bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of the transient electric birefringence response and its application to relaxation systems
Authors: Teraoka Iwao , Hayakawa Reinosuke
Published: July 2002

A new formulation of the transient electric birefringence (TEB) response is presented. By using the method of operator expansion for the nonlinear response function, the TEB rise and decay response functions are generally derived for solutions containing two types of polymer molecules: The first is of the polymer molecules with an induced dipole moment (anisotropy in electric polarizability) alone; and the second is of polymer molecules with a permanent dipole moment alone. For the first type of polymer of any main-chain conformation, the TEB rise and decay responses are related with each other by a simple equation, which is the same as in the linear response. In the second type, a simple relation between the two TEB responses is found to hold for particular cases. We find the examples in rod-like and flexible conformations of polymer molecules. TEB responses of rod-like molecules under various confinement conditions are also discussed.
Fractal quantum propagators
Authors: Dewey T. G.
Published: July 2002

Quantum time-evolution propagators are derived for a particle on a fractal lattice. It is shown that the path of such a particle represents a self-affine fractal. A relationship is obtained between the fractal dimension of the path (as determined by three different operational definitions) and the fractal dimension of the lattice. From these relationships it is seen that a quantum-mechanical particle in a one-dimensional Euclidean space also has a path which is a self-affine fractal. A strong analogy exists between these observations and the difference between Brownian motion and fractional Brownian motion. The uncertainty principle for a particle on a fractal lattice is derived and the phenomena of persistence and antipersistence is related to the uncertainty in momentum. The fractal quantum propagators are then used to develop a quantum theory of fractal rate constants. The theory of Miller and co-workers [J. Chem. Phys. 79, 4889 (1983); 90, 904 (1989)] is used to derive expressions for a bimolecular rate constant. Using the position-flux cross correlation function, scaling laws for the time dependence of the ‘‘rate constant’’ is obtained. These results are discussed in relation to experimental and theoretical results for time-dependent rate constants in percolation clusters.
Models of polymer and solvent dynamics
Authors: Fixman Marshall
Published: July 2002

Some solute–solvent systems show vanishing or negative dynamic intrinsic viscosity [η]ω at any frequency ω. For consistency with this observation the conventional model of dilute polymer dynamics is modified to account for the gradient of solvent velocity in the vicinity of a polymer bead. With simplifications which are strictly valid only for polymers of low molecular weight M or for large ω, [η]ω is changed only by the addition of a term [η]γ. In units of ml/g [η]γ is independent of M and ω and may be positive or negative. The same type of theory is applied to the effect of polymer on the translational and rotational friction constants of small solute molecules A, e.g., labeled solvent. With reasonable estimates of a distance of closest approach between polymer beads and molecules A, the friction constants of A increase with polymer concentration at roughly the same rate as the viscosity of an oligomer solution of the same polymer species. A molecular theory of the coupling constant between a polymer bead and a solvent velocity gradient is not essential, but a few possibilities are considered. The coupling constant may reflect modifications of the solvent by the polymer, as has been suggested by others, or differences in the deformability of oligomers and solvent, etc. The deformability argument seems to necessitate friction matrices with negative eigenvalues, and a reconciliation of such behavior with stability requirements is presented.
Theoretical potential energy and electric dipole moment functions of HCF (X 1A′ and a 3A″)
Authors: Weis Bernhard , Rosmus Pavel , Yamashita Koichi , Morokuma Keiji
Published: July 2002

Highly correlated CEPA electronic wave functions have been used to calculate the three-dimensional potential energy and electric dipole moment functions of the X 1A′ and a 3A″ states of HCF. The analytic expansions of these functions have been employed in variational and perturbational calculations of the vibrational band origins and spectroscopic constants. For the singlet ground state the vibrational band origins agree with available experiments to within 2 to 20 cm−1, the rotational constants to within 0.04 cm−1. Theoretical spectroscopic constants of similar accuracy are presented also for the triplet state. The singlet–triplet separation is calculated to be 13.9 kcal/mol, in agreement with the experimental upper bound of 14.7±0.2 kcal/mol. The dipole moments (μ0) have been calculated to be 1.394±0.05 D (X 1A′) or 1.049±0.05 D (a 3A″), respectively, and vibrational radiative transition probabilities are also given. Anomalous variations of radiative lifetimes in some low-lying vibrational levels have been found in the singlet state of HCF which are due to anharmonic coupling effects.
Vibrational analysis of the 460 nm band system of nickel dichloride produced in a free jet expansion
Authors: Grieman F. J. , Ashworth S. H. , Brown J. M. , Beattie I. R.
Published: July 2002

Using a free-jet expansion which incorporates a heated nozzle, we have recorded the laser excitation spectrum of the 460 nm band system of NiCl2 at a rotational temperature of ∼40 K. 35Cl/37Cl isotope shifts were resolved which permit the assignment of progressions involving the symmetric stretching vibrational mode and identify a triplet splitting with spacings of 96 and 149 cm−1 which is believed to be due to spin–orbit coupling. Sequence bands involving the bending vibrational mode are also tentatively assigned. Only a small change in the symmetric stretching vibrational wave number is found between the electronic states involved in this transition (ν̃′1 =356 cm−1, ν̃″1 =360 cm−1). This result and the triplet splitting observed are discussed with respect to the possible electronic states involved and the assignment of this band system as either a Laporte forbidden g↔g transition involving the d orbitals on the Ni atom or an allowed u↔g charge transfer transition.
Interaction of reactive ions with Pt(100). I. Neutralization and surface trapping
Authors: Akazawa Housei , Murata Yoshitada
Published: July 2002

Scattering of (10–400 eV) O+, O+2 , C+, CO+, and CO+2 ions from a Pt(100) surface has been studied. Below 100 eV, the peak position of the angular distribution for survival ions was shifted parallel to the surface, and the lobe width was very narrow in comparison with noble-gas ions. This suggests that surface trapping due to chemical interaction takes place at very low energies. The importance of collisional neutralization at high energies is demonstrated by the result that the yields of reactive ions decrease steeply with increasing incident energy. The scattering ion yields of O+ and O+2 ions, especially, were very low, being less than 1/100 and 1/10 of those of nitrogen ions, respectively. These results show that a chemical interaction effect is significant for the scattering of oxygen ions.
Potential energy surface for large-amplitude motion and vibrational spacings for FH+2
Authors: Petsalakis I. D. , Theodorakopoulos G. , Wright J. S. , Hamilton I. P.
Published: July 2002

Multireference configuration interaction calculations have been carried out on the ground electronic state of the fluoronium ion FH+2 . Both local (expansion about equilibrium geometry) and global (expansion about linear equidistant geometry) surface fits are obtained. The equilibrium geometry occurs at Re=1.812 35 bohr and ∠HFH=112.30 deg. The proton affinity is 116.5 kcal/mol and the inversion barrier height is 19.25 kcal/mol. The surface is suitable for the study of large-amplitude motion, and we obtain vibrational energies up to 2 eV, which is well above the barrier height. For higher vibrational levels, we note the effect of the potential energy barrier on the vibrational spacing. The minimum in vibrational spacing for the bending progression is found to be in excellent agreement with the calculated barrier height.
Frequency-dependent viscosity of linear, ring, and star Gaussian chains with fluctuating hydrodynamic interactions
Authors: Rey Antonio , Freire Juan J. , Torre José García de la
Published: July 2002

Numerical values for the stress correlation function and the frequency-dependent complex viscosity of linear, ring, and star Gaussian chains with fluctuating hydrodynamic interactions have been obtained from Brownian dynamics simulation. Numerical procedures to calculate these properties (inspired by the previous work of Fixman) are devised. The numerical values are significantly smaller than those obtained with preaveraged hydrodynamic interactions (employed in the standard theories), especially in the low frequency region. Differences are very important (about 100%) for the star chains. These differences tend to decrease for higher frequencies but are still remarkable in the intermediate frequency region (the high frequency predictions for the Gaussian model are not of practical interest).
Relaxation of excited CH stretching modes in toluene
Authors: Guan Yuhua , Thompson Donald L.
Published: July 2002

Classical trajectories have been used to investigate intramolecular energy transfer in toluene for a potential-energy surface based on the ab initio force field by Xie and Boggs [J. Comp. Chem. 7, 158 (1986)]. Various CH bond stretching local modes were initially excited to the v=6 state. The calculated relaxation time of an excited methyl–CH stretching mode is approximately twice that of an excited ring–CH stretching mode, in qualitative agreement with experiment. The time scale of the energy transfer from the methyl group to the ring or from the ring to the methyl group is approximately 3 to 5 times longer than that of the relaxation of the excited CH bonds. The pathways of the intramolecular energy transfer were examined.
Reference interaction site model polaron theory of electron mobility in fluids
Authors: Hsu David , Chandler D.
Published: July 2002

The reference interaction site model (RISM)-polaron model of excess electrons in liquids is extended to treat the competition between attractive and repulsive branches of electron-liquid atom pseudopotentials. For certain choices of parameters, a delicate cancellation occurs leading to unusually large values of electron mobility over a narrow range of liquid densities. This behavior has also been observed in experiment. The RISM-polaron theory is used to interpret these experiments. It is shown that because of the topological disorder of a liquid, attractive interactions alone lead to electron localization and no anomalously large mobilities. Similarly, repulsions by themselves do not produce the anomaly. The cancellation that can occur is a manifestation of the quantum nature of electronic states in an annealed random system. Comparison of the present results with those that might follow from a classical percolation model suggests that the latter does not provide a correct description of electron mobilities in liquids. The cancellation is different but analogous to the Ramsauer–Townsend effect.
Nonadditive hard-sphere reference system for a perturbative liquid state theory of binary systems
Authors: Kahl Gerhard
Published: July 2002

Up to now additive hard spheres have been used as reference systems in perturbation theories of binary liquid systems; this is due to the fact that only for this case are analytic expressions for the direct correlation functions available within the Percus–Yevick approximation. Here for the first time a Weeks–Chandler–Andersen perturbation theory for binary systems, using nonadditive hard spheres as a reference system for the repulsive parts of the potentials, is presented. The nonadditivity of realistic systems−as binary metal alloys−can therefore properly be taken into account. Treating nonadditive systems with additive reference systems by introducing additional (sometimes unphysical) parameters is no longer necessary, and our parameters−i.e., the three hard-sphere diameters−are determined uniquely. Including in a subsequent step the attractive forces by means of the optimized random phase approximation, it is found that agreement with other liquid state theories as well as with experimental scattering data is very good, even for extremely nonadditive systems.
Pumping reactions in a photoinitiated XeF2–D2 chemical laser
Authors: Searles S. K. , Winings M. J.
Published: July 2002

The laser emission spectrum of a flash initiated XeF2–D2 chemical laser indicated that translationally hot F atoms (31 kcal/mol) react with D2 to yield DF primarily in the v=2 state. Reaction of D+XeF2 was found to be too slow to contribute to the observed laser emission.
Spectral and kinetic characteristics of low-temperature luminescence of adeninium sulphate single crystals
Authors: Večeř J. , Jelínek O.
Published: July 2002

Measurements of low-temperature luminescence of adeninium sulphate single crystal are reported. At the first time monomer and excimer fluorescence were observed in both spectral and time domain. The spectrum of monomer fluorescence shows well-resolved vibronic structure which is different from that found for adenine at low temperature in polyalcoholic glasses. The vibration which builds the main equidistant fluorescence maxima corresponds to about 1450 cm−1. Complex fluorescence decay composed from both monomer and excimer part of emission was interpreted on assumption that an extensive energy transfer takes place. The excimer fluorescence decays monoexponentially at 6 K with a lifetime of about 280 ps.
Excimer emission of molecular systems with energy transfer
Authors: Večeř J.
Published: July 2002

The exact solution of kinetic equations of a simple chain of molecular excimer forming system is derived. The influence of energy transfer on both monomer and excimer emission kinetic is discussed.
High-resolution rotation–vibration spectroscopy of difluorophosphorane: A combined theoretical and experimental study
Authors: Beckers H. , Breidung J. , Bürger H. , Kuna R. , Rahner A. , Schneider W. , Thiel W.
Published: July 2002

The harmonic and anharmonic force fields of PH3F2 have been calculated at the ab initio self-consistent-field level using polarized split-valence and triple-zeta basis sets. PH3F2 has been prepared in pure form and identified unambiguously in the gas phase by Doppler-limited Fourier transform infrared spectroscopy. Guided by the theoretical predictions for the rotation–vibration spectra and the spectroscopic constants, the observed bands have been assigned and several of them rotationally analyzed, in particular ν4/2ν±27, ν2+ν4/ν2+2ν±27, and ν5/ν3+ν8. PH3F2 is found to have a D3h structure, ro(PH)=1.394(4) Å and ro(PF)=1.6468(2) Å. The theoretical results are in good agreement with experiment, both for the structure and for the available spectroscopic constants. The present study demonstrates the advantages of a combined theoretical and experimental approach to the spectroscopy of reactive molecules.
Photoemission studies of Ru3(CO)12 adsorption on Cu3Au
Authors: Sham T. K. , Liu Z.-F. , Tan K. H.
Published: July 2002

Photoemission spectra of Ru3(CO)12 adsorbed on polycrystalline ordered and disordered Cu3Au surfaces and its decomposition products induced by zero order light and electron bombardment are reported. The results are compared with multiple-scattering–X-alpha (MS–Xα) calculations and recent studies of Ru3(CO)12 on Cu.
The study of the internal and collision energy dependence of the two microscopic reaction mechanisms in the ion–molecule reactions MH++MH→MH+2+M (MH=CH3F, CH3Cl, CH4)
Authors: Suzuki Shinzo
Published: July 2002

The ion–molecule reactions of the type MH++MH→MH+2 +M (MH=CH3F, CH3Cl, CH4) have been investigated using the threshold electron secondary ion coincidence (TESICO) technique. Two peaks observed in the time-of-flight coincidence spectra of mass-selected product ions MH+2 have been interpreted as arising from the two microscopic reaction mechanisms of the MH+2 formation, i.e., the hydrogen atom abstraction by the ion (HA) and the proton transfer from the ion (PT). Relative reaction cross sections (σHA and σPT) have been determined for each of the two mechanisms as a function of both the internal energy of the reactant ion and the center-of-mass collision energy. The results indicate that these reaction systems are classified into two types according to the relative importance of the two mechanisms and its energy dependence: Type (I) in which the ratio σPT/σHA is almost unity and independent of the total energy (CH3Cl system) and Type (II) in which PT dominates over HA at all energies with the ratio σPT/σHA increasing with the total energy (CH3F and CH4 systems). A reaction model which regards the HA mechanism as the electron transfer process followed by proton transfer has been proposed to interpret the experimental results. In this model, the difference in the behavior of the ratio σPT/σHA between the two types is ascribed to the difference in the ease with which the electron hopping takes place in the entrance channel of the reaction. In addition, the upper limit of the barrier height for this electron hopping has been calculated using an ab initio method for the CH3Cl++CH3Cl and CH3F++CH3F systems, with the results which support the above model.
A one-electron perturbation theory of chemisorption
Authors: Basilevsky Mikhail V. , Hoffmann Roald
Published: July 2002

We present a general one-electron perturbation theoretic formalism for the interaction of discrete molecules or a translationally periodic array of molecules with a surface. The approach uses a Green’s function formalism, a perturbation expansion and a technique of calculating the imaginary parts of traces over matrix products. The methodology, applicable to both Hückel and extended Hückel calculations, introduces projected Green’s functions which serve as natural indices for the reactivity, inherent and mutual, of different surface sites.
Comment on: Highly vibrationally excited HCN
Authors: Carter Stuart , Mills Ian M. , Handy Nicholas C.
Published: July 2002

The highly vibrationally excited states of the HCN molecule reported recently by Yang, Rogaski, and Wodtke [J. Chem. Phys. 92, 2111 (1990)] are assigned as states involving excitation of the CN stretching mode ν1 and the bending mode ν2 . The assignments are made on the basis of variational calculations of the rovibrational energy levels of HCN which we have recently reported. Our calculations give a satisfactory fit to the observed values of both the vibrational energy levels and the rotational constants.
Tunneling rates in bound systems using smooth exterior complex scaling within the framework of the finite basis set approximation
Authors: Rom Naomi , Engdahl Erik , Moiseyev Nimrod
Published: July 2002

A basis-set time-independent method to calculate tunneling rates in bound systems through a potential barrier is presented. The tunneling decay rates are associated with the imaginary parts of the complex eigenvalues of the Schrödinger equation where the reaction coordinate r′ is complex scaled such that, dr = dr′[1/cos θ(r′)]exp (iθ(r′)), where tan θ(r′) = tan θ∞g(r′). The function g(r′) fulfills 0 ≤ g(r′) ≤ 1 and shows a smooth transition from 0 to 1 near r′ = r0 which is the location of the top of the barrier. The value of θ∞ should be larger than a critical value for which a sharp transition from a real eigenvalue spectrum to a complex one is obtained. Illustrative numerical applications to two isomerization reaction models are given.
Influence of radiative transport on energy transfer
Authors: Martinho J. M. G. , d’Oliveira J. M. R.
Published: July 2002

A model describing the radiative processes occurring in concentrated solutions of a donor able to transfer its electronic energy to an acceptor is presented. It was found that both radiative transport over donors and transfer to the acceptor modify the decay curves of the donor, the effect being more pronounced at low acceptor concentrations owing to a small absorption of the donor emission by the acceptor and an inefficient donor–acceptor nonradiative energy transfer process. Fitting or decay curves influenced by radiative transport can lead to incorrect evaluation of nonradiative energy transfer parameters if the radiative processes are not accounted for. The true nonradiative parameters can be evaluated using the theoretical decay law predicted by the model.
Computer simulation of steady-state diffusion-controlled reaction rates in dispersions of static sinks: Effect of sink sizes
Authors: Zheng Lihua , Chiew Yee C.
Published: July 2002

The steady state diffusion-controlled reaction or trapping rate k2 in binary mixtures of impenetrable, nonoverlapping static sinks or traps are determined through random-walk simulations. The simulations are carried out using the first passage time technique. Exact values of the reaction rate k2 are obtained as a function of the total sink volume fraction φ, sink size ratio β, and sink number fraction xA. The reaction rate k2 is found to increase with increasing surface area of the sinks. Specifically, for dispersions at low volume fraction φ and small values of β, we observe from our data that the ratio of the reaction rate in a binary sink dispersion to that of the monodisperse system is directly proportional to the square of the ratio of the specific surface areas of the two systems. In addition, it is found that the quantity l=〈R3〉/〈R2〉 serves as an appropriate scaling parameter for the reaction rate k2.
Experimental results for nitrogen condensation into silica pores. Dielectric measurements at microwave frequencies
Authors: Biquard Francis , Guermeur Robert , Jacolin Christian
Published: July 2002

Experimental measurements on nitrogen condensation in silica pores of 70, 117, and 159 Å diameters give measured values of the surface tension in reasonable agreement with computed results based on a very simple thermodynamic model of a fluid interface. Adsorption and desorption isotherms are drawn by recording the dielectric susceptibility of the fluid at microwave frequencies. Hysteresis loop in pores of 159 Å diameter accurately fit a theory published earlier by Saam and Cole.
Gas-phase x-ray photoelectron spectroscopy of model molecules relating to the thermochromism in poly(3-alkylthiophene)
Authors: Keane M. P. , Svensson S. , Naves de Brito A. , Correia N. , Lunell S. , Sjögren B. , Inganäs O. , Salaneck W. R.
Published: July 2002

Previously, a geometrical model of the thermochromism in poly(3-alkylthiophene) was proposed, based upon an analysis of optical absorption spectra as well as ultraviolet and x-ray photoelectron spectra (UPS and XPS). In the present contribution, the shake-up features in the XPS C(1s) spectra of thiophene, hexyl-substituted thiophene, and bithiophene molecules in the gas phase, are compared with the shake-up features in previously published XPS C1s spectra of poly(3-hexylthiophene) and poly(3-butylthiophene). An analysis of these gas phase molecular data confirms the geometric model of electronic localization in the polymer materials proposed previously.
Spectral hole burning and holography. III. Electric field induced interference of holograms
Authors: Renn Alois , Meixner Alfred J. , Wild Urs P.
Published: July 2002

The electric field induced superposition of holograms recorded by spectral hole burning is investigated. Holograms have been burned at adjacent positions in a plane defined by wavelength and electric field. Application of an appropriate electric field to the sample causes the components of adjacent holograms to overlap as the spectral holes split due to Stark shifts of molecular transition frequencies. The diffraction efficiency of such superimposed holograms depends on their relative phase and has been studied theoretically and experimentally. It is shown that for zero phase difference, constructive interference leads to a strong diffraction efficiency whereas for a phase difference of π, the gratings cancel leading to zero diffraction efficiency. Experiments have been performed with the dye cresyl violet in a polyvinylbutyral film at a temperature of 1.7 K and the data are compared with computer simulations.
Estimating carbon cluster binding energies from measured Cn distributions, n≤10
Authors: Pargellis A. N.
Published: July 2002

Experimental data are presented for the cluster distribution of sputtered negative carbon clusters, C−n, with n≤10. Additionally, clusters have been observed with masses indicating they are CsC−2n, with n≤4. The C−n data are compared with the data obtained by other groups, for neutral and charged clusters, using a variety of sources such as evaporation, sputtering, and laser ablation. The data are used to estimate the cluster binding energies En, using the universal relation, En=(n−1)ΔHn+RTe [ln(Jn/J1)+0.5 ln(n)−α−(ΔSn−ΔS1)/R], derived from basic kinetic and thermodynamic relations. The estimated values agree astonishingly well with values from the literature, varying from published values by at most a few percent. In this equation, Jn is the observed current of n-atom clusters, ΔHn is the heat of vaporization, ΔH1=7.41 eV, and Te ≊0.25 eV (2900 K) is the effective source temperature. The relative change in cluster entropy during sublimation from the solid to vapor phase is approximated to first order by the relation (ΔSn−ΔS1)/R =3.1+0.9(n−2), and is fit to published data for n between 2 and 5 and temperatures between 2000 and 4000 K. The parameter α is empirical, obtained by fitting the data to known binding energies for Cn≤5 clusters. For evaporation sources, α must be zero, but α∼7 when sputtering with Cs+ ions, indicating the sputtered clusters appear to be in thermodynamic equilibrium, but not the atoms. Several possible mechanisms for the formation of clusters during sputtering are examined. One plausible mechanism is that atoms diffuse on the graphite surface to form clusters which are then desorbed by energetic, recoil atoms created in subsequent sputtering events.
Theory of dipolar relaxation in lamellar system: Application to lyotropic liquid crystals
Authors: Korb J.-P. , Bredel Th. , Chachaty C. , Van Der Maarel J. R. C.
Published: July 2002

We propose a theory of dipolar spin relaxation for lamellar geometry where one of the spin species diffuses on an infinite plane while the other diffuses within an infinite layer of finite thickness. Analytical expressions of the frequency dependence of the spectral densities and spin relaxation rates are given. The theoretical frequency variation of the longitudinal relaxation rate appears to be drastically dependent of the anisotropic diffusion ratio and on the thickness of the layer. An application of this theory to lamellar lyotropic liquid crystal gives the spatial distribution of an organic counterion solute in the bilayer from the frequency variation of the 31P longitudinal relaxation rates of the surfactant. This gives some information about the surfactant-organic counterion interaction and the hydration degree of the phosphate group.
Magnetic circular dichroism and ground state splittings
Authors: Wang Qingsheng , Wybourne B. G.
Published: July 2002

Recently reported measurements of the ground state splitting of atomic rhenium in a krypton matrix by the observation of MCD saturation phenomena are considered. It is shown that the suggestion that this splitting comes from the admixing, via the spin–orbit interaction, of some 4P5/2 character into the 6S5/2 ground state cannot lead to a ground state splitting and higher order mechanisms must be invoked. The special properties of half-filled shells are considered and the splitting mechanism outlined. Detailed calculations show the significance of configuration interaction.
Complex kinetics of systems with multiple stationary states at equilibrium
Authors: Chu X. -L. , Ross John
Published: July 2002

We consider chemical reactions which at equilibrium have multiple stationary states due to nonidealities of chemical species. When such reactions are included in a simple reaction mechanism open to mass flow, without autocatalysis or feedback steps, there may occur complex dynamics such as relaxation oscillations, as reported earlier for regular solutions. Here we consider both regular solution and ionic species (Debye–Hückel nonideality), show that chemical oscillations may occur arbitrarily close to chemical equilibrium, and trace the topological structure of the complex dynamics of relaxation oscillations, sustained oscillations, stable focus, and stable nodes to the multiplicity of equilibrium states, for stated constraints. Relaxation oscillations occur around an unstable stationary state which, on approach to equilibrium, connects to an unstable equilibrium state. Thus, there is no bifurcation to oscillations on removing the systems from equilibrium. Neither is there a region where linear irreversible thermodynamics is valid close to equilibrium. Earlier work on ionic systems is found to be in error.
NaSO→NaOS potential energy hypersurface
Authors: Jin Suqian , Schaefer F.
Published: July 2002

For the ground and first excited electronic states of NaOS three minima and three transition states for interconversion have been determined by means of self-consistent field (SCF) and single and double excitation configuration interation (CISD) analytic gradient methods. The relationships between these structures have been clarified by vibrational analyses of the transition states. One of the NaOS equilibrium geometries is linear and the other two are bent. The chemical bonds between the two component parts of NaOS, Na and SO, for both 2A′ and 2A″ bent structures have ionic character, although differing in degree. In all studies both double-zeta-plus polarization and triple-zeta-plus double polarization basis sets were used.
Conformational stability, barriers to internal rotation, vibrational assignment, and a
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o calculations of 2-chloropropenoyl fluoride
Authors: Durig J. R. , Wang A. Y. , Little T. S. , Brletic P. A.
Published: July 2002

The far-infrared spectrum of gaseous 2-chloropropenoyl fluoride, CH2 CClCFO, has been recorded at a resolution of 0.10 cm−1 in the region of 350–35 cm−1. The fundamental asymmetric torsional frequencies of the more stable s-trans (two double bonds oriented trans to one another) and the high energy s-cis conformations have been observed at 67.80 and 49.96 cm−1, respectively, each with several excited states falling to lower frequencies. From these data the asymmetric torsional potential function governing the internal rotation about the C–C bond has been determined. The potential coefficients are V1 =−125±1, V2 =1586±6, V3 =375±2, V4 =−36±2, and V5 =−65±1 cm−1. The s-trans to s-cis and s-cis to s-trans barriers have been determined to be 1755 and 1570 cm−1, respectively, with an energy difference between the conformations of 185±9 cm−1 (529±26 cal/mol). From studies of the Raman spectrum at variable temperatures, the conformational enthalpy difference has been determined to be 176±40 cm−1 (503±114 cal/mol) and 625±51 cm−1 (1787±146 cal/mol) for the gas and liquid, respectively. A complete assignment of the vibrational fundamentals observed from the infrared spectra (3500–50 cm−1) of the gas and solid and the Raman spectra (3200–10 cm−1) of all three physical states is proposed. All of these data are compared to the corresponding quantities obtained from ab initio Hartree–Fock gradient calculations employing both the 3-21G* and 6-31G* basis sets. Additionally, complete equilibrium geometries have been determined for both rotamers. The results are discussed and compared with the corresponding quantities obtained for some similar molecules.
Effects of collision-induced perturbation of atomic motions on the vibrational relaxation of polyatomic molecules
Authors: Torii Hajime , Tasumi Mitsuo
Published: July 2002

We have performed model calculations on the vibrational relaxation (including population relaxation and dephasing) induced by intermolecular interactions in the liquid phase. Taking into account the points that (1) intermolecular interactions are primarily of atom–atom origin, and (2) the relaxation resulting from quasielastic collisions are considered to be dominant, we have calculated how the eigenvector (on the Cartesian coordinate basis) of an initially excited normal mode is transformed when the three components corresponding to one atom are displaced without change in the vibrational energy. On this basis, the relative efficiency of intramolecular energy flow from the initial state has been estimated. Calculations on the CH stretches of dichloromethane and the OH stretch of methanol are compared with existing experimental results.
Infrared spectrum of a chemisorbed molecule: Computational aspects, analysis of experimental data for ethylidyne on Pt(111)
Authors: Johnson W. G. , Buch V. , Trenary M.
Published: July 2002

A microscopic model is presented for anharmonic vibrations of ethylidyne, 3/4 CCH3, chemisorbed on the Pt(111) surface. The model includes 24 vibrational modes of the adsorbate and of the solid. A quantum-mechanical calculation based on second-order perturbation theory is used to interpret experimental data on vibrations of 3/4 CCH3/Pt(111) and 3/4 CCD3/Pt(111). The measured temperature dependence of the CC infrared fundamental and of the umbrella mode fundamental can be accounted for by anharmonic coupling between the CC stretch and the three PtPt stretch coordinates at the base of the adsorbate. Line shapes calculated using classical molecular dynamics disagree significantly with quantum-mechanical results, the apparent reason being overestimation of vibrational energy transfer in the classical calculation. A semiclassical approximation is suggested, in which all the high frequency adsorbate modes except the infrared absorbing mode are frozen; the remaining modes are treated by classical mechanics. The semiclassical calculation agrees much better with the quantum-mechanical results, and can be extended to higher dimension in a straightforward fashion.
Rotational Raman spectrum of ketene
Authors: Escribano R. , Ortigoso J. , Cutín E. , García-Moreno I.
Published: July 2002

The Raman spectrum of ketene has been recorded for the first time since 1936. The rotational part of this spectrum shows Δkp=2, ΔJ=0 peaks with an intensity nearly four orders of magnitude smaller than that of the usual R/S structure. Computer simulation is used to reproduce the whole rotational spectrum. The observation of these peaks allows a fairly accurate determination of the R20 intensity ratio.
Quantum rotations of the ammonium ions in ammonium tetraphenyl–borate. III. Inelastic neutron scattering results
Authors: Roberts Malcolm P. , Lucazeau Guy , Kearley Gordon J. , Dianoux A. J.
Published: July 2002

Incoherent inelastic neutron scattering experiments have been performed on polycrystalline samples of NH4B(C6H5)4 and NH4B(C6D5)4 in the 1.5–120 K temperature range. A high-resolution inelastic neutron scattering spectrum at the lowest temperatures reveals a rotational tunneling spectrum containing two peaks at 26.5 and 53.0 μeV and is characteristic of ammonium ions in a cubic environment. From the intensities of these peaks it seems that about half of the ammonium ions are involved in this tunneling. Two further peaks are found at higher energy, 4.3 and 8.2 meV, either of which may be correlated as the libration associated with the observed tunnel splitting depending on the form of the potential. An alternative assignment of the peaks at 4.3 and 8.2 meV as transitions of a free rotor from the ground state to the J=2 and J=3 levels is also discussed.
Calculated vs measured scattering and kinetic data for the Li+HCl reaction
Authors: Laganà A. , Palmieri P. , Alvariño J. M. , Garcia E.
Published: July 2002

A study of the Li+HCl reaction has been carried out using classical trajectories. A comparison with detailed scattering data has given sufficient indications on the accuracy of the overall shape of a previous bond order potential energy surface derived from ab initio values. Calculations performed on a new bond order surface having a lower transition state has led to a more realistic estimate of the threshold energy and the ratio between high and low collision energy reactive cross sections. The comparison has been extended to rate constants. Calculated values agree with measured ones within the given error boundaries
Electric microfield distribution at an Ar atom dissolved in molten KCl
Authors: Fukase Shoji , Takagi Ryuzo
Published: July 2002

The electric microfield distribution at an Ar atom dissolved in molten KCl at 1173 K is calculated based on the Morita–Iglesias formalism and the mean-spherical approximation for charged hard particles fluid. The results are compared with those of a molecular dynamics simulation which is carried out for a realistic potential system. The theory provides a good estimate of the second moment of the microfield distribution. A very good result for the distribution itself is obtained by introducing an adjustable parameter.
Model for micelle formation in copolymer/homopolymer blends
Authors: Kao Chengheng R. , de la Cruz Monica Olvera
Published: July 2002

Polydisperse micelle formation in dilute solutions of A–B diblock copolymer in A homopolymer is studied. The standard free energy of micellization, the critical micelle concentration (c.m.c.), the average micelle sizes, and the micelle size distribution are determined. The effects of copolymer concentration, B block length nB, and temperature (in terms of the Flory’s interaction parameter χ) on micellar behavior are examined. The width of the micelle size distribution is shown to be inversely proportional to the square root of the curvature of the standard free energy of micellization. The polydispersity of the micelles decreases with increasing copolymer concentration, being high for concentration below and around the c.m.c. The polydispersity also depends on nBχ, with high polydispersity corresponding to small nBχ values. The average micelle size exhibits sudden growth at the c.m.c. and increases slightly beyond the c.m.c.
Order/disorder phase transitions of liquid-crystalline polymers with rigid groups in the side chains. A lattice theory
Authors: Auriemma Finizia , Corradini Paolo , Vacatello Michele
Published: July 2002

We present, in this paper, a lattice model of liquid-crystalline polymers with rigid groups attached to a semiflexible main chain through semiflexible spacers. The polymers are modeled as sequences of isodiametric units allocated at the nodes of the face-centered-cubic lattice. The model allows study of the phase behavior in the liquid state of oligomers and polymers with various constitutions. Uniaxially ordered phases (nematic mesophases) with the rigid groups and/or the main chains partially aligned to the preferred direction are predicted to be stable in suitable conditions. The predicted general trends are in agreement with experiments.
Viscosity study of the collapse state of a polystyrene
Authors: Sun S. F. , Chou Chen-Cheng , Nash R. A.
Published: July 2002

Intrinsic viscosity measurements were carried out with a polystyrene (M̄w3.2×106, M̄w/M̄n=1.03) in cyclohexane at temperatures near and including θ down to the point before precipitation occurs. The transition of coil conformation from θ state to the collapse state seems to be relatively smooth. The onset of the collapse is estimated to be at 32.9 °C.
Interaction induced contributions to the far infrared spectrum of a polar fluid: Zeroth and second spectral moments
Authors: Palting Pancracio , McHale Jeanne L.
Published: July 2002

The zeroth and second spectral moments for the far infrared spectral intensity of a polar liquid are analyzed from first principles, taking into account the first-order dipole–induced dipole contribution. The results, based on evaluating the equilibrium averages of appropriate correlation functions, are simplified by considering that the liquid pair distribution function can be approximated by a truncated expansion in terms of Wigner rotation functions. Averages involving three- and four-molecule distribution functions are not considered in the present calculation. The calculated zeroth moment for acetonitrile, M(0)=17.5 D2, compares favorably with the experimental value of 20.7 D2. The difference probably reflects the neglect of three- and four-molecule terms as well as higher order induction effects.
The effect of pressure on the Raman spectra of solids. VII. The internal Raman bands in solid and coordinated pyridine
Authors: Heyns A. M. , Venter M. W.
Published: July 2002

The pressure dependences of the internal Raman-active modes of solid pyridine and pyridine-d5 in both the crystalline and glassy modifications as well as of the complexes Zn(py)2Cl2, Ni(py)2Cl2, and Ni(py)4Cl2 are reported. When pyridine is frozen by the application of pressure, some ring modes as well as those involving the hydrogen atoms reflect this transformation. Upon the coordination of pyridine to metal ions, the ring vibrations show appreciable blue shifts. The pressure dependences of ν1, the C–C stretching mode, and ν12, the in-plane ring bending mode of the pyridine rings, are discussed in detail. The unusually high d5–h5 isotopic ratio of ν12 and its contrasting pressure dependences in the liquid and condensed phases of pyridine-d5 are explained. The association of pyridine molecules in the condensed phase does not occur through hydrogen bonds and the C–H stretching modes, in particular, show that repulsive intermolecular forces become very significant at higher pressures. The ratio of the intensities Iν12/Iν1 varies linearly with the strength of the M–N bonds in a series of pyridine complexes and a correlation also exists between Iν12/Iν1 and ∂ν12/∂p. The vibrations ν1 and ν2 are coupled through Fermi resonance in pyridine and its complexes and the pressure dependence of the Fermi resonance constant W is calculated for Zn(py)2Cl2. The C–H stretching modes reflect the presence of more than one distinct pyridine group in the lattice and are of much lower intensity than in complexes where only one distinct pyridine group is found.
Potential energy surfaces for Ir+H2 and Ir++H2 reactions
Authors: Balasubramanian K. , Dai Dingguo
Published: July 2002

Potential energy surfaces of 10 electronic states of IrH2 and 12 electronic states of IrH+2 are computed. A complete active space multi-configuration self-consistent field (CAS-MCSCF) followed by multireference configuration interaction (MRCI) calculations which included up to 270 000 configurations are employed. In addition spin–orbit effects are studied using the relativistic configuration interaction (RCI) method. It is found that the Ir(2F) state inserts spontaneously into H2 to form a stable IrH2 molecule in a 2A1 ground state which is 28 kcal/mol more stable than Ir(4F)+H2 in the absence of spin–orbit effects. The spin–orbit coupling of the quartet and doublet states provides nonzero transition probability for the insertion of Ir (4F) state into H2. The 3P state of Ir+ was found to insert spontaneously into H2 to form the 3A2 ground state of IrH+2 which is 30 kcal/mol more stable than Ir+(5D)+H2.

An excited singlet state of Ir+ also was found to insert into H2 spontaneously. The spin–orbit couplings of quintet and triplet states of IrH+2 at the crossing of these curves provide nonzero transition probability for the insertion of Ir+ (5D) into H2. The bent E ground state of IrH2 in the C22v group was found to be a 63% 2A1, 16% 2B1 and 17% 2A2 mixture. This strong mixing induces a large H–Ir–H bond angle change of 9.5° in the E(III) state of IrH2. The 3A2 (A1) ground state of IrH+2 was found to be a 63% 3A2, 15% 3B2, 12% 3B1 and 7% 1A1 mixture. This strong spin–orbit mixing induces a θe change of almost 9° in the ground state of IrH+2. The adiabatic ionization potential including spin–orbit effects for IrH2 and Ir are calculated as 8.2 and 8.6 eV, respectively. The ground state of IrH2 was found to be ionic (μe=2.2 D) with Ir+H− polarity exhibiting Ir(6s0.756p0.125d8.06) hybridization. The IrH+2 ion in its 3A2 state exhibits Ir+(6s0.626p0.125d7.51) hybridization character.
On the nature of the orientational transition in crystalline A–TCNB
Authors: Kuchta B. , Luty T. , Etters R. D.
Published: July 2002

The orientational properties of crystalline A–TCNB are calculated using a Monte Carlo procedure, based upon a previously reported site–site expression for the interactions between molecules. The nearly static TCNB complexes are orientationally quiescent. The A molecules respond to an orientational double well potential provided by the TCNB, and by their mutual interactions. As a consequence, the dominant part of the orientational Hamiltonian depends on only a single degree of freedom, from which the results are determined. Properties calculated include the orientational structures, internal energy, specific heat, and the phase transition temperature. Various order parameters are calculated to understand the microscopic nature of the transition, which seems to show features of both an order–disorder and displacive character, much like experimental interpretations.
Correlations between hydrodynamic and intermolecular interactions
Authors: Washington G.
Published: July 2002

Dynamic light scattering can be used to measure the intensity autocorrelation function. The limiting initial slope (the first cumulant) is susceptible to variation due to hydrodynamic and intermolecular interactions. The first cumulant of the intermediate scattering function is calculated for several interaction potentials with hydrodynamic interaction in the Oseen approximation. Solutions of the Percus–Yevick equation provide the required radial distribution functions for the equations derived by Ackerson and Felderhof. Spherically symmetric particles are considered at volume fractions of 0.0262 to 0.10. Corrections to the first cumulant are found to be as large as 40%. The model potentials were chosen to probe the dependence of the hydrodynamic interaction effect on the details of the interaction potential. This study represents an effort to explore such effects on the measured first cumulant. Qualitative agreement is found for experimental results. Some qualitative features of the solute–solute interactions can be determined from comparisons of measured and calculated hydrodynamic effects of several model potentials.