bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser-induced fluorescence and fluorescence depletion spectroscopy of SCCS−
Authors: Nakajima Masakazu , Yoneda Yu , Sumiyoshi Yoshihiro , Nagata Takashi , Endo Yasuki
Published: October 2003

In a discharged supersonic jet of carbon disulfide, a band system of a new species is observed by laser-induced fluorescence (LIF) spectroscopy. Rotationally resolved spectra show that the observed electronic transition is Π23/2−Π23/2. Since both sulfur and carbon atoms have even numbers of electrons, it is concluded that the spectral carrier is an ionic species. Furthermore, the spectral carrier is confirmed to have two equivalent carbon atoms from the LIF spectra of the C13-substituted species. With a help of ab initio calculations, the carrier is identified as the linear negative ion SCCS−, where the observed electronic transition is considered to be Ã 2Πg–X̃ 2Πu. A mass spectrometric measurement also gives evidence that SCCS− is produced in the discharged jet. The vibrational structure for the upper electronic state is determined by both LIF and fluorescence depletion spectroscopy. A dispersed fluorescence spectrum is also observed to determine the vibrational structure of the lower electronic state. Frequencies of the ν1 (C–C stretching) and ν2 (C–S symmetric stretching) vibrational modes are determined for both the electronic states, which are in good agreement with the theoretically calculated values. Fluorescence decay profiles are obtained for many vibronic levels, and the excited-state dynamics is discussed based on the determined fluorescence lifetimes and results of ab initio calculations.
Inner-valence states of O2+ and dissociation dynamics studied by threshold photoelectron spectroscopy and a configuration interaction calculation
Authors: Hikosaka Yasumasa , Aoto Tomohiro , Hall Richard I. , Ito Kenji , Hirayama Ryo , Yamamoto Norifumi , Miyoshi Eisaku
Published: October 2003

High-resolution threshold photoelectron spectroscopy has been used to study O2 in the 24–50 eV photon energy region, where several broad bands with superimposed fine peaks are observed. Theoretical calculations on the basis of the state-averaged complete-active-space self-consistent-field method followed by the second order configuration interaction method reproduce well the general band features of the threshold photoelectron spectrum, enabling us to assign the bands to inner-valence O2+ states. Dissociation products formed from the inner-valence O2+ states have been investigated by threshold photoelectron–photoion coincidence spectroscopy and their dissociation dynamics discussed with reference to the theoretical potential energy curves.
Effects of weak surface fields on the density profiles and adsorption of a confined fluid near bulk criticality
Authors: Maciołek A. , Evans R. , Wilding N. B.
Published: October 2003

The density profile ρ(z) and Gibbs adsorption Γ of a near-critical fluid confined between two identical planar walls is studied by means of Monte Carlo simulation and by density functional theory for a Lennard-Jones fluid. By reducing the strength of wall–fluid interactions relative to fluid–fluid interactions we observe a crossover from behavior characteristic of the normal surface universality class, strong critical adsorption, to behavior characteristic of a “neutral” wall. The crossover is reminiscent of that which occurs near the ordinary surface transition in Ising films subject to vanishing surface fields. For the “neutral” wall ρ(z), away from the walls, is almost constant throughout the slit capillary and gives rise to a Γ that is constant along the critical isochore. The same “neutral” wall yields a line of capillary coexistence that is almost identical to the bulk coexistence line. In the crossover regime we observe features in ρ(z) similar to those found in the magnetization profile of the critical Ising film subject to weak surface fields, namely two smooth maxima, located away from the walls, which merge into a single maximum at midpoint as the strength of the wall–fluid interaction is reduced or as the distance between walls is decreased. We discuss similarities and differences between the surface critical behavior of fluids and of Ising magnets.
Relaminarization of Reτ=100 turbulence using gain scheduling and linear state-feedback control
Authors: Högberg M. , Bewley T. R. , Henningson D. S.
Published: October 2003

The first successful application of linear full-state feedback optimal control theory to consistently relaminarize turbulent channel flow at Reτ=100 with full state information and gain scheduling is reported. The actuation is zero-net mass-flux blowing and suction on the channel walls. Two key issues central to the success of this strategy are: (a) the choice of the mean-flow profile about which the equations are linearized for the computation of the linear feedback gains, and (b) the choice of an objective function which targets the control effort on the flow perturbations of interest. A range of mean-flow profiles between the laminar and fully turbulent profiles and a weighted energy measure which targets flow perturbations in the near-wall region were found to provide effective feedback gains. A gain-scheduling strategy to tune the feedback gains to the nonstationary mean-flow profile is introduced, resulting in consistent relaminarization of the turbulent flow in all realizations tested.
Calculation of ionic charging free energies in simulation systems with atomic charges, dipoles, and quadrupoles
Authors: Herce David H. , Darden Thomas , Sagui Celeste
Published: October 2003

The ionic charging free energy is a very sensitive probe for the treatment of electrostatics in any given simulation setting. In this work, we present methods to compute the ionic charging free energy in systems characterized by atomic charges and higher-order multipoles, mainly dipoles and quadrupoles. The results of these methods for periodic boundary conditions and for spherical clusters are then compared. For the treatment of spherical clusters, we introduce a generalization of Gauss’ law that links the microscopic variables to the measurable macroscopic electrostatics via a work function.
Liquid–vapor criticality in a fluid of charged hard dumbbells
Authors: Daub Christopher D. , Patey G. N. , Camp Philip J.
Published: October 2003

The vapor–liquid criticality of a fluid of charged hard dumbbells is investigated employing grand canonical Monte Carlo simulations and mixed-field finite-size scaling methods. The reduced critical temperature and density obtained are Tc*=0.04911±0.00003 and ρc*=0.101±0.003, respectively. The critical temperature is very close to that of the restricted primitive model (RPM) for ionic fluids, while the critical density is ∼25% larger than that of the RPM. The “fits” to the Ising ordering operator distribution are good, and are of similar quality to those found for the RPM with systems of comparable size. However, for the finite-size systems simulated, the constant volume heat capacity, CV, gives no indication of an Ising-type “divergence” at Tc. This is analogous to the RPM, and serves to demonstrate that this still puzzling behavior is not restricted to that model.
Neutron spin-echo investigation of the dynamics of block copolymer micelles
Authors: Castelletto V. , Hamley I. W. , Yang Z. , Haeussler W.
Published: October 2003

The dynamics of E92B18 (E=OCH2CH2: oxyethylene, B=OCH2CH(C2H5): oxybutylene; the subscripts are the number of repeats) block copolymer micelles is investigated by neutron spin-echo (NSE). The dynamics of chains in E92B18 micelles is investigated in the hard gel and soft gel phases of the E92B18 in D2O, as well as in the micellar solution. NSE revealed the presence of two dynamic modes, i.e., “fast” and “slow” modes, which are observed independent of the phase, i.e., micellar liquid, soft gel or hard gel. A “slow” mode that dominates at low scattering angles corresponds to the translational diffusion of micelles, the micellar size Rs being in good agreement with the apparent hydrodynamic radius from dynamic light scattering experiments on a dilute solution. An additional “fast” mode was observed, and ascribed to internal “blob scattering” in the micellar corona.
Reaching large lengths and long times in polymer dynamics simulations
Authors: van Heukelum A. , Barkema G. T.
Published: October 2003

A lattice model is presented for the simulation of dynamics in polymeric systems. Each polymer is represented as a chain of monomers, residing on a sequence of nearest-neighbor sites of a face-centered-cubic lattice. The polymers are self- and mutually avoiding walks: no lattice site is visited by more than one polymer, nor revisited by the same polymer after leaving it. The dynamics occurs through single-monomer displacements over one lattice spacing. To demonstrate the high computational efficiency of the model, we simulate a dense binary polymer mixture with repelling nearest-neighbor interactions between the two types of polymers, and observe the phase separation over a long period of time. The simulations consist of a total of 46 080 polymers, 100 monomers each, on a lattice with 13 824 000 sites, and an interaction strength of 0.1kBT. In the final two decades of time, the domain-growth is found to be d(t)∼t1/3, as expected, since the lattice model shows the dynamical scaling of “Model B,” once the domains are bigger than the radius of gyration.
Thermal bending of liquid sheets and jets
Authors: Brenner Michael P. , Paruchuri Srinivas
Published: October 2003

We present an analytical model for the bending of liquid jets and sheets from temperature gradients, as recently observed by Chwalek et al. [Phys. Fluids 14, L37 (2002)]. The bending arises from a local couple caused by Marangoni forces. The dependence of the bending angle on experimental parameters is presented, in qualitative agreement with reported experiments. The methodology gives a simple framework for understanding the mechanisms for jet and sheet bending.
Electrical properties of zinc oxide nanowires and intramolecular p–n junctions
Authors: Liu C. H. , Yiu W. C. , Au F. C. K. , Ding J. X. , Lee C. S. , Lee S. T.
Published: October 2003

Electrical properties of ZnO nanowires and intramolecular p–n junctions were characterized by I–V measurements. These nanowires were grown embedded in anodic aluminum oxide (AAO) templates by vapor-phase-transport growth method. The nanowires were dense, continuous, and uniform in diameter along the length of the wires. I–V measurements showed the average resistivity of the ZnO nanowires in AAO templates was about one order of magnitude higher than that of the naked single ZnO nanowire. The p–n junctions in ZnO nanowires were fabricated by a two-step growth of ZnO with and without dopant of boron (∼1 wt %) in the source. I–V results suggested that p–n junctions in ZnO nanowires were formed by the two-step method.
A one-photon laser induced fluorescence and a sequential two-photon optical–optical double resonance excitation study of the vibrational structure of the B̃ 1A1(ππ*) state of thiophosgene, Cl2CS
Authors: Fujiwara Takashige , Lim Edward C. , Moule David C.
Published: October 2003

The vibrational structure of the B̃ 1A1(ππ*) electronic state of jet cooled thiophosgene, Cl2CS, has been studied by laser induced fluorescence (LIF) excitation spectroscopy through the one-photon process B̃ 1A1←X̃ 1A1 and by optical–optical double resonance (OODR), spectroscopy. Two OODR schemes were used to probe the B̃ 1A1 state. One uses selected vibronic levels of the singlet Ã 1A2(nπ*) state while the second scheme uses the companion triplet, ã 3A2(nπ*) as the intermediate level. The one-photon LIF and the two-photon OODR schemes use different optical selection rules and the two sets of spectra contain very different information. The analyses of the vibrational structure confirmed the existing assignments for the Q1 (C=S stretch), Q2 (C–Cl stretch), and Q4 (out-of-plane) modes, and reversed the assignments for the Q3 (sym. Cl–C–Cl bend) and Q6 (antisym. Cl–C–Cl bend) modes. The barrier height to molecular inversion was revised upwards to 1495 cm−1 from an analysis of the (−)−(+) inversion splittings extracted from the ν4″=471 cm−1 “hot” band intervals in the “warm jet” one-photon LIF spectra. The regularity of the patterns of the Dixon–Western bands and the constant connecting wave-number intervals allowed these bands to be assigned to the activity of ν3″. The loss of fluorescence and the shortening of the lifetime at higher vibrational excitation energies is attributed to the crossing of the B̃ 1A1(ππ*) and C̃ 1B2(nσ*) electronic states at longer C=S bond distances.
Investigation of some Rydberg states of ketene by two-photon resonance-enhanced multiphoton ionization spectroscopy
Authors: Wang Shiliang , Shi Yujun , Dénommée Stéphane , Simard Benoit , Lee Yuan-Pern
Published: October 2003

Rydberg states of CH2CO and CD2CO in the 54 000–72 000 cm−1 spectral range have been reinvestigated using two-photon resonance-enhanced multiphoton-ionization spectroscopy. Improved resolution and sensitivity has allowed for identifications of more Rydberg states than in previous work. Based on an analysis of rotational structures and quantum defects and a comparison with the results of theoretical calculations, transitions to the 3pz, 4py, 4pz, and 5py, three components of 4d, and two components of 4f Rydberg states with a ground-state ionic core (X̃ 2B1) are identified. Several transitions have been reassigned. Vibrational wave numbers indicate that the geometry of the [X̃ 2B1]3py(1A2) state is almost identical to that of the corresponding cation in its ground electronic state, with C2v symmetry, whereas that of the [X̃ 2B1]3px(1A1) state differs significantly from those of the neutral molecule and the cation in their ground states, consistent with previous quantum chemical calculations that indicated that the [X̃ 2B1]3px(1A1) state has Cs symmetry. The energy ordering of the three components of the 3p Rydberg states is found to be 3px<3py<3pz, in agreement with a previous theoretical prediction using the equation-of-motion coupled-cluster singles and doubles polarized basis set methods and a first-principles vibronic model simulation. Excitations of the vibrational modes of b1 (e.g., C=C=O out-of-plane bending, CH2 or CD2 wagging) and b2 symmetries (e.g., C=C=O in-plane bending) are observed in several Rydberg states of CH2CO and CD2CO.
H and CH3 eliminations in the photodissociation of chlorotoluene
Authors: Lin Ming-Fu , Huang Cheng-Liang , Kislov Vadim V. , Mebel A. M. , Lee Yuan T. , Ni Chi-Kung
Published: October 2003

Photodissociation of o-, m-, and p-chlorotoluene at 193 nm under collision-free conditions has been studied using multimass ion imaging techniques. In addition to the Cl atom elimination, photofragments corresponding to the reactions of C6H4ClCH3→C6H4ClCH2+H and C6H4ClCH3→C6H4Cl+CH3 were observed. Dissociation rates and fragment translational energy distributions were measured. A comparison with RRKM calculation has been made and the possible dissociation mechanism was discussed.
Global ab initio potential energy surfaces for the lowest three doublet states (1 2A′, 2 2A′, and 1 2A″) of the BrH2 system
Authors: Kurosaki Yuzuru , Takayanagi Toshiyuki
Published: October 2003

Global adiabatic potential energy surfaces (PESs) of the lowest three doublet states (1 A2A′, 2 2A′, and 1 2A″) for the BrH2 system have been calculated using the multireference configuration interaction (MRCI) method including the Davidson’s correction (Q) with the aug-cc-pVTZ basis set. Spin–orbit effects were considered on the basis of the Breit–Pauli Hamiltonian using the MRCI wave functions. The calculated adiabatic energies were fitted to the analytical functional form of many-body expansion. The barrier heights of the H+HBr→H2+Br abstraction and H+H′Br→H′+HBr exchange reactions on the ground-state PES were calculated to be 1.28 and 11.71 kcal mol−1, respectively, both of which are slightly smaller than the values obtained in the previous work [G. C. Lynch, D. G. Truhlar, F. B. Brown, and J.-G. Zhao, J. Phys. Chem. 99, 207 (1995)]. The fits for the 1 2A′, 2 2A′, and 1 2A″ PESs were successful within an accuracy of 0.1 kcal mol−1 in the important regions of PESs such as the transition states and van der Waals wells. Thermal rate constants for the abstraction and exchange reactions and their isotopic variants were calculated with the fitted 1 2A′ PES using the improved canonical variational transition-state theory with the least-action adiabatic ground-state approximation method. The calculated rate constants were found to agree better with experiment than those obtained by Lynch et al.
Spin-dependent pseudopotentials in the solid-state environment: Applications to ferromagnetic and antiferromagnetic metals
Authors: Cocula Vincent , Starrost Frank , Watson Stuart C. , Carter Emily A.
Published: October 2003

The standard density-functional theory (DFT) pseudopotential method often fails to properly describe transition-metal-containing materials because the commonly used spin-averaged pseudopotentials fail to capture environment-dependent magnetic effects. Based on a perturbationlike theory, the spin-dependent pseudopotentials have been shown to accurately reproduce properties of transition metal atoms and bulk crystals within real space DFT formalisms. In the present paper, we revisit the question of the transferability of pseudopotentials for the study of transition elements and implement the spin-dependent pseudopotentials in the more standard approach to condensed matter DFT calculations—namely, the plane-wave pseudopotential DFT method. Applications to bulk Ni, Fe, and Cr and comparison with other pseudopotential methods show that the method promises to provide an enhancement of the pseudopotential transferability compared to the standard norm-conserving or ultrasoft pseudopotentials, even beyond the nonlinear core correction.
Singular value decomposition approach for the approximate coupled-cluster method
Authors: Kinoshita Tomoko , Hino Osamu , Bartlett Rodney J.
Published: October 2003

We present a method for the approximate solution of the coupled-cluster (CC) equation, based upon the singular value decomposition (SVD). The key idea of this method is that we use SVD for the cluster amplitudes to exploit the physically important states in the CC equation. This method enables us to significantly reduce the computational requirements for CC calculations without losing the essence of the method. Relationships to the density matrix renormalization group theory and the local correlation methods are mentioned. We perform pilot calculations on some atoms and molecules to investigate the applicability of the method.
Microwave and ab initio studies of the internal rotation of ethylene in the Ar-ethylene and Ne-ethylene van der Waals complexes
Authors: Liu Yaqian , Jäger Wolfgang
Published: October 2003

Rotational spectra of the weakly bound complexes Ar-ethylene and Ne-ethylene were measured with a pulsed molecular beam Fourier transform microwave spectrometer in the range from 3.5 to 26 GHz. Spectra of five isotopomers of Ar-ethylene, namely Ar–C2H4, Ar–13C2H4, Ar–C2D4, Ar-trans-1,2-C2D2H2, and Ar-cis-1,2-C2D2H2, and of eight isotopomers of Ne-ethylene, namely Ne20-C2H4, Ne20-C2D4, Ne20-trans-1,2-C2D2H2, Ne20-cis-1,2-C2D2H2, Ne20-C2H4, Ne22-C2D4, Ne22-trans-1,2-C2D2H2, and Ne22-cis-1,2-C2D2H2, were assigned and analyzed. The spectra are in accord with T-shaped, planar structures, where the rage gas atoms are located on the b-principal inertial axis of the ethylene monomer. For isotopomers containing C2H4, C132H4, C2D4, and trans-1,2-C2D2H2, all observed transitions are doubled due to an internal rotation motion of the ethylene subunit within the complexes. The observed transition intensities are in agreement with nuclear spin statistical weights obtained from molecular symmetry group analyses under the assumption of an internal rotation of the ethylene unit about the C=C bond, i.e., the out-of-plane motion. The observation of Ka=1, m=0 transitions in Ne-trans-1,2-C2D2H2 provides further proof that the out-of-plane motion is responsible for the observed tunneling splittings. Information about the energy level ordering of the Ka=1, m=0 and Ka=0, m=1 states was obtained from the rotational spectra of the Ne-trans-1,2-C2D2H2 isotopomers. Electronic structure calculations of Ne-C2H4 were done at the CCSD(T) level of theory with the aug-cc-pVTZ basis set for all atoms, supplemented with bond functions. The global minimum is at the T-shaped, planar configuration, with a distance of R=3.55 Å between the Ne atom and the center-of-mass of ethylene and a well depth of −81.5 cm−1. One-dimensional minimum potential energy paths for possible internal rotation motions were determined. The results confirm that the out-of-plane motion is the preferred internal motion. The out-of-plane minimum potential energy path was used to determine the energy difference between the two lowest tunneling states using the one-dimensional flexible model by Meyer [R. Meyer, J. Mol. Spectrosc. 76, 266 (1979)].
Ionization of the xenon fluorides
Authors: Buth Christian , Santra Robin , Cederbaum Lorenz S.
Published: October 2003

The noble-gas atom xenon can bind fluorine atoms and form several stable compounds. We study the electronic structure of the xenon fluorides (XeFn, n=2, 4, 6) by calculating their ionization spectra using a Green’s function method, which allows one to treat many-body effects at a high level. Our focus is on the valence region and on the Xe 4d core hole. We observe a sensitive dependence of the spectra on the number of fluorine ligands. Systematic line shifts are uncovered and explained. In the Xe 5s and F 2s inner-valence regimes, from XeF2 to XeF6, the usefulness of the one-particle picture of ionization is found to become progressively worse. Moreover, adding the electronegative fluorine ligands seems to enhance—not suppress—the Auger decay of a Xe 4d core hole.
Vacuum ultraviolet laser pulsed field ionization photoelectron study of trans-2-butene
Authors: Woo H. K. , Lau K.-C. , Zhan Jiping , Ng C. Y. , Li Chi-Lun , Li Wai-Kee , Johnson Philip M.
Published: October 2003

The single-photon pulsed field ionization photoelectron (PFI-PE) spectrum of trans-2-butene (trans-CH3CH=CHCH3) in the energy range of 73 500–75 850 cm−1 has been measured using vacuum ultraviolet laser sources. The semi-empirical simulation of fine structures resolved in the original PFI-PE band yields a value of 73 624.7±2.0 cm−1 for the ionization energy (IE) of trans-2-butene. The vibrational bands for trans-CH3CH=CHCH3+ resolved in the PFI-PE spectrum are assigned based on ab initio calculations of the vibrational frequencies and Franck-Condon factors (FCFs) for ionization transitions. This assignment has provided reliable vibrational frequencies (ν1+=104 cm−1, ν2+=127 cm−1, ν3+=131 cm−1, ν5+=484 cm−1, ν8+=798 cm−1, ν13+=1164 cm−1, ν14+=1264 cm−1, ν16+=1307 cm−1, ν20+=1407 cm−1, and ν22+=1567 cm−1) for trans-CH3CH=CHCH3+. The PFI-PE spectrum is compared to the recently reported PFI-photoion (PFI-PI) spectrum for trans-2-butene. The major difference observed between the PFI-PE and PFI-PI spectra is that the intensities for excited vibrational bands were significantly suppressed or indiscernible in the PFI-PI spectrum, suggesting that the lifetimes for high-n Rydberg states associated with these excited vibrational bands were greatly reduced under the conditions used in the PFI-PI study. The experimental conditions used in the PFI-PI study also led to an IE value of about 20 cm−1 lower than that obtained in the PFI-PE measurement. We have also reassigned the vibrational bands resolved in the PFI-PE spectrum for cis-2-butene based on the FCF calculation and a more reliable set of theoretical vibrational frequencies.
The Ar–HCCCN van der Waals complex: Microwave spectroscopy and coupled cluster calculations
Authors: Huckauf Aiko , Jäger Wolfgang , Botschwina Peter , Oswald Rainer
Published: October 2003

Large-scale coupled cluster calculations have yielded an almost T-shaped equilibrium structure for the Ar–HCCCN van der Waals complex, with an equilibrium dissociation energy of De=221 cm−1. The theoretical predictions are confirmed by pulsed-nozzle Fourier transform microwave spectroscopy in the frequency range from 3 to 26 GHz. Strong b-type and much weaker a-type transitions have been observed, and the N14 nuclear quadrupole hyperfine components of the rotational transitions have been resolved. The spectral analysis has produced rotational, centrifugal distortion, and N14 nuclear quadrupole coupling constants. Structural parameters describing a (vibrationally averaged) T-shaped complex geometry have been derived.
Dynamics of radiationless transitions in large molecular systems: A Franck–Condon-based method accounting for displacements and rotations of all the normal coordinates
Authors: Borrelli Raffaele , Peluso Andrea
Published: October 2003

An efficient method to study the dynamics of radiationless transition in large molecular systems is proposed. It is based on the use of the whole set of normal coordinates of vibration and allows for taking properly into account both the displacements and the mix of the normal modes upon transition between two electronic states. The Hamiltonian matrix elements are written in terms of generalized Franck–Condon integrals and are analytically evaluated by recursion formulas. Applications to the S2→S1 internal conversion in pyrazine and to long-range electron transfer between quinones in photosynthetic reaction centers are given.
Chaotropic effect and preferential binding in a hydrophobic interaction model
Authors: Moelbert Súsanne , De Los Rios Paolo
Published: October 2003

Chaotropic substances such as urea and guanidinium chloride, which tend to increase the solubility of hydrophobic particles in aqueous solutions, are used frequently to destabilize aggregations of nonpolar solute particles and micelles, or to denature proteins. Their important applications have generated a growing interest in the physical origin of the chaotropic effect, which to date remains unclear. In this study, the two-state Muller–Lee–Graziano model for water is adapted to describe the ternary system of water, chaotropic cosolvents, and hydrophobic particles in order to analyze the effect of chaotropic substances on hydrophobic interactions. A mean-field approximation confirms the destabilizing effect of chaotropic substances on aggregates of hydrophobic solute particles. In agreement with a pair approximation, detailed Monte Carlo simulations of a three-dimensional system show preferential binding of chaotropic substances to the nonpolar particles and an increase in solubility of the latter due to the cosolvent. The modification of effective hydrophobic interactions in the presence of chaotropic substances is shown to be reproduced within a simple model where the ternary system is described only in terms of the induced alterations in hydrogen bonding between solvent molecules.
Molecular dynamics simulation of molten sodium chlorate
Authors: Siqueira Leonardo J. A. , Urahata Sérgio M. , Ribeiro Mauro C. C.
Published: October 2003

Molecular dynamics (MD) simulation has been used in a detailed investigation of structure and dynamics of molten sodium chlorate, NaClO3. Results obtained with nonpolarizable and polarizable models are compared, the latter being implemented by using a fluctuating charges approach for the anions. The partial charges of the nonpolarizable model and the parameters of the polarizable model were obtained by ab initio calculations of a single ClO3− anion. The calculated static structure factor of molten NaClO3 is in good agreement with recent neutron scattering results. A detailed picture of the distribution of cations-around the anions is provided. Proper to the rather large dipole moment of the ClO3− anion, short-range dipole ordering between pair of anions is discernible in the MD simulations. The equilibrium structure of molten NaClO3 is not too affected by including polarization effects on the anions, but significant polarization effects are observed in the dynamics of the simulated system. The ionic diffusion coefficients increase by including polarization effects, so that the polarizable model gives higher conductivity and lower viscosity than the nonpolarizable model.
Surface forces induced by ideal equilibrium polymers
Authors: van der Gucht J. , Besseling N. A. M. , Fleer G. J.
Published: October 2003

The behavior of a dilute solution of ideal equilibrium (or “living”) polymers confined between two surfaces and the effect on the surface forces are investigated theoretically. Exact analytical expressions are obtained for the concentration profile and the average length of chains in the gap, the adsorbed amount, and the disjoining pressure for chains with an arbitrary interaction with the surfaces. If the adsorption energy of the segments increases, the excess amount of segments in the gap and the average chain length increase and diverge continuously at a critical value of the adsorption energy which depends on the average length of the chains in the bulk and on the width of the gap. If the chain ends have no specific interaction with the surfaces, the equilibrium polymers cause an attraction between the surfaces, either via the depletion mechanism in the case of nonadsorbing polymers or via the formation of bridges in the case of adsorbing polymers. If only one of the functional groups adsorbs preferentially on the surface, the interaction becomes repulsive (if the main-chain segments do not adsorb), due to steric repulsion. On the other hand, if both functional groups adsorb preferentially, the interaction is attractive as a result of the formation of bridges with one adsorbed end on either surface.
Drop impact on a liquid–liquid interface
Authors: Mohamed-Kassim Zulfaa , Longmire Ellen K.
Published: October 2003

The effects of Reynolds number (Re) on the gravity-driven impact of a single drop onto a liquid–liquid interface were studied experimentally using the particle image velocimetry method. The liquid beneath the interface was identical to the drop liquid. Two liquids with different viscosities were used as the ambient above the interface resulting in viscosity ratios (drop to ambient) of 0.14 and 0.33. Index matching and a slight camera inclination were employed to eliminate optical distortion. Image planes were captured at a rate of 500 Hz, and velocity fields were determined from consecutive images. The flow Reynolds numbers based on drop impact velocity and ambient viscosity were 20 and 68 for the lower and higher viscosity ratios, respectively. During the approach toward the interface, the drop shape was more oblate for the higher Re case. At the same time, viscous stresses generated a vortex ring inside each drop and a wake behind it. Each wake contained a detached ring of similar sign to the ring inside the drop. The subsequent deformation of the drop and the interface due to impact was observed to be more radical in the higher Re case. The impingement and shearing of the trailing wake on the upper surface of each drop played a significant role in dissipating the vorticity inside both drops, and the vorticity dissipated faster for lower Re.
Effects of copolymer segment length and reversible deformation on the molecular surface structure of polyurethane
Authors: Amitay-Sadovsky E. , Komvopoulos K. , Ward R. , Somorjai G. A.
Published: October 2003

The surface molecular structure and the deformation mechanisms of two polyurethane (PUR) short-segmented copolymers were studied by sum frequency generation (SFG) vibrational spectroscopy. These PURs differ only in the length of their hard segment. Surface deformation was induced by cyclically stretching the PUR films to a macroscopic elastic elongation. Results for both PUR compositions indicate that the upward orientation of the methylene groups increases with elongation and decreases upon relaxation. The surface of the stretched PUR films with shorter hard segments exhibited irreversible deformation at the molecular level. This produced a surface composition similar to that of PUR with longer hard segments that deformed only elastically after three stretching cycles. This behavior indicates that the surface structure of PUR copolymers can be controlled by mechanical manipulation or by modification of the copolymer segment length.
Plasma etching and hydrogen blocking characteristics of PtOx thin films in ferroelectric capacitor fabrication
Authors: Huang Chun-Kai , Wu Tai-Bor
Published: October 2003

The use of a PtOx thin film as a transient template of Pt electrode in the fabrication of ferroelectric capacitor for memory devices was investigated. Fence-free patterning with a significantly high etch rate, selectivity, and sidewall slope was obtained from dry etching the photoresist-masked PtOx films using Ar/Cl2/O2 helicon wave plasma. The x-ray photoelectron spectroscopy analysis indicates that the redeposition of PtClx etch product can be repressed due to an in situ sidewall passivation with a PtO2 layer resulting from a further oxidation of the etched surface of PtOx film by the introduction of oxygen in the etching gas. Due to the chemical instability of oxygen in the PtOx film, a superior hydrogen blocking effect was also achieved in hydrogen plasma annealing of the Pb(Zr0.5Ti0.5)O3 (PZT) ferroelectric capacitors with the use of PtOx as the top electrode, and the hydrogen degradation of the PZT capacitor was repressed.
On the electronic structures of gaseous transition metal halide complexes, FeX4− and MX3− (M=Mn, Fe, Co, Ni, X=Cl, Br), using photoelectron spectroscopy and density functional calculations
Authors: Yang Xin , Wang Xue-Bin , Wang Lai-Sheng , Niu Shuqiang , Ichiye Toshiko
Published: October 2003

We report a photoelectron spectroscopy (PES) and theoretical study on a series of transition metal halide complexes: FeX4− and MX3− (M=Mn, Fe, Co, Ni, X=Cl, Br). PES spectra were obtained at two photon energies (193 and 157 nm), revealing the complicated electronic structures of these metal complexes and their variation with the ligand-field geometry and metal center substitution. Density functional calculations were carried out to obtain information about the structures, energetics, and molecular orbitals of the metal complexes and used to interpret the PES spectra. For the tetrahedrally coordinated ferric complexes (FeX4−), the PES data directly confirm the “inverted level scheme” electronic structure, where the Fe 3d electrons lie below those of the ligands due to a strong spin-polarization of the Fe 3d levels. For the three-coordinate complexes (MX3−), the calculations also revealed strong spin polarizations, but the molecular orbital diagrams present a “mixed level scheme,” in which the ligand orbitals and the Fe 3d majority spin orbitals are spaced closely in the same energy regions. This “mixed level scheme” is due to the larger splitting of the 3d orbitals in the stronger D3h ligand field and the smaller spin polarizations of the divalent metal centers. The calculations show that the metal 3d orbitals are stabilized gradually relative to the ligand orbitals from Mn to Ni in the tri-halide complexes consistent with the PES spectral patterns.
On the role of the electron density difference in the interpretation of molecular properties
Authors: Harrison James F.
Published: October 2003

In this report we use the electron density difference function, δη(r), to present an interesting and useful interpretation of several molecular properties. For example, all of the electric multipole moments of a molecule may be written as Mαβ⋯γmolecule=Mαβ⋯γatoms+Mαβ⋯γcr where Mαβ⋯γatoms is the sum of the moments of the non-interacting atoms and Mαβ⋯γcr depends on δη(r) and is the contribution to Mαβ⋯γmolecule due to charge redistribution upon molecule formation. This interpretation has implications for attempts to represent the multipole moments of an in situ charge distribution by an array of algebraic point charges.
Structural properties of CuO4 and CuO5 clusters: A density functional study
Authors: Massobrio Carlo , Pouillon Yann
Published: October 2003

We determine the equilibrium structures of CuO4 and CuO5 clusters within the framework of density functional theory and a plane-wave approach. Our calculations go beyond qualitative structural assignments proposed to interpret photoelectron spectroscopy measurements. We found that the lowest energy structures for CuO4 are based on Cu(O2) units, isomers containing Cu(O3) ozonide units being higher in energy. A different situation is observed in the case of CuO5, where several isomers with one O3 motif lie at lower energy than those made of Cu(O2) units only. Ozonide units appear crucial to ensure the stability of CuO5 clusters. This is achieved by a larger hybridization between Cu3d-like and O2p-like states, which persists when the ozonide unit transforms into an O3 chain.
Split-localized orbitals can yield stronger configuration interaction convergence than natural orbitals
Authors: Bytautas Laimutis , Ivanic Joseph , Ruedenberg Klaus
Published: October 2003

The convergence of configuration interaction (CI) expansions depends upon the orbitals from which the configurations are formed. Since their introduction half a century ago, natural orbitals have gained an increasing popularity for generating rapidly converging CI expansions and the notion has become widespread that they always yield the fastest CI convergence. It is shown here that, in fact, certain localized orbitals often yield a better CI convergence than natural orbitals, as measured by a wave function criterion as well as by an energy criterion.
Hydrated structure of ammonia–water molecule pair via the free energy gradient method: Realization of zero gradient and force balance on free energy surfaces
Authors: Nagae Yukihiko , Oishi Yuki , Naruse Norihiro , Nagaoka Masataka
Published: October 2003

The hydrated structure of ammonia molecule in aqueous solution was theoretically optimized as an ammonia–water molecule pair (H3N⋯H2O) by the free energy gradient (FEG) method [J. Chem. Phys. 113, 3516 (2000)]. The interaction between the pair and a solvent water molecule (TIP3P) [J. Chem. Phys. 79, 926 (1983)] was described by a hybrid quantum mechanical and molecular mechanical method combined with a semiempirical molecular orbital method at the PM3 level of theory. It is concluded that the present FEG method works quite well in spite of a simple steepest descent optimization scheme equipped with the adaptive displacement vector. The free energy stabilization was estimated −0.3 kcal/mol from the free energy for the same structure as that of the cluster in the gas phase. The optimized structure was found to be almost the same as that in the gas phase except for a longer OH bond length of the water molecule. However, its realization in aqueous solution is accomplished by virtue of the fulfillment of both “zero gradient” and “force balance” conditions. Finally, we discuss also the effect of microscopic “solvation entropy,” compared with the result by the conductorlike screening model method.
Semiclassical mode-coupling factorizations of coherent nonlinear optical response
Authors: Jansen Thomas la Cour , Mukamel Shaul
Published: October 2003

The identification of relevant collective coordinates is crucial for the interpretation of coherent nonlinear spectroscopies of complex molecules and liquids. Using an ℏ expansion of Liouville space generating functions, we show how to factorize multitime nonlinear response functions into products of lower-order correlation functions of collective coordinates, and derive closed expressions for linear, second- and third-order response functions. In addition to providing systematic quantum corrections, ℏ offers a convenient bookkeeping device even for the purely classical response, since including quantum fluctuations allows to circumvent the expensive computation of stability matrices which is a major bottleneck in molecular dynamics simulations. The existing classical simulation strategies, including mode coupling in k space and in real space, Langevin equations, and instantaneous normal modes are compared from a unified viewpoint.
Brillouin and boson peaks in glasses from vector Euclidean random matrix theory
Authors: Ciliberti S. , Grigera T. S. , Martı́n-Mayor V. , Parisi G. , Verrocchio P.
Published: October 2003

A simple model of harmonic vibrations in topologically disordered systems, such as glasses and supercooled liquids, is studied analytically by extending Euclidean random matrix theory to include vector vibrations. Rather generally, it is found that (i) the dynamic structure factor shows soundlike Brillouin peaks whose longitudinal/transverse character can only be distinguished for small transferred momentum, p; (ii) the model presents a mechanical instability transition at small densities, for which scaling laws are analytically predicted and confirmed numerically; (iii) the Brillouin peaks persist deep into the unstable phase, the phase transition being noticeable mostly in their linewidth; (iv) the Brillouin linewidth scales like p2 in the stable phase, and like p in the unstable one. The analytical results are checked numerically for a simple potential. The main features of glassy vibrations previously deduced from scalar are not substantially altered by these new results.
Quantum mechanical/molecular mechanical studies of a novel reaction catalyzed by proton transfers in ambient and supercritical states of water
Authors: Takahashi H. , Hashimoto H. , Nitta T.
Published: October 2003

Real-space grid quantum mechanical/molecular mechanical (QM/MM) simulations have been carried out to investigate the role of the water solvent on the novel ethanol oxidation reaction catalyzed by two water molecules through proton transfer mechanism. We have considered two thermodynamical conditions of solutions for the calculations; ambient (AW) and supercritical water (SCW). The QM/MM simulations have revealed that the solvation energy for the transition state (TS) is larger than that for the reactant state in the SCW, resulting in the reduction of the activation energy by 3.7 kcal/mol. Meanwhile, in the AW, the energy barrier is raised by 7.2 kcal/mol. Radial distribution functions show that hydrogen bondings between the solvent and the water molecules that participate in the reaction seriously collapse when the complex is changed from the reactant to the TS in AW, suggesting that the closely packed hydrogen bond network attached to the reactant disturbs the proton migration to take place. A reaction mechanism by stepwise proton translocations has also been examined and found to be competing with the concerted one.
Two-dimensional infrared correlation spectroscopy as a probe of sequential events in the diffusion process of water in poly(ε-caprolactone)
Authors: Peng Yun , Wu Peiyi , Yang Yuliang
Published: October 2003

In this study, the diffusion process of water molecules in poly(ε-caprolactone) (PCL) has been investigated using in-situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. In our system, the original broad water OH bands in 1D IR spectra can be effectively differentiated into four bands, located at 3641, 3593, 3410, and 3203 cm−1, respectively, using 2D correlation analysis. The bands at 3641 cm−1 (antisymmetric) and 3593 cm−1 (symmetric) are assigned to the OH stretching vibration of water partially hydrogen bonded with hydrophilic carbonyl group (C=O) of PCL, while the other band pair at 3410 cm−1 (antisymmetric) and 3203 cm−1 (symmetric) could be attributed to the stretching vibration of water fully hydrogen bonded with another water molecule. According to the result of the asynchronous correlation, it was concluded that the water molecules at first diffuse into free volume (microvoids) or are molecularly dispersed into the PCL matrix and then form hydrogen bond with the C=O group of the polymer during the process of water diffusion. In addition, the diffusion coefficient was estimated using nonlinear curve fitting of OH band areas in the range of 3800–3000 cm−1.
Hydrodynamic boundary conditions, the Stokes–Einstein law, and long-time tails in the Brownian limit
Authors: Schmidt J. R. , Skinner J. L.
Published: October 2003

Using molecular dynamics computer simulation, we have calculated the velocity autocorrelation function and diffusion constant for a spherical solute in a dense fluid of spherical solvent particles. The size and mass of the solute particle are related in such a way that we can naturally approach the Brownian limit (when the solute becomes much larger and more massive than the solvent particles). We find that as long as the solute radius is interpreted as an effective hydrodynamic radius, the Stokes–Einstein law with slip boundary conditions is satisfied as the Brownian limit is approached (specifically, when the solute is roughly 100 times more massive than the solvent particles). In contrast, the Stokes–Einstein law is not satisfied for a tagged particle of the neat solvent. We also find that in the Brownian limit the amplitude of the long-time tail of the solute’s velocity autocorrelation function is in good agreement with theoretical hydrodynamic predictions. When the solvent density is substantially lower than the triple density, the Stokes–Einstein law is no longer satisfied, and the amplitude of the long-time tail is not in good agreement with theoretical predictions, signaling the breakdown of hydrodynamics.
Monte Carlo simulations of infinitely dilute solutions of amphiphilic diblock star copolymers
Authors: Connolly Ronan , Timoshenko Edward G. , Kuznetsov Yuri A.
Published: October 2003

Single-chain Monte Carlo simulations of amphiphilic diblock star copolymers were carried out in continuous space using implicit solvents. Two distinct architectures were studied: stars with the hydrophobic blocks attached to the core and stars with the polar blocks attached to the core, with all arms being of equal length. The ratio of the lengths of the hydrophobic block to the length of the polar block was varied from 0 to 1. Stars with 3, 6, 9 or 12 arms, each of length 10, 15, 25, 50, 75 and 100 Kuhn segments, were analyzed. Four distinct types of conformations were observed for these systems. These, apart from studying the snapshots from the simulations, have been quantitatively characterized in terms of the mean-squared radii of gyration, mean-squared distances of monomers from the center of mass, asphericity indices, and static scattering form factors in the Kratky representation as well as the intrachain monomer–monomer radial distribution functions.
Maximum-entropy calculation of the end-to-end distance distribution of force-stretched chains
Authors: Dai Luru , Liu Fei , Ou-Yang Zhong-can
Published: October 2003

Using the maximum-entropy method, we calculate the end-to-end distance distribution of the force-stretched chain from the moments of the distribution, which can be obtained from the extension-force curves measured in single-molecule experiments. If one knows the force expansion of the extension through the (n−1)th power of a force, that is enough to calculate the n moments of the distribution. We examine the method with three force-stretched chain models: the Gaussian chain, free-joined chain, and self-avoiding chain on a two-dimensional lattice. The method reconstructs all distributions precisely. We also apply the method to force-stretched complex chain molecules: the hairpin and secondary structure conformations. We find that the distributions of homogeneous chains of the two conformational classes are quite different: there are two independent peaks in the hairpin distribution, while only one peak is observed in the distribution of secondary structure conformations. Our discussion shows that the end-to-end distance distribution, instead of extension-force curves, can reveal more important physical information.