bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrogen bonding in liquid methanol
Authors: Matsumoto M. , Gubbins K. E.
Published: July 2002

Molecular-dynamics simulations of liquid methanol have been carried out at two temperatures (T=300 and 200 K) to investigate the dynamics of hydrogen bonding. The mean lifetime of hydrogen bonds (defined in terms of a time-averaged pair energy) is calculated and found to be 5–7 ps at 300 K, through the results depend on the averaging time used in the hydrogen bond definition. At 200 K the lifetime becomes much longer, by one order of magnitude or more. A bonding state is defined for each molecule according to the number of hydrogen bonds, and the mean lifetime of the states and the rate constants of transition between states are calculated. Molecules with two hydrogen bonds have much longer lifetimes than expected from the assumption that forming and breaking of hydrogen bonds occur randomly. Bonding autocorrelation and state autocorrelation functions are calculated, which enable us to have another definition of lifetimes and to discuss the way in which local diffusion occurs near molecules.
Collision of hyperthermal atoms with a solid surface. I. Energy dissipation in the solid
Authors: Zeiri Yehuda , Lucchese Robert R.
Published: July 2002

It is well established that when a hyperthermal atom collides with a solid surface, a large fraction of the atom’s translational energy may be transferred to the solid in a single collision. The energy transferred to the solid may be channeled into two modes, which are electronic excitation and energy transfer to phonons. In the present work, electronic excitation in the solid was not considered. Thus, it was assumed that energy is transferred during the scattering event from the projectile to the solid vibrational modes only. Since the gas particle interacts with a limited small number of surface atoms, a ‘‘hot spot’’ is formed on the surface. We found that the excitation of the vibrational modes of the solid decays initially with a decay constant of less than 0.5 ps and then more slowly with a decay constant of 2.5–3.5 ps. A discussion of which vibrational modes are excited is also given.
Rotationally resolved threshold photoelectron spectra of OH and OD
Authors: Wiedmann R. T. , Tonkyn R. G. , White M. G. , Wang Kwanghsi , McKoy V.
Published: July 2002

The results of combined experimental and theoretical studies of the rotationally resolved photoelectron spectra of OH and OD following single-photon ionization are presented. The measured zero-kinetic-energy (ZEKE) spectra were obtained using pulsed field ionization in conjunction with a vacuum ultraviolet laser source. The OH+ and OD+ (X 3Σ−, v+=0) rotational distributions were studied over the range 95.0–95.4 nm. Agreement between the observed and calculated spectra is very encouraging. Improved values for the ionization potentials of OH and OD (104 989 and 105 085±2 cm−1, respectively) are reported and the unusual dynamics favoring ΔN<0 transitions are discussed.
Adsorption kinetics of ‘‘hot’’ dimers
Authors: Albano Ezequiel V. , Pereyra Victor D.
Published: July 2002

In this work we study, by means of the Monte Carlo technique, the adsorption kinetics of ‘‘hot’’ dimers, i.e., molecules which after adsorption dissociate and each of the remaining monomers fly apart up to a maximum distance R from the original adsorption site. We have evaluated the jamming coverage (θj) which depends on R and differs from the standard random dimer filling problem. Also the dependence of both the sticking coefficient and the average distance traveled by the monomers on θ is studied and discussed. ‘‘Hot’’ monomers exhibit an enhanced probability for encounters with other adparticles. This behavior may be relevant in the dynamic of some catalytic processes.
Comparisons between coupling model and molecular dynamics simulation for local chain motions in bulk amorphous polymers
Authors: Ngai K. L.
Published: July 2002

Recent molecular dynamics simulation of the local chain dynamics of bulk amorphous polymers by Takeuchi and Roe [J. Chem. Phys. 94, 7446 (1991)] have brought out many interesting features of various time-correlation functions of bond reorientational motion. It is pointed out here that these features are in good agreement with what is predicted by the coupling model for local chain motions of amorphous polymers, and furthermore these features are common to relaxations in a number of interacting many body systems.
Stability domain of the ice VIII proton-ordered phase at very high pressure and low temperature
Authors: Pruzan Ph. , Chervin J. C. , Canny B.
Published: July 2002

The transition line between ice VII and ice VIII has been determined by Raman scattering for H2O and D2O. Above 15 GPa the transition temperature decreases linearly with pressure, and then drops to 0 K around 62 and 72 GPa for H2O and D2O, respectively. An analysis, using the pseudospin formalism, shows that the linear regime is due to the decrease with pressure of the dipolar interaction, while the proton tunnelling remains negligible. The proton disorder becomes efficient only from 60 GPa for H2O (or 72 for D2O) where it limits the stability range of the ordered phase VIII. Our analysis suggests that ice X, the so-called ice with hydrogen at the midpoint of the O---O bonds, would be obtained above 80 GPa (H2O) or 100 GPa (D2O).
Statistical mechanics of viscous flow in nematic fluids
Authors: Sarman Sten , Evans Denis J.
Published: July 2002

We derive Green–Kubo (GK) relations for the viscosity coefficients of nematic liquid crystals. These GK relations are similar to, but considerably more complicated than, those of an isotropic fluid. In addition to shear viscosities there are also twist viscosities and cross couplings between the symmetric strain rate and the antisymmetric pressure tensor and vice versa. We show that the twist viscosity is inversely proportional to the mean square displacement of the director. Using the so-called SLLOD equations of motion we construct nonequilibrium molecular dynamics (NEMD) algorithms that can be used to efficiently calculate the viscosity coefficients of nematic liquid crystals from atomistic computer simulations. We also devise an additional NEMD algorithm for controlling the angular velocity of the director in a nematic fluid. We derive a fluctuation relation for the alignment angle between the director and the streamlines in planar Couette flow and also for the shear induced molecular angular velocity. In an isotropic fluid, close to equilibrium, this angular velocity is equal to half the vorticity. In a nematic liquid crystal it is nearly zero because of cross couplings with the symmetric part of the strain rate tensor. We test the Green–Kubo relations and the NEMD algorithms in a nematic liquid crystal modeled using a modified version of the Gay–Berne potential. In general, the Green–Kubo and NEMD results agree very well.
A multiconfiguration self-consistent reaction field response method
Authors: Mikkelsen Kurt V. , Jo/rgensen Poul , Jensen Hans Jo/rgen Aagaard
Published: July 2002

A multiconfiguration self-consistent reaction field linear response method is presented for calculating frequency-dependent molecular properties as well as electronic excitation energies and transition moments of solvated molecules. Sample calculations are presented of a solvated water molecule and show a substantial dependence on the properties of the surrounding solvent. The solvent effect cannot be described as a correction to the vacuum value involving simple scalar factors.
On the mechanism and surface morphology of gallium arsenide laser-assisted etching by chlorine at 193 nm
Authors: Tejedor P. , Briones F.
Published: July 2002

Laser-assisted etching of (100) n-doped GaAs in a Cl2/Ar atmosphere performed with a pulsed ArF excimer laser (λ=193 nm, τ=17 ns) was investigated as a function of laser fluence, process thermodynamical parameters (pressure, temperature, and gas phase composition), and carrier concentration. The etching process is shown to result from a combination of photochemically and thermally activated reaction steps. Etch reaction kinetics were found to be 3/2 order in Cl2 at pressures below 7×10−3 Torr with an activation energy of 7.8 kcal/mol, attributable to the formation of GaCl3 via the reaction between chemisorbed GaCl2 and Cl radicals from the gas phase. The influence of the etching parameters on surface morphology was also examined. Mirror-like morphologies were achieved using laser fluences below 25 mJ/cm2, substrate temperatures between 100 and 200 °C, and concentrations of Cl2 in Ar below 2%.
Molecular dynamics free energy simulations: Influence of the truncation of long-range nonbonded electrostatic interactions on free energy calculations of polar molecules
Authors: Chipot Christophe , Millot Claude , Maigret Bernard , Kollman Peter A.
Published: July 2002

The introduction of a reaction field dipolar contribution in free energy calculations is considered. The method is applied to a series of polar compounds, namely TIP3P water, methanol, and acetamide. The hydration free energies computed with both spherical cutoff and reaction field geometries are critically compared. Although the estimated quantities appear to be very similar, the use of a reaction field correction offers a better representation of the liquid structure. In the case of methanol, different potential derived point charge models of increasing complexity are investigated. It is found that the sophisticated models, involving either lone pairs or bond center charges, do not lead to any significant improvement over the simple atomic charge distribution. This trend is correlated to the variable strength of the modeled hydrogen bonds in solution.
Spin selectivity in the ultraviolet photodissociation of phosgene
Authors: Maul Christof , Haas Tobias , Gericke Karl-Heinz , Comes Franz Josef
Published: July 2002

The ultraviolet photodissociation of phosgene in its first absorption band 1A2←1A1 was investigated by resonance enhanced multiphoton ionization and time of flight techniques. Nascent atomic chlorine fragments were observed and their state specific kinetic energy distributions were determined. Of the chlorine atoms 15% are produced in the excited 2P1/2 spin–orbit state with a mean kinetic energy of 3200 cm−1 compared to a value of 1500 cm−1 for the mean kinetic energy of the ground state chlorine atoms. The analysis of the kinetic energy spectra yielded evidence for a concerted three-body decay. The formation of intermediate COCl is of minor importance in the dissociation process, the formation of a stable final COCl product can be excluded. Competing pathways on the upper potential energy surface are discussed. A significant excitation of the carbon monoxide CO fragments is predicted.
Electronic absorption spectra of linear carbon chains in neon matrices. III. HC2n+1H
Authors: Fulara Jan , Freivogel Patrick , Forney Daniel , Maier John P.
Published: July 2002

The electronic absorption spectra of HC2n+1H and HC2n+1H+ (n=2−7) in neon matrices have been obtained. The species were prepared by codeposition of mass selected HC2n+1H+ ions with neon at 5 K. For each species the 000 band of the electronic transition as well as frequencies of fundamental vibrations in the excited state have been determined. The wavelength of the origin band in this homologous series is linearly dependent on the number of carbon atoms. Isotopic labeling supports the vibrational assignment and confirms the presence of two equivalent hydrogen atoms for HC2n+1H and HC2n+1H+. Based on spectroscopic considerations, a linear geometry is assumed with one hydrogen atom located at each end, and that the observed spectra of HC2n+1H are their 3Σu−←X 3Σg− transition.
Impulsive stimulated thermal scattering study of α relaxation dynamics and the Debye–Waller factor anomaly in Ca0.4K0.6(NO3)1.4
Authors: Yang Yongwu , Nelson Keith A.
Published: July 2002

Impulsive stimulated light scattering experiments were carried out on an ionic glass former Ca0.4K0.6(NO3)1.4 to determine the temperature dependence of the Debye–Waller factor fq(T) in the q→0 limit and to investigate the structural relaxation dynamics. A square-root cusp anomaly was observed in fq→0(T) at a crossover temperature Tc of 378 K. This and the relaxation dynamics observed were consistent with predictions of the mode-coupling theory of the liquid–glass transition.
Polyamorphism and density anomalies in network-forming fluids: Zeroth- and first-order approximations
Authors: Roberts C. J. , Debenedetti Pablo G.
Published: July 2002

A molecular model of network-forming liquids has been formulated in terms of a lattice fluid in which bond formation depends strongly on molecular orientations and local density. The model has been solved in the zeroth- and first-order approximations for molecular and bond geometries similar to water or silica. Results are presented in the form of fluid-phase boundaries, limits of stability, and loci of density extrema. At low temperatures and high pressures the first-order solution shows a liquid–liquid transition with upper and lower consolute temperatures, in addition to vapor–liquid equilibrium; and two loci of density extrema. In contrast to previous models which display a second fluid–fluid transition, the phase behavior of the present model fluid does not result from an a priori imposed dependence of the bonding interaction upon bulk density. The zeroth-order solution shows only one, vapor–liquid, phase transition; and a single, continuous locus of density maxima. The results suggest that low-temperature polyamorphic phase transitions in a pure substance can arise from orientation-dependent interactions; and in particular that a phase transition between two dense fluids can be driven by the greater orientational entropy of high density states which are not fully bonded. The predicted phase behavior is, however, sensitive to the level of approximation used to solve the partition function.
Exact six-dimensional quantum calculations of the rovibrational levels of (HCl)2
Authors: Qiu Yanhui , Bačić Zlatko
Published: July 2002

Results of comprehensive full-dimensional (6D) quantum calculations of the rovibrational levels of (HCl)2, for total angular momentum J=0,1 are presented. The calculations employed two 6D potential energy surfaces (PES)—the ab initio PES of Bunker and co-workers, and the semiempirical PES of Elrod and Saykally. This 6D study provides the first rigorous, approximation-free description of the bound state properties of (HCl)2, including the dissociation energy, tunneling splittings and their J, K dependence, frequencies of intermolecular vibrations and associated J=0→1 spacings, and quantum number assignments of the 6D eigenstates. Detailed comparison with 4D bound state calculations (for fixed HCl bond length) was made in order to assess the importance of including the intramolecular vibrations of the two HCl subunits for accurate calculation of various spectroscopic properties of (HCl)2. Comparison of the 6D results with experimental data, while confirming that the ES1 PES is substantially more accurate than the ab initio PES, shows that there is room for further refinements, preferably using 6D bound state calculations.
Analysis of dynamical and nondynamical components of electron correlation energy by means of local-scaling density-functional theory
Authors: Valderrama E. , Ludeña E. V. , Hinze J.
Published: July 2002

The partitioning of electron correlation energy into dynamical and nondynamical components is examined in the context of the local-scaling transformation version of density-functional theory and its connection with the Hohenberg–Kohn–Sham density-functional-theory definition of electron correlation is discussed. The relative importance of these components is analyzed with reference to the helium atom and its isoelectronic series. The present results attest to the preponderantly dynamical character of the recovered correlation energy.
High resolution threshold photoelectron spectrum of oxygen in the 12–19 eV region
Authors: Akahori T. , Morioka Y. , Tanaka T. , Yoshii H. , Hayaishi T. , Ito K.
Published: July 2002

The threshold photoelectron spectrum of oxygen has been measured with high resolution in the photon energy range of 12–19 eV using a penetrating field technique and a synchrotron radiation source. The long vibrational progression of the X2Πg state of O2+ was observed to v′=45. An extrapolation in a Birge–Sponer plot (ΔG versus v′+1/2) gives a maximum vibrational level vmax′=56. The A2Πu state was also measured in detail. Most vibrational levels of the A2Πu state of O2+ (from v′=0 to 24) were observed for the first time. A Birge–Sponer plot of the A2Πu state gives a maximum vibrational level vmax′=31. The dissociation limit of the A2Πu state is slightly higher (76 meV) than the well-known dissociation limit O(3P2)+O+(3S0) 18.733 eV. Therefore the A2Πu state may be considered to have a hump. We observed new states which were assigned to Σg+4 and Σu+2 according to a previous theoretical investigation [Beebe et al., J. Chem. Phys. 64, 2080 (1976)]. Potential curves of the X2Πg and A2Πu states were calculated by the Rydberg–Klein–Rees method using both the rotational constants obtained previously by others [K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure, Constants of Diatomic Molecules Volume IV (Van Nostrand, New York, 1974)] and the vibrational energy values observed in the present experiment. A Le Roy–Bernstein plot as well as a Birge–Sponer plot were used to determine the dissociation energy of the X2Πg state. However, the plot gave an unreasonably large dissociation limit.
Spectroscopic constants and potential energy functions of OCCl+, ONP, ONS+, ArCN+, OCS, and NCCl using the coupled cluster method
Authors: Pak Youngshang , Woods R. Claude
Published: July 2002

Large basis set ab initio calculations have been carried out on the three-dimensional near- equilibrium potential energy surfaces of the spectroscopically unknown species OCCl+, ONP, ONS+, and ArCN+ and the isoelectronic reference molecules OCS and NCCl, using a correlation consistent polarized valence quadruple zeta (cc-pVQZ) basis set and the coupled cluster method with single and double substitutions, augmented by a perturbative estimate of triple excitations [CCSD(T)]. A complete set of spectroscopic constants for each species has been obtained from the CCSD(T)/cc-pVQZ potential energy surfaces using the standard second-order perturbation theory formulas. In order to predict equilibrium bond distances of the unknown species as accurately as possible, their resulting CCSD(T) structures have been corrected based on identical calculations on both the diatomics CO, CN, NO, CS, CCl+, and NP and the linear triatomics OCS and NCCl. The second-order spectroscopic constants and anharmonic force fields for OCS and OCCl+ previously calculated with the MP4SDQ and CISD(s) methods are in good agreement with the present CCSD(T) results.
Thermodynamic variables in the context of a nonequilibrium statistical ensemble approach
Authors: Luzzi Roberto , Vasconcellos Áurea R. , Jou David , Casas-Vázquez José
Published: July 2002

We consider the question of the definition of thermodynamic-like variables in the context of a statistical thermodynamics, which is a large generalization of Gibbs statistical thermostatics and linear and local-equilibrium classical irreversible thermodynamics. It is based on a nonequilibrium ensemble approach known as the nonequilibrium statistical operator method. Some of these quasithermodynamic variables are characteristic of the nonequilibrium state and go to zero in the limit of local or global equilibrium, but others go over the thermodynamic variables that are present in such a limit. We consider in particular temperature-like variables for the different subsystems of the sample. For illustration we apply the theory to the study of optical properties of highly photoexcited plasma in semiconductors, following a good agreement between theory and experimental data. It is shown that high-resolution spectroscopy provides an excellent experimental testing ground for corroboration of the theoretical concepts, and a quite appropriate way for characterizing and measuring nonequilibrium thermodynamic-like variables.
Dielectric investigations of the molecular dynamics of propanediol in mesoporous silica materials
Authors: Huwe A. , Arndt M. , Kremer F. , Haggenmüller C. , Behrens P.
Published: July 2002

Broadband dielectric spectroscopy (10−2–1.8×109 Hz) is employed to study the molecular dynamics of the glass-forming hydrogen-bonded liquid propanediol confined to mesoporous M41S silica materials having two different topologies. It is shown that the dynamic glass transition takes place in the mesoporous system (diameter 2.7 nm). With respect to the bulk its relaxation rates are decreased when approaching the calorimetric glass transition. Silanization of the inner surfaces acts as a molecular lubrication and makes the molecular dynamics of the confined liquid comparable to the bulk.
High resolution vacuum ultraviolet pulsed field ionization photoelectron band for OCS+(X 2Π): An experimental and theoretical study
Authors: Stimson S. , Evans M. , Ng C. Y. , Hsu C.-W. , Heimann P. , Destandau C. , Chambaud G. , Rosmus P.
Published: July 2002

The vacuum ultraviolet pulsed field ionization photoelectron (PFI-PE) band for OCS+(X 2Π) in the energy region of 11.09–11.87 eV has been measured using high resolution monochromatized synchrotron radiation. The ionization energies (IEs) for the formation of the (0,0,0) X 2Π3/2 and (0,0,0) 2Π1/2 states of OCS+ are determined to be 11.1831±0.0005 and 11.2286±0.0005 eV, respectively, yielding a value of 367±1.2 cm−1 for the spin–orbit splitting. Using the internally contracted multireference configuration interaction approach, three-dimensional potential energy functions (PEFs) for the OCS+(X 2Π) state have been generated and used in the variational Renner–Teller calculations of the vibronic states. The energies of all vibronic states (J=P) for J=1/2, 3/2, 5/2, and 7/2 have been computed in the energy range of ≈4000 cm−1 above the IE[OCS+(X 2Π3/2)] for the assignment of the experimental spectrum. By a minor modification of the ab initio PEFs, good correlations are found between the experimental and theoretical Renner–Teller structures. Similar to the PFI-PE bands for CO2+(X 2Πg) and CS2+(X 2Πg), weak transitions have been detected in the PFI-PE band for OCS+(X 2Π), which are forbidden in the Franck–Condon approximation. The nonvanishing single-photon ionization cross sections involving the excitation of the bending vibrational modes of OCS+, CO2+, and CS2+, in their ground electronic states are attributed to the symmetries of the geometry-dependent electronic transition dipole operator components.
Ab initio calculations on bromine oxide and dioxides and their corresponding anions
Authors: Alcamı́ M. , Cooper I. L.
Published: July 2002

Neutral bromine oxides and dioxides as well as their corresponding anions have been studied by means of ab initio molecular orbital calculations. To test the importance of static and dynamic correlation in these systems both single-configuration-based methods [MP2, QCISD, and QCISD(T)] and multiconfiguration-based methods (CASSCF and CASMP2) have been used. Equilibrium geometries and harmonic vibrational frequencies have been obtained for BrO and the two bromine dioxide isomers (OBrO and BrOO). For the corresponding anionic species, excellent agreement has been obtained for the predicted geometries at QCISD(T) and CASMP2 levels, while frequencies obtained at QCISD(T) agree to within 10 cm−1 with the available experimental data. An analysis of the charge density shows that the nature of the BrO bond is very different within OBrO and BrOO, and that the BrO charge density is reinforced in OBrO relative to BrO itself.
Predictions of rate constants and estimates for tunneling splittings of concerted proton transfer in small cyclic water clusters
Authors: Loerting Thomas , Liedl Klaus R. , Rode Bernd M.
Published: July 2002

We present transfer rates for the concerted hydrogen exchange in cyclic water clusters (H2O)n (n=3,4) based on ab initio hypersurfaces. The studied hydrogen exchange involves bond breaking and forming and is in contrast to flipping motions of “free” hydrogen atoms in a “chemical” reaction. The rates are calculated for gas-phase systems using canonical, variational transition state theory. Multidimensional tunneling corrections are included assuming both a small and a large reaction path curvature. Hybrid density functional theory [B3LYP/6-31+G(d)] was used to evaluate the potential energy hypersurface with interpolated corrections of second order perturbation theory [MP2/6-311++G(3pd,3df)] at the three stationary points for both systems. Large curvature tunneling corrections are included in dual-level direct ab initio dynamics for the cyclic tri- and tetramer of water. The ridge of the reaction swath serves as an estimate for the tunneling probability of various straight-line corner cutting paths. Our results suggest that the investigated species interconvert on a time scale of seconds. The ground-state tunneling splitting is proportional to the square root of the transition probability at the energy of the minima, which is available from the calculation of tunneling corrections. The associated tunneling splittings are estimated to be between 10−4 and 10−5 cm−1, which is close to the experimental resolution limit.
Dynamic evidence of chemical and physical traps in H-bonded confined liquids
Authors: Crupi V. , Maisano G. , Majolino D. , Migliardo P. , Venuti V.
Published: July 2002

Rayleigh wing, infrared (IR) absorption, and Raman-scattering measurements are employed to investigate the reorientational and vibrational dynamics of ethylene glycol and its homologous systems, namely ethylene glycol monomethyl ether and ethylene glycol dimethyl ether, in the bulk state and confined into 25 Å pores of a sol-gel porous glass. As far as the Rayleigh wing data are concerned, the quantitative analysis of the different contributions in the spectra shows the clear influence of the physical and chemical confinement on the mobility of the studied liquids. In addition the IR and Raman measurements, performed in the O–H stretching region, allowed to identify the intramolecular, H-bond imposed, sub-band, as well as to connect the various sub-bands to different intermolecular environments originated by the existence of the H-bond potential. The observed dynamics is discussed on the basis of current theories for associated liquids.
π-systems as lithium/hydrogen bond acceptors: Some theoretical observations
Authors: Ammal S. Salai Cheettu , Venuvanalingam P.
Published: July 2002

Ab initio calculations at the Hartree–Fock and correlated levels and density functional theory calculations have been performed with 6-31++G(d,p) and 6-311++G(d,p) basis sets on LiF and HF complexes of benzene, ethylene, and acetylene. Complex binding energies have been corrected for basis set superposition error, and zero point energy corrections have been done on Hartree–Fock binding energies. Computed results indicate that the complexes exist in different conformations and among them those with π-lithium and π-hydrogen bonds are the most stable. π-lithium bonds are stronger than π-hydrogen bonds. The computed binding energies and geometry of HF complexes correlate well with the available experimental results. LiF complexes with these π systems are found to be weaker than Li+ complexes but they are stronger than Li atom complexes. Natural bond orbital analysis traces the origin of the weak interactions that stabilize the complex. Li, as found in earlier cases, prefers the most symmetric site for interaction whereas proton prefers a nonsymmetric site in benzene complexes. Surprisingly, such a change of interaction geometry in LiF and HF complexes is found to change the donating π-orbitals in the benzene complexes.
A fully relativistic Dirac–Hartree–Fock and second-order Mo/ller–Plesset study of the lanthanide and actinide contraction
Authors: Laerdahl J. K. , Fægri K. , Visscher L. , Saue T.
Published: July 2002

Fully relativistic four-component self-consistent field and correlated calculations at the Mo/ller–Plesset second-order perturbation theory level (MP2) have been performed for the monofluorides and mono- and trihydrides of lanthanum, lutetium, actinium, and lawrencium. The calculated spectroscopic constants are in good agreement with available experimental data. The calculated bond lengths have been compared with values from nonrelativistic calculations to give an estimate of the effect of relativity on the molecular lanthanide and actinide contraction. The calculated lanthanide contraction at the relativistic MP2 level is 0.12, 0.12, and 0.19 Å for the monohydrides, monofluorides, and trihydrides, respectively. The corresponding results for the actinides are 0.20, 0.15, and 0.28 Å, and we demonstrate that the larger size of the actinide contraction is a consequence of relativistic effects. Between 10% and 30% of the lanthanide contraction and between 40% and 50% of the actinide contraction is caused by relativity in these compounds.
Multireference coupled cluster based analytic response approach for evaluating molecular properties: Some pilot results
Authors: Ajitha D. , Vaval Nayana , Pal Sourav
Published: July 2002

In this paper we present the first results for linear response theory in the multireference Fock space framework. Dipole moments of the open shell radicals hydro peroxy radical, hydroxyl radical, and formyloxyl radical are discussed in this paper. The results obtained from the analytic response are compared with the experimental as well as the finite field results including relaxation of the orbitals and the results suggest that the effects of relaxation are substantial. The Fock space approach enables us to obtain the properties of excited states of these radicals in a single calculation. The dipole moments of the first excited states of the above radicals are also reported. The results of the lower Fock space sector energy derivatives are also presented.
The spectral density in simple organic glass formers: Comparison of dielectric and spin-lattice relaxation
Authors: Blochowicz T. , Kudlik A. , Benkhof S. , Senker J. , Rössler E. , Hinze G.
Published: July 2002

The spin-lattice relaxation time T1 of simple organic glass formers is analyzed by introducing a spectral density obtained from broadband dielectric susceptibility data χ″(ω). For this purpose χ″(ω) was measured for several glass formers, that do not exhibit a Johari-type secondary relaxation process, covering a frequency range between 10−2 Hz and 109 Hz at temperatures above and below the glass transition temperature Tg. We introduce an analytical function to fit the shape of the main relaxation (α-process) above Tg, in particular taking into account high-frequency contributions in χ″(ω) commonly known as high-frequency wing. Below Tg the latter feature appears as a power law susceptibility χ″(ω)∝ω−γ, with γ<0.1 and a characteristic temperature dependence χ″(T)∝exp(T/const.), yielding almost 1/ω behavior in the spectral density. On the base of this complete description of χ″(ω), a quantitative comparison of dielectric and NMR spectroscopy is possible, which is carried out in full detail for glycerol-d3 (2H-NMR), yielding almost identical spectral densities at the Larmor frequency in both cases. In particular the temperature dependence of the high-frequency wing reappears in that of the spin lattice relaxation rate. In addition a semiquantitative analysis is given for trinaphthyl benzene (1H-NMR) and tricresyl phosphate (31P-NMR).
A first-principle computation of the thermodynamics of glasses
Authors: Mézard Marc , Parisi Giorgio
Published: July 2002

We propose a first-principle computation of the equilibrium thermodynamics of simple fragile glasses starting from the two-body interatomic potential. A replica formulation translates this problem into that of a gas of interacting molecules, each molecule being built of m atoms, and having a gyration radius (related to the cage size) which vanishes at zero temperature. We use a small cage expansion, valid at low temperatures, which allows to compute the cage size, the specific heat (which follows the Dulong and Petit law), and the configurational entropy.
Viscoelastic response of hyperstar polymers in the linear regime
Authors: Kapnistos Michael , Semenov Alexander N. , Vlassopoulos Dimitris , Roovers Jacques
Published: July 2002

We compare the linear viscoelastic spectra of star polymer melts, with varying functionality (4-128) and chemistry (isoprenes, butadienes), with a recent parameter-free theory of arm relaxation [S. T. Milner and T. C. B. McLeish, Macromolecules 30, 2159 (1997)]. The theory, which considers this activated process within the framework of dynamic dilution and with appropriate account of the entanglement length scaling and the higher Rouse modes, is universal as it works remarkably well for a very wide range of star functionalities and arm molecular weights. However, for hyperstars consisting of 64 or 128 arms, the viscoelastic response is characterized by the presence of a slow relaxation process in addition to the faster arm relaxation. This additional process is due to the soft ordering of these systems because of their nonuniform monomer density distribution, and exhibits a very strong functionality and molecular weight dependence. It is accounted for by a mean field approach which considers the structural relaxation of the ordered stars as an activated process involving partial disentanglement of the interpenetrating arms and a jump of the star over a distance of its size, in good qualitative agreement with the experimental findings.
Nuclear magnetic shielding in the acetylene isotopomers calculated from correlated shielding surfaces
Authors: Wigglesworth Richard D. , Raynes William T. , Kirpekar Sheela , Oddershede Jens , Sauer Stephan P. A.
Published: July 2002

Ab initio, symmetry-coordinate and internal valence coordinate carbon and hydrogen nuclear shielding surfaces for the acetylene molecule are presented. Calculations were performed at the correlated level of theory using gauge-including atomic orbitals and a large basis set. The shielding was calculated at equilibrium and at 34 distinct geometries corresponding to 53 distinct sites for each nucleus. The results were fitted to fourth order in Taylor series expansions and are presented to second order in the coordinates. The carbon-13 shielding is sensitive to all geometrical parameters and displays some unexpected features; most significantly, the shielding at a carbon nucleus (C1, say) is six times more sensitive to change of the C1C2H2 angle than it is to change of the H1C1C2 angle. In addition, for small changes, σ(C1) is more sensitive to the C2H2 bond length than it is to the C1H1 bond length. These, and other, examples of “unexpected differential sensitivity” are discussed. The proton shielding surface is much more as expected with σ(H1) being most sensitive to the C1H1 bond length, less so to the CC bond length and hardly at all to the C2H2 bond length. The surfaces have been averaged over a very accurate force field to give values of σ(C), σ(H), and σ(D) for the ten isotopomers containing all possible combinations of C12, C13, H1, and H2 nuclei at 0 K and at a number of selected temperatures in the range accessible to experiment. For the carbon shielding the dominant nuclear motion contribution comes from the bending at “the other” carbon atom with the combined stretching contributions being only 20% of those from bending. For the proton shielding it is the stretching of the CH bond containing the proton of interest which provides the major nuclear motion contribution. For σ(C) in H13C13CH at 300 K our best result is 117.59 ppm which is very close to the experimental value of 116.9 (±0.9) ppm. For σ(H) in H13C13CH at 300 K we obtain 29.511 ppm which is also in very close agreement with the experimental value of 29.277 (±0.001) ppm. Calculated values are also very close to recent, highly accurate carbon and proton isotope shifts in the ten isotopomers; carbon isotope shifts differ by no more than 10% from the measured values and proton isotope shifts are generally in even better agreement than this. The observed anomaly whereby the C13 isotope shift in H13C12CD is greater than that in D13C12CH both with respect to H13C12CH is explained in terms of the bending contribution at “the other” carbon. The observed nonadditivity of deuterium isotope effects on the carbon shielding can be traced to a cross term involving second order bending.
Determination of the helium/Si(111)–(1×1)H potential
Authors: Buckland J. R. , Allison W.
Published: July 2002

We have performed a detailed study of the helium/Si(111)–(1×1)H interaction, using a thorough set of experimental measurements combined with a first principles theoretical approach. An empirical potential is presented, which describes both diffraction from the repulsive part and selective adsorption resonances resulting from the helium–surface potential well. The 80 meV potential energy contour has a corrugation of 0.6 Å along the [1̄10] direction, and the well depth is 7.5 meV. The study is completed by a calculation of the helium/Si(111)–(1×1)H potential, based on the surface electron density using effective medium models. Comparison with the empirical potential provides insight into the nature of the helium–semiconductor interaction.
Computer simulation studies of liquid lenses at a liquid–liquid interface
Authors: Bresme Fernando , Quirke Nicholas
Published: July 2002

We simulate using molecular dynamics the wetting behavior of nanometer scale liquid lenses at a liquid–liquid interface. The spreading of the lens is controlled by changing the lens–liquid surface tension. We have measured the contact angle that the lens makes with the interface for several values of the surface tension. We find that the macroscopic description provided by Neumann’s equation describes the wetting behavior of lenses of nanometer size very accurately. In addition Laplace’s equation for the pressure difference between the interior of the lens and the liquid phases is obeyed.
Surface tension of the three-dimensional Lennard-Jones fluid from histogram-reweighting Monte Carlo simulations
Authors: Potoff Jeffrey J. , Panagiotopoulos Athanassios Z.
Published: July 2002

The surface tension of the full three-dimensional Lennard-Jones potential is calculated from grand canonical Monte Carlo simulations with the finite-size scaling methodology outlined by Binder [Phys. Rev. A 25, 1699 (1982)]. Surface tensions are determined for the range of reduced temperatures T*=0.95–1.312 and are found to be in good agreement with molecular-dynamics calculations. A critical temperature Tc*=1.311±0.002 is established by locating the T* where the surface tension of the infinite system size vanishes. In addition, with this method it is possible to determine the critical exponent 2ν. For the Lennard-Jones fluid we found 2ν=1.42±0.08, which differs from the accepted value of 2ν=1.26.
Solvent-induced stabilization of the naphthalene anion by water molecules: A negative cluster ion photoelectron spectroscopic study
Authors: Lyapustina Svetlana A. , Xu Shoujun , Nilles J. Michael , Bowen Kit H.
Published: July 2002

We show that (a) only a single water molecule is needed to stabilize the naphthalene anion, (b) the EAa of naphthalene is −0.20 eV, in agreement with determinations by electron transmission spectroscopy, (c) the energetics are consistent with the number of waters required to stabilize the naphthalene anion, and (d) the excess electron is located on the naphthalene moiety of Nph1−(H2O)n.
Femtosecond pump–probe photoelectron spectroscopy of predissociative Rydberg states in acetylene
Authors: Sorensen S. L. , Björneholm O. , Hjelte I. , Kihlgren T. , Öhrwall G. , Sundin S. , Svensson S. , Buil S. , Descamps D. , L’Huillier A. , Norin J. , Wahlström C.-G.
Published: July 2002

We employ a pump–probe approach to molecular photoionization to study fast dissociation of Rydberg states in acetylene. By using time-resolved photoelectron spectroscopy to study the electronic state of the resulting ions we are able to monitor the system continuously during dissociation or rearrangement. We find that the predissociative lifetime for the 3R′′′ (v2′=1) Rydberg state is about 150 fs. We demonstrate a powerful new technique using time-correlated femtosecond harmonic generation and laser light pulses to study the time evolution of ultrafast dynamic processes in molecules.
On spherically symmetric shear-free perfect fluid configurations (neutral and charged). II. Equation of state and singularities
Authors: Sussman Roberto A.
Published: July 2002

Geometrical and physical properties of the solutions derived and classified in Part I [J. Math. Phys. 28, 1118 (1987)] are examined in detail. It is shown how the imposition of zero shear restricts the possible choices of equations of state. Two types of singular boundaries arising in these solutions are examined by verifying the local behavior of causal curves approaching these boundaries. For this purpose, a criterion due to C. J. S. Clarke (private communication) is given, allowing one to test the completeness of arbitrary accelerated timelike curves in terms of their acceleration and proper time. One of these boundaries is a spacelike singularity at which causal curves terminate as pressure diverges but matter-energy and charge densities remain finite. At the other boundary, which is timelike if the expansion Θ is finite, proper volume of local fluid elements vanishes as all state variables diverge but causal curves are complete. If Θ diverges at this boundary, a null singularity arises as the end product of the collapse of a two-sphere generated by a given class of timelike curves. The gravitational collapse of bounded spheres matched to a Schwarzschild or Reissner–Nordstro/m exterior is also examined in detail. It is shown that the spacelike singularity mentioned above could be naked under certain parameter choices. Solutions presenting the other boundary produce very peculiar black holes in which the ‘‘surface’’ of the sphere collapses into the above mentioned null singularity, while the ‘‘interior’’ fluid layers avoid this singularity and evolve towards their infinite future.
Symbols of operators and quantum evolution
Authors: Borsari I. , Graffi S.
Published: July 2002

An algebraic procedure to compute the higher order symbols of the Heisenberg quantum observables is explicitly implemented. As an application, it is proven in a very simple way that a time evolution under which the symbol of any Heisenberg quantum observable is exactly given by the evolution along the classical flow is necessarily generated by a quadratic Hamiltonian.
Setting hidden symmetries free by the noncommutative Veronese mapping
Authors: Juriev D.
Published: July 2002

This paper is devoted to setting free hidden symmetries in Verma modules over 𝔰𝔩 (2,C) by the noncommutative Veronese mappings.
Two-body scattering on a graph and application to simple nanoelectronic devices
Authors: Melnikov Yu. B. , Pavlov B. S.
Published: July 2002

The two-body system on a graph with one junction is considered. The effective three-body scattering problem turns out to be exactly solvable for pointwise interactions. Additional degrees of freedom corresponding to a dynamics of some structure (e.g., an atomic cluster) located in the junction (point of common contact) of three thin electrodes are considered. These degrees of freedom bring effective energy-dependent interaction into the effective Schrödinger equation in the scattering channel. The wave function of the system is constructed in the explicit form using the extension theory methods. The obtained results are applied to the qualitative description of a simple three-electrode nanoelectronic device. The perturbation theory approach based on the analysis of the Liouville equation is suggested for calculation of the conductivity for such a device in terms of the obtained wave function.
Rigorous estimates of small scales in turbulent flows
Authors: Constantin Peter , Doering Charles R. , Titi Edriss S.
Published: July 2002

We derive rigorous bounds on the length scale of determining local averages (volume elements) for the 3-D Navier-Stokes Equations. These length scale estimates are related to Kolmogorov’s notion of a dissipation length scale in turbulent flows.
Superintegrability and associated polynomial solutions: Euclidean space and the sphere in two dimensions
Authors: Kalnins E. G. , Miller W. , Pogosyan G. S.
Published: July 2002

In this work we examine the basis functions for those classical and quantum mechanical systems in two dimensions which admit separation of variables in at least two coordinate systems. We do this for the corresponding systems defined in Euclidean space and on the two-dimensional sphere. We present all of these cases from a unified point of view. In particular, all of the special functions that arise via variable separation have their essential features expressed in terms of their zeros. The principal new results are the details of the polynomial bases for each of the nonsubgroup bases, not just the subgroup Cartesian and polar coordinate cases, and the details of the structure of the quadratic algebras. We also study the polynomial eigenfunctions in elliptic coordinates of the n-dimensional isotropic quantum oscillator.
Symplectic geometry and topology
Authors: Arnold V. I.
Published: July 2002

This is a review of the ideas underlying the application of symplectic geometry to Hamiltonian systems. The paper begins with symplectic manifolds and their Lagrangian submanifolds, covers contact manifolds and their Legendrian submanifolds, and indicates the first steps of symplectic and contact topology.
Diffusion in liquid and solid solutions He3–4He
Authors: Adamenko I. N. , Zhukov A. V. , Nemchenko K. È. , George T. F.
Published: July 2002

An exact expression for diffusion time, which depends on the interaction rates for particles of not only different, but also of the same species, has been derived from the system of kinetic equations. The result is valid for particles with arbitrary statistics and energy–momentum relations. The derived general relations are valid for investigating diffusion in liquid and solid He3–4He mixtures. The contribution of interaction between quasiparticles of the same type to the diffusion coefficient and effective thermal conductivity of superfluid solutions is analyzed. The calculated values are compared with experimental data. The calculated diffusion coefficient of He3–4He solid solutions differs from the previous theoretical results. A comparison of the obtained diffusion coefficient with experimental data makes it possible to determine the numerical value of the energy band width for impurity quasiparticles.
Study of phase separation kinetics of He3–4He solid mixtures by precision pressure measurements
Authors: Ganshin A. N. , Maidanov V. A. , Omelaenko N. F. , Penzev A. A. , Rudavskii E. Ya. , Rybalko A. S.
Published: July 2002

The kinetics of isotopic phase separation of He3–4He solid mixtures for various molar volumes has been studied by precision pressure measurements at a constant volume. It is found that the attainment of equilibrium between coexisting phases formed as a result of stratification is described correctly by an exponential dependence for various modes of crystal cooling and heating. The characteristic phase separation time decreases with temperature, thus confirming the athermal quantum nature of the growth of a new phase during the phase transition. The phase separation time is found to increase considerably with crystal pressure. It is shown that the prevailing theory can provide only a qualitative description of the established regularities. A quantitative description of experimentally observed decay times requires an analysis of diffusion processes in a gas of impurity excitations in the presence of a concentration gradient.