bluuebunny/crossref_metadata_2025 huggingface dataset:
Dissociative ionization of ethanol in chirped intense laser fields
Authors: Itakura Ryuji , Yamanouchi Kaoru , Tanabe Takasumi , Okamoto Tatsuyoshi , Kannari Fumihiko
Published: August 2003

The dissociative ionization of ethanol C2H5OH in an intense laser field is investigated with a chirped laser pulse. From the sensitive dependence of the relative yields of the fragment ions on the absolute values of the linear chirp rate, it is shown that the light-dressed potential-energy surface (LDPES) at the singly charged stage governs the nuclear dynamics, and that the nuclear wave packet flow into the breaking of either of the C–C and C–O chemical bonds could be characterized by the holding time thold during which the LDPESs are maintained. It is also understood in term of the holding time that the enhanced ionization into the doubly charged stage followed by the Coulomb explosion at C–C or C–O proceeds when the nuclear wave packet at the singly charged stage reaches the critical distance for the further ionization.
Effects of intermolecular interaction on proton tunneling: Theoretical study on two-dimensional potential energy surfaces for 9-hydroxyphenalenone-CO2/H2O complexes
Authors: Mori Hirotoshi , Sekiya Hiroshi , Miyoshi Eisaku , Mogi Koichi , Sakai Yoshiko
Published: August 2003

The effects of binding of CO2 or H2O with 9-hydroxyphenalenone (9HPO) on proton tunneling in the S0 state have been theoretically investigated. High-level ab initio calculations predict that CO2 is van der Waals-bonded to the C=O⋯OH moiety of 9HPO in the most stable structure. This planar structure is more stable than the nonplanar structure where CO2 is bonded above the aromatic rings of 9HPO. In the 9HPO–H2O complex, H2O is hydrogen-bonded to the carbonyl group in the most stable structure. Two-dimensional potential energy surfaces (PESs) for 9HPO–CO2 and 9HPO–H2O have been calculated with the reaction surface method, and the contour plots of PESs for the complexes are compared with those for the 9HPO monomer. The binding of CO2 with 9HPO induces slight asymmetry in the double-minimum potential well, whereas the asymmetry of the PES is very large for the binding of H2O. The transition state energy for 9HPO–CO2 drastically decreases to be about a half that of 9HPO, while that for 9HPO–H2O is only slightly smaller than the transition energy for 9HPO. The vibrational wave function for in 9HPO–CO2 is substantially delocalized over two potential minima, but that for 9HPO–H2O is completely localized around a single potential minimum. The calculated tunneling splitting of the zero-point level in 9HPO–CO2 is only 10% smaller than the corresponding splitting of 9HPO, whereas proton tunneling is quenched in 9HPO–H2O. The calculated results are consistent with the prediction from the electronic spectra measured in a supersonic free jet.
Photoelectron spectroscopy of s-triazine anion clusters: Polarization-induced electron binding in aza-aromatic molecule
Authors: Kim Jeong Hyun , Song Jae Kyu , Park Hyokeun , Lee Sang Hak , Han Sang Yun , Kim Seong Keun
Published: August 2003

Photoelectron spectroscopy was carried out for the mass-selected cluster anions of s-triazine molecule, Tzn− (n=1–6). The mass spectrum and vibrationally resolved photoelectron spectrum of Tz− showed that unlike pyridine and pyrazine, Tz binds an electron and thus becomes the first molecule in the azabenzene series with a positive electron affinity (0.03 eV). This indicates that the local charge polarization in the aromatic ring by the three nitrogen atoms is large enough to facilitate electron binding to a homologue of benzene. A Jahn–Teller distortion was proposed to explain the vibrational progressions of the photoelectron spectrum of Tz−. A series of Ar-solvated clusters of Tz−, Tz−⋅Arm (m=1–7), have been also studied. Their photoelectron spectra showed a drop in the incremental electron binding energy when going from m=4 to 5, indicating the closure of a solvation shell with four Ar atoms. In the mass abundance spectrum of Tzn−, a distinctly high intensity for Tz2− indicated its exceptional stability, which was also manifested by the large increase by more than 0.5 eV in the vertical detachment energy of the photoelectron spectrum. Theoretical calculations were carried out to obtain optimized geometries of the neutral and anion of Tz and Tz2. We confirmed the Jahn–Teller distortion in Tz− and also addressed the role of hydrogen bonding in determining the geometries of Tz2−. A common feature for the two most stable forms of Tz2− with comparable energies was that they achieve their unique stability through equal sharing of the negative charge between their two molecular constituents. A new photoelectron band was found to emerge from Tzn− for n⩾2 by the 355 nm light, in addition to the photoelectron band at lower electron binding energy observed for n⩾1 at 532 nm. The relative intensity of this new band decreased as n increased, and its position was 1.6–1.8 eV above the first band. Photodetachment to an electronically excited state was suggested to give rise to the second photoelectron band. The nature of the excited state should be cluster-derived, not molecular, and it is highly likely that it is dimeric. A parallel-displaced geometry for Tz2− may upon photodetachment lead to a neutral excited state with a similar geometry and a strong excimer type character.
Reaction dynamics of Cl+H2S: Rotational and vibrational distribution of HCl probed with time-resolved Fourier-transform spectroscopy
Authors: Chen Kan-Sen , Cheng Shin-Shin , Lee Yuan-Pern
Published: August 2003

Following laser irradiation of a flowing mixture of S2Cl2 and H2S at 308 nm to initiate the reaction of Cl+H2S, vibration–rotation resolved emission spectra of HCl(v=1,2) in the spectral region 2436–3310 cm−1 are detected with a step-scan time-resolved Fourier-transform spectrometer. The Boltzmann-type rotational distributions of HCl(v=1) and HCl(v=2) yield rotational temperatures that decrease with reaction time; extrapolation to time zero based on data in the range 0.5–4.0 μs yields nascent rotational temperatures of 1250±70 K and 1270±120 K, respectively; an average rotational energy of 8.3±1.5 kJ mol−1 is determined for HCl(v=1,2), much greater than a previous report. Observed temporal profiles of the vibrational population of HCl(v=1,2) are fitted with a kinetic model that includes formation and quenching of HCl(v=1,2) to yield a branching ratio of 0.14±0.01 for formation of HCl(v=2)/HCl(v=1) and a thermal rate coefficient of k1=(3.7±1.5)×10−11 cm3 molecule−1 s−1. Combining an estimate of the vibrational population of HCl(v=0) based on a surprisal analysis of previous investigations on the reaction Cl+D2S, we report a ratio of vibrational distributions of HCl(v=0):(v=1):(v=2)=0.41:0.52:0.07, which gives an average vibrational energy of 23±4 kJ mol−1 for HCl. Internal energies, especially rotational energy, of HCl derived with this method is more reliable than with previous techniques; the fractions of available energy going into rotation and vibration of HCl are fr=0.12±0.02 and fv=0.33±0.06, respectively.
Molecular dynamics with quantum transitions for proton transfer: Quantum treatment of hydrogen and donor–acceptor motions
Authors: Kim Soo Young , Hammes-Schiffer Sharon
Published: August 2003

The mixed quantum/classical molecular dynamics with quantum transitions (MDQT) method is extended to treat the donor–acceptor vibrational motion as well as the hydrogen motion quantum mechanically for proton transfer reactions. The quantum treatment of both the hydrogen and the donor–acceptor motions requires the calculation of two-dimensional vibrational wave functions. The MDQT surface hopping method incorporates nonadiabatic transitions among these adiabatic vibrational states. This approach is applied to a model representing intramolecular proton transfer within a phenol-amine complex in liquid methyl chloride. For this model, the rates and kinetic isotope effects are the same within statistical uncertainty for simulations in which only the hydrogen motion is treated quantum mechanically and simulations in which both the hydrogen and the donor–acceptor vibrational motions are treated quantum mechanically. The analysis of these simulations elucidates the fundamental issues arising from a quantum mechanical treatment of the donor–acceptor vibrational motion as well as the hydrogen motion. This insight is relevant to future mixed quantum/classical molecular dynamics simulations of proton and hydride transfer reactions in solution and in enzymes.
Spectroscopic characterization of collision-induced electronic deformation energy using sum rules
Authors: Gross A. , Levine R. D.
Published: August 2003

Collision induced spectra allow a characterization of the rate of change of the dipolar asymmetry of the electronic charge distribution. We compute such spectra using classical trajectories but include essential quantal corrections. These corrections are necessary to satisfy the sum rules to leading order in Planck’s constant. A corrected computation using classical dynamics for the motion during the collision results when the spectrum is computed from the dipole velocity rather than from the dipole itself. The resulting spectrum is then an asymmetric function of frequency. The Laplace distribution is discussed as a convenient representation of the asymmetric spectrum over both the negative and positive frequency axis. For the emission spectrum the frequency distribution corresponds to the Planck equation with a radiation temperature that is equal to the mean deformation energy of the electronic charge distribution. Therefore, collision induced emission provides a thermometer for the electronic deformation during the collision.
Symmetry-adapted direct product discrete variable representation for the coupled angular momentum operator: Application to the vibrations of (CO2)2
Authors: Lee Hee-Seung , Chen Hua , Light John C.
Published: August 2003

The theoretical (quantum) description of large amplitude vibrations of systems containing four or more atoms using orthogonal internal coordinates requires three or more angular coordinates. The basis commonly used to represent these coordinates is the coupled angular momentum basis. We show that a direct product angular discrete variable representation (DVR) can be used advantageously, particularly for systems with high permutation-inversion symmetry and nonlinear equilibrium geometry. The DVR permits full symmetry projection and solution by the sequential diagonalization and truncation method. Application to the dimer of rigid CO2 demonstrates the accuracy and efficiency of the approach.
Vacuum ultraviolet mass-analyzed threshold ionization spectroscopy of benzene: Vibrational analysis of C6H6+ and C6D6+ in the B̃ 2E2g state
Authors: Kwon Chan Ho , Kim Hong Lae , Kim Myung Soo
Published: August 2003

Vibrational spectra of C6H6+ and C6D6+ in the first excited electronic state, B̃ 2E2g, have been measured by one-photon mass-analyzed threshold ionization spectroscopy using coherent vacuum ultraviolet radiation generated by four-wave sum frequency mixing in Hg. Ionization energies to C6H6+ and C6D6+ in the B̃ 2E2g state have been determined to be 11.4897±0.0006 and 11.5235±0.0006 eV, respectively. Vibrational spectra were much simpler than and different from those of the same state recorded by the gerade photo-induced Rydberg ionization technique reported previously. For some vibrations not much affected by the Jahn–Teller effect, assignments were possible by comparing with the calculated results. Assignments for the Jahn–Teller components were not definite, or rather arbitrary, even though decent fits were possible through multimode Jahn–Teller calculations.
Short-range order in liquid N-methylformamide HCONHCH3, as studied by x-ray scattering and density functional theory calculations
Authors: Hammami Férid , Bahri Mohamed , Nasr Salah , Jaidane Nejmeddine , Oummezzine Mohamed , Cortes Robert
Published: August 2003

The local order in liquid N-methylformamide has been studied by using x-ray diffraction and a density functional theory (DFT). Experimental data were analyzed to yield the total structure function SM(q) and the intermolecular pair correlation function gL(r). DFT calculations, using, namely, the standard TZV basis set, were performed to study the relative stability of the two possible isomers (cis and trans) and to examine some possible intermolecular arrangements in the liquid state. X-ray measurements can be interpreted in term of cyclic trimers of cis form molecules where each monomer can establish two N–H⋯O hydrogen bonds that are described.
Drift velocity of rotating spiral waves in the weak deformation approximation
Authors: Zhang Hong , Hu Bambi , Hu Gang , Xiao Jinghua
Published: August 2003

The drift velocities of spiral waves driven by a periodic mechanic deformation or a constant or periodic electric field are obtained under the weak deformation approximation around the spiral wave tip. An approximate formula is derived for these drift velocities and some significant results, such as the drift of spiral waves induced by a mechanical deformation with ω=3ω0, are predicted. Numerical simulations are performed demonstrating qualitative agreement with the analytical results.
Correlations between heterocycle ring size and x-ray spectra
Authors: Doomes E. E. , McCarley R. L. , Poliakoff E. D.
Published: August 2003

X-ray absorption spectra are reported for two classes of ring systems, cyclic polymethylene sulfides and organochromium ring compounds with phosphorus-complexing bidentate ligands. For the cyclic polymethylene sulfides, spectra were acquired in the region of the sulfur K-edge. For the organochromium complexes, spectra were acquired at both the chromium K-edge and at the phosphorus K-edge. These systems allow one to interrogate how the spectra evolve as the bond angle about the absorbing atom is varied. Systematic trends are observed as a function of ring size/bond angle. For the cyclic sulfides, the peaks in the continuum above the sulfur K-edge shift to higher energy and broaden with increasing ring size. These continuum features are assigned to shape resonances. In the chromium K-edge measurements, changes in the P–Cr–C bond angle do not influence the spectra appreciably, indicating that the four carbonyl groups dominate the photoelectron scattering processes. However, the phosphorus K-edge spectra are sensitive to changes in the endocyclic Cr–P–C bond angle. The trends observed in the phosphorus K-edge region for the organometallic continuum features are consistent with those observed for the cyclic polymethylene sulfides.
Quasiperiodic orbit analysis of nonadiabatic cis–trans photoisomerization dynamics
Authors: Balzer Birgit , Dilthey Stefan , Hahn Susanne , Thoss Michael , Stock Gerhard
Published: August 2003

Adopting a multidimensional model of nonadiabatic cis–trans photoisomerization, quantum-mechanical and classical simulations of the ultrafast wave-packet dynamics associated with this photoreaction are presented. The quantum calculations demonstrate that nonadiabatic photoisomerization typically leads to a largely delocalized and diffuse wave function, which hampers an intuitive understanding of the dynamics in terms of specific nuclear motion. To facilitate a classical description, a recently proposed theoretical formulation is employed that affords an exact mapping of discrete electronic states onto continuous degrees of freedom and therefore provides a well-defined classical limit of a nonadiabatically coupled system. It is shown that a simple quasiclassical implementation of the mapping formulation is able to reproduce at least qualitatively the complex quantum dynamics of the system. In addition, the classical description allows us to characterize the nonadiabatic photoisomerization dynamics in terms of a few “quasiperiodic orbits.” These orbits are close to a true unstable periodic orbit but are exactly periodic only with respect to the slow reaction coordinate of the system. Various types of quasiperiodic orbits of nonadiabatic photoisomerization are identified and analyzed. It is shown that the diffuse appearance of the quantum-mechanical wave function can be directly connected to irregular classical orbits propagating on vibronically coupled potential-energy surfaces. The chaotic behavior of the system is mainly caused by the relatively high energy corresponding to photoexcitation, the large anharmonicity of the isomerization potentials, and the reflection of the trajectory at surface crossings. The results demonstrate that quasiperiodic orbits represent a concept well suited to analyze the quantum dynamics of complex systems in terms of classical trajectories without the cumbersome search for periodic orbits.
Protein folding simulations of the hydrophobic–hydrophilic model by combining tabu search with genetic algorithms
Authors: Jiang Tianzi , Cui Qinghua , Shi Guihua , Ma Songde
Published: August 2003

In this paper, a novel hybrid algorithm combining genetic algorithms and tabu search is presented. In the proposed hybrid algorithm, the idea of tabu search is applied to the crossover operator. We demonstrate that the hybrid algorithm can be applied successfully to the protein folding problem based on a hydrophobic–hydrophilic lattice model. The results show that in all cases the hybrid algorithm works better than a genetic algorithm alone. A comparison with other methods is also made.
The statistical mechanics of the electro-acoustic effects of liquids
Authors: Yamaguchi T. , Matsuoka T. , Koda S.
Published: August 2003

The ultrasonic vibration potential (UVP) and the electrokinetic sonic amplitude (ESA) are described in terms of equilibrium time-correlation functions using the linear response theory. The reciprocal relationship between UVP and ESA is shown based on the formulation. By introducing the generalized Langevin theory and taking the hydrodynamic limit, it is discussed how the effective volume of ions in the UVP measurement is related to their partial molar thermodynamic quantities. The effective volume is proven exactly equal to the isothermal partial molar volume in the isothermal formulation. The effect of the adiabaticity of sound wave is also investigated.
The transient rise of a bubble subject to shape or volume changes
Authors: Yang B. , Prosperetti A. , Takagi S.
Published: August 2003

This paper deals with two problems in which the rectilinear rise of a gas bubble in a liquid undergoes a transient behavior. In the first problem, the bubble is released with a spherical, oblate, prolate, or oval shape and its evolution to steady state is simulated numerically. Contrary to some recently reported experiments, it is found that the terminal velocity and final shape are independent of the initial shape. This result suggests that the experimental observations may be influenced by uncontrolled effects rather than a genuine multivaluedness of the fluid-dynamic solution for a steadily rising bubble. The second problem concerns the ascent of a bubble which expands, or contracts, due to a change in the ambient pressure. The ensuing behavior of the rise velocity is strongly influenced by added mass effects.
Hydrogen bonding and proton transfer in small hydroxylammonium nitrate clusters: A theoretical study
Authors: Alavi Saman , Thompson Donald L.
Published: August 2003

Structures and energies of gas-phase hydroxylammonium nitrate (HAN), HONH3NO3, are determined using density functional theory and the 6-311++G(d,p) basis set. Three stable configurations are found for HAN which involve strong hydrogen bonding between hydroxylamine and nitric acid molecules. In the most stable configuration, both the oxygen and the nitrogen of hydroxylamine are hydrogen bonded to sites on the nitric acid molecule. In the less stable HAN structures only the oxygen or the nitrogen of hydroxylamine are hydrogen bonded. Two stable structures for the (HAN)2 complex are investigated. The more stable structure is ionic, with the nitric acid proton having transferred to the nitrogen of hydroxylamine. Strong electrostatic and hydrogen-bonding interactions stabilize this structure. The other stable form of (HAN)2 has fewer hydrogen bonds and is composed of interacting neutral nitric acid and hydroxylamine molecules. Binding energies are determined for all structures along with corrections for basis set superposition errors in the HAN molecules. Proton exchange reaction paths are studied for the HAN configurations. The saddle points for the proton exchange process are ionic forms of HAN with interacting HONH3+ and NO3− moieties. These ionic structures are 13.5 and 13.6 kcal/mol higher in energy than the neutral hydrogen-bonded complexs of HONH2 and HNO3 from which they are formed. The electrostatic attractions between the ions are sufficient to stabilize the ionic form of (HAN)2, whereas in the HAN “monomer” the interaction energy for single HONH3+ and NO3− ions is not sufficient to compensate for the energy required for proton transfer from nitric acid to the hydroxylamine group. A correlation based on the bond-valence theory which describes the bond lengths of the hydrogen bonds is examined for the complexes. All the hydrogen bonds follow the correlation well.
Current transport through molecular electronic devices
Authors: Ernzerhof Matthias , Zhuang Min
Published: August 2003

A new formalism for the calculation of the conductance of a molecule attached to two macroscopic metal contacts is proposed. Starting from an effective one-electron picture, the contacts are accounted for by certain potentials that are added to the molecular Hamiltonian. By choosing appropriate boundary conditions for the molecular eigenvalue problem, stationary states can be obtained describing the current transport through the molecule. The approach presented here is not restricted to the zero-voltage and zero-current limit. A simple and transparent formula for the conductance is derived that resembles Fermi’s golden rule. The relation of the proposed method to nonequilibrium transport theory is discussed.
Microwave spectrum of o-benzyne produced in a discharge nozzle
Authors: Kukolich S. G. , Tanjaroon C. , McCarthy M. C. , Thaddeus P.
Published: August 2003

The microwave spectrum for o-benzyne was obtained by passing a dilute (<1%) mixture of benzene in neon through a pulsed-DC discharge nozzle source into a pulsed-beam, Fourier transform spectrometer. Rotational transitions were measured for the normal isotopomer, the two unique single-D isotopomers, and the C13 isotopomer and one of the C13 isotopomers. Benzynes have been known as reactive intermediates in organic reactions for many years, and have recently been implicated in gasoline combustion reactions and antitumor activity of enediynes. Twenty-seven b-type transitions for the normal isotopomer were fit to obtain A=6989.7292(6), B=5706.8062(6), and C=3140.3708(4) MHz, and five centrifugal distortion constants. The inertial defect is Δ=0.069 4 amu Å2, consistent with a planar structure. Hyperfine structure for the D1 (closest to the C≡C bond) and D2 (furthest from the C≡C bond), was analyzed to obtain deuterium quadrupole coupling strengths eQqaa(D1)=185(3) kHz, eQqbb(D1)=−85(2) kHz, eQqaa(D2)=5(13), and eQqbb(D2)=86(13) kHz. The C–D, bond axis quadrupole coupling strengths are compared with values for benzene. Spectra for the C613 and one of the C113 isotopomers were analyzed to obtain rotational constants. Kraitchman analysis and least-squares fitting provided nearly all of the structural parameters. The preliminary structural analysis yields an acetylenic C≡C bond length of 1.24 Å, in agreement with a recent NMR value. Density functional theory (DFT) calculations were used to obtain structural parameters, and values obtained are in very good agreement with present experimental results.
The effects of temperature on the hydration structure around Ni2+ in concentrated aqueous solution
Authors: Badyal Y. S. , Simonson J. M.
Published: August 2003

A preliminary investigation has been made of the effects of temperature on the hydration structure around Ni2+ in a concentrated (nominally 4 m) aqueous solution of nickel (II) chloride using the technique of neutron diffraction with isotope substitution. The scattering from two heavy water solutions containing, respectively, nickel in natural abundance and enriched in the Ni62 isotope, were measured at temperatures of 90, 175, and 230 °C using the general liquids and amorphous materials diffractometer at the intense pulsed neutron source, Argonne National Laboratory. The Ni2+ hydration structure was seen to become progressively weaker and broader with increasing temperature, consistent with the findings of previous experiments. A more subtle effect of temperature on hydration structure has also been highlighted for the first time, namely, gradual shifts in the first hydration peak positions in the real-space difference function. Our findings point to the importance of following changes in hydration structure closely by measuring as many state points as possible, and the desirability of complementary approaches such as EXAFS (extended x-ray absorption fine structure) and quasielastic neutron scattering. Our initial study has also demonstrated the successful performance of a new sample cell designed at Oak Ridge National Laboratory for handling corrosive aqueous solutions under conditions of elevated temperatures and pressures.
A statistical mechanical model for inverse melting
Authors: Feeney Melissa R. , Debenedetti Pablo G. , Stillinger Frank H.
Published: August 2003

Inverse melting is the situation in which a liquid freezes when it is heated isobarically. Both helium isotopes exhibit intervals of inverse melting at low temperature, and published data suggests that isotactic poly (4-methylpentene-1) also displays this unusual phase behavior. Here we propose a statistical mechanical model for inverse melting. It is a decorated modification of the Gaussian core model, in which particles possess a spectrum of thermally activated internal states. Excitation leads to a change in a particle’s Gaussian interaction parameters, and this can result in a spatially periodic crystal possessing a higher entropy than the fluid with which it coexists. Numerical solution of the model, using integral equations and the hypernetted chain closure for the fluid phase, and the Einstein model for the solid phases, identifies two types of inverse melting. One mimics the behavior of the helium isotopes, for which the higher-entropy crystal is denser than the liquid. The other corresponds to inverse melting in poly(4-methylpentene-1), where the high-entropy crystal is less dense than the liquid with which it coexists.
Dynamics of supercooled liquids: Universality of relaxation time near the crossover temperature
Authors: Gerardin Jaline , Mohanty Sudarsana , Mohanty Udayan
Published: August 2003

We investigate the nature of cooperative relaxation at the crossover temperature. The relaxation time for a cooperative rearranging region at the crossover temperature is related to the ratio of the entropy and the heat capacity of the supercooled liquid, and the ratio of the glass transition to the crossover temperatures. The lifetime of “elementary” excitations in supercooled liquid is determined by a variational technique. By imposing self-consistency between lifetime of elementary excitations and hopping relaxation time on the potential energy surface, the relaxation time at the crossover temperature is estimated. The predictions are in excellent agreement with available experimental data.
Nontopographic description of inherent structure dynamics in glassformers
Authors: Berthier Ludovic , Garrahan Juan P.
Published: August 2003

We show that the dynamics between inherent structures in glassforming systems can be understood in purely dynamical terms, without any reference to “topographic” features of the potential energy landscape. This “nontopographic” interpretation is based instead on the existence of dynamical heterogeneities and on their statistical properties. Our view is supported by the study of simple dynamically facilitated models of glassformers. These models also allow for the formulation of quantitative theoretical predictions which are successfully compared to published data obtained in numerical and experimental studies of local dynamics of supercooled liquids.
Breakup length of forced liquid jets
Authors: Kalaaji A. , Lopez B. , Attané P. , Soucemarianadin A.
Published: August 2003

The experimental breakup of liquid jets subjected to a sinusoidal perturbation is investigated in the Rayleigh and first wind-induced regimes. Stroboscopic illumination of the jet and laser photometry method are used. The ability of linear spatial and temporal theories to describe certain aspects of the phenomenon is stressed. A review of data in the literature shows that the limited experimental windows investigated so far do not allow definite conclusions to be drawn. Our results, obtained over a wide range of fluid viscosity and jet velocity values, show that the linear theory of Sterling and Sleicher accurately predicts the variation in breakup length with jet velocity. The exponential character of the initial growth of a monochromatic perturbation along the jet is also described quantitatively. These results were obtained by carefully controlling the initial jet surface perturbation. It is also shown that transient surface tension and jet contraction have to be taken into account to analyze the experimental results.
CO on Pt(111): A puzzle revisited
Authors: Olsen R. A. , Philipsen P. H. T. , Baerends E. J.
Published: August 2003

Today’s state-of-the-art method for calculating the interaction of atoms or small molecules with metal surfaces is considered to be density functional theory (DFT) at the generalized gradient approximation (GGA) level employing a slab or supercell representation of the surface. The method is widely used and by many assumed to be both qualitatively and quantitatively accurate. This notion has recently been challenged by Feibelman et al. [J. Phys. Chem. B 105, 4018 (2001)] who suggest that the DFT/GGA method does not correctly predict the most stable adsorption site for the CO/Pt(111) system, and they conclude that the method is not qualitatively accurate. However, using a different calculational approach we find a good agreement between the calculated potential energy surface for this system and the one inferred from experiments, indicating that the evidence supporting the view of Feibelman et al. is not yet conclusive. On the contrary, we advocate the view that the DFT/GGA method should at the moment be considered qualitatively accurate for predicting the most stable CO adsorption sites on metal surfaces. This view is supported by (i) our results for the Pt(111) surface which in agreement with experiments favors the top site, (ii) an assessment of literature results for other surfaces, suggesting that the error in the relative stability of the CO adsorption sites on a given surface is within ±0.1 eV when compared to experiments, (iii) the considerable challenge one faces when trying to converge DFT/GGA calculations within ±0.1 eV with respect to all computational parameters, (iv) and that for energy differences smaller than say 0.1 eV, calculated quantities like, e.g., vibrational frequencies and geometries discriminate correctly between sites, being in agreement with experiments at the correct adsorption site.
Ab initio simulation of the ice II structure
Authors: Fortes A. D. , Wood I. G. , Brodholt J. P. , Vočadlo L.
Published: August 2003

We have carried out ab initio simulations on the high-pressure polymorph of solid water, ice II, a phase for which there is a surprising lack of experimental data. We report our calculated third-order Birch–Murnaghan equation of state for ice II: the zero pressure and temperature density, ρ0=1240.27±0.62 kg m−3, bulk modulus, K0=16.18±0.12 GPa, with the first pressure derivative of the bulk modulus, K0′, fixed equal to 6.0. These parameters, the unit cell dimensions, and the atomic positions are in good agreement with experimental values. We also describe the way in which the change in unit cell volume is accommodated within the structure, primarily by contraction of the distance between neighboring hexagonal tubes—the principal structural element of ice II. This is in agreement with existing experimental data.
Electron–hole pair creation by atoms incident on a metal surface
Authors: Trail J. R. , Bird D. M. , Persson M. , Holloway S.
Published: August 2003

Electron–hole pair creation by an adsorbate incident on a metal surface is described using ab initio methods. The approach starts with standard first principles electronic structure theory, and proceeds to combine classical, quantum oscillator, and time dependent density functional methods to provide a consistent description of the nonadiabatic energy transfer from adsorbate to substrate. Of particular interest is the conservation of the total energy at each level of approximation, and the importance of a spin transition as a function of the adsorbate/surface separation. Results are presented and discussed for H and D atoms incident on the Cu(111) surface.
Can trimers influence the free surface density profile of liquid He4 at zero temperature?
Authors: March N. H. , Tosi M. P. , Minguzzi A.
Published: August 2003

In the ground state of liquid He4, the density profile must display a huge decrease from passing from the bulk quantal liquid to dilute quantal vapor. Motivated by the recent work of Bulgac [Phys. Rev. Lett. 88, 050402 (2002)] we have reopened the question of the nature of the density profile through an assumed planar surface. We predict that in the low density tail of the still inhomogeneous profile there will be a transition as the density is lowered from monomer to trimer quantal vapors. If true, there should be two “transition” regions: the customary high-density liquid to low-density vapor now supplemented by a further quantal vapor transition.
Low barrier hydrogen bond in protonated proton sponge. X-ray diffraction, infrared, and theoretical ab initio and density functional theory studies
Authors: Bieńko Agnieszka J. , Latajka Zdzisław , Sawka-Dobrowolska Wanda , Sobczyk Lucjan , Ozeryanskii Valery A. , Pozharskii Alexander F. , Grech Eugeniusz , Nowicka-Scheibe Joanna
Published: August 2003

A new proton sponge, 2,7-dibromo-1,8-bis(dimethylamino)naphthalene (Br2DMAN), and its protonated (HBr) or deuterated (DBr) forms were studied by using x-ray diffraction and infrared spectroscopy, as well as ab initio and density functional theory calculations. In the crystalline lattice of the Br2DMAN.HBr salt, symmetrical (NHN)+ hydrogen bonding of length 2.547(3) Å is observed. No deuterium geometrical isotope effect was detected. The structure refinement suggests disordering of protons between two equivalent positions at the nitrogen atoms. These findings are in agreement with infrared spectra, which are characterized by an intense band centered at ∼560 cm−1 assigned to the ν(NHN) protonic transition. Deuteration leads to a shift of this band to ∼340 cm−1, so that the isotopic ratio νH/νD (ISR) of 1.65 is characteristic of an unusual potential for the proton motion. The results of MP2 calculations are in fairly good agreement with the experimental data. The theoretical N…N hydrogen bond length is 2.575 Å, while the distance between the minima equals to ca. 0.5 Å with a barrier height of 0.70 kcal/mol. The calculated difference between the 0→1 proton (deuteron) levels is 509 (284) cm−1, giving an ISR value of 1.76.
Extended Douglas–Kroll transformations applied to the relativistic many-electron Hamiltonian
Authors: Nakajima Takahito , Hirao Kimihiko
Published: August 2003

A new generalized Douglas–Kroll (DK) approach is proposed for the relativistic many-electron Hamiltonian including the electron–electron interaction. In order to consider the higher-order DK transformation to the two-electron interaction, the present approach adopts the effective one-electron potential in the Dirac–Hartree–Fock/Dirac–Kohn–Sham operator as an expansion parameter in the DK transformation. Its numerical performance is tested for the atomic Hg and molecular HAt and At2 systems. The third-order DK transformation to both one-electron and two-electron Hamiltonians, which is the highest level of theory treated in this study, gives excellent agreement with the four-component relativistic approach. The first-order DK correction to the two-electron interaction is shown to be satisfactory for both atomic and molecular systems.
Variational calculations of HBN energy levels in the X 2Π and A 2Σ+ states
Authors: Biczysko Małgorzata , Tarroni Riccardo , Carter Stuart
Published: August 2003

A theoretical study of the HBN radical in the X 2Π and A 2Σ+ states, taking into account vibronic coupling effects, is reported. The lowest (1 2A′,1 2A″,2 2A′) potential energy surfaces (PES) of the HBN–BNH system have been studied to identify all stationary points. The HBN minimum was found to be 20.0 kcal/mol above BNH, with an isomerization barrier of ≈11 000 cm−1 on the 1 2A′ surface. For the HBN isomer, accurate near-equilibrium three-dimensional diabatic PESs for the ground X 2Π (1 2A′,1 2A″) and first excited A 2Σ+ (2 2A′) electronic states have been calculated at the multireference configuration interaction level of theory, with extended basis set. A vibronic coupling between bend and BN stretch, analogous to that found in the isoelectronic C2H and HCN+ radicals, has been found to take place due to the crossing of the X 2Π and A 2Σ+ states at energies close to 11 000 cm−1. Vibronic energy levels of HBN and DBN have been calculated variationally using a previously developed method [Carter et al., Mol. Phys. 98, 1967 (2000)] suitable for three-atomic molecules showing three-state vibronic interactions. Energy levels of Σ and Π symmetry up to 10 000 cm−1 for HBN, and 8800 cm−1 for DBN, are reported. It is shown that due to the high-energy surface crossing, the vibronic interaction becomes non-negligible only for levels above 8500 cm−1. For all levels, Renner–Teller effects and Fermi resonances are analyzed.
Surface potential measurements as a probe of the charge localization in assemblies of metallic quantum dots: A computational study
Authors: Remacle F.
Published: August 2003

We report a systematic computational study of the surface charge density of assemblies of metallic quantum dots as a function of the compression of the array, the applied voltage and the temperature. The computations also take into account the inherent disorder that arises from the dispersion in the sizes of the individual dots and from geometrical packing defects. They are carried out quantum mechanically using a Hückel-type (tight-binding) Hamiltonian. Surface potential contours allow characterizing the distinct coupling regime (domain-localized phase) that occurs at intermediate compression of the array, between the insulating and the conducting phase. This phase is made of super exchange coupled islands. We show how the shape of the islands depends not only on the direction and on the strength of the applied voltage but also significantly on the temperature. This temperature effect is due to the variation of the delocalization of the excited electronic states with energy. Finally, we investigate in the time domain the rate of propagation of an initially localized charge in the presence of an external bias. The super exchange coupled islands are built at a finite rate that depends on the amount of compression. When an external bias is applied, the rate of charge delocalization in the direction of the voltage gradient is faster than in the direction perpendicular to it.
Isotopic effect on phase equilibria of atomic fluids and their mixtures: A direct comparison between molecular simulation and experiment
Authors: Chialvo Ariel A. , Horita Juske
Published: August 2003

Vapor–liquid and vapor–solid isotopic fractionation of noble gases and their mixtures are studied by molecular-based simulation of atomic Lennard-Jones fluids. The temperature dependence of the fractionation factors for Ar36/40Ar, Ne20/22Ne, Kr80/84Kr and the composition dependence of the corresponding fractionation factors for binary Ar–Kr mixtures as predicted by simulation are compared with the existing experimental data, to assess the accuracy of ℏ2-order Kirkwood–Wigner free energy expansion for specific Lennard-Jones parametrizations. Predictions of the fractionation factors for other isotopic pairs, including Ne20/21Ne, and Xe132/136Xe as well as tests of some premises behind the microscopic interpretation of the fractionation factors are also given.
Crossover critical phenomena in an aqueous electrolyte solution: Light scattering, density and viscosity of the 3-methylpyridine+water+NaBr system
Authors: Hernández Marı́a Paula , Ortega Francisco , Rubio Ramón G.
Published: August 2003

We have measured the light scattered by critical mixtures of 3-methylpyridine+water+NaBr, at three different salt concentrations, as a function of temperature and wave vector, in the one-phase region. From the data, we have calculated the susceptibility χ and the correlation length ξ. We have also measured the density and the shear viscosity for the same critical mixtures over a broad temperature range. The analysis of the χ and ξ data in terms of the Wegner expansion lead to negative values for the amplitudes of the first correction-to-scaling terms. This is consistent with the nonmonotonic crossover from Ising to mean-field critical behavior. The analysis of the light scattering data in terms of the crossover theory of Anisimov et al. [Phys. Rev. Lett. 75, 3146 (1995)] leads to a good fit of the data, and allows one to describe accurately the behavior of the effective critical exponents γ and ν. The thermal expansivity calculated from the density measurements is consistent with a (1-α) critical anomaly, with α=0.11 for the three critical mixtures studied. Finally, the shear viscosity has been analyzed in terms of the dynamic crossover function and the ξ values calculated from the theory of Anisimov et al. [Phys. Rev. Lett. 75, 3146 (1995)]. The values of the critical exponent z are consistent with the theoretical predictions.
Density of states of a binary Lennard-Jones glass
Authors: Faller Roland , de Pablo Juan J.
Published: August 2003

We calculate the density of states of a binary Lennard-Jones glass using a recently proposed Monte Carlo algorithm. Unlike traditional molecular simulation approaches, the algorithm samples distinct configurations according to self-consistent estimates of the density of states, thereby giving rise to uniform internal-energy histograms. The method is applied to simulate the equilibrium, low-temperature thermodynamic properties of a widely studied glass former consisting of a binary mixture of Lennard-Jones particles. We show how a density-of-states algorithm can be combined with particle identity swaps and configurational bias techniques to study that system. Results are presented for the energy and entropy below the mode coupling temperature.
Solvent dependence of solvatochromic shifts and the first hyperpolarizability of para-nitroaniline: A nonmonotonic behavior
Authors: Wang Chuan-Kui , Wang Yan-Hua , Su Yan , Luo Yi
Published: August 2003

Solvent dependence of the electronic structure and nonlinear optical properties of the para-nitroaniline (pNA) molecule on the polarity of the solutions has been studied using the polarizable continuum model in combination with the hybrid density functional theory. With a supermolecular approach, specific hydrogen bonding effects have also been fully considered. Good agreement between theory and experiments are obtained for both solvatochromic shifts of the charge transfer state and the solvent-induced first hyperpolarizability of pNA.
Rotational dynamics of colloidal tracer spheres in suspensions of charged rigid rods
Authors: Koenderink Gijsberta H. , Aarts Dirk G. A. L. , Philipse Albert P.
Published: August 2003

The short-time rotational dynamics of colloidal silica tracer spheres in suspensions of rigid silica rods is investigated, using time-resolved phosphorescence anisotropy, as a function of tracer radius aT, rod volume fraction φ, and the range κ−1 of the double-layer repulsions between the like-charged rods and tracer spheres. A large tracer size aT and a small screening length κ−1 appear to maximize hydrodynamic hindrance of tracer diffusion for given φ. The marked φ-dependence of the rotational dynamics is primarily determined by the large excluded volumes of the high-aspect ratio rods. Stokes–Einstein–Debye (SED) scaling of the rotational diffusion coefficients with the inverse viscosity of the rod suspensions holds fairly well, expect for small aT and large κ−1. The ionic strength dependence of deviations from SED scaling is rationalized in terms of an effective hard-rod model with the bare length L replaced by an effective length L+4κ−1.
An ab initio, analytically fitted, global potential energy surface for the ground electronic state of He3+
Authors: Chang Daniel T. , Gellene Gregory I.
Published: August 2003

An analytical, global potential energy surface for the ground electronic potential energy surface (PES) for the He3+ ion has been constructed by fitting ab initio energy values calculated at the QCISD(T)/aug-cc-pVTZ level of theory for 935 geometric configurations to a many body expansion type functional form appended with ion-induced dipole terms to describe the long range interactions. The PES is adiabatically constrained to the ground electronic state by requiring the two atoms with the shortest separation in any particular geometry to be described by the embedded two-body He2+ potential. A transition state for the positional interchange of the middle and end atoms of the linear, centrosymmetric equilibrium geometry is identified and lies about 300 cm−1 below the energy of the He2++He dissociation products. The nature of the PES near a seam of conical intersections between the ground and first excited electronic states occurring at D3h geometries is discussed.
Theoretical study of the potential stability of the peroxo nitrate radical
Authors: Eisfeld Wolfgang , Morokuma Keiji
Published: August 2003

The existence of the peroxo nitrate radical (ONOO) has been discussed for some time and its formation has been used to explain aspects of the NO3 scavenging in the Earth’s atmosphere. In this study we report our thorough investigation of the stability of this species by means of highly correlated ab initio calculations. Single-reference coupled-cluster singles and doubles (CCSD) as well as multireference configuration interaction (MRCI) calculations were performed to optimize equilibrium structures and obtain harmonic force fields. The force fields were used to calculate the harmonic frequencies as well as isotopic shifts. The CCSD calculations result in shallow minima for both the |2A″〉 ground as well as the |2A′〉 excited state. However, the calculated isotopic shifts of the ground state show that the experimentally observed shift of 50 cm−1 cannot be due to ONOO. In contrast, no minima were found by the MRCI calculations. The analysis of the wave functions indicates that the potential wells obtained by CCSD are artifacts which are due to the single-reference nature of the CCSD method. Our conclusion is that ONOO is not a bound structure and cannot be observed experimentally. Our calculations also show that thermal decomposition of NO3 into NO and O2 is not possible under atmospheric conditions and thus this channel cannot be responsible for the unknown NO3 scavenging process discussed in the literature.
Density fitting in second-order linear-r12 Møller–Plesset perturbation theory
Authors: Manby Frederick R.
Published: August 2003

Density fitting is used to approximate all of the 4-index 2-electron integrals in the explicitly correlated MP2-R12 theory of Kutzelnigg and Klopper. The resulting method—DF-MP2-R12—requires only 2- and 3-index integrals over various 2-electron operators, and is extremely efficient. The errors arising from the fitting process can be made small by using robust fitting formulas throughout, such that the error in each fitted integral is quadratic in the error of the fitted orbital product densities. Sample calculations on glycine reveal that for large basis sets DF-MP2-R12 is faster than a standard MP2 calculation and takes only a small fraction of the time for the Hartree–Fock calculation.