bluuebunny/crossref_metadata_2025 huggingface dataset:
Point groups in the Vibron model
Authors: Leviatan Amiram
Published: July 2002

The question of incorporating the notion of point groups in the algebraic Vibron model for molecular rotation–vibration spectra is addressed. Boson transformations which act on intrinsic states are identified as the algebraic analog of the discrete point group transformations. A prescription for assigning point group labels to states of the Vibron model is obtained. In case of nonlinear triatomic molecules the Jacobi coordinates are found to be a convenient possible choice for the geometric counterparts of the algebraic shape parameters. The work focuses on rigid diatomic and triatomic molecules (linear and bent).
Investigation of diffusion processes in poly(ethylene oxide)/poly(methyl methacrylate) blends by laser light scattering spectroscopy
Authors: Wang C. H. , Zhang X. Q. , Fytas G. , Kanetakis J.
Published: July 2002

Mutual diffusion in poly(ethylene oxide)/polymethyl methacrylate blends is investigated by using the photon correlation spectroscopic technique. The mutual diffusion coefficient and the static structural factor are measured as a function of concentration for various temperatures. The Onsager coefficient is obtained by simultaneous measurements of the diffusion coefficient and static structural factor. The result is employed to test theoretical predictions on the concentration dependence of the mutual diffusion coefficient of the polymer blend. The experiment results are found not in agreement with theoretical predictions.
Pair dynamics in hard-sphere fluids
Authors: Leegwater Jan A.
Published: July 2002

The short- as well as the intermediate- and long-time behavior of velocity-dependent pair-time correlation functions are calculated, with the aid of a kinetic theory that is an extension of the Lorentz–Enskog equation. The numerical solution to this equation reproduces molecular-dynamics simulation results reasonably well for all times at an intermediate density, and up to a few mean free times at high density. At high densities and long times the solution of a Smoluchowski equation gives an accurate description.
Stereoselectivity of energy transfer in chiral lanthanide systems
Authors: Sztucki J. , Strek W.
Published: July 2002

A theory of resonant energy transfer in lanthanide complexes with chiral ligands is developed within the independent systems model. The second- and third-order expressions for the amplitude of energy transfer are derived and their sensitivity to the ligand chirality is discussed. It is shown that within the presented model only the dynamic coupling mechanism gives different energy transfer rates for racemic and resolved systems. The general expression for the stereoselectivity of energy transfer is presented and its approximate value is estimated.
Molecular weight dependence in Flory’s theory of crystallization of copolymers
Authors: Bryant J. L. , Lacher R. C.
Published: July 2002

We investigate molecular weight effects on the melting temperature of a branched semicrystalline polymer. Flory’s model for infinite chains in equilibrium is extended to the case of finite chains. This model predicts an increase in the melting temperature of crystals of fixed size with increasing molecular weight. Recent experimental studies of Alamo, Chan, and Mandelkern, however, provide evidence to the contrary. In order to explain, at least in part, their observations, we compute the expected number of chain segments that are available for taut folds. The number of such segments increases with molecular weight, and, hence, contribute an increasingly powerful suppressing force on melting temperature.
X-ray reflectivity on perfluoropolyether polymer molecules on amorphous carbon
Authors: Toney Michael F. , Thompson Carol
Published: July 2002

The mass density profile from thin (∼25 Å) layers of polymer molecules adsorbed on amorphous carbon thin films is determined from measurements of the specular reflectivity of x rays. Important information on the conformation of the polymer molecules is obtained from the density profile (average density as a function of position above the surface). The polymer is a perfluoropolyether (PFPE) with piperonyl end groups and has a molecular weight of 2000–3000 Daltons. Three samples are measured: a nonbonded sample with an approximately 25 Å layer applied by dipping, a bonded sample with the layer applied by dipping but followed by a process to attach the molecule to the carbon, and a cleaned sample which is the nonbonded sample after the polymer had been removed. The density profile of the nonbonded polymer shows that the density within 10 Å of the carbon surface is ∼1.6 gm/cc, which is smaller than the density in the region between 10 and 25 Å (∼1.8 gm/cc). This indicates that the less dense piperonyl end groups are preferentially adsorbed near the carbon surface, which provides a possible explanation of the observation that the addition of the piperonyl end group to PFPE improves adhesion of the polymer to surfaces. The bulk-like density in the region between 10 and 25 Å and the compactness of the layer suggest that the preponderance of molecules have both end groups preferentially adsorbed; consequently, the PFPE chains remain close to the surface. The data from the bonded and nonbonded polymer layers are essentially the same, which indicates the molecular conformation is not strongly affected by the bonding treatment.
On the mechanistic dependence of the affinity decay
Authors: Hjelmfelt Allen , Brauman John I. , Ross John
Published: July 2002

In a series of articles M. Garfinkle has presented an empirical thermodynamic approach to chemical reactions from an initial nonequilibrium state to equilibrium in a closed isothermal system. He claims that (1) (essential points made by M. Garfinkle are numbered for reference later in the text) ‘‘a stoichiometric chemical reaction in a closed system traverses a unique natural path from reaction initiation to equilibrium. Along such a natural reaction path the time rate of change of the thermodynamic functions can be analytically described independently of phenomenological or mechanistic consideration’’ [M. Garfinkle, J. Phys. Chem. 93, 2158 (1989)]. We show these and other claims not to be correct; this approach has validity limited to: reaction mechanisms with essentially only one velocity (mechanisms with one rate-determining step or mechanisms in a quasi-stationary state); reactions occurring at times close to the initial time; and no products present at the initial time. Garfinkle’s method of plotting kinetic data, as a function of t−1, suppress information at later times, which shows the inadequacy of his proposed form of the affinity decay, and leads to the erroneous conclusion that a parameter in this form, tk equal to the most probable time to reach equilibrium, is finite, when in fact it is infinite. The affinity decay rate in general depends on the reaction mechanism, or on the order of the empirical rate equation if determined experimentally.
A study of the reaction O+(4S)+N2 using the tandem photoionization mass spectrometric method
Authors: Flesch G. D. , Ng C. Y.
Published: July 2002

The reaction between oxygen ions and nitrogen molecules is studied by using tandem photoionization mass spectroscopy. This reaction is pertinent to the study of reaction occuring in the inosphere. (AIP)
Continuous wave–continuous wave molecular double resonance spectroscopy: Lifetimes and term energies of individual rovibronic levels of the (4pπ)K 2Π(v=2) Rydberg state of nitric oxide
Authors: Miller R. J. , Bushaw B. A.
Published: July 2002

The (4pπ)K 2Π(v=2)←(3sσ)A 2Σ+(v=1)←X2Π(v=0) system of NO has been studied by (2+1) optical-optical double resonance laser induced fluorescence (LIF) dip techniques. These experiments utilized two high resolution, continuous-wave lasers. The spectral resolution obtained under these conditions has provided measurements of the frequencies to an absolute accuracy of better than 0.002 cm−1, and of the widths to an average precision of 3% of the K←A(2,1) rotational transitions of interest. Term energies of individual rovibronic levels of both the Ω=0.5 and Ω=1.5 spin–orbit components of the (4pπ)K 2Π(v=2) Rydberg state of 14N16O have been determined. For values of J=2.5 to 4.5, the lifetimes of these levels range from 189 to 410 ps. These results demonstrate the potential of high resolution, cw lasers in double resonance studies of molecules. The ability to excite selectively to a single, completely specified quantum level, e.g., one hyperfine level, within the resonant intermediate state will ultimately allow studies of transition frequencies and lifetimes as functions of Ω, J, F, and parity providing a more explicit description of the structural and dynamical ramifications of complex multistate interactions.
The effect of discretization on a path integral expression for the one-electron density
Authors: Hoffman Gary G.
Published: July 2002

Using an integral expression which is based on the use of discretized path integrals, the one-particle density matrix is evaluated for individual fermions in a one- and three-dimensional harmonic well. In this regard, the present paper improves and extends work previously done by Handler. By deriving a closed form expression for the path integral with finite discretization, the density is expressed as a one-dimensional integral that can be evaluated numerically. In addition, the trace of this density matrix, which corresponds to the number of particles present as a function of the Fermi energy, is evaluated in closed form. For finite discretization, the function is continuous in the Fermi energy, but approaches the correct discontinuous limit as the discretization becomes large. Oscillations are observed at the discontinuities analogous to the Gibbs phenomenon of Fourier analysis. Calculations of the density show a marked improvement in the classically allowed region when the discretization is only one level beyond the simple Thomas–Fermi theory. The density also penetrates into the classically forbidden region as the discretization is increased, but the presence of negative oscillations requires a higher level of discretization for a proper description in this region.
Angular distribution of photoelectrons from two-photon ionization in molecules: H2O
Authors: Cacelli I. , Carravetta V. , Rizzo A. , Moccia R.
Published: July 2002

The angular distribution of the photoejected electrons in a nonresonant two-photon ionization process in H2O is obtained by ab initio calculations for selected choices of photon polarization and experimental set-up. Within the framework of the second-order perturbation theory in the dipole and vertical transition approximations, both intermediate and final states are described in the static-exchange approximation. The continuum orbitals are obtained via a K-matrix technique, by adopting a large basis set of L2 integrable functions and an interpolation procedure.
Theory of multiphoton processes by the Fourier-expansion density matrix method
Authors: Lin S. H. , Nomura Y. , Fujimura Y.
Published: July 2002

The Fourier-expansion density matrix method is developed to describe the multiphoton processes of molecules interacting with the heat bath under the strong laser light. This method is applied to deriving expressions for the absorption spectra in the case in which a single-mode laser interacts with the molecular system of a three-level taking into account the dynamic Stark effect. Model calculations are performed to demonstrate the dynamic Stark effects on the absorption ability in the three-level system, and compared with the results of the weak laser light case. The calculated band shapes of the two-photon absorption are analyzed in terms of the simultaneous and sequential mechanisms. The sequential mechanism is characterized by bath-induced intramolecular transitions. As the laser intensity is increased the simultaneous mechanism makes a dominant contribution with increased dynamic Stark effects.
Holographic method for investigating the diffusion of dye molecules in the polymer host
Authors: Wang C. H. , Xia J. L.
Published: July 2002

Laser induced holographic grating relaxation studies of thymoquinone dissolved in amorphous poly(α-methyl styrene) have been carried out. The Onsager theory of mutual diffusion for binary and tertiary systems are utilized to analyze the shape of the diffraction intensity curve. Different line shapes that are associated with the relaxation of the diffraction intensity are interpreted in terms of the diffusion processes. Diffusion coefficients are obtained as a function of thymoquinone concentration from 0.3 to 20 wt. % at various temperatures. It is shown that at very low concentrations (less than 0.5%), the self-diffusion coefficients of the dye molecule and its photoproduct are obtained. Above 0.5% concentrations the diffusion coefficient rapidly increases with increasing dye concentration. The temperature dependence of the self-diffusion coefficient follows the Williams–Landel–Ferry equation, whereas the mutual diffusion coefficient at higher dye concentrations follows the Arrhenius equation. The self-diffusion coefficient rapidly decreases as the sample temperature is traversed across the glass transition temperature (Tg). However at finite dye concentrations there is no detectable effect owing to the onset of Tg on the mutual diffusion coefficient. The difference is attributed to the plasticizing effect of the dye molecules.
Site-selective laser spectroscopy of deuterated SrF2:Er3+
Authors: Cockroft N. J. , Jones G. D. , Syme R. W. G.
Published: July 2002

Laser selective excitation and optical absorption of deuterated SrF2:0.05% Er3+ crystals have revealed eight Er3+ ion centers involving D− ion charge compensation, nine new Er3+–F− centers not associated with D− ions and several approximately cubic symmetry Er3+ centers. In contrast to the trigonal symmetry of the principal F− center, the dominant arrangements in the D− ion charge compensation case are derived from a tetragonal symmetry center. Detailed spectroscopic results for the new centers are presented. Fluorescence polarization ratios are listed for three centers ( J, B, and G1) present in either SrF2:Er3+ or CaF2:Er3+ and crystal-field analyses of these, based on assumed trigonal symmetry, are also reported.
Fluorescence lifetime of the CO D′ 1Σ+ electronic state
Authors: DeLeon R. L.
Published: July 2002

The lifetime of the CO D′ 1Σ+ electronic state has been measured by laser induced fluoresence. A highly vibrationally excited CO(X) state population distribution was created by optical vibration–vibration pumping. The D′ population was created by a one photon UV laser excitation of CO(X,v″>30) and the fluorescence from D′–X was time resolved. The measured fluorescence lifetime of D′v′=2 is 3.87(30) ns.
Low energy electron induced decomposition of phosgene on Ag(111)
Authors: Zhou X.-L. , Coon S. R. , White J. M.
Published: July 2002

The decomposition, induced by low energy electrons (0–23 eV), of adsorbed phosgene (Cl2CO) on Ag(111) has been studied using temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS). The electron induced decomposition (EID) products are surface Cl(a) and gas phase CO(g). There is no electron stimulated desorption (ESD) of molecular Cl2CO or atomic Cl. The evolution of CO during EID is readily monitored with a mass spectrometer. The electron kinetic energy threshold for the EID of Cl2CO is near zero eV. The EID cross section is in the range of 10−16–10−15 cm2 and increases with incident electron energy. The EID process is attributed to dissociative electron attachment (DEA) in which incident electrons attach themselves to adsorbed Cl2CO forming Cl2CO− ions as intermediates that dissociate. These results are compared with the photodissociation of Cl2CO on Ag(111).
Do classical oscillators with quantum effective potentials simulate quantal oscillators in energy transfer collisions?
Authors: Cochrane David L. , Truhlar Donald G.
Published: July 2002

The use of quantum effective potentials in classical simulations of dynamical processes is tested against exact quantum mechanics.
Diffusion coefficient and interatomic potential of He–Ar at high temperatures
Authors: Taylor W. L. , Wyrick S. B. , Hurly J. J. , Meeks F. R.
Published: July 2002

Measurements of the mutual diffusion coefficient D12 for the He/Ar gaseous system have been extended to 2050 K, approximately 600 deg beyond any previous work. The results, obtained in a tungsten–tantalum–hafnium alloy (‘‘T-111’’) two-bulb cell, are in excellent agreement with previous studies in the 200–1400 K range. An equation is presented which has been fitted to all available published D12 results. An HFD-B interatomic potential is proposed which accurately predicts D12 within accepted experimental uncertainties.
Disorder in paraffin chains of urea adducts and n-paraffins
Authors: Fukao Koji
Published: July 2002

In urea adducts with n-paraffins, the dependence of the rotational transition temperature on the chain length is analyzed, assuming that the paraffin molecules are in the all-trans conformation in the low temperature phase and contain conformational defects in the high temperature phase. The nature of the conformational defect is discussed on the basis of the conformational energy calculated. It is found that the conformational defect is a 60° twist and can be expressed as a soliton. The rotational phase transition of pure paraffins can be treated in the same manner as that of the urea adducts.
A reactive-flux theory of chemical surface diffusion
Authors: Rejto Paul A. , Andersen Hans C.
Published: July 2002

A theory for calculating the surface chemical diffusion coefficient of adsorbates strongly bound to localized adsorption sites on a crystal surface is presented. The coefficient is expressed as the product of a transition state theory value that may be calculated by Monte Carlo methods and a dynamical correction factor that may be calculated by molecular dynamics. An algorithm for determining the dynamical correction factor is presented and its fluctuation properties evaluated.
Electric double layer interactions in reverse micellar systems: A Monte Carlo simulation study
Authors: Luzar A. , Bratko D.
Published: July 2002

The electrostatic contribution to the interaction between reverse micelles in water-in-oil microemulsions formed in the presence of ionizing surfactant is studied by means of Monte Carlo simulation. The inverted micelles are treated as spherical entities consisting of charged surfactant shell and aqueous core with neutralizing counterions. The distributions of simple ions in the core determined by simulation are compared with the predictions of the Poisson–Boltzmann approximation. A good agreement is observed, particularly for monovalent simple ions. The dispersion force due to the correlated fluctuations in ionic distribution within electroneutral micelles is found to be of comparable magnitude as classical van der Waals interaction and may represent a significant contribution to the total pair potential estimated from recent small angle neutron scattering (SANS) measurements of intermicellar correlations.
Photoionization of the 3σ and 1π orbitals of CH
Authors: Lee M.-T. , Stephens J. A. , McKoy V.
Published: July 2002

We report the results of theoretical studies of photoionization cross sections and photoelectron angular distributions for the 3σ and 1π levels of CH leading to the A 1Π, a 3Π, and X 1Σ+ molecular ions. The calculations employed multiplet-specific Hartree–Fock potentials and numerical photoelectron continuum orbitals, obtained using the iterative Schwinger variational method. Noticeable nonstatistical behavior of the cross sections is seen for the 3σ level near threshold, although deviations are not significant at higher photon energies. A comparison with some previous theoretical studies is made.
Analytic expressions for equilibrium distributions of isomer groups in homologous series of alkanes, alkenes, and alkynes at a specified partial pressure of molecular hydrogen
Authors: Alberty Robert A.
Published: July 2002

The chemical equilibrium distributions of isomer groups in a homologous series of hydrocarbons can be calculated at a specified temperature, total pressure, and partial pressure of molecular hydrogen. If the standard Gibbs energies of formation of the successive isomer groups in the homologous series are given by A+Bn, where n is the carbon number of the isomer group and A and B are functions of temperature only, the equilibrium distribution is given by an analytic function that depends only on A for ideal gases. The analytic functions for the equilibrium mole fraction distributions yn and equilibrium mass fraction distributions wn are derived for the alkanes, alkenes, and alkynes. Equations for the mean carbon number n̄, standard deviation σ, the carbon number nmax at which wn is a maximum, and the mass-average carbon number n̄m are also derived.
Orientational correlation in liquid phosphorous tribromide studied by pulsed neutron total scattering
Authors: Misawa M. , Fukunaga T. , Suzuki K.
Published: July 2002

Structure factor Sm(Q) of liquid phosphorous tribromide (PBr3) has been measured at room temperature by means of pulsed neutron total scattering technique. Characteristic features of the experimental Sm(Q) are analyzed in terms of preferred orientations introduced between the nearest neighbors as well as a packing of effectively uncorrelated molecules. The preferred orientation estimated in this analysis is such that a top (or a P atom) of pyramidal shape of each PBr3 molecule points in nearly the same direction.
Internal rotation of the methyl group in the radical cation of dimethyl ether
Authors: Matsushita Michio , Momose Takamasa , Shida Tadamasa
Published: July 2002

The radical cation of dimethyl ether has been studied by ESR in the temperature region of 6–140 K focusing on the internal rotation of the methyl groups. The methyl groups rotate almost freely at above ∼70 K to give a septet ESR spectrum. At temperatures below 40 K there emerge extra lines due to the tunneling rotation of the methyl groups. From the analysis of the line shape, the interaction potential for the rotation of the two methyl groups, if any, should be approximated as proportional to cos 3θ1 cos 3θ2, where θ1 and θ2 denote the rotational angles of the methyl groups measured from the potential minima of the internal rotation of the methyl groups. The activation energy for the thermally induced internal rotation is determined to be ∼100 cal/mol at temperatures above 25 K, whereas at lower temperatures the apparent activation energy drops sharply, which is consistent with the quantum tunneling of the methyl protons. The small activation energy of 100 cal/mol for the radical cation is compatible with the result of ab initio MO calculation for the potential barrier.
Geminate electron–cation recombination in disordered solids
Authors: Berlin Yu. A. , Chekunaev N. I. , Goldanskii V. I.
Published: July 2002

A theory of a geminate electron–cation recombination has been developed using the percolation approach to the description of the electron transport in disordered solids. Following this approach all trapping sites are separated into two groups. The first group forms a diffusion cluster responsible for the macroscopic charge transfer in disordered media whilethe second group consists of isolated traps playing the role of origins and sinks for mobile electrons. In the framework of such a model an equation has been derived describing the electron motion in the Coulomb field of a parent cation. The solution of this equation in the long time limit shows that the recombination rate decreases vs time as t−(1+α/2) with α being a positive constant or a very weak function of t. In the particular case of Gaussian diffusion α=1 and the kinetic law obtained reduces to that predicted by the well-known Onsager–Smoluchowski theory. However for the dispersive (non-Gaussian) transport in highly disordered systems α<1 and its value depends on the type of disorder, on the energy level structure of trapped electrons and on the specific mechanism of electron migration through the medium.
Quantitative determination of hole burning-induced changes of site energy in glassy matrices
Authors: Glatz Dieter , Fünfschilling Jürg , Zschokke-Gränacher Iris
Published: July 2002

Nonphotochemical hole burning in glassy host/guest matrices generates a change of the site energy distribution of the guest molecules. This distribution of shifted energies has been determined by deconvoluting the difference of white-light excited fluorescence spectra before and after hole burning. For this aim, a special numeric algorithm has been developed. For the host/guest-system tetracene in ethanol, the observed shifts are within the inhomogeneously broadened line, but a shift to higher energies is predominant and amounts to about 20 wave numbers.
On the relation between electronic structure and molecular dynamics
Authors: Lazarides Anne A. , Rabitz Herschel
Published: July 2002

A formalism is developed for relating dynamic observables of collision processes to the electronic structure of the colliding species. Expressions are derived for functional derivatives of dynamic observables with respect to the full electronic wavefunction for the case of indistinguishable collision partners as well as for nonidentical partners. For wavefunctions described by orbitals, the formalism is extended to relate dynamic observables to electronic orbitals and orbital coefficients. The formalism is illustrated with the simple example of H+D and H+H elastic scattering cross sections at energies between 0.5 and 5.0 eV. Regions of the wavefunction which have particularly strong influence on the cross sections are identified by the functional derivatives. The manner in which the dynamics enters into the sensitivity is discussed. Particle indistinguishability is seen to influence the sensitivity of the collision to electronic structure.
Cellular automaton model of chemical wave propagation on fractals
Authors: Irwin Andrew J. , Fraser Simon J.
Published: July 2002

A three-state cellular automaton (CA) model of nucleation and chemical wave propagation on fractal lattices is discussed. In the CA, seeds produce spreading wavefronts of active or transformed sites which mutually annihilate on collision. Many chemical and biological growth processes display this behavior. Pattern formation and growth from isolated seeds and from random initial distributions of seeds are considered. Steady-state behavior for continuous seeding is also discussed. For isolated seeds, surface and volume growth exponents on fractals do not show the simple relation that holds for homogeneous lattices, and lattice topology plays an important dynamical role. For initial seeding, mean-field theory predicts that growth depends on the fractal dimension D (since the minimum path dimension is one). However the fractal gap hierarchy (lacunarity) introduces fluctuation contributions. For continuous seeding entirely new effects arise. On sponge-like fractals oscillators are created; these eventually fill the lattice even at low seeding density. However tree-like fractals cannot support oscillators, and instead exhibit dynamical scaling behavior. For mixed fractals complicated periodic phenomena can arise.
The metastable triplet state of CrO2−4 in a calcium sulphate host: Electron-spin-echo experiments
Authors: Coremans C. J. M. , Groenen E. J. J. , van der Waals J. H.
Published: July 2002

An electron paramagnetic resonance (EPR) study with laser flash excitation and electron-spin-echo detection is reported on the very weakly luminescent state of the CrO2−4 ion in an anhydrite (CaSO4) host. On excitation a lowering of symmetry of the chromate ion occurs, and four sets of congruent excited species are observed, interrelated by the orthorhombic symmetry of the crystal. The results can be fitted to a spin Hamiltonian for an orbitally nondegenerate triplet state with parameters D=−20.337 GHz, E=−0.211 GHz, g11=1.961, g22= 1.989, and g33=1.9817. The relaxation behavior of the triplet state has been studied by varying (1) the delay between the laser flash and the first microwave pulse and (2) the interval τ between the microwave pulses. The lifetimes of the zero-field spin states are τx=2.2, τy=0.73, and τz=0.023 μs. Because of the very fast decay of the Tz level and attendant very short relaxation time T2 for most orientations of the magnetic field, the four ‘‘allowed’’ stationary EPR transitions in our X-band experiment could only be observed by using a stripline cavity and reducing τ to less than 100 ns.
A laser-induced fluorescence determination of the internal state distribution of NO produced in the reaction: H+NO2→OH+NO
Authors: Irvine Alistair M. L. , Smith Ian W. M. , Tuckett Richard P.
Published: July 2002

Laser-induced fluorescence (LIF) spectra have been recorded of NO produced when H atoms and NO2 react in thermal energy collisions in the region where two uncollimated jets containing the reagents intersect. Spectra of the (0,0), (1,1) and (2,2) bands and the (0,2) and (1,3) bands of the A 2Σ+–X 2Π γ-band system have been observed. Distributions of NO over rovibrational levels have been determined by matching the experimental spectra to simulated spectra. The high J tail of the rotational distributions fit a linear surprisal plot. The analysis leads to average fractional yields of vibration and rotation energy, 〈fvib〉NO=0.056 and 〈frot〉NO=0.10, as well as branching ratios into vibrational (v=0–3), spin–orbit and Λ-doublet states. Preferences are found for the lower 2Π1/2 spin–orbit substate and for the Π(A′) Λ-doublet levels. Combined with results from the preceding paper, the data indicate that ∼31% of the energy released in the reaction should appear as relative translational motion of OH and NO. The reaction appears to proceed via the ground state HONO surface but the complex does not survive sufficiently long for complete energy randomisation: OH is more excited, NO less excited, than would be expected on a purely statistical basis.
Diode laser probing of vibrational, rotational, and translational excitation of CO2 following collisions with O(1D). I. Inelastic scattering
Authors: Zhu Lei , Kreutz Thomas G. , Hewitt Scott A. , Flynn George W.
Published: July 2002

Time domain diode laser absorption spectroscopy has been used to measure state-specific energy deposition in the vibrational, rotational, and translational degrees of freedom of CO2 following the 248 nm photolysis of ozone in a low pressure mixture of CO2, O3, and O2. Nascent rotational population distributions have been measured in a number of low-lying CO2 vibrational levels, including 0000, 0110, 0220, 0200, 0330, 1000, and 0001. In addition, measurements of CO2 translational excitation have been obtained for the majority of the rovibrational states which were probed. The results suggest that the prompt absorption signals observed so far arise from inelastic scattering between CO2 and the translationally hot O(1D) and O2(1Δ) photofragments rather than electronic quenching of O(1D) to O(3P) by collisions with CO2. Simple calculations indicate that the latter process should provide substantially more CO2 rotational and translational excitation than is observed here.
Lifetimes of electronically metastable double-Rydberg anions: FH−2
Authors: Gutowski Maciej , Simons Jack
Published: July 2002

The method of analytic continuation of real stabilization graphs was applied to calculate positions and widths of electronic resonances of the FH−2 double-Rydberg anion at the experimental geometry of the parent FH+2 cation. In correlated calculations on FH−2, a full configuration interaction calculation was performed on the two outermost electrons; the remaining electrons occupied orbitals taken from the SCF-level treatment of the FH+2 core. All spatial symmetries and both singlet and triplet spin multiplicities were considered. Many Feshbach and core-excited shape resonances were found with lifetimes in the range (1 to 80) ×10−14 s. Different methods of fitting the coefficients of the characteristic polynomial used in the stabilization calculations were considered. Techniques to suppress incomplete basis set artifacts in the stabilization calculations were examined.
Frame transformation theory for heavy particle scattering: Application to the rotational predissociation of Ar–H2
Authors: Raoult M. , Balint-Kurti G. G.
Published: July 2002

The frame transformation concept, which is standardly used in discussions of atomic and molecular Rydberg spectra, is applied to heavy particle scattering theory. It is shown how this approach permits the use of an optimal reference frame in the various different ranges of the scattering coordinate. It is further argued that the accuracy of the coupled states or p-helicity decoupling approximations may be significantly improved without substantial additional computational effort especially for low energy scattering processes, through the use of frame transformation procedures. The method is then applied to the calculation of the photodissociation line shapes for the rotational predissociation of Ar–H2 within the framework of generalized multichannel quantum defect theory (MQDT). It is shown how the use of the frame transformation procedure yields reasonably correct product rotational state distributions in situations where the standard coupled states or body-fixed decoupling procedure fails even at the qualitative level. The paper also reviews the application of generalized MQDT to heavy particle scattering processes.
Comment on: Deuterium nuclear fusion at room temperature: A pertinent inequality on barrier penetration
Authors: Durup Jean
Published: July 2002

Gerald Rosen’s formula (Ref. 1) and the inequality derived by hin on Coulomb barrier penetration is found to be incorrect. (AIP)
An investigation of hydrogen bonding between HCl and vinylacetylene: A molecule with two different π-acceptor sites
Authors: Kisiel Z. , Fowler P. W. , Legon A. C. , Devanne D. , Dixneuf P.
Published: July 2002

The ground state rotational spectrum of a hydrogen-bonded dimer formed by vinylacetylene and hydrogen chloride has been detected by the pulsed-nozzle, Fourier-transform microwave technique. Vinylacetylene has been chosen as a prototype acceptor molecule containing two different π-acceptor sites. Rotational constants 𝒜0, ℬ0, 𝒞0, centrifugal distortion constants ΔJ, ΔJK, δJ, δK, and three components χaa, χbb−χcc, and χab of the Cl nuclear quadrupole coupling tensor have been determined for each of the three isotopomers CH2CHCCH⋅⋅⋅ H35Cl, CH2CHCCH⋅⋅⋅H37Cl, and CH2CHCCH⋅⋅⋅D35Cl. These spectroscopic constants have been interpreted in terms of a dimer in which the HCl subunit forms a hydrogen bond to the C 3/4 C triple bond in a T-shape configuration, but is displaced from the center of the triple bond by d=0.04 Å towards the inner C atom, and makes an angle φ=34° with the vinylacetylene plane. The experimental angular geometry is in excellent agreement with that predicted by the Buckingham–Fowler electrostatic model which gives φ=27°.
The Na 7Li 3 1Σ+(C) and 1 1Π(B) electronic states through collision energy transfer
Authors: Fellows C. E. , Vergès J. , Amiot C.
Published: July 2002

The NaLi 3 1Σ+(C)→2 1Σ+(A) electronic transition has been observed in the infrared region after laser excitation of the 1 1Π(B) electronic state and subsequent collisional energy transfer between the 1 1Π(B) and 3 1Σ+(C) electronic states. The spectra were recorded at high resolution by Fourier-transform spectroscopy. Thirteen vibrational bands were analyzed, providing detailed information for the 2 1Σ+(A) (v=0,...,4) and 3 1Σ+(C) (v=5,...,13) vibrational levels. Rotational perturbations have been observed in the spectra. The nearly 1200 observed lines belonging to 1 1Π(B)→2 1Σ+(A) and 3 1Σ+(C)→2 1Σ+(A) transitions have been assigned and reduced to molecular constants in a linear least-squares fit. Perturbations observed in the upper electronic states have been reduced using a nonlinear least-squares fit to a 1Σ∼1Π effective Hamiltonian matrix model. Deperturbed molecular constants and perturbation parameters are obtained for the 1 1Π(B) electronic state (v=0,...,6) and the 3 1Σ+(C) electronic state (v=5,...,13) levels. Propensity rules concerning the energy gaps and the conservation of angular momentum, during the energy transfer, are inferred from the intensity distributions of anomalous lines.
Axial and circular birefringence due to static electric and magnetic field combinations
Authors: Evans M. W.
Published: July 2002

Axial and circular birefringence are derived for a combination of static electric field strength (ES) and static magnetic flux density (BS). For ES parallel to BS in the Z axis of the laboratory frame (X, Y, Z) the refractive index measured in a chiral ensemble with unpolarized light with wave vector KZ, propagating in Z, is different for KZ parallel and antiparallel to ESZ for fixed BSZ or vice versa. The effect is c times greater in magnitude than axial birefringence due to BSZ alone and is proportional to the product BS⋅ES and to the ensemble average 〈A′1XXZZ〉, where A1 is an odd parity tensor mediating the effect of BS⋅ES on the molecular polarizability. Circular birefringence due to ES⋅BS also occurs in chiral ensembles only, but is c times smaller than axial birefringence. It is proportional to the ensemble average 〈A′2XXZZ〉, where A2 is an even parity tensor mediating the effect of ES⋅BS on the molecular Rosenfeld tensor. There are no equivalent effects due to ES alone, ES⋅ES or BS⋅BS, because they violate reversality. The ES⋅BS effects conserve reversality both in achiral and chiral ensembles, and provide information on new molecular property tensors. Their frequency dependencies provide novel molecular spectroscopies, and experimental configurations are suggested.
On the exponential energy gap law in He–I2 vibrational relaxation
Authors: Maricq M. Matti
Published: July 2002

A comparison between coupled states, infinite order sudden, and classical path calculations is used to elucidate the origin of an exponential energy gap law recently observed for vibrational relaxation from highly excited states in the B 0+u state of I2 due to collisions with He. All three methods provide relaxation cross sections in good agreement with experiment. Anharmonic effects play an important role, with accurate results obtained with a Morse, but not harmonic, oscillator description of the I*2 molecule. The nearly exact agreement between rotationally summed coupled states cross sections and the IOSA is consistent with the view that the I*2 molecule does not rotate significantly during a collision. A closed form solution of the forced harmonic oscillator, valid for highly excited states, predicts a J2‖Δv‖ distribution of vibrationally relaxed states at a given collision angle and impact parameter. The vibrationally close coupled-infinite order sudden (VCC-IOSA) results bear this out and show that the observed exponential scaling law arises from a superposition of such distributions over θ and b.
Dynamic contribution of the Brillouin zone center to the floating transition of adsorbed monolayers
Authors: Hilliker P. R. , Hakim T. M.
Published: July 2002

The Monkhorst–Pack (MP) triangular distribution of q points in the Brillouin zone is used to probe the floating transition of krypton solid monolayers on graphite. Different orders of points are used in the computation. Despite the presence of the 0-point in the MP sets, a very large order is needed to observe the disappearance of the gap at the critical temperature. The MP method is comparable to the Chadi–Cohen/Cunningham but neither is practical in predicting the commensurate–incommensurate transition.
The He–Co2 interaction revisited: Approximate rotational energy transfer efficiency indices and computed transport coefficients
Authors: Gianturco F. A. , Toennies J. P. , Bernardi M. , Venanzi M.
Published: July 2002

Of the several anisotropic interactions suggested over the years for the title system, two of the most recent ones have been tested against experimental total differential cross sections, energy loss angular distributions, and transport coefficients. In the present work, they are examined again in order to compare them in a calculation over a broader range of transport properties, using the approximate infinite order sudden approximation (IOSA) scheme for the dynamics and getting first- and second-order contributions to the Chapman–Cowling expansion in the kinetic theory of dilute gaseous mixtures. The various observables are found to be very close to the experiments for both potential functions, thereby making it still difficult to establish clearcut differences between them from the study of the above properties alone. The novelty of the present study, however, is to show that various recently proposed efficiency indices for the rotational energy transfer (RET) collisions are able to exhibit marked differences between the two surfaces and to unequivocally select one of them as the more anisotropic of the two. Because of the low value of such indices, one is also able to explain why the IOSA approximation should work well for computing the transport coefficients of this system.
Calculation of partial widths for autoionization of the 1P (3s3p) resonance state of helium
Authors: Bentley John , Chipman Daniel M.
Published: July 2002

Partial widths for the autoionization of He** 1P (3s3p) into various decay channels are calculated by an analytic continuation method that makes use only of real eigenvalues from stabilization graphs. Agreement with experiment and with more elaborate theoretical calculations is satisfactory, more closely in accord with the latter where discrepancies exist.
Fine structure of the lowest triplet states in He2
Authors: Kristensen Martin , Bjerre Nis
Published: July 2002

Laser driven transitions from the metastable a 3Σ+u state to the predissociating level v′=4 of the electronic state c 3Σ+g of He2 are investigated by fast beam laser spectroscopy. For transitions to the rotational levels N′=8, 10, and 12 of the c 3Σ+g state, the fine structure is resolved and the fine structure parameters of both electronic states can be determined. The fine structure in the rotational levels N″=7, 9, and 11 of v″=0 in the a 3Σ+u state is measured to 20 kHz precision (3σ) using laser–radio frequency double-resonance spectroscopy. These measurements are complementary to the previous radio frequency (rf) measurements for the levels N″=1, 3, and 5 by Lichten et al. The fine structure parameters are compared to theoretical calculations and simple models for the electronic interactions and the couplings between different electronic states.
The osmotic pressure in polyelectrolyte solutions: Exact and mean-field results
Authors: Miklavic S. J. , Woodward C. E.
Published: July 2002

We derive, from statistical mechanical arguments, exact expressions for the osmotic pressure in a system involving two charged, hard walls in a solution containing polyelectrolytes. Relations are given appropriate to the polyelectrolyte molecules being either dispersed, i.e., free in solution or grafted to the surfaces. Our results appear as direct generalizations of existing osmotic pressure equations, well known for simple electrolyte systems. In the case of free polyions the corresponding equation is shown to take precisely the same form as found for ordinary electrolytes. We show also that these expressions, which appear in simple form, are satisfied by an appropriate mean-field theory for polyelectrolytes. Thus the relations provide for consistent comparisons of this mean-field approximation with exact results.
Cs cluster binding to a GaAs surface
Authors: Krauss M. , Stevens W. J.
Published: July 2002

A cluster model for the binding of Cs atoms on the (110) surface of GaAs is examined for polarization, charge transfer, and dispersion interactions. Binding energies for two or three atom clusters on GaAs are calculated to be less than 0.1 eV per Cs atom indicating only small binding contributions from charge transfer and polarization. Orbital and total charge density plots reveal an alkali valence charge weakly bonded between the alkali atoms and polarized toward the Ga atom. A London analysis of the dispersion energy between quasilinear Cs clusters and GaAs clusters finds it is large compared to the difference in stability between polyhedral clusters and the quasilinear clusters that are experimentally observed on the GaAs surface. The large dispersion energy is due to the large polarizabilities for quasilinear chains of Cs atoms whose longitudinal component increases approximately with the square of the chain length.
Memory kernel for a multilevel quantum system driven by colored thermal noise
Authors: Velasco S. , White J. A. , Calvo Hernández A.
Published: July 2002

The memory kernel appearing in a non-Markovian population equation for a multilevel quantum system stochastically coupled to a colored Gaussian bath is calculated on the basis of a fully quantum-mechanical treatment to construct the time autocorrelation function (TAF) associated to the system–bath interaction Hamiltonian. The limiting cases of high and low temperatures and white noise bath are also analyzed. These examples allow us to discuss in a very simple way the dependence of the memory kernel on the Bohr frequencies of the system, the intensity of the system–bath interaction, its correlation time, and the bath temperature. In particular, it is shown that a true Markovian population equation is only achieved at high temperatures with a bath correlation time much shorter than the relaxation process characteristic time.
Limit cycles and discontinuous entropy production changes in the reversible Oregonator
Authors: Dutt Arun K. , Bhattacharya D. K. , Eu Byung Chan
Published: July 2002

We show that the chemical entropy production in the reversible Oregonator changes discontinuously at critical values of the concentration parameter at which points a limit cycle bifurcates out of an unstable steady state. The discontinuities in the entropy production are reminiscent of the behavior of the entropy change accompanying a first order phase transition in thermodynamics. They appear to be an example of dynamic phase transitions. For this model, by using Poore’s algorithm, we show that in the case of f=1 the limit cycle is orbitally asymptotically unstable and the bifurcation is subcritical, but in the case of f=0.5 the limit cycle bifurcation at the higher critical concentration of P is subcritical whereas the one at the lower critical concentration of P is supercritical. Therefore, a discontinuous change in chemical entropy production accompanies subcritical Hopf bifurcations and possibly a supercritical Hopf bifurcation. It is conjectured that if a bifurcation is subcritical, attractors of different topological dimensions have different characteristic entropy productions in the same manner as two different states of aggregation of matter have different entropies associated with them.
Repulsive binary alloys and the absence of localization: Application to Fibonacci lattices and molecularly based electronic filters
Authors: Wu H. -L. , Phillips P. W.
Published: July 2002

We show here that a static disordered binary alloy in which one of the impurities is prevented from clustering in the lattice as a result of strong repulsive interactions, e.g., will possess a localization–delocalization transition regardless of the spatial dimension. We show explicitly that (N)1/2 of the electronic states are completely unscattered by the disorder and lead to superdiffusive transport with a mean-square displacement growing in time as t3/2 over a wide range of the static disorder in one dimension. The model is shown to be applicable to electron transport in Fibonacci lattices fabricated from two kinds of materials such as GaAs and AlAs. It is shown explicitly that transient grating experiments can be used to probe the location of the unattenuated states in the energy band. We propose that this model can be used to design molecularly based electronic filters.