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28 Jun 2009

Volume 130, Issue 24, Articles (24xxxx)

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J. Chem. Phys. 130, 244701 (2009); http://dx.doi.org/10.1063/1.3152332 (17 pages)

Shihao Wang and N. M. Cann
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Local explicitly correlated coupled-cluster methods: Efficient removal of the basis set incompleteness and domain errors

Thomas B. Adler and Hans-Joachim Werner

J. Chem. Phys. 130, 241101 (2009); http://dx.doi.org/10.1063/1.3160675 (5 pages) | Cited 26 times

Online Publication Date: 25 June 2009

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We propose an explicitly correlated local LCCSD-F12 method in which the basis set incompleteness error as well as the error caused by truncating the virtual orbital space to pair-specific local domains are strongly reduced. This is made possible by including explicitly correlated terms that are orthogonalized only to the pair-specific configuration space. Thus, the contributions of excitations outside the domains are implicitly accounted for by the explicitly correlated terms. It is demonstrated for a set of 54 reactions that the reaction energies computed with the new LCCSD-F12 method and triple-zeta basis sets deviate by at most 2.5 kJ/mol from conventional CCSD complete basis set results (RMS: 0.6 kJ/mol). The local approximations should make it possible to achieve linear scaling of the computational cost with molecular size.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.-w Chemical kinetics and dynamics
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back to top Theoretical Methods and Algorithms

Quantum mechanics with the basis set guided by Ehrenfest trajectories: Theory and application to spin-boson model

Dmitrii V. Shalashilin

J. Chem. Phys. 130, 244101 (2009); http://dx.doi.org/10.1063/1.3153302 (11 pages) | Cited 5 times

Online Publication Date: 22 June 2009

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In this article a method of numerical solution of the Schrödinger equation is proposed. The approach corrects the Ehrenfest approximation by using several trajectories/configurations with their amplitudes coupled within and across configurations, thus making the method formally exact. Accurate results are obtained for the spin-boson model with up to 2000 bath modes treated on fully quantum level without approximations.
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03.65.Ge Solutions of wave equations: bound states
05.30.Jp Boson systems
02.60.-x Numerical approximation and analysis

Relativistic, QED, and nuclear mass effects in the magnetic shielding of mathe

Adam Rudziński, Mariusz Puchalski, and Krzysztof Pachucki

J. Chem. Phys. 130, 244102 (2009); http://dx.doi.org/10.1063/1.3159674 (5 pages)

Online Publication Date: 24 June 2009

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The magnetic shielding σ of mathe is studied. The complete relativistic corrections of order O(α2), leading QED corrections of order O(α3 ln α), and finite nuclear mass effects of order O(m/mN) are calculated with high numerical precision. The resulting theoretical predictions for σ = 59.967 43(10)×10−6 are the most accurate to date among all elements and support the use of mathe as a NMR standard.
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31.30.jc Relativistic corrections to atomic structure and properties
32.30.Dx Magnetic resonance spectra
31.30.jf QED calculations of level energies, transition frequencies, fine structure intervals (radiative corrections, self-energy, vacuum polarization, etc.)
32.30.Rj X-ray spectra
32.30.-r Atomic spectra

Variable Lieb–Oxford bound satisfaction in a generalized gradient exchange-correlation functional

A. Vela, V. Medel, and S. B. Trickey

J. Chem. Phys. 130, 244103 (2009); http://dx.doi.org/10.1063/1.3152713 (6 pages) | Cited 3 times

Online Publication Date: 24 June 2009

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We propose a different way to satisfy both gradient expansion limiting behavior and the Lieb–Oxford bound in a generalized gradient approximation exchange functional by extension of the Perdew–Burke–Ernzerhof (PBE) form. Motivation includes early and recent exploration of modified values for the gradient expansion coefficient in the PBE exchange-correlation functional (cf. the PBEsol functional) and earlier experience with a numerical cutoff for large-s (s∝|∇n|/n4/3) in a version of the deMon molecular code. For either the original PBE or the PBEsol choice of the gradient coefficient, we find improved performance from using an s-dependent (spatially varying) satisfaction of the Lieb–Oxford bound which quenches to uniform electron gas behavior at large s. The mean absolute deviations (MADs) in atomization energies for a widely used test set of 20 small molecules are reduced by about 22% relative to PBE and PBEsol. For these small molecules, the bond length MADs are essentially unchanged.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics
33.15.Dj Interatomic distances and angles

A new class of highly efficient exact stochastic simulation algorithms for chemical reaction networks

Rajesh Ramaswamy, Nélido González-Segredo, and Ivo F. Sbalzarini

J. Chem. Phys. 130, 244104 (2009); http://dx.doi.org/10.1063/1.3154624 (13 pages) | Cited 7 times

Online Publication Date: 25 June 2009

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We introduce an alternative formulation of the exact stochastic simulation algorithm (SSA) for sampling trajectories of the chemical master equation for a well-stirred system of coupled chemical reactions. Our formulation is based on factored-out, partial reaction propensities. This novel exact SSA, called the partial-propensity direct method (PDM), is highly efficient and has a computational cost that scales at most linearly with the number of chemical species, irrespective of the degree of coupling of the reaction network. In addition, we propose a sorting variant, SPDM, which is especially efficient for multiscale reaction networks.
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82.20.Fd Collision theories; trajectory models
82.20.Uv Stochastic theories of rate constants

Relationships between the third-order reactivity indicators in chemical density-functional theory

Carlos Cárdenas, Eleonora Echegaray, Debajit Chakraborty, James S. M. Anderson, and Paul W. Ayers

J. Chem. Phys. 130, 244105 (2009); http://dx.doi.org/10.1063/1.3151599 (9 pages) | Cited 4 times

Online Publication Date: 25 June 2009

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Relationships between third-order reactivity indicators in the closed system [N, v(r)], open system [μ, v(r)], and density [ρ(r)] pictures are derived. Our method of derivation unifies and extends known results. Among the relationships is a link between the third-order response of the energy to changes in the density and the quadratic response of the density to changes in external potential. This provides a link between hyperpolarizability and the system’s sensitivity to changes in electron density. The dual descriptor is a unifying feature of many of the formulas we derive.
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82.20.-w Chemical kinetics and dynamics

From power law intermittence to macroscopic coherent regime

Mauro Bologna, Adrián A. Budini, Filippo Giraldi, and Paolo Grigolini

J. Chem. Phys. 130, 244106 (2009); http://dx.doi.org/10.1063/1.3156807 (9 pages) | Cited 2 times

Online Publication Date: 25 June 2009

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We address the problem of establishing which is the proper form of quantum master equation generating a survival probability identical to that corresponding to the nonergodic sequence of “light on” and “light off” fluorescence fluctuations in blinking quantum dots. We adopt a theoretical perspective based on the assumption that the abrupt transitions from the light on to light off state are the results of many collisions between system and environment, properly described by the Lindblad equation, and that between two consecutive collisions the system dynamics are frozen. This generates a quantum master equation belonging to the recently proposed class of generalized Lindblad equations, with a time convoluted structure, involving in the specific case of this paper both the unitary and the nonunitary contribution of the Lindblad equation. This is the property that under the low-frequency condition makes the new class of generalized Lindblad equation generates the required survival probability. We make the conjecture that this equation corresponds to the cooperative dynamics of many units that, in isolation, are described by the ordinary Lindblad equation. When the time scale of the unitary term of the Lindblad equation is shorter than the dephasing time, the cooperation generates a surprisingly extended macroscopic coherence.
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78.55.-m Photoluminescence, properties and materials
78.67.Hc Quantum dots
05.45.Xt Synchronization; coupled oscillators
05.40.Fb Random walks and Levy flights
03.65.Ta Foundations of quantum mechanics; measurement theory

Decoherence and dissipation in a molecular system coupled to an environment: An application of semiclassical hybrid dynamics

Christoph-Marian Goletz and Frank Grossmann

J. Chem. Phys. 130, 244107 (2009); http://dx.doi.org/10.1063/1.3157162 (12 pages) | Cited 7 times

Online Publication Date: 25 June 2009

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Applying the recently developed semiclassical hybrid dynamics [ Grossmann, J. Chem. Phys. 125, 014111 (2006) ], we study the decay of interference patterns in the reduced density as well as of the purity in a Morse oscillator test system due to the interaction with a finite harmonic bath at zero temperature. In the case that the bath mimics a continuous Ohmic spectral density, in addition to the quantum classical transition induced by the interaction with the environment, we corroborate the existence of a blueshift due to the bath coupling, predicted by Pollak [Phys. Rev. A 33, 4244 (1986)] . Furthermore, the decoherence dynamics of cat states is confirmed to be faster than that of single coherent states and we show that for a resonant bath the dissipation leads to an increase in the decoherence rate as compared to the low frequency bath.
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03.65.Sq Semiclassical theories and applications
05.45.-a Nonlinear dynamics and chaos

Transition state-finding strategies for use with the growing string method

Anthony Goodrow, Alexis T. Bell, and Martin Head-Gordon

J. Chem. Phys. 130, 244108 (2009); http://dx.doi.org/10.1063/1.3156312 (14 pages) | Cited 13 times

Online Publication Date: 26 June 2009

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Efficient identification of transition states is important for understanding reaction mechanisms. Most transition state search algorithms require long computational times and a good estimate of the transition state structure in order to converge, particularly for complex reaction systems. The growing string method (GSM) [ B. Peters et al., J. Chem. Phys. 120, 7877 (2004) ] does not require an initial guess of the transition state; however, the calculation is still computationally intensive due to repeated calls to the quantum mechanics code. Recent modifications to the GSM [A. Goodrow et al., J. Chem. Phys. 129, 174109 (2008) ] have reduced the total computational time for converging to a transition state by a factor of 2 to 3. In this work, three transition state-finding strategies have been developed to complement the speedup of the modified-GSM: (1) a hybrid strategy, (2) an energy-weighted strategy, and (3) a substring strategy. The hybrid strategy initiates the string calculation at a low level of theory (HF/STO-3G), which is then refined at a higher level of theory (B3LYP/6-31G∗). The energy-weighted strategy spaces points along the reaction pathway based on the energy at those points, leading to a higher density of points where the energy is highest and finer resolution of the transition state. The substring strategy is similar to the hybrid strategy, but only a portion of the low-level string is refined using a higher level of theory. These three strategies have been used with the modified-GSM and are compared in three reactions: alanine dipeptide isomerization, H-abstraction in methanol oxidation on VOx/SiO2 catalysts, and C–H bond activation in the oxidative carbonylation of toluene to p-toluic acid on Rh(CO)2(TFA)3 catalysts. In each of these examples, the substring strategy was proved most effective by obtaining a better estimate of the transition state structure and reducing the total computational time by a factor of 2 to 3 compared to the modified-GSM. The applicability of the substring strategy has been extended to three additional examples: cyclopropane rearrangement to propylene, isomerization of methylcyclopropane to four different stereoisomers, and the bimolecular Diels–Alder condensation of 1,3-butadiene and ethylene to cyclohexene. Thus, the substring strategy used in combination with the modified-GSM has been demonstrated to be an efficient transition state-finding strategy for a wide range of types of reactions.
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82.20.Db Transition state theory and statistical theories of rate constants
82.20.Wt Computational modeling; simulation
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.30.Qt Isomerization and rearrangement
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.30.Rs Hydrogen bonding, hydrophilic effects

Phase equilibria of molecular fluids via hybrid Monte Carlo Wang–Landau simulations: Applications to benzene and n-alkanes

Caroline Desgranges and Jerome Delhommelle

J. Chem. Phys. 130, 244109 (2009); http://dx.doi.org/10.1063/1.3158605 (7 pages) | Cited 9 times

Online Publication Date: 26 June 2009

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In recent years, powerful and accurate methods, based on a Wang–Landau sampling, have been developed to determine phase equilibria. However, while these methods have been extensively applied to study the phase behavior of model fluids, they have yet to be applied to molecular systems. In this work, we show how, by combining hybrid Monte Carlo simulations in the isothermal-isobaric ensemble with the Wang–Landau sampling method, we determine the vapor-liquid equilibria of various molecular fluids. More specifically, we present results obtained on rigid molecules, such as benzene, as well as on flexible chains of n-alkanes. The reliability of the method introduced in this work is assessed by demonstrating that our results are in excellent agreement with the results obtained in previous work on simple fluids, using either transition matrix or conventional Monte Carlo simulations with a Wang–Landau sampling, and on molecular fluids, using histogram reweighting or Gibbs ensemble Monte Carlo simulations.
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64.70.F- Liquid-vapor transitions
61.20.Ja Computer simulation of liquid structure
61.25.Em Molecular liquids

Electronic structure and molecular dynamics of breaking the RO–NO2 bond

Igor V. Schweigert and Brett I. Dunlap

J. Chem. Phys. 130, 244110 (2009); http://dx.doi.org/10.1063/1.3155081 (7 pages) | Cited 3 times

Online Publication Date: 26 June 2009

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Decomposition of energetic molecules such as pentaerythritol tetranitrate is accompanied by extensive changes in their electronic configuration and thus is challenging for ab initio Born–Oppenheimer molecular dynamics simulations. The performance of single-determinant methods (in particular, density-functional theory) is validated on electronic structure and molecular dynamics simulations of RO–NO2 bond dissociation in a smaller nitric ester, ethyl nitrate. Accurate description of dissociating molecule requires using unrestricted, spin-symmetry-broken orbitals. However, the iterative self-consistent field procedure is prone to convergence failures in the bond-breaking region even if robust convergence algorithms are employed. As a result, molecular dynamics simulations of unimolecular decomposition need to be closely monitored and manually restarted to ensure seamless transition from the closed-shell to open-shell configuration.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.20.Db Transition state theory and statistical theories of rate constants
82.20.Hf Product distribution
71.20.Rv Polymers and organic compounds

Analytic dynamics of the Morse oscillator derived by semiclassical closures

Eric M. Heatwole and Oleg V. Prezhdo

J. Chem. Phys. 130, 244111 (2009); http://dx.doi.org/10.1063/1.3154143 (12 pages) | Cited 2 times

Online Publication Date: 29 June 2009

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The quantized Hamilton dynamics methodology [ O. V. Prezhdo and Y. V. Pereverzev, J. Chem. Phys. 113, 6557 (2000) ] is applied to the dynamics of the Morse potential using the SU(2) ladder operators. A number of closed analytic approximations are derived in the Heisenberg representation by performing semiclassical closures and using both exact and approximate correspondence between the ladder and position-momentum variables. In particular, analytic solutions are given for the exact classical dynamics of the Morse potential as well as a second-order semiclassical approximation to the quantum dynamics. The analytic approximations are illustrated with the O–H stretch of water and a Xe–Xe dimer. The results are extended further to coupled Morse oscillators representing a linear triatomic molecule. The reported analytic expressions can be used to accelerate classical molecular dynamics simulations of systems containing Morse interactions and to capture quantum-mechanical effects.
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34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
31.15.xv Molecular dynamics and other numerical methods
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Threshold photoionization and density functional theory studies of bimetallic-carbide nanocrystals and fragments: Ta3ZrCy (y = 0–4)

V. Dryza and G. F. Metha

J. Chem. Phys. 130, 244301 (2009); http://dx.doi.org/10.1063/1.3154384 (10 pages)

Online Publication Date: 23 June 2009

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Gas-phase bimetallic tantalum-zirconium-carbide clusters are generated using a constructed double ablation cluster source. The Ta3ZrCy (y = 0–4) clusters are examined by photoionization efficiency spectroscopy to extract experimental ionization energies (IEs). The IE trend for the Ta3ZrCy cluster series is reasonably similar to that of the Ta4Cy cluster series [ V. Dryza et al., J. Phys. Chem. A 109, 11180 (2005) ], although the IE reductions upon carbon addition are greater for the former. Complementary density functional theory calculations are performed for the various isomers constructed by attaching carbon atoms to the different faces of the tetrahedral Ta3Zr cluster. The good agreement between the experimental IE trend and that calculated for these isomers support a 2×2×2 face centered cubic nanocrystal structure for Ta4ZrC4 and nanocrystal fragment structures for the smaller clusters.
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61.46.Hk Nanocrystals
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Ps Other inorganic compounds

The dynamics of the H2+CO+ reaction on an interpolated potential energy surface

Shapour Ramazani, Terry J. Frankcombe, Stefan Andersson, and Michael A. Collins

J. Chem. Phys. 130, 244302 (2009); http://dx.doi.org/10.1063/1.3156805 (9 pages) | Cited 2 times

Online Publication Date: 23 June 2009

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A potential energy surface that describes the title reaction has been constructed by interpolation of ab initio data. Classical trajectory studies on this surface show that the total reaction rate is close to that predicted by a Langevin model, although the mechanism is more complicated than simple ion-molecule capture. Only the HCO++H product is observed classically. An estimate of the magnitude of rotational inelastic scattering is also reported.
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82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Fd Collision theories; trajectory models
82.20.Hf Product distribution

On the accuracy of thermionic electron emission models. I. Electron detachment from SF6−

Jürgen Troe, Thomas M. Miller, and Albert A. Viggiano

J. Chem. Phys. 130, 244303 (2009); http://dx.doi.org/10.1063/1.3149782 (12 pages) | Cited 8 times

Online Publication Date: 24 June 2009

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Detailed statistical rate calculations combined with electron capture theory and kinetic modeling for the electron attachment to SF6 and detachment from SF6− [ Troe et al., J. Chem. Phys. 127, 244303 (2007) ] are used to test thermionic electron emission models. A new method to calculate the specific detachment rate constants kdet(E) and the electron energy distributions f(E,ε) as functions of the total energy E of the anion and the energy ε of the emitted electrons is presented, which is computationally simple but neglects fine structures in the detailed kdet(E). Reduced electron energy distributions f(E,ε/〈ε〉) were found to be of the form (ε/〈ε〉)n exp(−ε/〈ε〉) with n ≈ 0.15, whose shape corresponds to thermal distributions only to a limited extent. In contrast, the average energies 〈ε(E)〉 can be roughly estimated within thermionic emission and finite heat bath concepts. An effective temperature Td(E) is determined from the relation E−EA = 〈ESF6(Td)〉+kTd, where 〈ESF6(Td)〉 denotes the thermal internal energy of the detachment product SF6 at the temperature Td and EA is the electron affinity of SF6. The average electron energy is then approximately given by 〈ε(E)〉 = kTd(E), but dynamical details of the process are not accounted for by this approach. Simplified representations of kdet(E) in terms of Td(E) from the literature are shown to lead to only semiquantitative agreement with the equally simple but more accurate calculations presented here. An effective “isokinetic” electron emission temperature Te(E) does not appear to be useful for the electron detachment system considered because it neither provides advantages over a representation of kdet(E) as a function of Td(E), nor are recommended relations between Te(E) and Td(E) of sufficient accuracy.
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34.50.Gb Electronic excitation and ionization of molecules
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
34.70.+e Charge transfer

Correction for dispersion and Coulombic interactions in molecular clusters with density functional derived methods: Application to polycyclic aromatic hydrocarbon clusters

Mathias Rapacioli, Fernand Spiegelman, Dahbia Talbi, Tzonka Mineva, Annick Goursot, Thomas Heine, and Gotthard Seifert

J. Chem. Phys. 130, 244304 (2009); http://dx.doi.org/10.1063/1.3152882 (10 pages) | Cited 9 times

Online Publication Date: 24 June 2009

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The density functional based tight binding (DFTB) is a semiempirical method derived from the density functional theory (DFT). It inherits therefore its problems in treating van der Waals clusters. A major error comes from dispersion forces, which are poorly described by commonly used DFT functionals, but which can be accounted for by an a posteriori treatment DFT-D. This correction is used for DFTB. The self-consistent charge (SCC) DFTB is built on Mulliken charges which are known to give a poor representation of Coulombic intermolecular potential. We propose to calculate this potential using the class IV/charge model 3 definition of atomic charges. The self-consistent calculation of these charges is introduced in the SCC procedure and corresponding nuclear forces are derived. Benzene dimer is then studied as a benchmark system with this corrected DFTB (c-DFTB-D) method, but also, for comparison, with the DFT-D. Both methods give similar results and are in agreement with references calculations (CCSD(T) and symmetry adapted perturbation theory) calculations. As a first application, pyrene dimer is studied with the c-DFTB-D and DFT-D methods. For coronene clusters, only the c-DFTB-D approach is used, which finds the sandwich configurations to be more stable than the T-shaped ones.
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34.20.Gj Intermolecular and atom-molecule potentials and forces
36.40.Cg Electronic and magnetic properties of clusters
31.15.xr Self-consistent-field methods
31.15.E- Density-functional theory

Ab initio study of methyl-bromide photodissociation in the math band

Christelle Escure, Thierry Leininger, and Bruno Lepetit

J. Chem. Phys. 130, 244305 (2009); http://dx.doi.org/10.1063/1.3154140 (10 pages) | Cited 5 times

Online Publication Date: 25 June 2009

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We performed a theoretical study of the photodissociation dynamics of CH3Br in the math band using a wave packet propagation technique on coupled ab initio potential energy curves. The present model involves the 3Q1 and 1Q1 excited states which can be populated from the ground state by a perpendicular transition and which are correlated at large methyl-bromide distance to the ground bromide spin-orbit state, as well as the 3Q0 and 4E states which can be excited by a parallel and perpendicular transition (respectively) and both correlate to excited Br∗ spin-orbit state. The model provides absorption cross sections and branching ratios in excellent agreement with experimental results. Due to weak spin-orbit interaction, the 1Q1 state is the dominant contributor to the absorption cross section, except for the red wing of the band where 3Q0 and 3Q1 states have significant absorption. However, spin-orbit coupling is strong enough to induce nonadiabatic transitions between the 3Q1 and 1Q1 states during the dissociation process which should be experimentally detectable in the alignment properties of the fragments. Nonadiabatic transitions at the conical intersection between 3Q0 and 1Q1 are shown to play a minor role in this system.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
33.20.Lg Ultraviolet spectra
31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure
33.15.Bh General molecular conformation and symmetry; stereochemistry

Ab initio study of valence and Rydberg states of CH3Br

Christelle Escure, Thierry Leininger, and Bruno Lepetit

J. Chem. Phys. 130, 244306 (2009); http://dx.doi.org/10.1063/1.3152865 (8 pages) | Cited 5 times

Online Publication Date: 25 June 2009

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We performed configuration interaction ab initio calculations on the valence and 5s, 5pa1, and 5pe Rydberg bands of the CH3Br molecule as a function of the methyl-bromide distance for frozen C3v geometries. The valence state potential energy curves are repulsive, the Rydberg state ones are similar to the one of the CH3Br+ ion with a minimum at short distance. One state emerging from the 5pe band has valence and ion-pair characters as distance increases and the corresponding potential curve has a second minimum at large distance. This state has a very strong parallel electric dipole transition moment with the ground state and plays a central role in UV photon absorption spectra. It is also responsible for the parallel character of the anisotropy parameters measured in ion-pair production experiments. In each band, there is a single state, which has a non-negligible transition moment with the ground state, corresponding to a transition perpendicular to the molecular axis of symmetry, except for the 5pe band where it is parallel. The perpendicular transition moments between ground and valence states increase sharply as methyl-bromide distance decreases due to a mixing between valence and 5s Rydberg band at short distance. In each band, spin orbit interaction produces a pair of states, which have significant transition moments with the ground one. In the valence band, the mixing between singlet and triplet states is weak and the perpendicular transition to the 1Q1 state is dominant. In each Rydberg band, however, spin-orbit interaction is larger than the exchange interaction and the two significant transition moments with the ground state have comparable strengths. The valence band has an additional state (1Q0) with significant parallel transition moment induced by spin-orbit interaction with the ground state at large distance.
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31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
33.20.Lg Ultraviolet spectra
31.50.Df Potential energy surfaces for excited electronic states
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.80.-b Photon interactions with molecules

Theoretical investigation of the Ωg,u(+/−) states of K2 dissociating adiabatically up to K(4p 2P3/2)+K(4p 2P3/2)

A. Jraij, A. R. Allouche, S. Magnier, and M. Aubert-Frécon

J. Chem. Phys. 130, 244307 (2009); http://dx.doi.org/10.1063/1.3158361 (12 pages) | Cited 6 times

Online Publication Date: 25 June 2009

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A theoretical investigation of the electronic structure of the K2 molecule, including spin-orbit effects, has been performed. Potential energies have been calculated over a large range of R up to 75a0 for the 88 Ωg,u(+/−) states dissociating adiabatically into the limits up to K(4p 2P3/2)+K(4p 2P3/2). Equilibrium distances, transition energies, harmonic frequencies, as well as depths for wells and heights for barriers are reported for all of the bound Ωg,u(+/−) states. Present ab initio calculations are shown to be able to reproduce quite accurately the small structures (wells and barrier) displayed at very long-range (R>50a0) by the (2,3)1u and (2)0g− purely long-range states. As the present data could help experimentalists, we make available extensive tables of energy values versus internuclear distances in our database at the web address http://www-lasim.univ-lyon1.fr/spip.php?rubrique99.
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31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure
31.15.xr Self-consistent-field methods
31.50.Df Potential energy surfaces for excited electronic states
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Dj Interatomic distances and angles
33.15.Mt Rotation, vibration, and vibration-rotation constants

The mechanism of the interstellar isomerization reaction HOC+→HCO+ catalyzed by H2: New Insights from the reaction electronic flux

Stefan Vogt-Geisse and Alejandro Toro-Labbé

J. Chem. Phys. 130, 244308 (2009); http://dx.doi.org/10.1063/1.3147702 (7 pages) | Cited 11 times

Online Publication Date: 26 June 2009

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A theoretical study of the mechanism of the isomerization reaction HOC+→HCO+ is presented. The mechanism was studied in terms of reaction force, chemical potential, reaction electronic flux (REF), and bond orders. It has been found that the evolution of changes in REF along the intrinsic reaction coordinate can be explained in terms of bond orders. The energetic lowering of the hydrogen assisted (catalyzed) reaction has been identified as being due to the stabilization of the H3+ transition state complex and the stepwise bond dissociation and formation of the H–O and H–C bonds, respectively.
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82.30.Qt Isomerization and rearrangement
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
95.30.Ft Molecular and chemical processes and interactions
82.33.-z Reactions in various media
82.60.-s Chemical thermodynamics
98.58.Bz Atomic, molecular, chemical, and grain processes

Slow photoelectron velocity-map imaging spectroscopy of the vinoxide anion

Tara I. Yacovitch, Etienne Garand, and Daniel M. Neumark

J. Chem. Phys. 130, 244309 (2009); http://dx.doi.org/10.1063/1.3157208 (8 pages) | Cited 6 times

Online Publication Date: 26 June 2009

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High resolution photoelectron spectra of the vinoxide anion are obtained by slow electron velocity-map imaging. Transitions between the anion math 1A′ ground electronic state and the radical math 2A″ and math 2A′ states are observed. This experiment yields a precise value of 1.8250±0.0012 eV for the adiabatic electron affinity and 0.996±0.003 eV for the math-math term energy of the vinoxy radical. Franck–Condon simulations of the math 2A″←math 1A′ transition are performed at varying levels of approximation. Full treatment with Duschinsky rotation is necessary to reproduce experimental results. Comparison of the experimental and simulated spectra leads to the assignment of previously unresolved transitions, notably between levels of a″ symmetry.
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33.60.+q Photoelectron spectra
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Mt Rotation, vibration, and vibration-rotation constants

An exchange-Coulomb model potential energy surface for the Ne–CO interaction. I. Calculation of Ne–CO van der Waals spectra

Ashok K. Dham, Frederick R. W. McCourt, and William J. Meath

J. Chem. Phys. 130, 244310 (2009); http://dx.doi.org/10.1063/1.3157169 (16 pages) | Cited 2 times

Online Publication Date: 26 June 2009

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Exchange-Coulomb model potential energy surfaces have been developed for the Ne–CO interaction. The initial model is a three-dimensional potential energy surface based upon computed Heitler–London interaction energies and literature results for the long-range induction and dispersion energies, all as functions of interspecies distance, the orientation of CO relative to the interspecies axis, and the bond length of the CO molecule. Both a rigid-rotor model potential energy surface, obtained by setting the CO bond length equal to its experimental spectroscopic equilibrium value, and a vibrationally averaged model potential energy surface, obtained by averaging the stretching dependence over the ground vibrational motion of the CO molecule, have been constructed from the full data set. Adjustable parameters in each model potential energy surface have been determined through fitting a selected subset of pure rotational transition frequencies calculated for the mathe–mathmath isotopolog to precisely known experimental values. Both potential energy surfaces provide calculated results for a wide range of available experimental microwave, millimeter-wave, and midinfrared Ne–CO transition frequencies that are generally far superior to those obtained using the best current literature potential energy surfaces. The vibrationally averaged CO ground state potential energy surface, employed together with a potential energy surface obtained from it by replacing the ground vibrational state average of the CO stretching dependence of the potential energy surface by an average over the first excited CO vibrational state, has been found to be particularly useful for computing and/or interpreting mid-IR transition frequencies in the Ne–CO dimer.
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31.50.Df Potential energy surfaces for excited electronic states
34.20.Gj Intermolecular and atom-molecule potentials and forces
33.15.Dj Interatomic distances and angles
33.20.Tp Vibrational analysis

Temperature dependence of reactions involving electron transfer in K(np)/C2Cl4 collisions

M. Cannon, C. H. Wang, Y. Liu, F. B. Dunning, and J. D. Steill

J. Chem. Phys. 130, 244311 (2009); http://dx.doi.org/10.1063/1.3158604 (9 pages) | Cited 1 time

Online Publication Date: 26 June 2009

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Electron transfer in K(np)–C2Cl4 collisions, which leads to formation of both Cl− and C2Cl4− anions, is investigated as a function of target temperature over the range of 300–650 K. Measurements at high n (n ∼ 30) show that the likelihood of Cl− production increases rapidly with temperature indicating the presence of a dissociation barrier. The data yield an activation energy of ∼ 0.1 eV. A broad distribution of product C2Cl4− lifetimes is observed that extends from microseconds to milliseconds, this distribution moving toward shorter lifetimes as the target temperature is increased. The measured lifetimes are consistent with the predictions of quasiequilibrium theory. Studies at low n (n ∼ 14) show a substantial fraction of the product K+–Cl− and K+–C2Cl4− ion pairs is electrostatically bound leading to creation of heavy-Rydberg ion-pair states. Variations in target temperature lead to changes in kinetic energy of relative motion of the reactants that can result in marked changes in the fraction of ion pairs that is bound, especially at low Rydberg atom velocities. In the case of bound K+–C2Cl4− ion pairs a few percent subsequently dissociate by the conversion of internal energy in the anion into translational energy of the ion pair. Analysis of the data points to a mean energy conversion of ∼ 60–90 meV, much less than the available excess energy of reaction, ∼ 0.7 eV.
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34.70.+e Charge transfer
34.50.Gb Electronic excitation and ionization of molecules
34.50.Ez Rotational and vibrational energy transfer
32.80.Ee Rydberg states

Vibration energy levels of the PH3, PH2D, and PHD2 molecules calculated from high order potential energy surface

Andrei V. Nikitin, Filip Holka, Vladimir G. Tyuterev, and Julien Fremont

J. Chem. Phys. 130, 244312 (2009); http://dx.doi.org/10.1063/1.3156311 (13 pages) | Cited 5 times

Online Publication Date: 29 June 2009

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Vibrational energy levels of the PH3, PH2D, and PHD2 molecules were calculated from the new extended potential energy surface (PES) determined in this work. The coupled-cluster approach with the perturbative inclusion of the connected triple excitations CCSD(T) and correlation consistent polarized valence basis set cc-pV5Z was employed in the ab initio calculations of electronic ground state energies. The contribution of relativistic effects to the overall electronic energy surface was computed using quasirelativistic mass-velocity-Darwin approach. These ab initio points were fitted by a parametrized function with one parameter empirically adjusted. The grid of 11 697 geometrical nuclear configurations covers a large domain of the six dimensional internal coordinate space and was designed to provide vibration energy levels of phosphine molecule up to 7000 cm−1 above the zero point vibration energy with reasonable accuracy. The analytical representation of the PES was determined through the expansion in symmetry adapted products of nonlinear internal coordinates for various orders of analytical expansions up to the tenth order. The dependence of calculated vibration energy levels on the analytical representation of PES and on the coordinate choice was studied. Calculated vibration levels are in very good agreement with observations: The root mean squares deviation between theoretically calculated and observed band centers is 1.4 cm−1 for PH3, 0.4 cm−1 for PH2D, and 0.6 cm−1 for PHD2.
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33.20.Tp Vibrational analysis
31.15.A- Ab initio calculations
31.15.bw Coupled-cluster theory
31.50.Bc Potential energy surfaces for ground electronic states
33.15.Mt Rotation, vibration, and vibration-rotation constants

Chirped pulse multiphoton ionization of nitrogen: Control of selective rotational excitation in N2+(B 2Σu+)

J. Plenge, A. Wirsing, C. Raschpichler, M. Meyer, and E. Rühl

J. Chem. Phys. 130, 244313 (2009); http://dx.doi.org/10.1063/1.3158603 (8 pages) | Cited 3 times

Online Publication Date: 30 June 2009

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We report on fluorescence spectra of N2+(B 2Σu+)→N2+(X 2Σg+) obtained from multiphoton ionization of molecular nitrogen by 804 nm femtosecond laser pulses. The analysis of the fluorescence spectra reveals that the vibrational levels v = 0 and v = 4 in the B 2Σu+-state of N2+ are primarily populated. The rotational state distribution of N2+(B 2Σu+, v = 0) is determined from the rotationally resolved fluorescence spectra. It is demonstrated that the linear chirp of the 804 nm femtosecond laser pulse has a strong influence on the rotational state distribution of the vibrational ground state of the molecular cation N2+(B 2Σu+, v = 0). Possible mechanisms leading to the experimental results are discussed. The particular population of the vibrational levels as well as the linear chirp dependence of the fluorescence signal gives evidence for the importance of a resonant intermediate state. The N2 a 1Π-state is likely involved in a resonant multiphoton excitation process. This permits to selectively control the rotational population of the cation that is formed via chirped pulse multiphoton ionization.
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33.50.Dq Fluorescence and phosphorescence spectra
33.80.Eh Autoionization, photoionization, and photodetachment
33.15.Mt Rotation, vibration, and vibration-rotation constants
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