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14 Jan 2010

Volume 132, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

J. Chem. Phys. 132, 025101 (2010); http://dx.doi.org/10.1063/1.3285269 (10 pages)

Atefeh Khoshnood, Hiroshi Noguchi, and Gerhard Gompper
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Communications: Explicitly correlated equation-of-motion coupled cluster method for ionized states

Denis Bokhan and Seiichiro Ten-no

J. Chem. Phys. 132, 021101 (2010); http://dx.doi.org/10.1063/1.3291042 (4 pages) | Cited 1 time

Online Publication Date: 14 January 2010

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The ionization potential equation-of-motion (IP-EOM) method, based on linear explicitly correlated coupled cluster singles and doubles theory [CCSD(F12)] is reported. Numerical tests have shown that the present IP-EOM-CCSD(F12) method provides vertical IPs accurate to 0.05 eV compared to those in the complete basis set limit. The corresponding error in vertical IP of 2s shells does not exceed 0.1 eV.
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31.15.bw Coupled-cluster theory
32.50.+d Fluorescence, phosphorescence (including quenching)
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
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Communications: Nanomagnetic shielding: High-resolution NMR in carbon allotropes

Y. Kim, E. Abou-Hamad, A. Rubio, T. Wågberg, A. V. Talyzin, D. Boesch, S. Aloni, A. Zettl, D. E. Luzzi, and C. Goze-Bac

J. Chem. Phys. 132, 021102 (2010); http://dx.doi.org/10.1063/1.3284740 (4 pages) | Cited 2 times

Online Publication Date: 14 January 2010

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The understanding and control of the magnetic properties of carbon-based materials is of fundamental relevance in applications in nano- and biosciences. Ring currents do play a basic role in those systems. In particular the inner cavities of nanotubes offer an ideal environment to investigate the magnetism of synthetic materials at the nanoscale. Here, by means of math high resolution NMR of encapsulated molecules in peapod hybrid materials, we report the largest diamagnetic shifts (down to −68.3 ppm) ever observed in carbon allotropes, which is connected to the enhancement of the aromaticity of the nanotube envelope upon doping. This diamagnetic shift can be externally controlled by in situ modifications such as doping or electrostatic charging. Moreover, defects such as C-vacancies, pentagons, and chemical functionalization of the outer nanotube quench this diamagnetic effect and restore NMR signatures to slightly paramagnetic shifts compared to nonencapsulated molecules. The magnetic interactions reported here are robust phenomena independent of temperature and proportional to the applied magnetic field. The magnitude, tunability, and stability of the magnetic effects make the peapod nanomaterials potentially valuable for nanomagnetic shielding in nanoelectronics and nanobiomedical engineering.
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76.60.-k Nuclear magnetic resonance and relaxation
61.72.up Other materials
75.20.Ck Nonmetals
75.50.Tt Fine-particle systems; nanocrystalline materials
61.72.jd Vacancies
61.46.Np Structure of nanotubes (hollow nanowires)
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back to top Theoretical Methods and Algorithms

Towards the Hartree–Fock and coupled-cluster singles and doubles basis set limit: A study of various models that employ single excitations into a complementary auxiliary basis set

Andreas Köhn and David P. Tew

J. Chem. Phys. 132, 024101 (2010); http://dx.doi.org/10.1063/1.3291040 (10 pages) | Cited 7 times

Online Publication Date: 11 January 2010

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In explicitly correlated coupled-cluster singles and doubles [CCSD(F12)] calculations, the basis set incompleteness error in the double excitations is reduced to such an extent that the error in the Hartree–Fock energy and the error in the single excitations become important. Using arguments from perturbation theory to systematically truncate the coupled-cluster singles and CCSD(F12) Lagrangians, a series of coupled-cluster models are proposed and studied that reduce these basis set incompleteness errors through additional single excitations into a complementary auxiliary basis. Convergence with model and size of complementary basis is rapid and there appears to be no need to go beyond second-order models. Our iterative second-order approach is a slight improvement over the existing noniterative approach, but its main advantage is that it is suitable for response theory.
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31.15.xr Self-consistent-field methods
31.15.bw Coupled-cluster theory

The direct approach to gravitation and electrostatics method for periodic systems

S. A. Losilla, D. Sundholm, and J. Jusélius

J. Chem. Phys. 132, 024102 (2010); http://dx.doi.org/10.1063/1.3291027 (7 pages) | Cited 2 times

Online Publication Date: 11 January 2010

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The direct approach to gravitation and electrostatics (DAGE) algorithm is an accurate, efficient, and flexible method for calculating electrostatic potentials. In this paper, we show that the algorithm can be easily extended to consider systems with many different kinds of periodicities, such as crystal lattices, surfaces, or wires. The accuracy and performance are nearly the same for periodic and aperiodic systems. The electrostatic potential for semiperiodic systems, namely defects in crystal lattices, can be obtained by combining periodic and aperiodic calculations. The method has been applied to an ionic model system mimicking NaCl, and to a corresponding covalent model system.
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61.66.Fn Inorganic compounds

Ghost transmission: How large basis sets can make electron transport calculations worse

Carmen Herrmann, Gemma C. Solomon, Joseph E. Subotnik, Vladimiro Mujica, and Mark A. Ratner

J. Chem. Phys. 132, 024103 (2010); http://dx.doi.org/10.1063/1.3283062 (17 pages) | Cited 3 times

Online Publication Date: 12 January 2010

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The Landauer approach has proven to be an invaluable tool for calculating the electron transport properties of single molecules, especially when combined with a nonequilibrium Green’s function approach and Kohn–Sham density functional theory. However, when using large nonorthogonal atom-centered basis sets, such as those common in quantum chemistry, one can find erroneous results if the Landauer approach is applied blindly. In fact, basis sets of triple-zeta quality or higher sometimes result in an artificially high transmission and possibly even qualitatively wrong conclusions regarding chemical trends. In these cases, transport persists when molecular atoms are replaced by basis functions alone (“ghost atoms”). The occurrence of such ghost transmission is correlated with low-energy virtual molecular orbitals of the central subsystem and may be interpreted as a biased and thus inaccurate description of vacuum transmission. An approximate practical correction scheme is to calculate the ghost transmission and subtract it from the full transmission. As a further consequence of this study, it is recommended that sensitive molecules be used for parameter studies, in particular those whose transmission functions show antiresonance features such as benzene-based systems connected to the electrodes in meta positions and other low-conducting systems such as alkanes and silanes.
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73.40.Gk Tunneling
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Field-theoretic simulations in the Gibbs ensemble

Robert A. Riggleman and Glenn H. Fredrickson

J. Chem. Phys. 132, 024104 (2010); http://dx.doi.org/10.1063/1.3292004 (12 pages) | Cited 2 times

Online Publication Date: 12 January 2010

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Calculating phase diagrams and measuring the properties of multiple phases in equilibrium is one of the most common applications of field-theoretic simulations. Such a simulation often attempts to simulate two phases in equilibrium with each other in the same simulation box. This is a computationally demanding approach because it is necessary to perform a large enough simulation so that the interface between the two phases does not affect the estimate of the bulk properties of the phases of interest. In this paper, we describe an efficient method for performing field-theoretic simulations in the Gibbs ensemble, a familiar construct in particle-based simulations where two phases in equilibrium with each other are simulated in separate simulation boxes. Chemical and mechanical equilibrium is maintained by allowing the simulation boxes to swap both chemical species and volume. By fixing the total number of each chemical species and the total volume, the Gibbs ensemble allows for the efficient simulation of two bulk phases at equilibrium in the canonical ensemble. After providing the theoretical framework for field-theoretic simulations in the Gibbs ensemble, we demonstrate the method on two two-dimensional model polymer test systems in both the mean-field limit (self-consistent field theory) and in the fluctuating field theory.
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64.70.-p Specific phase transitions
64.75.-g Phase equilibria
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
81.30.Dz Phase diagrams of other materials

Multireference quantum chemistry through a joint density matrix renormalization group and canonical transformation theory

Takeshi Yanai, Yuki Kurashige, Eric Neuscamman, and Garnet Kin-Lic Chan

J. Chem. Phys. 132, 024105 (2010); http://dx.doi.org/10.1063/1.3275806 (9 pages) | Cited 18 times

Online Publication Date: 13 January 2010

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We describe the joint application of the density matrix renormalization group and canonical transformation theory to multireference quantum chemistry. The density matrix renormalization group provides the ability to describe static correlation in large active spaces, while the canonical transformation theory provides a high-order description of the dynamic correlation effects. We demonstrate the joint theory in two benchmark systems designed to test the dynamic and static correlation capabilities of the methods, namely, (i) total correlation energies in long polyenes and (ii) the isomerization curve of the [Cu2O2]2+ core. The largest complete active spaces and atomic orbital basis sets treated by the joint DMRG-CT theory in these systems correspond to a (24e,24o) active space and 268 atomic orbitals in the polyenes and a (28e,32o) active space and 278 atomic orbitals in [Cu2O2]2+.
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31.15.V- Electron correlation calculations for atoms, ions and molecules
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
82.30.Qt Isomerization and rearrangement

Strongly contracted canonical transformation theory

Eric Neuscamman, Takeshi Yanai, and Garnet Kin-Lic Chan

J. Chem. Phys. 132, 024106 (2010); http://dx.doi.org/10.1063/1.3274822 (13 pages) | Cited 9 times

Online Publication Date: 13 January 2010

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Canonical transformation (CT) theory describes dynamic correlation in multireference systems with large active spaces. Here we discuss CT theory’s intruder state problem and why our previous approach of overlap matrix truncation becomes infeasible for sufficiently large active spaces. We propose the use of strongly and weakly contracted excitation operators as alternatives for dealing with intruder states in CT theory. The performance of these operators is evaluated for the H2O, N2, and NiO molecules, with comparisons made to complete active space second order perturbation theory and Davidson-corrected multireference configuration interaction theory. Finally, using a combination of strongly contracted CT theory and orbital-optimized density matrix renormalization group theory, we evaluate the singlet-triplet gap of free base porphin using an active space containing all 24 out-of-plane 2p orbitals. Modeling dynamic correlation with an active space of this size is currently only possible using CT theory.
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31.15.xr Self-consistent-field methods
31.15.xp Perturbation theory

Excited-state polarizabilities of solvated molecules using cubic response theory and the polarizable continuum model

Lara Ferrighi, Luca Frediani, and Kenneth Ruud

J. Chem. Phys. 132, 024107 (2010); http://dx.doi.org/10.1063/1.3291026 (12 pages) | Cited 1 time

Online Publication Date: 13 January 2010

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The theory and an implementation of the solvent contribution to the cubic response function for the polarizable continuum model for multiconfigurational self-consistent field wave functions is presented. The excited-state polarizability of benzene, para-nitroaniline, and nitrobenzene has been obtained from the double residue of the cubic response function calculated in the presence of an acetonitrile and dioxane solvent. The calculated excited-state polarizabilities are compared to results obtained from the linear response function of the explicitly optimized excited states.
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61.20.Gy Theory and models of liquid structure

Efficient hybrid evolutionary optimization of interatomic potential models

W. Michael Brown, Aidan P. Thompson, and Peter A. Schultz

J. Chem. Phys. 132, 024108 (2010); http://dx.doi.org/10.1063/1.3294562 (13 pages) | Cited 1 time

Online Publication Date: 14 January 2010

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The lack of adequately predictive atomistic empirical models precludes meaningful simulations for many materials systems. We describe advances in the development of a hybrid, population based optimization strategy intended for the automated development of material specific interatomic potentials. We compare two strategies for parallel genetic programming and show that the Hierarchical Fair Competition algorithm produces better results in terms of transferability, despite a lower training set accuracy. We evaluate the use of hybrid local search and several fitness models using system energies and/or particle forces. We demonstrate a drastic reduction in the computation time with the use of a correlation-based fitness statistic. We show that the problem difficulty increases with the number of atoms present in the systems used for model development and demonstrate that vectorization can help to address this issue. Finally, we show that with the use of this method, we are able to “rediscover” the exact model for simple known two- and three-body interatomic potentials using only the system energies and particle forces from the supplied atomic configurations.
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34.20.Cf Interatomic potentials and forces

Kirkwood–Buff derived force field for alkali chlorides in simple point charge water

Benjamin Klasczyk and Volker Knecht

J. Chem. Phys. 132, 024109 (2010); http://dx.doi.org/10.1063/1.3273903 (12 pages) | Cited 5 times

Online Publication Date: 14 January 2010

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Solvated ions are a fundamental constituent of many biological systems. An important class consists of the alkali cations. In particular, potassium (K+) is the most abundant ion in the cytoplasm, whereas lithium (Li+), rubidium (Rb+), and cesium (Cs+) are of fundamental physicochemical and medical relevance. A powerful tool to understand ion specificity and cellular systems on a microscopic level is provided by molecular dynamics simulations. Previously, reliable force field parameters for Li+, K+, Rb+, and Cs+ in aqueous solution have not been available for the simple point charge (SPC) water model widely used in conjunction with the GROMOS force field. We used the Kirkwood–Buff theory to develop force fields for Li+, K+, Rb+, and Cs+ in SPC water to reproduce experimental data on respective aqueous alkali chloride solutions (LiCl, KCl, RbCl, CsCl). The force field developed reproduces many of the known properties of alkali metal chlorides solutions including densities and partial molar volumes. Our force field is shown to be superior to other common alkali chloride force fields in terms of reproducing the activity derivative, as a prerequisite for a realistic measure of ion-solute association underlying ion-specific phenomena (Hofmeister effects). For lithium and potassium, the ionic radii from cation-water oxygen pair correlation functions and hydration numbers are well reproduced. The force field developed will be useful for modeling physiological conditions and ion-specific phenomena for biomolecular systems.
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87.16.dp Transport, including channels, pores, and lateral diffusion
87.16.Vy Ion channels
87.15.R- Reactions and kinetics
87.15.ap Molecular dynamics simulation

Variational solution of the Schrödinger equation using plane waves in adaptive coordinates: The radial case

José M. Pérez-Jordá

J. Chem. Phys. 132, 024110 (2010); http://dx.doi.org/10.1063/1.3291345 (11 pages) | Cited 2 times

Online Publication Date: 14 January 2010

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A new method for solving the Schrödinger equation is proposed, based on the following details. First, a map u = u(r) from Cartesian coordinates r to a new coordinate system u is chosen. Second, the solution (orbital) ψ(r) is written in terms of a function U depending on u so that ψ(r) = |Ju|−1/2U(u), where |Ju| is the Jacobian determinant of the map. Third, U is expressed as a linear combination of plane waves in the u coordinate, U(u) = ∑kckeik⋅u. Finally, the coefficients ck are variationally optimized to obtain the best energy, using a generalization of an algorithm originally developed for the Coulomb potential [ J. M. Pérez-Jordá, Phys. Rev. B 58, 1230 (1998) ]. The method is tested for the radial Schrödinger equation in the hydrogen atom, resulting in micro-Hartree accuracy or better for the energy of ns and np orbitals (with n up to 5) using expansions of moderate length.
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31.15.xr Self-consistent-field methods
34.20.Cf Interatomic potentials and forces

Constrained-pairing mean-field theory. III. Inclusion of density functional exchange and correlation effects via alternative densities

Takashi Tsuchimochi, Gustavo E. Scuseria, and Andreas Savin

J. Chem. Phys. 132, 024111 (2010); http://dx.doi.org/10.1063/1.3292640 (9 pages) | Cited 11 times

Online Publication Date: 14 January 2010

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The recently proposed constrained-pairing mean-field theory (CPMFT) is here extended to include exchange and correlation effects from density functional theory (DFT) via alternative densities. We transform from α and β spin densities to alternatives based on the total and on-top pair densities. This transformation is needed because CPMFT produces correct spin-symmetry and space-symmetry adapted densities that traditional DFT functionals are not designed to work with. The inclusion of DFT exchange and correlation effects in CPMFT is well founded both on practical and methodological reasons. We present multiple benchmarks showing that in many cases our model accurately reproduces unrestricted hybrid functional energies (both regular and range separated) and does so on the correct space-symmetry and spin-symmetry surface. Our approach affords efficient inclusion of dynamical correlation effects absent in CPMFT.
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31.15.eg Exchange-correlation functionals (in current density functional theory)
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Theoretical studies of absorption cross sections for the math math2-math math1 system of sulfur dioxide and isotope effects

Ikuo Tokue and Shinkoh Nanbu

J. Chem. Phys. 132, 024301 (2010); http://dx.doi.org/10.1063/1.3277191 (10 pages) | Cited 2 times

Online Publication Date: 8 January 2010

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The math math2-math math1 photoexcitation of SO2 was studied to investigate excited-state dynamics and the effects of the initial vibrational state. Ultraviolet photoabsorption cross sections (σ's) of seven isotopologues (math math2, math math2, math math2, math math2, mathmathmath, mathmathmath, mathmathmath) were computed using the wave packet propagation technique based on the three-dimensional potential energy surfaces of the math and math states, which were calculated using the ab initio molecular orbital configuration interaction method. Numerous wave packet simulations were carried out under the adiabatic approximation and used to calculate the σ’s of the seven isotopologues at 298 K; we concluded that the absorption spectrum of SO2 can be reliably modeled within the adiabatic framework based on the analysis of the time evolution of the wave packet. The calculated σ’s are in reasonable agreement with the recent experiment in the 190–228 nm region, and the isotope shifts of the peaks for math math2 and math math2 relative to the corresponding peaks for math math2 are in good agreement with the observed data. Relative to the σ of math math2, isotopic substitution shows a significant increment for those of math math2 and math math2 in the 190–228 nm region. This trend is consistent with the observed data.
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31.30.Gs Hyperfine interactions and isotope effects
33.80.-b Photon interactions with molecules
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
33.20.Lg Ultraviolet spectra
31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations

State resolved measurements of a mathH2 removal confirm predictions of the gateway model for electronic quenching

K. L. Gannon, M. A. Blitz, T. Kovács, M. J. Pilling, and P. W. Seakins

J. Chem. Phys. 132, 024302 (2010); http://dx.doi.org/10.1063/1.3263617 (8 pages) | Cited 4 times

Online Publication Date: 8 January 2010

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Collisional quenching of electronically excited states by inert gases is a fundamental physical process. For reactive excited species such as singlet methylene, mathH2, the competition between relaxation and reaction has important implications in practical systems such as combustion. The gateway model has previously been applied to the relaxation of mathH2 by inert gases [ U. Bley and F. Temps, J. Chem. Phys. 98, 1058 (1993) ]. In this model, gateway states with mixed singlet and triplet character allow conversion between the two electronic states. The gateway model makes very specific predictions about the relative relaxation rates of ortho and para quantum states of methylene at low temperatures; relaxation from para gateway states leads to faster deactivation independent of the nature of the collision partner. Experimental data are reported here which for the first time confirm these predictions at low temperatures for helium. However, it was found that in contrast with the model predictions, the magnitude of the effect decreases with increasing size of the collision partner. It is proposed that the attractive potential energy surface for larger colliders allows alternative gateway states to contribute to relaxation removing the dominance of the para gateway states.
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31.50.Df Potential energy surfaces for excited electronic states
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.30.-b Specific chemical reactions; reaction mechanisms
34.50.-s Scattering of atoms and molecules
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions

Rotational excitation of CN(X math+) by He: Theory and comparison with experiments

François Lique, Annie Spielfiedel, Nicole Feautrier, Ioan F. Schneider, Jacek Kłos, and Millard H. Alexander

J. Chem. Phys. 132, 024303 (2010); http://dx.doi.org/10.1063/1.3285811 (6 pages) | Cited 13 times

Online Publication Date: 8 January 2010

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Rotational excitation of the CN(X math+) molecule with He is investigated. We present a new two-dimensional potential energy surface (PES) for the He–CN system, calculated at an internuclear CN distance frozen at its experimental equilibrium distance. This PES was obtained using an open-shell, coupled-cluster method including all single and double excitations, as well as the perturbative contributions of connected triple excitations [RCCSD(T)]. Bond functions were placed at mid-distance between the center of mass of the CN molecule and He atom for a better description of the van der Waals interaction. State-to-state collisional excitation cross sections of the fine-structure levels of CN by He are calculated for energies up to 2500 cm−1, which yield after thermal averaging, rate coefficients up to 350 K. The exact spin splitting of the energy levels is taken into account. The propensity rules between fine-structure levels are studied, and it is shown that the rate constants for Δj = ΔN transitions are much larger than those for Δj ≠ ΔN transitions, as expected from theoretical considerations. Our calculated rate coefficients are compared to experimental results at 295 K of Fei et al. [J. Chem. Phys. 100, 1190 (1994) ]. The excellent agreement confirms the accuracy of the PESs and of the scattering calculations.
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34.50.Ez Rotational and vibrational energy transfer
33.15.Pw Fine and hyperfine structure
34.20.Gj Intermolecular and atom-molecule potentials and forces
31.15.bw Coupled-cluster theory

The role of cluster energy nonaccommodation in atmospheric sulfuric acid nucleation

Theo Kurtén, Chongai Kuang, Pedro Gómez, Peter H. McMurry, Hanna Vehkamäki, Ismael Ortega, Madis Noppel, and Markku Kulmala

J. Chem. Phys. 132, 024304 (2010); http://dx.doi.org/10.1063/1.3291213 (8 pages) | Cited 2 times

Online Publication Date: 11 January 2010

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We discuss the possible role of energy nonaccommodation (monomer-cluster collisions that do not result in stable product formation due to liberated excess energy) in atmospheric nucleation processes involving sulfuric acid. Qualitative estimates of the role of nonaccommodation are computed using quantum Rice–Ramsberger–Kassel theory together with quantum chemically calculated vibrational frequencies and anharmonic coupling constants for small sulfuric acid—containing clusters. We find that energy nonaccommodation effects may, at most, decrease the net formation rate of sulfuric acid dimers by up to a factor of 10 with respect to the hard-sphere collision rate. A decrease in energy nonaccommodation due to an increasing number of internal degrees of freedom may kinetically slightly favor the participation of amines rather than ammonia as stabilizing agents in sulfuric acid nucleation, though the kinetic enhancement factor is likely to be less than three. However, hydration of the clusters (which always occurs in ambient conditions) is likely to increase the energy accommodation factor, reducing the role that energy nonaccommodation plays in atmospheric nucleation.
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92.60.hf Tropospheric composition and chemistry, constituent transport and chemistry
92.60.Jq Water in the atmosphere

Accurate evaporation rates of pure and doped water clusters in vacuum: A statistico-dynamical approach

F. Calvo, J. Douady, and F. Spiegelman

J. Chem. Phys. 132, 024305 (2010); http://dx.doi.org/10.1063/1.3280168 (12 pages) | Cited 2 times

Online Publication Date: 12 January 2010

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Unimolecular evaporation of selected pure (H2O)n and heterogeneous (H2O)n−1X+ water clusters containing a single hydronium or ammonium impurity is investigated in the framework of phase space theory (PST) in its orbiting transition state version. Using the many-body polarizable Kozack–Jordan potential and its extensions for X+ = H3O+ and NH4+, the thermal evaporation of clusters containing 21 and 50 molecules is simulated at several total energies. Numerous molecular dynamics (MD) trajectories at high internal energies provide estimates of the decay rate constant, as well as the kinetic energy and angular momentum released upon dissociation. Additional Monte Carlo simulations are carried out to determine the anharmonic densities of vibrational states, which combined with suitable forms for the rotational densities of states provide expressions for the energy-resolved differential rates. Successful comparison between the MD results and the independent predictions of PST for the distributions of kinetic energy and angular momentum released shows that the latter statistical approach is quantitative. Using MD data as a reference, the absolute evaporation rates are calculated from PST over broad energy and temperature ranges. Based on these results, the presence of an ionic impurity is generally found to decrease the rate, however the effect is much more significant in the 21-molecule clusters. Our calculations also suggest that due to backbendings in the microcanonical densities of states the variations of the evaporation rates may not be strictly increasing with energy or temperature.
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61.20.Ja Computer simulation of liquid structure
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
68.03.Fg Evaporation and condensation of liquids
63.20.Ry Anharmonic lattice modes

Guided ion beam and theoretical studies of the reaction of Ag+ with CS2: Gas-phase thermochemistry of AgS+ and AgCS+ and insight into spin-forbidden reactions

P. B. Armentrout and Ilona Kretzschmar

J. Chem. Phys. 132, 024306 (2010); http://dx.doi.org/10.1063/1.3285837 (10 pages) | Cited 4 times

Online Publication Date: 12 January 2010

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The gas-phase reactivity of the atomic transition metal cation, Ag+, with CS2 is investigated using guided-ion beam mass spectrometry. Endothermic reactions forming AgS+ and AgCS+ are observed but are quite inefficient. This observation is largely attributed to the stability of the closed shell Ag+(math,4d10) ground state, but is also influenced by the fact that the reactions producing ground state AgS+ and AgCS+ products are both spin forbidden. Analysis of the kinetic energy dependence of the cross sections for formation of these two products yields the 0 K bond energies of D0(Ag+S) = 1.40±0.12 eV and D0(Ag+CS) = 1.98±0.14 eV. Quantum chemical calculations are used to investigate the electronic structure of the two product ions as well as the potential energy surfaces for reaction. The primary mechanism involves oxidative addition of a CS bond to the metal cation followed by simple AgS or AgCS bond cleavage. Crossing points between the singlet and triplet surfaces are located near the transition states for bond activation. Comparison with analogous work on other late second-row transition metal cations indicates that the location of the crossing points bears directly on the efficiency of these spin-forbidden processes.
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82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.20.Db Transition state theory and statistical theories of rate constants
82.20.Kh Potential energy surfaces for chemical reactions
82.60.-s Chemical thermodynamics
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
82.30.Nr Association, addition, insertion, cluster formation

Homogeneous nucleation of a homologous series of n-alkanes (CiH2i+2, i = 7–10) in a supersonic nozzle

David Ghosh, Dirk Bergmann, Regina Schwering, Judith Wölk, Reinhard Strey, Shinobu Tanimura, and Barbara E. Wyslouzil

J. Chem. Phys. 132, 024307 (2010); http://dx.doi.org/10.1063/1.3274629 (17 pages) | Cited 9 times

Online Publication Date: 13 January 2010

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Homogeneous nucleation rates of the n-alkanes (CiH2i+2; i = 7–10) were determined by combining information from pressure trace measurements and small angle x-ray scattering (SAXS) experiments in a supersonic Laval nozzle. The condensible vapor pressure pJ max, the temperature TJ max, the characteristic time ΔtJ max, and supersaturation SJ max corresponding to the peak nucleation rate Jmax were determined during the pressure trace measurements. These measurements also served as the basis for the subsequent SAXS experiments. Fitting the radially averaged SAXS spectrum yielded the mean droplet radius 〈r〉, 5<〈r〉/nm<31, the width of the aerosol size distribution σ, 2<σ/nm<6, and the particle number density N, 7×1010<N/cm−3<2.2×1012. The nucleation rates for the n-alkanes Jmax, 4×1015<Jmax/cm−3 s−1<2×1018, vary by almost three orders of magnitude as the temperature TJmax decreases from ∼ 200 K to as low as 150 K. At the lowest temperatures, the supersaturations SJmax are on the order of 105. In spite of these extreme operating conditions, we find good agreement between the current experimental results and those available in the literature using Hale’s scaling formalism [ Phys. Rev. A 33, 4156 (1986) ; Metall. Trans. A 23, 1863 (1992) ] and the scaling parameters reported by Rusyniak and El-Shall [ J. Phys. Chem. B 105, 11873 (2001) ]. Comparing the experimental nucleation rates with the predictions of classical nucleation theory, we find that our experimental nucleation rates are 4.5–8 orders of magnitude higher than the predictions.
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78.70.Ck X-ray scattering
82.70.Rr Aerosols and foams

An exchange-Coulomb model potential energy surface for the Ne–CO interaction. II. Molecular beam scattering and bulk gas phenomena in Ne–CO mixtures

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

J. Chem. Phys. 132, 024308 (2010); http://dx.doi.org/10.1063/1.3285721 (18 pages) | Cited 3 times

Online Publication Date: 13 January 2010

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Four potential energy surfaces are of current interest for the Ne–CO interaction. Two are high-level fully ab initio surfaces obtained a decade ago using symmetry-adapted perturbation theory and supermolecule coupled-cluster methods. The other two are very recent exchange-Coulomb (XC) model potential energy surfaces constructed by using ab initio Heitler–London interaction energies and literature long range dispersion and induction energies, followed by the determination of a small number of adjustable parameters to reproduce a selected subset of pure rotational transition frequencies for the mathe–mathmath van der Waals cluster. Testing of the four potential energy surfaces against a wide range of available experimental microwave, millimeter-wave, and mid-infrared Ne–CO transition frequencies indicated that the XC potential energy surfaces gave results that were generally far superior to the earlier fully ab initio surfaces. In this paper, two XC model surfaces and the two fully ab initio surfaces are tested for their abilities to reproduce experiment for a wide range of nonspectroscopic Ne–CO gas mixture properties. The properties considered here are relative integral cross sections and the angle dependence of rotational state-to-state differential cross sections, rotational relaxation rate constants for CO(v = 2) in Ne–CO mixtures at T = 296 K, pressure broadening of two pure rotational lines and of the rovibrational lines in the CO fundamental and first overtone transitions at 300 K, and the temperature and, where appropriate, mole fraction dependencies of the interaction second virial coefficient, the binary diffusion coefficient, the interaction viscosity, the mixture shear viscosity and thermal conductivity coefficients, and the thermal diffusion factor. The XC model potential energy surfaces give results that lie within or very nearly within the experimental uncertainties for all properties considered, while the coupled-cluster ab initio surface gives results that agree similarly well for all but one of the properties considered. When the present comparisons are combined with the ability to give accurate spectroscopic transition frequencies for the Ne–CO van der Waals complex, only the XC potential energy surfaces give results that agree well with all extant experimental data for the Ne–CO interaction.
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31.50.-x Potential energy surfaces
33.70.Jg Line and band widths, shapes, and shifts
31.15.xp Perturbation theory
31.15.A- Ab initio calculations
33.15.Mt Rotation, vibration, and vibration-rotation constants
34.20.Gj Intermolecular and atom-molecule potentials and forces

The Sc2 dimer revisited

Apostolos Kalemos, Ilya G. Kaplan, and Aristides Mavridis

J. Chem. Phys. 132, 024309 (2010); http://dx.doi.org/10.1063/1.3290951 (7 pages) | Cited 7 times

Online Publication Date: 13 January 2010

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Thirty two states of the homonuclear neutral diatomic Sc2 molecule have been studied by multireference methods using basis sets of quadruple quality. For all 30 states resulting from the ground state Sc atoms, Sc(mathg)+Sc(mathg), and two out of 80, X mathu− and 1 mathu−, issued from the first excited channel Sc(mathg)+Sc(a mathg), we have constructed full potential energy curves and extracted the standard spectroscopic parameters. With the exception of X mathu− and 1 mathu− which are covalently bound, the 30 states related to the ground state Sc atoms are of van der Waals nature with interaction energies of 3–5 kcal/mol at distances of 7–7.5 bohr. For the X mathu− state the proposed De value is 48 kcal/mol, with respect to the adiabatic fragments and with the 1 mathu− state just 380 cm−1 above it.
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31.50.Df Potential energy surfaces for excited electronic states

The complete iodine and nitrogen nuclear electric quadrupole coupling tensors for fluoroiodoacetonitrile determined by chirped pulse Fourier transform microwave spectroscopy

G. S. Grubbs, G. Kadiwar, W. C. Bailey, and S. A. Cooke

J. Chem. Phys. 132, 024310 (2010); http://dx.doi.org/10.1063/1.3291619 (6 pages) | Cited 6 times

Online Publication Date: 13 January 2010

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Molecular pulsed jet, chirped-pulse Fourier transform microwave spectroscopy has been used to record 499 transitions for the title molecule. Measurements have been made in the 8–16 GHz regions. Vibrational and electronic ground state rotational constants A, B, and C have been obtained, together with centrifugal distortion terms. The complete iodine and nitrogen nuclear quadrupole coupling tensors have been determined for the first time. Quantum chemical calculations have been performed to aid with analyses and, in particular, to aid in determining the signs of the off-diagonal components of the nuclear quadrupole coupling tensors. An experimentally determined relative electronegativity scale for several polyhalomethyl groups is proposed.
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33.25.+k Nuclear resonance and relaxation
33.20.Bx Radio-frequency and microwave spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
33.20.Sn Rotational analysis

An interpretation of the anomalous math vibronic structure in the far-UV spectrum of CO

H. Lefebvre-Brion, H. P. Liebermann, and G. J. Vázquez

J. Chem. Phys. 132, 024311 (2010); http://dx.doi.org/10.1063/1.3276453 (6 pages) | Cited 2 times

Online Publication Date: 13 January 2010

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The far-UV spectrum of carbon monoxide presents numerous abnormal math rovibronic levels in the region 92 000–105 000 cm−1 which have been observed by several experimentalists. Yet, and in spite of various attribution attempts carried out over the past two decades, the nature of these levels is poorly understood and they still lack a definitive assignment. The absorption lines in this energy region are characterized by irregular energy level positions and spacings, and odd, smaller than expected, rotational constants. In the current contribution we address this puzzle by relying on recent ab initio calculations of several Rydberg and valence states of CO [ G. J. Vázquez, J. M. Amero, H. P. Liebermann, and H. Lefebvre-Brion, J. Phys. Chem. A 113, 13395 (2009) ], and on further new calculations in which we compute electronic transition moments between the ground state and several excited math states. We focus on the perturbations between the adiabatic math states, specifically on the interaction between the second and third potential energy curves, reported in our previous paper. The second adiabatic potential energy curve, which we refer to as E-E′, displays a distorted shape with two minima as a result of an avoided crossing with the third one. We report here the computation of the lowest vibronic levels of a system of two electronic states which undergo a strong Rydberg-valence interaction. Our vibronic calculations proceed as follows: from the second and third computed adiabatic curves we first obtain approximate diabatic curves for the (X math+)3pπ E math Rydberg state and for the valence E′ math state. Then we solve a system of 2×2 coupled equations in order to obtain the perturbed vibronic energy levels and wave functions for the interacting E and E′ states. The computed vibronic levels obtained from the coupled equation treatment are compared to the first six observed math levels. A good agreement is found with experiment for the four lowest vibronic levels and a reasonable accord for two higher levels.
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33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.20.Lg Ultraviolet spectra
33.20.Sn Rotational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.15.ae Electronic structure and bonding characteristics
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Electronic structure and spin coupling of the manganese dimer: The state of the art of ab initio approach

Alexei A. Buchachenko, Grzegorz Chałasiński, and Małgorzata M. Szczęśniak

J. Chem. Phys. 132, 024312 (2010); http://dx.doi.org/10.1063/1.3292572 (10 pages) | Cited 4 times

Online Publication Date: 14 January 2010

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A thorough ab initio study of the Mn2 dimer in its lowest electronic states that correlate to the ground Mn(math)+Mn(math) dissociation limit is reported. Performance of multireference methods is examined in calculations of the fully spin-polarized S = 5(math) state against the recent accurate single-reference coupled cluster CCSD(T) results [ A. A. Buchachenko, Chem. Phys. Lett. 459, 73 (2008) ]. The detailed comparison reveals a serious disagreement between the multireference configuration interaction (MRCI) and related nonperturbative results on the one hand and the complete active space perturbation theory (CASPT) calculations on the other. A striking difference found in the CASPT results of the second and third orders indicates poor perturbation expansion convergence. It is shown that a similar problem has affected most of the previous calculations performed using CASPT2 and similar perturbative approximations. The composition of the active space in the reference multiconfigurational self-consistent field calculations, the core correlation contribution, and basis set saturation effects are also analyzed. The lower spin states, S = 0–4, are investigated using the MRCI method. The results indicate a similar dispersion binding for all the spin states within the manifold related to the closed 4s shells, which appears to screen and suppress the spin coupling between the half-filled 3d atomic shells. On this premise, the full set of model potentials is built by combining the accurate reference CCSD(T) interaction potential for S = 5 and the MRCI spin-exchange energies for the S<5 states. This approach leads to the value of 550 cm−1 as a lower bound for the math ground-state dissociation energy. The spin-exchange energies themselves are found to comply with the simple Heisenberg model. The effective spin-coupling parameter J is estimated as −3.9 cm−1, a value roughly 2.5 times smaller in magnitude than those measured in the inert gas cryogenic matrices. Compressing of the Mn2 dimer in the matrix cage is suggested as the prime cause of this disagreement.
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31.15.ae Electronic structure and bonding characteristics
31.15.xr Self-consistent-field methods
33.15.Fm Bond strengths, dissociation energies
31.15.ve Electron correlation calculations for atoms and ions: ground state
31.15.bw Coupled-cluster theory
31.15.xp Perturbation theory
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