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21 Sep 2009

Volume 131, Issue 11, Articles (11xxxx)

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J. Chem. Phys. 131, 114302 (2009); http://dx.doi.org/10.1063/1.3222640 (8 pages)

Javier Eduardo Cuervo and Pierre-Nicholas Roy
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Ortho-para mixing interaction in the vinyl radical detected by millimeter-wave spectroscopy

Keiichi Tanaka, Masato Hayashi, Mitsuhiko Ohtsuki, Kensuke Harada, and Takehiko Tanaka

J. Chem. Phys. 131, 111101 (2009); http://dx.doi.org/10.1063/1.3231491 (4 pages) | Cited 2 times

Online Publication Date: 15 September 2009

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Ortho-para mixing interaction due to the coupling of nuclear and electron spins was detected for the first time by millimeter-wave spectroscopy of the deuterated vinyl radical H2CCD. The ground state of H2CCD is split by the deuteron tunneling into two components 0+ and 0− separated by ΔE0 = 1186.794(16) MHz. Rotational levels in the 0+ and 0− states, one being an ortho level and the other a para level, are coupled by the interaction expressed by 〈0±|H′|0∓〉 = (δaF/2)S⋅(I1−I2), where I1 and I2 are spins of the two protons and S is the electron spin. The δaF constant has been determined to be 68.06(52) MHz. The para to ortho conversion rate constant is predicted to be 1.2×105 s−1 torr−1.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
33.20.Bx Radio-frequency and microwave spectra
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Diversity of kinetic pathways in amyloid fibril formation

Giovanni Bellesia and Joan-Emma Shea

J. Chem. Phys. 131, 111102 (2009); http://dx.doi.org/10.1063/1.3216103 (4 pages) | Cited 17 times

Online Publication Date: 17 September 2009

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The kinetics of peptide oligomerization was investigated using Langevin Dynamics simulations and a coarse-grained peptide model. The simulations show a rich diversity of aggregation pathways, modulated by the β-sheet propensity (flexibility) of the peptide. Aggregation into amyloidlike fibrils occurs via three main mechanisms: (i) formation of fibrils directly from the assembly of early ordered oligomers, (ii) fibril formation via the formation of on-pathway, nonfibrillar aggregates high in β-sheet content, and (iii) formation of amorphous aggregates followed by reorganization to β-sheet aggregates and to fibrils. β-sheet, nonfibrillar aggregates also appeared as long-lived, “off-pathway” end-product species.
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87.15.nr Aggregation
87.14.E- Proteins
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back to top Theoretical Methods and Algorithms

All-electron calculation of nonadiabatic couplings from time-dependent density functional theory: Probing with the Hartree–Fock exact exchange

Chunping Hu, Osamu Sugino, and Yoshitaka Tateyama

J. Chem. Phys. 131, 114101 (2009); http://dx.doi.org/10.1063/1.3226344 (8 pages) | Cited 5 times

Online Publication Date: 15 September 2009

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We present the all-electron scheme of calculating nonadiabatic couplings (NACs) from time-dependent density functional theory (TDDFT) using atomic orbital basis. The formal expression for calculating NAC from linear response TDDFT [ Hu et al., J. Chem. Phys. 127, 064103 (2007) ] can be straightforwardly adapted to the all-electron TDDFT scheme. However, in contrast to the planewave basis, the nuclear coordinate dependence of atomic orbital basis needs to be considered when constructing the matrix elements of the nuclear derivative of Hamiltonian. Practical calculations show that the contribution of atomic orbital basis (“Pulay term”) is significant and comparable to that of the Hellmann–Feynman term. In particular, we probe the all-electron formalism of NAC with the Hartree–Fock exact exchange, which serves as the prerequisite for hybrid functionals. It is validated that in the present framework the sum rule of NAC is rigorously satisfied, which has not been the case in the pseudopotential planewave calculations. Reasonably good results can be obtained in the vicinity of various Renner–Teller (and also Jahn–Teller) intersections when the intersection point is not too closely approached, while further tests show that correlation effects should be taken into account in general cases.
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33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
31.50.-x Potential energy surfaces
31.30.jh QED corrections to long-range and weak interactions
31.15.ee Time-dependent density functional theory
31.15.eg Exchange-correlation functionals (in current density functional theory)
31.15.xr Self-consistent-field methods

A thermal self-consistent field theory for the calculation of molecular vibrational partition functions

Tapta Kanchan Roy and M. Durga Prasad

J. Chem. Phys. 131, 114102 (2009); http://dx.doi.org/10.1063/1.3213568 (7 pages) | Cited 1 time

Online Publication Date: 15 September 2009

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A new approach for the calculation of anharmonic molecular vibrational partition functions is developed based on a separable ansatz to the thermal density matrix. The parameters appearing in the effective single particle Hamiltonians that generate the thermal density matrices are determined variationally. The resulting equations are the thermal analogs of the vibrational self-consistent field approximation. The method has the formal property that the free energy calculated by this approach is an upper bound to the exact free energy. Thermodynamic quantities calculated by this approach are generally in good agreement with the results of numerically converged calculations. This approach is more efficient than the standard sum over state approaches in that the computational resources scale with N4 where N is the number of vibrational degrees of freedom. Thus it can be applied to fairly large systems.
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31.15.xr Self-consistent-field methods
33.15.Mt Rotation, vibration, and vibration-rotation constants
05.70.Ce Thermodynamic functions and equations of state

Accounting for the exact degeneracy and quasidegeneracy in the automerization of cyclobutadiene via multireference coupled-cluster methods

Xiangzhu Li and Josef Paldus

J. Chem. Phys. 131, 114103 (2009); http://dx.doi.org/10.1063/1.3225203 (10 pages) | Cited 19 times

Online Publication Date: 15 September 2009

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The automerization of cyclobutadiene (CBD) is employed to test the performance of the reduced multireference (RMR) coupled-cluster (CC) method with singles and doubles (RMR CCSD) that employs a modest-size MR CISD wave function as an external source for the most important (primary) triples and quadruples in order to account for the nondynamic correlation effects in the presence of quasidegeneracy, as well as of its perturbatively corrected version accounting for the remaining (secondary) triples [RMR CCSD(T)]. The experimental results are compared with those obtained by the standard CCSD and CCSD(T) methods, by the state universal (SU) MR CCSD and its state selective or state specific (SS) version as formulated by Mukherjee et al. (SS MRCC or MkMRCC) and, wherever available, by the Brillouin–Wigner MRCC [MR BWCCSD(T)] method. Both restricted Hartree-Fock (RHF) and multiconfigurational self-consistent field (MCSCF) molecular orbitals are employed. For a smaller STO-3G basis set we also make a comparison with the exact full configuration interaction (FCI) results. Both fundamental vibrational energies—as obtained via the integral averaging method (IAM) that can handle anomalous potentials and automatically accounts for anharmonicity– and the CBD automerization barrier for the interconversion of the two rectangular structures are considered. It is shown that the RMR CCSD(T) potential has the smallest nonparallelism error relative to the FCI potential and the corresponding fundamental vibrational frequencies compare reasonably well with the experimental ones and are very close to those recently obtained by other authors. The effect of anharmonicity is assessed using the second-order perturbation theory (MP2). Finally, the invariance of the RMR CC methods with respect to orbital rotations is also examined.
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31.15.bw Coupled-cluster theory
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.15.xr Self-consistent-field methods
31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations

A computationally less demanding charge-on-spring model for the water molecule

András Baranyai

J. Chem. Phys. 131, 114104 (2009); http://dx.doi.org/10.1063/1.3227906 (6 pages)

Online Publication Date: 15 September 2009

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We developed a new charge-on-spring model for the water molecule with the advantage of being computationally less demanding. We start from the basic geometry of Lamoureux et al. [J. Chem. Phys. 119, 5185 (2003) ; Chem. Phys. Lett. 418, 245 (2006)] in order to have a good approximation for the quadrupole moment of the gas phase molecule, but we use only four charged sites. We polarize the molecules in two steps. First, the three sites of the equilibrium gas phase molecule are polarized and this process is accompanied by a charge rearrangement. This step creates the massless spring particle connected to the uncharged oxygen atom. The equilibrium position of the spring particle is found by iteration. We describe the construction of the model and present details of the results obtained by molecular dynamics simulation for the properties of liquid water, hexagonal ice, and gas clusters. Our results are comparable in quality to that of Lamoureux et al. [Chem. Phys. Lett. 418, 245 (2006)] and show good agreements with experiments.
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61.25.Em Molecular liquids
61.20.Ja Computer simulation of liquid structure

A global search algorithm of minima exploration for the investigation of low lying isomers of clusters from density functional theory-based potential energy surfaces: The example of Sin (n = 3,15) as a test case

Rémi Marchal, Philippe Carbonnière, and Claude Pouchan

J. Chem. Phys. 131, 114105 (2009); http://dx.doi.org/10.1063/1.3216382 (9 pages) | Cited 6 times

Online Publication Date: 16 September 2009

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Using an effective generation algorithm coupled with a PBE0/LANL2DZdp level of theory, 905 stable structures of Sin (n = 3,15) have been found. This global search algorithm of minima exploration includes two original parts: the spheroidal generation, allowing the generation of rings, sphericals, m rings cylinders, and planar structures, and the raking optimization, which discards step by step the conformations that become physically unreasonable during the optimization process. The 142 isomers lying below 1 eV are reported and include the 28 structures reported in the literature. Conformational energies are well reproduced with respect to the values previously published (ΔE = 0,00±0,09 eV).
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36.40.-c Atomic and molecular clusters
33.15.Bh General molecular conformation and symmetry; stereochemistry
31.15.E- Density-functional theory
31.50.-x Potential energy surfaces

Potentialphilicity and potentialphobicity: Reactivity indicators for external potential changes from density functional reactivity theory

Shubin Liu, Tonglei Li, and Paul W. Ayers

J. Chem. Phys. 131, 114106 (2009); http://dx.doi.org/10.1063/1.3231687 (7 pages) | Cited 6 times

Online Publication Date: 16 September 2009

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In analogy to the electrophilicity, we define potentialphilicity indicators that represent energetically favorable ways to change the external potential of a molecule at fixed electron number. Similarly, we define a potentialphobicity to represent the least favorable way to change the external potential of a molecule. The resulting indicators should be useful for describing how molecular geometries change and predicting favorable and unfavorable ways for a reagent to approach a molecule. The linear response function enters plays a very important role in this approach, analogous to the role of the hardness for the electrophilicity or the hardness kernel for the Fukui function. The mathematical properties of the response function and its implications for these reactivity indicators are discussed in depth.
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82.20.Db Transition state theory and statistical theories of rate constants

Configuration interaction calculations of potential curves and annihilation rates for positronic complexes of alkali monoxides

Robert J. Buenker and Heinz-Peter Liebermann

J. Chem. Phys. 131, 114107 (2009); http://dx.doi.org/10.1063/1.3231685 (9 pages) | Cited 1 time

Online Publication Date: 17 September 2009

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Ab initio multireference single- and double-excitation configuration interaction calculations have been carried out to compute the potential curves and annihilation rates (ARs) of positronic molecular complexes of a series of alkali monoxides. The dissociation limit for the lowest states of these systems consists of the positive alkali ion ground state (M+) and the OPs (e+O−) complex formed by attaching the positron to O−, even though the ground state of the corresponding neutral molecule always correlates with uncharged fragments (M+O). The positron affinity of the neutral oxide 2Π state is greater than that of 2Σ+ in each case, so that the e+MO ground state always has 3,1Π symmetry, despite the fact that both KO and RbO have 2Σ+ ground states. The bonding in the positronic systems is highly ionic at all internuclear distances and this causes their ARs to decrease gradually as the positive alkali ion approaches the OPs fragment.
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34.80.Uv Positron scattering
34.80.Ht Dissociation and dissociative attachment
31.15.vn Electron correlation calculations for diatomic molecules
31.15.A- Ab initio calculations
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions

Divide-and-conquer-based linear-scaling approach for traditional and renormalized coupled cluster methods with single, double, and noniterative triple excitations

Masato Kobayashi and Hiromi Nakai

J. Chem. Phys. 131, 114108 (2009); http://dx.doi.org/10.1063/1.3211119 (9 pages) | Cited 16 times

Online Publication Date: 18 September 2009

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We have reported the divide-and-conquer (DC)-based linear-scaling correlation treatment of coupled-cluster method with single and double excitations (CCSD) [ Kobayashi and Nakai, J. Chem. Phys. 129, 044103 (2009) ]. In the DC-CCSD method, the CCSD equations derived from subsystem orbitals are solved for each subsystem in order to obtain the total correlation energy by summing up subsystem contributions using energy density analysis. In this study, we extend the DC-CCSD method for treating noniterative perturbative triple excitations using CCSD T1 and T2 amplitudes, namely, CCSD(T). In the DC-CCSD(T) method, the so-called (T) corrections are also computed for each subsystem. Numerical assessments indicate that DC-CCSD(T) reproduces the CCSD(T) results with high accuracy and significantly less computational cost. We further extend the DC-based correlation method to renormalized CCSD(T) [ Kowalski and Piecuch, J. Chem. Phys. 113, 18 (2000) ] for avoiding the divergence that occurs in multireference problems such as bond dissociation.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.20.Kh Potential energy surfaces for chemical reactions

Local correlation calculations using standard and renormalized coupled-cluster approaches

Wei Li, Piotr Piecuch, Jeffrey R. Gour, and Shuhua Li

J. Chem. Phys. 131, 114109 (2009); http://dx.doi.org/10.1063/1.3218842 (30 pages) | Cited 32 times

Online Publication Date: 18 September 2009

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The linear scaling local correlation approach, termed “cluster-in-molecule” (CIM), is extended to the coupled-cluster (CC) theory with singles and doubles (CCSD) and CC methods with singles, doubles, and noniterative triples, including CCSD(T) and the completely renormalized CR-CC(2,3) approach. The resulting CIM-CCSD, CIM-CCSD(T), and CIM-CR-CC(2,3) methods are characterized by (i) the linear scaling of the CPU time with the system size, (ii) the use of orthonormal orbitals in the CC subsystem calculations, (iii) the natural parallelism, (iv) the high computational efficiency, enabling calculations for much larger systems and at higher levels of CC theory than previously possible, and (v) the purely noniterative character of local triples corrections. By comparing the results of the canonical and CIM-CC calculations for normal alkanes and water clusters, it is shown that the CIM-CCSD, CIM-CCSD(T), and CIM-CR-CC(2,3) approaches accurately reproduce the corresponding canonical CC correlation and relative energies, while offering savings in the computer effort by orders of magnitude.
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31.15.bw Coupled-cluster theory
31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations

Determination of the solid-liquid interfacial free energy along a coexistence line by Gibbs–Cahn integration

Brian B. Laird, Ruslan L. Davidchack, Yang Yang, and Mark Asta

J. Chem. Phys. 131, 114110 (2009); http://dx.doi.org/10.1063/1.3231693 (8 pages) | Cited 6 times

Online Publication Date: 18 September 2009

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We calculate the solid-liquid interfacial free energy γsl for the Lennard-Jones (LJ) system at several points along the pressure-temperature coexistence curve using molecular-dynamics simulation and Gibbs–Cahn integration. This method uses the excess interfacial energy (e) and stress (τ) along the coexistence curve to determine a differential equation for γsl as a function of temperature. Given the values of γsl for the (100), (110), and (111) LJ interfaces at the triple-point temperature (T∗ = kT/ϵ = 0.618), previously obtained using the cleaving method by Davidchack and Laird [ J. Chem. Phys. 118, 7657 (2003) ], this differential equation can be integrated to obtain γsl for these interfaces at higher coexistence temperatures. Our values for γsl calculated in this way at T∗ = 1.0 and 1.5 are in good agreement with those determined previously by cleaving, but were obtained with significantly less computational effort than required by either the cleaving method or the capillary fluctuation method of Hoyt, Asta, and Karma [ Phys. Rev. Lett. 86, 5530 (2001) ]. In addition, the orientational anisotropy in the excess interface energy, stress and entropy, calculated using the conventional Gibbs dividing surface, are seen to be significantly larger than the relatively small anisotropies in γsl itself.
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68.35.Md Surface thermodynamics, surface energies
65.40.gd Entropy
64.60.Kw Multicritical points
64.70.D- Solid-liquid transitions
65.40.G- Other thermodynamical quantities

Non-Markovian theory for the waiting time distributions of single electron transfers

Sven Welack and YiJing Yan

J. Chem. Phys. 131, 114111 (2009); http://dx.doi.org/10.1063/1.3225244 (7 pages)

Online Publication Date: 18 September 2009

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We derive a non-Markovian theory for waiting time distributions of consecutive single electron transfer events. The presented microscopic Pauli rate equation formalism couples the open electrodes to the many-body system, allowing to take finite bias and temperature into consideration. Numerical results reveal transient oscillations of distinct system frequencies due to memory in the waiting time distributions. Memory effects can be approximated by an expansion in non-Markovian corrections. This method is employed to calculate memory landscapes displaying preservation of memory over multiple consecutive electron transfers.
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73.23.-b Electronic transport in mesoscopic systems

Perturbative triples correction for the equation-of-motion coupled-cluster wave functions with single and double substitutions for ionized states: Theory, implementation, and examples

Prashant U. Manohar, John F. Stanton, and Anna I. Krylov

J. Chem. Phys. 131, 114112 (2009); http://dx.doi.org/10.1063/1.3231133 (13 pages) | Cited 5 times

Online Publication Date: 18 September 2009

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A noniterative N6 triples energy correction is presented for the equation-of-motion coupled-cluster method with single and double substitutions for ionized states (EOM-IP-CCSD). The correction, which is size intensive, is derived using a second-order Rayleigh–Schrödinger perturbative treatment and is similar to the approach of Stanton and Gauss [Theor. Chim. Acta 93, 303 (1996)] . In the present implementation, only the target EOM-IP states are corrected, and the reference state is described by CCSD; the method is therefore more useful for the study of the target states themselves than ionization potentials. The performance of the correction, which demonstrates the caveat above, is demonstrated by applications to singlet methylene, BNB−, nitrogen, carbon monoxide, acetylene, benzene, thymine, and adenine.
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31.15.bw Coupled-cluster theory
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
31.15.xp Perturbation theory

Full-electron calculation of effective electronic couplings and excitation energies of charge transfer states: Application to hole transfer in DNA π-stacks

Agostino Migliore

J. Chem. Phys. 131, 114113 (2009); http://dx.doi.org/10.1063/1.3232007 (12 pages) | Cited 5 times

Online Publication Date: 21 September 2009

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In this work I develop and apply a theoretical method for calculating effective electronic couplings (or transfer integrals) between redox sites involved in hole or electron transfer reactions. The resulting methodology is a refinement and a generalization of a recently developed approach for transfer integral evaluation. In fact, it holds for any overlap between the charge-localized states used to represent charge transfer (CT) processes in the two-state model. The presented theoretical and computational analyses show that the prototype approach is recovered for sufficiently small overlaps. The method does not involve any empirical parameter. It allows a complete multielectron description, therefore including electronic relaxation effects. Furthermore, its theoretical formulation holds at any value of the given reaction coordinate and yields a formula for the evaluation of the vertical excitation energy (i.e., the energy difference between the adiabatic ground and first-excited electronic states) that rests on the same physical quantities used in transfer integral calculation. In this paper the theoretical approach is applied to CT in B-DNA base dimers within the framework of Density Functional Theory (DFT), although it can be implemented in other computational schemes. The results of this work, as compared with previous Hartree–Fock (HF) and post-HF evaluations, support the applicability of the current implementation of the method to larger π-stacked arrays, where post-HF approaches are computationally unfeasible.
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87.15.Pc Electronic and electrical properties
87.14.gk DNA
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Vibration-rotation pattern in acetylene. II. Introduction of Coriolis coupling in the global model and analysis of emission spectra of hot acetylene around 3 μm

Badr Amyay, Séverine Robert, Michel Herman, André Fayt, Balakrishna Raghavendra, Audrey Moudens, Jonathan Thiévin, Bertrand Rowe, and Robert Georges

J. Chem. Phys. 131, 114301 (2009); http://dx.doi.org/10.1063/1.3200928 (14 pages) | Cited 11 times

Online Publication Date: 15 September 2009

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A high temperature source has been developed and coupled to a high resolution Fourier transform spectrometer to record emission spectra of acetylene around 3 μm up to 1455 K under Doppler limited resolution (0.015 cm−1). The ν3-ground state (GS) and ν2+ν4+ν5 (Σu+ and Δu)-GS bands and 76 related hot bands, counting e and f parities separately, are assigned using semiautomatic methods based on a global model to reproduce all related vibration-rotation states. Significantly higher J-values than previously reported are observed for 40 known substates while 37 new e or f vibrational substates, up to about 6000 cm−1, are identified and characterized by vibration-rotation parameters. The 3 811 new or improved data resulting from the analysis are merged into the database presented by Robert et al. [ Mol. Phys. 106, 2581 (2008) ], now including 15 562 lines accessing vibrational states up to 8600 cm−1. A global model, updated as compared to the one in the previous paper, allows all lines in the database to be simultaneously fitted, successfully. The updates are discussed taking into account, in particular, the systematic inclusion of Coriolis interaction.
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33.20.Vq Vibration-rotation analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.50.Dq Fluorescence and phosphorescence spectra
33.20.Tp Vibrational analysis
33.20.Sn Rotational analysis

Weakly bound complexes trapped in quantum matrices: Structure, energetics, and isomer coexistence in (para-H2)N(ortho-D2)3 clusters

Javier Eduardo Cuervo and Pierre-Nicholas Roy

J. Chem. Phys. 131, 114302 (2009); http://dx.doi.org/10.1063/1.3222640 (8 pages) | Cited 2 times

Online Publication Date: 15 September 2009

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The ground state of mixed (para-H2)N(ortho-D2)3 clusters of sizes ranging from N = 8 to 37 is examined by means of the path integral ground state method. The chemical potential is calculated and reveals that magic numbers are consistent with those found in pure para-H2 and ortho-D2 clusters. The structural features of the mixed clusters are examined by analyzing density profiles, one-dimensional Pekeris distribution functions of the (ortho-D2)3 subsystem, and by direct visualization of density isosurfaces of the systems. The heavier (ortho-D2)3 complex resides in the center of the cluster for the various sizes under consideration. It is found that certain cluster sizes favor either equilateral, or near-linear isosceles (ortho-D2)3 configurations, while others show a coexistence between those two triangular geometries.
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36.40.Cg Electronic and magnetic properties of clusters
31.50.Bc Potential energy surfaces for ground electronic states
36.40.Mr Spectroscopy and geometrical structure of clusters
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)

Born–Oppenheimer quantum dynamics of the C(1D)+H2 reaction on the CH2 math 1A1 and math 1B1 surfaces

Paolo Defazio, Carlo Petrongolo, Béatrice Bussery-Honvault, and Pascal Honvault

J. Chem. Phys. 131, 114303 (2009); http://dx.doi.org/10.1063/1.3226573 (6 pages) | Cited 5 times

Online Publication Date: 15 September 2009

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We present the Born–Oppenheimer coupled-channel dynamics of the reaction 12C(1D)+1H2(X 1Σg+)→CH(X 2Π)+H(2S), considering the uncoupled CH2 states math 1A1 and math 1B1, the permutation-inversion symmetry, and Coriolis interactions. Using accurate MRCI potential energy surfaces (PESs), we obtain initial-state-resolved reaction probabilities, cross sections, and rate constants through the time-dependent, real wavepacket (WP) and flux methods, taking into account the proton-spin statistics for both electronic species. Comparing results on both PESs, we point out the role of the math 1B1 upper state on the initial-state-resolved dynamics and on the thermal kinetic rate. WP probabilities at J = 0 and cross sections at Ecol = 0.080 eV agree quite well with quantum-mechanical time-independent findings. Probabilities and WP snapshots show the different reaction mechanisms on the PESs, i.e., an math 1A1 indirect perpendicular insertion and a math 1B1 direct sideways collision, associated with many and few sharp resonances, respectively. All cross sections are very large at low Ecol, decrease at high energies, and that of the lowest reactant state presents some weak resonances. As the temperature increases from 100 to 400 K, the math 1A1 rate constant increases slightly from 1.37×10−10 to 1.43×10−10 cm3 s−1, whereas the math 1B1 one decreases from 1.30×10−10 to 0.98×10−10 cm3 s−1. In this temperature range, the math 1B1 contribution to the total rate constant thus decreases from 49% to 41%. At 300 K, the WP and experimental rates are equal to (2.45±0.08)×10−10 and (2.0±0.6)×10−10 cm3 s−1, respectively.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Ej Quantum theory of reaction cross section
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies

Laser-induced electron dynamics including photoionization: A heuristic model within time-dependent configuration interaction theory

Stefan Klinkusch, Peter Saalfrank, and Tillmann Klamroth

J. Chem. Phys. 131, 114304 (2009); http://dx.doi.org/10.1063/1.3218847 (8 pages) | Cited 7 times

Online Publication Date: 16 September 2009

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We report simulations of laser-pulse driven many-electron dynamics by means of a simple, heuristic extension of the time-dependent configuration interaction singles (TD-CIS) approach. The extension allows for the treatment of ionizing states as nonstationary states with a finite, energy-dependent lifetime to account for above-threshold ionization losses in laser-driven many-electron dynamics. The extended TD-CIS method is applied to the following specific examples: (i) state-to-state transitions in the LiCN molecule which correspond to intramolecular charge transfer, (ii) creation of electronic wave packets in LiCN including wave packet analysis by pump-probe spectroscopy, and, finally, (iii) the effect of ionization on the dynamic polarizability of H2 when calculated nonperturbatively by TD-CIS.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
34.70.+e Charge transfer
31.15.vq Electron correlation calculations for polyatomic molecules
31.15.vn Electron correlation calculations for diatomic molecules

Structural characterization of (C2H2)1–6+ cluster ions by vibrational predissociation spectroscopy

Rachael A. Relph, Joseph C. Bopp, Joseph R. Roscioli, and Mark A. Johnson

J. Chem. Phys. 131, 114305 (2009); http://dx.doi.org/10.1063/1.3212595 (7 pages) | Cited 3 times

Online Publication Date: 16 September 2009

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Vibrational predissociation spectra are reported for the cationic acetylene clusters, (C2H2)n+, n = 1–6, in the region of the C–H stretching fundamentals. For n = 1 and 2, predissociation could only be observed for the Ar-tagged clusters. These were prepared by charge-transfer collisions of Ark+ with C2H2 to create C2H2+⋅Arm clusters, which were then converted into larger members of the (C2H2)n+⋅Ar series by sequential addition of acetylene molecules. The (C2H2)2+⋅Ar spectrum indicates that this species is predominantly present as the cyclobutadiene cation. Although mobility measurements on the electron-impact-generated (C2H2)3+ ion indicated that it primarily occurs as the benzene cation, [ P. O. Momoh, J. Am. Chem. Soc. 128, 12408 (2006) ] photofragmentation of (C2H2)3+⋅Ar in the C–H stretching region is dominated by the loss of C2H2 in addition to the weakly bound Ar atom. This suggests that the dominant n = 3 species formed by sequential addition of C2H2 is based on a covalently bound C4H4+ core ion. Interestingly, the spectrum of this core C4H4+ species is different from that found for the cyclobutadiene cation, displaying instead a new band pattern that is retained in the higher (C2H2)3–6+ clusters. Multiple isomers are clearly involved, as yet another pattern of bands is recovered when the (C2H2)3+⋅Ar action spectrum is recorded in the (minor) Ar loss fragmentation channel. One of these features does appear in the location of the single band characteristic of the Ar-tagged benzene cation reported earlier [ Phys. Chem. Chem. Phys. 4, 24 (2002) ], supporting a scenario where the benzene cation is one of the isomers present. We then compare the Ar predissociation results with (C2H2)n+ spectra obtained when the ions are prepared by electron impact ionization of neutral acetylene clusters. The photofragmentation behavior and vibrational spectra indicate that the dominant species formed in this way also occur with a covalently bound C4H4+ core. There are absorptions, however, which are consistent with a minor contribution from (C2H2)n+ clusters based on the benzene cation.
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36.40.Mr Spectroscopy and geometrical structure of clusters
36.40.Qv Stability and fragmentation of clusters
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.20.Tp Vibrational analysis
34.80.Gs Molecular excitation and ionization
34.70.+e Charge transfer

Postionization fragmentation of rare-gas trimers revisited with new theoretical approaches

Ivan Janeček, Silvie Cintavá, Daniel Hrivňák, René Kalus, Michal Fárník, and Florent Xavier Gadea

J. Chem. Phys. 131, 114306 (2009); http://dx.doi.org/10.1063/1.3224855 (9 pages) | Cited 5 times

Online Publication Date: 16 September 2009

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A new theoretical approach is presented for the general treatment of nonadiabatic hybrid dynamics (mixing classical and quantum approach) and applied to the postionization of rare-gas trimers. There was an important disagreement between trajectory surface hopping (TSH) or mean field (MF) approaches and the experimental results; noteworthy, with the new method qualitative and almost quantitative agreement is found for the fragmentation ratios of ionic monomers and dimers. For the first time in the theory as in the experiment, the dimers prevail for argon while monomers strongly dominate for the heavier rare gases, krypton and xenon. A new compromise between MF and TSH approaches is proposed and the new method is found quite robust with results not too sensitive to various possible implementations.
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36.40.Qv Stability and fragmentation of clusters
31.15.-p Calculations and mathematical techniques in atomic and molecular physics

Cross sections for electron impact excitation of the C 1Π and D 1Σ+ electronic states in N2O

H. Kawahara, D. Suzuki, H. Kato, M. Hoshino, H. Tanaka, O. Ingólfsson, L. Campbell, and M. J. Brunger

J. Chem. Phys. 131, 114307 (2009); http://dx.doi.org/10.1063/1.3230150 (9 pages) | Cited 6 times

Online Publication Date: 16 September 2009

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Differential and integral cross sections for electron-impact excitation of the dipole-allowed C 1Π and D 1Σ+ electronic states of nitrous oxide have been measured. The differential cross sections were determined by analysis of normalized energy-loss spectra obtained using a crossed-beam apparatus at six electron energies in the range 15–200 eV. Integral cross sections were subsequently derived from these data. The present work was undertaken in order to check both the validity of the only other comprehensive experimental study into these excitation processes [ Marinković et al., J. Phys. B 32, 1949 (1998) ] and to extend the energy range of those data. Agreement with the earlier data, particularly at the lower common energies, was typically found to be fair. In addition, the BEf-scaling approach [ Kim, J. Chem. Phys. 126, 064305 (2007) ] is used to calculate integral cross sections for the C 1Π and D 1Σ+ states, from their respective thresholds to 5000 eV. In general, good agreement is found between the experimental integral cross sections and those calculated within the BEf-scaling paradigm, the only exception being at the lowest energies of this study. Finally, optical oscillator strengths, also determined as a part of the present investigations, were found to be in fair accordance with previous corresponding determinations.
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34.80.Gs Molecular excitation and ionization
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors

Must Kohn–Sham oscillator strengths be accurate at threshold?

Zeng-hui Yang, Meta van Faassen, and Kieron Burke

J. Chem. Phys. 131, 114308 (2009); http://dx.doi.org/10.1063/1.3222638 (7 pages)

Online Publication Date: 16 September 2009

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The exact ground-state Kohn–Sham (KS) potential for the helium atom is known from accurate wave function calculations of the ground-state density. The threshold for photoabsorption from this potential matches the physical system exactly. By carefully studying its absorption spectrum, we show the answer to the title question is no. To address this problem in detail, we generate a highly accurate simple fit of a two-electron spectrum near the threshold, and apply the method to both the experimental spectrum and that of the exact ground-state Kohn–Sham potential.
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32.70.Cs Oscillator strengths, lifetimes, transition moments
32.80.-t Photoionization and excitation
31.15.-p Calculations and mathematical techniques in atomic and molecular physics

Dissociation dynamics of C6H6 and C6H5F molecules following carbon 1s and fluorine 1s photoionization studied by three-dimensional momentum imaging method

A. Sugishima, K. Nagaya, H. Iwayama, M. Yao, J. Adachi, Y. Kimura, M. Yamazaki, and A. Yagishita

J. Chem. Phys. 131, 114309 (2009); http://dx.doi.org/10.1063/1.3224117 (6 pages) | Cited 2 times

Online Publication Date: 17 September 2009

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Benzene and fluorobenzene molecules were multiply ionized through Auger decay following from the C 1s or the F 1s photoionization and their subsequent dissociations were studied utilizing position-sensitive time-of-flight measurements. The angular correlation between the momenta of (H+–H+) and (H+–F+) fragment ions derived from the multiply ionized benzene or fluorobenzene clearly reflects the hexagonal structure of the parent molecules, though the dissociations are not described by the simple Coulomb explosion model. Also, analysis on the planarity between the momentum of H+, C+, and F+ reveals that these three ions are emitted almost in a single plane.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Gj Diffuse spectra; predissociation, photodissociation

Heavy atom nitroxyl radicals. I: An ab initio study of the ground and lower electronic excited states of the H2As = O free radical

Riccardo Tarroni and Dennis J. Clouthier

J. Chem. Phys. 131, 114310 (2009); http://dx.doi.org/10.1063/1.3230132 (10 pages) | Cited 5 times

Online Publication Date: 18 September 2009

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A series of ab initio calculations have been undertaken to predict the spectroscopic properties of the ground and first two excited states of the recently discovered arsenyl (H2AsO) free radical. This 13 valence electron species can be viewed as similar to the formaldehyde radical anion with a ground state electron configuration of ⋯(π)2(n)2(π∗)1. The arsenyl radical is nonplanar (pyramidal) in the ground state with a 59° out-of-plane angle and a 1.67 Å AsO bond length. It has a low-lying n-π∗(math 2A″) excited state (Te ∼ 5000 cm−1) which has a much larger out-of-plane angle (86°) and longer AsO bond length (1.81 Å). The π-π∗(math 2A′) excited state at ∼ 20 500 cm−1 is less pyramidal (out-of-plane angle = 70°) and has a somewhat shorter AsO bond (1.77 Å). Similar trends are found for the H2PO and H2NO free radicals, although the latter has a planar ground state, due to sp2 hybridization of the N atom, and a very long math state AsO bond length. The geometric variations of the ground and excited states of the H2EO (E = N, P, As) radicals, as well as the ground states of the corresponding anions and cations, can be readily rationalized from the Walsh diagram of the anion. The variations in the E-O bond length are a result of changes in both the orbital occupancy and pyramidalization of the molecule. The results of the present work have been employed in the analysis of the math 2A′-math 2A′ electronic band system of the H2AsO free radical as reported in the companion paper.
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31.15.A- Ab initio calculations
33.15.Dj Interatomic distances and angles
33.20.Ea Infrared spectra
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
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