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28 Sep 2007

Volume 127, Issue 12, Articles (12xxxx)

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Announcement: Search for new editor for The Journal of Chemical Physics

H. Frederick Dylla

J. Chem. Phys. 127, 120201 (2007); http://dx.doi.org/10.1063/1.2798324 (1 page)

Online Publication Date: 28 September 2007

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01.10.Cr Announcements, news, and awards
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Tuning ab initio data to scattering length: The a math state of KRb

Pavel Soldán and Vladimír Špirko

J. Chem. Phys. 127, 121101 (2007); http://dx.doi.org/10.1063/1.2790004 (4 pages) | Cited 4 times

Online Publication Date: 26 September 2007

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Interaction energies for the lowest triplet state a math of KRb are calculated using high level ab initio methods. The interaction energies are then morphed so that the resulting potential energy curve yields 32 bound states and the correct scattering length for mathmath. Calculated vibrational spacings are shown to be in very good agreement with the available experimental Fourier transform and photoassociation vibrational data, but a different numbering scheme has to be used for the experimental vibrational assignment.
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31.15.A- Ab initio calculations
31.50.Df Potential energy surfaces for excited electronic states
33.20.Tp Vibrational analysis

The effect of self-assembled monolayers on polarization-dependent two-photon photoemission and on the angular distribution of the photoelectrons

Z. Fradkin, D. Oron, and R. Naaman

J. Chem. Phys. 127, 121102 (2007); http://dx.doi.org/10.1063/1.2789413 (4 pages) | Cited 2 times

Online Publication Date: 28 September 2007

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The effect of a self-assembled organized organic monolayer on the two-photon photoemission from semiconductor substrates was investigated. It has been found that the monolayer affects the relative yield of photoelectrons emitted by p-polarized versus s-polarized light. In addition, the monolayer affects the angular distribution of the ejected electrons. The effect on the photoelectron yield is attributed to the monolayer “smoothing” the electronic potential on the surface by eliminating surface states and dangling bonds. The effect on the angular distribution is attributed to a post-ejection interaction between the photoelectrons and the adsorbed molecules.
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68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
79.60.-i Photoemission and photoelectron spectra
73.20.-r Electron states at surfaces and interfaces
71.55.-i Impurity and defect levels
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back to top Theoretical Methods and Algorithms

Generator coordinate method in time-dependent density-functional theory: Memory made simple

E. Orestes, K. Capelle, A. B. F. da Silva, and C. A. Ullrich

J. Chem. Phys. 127, 124101 (2007); http://dx.doi.org/10.1063/1.2768368 (10 pages) | Cited 8 times

Online Publication Date: 24 September 2007

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The generator coordinate (GC) method is a variational approach to the quantum many-body problem in which interacting many-body wave functions are constructed as superpositions of (generally nonorthogonal) eigenstates of auxiliary Hamiltonians containing a deformation parameter. This paper presents a time-dependent extension of the GC method as a new approach to improve existing approximations of the exchange-correlation (XC) potential in time-dependent density-functional theory (TDDFT). The time-dependent GC method is shown to be a conceptually and computationally simple tool to build memory effects into any existing adiabatic XC potential. As an illustration, the method is applied to driven parametric oscillations of two interacting electrons in a harmonic potential (Hooke’s atom). It is demonstrated that a proper choice of time-dependent generator coordinates in conjunction with the adiabatic local-density approximation reproduces the exact linear and nonlinear two-electron dynamics quite accurately, including features associated with double excitations that cannot be captured by TDDFT in the adiabatic approximation.
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31.15.E- Density-functional theory
31.15.xt Variational techniques
31.15.V- Electron correlation calculations for atoms, ions and molecules

Design-atom approach for the quantum mechanical/molecular mechanical covalent boundary: A design-carbon atom with five valence electrons

Chuanyun Xiao and Yingkai Zhang

J. Chem. Phys. 127, 124102 (2007); http://dx.doi.org/10.1063/1.2774980 (9 pages) | Cited 7 times

Online Publication Date: 24 September 2007

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A critical issue underlying the accuracy and applicability of the combined quantum mechanical/molecular mechanical (QM/MM) methods is how to describe the QM/MM boundary across covalent bonds. Inspired by the ab initio pseudopotential theory, here we introduce a novel design atom approach for a more fundamental and transparent treatment of this QM/MM covalent boundary problem. The main idea is to replace the boundary atom of the active part with a design atom, which has a different number of valence electrons but very similar atomic properties. By modifying the Troullier-Martins scheme, which has been widely employed to construct norm-conserving pseudopotentials for density functional calculations, we have successfully developed a design-carbon atom with five valence electrons. Tests on a series of molecules yield very good structural and energetic results and indicate its transferability in describing a variety of chemical bonds, including double and triple bonds.
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31.15.A- Ab initio calculations
31.15.E- Density-functional theory
31.15.xv Molecular dynamics and other numerical methods
31.15.xw Valence bond calculations

Orbital currents in the Colle-Salvetti correlation energy functional and the degeneracy problem

S. Pittalis, S. Kurth, S. Sharma, and E. K. U. Gross

J. Chem. Phys. 127, 124103 (2007); http://dx.doi.org/10.1063/1.2777140 (4 pages) | Cited 1 time

Online Publication Date: 25 September 2007

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Popular density functionals for the exchange-correlation energy typically fail to reproduce the degeneracy of different ground states of open-shell atoms. As a remedy, functionals which explicitly depend on the current density have been suggested. We present an analysis of this problem by investigating functionals that explicitly depend on the Kohn-Sham orbitals. Going beyond the exact-exchange approximation by adding correlation in the form of the Colle-Salvetti functional, we show how current-dependent terms enter the Colle-Salvetti expression and their relevance is evaluated. A very good description of the degeneracy of ground states for atoms of the first and second rows of the Periodic Table is obtained.
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31.15.E- Density-functional theory

Modified Morse potential for unification of the pair interactions

Longjiu Cheng and Jinlong Yang

J. Chem. Phys. 127, 124104 (2007); http://dx.doi.org/10.1063/1.2777148 (5 pages) | Cited 9 times

Online Publication Date: 26 September 2007

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We designed a novel model potential that unifies the pair interactions including the well known Morse and Lennard-Jones potentials. Using two parameters, the interactions at the minimum, short range, and long range of the new model potential can be controlled separately, so the potential is very flexible to fit various systems. It is found that for potentials with similar range with the Lennard-Jones potential at the minimum, due to the difference at the short and long ranges, the favorite structures can be very different, and some previously unknown magic numbers are located.
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34.20.Gj Intermolecular and atom-molecule potentials and forces
34.20.Cf Interatomic potentials and forces

Gaussian-4 theory using reduced order perturbation theory

Larry A. Curtiss, Paul C. Redfern, and Krishnan Raghavachari

J. Chem. Phys. 127, 124105 (2007); http://dx.doi.org/10.1063/1.2770701 (8 pages) | Cited 47 times

Online Publication Date: 26 September 2007

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Two modifications of Gaussian-4 (G4) theory [ L. A. Curtiss et al., J. Chem. Phys. 126, 084108 (2007) ] are presented in which second- and third-order perturbation theories are used in place of fourth-order perturbation theory. These two new methods are referred to as G4(MP2) and G4(MP3), respectively. Both methods have been assessed on the G3/05 test set of accurate experimental data. The average absolute deviation from experiment for the 454 energies in this test set is 1.04 kcal/mol for G4(MP2) theory and 1.03 kcal/mol for G4(MP3) theory compared to 0.83 kcal/mol for G4 theory. G4(MP2) is slightly more accurate for enthalpies of formation than G4(MP3) (0.99 versus 1.04 kcal/mol), while G4(MP3) is more accurate for ionization potentials and electron affinities. Overall, the G4(MP2) method provides an accurate and economical method for thermochemical predictions. It has an overall accuracy for the G3/05 test set that is much better than G3(MP2) theory (1.04 versus 1.39 kcal/mol) and even better than G3 theory (1.04 versus 1.13 kcal/mol). In addition, G4(MP2) does better for challenging hypervalent systems such as H2SO4 and for nonhydrogen species than G3(MP2) theory.
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31.15.xp Perturbation theory
32.50.+d Fluorescence, phosphorescence (including quenching)
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
82.60.Cx Enthalpies of combustion, reaction, and formation

Analyzing molecular properties calculated with two-component relativistic methods using spin-free natural bond orbitals: NMR spin-spin coupling constants

Jochen Autschbach

J. Chem. Phys. 127, 124106 (2007); http://dx.doi.org/10.1063/1.2768363 (11 pages) | Cited 15 times

Online Publication Date: 26 September 2007

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An analysis method for static linear response properties employing two-component (spin-orbit) relativistic density functional theory along with scalar relativistic “natural localized molecular orbitals” (NLMOs) and “natural bond orbitals” (NBOs) has been developed. The spin-orbit NLMO/NBO analysis has been applied to study the indirect spin-spin coupling (J-coupling) constants in Tl–I, PbH4, and a dinuclear Pt–Tl bonded complex with a very large Pt–Tl coupling constant (expt.: 146.8 kHz). For Tl–I it is shown that the analysis scheme based on scalar relativistic NLMOs is applicable even if spin-orbit coupling is responsible for most of the coupling’s magnitude. For PbH4 it is shown that electron delocalization plays a much larger role for the Pb–H coupling than it is the case for the C–H coupling in methane. For the Pt–Tl complex the analysis clearly demonstrates the strong influence of the ligands on the Pt–Tl coupling constant and quantifies the effect of the delocalization of the Pt–Tl bond on the Pt–Tl coupling constant.
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31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
31.15.E- Density-functional theory
33.25.+k Nuclear resonance and relaxation
33.15.Fm Bond strengths, dissociation energies
31.15.xp Perturbation theory

Quantum dynamics in macrosystems with several coupled electronic states: Hierarchy of effective Hamiltonians

Etienne Gindensperger and Lorenz S. Cederbaum

J. Chem. Phys. 127, 124107 (2007); http://dx.doi.org/10.1063/1.2778682 (13 pages) | Cited 8 times

Online Publication Date: 27 September 2007

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We address the nonadiabatic quantum dynamics of macrosystems with several coupled electronic states, taking into account the possibility of multistate conical intersections. The general situation of an arbitrary number of states and arbitrary number of nuclear degrees of freedom (modes) is considered. The macrosystem is decomposed into a system part carrying a few, strongly coupled modes and an environment, comprising the vast number of remaining modes. By successively transforming the modes of the environment, a hierarchy of effective Hamiltonians for the environment is constructed. Each effective Hamiltonian depends on a reduced number of effective modes, which carry cumulative effects. By considering the system’s Hamiltonian along with a few members of the hierarchy, it is shown mathematically by a moment analysis that the quantum dynamics of the entire macrosystem can be numerically exactly computed on a given time scale. The time scale wanted defines the number of effective Hamiltonians to be included. The contribution of the environment to the quantum dynamics of the macrosystem translates into a sequential coupling of effective modes. The wave function of the macrosystem is known in the full space of modes, allowing for the evaluation of observables such as the time-dependent individual excitation along modes of interest as well as spectra and electronic-population dynamics.
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31.10.+z Theory of electronic structure, electronic transitions, and chemical binding

A unified density-functional treatment of dynamical, nondynamical, and dispersion correlations

Axel D. Becke and Erin R. Johnson

J. Chem. Phys. 127, 124108 (2007); http://dx.doi.org/10.1063/1.2768530 (8 pages) | Cited 18 times

Online Publication Date: 27 September 2007

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In previous work we have introduced exact-exchange-based density-functional models of dynamical, nondynamical, and dispersion correlations. We have not yet, however, been able to combine these models into a single energy functional. The problem is that interaction curves in van der Waals complexes are too repulsive. A simple solution is proposed in the present work resulting in an exact-exchange-based energy functional for all chemical interactions, from the weakest (dispersion) to the strongest (molecular bonds).
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33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
31.15.E- Density-functional theory
33.15.Fm Bond strengths, dissociation energies

Trotter derivation of algorithms for Brownian and dissipative particle dynamics

Fabrice Thalmann and Jean Farago

J. Chem. Phys. 127, 124109 (2007); http://dx.doi.org/10.1063/1.2764481 (20 pages) | Cited 4 times

Online Publication Date: 28 September 2007

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This paper focuses on the temporal discretization of the Langevin dynamics, and on different resulting numerical integration schemes. Using a method based on the exponentiation of time dependent operators, we carefully derive a numerical scheme for the Langevin dynamics, which we found equivalent to the proposal of Ermak and Buckholtz [J. Comput. Phys. 35, 169 (1980)] and not simply to the stochastic version of the velocity-Verlet algorithm. However, we checked on numerical simulations that both algorithms give similar results, and share the same “weak order two” accuracy. We then apply the same strategy to derive and test two numerical schemes for the dissipative particle dynamics. The first one of them was found to compare well, in terms of speed and accuracy, with the best currently available algorithms.
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05.40.Jc Brownian motion
02.50.Ey Stochastic processes

Behavior of density functionals with respect to basis set. VI. Truncation of the correlation consistent basis sets

Brian P. Prascher, Brent R. Wilson, and Angela K. Wilson

J. Chem. Phys. 127, 124110 (2007); http://dx.doi.org/10.1063/1.2768602 (14 pages) | Cited 5 times

Online Publication Date: 28 September 2007

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Systematic truncation of the correlation consistent basis sets has been investigated in first and second row atoms and molecules to better understand basis set requirements for density functional theory, particularly the need for high angular momentum functions, as well as to understand possible computational cost savings that could be achieved by using reduced basis sets. The truncation scheme employed follows that recently introduced for ab initio methods [ B. Mintz et al., J. Chem. Phys. 121, 5629 (2004) ]. Properties examined in the current study include geometries, ionization potentials, electron affinities, and dissociation energies. In general, this investigation shows that a degree of truncation of higher angular momentum functions is possible with limited impact upon energetic properties, and does result in useful CPU time savings. However, not all properties investigated have the same level of dependence upon high angular momentum functions, and, thus, careful selection of truncated basis sets should be made.
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31.15.E- Density-functional theory
32.50.+d Fluorescence, phosphorescence (including quenching)
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Fm Bond strengths, dissociation energies
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Dianions of 7,7,8,8-tetracyano-p-quinodimethane and perfluorinated tetracyanoquinodimethane: Information on excited states from lifetime measurements in an electrostatic storage ring and optical absorption spectroscopy

Subhasis Panja, Umesh Kadhane, Jens Ulrik Andersen, Anne I. S. Holm, Preben Hvelplund, Maj-Britt Suhr Kirketerp, Steen Brøndsted Nielsen, Kristian Støchkel, Robert N. Compton, James S. Forster, Kristine Kilså, and Mogens Brøndsted Nielsen

J. Chem. Phys. 127, 124301 (2007); http://dx.doi.org/10.1063/1.2771177 (6 pages) | Cited 6 times

Online Publication Date: 24 September 2007

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We have developed an experimental technique that allows us to study the physics of short lived molecular dianions in the gas phase. It is based on the formation of monoanions via electrospray ionization, acceleration of these ions to keV energies, and subsequent electron capture in a sodium vapor cell. The dianions are stored in an electrostatic ion storage ring in which they circulate with revolution times on the order of 100 μs. This enables lifetime studies in a time regime covering five orders of magnitude, 10−5–1 s. We have produced dianions of 7,7,8,8-tetracyano-p-quinodimethane and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-p-quinodimethane (TCNQ-F4) and measured their lifetimes with respect to electron autodetachment. Our data indicate that most of the dianions were initially formed in electronically excited states in the electron transfer process. Two levels of excitation were identified by spectroscopy on the dianion of TCNQ-F4, and the absorption spectrum was compared with spectra obtained from spectroelectrochemistry of TCNQ-F4 in acetonitrile solution.
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33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
34.70.+e Charge transfer
33.80.Eh Autoionization, photoionization, and photodetachment

Permanent electric dipole moment of molybdenum carbide

Hailing Wang, Wilton L. Virgo, Jinhai Chen, and Timothy C. Steimle

J. Chem. Phys. 127, 124302 (2007); http://dx.doi.org/10.1063/1.2778427 (6 pages) | Cited 1 time

Online Publication Date: 24 September 2007

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High resolution optical spectroscopy has been used to study a molecular beam of molybdenum monocarbide (MoC). The Stark effect of the Re(0) and Qfe(1) branch features of the [18.6] 3Π1-X 3Σ−(0,0) band system of 98MoC were analyzed to determine the permanent electric dipole moments μe of 2.68(2) and 6.07(18) D for the [18.6] 3Π1(ν = 0) and X 3Σ−(ν = 0) states, respectively. The dipole moments are compared with the experimental value for ruthenium monocarbide [ T. C. Steimle et al., J. Chem. Phys. 118, 2620 (2003) ] and with theoretical predictions. A molecular orbital correlation diagram is used to interpret the observed and predicted trends of ground state μe values for the 4d-metal monocarbides series.
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33.50.Dq Fluorescence and phosphorescence spectra
33.57.+c Magneto-optical and electro-optical spectra and effects
31.15.-p Calculations and mathematical techniques in atomic and molecular physics
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Pair potential for helium from symmetry-adapted perturbation theory calculations and from supermolecular data

Małgorzata Jeziorska, Wojciech Cencek, Konrad Patkowski, Bogumił Jeziorski, and Krzysztof Szalewicz

J. Chem. Phys. 127, 124303 (2007); http://dx.doi.org/10.1063/1.2770721 (13 pages) | Cited 39 times

Online Publication Date: 25 September 2007

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Symmetry-adapted perturbation theory (SAPT) was applied to the helium dimer for interatomic separations R from 3 to 12 bohrs. The first-order interaction energy and the bulk of the second-order contribution were obtained using Gaussian geminal basis sets and are converged to about 0.1 mK near the minimum and for larger R. The remaining second-order contributions available in the SAPT suite of codes were computed using very large orbital basis sets, up to septuple-zeta quality, augmented by diffuse and midbond functions. The accuracy reached at this level was better than 1 mK in the same region. All the remaining components of the interaction energy were computed using the full configuration interaction method in bases up to sextuple-zeta quality. The latter components, although contributing only 1% near the minimum, have the largest uncertainty of about 10 mK in this region. The total interaction energy at R = 5.6 bohrs is −11.000±0.011 K. For R ⩽ 6.5 bohrs, the supermolecular (SM) interaction energies computed by us recently turned out to be slightly more accurate. Therefore, we have combined the SM results for R ⩽ 6.5 bohrs with the SAPT results from 7.0 to 12 bohrs to fit analytic functions for the potential and for its error bars. The potential fit uses the best available van der Waals constants C6 through C16, including C11, C13, and C15, and is believed to be the best current representation of the Born-Oppenheimer (BO) potential for helium. Using these fits, we found that the BO potential for the helium dimer exhibits the well depth De = 11.006±0.004 K, the equilibrium distance Re = 5.608±0.012 bohrs, and supports one bound state for math with the dissociation energy D0 = 1.73±0.04 mK, and the average interatomic separation 〈R〉 = 45.6±0.5 Å.
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34.20.Cf Interatomic potentials and forces
33.15.Fm Bond strengths, dissociation energies
31.15.xp Perturbation theory
31.15.V- Electron correlation calculations for atoms, ions and molecules
33.15.Bh General molecular conformation and symmetry; stereochemistry

Proton formation in 2+1 resonance enhanced multiphoton excitation of HCl and HBr via (Ω = 0) Rydberg and ion-pair states

Constantin Romanescu and Hans-Peter Loock

J. Chem. Phys. 127, 124304 (2007); http://dx.doi.org/10.1063/1.2767259 (13 pages) | Cited 8 times

Online Publication Date: 25 September 2007

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Molecular beam cooled HCl was state selected by two-photon excitation of the V 1∑(0+) [v = 9,11–13,15], E 1∑(0+) [v = 0], and g 3∑−(0+) [v = 0] states through either the Q(0) or Q(1) lines of the respective 1,3∑(0+)←←X 1∑(0+) transition. Similarly, HBr was excited to the V 1∑(0+) [v = m+3, m+5−m+8], E 1∑(0+) [v = 0], and H 1∑(0+) [v = 0] states through the Q(0) or Q(1) lines. Following absorption of a third photon, protons were formed by three different mechanisms and detected using velocity map imaging. (1) H*(n = 2) was formed in coincidence with 2Pi halogen atoms and subsequently ionized. For HCl, photodissociation into H*(n = 2)+Cl(2P1/2) was dominant over the formation of Cl(2P3/2) and was attributed to parallel excitation of the repulsive [(2) 2Π∙∙4lλ] superexcited (Ω = 0) states. For HBr, the Br(2P3/2)/Br(2P1/2) ratio decreases with increasing excitation energy. This indicates that both the [(3) 2Π1/2∙∙5lλ] and the [B 2∑∙∙5lλ] superexcited (Ω = 0) states contribute to the formation of H*(n = 2). (2) For selected intermediate states HCl was found to dissociate into the H++Cl− ion pair with over 20% relative yield. A mechanism is proposed by which a bound [A 2∑∙∙nlσ] 1∑(0+) superexcited state acts as a gateway state to dissociation into the ion pair. (3) For all intermediate states, protons were formed by dissociation of HX+[v+] following a parallel, ΔΩ = 0, excitation. The quantum yield for the dissociation process was obtained using previously reported photoionization efficiency data and was found to peak at v+ = 6–7 for HCl and v+ = 12 for HBr. This is consistent with excitation of the repulsive A2∑1/2 and (2) 2Π states of HCl+, and the (3) 2Π state of HBr+. Rotational alignment of the Ω = 0+ intermediate states is evident from the angular distribution of the excited H*(n = 2) photofragments. This effect has been observed previously and was used here to verify the reliability of the measured spatial anisotropy parameters.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.80.Gj Diffuse spectra; predissociation, photodissociation
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Probing coherence aspects of adiabatic quantum computation and control

Debabrata Goswami

J. Chem. Phys. 127, 124305 (2007); http://dx.doi.org/10.1063/1.2768954 (10 pages)

Online Publication Date: 25 September 2007

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Quantum interference between multiple excitation pathways can be used to cancel the couplings to the unwanted, nonradiative channels resulting in robustly controlling decoherence through adiabatic coherent control approaches. We propose a useful quantification of the two-level character in a multilevel system by considering the evolution of the coherent character in the quantum system as represented by the off-diagonal density matrix elements, which switches from real to imaginary as the excitation process changes from being resonant to completely adiabatic. Such counterintuitive results can be explained in terms of continuous population exchange in comparison to no population exchange under the adiabatic condition.
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42.50.-p Quantum optics
03.67.Lx Quantum computation architectures and implementations

Dissociation energy of the water dimer from quantum Monte Carlo calculations

I. G. Gurtubay and R. J. Needs

J. Chem. Phys. 127, 124306 (2007); http://dx.doi.org/10.1063/1.2770711 (8 pages) | Cited 15 times

Online Publication Date: 25 September 2007

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We report a study of the electronic dissociation energy of the water dimer using quantum Monte Carlo techniques. We have performed variational quantum Monte Carlo and diffusion quantum Monte Carlo (DMC) calculations of the electronic ground state of the water monomer and dimer using all-electron and pseudopotential approaches. We have used Slater-Jastrow trial wave functions with B3LYP type single-particle orbitals, into which we have incorporated backflow correlations. When backflow correlations are introduced, the total energy of the water monomer decreases by about 4–5 mhartree, yielding a DMC energy of −76.428 30(5) hartree, which is only 10 mhartree above the experimental value. In our pseudopotential DMC calculations, we have compared the total energies of the water monomer and dimer obtained using the locality approximation with those from the variational scheme recently proposed by Casula [Phys. Rev. B 74, 161102(R) (2006)] . The time step errors in the Casula scheme are larger, and the extrapolation of the energy to zero time step always lies above the result obtained with the locality approximation. However, the errors cancel when energy differences are taken, yielding electronic dissociation energies within error bars of each other. The dissociation energies obtained in our various all-electron and pseudopotential calculations range between 5.03(7) and 5.47(9) kcal/mol and are in good agreement with experiment. Our calculations give monomer dipole moments which range between 1.897(2) and 1.909(4) D and dimer dipole moments which range between 2.628(6) and 2.672(5) D.
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31.15.xt Variational techniques
33.15.Fm Bond strengths, dissociation energies
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Structure and properties of the low-lying electronic states of CeC2 and CeC2+

Pawel Wielgus, D. Majumdar, Szczepan Roszak, and Jerzy Leszczynski

J. Chem. Phys. 127, 124307 (2007); http://dx.doi.org/10.1063/1.2770698 (13 pages)

Online Publication Date: 26 September 2007

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Theoretical studies on the electronic and thermodynamic properties of several electronic states of CeC2 and CeC2+ have been carried out employing state-of-the-art single- and multireference techniques. The ground and the low-lying electronic states of these two species have been found to possess C2v triangular structures. A 3B2 state has been found to be the ground state of CeC2 while for CeC2+ 2A2 is the ground state. The computed electron ionization energy is in excellent agreement with experiment. The experimentally observed thermodynamic properties (dissociation and atomization energies) of reactions involving CeC2 dissociation are corrected using the computed gas-phase properties of the molecule and the partition functions. The bent triplet and singlet state of CeC2 exhibit large dipole moments (7.0–10.5 D) and it is consistent with the ionic character (through dative charge transfer) of the cluster in ground and excited states.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Fm Bond strengths, dissociation energies
82.60.-s Chemical thermodynamics
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

A Fock space coupled cluster study on the electronic structure of the UO2, UO2+, U4+, and U5+ species

Ivan Infante, Ephraim Eliav, Marius J. Vilkas, Yasuyuki Ishikawa, Uzi Kaldor, and Lucas Visscher

J. Chem. Phys. 127, 124308 (2007); http://dx.doi.org/10.1063/1.2770699 (12 pages) | Cited 15 times

Online Publication Date: 26 September 2007

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The ground and excited states of the UO2 molecule have been studied using a Dirac-Coulomb intermediate Hamiltonian Fock-space coupled cluster approach (DC-IHFSCC). This method is unique in describing dynamic and nondynamic correlation energies at relatively low computational cost. Spin-orbit coupling effects have been fully included by utilizing the four-component Dirac-Coulomb Hamiltonian from the outset. Complementary calculations on the ionized systems UO2+ and UO22+ as well as on the ions U4+ and U5+ were performed to assess the accuracy of this method. The latter calculations improve upon previously published theoretical work. Our calculations confirm the assignment of the ground state of the UO2 molecule as a 3Φ2u state that arises from the 5f17s1 configuration. The first state from the 5f2 configuration is found above 10 000 cm−1, whereas the first state from the 5f16d1 configuration is found at 5 047 cm−1.
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31.15.bw Coupled-cluster theory
31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions

Dissociative recombination of H3+ in the ground and excited vibrational states

Samantha Fonseca dos Santos, Viatcheslav Kokoouline, and Chris H. Greene

J. Chem. Phys. 127, 124309 (2007); http://dx.doi.org/10.1063/1.2784275 (8 pages) | Cited 35 times

Online Publication Date: 27 September 2007

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The article presents calculated dissociative recombination (DR) rate coefficients for H3+. The previous theoretical work on H3+ was performed using the adiabatic hyperspherical approximation to calculate the target ion vibrational states and it considered just a limited number of ionic rotational states. In this study, we use accurate vibrational wave functions and a larger number of possible rotational states of the H3+ ground vibrational level. The DR rate coefficient obtained is found to agree better with the experimental data from storage ring experiments than the previous theoretical calculation. We present evidence that excited rotational states could be playing an important role in those experiments for collision energies above 10 meV. The DR rate coefficients calculated separately for ortho- and para-H3+ are predicted to differ significantly at low energy, a result consistent with a recent experiment. We also present DR rate coefficients for vibrationally excited initial states of H3+, which are found to be somewhat larger than the rate coefficient for the ground vibrational level.
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33.15.Mt Rotation, vibration, and vibration-rotation constants
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.37.Np Single molecule reaction kinetics, dissociation, etc.
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies

Vibrational state dependence of β and D asymmetry parameters: The case of the highest occupied molecular orbital photoelectron spectrum of methyl-oxirane

G. Contini, N. Zema, S. Turchini, D. Catone, T. Prosperi, V. Carravetta, P. Bolognesi, L. Avaldi, and V. Feyer

J. Chem. Phys. 127, 124310 (2007); http://dx.doi.org/10.1063/1.2779324 (7 pages) | Cited 3 times

Online Publication Date: 27 September 2007

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The β angular asymmetry and D dichroic asymmetry parameters of the methyl-oxirane highest occupied molecular orbital (HOMO) band have been experimentally investigated with vibrational resolution using synchrotron radiation. A theoretical calculation of the Franck-Condon factors between vibrational ground state and different ionic vibrational states, in the Born-Oppenheimer harmonic approximation, has been performed in order to gain information on the vibrational states mainly involved in the HOMO photoelectron band. The general good agreement between theoretical and experimental results allows a reliable assignment of the major features. The experimental determination of β and D shows their dependence on the different final vibrational states. This paper reports, for the first time, experimental evidence of the dependence of the dichroic D parameter on the vibrational excitation of the ion.
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33.55.+b Optical activity and dichroism
33.57.+c Magneto-optical and electro-optical spectra and effects
33.60.+q Photoelectron spectra
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.20.Tp Vibrational analysis

Molecular beam optical Stark study of the [18.1] 2Π1/2-X 4Σ1/2− band system of rhodium monosulfide

Tongmei Ma, Hailing Wang, and Timothy C. Steimle

J. Chem. Phys. 127, 124311 (2007); http://dx.doi.org/10.1063/1.2778683 (6 pages)

Online Publication Date: 27 September 2007

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The optical Stark effect in the RR13(0.5) branch feature of the [18.1] 2Π1/2-X 4Σ1/2− (v′,v″ = 0) band of rhodium monosulfide (RhS) has been recorded and analyzed to determine the permanent electric dipole moment μe of 3.40(2) D for the ground X 4Σ1/2− (v = 0) state and an upper limit of 1.5 D for the [18.1] 2Π1/2 state. Molecular orbital correlation diagrams are used to interpret the relative values of μe for RhN, RhO, and RhS. The 103Rh(I = 1/2) magnetic hyperfine interaction in the X 4Σ1/2− and [18.1] 2Π1/2 states is analyzed.
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33.57.+c Magneto-optical and electro-optical spectra and effects
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Controlling the dissociative ionization of ethanol with 800 and 400 nm two-color femtosecond laser pulses

H. Yazawa, T. Shioyama, Y. Suda, M. Yamanaka, F. Kannari, R. Itakura, and K. Yamanouchi

J. Chem. Phys. 127, 124312 (2007); http://dx.doi.org/10.1063/1.2780156 (5 pages) | Cited 1 time

Online Publication Date: 27 September 2007

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Ethanol molecules were irradiated with a pair of temporally overlapping ultrashort intense laser pulses (1013–1014 W/cm2) with different colors of 400 and 800 nm, and the dissociative ionization processes have been investigated. The yield ratio of the C–O bond breaking with respect to the C–C bond breaking was varied in the range of 0.17–0.53 sensitively depending on the delay time between the two laser pulses, and the absolute value of the yield of the C–O bond breaking was found to be increased largely when the Fourier-transform limited 800 nm laser pulse overlaps the stretched 400 nm laser pulse, demonstrating an advantage of the two-color intense laser fields in controlling chemical bond breaking processes.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.50.-m Photochemistry
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