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8 Dec 2004

Volume 121, Issue 22, pp. 10839-11508

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Rydberg–London potential for diatomic molecules and unbonded atom pairs

Kevin Cahill and V. Adrian Parsegian

J. Chem. Phys. 121, 10839 (2004); http://dx.doi.org/10.1063/1.1830011 (4 pages) | Cited 11 times

Online Publication Date: 30 November 2004

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We propose and test a pair potential that is accurate at all relevant distances and simple enough for use in large-scale computer simulations. A combination of the Rydberg potential from spectroscopy and the London inverse-sixth-power energy, the proposed form fits spectroscopically determined potentials better than the Morse, Varnshi, and Hulburt–Hirschfelder potentials and much better than the Lennard-Jones and harmonic potentials. At long distances, it goes smoothly to the London force appropriate for gases and preserves van der Waals’s “continuity of the gas and liquid states,” which is routinely violated by coefficients assigned to the Lennard-Jones 6-12 form. © 2004 American Institute of Physics.
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34.20.Cf Interatomic potentials and forces
34.20.Gj Intermolecular and atom-molecule potentials and forces

Fragile-to-strong liquid transition in deeply supercooled confined water

A. Faraone, L. Liu, C.-Y. Mou, C.-W. Yen, and S.-H. Chen

J. Chem. Phys. 121, 10843 (2004); http://dx.doi.org/10.1063/1.1832595 (4 pages) | Cited 93 times

Online Publication Date: 30 November 2004

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Confining water in lab synthesized nanoporous silica matrices MCM-41-S with pore diameters of 18 and 14 Å, we have been able to study the molecular dynamics of water in deeply supercooled states, down to 200 K. Using quasielastic neutron scattering and analyzing the data with the relaxing cage model, we determined the temperature variation of the average translational relaxation time and its Q-dependence. We find a clear evidence of an abrupt change of the relaxation time behavior at T ≈ 225 K, which we interpreted as the predicted fragile-to-strong liquid–liquid transition.© 2004 American Institute of Physics.
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64.70.Ja Liquid-liquid transitions

Atomistic simulations of biologically realistic transmembrane potential gradients

Jonathan N. Sachs, Paul S. Crozier, and Thomas B. Woolf

J. Chem. Phys. 121, 10847 (2004); http://dx.doi.org/10.1063/1.1826056 (5 pages) | Cited 22 times

Online Publication Date: 30 November 2004

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We present all-atom molecular dynamics simulations of biologically realistic transmembrane potential gradients across a DMPC bilayer. These simulations are the first to model this gradient in all-atom detail, with the field generated solely by explicit ion dynamics. Unlike traditional bilayer simulations that have one bilayer per unit cell, we simulate a 170 mV potential gradient by using a unit cell consisting of three salt-water baths separated by two bilayers, with full three-dimensional periodicity. The study shows that current computational resources are powerful enough to generate a truly electrified interface, as we show the predicted effect of the field on the overall charge distribution. Additionally, starting from Poisson’s equation, we show a new derivation of the double integral equation for calculating the potential profile in systems with this type of periodicity. © 2004 American Institute of Physics.
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87.16.D- Membranes, bilayers, and vesicles
87.16.Uv Active transport processes
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back to top Theoretical Methods and Algorithms

Correlation energy extrapolation by intrinsic scaling. III. Compact wave functions

Laimutis Bytautas and Klaus Ruedenberg

J. Chem. Phys. 121, 10852 (2004); http://dx.doi.org/10.1063/1.1814937 (11 pages) | Cited 13 times

Online Publication Date: 30 November 2004

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The information gained in the context of extrapolating the correlation energy by intrinsic scaling is used to shorten the full configurational expansions of electronic wave function without compromising their chemical accuracy. The truncations are accomplished by judiciously limiting the participation of the ranges of predetermined approximate sets of natural orbitals in the various excitation categories. © 2004 American Institute of Physics.
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31.15.V- Electron correlation calculations for atoms, ions and molecules

Globally convergent trust-region methods for self-consistent field electronic structure calculations

Juliano B. Francisco, José Mario Martínez, and Leandro Martínez

J. Chem. Phys. 121, 10863 (2004); http://dx.doi.org/10.1063/1.1814935 (16 pages) | Cited 9 times

Online Publication Date: 30 November 2004

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As far as more complex systems are being accessible for quantum chemical calculations, the reliability of the algorithms used becomes increasingly important. Trust-region strategies comprise a large family of optimization algorithms that incorporates both robustness and applicability for a great variety of problems. The objective of this work is to provide a basic algorithm and an adequate theoretical framework for the application of globally convergent trust-region methods to electronic structure calculations. Closed shell restricted Hartree–Fock calculations are addressed as finite-dimensional nonlinear programming problems with weighted orthogonality constraints. A Levenberg–Marquardt-like modification of a trust-region algorithm for constrained optimization is developed for solving this problem. It is proved that this algorithm is globally convergent. The subproblems that ensure global convergence are easy-to-compute projections and are dependent only on the structure of the constraints, thus being extendable to other problems. Numerical experiments are presented, which confirm the theoretical predictions. The structure of the algorithm is such that accelerations can be easily associated without affecting the convergence properties. © 2004 American Institute of Physics.
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31.15.xr Self-consistent-field methods

Variationally optimized basis orbitals for biological molecules

T. Ozaki and H. Kino

J. Chem. Phys. 121, 10879 (2004); http://dx.doi.org/10.1063/1.1794591 (10 pages) | Cited 14 times

Online Publication Date: 30 November 2004

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Numerical atomic basis orbitals are variationally optimized for biological molecules such as proteins, polysaccharides, and deoxyribonucleic acid within a density functional theory. Based on a statistical treatment of results of a fully variational optimization of basis orbitals ( full optimized basis orbitals) for 43 biological model molecules, simple sets of preoptimized basis orbitals classified under the local chemical environment (simple preoptimized basis orbitals) are constructed for hydrogen, carbon, nitrogen, oxygen, phosphorous, and sulfur atoms, each of which contains double valence plus polarization basis function. For a wide variety of molecules we show that the simple preoptimized orbitals provide well convergent energy and physical quantities comparable to those calculated by the full optimized orbitals, which demonstrates that the simple preoptimized orbitals possess substantial transferability for biological molecules.© 2004 American Institute of Physics.
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36.20.Kd Electronic structure and spectra
36.20.Hb Configuration (bonds, dimensions)
87.14.E- Proteins
87.14.G- Nucleic acids
87.15.B- Structure of biomolecules
87.15.A- Theory, modeling, and computer simulation
87.15.-v Biomolecules: structure and physical properties
31.15.E- Density-functional theory
87.10.-e General theory and mathematical aspects

Lower and upper bounds for the absolute free energy by the hypothetical scanning Monte Carlo method: Application to liquid argon and water

Ronald P. White and Hagai Meirovitch

J. Chem. Phys. 121, 10889 (2004); http://dx.doi.org/10.1063/1.1814355 (16 pages) | Cited 13 times

Online Publication Date: 30 November 2004

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The hypothetical scanning (HS) method is a general approach for calculating the absolute entropy S and free energy F by analyzing Boltzmann samples obtained by Monte Carlo or molecular dynamics techniques. With HS applied to a fluid, each configuration i of the sample is reconstructed by gradually placing the molecules in their positions at i using transition probabilities (TPs). At each step of the process the system is divided into two parts, the already treated molecules (the “past”), which are fixed, and the as yet unspecified (mobile) “future” molecules. Obtaining the TP exactly requires calculating partition functions over all positions of the future molecules in the presence of the frozen past, thus it is customary to invoke various approximations to best represent these quantities. In a recent publication [Proc. Natl. Acad. Sci. USA 101, 9235 (2004)] we developed a version of HS called complete HSMC, where each TP is calculated from an MC simulation involving all of the future molecules (the complete future); the method was applied very successfully to Lennard-Jones systems (liquid argon) and a box of TIP3P water molecules. In its basic implementation the method provides lower and upper bounds for F, where the latter can be evaluated only for relatively small systems. Here we introduce a new expression for an upper bound, which can be evaluated for larger systems. We also propose a new exact expression for F and verify its effectiveness. These free energy functionals lead to significantly improved accuracy (as applied to the liquid systems above) which is comparable to our thermodynamic integration results. We formalize and discuss theoretical aspects of HSMC that have not been addressed in previous studies. Additionally, several functionals are developed and shown to provide the free energy through the analysis of a single configuration. © 2004 American Institute of Physics.
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61.20.Ja Computer simulation of liquid structure
65.20.-w Thermal properties of liquids

Correlation energy extrapolation by intrinsic scaling. I. Method and application to the neon atom

Laimutis Bytautas and Klaus Ruedenberg

J. Chem. Phys. 121, 10905 (2004); http://dx.doi.org/10.1063/1.1811603 (14 pages) | Cited 21 times

Online Publication Date: 30 November 2004

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Remarkably accurate scaling relations are shown to exist between the correlation energy contributions from various excitation levels of the configuration interaction approach, considered as functions of the size of the correlating orbital space. These relationships are used to develop a method for extrapolating a sequence of smaller configuration interaction calculations to the full configuration-interaction energy. Calculations of the neon atom ground state with the Dunning’s quadruple ζ basis set demonstrate the ability of the method to obtain benchmark quality results. © 2004 American Institute of Physics.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics
34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)

Correlation energy extrapolation by intrinsic scaling. II. The water and the nitrogen molecule

Laimutis Bytautas and Klaus Ruedenberg

J. Chem. Phys. 121, 10919 (2004); http://dx.doi.org/10.1063/1.1811604 (16 pages) | Cited 17 times

Online Publication Date: 30 November 2004

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The extrapolation method for determining benchmark quality full configuration-interaction energies described in preceding paper [L. Bytautas and K. Ruedenberg, J. Chem. Phys. 121, 10905 (2004)] is applied to the molecules H2O and N2. As in the neon atom case, discussed in preceding paper [L. Bytautas and K. Ruedenberg, J. Chem. Phys. 121, 10905 (2004)] remarkably accurate scaling relations are found to exist between the correlation energy contributions from various excitation levels of the configuration-interaction approach, considered as functions of the size of the correlating orbital space. The method for extrapolating a sequence of smaller configuration-interaction calculations to the full configuration-interaction energy and for constructing compact accurate configuration-interaction wave functions is also found to be effective for these molecules. The results are compared with accurate ab initio methods, such as many-body perturbation theory, coupled-cluster theory, as well as with variational calculations wherever possible. © 2004 American Institute of Physics.
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31.15.vn Electron correlation calculations for diatomic molecules
31.15.vq Electron correlation calculations for polyatomic molecules

A natural linear scaling coupled-cluster method

N. Flocke and Rodney J. Bartlett

J. Chem. Phys. 121, 10935 (2004); http://dx.doi.org/10.1063/1.1811606 (10 pages) | Cited 64 times

Online Publication Date: 30 November 2004

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It is shown that using an appropriate localized molecular orbital (LMO) basis, one is able to calculate coupled-cluster singles and doubles (CCSD) wave functions and energies for very large systems by performing full CCSD calculations on small subunits only. This leads to a natural linear scaling coupled-cluster method (NLSCC), in which total correlation energies of extended systems are evaluated as the sum of correlation energy contributions from individual small subunits within that system. This is achieved by defining local occupied orbital correlation energies. These are quantities, which in the LMO basis become transferable between similar molecular fragments. Conventional small scale existing molecular CCSD codes are all that is needed, the local correlation effect being simply transmitted via the appropriate LMO basis. Linear scaling of electronic correlation energy calculations is thus naturally achieved using the NLSCC approach, which in principle can treat nonperiodic extended systems of infinite basis set size. Results are shown for alkanes and several polyglycine molecules and the latter compared to recent results obtained via an explicit large scale LCCSD calculation.© 2004 American Institute of Physics.
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31.15.bw Coupled-cluster theory
31.15.V- Electron correlation calculations for atoms, ions and molecules
36.20.Kd Electronic structure and spectra

Exact decoupling of the Dirac Hamiltonian. II. The generalized Douglas–Kroll–Hess transformation up to arbitrary order

Markus Reiher and Alexander Wolf

J. Chem. Phys. 121, 10945 (2004); http://dx.doi.org/10.1063/1.1818681 (12 pages) | Cited 94 times

Online Publication Date: 30 November 2004

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In order to achieve exact decoupling of the Dirac Hamiltonian within a unitary transformation scheme, we have discussed in part I of this series that either a purely numerical iterative technique (the Barysz–Sadlej–Snijders method) or a stepwise analytic approach (the Douglas–Kroll–Hess method) are possible. For the evaluation of Douglas–Kroll–Hess Hamiltonians up to a pre-defined order it was shown that a symbolic scheme has to be employed. In this work, an algorithm for this analytic derivation of Douglas–Kroll–Hess Hamiltonians up to any arbitrary order in the external potential is presented. We discuss how an estimate for the necessary order for exact decoupling (within machine precision) for a given system can be determined from the convergence behavior of the Douglas–Kroll–Hess expansion prior to a quantum chemical calculation. Once this maximum order has been accomplished, the spectrum of the positive-energy part of the decoupled Hamiltonian, e.g., for electronic bound states, cannot be distinguished from the corresponding part of the spectrum of the Dirac operator. An efficient scalar-relativistic implementation of the symbolic operations for the evaluation of the positive-energy part of the block-diagonal Hamiltonian is presented, and its accuracy is tested for ground-state energies of one-electron ions over the whole periodic table. Furthermore, the first many-electron calculations employing sixth up to fourteenth order DKH Hamiltonians are presented. © 2004 American Institute of Physics.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics
03.65.Ge Solutions of wave equations: bound states
02.60.-x Numerical approximation and analysis

First-order semidefinite programming for the direct determination of two-electron reduced density matrices with application to many-electron atoms and molecules

David A. Mazziotti

J. Chem. Phys. 121, 10957 (2004); http://dx.doi.org/10.1063/1.1810134 (10 pages) | Cited 57 times

Online Publication Date: 30 November 2004

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Direct variational calculation of two-electron reduced density matrices (2-RDMs) for many-electron atoms and molecules in nonminimal basis sets has recently been achieved through the use of first-order semidefinite programming [D. A. Mazziotti, Phys. Rev. Lett. (in press)]. With semidefinite programming, the electronic ground-state energy of a molecule is minimized with respect to the 2-RDM subject to N-representability constraints known as positivity conditions. Here we present a detailed account of the first-order algorithm for semidefinite programming and its comparison with the primal-dual interior-point algorithms employed in earlier variational 2-RDM calculations. The first-order semidefinite-programming algorithm, computations show, offers an orders-of-magnitude reduction in floating-point operations and storage in comparison with previous implementations. We also examine the ability of the positivity conditions to treat strong correlation and multireference effects through an analysis of the Hamiltonians for which the conditions are exact. Calculations are performed in nonminimal basis sets for a variety of atoms and molecules and the potential-energy curves for CO and H2O. © 2004 American Institute of Physics.
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31.15.xt Variational techniques
31.15.V- Electron correlation calculations for atoms, ions and molecules
31.50.Bc Potential energy surfaces for ground electronic states
02.10.Yn Matrix theory
02.60.Pn Numerical optimization
02.60.Dc Numerical linear algebra

A canonical averaging in the second-order quantized Hamilton dynamics

Eric Heatwole and Oleg V. Prezhdo

J. Chem. Phys. 121, 10967 (2004); http://dx.doi.org/10.1063/1.1812749 (9 pages) | Cited 15 times

Online Publication Date: 30 November 2004

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Quantized Hamilton dynamics (QHD) is a simple and elegant extension of classical Hamilton dynamics that accurately includes zero-point energy, tunneling, dephasing, and other quantum effects. Formulated as a hierarchy of approximations to exact quantum dynamics in the Heisenberg formulation, QHD has been used to study evolution of observables subject to a single initial condition. In present, we develop a practical solution for generating canonical ensembles in the second-order QHD for position and momentum operators, which can be mapped onto classical phase space in doubled dimensionality and which in certain limits is equivalent to thawed Gaussian. We define a thermal distribution in the space of the QHD-2 variables and show that the standard β = 1/kT relationship becomes β′ = 2/kT in the high temperature limit due to an overcounting of states in the extended phase space, and a more complicated function at low temperatures. The QHD thermal distribution is used to compute total energy, kinetic energy, heat capacity, and other canonical averages for a series of quartic potentials, showing good agreement with the quantum results. © 2004 American Institute of Physics.
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03.65.Xp Tunneling, traversal time, quantum Zeno dynamics
03.65.Sq Semiclassical theories and applications
03.65.Ge Solutions of wave equations: bound states
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Methane activation by nickel cluster cations, Nin+ (n = 2–16): Reaction mechanisms and thermochemistry of cluster-CHx (x = 0–3) complexes

Fuyi Liu, Xiao-Guang Zhang, Rohana Liyanage, and P. B. Armentrout

J. Chem. Phys. 121, 10976 (2004); http://dx.doi.org/10.1063/1.1814095 (15 pages) | Cited 10 times

Online Publication Date: 30 November 2004

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The kinetic energy dependences of the reactions of Nin+ (n = 2–16) with CD4 are studied in a guided ion beam tandem mass spectrometer over the energy range of 0–10 eV. The main products are hydride formation NinD+, dehydrogenation to form NinCD2+, and double dehydrogenation yielding NinC+. These primary products decompose at higher energies to form NinCD+, Nin−1D+, Nin−1C+, Nin−1CD+, and Nin−1CD2+. NinCD2+ (n = 5–9) and Nin−1CD2+ (n ≥ 4) are not observed. In general, the efficiencies of the single and double dehydrogenation processes increase with cluster size. All reactions exhibit thresholds, and cross sections for the various primary and secondary reactions are analyzed to yield reaction thresholds from which bond energies for nickel cluster cations to C, CD, CD2, and CD3 are determined. The relative magnitudes of these bond energies are consistent with simple bond order considerations. Bond energies for larger clusters rapidly reach relatively constant values, which are used to estimate the chemisorption energies of the C, CD, CD2, and CD3 molecular fragments to nickel surfaces. © 2004 American Institute of Physics.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
36.40.Jn Reactivity of clusters
36.40.Wa Charged clusters
82.60.-s Chemical thermodynamics
82.20.Pm Rate constants, reaction cross sections, and activation energies
33.15.Ta Mass spectra
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Fm Bond strengths, dissociation energies

Quantum effect on the internal proton transfer and structural fluctuation in the H5+ cluster

Yasuhito Ohta, Koji Ohta, and Kenichi Kinugawa

J. Chem. Phys. 121, 10991 (2004); http://dx.doi.org/10.1063/1.1812739 (9 pages) | Cited 10 times

Online Publication Date: 30 November 2004

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The thermal equilibrium state of H5+ is investigated by means of an ab initio path integral molecular dynamics (PIMD) method, in which degrees of freedom of both nuclei and electrons at finite temperature are quantized within the adiabatic approximation. The second-order Møller-Plesset force field has been employed for the present ab initio PIMD. At 5–200 K, H5+ is shown to have the structure that the proton is surrounded by the two H2 units without any exchange of an atom between the central proton and the H2 unit. At 5 K, the quantum tunneling of the central proton occurs more easily when the distance between the two H2 units is shortened. At the high temperature of 200 K, the central proton is more delocalized in space between the two H2 units, with less correlation with the stretching of the distance between the two H2 units. As for the rotation of the H2 units around the C2 axis of H5+, the dihedral angle distribution is homogeneous at all temperatures, suggesting that the two H2 units freely rotate around the C2 axis, while this quantum effect on the rotation of the H2 units becomes more weakened with increasing temperature. The influence of the structural fluctuation of H5+ on molecular orbital energies has been examined to conclude that the highest occupied molecular orbital–lowest unoccupied molecular orbital energy gap is largely reduced with the increase of temperature because of the spatial expansion of the whole cluster. © 2004 American Institute of Physics.
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36.40.Wa Charged clusters
82.33.Fg Reactions in clusters
31.15.A- Ab initio calculations
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
36.40.Mr Spectroscopy and geometrical structure of clusters
31.15.xk Path-integral methods
31.15.xp Perturbation theory
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Dj Interatomic distances and angles
33.15.Bh General molecular conformation and symmetry; stereochemistry

Multireference calculations of the phosphorescence and photodissociation of chlorobenzene

Ya-Jun Liu, Petter Persson, and Sten Lunell

J. Chem. Phys. 121, 11000 (2004); http://dx.doi.org/10.1063/1.1810135 (7 pages) | Cited 10 times

Online Publication Date: 30 November 2004

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Multireference complete active space self-consistent-field (CASSCF) and multireference CASSF second-order perturbation theory (MSCASPT2) calculations were performed on the ground state and a number of low-lying excited singlet and triplet states of chlorobenzene. The dual phosphorescence observed experimentally is clearly explained by the MSCASPT2 potential-energy curves. Experimental findings regarding the dissociation channels of chlorobenzene at 193, 248, and 266 nm are clarified from extensive theoretical information including all low-energy potential-energy curves. © 2004 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
82.50.Hp Processes caused by visible and UV light
33.50.Dq Fluorescence and phosphorescence spectra
31.15.xr Self-consistent-field methods
31.15.xp Perturbation theory
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions

Electronic structure, vibrational stability, and predicted infrared-Raman spectra of the As20, AsNi12, and AsNi12As20 clusters

Tunna Baruah, Rajendra R. Zope, Steven L. Richardson, and Mark R. Pederson

J. Chem. Phys. 121, 11007 (2004); http://dx.doi.org/10.1063/1.1803539 (9 pages) | Cited 3 times

Online Publication Date: 30 November 2004

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Recently an inorganic fullerine-like [AsNi12As20]3− onion with near-perfect icosahedral symmetry in the crystalline phase was reported [M. J. Moses, J. C. Fettinger, and B. W. Eichhorn, Science 300, 778 (2003)]. This paper presents a detailed computational study in the framework of density functional theory on various aspects of this molecule. The electronic structure of the AsNi12As20 is investigated in its neutral as well as −3 charged state together with its subunits As20 and AsNi12 by the all electron linear combination of Gaussian-type orbitals method. The bonding is studied by examining the integrated charge within atomic sphere, the electron localization function, changes in the electron density distribution, and from vibrational modes. We find that strong covalent As-As bonds seen in isolated As20 become weaker in the AsNi12As20 and strong covalent As-Ni bonds are formed. The structural stability of all four clusters is examined by analyzing the energetics and by calculating the vibrational frequencies. Further, the infrared and Raman spectra is predicted for both the neutral and charged AsNi12As20 clusters. Finally, the energy barrier for removal of a single arsenic atom is calculated for the neutral AsNi12As20 cluster. © 2004 American Institute of Physics.
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36.40.Mr Spectroscopy and geometrical structure of clusters
36.40.Wa Charged clusters
33.20.Ea Infrared spectra
33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Fm Bond strengths, dissociation energies
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.15.E- Density-functional theory

C–Cl bond fission dynamics and angular momentum recoupling in the 235 nm photodissociation of allyl chloride

Yi Liu and Laurie J. Butler

J. Chem. Phys. 121, 11016 (2004); http://dx.doi.org/10.1063/1.1812757 (7 pages) | Cited 22 times

Online Publication Date: 30 November 2004

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The photodissociation dynamics of allyl chloride at 235 nm producing atomic Cl(2PJ;J = 1/2,3/2) fragments is investigated using a two-dimensional photofragment velocity ion imaging technique. Detection of the Cl(2P1/2) and Cl(2P3/2) products by [2+1] resonance enhanced multiphoton ionization shows that primary C–Cl bond fission of allyl chloride generates 66.8% Cl(2P3/2) and 33.2% Cl(2P1/2). The Cl(2P3/2) fragments evidenced a bimodal translational energy distribution with a relative weight of low kinetic energy Cl(2P3/2)/high kinetic energy Cl(2P3/2) of 0.097/0.903. The minor dissociation channel for C–Cl bond fission, producing low kinetic energy chlorine atoms, formed only chlorine atoms in the Cl(2P3/2) spin–orbit state. The dominant C–Cl bond fission channel, attributed to an electronic predissociation that results in high kinetic energy Cl atoms, produced both Cl(2P1/2) and Cl(2P3/2) atomic fragments. The relative branching for this dissociation channel is Cl(2P1/2)/[Cl(2P1/2)+Cl(2P3/2)] = 35.5%. The average fraction of available energy imparted into product recoil for the high kinetic energy products was found to be 59%, in qualitative agreement with that predicted by a rigid radical impulsive model. Both the spin–orbit ground and excited chlorine atom angular distributions were close to isotropic. We compare the observed Cl(2P1/2)/[Cl(2P1/2)+Cl(2P3/2)] ratio produced in the electronic predissociation channel of allyl chloride with a prior study of the chlorine atom spin–orbit states produced from HCl photodissociation, concluding that angular momentum recoupling in the exit channel at long interatomic distance determines the chlorine atom spin–orbit branching. © 2004 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
33.15.Fm Bond strengths, dissociation energies
33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)

Anchoring the potential energy surface of the cyclic water trimer

Julie A. Anderson, Kelly Crager, Lisa Fedoroff, and Gregory S. Tschumper

J. Chem. Phys. 121, 11023 (2004); http://dx.doi.org/10.1063/1.1799931 (7 pages) | Cited 21 times

Online Publication Date: 30 November 2004

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Six cyclic stationary points on the water trimer potential energy surface have been fully optimized at the MP2 level with the aug-cc-pVQZ basis set. In agreement with previous work, harmonic vibrational frequencies indicate that two structures are minima, three are transition states connecting minima on the surface while the remaining stationary point is a higher-order saddle point. The 1- and n-particle limits of the electronic energies of each of these six structures were estimated by systematically varying both the basis sets and theoretical methods. The former limit was approached with the cc-pVXZ and aug-cc-pVXZ families of basis sets (X = 2–7) while MP2, CCSD(T), and BD(TQ) calculations helped examine the latter. Core correlation effects have also been assessed at the MP2 level with the cc-pCVXZ series of basis sets (X = 2–5). These data have been combined to provide highly accurate relative energies and dissociation energies for these stationary points. © 2004 American Institute of Physics.
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31.50.-x Potential energy surfaces
82.20.Kh Potential energy surfaces for chemical reactions
31.15.bw Coupled-cluster theory
31.15.vq Electron correlation calculations for polyatomic molecules
33.15.Fm Bond strengths, dissociation energies
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Mt Rotation, vibration, and vibration-rotation constants

Action spectroscopy and temperature diagnostics of H3+ by chemical probing

J. Mikosch, H. Kreckel, R. Wester, R. Plašil, J. Glosík, D. Gerlich, D. Schwalm, and A. Wolf

J. Chem. Phys. 121, 11030 (2004); http://dx.doi.org/10.1063/1.1810512 (8 pages) | Cited 23 times

Online Publication Date: 30 November 2004

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Infrared absorption spectroscopy of few hundred H3+ ions trapped in a 22-pole ion trap is presented using chemical probing as a sensitive detection technique down to the single ion level. By exciting selected overtone transitions of the (v1 = 0,v2l = 31)←(0,00) vibrational band using an external cavity diode laser an accurate diagnostics measurement of the effective translational and rotational temperatures of the trapped ions was performed. The absolute accuracy of the measured transition frequencies was improved by a factor of four compared to previous plasma spectroscopy measurements using velocity modulation [Ventrudo et al., J. Chem. Phys. 100, 6263 (1994)]. The observed buffer gas cooling conditions in the ion trap indicate how to cool trapped H3+ ions into the lowest ortho and para rotational states. Future experiments will utilize such an internally cold ion ensemble for state-selected dissociative recombination experiments at the heavy ion storage ring Test Storage Ring (TSR). © 2004 American Institute of Physics.
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33.20.Ea Infrared spectra
37.10.Mn Slowing and cooling of molecules
37.10.Pq Trapping of molecules
33.20.Tp Vibrational analysis
34.80.Lx Recombination, attachment, and positronium formation
33.20.Sn Rotational analysis

Isotope branching and tunneling in O(3P)+HD→OH+D; OD+H reactions

Renat A. Sultanov and N. Balakrishnan

J. Chem. Phys. 121, 11038 (2004); http://dx.doi.org/10.1063/1.1810478 (7 pages) | Cited 9 times

Online Publication Date: 30 November 2004

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The O(3P)+HD and O(3P)+D2 reactions are studied using quantum scattering calculations and chemically accurate potential energy surfaces developed for the O(3P)+H2 system by Rogers et al. [J. Phys. Chem. A 104, 2308 (2000)]. Cross sections and rate coefficients for OH and OD products are calculated using accurate quantum methods as well as the J-shifting approximation. The J-shifting approach is found to work remarkably well for both O+HD and O+D2 collisions. The reactions are dominated by tunneling at low temperatures and for the O+HD reaction the hydrogen atom transfer leading to the OH product dominates at low temperatures. Our result for the OH/OD branching ratio is in close agreement with previous calculations over a wide range of temperatures. The computed OH/OD branching ratios are also in close agreement with experimental results of Robie et al. [Chem. Phys. Lett. 134, 579 (1987)] at temperatures above 400 K but the theoretical results do not reproduce the rapid rise in the experimental values of the branching ratio for temperatures lower than 350 K. We believe that new measurements could resolve the long-standing discrepancy between experiment and theory for this benchmark reaction.© 2004 American Institute of Physics.
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82.20.Tr Kinetic isotope effects including muonium
82.20.Xr Quantum effects in rate constants (tunneling, resonances, etc.)
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.20.Kh Potential energy surfaces for chemical reactions

ArnHF van der Waals clusters revisited. I. New low-energy isomeric structures for n = 6–13

Minzhong Xu, Hao Jiang, and Zlatko Bačić

J. Chem. Phys. 121, 11045 (2004); http://dx.doi.org/10.1063/1.1811612 (8 pages) | Cited 4 times

Online Publication Date: 30 November 2004

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New low-lying isomeric structures of ArnHF clusters are reported for n = 6–13. They were determined using simulated annealing and evolutionary programing, for pairwise additive intermolecular potential energy surfaces. New global minima were found for the clusters with n = 7, 10, 11. The new lowest-energy structure of Ar7HF and several new local minima for n = 6, 7 clusters have the HF bound on a threefold surface site, consistent with the recent spectroscopic data for ArnHF clusters in helium nanodroplets. A new type of low-energy local minima were determined for n = 9–13 clusters. © 2004 American Institute of Physics.
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36.40.Mr Spectroscopy and geometrical structure of clusters
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
31.50.Bc Potential energy surfaces for ground electronic states

Distributions of angular anisotropy and kinetic energy of products from the photodissociation of methanol at 157 nm

Shih-Huang Lee, Hsin-I. Lee, and Yuan T. Lee

J. Chem. Phys. 121, 11053 (2004); http://dx.doi.org/10.1063/1.1814099 (7 pages) | Cited 15 times

Online Publication Date: 30 November 2004

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We investigated distributions of angular-anisotropy parameter β and kinetic energy of fragments after photodissociation of methanol using time-of-flight (TOF) mass spectrometry. Fragments, in particular CH3O and CO, were successfully detected using tunable radiation from a synchrotron for photoionization. Following O–H bond fission, a CH3O fragment with internal energy greater than 104 kJ mol−1 dissociates to CH2O+H. Elimination of two H2 accompanies formation of CO. The 〈β〉 value of hydroxyl hydrogen is −0.26 whereas that of methyl hydrogen is zero. H2 has two distinct components in TOF spectra; these rapid and slow components have 〈β〉 values −0.30 and −0.18, respectively. The CH3+OH dissociation exhibits a highly anisotropic angular distribution with 〈β〉=−0.75. The β values of fragments from CD3OH photolysis are addressed. From measurements of angular-anisotropy parameters of various fragments, we surmise that the transition dipole moment μ is almost perpendicular to the C–O–H plane and that n−3px (2 1A″) is the major photoexcited state at 157 nm. © 2004 American Institute of Physics.
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82.50.Hp Processes caused by visible and UV light
82.20.Hf Product distribution
82.80.Rt Time of flight mass spectrometry
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.80.Eh Autoionization, photoionization, and photodetachment
33.15.Fm Bond strengths, dissociation energies
33.15.Ta Mass spectra

Three-photon absorption in anthracene-porphyrin-anthracene triads: A quantum-chemical study

Lingyun Zhu, Xia Yang, Yuanping Yi, Pengfei Xuan, Zhigang Shuai, Dezhan Chen, Egbert Zojer, Jean-Luc Brédas, and David Beljonne

J. Chem. Phys. 121, 11060 (2004); http://dx.doi.org/10.1063/1.1813437 (8 pages) | Cited 6 times

Online Publication Date: 30 November 2004

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We have applied correlated quantum-chemical methods to investigate the three-photon absorption (3PA) response of a porphyrin triad derivative, where the central macrocycle is linked in mesopositions to two anthracene units via acetylenic bridges. The 3PA frequency-dependent spectrum of this derivative is dominated by a single resonance feature in the transparent region, associated with charge-transfer states between porphyrin and anthracene. The calculations indicate a two order of magnitude enhancement in the 3PA cross section in the triad molecule with respect to the individual entities, which is attributed to close one-, two-, and three-photon resonances together with strong electronic couplings among the units. © 2004 American Institute of Physics.
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33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
82.50.Pt Multiphoton processes
34.70.+e Charge transfer

Nonadiabatic transitions in the exit channel of atom-molecule collisions: Fine-structure branching in Na+N2

C. Figl, R. Goldstein, J. Grosser, O. Hoffmann, and F. Rebentrost

J. Chem. Phys. 121, 11068 (2004); http://dx.doi.org/10.1063/1.1818121 (5 pages) | Cited 2 times

Online Publication Date: 30 November 2004

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We study Na+N2 collisions by laser excitation of the collision complex in a differential scattering experiment. The measured relative population of the Na(3p) fine-structure levels reflects the nonadiabatic transitions occuring in the exit channel of the collision. Theoretical results obtained with a classical-path formalism and accurate quantum chemical data for NaN2 are found to be in good agreement. The presence of a conical intersection for the T-shaped geometry has a profound influence on the observed fine-structure branching.© 2004 American Institute of Physics.
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34.50.Gb Electronic excitation and ionization of molecules
33.15.Pw Fine and hyperfine structure
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.80.-b Photon interactions with molecules
31.15.-p Calculations and mathematical techniques in atomic and molecular physics
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