bluuebunny/crossref_metadata_2025 huggingface dataset:
Persistent spectral hole-burning, luminescence line narrowing and selective excitation spectroscopy of the R lines of Cr(III) tris(2,2′-bipyridine) in amorphous hosts
Authors: Riesen Hans , Krausz Elmars
Published: July 2002

The distributions of the 2E and the 4A2 splittings of Cr(III) tris(2,2′-bipyridine) embedded in a wide range of amorphous hosts are investigated by means of luminescence line narrowing and hole-burning spectroscopies. A large spread of the 2E splitting is observed for all amorphous matrices and this is attributed mainly to low symmetry field contributions. A simple model is proposed which rationalizes the observed non-Gaussian distribution of R2 energies as a function of the selected R1 energy. The zero field splitting of the 4A2 ground state also shows a significant variation in all the investigated samples. An important conclusion is that optically detected magnetic resonance and electron paramagnetic resonance measurements of transition metal complexes in amorphous hosts need to be interpreted with care. The homogeneous linewidth of the R1 line was measured at 1.5 K for five hosts and ranged from 80 MHz in glycerol to 460 MHz in 4:1 ethanol/methanol.
Breakdown of the Rouse model for polymers near the glass transition temperature
Authors: Plazek D. J. , Schlosser E. , Schönhals A. , Ngai K. L.
Published: July 2002

The bead-spring model pioneered by Rouse is generally considered to be the basis of polymer physics. We show generally that it breaks down dramatically near the glass transition temperature by shear creep measurements on several polymers with very different backbone structures. The physical origin of this breakdown is traced to the segmental relaxation time having a much stronger temperature dependence than that of the Rouse spectrum. This property, a consequence of the cooperative nature of segmental relaxation in dense packed polymers, was predicted before by a coupling model. We verify this property directly by dielectric relaxation measurements with a wide frequency window of ten decades.
Exchange and vibronic interactions in a tetrahedral, five-electron mixed-valence cluster
Authors: Marks Alison J. , Prassides Kosmas
Published: July 2002

The distribution of an ‘‘excess’’ electron in a model mixed-valence tetranuclear metal cluster with open-shell ion cores is explored as a function of vibronic coupling, electron transfer, and electron exchange interactions. The system comprises five electrons, one ‘‘core electron’’ at each metal center, and one electron in a different local orbital which can delocalize among the sites. Vibronic coupling is introduced as the interaction of the electronic states with nontotally symmetric combinations of the subunit ligand vibrations. An extension of the Anderson–Hasegawa Hamiltonian is developed to describe the system, and adiabatic potential energy surfaces for the different spin states are obtained. From these, the excess electron distribution is deduced. The model is designed to be a prototype for understanding the excess electron distributions in tetranuclear iron–sulfur clusters. Examples of electron delocalization over three sites in an S=3/2 ground state and over two sites in an S=1/2 state are found. These distributions cannot arise in a tetranuclear cluster having closed-shell ion cores and are attributed to favorable double exchange interactions. The occurrence of pair delocalization in an S=1/2 ground state is consistent with experimental observations of (Fe4S4)3+ iron–sulfur clusters.
Bloch equations applied to ion cyclotron resonance spectroscopy: Broadband interconversion between magnetron and cyclotron motion for ion axialization
Authors: Guan Shenheng , Marshall Alan G.
Published: July 2002

Conversion of magnetron motion to cyclotron motion combined with collisional cooling of the cyclotron motion provides an efficient way to reduce the kinetic energy of trapped heavy ions and to reduce their magnetron radii in an ion cyclotron resonance (ICR) ion trap. The coupling of magnetron and cyclotron motion can be realized by azimuthal quadrupolar excitation. Theoretical understanding of the coupling process has until now been based on resonant single-frequency quadrupolar excitation at the combination frequency ωc=ω++ω−, in which ωc is the ion cyclotron orbital frequency in the absence of electrostatic field; and ω+ and ω− are the reduced cyclotron and magnetron frequencies in the presence of an electrostatic trapping potential. In this work, we prove that the magnetron/cyclotron coupling is closely related to a two energy level system whose behavior is described by the well-known Bloch equations. By means of a special transformation, the equations of motion for the coupling may be expressed in Bloch-type equations in spherical coordinates. We show that magnetron-to-cyclotron conversion by single-frequency quadrupolar excitation in ICR is analogous to a 180° pulse in nuclear magnetic resonance (NMR). We go on to show that simultaneous magnetron-to-cyclotron conversion of ions over a finite mass-to-charge ratio range may be produced by quadrupolar frequency-sweep excitation, by analogy to adiabatic rapid passage in magnetic resonance. Axialization by broadband magnetron-to-cyclotron conversion followed by cyclotron cooling is successfully demonstrated experimentally for a crude oil distillate sample.
A distorted wave impulse approach for atom–diatom collisions
Authors: Dothe Hoang , Sharma Ramesh D.
Published: July 2002

A formalism is derived to include the effects of the long-range attractive part of the interaction potential in the calculation of atom–diatom collision cross sections using the impulse approach (IA). These calculations have, until now, assumed the atom–diatom potential given by a sum of two atom–atom interactions, consequently yielding a poor representation of the long-range attractive part. In the distorted wave impulse approach (DWIA) the long-range attractive part, located at the center of mass of the diatom, is a spherically symmetric potential which ‘‘distorts’’ the incoming and outgoing waves. The DWIA formalism is used to calculate differential cross sections for the rotationally inelastic process Li++N2(v=0, j=2)→Li++N2(v′=0, j′), as a function of the final rotational level j′, at a relative kinetic energy of 4.23 eV and center of mass scattering angles of 49.2° and 37.1°. It is shown that differential cross sections calculated using the DWIA formalism are in much better agreement with experimentally measured ones than IA differential cross sections using atom–atom interactions expressed by either hard-core, or exponential repulsive, functions.
A continuous Monte Carlo method for growth and equilibration of polymer chains at high densities
Authors: Gupta S. , Westermann-Clark G. B. , Bitsanis I.
Published: July 2002

We have developed an off-lattice Monte Carlo method for growth and equilibration of dense liquids consisting of polymer chains with realistic intramolecular architecture. Our technique is a continuous generalization of the lattice scheme developed by Kolinski et al. [J. Chem. Phys. 84, 1922 (1986)]. The method succeeded in growing alkane chains with chain length up to 25 at high liquid densities. Comparison with earlier molecular dynamics studies shows that our method produces fully equilibrated configurations of dense alkane liquids very efficiently.
Infrared absorption of 2-hydroxyethyl (HOCH2CH2) in solid Ar
Authors: Kuo Yu-Ping , Wann Gwo-Huei , Lee Yuan-Pern
Published: July 2002

An argon matrix containing C2H4 and H2O2 was irradiated at 12 K with the 248 nm emission of a KrF excimer laser; IR spectra were recorded after various periods of photolysis. In addition to lines ascribed to ethylene oxide, acetaldehyde, and vinyl alcohol, absorptions at 2991.0, 2842.7, 1355.4, 1172.5, and 1040.1 cm−1 have been assigned to HOCH2CH2; weaker lines at 3625.8, 2922.4, and 873.9 cm−1 may also be due to HOCH2CH2. Corresponding lines at 2970.6, 2829.3, 1346.5, 1171.3, and 1020.5 (and probably 3625.8, 2915.1, and 860.7) cm−1 were observed for HO13CH2 13CH2. The results are consistent with ab initio calculations.
High resolution photoacoustic overtone spectroscopy of monofluoroacetylene, HCCF, with a titanium:sapphire ring laser
Authors: Vaittinen Olavi , Saarinen Maria , Halonen Lauri , Mills Ian M.
Published: July 2002

Intracavity photoacoustic overtone spectrum of monofluoroacetylene, HCCF, has been recorded in the wave number region 10 750–14 500 cm−1 with a titanium:sapphire ring laser. The spectrum contains many dense vibration–rotation band systems which can be resolved with Doppler limited resolution. Altogether 58 individual overtone bands have been analyzed rotationally. Many of the observed bands show perturbations of which some have been attributed to anharmonic resonance interactions. A Fermi resonance model based on conventional rectilinear normal coordinate theory has been used to assign vibrationally bands from this work and from earlier studies. Many of the observed vibrational term values and rotational constants can be reproduced well with this model. The results show the importance of the Fermi resonance interactions at the high overtone excitations.
A 9 GHz cw-electron-paramagnetic resonance study of the sulphate salts of tridecameric [MnxAl13−xO4(OH)24(H2O)12](7−x)+
Authors: Kudynska J. , Buckmaster H. A. , Kawano K. , Bradley S. M. , Kydd R. A.
Published: July 2002

The results of a 13 °C, 9 GHz electron-paramagnetic resonance (EPR) investigation of the sulfate salts of the species formed by the base hydrolyses of solutions containing Mn2+ and Al3+, in the molar concentration range 1≤Mn/(Al+Mn)≤10% is reported. The EPR spectra of the microcrystalline samples consisted of the superposition of two overlapping axial, hyperfine structure (hfs) central transition Mn2+ resonances with g=1.9994(2) D=6.93(3) mT, A=8.56(3) mT, A=8.49(2), P=0.4(1)×10−4 mT, and gn=0.7(1)×10−3, and an unresolved resonance due to exchange coupled Mn2+ ions. The results are consistent with the interpretation that the resolved axial symmetry hfs central transition spectrum arises from Mn2+ ions replacing aluminum in either the tetrahedral or octahedral sites of the tridecameric Keggin-like cation [AlO4Al12(OH)24H2O)12]7+, which is known to form when Al3+ solutions are hydrolyzed under these conditions. The unresolved, exchange coupled spectrum must arise when two or more Mn2+ ions substitute into the same cation. The ratio of the intensities of the axial and exchange coupled Mn2+ centers had a maximum near the stoichiometric molar concentration 7.69% [i.e., Mn/(Al+Mn)=1:13]. The temperature dependence of the EPR spectral intensity and total hfs splitting for the resolved hfs central transition spectrum revealed that a first-order isomorphous phase transition occurred at 120 °C. .
Theory of melting in multicomponent systems of polymers
Authors: Hirami Matsuo
Published: July 2002

A theory is developed for the equilibrium crystalline state and melting in multicomponent systems of crystallizable polymers (species μ) and solvents (species m) by extending the Flory theory for binary systems of a single polymer and a solvent. Relationships deduced from the free energy of fusion for multicomponent systems are examined. The formula for the equilibrium crystallite length ζα for μ=α is common for all polymer components μ. The relationship of melting temperature Tm(α) for μ=α involves the degree of crystallinity (1−λμ) for all μ and interaction parameters of all polymer–polymer, polymer–solvent, and solvent–solvent contacts, i.e., χμν, χμm, and χmn. The degree of crystallinity (1−λα) for each component μ=α can be obtained by solving the simultaneous equations of melting temperatures Tm(μ) for the components μ which are coexistent in the crystalline state under a given condition of the system. The theory is applied to systems involving two crystallizable polymer components and the features of melting temperature diagram predicted from the theory are examined.
Long-range interaction coefficients for the metastable states of He
Authors: Spelsberg Dirk , Meyer Wilfried
Published: July 2002

Following the lines presented in a recent paper [J. Chem. Phys. (unpublished)] reduced spectra representing the dynamic polarizabilities are reported with special emphasis on accurate values for the metastable states of the He atom. Together with the reduced spectra taken from Ref. 1, long range interaction coefficients are computed for all combinations between the three lowest He states and the atoms H, Li, Na, K, and H−.
The adsorption of H2 on Fe(111) studied by thermal energy atom scattering
Authors: Jiang P. , Zappone M. , Bernasek S. L.
Published: July 2002

The interaction of H2 with Fe(111) has been studied by thermal energy atom scattering (TEAS). The specularly scattered He intensity as a function of hydrogen coverage exhibits a concave drop in scattered He intensity up to 30% coverage, followed by a plateau and another drop in intensity at 80% coverage. A model has been developed to account for this data which assumes three adsorption sites for H on Fe(111), in analogy with the three desorption peaks seen in temperature-programmed desorption (TPD). The adsorption sites have not been definitely assigned, but are labeled ‘‘deep–hollow,’’ ‘‘shallow–hollow,’’ and ‘‘on-top.’’ Competitive adsorption into the deep-hollow and shallow-hollow sites is assumed to account for the initial concavity of the data. Adsorption into on-top sites only becomes significant at 80% coverage. Effective cross sections and reflectivities for the three sites have been obtained for θi=60° and 40°. When a H saturated surface is heated, the scattered He intensity decreases upon heating from 173 to 240 K, at which point desorption has already begun. This drop in intensity is not completely explicable by a Debye–Waller attenuation. It is proposed to be due to a shift in population of the adsorbed H to more exposed, on-top sites, in accord with a Boltzmann distribution of adsorption sites. The scattered He intensity increases upon further heating from 240 to 400 K, corresponding to the desorption of recombined H2 from the surface. Comparison of the He/H/Fe(111) system is made with the He/H/Pt(111) and He/H/Fe(110) systems.
He scattering from substitutionally disordered mixed monolayers: Experimental and theoretical studies of Xe+Kr on Pt(111)
Authors: Yanuka M. , Yinnon A. T. , Gerber R. B. , Zeppenfeld P. , Kern K. , Becher U. , Comsa G.
Published: July 2002

The diffraction of thermal He atoms from mixed Xe+Kr monolayers on Pt(111) was measured, and the results were compared with theoretical studies of these systems. The results shed light on the structural properties of these disordered systems, and on their relation to the He diffraction intensities. Experimentally, the specular (0,0), the (1,0), and the (2,0) Bragg peak intensities were measured for monolayers of different Kr:Xe concentration ratios. The theoretical calculations included Monte Carlo simulations of the mixed disordered monolayers, and quantum calculations in the Sudden approximation of the scattering intensities from the simulated disordered structures. The following main results were obtained: (1) Both experiment and the Monte Carlo simulations suggest that the mixed Xe+Kr monolayers are periodic for all Xe:Kr concentration ratios, the lattice constant varies linearly with the Xe:Kr ratio. The domain size of the 2D crystals, from experiment and theory, is found to be larger than 100 Å. (2) The Monte Carlo simulations suggest that the Xe+Kr monolayers form an almost ideal substitutionally disordered lattice. (3) Using a semiempirical Debye–Waller factor, reasonable agreement is found between the theoretical and the measured diffraction intensities, thus supporting the calculated structural model for the disordered surface. (4) The theoretical scattering calculations show that in addition to the diffraction peaks, there are also intensity maxima at non-Bragg positions. These are entirely due to the lattice disorder, and are identified as a recently found new type of Rainbow effect that can furnish important information on disordered surfaces. The results demonstrate the power of He scattering as a tool for exploring substitutionally disordered surfaces.
Critical analysis of the band-shape function of a molecular system imbedded in a host crystal: Application to F centers
Authors: West J. , Lin S. H. , Tsen K. T.
Published: July 2002

We present an investigation of the accuracy of the saddle-point method in application to band-shape functions and find that it gives excellent results for most commonly encountered situations. We also present a comparison with a new improved short-time approximation which shows promise in applications. We use this new method to examine the behavior of the band-shape function in a distorted oscillator model. As an application, we have used these methods to explain the absorption and emission spectra of an F-center defect (a prototype defect system) in four different host crystals KCl, KI, KBr, and NaCl.
Orientational order in liquid crystal solutions of polyhexylisocyanate. II. Deuterium nuclear magnetic resonance
Authors: Wang Honghui , Wittebort R. J. , DuPré Donald B.
Published: July 2002

The concentration dependence of the order parameter was measured for liquid crystal solutions of deuterated samples of polyhexylisocyanate of two molecular weights in two solvents, chloroform and toluene. Trends in and values of order parameters determined from deuterium nuclear magnetic resonance (DNMR) spectroscopy for this semiflexible polymer were analyzed in terms of a recent modification [DuPré and Yang, J. Chem. Phys. 94, 7466 (1991)] of the Onsager theory that takes into account macromolecular flexibility and the higher solute densities characteristic of these polymer liquid crystals. Computer simulation of DNMR spectra with the consideration of internal flexibility of the polymer main chain was performed also to interpret unusual line shape features observed in liquid crystal solutions of this polymer.
Enhanced second harmonic generation in a silver–spacer–islands multilayer system
Authors: Bingler H. G. , Brunner H. , Klenke M. , Leitner A. , Aussenegg F. R. , Wokaun A.
Published: July 2002

Second harmonic radiation from a silver island film may be enhanced by two orders of magnitude in multilayer structures in which the film is placed on top of a silver mirror, with an interlying quartz spacer layer of variable height. The dependence of the enhancement on spacer thickness is distinctly different for s and p polarization of the fundamental beam; minimum enhancement for p-polarized excitation coincides with an enhancement maximum for s polarization. The origin of this phenomenon is discussed in terms of stratified medium theory: It arises from an amplification of the field in the island film layer, as a consequence of coherent superposition of the multiply reflected partial waves. The excitation of localized surface plasmons in the island film is taken into account in terms of an effective dielectric constant. In agreement with symmetry arguments, the produced second harmonic radiation is predominantly p-polarized, even for s-polarized excitation. Good agreement between the model calculations and the experimentally observed thickness dependence is achieved when this tensorial character of the SHG process is taken into account.
Tunneling in presence of coupling to other modes: Application to scanning tunneling microscopy
Authors: Sebastian K. L. , Doyen G.
Published: July 2002

Using path integral techniques, we investigate the problem of estimating the tunneling probability in the case where the tunneling particle is coupled to the medium through which it tunnels. We develop methods for estimating the tunneling probability in the cases where (1) the tunneling is elastically and the medium is at zero temperature and (2) the medium is at a finite temperature and the tunneling could happen inelastically. We point out that the second method makes clearer the basis for the approach of Persson and Baratoff [Phys. Rev. B 38, 9616 (1988)], in which they heuristically extended the method of Caldeira and Leggett [Phys. Rev. Lett. 46, 211 (1981)] to account for dynamical image effects in scanning tunneling microscopy. Our analysis, however, brings out a defect of their approach. It leads to an energy loss to the system of plasmons, even when there is no possibility of exciting plasmons, because the tunneling particle does not have enough energy to cause this. Therefore, for this problem, we suggest that one has to make use of a method which has the condition that the tunneling is elastically built into it. We demonstrate how this can be done and find that the dynamical effects are more important than pointed out by Persson and Baratoff. We have also investigated the tunneling of an electron through a liquid in between the electrode and the tip, a situation of great interest in the study of the electrochemical interface. It has been suggested that the solvent might play a dynamical role in the tunneling, leading to a lowering of the barrier height for tunneling. We find that the time spent by the electron inside the liquid is much shorter than the time needed for the orientational polarization of the liquid to respond. Consequently, the tunneling has to be thought of as occurring through a random distribution of stationary solvent molecules. The randomness leads to an enhancement of the tunneling probability, due to which the tunneling current increases with temperature. We have investigated the temperature dependence and found it to be rather weak. We conclude that coupling to the orientational polarization of the liquid cannot explain the large lowering of the barrier that has been observed in some experiments.
Structure and thermochemistry of hydrochlorous acid, HOCl
Authors: Francisco J. S. , Sander S. P.
Published: July 2002

The structure and heat of formation for hydrochlorous acid (HOCl) has been examined using post-Hartree methods which include second-order Mo/ller–Plesset theory perturbation and quadratic configuration interaction theory. The heat formation of HOCl is theoretically estimated to be −19.9±1 kcal mol−1 and compared well with the experimental determinations.
An analysis of the fractal properties of the surfaces of globular proteins
Authors: Fedorov Boris A. , Fedorov Boris B. , Schmidt Paul W.
Published: July 2002

The fractal properties of the surfaces of ten globular protein molecules have been investigated by calculations that made use of crystallographic data on the atomic coordinates of these proteins. On length scales from about 1.5 to at least 7.5 Å, the fractal dimensions Ds of the protein surfaces were found to lie between 2.10 and 2.17 and thus were not much greater than the value Ds=2 characteristic of a smooth surface. The calculated fractal dimensions Ds did not depend on the molecular mass, molecular diameter, biological function, or origin of the proteins.
Substrate-mediated dispersion interaction effects in the properties of a physisorbed gas
Authors: Elliott G. S. , Wei D. H. , Wu K. J. , Kevan S. D.
Published: July 2002

The theory of substrate-mediated dispersion interactions is applied to analyze a set of quasiequilibrium measurements of adsorption isobars and desorption isotherms of the CH4/Ag(011) physisorption system. The theory provides for the construction of an adsorbate intermolecular potential from the gas phase potential, with the spacing between the metal surface and the adsorbed layer as the sole adjustable parameter. The best fits to the kinetic and thermodynamic data yield a consistent intermolecular potential, with a well depth of approximately two-thirds of the free space value. The limited dynamic range of the measurements does not permit a determination of the form of the intermolecular potential. However, the good agreement of the theory with both data sets lends strong support for the quasiequilibrium model, and supports the proposition that the properties of physisorbed layers can be predicted using gas phase potentials while accounting for substrate-mediated dispersion interaction effects.
A theoretical model for copolymer–bilayer interactions
Authors: Li Weixiong , Gersappe Dilip , Balazs Anna C.
Published: July 2002

We develop a theory to model the interactions between an amphiphilic copolymer and a bilayer. The copolymer is represented as a Gaussian chain, which contains an alternating arrangement of hydrophobic and hydrophilic sites along the length of the chain. The bilayer is modeled as a hydrophobic layer embedded in a hydrophilic environment. We use the transfer matrix technique to determine the polymer density profiles and the phase diagram for this system. Two distinct phases are observed. In one phase, the copolymer is localized at the surface or within the bilayer. In the second phase, the polymer is unbound or ‘‘delocalized.’’ There is a continuous transition between the two phases. We also determine the scaling behavior for the density profiles. The scaling exponents agree with our analytical arguments. We discuss the implications of our findings on designing copolymers that can act as adhesives or macromolecular surfactants.
Molecular solvent model for an electrical double layer: Effects of ionic polarizability
Authors: Wei Dongqing , Torrie G. M. , Patey G. N.
Published: July 2002

The effect of ionic polarizability on properties of the electrical double layer is considered by extending a theory of Kusalik and Patey [J. Chem. Phys. 92, 1345 (1990)] to the case of an ion at a distance r from a charged macroion. The reference hypernetted-chain theory is solved for a fully molecular model of the double layer and the results are compared with previous results for an identical model without polarizability and with experimental data for double layers in alkali halide solutions. Polarizability is found to have a large effect on the differential capacitance at high surface charges and to make a substantial contribution to the experimentally observed asymmetry in this quantity. This effect is shown to have its origin, not in any structural change in the double layer, but in the contribution to the potential from the induced polarization of the ions themselves.
A thermodynamic basis for transport phenomena in viscoelastic fluids
Authors: Goldstein Patricia , García-Colín L. S.
Published: July 2002

A calculation for the longitudinal stress modulus in a viscoelastic medium is obtained introducing the stress tensor, its trace and the heat flux as additional variables, without requiring the specific form of the dynamic structure factor of the system. By using extended irreversible thermodynamics, we derive the time evolution equations for the state variables. These equations are used to obtain general wave vector and frequency dependent expressions for measurable properties of the system. We recover for a particular case results that have been derived previously in the literature.
Pattern formation of constrained acrylamide/sodium acrylate copolymer gels in acetone/water mixture
Authors: Li Yong , Li Chunfang , Hu Zhibing
Published: July 2002

Pattern formation and evolution in constrained acrylamide/sodium acrylate (PAAM/SA) gels have been investigated in acetone/water mixture. The constraint is achieved by cross linking the gel slabs onto a rigid substrate. All samples are initially kept in water with the hexagonal pattern develop on the surface before being immersed in the acetone/water mixture. Depending on the solvent composition and ionic strength of the sample, different patterns, i.e., hexagonal, grains, and bubbles, have been observed. These patterns are formed at acetone concentration below, near, and above the concentration at which the gel volume phase transition occurs. The wavelengths of hexagonal and bubble patterns are found to be the same, while that of the grain pattern is four times smaller. It is suggested that the shrinking patterns are formed due to the dense gel surface produced during the shrinking process.
Interpretation of new 13CD3F submillimeter-wave laser lines using high resolution infrared spectroscopy
Authors: Lummila Juha , Halonen Lauri , Lang P. T. , Schatz W. , Renk K. F. , Koivusaari Matti
Published: July 2002

A high resolution infrared spectrum of 13CD3F has been recorded in the wave number region 820–1350 cm−1 which covers four fundamentals ν2(A1), ν3(A1), ν5(E), and ν6(E). All strong and medium strong vibration-rotation lines have been assigned in terms of a model which treats simultaneously these strongly Coriolis coupled four fundamentals. Fifty-nine upper state parameters have been determined with the least squares method including 4390 infrared transitions as data. The standard deviation of the fit obtained is 0.56×10−3 cm−1. Ground state rotational parameters have been determined using ground state combination differences. Due to strong vibration–rotation interactions a large number of normally forbidden transitions have been observed which have allowed an accurate determination of the ground state axial rotational constant A0 and the centrifugal distortion constant DK0. The results of the analyzed infrared spectrum have made it possible to interpret many new laser emission lines from 13CD3F gas optically pumped with a continuously tunable high pressure pulsed CO2 laser. Making use of the coincidence of the 10 μm P and R branches of CO2 with the ν2, ν3, ν5, and ν6 bands, altogether 151 laser lines of 13CD3F between 10 and 61 cm−1 have been observed. These emission lines have been assigned as rotational transitions within the excited vibrational states and the ground vibrational state.
Electronic structure of BaLi. II. First observation of the Ba6,7Li spectrum: Analysis of the (2)2Π→X 2Σ+ system
Authors: D’Incan J. , Effantin C. , Bernard A. , Fabre G. , Stringat R. , Boulezhar A. , Vergès J.
Published: July 2002

The thermal emission at high temperature (1100 °C) of BaLi has been analyzed spectroscopically at high resolution with a Fourier transform spectrometer. Molecular emission in the infrared region is observed and is ascribed to a transition from the (2)2Π state towards the ground state X 2Σ+ of BaLi. These states (among several others) have been predicted from ab initio calculations [see part I, A. R. Allouche and M. Aubert-Frécon, J. Chem. Phys. 100, 938 (1994)]. Very good agreement is observed between theoretical predictions and experiment for the energy of the (2)2Π state and spectroscopic constants of both states. Both isotopic species Ba7Li and Ba6Li have been investigated and molecular parameters are derived from the analysis of the (2)2Π→X 2Σ+(0,0) band (the one analyzable band). No irregularities appear in the rotational structure.
Gas phase clustering of N2 molecules on to TiO+: Comparison with Ti+ and evidence for the octahedral structure of TiO+(N2)5
Authors: Daly George M. , El-Shall M. Samy
Published: July 2002

A striking difference in the clustering efficiency of Ti+ and TiO+ toward N2 or O2 has been observed in a laser vaporization high pressure mass spectrometric source. Evidence for the magic number n=5 within the sequence TiO+(N2)n is presented. The results are consistent with an octahedral structure for TiO+(N2)5.
Synchronization and spatiotemporal self-organization in the NO+CO reaction on Pt(100). II. Synchronized oscillations on the hex-substrate
Authors: Veser G. , Imbihl R.
Published: July 2002

The NO+CO reaction exhibits sustained rate oscillations on Pt(100) under conditions where the surface is mostly hex-reconstructed. These rate oscillations have been investigated in the 10−6 mbar range using photoemission electron microscopy as a spatially resolving method. During the rate oscillations which appear in a temperature-window ranging from 490 to 478 K, the surface reacts in a spatially homogeneous way. At the upper T-boundary of the oscillatory range, the oscillations develop via a Feigenbaum scenario leading from chaotic small amplitude oscillations at high T to regular period-1 oscillations at lower T. At the lower T-boundary of the oscillatory range, at T=478 K, target patterns appear, causing the collapse of the amplitude of the rate oscillations. As the temperature is lowered further, the parallel wave trains become increasingly irregular. Spiral waves form, and finally one observes only local reaction outbursts. A model for the synchronization mechanism in the rate oscillations is proposed based on the 1×1⇔hex-phase transition, while the origin of the chaotic oscillations in this reaction system is discussed in terms of a transition from unsynchronized to synchronized oscillations.
A discrete-continuum hybrid model for vibrational energy transfer at the gas–solid interface. II. The quantal evolution of coupled localized-collective motions
Authors: Vilallonga Eduardo , Rabitz Herschel
Published: July 2002

We analyze a new approach to the vibration of inhomogeneous surfaces whereby surface defects and their surroundings are properly treated as discrete atoms while the remainder of the solid is represented by an elastic continuum of equivalent mass density and elasticity with quantized vibrational waves. Such a hybrid treatment is aimed at describing defect-local motion while fully coupled to collective vibrational waves in a quantum-mechanical fashion appropriate to inelastic gas–surface scattering. We assess how the hybrid model reproduces the response of the surface by following the quantum-statistical moments of vibrational displacements as the collision progresses. The results suggest that the discrete-continuum approach can provide a powerful tool for describing collisional excitation of defect-laden surfaces within a fully quantal treatment of surface motion.
Critical-scaling theory of binary excess enthalpies and its use to determine liquid–liquid equilibrium phase compositions
Authors: Lim Kyung-Hee , Ferer M. , Smith Duane H.
Published: July 2002

From the Widom–Kadanoff scaling theory, predictions are made for the temperature and composition dependence of excess enthalpies for binary mixtures. The predictions are tested with one- and two-phase heats of mixing (or excess enthalpies) measured by flow calorimetry for the system C4H9OC2H4OH/H2O over the entire composition range and at temperatures from the lower consolute temperature (Tc) to about 20 °C above Tc. Compositions of conjugate phases at each temperature are obtained by solving for points of intersection between fits of the scaling equations to single-phase data and fits of equations for straight lines to two-phase data. The compositions thus obtained are in excellent agreement with literature data. For all but the very highest amphiphile concentrations, the agreement of theory with the data is excellent when a ‘‘new’’ order parameter is used.
Characterization of particles by modulated dynamic light scattering. II. Experiment
Authors: Hutchins Darrell K. , Dahneke Barton E.
Published: July 2002

In an earlier paper we described the theoretical foundations of modulated dynamic light scattering (MDLS) and indicated how these methods can be implemented in the characterization of particles. In this paper we illustrate the range of application of MDLS methods by describing eight types of MDLS experiments we have performed. In addition to illustrating the range of application of MDLS methods, the results of these experiments validate our theoretical predictions. The experiments were done with an MDLS apparatus in which the requisite modulation is produced by frequency-biasing two intersecting laser beams with acousto-optic modulators. Measurements were made by introducing a single sample particle into the intersection volume of the two beams and processing the scattered light signal from the particle. Data from these experiments typically provide detailed records of the translational and/or rotational Brownian motion for one or more single particles suspended in a fluid medium. Dynamic particle properties are inferred by comparing measured results with theoretical results based on models of Brownian motion. Described MDLS method experiments include (a) simultaneous measurement of the translational diffusion coefficient and velocity component of particles suspended in air; (b) simultaneous measurement of the translational and rotational Brownian motion of hematite ellipsoids and spindles with submicrometer dimensions suspended in water; (c) determination of the diameters and slip correction factors of micrometer-sized spheres suspended in air; (d) determination of the precision of the present MDLS apparatus for finding sphere diameters; (e) precise measurement of sphere diameters; (f) simultaneous measurement of the mass and friction coefficient of a particle suspended in air and verification of predicted effects of particle inertia on Brownian translation and rotation; (g) measurement of translational Brownian displacement distributions; and (h) determination of precision vs measurement time for an MDLS method.
Hartree–Fock operators to improve virtual orbitals and configuration interaction energies
Authors: Palmieri Paolo , Tarroni Riccardo , Rettrup Sten
Published: July 2002

The definitions of Hartree–Fock operators able to provide virtual orbitals more suited for correlation and excited electronic states and for configuration interaction (CI) treatments have been reviewed. From the comparisons, a simple procedure to improve these operators has emerged and discussed. In our approach, the sign of the pair and total electronic densities is changed to make the interelectron potential attractive for excited electrons. The orbitals generated from the modified operators have been compared to canonical HF orbitals by performing large scale CI computations on ground and excited states of the NO+ molecule improving the CI energies and the dipole moments for all states and the convergence properties of CI. Similarly, using truncated orbital subspaces, the ground state MP2 correlation energy becomes closer to the basis limit for this property.
High-resolution zero kinetic energy photoelectron spectra of para-n-propylaniline
Authors: Song Xinbei , Davidson Ernest R. , Gwaltney Steven R. , Reilly James P.
Published: July 2002

ZEKE spectra of propylaniline were recorded by exciting 13 vibronic levels in the S1 electronic state. All ZEKE spectra show well resolved vibrational structure of the anti and gauche cations. Adiabatic ionization potentials of the anti and gauche conformations were determined to be 59 717±3 cm−1 (7.4040 eV) and 59 793±3 cm−1 (7.4134 eV), respectively. A number of ring modes as well as several low-frequency torsional and bending chain modes have been identified. Spectra demonstrate that low-frequency chain modes are sensitive to the molecular conformation. Ab initio calculations were performed to understand the nature of these low-frequency chain modes. S1←S0 vibronic transitions involving anti and gauche conformations can easily be distinguished using the ZEKE method.
The formulation of quantum statistical mechanics based on the Feynman path centroid density. I. Equilibrium properties
Authors: Cao Jianshu , Voth Gregory A.
Published: July 2002

A formulation of quantum statistical mechanics is discussed in which the Feynman path centroid density in Feynman path integration is recast as the central statistical distribution used to average equilibrium and dynamical quantities. In this formulation, the path integral centroid density occupies the same role as the Boltzmann density in classical statistical mechanics. Therefore, the statistical ensemble of imaginary time path centroid configurations provides the distribution which is used to average the appropriately formulated effective operators and imaginary time correlation functions. An accurate renormalized diagrammatic perturbation theory for the centroid density and centroid-constrained imaginary time propagator will also be described with particular emphasis given to the mathematical advantages arising from the centroid-based formulation. The present paper is concerned with the calculation of equilibrium properties from the centroid perspective, while the companion paper describes a centroid-based formalism for calculating dynamical time correlation functions.
Effects of molecular fluctuations on chemical oscillations and chaos
Authors: Wu Xiao-Guang , Kapral Raymond
Published: July 2002

The effects of molecular fluctuations on chemical oscillations and chaos are investigated. The calculations are carried out using a reactive lattice-gas automaton which provides a mesoscopic description of the reactive dynamics. A specific chemical model, the Willamowski–Rössler reaction, is used to illustrate the effects. The applicability of mass-action rate laws and reaction-diffusion equations are considered and the character of the fluctuations in various dynamical regimes for both spatially-distributed and spatially-homogeneous systems are examined. The work provides information on the molecular origin of macroscopic, self-organized structures in far-from-equilibrium reacting systems.
Orthogonal polynomials in phase space and classical analogs to quantum eigenstates with an application to the transmission flux for the potential step
Authors: Torres-Vega Go. , Morales-Guzmán J. D.
Published: July 2002

We introduce a set of orthogonal polynomials in phase space with similar properties, and which can be reduced to the usual Hermite polynomials. Based on these polynomials, we develop a method that allows the finding of classical analogs to quantum eigenstates. This method is applied to the free particle scattered by a potential step and the transmission flux is calculated and compared with the quantum one.
A time-dependent formulation of the Born–Oppenheimer approximation to describe vibronic nonlinear optical effects
Authors: Das G. P.
Published: July 2002

A time-dependent analog of the Born–Oppenheimer approximation is derived. The resulting wave function furnishes an alternative route to obtain the vibronic corrections to the frequency-dependent nonlinear optical effects.
X-ray scattering and disordered structure of n-tetracosane in urea adducts. II. Averaged disorder, spatial correlation, and phase transition
Authors: Fukao Koji
Published: July 2002

Bragg reflections and diffuse scattering from n-tetracosane molecules included in urea adducts have been investigated from 136 to 355 K. Analysis of the Bragg reflections leads to mean-squared translational displacements uz along the chain axis and rotational displacement around the chain axis. The B factor (B=8π2〈u2z〉) in the Debye–Waller factor e−Bq2z/8π2 obtained from the meridional reflections shows a qz dependence, which cannot be accounted for within the harmonic approximation. The qz dependence could be explained by introducing anharmonic contributions to the Debye–Waller factor. From the distribution of the diffuse scattering intensity three different correlation lengths were obtained. The correlation length of the rotational displacement between molecules neighboring laterally increases anomalously as the temperature approaches the transition temperature, while the correlation length of the translational displacements between molecules neighboring laterally is independent of temperature. The correlation length of the translational displacements between molecules neighboring longitudinally is constant over a wide temperature range and even across the phase transition temperature.
Time and internal energy dependent fluorescence spectra of naphthol⋅water clusters
Authors: Knochenmuss Richard D. , Smith David E.
Published: July 2002

Time-resolved fluorescence spectra of 1-naphthol⋅(H2O)n clusters formed in a supersonic jet were measured under conditions of strong and weak cooling. Wavelength selectivity was used to excite very similar size distributions in both cases, thereby allowing controlled study of temperaturelike effects of internal energy in clusters. In both warm and cold clusters, long wavelength fluorescence from 1-naphtholate formed via an intermolecular excited state proton transfer (ESPT) reaction is observed, but this emission was significantly more red-shifted in warmer clusters. The fluorescence spectra of warmer clusters also shift strongly to the red after excitation, on a time scale of about 10 ns. Colder clusters showed no spectral shifts on this time scale. A weak solvent isotope effect was also observed. Similar clusters of 2-naphthol with water were not observed to undergo ESPT under any conditions. The time-dependent spectra indicate that ESPT in warm 1-naphthol⋅water clusters is not prompt, but continues on a ∼10 ns time scale, as does dynamic stabilization of previously reacted clusters. The ESPT rate is believed to be controlled by the rate at which the water relaxes around the naphthol, via interaction with two electronic excited states. The 10 ns and the two faster [R. Knochenmuss, G. R. Holtom, and D. Ray, Chem. Phys. Lett. 215, 188 (1993)] time scales now known in the spectral dynamics are discussed in terms of water solvation relaxation, and connected to the bulk by means of molecular dynamics simulations.
Spectroscopic analysis of the open 3d subshell transition metal aluminides: AlV, AlCr, and AlCo
Authors: Behm Jane M. , Brugh Dale J. , Morse Michael D.
Published: July 2002

Three open 3d subshell transition metal aluminides, AlV, AlCr, and AlCo, have been investigated by resonant two-photon ionization spectroscopy to elucidate the chemical bonding in these diatomic molecules. The open nature of the 3d subshell results in a vast number of excited electronic states in these species, allowing bond strengths to be measured by the observation of abrupt predissociation thresholds in a congested optical spectrum, giving D00(AlV)=1.489±0.010 eV, D00(AlCr)=2.272±0.009 eV, and D00(AlCo)=1.844±0.002 eV. At lower excitation energies the presence of discrete transitions has permitted determinations of the ground state symmetries and bond lengths of AlV and AlCo through rotationally resolved studies, giving r0″ (AlV, Ω″=0)=2.620±0.004 Å and r0″ (AlCo, Ω″=3)=2.3833±0.0005 Å. Ionization energies were also measured for all three species, yielding IE(AlV)=6.01±0.10 eV, IE(AlCr)=5.96±0.04 eV, and IE(AlCo)=6.99±0.17 eV. A discussion of these results is presented in the context of previous work on AlCu, AlNi, AlCa, and AlZn.
Stability of CdxSn1−xTe in rocksalt structure: A study of zero-flux surfaces and bonding character
Authors: Grosch G. H. , Freytag B. , Range K.-J. , Rössler U.
Published: July 2002

In the mixed crystal system CdxSn1−xTe the transition from a ten- (x=0) to an eight-electron system (x=1) is realized with a simultaneous change from rocksalt (SnTe) to zinc blende structure (CdTe). From previous calculations using density functional theory (DFT) [in the local density approximation (LDA) together with normconserving pseudopotentials and the virtual crystal approximation (VCA)] we know, that the rocksalt structure is stable up to x=0.93. As a possible reason for this stability we investigate the valence charge transfer connected with the formation of the solid by employing the concept of zero-flux surfaces, which has been used so far only for molecules. We find an increasing charge transfer when going from CdTe to SnTe in the rocksalt structure. In addition we analyze the bonding character of the individual valence bands and find partial antibonding for CdTe in zinc blende. Both support the stability of the rocksalt structure, which is found experimentally.
Observation of the PF2 radical by resonance enhanced multiphoton ionization spectroscopy
Authors: Howe J. D. , Ashfold M. N. R. , Hudgens J. W. , Johnson R. D.
Published: July 2002

We have observed nine new excited electronic states of the PF2 radical in the wave number range 50 000–71 000 cm−1 via the two photon resonance enhancements they provide in mass resolved multiphoton ionization spectroscopy. We also report ab initio calculations which yield optimized energies, geometries, and vibrational frequencies for the ground states of PF2 and of the PF+2 ion. Energetic considerations, and the observation that the frequencies of the ν1′ (symmetric stretch) and ν2′ (bending) modes in these excited states closely parallel those of the ground state ion, lead us to conclude that all nine excited states are Rydberg states belonging to series that converge to the ground state ionization limit. Polarization analyses and band contour simulations allow us to identify the electronic symmetries of the first two of these newly identified states (2B1 and 2A1, respectively) and to provide an estimate of the excited state geometries [r(P–F)≊1.49 Å, ∠F–P–F≊109°].