bluuebunny/crossref_metadata_2025 huggingface dataset:
Electronic state distributions of Kr+* formed by excitation transfer from He(2 3S) to Kr+(2P3/2) and Kr+(2P1/2) at thermal energy
Authors: Tsuji Masaharu , Kaneko Nobuo , Nishimura Yukio
Published: July 2002

The He(2 3S)+Kr+(4p5 2P3/2,1/20) excitation-transfer reaction has been studied by observing ultraviolet (UV) and visible emissions from Kr+* in the He flowing afterglow. The relative contribution of Kr+(2P3/20) and Kr+(2P1/20) to the excitation of Kr+* was examined by changing the [Kr+(2P1/20)]/[Kr+(2P3/20)] ratio with the addition of SF6 as a remover of the lower spin–orbit component. The He(2 3S)+Kr+(2P3/20) reaction gives 13 Kr+(5p,5p′,6s) levels in the 16.60–19.58 eV range, while the He(2 3S)+Kr+(2P1/20) reaction populates 26 Kr+(5p,5p′,5d,6s,6s″) levels in the 16.60–20.47 eV range. The electronic state distributions of individual Kr+* levels have been determined by taking account of radiative cascade for low lying electronic levels. The favored product levels are the 6s 4P5/2 level at 19.48 eV for both reactions. Since these product channels are 0.34 and 1.00 eV below the entrance channels, attractive entrance potentials are probably important. The total formation rate of Kr+* in the He(2 3S)+Kr+(2P1/20) reaction is larger than that in the He(2 3S)+Kr+(2P3/20) reaction by a factor of 2.4. No evidence of the formation of Kr+* by the He++Kr(3P2,00) charge-transfer reaction is found.
CH+5: The never-ending story or the final word?
Authors: Schreiner Peter R. , Kim Seung-Joon , Schaefer Henry F. , von Ragué Schleyer Paul
Published: July 2002

The closely related Cs(1), Cs(2), and C2v(3) structures of CH5+ have been reinvestigated with high level ab initio theory through the coupled cluster with single and double substitutions (CCSD), and CCSD with perturbatively included connected triple excitations [CCSD(T)] levels, employing a triple-ζ plus double polarization functions basis set, with f-functions on carbon as well as d-functions on the hydrogens [TZ2P(f,d)]. Vibrational frequencies have been computed up to TZ2P+f CCSD; the inclusion of f-functions on carbon is critical for the configuration interaction with single and double excitations (CISD) and coupled cluster methods using the triple-ζ basis sets. The changes in geometries between the CISD and CCSD levels are very small, e.g., the C–H bond lengths vary by at most 0.005 Å. Thus, the optimizations are essentially converged within theoretical limits. The differences in energies of 1, 2, and 3 decrease and essentially vanish at the most sophisticated levels when the zero point vibrational energy corrections are applied. Hence, there is essentially no barrier to complete hydrogen scrambling.
Elastic constants, interatomic forces, and equation of state of β-oxygen at high pressure
Authors: Abramson E. H. , Slutsky L. J. , Brown J. M.
Published: July 2002

The six independent elastic constants of β-oxygen have been measured over a pressure range extending from 6.0 to 9.5 GPa. Neither central forces between individual atoms, nor central forces augmented by the interactions between axial distributions of charge can give a reasonable account of the data. Force constant matrices were found which can account for the elastic data and the previously observed librational frequency. These matrices are based on general, short range forces with many-body interactions only among atoms contained in the same pair of molecules. Vibrational densities of states, distributions of individual-mode Grüneisen parameters, heat capacities, and the equation of state derived from the pressure dependence of the elastic moduli are presented.
Interface roughening and kinetics of poisoning in a surface reaction
Authors: Kang H. Chuan , Weinberg W. Henry
Published: July 2002

We investigate the roughening of the reaction front in a monomer–monomer surface reaction and determine its fractal dimension. The poisoning kinetics are also investigated. We find that the roughness of the interface obeys a power law, σ∼tβ, and that the reaction rate also obeys a power law, R∼tα−1. We conjecture that the relation α=2β holds for these exponents and find this conjecture is very well supported by our simulation results.
Transverse deuteron spin relaxation studies of a smectic liquid crystal polymer: Local motions, order director fluctuations, and the glass transition process
Authors: Reimer D. , Heaton N. , Schleicher A. , Müller K. , Kothe G. , Vilfan M.
Published: July 2002

Molecular dynamics of a main chain thermotropic liquid crystal polymer in the smectic A phase has been investigated using multipulse dynamic nuclear magnetic resonance (NMR) techniques. Transverse deuteron spin relaxation times T2ECP from quadrupole echo pulse trains (modified Carr–Purcell–Meiboom–Gill sequence) measured for deuterons in the aromatic rings of the mesogenic units are obtained as a function of pulse spacing τ sample orientation θN, and temperature. Just below the nematic–smectic A phase transition, the relaxation times exhibit a linear dispersion regime T2ECP ∼ τ−1 consistent with smectic director fluctuations. At lower temperatures, the dispersion step gradually disappears, indicating that faster molecular motions are the dominant transverse relaxation process. The observed anisotropy in T2ECP, measured at short pulse spacings, approximately follows the (sin4θN)−1 dependence expected for axial diffusion in a highly ordered medium. Analysis of the experiments is achieved employing a density operator treatment based on the stochastic Liouville equation. The intramolecular motion is identified with phenyl ring flips and is the fastest process studied, with correlation times varying from 10−10 to 10−7 s over the temperature range investigated.

Intermolecular (individual molecule) dynamics are somewhat slower and have been interpreted as rotational diffusion in an orienting potential. The correlation times for intermolecular motion exhibit non-Arrhenius behavior approaching the glass transition, following a temperature dependence described by the Williams–Landel–Ferry equation over six orders of magnitude. This result indicates a strong coupling of the intermolecular motion to the glass transition process. The slowest motion affecting transverse deuteron spin relaxation is assigned to smectic director fluctuations or undulation waves. Analysis of the T2ECP dispersion yields information concerning the viscoelastic properties of the polymer. At T=418 K, a splay elastic constant of K1=2×10−11N has been estimated. Using the experimentally accessible value for the long wavelength cutoff of the elastic modes, the root mean square fluctuation 〈θ20〉1/2 of the director is calculated to be 4°.
Multiphoton dissociative ionization of O2: Competition between dissociation and ionization in excited states
Authors: Yang S. , Hill W. T. , Dixit S. N.
Published: July 2002

A mass and energy resolved photoion spectrum of O2 induced by 12 ns 193 nm radiation with an intensity of 1010–1011 W/cm2 is presented. The analysis of the spectrum gives (1) the two-photon ionization cross section (≊1.1×10−54 cm4 s) of the X 3Σ−g of O2 and (2) the intensity dependent branching ratios between photoionization and predissociation of the B 3Σ−u state of O2. The two-photon ionization cross section of O2 is linked to our ab initio calculation of the three-photon ionization cross section (≊7.5×10−84 cm6 s2) of atomic oxygen.
Time-resolved double resonance study of J- and K-changing rotational collisional processes in CH3Cl
Authors: Pape Travis W. , De Lucia Frank C. , Skatrud David D.
Published: July 2002

Time-resolved double resonance spectroscopy using infrared pump radiation and millimeter-wave and submillimeter-wave probe radiation (IRMMDR) has been used to study rotational energy transfer (RET) in CH3Cl. A collisional energy transfer model using only five parameters for RET plus those needed for vibrational processes is shown to accurately model 350 IRMMDR time responses for two different pump states and 43 probe transitions covering a wide range of rotational states. Previous studies in this laboratory have revealed that J- and K-changing RET have vastly different characters in CH3F [J. Chem. Phys. 92, 6480 (1990)]. Both J- and K-changing RET were accurately modeled with four parameters—one for dipole–dipole collisions, two for the ΔJ scaling law, and one for the cumulative rate of K-changing collisions. As was found for CH3F, J-changing rotational collision rates in CH3Cl are modeled accurately by both the statistical power gap (SPG) law and the infinite order sudden approximation using a power law expression for the basis rates (IOS-P). However, in contrast to CH3F, where all IRMMDR time responses for K-changing collisions have the same shape, many time responses of CH3Cl states populated by K-changing collisions contain an additional early time feature (ETF) that varies with pump and probe states. Nonetheless, a simple generalization of the previously reported model for K-changing collisions is shown to account for all of the additional features observed in CH3Cl. Rather than observing a fixed temperature for K-changing collisions as was the case for CH3F, the temperature is found to be a function of time for CH3Cl. Moreover, the two new parameters this adds to the RET model are related to known physical quantities. A qualitative argument of K-changing collisions based on a classical picture is offered to explain the difference between the measured J- and K-changing state-to-state rates in CH3Cl.
Analysis of electron interaction and atomic shell structure in terms of local potentials
Authors: Gritsenko Oleg , van Leeuwen Robert , Baerends Evert Jan
Published: July 2002

The Kohn–Sham potential vs of an N-electron system and the potential veff of the Euler–Lagrange equation for the square root of the electron density are expressed as the sum of the external potential plus potentials related to the electronic structure, such as the potential of the electron Coulomb repulsion, including the Hartree potential and the screening due to exchange and correlation, a potential representing the effect of Fermi–Dirac statistics and Coulomb correlation on the kinetic functional, and additional potentials representing ‘‘response’’ effects on these potentials. For atoms several of these potentials have distinct atomic shell structure: One of them has peaks between the shells, while two others are step functions. In one of those step functions the steps represent characteristic shell energies. Examples of the potentials extracted from the optimized potential model (OPM) are presented for Kr and Cd. Correlation potentials, obtained by subtracting the exchange potential of the OPM from (nearly) exact Kohn–Sham potentials, are discussed for Be and Ne.
Electron tunneling through a dielectric barrier
Authors: Rostkier-Edelstein Dorita , Urbakh Michael , Nitzan Abraham
Published: July 2002

Electron tunneling through a dielectric barrier is considered with special attention given to questions relevant for STM experiments in dielectric liquids. The effect of the barrier dielectric response on the tunneling probability is studied using the effective Hamiltonian formalism for the polarization dynamics in the barrier, and two different theoretical approaches for the calculation of the tunneling probability: A generalization of the Bardeen’s formalism to inelastic tunneling and the quasiclassical of Brink, Nemes, and Vautherin as expanded by Sumetskii. Although based on different approximations, both approaches yield similar results in the slow barrier limit, where their ranges of validity coincide. The approach based on the Bardeen’s formalism relies on the adiabatic approximation and fails for fast barrier dynamics. The overall effect of the barrier dielectric response is to enhance the tunneling probability relative to the rigid barrier case. The enhancement factor is larger for thicker barrier, higher temperature and faster barrier dynamics. Both the elastic and inelastic components of the tunneling current show these trends in the relevant range of parameters.
Brownian dynamics in amorphous solids
Authors: Tsekov Roumen , Ruckenstein Eli
Published: July 2002

The dynamics of a mechanical subsystem interacting with an amorphous solid is studied. The Hamilton equations are transformed to a set of stochastic Langevin equations governing the random evolution of the coordinates of the subsystem particles. An explicit expression for the friction tensor is obtained which accounts both for the subsystem–solid interactions and for the thermal vibrations of the atoms of the amorphous solid. The possibility to calculate the diffusion coefficient of a Brownian particle in an amorphous solid is examined. Finally, a new approach for the description of the Brownian dynamics in liquids based on the results obtained for amorphous solids is proposed.
X-ray scattering and disordered structure of n-tetracosane in urea adducts. I. A model for the x-ray scattering pattern
Authors: Fukao Koji
Published: July 2002

The x-ray scattering pattern of a single crystal of n-tetracosane-urea adducts was investigated by photographic and counter methods. Two different kinds of diffuse scatterings were found in addition to Bragg reflections; s-diffuse scattering and d-diffuse scattering. The s-diffuse scattering exists on the layers corresponding to the molecular length of n-tetracosane and its width along the c* axis is as sharp as that of the Bragg reflections. The d-diffuse scattering exists on the layers corresponding to the repeating period of C2H4 units and the width is broad. The two-dimensional distribution normal to the c* axis of the intensity of the diffuse scattering shows maxima on hexagonal reciprocal lattice points. A model is proposed on the assumption that the n-alkane molecule has a translational displacement along the chain axis and a rotational displacement around the chain axis. The model can reproduce the observed x-ray scattering pattern and gives us three different spatial correlation lengths.
Mercury 61P1 relaxation, singlet to triplet transfer under collisions with molecular hydrogen
Authors: Bras N. , Jeannet J. C.
Published: July 2002

Quenching of Hg(61P1) and Hg(63P0,1,2←61P1) intermultiplet transfer induced by collisions with H2 molecules have been studied. The 61P1 state was excited by a 185 nm radiation generated by two photon resonant four wave sum mixing in Hg vapor, the 61P1 and 61P0,1,2 state populations were probed by laser induced fluorescence. The Hg(61P1) quenching rate constant has been found equal to 6±0.9×10−10 s−1 cm3 in good agreement with a previous determination. The ratio of the 63P2←61P1 and 63P1←61P1 transfer rate constants has been determined; no transfer to the 63P0 state was observed.
Fragmentation of methyl chloride photoexcited near Cl (2p) by mass spectrometry
Authors: Thissen Roland , Simon Marc , Hubin-Franskin M.-J.
Published: July 2002

The evolution of the fragmentation pathways of the methylchloride around the Cl 2p edge has been studied by use of charge separation mass spectrometry. Some fragmentation patterns are discussed in the frame of rapid fragmentation of the neutral and dissociation pathways characteristic of singly or multiply charged species. The correlation of the evolution of the charge separation spectra with the initial excitation process is used to give a definitive attribution to the pre-edge features present in the absorption spectrum.
Shell boundaries in rare earth atoms and tripositive ions using average local electrostatic potential
Authors: Krishnaveni R. , Sen K. D.
Published: July 2002

It is shown that the locations of the characteristic topological features in the average local electrostatic potential defined by the ratio of the electrostatic potential V(r) and the spherically averaged electron density ρ(r) can be identified with the intershell boundaries in the lanthanoid atoms and their tripositive ions. Numerical tests carried out using the nonrelativistic numerical Hartree–Fock densities establish the validity of the Politzer–Parr partitioning of the core-valence region for the heavier atoms and ions.
The role of adsorbate–adsorbate interactions in the rate oscillations in catalytic CO oxidation on Pd (110)
Authors: Hartmann N. , Krischer K. , Imbihl R.
Published: July 2002

The CO+O2 reaction on Pd(110) exhibits kinetic oscillations above pO2≊ 10−3 Torr and bistability below this pressure. Based on the reversible formation of subsurface oxygen and the Langmuir Hinshelwood mechanism of catalytic CO oxidation, a mathematical model had been developed which described the occurrence of rate oscillations and most of the qualitative features of the oscillations. This model, however, failed to reproduce the change from bistability to oscillatory behaviour with increasing pO2. In this paper we demonstrate that by introducing repulsive interactions between COad and Oad, the subsurface oxygen model correctly reproduces the experimentally determined stability diagram in pO2,pCO parameter space. The effect of the repulsive interactions is to reduce the activation barrier for penetration of chemisorbed oxygen into the subsurface region, thus facilitating the formation of subsurface oxygen at high coverages. For the improved subsurface oxygen model a bifurcation analysis has been conducted in pO2,pCO parameter space. The influence of the constants in the model has been analyzed likewise with bifurcation theory.
Application of the elongation method to the calculation of electronic structures of the interface and the local defect states in a polymer: An analysis of the periodicity in the electronic states of a nonperiodic polymer by using the cluster-series calculation
Authors: Mitani Masaki , Imamura Akira
Published: July 2002

We have developed an approach at the Hartree–Fock level by which it is possible to calculate the electronic structures of large polymers with or without periodic sequences systematically. This elongation method is based on the concept of a cluster-series calculation which means the successive connection of cluster molecules at the molecular orbital level in approximating a large polymer as a cluster molecule. It has already been reported that we can extract the periodic condition of the electronic states within the series of extended clusters by using the cluster-series model. Recently, we tried to introduce the elongation method into the program package of semiempirical molecular orbital methods mopac. In the present paper, we report results of applications to the calculations of three polymer systems by using AM1 parameters, that is, the first system is the periodic polymer, the second is the interface between two blocks in a polymer chain, and the third is the local defect within a periodic polymer. In calculations of periodic polymers, clusters of polyethylene, polytetrafluoroethylene, polyacetylene, or polydifluoroacetylene were elongated in one direction, and the interfaces between the above polymer blocks with ethylene- or acetylene-type chain were dealt with by the two-directional elongation method. Also, the solitonic structures with one plus or minus charge within polyacetylene chain were created in elongation calculations of the bidirectional extension as models for the local defect in a periodic polymer. Moreover, we discussed periodic states of electronic structures in these systems from cluster-series calculations.
Many-body effects and resonances in universal quantum sticking of cold atoms to surfaces
Authors: Bittner Eric R. , Light John C.
Published: July 2002

The role of shape resonances and many-body effects on universal quantum sticking of ultracold atoms onto solid surfaces is examined analytically and computationally using an exactly solvable representation of the Dyson equation. We derive the self-energy renormalization of the transition amplitude between an ultracold scattering atom and the bound states on the surface in order to elucidate the role of virtual phonon exchanges in the limiting behavior of the sticking probability. We demonstrate that, to first order in the interactions for finite ranged atom–surface potentials, virtual phonons can only rescale the strength of the atom–surface coupling and do not rescale the range of the coupling. Thus, universal sticking behavior at ultralow energies is to be expected for all finite ranged potentials. We demonstrate that the onset of the universal sticking behavior depends greatly on the position of the shape resonance of the renormalized potential and for sufficiently low energy shape resonances, deviations from the universal s(E)∝√E can occur near these energies. We believe that this accounts for many of the low energy sticking trends observed in the scattering of submillikelvin H atoms from superfluid 4He films.
Disorder induced enhancement of the third order optical nonlinearity in a conjugated polymer
Authors: Hambir S. A. , Blanchard G. J. , Baker G. L.
Published: July 2002

We report on the relationship between material disorder and nonlinear optical response for a conjugated polymer. Inverse Raman scattering, the technique used here, is sensitive to the transition cross sections of both the purely electronic (Sv=01↔Sv=00) and vibronic (Sv=01↔Sv=10) transitions accessed, and both of these quantities are related to the extent of disorder in the polymer backbone. We have verified these morphology dependencies using crystalline and amorphous samples of the polydiacetylene poly(4BCMU). The magnitude of the nonlinear response per backbone repeat unit in the amorphous material is comparable to that of the crystalline form because of the large potential well displacement between the ground and excited electronic states characteristic of the disordered material. This increased potential well displacement compensates for the nonlinear response lost to the reduced macroscopic polymer alignment associated with the two-dimensionally isotropic spin cast film.
Gas phase reactions of N2O5 with NO−2(H2O)n=0–2, NO−3(H2O)n=1,2, and NO−n=2,3HNO2
Authors: Wincel H. , Mereand E. , Castleman A. W.
Published: July 2002

The reactions of N2O5 with the NO−2(H2O)n=0–2, NO−3(H2O)n=1,2, and NO−n=2,3HNO2 ions were studied in a flow-tube apparatus in a He-buffer gas at several temperatures within the range 167–298 K and at a pressure of 0.28 Torr. All these ions were observed to react quite efficiently with N2O5, giving rise to the main product ion NO−3HNO3. This finding is of atmospheric interest since these reactions may occur in the atmosphere and are potentially relevant to the chemistry of reactive nitrogen species involved in ozone destruction. These results also have implications for the derivation of the HNO3 concentration in the upper earth’s atmosphere from ion composition measurements. The rate constants of the observed reactions were determined and mechanisms are proposed which account for the findings.
The dissociative recombination of OH+
Authors: Guberman Steven L.
Published: July 2002

Theoretical quantum chemical calculations of the cross sections and rates for the dissociative recombination of the v=0 level of the ground state of OH+ show that recombination occurs primarily along the 2 2Π diabatic route. The products are O(1D) and a hot H atom with 6.1 eV kinetic energy. The coupling to the resonances is very small and the indirect recombination mechanism plays only a minor role. The recommended value for the rate coefficient is (6.3±0.7) ×10−9×(Te/300)−0.48 cm3/s for 10<Te<1000 K.
Microwave electronic spectrum of the He+2 ion
Authors: Carrington Alan , Pyne Christopher H. , Knowles Peter J.
Published: July 2002

We have observed and assigned seven microwave and millimeter wave lines arising from rovibronic components of the A 2Σ+g←X 2Σ+u electronic spectrum of the He+2 ion; this is the first observation of any spectrum of the homonuclear 4He4He+ species. The vibration-rotation levels involved in our observations all lie within 8 cm−1 of the lowest degenerate He(1S)+He+(2S) dissociation limits for both electronic states. We use an ion beam technique in which weakly bound levels dissociate in an applied electric field to produce He+ fragments. These fragments are separated from all other ions with an electrostatic kinetic energy analyzer, and microwave transitions are detected as changes in the He+ fragment current arising from resonant population transfer. Four of the transitions are detected using a single microwave frequency; the remaining three are measured by means of a microwave–microwave double resonance method. The assignment of the spectrum is achieved by means of ab initio electronic structure calculations, made within the Born–Oppenheimer approximation. The agreement between experiment and theory is excellent and leads to an accurate characterization of the He...He+ 2Σ+g charge/induced-dipole state.
Microemulsions as macroelectrolytes
Authors: Halle Bertil , Björling Mikael
Published: July 2002

Water-in-oil microemulsions, composed of discrete aqueous droplets dispersed in a continuous oil medium, constitute a special class of electrolyte solutions. Such macroelectrolytes are analogous to conventional electrolyte solutions in most respects, with the notable difference that, in a microemulsion, the ionic (droplet) charge is not fixed but depends on the droplet interactions. Describing the microemulsion as a primitive-model electrolyte mixture with ions of variable charge and evaluating the statistical mechanics within the mean-spherical approximation (MSA), we construct a self-consistent theory of charge fluctuations and droplet interactions in ionic microemulsions. The droplet charge distribution is calculated as a function of the size, shape, polydispersity, and volume fraction of the droplets. We argue that the net droplet charges can have a decisive influence on microemulsion structure, especially at the higher volume fractions where clustering and spinodal decomposition are observed. At lower volume fractions, where the MSA treatment should be quantitatively accurate, the Coulomb interaction between charged droplets has no effect on the structure factor deduced from scattering data.
Incorporation of solvent effects into density functional calculations of molecular energies and geometries
Authors: Andzelm Jan , Kölmel Christoph , Klamt Andreas
Published: July 2002

In this paper, we present the implementation of the ‘‘conductorlike screening model’’ (COSMO) into the density functional program DMol. The electronic structure and geometry of the solute are described by a density functional method (DFT). The solute is placed into a cavity which has the shape of the solute molecule. Outside of the cavity, the solvent is represented by a homogeneous dielectric medium. The electrostatic interaction between solute and solvent is modeled through cavity surface charges induced by the solvent. The COSMO theory, based on the screening in conductors, allows for the direct determination of the surface charges within the SCF procedure using only the electrostatic potentials. This represents the major computational advantage over many of other reaction field methods. Since the DMol/COSMO energy is fully variational, accurate gradients with respect to the solute coordinates can be calculated for the first time, without any restriction on the shape of the cavity. The solvation energies and optimized molecular structures are calculated for several polar solutes. In addition, the trends in basicity of amines and the relative stabilities of molecular conformers are studied. Our results suggest that for neutral solutes, agreement between calculated and experimental solvation energies of better than about 2 kcal/mol can be achieved.
Comparison of experimental and computed vibrationally inelastic rate constants for Li2 A 1Σ+u–Ne collisions
Authors: Gao Yunxiao , Stewart Brian
Published: July 2002

We report measurements of level-resolved rate constants for inelastic scattering in the Li2 A 1Σ+u–Ne system, with initial molecular quantum numbers vi=2 and ji=30. The measurements include rotationally and vibrationally inelastic rate constants with ‖Δv‖≤2. Comparison is made with rate constants computed from classical trajectories on a recently reported ab initio potential energy surface. Our work constitutes the first comparison between experiment and calculation on an accurate potential for level-resolved vibrationally inelastic scattering.
Theory of diatomic photodissociation involving several atomic term limits: Quantum interference and product control in OH photodissociation
Authors: Lee Sungyul
Published: July 2002

A quantum mechanical theory is described for diatomic photodissociation processes to atomic fine structure states for which more than one atomic term limit must be explicitly considered. The theory is employed to treat the photodissociation of OH molecule. Two frame transformation matrices are constructed and incorporated, for the first time, to describe the correlations between two oxygen terms [O(3P) and O(1D)] and the adiabatic Born–Oppenheimer states. We find that very interesting dynamics results from the quantum interferences between electronic states. Near the dissociation threshold to O(3P), asymptotic interactions between asymptotically degenerate states correlating to O(3P) term are shown to manifest as multichannel resonances. At energies between thresholds to O(3P) and O(1D) terms, quantum interferences between A 2Σ+ and 2Σ− states are predicted to result in asymmetric resonances. Partial cross sections to the triplet oxygen fine structure states O(3Pj, j=0,1,2) exhibit different degrees of asymmetry due to the combined effects of the quantum interference between A 2Σ+ and 2Σ− states crossing in the Franck–Condon region, and the asymptotic interactions among 4Σ−, 2Σ−, and 4Π states correlating to O(3P). Consequently, the branching ratios of O(3Pj, j=0,1,2) exhibit strong variations across the asymmetric resonances, suggesting the possibility of controlling the product distributions by tuning at the excitation wavelengths across a single asymmetric resonance in one-photon process. Interference between the dissociative 2Δ and 2 2Π states, correlating with O(1D) term, are shown to give rise to highly oscillatory variations of the dissociation cross sections to O(1D) at energies above the threshold to O(1D).
The study of translational excitation of CO2 produced from CO oxidation on Pd using high resolution infrared chemiluminescence spectroscopy
Authors: Wei Cong , Haller Gary L.
Published: July 2002

The translational energy of CO2 produced from CO oxidation on Pd foil at 600 K was studied using high resolution infrared chemiluminescence spectroscopy. Rotational structure of certain vibrational transitions was fully resolved using a Fourier transform infrared (FTIR) spectrometer operating at 0.006 cm−1 resolution. The Doppler line broadening of each rovibrational transition was also resolved, and information on translational energy of CO2 was therefore obtained. It was observed that the translational excitation of CO2 was independent of the specific rovibrational state. The sensitivity to angular and velocity distribution of the translational energy of CO2 was also evaluated.
Solid–solid phase transitions in n-alkanes C23H48 and C25H52: X-ray power diffraction study on new layer stacking in phase V
Authors: Nozaki Koji , Higashitani Naoki , Yamamoto Takashi , Hara Tetsuhiko
Published: July 2002

The solid–solid phase transitions and the crystal structures of odd n-alkanes, n-C23H48, and n-C25H52, were investigated by x-ray powder diffraction. The phase transitions, I→V→RI for n-C23H48 and I→V→IV→RI for n-C25H52, were observed, where phases I, V, IV are the low-temperature ordered phases, and the phase RI is the rotator phase. The crystal structure of phase V was determined by the Rietveld profile refinement method. Phase V is orthorhombic (Pbnm). New molecular layer stacking appears in phase V, while the lamellar structure and the lateral packing of molecules are same as those in phase I and phase IV. The solid–solid phase transitions below the rotator phase transition of odd n-alkanes found to be characterized by the changes in molecular layer stacking are considered to be caused by the increased disorder in the layer surface.
CO on Pt(335): Electric field screening on a stepped surface
Authors: Wang Hong , Tobin R. G. , Lambert David K. , Fisher Galen B. , DiMaggio Craig L.
Published: July 2002

We compare CO’s response to electric fields at edge and terrace sites on the stepped Pt(335) surface. The comparison is made at zero frequency and at the frequency of the C–O stretch vibration. Atop-bonded CO is observed with reflection–absorption ir spectroscopy (RAIRS), electroreflectance vibrational spectroscopy (EVS), and high-resolution electron energy loss spectroscopy (HREELS). Coadsorbed H or O is used to control the CO adsorption site. With both RAIRS and HREELS the measured vibrational cross-section of atop CO at the step edge is 2.0±0.2 times greater than for CO on the terrace. The vibrational Stark effect—the change of CO’s vibrational frequency with externally applied electrostatic field—is also a factor 2.0±0.2 larger for atop CO at the step edge than it is for atop CO on the terrace. Because the vibrational cross section varies as the square of the field while the Stark effect is linear, a model in which CO responds to the screened local field at a single point cannot simultaneously explain the observed site dependence of both the vibrational Stark effect and the vibrational cross section. The most plausible explanation is that CO’s response to electric fields is nonlocal. A simple model is presented that can account for our data.
The photoionization of large pure and doped helium droplets
Authors: Fröchtenicht R. , Henne U. , Toennies J. P. , Ding A. , Fieber-Erdmann M. , Drewello T.
Published: July 2002

The photoionization of neutral liquid helium droplets (mean particle number 〈N〉=102–107) was studied using synchrotron radiation at photon energies ranging from 15 to 30 eV. Mass spectra as well as total and mass selective ion yields were measured as a function of the photon energy for different droplet sizes. The experiments indicate that ionization occurs not only by a direct process at photon energies above the atomic ionization potential but also at energies below the threshold by an autoionization process. The latter ionization mechanism proceeds via the electronically excited states of the neutral droplet, which show a strong neutral droplet size dependence. For large neutral droplets HeN(〈N〉≳104) retarding field measurements established that a predominant part of the total ion yield results from larger cluster ions He+k(k≳103). These measurements also show that a decay by fluorescence emission is much more probable than one by ionization following the photoexcitation process. In droplets with embedded SF6 molecules these are ionized indirectly by Penning ionization via excitons which leads to a large ion signal on the mass of the embedded species. No evidence for direct photoionization of the impurities was found.
Ab initiomolecular dynamics studies on volume stability of Voronoi polyhedra under pressures in a metal glass
Authors: Aoki Masaru I. , Tsumuraya Kazuo
Published: July 2002

We study volume stability of Voronoi polyhedra under hydrostatic pressures in a sodium glass. We optimize the atom positions under the pressures by an ab initio molecular dynamics method with an orbital-free density functional. The number of atoms in the supercell is 128. The change of the volumes is insensitive to pressure for the Voronoi polyhedra with smaller volumes. We introduce a method to evaluate the average charge density around individual atom. The average electron charge density around individual atom increases with decreasing Voronoi volume. The volume change of Voronoi polyhedron with signature (0,0,12,0) is the most stable to the applied pressures. The density around the atoms with the signature (0,0,12,0) is the greatest among the signatures.
Effects of the interactions between dissociative states and control of the product branching ratios in predissociation
Authors: Lee Sungyul
Published: July 2002

The influence of the interactions between the dissociative states on the product branching ratios in predissociation is theoretically analyzed. We adopt the OH molecule as a model system and treat indirect dissociation processes with quantum interferences from the direct dissociation pathways eliminated. Various hypothetical coupling schemes between the bound electronic state and the dissociative states, and those among the dissociative states are employed. When a single dissociative state is involved in the dissociation with no interactions among the asymptotically degenerate states, recoil limit branching ratios of the triplet oxygen fine structure components O(3Pj, j=0,1,2) are attained at all energies. When a dissociative state, coupled with the bound state, is allowed to interact with other dissociative states correlating to the same atomic term, the product branching ratios approach recoil limit values only at a high energy limit. Predissociation through more than one dissociative state, interacting with each other, results in branching ratios that highly depend on the vibrational and angular momentum quantum numbers of the bound electronic state at energies below the dissociation limit to O(1D). Above the threshold to O(1D), the interactions between the dissociation channels give rise to highly oscillating branching ratios as a function of excitation energy. These findings are discussed in connection with the recent experiment of Gordon and co-workers [J. Chem. Phys. 103, 6811 (1995)] on the spin–orbit control in the predissociation of HCl.
Squeezed states in the trimer problem
Authors: Eiermann H. , Wagner M.
Published: July 2002

In the present work we study unconventional (‘‘squeezed’’) exciton–phonon states in the trimer model. These quasifree states, which do not undergo self-trapping, are characterized by a nearly vanishing lattice distortion and a stiffening in the phonon part as well as a large amount of kinetic energy in the excitonic subsystem. In contrast, the ‘‘conventional’’ exciton–phonon states are characterized by a strong lattice distortion and physically amount to a self-trapping of the exciton. In the trimer model a third type of exciton–phonon states have been found, which are a kind of ‘‘dimerized’’ states, where self-trapping has taken place only partially. The different types of states are analyzed and discussed.
Theory of binary mixtures of a flexible polymer and a liquid crystal
Authors: Matsuyama Akihiko , Kato Tadaya
Published: July 2002

A simple model is presented to describe the phase behavior in binary mixtures of a flexible polymer and a liquid crystal. By using the incompressible approximation to the Onsager theory which combined both the excluded volume interactions between the liquid crystals and the attractive interaction due to the alignment of the liquid crystals, we obtain the free energy of mixing of the binary mixtures. The derived free energy consists of two terms: the free energy of mixing of Flory–Huggins type for polymer blends and the free energy change due to the alignment of the liquid crystals. We predict the nematic–isotropic phase separation and the isotropic–isotropic one with a critical point in terms of the Flory–Huggins and Maier–Saupe interaction parameters. The results are compared with the observed phase diagrams. We also discuss the phase separation in solutions of rigid-rodlike molecules.
Excited state absorption and fluorescence line narrowing studies of Cm3+ in LuPO4
Authors: Murdoch K. M. , Edelstein N. M. , Boatner L. A. , Abraham M. M.
Published: July 2002

Laser selective excitation, fluorescence line narrowing, and excited state absorption techniques have been used to investigate the electronic-energy-level structure of the 5f7 ion Cm3+ in the host crystal LuPO4. Crystal-field levels have been determined up to 35 700 cm−1 for the principal D2d symmetry site. Eighty levels have been assigned and fitted to a parametric Hamiltonian with an rms deviation of 28.4 cm−1. Inhomogeneous broadening of the electronic transitions and the small 9.5 cm−1 splitting of the nominally 8S7/2 ground multiplet are responsible for satellite lines reported previously. Time resolved fluorescence line narrowing was used to observe energy transfer between different subsites of the intrinsic Cm3+ center. It was found that electric-dipole interactions mediate this energy transfer.
Visible to near-infrared femtosecond dynamics of photoexcited gap states in substituted polyacetylenes
Authors: Takeuchi Satoshi , Masuda Toshio , Kobayashi Takayoshi
Published: July 2002

Visible to near-infrared transient spectra were measured for thin films of three substituted polyacetylenes with a time-resolution ≤300 fs. A hot self-trapped exciton (STE) and an oppositely charged, spatially confined soliton–antisoliton pair were temporally and spectrally resolved in detail, which reveals a formation process of the localized excitations with geometrical relaxation taking place within a subpicosecond time scale. The hot STE showing an exponential decay (τ=115–135 fs) has a spectral peak in the energy region of 1.4–1.5 eV. The transition energies from the hot STE both to continuum state and to a biexciton state are discussed with referring to strength of the Coulomb interactions between the conjugated π electrons. The soliton–antisoliton pair which decays with a power-law behavior has a dual-peaks spectrum below the band gap energy and the two peak energies vary depending on the polymers. A π-conjugation length (λc), a soliton size (ξ), and a distance (d) between the soliton and antisoliton were evaluated based on the experimental results for each polymer. The distance was found to be nearly proportional to the conjugation length with a ratio of d/λc=0.4, indicating that an overall size of the soliton–antisoliton pair approximatedly given by 2ξ+d is limited just within a segmented conjugation chain. The decay kinetics of photoexcitations in both degenerate and nondegenerate systems has been discussed together using an adiabatic potential surface in a configuration space.
Characterization of spin–orbit autoionizing Rydberg states excited via one-photon absorption from the F 1Δ2 Rydberg state of HBr
Authors: Wales N. P. L. , Buma W. J. , de Lange C. A. , Lefebvre-Brion H.
Published: July 2002

Rotationally and parity resolved excitation spectra of autoionizing Rydberg states of HBr in the energy region between the 2Π3/2 and 2Π1/2 ionic thresholds have been obtained in a double resonant excitation scheme via single rotational levels of the vibrationless F 1Δ2 Rydberg state. A cursory examination of these spectra reveals the presence of s, p, d, and f Rydberg series. Apart from the f series, which show almost Hund’s case (e) coupling, these series clearly exhibit an angular momentum coupling scheme intermediate between Hund’s case (c) and (e). As a result it is difficult to assign them as converging upon specific ionic rotational thresholds. A detailed analysis of the excitation spectra has consequently been performed employing multichannel quantum defect theory calculations, allowing for a determination of the quantum defects of the Hund’s case (a) basis states and the relevant transition moments, and, concurrently, the assignment of nearly all the observed autoionizing resonances.
Resonance-enhanced multiphoton ionization spectroscopy of X 1Σ+ and a 3Π carbon monoxide using electron stimulated desorption as a source for rovibronically excited species
Authors: Wurm S. , Feulner P. , Menzel D.
Published: July 2002

Electron stimulated desorption from CO monolayers chemisorbed on transition metal surfaces and from condensed CO layers were utilized as new sources for the production of nonthermal rovibrational distributions of CO probed by resonance-enhanced multiphoton ionization spectroscopy (REMPI). Highly vibrationally excited ground state CO molecules were studied by (1+1)-REMPI via the A 1Π and D′ 1Σ+ intermediate states, and metastable CO via the b 3Σ+ and c 3Π intermediate states. Rotationally resolved (1+1) spectroscopy via A 1Π (v′≥20) allowed the verification of the intermediate term energies, including the existence of a potential barrier for the A 1Π state. (1+1) spectroscopy via D′ 1Σ+ is shown to provide the possibility to directly probe the D′ 1Σ+ potential curve. Additional spectral features accompanying the b 3Σ+←a 3Π (1+1) spectra which cannot be explained by known perturbations were found. In gas phase (2+1) spectroscopy via the B 1Σ+ and C 1Σ+ intermediate states, O- and S-branches could be detected even with linearly polarized light at very low CO densities (some 10−6 Pa).
Electron-spin resonance studies of the titanium cation (Ti+,3d3,4F) in rare gas matrices at 4 K: A crystal field interpretation
Authors: Knight Lon B. , Keller Keith A. , Babb Robert M. , Morse Michael D.
Published: July 2002

Electron-spin resonance studies of laser-ablated titanium metal isolated in neon and argon display an intense feature which exhibits a symmetric, narrow line and a large matrix-dependent g shift. On the basis of a number of experiments, this is assigned to a matrix isolated 3d3,4F Ti+ ion in an octahedral matrix environment. Although the ground state of the gas-phase Ti+ ion is 3d24s1,4F, the assignment to the 3d3,4F state is supported by the small hyperfine structure which is observed. The neon magnetic parameters are: g=1.934(1) and A(47Ti)=64(1) MHz; for argon, g=1.972(1) and A=56(1) MHz. This unusual stabilization of an excited atomic state by a rare gas matrix is consistent with ab initio studies, and has been previously found for atomic nickel. A crystal-field study of the expected behavior of a d3,4F ion isolated in a tetrahedral, octahedral, or cuboctahedral environment supports the assignment to an octahedral Ti+(Rg)6 species, and using the atomic spin–orbit parameter, ζ permits accurate values of Dq to be derived from the measured g values. Finally, it is also noted that for small values of Dq/(Dq+ζ), or for a d3,4F ion in a tetrahedral environment, an as yet unobserved, unequal Zeeman splitting of the fourfold degeneracy occurs, causing a departure of the Zeeman energies from the standard formula of EZeeman=βeH0gM, with M=±3/2, ±1/2. For these situations it becomes necessary to define two values of g, corresponding to the more strongly (g3/2) and less strongly (g1/2) affected Zeeman levels, respectively.
An internal coordinate quantum Monte Carlo method for calculating vibrational ground state energies and wave functions of large molecules: A quantum geometric statement function approach
Authors: Tuzun Robert E. , Noid Donald W. , Sumpter Bobby G.
Published: July 2002

An internal coordinate quantum Monte Carlo (ICQMC) method using importance sampling is illustrated for a 100 atom model polyethylene chain. Importance sampling with an internal coordinate guiding wave function yields smoother, more physically reasonable wave functions and lower ground state energies than Cartesian importance sampling, in good agreement with normal coordinate analysis results. A novel geometric statement function (GSF) method for economizing expressions involving first and second derivatives of stretch, bend, and torsion internal coordinates by up to 2 orders of magnitude allows QMC calculations to be performed even for large molecules in reasonable times on standard workstations. The ICQMC method with quantum GSF is eminently suitable for large molecules with complicated, strongly coupled potential energy surfaces such as polymer chains.
On the pair approximation method in a nonreactive catalytic system
Authors: Cortés Joaquín , Puschmann Heinrich , Valencia Eliana
Published: July 2002

The nonreactive catalytic system made up of the reduction of NO by CO on a square lattice of sites is studied by means of dynamic equations in the pair approximation, showing some characteristics and limitations of the model in systems with a nontrivial behavior.