very close to the Debye–Hückel results. Larger nonequilibrium effects are expected for multivalent electrolytes.
Dynamics of helical worm-like chains. X. Oscillatory flow birefringence
Authors: Nagasaka Kyosuke , Yoshizaki Takenao , Yamakawa Hiromi
Published: July 2002

Oscillatory flow birefringence of flexible chain polymers in dilute solution is studied on the basis of the discrete helical worm-like chain such that a local polarizability tensor is attached rigidly to each of the subbodies composing the chain. The mechano-optic coefficient S is formulated by the time-correlation function formalism, and is expressed in terms of the (1,1)- and (1,2)-body time-correlation functions of ‘‘total angular momentum quantum number’’ L=2. The (1,2)-body time-correlation functions are evaluated following a procedure analogous to the one developed previously in the higher-order subspace approximations. It is then shown that the three branches (one global and two local) of the viscoelastic eigenvalue spectrum and the five local branches of the magnetic one make contributions to S. With these results, examination is made of the frequency behavior of the phase angle θs of S and also of its dependence on the local polarizability tensor. It is found that the high-frequency behavior of observed θs, which deviates from the prediction for the Zimm spring–bead model, may well be explained by the contributions from the local chain motions with proper local polarizability tensors. A comparison of theory with experiment is made for atactic polystyrene with respect to the frequency dependence of θs, and the good agreement is found with the model parameters determined from an analysis of experimental data for equilibrium properties.
Static and dynamic properties of solid CO2 at various temperatures and pressures
Authors: Etters R. D. , Kuchta Bogdan
Published: July 2002

A constant pressure Monte Carlo formalism, lattice dynamics, and classical perturbation theory are used to calculate the thermal expansion, pressure–volume relation at room temperature, the temperature dependence of the zone center libron frequencies, and the pressure dependence of the three vibron modes of vibration, in solid CO2 at pressures 0≤p≤16 GPa and temperatures 0≤T≤300 K. The agreement with experiment is good. At room temperature the observed Pa3 phase is predicted for P≤11 GPa, above which a transition occurs into an orthorhombic Cmca structure, with a volume change upon transition of ΔV=0.4 cm3 /mol. Calculated physical quantities in this phase are consistent with experiment.
The generation and electron spin resonance characterization of 63,65Cu12CH2 and 63,65Cu13CH2 in neon matrices
Authors: Knight Lon B. , Cobranchi S. T. , Petty Jeff , Cobranchi D. P.
Published: July 2002

The first ESR (electron spin resonance) results are reported for a metal–methylene radical. The CuCH2 molecule was generated by trapping the products of the pulsed laser vaporization of copper in the presence of cyclopropane in neon matrices at 4 K. A second generation procedure involved the laser vaporization of elemental carbon and copper in the presence of H2(g). The unpaired electron in CuCH2 was found to occupy primarily the carbon p orbital which was perpendicular to the C2v molecular plane. This electronic distribution confirms the 2B1 ground state assignment predicted by previous theoretial calculations. The neon matrix magnetic parameters (MHz) were: g⊥=2.000(3); g∥=2.0027(3); 63Cu: A∥=303(1); A⊥=306(1); H:‖A∥‖=66.6(3); ‖A⊥‖ =43.1(3) and 13C:‖Aiso‖=124.3(5).
Variational Monte Carlo method in the connected moments expansion: H, H−, Be, and Li2
Authors: Yoshida Takashi , Iguchi Kaoru
Published: July 2002

The connected moments expansion with use of variational Monte Carlo technique (CMX-VMC) is applied to the calculation of the ground state energies of H, H−, Be, and Li2. Exponential-type wave functions for H, Hylleraas-type wave functions for H−, and a Hartree–Fock single determinant constructed with a single-zeta Slater-type orbital multiplied by a pair correlation factor of Jastrow-type for Be and Li2 are employed as approximate trial wave function. The results of the present computation are found to agree with the corresponding exact values quite well. The overlap between the approximate and exact wave function is also estimated simultaneously by the new technique.
Noise-induced transitions in an excitable system
Authors: L’Heureux Ivan , Kapral Raymond , Bar-Eli Kedma
Published: July 2002

A numerical study of dichotomous noise-induced transitions is presented for an example of a two-dimensional excitable system exhibiting bistability between a limit cycle and a fixed point: the simple Oregonator model. The decay of the average population number in the fixed-point region is investigated for various noise correlation times and for two different initial system preparations. The mean first passage time taken to leave the fixed-point region is determined and is compared with analytical results obtained from a simple stochastic model.
Statistical-mechanical theory of many-body effects in reaction rates
Authors: Tokuyama Michio , Ross John
Published: July 2002

Many-body effects in reaction rates depend on the ratio ε of a rate coefficient to the product of a diffusion coefficient and a radius, and on the reduced volume fraction φ0 of one or more reactants. We present a statistical-mechanical theory of the macroscopic kinetics (deterministic rates) of reactions in solutions, and fluctuations therefrom, for arbitrary ε and φ0, by deriving expressions for effective forward and reverse rate coefficients and their dependence on ε, φ0 to lowest order. We use an enzyme-catalyzed reaction as an example. There are two corrections to rate coefficients (for ε=0, φ0=0) at a given ε, φ0≠0, and both are proportional to φ1/20 (the square root of the total enzyme density in the example). The first is an uncorrelated screening term described by the single enzyme distribution function, which increases the rate; and the second a term described by correlations among enzymes, which decreases the rate. In the limit of very fast reactions the correlation term is negligible, and the screening term reduces to that previously obtained for diffusion controlled reactions. For other cases both terms contribute: for example, in the range φ0∼10−2 to 10−1 and ε∼1–10 the corrections vary from a few percent to 30%, as obtained from numerical solutions of the corrections for the enzyme example. We discuss a quasistationary state of the example and derive a generalization of the Michaelis–Menten equation for all ε, φ0. Fluctuations from the deterministic motion are shown to be small for three-dimensional systems.
The Thouless–Anderson–Palmer approach to random copolymer glasses
Authors: Kholodenko A. L.
Published: July 2002

The experimental evidence that the critical properties of homopolymer solutions are the same as Ising-type ferromagnets suggests that the critical properties of the random copolymer solutions might be analogous to that of Ising spin glasses. Using newly developed path integral methods, the analogy between the polymer and the magnets is carefully analyzed in order to be extended to the case of random copolymers. Established similarities permit one to use the Thouless–Anderson–Palmer (TAP) method in order to investigate the possibility of the formation of the new phase for random copolymers analogous to the spin glass phase for the magnets.
Reaction paths and generalized valley approximation
Authors: Walet Niels R. , Klein Abraham , Do Dang G.
Published: July 2002

The generalized valley approximation has been developed as a method of approximately decoupling one or a few low-frequency nonlinear modes from the remaining higher frequency modes of a multiparticle system. This decoupling will be best when the difference in frequencies is large; this is the case of adiabatic motion. We describe the application of this method to chemical reactions, relying in some measure on our earlier work, and contrast it with reaction-path theories. We give an algorithm for the incorporation of our method in a chemical calculation of the Born–Oppenheimer type. Detailed calculations are reported for several standard models that couple a double well to a harmonic oscillator. The decoupling procedure leads to an effective or renormalized one-dimensional double-well problem. The energy splitting of the lowest doublet in this well is contrasted with the exact splitting obtained by numerical integration of the two-dimensional Schrödinger equation. Results are good when the adiabatic condition is well satisfied. For future applications the most important feature of our theory is that it allows the decoupling of more than one degree of freedom.
Level shifts of discrete states embedded in a continuum
Authors: Du M. L. , Dalgarno A. , Jamieson M. J.
Published: July 2002

A procedure which offers computational advantages over the customary formalism is presented for calculating the shifts of the energy levels of discrete states embedded in a continuum. Numerical procedures are described and applied to the vibrational level shifts of the B 3Σ−u state of 16O2 interacting with the 5Πu continuum.
Electronic quenching, fluorescence lifetime, and spectroscopy of the A 3Πu state of NCN
Authors: Smith Gregory P. , Copeland Richard A. , Crosley David R.
Published: July 2002

Laser-induced fluorescence of the NCN radical was observed downstream of a microwave discharge of N2 and CF4 in He via the A 3Πu–X 3Σ−g transition near 329 nm. The zero-pressure fluorescence lifetime of the 000 vibrational level of the A state was measured from the time-resolved laser-induced fluorescence to be 183±6 ns. Other spectral features were observed both to the blue and red of the 000–000 band. The blue-shifted features are tentatively assigned to the 020–000, 100–000, 030–010, and 110–010 vibrational bands. Quenching cross sections were determined for NCN (A 3Πu, 000) at 300 K for Ar, Kr, Xe, O2, CO, CO2, N2O, SF6, NO, and NO2. The molecules He, N2, and CF4 are inefficient quenchers and upper limits only were obtained. The large variation in cross section among the colliders does not correlate with predictions of simple electronic quenching models.
Complex angular momentum analysis of rotationally inelastic diffraction scattering in sudden atom-homonuclear–molecule collisions
Authors: Thylwe K.-E. , Connor J. N. L.
Published: July 2002

A new complex angular momentum (CAM) theory of rotationally inelastic scattering has been developed for atom homonuclear–diatomic molecule collisions. The CAM theory is valid for sudden collisions, when the infinite-order-sudden (IOS) approximation for atom rigid-rotator scattering is appropriate. In the IOS/CAM theory, the inelastic scattering amplitude is written in terms of two subamplitudes: a background integral and a residue series. Physically the background integral corresponds to particles scattered by the repulsive potential core, while the residue series corresponds to short lived surface waves that propagate around the potential core. Diffraction effects arise from the interference of these two subamplitudes. The IOS/CAM theory is more general and accurate than the simple Drozdov–Blair theory of inelastic diffraction scattering. The weak coupling limit of the IOS/CAM equations has also been investigated and a new phase rule has been derived that is more general than the Blair phase rule. Approximate conditions for the validity of the new phase rule have been investigated using a model anisotropic potential of the form [g(γ)/r]n, n≥3. Numerical calculations of inelastic angular distributions using the IOS/CAM equations have been made for the strongly anisotropic He–N2 and weakly anisotropic Ne–D2 collision systems. Using a semiclassical approximation to the background integral and a single Regge pole term in the residue series, we obtain good agreement with conventional partial wave IOS angular distributions.
Polaritons and retarded interactions in nonlinear optical susceptibilities
Authors: Knoester Jasper , Mukamel Shaul
Published: July 2002

The role of retarded intermolecular interactions (polariton effects) in the nonlinear optical susceptibilities of condensed phases is studied. A systematic method for calculating these susceptibilities is developed, based on the derivation of reduced equations of motion which couple the electronic variables to the Maxwell (internal) electric field E. The susceptibilities are obtained by iteratively solving these equations in powers of E. Thus, the common introduction of intermediate susceptibilities with respect to either the external or the local electric field is avoided. Our method allows for the incorporation of polariton dynamics into the equations of motion. A clear distinction between microscopic and macroscopic polariton effects is made. Explicit forms for the linear (χ(1)) and second order (χ(2)) susceptibilities in molecular crystals are derived, which microscopically account for polariton–phonon scattering. Our theory provides an explanation for a recent series of linear and nonlinear optical experiments in naphthalene crystals which were found to contradict existing theories of nonlinear susceptibilities.
The calculation of electric dipole moments from the polarization propagator. Theory and application
Authors: Geertsen Jan , Jensen Frank , Scuseria Gustavo E.
Published: July 2002

A method for computation of dipole moments from the polarization propagator is presented and applied to the H2O molecule. Using extended basis sets it is shown that the coupled cluster singles doubles polarization propagator approximation (CCSDPPA) reproduces the experimental dipole moment to a high degree of accuracy
The thermodynamics of perchlorates. I. Heat capacity of ND4ClO4 from 7 to 345 K and the analysis of heat capacities and related data of NH4ClO4 and ND4ClO4
Authors: Brown R. J. C. , Weir R. D. , Westrum E. F.
Published: July 2002

The heat capacity of the orthorhombic salt: deuterated ammonium perchlorate, ND4 ClO4 , was measured from 7 to 345 K using adiabatic calorimetry. The heat capacity against temperature curve is smooth, continuous and without anomaly. Values of the standard molar thermodynamic quantities are presented up to 340 K. The heat capacities of ND4 ClO4 and NH4 ClO4 have been analyzed. The contributions to the vibrational heat capacity from the external optical modes of NH+4 or ND+4, ClO−4 and libration from the external modes of ClO−4 along with those of vibration from the internal optical modes of NH+4 or ND+4 and ClO−4, and the acoustic lattice modes for these ions have been calculated. The difference between the experimental and calculated heat capacity, called the residual heat capacity, equals the contribution from ammonium ion rotation and the thermal expansion of the lattice. With recent thermal expansion data, the correction from constant stress to constant strain has been applied and the derived rotational heat capacities of the NH+4 and ND+4 are determined to be in qualitative agreement with those derived from various rotational models.
Resonance Raman scattering of a Peierls–Hubbard dimer
Authors: Bozio R. , Feis A. , Zanon I. , Pecile C.
Published: July 2002

The resonance Raman scattering spectra of a Peierls–Hubbard dimer with explicit inclusion of electron coupling to both intramolecular vibration and intermolecular phonon modes are discussed theoretically and investigated experimentally. When the exciting wavelength is in resonance with the charge transfer band of a symmetric dimer the intermolecular phonon modes which modulate the transfer integral are selectively enhanced through both Albrecht’s A and C mechanisms. No enhancement occurs for the intramolecular modes. This prediction is strikingly demonstrated by reporting the low temperature resonance Raman spectra of crystalline (TTF)Br (TTF=tetrathiafulvalene) whose structure consists of almost isolated (TTF+)2 dimers. Fourteen bands are observed at low frequencies whereas the intramolecular mode region is silent. The observed bands are tentatively assigned to intermolecular modes in which the TTF+ cations in a dimer translate antiphase and to one low frequency out-of-plane molecular vibration. It is argued that a detailed study of the resonance enhancement mechanism may provide information on the electron correlation in a Peierls–Hubbard dimer.
Desorption kinetics and excimer formation of pyrene on Al2O3(112̄0)
Authors: Tro N. J. , Haynes D. R. , Nishimura A. M. , George S. M.
Published: July 2002

Laser-induced fluorescence (LIF) and electronic absorption spectroscopy (EAS) were used to examine pyrene adsorbed on Al2O3(112̄0) as a function of surface coverage, temperature, and adlayer order. Temperature-programmed LIF and EAS techniques were employed to measure the desorption kinetics of pyrene from Al2O3(112̄0). An activation energy of Ed=18±1 kcal/mol was obtained for pyrene desorption in the submonolayer regime assuming a first-order desorption pre-exponential of ν1=1×1013 s−1. Multilayer desorption studies revealed zero-order desorption kinetics with an activation energy of Ed =20±2 kcal/mol and a pre-exponential of ν0=3×1026±1.5 molecules/cm2 s. The formation of pyrene excimers and the structure of the pyrene adlayer were also investigated using LIF and EAS techniques. The LIF spectra for pyrene adlayers on Al2O3(112̄0) at 21 K exhibited both monomer and excimer emission. The relative amount of excimer emission at 21 K increased vs pyrene coverage from Θ=0.30 monolayers (ML) to Θ=4.5 ML. In addition, the excimer emission increased and the monomer emission decreased vs surface temperature between 21 and 150 K at all measured coverages. The temperature and coverage dependence of the LIF spectra suggested that excimer formation was dependent on pyrene mobility. In support of a mobility mechanism for excimer formation, LIF studies demonstrated that the excimer emission at Θ=0.25 ML was quenched by xenon adsorption on the pyrene adlayer. LIF and EAS measurements also indicated that the pyrene adlayer crystallized when the adlayer was annealed above 230 K. The LIF spectra of the crystalline pyrene adlayers on the Al2O3(112̄0) surface displayed only excimer emission.
The thermodynamic barrier to nucleation near a critical point
Authors: McGraw Robert
Published: July 2002

The revised capillarity approximation (RCPA) of McGraw and Reiss [J. Stat. Phys. 20, 385 (1979)] is reexamined using established liquid drop models to evaluate the effects of physical cluster excluded volume on the thermodynamic barrier to nucleation near a critical temperature Tc. A significant heightening of the nucleation barrier is predicted, and the anomalous behavior observed experimentally near Tc is examined within the framework of classical nucleation theory using the RCPA. Definitive methods for experimentally separating this pure nucleation effect from those dependent on slowing down of the post-nucleation completion times for phase separation are described.
Single-particle density matrix method for the solution of the many-electron problem
Authors: Redondo Antonio , Marshall Jean C.
Published: July 2002

A new calculational method for the solution of the many-electron problem, the single-particle density matrix (SPDM) method, is presented. The method is based on a generalization of the Hohenberg–Kohn theorem [A. Redondo, Phys. Rev. A 39, 4366 (1989)] which states that the ground-state energy of a many-body Hamiltonian is a universal functional of the single-particle density matrix. The calculational technique involves the minimization of the total energy, employing the methods of nonlinear programming. Using the Hartree–Fock approximation, we compare the results of the SPDM calculations with the standard diagonalization method for the molecules H2, LiH, and N2. Calculations are also presented in which correlation is introduced by means of the local density approximation.
A theoretical intensity study of the interaction induced Raman spectra of the ν2(πu) mode of CO2 between 100 and 3000 bars of pressure
Authors: Yoon Jong-Ho , Hacura Andrzej , Baglin Frank G.
Published: July 2002

The density dependent integrated intensities of the interaction induced (ii) dipole forbidden Raman spectra of the CO2 ν2(πu) mode have been calculated by the use of statistical mechanics based on the quadrupole–induced-dipole (QID) mechanism. The calculated intensities were compared with experimentally determined intensities. The intensities examined were between 5.03 to 17.00×1021 molecules/cm3 and the temperatures examined were 50 and 75 °C. The results indicated that at densities up to approximately 2.5× the triple point density, the integrated intensities can be expressed as a function of the density squared. This density square dependence of the integrated intensity may be due to almost perfect cancellation between constructive intensity originated from (CO2)2 dimers and the destructive intensity of classical three body interactions which have also been calculated. In any case, extra intensity was present as a high frequency shoulder at all densities except the lowest and highest values and was not accounted for by our calculations.
Rotationless molecular vibrations. II. Molecules containing three identical atoms
Authors: Shipsey E. J.
Published: July 2002

Coordinates are introduced which are irreducible representations of the permutation–inversion group. For triatomic molecules these become essentially hyperspherical coordinates. The system can thus be regarded as a hyperspherical coordinate system for the three identical atoms augmented by coordinates for the remaining atoms symmetry adapted to the environment of the three identical atoms.
Collisional electron detachment and decomposition rates of SF−6, SF−5, and F− in SF6: Implications for ion transport and electrical discharges
Authors: Olthoff J. K. , Van Brunt R. J. , Wang Yicheng , Champion R. L. , Doverspike L. D.
Published: July 2002

Measured cross sections for prompt collisional detachment and decomposition of SF−6, SF−5, and F− in SF6 reported in the preceding companion paper are used to calculate detachment coefficients and ion-conversion reaction coefficients as functions of electric field-to-gas density ratio (E/N) for ion drift in SF6. Analysis from a model presented here using these coefficients suggests that prompt electron detachment from SF−6 and SF−5 in SF6 are insignificant processes in such ion-drift experiments. Calculated rates for ion-conversion processes indicate the necessity to: (1) reexamine the previously measured rates in SF6 from drift-tube experiments, and (2) use ion kinetic-energy distributions with larger high-energy tails than the standard distributions assumed in earlier calculations. The calculated detachment and reaction coefficients are used in a model which invokes detachment from long-lived energetically unstable states of collisionally excited SF−6 to explain the pressure dependence of previously measured detachment coefficients and the high detachment thresholds implied by analysis of electrical-breakdown probability data for SF6. Consistent with the interpretation of results from earlier work, the model indicates that at high pressure, measured detachment coefficients depend primarily upon rates for ion conversion and prompt collisional detachment from F−.
Electron paramagnetic resonance, electron nuclear double resonance, and electron spin echo envelope modulation of Fe(CN)3−6 in a KCl lattice
Authors: Wang D. M. , de Boer E.
Published: July 2002

An electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), and electron spin echo envelope modulation (ESEEM) study has been carried out on Fe(CN)3−6 in a KCl lattice. The EPR spectrum showed the formation of a large number of centers, which correspond to different configurations of the charge compensating cation vacancies. The two major centers called center Ia and Ib have been well characterized. Both centers have orthorhombic symmetry and show a large g anisotropy. The principle g values are: gx =2.079, gy =3.054, and gz =0.400 for center Ia; gx =2.007, gy =3.177, and gz =0.752 for center Ib. The ligand field splitting and the orbital reduction factor k have been obtained through analyzing the spectra in terms of the generalized spin Hamiltonian. A number of unusual features observed in the EPR spectra have been found to be due to the high level of g anisotropy. The ENDOR and ESEEM measurements performed on center Ia revealed nearly all the coupling tensors between the unpaired electron and the 13C and 14N nuclei. The principle values and tensor orientations were precisely determined by least-squares fitting. The orientations of the coupling tensors give a detailed picture of the complex under the influence of the two cation vacancies. The coupling constants of 13C were found to be an order of magnitude larger than those of 14N. Level anticrossing was observed for the nuclear spin states of 14N.
The ionization of thermal and hyperthermal beams of Na, K, and Cs on Si(111) surfaces
Authors: Bu Y. , Greene E. F. , Stewart D. K.
Published: July 2002

Measurement of the energy dependence of the yields of Na+, K+, and Cs+ ions formed when beams of the corresponding alkali atoms M hit a Si(111) surface and of Na+ for Na striking a Pt surface at a temperature T are those expected for equilibrium for thermal kinetic energies E of the incident atoms. Above a threshold energy of 0.5–1.0 eV the yields rise rapidly to maxima greater than 0.1 and then remain approximately constant as the energy increases to 100 eV. They are nearly independent of T in the range 300–1100 K. The results are represented well by a classical model having (1) a rate of electron transfer that varies exponentially with the distance z of M from the surface, (2) potentials that slow the incoming atom down as it nears the surface, and (3) energy transfer by elastic two-body collisions with the surface represented as hard cubes, each having the mass of an integral number n of surface atoms. At z=5 Å the rate on Si for Na and K is 1012.5±0.2 s−1 with n equal to 3 and 5, respectively, while for Cs it is three times less with n equal to 20. For Na on Pt it is 1012.9±0.1 s−1 with n equal to 1.
The effect of adsorbate-induced surface reconstruction on the apparent Arrhenius parameters for desorption
Authors: Myshlyavtsev A. V. , Zhdanov V. P.
Published: July 2002

The effect of adsorbate-induced surface reconstruction on the apparent preexponential factor and activation energy for desorption is analyzed and discussed. The reconstruction is assumed to be a continuous order–disorder phase transition. The adsorbate-induced changes in the surface are shown to result in a rather strong (of the order of 102) coverage dependence of the preexponential factor for desorption. The direction of the variation is in accordance with the compensation effect (the preexponential factor and the activation energy decrease with increasing coverage).
Nematic to smectic-A transition of parallel dipolar hard spherocylinders and ellipsoids, a hypernetted chain equation study
Authors: Caillol J. M. , Weis J. J.
Published: July 2002

The thermodynamic, dielectric, and structural properties of systems of dipolar hard spherocylinders and ellipsoids with perfect nematic order are investigated by means of the hypernetted chain (HNC) equation. The density, temperature domain for which the HNC equation admits a stable solution is determined. For spherocylinders a large increase of the main peak of the total structure factor in the vicinity of the stability limit of the HNC equation is, tentatively, associated with the onset of a nematic–smectic-A transition. The situation seems less clear for dipolar ellipsoids, though the results are in many aspects qualitatively similar to the spherocylinder case. The pair structure near the transition is analyzed. It is not characteristic of any of the smectic-A phase structures typical of strongly polar liquid crystals. This is probably a consequence of the highly symmetric nature of the model.
The size and flexibility of grown sodium dodecyl sulfate micelles in aqueous sodium chloride solutions
Authors: Mishic J. R. , Fisch M. R.
Published: July 2002

We have used light scattering techniques to measure the size and flexibility of grown sodium dodecyl sulfate (SDS) micelles in aqueous NaCl solutions as a function of temperature, surfactant concentration, and salt concentration. The mean hydrodynamic radius (R̄h) was determined using quasielastic light scattering, and the mean radius of gyration (R̄g) was measured using static light scattering. A theory of flexible rod-like objects is compared to the data. This theory predicts that for flexible rod-like micelles R̄g/R̄h will depend not only on R̄h but also on the persistence length, a measure of micellar flexibility. The data are found to be consistent with flexible rod-like micelles whose mean persistence length (〈l〉) depends weakly on SDS concentration and strongly on temperature and NaCl concentration. In the temperature range from 20–37 °C in 0.8 M NaCl and 30–50 °C in 1 M NaCl solution we find 〈l〉∝exp(−w/kBT) with w=4.7±0.5×10−12 erg.
Fluctuation in rate coefficients, induced by dichotomous noise, and the rate of chemical reactions
Authors: Morita Akio
Published: July 2002

The effect on the dynamics of irreversible first- and second-order chemical reactions caused by random changes in the rate coefficients is calculated. The changes in the rate coefficients are assumed to be dichotomous, being generated by a Poisson process. The conditions are determined under which the average values of the concentrations of the reactants can differ appreciably from the values obtained in the absence of fluctuations. The initial concentration for the variance is taken to be zero. It achieves a unique maximum and decreases monotonically thereafter.
2H-nuclear magnetic resonance study of the host lattice dynamics in the clathrate of Dianin’s compound. Concerted rotational jumps of six hydroxyl groups
Authors: Bernhard T. , Zimmermann H. , Haeberlen U.
Published: July 2002

2H-nuclear magnetic resonance was applied to single crystals of the clathrate of Dianin’s compound with ethanol as a guest. The hydroxyl groups of both the host lattice and the guest were deuterated. The temperature dependences of the 2H spectra and of the quadrupole coupling tensors of the host lattice deuterons provide evidence that these deuterons carry out jumps between two unequally populated sites. These jumps may be visualized as approximate rotations of the hydroxyl groups about the C–O bonds. The occupancies of the two sites were measured and found to follow a Boltzmann distribution at T>145 K. At lower temperatures the minority sites are overpopulated. The temperature dependence of the jump rate was determined by line shape analyses and relaxation time measurements. From the absence of dipolar fine structure in the 2H spectra recorded for specially chosen crystal orientations it is concluded that groups of six hydroxyl units carry out their rotational jumps in a concerted manner.
Semiempirical determination of molecular motions associated with phonon modes in molecular crystals
Authors: White K. M. , Eckhardt C. J.
Published: July 2002

An approach using piezomodulated Raman scattering is presented which permits determination of the molecular motions associated with the eigenmodes of molecular crystals. When coupled with a lattice dynamical calculation for the eigenmodes, the experiment can be used to validate the calculation. The case of 1,2,4,5-tetrabromobenzene is treated and it is shown that the phase relations of the piezomodulated Raman signals confirm the calculated eigenmodes.
Perturbations, inhibition, and promotion of ultraviolet surface photochemistry: CH3 Br on Br/Ni(111)
Authors: Marsh E. P. , Tabares F. L. , Schneider M. R. , Gilton T. L. , Meier W. , Cowin J. P.
Published: July 2002

The inhibition and perturbations of surface photochemistry, due to the coupling of the excited state to the surface, are discussed as it pertains to CH3 Br adsorbed on nickel. Photofragmentation of CH3 Br was observed on a brominated Ni(111) surface, with the fragmentation process being strongly perturbed at low coverages. The perturbations are attributed to charge transfer processes. Direct photofragmentation was observed as well as a surface specific dissociative electron attachment channel. Cross section values are reported for fragmentation at 193 and 248 nm.
Method-dependent diffusion coefficients on interactive systems
Authors: Tringides M. C.
Published: July 2002

Diffusion coefficients are examined in interactive models by using different methods and different overlayer configurations. Comparison between the fluctuation and laser-induced-desorption method on well-equilibrated overlayers can lead to large differences depending on the ordered structures formed. If comparison is made between well-equilibrated and faraway-from-equilibrium configurations different diffusion coefficients and activation energies are obtained. Finally, the activation energy ΔEc obtained from growth rates in coarsening experiments is shown to verify ΔEc=xΔEd, where x is the growth exponent and ΔEd the activation energy of diffusion.
Time-resolved fluorescence spectroscopy of matrix-isolated silver atoms after pulsed excitation of inner-shell transitions
Authors: Hebert T. , Wiggenhauser H. , Schriever U. , Kolb D. M.
Published: July 2002

The energy dissipation in matrix-isolated silver atoms after pulsed vacuum ultraviolet (VUV) excitation of 4d–5p transitions has been studied by time-resolved fluorescence spectroscopy. The decay behavior of the various fluorescence bands has been analyzed and a model for the relaxation process proposed within the framework of a two-dimensional configuration-coordinate diagram. If minute quantities of Ag2 are present in the matrix, the analysis requires consideration of energy transfer between silver atoms and dimers.
Evolution of molecular dissociation through an electronic curve crossing: Polarized emission spectroscopy of CH3I at 266 nm
Authors: Lao K. Q. , Person M. D. , Xayariboun P. , Butler L. J.
Published: July 2002

We present a study of the dissociation of CH3I on coupled repulsive electronic potential energy surfaces by the technique of polarized emission spectroscopy. We excite CH3I at 266 nm and disperse the photons emitted from the dissociating molecule by both frequency and angular distribution with respect to the polarization direction of the excitation laser. We thus measure the polarization of the first 12 C–I stretching emission features, corresponding to the spectral region between 266 and 317 nm. We also obtain the rotational envelope of selected emission features in higher resolution scans and model the lineshapes with parameters derived from the polarization results. The polarization measurements show the emission into the first few low-lying C–I stretching vibrational levels is via a transition moment parallel to the absorbing one, consistent with excitation to and emission from the 3Q0(2A1) repulsive surface. Emission to higher C–I stretching overtones shows an increasing contribution from emission via a transition moment perpendicular to the absorbing one, consistent with emission from a repulsive surface of E symmetry following excitation to the 3Q0(2A1) state.

We extract from the data the fraction of photons emitted via a perpendicular transition for each of the C–I stretch emission features. The analysis includes the derivation of analytic expressions for the angular distribution of the photons, with and without integration over the rotational contour, when the detector has a finite acceptance angle. We discuss the results in relation to a simple model where photoabsorption excites the molecule to the 3Q0(2A1) repulsive surface (parallel transition moment) and amplitude develops on the 1Q1(3E) repulsive surface as the molecule dissociates through a curve crossing. The changes in amplitude of the molecular wavefunction on the A1 vs the E repulsive surfaces during dissociation is thus probed. We outline a crude classical quasidiatomic approximation for roughly extracting from our data the electronic energy at which the ‘‘curve crossing’’ occurs. This derived energy is compared to that given in model and ab initio calculations of the excited electronic potential energy surfaces. Finally, we discuss the results in relation to the simple quasidiatomic Landau–Zener crossing model utilized by other workers, a model which does not fully explain the collection of experimental results over the last decade on the iodoalkane curve crossing.
The origin of the superposition principle for circular intensity differential scattering by hierarchical chiral structures
Authors: Ulibarri Laura , Bustamante Carlos
Published: July 2002

The superposition principle states that the angle-dependent difference in scattering intensities for right and left circularly polarized light, for chiral structures composed of various hierarchical levels, is the sum of the contributions from each level taken separately. Analytic expressions describing this superposition are obtained for oriented and rotationally averaged hierarchical chiral structures. It is shown that the superposition principle holds only when the coiling levels in the chiral structure are disparate. In particular, for a structure composed of two chiral levels, the lower order structure must be much smaller than both the wavelength of light and the higher order structure. Numerical calculations using these expressions are carried out for superhelices of varying dimensions.
Comment on: ‘‘Ionic hydration in sodium chloride solutions’’
Authors: Kumar Anil
Published: July 2002

The ionic hydration model of Onori has been found to yield incorrect magnitude and temperature dependence of hydration numbers of NaCl at various concentrations.