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7 Jul 2007

Volume 127, Issue 1, Articles (01xxxx)

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Announcement: New Interim Editor Appointed

H. Frederick Dylla

J. Chem. Phys. 127, 010201 (2007); http://dx.doi.org/10.1063/1.2759507 (1 page)

Online Publication Date: 3 July 2007

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back to top Theoretical Methods and Algorithms

Computation and interpretation of molecular Omega intracules

Deborah L. Crittenden and Peter M. W. Gill

J. Chem. Phys. 127, 014101 (2007); http://dx.doi.org/10.1063/1.2746028 (9 pages) | Cited 14 times

Online Publication Date: 2 July 2007

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The Omega intracule is a three-dimensional function that describes the relative positions, momenta, and directions of motion of pairs of electrons in a system. In this paper, we describe the computation of the Omega intracule for a molecular system whose electronic wave function is expanded in a Gaussian basis set. This is followed by implementation details and numerical tests. Finally, we use the Omega intracules of a number of small systems to illustrate the power of this function to extract simple physical insights from complicated wave functions.
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31.10.+z Theory of electronic structure, electronic transitions, and chemical binding

Perturbative treatment of the electron-correlation contribution to the diagonal Born-Oppenheimer correction

Attila Tajti, Péter G. Szalay, and Jürgen Gauss

J. Chem. Phys. 127, 014102 (2007); http://dx.doi.org/10.1063/1.2744014 (8 pages) | Cited 9 times

Online Publication Date: 2 July 2007

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A perturbative scheme for the treatment of electron-correlation effects on the diagonal Born-Oppenheimer correction (DBOC) is suggested. Utilizing the usual Møller-Plesset partitioning of the Hamiltonian formulas for first and second orders (termed as MP1 and MP2) are obtained by expanding the wave function in the corresponding coupled-cluster expressions for the DBOC[ J. Gauss et al., J. Chem. Phys. 125, 144111 (2006) ]. The obtained expressions are recast in terms of one- and two-particle density matrices in order to take advantage of existing analytic second-derivative implementations for many-body methods. Test calculations show that both MP1 and MP2 recover large fractions (on average 90% and 95%, respectively) of the coupled-cluster singles and doubles (CCSD) electron-correlation corrections to the DBOC and thus render the suggested MP treatments cost-effective (though still accurate) alternatives to high-level coupled cluster (CC) treatments. The applicability of the MP1 and MP2 schemes for treating DBOC is demonstrated in calculations for the atomization energies of benzene, naphthalene, anthracene, and tetracene. The corresponding corrections are surprisingly large (about 0.6 kJ/mol for benzene, 1.1 kJ/mol for naphthalene, 1.5 kJ/mol for anthracene, and 1.8 kJ/mol for tetracene) with the electron-correlation corrections reducing the corresponding Hartree-Fock self-consistent field values by 25%–30%.
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31.15.V- Electron correlation calculations for atoms, ions and molecules
31.15.bw Coupled-cluster theory
31.15.xr Self-consistent-field methods

Using redundant coordinates to represent potential energy surfaces with lower-dimensional functions

Sergei Manzhos and Tucker Carrington, Jr.

J. Chem. Phys. 127, 014103 (2007); http://dx.doi.org/10.1063/1.2746846 (10 pages) | Cited 26 times

Online Publication Date: 2 July 2007

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We propose a method for fitting potential energy surfaces with a sum of component functions of lower dimensionality. This form facilitates quantum dynamics calculations. We show that it is possible to reduce the dimensionality of the component functions by introducing new and redundant coordinates obtained with linear transformations. The transformations are obtained from a neural network. Different coordinates are used for different component functions and the new coordinates are determined as the potential is fitted. The quality of the fits and the generality of the method are illustrated by fitting reference potential surfaces of hydrogen peroxide and of the reaction OH+H2→H2O+H.
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82.20.Ej Quantum theory of reaction cross section
82.20.Kh Potential energy surfaces for chemical reactions
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
31.50.-x Potential energy surfaces

Ab initio electron propagators in molecules with strong electron-phonon interaction: II. Electron Green’s function

Yuri Dahnovsky

J. Chem. Phys. 127, 014104 (2007); http://dx.doi.org/10.1063/1.2749511 (11 pages) | Cited 3 times

Online Publication Date: 2 July 2007

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Ab initio electron propagator methods are developed to study electronic properties of molecular systems with strong electron-electron and electron-phonon interactions. For the calculation of electron Green’s functions we apply a canonical small polaron transformation that intrinsically contains strong electron-phonon effects. In the transformed Hamiltonian, the energy levels for the noninteracting particles are shifted down by the relaxation (solvation) energies. The Coulomb integrals are also renormalized by the electron-phonon interaction. For certain values of the electron-phonon coupling constants, the renormalized Coulomb integrals can be negative which implies the attraction between two electrons. Within the small polaron transformation we develop a diagrammatic technique for the calculation of electron Green’s function in which the electron-phonon interaction is already included into the multiple phonon correlation functions. Since the decoupling of the phonon correlation functions is impossible, and therefore, a Wick’s theorem for such correlation functions is invalid, there is no Dyson equation for the electron Green’s function. To find the electron Green’s function, we use different approximations. One of them is a link-cluster approximation that includes diagonal transitions for the renormalized zeroth Green’s function. In the linked-cluster approach the Dyson equation is derived in the most general case, where the self-energy operator is an arbitrary functional (not only in the Hartree-Fock approximation). It is shown that even a Hartree-Fock electron (hole) is not a particle any longer. It is a quasiparticle with a finite lifetime that depends on energy of particle and hole states in different ways. As a consequence of this, a standard description of a Hartree-Fock approximation in terms of wave functions becomes inappropriate in this problem. To challenge the linked-cluster approximation we develop a different approach: a sequential propagation approximation where scattering events occur only for sequential transitions. A self-consistent Hartree-Fock equation for a four-index Green’s function matrix is derived. In conclusion, the proposed schemes can be considered for future method developments for quantum chemical calculations for large molecules with strong nonadiabatic effects, e-e correlated electron transfer reactions, and electron transport in molecular transport junctions.
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71.38.-k Polarons and electron-phonon interactions
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.30.Nr Association, addition, insertion, cluster formation

Weak binding between two aromatic rings: Feeling the van der Waals attraction by quantum Monte Carlo methods

Sandro Sorella, Michele Casula, and Dario Rocca

J. Chem. Phys. 127, 014105 (2007); http://dx.doi.org/10.1063/1.2746035 (12 pages) | Cited 22 times

Online Publication Date: 2 July 2007

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We report a systematic study of the weak chemical bond between two benzene molecules. We first show that it is possible to obtain a very good description of the C2 dimer and the benzene molecule by using pseudopotentials for the chemically inert 1s electrons and a resonating valence bond wave function as a variational ansatz, expanded on a relatively small Gaussian basis set. We employ an improved version of the stochastic reconfiguration technique to optimize the many-body wave function, which is the starting point for highly accurate simulations based on the lattice regularized diffusion Monte Carlo method. This projection technique provides a rigorous variational upper bound for the total energy, even in the presence of pseudopotentials, and substantially improves the accuracy of the trial wave function, which already yields a large fraction of the dynamical and nondynamical electron correlation. We show that the energy dispersion of two benzene molecules in the parallel displaced geometry is significantly deeper than the face-to-face configuration. However, contrary to previous studies based on post-Hartree-Fock methods, the binding energy remains weak ( ≃ 2 kcal/mol) also in this geometry, and its value is in agreement with the most accurate and recent experimental findings [ H. Krause et al., Chem. Phys. Lett. 184, 411 (1991) ].
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34.20.Cf Interatomic potentials and forces
33.15.Fm Bond strengths, dissociation energies
31.15.vq Electron correlation calculations for polyatomic molecules

New results from the contact theorem for the charge profile for symmetric electrolytes

M. Holovko, J. P. Badiali, and D. di Caprio

J. Chem. Phys. 127, 014106 (2007); http://dx.doi.org/10.1063/1.2750336 (3 pages) | Cited 9 times

Online Publication Date: 2 July 2007

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In this paper the contact value of the charge profile at a charged interface is presented as the sum of the normal component of the Maxwell electrostatic tensor and a new electrostatic property defined by the integral from the product of the gradient of the electrical potential and the singlet distribution function of coions (ions with sign of the charge equal to that of the interface). On physical arguments, it is conjectured that this new property is a monotonic function of the electrical charge at the wall and is limited by the bulk electrolyte pressure for large electrical charges at the wall. Using the contact theorems for the density and the charge profiles, the exact expressions for the contact values of the profiles of coions and counterions are derived and some related general properties are discussed.
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82.45.Gj Electrolytes
41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems

Efficient calculation of van der Waals dispersion coefficients with time-dependent density functional theory in real time: Application to polycyclic aromatic hydrocarbons

Miguel A. L. Marques, Alberto Castro, Giuliano Malloci, Giacomo Mulas, and Silvana Botti

J. Chem. Phys. 127, 014107 (2007); http://dx.doi.org/10.1063/1.2746031 (6 pages) | Cited 9 times

Online Publication Date: 5 July 2007

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The van der Waals dispersion coefficients of a set of polycyclic aromatic hydrocarbons, ranging in size from the single-cycle benzene to circumovalene (C66H20), are calculated with a real-time propagation approach to time-dependent density functional theory (TDDFT). In the nonretarded regime, the Casimir-Polder integral is employed to obtain C6, once the dynamic polarizabilities have been computed at imaginary frequencies with TDDFT. On the other hand, the numerical coefficient that characterizes the fully retarded regime is obtained from the static polarizabilities. This ab initio strategy has favorable scaling with the size of the system—as demonstrated by the size of the reported molecules—and can be easily extended to obtain higher order van der Waals coefficients.
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31.15.E- Density-functional theory
34.20.Cf Interatomic potentials and forces
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.A- Ab initio calculations

New method for calculating bound states: The A1 states of Li3 on the spin-aligned Li3(1 4A′) potential energy surface

Xuan Li, Daniel A. Brue, and Gregory A. Parker

J. Chem. Phys. 127, 014108 (2007); http://dx.doi.org/10.1063/1.2753157 (9 pages) | Cited 2 times

Online Publication Date: 6 July 2007

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In this paper, we present a calculation for the bound states of A1 symmetry on the spin-aligned Li3(1 4A′) potential energy surface. We apply a mixture of discrete variable representation and distributed approximating functional methods to discretize the Hamiltonian. We also introduce a new method that significantly reduces the computational effort needed to determine the lowest eigenvalues and eigenvectors (bound state energies and wave functions of the full Hamiltonian). In our study, we have found the lowest 150 energy bound states converged to less than 0.005% error, and most of the excited energy bound states converged to less than 2.0% error. Furthermore, we have estimated the total number of the A1 bound states of Li3 on the spin-aligned Li3(1 4A′) potential surface to be 601.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics
31.50.Df Potential energy surfaces for excited electronic states

New parametrization method for dissipative particle dynamics

Karl P. Travis, Mark Bankhead, Kevin Good, and Scott L. Owens

J. Chem. Phys. 127, 014109 (2007); http://dx.doi.org/10.1063/1.2746325 (12 pages) | Cited 8 times

Online Publication Date: 6 July 2007

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We introduce an improved method of parametrizing the Groot-Warren version of dissipative particle dynamics (DPD) by exploiting a correspondence between DPD and Scatchard-Hildebrand regular solution theory. The new parametrization scheme widens the realm of applicability of DPD by first removing the restriction of equal repulsive interactions between like beads, and second, by relating all conservative interactions between beads directly to cohesive energy densities. We establish the correspondence by deriving an expression for the Helmoltz free energy of mixing, obtaining a heat of mixing which is exactly the same form as that for a regular mixture (quadratic in the volume fraction) and an entropy of mixing which reduces to the ideal entropy of mixing for equal molar volumes. We equate the conservative interaction parameters in the DPD force law to the cohesive energy densities of the pure fluids, providing an alternative method of calculating the self-interaction parameters as well as a route to the cross interaction parameter. We validate the new parametrization by modeling the binary system SnI4/SiCl4, which displays liquid-liquid coexistence below an upper critical solution temperature around 140 °C. A series of DPD simulations were conducted at a set of temperatures ranging from 0 °C to above the experimental upper critical solution temperature using conservative parameters based on extrapolated experimental data. These simulations can be regarded as being equivalent to a quench from a high temperature to a lower one at constant volume. Our simulations recover the expected phase behavior ranging from solid-liquid coexistence to liquid-liquid coexistence and eventually leading to a homogeneous single phase system. The results yield a binodal curve in close agreement with the one predicted using regular solution theory, but, significantly, in closer agreement with actual solubility measurements.
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64.75.-g Phase equilibria
64.70.Ja Liquid-liquid transitions
65.20.-w Thermal properties of liquids
61.20.Gy Theory and models of liquid structure
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Space-time contours to treat intense field-dressed molecular states. I. Theory

Biplab Sarkar, Satrajit Adhikari, and Michael Baer

J. Chem. Phys. 127, 014301 (2007); http://dx.doi.org/10.1063/1.2743437 (9 pages) | Cited 3 times

Online Publication Date: 2 July 2007

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A molecular system exposed to an intense external field is considered. The strength of the field is measured by the number L of electronic states that become populated during this process. In the present article the authors discuss a rigorous way, based on the recently introduced space-time contours [ R. Baer, et al., J. Chem. Phys. 119, 6998 (2003) ], to form N coupled Schrödinger equations where N<L, which maintains the effects due to the remaining (L−N) populated states. It is shown that whereas the size of L is unlimited, the main requirement concerning N is that the original group of N field-free states forms a Hilbert subspace in the spatial region of interest. From previous studies it is known that a group of states forms a Hilbert subspace if and only if the corresponding topological D matrix is diagonal [ M. Baer, et al., Farad, Discuss 127, 337 (2004) ].
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33.80.-b Photon interactions with molecules
31.15.-p Calculations and mathematical techniques in atomic and molecular physics

Space-time contours to treat intense field-dressed molecular states. II. Applications

Biplab Sarkar, Satrajit Adhikari, and Michael Baer

J. Chem. Phys. 127, 014302 (2007); http://dx.doi.org/10.1063/1.2743438 (12 pages)

Online Publication Date: 2 July 2007

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This second article in the two back-to-back articles presents a numerical application to support and strengthen two theoretical findings extensively discussed in the previous article (article I). In I, we found that introducing the space-time contours enables to distinguish between N, the number of nuclear Schrödinger equations to be solved, and L, the number of field-free states that become populated by the external field (in the ordinary, perturbative approaches this distinction is not apparent). In the numerical study we show, employing the electronic transition probability matrix P(s,t) [which closely is related to the transformation matrix ω(s,t)—see Eqs. (21) and (25) in I], that the N = L case is rare and in most cases we have N<L. Since the perturbative approach can be shown to follow when N = L (see Sec. III C in I) the numerical study implies that in most cases the perturbative approach is not reliable. The second issue that is studied is related to the diabatization process. It is shown, numerically, that the N<L case, in general, does not lead to field-dressed diabatic potentials which are single valued. However, if N is chosen to be identical to the number of field-free states that yield field-free single-valued diabatic potentials in a given spatial region then the corresponding N field-dressed states also yield single-valued (field-dressed) diabatic potentials. This result is independent of L. The numerical study is carried out for an eigenvalue problem based on the Mathieu equation.
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33.80.-b Photon interactions with molecules
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
31.15.-p Calculations and mathematical techniques in atomic and molecular physics

Ab initio molecular orbital study of ground and low-lying electronic states of CoCN

Tsuneo Hirano, Rei Okuda, Umpei Nagashima, and Per Jensen

J. Chem. Phys. 127, 014303 (2007); http://dx.doi.org/10.1063/1.2723110 (7 pages) | Cited 2 times

Online Publication Date: 2 July 2007

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The ground and low-lying excited states of CoCN have been studied by ab initio multireference single and double excitation configuration interaction (MR-SDCI) calculations with Davidson’s correction Q and Cowan-Griffin’s relativistic corrections. The electronic ground state of CoCN is 3Φi and the equilibrium geometry is linear with bond lengths of re(Co–C) = 1.8540 Å and re(C–N) = 1.1677 Å, substantially different from the experimentally derived values of r0(Co–C) = 1.8827(7) Å and r0(C–N) = 1.1313(10) Å. The first excited state is 3Δi, separated from the ground state by 727 cm−1. Larger dynamical electron correlation energy for the low-spin 3Φ state than for the high-spin 5Φ state makes the 3Φ state to be the ground state, which is discussed in terms of the differences in natural orbitals. A new spin-orbit interaction scheme between the math 3Φi and 1 3Δi states is proposed.
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31.15.A- Ab initio calculations
31.15.vj Electron correlation calculations for atoms and ions: excited states
31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Dj Interatomic distances and angles

Production yields of H(D) atoms in the reactions of N2(A 3Σu+) with C2H2, C2H4, and their deuterated variants

Hironobu Umemoto

J. Chem. Phys. 127, 014304 (2007); http://dx.doi.org/10.1063/1.2746851 (7 pages) | Cited 4 times

Online Publication Date: 2 July 2007

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The production yields of H(D) atoms in the reactions of N2(A 3Σu+) with C2H2, C2H4, and their deuterated variants were determined. N2(A 3Σu+) was produced by excitation transfer between Xe(6s[3/2]1) and ground-state N2 followed by collisional relaxation. Xe(6s[3/2]1) was produced by two-photon laser excitation of Xe(6p[1/2]0) followed by concomitant amplified spontaneous emission. H(D) atoms were detected by using vacuum-ultraviolet laser-induced fluorescence (LIF). The H(D)-atom yields were evaluated from the LIF intensities and the overall rate constants for the quenching, which were determined from the temporal profiles of the NO tracer emission. The absolute yields were evaluated by assuming that the yield for NH3(ND3) is 0.9. Although no H/D isotope effects were observed in the overall rate constants, there were isotope effects in the H(D)-atom yields. The H-atom yields for C2H2 and C2H4 were 0.52 and 0.30, respectively, while the D-atom yields for C2D2 and C2D4 were 0.33 and 0.13, respectively. The presence of isotope effects in yields suggests that H2(D2) molecular elimination processes are competing and that molecular elimination is more dominant in deuterated species than in hydrides.
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82.80.Dx Analytical methods involving electronic spectroscopy
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.20.Tr Kinetic isotope effects including muonium
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions

Dissociative recombination study of N3+: Cross section and branching fraction measurements

V. Zhaunerchyk, W. D. Geppert, E. Vigren, M. Hamberg, M. Danielsson, M. Larsson, R. D. Thomas, M. Kaminska, and F. Österdahl

J. Chem. Phys. 127, 014305 (2007); http://dx.doi.org/10.1063/1.2747601 (5 pages) | Cited 5 times

Online Publication Date: 2 July 2007

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We report an investigation into the dissociative recombination of the azide radical cation, N3+. The reaction rate constant has been measured to be 6.47×10−7 cm3 s−1 at room temperature. This value is smaller than those reported earlier for the ion-electron neutralization of N3+ at nitrogen atmospheric pressure. A strong propensity to dissociate through the N2+N channel has been observed.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions

In search of definitive signatures of the elusive NCCO radical

Andrew C. Simmonett, Francesco A. Evangelista, Wesley D. Allen, and Henry F. Schaefer, III

J. Chem. Phys. 127, 014306 (2007); http://dx.doi.org/10.1063/1.2747241 (9 pages) | Cited 10 times

Online Publication Date: 2 July 2007

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Previous experimental assignments of the fundamental vibrational frequencies of NCCO have been brought into question by subsequent unsuccessful attempts to observe IR signatures of this radical at these frequencies. Here we compute the fundamental vibrational frequencies by applying second-order vibrational perturbation theory to the complete quartic force field computed at the all-electron (AE) coupled cluster singles, doubles, and perturbative triples level [CCSD(T)] with the correlation-consistent, polarized core-valence quadruple-zeta (cc-pCVQZ) basis set, which has tight functions to correctly describe core correlation. The AE-CCSD(T)/cc-pCVQZ geometric parameters are re(N–C) = 1.1623 Å, re(C–C) = 1.4370 Å, re(C–O) = 1.1758 Å, θe(N–C–C) = 168.55°, and θe(C–C–O) = 132.22°. Our CCSD(T)/cc-pCVQZ values of the characteristic stretching frequencies ν1 and ν2 are 2171 and 1898 cm−1, respectively, in stark contrast to the experimentally derived values of 2093 and 1774 cm−1. Finally, focal-point extrapolations using correlation-consistent basis sets cc-pVXZ (X = D,T,Q,5,6) and electron correlation treatments as extensive as full coupled cluster singles, doubles, and triples (CCSDT) with perturbative accounting of quadruple excitations [CCSDT(Q)] determine the vibrationless barrier to linearity of NCCO and the dissociation energy (D0) of NCCO→NC+CO to be 8.4 and 26.5 kcal mol−1, respectively. Using our precisely determined dissociation energy, we recommend a new 0 K enthalpy of formation for NCCO of 50.9±0.3 kcal mol−1.
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33.20.Tp Vibrational analysis
31.15.bw Coupled-cluster theory
33.15.Fm Bond strengths, dissociation energies
33.15.Bh General molecular conformation and symmetry; stereochemistry

OH3− and O2H5− double Rydberg anions: Predictions and comparisons with NH4− and N2H7−

Junia Melin and J. V. Ortiz

J. Chem. Phys. 127, 014307 (2007); http://dx.doi.org/10.1063/1.2741558 (7 pages) | Cited 4 times

Online Publication Date: 2 July 2007

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A low barrier in the reaction pathway between the double Rydberg isomer of OH3− and a hydride-water complex indicates that the former species is more difficult to isolate and characterize through anion photoelectron spectroscopy than the well known double Rydberg anion (DRA), tetrahedral NH4−. Electron propagator calculations of vertical electron detachment energies (VEDEs) and isosurface plots of the electron localization function disclose that the transition state’s electronic structure more closely resembles that of the DRA than that of the hydride-water complex. Possible stabilization of the OH3− DRA through hydrogen bonding or ion-dipole interactions is examined through calculations on O2H5− species. Three O2H5− minima with H−(H2O)2, hydrogen-bridged, and DRA-molecule structures resemble previously discovered N2H7− species and have well separated VEDEs that may be observable in anion photoelectron spectra.
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82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
82.20.-w Chemical kinetics and dynamics

H3+ as a trap for noble gases - 2: structure and energetics of XH3+ complexes from X = neon to xenon

F. Pauzat and Y. Ellinger

J. Chem. Phys. 127, 014308 (2007); http://dx.doi.org/10.1063/1.2746033 (13 pages) | Cited 7 times

Online Publication Date: 3 July 2007

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The affinity of H3+ to combine with noble gases X has been investigated from neon to xenon using ab initio coupled cluster [CCSD and CCSD(T)] and density functional BH&HLYP levels of theory. For all noble gases, the stable structures belong to a C2v symmetry with an apex of the H3+ triangle pointing to the noble gas. The structure of the complexes changes gradually from a practically pure Ne–H3+ arrangement to a situation close to XeH+–H2. A topological analysis of the electron localization function is used to illustrate the changes in the bonding along the series. The lowest dissociation energies of NeH3+ and ArH3+ ( ∼ 1 and ∼ 7 kcal/mol) correspond to the breaking of the complexes according to X+H3+, while the lowest dissociation energies of KrH3+ and XeH3+ ( ∼ 8 and ∼ 3 kcal/mol) correspond to the breaking according to XH++H2. Rotational constants and harmonic frequencies are reported. Apart from XeH3+ whose dipole moment (μ = 2.6 D) may not be large enough, all the other complexes with dipole moments in the range of 6–8 D should be reasonable targets for detection by microwave spectroscopy. The present calculations are intended to stimulate both laboratory experiments and spatial observations since the possible sequestration of noble gases by H3+ may have strong implications on the composition of astrophysical objects.
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31.15.A- Ab initio calculations
31.15.bw Coupled-cluster theory
31.15.E- Density-functional theory
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Fm Bond strengths, dissociation energies
33.20.Bx Radio-frequency and microwave spectra

Ground and asymmetric CO-stretch excited state tunneling splittings in the formic acid dimer

I. Matanović, N. Došlić, and O. Kühn

J. Chem. Phys. 127, 014309 (2007); http://dx.doi.org/10.1063/1.2748048 (7 pages) | Cited 9 times

Online Publication Date: 5 July 2007

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There has been some controversy concerning the assignment of measured tunneling splittings for the formic acid dimer in the vibrational ground state and the asymmetric CO-stretching excited state. The discussion is intimately related to the question whether the fundamental excitation of the CO-vibration promotes or hinders tunneling. Here we will address this issue on the basis of a five-dimensional reaction space Hamiltonian which includes three large amplitude coordinates as well as two harmonic modes whose linear superposition reproduces the asymmetric CO-vibrational mode. Within density functional theory using the B3LYP functional together with a 6-311++G(3df,3pd) basis set we obtain a ground state tunneling splitting which is about 2.4 larger than the one for the CO-stretching excited state.
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33.20.Tp Vibrational analysis
31.15.E- Density-functional theory
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Mt Rotation, vibration, and vibration-rotation constants

Photoionization of C4 molecular beam: Ab initio calculations

Majdi Hochlaf, Christophe Nicolas, and Lionel Poisson

J. Chem. Phys. 127, 014310 (2007); http://dx.doi.org/10.1063/1.2746032 (6 pages) | Cited 8 times

Online Publication Date: 5 July 2007

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Large computations are performed on the C4+ cation in order to characterize its stable isomers and its lowest electronic excited states using configuration interaction methods and large basis sets. Several stable isomers are found including a linear C4+(l-C4+), a rhombic C4+(r-C4+) (or cyclic), and a branched (d-C4+) structure. Our calculations show a high density of electronic states for all of these isomers favoring their interactions. By combining the present ab initio data and those on neutral C4, the l-C4(math)+hν→l-C4+(math+)+e−, d-C4(math)+hν→d-C4+(math+)+e−, and r-C4(math)+hν→r-C4+(math+)+e− vertical photoionization transition energies are computed at 10.87, 10.92, and 10.77 eV, respectively. Photoionizing a C4 molecular beam results on an onset at 10.4–10.5 eV and then to a linear increase of the signal due to the opening of several ionization channels involving most of the C4 and C4+ isomers and electronic states.
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31.15.A- Ab initio calculations
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
31.15.vq Electron correlation calculations for polyatomic molecules
36.40.Wa Charged clusters
33.80.Eh Autoionization, photoionization, and photodetachment

Rotationally resolved spectra of jet-cooled VMo

Ramya Nagarajan, Shane M. Sickafoose, and Michael D. Morse

J. Chem. Phys. 127, 014311 (2007); http://dx.doi.org/10.1063/1.2747617 (8 pages) | Cited 1 time

Online Publication Date: 5 July 2007

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The authors report the first gas-phase spectroscopic investigation of diatomic vanadium molybdenum (VMo). The molecules were produced by laser ablation of a VMo alloy disk and cooled in a helium supersonic expansion. The jet-cooled VMo molecules were studied using resonant two-photon ionization spectroscopy. The ground state has been demonstrated to be of 2Δ5/2 symmetry, deriving from the dσ2dπ4dδ3sσ2 electronic configuration. Rotational analysis has established the ground state bond length and rotational constant as r0″ = 1.876 57(23) Å and B0″ = 0.142 861(35) cm−1, respectively, for 51V98Mo (1σ error limits). Transitions to states with Ω′ = 2.5, Ω′ = 3.5, and Ω′ = 1.5 have been recorded and rotationally analyzed. A band system originating at 15 091 cm−1 has been found to exhibit a vibrational progression with ωe′ = 752.7 cm−1, ωe′xe′ = 12.8 cm−1, and r0′ = 1.90 Å for 51V98Mo. The measured bond lengths (r0) of V2, VNb, Nb2, Cr2, CrMo, Mo2, VCr, NbCr, and VMo have been used to derive multiple bonding radii for these elements of r(V) = 0.8919 Å, r(Nb) = 1.0424 Å, r(Cr) = 0.8440 Å, and r(Mo) = 0.9725 Å. These values reproduce the bond lengths of all nine diatomics to an accuracy of ±0.012 Å or better.
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33.20.Sn Rotational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.80.Eh Autoionization, photoionization, and photodetachment
33.15.Dj Interatomic distances and angles

Control of wave packets in Li2 by shaping the pump and probe pulses for a state-selected pump-probe analysis of the ionization continuum

Xingcan Dai and Stephen R. Leone

J. Chem. Phys. 127, 014312 (2007); http://dx.doi.org/10.1063/1.2745793 (8 pages) | Cited 3 times

Online Publication Date: 5 July 2007

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Wave packet signals in Li2 prepared by shaped pump pulses are also detected with state-selected shaped probe pulses in the ionization continuum. The results show that the final states are discrete Rydberg states instead of continuum states. Final autoionizing states in the continuum are observed and characterized. By selecting specific resonant rovibrational electronic transitions from the superposition states prepared in the wave packets to the final autoionizing states with the pulse shaping system, the modulation depths of the wave packet signals are increased by as much as 5.20±0.03 times. Control of the wave packets is also realized by shaping the probe pulses to select specific resonant transitions between the states in the wave packets and the highly excited Rydberg states. The detected amplitude ratio of one specific vibrational quantum beat to one specific rotational quantum beat can be decreased by ten times.
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33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.20.Vq Vibration-rotation analysis
33.80.Eh Autoionization, photoionization, and photodetachment

High resolution infrared spectra of the linear carbon cluster C7: The ν4 stretching fundamental band and associated hot bands

P. Neubauer-Guenther, T. F. Giesen, S. Schlemmer, and K. M. T. Yamada

J. Chem. Phys. 127, 014313 (2007); http://dx.doi.org/10.1063/1.2749520 (8 pages) | Cited 4 times

Online Publication Date: 6 July 2007

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High resolution infrared spectra of the ν4 fundamental antisymmetric stretching mode and associated hot bands of the linear carbon cluster C7 were recorded using a tunable diode laser spectrometer in the frequency range of 2135–2141 cm−1. Spectra of the ν4 fundamental, ν4+ν11−ν11, ν4+2ν11−2ν11, and ν4+ν8−ν8, bands have been analyzed and are compared to recent experimental results and high level ab initio calculations. In particular, the presented results give experimental evidence for the rigidity of C7 and confirm theoretical predictions of a rather regular chain molecule, similar to the cases of C4, C5, and C9. For the two energetically low-lying bending modes, ν8 and ν11, the rotational constants differ by less than 0.2%, from the ground state value, B0 = 0.030 624 4(28) cm−1, in good agreement with the recent calculations by Botschwina [Chem. Phys. Lett. 354, 148 (2002)] . From the hot band analysis and the ℓ-type doubling constant q, experimental values for the band origins of the ν8 and ν11 fundamentals have been derived.
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33.20.Ea Infrared spectra
36.40.Mr Spectroscopy and geometrical structure of clusters
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
42.55.Px Semiconductor lasers; laser diodes

Fluxional and aromatic behavior in small magic silicon clusters: A full ab initio study of Sin, Sin1−, Sin2−, and Sin1+, n = 6, 10 clusters

Aristides D. Zdetsis

J. Chem. Phys. 127, 014314 (2007); http://dx.doi.org/10.1063/1.2746030 (10 pages) | Cited 21 times

Online Publication Date: 6 July 2007

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The structural, electronic, vibrational, optical, magnetic, and aromatic characteristics of Sin, Sin1−, Sin2−, and Sin1+, clusters have been calculated very accurately with a variety of high level ab initio techniques. These calculations have been performed with the aim to clarify existing ambiguities in the literature and to bring up the fluxional and aromatic characteristics of these species. The fluxional behavior, according to earlier conjecture of the present author, could be connected to the magic property. In addition such behavior could also explain the existence of conflicting results. The ab initio techniques include quadratic configuration interaction, coupled cluster, and multireference second order perturbation theory, together with density functional theory (“static” and time dependent) with the hybrid B3LYP functional. Various high quality correlation-consistent basis sets, ranging from 2Z up to 5Z quality, were employed. It is demonstrated that Si6 is fluxional, fluctuating around a symmetric D4h structure. Si10 is also fluxional but to a lesser degree, in contrast to Si101− anion which is highly fluxional. For both clusters, in full agreement with Wade’s and Lipscomb’s rules for deltahedral boranes, the corresponding dianions have higher symmetry (Oh and D4d, respectively) and lower energy than the neutral clusters. The aromatic behavior of Si6 fits better to a mixed conflicting aromaticity picture. This type of aromatic and fluxional behavior has also been observed in stable “magic” carbon clusters as C6 and carbon fullerenes such as C20. The present results, which support possible connection of fluxional and magic properties, are in excellent agreement with experimental measurements of ionization energies, electron affinities, and vibrationally resolved photoelectron spectra.
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36.40.Cg Electronic and magnetic properties of clusters
36.40.Wa Charged clusters
36.40.Vz Optical properties of clusters
36.40.Mr Spectroscopy and geometrical structure of clusters
31.15.bw Coupled-cluster theory
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation

Molecular dynamics simulations of local field factors

Qiong Zhang, Yaoquan Tu, He Tian, and Hans Ågren

J. Chem. Phys. 127, 014501 (2007); http://dx.doi.org/10.1063/1.2743970 (6 pages)

Online Publication Date: 2 July 2007

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In the present work, the authors evaluate a scheme based on molecular dynamics to derive local field factors. These are given without any assumption of a cavity by fitting the Langevin functions to the order parameters obtained from the molecular dynamics simulations. The local field factors so obtained, with the detailed chromophore-solvent interactions and solvent structures taken into account, are much smaller than those calculated from the conventional Onsager and Lorentz models. A numerical demonstration is given for two typical organic chromophore molecules, p-nitroaniline and p-nitro-N,N-dimethylaniline dissolved in chloroform.
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61.20.Ja Computer simulation of liquid structure
61.25.Em Molecular liquids
31.15.xv Molecular dynamics and other numerical methods
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