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21 Mar 2008

Volume 128, Issue 11, Articles (11xxxx)

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An alternative near-neighbor definition of hydrogen bonding in water

A. D. Hammerich and V. Buch

J. Chem. Phys. 128, 111101 (2008); http://dx.doi.org/10.1063/1.2889949 (4 pages) | Cited 13 times

Online Publication Date: 17 March 2008

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A definition of hydrogen bonding in water is proposed in which an H⋯O pair forms a hydrogen bond if (a) an oxygen atom is the nearest nonchemically bonded neighbor of a hydrogen atom; and (b) the hydrogen is the first or the second intermolecular near-neighbor of the oxygen. Unlike the commonly employed hydrogen-bond definitions, this definition does not depend on the choice of geometric or energetic cutoffs applied to continuous distributions of properties. With the present definition, the distribution of O⋯H bond lengths decays smoothly to zero in a physically reasonable range. After correction for the presence of intermittent hydrogen bonds, this definition appears to provide a more stable description of hydrogen bonds and coordination shells than the more conventional cutoff-based definition. “Partial” H bonds satisfying only one of the two bonding requirements serve as transition states in the H-bond network evolution.
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33.15.Dj Interatomic distances and angles
34.20.Gj Intermolecular and atom-molecule potentials and forces

Ruelle–Takens–Newhouse scenario in reaction-diffusion-convection system

Marcello Antonio Budroni, Marco Masia, Mauro Rustici, Nadia Marchettini, Vitaly Volpert, and Pier Carlo Cresto

J. Chem. Phys. 128, 111102 (2008); http://dx.doi.org/10.1063/1.2894480 (4 pages) | Cited 6 times

Online Publication Date: 17 March 2008

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Direct numerical simulations of the transition process from periodic to chaotic dynamics are presented for two variable Oregonator-diffusion model coupled with convection. Numerical solutions to the corresponding reaction-diffusion-convection system of equations show that natural convection can change in a qualitative way, the evolution of concentration distribution, as compared with convectionless conditions. The numerical experiments reveal distinct bifurcations as the Grashof number is increased. A transition to chaos similar to Ruelle–Takens–Newhouse scenario is observed. Numerical results are in agreement with the experiments.
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44.25.+f Natural convection
47.27.te Turbulent convective heat transfer
47.27.Cn Transition to turbulence
47.70.Fw Chemically reactive flows
47.20.Ky Nonlinearity, bifurcation, and symmetry breaking

Influence of functional groups on charge transport in molecular junctions

D. J. Mowbray, G. Jones, and K. S. Thygesen

J. Chem. Phys. 128, 111103 (2008); http://dx.doi.org/10.1063/1.2894544 (5 pages) | Cited 20 times

Online Publication Date: 18 March 2008

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Using density functional theory (DFT), we analyze the influence of five classes of functional groups, as exemplified by NO2, OCH3, CH3, CCl3, and I, on the transport properties of a 1,4-benzenedithiolate (BDT) and 1,4-benzenediamine (BDA) molecular junction with gold electrodes. Our analysis demonstrates how ideas from functional group chemistry may be used to engineer a molecule’s transport properties, as was shown experimentally and using a semiempirical model for BDA [ Nano Lett. 7, 502 (2007) ]. In particular, we show that the qualitative change in conductance due to a given functional group can be predicted from its known electronic effect (whether it is σ/π donating/withdrawing). However, the influence of functional groups on a molecule’s conductance is very weak, as was also found in the BDA experiments. The calculated DFT conductances for the BDA species are five times larger than the experimental values, but good agreement is obtained after correcting for self-interaction and image charge effects.
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85.65.+h Molecular electronic devices
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back to top Theoretical Methods and Algorithms

Simple finite field nuclear relaxation method for calculating vibrational contribution to degenerate four-wave mixing

Bernard Kirtman and Josep M. Luis

J. Chem. Phys. 128, 114101 (2008); http://dx.doi.org/10.1063/1.2889950 (4 pages) | Cited 6 times

Online Publication Date: 18 March 2008

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A simple extended finite field nuclear relaxation procedure for calculating vibrational contributions to degenerate four-wave mixing (also known as the intensity-dependent refractive index) is presented. As a by-product one also obtains the static vibrationally averaged linear polarizability, as well as the first and second hyperpolarizability. The methodology is validated by illustrative calculations on the water molecule. Further possible extensions are suggested.
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33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Investigation of the benzene-dimer potential energy surface: DFT/CCSD(T) correction scheme

Ota Bludský, Miroslav Rubeš, Pavel Soldán, and Petr Nachtigall

J. Chem. Phys. 128, 114102 (2008); http://dx.doi.org/10.1063/1.2890968 (8 pages) | Cited 33 times

Online Publication Date: 18 March 2008

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A novel method, designated as the density functional theory/coupled-cluster with single and double and perturbative triple excitation [DFT/CCSD(T)] correction scheme, was developed for precise calculations of weakly interacting sp2 hydrocarbon molecules and applied to the benzene dimer. The DFT/CCSD(T) interaction energies are in excellent agreement with the estimated CCSD(T)/complete basis set interaction energies. The tilted T-shaped structure having Cs symmetry was determined to be a global minimum on the benzene-dimer potential energy surface (PES), approximately 0.1 kcal/mol more stable than the parallel-displaced structure. A fully optimized set of ten stationary points on the benzene-dimer PES is proposed for the evaluation of the reliability of methods for the description of weakly interacting systems.
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31.15.E- Density-functional theory
31.50.-x Potential energy surfaces
31.15.bw Coupled-cluster theory
31.15.xp Perturbation theory
33.15.Bh General molecular conformation and symmetry; stereochemistry

Performance of the M06 family of exchange-correlation functionals for predicting magnetic coupling in organic and inorganic molecules

Rosendo Valero, Ramon Costa, Ibério de P. R. Moreira, Donald G. Truhlar, and Francesc Illas

J. Chem. Phys. 128, 114103 (2008); http://dx.doi.org/10.1063/1.2838987 (8 pages) | Cited 27 times

Online Publication Date: 19 March 2008

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The performance of the M06 family of exchange-correlation potentials for describing the electronic structure and the Heisenberg magnetic coupling constant (J) is investigated using a set of representative open-shell systems involving two unpaired electrons. The set of molecular systems studied has well defined structures, and their magnetic coupling values are known experimentally. As a general trend, the M06 functional is about equally as accurate as B3LYP or PBE0. The performance of local functionals is important because of their economy and convenience for large-scale calculations; we find that M06-L local functional of the M06 family largely improves over the local spin density approximation and the generalized gradient approximation.
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31.15.eg Exchange-correlation functionals (in current density functional theory)

Calculation of free-energy differences and potentials of mean force by a multi-energy gap method

Huan-Xiang Zhou

J. Chem. Phys. 128, 114104 (2008); http://dx.doi.org/10.1063/1.2841942 (8 pages) | Cited 1 time

Online Publication Date: 19 March 2008

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A method is proposed to significantly accelerate the convergence of free-energy calculations. It introduces a bias factor in Monte Carlo simulations or, equivalently, a bias force in molecular dynamics simulations. The bias factor targets the energy gap, i.e., the difference in energy function between two states, and is therefore specifically designed for calculating free-energy differences. The goal is to make the probability density of the energy gap as uniform as possible, thus allowing for its accurate determination. An iterative procedure, based on simulations at higher temperatures, is devised to obtain the bias factor. The same method naturally extends to the calculation of potentials of mean force. The generalized coordinate, for which the potential of mean force is to be calculated, now plays the role of the energy gap. Applications to model systems confirm the expected increase in accuracy of calculated free-energy differences and potentials of mean force.
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05.70.Ce Thermodynamic functions and equations of state
02.50.Cw Probability theory
02.50.Ng Distribution theory and Monte Carlo studies

An analysis through order ℏ2 of a surface hopping expansion of the nonadiabatic wave function

Michael F. Herman and Yinghua Wu

J. Chem. Phys. 128, 114105 (2008); http://dx.doi.org/10.1063/1.2837803 (11 pages) | Cited 10 times

Online Publication Date: 19 March 2008

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It is shown that a surface hopping expansion of the semiclassical wave function formally satisfies the time independent Schrödinger equation for many-state, multidimensional problems. This wave function includes terms involving hops between different adiabatic quantum states as well as momentum changes without change of state at each point along classical trajectories. The single-state momentum changes correct for the order ℏ2 errors due to the semiclassical approximation that are present even in single surface problems. A prescription is provided for the direction of this momentum change and the amplitude associated with it. The direction of the momentum change for energy conserving hops between adiabatic states is required to be in the direction of the nonadiabatic coupling vector. The magnitude of the posthop momentum in this direction is determined by the energy, but the sign is not. Hops with both signs of this momentum component are required in order for the wave function to formally satisfy the Schrödinger equation. Numerical results are presented which illustrate how the surface hopping expansion can be implemented and the accuracy that can be obtained.
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03.65.Ge Solutions of wave equations: bound states
03.65.Sq Semiclassical theories and applications

Electron-nucleus cusp correction and forces in quantum Monte Carlo

Manolo C. Per, Salvy P. Russo, and Ian K. Snook

J. Chem. Phys. 128, 114106 (2008); http://dx.doi.org/10.1063/1.2890722 (6 pages) | Cited 6 times

Online Publication Date: 19 March 2008

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A simple method is presented which ensures the electron-nucleus cusp condition is satisfied by the Slater-Jastrow wavefunctions commonly employed in quantum Monte Carlo simulations. The method is applied in variational energy calculations of the neon atom and a selection of molecules using both Gaussian and Slater basis sets. In addition, we discuss the relationship between the electron-nucleus cusps and the variance of forces, and investigate the sensitivity of forces to the quality of the cusps for various diatomic molecules.
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34.80.Bm Elastic scattering
02.70.Ss Quantum Monte Carlo methods
31.15.xt Variational techniques

Energy and energy gradient matrix elements with N-particle explicitly correlated complex Gaussian basis functions with L = 1

Sergiy Bubin and Ludwik Adamowicz

J. Chem. Phys. 128, 114107 (2008); http://dx.doi.org/10.1063/1.2894866 (15 pages) | Cited 9 times

Online Publication Date: 20 March 2008

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In this work we consider explicitly correlated complex Gaussian basis functions for expanding the wave function of an N-particle system with the L = 1 total orbital angular momentum. We derive analytical expressions for various matrix elements with these basis functions including the overlap, kinetic energy, and potential energy (Coulomb interaction) matrix elements, as well as matrix elements of other quantities. The derivatives of the overlap, kinetic, and potential energy integrals with respect to the Gaussian exponential parameters are also derived and used to calculate the energy gradient. All the derivations are performed using the formalism of the matrix differential calculus that facilitates a way of expressing the integrals in an elegant matrix form, which is convenient for the theoretical analysis and the computer implementation. The new method is tested in calculations of two systems: the lowest P state of the beryllium atom and the bound P state of the positronium molecule (with the negative parity). Both calculations yielded new, lowest-to-date, variational upper bounds, while the number of basis functions used was significantly smaller than in previous studies. It was possible to accomplish this due to the use of the analytic energy gradient in the minimization of the variational energy.
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31.15.xt Variational techniques

Calculation of electric dipole (hyper)polarizabilities by long-range-correction scheme in density functional theory: A systematic assessment for polydiacetylene and polybutatriene oligomers

Bernard Kirtman, Sean Bonness, Alejandro Ramirez-Solis, Benoit Champagne, Hironori Matsumoto, and Hideo Sekino

J. Chem. Phys. 128, 114108 (2008); http://dx.doi.org/10.1063/1.2885051 (5 pages) | Cited 42 times

Online Publication Date: 20 March 2008

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The long-range correction (LC) for treating electron exchange in density functional theory, combined with the Becke–Lee–Yang–Parr (BLYP) exchange-correlation functional, was used to determine (hyper)polarizabilities of polydiacetylene/polybutatriene oligomers. In comparison with coupled-cluster calculations including single and double excitations as well as a perturbative treatment of triple excitations, our values indicate that the tendency of conventional functionals to result in a catastrophic overshoot for these properties is alleviated but not eliminated. No clear-cut preference for LC-BLYP over Hartree–Fock values is obtained. This analysis is consistent with the calculations of Sekino et al. [J. Chem. Phys. 126, 014107 (2007)] on polyacetylene and molecular hydrogen oligomers. Thus, the performance of LC-BLYP with regard to (hyper)polarizabilities of quasilinear conjugated systems is now well characterized.
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33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.eg Exchange-correlation functionals (in current density functional theory)
31.15.bw Coupled-cluster theory

Electronic excited-state energies from a linear response theory based on the ground-state two-electron reduced density matrix

Loren Greenman and David A. Mazziotti

J. Chem. Phys. 128, 114109 (2008); http://dx.doi.org/10.1063/1.2890961 (7 pages) | Cited 9 times

Online Publication Date: 20 March 2008

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Ground-state two-particle reduced density matrices (2-RDMs) are used to calculate excited-state energy spectra. Solving the Schrödinger equation for excited states dominated by single excitations from the ground-state wavefunction requires the ground-state 2- and 3-RDMs. The excited states, however, can be obtained without a knowledge of the ground-state 3-RDM by two methods: (i) cumulant expansion methods which build the 3-RDM from the 2-RDM, and (ii) double commutator methods which eliminate the 3-RDM. Previous work [ Mazziotti, Phys. Rev. A 68, 052501 (2003) ] examined the accuracy of excited states extracted from ground-state 2-RDMs, which were calculated by full configuration interaction or the variational 2-RDM method. In this work we employ (i) advances in semidefinite programming to treat the excited states of water and hydrogen fluoride and chains of hydrogen atoms, and (ii) the addition of partial three-particle N-representability conditions to compute more accurate ground-state 2-RDMs. With the hydrogen chains we examine the metal-to-insulator transition as measured by the band gap (the difference between the ground-state and the first excited-state energies), which is difficult for excited-state methods to capture.
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71.30.+h Metal-insulator transitions and other electronic transitions
71.15.Qe Excited states: methodology
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Concurrent triple-scale simulation of molecular liquids

Rafael Delgado-Buscalioni, Kurt Kremer, and Matej Praprotnik

J. Chem. Phys. 128, 114110 (2008); http://dx.doi.org/10.1063/1.2890729 (9 pages) | Cited 25 times

Online Publication Date: 20 March 2008

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We present a triple-scale simulation of a molecular liquid, in which the atomistic, coarse-grained, and continuum descriptions of the liquid are concurrently coupled. The presented multiscale approach, which covers the length scales ranging from the micro- to macroscale, is a combination of two dual-scale models: a particle-based adaptive resolution scheme (AdResS), which couples the atomic and mesoscopic scales, and a hybrid continuum-molecular dynamics scheme (HybridMD). The combined AdResS-HybridMD scheme successfully sorts out the problem of large molecule insertion in the hybrid particle-continuum simulations of molecular liquids. The combined model is shown to correctly describe the hydrodynamics within a hybrid particle-continuum framework. The presented approach opens up the possibility to perform efficient grand-canonical molecular dynamics simulations of truly open molecular liquid systems.
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61.20.Ja Computer simulation of liquid structure

High-accuracy extrapolated ab initio thermochemistry. III. Additional improvements and overview

Michael E. Harding, Juana Vázquez, Branko Ruscic, Angela K. Wilson, Jürgen Gauss, and John F. Stanton

J. Chem. Phys. 128, 114111 (2008); http://dx.doi.org/10.1063/1.2835612 (15 pages) | Cited 55 times

Online Publication Date: 21 March 2008

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Effects of increased basis-set size as well as a correlated treatment of the diagonal Born-Oppenheimer approximation are studied within the context of the high-accuracy extrapolated ab initio thermochemistry (HEAT) theoretical model chemistry. It is found that the addition of these ostensible improvements does little to increase the overall accuracy of HEAT for the determination of molecular atomization energies. Fortuitous cancellation of high-level effects is shown to give the overall HEAT strategy an accuracy that is, in fact, higher than most of its individual components. In addition, the issue of core-valence electron correlation separation is explored; it is found that approximate additive treatments of the two effects have limitations that are significant in the realm of <1 kJ mol−1 theoretical thermochemistry.
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31.15.A- Ab initio calculations
31.15.V- Electron correlation calculations for atoms, ions and molecules
82.60.-s Chemical thermodynamics

Directionally negative friction: A method for enhanced sampling of rare event kinetics

James MacFadyen, Jeff Wereszczynski, and Ioan Andricioaei

J. Chem. Phys. 128, 114112 (2008); http://dx.doi.org/10.1063/1.2841102 (9 pages) | Cited 2 times

Online Publication Date: 21 March 2008

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A method exploiting the properties of an artificial (nonphysical) Langevin dynamics with a negative frictional coefficient along a suitable manifold and positive friction in the perpendicular directions is presented for the enhanced calculation of time-correlation functions for rare event problems. Exact time-correlation functions that describe the kinetics of the transitions for the all-positive, physical system can be calculated by reweighting the generated trajectories according to stochastic path integral treatment involving a functional weight based on an Onsager–Machlup action functional. The method is tested on a prototypical multidimensional model system featuring the main elements of conformational space characteristic of complex condensed matter systems. Using the present method, accurate estimates of rate constants require at least three order of magnitudes fewer trajectories than regular Langevin dynamics. The method is particularly useful in calculating kinetic properties in the context of multidimensional energy landscapes that are characteristic of complex systems such as proteins and nucleic acids.
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82.20.Wt Computational modeling; simulation
82.20.Uv Stochastic theories of rate constants

Dynamics of molecules in strong oscillating electric fields using time-dependent Hartree–Fock theory

Henk Eshuis, Gabriel G. Balint-Kurti, and Frederick R. Manby

J. Chem. Phys. 128, 114113 (2008); http://dx.doi.org/10.1063/1.2850415 (6 pages) | Cited 3 times

Online Publication Date: 21 March 2008

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Restricted and unrestricted forms of time-dependent Hartree–Fock theory have been implemented and used to study the electronic dynamics of ethene, benzene, and the formaldehyde cation subjected to both weak and strong oscillating electric fields. Absorption spectra and frequency-dependent polarizabilities are calculated via the instantaneous dipole moment and its derivative. In the weak field limit the computed excitation energies agree very well with those obtained using linearized time-dependent Hartree–Fock theory, which is valid only in the low-field perturbation limit. For strong fields the spectra show higher-order excitations, and a shift in the position of the excitations, which is due to the nonadiabatic response of the molecules to the field. For open-shell systems in the presence of strong oscillating electric fields, unrestricted time-dependent Hartree–Fock theory predicts the value of math2 to vary strongly with time.
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31.15.xr Self-consistent-field methods
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.20.-t Molecular spectra

Global fitting without a global model: Regularization based on the continuity of the evolution of parameter distributions

Jason T. Giurleo and David S. Talaga

J. Chem. Phys. 128, 114114 (2008); http://dx.doi.org/10.1063/1.2837293 (18 pages) | Cited 1 time

Online Publication Date: 21 March 2008

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We introduce a new approach to global data fitting based on a regularization condition that invokes continuity in the global data coordinate. Stabilization of the data fitting procedure comes from probabilistic constraint of the global solution to physically reasonable behavior rather than to specific models of the system behavior. This method is applicable to the fitting of many types of spectroscopic data including dynamic light scattering, time-correlated single-photon counting (TCSPC), and circular dichroism. We compare our method to traditional approaches to fitting an inverse Laplace transform by examining the evolution of multiple lifetime components in synthetic TCSPC data. The global regularizer recovers features in the data that are not apparent from traditional fitting. We show how our approach allows one to start from an essentially model-free fit and progress to a specific model by moving from probabilistic to deterministic constraints in both Laplace transformed and nontransformed coordinates.
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78.20.Fm Birefringence
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Electron-electron cusp condition and asymptotic behavior for the Pauli potential in pair density functional theory

Á. Nagy and C. Amovilli

J. Chem. Phys. 128, 114115 (2008); http://dx.doi.org/10.1063/1.2838201 (4 pages) | Cited 5 times

Online Publication Date: 21 March 2008

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In the ground state, the pair density n can be determined by solving a single auxiliary equation of a two-particle problem. Electron-electron cusp condition and asymptotic behavior for the Pauli potential of the effective potential of the two-particle equation are presented.
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31.15.E- Density-functional theory
31.15.ve Electron correlation calculations for atoms and ions: ground state

The three-dimensional nonadiabatic dynamics calculation of DH2+ and HD2+ systems by using the trajectory surface hopping method based on the Zhu–Nakamura theory

Bin Li and Ke-Li Han

J. Chem. Phys. 128, 114116 (2008); http://dx.doi.org/10.1063/1.2884928 (7 pages) | Cited 4 times

Online Publication Date: 21 March 2008

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A theoretical investigation on the nonadiabatic processes of the full three-dimensional D++H2 and H++D2 reaction systems has been performed by using trajectory surface hopping (TSH) method based on the Zhu–Nakamura (ZN) theory. This ZN-TSH method refers to not only classically allowed hops but also classically forbidden hops. The potential energy surface constructed by Kamisaka et al. is employed in the calculation. A new iterative method is proposed to yield the two-dimensional seam surface from the topography of the adiabatic potential surfaces, in which the inconvenience of directly solving the first-order partial differential equation is avoided. The cross sections of these two systems are calculated for three competing channels of the reactive charge transfer, the nonreactive charge transfer, and the reactive noncharge transfer, for ground rovibrational state of H2 or D2. Also, this study provides reaction probabilities of these three processes for the total angular momentum J = 0 and ground initial vibrational state of H2 or D2. The calculated results from ZN-TSH method are in good agreement with the exact quantum calculations and the experimental measurements.
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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

First-principles calculations of magnetic circular dichroism spectra

Dmitry Ganyushin and Frank Neese

J. Chem. Phys. 128, 114117 (2008); http://dx.doi.org/10.1063/1.2894297 (13 pages) | Cited 16 times

Online Publication Date: 21 March 2008

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An elaborate approach for the prediction of magnetic circular dichroism (MCD) spectra in the framework of highly correlated multiconfigurational ab initio methods is presented. The MCD transitions are computed by the explicit treatment of spin-orbit coupled (SOC) and spin-spin coupled (SSC) N-electron states. These states are obtained from the diagonalization of the SOC and SSC operators along with the spin and orbital Zeeman operators in the basis of a preselected number of roots of the spin-free Hamiltonian. Therefore, zero-field splittings due to the SOC and SSC interactions along with the magnetic field splittings are explicitly accounted for in the ground as well as the excited states. This makes it possible to calculate simultaneously all MCD A, B, and C terms even beyond the linear response limit. The SOC is computed using a multicenter mean-field approximation to the Breit–Pauli Hamiltonian. Two-electron SSC terms are included in the treatment without further approximations. The MCD transition intensities are subjected to numerical orientational averaging in order to treat the most commonly encountered case of randomly oriented molecules. The simulated MCD spectra for the OH, NH, and CH radicals as well as for [Fe(CN)6]3− are in good agreement with the experimental spectra. In the former case, the significant effects of the inert gas matrices in which the experimental spectra were obtained were modeled in a phenomenological way.
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78.20.Ls Magneto-optical effects
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

CCSD calculations on C14, C18, and C22 carbon clusters

Sundaram Arulmozhiraja and Takahisa Ohno

J. Chem. Phys. 128, 114301 (2008); http://dx.doi.org/10.1063/1.2838200 (9 pages) | Cited 4 times

Online Publication Date: 17 March 2008

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The structure and energetics of the ring isomers of C4n+2 (n = 3–5) carbon clusters were studied by using coupled-cluster singles and doubles excitation theory to overcome the vast differences existing in the literature. The results obtained in the present study clearly indicate that C14, C18, and C22 carbon rings have bond-length and bond-angle alternated acetylenic minimum energy structures. Contrarily, density functional theory calculations were unable to predict these acetylenic-type structures and they ended up with the cumulenic structures. It is found from the coupled-cluster studies that the lowest-energy ring isomer for the first two members of C4n+2 series is a bond-angle alternated cumulenic D(2n+1)h symmetry structure while the same for the remaining members is a bond-length and bond-angle alternated C(2n+1)h symmetry structure. In C4n+2 carbon rings, Peierls-type distortion, transformation from bond-angle alternated to bond-length alternated minimum energy structures, occurs at C14 carbon ring.
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36.40.Mr Spectroscopy and geometrical structure of clusters
31.15.bw Coupled-cluster theory
31.15.es Applications of density-functional theory (e.g., to electronic structure and stability; defect formation; dielectric properties, susceptibilities; viscoelastic coefficients; Rydberg transition frequencies)
33.15.Dj Interatomic distances and angles

Oscillator strengths and line widths of dipole-allowed transitions in 14N2 between 89.7 and 93.5 nm

G. Stark, B. R. Lewis, A. N. Heays, K. Yoshino, P. L. Smith, and K. Ito

J. Chem. Phys. 128, 114302 (2008); http://dx.doi.org/10.1063/1.2834933 (10 pages) | Cited 11 times

Online Publication Date: 17 March 2008

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Line oscillator strengths in the 20 electric dipole-allowed bands of 14N2 in the 89.7–93.5 nm (111480–106950 cm−1) region are reported from photoabsorption measurements at an instrumental resolution of ∼ 6 mÅ (0.7 cm−1) full width at half maximum. The absorption spectrum comprises transitions to vibrational levels of the 3pσu c4′ 1Σu+, 3pπu c3 1Πu, and 3sσg o3 1Πu Rydberg states and of the b′ 1Σu+ and b 1Πu valence states. The J dependences of band f values derived from the experimental line f values are reported as polynomials in J′(J′+1) and are extrapolated to J′ = 0 in order to facilitate comparisons with results of coupled Schrödinger-equation calculations. Most bands in this study are characterized by a strong J dependence of the band f values and display anomalous P-, Q-, and R-branch intensity patterns. Predissociation line widths, which are reported for 11 bands, also exhibit strong J dependences. The f value and line width patterns can inform current efforts to develop comprehensive spectroscopic models that incorporate rotational effects and predissociation mechanisms, and they are critical for the construction of realistic atmospheric radiative-transfer models.
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33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.70.Jg Line and band widths, shapes, and shifts
33.20.Tp Vibrational analysis
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.80.Gj Diffuse spectra; predissociation, photodissociation

Photofragment translational spectroscopy of propargyl radicals at 248 nm

Scott J. Goncher, David T. Moore, Niels E. Sveum, and Daniel M. Neumark

J. Chem. Phys. 128, 114303 (2008); http://dx.doi.org/10.1063/1.2840350 (8 pages) | Cited 10 times

Online Publication Date: 17 March 2008

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The photodissociation of propargyl radical, C3H3, and its perdeuterated isotopolog was investigated using photofragment translational spectroscopy. Propargyl radicals were produced by 193 nm photolysis of allene entrained in a molecular beam expansion and then photodissociated at 248 nm. Photofragment time-of-flight spectra were measured at a series of laboratory angles using electron impact ionization coupled to a mass spectrometer. Data for ion masses corresponding to C3H2+, C3H+, C3+, and the analogous deuterated species show that both H and H2 loss occur. The translational energy distributions for these processes have average values 〈ET〉 = 5.7 and 15.3 kcal/mol, respectively, and are consistent with dissociation on the ground state following internal conversion, with no exit barrier for H loss but a tight transition state for H2 loss. Our translational energy distribution for H atom loss is similar to that in a previous work on propargyl in which the H atom, rather than the heavy fragment, was detected. The branching ratio for H loss/H2 loss was determined to be 97.6/2.4±1.2, in good agreement with previous calculations.
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82.50.Hp Processes caused by visible and UV light
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.80.Dx Analytical methods involving electronic spectroscopy

Vibrational effects on the reaction of NO2+ with C2H2: Effects of bending and bending angular momentum

Jason M. Boyle, Brady W. Uselman, Jianbo Liu, and Scott L. Anderson

J. Chem. Phys. 128, 114304 (2008); http://dx.doi.org/10.1063/1.2889953 (12 pages) | Cited 5 times

Online Publication Date: 18 March 2008

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NO2+ in six different vibrational states was reacted with C2H2 over the center-of-mass energy range from 0.03 to 3.3 eV. The reaction, forming NO++C2H2O and NO+C2H2O+, shows a bimodal dependence on collision energy (Ecol). At low Ecol, the reaction is quite inefficient (<2%) despite this being a barrierless, exoergic reaction, and is strongly inhibited by Ecol. For Ecol> ∼ 0.5 eV, a second mechanism turns on, with an efficiency reaching ∼ 27% for Ecol>3 eV. The two reaction channels have nearly identical dependence on Ecol and NO2+ vibrational state, and identical recoil dynamics, leading to the conclusion that they represent a single reaction path throughout most of the collision. All modes of NO2+ vibrational excitation enhance both channels at all Ecol, however, the effects of bend (010) and bend overtone (0200) excitation are particularly strong (factor of 4). In contrast, the asymmetric stretch (001), which intuition suggests should be coupled to the reaction coordinate, leads to only a factor of ∼ 2 enhancement, as does the symmetric stretch (100). Perhaps the most surprising effect is that of the bending angular momentum, which strongly suppress reaction, even though both the energy and angular momentum involved are tiny compared to the collision energy and angular momentum. The results are interpreted in light of ab initio and Rice-Ramsperger-Kassel-Marcus calculations.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Fd Collision theories; trajectory models

Rovibrational spectroscopy and intramolecular dynamics of 1,2-trans-d2-ethene in the first C–H stretch overtone region

Amir Zwielly, Alexander Portnov, Chen Levi, Salman Rosenwaks, and Ilana Bar

J. Chem. Phys. 128, 114305 (2008); http://dx.doi.org/10.1063/1.2890041 (6 pages)

Online Publication Date: 18 March 2008

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The first overtone region of the C–H stretching vibration of 1,2-trans-d2-ethene (HDC=CDH) was monitored via jet-cooled action spectroscopy and room temperature photoacoustic spectroscopy. The spectra include a strong band, which we assigned as the ν1+ν9 C–H stretch vibration, and five additional bands related to transitions to coupled states. The spectral features were modeled in terms of a six-state deperturbation analysis, revealing the energies of the zero-order states and the relatively strong couplings between the initially excited ν1+ν9 state and the doorway states. Considering these energies and the fundamental frequencies of 1,2-trans-d2-ethene and presuming that only low-order resonances are involved in the couplings enabled the assignment of the states. The analysis also allowed obtaining insight on energy flow and to find out that the energy oscillations between the C–H stretch state and the doorway states occur on a subpicosecond time scale.
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33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Vq Vibration-rotation analysis
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