bluuebunny/crossref_metadata_2025 huggingface dataset:
On the photoisomerization of 5-hydroxytropolone: An ab initio and nuclear wave function study
Authors: Paz Juan J. , Moreno Miquel , Lluch José M.
Published: July 2002

In this paper we perform ab initio calculations for the stable conformations and the transition states for the isomerization processes in 5-hydroxytropolone in both the ground (S0) and first excited (S1) singlet electronic states. The Hartree–Fock self-consistent field (SCF) level and a complete active space SCF (CASSCF) level for S0 are considered, whereas the configuration interaction all single excitation method (CIS) and the CASSCF levels are used to deal with the S1 state. Energies are reevaluated at all levels through perturbation theory up to second order: Mo/ller–Plesset for the Hartree–Fock and CIS methods, and the CASPT2 method for CAS results. The ab initio results are then used to perform different monodimensional fits to the potential energy surfaces in order to analyze the wave functions for the nuclear motions in both electronic states. Our best results predict that for the S0 state two stable conformers, syn and anti, can exist in thermal equilibrium. In accordance with experimental expectations the syn isomer is the most stable. As for the S1 state, and again in accord with experimental spectroscopical data, the order of stability reverses, the anti being the most stable. A more interesting result is that analysis of the nuclear wave functions shows an important syn–anti mixing in the S1 state that does not appear in S0. This result explains the appearance of syn–anti and anti–syn crossover transitions observed in the electronic spectra of 5-hydroxytropolone so that syn–anti reaction may take place through photoisomerization.
Isotope and temperature effects on the 13C and 77Se nuclear shielding in carbon diselenide
Authors: Lounila Juhani , Vaara Juha , Hiltunen Yrjö , Pulkkinen Anja , Jokisaari Jukka , Ala-Korpela Mika , Ruud Kenneth
Published: July 2002

A comprehensive theoretical and experimental study of the 13C and 77Se nuclear magnetic shieldings and their rovibrational corrections in carbon diselenide (CSe2) has been undertaken. The 13C and 77Se shielding tensors as well as all their first and second derivatives with respect to the internal displacement coordinates of the molecule have been calculated by several first principles gauge-including atomic orbital (GIAO) methods. Hartree-Fock (HF), multiconfiguration Hartree-Fock (MCHF), and density-functional (DFT) theories have been compared, the latter both in the local density approximation (LDA) and by using two gradient corrected exchange-correlation functionals. The shielding derivatives calculated with MCHF and DFT are very much smaller in magnitude than the derivatives obtained by using HF, being in reasonable mutual agreement. By using the theoretical shielding derivatives and the cubic anharmonic force constants calculated within LDA, together with an experimental harmonic force field, all the first and second order terms in the rovibrational contributions to the shielding constants and anisotropies have been worked out. The contributions to the shielding constants have been calculated for the various isotopomers of CSe2 at several temperatures, and the resulting theoretical temperature dependencies of the shielding constants, the isotope shifts and the temperature dependencies of the isotope shifts have been compared with the experimental results. There is excellent agreement between the theoretical and experimental results for 77Se. The agreement is not quite as good for the (anomalously small) shielding constant of 13C and its rovibrational corrections. Contrary to what has been frequently assumed, none of the first and second order terms in the rovibrational contributions to the shielding constants can safely be neglected. In particular, the first order isotope effect due to change in the bond not directly attached to the observed nucleus is very important. Furthermore, the second order terms — including the bending and even cross terms — are essential in order to give a correct description of the isotope shifts.
All-electron Dirac–Fock–Roothaan calculations for the ThO molecule
Authors: Watanabe Yoshihiro , Matsuoka Osamu
Published: July 2002

Accurate all-electron Dirac–Fock–Roothaan calculations were performed for the 1Σ+ ground state of ThO using Gaussian basis sets of Th (24s20p16d12f)/[19s15p12d5f] and O (10s6p1d)/[7s4p1d]. The relativistic effects in ThO were found to slightly extend the bond length re, to increase the dissociation energy De, and to decrease the harmonic frequency ωe.
Dynamics around a multidimensional conical intersection: A mixed quantum-classical model
Authors: Ferretti Alessandro , Lami Alessandro , Villani Giovanni
Published: July 2002

We investigate the dynamics around a two-state conical intersection in a polyatomic molecule. The simplified model considered is an extension of that proposed and tested previously for the case of one active (coupling) mode and one passive mode. Here we study a multidimensional conical intersection built adding many other passive modes, which globally share a small fraction (up to 20%) of the total vibrational energy. The model simply consists in treating the coupling mode quantum mechanically, while the others are described as classical oscillators running unperturbed trajectories on the initial diabatic surface. The computed adiabatic transition probabilities show, in some conditions, a marked effect of the extra passive modes, which can be explained in terms of the time spent by the classical trajectories in the region where the diabatic coupling is at its maximum.
Collision-induced first overtone band of H2 in H2–Kr and H2–Xe mixtures
Authors: Prasad R. D. G. , Gillard P. G. , Reddy S. Paddi
Published: July 2002

Enhancement of the collision-induced absorption (CIA) spectra of the first overtone infrared band of H2 in the H2–Kr and H2–Xe binary mixtures were recorded at 295 K for base densities of H2 in the range 30–57 amagat and for partial densities in the range 50–250 amagat for each of Kr and Xe. The observed spectra consist of single transitions O2(J), Q2(J), and S2(J) corresponding to the selection rule ΔJ=−2, 0, and 2, respectively. Binary, ternary, and quarternary absorption coefficients of the band arising from collisions of the type H2–X, H2–X–X, H2–H2–X,H2–X–X–X, H2–H2–X–X, and H2–H2–H2–X, where X represents Kr or Xe, have been determined from the integrated absorption coefficients of the band. The spectra are interpreted in terms of the quadrupolar induction mechanism and no evidence of the contribution from the isotropic overlap induction mechanism is found unlike in the CIA spectra of the fundamental band of H2 [see S. P. Reddy, in Phenomena Induced by Intermolecular Interactions, edited by G. Birnbaum (Plenum, New York, 1985), p. 129]. Analysis of the absorption profiles of the observed spectra was carried out using the Birnbaum–Cohen line-shape function [G. Birnbaum and E. R. Cohen, Can. J. Phys. 54, 593 (1976)] for individual components of the band and characteristic line shape parameters were determined from the analysis.
Thermodynamics of the coil to frozen globule transition in heteropolymers
Authors: Pande Vijay S. , Grosberg Alexander Yu. , Tanaka Toyoichi
Published: July 2002

Recent analytic theories and computer simulations of heteropolymers have centered on the freezing transition of globular heteropolymers. We present a simple analytic theory to describe the coil to globule collapse in heteropolymers and compare this to the computer simulation of the exhaustive enumeration of all 18-mer cubic lattice polymer conformations. We find that the collapse transition from coil to frozen globule can either be first or second order. The relevance to protein folding is also discussed.
The current in magnetic field density functional theory and its application to the chemical shielding and magnetic susceptibility
Authors: Salsbury Freddie R. , Harris Robert A.
Published: July 2002

A gradient expansion of the electronic current in the electron density is used to obtain expressions for the magnetic susceptibity and chemical shielding. The first term in the expansion is the Thomas Fermi expression. All succeeding terms diverge for both properties. A renormalized functional is used which removes the divergences and gives asymptotic diamagnetism. A single parameter which depends linearly on the number of electrons gives all heavy rare gas susceptibities to within 1% of exact calculation using the same electron density. Similar results are found for the chemical shielding. Susceptibility and shielding calculations for the helium dimer and the hydrogen molecule in singlet and triplet states are presented. The results are compared with other calculations over a full range of internuclear distances.
Spectroscopic constants of the X 2Σ+ and A 2Π states of Sr+Ar from first principles: Comparison with experiment
Authors: Xantheas Sotiris S. , Fanourgakis George S. , Farantos Stavros C. , Velegrakis Michalis
Published: July 2002

We present the first nonempirically calculated spectroscopic constants for the recently observed [J. Chem. Phys. 105, 2167 (1996)] ground (X 2Σ+) and excited (A 2Π) states of Sr+Ar. Our best results yield De=694 cm−1, Re=3.662 Å, and ωe=38.7 cm−1 for the ground and De=1967 cm−1, Re=3.169 Å, and ωe=99.1 cm−1 for the excited state. The calculated De’s are within the error bars of the experimentally determined one for the ground state favoring the low end and underestimate the corresponding one for the excited state by about 7%. The equilibrium separations (Re’s) for the two states have not been experimentally determined, however our results accurately reproduce the estimated shift, ΔRe, between the two states. The interaction is mainly electrostatic for the ground state for which the contribution of dynamic electron correlation was found to be more important than for the excited state.
Shear-induced ordering kinetics of a triblock copolymer melt
Authors: Hajduk Damian A. , Tepe Thomas , Takenouchi Hiroshi , Tirrell Matthew , Bates Frank S. , Almdal Kristoffer , Mortensen Kell
Published: July 2002

Disorder-to-order transitions, in which an isotropic system acquires a spatially periodic structure, are common to a number of phenomena in materials science. Here, we employ small-angle neutron scattering to probe the effects of reciprocating shear on the isotropic-to-lamellar transition of a triblock copolymer composed of poly(ethylene-co-propylene) (PEP) and poly(ethylethylene) (PEE). Prior work has shown that the transition temperature decreases with increasing shear rate, implying that the isotropic state can be produced at low temperatures through application of a flow field [T. Tepe et al., J. Rheol. 41, 1147 (1987)]. Removing this field results in a “jump” to conditions under which the lamellar phase is stable with a time scale set by the relaxation of concentration fluctuations. We describe the ordering process which results, concentrating on the possible existence of a stability limit for the initial (isotropic) state.
Equation of state and stress tensor in inhomogeneous compressible copolymer melts: Dynamic mean-field density functional approach
Authors: Maurits N. M. , Zvelindovsky A. V. , Fraaije J. G. E. M.
Published: July 2002

We have derived an expression for the global stress in inhomogeneous complex copolymer liquids. We apply the principle of virtual work to the free energy as defined in the dynamic mean-field density functional method. This method automatically provides the full stress tensor (deviatoric and isotropic parts) and hence an equation of state for inhomogeneous compressible copolymer melts. The excluded volume interactions and cohesive interactions between chains have been explicitly taken into account. Therefore the expressions for the stress and thermodynamic pressure have a wide range of validity. The connectivity of the chains is automatically accounted for and the free energy adapts very well to changes in the molecule properties. In the limiting case of homogeneous systems it simplifies to known results. In order to study rheological properties of copolymer melts and npT-ensemble simulations, the pressure and stress components have to be calculated at any given moment in time. We show how the pressure and stress can be numerically evaluated during simulations using a Green propagator algorithm, instead of having to calculate the time dependent configuration distribution function explicitly from a Smoluchowski equation. We provide illustrative numerical results that indicate how the pressure changes during microphase separation.
Solvent effects on nuclear shieldings and spin–spin couplings of hydrogen selenide
Authors: Åstrand Per-Olof , Mikkelsen Kurt V. , Jo/rgensen Poul , Ruud Kenneth , Helgaker Trygve
Published: July 2002

Solvent effects on the nuclear shielding and indirect spin–spin coupling constants of H2Se have been calculated by modeling the surroundings as a continuous dielectric medium. Gauge-origin independence of the nuclear shieldings is ensured by using London atomic orbitals in combination with linear response theory. We present the linear response function of a solvated molecule subject to triplet perturbations and use a new implementation of this theory to evaluate the Fermi-contact and spin–dipole contributions to the indirect spin–spin coupling constants. We present high-level calculations of the nuclear shielding and indirect spin–spin coupling constants of H2Se in vacuum and different solvents. Our results represent the first ab initio calculations of the spin–spin coupling constants in H2Se as well as the first investigation of medium effects on these properties. It is demonstrated that the solvent shifts of the spin–spin couplings are caused by a polarization of the molecular electronic structure as well as by changes in the geometry upon solvation.
State-to-state differential cross sections for rotationally inelastic collisions of NO(2Π1/2,j⩽2.5) with CO(1Σ+) and O2(3Σg−) at a kinetic energy of 442 cm−1
Authors: Bacon Joel A. , Giese Clayton F. , Gentry W. Ronald
Published: July 2002

Crossed molecular beam measurements of state-resolved differential cross sections for NO+O2 and NO+CO inelastic collisions at a relative kinetic energy of 442 cm−1 are reported. The initial states (NO 2Π1/2, ν=0, j⩽2.5, CO 1Σ+, ν=0, O2 3Σg−, ν=0) were prepared by pulsed supersonic expansions of pure NO, O2, and CO gas. Scattered NO products were detected by resonance enhanced two-photon ionization. Product distributions were measured in both center-of-mass scattering angle and final rotational state (j′). Intensity maxima were found in both types of scans and comparable populations were found in both of the spin–orbit manifolds (2Π1/2 and 2Π3/2). The results are compared to previous inelastic scattering experiments of NO collisions with NO, Ar, CO, and O2.
Empirical exponent law of the second-order hyperpolarizability in small armchair and zig–zag nanotubes
Authors: Xie Rui-Hua
Published: July 2002

Our theoretical calculation has shown an empirical exponent law of the static second-order hyperpolarizabilities γ in armchair and zig–zag nanotubes, i.e., γ/γ60=(U/60)P, where U is the number of carbon atoms in nanotube, γ60 is the static γ value of C60, and P=3.15 and 2.98 for armchair and zig–zag nanotubes, respectively.
Kinetic model of coupled nonequilibrium condensation and radiative excitation of water molecules
Authors: Itkin A. L.
Published: July 2002

A new microscopic kinetic model of coupled nonequilibrium condensation and radiative excitation of water molecules effusing from a surface of a cometary nucleus is developed. The method is greatly based on the microscopic theory of nonequilibrium condensation (MTC) developed earlier by the author. To analyze vibrational and rotational excitation of the H2O molecule a kinetic model has been used which includes infrared rovibrational pumping by the solar radiation flux, thermal excitation by collisions, and radiation trapping in the rotational and rovibrational lines. Appropriate kinetic equations for cluster concentrations and populations of their energetic levels have been solved analytically. This permits one to reduce the coupled equations of the condensation and radiative balance to a closed system of differential equations involving the rotational populations of the water molecule. Prospects of the use of this model when studying an influence of the indicated processes on the structure of an inner coma are discussed.
One-fluid theory of liquid-vapor surface tension in simple multi-component mixtures
Authors: Kalikmanov V. I.
Published: July 2002

We propose a theory of surface tension in multi-component mixtures of simple fluids far from critical conditions based on the one-fluid van der Waals approximation and statistical mechanical perturbation approach. The theory contains no adjustable parameters. By comparison with molecular dynamics simulation of binary Lennard-Jones mixtures it is shown that the theory provides a quantitative (within a tolerance of ∼15%–20%) description of surface tension.
On the kinetic theory of rarefied gas suspensions
Authors: Gladkov M. Yu. , Heinz U.
Published: July 2002

The system of kinetic equations for a medium of finely dispersed particles in a rarefied gas is solved by the Chapman-Enskog method. The hydrodynamic transport equations and expressions for the transport coefficients are obtained. The contribution of the three-body interactions to the transport coefficients, determining the first-order corrections in the density expansion, has been calculated for a model of hard spheres. The many-body collision contribution to the dissipative characteristics of the medium is calculated under the condition that the gas-gas collisions in the ternary and higher order collision integrals can be neglected. We also suggest a system of effective kinetic equations which take into account these effects.
Phenyl ring dynamics and chain reorientation in liquid crystal polymers: A deuteron spin relaxation study
Authors: Heaton Nicholas J. , Kothe Gerd
Published: July 2002

A detailed description of phenyl ring dynamics and spin relaxation in a highly ordered main chain/side chain liquid crystal polymer is presented. Models for the different motional processes are discussed with reference to experimental measurements of the deuteron spectral densities, JM(Mω0), measured in the smectic A and nematic phases between 330 K and 500 K, and measured as a function of orientation at 410 K, close to the minima in the relaxation times for Zeeman and quadrupolar order, T1Z and T1Q. Intramolecular motion of phenyl rings about the para-axis is regarded as a diffusive process in a two-fold symmetric potential. Theoretical analysis of this model provides the rate constants and amplitudes for passage across the potential barriers and libration within the minima. These are governed entirely by the height of the potential barrier, the potential shape, and the diffusion constant. It is demonstrated that other models for the intramolecular ring dynamics cannot simultaneously account for the magnitudes of the observed JM(Mω0) in the vicinity of the T1Z and T1Q minima. Large amplitude reorientation of the polymer chain is regarded as rotational diffusion in an orienting potential. In order to reproduce both the temperature and orientation dependences of the JM(Mω0), an additional low amplitude motion of the polymer about the main chain axis, with correlation times in the 10−9 s regime at T∼400 K, must be included. This is modeled as a one-dimensional diffusion process modulated by a harmonic potential, representing torsional motion of the extented polymer chains. Analysis of the experimental deuteron spin relaxation data yields values for the correlation times and amplitudes for each of the individual processes, providing estimates for the parameters describing each of the potentials which modulate the intramolecular and whole molecule motion, as well as the temperature dependences of the various diffusion constants.
The role of surface corrugation in the rotational rainbow scattering of NO from Ag(111)
Authors: Duhoo Thierry , Lemoine Didier
Published: July 2002

We report the results of quantum calculations taking explicitly into account the surface corrugation in hyperthermal collisions of NO(X 2Π) with Ag(111). Our study is based on the potential-energy surfaces of DePristo and Alexander [J. Chem. Phys. 94, 8454 (1991)]. Parallel momentum transfer is found to be substantial. In addition, inclusion of the corrugation strongly attenuates the interference structures due to the rotational rainbows at either low or high angular momentum J. With a single direction of corrugation along the rigid surface and a rotationally cold (J⩽3/2) incident beam, a Boltzmann plot of the final J distribution no longer exhibits a sharp oscillatory behaviour, in qualitative agreement with the measurements of Rettner, Kimman, and Auerbach [J. Chem. Phys. 94, 734 (1991)]. Notably, the low-J rainbow vanishes. This quenching effect has often been attributed to the large energy transfer with the surface occurring in the experiments, and/or to the initial state distribution. Thus, the attenuation due to the surface corrugation, although predictable, is far more efficient at damping the quantum oscillations than expected.
Radiative decay processes in the 6s and 7s Rydberg states of NO studied by three-color laser-induced amplified spontaneous emission spectroscopy
Authors: Sugita Akihiro , Ikeda Masashi , Tsukiyama Koichi
Published: July 2002

A novel spectroscopic technique involving amplified spontaneous emission (ASE) is presented to excite single rotational levels of the 6sσT 2Σ+ and 7sσZ 2Σ+ Rydberg states of the NO molecule. In this excitation regime, the 3pπD 2Σ+ state, which is populated by the ASE deexcitation process from the 4sσE 2Σ+ Rydberg state, serves as the intermediate state. As the initial radiative decay channels form the T 2Σ+ and Z 2Σ+ states, the dipole allowed ASE transitions down to the nearest Rydberg states, i.e., T 2Σ+→5pσR 2Σ+ and Z 2Σ+→6pσY 2Σ+, are identified. The anomalous intensity distributions both in the excitation and emission spectra are well explained by s–d mixing and l uncoupling in the upper Rydberg states.
Dissociation energies of the Ga2, In2, and GaIn molecules
Authors: Balducci G. , Gigli G. , Meloni G.
Published: July 2002

The group III metal dimers Ga2 and In2 and the newly identified intermetallic molecule GaIn were investigated in a Knudsen cell-mass spectrometric study of the vapors over gallium–indium alloys. From the all-gas equilibria analyzed by the second-law and third-law methods the following dissociation energies were derived; D00 (Ga2)=110.8±4.9 kJ mol−1, D00 (In2)=74.4±5.7 kJ mol−1, D00 (GaIn)=90.7±3.7 kJ mol−1. The value here measured for the dissociation energy of In2 is discussed and compared with a previous experimental determination and with the results of more recent theoretical investigations.
Transfer matrix method for enumeration and generation of compact self-avoiding walks. I. Square lattices
Authors: Kloczkowski A. , Jernigan R. L.
Published: July 2002

The transfer matrix method has been developed to enumerate and generate compact self-avoiding walks in two dimensions on the square lattice within rectangular strips of size m×n. The method is significantly superior to the traditional method of computer generation of self-avoiding walks, because it is attrition-free, i.e., each computation leads to successful conformations, with no failures. The method is generalized to irregular shapes, and the extension of the method to the Monte Carlo sampling of the compact conformational space is proposed. Application of this new method to protein conformation generation is discussed, with the possibility of including several types of constraints.
The pure rotational spectrum of yttrium monobromide
Authors: Walker Kaley A. , Gerry Michael C. L.
Published: July 2002

The pure rotational spectrum of the X 1Σ+ ground electronic state of yttrium monobromide has been measured. This is the first high-resolution spectrum recorded for this molecule. Transitions in the ground and first excited vibrational states have been measured for both the Y79Br and Y81Br isotopomers. Equilibrium rotational parameters have been determined and an equilibrium bond distance has been calculated. Vibrational parameters have been estimated. Hyperfine structure due to the bromine nuclei has been observed and nuclear quadrupole and nuclear spin–rotation constants have been determined. These parameters have been used to investigate the ionic character of the Y–Br bond and comparisons have been made to several alkali and alkaline earth metal bromide species.
Rovibrational effects, temperature dependence, and isotope effects on the nuclear shielding tensors of water: A new O17 absolute shielding scale
Authors: Vaara Juha , Lounila Juhani , Ruud Kenneth , Helgaker Trygve
Published: July 2002

We calculate the rovibrational corrections, temperature dependence and isotope shifts of the isotropic and anisotropic nuclear shieldings of the water molecule. This is the first correlated study of rovibrational effects on the nuclear shieldings in the water molecule and the first study of these effects on the shielding anisotropies. The use of a large restricted active space self-consistent field wave function and a large basis set ensures that the results are of high accuracy. The rovibrational corrections are found to be substantial, 3.7% and 1.8% for the isotropic oxygen and hydrogen shieldings, respectively, in the H21O17 isotopomer at 300 K. For the shielding anisotropies and asymmetry parameters, the corresponding relative corrections are even larger. The changes in the shielding tensors due to molecular rotation and vibration are of the same order of magnitude as—and in some cases even exceed—the changes due to electron correlation. The accuracy of our calculated rovibrationally corrected oxygen shielding leads us to propose a new absolute shielding scale for the O17 nucleus: 324.0±1.5 ppm for the O17 shielding of H2171O in the gas phase (300 K). This shielding scale is supported by recent high-level CCSD(T) calculations on carbon monoxide. The absolute oxygen shielding constants of some oxygen-containing molecules are calculated using the new shielding scale and experimental data on oxygen chemical shifts, comparing the absolute shieldings to the results of recent high-level theoretical calculations.
Boson trimers with nonzero total angular momenta
Authors: Bruch L. W.
Published: July 2002

The lowest energy states of van der Waals trimers of identical spinless bosons with one and two units of total angular momentum are examined. Parameters corresponding to He4 and para-H2 are treated and the relation of the results to level orderings for the rotation of rigid symmetric molecules is discussed. The 2+ rotational state of the para-H2 trimer is bound by 3 K relative to the dimer, while the rotational states of He34, if any, have binding energies of less than 1 mK relative to He24.
Ammonia adsorbed on Cu(110): An angle resolved x-ray spectroscopic and ab initio study
Authors: Hasselström J. , Föhlisch A. , Karis O. , Wassdahl N. , Weinelt M. , Nilsson A. , Nyberg M. , Pettersson L. G. M. , Stöhr J.
Published: July 2002

We present a study of a monolayer of ammonia (NH3) adsorbed on Cu(110) using core level spectroscopies in combination with ab initio calculations based on density functional theory. In particular, x-ray emission spectroscopy has been applied, providing an unsurpassed view of the electronic structure of NH3 upon adsorption. The saturated NH3 monolayer, Θ∼0.4 ML, is found to induce strong adsorbate–adsorbate interaction, causing the molecules to tilt on the surface. Based on the angular distribution of the x-ray emission (XE) spectra, we have been able to estimate a mean tilt angle from the surface normal of 40°–45° for the saturated monolayer; the accompanying theoretical calculations for up to three NH3 molecules on a Cu21 all-electron cluster model support a tilted structure due to adsorbate–adsorbate dipole, and possibly hydrogen bonding, interactions. Since the creation of a core hole on the nitrogen atom site in the intermediate state of the XE process does not affect the symmetry of the molecule, a separation of valence electronic states having mainly e symmetry (N 2pxy) and a1 symmetry (N 2pz) has been achieved using angle resolved XE measurements. In addition to the electronic states of free NH3, evidence of new, substrate induced, states has been found, interpreted as ammonia 3a1/4a1-Cu 3d valence band hybrids. It is found that back donation into the previously unoccupied ammonia 4a1 orbital, and a simultaneous 3a1 donation into the substrate plays an important role in the surface chemical bond.
Density functional theory of nonuniform colloidal suspensions: 3D density distributions and depletion forces
Authors: von Grünberg H. H. , Klein R.
Published: July 2002

We present a density functional approach for inhomogeneous charge-stabilized colloidal suspensions which is based on the hybrid weighted-density approximation. Making use of an analytic expression recently proposed for the free energy of the homogeneous system, a free energy functional for the inhomogeneous fluid can be found that is particularly easy to evaluate numericalLY because of the explicit nature of its input functions. Due to this numerical efficiency our calculation can be extended to relatively large three dimensional systems. After performing various explicit tests of our model we consider the case of two large hard spheres immersed in the suspension and calculate from the 3D density distribution of the fluid the effective pair potential between the spheres.
The He isoelectronic series and the Hooke’s law model: Correlation measures and modifications of Collins’ conjecture
Authors: Ziesche Paul , Smith Vedene H. , Hô Minhhuy , Rudin Sven P. , Gersdorf Peter , Taut Manfred
Published: July 2002

The recently developed concept of a correlation entropy, S, as a quantitative measure of the correlation strength present in a correlated quantum many-body state is applied to the ground states of the He isoelectronic series He(Z) with varying nuclear charge Z and of the Hooke’s law model HLM(ω) with varying oscillator frequency ω. S is constructed from the natural orbital occupation numbers. It vanishes for weak correlation (large coupling constants Z or ω), and increases monotonically with decreasing Z or ω (strengthening correlation). A reduced correlation energy per particle Δecorr and a dimensionless ratio ε=|Ecorr/E| are introduced which vanish asymptotically in the weak correlation limit in contrast to Ecorr and ecorr=Ecorr/N. These two intensive quantities, Δecorr and ε, are compared with s=S/N. For both model systems, dΔecorr/ds⩾0 and dε/ds⩾0 (which modifies Collins’ conjecture that |Ecorr|∼S).
Comment on “On the Longuet-Higgins phase and its relation to the electronic adiabatic–diabatic transformation angle” [J. Chem. Phys. 107, 2694 (1997)]
Authors: Kendrick Brian K. , Mead C. Alden , Truhlar Donald G.
Published: July 2002

We show that the new equation for nuclear motion obtained by Baer et al. is based on an invalid and self-contradictory approximation, and leads to incorrect results for the wave functions, energy levels, degeneracies, and matrix elements. Baer’s conclusion about the connection between the Longuet–Higgins (LH) phase and the adiabatic-diabatic transformation (ADT) angle is also shown to be incorrect. Applications of the method by Baer et al. are shown to contain further errors.
Global nine-dimensional potential energy surface for the H5 system. I. Ab initio multiple reference single and double excitation configuration interaction computations
Authors: Aguado Alfredo , Tablero César , Paniagua Miguel
Published: July 2002

The ground-state adiabatic potential energy surface was computed for 2836 conformations of H5, using a multiple reference single and double excitation configuration interaction program and an extended basis set. The transition state obtained is that of a pentagon with D5h symmetry. We find the energy barrier to lie at 81 kcal/mol within ±1 kcal/mol if a multireference Davidson’s correction is employed, while the De(H2) at this level was 109 kcal/mol. The calculations presented here clearly show the energy of H5 in D5h symmetry to be 28 kcal/mol below the dissociation energy of H2, and therefore a bimolecular mechanism, in the presence of hydrogen atoms, could indeed be considered for the exchange process: H2+D2+H→2HD+H.
Sample morphology and porosity in electron stimulated desorption: N2* from N2 adsorbed onto glassy and crystalline n-hexane
Authors: Vichnevetski E. , Cloutier P. , Sanche L.
Published: July 2002

The electron-stimulated desorption of metastable molecular nitrogen (N2*) from N2 condensed onto n-hexane spacer films deposited on Pt(111) is investigated as a function of electron-impact energy (5–25 eV), and thickness (1–20 monolayers) and deposition temperature (T=20–80 K) of the n-hexane layer. At low T, the N2* yield is found to be inversely proportional to the thickness of the amorphous n-hexane layer. This behavior is explained by the existence of a porous structure in the n-hexane film which efficiently absorbs N2. The metastable signal is also strongly dependent on the temperature of n-hexane deposition, which controls the morphology of the spacer from amorphous at low T to crystalline at T>70 K. Increasing the deposition temperature of n-hexane from 20 to 70 K results in an increase of the N2* signal due to the decrease of the pore volume. Formation of the n-hexane layers in the crystalline state at higher temperatures further inhibits N2 migration into the spacer which results in further increases in the magnitude of the N2* desorption signal.
Complexes of neon with nonaromatic ring molecules: Rotational spectrum, dynamics, and bond energy of 2,5-dihydrofuran–neon
Authors: Maris Assimo , Favero Paolo G. , Dell’Erba Adele , Caminati Walther
Published: July 2002

The equilibrium configuration, dynamics, and dissociation energy of the very weakly bonded 2,5-dihydrofuran⋯Ne complex have been deduced from its free jet millimeter wave spectrum. The equilibrium distance of Ne with respect to the center of mass of the molecule is 3.30 Å, with Ne tilted 7.3° from the perpendicular to the center of mass of the ring toward the oxygen atom. The dissociation energy is estimated, from the centrifugal distortion constant DJ, to be ca. 1.1 kJ/mol.
Cation–anion versus cation–framework interactions in sodalites: First-principles study of model Cu-exchanged sodalites
Authors: Bernasconi L. , Fois E. , Selloni A.
Published: July 2002

We present Local Density Functional calculations of the structural and electronic properties of halosodalite systems in which the Na+ cations are progressively exchanged by Cu+. The calculated lattice constant decreases with increasing Cu loading up to about two Cu/cage, while it is approximately independent of Cu content at higher loadings, in qualitative agreement with experimental observations for silver-exchanged sodalites. The reduction of the lattice parameter is accompanied by the formation of partially covalent Cu–X bonds (X=Cl, Br). The length of these bonds increases with increasing the number of Cu ions per cage, resulting in a simultaneous reduction of Cu–framework distances. For fully exchanged sodalites, the competition between Cu–X and Cu–framework interactions leads to a splitting of the enclosed Cu4X3+ aggregates in fragments. In the electronic density of states, Cu 3d states give rise to a narrow band above the top of the valence band of natural sodalite. Thus the band gap is strongly reduced w.r.t. that of natural sodalite, consistent with experiments for silver-exchanged sodalites. This reduction of the gap is largely independent of the Cu content, i.e., it already occurs at low Cu loading.
Diffusional growth of colloids
Authors: Mozyrsky Dima , Privman Vladimir
Published: July 2002

We consider incorporation of particle detachment in the Smoluchowski model of colloidal growth. Two approaches are considered, utilizing phenomenological rate equation and exact large-time results. Our main conclusion is that the value of the large-time diffusing particle concentration at the aggregate surface is the only parameter needed to describe the added effect of detachment. Explicit expression is given for the particle intake rate.
Numerical inversion of the Laplace transform
Authors: Hüpper Bruno , Pollak Eli
Published: July 2002

A generalization of Doetsch’s formula [Math. Z. 42, 263 (1937)] is derived to develop a stable numerical inversion of the one-sided Laplace transform Ĉ(β). The necessary input is only the values of Ĉ(β) on the positive real axis. The method is applicable provided that the functions Ĉ(β) belong to the function space Lα2 defined by the condition that G(x)=exαĈ(ex), α>0 has to be square integrable. The inversion algorithm consists of two sequential Fourier transforms where the second Fourier integration requires a cutoff, whose magnitude depends on the accuracy of the data. For high accuracy data, the cutoff tends to infinity and the inversion is very accurate. The presence of noise in the signal causes a lowering of the cutoff and a lowering of the accuracy of the inverted data. The optimal cutoff value is shown to be one which leads to an inversion which remains consistent with the original data and its noise level. The method is demonstrated for some model problems: a harmonic partition function, resonant transmission through a barrier, noisy correlation functions, and noisy Monte Carlo generated data for tunneling coefficients obtained via the recently introduced quantum transition state theory (QTST).
Beyond Born–Oppenheimer spectroscopic study for the
C
state of LiH
Authors: Gemperle F. , Gadea F. X.
Published: July 2002

A theoretical spectroscopic study is performed for the C state of LiH using eight diabatic or adiabatic states of symmetry Σ1 beyond the Born–Oppenheimer approximation. For the position of the vibrational levels, an excellent agreement is found with the ten recently observed ones giving confidence to the present study. The vibrational levels present rather strong vibronic shifts (rising to about 10 cm−1 for v=37) particularly for the highest ones. Two approximate methods are tested for their estimation and a new method is presented for the evaluation of the vibronic part of the adiabatic correction. The new method involves the diabatic picture and the discrete variable representation. It leads to nonlocal corrections but avoids the calculation of radial couplings. Nonradiative lifetimes are accurately determined. They range over six orders of magnitude, from nanoseconds to milliseconds. Similarities of the LiH molecule in the C state and in higher excited states at large internuclear distances with highly excited Rydberg atoms are emphasized.
Calculation of reduced partial cross sections of molecules photodesorbing from a cold crystal surface with internal vibrations: Inclusion of curve-crossing effects
Authors: Cárdenas A. E. , Coalson R. D.
Published: July 2002

A Gaussian wave packet/path integral (GWD/PI) method is used to compute final internal state distributions for a molecule photodesorbing from the surface of a zero-temperature crystal with internal vibrations in the situation where nonadiabatic coupling between two excited state potential surfaces is significant. The internal state distributions of the desorbed molecule are influenced by vast numbers of internal vibrational state transitions in the crystal which are not resolved in the calculation (or in experiment). A correlation function technique, introduced previously for the case of direct photodissociation on a single excited potential surface, is generalized to systems where two or more excited potential surfaces are nonadiabatically coupled. The accuracy of the method is successfully tested on a two-dimensional model for which numerically exact results can be computed. The method is then applied to a collinear model of a diatomic molecule photodesorbing from a chain of atoms coupled by Hooke’s law springs. While exact results cannot be obtained in this case, sum rule checks suggest that the results of the GWD/PI are of acceptable accuracy (fractional error of several percent). It is found that for the class of problems under study, which feature nonadiabatic coupling that decays to zero along the photodesorption coordinate, only a few paths through the electronic state space have significant weight. This suggests that the method can be utilized to treat more complicated problems.
Scratching the surface of the water dication
Authors: Van Huis Timothy J. , Wesolowski Steven S. , Yamaguchi Yukio , Schaefer Henry F.
Published: July 2002

The X̃ 3Σg−, ã 1Δg, and b̃ 1Σg+ states of the water dication, H2O2+, have been investigated using several high-level ab initio methods and a range of basis sets. With Dunning’s augmented correlation consistent polarized valence quadruple-ζ (aug-cc-pVQZ) basis set at the complete active space self-consistent field second-order configuration interaction (CAS-SOCI) level, it is confirmed that the ground and first two excited states of H2O2+ are all of D∞h symmetry, in violation of Walsh’s rules for 6 valence electron AH2 systems. The singlet–triplet splitting (X̃ 3Σg−—ã 1Δg) is predicted to be 53.6 kcal/mol (2.32 eV, 18 700 cm−1), while the X̃ 3Σg−—b̃ 1Σg+ separation is predicted to be 91.1 kcal/mol (3.95 eV, 31 900 cm−1). The vertical double ionization potentials (IPs) from X̃ 1A1 H2O to the X̃ 3B1, 1 1A1, b̃ 1B1, and 2 1A1 states of H2O2+ are predicted within the cc-pVQZ basis to be 40.1, 41.2, 42.6, and 46.1 eV, respectively, in good agreement with recent double-charge-transfer spectroscopic results. The corresponding adiabatic double IPs are 37.0, 39.3, and 41.0 eV to the X̃ 3Σg−, ã 1Δg, and b̃ 1Σg+ states of H2O2+, respectively. The activation barrier to fragmentation of H2O2+ (X̃ 3Σg− H2O2+→3Σ− OH++H+) at the cc-pVQZ CAS-SOCI level is predicted to be 2.1 kcal/mol (0.10 eV, 738 cm−1), and the reaction is exothermic by 126.4 kcal/mol (5.48 eV, 44 210 cm−1), providing a challenge for direct experimental detection of this elusive molecule.
Manifestation of anisotropic reactivity and molecular interactions in chemical reaction kinetics
Authors: Shushin A. I.
Published: July 2002

The effect of highly anisotropic reactivity and interaction between molecules on kinetics of diffusion-influenced liquid-phase reactions is analyzed in detail. The Smoluchowski equation (SE) that describes the space/time evolution of pairs of reacting molecules is solved analytically by the method proposed earlier [A. I. Shushin, Chem. Phys. Lett. 130, 452 (1986); Chem. Phys. 120, 91 (1988)]. The method allows for reducing the original SE in curvilinear translational/rotational coordinates of reacting molecules to the SE in the local Cartesian coordinates in the vicinity of reactive relative orientations. Many formulas for the reaction rate are derived in the realistic models of reactivity using this method. Analysis demonstrates high accuracy of these formulas. The model of reactive patches is shown to give reaction rates that are considerably smaller than those predicted here. Peculiarities of reaction kinetics for molecules with anisotropic reactivity and interaction potential are analyzed in detail. Possible applications of the obtained formulas are briefly discussed.
Polymer chain dynamics in dilute solution under Couette flow: Behavior of poly(α-methylstyrene) in good solvent
Authors: Tsunashima Yoshisuke
Published: July 2002

Chain dynamics of poly(α-methylstyrene) of high molecular weight in benzene, a good solvent, in dilute solution was investigated by dynamic light scattering under Couette flow, or the one-dimensional simple shear flow. At the velocity gradient γ=0.34–5.2 s−1 measured, two modes of the translational diffusion and the intramolecular motions were detected. However, the latter was suppressed with the increase of γ. The suppression occurred only in the amplitude without any change in the inherent internal-mode frequencies. The universal ratio Ω/D0q2, estimated as a γ-independent characteristic value in good solvents, agreed well with the theoretical curve predicted for the nondraining Gaussian chain with the microscopic description of chain dynamics, and differed from the macroscopic one with the preaveraged Oseen hydrodynamics. This quantitative agreement suggests that (1) the coupled kinetic equations for chain segments and solvent in the same dynamic level are indispensable for describing rigorous chain dynamics in dilute solution, and (2) the internal motions in the shear field suffer the hydrodynamic interaction strongly (to the level of the Zimm limit), the interaction being compensated for the intramolecular excluded volume effect and making the chain quasi-ideal even in good solvents.
Rigid diffusion paths in droplet growth
Authors: ten Bosch A.
Published: July 2002

A theory for growth of a single droplet of the new stable phase during a first-order phase transition is developed. In the early stage, growth occurs through particle diffusion inhibited by the surface pressure of the spherical droplet. As the droplet grows, the surface curvature diminishes and a transition to rapid propagation of the concentration front occurs. Results are given for the initial and asymptotic droplet distribution function and for the single droplet growth law.
Range definitions for Gaussian-type charge distributions in fast multipole methods
Authors: Kudin Konstantin N. , Scuseria Gustavo E.
Published: July 2002

Replacement of the exact analytic two electron integrals over Gaussian type orbitals by multipole–multipole interaction terms leads to discretization errors. Such errors are important in Fast Multipole Methods as well as in a number of other tree-based algorithms. We investigate the source of these errors and estimate its dependence on the angular momentum of charge distributions. Two new range schemes suitable for use in any multipole method are presented. Our best scheme allow us to achieve one and a half to two orders of magnitude higher accuracy in the total electron–electron energy than the previously proposed range scheme while requiring the same amount of CPU time. Several benchmarks are presented to illustrate the advantages of this new approach.
Valence-level photofragmentation of gaseous Si(CH3)Cl3 and solid-state analogs studied with synchrotron radiation
Authors: Lu K. T. , Chen J. M. , Chiang S. Y.
Published: July 2002

The dissociative photoionization channels of gaseous Si(CH3)Cl3 and ion desorption mechanisms of solid-state analogs following valence-level excitation have been investigated by means of photoionization mass spectroscopy, threshold photoelectron spectroscopy (TPES), and photon-stimulated ion desorption (PSID) using synchroton radiation. The adiabatic ionization threshold of the parent molecular ion was determined to be 11.18 eV, consistent with the value of 11.16 eV obtained from the TPES spectrum. An energy shift ∼0.8 eV toward lower binding energies for the orbitals of solid Si(CH3)Cl3 with respect to the gas phase values was observed. Two thresholds at 14.97 and 17.51 eV in the CH3+ photoionization efficiency spectrum are probably associated with the ionization of 2e″ and 11a1 orbitals, respectively. The H+ desorption threshold at 20.1 eV in the PSID spectrum may be attributed to the excitation of C 2s electron correlation states to the unoccupied states. The Cl+ desorption threshold at 19.9 eV is likely initiated by an Auger-stimulated desorption process.
Comment on “Reversible work of formation of an embryo of a new phase within a uniform macroscopic mother phase” [J. Chem. Phys. 108, 5498 (1998)]
Authors: Kusaka Isamu
Published: July 2002

We examine recently obtained expressions for the reversible work required to form a noncritical nucleus in a metastable vapor. We demonstrate that the expression obtained in by Debenedetti and Reiss [J. Chem. Phys. 108, 5498 (1998)] is identical to that in by Nishioka and Kusaka [J. Chem. Phys. 96, 5370 (1992)], thereby resolving the apparent contradiction between these two papers.