bluuebunny/crossref_metadata_2025 huggingface dataset:
Quadrature integration for orthogonal wavelet systems
Authors: Johnson Bruce R. , Modisette Jason P. , Nordlander Peter J. , Kinsey James L.
Published: July 2002

Wavelet systems can be used as bases in quantum mechanical applications where localization and scale are both important. General quadrature formulas are developed for accurate evaluation of integrals involving compact support wavelet families, and their use is demonstrated in examples of spectral analysis and integrals over anharmonic potentials. In contrast to usual expectations for these uniformly spaced basis functions, it is shown that nonuniform spacings of sample points are readily allowed. Adaptive wavelet quadrature schemes are also presented for the purpose of meeting specific accuracy criteria without excessive oversampling.
Six-dimensional calculation of intermolecular states in molecule-large molecule complexes by filter diagonalization: Benzene–H2O
Authors: Kim Wousik , Neuhauser Daniel , Wall Michael R. , Felker Peter M.
Published: July 2002

We present an approach toward the dynamically exact calculation of intermolecular states in molecule-large molecule complexes. The approach employs an intermolecular Hamiltonian specifically formulated with the case of molecule-large molecule complexes in mind. In addition, it makes use of filter diagonalization techniques to diagonalize that Hamiltonian. The approach is applied to the calculation of J=0 intermolecular states below about 110 cm−1 in the benzene–H2O complex. The results of the calculation are interpreted in terms of five internal rotation states, a doubly degenerate bending mode and a singly degenerate stretching mode, the latter two modes involving the relative translation of the monomer moieties in the complex. The internal rotation states are discussed in the context of the two-dimensional, free internal rotation/water in-plane torsion model of Pribble et al. [J. Chem. Phys. 103, 531 (1995)]. It is shown that that model is largely successful in identifying the important features of the low-energy benzene–H2O states that involve rotation and/or libration of water. It is also shown, though, that multimode couplings can have major effects on the detailed nature of the intermolecular level structure of the species.
Ab initio theoretical study of dipole–bound anions of molecular complexes: Water pentamer anions
Authors: Smith Dayle M. A. , Smets Johan , Adamowicz Ludwik
Published: July 2002

Results of ab initio calculations of the (H2O)5/(H2O)5− systems are presented. The main conclusions of the study are as follows: Based on the calculations we predict that water pentamer anions are metastable systems in agreement with their weak spectral manifestation in the gas-phase experiments of Bowen and co-workers; the excess electrons in all five structural isomers of the water pentamer anion found in the calculations are attached to the clusters by virtue of a dipole–electron interaction; the (H2O)5− anions found in the calculations are close in energy but have different vertical electron detachment energies ranging from 143 to 395 meV.
Time-integrated form of the semiclassical initial value method
Authors: Elran Y. , Kay K. G.
Published: July 2002

A method is presented that greatly improves the efficiency of semiclassical initial value representation treatments by transforming phase space integration variables to time, energy, and additional coordinates and momenta on a Poincare surface. Since the integration over time can be treated as an integration along the classical motion, the number of trajectories needed to obtain convergence is significantly reduced. The technique is applied to test cases involving bounded motion with very encouraging results.
Experimental determination of the reaction time for hydrogen isotope exchange H2+D2→2HD on Ni(110)
Authors: Bertino Massimo F. , Toennies J. Peter
Published: July 2002

The mean reaction time of the hydrogen isotope exchange reaction H2+D2→2HD on the Ni(110) surface has been measured in a high-resolution time-of-flight (TOF) scattering experiment. The reactants were supplied by a pulsed supersonic D2 nozzle beam with incident energy Ei⩽120 meV and by a room temperature effusive H2 source. The TOF spectra of the product HD molecules measured with a chopper located between the incident D2 beam and the sample are a convolution of the reaction time τ on the surface and the velocity distribution of the desorbing HD products. The latter distribution is then measured with a chopper placed between the sample and the detector. The reaction time τ as determined from a deconvolution of the two spectra decreases with increasing surface temperature Ts from τ∼3000 μs at Ts=450 K to τ∼10 μs at Ts=700 K. An Arrhenius plot of the reaction time reveals that the reaction energy is Er=440 meV at surface temperatures below about Ts=600 K and Er=790 meV for temperatures Ts>700 K. Possible interpretations for the two reaction channels are proposed.
Coherent control of multisubband wavepackets with terahertz (Thz) pulses
Authors: Tamborenea P. I. , Metiu H.
Published: July 2002

We perform numerical calculations to study coherent control of multisubband wavepackets by means of pairs of subpicosecond terahertz laser pulses in suitably designed quantum well structures. We employ a single-particle, effective-mass model of the semiconductor structures. Our purpose is to explore the applicability of the ideas of coherent control and wavepacket interferometry to a new physical system (multisubband wavepackets in doped semiconductor quantum wells) and in a new frequency range (terahertz radiation). Similar ideas have been successfully demonstrated in recent years in atomic, molecular, and excitonic systems, in the optical or near-infrared spectrum. We analyze in detail four quantum well structures, with emphasis on the wavepacket dynamics and interference, and demonstrate numerically the possibility of measurable coherent control of the population of the excited electrons. These wavepacket-interference effects could be used to study decoherence times in doped semiconductor structures. Also, due to the sensitivity of the interference effects to the potential energy, the scheme could be employed to detect defects in the sample. The article also presents a study to determine whether an absorption experiment in a quantum well can be used to determine the shape of a subcycle laser pulse. We show that it is difficult to distinguish pulses with a Gaussian envelope of the vector potential from pulses in which the electric field envelope is Gaussian.
Simulation of excited state proton transfer reaction kinetics
Authors: Cukier R. I. , Zhu Jianjun
Published: July 2002

A simulation method suited to characterize excited state proton transfer reaction kinetics in a polar solvent is developed, and applied to an intramolecular reaction of the form A–HB*→AH–B*. The model is applicable to an exothermic electronically excited proton potential energy surface (pes). The solvent modulates this surface but does not have enough coupling strength to symmetrize the proton pes with any significant probability. The proton transfer mechanism then is tunneling through an asymmetric proton pes. As the proton is a fast, quantum object relative to the solvent degrees of freedom, the tunneling is solvent configuration dependent. For each configuration, a rate constant is evaluated by a Wentzel–Kramers–Brillouin (WKB) method. Excitation to the excited reactant state initiates a coupled process of solvent relaxation to equilibrate to the new solute charge state and proton transfer. Hence, the kinetics of the reaction may be inhomogeneous. A survival time formalism is introduced to carry out the average over the solvent fluctuations. The kinetics is roughly exponential. However, the long-time rate constant obtained from the survival probability (0.160 ps−1) is somewhat slower than the rate constant (0.260 ps−1) obtained by assuming that the proton transfer is slow compared to solvent relaxation. The kinetics is fast, in accord with that found in many experimental studies of excited state intramolecular proton transfer.
Rate constants of spherical dispersions: From diffusion-limited data to nondiffusion limited results
Authors: Lu Shih-Yuan
Published: July 2002

A simple but accurate equation is derived for calculation of the overall rate constants of nondiffusion-limited incorporation of diffusing species in spherical dispersions, based on the corresponding results of the diffusion-limited cases. The proposed equation checks very well with the accurate nondiffusion limited rate constant data of three regular spherical arrays computed by Lu [J. Chem. Phys. 109, 4985 (1998)]. The relative errors are less than 5% for volume fractions as high as 0.45 for the simple cubic array and 0.6 for both the face-centered and body-centered cubic arrays. Results from the proposed equation deviate the most from the accurate data at intermediate P. Here P is a dimensionless parameter characterizing the relative rate of diffusive transport versus surface incorporation.
Reactive quenching of electronically excited OH radicals in collisions with molecular hydrogen
Authors: Anderson David T. , Todd Michael W. , Lester Marsha I.
Published: July 2002

The hydrogen atom products of the OH A 2Σ+ (v=0)+H2→H+H2O quenching reaction have been characterized by Doppler spectroscopy. The translational energy distribution of the products is bimodal, with the two components accounting for approximately 3% and 40% of the 4.72 eV of available energy.
Imaging of charged atomic reaction products: Inversion by a two-dimensional regularization method
Authors: Winterhalter J. , Maier D. , Honerkamp J. , Schyja V. , Helm H.
Published: July 2002

An improved inversion method is presented for the analysis of data obtained by imaging techniques. We apply the inversion method for the investigation of photoelectron images in order to determine the distribution of kinetic energy and emission angle of photoelectrons. The conventional inversion approach relies on an Abel-inversion formalism, valid only in a limited case of small kinetic energies of the photoelectrons. In contrast, the improved approach is valid for arbitrary kinetic energies because it explicitly accounts for the image distortion by the projection technique. The conventional and the improved approach are compared with simulated data and with measured data from photoionization of the rare gases, xenon and argon, in a strong laser field. At small energies the conventional and the new approach yield the same results, whereas for larger energies the conventional method fails but our method is still applicable. Most importantly our inversion method is applicable to arbitrary homogeneous and inhomogeneous field geometries and hence to all types of imaging spectrometers currently in use.
Time-dependent quantum studies of the O(3P)+HCl(X 1Σ+) reaction
Authors: Wang Lichang , Kalyanaraman C. , McCoy Anne B.
Published: July 2002

Time-dependent quantum wave packet calculations are carried out for the O(3P)+HCl reaction using the Koizumi, Schatz, and Gordon (KSG) and the Ramachandran, Senekowitsch, and Wyatt (RSW) potentials for the total angular momentum J=0. A detailed study is performed on the KSG surface for which reaction probabilities for the formation of the OH product as a function of collision energies are reported for the v0=0,1 and j0⩽10 states of HCl. The present results are in good agreement with previous time-independent quantum treatments, and physical insights into the reaction dynamics based on an analysis of the calculated wave packet are explored, for example, mechanisms for the rotationally enhanced reaction probabilities that have been observed at both v0=0 and 1. The most profound effects are observed when HCl is initially in states with j0>5 or v0=1. A comparison of the results for v0=0, j0=0 with those obtained from the RSW surface indicates that the width of barrier and the topology of the potential play crucial roles in governing the dynamics of the O(3P)+HCl reaction.
NO monomer and (NO)x polymeric chain chemisorption on Pt{110}: Structure and energetics
Authors: Ge Q. , Brown W. A. , Sharma R. K. , King D. A.
Published: July 2002

The chemisorption of NO on Pt{110}-(1×1) and -(1×2) has been studied using density functional theory slab calculations with the generalized gradient corrections. On both surface phases the monomeric species is the most stable and the short-bridge sites are energetically the most favorable adsorption sites. Monomeric NO is adsorbed upright with its molecular axis normal, bonded to the surface through the N atom. On the (1×2) surface at high coverage a polymeric (NO)x chain structure is identified; this may well correspond to the structure experimentally observed at high coverage on the (1×2) surface formed after heating a multilayer to temperatures between 80 K and 200 K, characterized by an NO IR band at 1760 cm−1.
Calculation of frequency-dependent first hyperpolarizabilities using the second-order Møller–Plesset perturbation theory
Authors: Kobayashi Takao , Sasagane Kotoku , Aiga Fumihiko , Yamaguchi Kizashi
Published: July 2002

We perform the first calculations of frequency-dependent first hyperpolarizabilities in the second-order Møller–Plesset perturbation theory (MP2) as analytical third derivatives of the time-averaged MP2 quasienergy with respect to electric field strengths. The calculations of frequency-dependent first hyperpolarizabilities using the quasienergy derivative (QED) method-based MP2 (QED-MP2) response theory are presented for the electro-optic Pockels effect (EOPE) [β(−ω;ω,0)] and second harmonic generation (SHG) [β(−2ω;ω,ω)] of the FH, H2O, CO, and NH3 molecules. The QED-MP2 values of the SHG first hyperpolarizabilities β∥(−2ω;ω,ω) for the H2O, CO, and NH3 molecules show good agreement with the experimental values. The QED-MP2 response theory is the simplest in ab initio methods for including dynamical electron correlation effects in dynamic response properties efficiently.
Intermediate-time tracer-diffusion of nonspherical Brownian particles
Authors: de J. Guevara-Rodrı́guez F. , Medina-Noyola M.
Published: July 2002

The time-dependent tracer-diffusion properties of a nonspherical Brownian particle that interacts with a suspension of spherical particles are studied in terms of an idealized but nontrivial model system for which the predictions of the generalized Langevin equation approach to tracer diffusion can be calculated, and compared with the results of a computer simulation experiment. In the model, the nonspherical particle is represented by a linear array of NT (=2 or 3) spherical particles with nearest-neighbor separation ΔL. For this model, we calculate the rotational and the (transversal and longitudinal) translational mean squared displacements, both, directly from the computer simulation, and approximately using the generalized Langevin equation approach. The theory is found to reproduce qualitatively and quantitatively the main features of the results of the simulation experiment for these properties.
Revisiting angular jump models of molecular reorientations in viscous liquids
Authors: Diezemann Gregor , Sillescu Hans
Published: July 2002

We generalize the frequently used model of isotropic reorientational Brownian motion via small but finite angular steps to the case in which molecular reorientations by different angles take place around arbitrary axes. A simple approximation allows to give analytical expressions for experimentally relevant correlation functions, including spin lattice relaxation rates. We compare the results of our model to earlier treatments of rotational Brownian motion.
Fundamental measure theory for mixtures of parallel hard cubes. II. Phase behavior of the one-component fluid and of the binary mixture
Authors: Martı́nez-Ratón Yuri , Cuesta José A.
Published: July 2002

A previously developed fundamental measure functional [J. Chem. Phys. 107, 6379 (1997)] is used to study the phase behavior of a system of parallel hard cubes. The single-component fluid exhibits a continuous transition to a solid with an anomalously large density of vacancies. The binary mixture has a demixing transition for edge–length ratios below 0.1. Freezing in this mixture reveals that at least the phase rich in large cubes always lies in the region where the uniform fluid is unstable, hence suggesting a fluid–solid phase separation. A method is developed to study very asymmetric binary mixtures by taking the limit of zero size ratio at fixed solvent fugacity. With this procedure the mixture is exactly mapped onto a one-component fluid of parallel adhesive hard cubes. At any density and solvent fugacity the large cubes are shown to collapse into a close-packed solid. Nevertheless the phase diagram contains a large metastability region with fluid and solid phases. Upon introduction of a slight polydispersity in the large cubes, the system shows the typical phase diagram of a fluid with an isostructural solid–solid transition (with the exception of a continuous freezing). Consequences about the phase behavior of binary mixtures of hard core particles are then drawn.
A simple model of tracer-diffusion of nonspherical Brownian particles
Authors: de J. Guevara-Rodrı́guez F. , Medina-Noyola M.
Published: July 2002

We present a Brownian dynamic simulation of the translational and rotational motion of an interacting nonspherical Brownian particle. This simulation experiment involves an idealized model system of a suspension of spherical colloidal particles with which the nonspherical particle interacts. The latter is represented as a rigid linear array of (two or three) spherical particles. The direct pair interactions between all the spheres in the system (including those of the tracer particle) are modeled by a repulsive Yukawa potential. For simplicity, the two-dimensional version of this simulation experiment is considered, and hydrodynamic interactions are ignored. From the simulation experiment, we determine the translational and rotational mean-square-displacement of the nonspherical tracer particle. Here we focus only on the early deviations, due to the direct interactions, from the short-time, free-diffusion regime. In the analysis of these results, use is made of the recently developed Generalized Langevin equation theory of tracer diffusion of nonspherical Brownian particles.
Hard core Yukawa fluid with temperature and density dependent interaction: Phase diagram of the AOT/water/decane microemulsion
Authors: Bouaskarne M. , Amokrane S. , Regnaut C.
Published: July 2002

A fluid with an interaction potential consisting of a hard core and an attractive Yukawa tail is considered. The strength of the attraction is taken to depend both on density and temperature in order to take into account the state dependence of the effective interaction suggested by the analysis of structural data of several colloidal suspensions, in particular microemulsions of AOT reverse micelles. The thermodynamics of this fluid is investigated starting from the inverse temperature expansion of the free energy in the mean spherical approximation. The temperature and density dependence of the interaction is incorporated in consistent expressions for the pressure, isothermal compressibility, and chemical potential. The phase diagram predicted by this method is in agreement with experimental data on AOT reverse micelles analyzed in the effective one component approach.
Ab initio calculation of the interaction potential for the krypton dimer: The use of bond function basis sets
Authors: Tao Fu-Ming
Published: July 2002

The Kr2 interaction potential is studied by ab initio calculations using several large basis sets containing high polarization functions and/or bond functions. It is shown that the addition of bond functions results in a dramatic improvement for the convergence of the calculated interaction energies. At the frozen-core MP4 level, the large atomic basis set such as [9s7p4d3f2g] recovered less than 75% of the experimental well depth. In contrast, the bond function basis set such as [9s7p4d3f]-{3s3p2d1f} produced a well depth of 617 μhartrees, over 99% of the experimental well depth. The frozen-core MP4 calculation appears to overestimate the well depth by about 25 μhartrees as compared to the calculation at the CCSD(T) level. On the other hand, the inclusion of core electron correlation at the MP4 level may contribute 13 μhartrees to the well depth. Beyond the potential minimum, the use of bond functions consistently gives significant improvement in the calculated potential from the highly repulsive wall to the attractive tail region. Final remarks are made about the counterpoise method and the use of bond functions.
ArHF vibrational predissociation dynamics using the diatomics-in-molecule potential energy surface
Authors: Buchachenko A. A. , Stepanov N. F. , Grigorenko B. L. , Nemukhin A. V.
Published: July 2002

Vibrational predissociation dynamics of ArHF and ArDF complexes is investigated theoretically for the first time owing to the use of three-dimensional potential energy surfaces (PES’s) based on the diatomics-in-molecule approach [J. Chem. Phys. 104, 5510 (1996)]. The original PES is improved empirically to yield a reasonable description of the lowest vibrational energy levels of the ArHF complex at J=0. Predissociation dynamics is studied by means of line shape and diabatic Fermi Golden Rule methods. The latter is found to provide excellent results for the total decay widths but only a qualitative estimate for the product rotational distributions. It is shown that predissociation dynamics is governed by vibrational to rotational energy transfer. The decay proceeds almost entirely into the highest accessible rotational product channel. This propensity manifests itself in the decrease of the predissociation lifetime upon increasing vibrational excitation of the diatomic fragment when the highest rotational channel appears to be closed. Another source of state specificity in the vibrational predissociation is the anisotropy of the PES. Absolute calculated lifetime values are likely too small, but exhibit some qualitative trends observed experimentally.
Dynamical properties of the soft sticky dipole model of water: Molecular dynamics simulations
Authors: Chandra Amalendu , Ichiye Toshiko
Published: July 2002

Dynamical properties of the soft sticky dipole (SSD) model of water are calculated by means of molecular dynamics simulations. Since this is not a simple point model, the forces and torques arising from the SSD potential are derived here. Simulations are carried out in the microcanonical ensemble employing the Ewald method for the electrostatic interactions. Various time correlation functions and dynamical quantities associated with the translational and rotational motion of water molecules are evaluated and compared with those of two other commonly used models of liquid water, namely the transferable intermolecular potential-three points (TIP3P) and simple point charge/extended (SPC/E) models, and also with experiments. The dynamical properties of the SSD water model are found to be in good agreement with the experimental results and appear to be better than the TIP3P and SPC/E models in most cases, as has been previously shown for its thermodynamic, structural, and dielectric properties. Also, molecular dynamics simulations of the SSD model are found to run much faster than TIP3P, SPC/E, and other multisite models.
A transition-state theory approach to adsorbate dynamics at arbitrary loadings
Authors: Tunca Canan , Ford David M.
Published: July 2002

There has been much recent interest in using transition-state theory (TST) to extend the time and length scales accessible to molecular-level simulations of adsorbate transport in microsporous materials. However, the vast majority of this work has been performed on systems at infinite dilution. The objective of this paper is to obtain fundamental rate constants for adsorbate motion at nonzero loadings using multidimensional TST. More specifically, we focus on systems where the adsorption of a molecule is not highly localized in a single site, but rather distributed throughout an uncorrugated cage. We develop a theory in which high-dimensional TST integrals are approximated using exact lower-dimensional information. The evaluation of the resulting integrals is performed with an importance sampling method involving the insertion of a single molecule, thus improving the statistical quality of the results. The theory is applied to the motion of methane and xenon in the zeolite ZK4, where hopping between α cages is the rate-limiting event. Our results show that hopping rates increase with loading in the cage, which is consistent with experimental trends in the diffusivity. Agreement between our theory and corresponding molecular dynamics simulations is excellent.
Interaction-site-model description of collective excitations in liquid water. II: Comparison with simulation results
Authors: Chong Song-Ho , Hirata Fumio
Published: July 2002

Theoretical results for dynamical correlation functions characterizing collective excitations in liquid water reported in a previous paper are compared with molecular dynamics simulation results performed on the same system. We also examine the validity and accuracy of the approximation scheme for memory functions employed in our theory by investigating whether the assumed form for memory functions and resulting expressions for dynamical correlation functions can be used as faithful models to reproduce the “experimental” data determined from the simulation.
Photodissociation detection of microwave transitions in highly excited vibrational states
Authors: Muenter J. S. , Rebstein J. , Callegari A. , Rizzo T. R.
Published: July 2002

This paper describes a new spectroscopic technique which uses photodissociation to detect pure rotational transitions in highly excited vibrational energy levels of the ground electronic state. This method has initially been applied to the HO35Cl molecule in its second excited OH stretching vibration, the (200) state. In addition to observing the microwave signal, the Stark effect for this transition provides a dipole moment measurement in the (200) vibrational state. The (200) 180,18→171,17 transition occurs at 14 858.40(1) MHz and the b component of the dipole moment of this state is μb=1.515(5) D. The technique is quite general in that the rotational transition can involve energy levels up to, and exceeding, the dissociation threshold of the ground electronic state.
Interaction optimized basis sets for correlated ab initio calculations on the water dimer
Authors: van Duijneveldt-van de Rijdt J. G. C. M. , van Duijneveldt F. B.
Published: July 2002

A compact basis set is constructed for the water dimer by focusing directly on an optimal description of the counterpoise-corrected interaction energy (ΔE) rather than on the total energy of the fragments. The optimization criterion is that the basis set should be of uniform accuracy, i.e., the truncation error in ΔE due to the basis set incompleteness should be the same for all symmetry types at all sites. Aiming at a truncation error of 10 μhartree per symmetry at the SCF+MP2 (self-consistent field+Møller–Plesset second-order) frozen core level the resulting interaction optimized basis set comprises 249 functions. The composition of this IO249 set is O/5s3p4d3f2g1h, H(donor)/2s4p1d, H(else)/2s3p, bond function set/3s3p2d1f. An all-electron variant, IO275, is described as well. A recipe to obtain interaction optimized sets for other systems is given. The set IO249 yields a ΔE(fc) value at the Feller–Frisch geometry of −4.87 kcal/mol. Of the many orbital-based calculations that have been reported for this system only Schütz’ 1046-function calculation [J. Chem. Phys. 107, 4597 (1997)] was more accurate. The small size of the interaction optimized sets opens the possibility for high-accuracy SCF+MP2 work on larger systems than have been accessible before. It also brings higher-level correlated treatments within reach. An Appendix summarizes two additivity rules which allow the ΔE for a larger basis set to be estimated to very high accuracy from the results of smaller basis sets.
Theoretical study of low-lying electronic states of TiCl and ZrCl
Authors: Sakai Yoshiko , Mogi Koichi , Miyoshi Eisaku
Published: July 2002

Low-lying electronic states of TiCl and ZrCl were investigated by the complete active space SCF (CASSCF), multi-reference singly and doubly excited configuration interaction (MRSDCI), and multi-reference coupled pair approximation (MRCPA) calculations using the model core potential (MCP) method. Relativistic effects were incorporated in the MCP and basis sets for Zr at the level of Cowan and Griffin’s quasi-relativistic Hartree–Fock method. The 4Φ state was found to be the ground state of TiCl, whereas the 2Δ state was the ground state of ZrCl at all levels of calculation. Two low-lying excited states were very close in energy to the ground state. The excited 4Σ−and 2Δ states of TiCl were higher than the ground state by 0.102 eV and 0.458 eV, respectively, and the excited 4Φ and 4Σ− states of ZrCl were higher by 0.094 eV and 0.110 eV, respectively, at the MRCPA level. The calculated values of re(2.319 Å) and ωe(382 cm−1) for the ground 4Φ state of TiCl are quite close to the values of re(2.351 Å) and ωe(383 cm−1) for the ground 2Δ state of ZrCl. The values of re, ωe, Be, and αe are reasonably comparable to the observed values for both TiCl and ZrCl.
Nanoscale shock wave spectroscopy: A direct view of coherent ultrafast bath dynamics
Authors: Kohen Daniela , Martens Craig C.
Published: July 2002

We present molecular dynamics simulations of an idealized ultrafast pump-probe experiment that is designed to allow direct observation of the real-time dynamical response of an impulsively driven many-body bath. In this scheme, a pump laser pulse excites an impurity molecule embedded in a solid host to a repulsive electronic state. The resulting photofragments collide with neighboring host atoms and create localized excitations that travel through the lattice at supersonic velocities. We refer to these excitations as a nanoscale shock wave, as they are localized on the nanometer length scale of individual atoms in the solid. The probe laser is tuned to a transient absorption in the host that is induced by the collisions between neighboring lattice atoms that accompany the propagation of the localized disturbance. The resulting signal as a function of time delay then provides a view of the creation, evolution, and decay of the nanoscale shock waves. We apply the general approach to a two-dimensional model system representing I2 photodissociation in solid Ar. Pump-probe signals are synthesized, and the observed features are interpreted in terms of the microscopic dynamics of the system.
Calculated and experimental rotational constants of (D2O)3: Effects of intermolecular torsional and symmetric stretching excitations
Authors: Sabo Dubravko , Bačić Zlatko , Graf Stephan , Leutwyler Samuel
Published: July 2002

Calculations of the torsional state dependence of A=B and C rotational constants of (D2O)3 are reported, for torsional energies up to 100 cm−1 above the ground state, extending our work on the rotational constants of all isotopomers of water trimer using ab initio four-dimensional torsional-stretching intermolecular potential-energy surface [D. Sabo et al., J. Phys. Chem. 110, 5745 (1999)]. Direct composition was made to the rotational constants measured by Viant et al. [J. Chem. Phys. 110, 4369 (1999)] for the same nine torsional levels of (D2O)3. In order to consistently reproduce the pronounced variations of the A=B and C rotational constants from one torsional eigenstate to the other, theory must take into account both the changes of rms torsional angles of the “free” O–D bonds and the changes in the oxygen–oxygen separation which accompany torsional excitation. The changes of C with torsional state, ΔC(n), are distinctly non-monotonic; they depend mainly on the rms (root-mean-square) torsional angle and to a lesser degree on the interoxygen distance. The changes of A=B with torsional state, ΔA(n)=ΔB(n), depend on both rms torsional angles and interoxygen distance, but with opposite signs, giving rise to an apparent monotonic decrease with n which is smaller than the changes due to either mechanism alone. The ΔA(n)=ΔB(n) and ΔC(n) changes from the (3+1)D torsional-stretching calculations are in good agreement with experiment up to n=5.
van der Waals theory for the spatial distribution of the tension in an interface. I. Density functional theory
Authors: Lovett R. , Baus M.
Published: July 2002

The van der Waals theory for the thermodynamic properties of equilibrium fluids is usually presented as an example of a mean field approximation to a simple interaction model. We use density functional arguments to show that the van der Waals description can also be viewed as an exact consequence of a more complex interaction model. The relation to standard statistical mechanical quantities is constructed and the theory is used to determine the tension profile at a vapor–liquid–wall interface.
Core to surface exchange and the melting of Ar12–HF (η=0); A j-walking-molecular-dynamics simulation
Authors: Ghayal Madhavi Rajan , Curotto E.
Published: July 2002

We carry out a systematic investigation of the melting properties of Ar12–HF (with HF in the ground vibrational state) using a classical Monte Carlo simulation enhanced by the j-walking algorithm. We discover two distinct features in the heat capacity of the system. The first feature around 11 K corresponds to the exchange of HF with one of the 12 surface atoms of the cluster. The second feature around 30 K corresponds to the melting of the argon frame. We investigate the spectrum of the cluster as a function of temperature using MC-MD methods and we find two distinct phenomena taking place gradually, each identifiable with a phase transition of the cluster. Optimization results reveal that the anisotropic Ar–HF interaction has large effects in the liquidlike structure of the cluster.
The fluorescence excitation spectra of the A 1Au(S1)–X 1Ag(S) transition of biacetyl: Determination of the band origin
Authors: Chen Yang , Pei Linsen , Jin Jin , Gao Yide , Ma Xingxiao , Chen Congxiang
Published: July 2002

Laser-induced fluorescence spectra of the A 1Au(S1)–X 1Ag(S0) transition of biacetyl are observed under supersonic jet condition. Three weaker bands have been observed at 154, 67, and 58 cm−1 to the red of the previously presumed band origin 000 (at 22 336 cm−1). The observed tunneling splitting 1.05 cm−1 for the G01 band and 1.68 cm−1 for the A01 band are compared to the theoretical result. Based on the tunneling splitting, the true band origin 000 is determined for the first time as the furthest weaker band at 22 182 cm−1. The three weaker bands have been assigned as 000, G01, and A01 transitions, respectively.
Spectroscopic analysis of an unusual Ca⋅Xe[3Σ−]←Ca(4s4pπ 3P)⋅Xe[3Π−] transition
Authors: Leung Allen W. K. , Bellert D. , Breckenridge W. H.
Published: July 2002

From the partially resolved rotational structure of six vibrational bands at high resolution, a vibrational progression in the 22 400–22 900 cm−1 region has been assigned to a CaXe[3Σ−]←Ca(4s4pπ 3P0)⋅Xe[3Π0−] transition. It is suggested that the CaXe[3Σ−] state observed is a “mixed” state, having both Ca(4pπ4pπ 3PJ)⋅Xe[3Σ−] and Ca(3dπ4pπ 3DJ)⋅Xe[3Σ−] character due to an adiabatic avoided crossing between the two diabatic states.
Laser spectroscopy of the ν1+3ν3 absorption band in C212H2. II. Self-collisional lineshift measurements
Authors: Herregodts F. , Hepp M. , Hurtmans D. , Vander Auwera J. , Herman M.
Published: July 2002

We have recorded the spectrum of the ν1+3ν3 band in C212H2, around 12676 cm−1, using an autoscan Ti:Sa spectrometer. Pressure-dependent line positions were determined from an absorption spectrum recorded using a long White-type multiple-pass cell. An optoacoustic cell with a constant, low acetylene pressure allowed reference line position wavenumbers to be measured simultaneously. In different experiments, the multiple-pass cell was filled with increasing acetylene pressures. Self-collisional lineshifts were determined for more than 30 P and R lines in the band. Line wavenumbers for the stronger lines were separately measured from an optoacoustic spectrum calibrated using the results of a previous investigation in the literature [X. Zhan and L. Halonen, J. Mol. Spectrosc. 160, 464 (1993)] and corrected for their pressure dependence using the presently determined self-collisional lineshifts. Lineshift parameters that are significantly different from the overall behavior in the band are unexpectedly observed for the R(17) and P(19) lines. This result is explained in terms of a different intermolecular behavior of the molecule in the upper J=18 rotation level, attributed to an intramolecular Coriolis-type coupling with a nearby state tentatively assigned as containing important excitation in ν5, the cis-bend mode.
Chemical potentials and potential distributions of inclusion gas in quenched-annealed random porous media
Authors: Fernaud Maria-Jose , Lomba Enrique , Lee Lloyd L.
Published: July 2002

The adsorption of hard-sphere gas in a random porous media and/or in a disordered hard sphere matrix is studied by applying the replica-Ornstein–Zernike (ROZ) equations for the quenched-annealed systems. Our interests are (1) to derive new formulas for the chemical potentials and the potential distributions theorems for such systems and (2) to use these derivations as consistency requirements for improving the closure relations in the ROZ. Two types of consistencies are enforced: (i) bulk thermodynamic property consistencies, such as the Gibbs–Duhem relation and (ii) zero-separation theorems on the cavity functions. Five hard-sphere matrix/hard-sphere fluid systems have been investigated, representing different porosities and size ratios. Direct formulas for the chemical potentials and the zero-separation theorems for the fluid cavity functions are derived and tested. We find uniformly better agreement with Monte Carlo data when self-consistency is enforced, than the conventional closures: such as the Percus–Yevick and hypernetted chain equations. In general, the structural properties are improved, as well as the thermodynamic properties. There remains discrepancy in the fluid-replica structure h12(r) at coincidence, r=0. The nature of the h12(r) behavior is discussed in light of the consistency principles.
An ab initio molecular dynamics study of the SN2 reaction Cl−+CH3Br→CH3Cl+Br−
Authors: Raugei Simone , Cardini Gianni , Schettino Vincenzo
Published: July 2002

An ab initio molecular dynamics study of the SN2 reaction Cl−+CH3Br→CH3Cl+Br− has been performed at the Becke, Lee, Yang, and Parr (BLYP) level of theory by the blue-moon method. The potential energy and the free energy profile along the reaction coordinate have been determined and compared with the available experimental and calculated data. An analysis of the structural parameters along the reaction pathway is presented. Results of impact studies are also reported. It is shown that, depending on impact velocity, recrossing of the barrier can occur. Strong polarization effects are reported.
Integral equation theory for dipolar hard sphere fluids with fluctuating orientational order
Authors: Klapp S. H. L. , Patey G. N.
Published: July 2002

We present an integral equation approach to the structural and thermodynamic properties of a fluid of partially aligned dipolar hard spheres. To relate the two-particle correlation functions to the anisotropic singlet density, we mainly employ the Lovett–Mou–Buff–Wertheim equation. We show that, as in the isotropic case, the mean-spherical approximation and the reference hypernetted chain (RHNC) closures lead to quite different results. This is particularly true at high coupling strengths, where the RHNC theory shows a transition from an isotropic to a ferroelectric fluid phase. The predicted transition temperatures are very close to those one obtains from the RHNC theory for the isotropic fluid.
The formation of ClOO following the photoexcitation of aqueous OClO studied by two-color, time-resolved resonance Raman spectroscopy
Authors: Thomsen Carsten L. , Philpott Matthew P. , Hayes Sophia C. , Reid Philip J.
Published: July 2002

The photochemistry of chlorine dioxide (OClO) is investigated by two-color time-resolved resonance Raman spectroscopy. Pump and probe wavelengths of 390 and 260 nm, respectively, are used to monitor photoproduct formation following aqueous OClO photoexcitation. Depletion and subsequent recovery of the OClO scattering intensities is observed consistent with subpicosecond reformation of OClO via geminate recombination of the primary photoproducts. Intensity is observed at 1442 cm−1 consistent with ClOO formation that appears and decays with time constants of 27.9±4.5 ps and 398±50 ps, respectively. The results presented here represent the first direct evidence for ClOO formation following the photoexcitation of aqueous OClO.
Intermolecular potential energy surfaces and bound states in F–HF
Authors: Meuwly Markus , Hutson Jeremy M.
Published: July 2002

Semiempirical potential energy surfaces for F–HF are constructed, based on recent Ne–HF, Ne–F, and Ne–Ne potentials. The electrostatic forces due to the quadrupole of the F atom are included. The potentials are presented in diabatic and adiabatic representations, with and without spin–orbit coupling. Fully coupled bound-state calculations are carried out, and the resulting energy levels and wave functions are analyzed. The well depth is 317 cm−1, and the ground state is bound by 174 cm−1. The complex is a promising candidate for spectroscopic observation, which would provide detailed information on the potential energy surfaces in the entrance and exit valleys of the F+HF reaction.
On the application of canonical perturbation theory to floppy molecules
Authors: Sugny Dominique , Joyeux Marc
Published: July 2002

Canonical perturbation theory (CPT) is a powerful tool in the field of molecular physics. It consists of a series of coordinate transformations aimed at rewriting the Hamiltonian in a simpler form without modifying the geometry of the phase space. The major achievement of CPT is the straightforward derivation of relations between the physically meaningful parameters of potential energy surfaces and the coefficients of the so-called effective Hamiltonians. While most of the studies performed up to date deal with surfaces expanded in polynomial series around a single minimum, CPT has also been applied to mixed polynomial/trigonometric expansions in the treatment of torsions. In this latter case, however, the accuracy of CPT has not been verified. The goal of this article is to suggest some modifications of the procedures, which allow for the successful application of CPT to floppy molecules with several equilibrium positions and nonpolynomial expansions. The levels belonging to all the wells or located above the saddle points are satisfactorily reproduced by the perturbative Hamiltonian. More precisely, the vibrational modes are sorted into two categories, namely oscillator-like ones and hindered-rotor-like ones. The application of CPT enables the expression of the Hamiltonian in terms of the good quantum numbers and/or classical constants of the motion associated with the oscillator-like modes. The perturbative Hamiltonian then acts on the reduced dimensional space of the hindered-rotor-like modes. The validity and accuracy of this approach are tested on two-dimensional and three-dimensional models mimicking, respectively, nonlinear and linear HCN.
Ion pairing and dissociation at liquid/liquid interfaces: Molecular dynamics and continuum models
Authors: Schweighofer Karl , Benjamin Ilan
Published: July 2002

The thermodynamics and dynamics of NaCl ion-pair dissociation at the water/1,2-dichloroethane liquid/liquid interface are examined using a continuum electrostatic model, molecular dynamics free energy calculations, and nonequilibrium dynamic trajectory calculations. The continuum model shows increased stability of the ion pair relative to that in bulk water and strong dependence of the potential of mean force on the orientation and location of the ion pair relative to the interface. These are in qualitative agreement with the molecular dynamics results. In particular, the equilibrium free energy calculations show that the ion pair is locally stable at the interface and that the dissociation must involve ion transfer and considerable change in the interface structure. These are also confirmed by the nonequilibrium dynamics calculations: Dissociation of the ion pair at the interface involves a simultaneous transfer of both ions into the aqueous side of the interface. The faster transfer of the sodium than the chloride ion influences the lifetime of the ion pair at the interface. In particular, a strong dependence of the ion pair’s stability on its orientation is found.
State resolved reaction rates of the spin-forbidden predissociation of N2O: A quantum dynamics study of the rotational effect
Authors: Nakamura Hisao , Kato Shigeki
Published: July 2002

The predissociation of N2O into the 13A′ and 13A″ dissociative states for the total angular momentum J>0 is studied by quantum dynamics calculations. The effective Hamiltonian for describing the predissociation is derived from time-dependent wave packet propagation calculations on the triplet potential energy surfaces. The decay rates of individual rovibrational states in the singlet manifold are obtained by diagonalizing the effective Hamiltonian represented in terms of the singlet rovibrational wave functions. The Fermi golden rule is also applied to test its validity in estimating the decay rate distribution. For J=1 and 2, the rovibrational Hamiltonian is constructed by recoupling the coupled state wave functions obtained by a filter diagonalization. For higher values of J, a random coupling model deduced from the calculations for J=1 and 2 is introduced to estimate the decay rate distributions. In order to compare the calculated decay rate distributions with those by a random matrix/transition state theory (RM/TST), the transition states are defined as the eigenvectors of decay rate matrix whose eigenvalues are used for calculating the RM/TST distributions. It is found that the fluctuation of decay rate distribution decreases with increasing J though the calculated distribution shows significant deviation from the RM/TST prediction even for J=20. A simple model is employed to interpret the origin of the decrease of fluctuation in decay rates with J and the deviation from RM/TST. It is concluded that a sharp decay rate distribution comes from an increase of the absolute number of singlet rovibrational states accessible to the transition state due to the K-mixing, though such a K-mixing is limited. The deviation of calculated distribution from the RM/TST one is thus attributed to incomplete energy randomization in the singlet state N2O.
A novel iterative strategy for protein design
Authors: Rossi Andrea , Maritan Amos , Micheletti Cristian
Published: July 2002

We propose and discuss a novel strategy for protein design. The method is based on recent theoretical advancements which showed the importance to treat carefully the conformational free energy of designed sequences. In this work we show how computational cost can be kept to a minimum by encompassing negative design features, i.e., isolating a small number of structures that compete significantly with the target one for being occupied at low temperature. The method is successfully tested on minimalist protein models and using a variety of amino acid interaction potentials.
Comment on “Quantum Monte Carlo study of the dipole moment of CO” [J. Chem. Phys. 110, 11700 (1999)]
Authors: Huang K. C. , Needs R. J. , Rajagopal G.
Published: July 2002

Recently Schautz and Flad concluded that the Hellmann–Feynman theorem holds within the fixed-node diffusion quantum Monte Carlo (DMC) method. We show that the Hellmann–Feynman expression is not in general equal to the derivative of the DMC energy with respect to some parameter λ if the nodal surface depends on λ.