bluuebunny/crossref_metadata_2025 huggingface dataset:
A model for association in electrolytes. Analytic solution of the hypernetted-chain/mean spherical approximation
Authors: Lee Song Hi , Rasaiah Jayendran C. , Cummings Peter T.
Published: July 2002

We study the structural and thermodynamic properties of electrolytes in which the association between oppositely charged ions (A++B−⇄AB) is represented by a sticky electrolyte model (SEM) which allows positive and negative ions of diameter σ to be bonded at a distance L≤σ/2. The model is solved for a 2–2 electrolyte at concentrations up to 2 M and for L=σ/2 using the hypernetted-chain (HNC) approximation for the correlation functions within the spherical core and the mean spherical (MS) approximation outside. The number of AB dimers at a separation L is found to increase with concentration while there is a reduction in the number of contact ion pairs below that predicted by the restricted primitive model (RPM) from which stickiness is absent. The structural and thermodynamic properties of the SEM and RPM prove to be significantly different and sufficiently interesting to justify future applications of the SEM to molten salts and molecular solvents, especially if the ion–ion interactions can be treated with greater accuracy. The equilibrium properties of the fully associated system of extended dipoles with charges separated at a distance L=σ/2 are also given in the mean spherical approximation.
On the helium-alkali halide surface potential: Surface corrugation vs ionic size
Authors: Miglio L. , Quasso F. , Benedek G.
Published: July 2002

We evaluate the potential energy of a He atom near an ionic surface by summing a two-body potential as derived from molecular physics. Corrugation parameters and binding energy are derived for a set of four alkali halide surfaces and compared to recent atom scattering data. Finally we comment on the possibility of performing a surface crystallography of ionic crystals by means of atom scattering.
Conformational properties of a polymer chain confined between two plates
Authors: Ishinabe Takao
Published: July 2002

The behavior of a polymer chain confined between parallel plates a distance D apart is studied by Monte Carlo calculations of self-avoiding walks for up to 100 steps on the tetrahedral lattice. Scaling predictions of Daoud and de Gennes are tested using the data obtained; they are consistent with the predictions for D≥7. Dependencies of the end-to-end distance of the chain and the monomer density distribution on D are examined. An exponent related to polymer adsorption is also estimated. Some of the results are compared with those obtained from the exact enumerations for up to 20 steps.
Spin-dependent electrochemical kinetics at a semiconducting photocathode
Authors: Chazalviel J.-N.
Published: July 2002

We present experimental evidence that the electrochemical rate at a semiconducting photocathode can be affected by the relative spin orientations of the electrons in the semiconductor and of the redox species in the electrolyte. Here the spin orientations are acted upon independently by combination of a large magnetic field and optical pumping of the photoelectrons with circularly polarized light. The effect can be qualitatively understood in terms of the classical models for electrochemical transfer at a semiconducting photoelectrode. The results show that the spin polarization may not be drastically affected upon the electrochemical transfer and may provide a probe for the electrochemical interface.
Excitation of continuum radiation in collisions of (1) electrons and (2) metastable argon atoms with H2 and D2
Authors: Lishawa C. R. , Feldstein J. W. , Stewart T. N. , Muschlitz E. E.
Published: July 2002

Measurements have been made of the spectral distribution of continuum radiation arising from collisions of low energy electrons and of metastable (3P0,2) argon atoms with hydrogen and deuterium molecules. The electron impact spectra, a(3Σ+g, v′=0) → b(3Σ+u)+hν, are in good agreement with the calculations of James and Coolidge. The spectra originating from Ar*+H2, D2 were obtained using crossed supersonic beams. In both cases, an onset at 0.065 ± 0.009 eV relative collision energy was observed. For deuterium, this onset occurs below the energy required to produce D2(a 3Σ+g) . Calculations of the spectral distributions when compared to experiment showed that, at 0.07 eV, the observed radiation arises from the first two vibrational levels of ArD* in the ratio (v′=0)/(v′=1)=4. For hydrogen at this energy, both product channels are present in the ratio ArH*/H*2=2 . At higher energy, both product channels are found in both systems with D*2 predominating in the case of D2 and ArH* in the case of H2.
Computed rotational rainbows from realistic potential energy surfaces
Authors: Gianturco F. A. , Palma A.
Published: July 2002

The quantal IOS approximation in here employed to study interference structures in the rotationally inelastic, state-to-state differential cross sections for polar diatomic targets (LiH, FH, and CO) interacting with He atoms. Quite realistic expressions are used to describe the relevant potential energy surfaces (PES) which were taken from previous works that tested them against accurate experimental findings for total and partial differential cross sections. Specific features like short-range anisotropy and well depth, long-range attractive regions and overall range of action for each potential employed are analyzed and discussed in relation to their influence on rotational rainbows appearance and on the possible observation of cross section extrema in rotational energy distributions.
Critical behavior of modulus of gel
Authors: Tokita Masayuki , Niki Ryoya , Hikichi Kunio
Published: July 2002

The critical behavior of the shear modulus of casein gel is studied. The shear modulus of casein gel scales with the conductivity exponent in the immediate vicinity of the sol–gel transition point. The asymptotic behavior of the modulus in the region far above the transition point is governed by a different exponent which is much larger than the conductivity exponent. These results are explainable by the crossover behavior of the percolation process. This study shows that the gelation of the casein micelle solution is a realization of the percolation process.
Coexistence curve of polystyrene in methylcyclohexane. IV. Three-phase coexistence curve of ternary system
Authors: Dobashi Toshiaki , Nakata Mitsuo
Published: July 2002

Three-phase equilibria have been studied for the ternary system polystyrene (Mw=1.73×104)+polystyrene (Mw=7.19×105)+methylcyclohexane by numerical analyses of Gibbs free energy and experimental measurements. The calculation showed that the three-phase equilibrium appears at the temperature range from 21.4 to 23.4 °C. At these two temperatures two phases of the three coexisting phases coalesce into one phase and phase equilibria are represented by a tie line with one end being a critical point. The intersection of the two tie lines gives compositions the solution of which can give rise to the entire three-phase coexistence curve. The coexistence curve measurements were made for two solutions with different compositions near the calculated intersection. By a refractive index method coexistence curves were obtained in a temperature-total polymer composition diagram. The three-phase region was observed in a very narrow temperature range from 24.1 to 24.7 °C. The two solutions could give rise to almost entire three-phase coexistence curve and two critical points were predicted to be just above and below the three-phase region from strong opalescence. The mechanism of the three-phase separation was explained as due to the heterogeneous double plait point.
Internal viscosity in polymer chains: A critical analysis
Authors: Allegra Giuseppe
Published: July 2002

The theory relating internal viscosity to nonequilibrium statistics of chain rotational states is critically reinvestigated, to obtain a comprehensive formulation valid in the whole range of the Fourier normal modes, not necessarily under Θ-conditions. The internal viscosity force acting on a given atom is linearly related with the local strain rate or, more precisely, with the time rate of change of the local configurational free energy. An error by a factor 2 in the previously proposed numerical coefficient of the internal viscosity is pointed out. A simplified comparison with other internal viscosity theories deriving from the hindered rotation concept is carried out on the basis of linear Langevin equations of motion valid for collective chain modes. It is shown that the present theory obeys the twofold requirement of leading to a physically needed upper limit of the rate of propagation along the chain as well as to a spectrum of relaxation times in satisfactory agreement with experimental data.
Shape resonances in the photoionization of cyanogen
Authors: Lynch D. L. , Dixit S. N. , McKoy V.
Published: July 2002

We have studied the photoionization cross sections and photoelectron asymmetry parameters for ionization of the 1πg(X 2Πg), 5σg(A 2Σ+g), and 4σu(B 2Σ+u) levels of cyanogen using frozen-core Hartree–Fock photoelectron continuum orbitals. The main purpose of these studies has been to extend our understanding of the dynamics of shape resonances from earlier studies of diatomic and smaller polyatomic molecules to a larger polyatomic system. The results do, in fact, reveal a rich shape resonant structure in the electronic continuum of this polyatomic system. There is a low-energy σu resonance which, as expected, is the C–C analog of the l=3 shape resonance seen in N2(3σ−1g) and several other diatomics. In contrast to this diatomic-like behavior, the presence of the two CN groups in C2N2 results in a second σu and a σg resonance corresponding to linear combinations of a l=3 shape resonance localized on the CN sites. Moreover, our results also show a pronounced shape resonant behavior in the πu continuum, which, to our knowledge, has not been seen in smaller molecules.
Relaxation behavior in a bistable chemical system near the critical point and hysteresis limits
Authors: Ganapathisubramanian N. , Showalter Kenneth
Published: July 2002

Relaxation half-times have been measured in the bistable iodate-arsenous acid reaction near a hysteresis limit and the critical point. A one-variable empirical rate law model is used to examine the apparent divergence in the relaxation times at these points. Relaxation behavior very close to, and exactly at the critical point and hysteresis limits is considered.
Dynamics of helical worm-like chains. VII. General scheme of the higher-order subspace approximations
Authors: Yoshizaki Takenao , Yamakawa Hiromi
Published: July 2002

The higher-order subspace approximations to a solution of the eigenvalue problems relevant to the L(1) observables for the discrete helical worm-like chain are formulated. It consists of augmenting the L(1) subset of basis functions with those in the complementary subspace. The procedure is applied to a one-dimensional system of rotors, and it is found that there is good agreement between the higher-order approximations and the simulation results obtained by Cook and Livornese for certain correlation functions. For flexible chains, the analysis shows that it is sufficient to change the relaxation rates in the crude approximation by taking into account only a rather small number of basis functions in the subspace L(2) without changing the amplitudes and with neglect of any additional modes. This procedure is not effective at all for stiff chains.
Analysis of the reaction He++He+He→He+2+He. II. Improved sampling
Authors: Russell J. E.
Published: July 2002

The rate coefficient for He+ ions recombining in helium gas is computed using the Wigner–Keck Monte Carlo trajectory method. The present calculation is a refinement of a previous one, the principal difference between the two being that simpler, more reliable, and much less time consuming procedures are now employed to select the trajectories. The results of the new calculation are consistent with, and statistically more accurate than, those of the previous one. The improved sampling procedures, unlike those employed in the previous calculation, have the appearance of being easily applicable to other, similar three body association reactions.
The role of vibrational excitations in collision-induced dissociation using Faddeev–AGS theory
Authors: Haftel M. I. , Lim T. K.
Published: July 2002

This paper examines the role of vibrational (and rotational) excitations in collision-induced dissociation in atom–diatom reactions. We treat a model system of identical, bosonic hydrogen atoms and investigate the total H+H2→H+H+H cross section as functions of total center-of-mass (c.m.) energy and vibrational–rotational quantum numbers v, j. The investigations are based on Faddeev–AGS theory and both three-dimensional (3D) and collinear (one-dimensional, 1D) geometries are considered. We derive both low- and high-energy relations between the total dissociation cross section, c.m. energy, and the vibrational–rotational wave functions, employing the single-scattering approximation of Faddeev theory. We apply these relations to the spectrum of the Kolos–Wolniewicz potential, both in three dimensions and one dimension. For collisions with a fixed total c.m. energy, our investigations predict considerable vibrational enhancement of the total cross section in the low-energy limit, with this enhancement much more pronounced in the true 3D dynamics than in the artificial collinear geometry, indicating that translational energy is less effective than vibrational in CID. As the c.m. (or translational) energy increases, approaching infinity, a transition occurs to either no enhancement or inhibition, or to slight vibrational inhibition, depending on the nature of the underlying interaction. This property mainly results from how the momentum distributions of the diatomic wave functions sense the available phase space of the dissociation reaction. In light of the anticipated failure of the single-scattering approximation at low collision energies, the predicted trends for vibrational enhancement are tested by calculating dissociation cross sections with exact Faddeev theory for weakened H–H potentials. While the single-scattering approximation does indeed break down badly, the ratio of cross sections for different vibrational states is largely unchanged from the exact. An explanation of this fact, using a modified single-scattering argument with radially cut-off diatomic wave functions, is discussed and developed physically.
Consistently averaged hydrodynamic interaction for Rouse dumbbells. Series expansions
Authors: Öttinger Hans Christian
Published: July 2002

The consistent averaging approximation for the hydrodynamic interaction, which has been introduced very recently, is used to derive a retarded-motion expansion for Rouse dumbbells in slowly varying homogeneous flows. In the special case of shear flow, expansions for the viscometric functions are obtained for small and high shear rates. The effects of the consistently averaged hydrodynamic interaction are shown to be in reasonable agreement with experiment.
Resonances from the complex dilated Hamiltonians in a dilation-adapted basis set with a new stabilization parameter
Authors: Froelich Piotr , Goscinski Osvaldo , Moiseyev Nimrod
Published: July 2002

Explicit consideration of the analytic properties of the solutions to the dilated Hamiltonian is taken into account in the construction of the matrix representation of the latter in an L2 basis. The total dilated matrix is blocked according to division of the basis into ‘‘bound’’ and ‘‘scattering’’ subspaces, which are interacting via the off-diagonal blocks, leading to a coupling maintaining the adequacy of the bound part of the basis throughout the wide range of the dilation angle. The size of the bound subspace, M, becomes a new stabilization parameter; its variation covers the entire range of situations between a real stabilization calculation and the conventional complex-scaling calculation. This construction allows for a systematic analysis of the dilated Hamiltonian, bringing forward the physical interpretation of the configuration interaction while suppressing the disadvantageous effects of the dilation transformation, manifested by poor convergence. The connections to Junker’s complex stabilization method are discussed.
Label-free exchange perturbation approximation for the collision-induced dipole of He⋅⋅⋅H
Authors: Juanós i Timoneda J. , Hunt K. L. C.
Published: July 2002

A label-free exchange perturbation method is used in this work to calculate the net dipole μ(R) of interacting He and H atoms as a function of internuclear separation R. In the label-free formalism, the unperturbed Hamiltonian and perturbation terms are constructed so that each is invariant with respect to exchange of electrons between the interacting atoms; then a direct Rayleigh–Schrödinger perturbation expansion with a fully antisymmetrized set of zeroth-order wave functions yields the interaction energy and collision-induced properties. Good agreement with accurate ab initio results for the He ⋅⋅⋅ H dipole is obtained when a long-range dispersion contribution (varying as R−7) is added to the first-order overlap and exchange contributions, computed with an extended Gaussian basis. Near the van der Waals minimum and at short range the dipole vector points from the H nucleus to the He nucleus, but at long range the dipole orientation is reversed. Between R=4.0 and 8.0 a.u., the dipole decreases rapidly (with a roughly exponential R dependence) as the internuclear distance increases.
Binary nucleation and condensation in associated vapors
Authors: Studziński W. , Spiegel G. H. , Zahoransky R. A.
Published: July 2002

The binary nucleation theory is extended to include vapor phase association. Similar to the effects found for pure vapors, two opposite influences due to stable association complexes have been derived. A kinetic one increases the nucleation rate and a larger, thermodynamic effect acts contradictory. The developed theory is applied to the water–acetic acid system. Extensive experiments were performed in the unsteady rarefaction wave of a preheated shock tube. The variation of the measured critical supersaturation as a function of mixture composition was found to agree well with the predictions of the theory.
Vibronic band structure in the 270–330 nm photodissociation spectrum of (CO)+2
Authors: Ostrander Scott. C. , Sanders Lary , Weisshaar James C.
Published: July 2002

The photodissociation spectrum (CO)+2  →hν  CO++CO has been obtained in the near UV from 270–330 nm at 300 K in a fast flow reactor. Mass selected CO+ photofragments are detected following excitation with a frequency doubled pulsed dye laser. The spectrum exhibits a long progression of predissociative vibronic bands spaced by 475±20 cm−1, in contrast to the unstructured visible spectra of other dimer cations. Preliminary ab initio SCF calculations can qualitatively explain the unusual transparency of (CO)+2 in the visible.
Deuterium and sodium quadrupole interactions in sodium hydroxide. II. The monoclinic phase
Authors: Amm D. T. , Segel S. L. , Bastow T. J. , Jeffrey K. R.
Published: July 2002

The temperature dependence of the 23NaOH pure quadrupole resonance (NQR) frequency has been studied from 77 to 550 K and shows a change in slope and a discontinuous change in frequency of 6±2 kHz at the orthorhombic to monoclinic phase transition at 505 K. At 292 K the 23Na NQR frequency is 1.778±0.001 MHz, η<0.04. The temperature dependence of the deuterium quadrupole coupling was fit to a librating molecule model between 293 and 570 K (QCC=245±2 kHz, η=0.05±0.01 at 293 K) and confirms that the frequency of the OD− libration decreases in the high temperature monoclinic phase.
Shape resonances in the angle-resolved photoelectron spectroscopy of the Si 2p shell of SiCl4
Authors: Carlson Thomas A. , Svensson W. Agneta , Krause Manfred O. , Whitley Timothy A. , Grimm Frederick A. , Wald Grant Von , Taylor James W. , Pullen B. P.
Published: July 2002

The partial cross sections and angular distribution parameters, β, have been determined for the 2p subshell in SiCl4. These data were obtained with angle-resolved photoelectron spectroscopy and the use of synchrotron radiation for a range of photon energies from 114 to 150 eV. The same quantities were calculated by use of a multiple scattering Xα method, and the agreement between experiment and theory is very good. In particular, the behavior of shape resonances was well predicted. The nature of shape resonances as a function of molecular orbitals in SiCl4 is discussed, and the importance of such intercomparison is emphasized.
Vibrational distributions of CN(X 2Σ+) resulting from the C(3P)+NO and C(3P)+N2O reactions at 300 K
Authors: Sekiya Hiroshi , Tsuji Masaharu , Nishimura Yukio
Published: July 2002

The C(3P) atoms have been prepared from the dissociation of CO molecules by Ar(3P2,0) or He(2 3S) atoms in a flowing afterglow apparatus. The CN(B 2Σ+ ← X 2Σ+) laser induced fluorescence spectra have been observed from the reactions C(3P)+NO → CN(X 2Σ+)+O and C(3P)+N2O → CN(X 2Σ+)+NO at 300 K. The CN(X) state is observed in the vibrational levels up to v″=5 for the C(3P)+NO reaction, while it is detected up to v″=6 for the C(3P)+N2O reaction. In the C(3P)+NO reaction, the relative vibrational populations of CN(X) decrease with increasing the vibrational quantum number and the observed distribution is close to the ‘‘prior’’ one. In contrast to the C(3P)+NO reaction, the vibrational distribution of CN(X,v″=0–6) from the C(3P)+N2O reaction is inverted with a peak at v″=4. This agrees with the previous observation of Dorthe et al. However, the CN(A 2Π → X 2Σ+) chemiluminescence observed by them has never been detected.
Mechanism of thermal electron attachment to NO2
Authors: Shimamori Hiroshi , Hotta Hiroshi
Published: July 2002

The mechanism of thermal electron attachment to NO2 has been reexamined by observing the dependence of the attachment rates on the nature and the pressure of the environmental gases. Measurements for mixtures of NO2 with rare gases, H2, D2, N2, CO2, and n-C4H10 all showed two-body pressure dependence of the attachment rates at buffer-gas pressures of about 10 to 100 Torr. They gave the same two-body rate constant of (1.13±0.07)×10−10 cm3 molecule−1 s−1. The latter result disagrees with the data reported by Mahan and Walker in 1967. The present results indicate that the collisional electron detachment process introduced previously to interpret the effect of the nature of environmental gases should be negligible. We have also observed the decrease of the two-body rate constants at pressures below about 10 Torr for all the mixtures studied. This strongly suggests that the attachment mechanism is an ordinary two-step three-body process. The three-body rate constants then obtained are mostly of the orders of 10−27 cm6 molecule−2 s−1 and do not differ much with nature of the third bodies. An autoionization lifetime of 1×10−8 s has been estimated for the transient-negative ion of NO2. It has been found that even room light could cause appreciable decrease of the rate constants, probably through decomposition of NO2 molecules. The discrepancy between the present results and the previous ones may be due to such an effect.
A linear model of crystal field correlation effects in Mn2+
Authors: Ng Betty , Newman D. J.
Published: July 2002

Previous work on correlation effects in 3dn systems has been dominated by the nonlinear Koide and Pryce model which is based on a simplified picture of covalent bonding. Because of the deficiencies of this model, it is of interest to test linear correlation models which are not based on specific mechanisms. In this light, we assess the spin-correlated crystal field model, which has recently shown some success in explaining correlation effects in lanthanide crystal field splittings.
The effect of electron correlation in the interaction of atomic hydrogen with Ben clusters 3≤n≤7
Authors: Rubio J. , Illas F. , Ricart J. M.
Published: July 2002

The Ben and Ben –H (3≤n≤7) systems have been studied at the SCF and CI levels using nonempirical pseudopotentials for the Be atoms. While the effect of electron correlation is of great importance in correctly describing the cluster properties, the interaction of atomic hydrogen with those clusters can be described quite accurately at the SCF level. From a quantitative viewpoint the distances to the surface and interaction energies are changed by about 0.03–0.05 Å and 6–8 kcal/mol, respectively. Vibrational frequencies for the perpendicular motion to the surface are affected more.
The vibrational spectrum of the water dimer: Some model based predictions
Authors: Wójcik Marek J. , Rice Stuart A.
Published: July 2002

We report an analysis of the vibrational spectrum of the water dimer, including Fermi resonance and the adiabatic coupling between intra- and intermolecular modes. Three recently proposed pair potentials for water, each of which includes a representation of the intra- and intermolecular force fields, are tested by comparing the predicted and observed infrared spectra. Our results show that dynamical effects in the vibrational spectrum are underestimated by these potentials. Despite the considerable uncertainty in the experimental data it is clear that currently available water–water potentials are too inaccurate to be trusted except for predictions of the qualitative properties of the vibrational spectrum.
Density profiles and pair correlation functions of Lennard-Jones fluids near a hard wall
Authors: Plischke Michael , Henderson Douglas
Published: July 2002

We numerically solve the inhomogeneous Percus–Yevick equation for a system of particles interacting with each other through a Lennard-Jones potential in the vicinity of a flat impenetrable wall. The density profile and pair correlation function are determined self-consistently. We obtain density profiles which are, at least close to the wall, in good agreement with Monte Carlo results for low to intermediate densities. In one case for which a comparison of the entire profile with a Monte Carlo calculation is possible, we also obtain encouraging results.
Dissociative recombination of H+2 by collisions with slow electrons
Authors: Takagi Hidekazu , Nakamura Hiroki
Published: July 2002

Dissociative recombination of H2+ by collisions with slow electrons is investigated by the multichannel quantum defect theory. (AIP)
Molecular dynamics simulation of geminate recombination by electrons in liquid methane
Authors: Morgan Wm. Lowell
Published: July 2002

Geminate and homogeneous recombination of electrons in liquid CH4 has been simulated using molecular dynamics. The computed rate coefficients compare favorably with recently published measurements. A principal result of the simulation is that the energy transfer rate rather than diffusion is the rate limiting process in recombination. Other computational results include the effect of an external electric field and the effect of large dosage (high electron density) on the recombination rate coefficient, electron thermalization times, and the probability distribution of thermalization distances.
Total reactive cross sections for the reaction H+D2=HD+D
Authors: Tsukiyama K. , Katz B. , Bersohn R.
Published: July 2002

Total reactive cross sections for the reaction H+D2=HD+D with fast hydrogen atoms were measured in a single collision pump–probe experiment. With H atoms having translational energies of 0.84 and 1.95 eV relative to thermal D2 cross sections of 0.99±0.11 and 1.68±0.12 A2 were measured.
Generalized Langevin theory for many-body problems in chemical dynamics: The equivalent chain equations for solute motion in molecular solvents
Authors: Adelman Steven A. , Balk Michael W.
Published: July 2002

A generalized Langevin equation framework for the treatment of liquid state influence on solute dynamics in molecular solvents, which generalizes an earlier framework restricted to monatomic solvents [S. A. Adelman, Adv. Chem. Phys. 53, 61 (1983)], is developed. This framework permits one to realistically treat energy exchange between the solute atoms and the solvent vibrational (V) degrees of freedom. This energy exchange can qualitatively influence the rates of liquid state processes when the solute frequencies relevant to the process of interest (e.g., a solute normal mode frequency if one is interested in the vibrational energy relaxation of that mode) substantially overlap the V bands of the frequency spectrum describing local solvent density fluctuations. The main result of the present analysis is an infinite set of equivalent chain equations governing the dynamics of the solute configuration point in molecular solvents. These are equations of motion for the solute configuration point and for the coordinates of an infinite set of abstract chain ‘‘molecules’’. Each molecule is composed of r+1 ‘‘atoms’’ where r is the number of normal modes of a real solvent molecule. The nearest neighbor chain of fictitious molecules may alternatively be regarded as a set of r+1 nearest neighbor cross-linked ‘‘atomic’’ chains. Atomic chain 1 executes low frequency

‘‘acoustical’’ motions which simulate the influence of local solvent translational–rotational (TR) density fluctuations. Atomic chains 2,3,. . .,r+1 execute high frequency ‘‘optical’’ motions which simulate the influence of normal mode V local solvent density fluctuations. The coupling of the optical and acoustical branches of the chain by the crosslinks is the chain formalism equivalent of the physical coupling, due to liquid state effects, of the temporal development of the TR and V modes of motion. The theory presented in this paper provides a conceptual foundation for the treatment of liquid state reactions occuring in molecular solvents by stochastic dynamics techniques. This conceptual foundation may be made the basis of practical simulation methods for treating reactions of diatomic solutes in molecular solvents and may be further developed to provide practical simulation methods for polyatomic solutes in molecular solvents.
The microwave spectrum of propyne in the 17–52 GHz region for the V1=3 vibrational state
Authors: Prakash Vinod , Roberts J. A.
Published: July 2002

The rotational spectra in the V10=3 vibrational state of propyne have been determined in the frequency range 17–52 GHz. Molecular constants for this vibrationally excited state have been determined from more than 13 observed rotational transitions. Agreement between experimentally measured frequencies and those calculated using the results of Bauer et al. was found to be good.
Rotational analysis of the B̃ 2Σ+–X̃ 2Σ+ transition of BaOH and BaOD
Authors: Kinsey-Nielsen S. , Brazier C. R. , Bernath P. F.
Published: July 2002

The B̃ 2Σ+–X̃ 2Σ+ transitions of BaOH and BaOD were studied by the technique of dye laser spectroscopy. The 000–000 and 001–000 bands of BaOH and 000–000 band of BaOD were rotationally analyzed. The B̃ 2Σ+ state is perturbed by the Ã 2Π state and each parity (e/f) component of the B state was fit separately. BaOH is a linear molecule with r0(Ba–O)=2.201 Å and r0(O–H)=0.923 Å. The X̃ 2Σ+ vibrational frequencies for BaOH (BaOD) are 492.4 (482.4) cm−1 for Ba–O stretch and 341.6 (257.6) cm−1 for the bend.
Angularly resolved vibrational excitation in Na2–He collisions
Authors: Gottwald E. , Mattheus A. , Bergmann K. , Schinke R.
Published: July 2002

We report angle-resolved measurements of vi=0  → vf=1 vibrational transitions in Na2–He collisions at an energy of 90 meV. The agreement with calculated cross sections using an ab initio surface is good, both in the angular variation of the cross section as well as with respect to its magnitude relative to the vibrationally elastic process. The calculated (vi=0, ji=0)  → (vf=1, jf ) differential cross sections are discussed in some more detail. They show structure, in addition to the rainbow oscillations, related to the fact that the vibrational transition probability vanishes for a specific approach angle.
Electronic structure of polyhedral alkanes
Authors: Scamehorn Carol A. , Hermiller Susan M. , Pitzer Russell M.
Published: July 2002

Self-consistent-field wave functions have been obtained for tetrahedrane, cubane, and dodecahedrane with a flexible s, p basis set, (9s5p/4s), [4s3p/2s]. The CC and CH distances were optimized to 0.001 Å. Ionization potentials have been computed both by the ΔSCF and the Koopmans’ Theorem methods. The full spatial symmetry was used in the calculations, and some of the required considerations for dodecahedrane are discussed.
Influence of water on the infrared spectrum of crystalline N-methylacetamide
Authors: Häseler S. , Poglitsch A. , Bechtold G. , Peticolas W. L.
Published: July 2002

Infrared spectra of crystalline N-methylacetamide (NMA) at room temperature and near liquid helium temperature are reported for the pure vacuum distilled substance, and the same with defined amounts of water added. Several lines turn out to be highly water sensitive: those assigned to amide VI and IV, those at 804 and 1384 cm−1, and the one at 1413 cm−1 which is assigned to CH3(−N) sym. bend, the amide I and II bands, and two lines at 3103 and 3300 cm−1 mainly assigned to ν NH vibrations. It seems the spectra reported up to now have to be reconsidered cautiously concerning the water content of the samples and the assignments have to be thought through again.
More on the multidimensional surface intersection problem and classical trajectory surface hopping
Authors: Stine J. R. , Muckerman J. T.
Published: July 2002

We respond to the previous Comment by Mead and Truhlar pointing out a circularity in our published analysis of a trajectory passing through a locally avoided intersection of potential energy surfaces in a two state system. We did not distinguish clearly in that analysis between properties of the physical system and those of our model for it. Our ‘‘reduction’’ to a one-dimensional problem is rather a ‘‘mapping’’ onto a one-dimensional model. We present a clearer description of the actual procedures we used to demonstrate that our method is valid for the types of systems to which we have applied it.
Dihedral angle distribution in liquid n-butane: Molecular dynamics simulations
Authors: Wielopolski P. A. , Smith E. R.
Published: July 2002

We report molecular dynamics simulations of n-butane at the B1 state point of Ryckaert and Bellemans [Chem. Phys. Lett. 30, 23 (1975); Discuss. Chem. Soc. 6, 695 (1978)]. The results confirm those of Edberg et al. (preceding paper) in that we found 58.5±1.0% of the molecules in the trans state as opposed to the value of 54% reported by Ryckaert and Bellemans.
Two-dimensional crystal structure of single Langmuir–Blodgett films deposited on noble metal single crystals studied with LEED
Authors: Vogel Viola , Wöll Christof
Published: July 2002

Single fatty acid monolayers were deposited onto noble metal single crystals (Cu, Ag, Au).Low-energy electron diffraction (LEED) investigations of these 2D monolayer crystals reveal a structural quality comparable to that of single crystal metal surfaces. The monolayer crystal is aligned with respect to the metal substrate and the positional coherence extends over the whole monolayer coated metal substrate 20 mm in diameter.
Theoretical study of the 7Σ+u state of N2
Authors: Partridge Harry , Langhoff Stephen R. , Bauschlicher Charles W.
Published: July 2002

Theoretical potentials for the 7Σ+u state are reported using both extended Slater and Gaussian basis sets. Electron correlation is included using the interacting correlated fragments (ICF), the singles plus doubles configuration-interaction (SDCI), and the coupled-pair functional (CPF) approaches. Our best potential, corrected for basis set superposition errors, has a well depth of about 21 cm−1 and an re of 7.52 bohr. The inclusion of the nitrogen 2s correlation significantly increases the well depth. These results are in reasonably good agreement with the empirical potential of Ferrante and Stwalley, and support the contention that spin-polarized atomic nitrogen should behave like a classical solid such as Ne. It is shown that the modified Buckingham potential used by Ferrante and Stwalley is consistent with our ab initio potentials if smaller values are used for the dispersion coefficients of nitrogen atom.
Predissociation lifetimes in two excited electronic states of HCN and DCN
Authors: Meenakshi A. , Innes K. K.
Published: July 2002

Through computer simulation of predissociated absorption bands of HCN, DCN, D13CN, and DC15N, between 54 563 and 65 644 cm−1, average linewidths and lifetimes of representative upper-state levels are derived. Lifetimes of DC15N vary from 115 to 0.66 ps for Ã 1A″-state levels. Each of the three vibrations (a′) is found to couple efficiently the Ã state to a second 1A″ state, allowing radiationless transitions from the Ã state, and subsequent dissociation. The lifetime of HCN in the zero level of the C̃ 1A′ state is 0.95 ps, a value comparable to those of neighboring Ã-state levels; therefore the dominant predissociation mechanism for the C̃ state is assumed to be coupling of the C̃ and Ã electronic states by rotation, around one or both of the in-plane inertial axes.
Electronic quenching of I2 B 3Π(0+u) by He at low collision energies
Authors: Nicolai Jean-Philippe , Heaven Michael C.
Published: July 2002

Electronic quenching of I2 B 3Π(0+u), v′=11 by He has been investigated in a free jet expansion. The quenching cross section was found to be 0.33±0.08 Å2 at 9.4 K, which is significantly smaller than the room temperature value (0.89±0.02 Å2). The temperature dependence of the cross section has been quantitatively characterized in terms of a collision induced predissociation model. Calculations based on this model show that the predissociation is induced by dispersion forces acting between the collision partners, and they provide information about the symmetry of the repulsive state involved. The calculations are also shown to be compatible with the predissociation and fluorescence decay dynamics of the HeI2 (B) van der Waals complex.
Bulk properties of two-phase disordered media. III. New bounds on the effective conductivity of dispersions of penetrable spheres
Authors: Torquato S.
Published: July 2002

Rigorous upper and lower bounds on the effective electrical conductivity σ * of a two-phase material composed of equi-sized spheres distributed with an arbitrary degree of impenetrability in a matrix are obtained and studied. In general, the bounds depend upon, among other quantities, the point/n-particle distribution functions G(i)n, which are probability density functions associated with finding a point in phase i and a particular configuration of n spheres. The G(i)n are shown to be related to the ρn, the probability density functions associated with finding a particular configuration of n partially penetrable spheres in a matrix. General asymptotic and bounding properties of the G(i)n are given. New results for the G(i)n are presented for totally impenetrable spheres, fully penetrable spheres (i.e., randomly centered spheres), and sphere distributions between these latter two extremes. The so-called first-order cluster bounds on σ * derived here are given exactly through second order in the sphere volume fraction for arbitrary λ (where λ is the impenetrability or hardness parameter) for two different interpenetrable-sphere models. Comparison of these low-density bounds on σ * to an approximate low-density expansion of σ * derived here for interpenetrable-sphere models, reveals that the bounds can provide accurate estimates of the second-order coefficient for a fairly wide range of λ and phase conductivities. The results of this study suggest that general bounds derived by Beran, for dispersions of spheres distributed with arbitrary λ and through all orders in φ2, are more restrictive than the first-order cluster bounds for 0≤λ<1; with the two sets of bounds being identical for the case of totally impenetrable spheres (λ=1). For most values of λ in the range 0≤λ<1, however, the numerical differences between the Beran and cluster bounds should be small; the greatest difference occurring when λ=0. The analysis also indicates that the cluster bounds will be easier to compute than the Beran bounds for dispersions of partially penetrable spheres.
Wigner phase-space description above and below the classical threshold for the H+H2 reaction
Authors: Lee Hai-Woong , George Thomas F.
Published: July 2002

The Wigner phase-space representation offers a semiclassical way of describing molecular collisions. In this paper the collinear H+H2 exchange reaction is studied using the Wigner phase-space approach. The general behavior of the calculated Wigner reaction probabilities as a function of the collision energy is consistent with that of the exact quantum-mechanical probabilities reported in the past. Quantitative disagreements between the Wigner and quantum-mechanical probabilities arise mainly from the neglect of ‘‘dynamical’’ tunneling in the Wigner approach due to the use of real-valued classical trajectories. Nevertheless, the Wigner approach is capable of describing some aspect of tunneling as the high momentum tail of the initial Wigner distribution function is likely to exhibit tunneling. Thus the approach yields a nonzero reaction probability below the classical threshold energy.
An exact solution of the van der Waals interaction between two ground-state hydrogen atoms. II
Authors: Koga Toshikatsu , Ujiie Mitsuru
Published: July 2002

Systematic refinement and extension are presented for the momentum space approach proposed previously to the H(1s)–H(1s) van der Waals interaction. The results are applied to the solution of the first order perturbation equation in its Schrödinger form and almost exact perturbation wave functions are determined up to the order of R−5 where R is the internuclear distance. Using these functions, highly accurate values of the dipole–quadrupole, quadrupole–quadrupole, and dipole–octupole interaction energies are obtained in an extremely simple manner.
Theory of concentration depolarization in the presence of orientational correlations
Authors: Knoester J. , Van Himbergen J. E.
Published: July 2002

A theory is presented that incorporates the effect of orientational correlations between luminescent molecules on the fluorescence depolarization due to incoherent energy transfer. The luminescent molecules are embedded in a homogeneous two- or three-dimensional medium which is in an axially symmetric phase with the xy plane as a symmetry plane, and consists of axially symmetric molecules. For the general orientational singlet distribution and the general form of orientational correlations consistent with these symmetries, we derive analytical expressions for the anisotropy of fluorescence emission. In a no back transfer model, numerical results are evaluated for a simple choice of correlations that tend to align nearby molecules. In a pure donor system, the anisotropy of fluorescence is found to be strongly dependent on these correlations. By ignoring them, the critical transfer distance, as obtained from depolarization experiments, may be drastically underestimated. In a system where donors are surrounded by a huge majority of traps, the critical transfer distance can be determined from the intensity of trap fluorescence. Its anisotropy also strongly depends on correlations and may thus give an indication of the correlation length scale.
Visible and infrared spectroscopy of matrix-isolated PuF6
Authors: Dewey H. J. , Barefield J. E. , Rice W. W.
Published: July 2002

Absorption, emission, and excitation spectra have been obtained for the infrared and visible transitions of matrix-isolated PuF6 in argon. Analysis of the data yields ground-state vibrational frequencies for the six fundamentals, precise electronic state energies, and excited-state vibrational frequencies.
Frequency dependent biexponential 14N relaxation of methylisocyanide in nematic liquid crystals
Authors: Plomp L. , Loman A. C. , Bulthuis J.
Published: July 2002

The dynamical behavior of methylisocyanide, CH3NC, dissolved in two different nematic liquid crystals, has been studied for the first time by direct measurement of the spin-lattice relaxation of its 14N nucleus, at three different field strengths. The results show a frequency dependent relaxation behavior, that can be described by director fluctuations in the nematic solvents. The parameters of the relaxation model: the reorientational correlation time τ⊥, and the amplitude factor A and cut-off frequency ωc of the director fluctuation contributions, were estimated in dependence of the renormalization of the probe order parameter Sz′z. It is shown that the influence of the mean square of fluctuations 〈θ2〉 on the relaxation model can be far from negligible. Choosing literature values for the average elastic constant K and effective viscosity η in one solution (phase V), a reasonable value for the translational diffusion constant Dtr is found. The corresponding cut-off wavelength is L∼50 Å. For the other solution (ZLI 1167), using the same L and an estimated viscosity η, reasonable values for K and Dtr are obtained. Physical arguments are used to account for the differences between the two solutions and a comparison is made with previous studies of analogous systems. It is emphasized that the value of the director fluctuation model could be enhanced by carrying out more experiments to improve the accuracy of ωc, and by refining the theoretical description of the cut-off behavior.
A linear combination of Gaussian-type orbitals (LCGTO) Xα study of ferrocene: The metal-to-ring distance and ionization potentials
Authors: Rösch N. , Jörg H.
Published: July 2002

The metal-to-ring distance of ferrocene, Fe(C5H5)2, has been optimized using the LCGTO-Xα method. The resulting distance is 0.047 Å shorter than the experimental value of 1.65 Å. The corresponding symmetric stretching frequency of 331 cm−1 shows good agreement with experiment (303 cm−1). The two lowest (Fe 3d derived) ionization potentials are calculated almost degenerate but in reverse order compared to experiment (2A′1 below 2E2). The errors of all these results are discussed in the light of known inadequacies of the local density approximation.
Effects of substituent-induced strain on the electronic structure of polydiacetylenes
Authors: Eckhardt H. , Boudreaux D. S. , Chance R. R.
Published: July 2002

The valence effective Hamiltonian technique (VEH), and modified neglect of differential overlap (MNDO) calculations are used to study the influence of strain induced by side chains on the geometry of polydiacetylene backbones and the resulting polymer band structure, band gap, and ionization potential. Simulations of strain effects on the polymer backbone yield variations in optical properties which are similar to those observed experimentally during thermochromic phase changes in urethane-substituted polydiacetylenes. Our results suggest that these changes in optical properties are related to strain at points of substituent attachment and not to fundamental changes in the backbone geometry such as an acetylenic-to-butatrienic transformation.
Free jet infrared absorption spectroscopy of the ν3 band of TeF6
Authors: Matsumoto Yoshiyasu , Takami Michio
Published: July 2002

The ν3 band of TeF6 is studied at a low rotational and vibrational temperature using a tunable diode laser. The vibration–rotation lines are measured in the 752 to 759 cm−1 range with a Doppler-limited resolution. Five spectroscopic constants, ν3, B3, Bζ3, α220, and α224, are determined for the four major isotopic species, 130TeF6, 128TeF6, 126TeF6, and 125TeF6. Only the Q-branch peaks are measured for 124TeF6 and 122TeF6. Harmonic force constants for the F1u block and two anharmonic force constants, frrr and F335, are calculated for SeF6, TeF6, and WF6 from the spectroscopic constants determined by free jet measurements. Isotopic dependence of B0−B3, α220, and α224 are calculated for these molecules and compared with experimental values. Similarity in structure of the ν3 Q-branch of hexafluorides is discussed on the basis of frequency correlation between ω1 and ω2.