bluuebunny/crossref_metadata_2025 huggingface dataset:
Structures, barriers for internal rotation and inversion, vibrational frequencies, and thermodynamic functions of CH2FCF2, CHF2CF2, and CF3CF2 radicals: An a
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Authors: Chen Yonghua , Rauk Arvi , Tschuikow-Roux E.
Published: July 2002

The equilibrium geometries, rotational and inversion barriers, and harmonic vibrational frequencies for α,α,β-trifluoroethyl (CH2FCF2), α,α,β,β-tetrafluoroethyl (CHF2CF2), and pentafluoroethyl (CF3CF2) radicals have been determined by ab initio molecular orbital techniques using the GAUSSIAN 86 system of programs at the unrestricted Hartree–Fock level of theory with the 6-31G* basis set (UHF/6-31G*). Three conformational minima in the potential energy surface were found for the CH2FCF2 and the CHF2CF2 radicals, while only one was found for the CF3CF2 radical. The radical centers for all three species are nonplanar. The barriers hindering rotation about the C–C bond and inversion of the radical center were located for each compound by analytical methods. Vibrational frequencies, as well as moments of inertia for overall and internal rotation are reported for each species. Calculated heat capacities, entropies, and free energy functions are tabulated as a function of temperature. Several homodesmic reactions have been studied for the purpose of obtaining theoretical heats of formation of CH2FCF2 and CHF2CF2 radicals for which experimental values are not available. The theoretical heats of formation thus evaluated are −106.6 kcal/mol and −157.8 kcal/mol for CH2CF2 and CHF2CF2, respectively. These data and the experimental heat of formation of CF3CF2 (ΔH0f,298 =−213.0±1.3 kcal/mol) are used to evaluate ΔH0f ,T, ΔG0f ,T, and Kf ,T for all three radicals as a function of temperature.
Molecular dynamics in perfluoro-n-eicosane. III. Oscillatory and diffusive translational motion
Authors: Albrecht Thomas , Jaeger Raimund , Petry Winfried , Steiner Ralf , Strobl Gert , Stühn Bernd
Published: July 2002

The translational motion of C20F42 helices is investigated using a combination of x-ray scattering and coherent quasielastic and inelastic neutron scattering techniques. In phase I, the helices are ordered with respect to their orientation and the dominating mode of motion is an acoustic phonon. In the high temperature phase R, the helices are disordered with respect to their longitudinal position and the angle of rotation around their main axis. Neutron scattering reveals for the longitudinal disorder a wide spectrum of relaxation times (10−12–10−9 s). The rotational ordering of the helices leads to increased correlations and a slowing down in the diffusive longitudinal dynamics already above the phase transition.
Comment concerning the optimum control of transformations in an unbounded quantum system
Authors: Zhao Meishan , Rice Stuart A.
Published: July 2002

We discuss the achievability of optimal control of the evolution of an unbounded quantum system by the action of external fields. Previous work has established that the evolution of a quantum system with a nondegenerate discrete and bounded spectrum of states can, in principle, be fully controlled, i.e., that the system wave function can be guided by external fields to approach arbitrarily closely a selected target state wave function. The optimal control of the evolution of a quantum system with a discrete and bounded spectrum of states has also been studied, using a method of analysis that depends on the localized character of bound state wave functions and the fact that the spectrum of states is bounded. In this paper, we examine whether it is possible to control, partially or fully, the evolution of an unbounded quantum system. We show that optimal control of the evolution of an unbounded quantum system is possible, in the sense that it is possible to minimize the difference between the product function formed at time t0 from a localizing function and a continuum wave function and a similarly defined target function at time tf.

We have not been able to establish that such optimal control is equivalent to full control, i.e., that the difference between the initial and target functions can be made arbitrarily small, which would require showing that the set of control functions is complete with respect to the function space of the system. Our analysis establishes the existence of external fields that can optimally guide the unbounded system evolution in the absence of other constraints than the Schrödinger equation of motion, but does not provide an algorithm for the construction of such fields. The relationship between optimal control of the evolution of a quantum system and the existence of chaotic dynamics in the continuum domain is briefly discussed. We argue that the optimally controlled system cannot have chaotic dynamics even if the bare system does. As illustrations of the results obtained, we discuss briefly the optimal control of evolution in the subset of discrete states from a spectrum with both discrete and continuum states, the optimal control of evolution in resonant states, and the inversion of the optimally controlled localized product continuum target function to yield the corresponding system wave function.
Vibrational relaxation and dephasing of Fermi resonance states in molecular crystals
Authors: Bogani Franco , Cardini Gianni , Schettino Vincenzo
Published: July 2002

The vibrational relaxation of Fermi resonance bound states in molecular crystals is discussed. The anharmonic Hamiltonian includes two parts. The first, considered exactly, includes the single site cubic Fermi coupling term and gives rise to the formation of bound states. The second part, treated as a perturbation, includes cubic and quartic terms coupling the internal to the lattice phonons. These terms give rise to depopulation and dephasing processes of the bound states. Explicit expressions are obtained for the cubic and quartic contributions to the linewidths and frequency shifts. Model calculations are reported for a linear molecular crystal. On the basis of the theory and model calculations of the present paper, available experimental data on the CO2, N2O, CS2, NH4Cl, KClO4, and RbClO4 crystals are reviewed.
A family of equivalent expressions for the pressure of a fluid adjacent to a wall
Authors: Lovett Ronald , Baus Marc
Published: July 2002

A simple work-of-deformation calculation is shown to produce a family of equivalent expressions for the pressure of an equilibrium fluid adjacent to a mathematical wall. One of these expressions is a statement of the so-called wall theorem which asserts that the density of a fluid at contact with a wall is related to the pressure and temperature of the bulk fluid by the ideal gas equation of state. The work-of-deformation route provides a clear connection between macroscopic and microscopic quantities without requiring the singular limiting procedure used in earlier proofs. The standard expressions for the pressure and surface tension of the planar interface follow from particular interpretations of this family of expressions.
Vacancy-controlled interdiffusion: Nonlinear effects
Authors: Alexander S. , Rabin Y. , Zeitak R.
Published: July 2002

We derive the nonlinear equations governing vacancy-controlled interdiffusion in a two-component noninteracting lattice gas. We observe that when the diffusion constants of the two species are not equal, the problem cannot be reduced to a simple linear diffusion. In order to treat the strongly nonlinear limit of large kinetic asymmetry and small concentration of vacancies, we introduce an adiabatic approximation in which the ‘‘fast’’ species is in an equilibrium state defined by the instantaneous distribution of the ‘‘slow’’ species, which obeys a linear diffusion equation with a renormalized diffusion coefficient. Comparison with numerical solutions of the nonlinear equations shows that the adiabatic approximation captures the essential physics of the diffusion process.
Effect of ions on intermolecular association and sub-T
g dielectric relaxation in isomeric octanols
Authors: Hofer K. , Johari G. P.
Published: July 2002

The effect of ions on the H-bond association in 4-methyl-3, 2-methyl-1, and 2-methyl-6-heptanols has been studied from measurements of their dielectric properties in their pure state and their LiClO4 solutions over a temperature range from their glassy to a supercooled fluid state. The ions increase the equilibrium permittivity of 4-methyl-3 and decrease that of 2-methyl-1 and 2-methyl-6-heptanols. Ionic interaction breaks H bonds in their structures and converts ring dimers of virtually zero dipole moment to linear dimers or monomers for the 4-methyl-3 and converts chain n mers to shorter chains for the 2-methyl-1, and 2-methyl-6-heptanols, thus confirming our earlier interpretation of two types of H-bond association in isomeric octanols. The effect of ions on the permittivity and H-bond structure of 4-methyl-3 is similar to the effect of hydrostatic pressure and on those of 2-methyl-1 and 2-methyl-6-heptanols is opposite to that of hydrostatic pressure. On the addition of LiClO4, the height of the sub-Tg relaxation peak increases as does the permittivity at 100 K. The former is a reflection of less efficient molecular packing and the latter of an increase in the optical and infrared polarizabilities with increase in the LiClO4 concentration. Dielectric and conductivity measurements of ionic solutions are useful methods for studying the H-bond association in pure liquids.
Phase separation in polymer solutions near the critical point
Authors: Cherayil Binny J.
Published: July 2002

The Edwards path-integral description of chain statistics is used to derive an effective φ4 field theory of polymer solutions that is applicable near the temperature of critical phase separation Tc. The present formalism, an extension of the mean-field approach discussed in paper I [R. E. Goldstein and B. J. Cherayil, J. Chem. Phys. 90, 7448 (1989)], makes use of standard results from the theory of continuous phase transitions to account for the effects of previously neglected density fluctuations, and to obtain thereby, among other results, estimates for the temperature and molecular weight-scaling exponents of the coexistence curve in the vicinity of Tc. The critical monomer volume fraction ρc of the solution is shown to scale as the osmotic second virial coefficient below the theta point, providing a rigorous approach to the calculation of the molecular weight dependence of ρc. Experimental data on the phase separation of solutions of polystyrene in methylcyclohexane are shown to lie on a single universal curve when expressed in terms of the scaling variables suggested by the present analysis.
Plasma spectroscopy proposed for C60 and C70
Authors: Barton Gabriel , Eberlein Claudia
Published: July 2002

The fullerenes C60 (quasispherical though actually icosahedral) and C70 (quasispheroidal) are very like hollow shells (graphiteroles) made from a single hexagonal layer from a graphite crystal. They should support multipolar (l≥1) plasma oscillations, closely related to the plasmons seen in graphite. We estimate their frequencies using the so-called hydrodynamic model, with (provisionally) just one parameter calibrated on graphite. We predict π plasmons in the range between 6 and 8 eV, and σ plasmons near and above 25 eV. The best, if not the only way to observe them is by electron energy-loss spectroscopy. Only the dipole (l=1) excitation is allowed optically; in the solid, its frequency should be shifted according to the Lorentz–Lorenz formula. If, improbably, the l=1 π plasmon is observable in solution, its frequency should be unprecedentedly sensitive to the refractive index of the solvent. On C70, the multipoles are split and shifted relative to C60, but only by surprisingly little.
Finite-size effects in ionization potentials and electron affinities of metal clusters
Authors: Seidl M. , Meiwes-Broer K.-H. , Brack M.
Published: July 2002

Experimental ionization potentials (I) and electron affinities (A) of metal clusters MeN are compiled for a variety of systems and their size dependence is analyzed. In the theoretical part, we perform semiclassical density variational calculations using the spherical jellium model and the local density approximation. For alkali systems and, to some extent, also for some nonalkali systems, the calculated values of I and A reproduce very well the average size dependence of the measured quantities, if their common bulk limit W is adjusted to the experimental bulk work function. This holds even for rather small systems where I and A are no longer linear in N−1/3. We discuss the extent to which classical models for the energetics of charged metal spheres can account for the correct size dependence in the large-cluster limit. We point out that the deviation of the slope parameters α and β in the asymptotic expressions I∼W+α(e2/rs)N−1/3, A∼W−β(e2/rs)N−1/3 from the values (1)/(2) , which depends on the material via the Wigner–Seitz parameter rs, can be entirely accounted for by quantum-mechanical effects, namely the kinetic, exchange, and correlation energies and the diffuseness of the electron density.
Comparison of calculated cross sections for secondary electron emission from a water molecule and clusters of water molecules by protons
Authors: Long Keith A. , Paretzke Herwig G.
Published: July 2002

Double-differential cross sections for the emission of secondary electrons, as a function of emission angle and energy, from a water molecule, a cluster of water molecules, and liquid water due to proton impact have been calculated using the dielectric response function of the target material and a method which uses an integral formulation of the density-functional theory. From these double-differential cross sections, single-differential and total cross sections, and the energy loss per unit path length, have been calculated by successive integration. The results have been compared to available experimental results and, in the case of single-differential cross sections, also to empirical models. A comparison has been made between the results for the molecule and the central molecule of the cluster in order to obtain insight into how the cross sections might change in the condensed phase, namely in liquid water.
Brownian dynamics simulation of rotational correlation functions for a three-body macromolecular model
Authors: Ying Ruoxian , Peters Michael H.
Published: July 2002

A former investigation [R. Ying and M. H. Peters, J. Chem. Phys. 91, 1287 (1989)] on the rotational dynamics of rigid and partially flexible macromolecules in solution by means of Brownian dynamics simulation methods is extended to a trimer or three-body macromolecular model. We present expressions for the torque constraints in rigid and semirigid trimer systems that allows for a comprehensive simulation of the translational, rotational, and coupled translational–rotational motions of the three interacting spherical Brownian particles comprising the trimer (trumbell). The torque constraint expressions are verified by comparisons of the Brownian dynamics simulation results to exact analytical results for a rigid trimer system (Appendix). Computer simulations and analytical solutions for the rigid trimer system indicate that the inclusions of rotational motions of the model’s elements can have an appreciable effect on macromolecular dynamics. Macromolecular flexibility can also be easily introduced into the model through varying the parameters of the torque and force constraint expressions. Extensions to an N-body macromolecular model are also outlined based on the trimer system studied here.
Common microscopic origin of superconductivity and unusual temperature dependence of the dc electrical conductivity in strongly correlated organic donor–acceptor salts
Authors: Böhm Michael C.
Published: July 2002

Material properties of low-dimensional organic donor–acceptor (DA) metals are comparatively discussed. It is shown that the low-temperature superconductivity in organic solids and the nonconventional temperature dependence of the dc electrical conductivity σ have the same microscopic precursor, softening of lattice modes caused by a divergence of the generalized susceptibility on effectively flat Fermi surfaces (FS) (T dependence of σ), as well as the resulting enhancement of the electron–phonon coupling (superconductivity). Prerequisite for this behavior are sizeable electronic charge fluctuations 〈(Δn2i)〉 in the strongly correlated organic DA salts at any temperature. Nonvanishing fluctuations, which are maintained also in the limit of almost perfect interatomic correlations, are possible as a result of nonintegral effective electron densities n̄i≠1.0. The electronic charge fluctuations at T=0 K and finite temperature are studied by an analytic many-body model. The T dependence of the fluctuations is discussed as a function of the accessible electron density n̄i.

Charge densities n̄i≠1.0 as realized in the highly conducting organic metals attenuate a possible temperature control on the fluctuations. For the integral 1:1 charge transfer salts of D+A− stoichiometry, negligible fluctuations (insulating Mott configurations) for temperatures <500 K are predicted. In addition to the T dependence of the electronic fluctuations, the mean-squared atomic fluctuations are studied as a function of temperature. The fluctuation amplitude diverges with increasing mode softening. Experimental consequences of this behavior are touched. A Kubo–Mori projector technique in a single-particle approximation is adopted to quantify the strong interrelation between the T variation of σ and FS properties (mode softening). Boundary expressions following a T−2 and T−1 law of σ(T) are formulated. The first relation is valid for systems with sizeable frequency renormalization; the second one for conventional metals with vanishing mode softening. The theoretical results suggest a new subclassification of the DA salts into two classes; FS properties serve as underlying criterion. The validity of the transport theory is demonstrated for the two-dimensional (BEDT-TTF)2ClO4 system. A two-mode model in the strong-coupling approximation is used to calculate superconducting transition temperatures TC of organic superconductors in the presence of Kohn mode softening. A remarkable influence of the frequency renormalization on the magnitude of TC is evaluated. An additional enhancement of TC is possible due to the divergence of the mean-squared atomic (lattice) displacement. Calculated TC numbers of (BEDT-TTF)2A superconductors are in fair agreement with experimental results.
Transition matrix elements from multiple scattering wave functions for LiH
Authors: Till S. J. , Howard S. T. , Parsons I. W.
Published: July 2002

We outline the theory for computing radiative and nonradiative transition rates from MSXα wave functions. The electronic matrix elements involved are identified, and evaluated for LiH. Some radiative and nonradiative rates for this molecule are estimated within the framework of first-order time-dependent perturbation theory. The results suggest that the method has a general utility.
On the nonclassical asymptotic behavior of electronic properties in metal clusters
Authors: Makov Guy , Nitzan Abraham
Published: July 2002

The ionization potential I(R) of small metal spheres (of radius R) as well as the electronic chemical potential μ(R) in such particles are considered within a three-parameter variational local-density-functional calculation. The asymptotic (R→∞) deviations of I(R) and μ(R) from their bulk values behave as C/R and Cμ/R, respectively, where within the computational accuracy C+Cμ=0.5. These results are quantitatively similar to those obtained from a recent variational calculation by Engel and Perdew (EP), and identify the origin of the deviation of C from its classical value of 0.5 in the size dependence of μ(R). While EP show that this size dependence originates from the gradient terms in the energy functional, we find that its magnitude results from a delicate balance between different contributions. The classical limit C=0.5 is approached when both Z and R are large, where Z is the number of electrons involved in the transition. These results also lead to the resolution of an apparent paradox recently described by van Staveren et al.
Dynamics in concentrated polymer solutions by polarized Rayleigh–Brillouin scattering and dynamic light scattering
Authors: Brown Wyn , Johnsen Robert M. , Konak Cestmir , Dvoranek Ladislav
Published: July 2002

Solutions of polystyrene in toluene in the concentration range 0.1–1.0 g/ml have been examined using polarized Rayleigh–Brillouin scattering and dynamic light scattering. The purpose was to extend measurements to the hitherto little studied interval between semidilute solutions and the bulk polymer. The Brillouin shift increases monotonically with polymer volume fraction (Φp) and a linewidth maximum is observed at about Φp=0.6. Up to Φp=0.56, a single cooperative diffusion mode is found, which passes through a broad maximum at Φp=0.5. For the sample with Φp=0.78, the nature of the main component depends sensitively on temperature. At 17 °C it is purely relaxational (q independent), while at 40 and 50 °C, it is diffusive. At intermediate temperatures, mixed behavior is noted where the dynamic processes overlap because the slower relaxational mode has a stronger temperature dependence. At Φp=0.89, the correlation functions are highly nonexponential and strongly temperature dependent. The bimodal correlation function contains contributions from both concentration fluctuations due to cooperative diffusion and density fluctuations arising from segmental motions in the polymer.
Excitation and ionization of 4He clusters by electrons
Authors: Buchenau H. , Toennies J. P. , Northby J. A.
Published: July 2002

Clusters are produced by expanding high pressure (P0≤20 bar), low temperature (T0≥5 K) helium gas through a 5 μm nozzle into a vacuum. The neutral beam time-of-flight distribution has three peaks which we associate with distinct groups of large and small clusters, and atoms. The beam is ionized by electron impact and the resulting time resolved charged fragment mass distribution reveals in addition to previously observed anomalies (‘‘magic numbers’’) a new strong He+4 signal at high source pressures and low temperatures. The dependence of the various charged and neutral metastable fragment currents on the bombarding electron energy reveals that each has a unique appearance potential. A comparison with the calculated energy required for an electron to create various electronic excitations in the interior of a large cluster indicates that the production and dynamical evolution of metastable 3S1 atomic and a 3Σ+u molecular excitations plays a significant role in the formation of charged fragments from large clusters, but that the production of detectable metastable cluster fragments apparently proceeds via decay of high lying excitonic states. The strong He+4 signal does not appear until the incident electron has about enough energy to create two metastable 3S1 excitations in a cluster. Thus we propose that this ion signal results from the recombination of a pair of a 3Σ+u molecular excitons in or on a large cluster, or possibly from the dynamical evolution of a metastable spin quartet bound hole-exciton pair.
Exciton coherence-size and phonon-mediated optical nonlinearities in restricted geometries
Authors: Dubovsky Oleg , Mukamel Shaul
Published: July 2002

The magnitude of optical nonlinearities of molecular nanostructures is determined by a characteristic coherence-length which controls the cooperativity of the optical response. Equations of motion describing the evolution of the optical polarization coupled to two-exciton variables are derived, and used to calculate the third order optical response (χ(3)) of a one-dimensional molecular crystal or a polymer. We show that the coherence-length is determined by the interplay between intramolecular and intermolecular (nonlocal) nonlinearities and explore the limitations of the local-field approximation. Phonon-mediated exciton–exciton attractive interaction may result in the formation of bound exciton pairs (biexcitons). We show how unbound (two-exciton) as well as biexciton states could readily be observed as resonances in two-photon absorption and third harmonic generation.
The photoexcited triplet state as a probe of dynamics and phase memory in a multiphase liquid crystal: Time-resolved electron paramagnetic resonance spectroscopy
Authors: Regev Ayelet , Galili Tamar , Levanon Haim
Published: July 2002

Differences between mesophases and hysteresis effects can be examined by electron paramagnetic resonance (EPR) detection of light-induced transient triplets oriented in liquid crystals (LC). Time-resolved EPR spectroscopy (direct detection) has been applied to study the photoexcited triplet state dynamics of tetraphenylporphyrin (free-base) oriented in a multiphase LC, ZLI-1167, having a negative anisotropic susceptibility, Δχ<0. The feasibility of triplet detection over a temperature range of 100–370 K, enables one to monitor conspicuous changes of the triplet line shape associated with the different mesophases, i.e., cryst.↔(287 K) smec.↔(305 K) nem.↔(356 K) isot. Line shape analysis shows that all phases consist of domains having their directors spanned in a plane normal to the external magnetic field, as expected for Δχ<0. The triplet spectra in the fluid smectic phase depend on sample rotation, indicating the known rigidity of this phase. On the other hand, the spectra in the nematic phase are independent of the sample rotation but strongly depend on the temperature and sample alignment in the magnetic field. Two mechanisms of triplet dynamics are proposed; namely an inter- and intradomain triplet energy transfer between the porphyrin chromophores. In addition, the results suggest that, in a specific alignment procedure, the smectic character is maintained deep in the nematic and, to some extent, in the isotropic phases. Thus the EPR line shapes and temporal behavior of the nematic spectra, are associated with a phase memory effect (hysteresis), and the smectic phase persistence may indicate the existence of cybotactic groups within the nematic and isotropic phases.
Near infrared two-photon laser spectroscopy of the 2 1Σ+g state of 7Li2
Authors: He Chun , Gold L. P. , Bernheim R. A.
Published: July 2002

The results of a nonresonant near infrared two-photon laser spectroscopic study of the 2 1Σ+g state of 7Li2 are presented. Over 1000 rotationaly resolved 2 1Σ+g←X 1Σ+g transitions spanning 2300 cm−1 of the 2 1Σ+g potential well have been assigned and analyzed. Data from the v′=1 to v′=21 vibrational levels are used to obtain 2 1Σ+g state Dunham molecular constants as well as band-by-band constants. These data are also used to construct a Rydberg–Klein–Rees (RKR) potential which corresponds to 89% of the potential well depth. The results for the lower v′ levels are in agreement with the previously determined molecular constants for v′=0 to v′=16 [J. Mol. Spectrosc. 116, 271 (1986)]. For the higher v′ levels they reveal the perturbations from the 1 1Πg state. Comparisons with the results of ab initio calculations are made. In the 2 1Σ+g←X 1Σ+g nonresonant two-photon excitation only Q-branch transitions are observed with plane polarized radiation.
One-and-a-half-fluid theory: A new approach to conformal solutions
Authors: Kofke David A.
Published: July 2002

A theory is proposed that combines the most basic features of conformal solution theory and scaled particle theory (SPT). The treatment in essence provides a means for evaluating mixture properties from pure fluid data; however, two intermediate substances—the ‘‘infinitely polydisperse’’ (IP) mixture and the ‘‘one-and-a-half fluid’’—are used to implement the mapping. Associated with the IP mixture is a density-invariant surface onto which the properties of any mixture may be (approximately) mapped. This surface is itself evaluated through an inverse mapping of the properties of the 1 (1)/(2) fluid. This substance is a particularly simple type of binary mixture. It contains particles of zero diameter in an otherwise pure fluid. For hard, purely repulsive potentials, the properties of such a mixture may be evaluated exactly, using an elementary argument from SPT. Thus, the IP mixture serves as a bridge between the one-and-a-half fluid reference and any mixture of interest. Independent of these hypothetical substances, a ‘‘principle of component corresponding states’’ is elaborated. The principle states that the fugacity coefficients are equal for components having the same (density-)reduced diameter in different mixtures at the same reduced pressure. The one-and-a-half-fluid theory is demonstrated for mixtures of hard rods in one dimension, where it is seen to be exact, and for hard spheres in three dimensions. The treatment is demonstrably superior to standard conformal solution approaches, particularly at high density and for mixtures of components widely differing in size.
Stochastic dynamics of n-nonane and related molecules in solution compared with nuclear magnetic resonance coupled relaxation times
Authors: Xiang Tian-xiang , Liu Fang , Grant David M.
Published: July 2002

The motion of chain molecules in solution has been analyzed using both generalized Langevin equation (GLE) and ordinary Langevin equation (OLE) simulations. A numerical algorithm for solving the GLEs is developed in which the integrations over various forces have been performed explicitly. It is shown in the GLE simulations that the motion of chain segments is correlated closely with solvent relaxation giving significantly reduced friction forces. At temperatures higher than 233 K, a hydrodynamic description with a structure relaxation mode in the solvent (diglyme) is sufficient to yield Cartesian correlation times in good agreement with the NMR coupled relaxation results on n-nonane. The relative contributions of both overall tumbling and internal motion to the Cartesian and end-to-end direction relaxation and the possible couplings of these two motions are analyzed by calculating apparent activation energies for various motional modes and by using a harmonic approximation. It is found that the OLE model underestimates the contribution of internal motion to the relaxation of local Cartesian modes. The finite structural relaxation rate in the solvent can substantially alter not only the correlation times, but the dynamic features of the relevant relaxation processes in a full GLE calculation. In particular, it is shown that the short-time decay of the Cartesian correlation functions is underdamped oscillation in contrast with the overdamped behavior found from the OLE simulations.
Excited electronic states of the tropyl (cyclo-C7H7 ) radical
Authors: Johnson Russell D.
Published: July 2002

Two-photon electronic absorption spectra of the tropyl radical (cyclic C7H7 ) have been observed by resonance enhanced multiphoton ionization spectroscopy (REMPI) from 415 to 590 nm, corresponding to 34 000–48 000 cm−1. Two Rydberg series are assigned and an ionization potential determined: np, δ=0.35; nf, δ=0.05; I.P.=50 177 cm−1. Vibrational activity of the Rydberg states was observed and the frequencies were found to be similar to the ion: ω2=862 cm−1 (ring breathing); 2ω18=1528 cm−1 (ring bending); and 2ω20=1284 cm−1 (CH out-of-plane bend).
Near-infrared diode laser spectroscopy of the nitrogen molecule in Rydberg states
Authors: Kanamori Hideto , Takashima Shigehiro , Sakurai Katsumi
Published: July 2002

Two electronic bands of the nitrogen molecule were observed by near-infrared diode laser absorption spectroscopy around the 1.3 μm region. One band was assigned to the transition from the E 3Σ+g(v″=0) to D 3Σ+u(v′=0) state. Both states were previously assigned as Rydberg states with an s- or p-electron, and an N+2 X 2Σ+g core. Fine structure constants of these states were determined for the first time. The second band looked as if it belonged to a doublet system of the molecular ion, but it turned out to be that of the neutral when the doublet structure was resolved into triplet components by means of sub-Doppler saturation spectroscopy. This band was also assigned as a 3Σ+−3Σ+ transition and was tentatively assigned to a vibrational hot band of the D–E transition based on the rotational constants, lifetime, transition dipole moment, and systematic line broadening due to predissociation.
Rapid reconnaissance of a model of a chemical oscillator by numerical continuation of a bifurcation feature of codimension 2
Authors: Ringland J.
Published: July 2002

Many models have been proposed for the well-known Belousov–Zhabotinskii reaction. Partly for this reason, but also because the dimension of the models’ parameter spaces are very high, the phenomenology of even the most popular models has been investigated only lightly. The existence in the models of free parameters, i.e., those for which no values are supplied a priori, spreads the investigation even thinner. Consequently, the accuracy with which the models are capable of reproducing experimental phenomena is something that remains unknown. It therefore appears that there might be a use, in the investigation of such models, for a method by which large regions of a parameter space could be reconnoitered in some way. We describe a numerical calculation that constitutes a reconnaissance of a four-dimensional parameter subspace of a seven-species model of the Belousov–Zhabotinskii reaction. The calculation consists of following, or ‘‘continuing,’’ a bifurcation feature of codimension 2 throughout the parameter subspace. By comparing the results with experiment, we are able to circumscribe the region of the free-parameter space where qualitative agreement is possible, and we determine that, with the rate constants originally given by the authors of the model, quantitative agreement with experiment does not exist in any region of the free-parameter space. Moreover, we are able to determine that if a revised set of rate constants from the literature is used, nowhere in the free-parameter space is the model even qualitatively correct. We believe the method described may be helpful beyond the context discussed here.
Optical–optical double resonance spectroscopy of Cl2: First observation and analysis of the 0−g(3P1) ion-pair state and the lower-lying B′ 3Π(0−u) valence state
Authors: Ishiwata Takashi , Kasai Yasuko , Obi Kinichi
Published: July 2002

The perturbation facilitated optical–optical double resonance technique allows access to the 0−g(3P1) ion-pair state through the A 3Π(1u) v=9 intermediate state where the A 3Π(1u) ∼B′ 3Π(0−u) interaction occurs: 0−g(3P1) –{A 3Π(1u) ∼B′ 3Π(0−u) }–X 1Σ+g. Molecular constants of the 0−g(3P1) state are derived from 197 transitions in the 0≤v′≤15 and 9≤J′≤47 range, and a Rydberg–Klein–Rees (RKR) potential based on these constants is given. The dispersed fluorescence spectra of the 0−g(3P1) –B′ 3Π(0−u) system are used to establish the absolute vibrational numbering of the 0−g(3P1) state, and also to characterize the new B′ 3Π(0−u) state in view of the Franck–Condon factor consideration.
A theoretical treatment of thea 3Σ1+ →X1Σ++ spin-forbidden dipole-allowed radiative transition in NO+
Authors: Manaa M. Riad , Yarkony David R.
Published: July 2002

The radiative lifetime of the spin-forbidden dipole-allowed transition a 3Σ1+ →X1Σ0++is determined using ab initio electronic structure techniques. This transition acquires intensity as a result of the spin–orbit induced perturbations, a 3Σ+1∼1Π1 and X1Σ0++∼3Π0+ where the notation is meant to imply that the a 3Σ+1 and X1Σ0++ states are perturbed by all the states of the indicated symmetry in a given configuration state function (CSF) space. A near degeneracy of the A 1Π and a 3Σ+ potential energy curves necessitates the use of quasidegenerate perturbation theory when treating the a 3Σ+1∼1Π1 interaction. The nonrelativistic (zeroth order CI), and relativistic (first order perturbed), wave functions are expanded in CSF spaces of dimension 0.5–1.4×106. To our knowledge, this represents the first treatment of the spin–orbit interaction within the full microscopic Breit–Pauli approximation in a CSF space of greater than 1 million CSFs. The radiative lifetimes (τv) of the transitions (a 3Σ+,v)→X 1Σ+ were found to be τv=455, 467, 478, 488, 495 ms for v=0, 1, 2, 3, 4, respectively. These results are in good agreement with the experimental determination of Kuo et al. [J. Chem. Phys. 92, 4849 (1990)] who found τ=530(+300,−100) ms. The results of this treatment are compared with those of a single perturber model in which the a 3Σ+→X 1Σ+ transition is attributed exclusively to the a 3Σ+∼A 1Π perturbation. This model is shown to be only qualitatively correct.
A local-Gaussian approximation for the propagation of a classical distribution function
Authors: Walkup R. E.
Published: July 2002

A simple approximation method is described for the propagation of a classical Gaussian distribution function. This method is the classical analog of Heller’s well-known scheme for the propagation of Gaussian wave packets [E. J. Heller, J. Chem. Phys. 62, 1544 (1975)]. The classical version has the merit that thermal spreading of the distribution function can be accounted for. A simple method is proposed for treating the combined effects of quantum-mechanical and thermal spreading. In particular, it is shown that the classical approach can be used for an arbitrary initial temperature; it is only necessary to correctly specify the initial width of the distribution in configuration space and the initial root-mean-square momentum spread. Also, an improved method is presented which conserves the total energy of the system. The local-Gaussian method is useful when the force field is approximately linear over the width of the distribution function. In general, this criterion is more readily satisfied at low temperatures, where thermal spreading is not too severe, but where quantum effects can become important. The local-Gaussian method is applied to the dissociation of diatomic molecules by a sudden electronic transition, where a well-defined initial distribution function is propagated on a repulsive potential-energy curve. A comparison with ‘‘exact’’ classical and quantum-mechanical calculations is made.
The relaxation spectrum and diffusion in concentrated systems of spherical particles
Authors: Goodwin J. W. , Hughes R. W.
Published: July 2002

The viscoelastic properties of a concentrated monodisperse latex of polyvinylidene fluoride coated by a monolayer of the surfactant C12E6 has been examined as a function of volume fraction. This system shows solidlike behavior in the linear viscoelastic region. A model is developed to describe number density fluctuations in the sample in terms of the colloid pair interaction energy. This is used to determine the relaxation spectrum and is then compared with experimental data. Excellent agreement is found between the model and the measured stress relaxation response. This model has been compared to published data on polystyrene latex and has also shown excellent agreement. A tracer diffusion coefficient is calculated to illustrate that the dynamic processes controlling relaxation are slow.
Quantum scattering from disordered surfaces
Authors: Whaley K. B. , Bennett A.
Published: July 2002

A projected continuum formulation for time-independent quantum scattering from a continuum of channels is presented and applied to atomic scattering from disordered surfaces. Projecting out the channel continua gives rise to explicitly constructed optical potentials for the coherently diffracted scattering amplitudes, while the continuum diffuse scattering contribution is obtained in terms of these wave functions. Numerical application is made to atomic scattering from weakly corrugated disordered surfaces, for which a truncated set of coupled equations can be used within which the theory is shown to be unitary. The occurrence of a new phenomenon of disorder-induced sticking on rigid surfaces is demonstrated and comparison with phonon-induced sticking is made. These new disorder-induced sticking processes are shown to have very different energy dependence than phonon-induced sticking, with strong resonant sticking and oscillatory behavior seen at low incident energies.
The mechanism of kinetic oscillations in catalytic oxidation of CO on Pt(210)
Authors: Sander M. , Imbihl R. , Ertl G.
Published: July 2002

Under isothermal conditions at low pressure (10−4 Torr), the catalytic oxidation of CO on a Pt(210) surface exhibits kinetic oscillations which have been investigated using Video-LEED, measurement of the CO2 production rate and the variation of work function. An induction period of ∼30 to 60 min, which has been shown to be due to a facetting of the surface exists before the appearance of kinetic oscillations. If reaction conditions are chosen which correspond to the high rate branch of Langmuir Hinshelwood kinetics, the Pt(210) surface facets into (310) and (110) orientations. The facetting process is associated with a decrease in catalytic activity caused by a lowering of the oxygen sticking coefficient. In situ LEED experiments demonstrated that the oscillations in the reaction rate are associated with periodic intensity variations of the half-order LEED beams belonging to (110) facets. Thus, the oscillations appear to be driven by the CO-induced 1×1⇄1×2 phase transition on (110) facets in the same way as has been verified for the system Pt(110)/CO+O2. The involvement of a facetting process explains the characteristic properties of kinetic oscillations on Pt(210) such as the relatively low high-temperature limit of ≊500 K, the existence of an induction period and the period length which is on the order of minutes.
Effects of product occupancy on self-organization in heterogeneous catalysis. I. Multiple steady states and temporal oscillations
Authors: Li Ru-Sheng , Horsthemke W.
Published: July 2002

A Langmuir–Hinshelwood-type model for isothermal reactions in small pellets of microporous solids can exhibit multiple steady states, oscillations, and coexistence of one oscillatory state with up to two stationary states, if blocking of active sites by the product is taken into account.
Dispersion of linear and nonlinear optical properties of benzene: An a
b i
n
i
t
i
o time-dependent coupled-perturbed Hartree–Fock study
Authors: Karna Shashi P. , Talapatra Gautam B. , Prasad Paras N.
Published: July 2002

Frequency-dependent polarizability α and second hyperpolarizability γ corresponding to various third-order nonlinear optical processes have been calculated by ab initio time-dependent coupled-perturbed Hartree–Fock method. The selection of proper diffuse functions in the basis set is made from a comparison of the calculated values of a(ω) at two optical wavelengths (λ=589 and 632.3 nm) and that of γ (−2ω; 0, ω, ω) at λ=1064 nm with the reported experimental values at these wavelengths. It is found that a 4-31G basis with a diffuse p and a diffuse d function, in addition to properly describing various elements, yields the values of α and γ which are, respectively, within 7% and 5% of the corresponding experimental results. The in-plane components of α show a larger frequency dispersion compared to the out-of-plane component. The calculated values of γ for the electric field-induced second harmonic generation (EFISH) at five optical wavelengths are within 5%–14% of the reported experimental results. However, a somewhat larger discrepancy between the calculated and measured values of γ for third harmonic generation (THG) and γ for degenerate four wave mixing (DFWM) is found. The order of the γ values for various third-order processes is γ(THG) >γ(EFISH) >γ(DFWM) >γ(EFIKE) ≊γ(EFIOR), where EFIKE and EFIOR, respectively, represent electric field-induced Kerr effect and electric field-induced optical rectification. The elements of γ show deviation from the Kleinman symmetry even at lower optical frequencies.
Percolation and critical exponents on randomly close-packed mixtures of hard spheres
Authors: Frith W. J. , Buscall R.
Published: July 2002

This paper reports results for the percolation threshold and the critical exponents on a continuum model based on randomly close-packed mixtures of hard spherical particles. In the model, all the particles are identical in all respects save for their label (A or B). Each particle in the system has a variable number of neighbors that are defined by particle contacts, yielding a lattice of sites (the particles) with a distribution of coordination numbers. The percolation threshold for one type of particle was determined for this system, as were the exponents for the screening length, the susceptibility, and the strength of the largest cluster. The amplitude ratio for the susceptibility, below and above the percolation threshold, was also determined, and found to be in reasonable agreement with results for regular 3D lattices.
State-selective physisorption of deuterated ammonia on graphite (0001)
Authors: LaVilla Michael E. , Ionov Stanislav I.
Published: July 2002

Rotationally state-selected molecular beams of ND3 at 0.11 eV are directed at near-normal incidence to a graphite (0001) surface. The relative number density in the scattered beams, measured by photoionization spectroscopy, is found to be two times greater for the incident molecular beam of predominantly ‖JKM〉=‖222〉 rotational states as compared to the ‖111〉 beam, implying state-selective trapping.
Adiabatic channel potential curves for two linear dipole rotors. I. Classification of states and numerical calculations for identical rotors
Authors: Maergoiz A. I. , Nikitin E. E. , Troe J.
Published: July 2002

Adiabatic channel potential curves for a system of two linear dipole rotors are discussed. A general classification of states is given and a numerical procedure for calculating eigenvalues as a function of interrotor distance is formulated, both in a limited and extended basis set. A system of identical (but distinguishable) rotors is treated explicitly. Unexpectedly, the adiabatic potential curves show narrow avoided crossings which suggests the possibility of constructing diabatic channel potential curves. The validity of the adiabatic assumption for the relative motion of the dipoles is discussed.
General formula evaluation of the electron-repulsion integrals and the first and second integral derivatives over Gaussian-type orbitals
Authors: Ishida Kazuhiro
Published: July 2002

Recurrence relations between auxiliary functions to calculate the electron-repulsion integrals (ERIs) over Cartesian Gaussian-type orbitals (GTOs) can be derived. With the use of the Rys polynomials, this serves as a general formula method for evaluating ERIs and the ERI analytical derivatives. The computer code of the present method is quite general (i.e., it has no limitation for the shell type of GTOs), very compact (i.e., it has no coding difficulty), and extremely rapid (e.g., 2.1 μs per one ERI, 0.51 μs per one ERI first derivative, and 0.40 μs per one ERI second derivative for the [II‖II] shell block). It is found that the present method is especially efficient for evaluating ERIs including g-type or higher GTOs, the first derivatives including f-type or higher GTOs, and the second derivatives including d-type or higher GTOs.
Fourier transform microwave spectroscopy of Hg–CO2
Authors: Iida Minoru , Ohshima Yasuhiro , Endo Yasuki
Published: July 2002

Pure rotational spectra of the mercury–carbon dioxide complex have been observed by a Balle–Flygare-type Fourier-transform microwave spectrometer with a high temperature pulsed valve. From the nuclear spin statistics associated with the oxygen atoms of CO2, the complex has been found to be T-shaped with C2v symmetry, as in the analogous rare gas–carbon dioxide complexes. The rotational constants, B and C, and the harmonic force constants for the van der Waals (vdW) modes have been determined from a nonlinear least-squares fit of the transition frequencies. The mercury–carbon distance has been derived to be 3.695 Å from the determined rotational constants. The permanent dipole moment of the complex has been determined to be 0.107 (3) from Stark effect measurement, where the value in parentheses is twice the standard deviation.