bluuebunny/crossref_metadata_2025 huggingface dataset:
Fourier transform emission spectroscopy of new infrared systems of LaH and LaD
Authors: Ram R. S. , Bernath P. F.
Published: July 2002

The electronic emission spectra of LaH and LaD have been investigated in the 3 μm–700 nm spectral region using a Fourier transform spectrometer. The molecules were excited in a lanthanum hollow cathode lamp operated with neon gas and a trace of hydrogen or deuterium. The bands observed in the 1 μm–3 μm region have been assigned into two new electronic transitions; A 1Π–X 1Σ+ and d 3Φ–a 3Δ. The LaH bands with origins at 4533.5593(8) cm−1 and 4430.1916(13) cm−1 have been assigned as the 0-0 and 1-1 bands of the A1Π–X 1Σ+ transition. The rotational analysis of these bands provides the following principal molecular constants for the ground X 1Σ+ state, Be=4.080 534(80) cm−1 and αe=0.077 39(10) cm−1 and re=2.031 969(20) Å. To higher wave numbers, three subbands of LaH with origins at 5955.8568(16) cm−1, 6238.3768(8) cm−1, and 6306.6757(15) cm−1 have been assigned as the 3Φ2–3Δ1, 3Φ3–3Δ2, and 3Φ4–3Δ3 subbands of the d 3Φ–a 3Δ electronic transition. The rotational analysis of the 0-0 and 1-1 bands of the 3Φ2–3Δ1 and 3Φ4–3Δ3 subbands and the 0-0, 1-1, and 2-2 bands of the 3Φ3–3Δ2 subband has been obtained and effective equilibrium constants for the spin components of the d 3Φ and the a 3Δ states have been extracted. Magnetic hyperfine structure was also observed in the a 3Δ state. The rotational analysis of the corresponding LaD transitions has also been carried out and equilibrium constants for the ground and excited states have been determined. The singlet–triplet interval between the X 1Σ+ state and the a 3Δ state is not known but on the basis of ab initio calculation and by comparison with LaF and YH, we believe that the ground state of LaH is a 1Σ+ state.
A molecular dynamics simulation study of the effects of defects on the transformation pressure of polymorphic phase transformations
Authors: Devani Samir , Anwar Jamshed
Published: July 2002

The effect of defects (in the form of vacancies) on the transformation pressure of the Fm3m-Pm3m phase transition of KCl has been examined using molecular dynamics simulations. The simulated transformation has been found to be reversible, exhibiting a large hysteresis. Vacancy defects were systematically introduced into the crystal structure of the parent phase, and then a series of simulations using the Parrinello–Rahman method were performed to elucidate the transformation pressure. With an increase in the density of the defects, the hysteresis decreases. These results are entirely consistent with the observed behavior.
Structures, hyperfine parameters, and inversion barriers of cyclopropyl and oxiranyl radicals
Authors: Barone Vincenzo , Adamo Carlo , Brunel Yvon , Subra Robert
Published: July 2002

A comparative post-Hartree–Fock study has been performed on cyclopropyl and oxiranyl radicals in order to ascertain the role of the oxygen atom in modifying the hyperfine structure and height of the barrier governing inversion at the radical center. The structural parameters and harmonic force fields obtained for the parent molecules using second-order many-body perturbation theory with a large basis set are in good agreement with experiment. The same approach points out significant distortions upon breaking of a CH bond and a larger pyramidality for the radical center in oxiranyl with respect to cyclopropyl. Also inversion barriers of both radicals are in remarkable agreement with experimental estimates. Isotropic hyperfine parameters in good agreement with those obtained from electron spin resonance spectra can be computed only when using purposely tailored basis sets in the framework of a coupled cluster approach and taking into account vibrational averaging effects induced by the inversion motion. Interpretation of the results in terms of direct and spin polarization effects points out a number of general trends for germinal and vicinal atoms. Furthermore, it is well evidenced that replacement of a methylenic group by an oxygen atom modifies the hyperfine parameters through geometric rather than direct electronic effects.
The lower C2v potential energy surfaces of the doublet states of H2O+: A computational study
Authors: Schneider F. , Di Giacomo F. , Gianturco F. A.
Published: July 2002

In this paper we extend our previous study (F. Schneider, F. Di Giacomo, and F. A. Gianturco, J. Chem. Phys. 104, 5153) on the topology of the electronic states of the neutral H2O molecule in C2v symmetry by examining the lowest ten potential energy surfaces of the water molecular cation in its doublet states. The relevant electronic energy surfaces of H2O+ are shown as 2D contour maps where possible reaction pathways for several low-lying potential energy surfaces of H2O+ are clearly seen and therefore can be discussed and analyzed in some detail. The present results were obtained using ab initio multireference configuration interaction calculations at 184 nuclear arrangements, as described in our previous paper dealing with the neutral H2O.
Accurate diblock copolymer phase boundaries at strong segregations
Authors: Matsen M. W. , Whitmore M. D.
Published: July 2002

We examine the lamellar/cylinder and cylinder/sphere phase boundaries for strongly segregated diblock copolymer melts using self-consistent-field theory (SCFT) and the standard Gaussian chain model. Calculations are performed with and without the conventional unit-cell approximation (UCA). We find that for strongly segregated melts, the UCA simply produces a small constant shift in each of the phase boundaries. Furthermore, the boundaries are found to be linear at strong segregations when plotted versus (χN)−1, which allows for accurate extrapolations to χN=∞. Our calculations using the UCA allow direct comparisons to strong-segregation theory (SST), which is accepted as the χN=∞ limit of SCFT. A significant discrepancy between the SST and SCFT results indicate otherwise, suggesting that the present formulation of SST is incomplete.
Quasiclassical trajectory calculations for the OH(X 2Π) and OD(X 2Π)+HBr reactions: Energy partitioning and rate constants
Authors: Nizamov B. , Setser D. W. , Wang H. , Peslherbe G. H. , Hase W. L.
Published: July 2002

The quasiclassical trajectory (QCT) method was used to study the dynamics of the OH(X 2Π) and OD(X 2Π)+HBr chemical reactions on an empirical potential energy surface (PES). The main emphasis in the calculation was the vibrational energy distributions of H2O (and HDO) and the magnitude and temperature dependence of the rate constant. However, this PES also serves as a generic model for the dynamics of direct H atom abstraction by OH radicals. Since this PES has no formal potential energy barrier, variational transition-state theory was used to obtain rate constants for comparison with the QCT calculations and experimental results. The parameters of the potential energy surface were adjusted to obtain better agreement with the experimentally measured fraction of H2O vibrational energy, 〈fV(H2O)〉=0.6, without significantly changing the entrance channel. No isotope effect for the partition of energy to H2O vs HOD was found. Analysis of the trajectories indicates that the reactant OH(OD) bond is a spectator, until the system begins to traverse the exit channel, i.e., until H2O(HDO) starts to retreat from Br. The calculated average energy in the bending mode of H2O or HDO was lower than the experimental value, and the PES could not be adjusted in its present form to give a significantly larger fraction of energy to the bending mode. A nonlinear 1:2 resonance between the OH local mode and the bending mode was found to be the main mechanism leading to bending mode excitation for this PES. The QCT rate constant is larger than the value calculated by quantum methods or variational transition-state theory. This difference may arise from the absence of a zero point energy constraint in the QCT calculation.
Origin of chemical instability in the bromate–sulfite flow system
Authors: Hanazaki Ichiro , Rábai Gyula
Published: July 2002

The origin of the instability observed in the bromate–sulfite-proton system is discussed. This is known as the subsystem of some pH oscillators which provides the positive feedback channel for H+. It is composed of the following two fast equilibria: H++SO2−3↔HSO−3 and H++HSO−3↔H2SO3 and the oxidation of HSO−3 and H2SO3 by BrO−3 to recover the initially supplied proton as 3HSO−3+BrO−3→3SO2−4+Br−+3H+ and 3H2SO3+BrO−3→3SO2−4+Br−+6H+. This scheme exhibits bistability under flow conditions. It gives rise to chemical oscillations if it is coupled with a simple linear decay process of H+ as a negative feedback channel. It is also capable of exhibiting chaotic behavior in the presence of HCO−3. We analyze the nature of the strong nonlinearity provided by the above scheme in detail and show that it arises essentially from the fast reaction of H2SO3 with bromate. The simplicity of the scheme enables us to describe the system dynamics with three variables without any approximation. As a result, we now have a model in hand in which we can compare the theoretical results directly and quantitatively with the corresponding experiments. This situation may open a way to understand the complexity in nonlinear chemical systems in a more quantitative manner. Some recent experimental findings of complex oscillatory behavior including chaos for the system with more realistic negative feedback channels, or for the system in which BrO−3 is replaced with H2O2, are discussed on the basis of the present analysis.
Numerical analysis of Solomon echo amplitudes in static solids
Authors: Man Pascal P.
Published: July 2002

For the first time a numerical procedure for computing the Solomon echo amplitudes of half-integer quadrupole spins (I=3/2, 5/2, 7/2, and 9/2) has been derived from a detailed analysis of the evolution of the spin system using the density operator formalism. As the first-order quadrupole interaction is taken into account throughout the experiment, consisting in exciting the spin system with two pulses either in phase or in quadrature phase and separated by a delay τ2, the results are valid for any ratio of the quadrupole coupling, ωQ, to the amplitude of the pulses, ωrf. These results are applicable to light nuclei at high magnetic field, for which the second-order quadrupole interaction and the chemical shift anisotropy are negligible. We predict (4I2−1)(2I−1)/16 echoes and their positions in the detection period τ4, (I−1/2)2 of which are allowed echoes, the others being forbidden echoes. All of these echoes are satellite-transition signals, which are superimposed on the free induction decay (FID) of the central transition following the second pulse. This means that τ2 must be short when compared to the duration of the central-transition FID. In other words, during τ2 the magnetic dipole interactions have no time to affect the evolution of the spin system. The behavior of the τ4=τ2 echoes versus the second-pulse flip angle ωrft3 is analyzed: in the hard-pulse excitation condition (ωQ/ωrf≪1), the (±1/2↔±3/2) echoes generated by two pulses in quadrature phase are twice as large as those generated by two in-phase pulses; the echoes of the other transitions have comparable amplitudes. The echo amplitudes in the soft-pulse excitation condition (ωQ/ωrf=1) are also presented.
Electronic to vibrational energy transfer between Rb(5 2PJ) and H2
Authors: Chen Man-Lin , Lin Wei-Chou , Luh Wei-Tzou
Published: July 2002

We have investigated the electronic-to-vibrational (E-V) energy transfer between electronically excited rubidium atoms (Rb 5 2P1/2,3/2) and hydrogen molecules (H2). We have used the CARS (Coherent Anti-Stokes Raman Scattering) spectral technique to probe the internal state distribution of collisionally-populated H2 molecules. Both scanned CARS spectra and activated CARS spectra reveal that during E-V energy transfer processes H2 molecules are produced only at the v=1 and v=2 vibrational levels. From scanned and activated CARS spectral peaks two possible population ratios (n1/n2) are obtained. Through shape simulations of the time-resolved CARS profiles under a simple kinetic model, the actual population ratio n1/n2 is unambiguously determined to be of 0.59 (σ=0.05). This n1/n2 ratio indicates that the H2 molecules produced by the E-V energy transfer process are 37% populated at the v=1 vibrational level and 63% at v=2, and that the efficiency of the E-V energy transfer is 0.489 for the Rb 5 2P1/2−H2 system and 0.481 for the 5 2P3/2−H2 system, coincident with the highest E-V transfer fraction 0.489 under the impulsive model and a collinear collision geometry.
Hartree–Fock orbital instability envelopes in highly correlated single-reference wave functions
Authors: Crawford T. Daniel , Stanton John F. , Allen Wesley D. , Schaefer Henry F.
Published: July 2002

The effects of Hartree–Fock orbital instabilities on force constant predictions at both Hartree–Fock and correlated levels of theory are investigated. Due to the quadratic dependence of the second derivative of correlated energies on the orbital rotation parameters, anomalous force constant singularities enveloped by “instability volcanoes” are given by the single-reference correlation methods examined here. Infinite-order coupled-cluster methods are indeed affected by the reference instability, but over a rather small region of the potential surface, whereas perturbative triples corrections tend to widen the coupled-cluster volcano. Finite-order many-body perturbation theory yields very wide volcanoes, and corresponding predictions of vibrational spectra may be seriously compromised if the geometry of interest lies at all in the vicinity of an instability in the reference determinant.
Oscillating phase separation in microemulsions. II. Description by a bending free energy
Authors: Vollmer Jürgen , Vollmer Doris , Strey Reinhard
Published: July 2002

We propose a mechanism to describe the phase separation of a single phase of water-in-oil microemulsion droplets towards a phase of smaller water droplets coexisting with a water-rich excess phase. The phase separation shows oscillatory behavior when induced by a continuous temperature increase. A periodic clouding and clearing is observed in the extinction of transmitted light which is also reflected in the specific heat. To model this behavior the bending free energy describing the equilibrium phase transition is applied to identify the energy barriers in the dynamics of this transition. They are due to conservation laws preventing the relaxation to a close to equilibrium size distribution of droplets unless volume and surface is redistributed simultaneously for a large number of droplets. By numerical integration of an expression for the time evolution of the size distribution of droplets it is verified that constant heating gives rise to oscillations. Besides clarifying the origin of the oscillations this approach also gives good estimates for heat absorbed during a single oscillation.
Competitive adsorption of xenon and krypton in zeolite NaA: 129Xe nuclear magnetic resonance studies and grand canonical Monte Carlo simulations
Authors: Jameson Cynthia J. , Jameson A. Keith , Lim Hyung-Mi
Published: July 2002

Investigation of competitive adsorption is carried out using the Xe–Kr mixture in zeolite NaA as a model system. The XenKrm clusters are trapped in the alpha cages of this zeolite for times sufficiently long that it is possible to observe individual peaks in the nuclear magnetic resonance (NMR) spectrum for the clusters. The 129Xe nuclear magnetic resonance spectra of several samples of varying Xe and Kr loadings have been observed and analyzed to obtain the 129Xe chemical shifts and the intensities of the peaks which are dependent on the average krypton and xenon occupancies. The detailed distributions, f(XenKrm), the fractions of cages containing n Xe atoms and m Kr atoms can be observed directly in this system from the relative intensities since individual peaks for XenKrm mixed clusters are observed in the NMR spectrum. Grand canonical Monte Carlo (GCMC) simulations of mixtures of Xe and Kr in a rigid zeolite NaA lattice provide the detailed distributions and the average cluster shifts. The agreement with experiment is excellent. The calculated absolute chemical shifts for the Xen peaks and XenKr peaks at 300 K are in good agreement with experiment. A strictly statistical model of a binary mixture, derived from the hypergeometric distribution, in which the component atoms are distinguishable but equivalent in competition for eight lattice sites per cage under mutual exclusion provides a limiting case for the distributions, with which the GCMC simulations and the properties of the actual Xe–Kr system may be compared. The selectivity coefficients of the Xe–Kr mixture in zeolite NaA is well described by the ideal adsorbed solution model.
The formation of ArCO+ ions by dissociative ionization of argon/carbonmonoxide clusters
Authors: Mähnert Joachim , Baumgärtel Helmut , Weitzel Karl-Michael
Published: July 2002

The formation of ArCO+ ions has been investigated in a photoelectron photoion coincidence experiment by dissociative ionization of Ar2CO clusters. The kinetic energy released (KER) in this dissociation has been measured as a function of the internal energy of the parent cluster ion and compared to the KER expected on the basis of statistical theory of unimolecular reaction, e.g., phase space theory. The latter calculations are based on high level ab initio calculations of the ArCO+ ion and the Ar2CO+ ion. The ab initio calculations show a nonlinear equilibrium geometry of the ArCO+ ion. The comparison of experimental and theoretical KER leads to an adiabatic ionization potential of the ArCO of 13.03 eV and a dissociation energy of the ArCO+ ion of 1.00 eV.
Prewetting transition influenced by layeringlike transitions at a binary liquid/solid interface
Authors: Hamraoui A. , Privat M.
Published: July 2002

The prewetting transition in the silica-water-2,5-dimethylpyridine system has been studied through the adsorption isotherms. Steep wave shapes for these isotherms lead to the conclusion of alternate solid and liquid surface demixing very close to bulk coexistence and wetting temperature. Liquid demixing has the generic aspects of prewetting. An empirical model for demixings, surface phase diagrams in several representations, and critical end points are discussed, as well as the phenomena universality.
Line strengths of diatomics: The b 1Σ+v′=0→X 3Σ−v″=0 transition of the NF radical
Authors: Di Stefano G. , Lenzi M. , Piciacchia G. , Ricci A.
Published: July 2002

Line intensities in the (0,0) band of NF(b 1Σ+→X 3Σ−) spin forbidden emission have been observed in a microwave apparatus. Deduced line strengths of the OP and SR well resolved branches are shown differently, in contrast with the theoretical prevision, and are interpreted by taking into account some peculiarities of the NF radical. An intermediate (a) and (b) Hund case is seen to apply to OP and SR in the whole rotational range examined. Accordingly, a reliable value for the effective transition moment μe is evaluated from the experiment.
The electron affinities of PF and PF2
Authors: Gu Jiande , Chen Kaixian , Xie Yaoming , Schaefer Henry F. , Morris Robert A. , Viggiano A. A.
Published: July 2002

Theoretical investigations of the adiabatic electron affinities of PF and PF2 have been carried out. Large basis sets were used in this research, ranging from TZ2Pf+diff up to aug-cc-pVQZ. The theoretical methods applied here were Hartree–Fock self-consistent-field (SCF) theory, single and double excitation configuration interaction (CISD), single and double excitation coupled cluster (CCSD), and the CCSD(T) method, which adds perturbatively the connected triple excitations to the CCSD method. The results of this investigation show that three theoretical methods, DZP++ BHLYP, G2, and aug-cc-pVQZ CCSD(T) provide excellent agreement with each other for the adiabatic electron affinities of PF and PF2. The high level of theory used in this research suggests that the adiabatic electron affinity of PF is about 0.75 eV, and that of PF2 is about 0.76 eV. These predictions are in contrast to the experimental values of 3.4 eV (for PF) and 1.4–1.6 eV (for PF2).
Electrostatics of multilamellar vesicles: Legendre expansion and reaction-field Brownian dynamics
Authors: Zaloj Veaceslav , Agmon Noam
Published: July 2002

An analytic expression for the electrostatic potential of a point charge within a concentric multilayered dielectric medium is derived in terms of a Legendre expansion. A novel Brownian dynamics algorithm for solving the Poisson equation for the reaction-field potential of charges near dielectric interfaces is presented. To test both the computed and analytic solutions, the reaction-field potential and self-energy of a charge within a liposome are calculated and compared.
Mutual diffusion in binary systems
Authors: Sharma Raman , Tankeshwar K.
Published: July 2002

Expressions for the second and fourth sum rules of relative and cross velocity correlation functions are derived for two component systems. These sum rules and Mori’s memory function formalism have been used to study the mutual, self- and distinct diffusion in equimolar Ar–Kr mixture and molten salts. It is found that distinct diffusion, which is a measure of effect of cross correlations representing momentum spread to neighbouring particles, is positive for Ar–Kr mixture and is negative for molten salts. These findings are in agreement with molecular dynamics predictions. The positive value of distinct diffusion was not accounted for by Darken’s and common force models.
Weakened hydrogen bond interactions in the high pressure phase of ice: Ice II
Authors: Dong S. L. , Wang Y. , Kolesnikov A. I. , Li J. C.
Published: July 2002

The phonon density of states for ice II has been calculated using a lattice dynamics model. The force field for this system was parameterized based on two kinds of hydrogen bond model for ice Ih [J. C. Li and D. K. Ross, Nature 365, 327 (1993)] and a new force constant was introduced due to the distortion of the H-bond in the structure, in order to fit the measured inelastic neutron scattering spectra. The results showed that the hydrogen bond force constant between the six-molecule rings is significantly weaker, 0.75 eV/Å2, compared with the force constant, 2.1 eV/Å2, within the rings. The vectors of the molecular displacements due to translational normal modes were analyzed, and it was shown that the peak at 23 meV was mainly due to vertical “distorted H-bonds” between the rings and the feature at 19.5 meV was related to both lateral and vertical H-bonds. The peaks above 28 meV were related mainly to strong H-bonds inside six-molecule rings.
Spectra and time-dependent dynamics of H3 near the conical intersection in the (2p)1E′ ground electronic manifold
Authors: Mahapatra Susanta , Köppel Horst
Published: July 2002

We report on the spectra and dynamics of H3 near the conical intersection in its (2p)1E′ ground electronic manifold. The time-dependent wave packet approach and the double many-body expansion (DMBE) potential energy surface (PES) are employed for this purpose. We use Jacobi coordinates (R,r,γ) and employ the fast Fourier transform method for R and r, and the discrete variable representation method for γ, in conjunction with the split-operator formalism to describe the evolution of the wave packet (WP) in space and time, respectively. While the main focus of the present work is to explicitly reveal the effects of nonadiabatic coupling between the two sheets of the DMBE PES, companion calculations are also carried out to investigate the dynamics on the uncoupled upper and lower adiabatic sheets, both in two and three dimensions (for total angular momentum J=0). A set of pseudospectra is calculated by Fourier transforming the time autocorrelation function of suitably chosen Gaussian wave packets located initially at the minimum energy point of the seam of conical intersections. The eigenstates thus obtained are assigned by computing their eigenfunctions by spectral quantization. In the coupled states treatment the WP is propagated in the diabatic representation. The time dependence of the adiabatic populations is calculated by using suitable adiabatic projection operators. We find strong effects of nonadiabatic coupling on the discrete vibrational energy levels of the upper adiabatic sheet, which all change to quasibound states in the coupled manifold. The comparison of the decay dynamics of various levels of the upper adiabatic sheet indicates considerable mode specificity (their lifetimes typically vary between 3 and 6 fs). On the other hand, resonances are seen to be less pronounced near the conical intersection on the lower adiabatic sheet (when compared to those in the literature, obtained near the collinear saddle point region). The effect of nonadiabatic coupling on them is only minor. We also report preliminary results on the optical emission spectrum of H3 and compare them with the experimental findings.
Microscopic origin of the high-pressure-induced spectral shifts in ruby
Authors: Zhao M. G.
Published: July 2002

A microscopic model for the high-pressure-induced spectral shifts in ruby was developed based on both the exact microscopic complete energy matrix diagonalization procedure and an approximately equivalent self-consistent-field d-orbital model. The calculated results are in good agreement with the experimental data up to 1650 kbar. The predicted high-pressure-induced shifts of the optical and electron paramagnetic spectra can be tested by further measurements.
Structure and stability of the AlX and AlX− species
Authors: Gutsev Gennady L. , Jena Puru , Bartlett Rodney J.
Published: July 2002

The electronic and geometrical structures of the ground and low-lying excited states of the diatomic AlX and AlX− series (X=H, Li, Be, B, C, N, O, and F) are calculated by the coupled-cluster method with all singles and doubles and noniterative inclusion of triples using a large atomic natural orbital basis. All the ground-state AlX molecules except for AlF can attach an additional electron and form ground-state AlX− anions. The ground-state AlBe−, AlB−, AlC−, AlN−, and AlO− anions possess excited states that are stable toward autodetachment of an extra electron; AlBe− also has a second excited state. Low-lying excited states of all AlX but AlN can attach an extra electron and form anionic states that are stable with respect to their neutral (excited) parent states. The ground-state AlLi−, AlBe−, AlB−, AlN−, and AlO− anions are found to be thermodynamically more stable than their neutral parents. The most stable is AlO−, whose dissociation energy to Al+O− is 6.4 eV. Correspondingly, AlO possesses the largest electron affinity (2.65 eV) in the series.
Heterogeneous percolation-to-cluster transition in phase separation of an off-critical polymer mixture
Authors: Takeno Hiroyuki , Nakamura Eiji , Hashimoto Takeji
Published: July 2002

Phase separation kinetics of an off-critical polymer mixture involving percolation-to-cluster transition (PCT) was investigated by time-resolved light scattering and by transmission optical and electron microscopies. The process involving a splitting of a single peak in the light scattering profile into a double peak was observed for the first time after the onset of PCT. Each peak changes with time (t) according to different evolution modes, e.g., the first peak wave number qm,1 evolved according to the power law of percolated structures (qm∼t−α; α=0.9), while the time evolution of the second peak wave number qm,2 is very slow, which corresponds to the growth of cluster of the droplets after PCT. Furthermore, the real space pictures and the light scattering analysis reveal that a cluster of the small spherical droplets and the locally percolating domains coexist for a very long time. The percolating domains are larger than the small droplets, minor in volume fraction, and formed in bulk and they are developed into sheet-like grains with their surfaces parallel to the glass surface.
Surface relaxation in CdSe nanocrystals
Authors: Leung K. , Whaley K. B.
Published: July 2002

Total energy minimization is applied to semiempirical tight-binding CdSe nanocrystal models with diameter up to 31 Å. The crystallites have wurtzite lattice structure and ligand-terminated surfaces. It is found that the qualitative features of the surface relaxation in nanocrystals and at bulk surfaces are similar. When surface relaxation is incorporated, the onsets of absorption are determined by interior-to-interior transitions with little contribution from surface-localized states. The fine structure and exchange splittings derived from these clusters are in good agreement with experimental measurements. The effects of ligand parametrization, surface atom composition, and the contribution of surface states to the exciton fine structure are analyzed.
Monte Carlo simulation of the order–disorder transition of a symmetric cyclic diblock copolymer system
Authors: Jo Won Ho , Jang Seung Soon
Published: July 2002

The microphase separation of symmetric cyclic diblock copolymer with decreasing temperature is simulated using the Monte Carlo method. In order to investigate the effect of the ring-shape chain architecture on order–disorder transition (ODT), the microphase separation of the cyclic diblock copolymer is compared with that of a symmetric linear diblock copolymer with the same chain length. For both systems, the ODT is observed as a first-order transition, and the ordered structure formed through the ODT is lamellar. The ratio of the domain spacing in the cyclic diblock copolymer to that in the linear one is 0.7 at the ODT, and the scattering intensity of the former is weaker than that of the latter. The ring-shape chain architecture suppresses the random thermal force, so that the cyclic diblock copolymer still shows a mean-field behavior at the temperature at which the linear diblock copolymer does not obey the mean-field prediction. The value of (χeffN)ODT of the linear diblock copolymer is calculated to be in the range of 25.36<(χeffN)<26.04, which is in good agreement with the theoretical prediction, (χeffN)ODT=25.61, indicating that this simulation properly describes the ODT of the diblock copolymer. The value of (χeffN)ODT of the cyclic diblock copolymer is predicted to be in the range of 40.83<(χeffN)<43.02.
Hydrogen bonding, structure, and dynamics of benzonitrile–water
Authors: Melandri Sonia , Consalvo Daniela , Caminati Walther , Favero Paolo G.
Published: July 2002

Rotational transitions with high quantum numbers J and K of the 1:1 complex of benzonitrile with H2O and D2O have been investigated in the frequency range 60–78 GHz with the free jet absorption microwave technique to get detailed information on the unusual hydrogen bond and on the dynamics of the large amplitude motions of the water moiety. With respect to previous microwave studies [V. Storm, D. Consalvo, and H. Dreizler, Z. Naturforsch. A 52, 293 (1997); R. M. Helm, H.-P. Vogel, H. J. Neusser, V. Storm, D. Consalvo, and H. Dreizler, 52, 655 (1997); V. Storm, H. Dreizler, and D. Consalvo, Chem. Phys. 239, 109 (1998)] the position of the water oxygen has been confirmed and the planar configuration of the complex has been determined. The distance of the oxygen atom to the ortho hydrogen is 2.48 Å, the angle to the ortho C–H bond is 144° and the angle between the free hydrogen atom of water with the same C–H bond is 164°. A coupled analysis of the 0+ and 0− states observed for the normal species was performed and the experimental data were reproduced by a flexible model which allowed the determination of the barrier to internal rotation of water [V2=287(20) cm−1] and the structural relaxation associated with the dynamic process.
Photodissociation dynamics of ethanol at 193.3 nm: The H-atom channel and ethoxy vibrational distribution
Authors: Xu Kesheng , Amaral Gabriel , Zhang Jingsong
Published: July 2002

193.3 nm photodissociation of jet-cooled C2H5OH and C2H5OD has been studied by using the high-n Rydberg-atom time-of-flight technique. Isotope labeling study shows that the H-atom photofragment is produced preferentially from O–H bond fission upon ultraviolet excitation. Center-of-mass (c.m.) translational energy distribution of the H(D) atom and ethoxy radical photofragments has been obtained. Average c.m. product translational energy is large, with 〈ET〉=0.84Eavail for H+C2H5O and 〈ET〉=0.80Eavail for D+C2H5O, respectively. Maximum c.m. translational energy release yields an upper limit of the bond dissociation energy: D0(C2H5O–H)=103.7±0.5 kcal/mol and D0(C2H5O–D)=105.9±0.5 kcal/mol. The c.m. translational energy distribution of the C2H5O+H products reveals extensive C–O stretch and modest C–C–O bending excitation in the C2H5O radical, which can be rationalized by the geometric change in going from the parent molecule to the excited surface and then to the ethoxy radical product, and can be simulated by a simple Franck–Condon model. H-atom product angular distribution is anisotropic (with β≈−0.9), indicating a perpendicular electronic transition (Ã 1A″←X̃ 1A′) at 193.3 nm and a short excited-state lifetime (less than a rotational period). The obtained dynamic information implies that the C2H5O+H channel in 193.3 nm photodissociation of ethanol occurs via a prompt dissociation process and on a repulsive excited-state surface, and the ethoxy product vibrational distribution further reveals the detailed multidimensional features of this excited Ã 1A″ potential energy surface. Secondary photodissociation of the ethoxy radical has been observed and is briefly discussed.
Reaction of H2S with MgO(100) and Cu/MgO(100) surfaces: Band-gap size and chemical reactivity
Authors: Rodriguez José A. , Jirsak Tomas , Chaturvedi Sanjay
Published: July 2002

The interaction of H2S, SH, and S with MgO(100) and Cu/MgO(100) surfaces has been investigated using synchrotron-based high resolution photoemission and density functional calculations. Metallic magnesium reacts vigorously with H2S fully decomposing the molecule at temperatures below 200 K. In contrast, the Mg atoms in MgO exhibit a moderate reactivity. At 80 K, most of the H2S molecules (∼80%) chemisorb intact on a MgO(100) surface. Annealing to 200 K induces cleavage of S–H bonds leaving similar amounts of H2S and SH on the surface. The complete disappearance of H2S is observed at 300 K, and the dominant species on the oxide is SH which is coadsorbed with a small amount (∼10%) of atomic S. The adsorbed SH fully decomposes upon heating to 400 K producing S adatoms that are stable on the surface at temperatures well above 500 K. The results of density functional calculations indicate that the bonding interactions of SH and S with pentacoordinated Mg sites of a flat MgO(100) surface are strong, but the bonding of the H2S molecule is relatively weak. Defect sites probably play an important role in the dissociation of H2S. Cu adatoms facilitate the decomposition of H2S on MgO(100) by providing electronic states that are very efficient for interactions with the frontier orbitals of the molecule. The rate of H2S decomposition on MgO is substantially lower than those found on Cr3O4, Cr2O3, ZnO, and Cu2O. For these systems, the smaller the band-gap in the oxide, the bigger its reactivity towards H2S. Theoretical calculations indicate that this trend reflects the effects of band–orbital mixing. The electrostatic interactions between the dipole of H2S and the ionic field generated by the charges in an oxide play only a secondary role in the adsorption process.
Ion-stimulated desorption of O+ from the oxygenated TiC(111) surface: The role of nonadiabatic electronic transitions and the band effect
Authors: Souda R. , Kawanowa H. , Otani S. , Aizawa T.
Published: July 2002

The mechanism of secondary O+ ion emission from the oxygenated TiC(111) surface has been investigated by noble-gas ion irradiation. The O+ ion is ejected from the surface by He+ irradiation due to an electronic transition without violent collisions. The O+ ion occurs preferentially from the weakly bound oxygen species, but very little O+ arises from the strongly chemisorbed oxygen on the threefold hollow site. The O+ emission is not caused by two localized valence holes resulting from the Auger decay of the primary ions, but is rather initiated by the formation of a long-lived O 2s core-hole state with an antibonding character. The O 2s hole is created by He+ via the nonadiabatic electronic transition during moderate impact-parameter collisions (1.0–3.0 a.u.), which is accompanied by very little kinetic energy transfer (<1 eV) to the target oxygen atom. The probability for O 2s hole creation increases with increasing velocity of the primary ions. The ionization of oxygen occurs due to the Auger decay of the O 2s hole on the way out from the surface after breakage of the chemisorptive bond; this is essential for the emission of very low-energy (<10 eV) O+ ions without resonant neutralization. This mechanism is consistent with that developed in low-energy ion scattering and successfully explains the O+ emission even from metal surfaces without the need for any assumption of the localization of valence holes.
Induced nematic phase in a polymer/liquid crystal mixture
Authors: Matsuyama Akihiko , Kato Tadaya
Published: July 2002

A mean field theory is introduced to describe the phase separations in binary mixtures of a liquid crystal and a non-nematic polymer which means that nematic ordering is forbidden in the constituent pure polymers. The theory takes into account the partial orientational ordering of the polymer chain induced by the liquid crystal solvents. We predict that a triple point and a new stable nematic phase can be induced by the anisotropic coupling between the polymer and the liquid crystal. The new types of induced nematic phases are examined with respect to their dependence on polymer molecular weight and stiffness.
The gas-phase structure of chloroferrocene from microwave spectra
Authors: Drouin Brian J. , Dannemiller Jennifer J. , Kukolich Stephen G.
Published: July 2002

Rotational spectra for ten isotopomers of chloroferrocene were measured using pulsed-beam Fourier transform microwave spectroscopy. Rotational transitions due to both “a” and “b” dipole moments were measured in the 4–12 GHz range. Thirty rotational constants were determined from microwave data for the normal, Fe54, Fe57, Cl37, and six unique C13 isotopomers, by fitting the microwave data using a rigid rotor Hamiltonian with centrifugal distortion and quadrupole coupling terms. The moments of inertia of the isotopomers were used in Kraitchman and in least-squares fitting analyses to determine gas-phase structural parameters. The unsubstituted cyclopentadienyl (C5H5) ligand was determined to have essentially fivefold local symmetry, while the chlorinated cyclopentadienyl ligand shows small, but significant distortions from the fivefold symmetry. The C–Cl bond is bent 2.7(6)° from the plane of carbon atoms. This substituted C5H4Cl ligand is tilted 1.4(5)° with respect to the unsubstituted C5H5 ligand. The carbon atoms of the two cyclopentadienyl ligands are eclipsed, similar to normal ferrocene. The average Fe–C distance is 2.042(9) Å. The estimated displacement of C–H bonds out of the planes of the carbon atoms is 4(2)° away from the metal atom.
Studying vibrational wavepacket dynamics by measuring fluorescence interference fluctuations
Authors: Warmuth Ch. , Tortschanoff A. , Milota F. , Shapiro M. , Prior Y. , Averbukh I. Sh. , Schleich W. , Jakubetz W. , Kauffmann H. F.
Published: July 2002

The principle of coherence observation by interference noise [COIN, Kinrot et al., Phys. Rev. Lett. 75, 3822 (1995)] has been applied as a new approach to measuring wavepacket motion. In the COIN experiment pairs of phase-randomized femtosecond pulses with relative delay time τ prepare interference fluctuations in the excited state population, so the correlated noise of fluorescence intensity—the variance varF(τ)—directly mimics the dynamics of the propagating wavepacket. The scheme is demonstrated by measuring the vibrational coherence of wavepacket motion in the B-state of gaseous iodine. The COIN interferograms obtained recover propagation, recurrences and spreading as the typical signature of wavepackets. The COIN measurements were performed with precisely tuned excitation pulses which cover the bound part of the B-state surface up to the dissociative limit. In combination with preliminary numerical calculations, comparison has been made with results from previous phase-locked wavepacket interferometry and pump-probe experiments, and conclusions drawn about the limitations of the method and its applicability to quantum dynamical research.
A phenomenological description of the anomalous behavior of the electrical double layer at low temperatures
Authors: Henderson Douglas
Published: July 2002

A simple description that accounts for some recent simulations of the electric double layer of a charged hard sphere fluid that show anomalously large negative adsorption of the ions at a surface and an unusual positive temperature derivative for the capacitance at low temperatures is discussed. The treatment is phenomenological since it does not result from any controlled approximation but it is reasonably well founded. The mean spherical approximation expressions for the density profiles of this system, which do not exhibit anomalous behavior, are modified in light of an exact contact value condition, the Ornstein–Zernike theory of the critical point, and some plausible reasoning. The agreement with the simulation results is fairly good. At the moment, there is no theory that accounts for these recent simulation results.
Comment on “Frequency-dependent polarizabilities, hyperpolarizabilities, and excitation energies from time-dependent density-functional theory based on the quasienergy derivative method” [J. Chem. Phys. 111, 2878 (1999)]
Authors: Banerjee Arup , Harbola Manoj K.
Published: July 2002

In this comment we point out the similarity between the recent work of Aiga et al. [J. Chem. Phys. 111, 2878 (1999)] and our work [Phys. Lett. A 236, 525 (1997)], both developing perturbation methods within time-dependent density-functional theory for calculating frequency-dependent response properties of many-electron systems.
A quantitative study of non-Condon effects in the S2O C̃→X̃ emission spectrum
Authors: Iachello F. , Pérez-Bernal F. , Müller T. , Vaccaro P. H.
Published: July 2002

A novel technique has been developed for the quantitative study of vibronically-resolved transition intensities in polyatomic molecules beyond the Condon approximation. Matrix elements of coordinate-dependent transition moment operators are evaluated analytically with the pertinent vibrational wave functions obtained by means of Lie algebraic methods. Experimentally-observed S2O C̃ 1A′–X̃ 1A′(π*−π) emission intensities, in conjunction with previous Franck–Condon calculations, reveal pronounced non-Condon effects for vibronic bands terminating on higher-lying vibrational levels of the ground electronic state. The transition dipole moment is examined as a function of both the S–O and S–S local stretching coordinates.
Transferability in aldehydes and ketones. II. Alkyl chains
Authors: Graña Ana M. , Mosquera Ricardo A.
Published: July 2002

An analysis of the transferability of hydrocarbon chains in aldehydes and ketones was carried out, considering the values obtained for the atomic and bond properties of these chains in a series of 42 compounds. Likewise, the differences between the n-alkane groups and the methylene and methyl groups of a chain containing a carbonyl group were established. All the properties were calculated using the theory of atoms in molecules on 6-31++G**//6-31G* wave functions. The values of the atomic properties and their evolution with L(Ω) and the size of the molecule allow the carbon atoms of an alkyl skeleton to be classified considering both their position with respect to the C=O group (α, β, γ, δ or further) and their position in relation to the end of the chain (terminal C, C previous to the terminal, and the rest). For some of the properties of the carbons in α or β dispositions to the C=O group, it is also necessary to consider the nature of the other alkyl radical bonded to the carbonyl group (H,CH3,CH2CH3 or longer for C in α,H,CH3 or longer for C in β). The bond properties (the bond length, the distance to the critical point of the bond, the ellipticity, the charge density at the critical point, the Laplacian of the charge density at the critical point) display lower dependency on the position in relation to both elements, and only bring about a difference between the bonds including C in α or β to the C=O and/or C at the end of the chain, and a common behavior pattern for the other C–C bonds.
Tunneling through a singular potential barrier
Authors: Dittrich J. , Exner P.
Published: July 2002

Quantum tunneling of a nonrelativistic particle through a singular potential barrier V is studied on the line. The Hamiltonian is a self-adjoint extension of the operator H1=−d2/dx2+V(x). If H1 is essentially self-adjoint on its natural domain, the tunneling is forbidden for a class of potentials that includes all semiclassically impenetrable barriers. If H1 is not essentially self-adjoint, the Friedrichs extension of H1 yields no tunneling for another class of potentials which again includes the semiclassically impenetrable ones. In general, the occurrence of tunneling is not excluded and depends on the self-adjoint extension we choose as the Hamiltonian of our problem. As an example, we evaluate the transmission coefficient for all self-adjoint extensions of the operator H1 referring to V(x)=gx−2 with 0<g< 3/4 .
Irreducible *-representations of Lie superalgebras B(0,n) with finite-degenerated vacuum
Authors: Blank J. , Havlíček M.
Published: July 2002

The problem of getting irreducible *-representations π of Lie superalgebras B(0,n), n=1,2, is studied, starting with a recently constructed family of linear representations in terms of differential operators on the space C∞N of CN -valued C∞ -functions. Equivalent formulation via creation-annihilation operators of a para-Bose system with n degrees of freedom is used, and the domain 𝒟 of any π is shown to be a subset of C∞N containing a nonzero vacuum subspace. By assuming its dimension finite, the necessary conditions for existence of π are derived. The method is applied to the superalgebra B(0,1) and a one-parameter family Π of nonequivalent irreducible *-representations in terms of unbounded linear operators on L2(R+)⊗C2 is obtained. Each representation π∈Π has a nondegenerated vacuum and for all z∈B(0,1) satisfying z=z*, the operators π(z) are essentially self-adjoint.
Addition theorems for spherical wave solutions of the vector Helmholtz equation
Authors: Felderhof B. U. , Jones R. B.
Published: July 2002

Addition theorems for spherical wave solutions of the vector Helmholtz equation are discussed. The theorems allow one to expand a vector spherical wave about a given origin into spherical waves about a shifted origin. A simplified derivation of the results obtained earlier by Cruzan [O. R. Cruzan, Q. Appl. Math. 20, 33 (1962)] is presented.
Introducing division by an ‘‘a’’ number and a new ‘‘b’’ number in particle physics
Authors: Xiang-Lin Quan , Lian-Ji Wang , He-Shan Song
Published: July 2002

In this paper a new ‘‘b’’ number (b=a1a2⋅⋅⋅an, where n is even and each a is an anticommutative number or Grassmann number) is introduced, and the specialities of this ‘‘b’’ number are also expounded. Moreover, division by an ‘‘a’’ number is defined. At the same time a derivative concept of the functional containing an ‘‘a’’ number is also given in the traditional approach, and a new formula for the derivative of this functional is advanced. The new formula not only encompasses Berezin’s formula but also solves the problems that cannot be solved by Berezin’s formula. For ‘‘b’’ numbers, a unique infinitesimal calculus will be proposed.