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28 Apr 2011

Volume 134, Issue 16, Articles (16xxxx)

Issue Cover Spotlight Figure

J. Chem. Phys. 134, 165101 (2011); http://dx.doi.org/10.1063/1.3582336 (5 pages)

Ulrich Schmidt and Matthias Weiss
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Communication: Comment on the effective temporal and spectral resolution of impulsive stimulated Raman signals

Shaul Mukamel and Jason D. Biggs

J. Chem. Phys. 134, 161101 (2011); http://dx.doi.org/10.1063/1.3581889 (4 pages)

Online Publication Date: 22 April 2011

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A compact correlation-function expression for time-resolved stimulated Raman signals, generated by combining a spectrally narrow (picosecond) with a broad (femtosecond) pulse, is derived using a closed time path loop diagrammatic technique that represents forward and backward time evolution of the vibrational wave function. We show that even though the external spectral and temporal parameters of the pulses may be independently controlled, the effective temporal and spectral resolution of the experiment may not exceed the fundamental bandwidth limitation.
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87.15.M- Spectra of biomolecules
87.15.R- Reactions and kinetics
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back to top Theoretical Methods and Algorithms

Anharmonic rovibrational analysis for disilacyclopropenylidene (Si2CH2)

Tongxiang Lu, Jeremiah J. Wilke, Yukio Yamaguchi, and Henry F. Schaefer

J. Chem. Phys. 134, 164101 (2011); http://dx.doi.org/10.1063/1.3574344 (7 pages)

Online Publication Date: 25 April 2011

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The global minimum on the Si2CH2 electronic singlet potential energy surface has been theoretically predicted to be a peculiar hydrogen bridged (Si⋅⋅⋅H⋅⋅⋅Si) disilacyclopropenylidene structure (Si2CH2). An accurate quartic force field for Si2CH2 has been determined employing ab initio coupled-cluster theory with single and double excitations and a perturbative treatment for triple excitations [CCSD(T)], in combination with the correlation consistent core-valence quadruple zeta (cc-pCVQZ) basis set. The vibration–rotation coupling constants, equilibrium and zero-point vibration corrected rotational constants, centrifugal distortion constants, and harmonic and fundamental vibrational frequencies for six isotopologues of Si2CH2 are predicted using vibrational second-order perturbation theory (VPT2). The anharmonic corrections for the vibrational motions involving the H bridged bonds are found to be more than 5% with respect to the corresponding harmonic vibrational frequencies. In this light, an experimental detection and characterization of disilacyclopropenylidene (Si2CH2) is highly desired.
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33.20.Vq Vibration-rotation analysis
31.15.ae Electronic structure and bonding characteristics
31.15.bw Coupled-cluster theory
31.15.xp Perturbation theory
31.50.Df Potential energy surfaces for excited electronic states
33.15.Bh General molecular conformation and symmetry; stereochemistry

A natural orbital functional for multiconfigurational states

M. Piris, X. Lopez, F. Ruipérez, J. M. Matxain, and J. M. Ugalde

J. Chem. Phys. 134, 164102 (2011); http://dx.doi.org/10.1063/1.3582792 (6 pages) | Cited 5 times

Online Publication Date: 25 April 2011

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An explicit formulation of the Piris cumulant λ(Δ,Π) matrix is described herein, and used to reconstruct the two-particle reduced density matrix (2-RDM). Then, we have derived a natural orbital functional, the Piris Natural Orbital Functional 5, PNOF5, constrained to fulfill the D, Q, and G positivity necessary conditions of the N-representable 2-RDM. This functional yields a remarkable accurate description of systems bearing substantial (near)degeneracy of one-particle states. The theory is applied to the homolitic dissociation of selected diatomic molecules and to the rotation barrier of ethylene, both paradigmatic cases of near-degeneracy effects. It is found that the method describes correctly the dissociation limit yielding an integer number of electrons on the dissociated atoms. PNOF5 predicts a barrier of 65.6 kcal/mol for the ethylene torsion in an outstanding agreement with Complete Active Space Second-order Perturbation Theory (CASPT2). The obtained occupation numbers and pseudo one-particle energies at the ethylene transition state account for fully degenerate π orbitals. The calculated equilibrium distances, dipole moments, and binding energies of the considered molecules are presented. The values obtained are accurate comparing those obtained by the complete active space self-consistent field method and the experimental data.
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31.15.E- Density-functional theory
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
33.15.Fm Bond strengths, dissociation energies
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

Application of a semiclassical model for the second-quantized many-electron Hamiltonian to nonequilibrium quantum transport: The resonant level model

David W. H. Swenson, Tal Levy, Guy Cohen, Eran Rabani, and William H. Miller

J. Chem. Phys. 134, 164103 (2011); http://dx.doi.org/10.1063/1.3583366 (8 pages)

Online Publication Date: 25 April 2011

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A semiclassical approach is developed for nonequilibrium quantum transport in molecular junctions. Following the early work of Miller and White [J. Chem. Phys. 84, 5059 (1986)], the many-electron Hamiltonian in second quantization is mapped onto a classical model that preserves the fermionic character of electrons. The resulting classical electronic Hamiltonian allows for real-time molecular dynamics simulations of the many-body problem from an uncorrelated initial state to the steady state. Comparisons with exact results generated for the resonant level model reveal that a semiclassical treatment of transport provides a quantitative description of the dynamics at all relevant timescales for a wide range of bias and gate potentials, and for different temperatures. The approach opens a door to treating nontrivial quantum transport problems that remain far from the reach of fully quantum methodologies.
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85.65.+h Molecular electronic devices
73.40.Gk Tunneling
73.23.-b Electronic transport in mesoscopic systems

A strategy for reducing gross errors in the generalized Born models of implicit solvation

Alexey V. Onufriev and Grigori Sigalov

J. Chem. Phys. 134, 164104 (2011); http://dx.doi.org/10.1063/1.3578686 (15 pages)

Online Publication Date: 26 April 2011

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The “canonical” generalized Born (GB) formula [C. Still, A. Tempczyk, R. C. Hawley, and T. Hendrickson, J. Am. Chem. Soc. 112, 6127 (1990)] is known to provide accurate estimates for total electrostatic solvation energies ΔGel of biomolecules if the corresponding effective Born radii are accurate. Here we show that even if the effective Born radii are perfectly accurate, the canonical formula still exhibits significant number of gross errors (errors larger than 2kBT relative to numerical Poisson equation reference) in pairwise interactions between individual atomic charges. Analysis of exact analytical solutions of the Poisson equation (PE) for several idealized nonspherical geometries reveals two distinct spatial modes of the PE solution; these modes are also found in realistic biomolecular shapes. The canonical GB Green function misses one of two modes seen in the exact PE solution, which explains the observed gross errors. To address the problem and reduce gross errors of the GB formalism, we have used exact PE solutions for idealized nonspherical geometries to suggest an alternative analytical Green function to replace the canonical GB formula. The proposed functional form is mathematically nearly as simple as the original, but depends not only on the effective Born radii but also on their gradients, which allows for better representation of details of nonspherical molecular shapes. In particular, the proposed functional form captures both modes of the PE solution seen in nonspherical geometries. Tests on realistic biomolecular structures ranging from small peptides to medium size proteins show that the proposed functional form reduces gross pairwise errors in all cases, with the amount of reduction varying from more than an order of magnitude for small structures to a factor of 2 for the largest ones.
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87.15.R- Reactions and kinetics
87.15.B- Structure of biomolecules
87.15.A- Theory, modeling, and computer simulation

Unusual ground states via monotonic convex pair potentials

É. Marcotte, F. H. Stillinger, and S. Torquato

J. Chem. Phys. 134, 164105 (2011); http://dx.doi.org/10.1063/1.3576141 (12 pages)

Online Publication Date: 27 April 2011

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We have previously shown that inverse statistical-mechanical techniques allow the determination of optimized isotropic pair interactions that self-assemble into low-coordinated crystal configurations in the d-dimensional Euclidean space mathd. In some of these studies, pair interactions with multiple extrema were optimized. In the present work, we attempt to find pair potentials that might be easier to realize experimentally by requiring them to be monotonic and convex. Encoding information in monotonic convex potentials to yield low-coordinated ground-state configurations in Euclidean spaces is highly nontrivial. We adapt a linear programming method and apply it to optimize two repulsive monotonic convex pair potentials, whose classical ground states are counterintuitively the square and honeycomb crystals in math2. We demonstrate that our optimized pair potentials belong to two wide classes of monotonic convex potentials whose ground states are also the square and honeycomb crystal. We show that these unexpected ground states are stable over a nonzero number density range by checking their (i) phonon spectra, (ii) defect energies and (iii) self assembly by numerically annealing liquid-state configurations to their zero-temperature ground states.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
61.72.jj Interstitials
61.72.jd Vacancies
61.72.Cc Kinetics of defect formation and annealing

Use of correlated potential harmonic basis functions for the description of the 4He trimer and small clusters

Tapan Kumar Das, Barnali Chakrabarti, and Sylvio Canuto

J. Chem. Phys. 134, 164106 (2011); http://dx.doi.org/10.1063/1.3583365 (7 pages)

Online Publication Date: 27 April 2011

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A correlated many-body basis function is used to describe the 4He trimer and small helium clusters (4HeN) with N = 4 − 9. A realistic helium dimer potential is adopted. The ground state results of the 4He dimer and trimer are in close agreement with earlier findings. But no evidence is found for the existence of Efimov state in the trimer for the actual 4He-4He interaction. However, decreasing the potential strength we calculate several excited states of the trimer which exhibit Efimov character. We also solve for excited state energies of these clusters which are in good agreement with Monte Carlo hyperspherical description.
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36.40.Cg Electronic and magnetic properties of clusters
03.75.Nt Other Bose-Einstein condensation phenomena
03.75.Hh Static properties of condensates; thermodynamical, statistical, and structural properties
03.65.Ge Solutions of wave equations: bound states

Molecular dynamics scheme for precise estimation of electrostatic interaction via zero-dipole summation principle

Ikuo Fukuda, Yasushige Yonezawa, and Haruki Nakamura

J. Chem. Phys. 134, 164107 (2011); http://dx.doi.org/10.1063/1.3582791 (15 pages) | Cited 2 times

Online Publication Date: 28 April 2011

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We propose a novel idea, zero-dipole summation, for evaluating the electrostatic energy of a classical particle system, and have composed an algorithm for effectively utilizing the idea for molecular dynamics. It conceptually prevents the nonzero-charge and nonzero-dipole states artificially generated by a simple cutoff truncation. The resulting energy formula is nevertheless represented by a simple pairwise function sum, which enables facile application to high-performance computation. By following a heuristic approach to derive the current electrostatic energy formula, we developed an axiomatic approach to construct the method consistently. Explorations of the theoretical details of our method revealed the structure of the generated error, and we analyzed it by comparisons with other methods. A numerical simulation using liquid sodium chloride confirmed that the current method with a small damping factor yielded sufficient accuracy with a practical cutoff distance region. The current energy function also conducts stable numerical integration in a liquid MD simulation. Our method is an extension of the charge neutralized summation developed by Wolf et al. [J. Chem. Phys. 110, 8254 (1999)]. Furthermore, we found that the current method becomes a generalization of the preaveraged potential method proposed by Yakub and Ronchi [J. Chem. Phys. 119, 11556 (2003)], which is based on a viewpoint different from the neutrality. The current study presents these relationships and suggests possibilities for their further applications.
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61.20.Ja Computer simulation of liquid structure

Embedded density functional theory for covalently bonded and strongly interacting subsystems

Jason D. Goodpaster, Taylor A. Barnes, and Thomas F. Miller, III

J. Chem. Phys. 134, 164108 (2011); http://dx.doi.org/10.1063/1.3582913 (9 pages) | Cited 4 times

Online Publication Date: 28 April 2011

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Embedded density functional theory (e-DFT) is used to describe the electronic structure of strongly interacting molecular subsystems. We present a general implementation of the Exact Embedding (EE) method [J. Chem. Phys. 133, 084103 (2010)] to calculate the large contributions of the nonadditive kinetic potential (NAKP) in such applications. Potential energy curves are computed for the dissociation of Li+–Be, CH3–CF3, and hydrogen-bonded water clusters, and e-DFT results obtained using the EE method are compared with those obtained using approximate kinetic energy functionals. In all cases, the EE method preserves excellent agreement with reference Kohn–Sham calculations, whereas the approximate functionals lead to qualitative failures in the calculated energies and equilibrium structures. We also demonstrate an accurate pairwise approximation to the NAKP that allows for efficient parallelization of the EE method in large systems; benchmark calculations on molecular crystals reveal ideal, size-independent scaling of wall-clock time with increasing system size.
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31.15.E- Density-functional theory
31.50.-x Potential energy surfaces
33.15.Fm Bond strengths, dissociation energies
36.40.Cg Electronic and magnetic properties of clusters

Fluctuations in the ensemble of reaction pathways

G. Mazzola, S. a Beccara, P. Faccioli, and H. Orland

J. Chem. Phys. 134, 164109 (2011); http://dx.doi.org/10.1063/1.3581892 (15 pages) | Cited 1 time

Online Publication Date: 28 April 2011

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The dominant reaction pathway is a rigorous framework to microscopically compute the most probable trajectories, in nonequilibrium transitions. In the low-temperature regime, such dominant pathways encode the information about the reaction mechanism and can be used to estimate nonequilibrium averages of arbitrary observables. On the other hand, at sufficiently high temperatures, the stochastic fluctuations around the dominant paths become important and have to be taken into account. In this work, we develop a technique to systematically include the effects of such stochastic fluctuations, to order kBT. This method is used to compute the probability for a transition to take place through a specific reaction channel and to evaluate the reaction rate.
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82.20.Hf Product distribution
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.20.Uv Stochastic theories of rate constants
82.20.Db Transition state theory and statistical theories of rate constants

Ab initio lattice dynamics of nonconducting crystals by systematic fragmentation

Michael A. Collins

J. Chem. Phys. 134, 164110 (2011); http://dx.doi.org/10.1063/1.3581845 (14 pages)

Online Publication Date: 29 April 2011

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A systematic method for approximating the ab initio electronic energy of crystal lattices has been improved by the incorporation of long range electrostatic and dispersion interactions. The effect of these long range interactions on the optimization of the crystal structure is reported. The harmonic lattice dynamics have been evaluated to give phonon frequencies and neutron scattering intensities. Exemplary results are reported for diamond, silicon, and α-quartz using Hartree–Fock, Möller–Plesset perturbation, and coupled-cluster levels of ab initio theory.
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61.66.-f Structure of specific crystalline solids
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
71.15.-m Methods of electronic structure calculations
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

The photodissociation dynamics of tetrachloroethylene

Nuradhika Herath, Michael L. Hause, and Arthur G. Suits

J. Chem. Phys. 134, 164301 (2011); http://dx.doi.org/10.1063/1.3580282 (7 pages)

Online Publication Date: 22 April 2011

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We present a direct current slice imaging study of tetrachloroethylene (C2Cl4) photodissociation, probing the resulting ground state Cl (2P3/2) and spin-orbit excited state Cl* (2P1/2) products. We report photofragment images, total translational energy distributions and the product branching ratio of Cl*/Cl following dissociation at 235 and 202 nm, obtained using a two-color reduced-Doppler dissociation/probe. Near 235 nm, the Cl translational energy distribution shows a peak at the limit of the available energy, indicating a direct dissociation through a σ*(C–Cl) ← π (C=C) transition, which is superimposed on a broader underlying distribution. The ground state Cl image and associated translational energy distribution at 202 nm is broad and peaked at lower energy, suggesting either internal conversion to the ground state or a lower excited state prior to dissociation. The Cl* images are similarly broad at both wavelengths. The branching ratio is presented as a function of recoil energy, but after integration shows a near-statistical average of Cl:Cl* as 70:30 at both wavelengths. All the images are largely isotropic, with anisotropy parameters (β) of 0.05 ± 0.03.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
82.50.Hp Processes caused by visible and UV light

Two-dimensional resonance enhanced multiphoton ionization of HiCl; i = 35, 37: State interactions, photofragmentations and energetics of high energy Rydberg states

Kristján Matthíasson, Jingming Long, Huasheng Wang, and Ágúst Kvaran

J. Chem. Phys. 134, 164302 (2011); http://dx.doi.org/10.1063/1.3580876 (8 pages)

Online Publication Date: 22 April 2011

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Mass spectra were recorded for (2 + n) resonance enhanced multiphoton ionization (REMPI) of HCl as a function of resonance excitation energy in the 88865-89285 cm−1 region to obtain two-dimensional REMPI data. Band spectra due to two-photon resonance transitions to number of Rydberg states (Ω′ = 0, 1, and 2) and the ion-pair state V(1Σ+(Ω′ = 0)) for H35Cl and H37Cl were identified, assigned, and analyzed with respect to Rydberg to ion-pair interactions. Perturbations show as line-, hence energy level-, shifts, as well as ion signal intensity variations with rotational quantum numbers, J′, which, together, allowed determination of parameters relevant to the nature and strength of the state interactions as well as dissociation and ionization processes. Whereas near-resonance, level-to-level, interactions are found to be dominant in heterogeneous state interactions (ΔΩ ≠ 0) significant off-resonance interactions are observed in homogeneous interactions (ΔΩ = 0). The alterations in Cl+ and HCl+ signal intensities prove to be very useful for spectra assignments. Data relevant to excitations to the j3Σ(0+) Rydberg states and comparison with (3 + n) REMPI spectra allowed reassignment of corresponding spectra peaks. A band previously assigned to an Ω = 0 Rydberg state was reassigned to an Ω = 2 state (ν0 = 88957.6 cm−1).
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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
33.70.Jg Line and band widths, shapes, and shifts
33.15.Ta Mass spectra

Characterization of C4H in the A2Π and X2Σ+ states by double resonance four-wave mixing

Fabio J. Mazzotti, Ranjini Raghunandan, Aaseef Muhammed Esmail, Marek Tulej, and John P. Maier

J. Chem. Phys. 134, 164303 (2011); http://dx.doi.org/10.1063/1.3578188 (7 pages) | Cited 1 time

Online Publication Date: 22 April 2011

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The B2Π − X2Σ+ electronic spectrum of C4H has been studied by degenerate and double resonance four-wave mixing. The technique identifies vibrational levels in the X2Σ+ ground state. Its sensitivity and unique characteristics permit detection of new levels. The A2Π state lying 222 cm−1 above the X2Σ ground state is also observed, confirming the analysis from anion photoelectron spectroscopy but with improved accuracy. Vibrational level determination in the A2Π electronic manifold up to 700 cm−1 above v = 0 is made. A Renner–Teller analysis is carried out for the two lowest bending modes v6 and v7 in the A2Π state by diagonalization of the effective Hamiltonian matrix. The Renner–Teller parameters ∈ 6, ∈ 7, and ∈ 67, the vibrations ω6 and ω7 and the spin–orbit coupling constant Aso are determined.
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33.60.+q Photoelectron spectra
33.20.Tp Vibrational analysis
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.15.Mt Rotation, vibration, and vibration-rotation constants
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

First-principles determination of the structure of NaN and NaN− clusters with up to 80 atoms

Andrés Aguado and Oleg Kostko

J. Chem. Phys. 134, 164304 (2011); http://dx.doi.org/10.1063/1.3582911 (12 pages) | Cited 1 time

Online Publication Date: 25 April 2011

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We have performed an extensive computational search for the global minimum (GM) structures of both neutral and anionic sodium clusters with up to 80 atoms. The theoretical framework combines basin hopping unbiased optimizations based on a Gupta empirical potential (EP) and subsequent reoptimization of many candidate structures at the density functional theory level. An important technical point is that the candidates are selected based on cluster shape descriptors rather than the relative stabilities of the EP model. An explicit comparison of the electronic density of states of cluster anions to experimental photoemission spectra suggests that the correct GM structures have been identified for all but two sizes (N = 47 and 70). This comparison validates the accuracy of the proposed methodology. Furthermore, our GM structures either match or improve over the results of previous works for all sizes. Sodium clusters are seen to accommodate strain very efficiently because: (a) many structures are based on polyicosahedral packing; (b) others are based on Kasper polyhedra and show polytetrahedral order; (c) finally, some (N + 1)-atom structures are obtained by incorporating one adatom into the outermost atomic shell of a compact N-atom cluster, at the cost of increasing the bond strain. GM structures of neutrals and anions differ for most sizes. Cluster stabilities are analyzed and shown to be dominated by electron shell closing effects for the smaller clusters and by geometrical packing effects for the larger clusters. The critical size separating both regimes is around 55 atoms. Some implications for the melting behavior of sodium clusters are discussed.
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36.40.Mr Spectroscopy and geometrical structure of clusters
36.40.Cg Electronic and magnetic properties of clusters
33.60.+q Photoelectron spectra
31.15.E- Density-functional theory

Cr(CO)6 photochemistry: Semi-classical study of UV absorption spectral intensities and dynamics of photodissociation

Rachel Crespo-Otero and Mario Barbatti

J. Chem. Phys. 134, 164305 (2011); http://dx.doi.org/10.1063/1.3582914 (12 pages)

Online Publication Date: 25 April 2011

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The UV absorption spectrum of Cr(CO)6 (chromium hexacarbonyl) in gas phase is investigated by theoretical methods with focus on the absorption intensities. It is shown that in spite of good predictions for the excitation energies, the most frequently employed methods for excited-state calculations produce poor predictions for oscillator strengths and absorption cross sections. In particular, time-dependent DFT predicts relative intensities for the two main spectral bands to be up to five times larger than the experimental results depending on the functional. The best results are obtained by a multireference configuration interaction method based on DFT (DFT/MRCI). Spectral shoulders caused by vibronic-coupling absorption are assigned based on symmetry-restricted spectrum simulations. The dynamics of Cr(CO)6 photodissociation was also considered at TDDFT/B3LYP level. The estimated time constants for the Cr(CO)6 relaxation and dissociation are in excellent agreement with experimental values. The time constant for internal conversion, however, is longer than the experimentally observed by factor 2, presumably due to an underestimation of the experimental analysis.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
31.15.vj Electron correlation calculations for atoms and ions: excited states
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
31.15.E- Density-functional theory
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.20.Lg Ultraviolet spectra

H(D) → D(H) + Cu(111) collision system: Molecular dynamics study of surface temperature effects

Can D. Vurdu and Ziya B. Güvenç

J. Chem. Phys. 134, 164306 (2011); http://dx.doi.org/10.1063/1.3583811 (11 pages)

Online Publication Date: 25 April 2011

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All the channels of the reaction dynamics of gas-phase H (or D) atoms with D (or H) atoms adsorbed onto a Cu(111) surface have been studied by quasiclassical constant energy molecular dynamics simulations. The surface is flexible and is prepared at different temperature values, such as 30 K, 94 K, and 160 K. The adsorbates were distributed randomly on the surface to create 0.18 ML, 0.28 ML, and 0.50 ML of coverages. The multi-layer slab is mimicked by a many-body embedded-atom potential energy function. The slab atoms can move according to the exerted external forces. Treating the slab atoms non-rigid has an important effect on the dynamics of the projectile atom and adsorbates. Significant energy transfer from the projectile atom to the surface lattice atoms takes place especially during the first impact that modifies significantly the details of the dynamics of the collisions. Effects of the different temperatures of the slab are investigated in this study. Interaction between the surface atoms and the adsorbates is modeled by a modified London–Eyring–Polanyi–Sato (LEPS) function. The LEPS parameters are determined by using the total energy values which were calculated by a density functional theory and a generalized gradient approximation for an exchange-correlation energy for many different orientations, and locations of one- and two-hydrogen atoms on the Cu(111) surface. The rms value of the fitting procedure is about 0.16 eV. Many different channels of the processes on the surface have been examined, such as inelastic reflection of the incident hydrogen, subsurface penetration of the incident projectile and adsorbates, sticking of the incident atom on the surface. In addition, hot-atom and Eley-Rideal direct processes are investigated. The hot-atom process is found to be more significant than the Eley-Rideal process. Furthermore, the rate of subsurface penetration is larger than the sticking rate on the surface. In addition, these results are compared and analyzed as a function of the surface temperatures.
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34.35.+a Interactions of atoms and molecules with surfaces
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
31.15.xv Molecular dynamics and other numerical methods
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.43.Mn Adsorption kinetics
31.15.E- Density-functional theory
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions

Measurement of the electric quadrupole moment of CO

Naven Chetty and Vincent W. Couling

J. Chem. Phys. 134, 164307 (2011); http://dx.doi.org/10.1063/1.3585605 (5 pages) | Cited 1 time

Online Publication Date: 27 April 2011

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Measurements of the temperature dependence of the Buckingham effect (electric-field-gradient-induced birefringence, EFGIB) for gaseous carbon monoxide are presented. The measurements span the temperature range 301.2–473.9 K, which allows for separation of the temperature-independent hyperpolarizability contribution from the temperature-dependent quadrupole contribution. It is demonstrated that in the case of carbon monoxide, quantization of the rotational motion of the molecules needs to be considered, the analysis yielding a quadrupole moment of Θ = (−8.77 ± 0.31) × 10−40 C m2 and a hyperpolarizability term of b′ = (−0.1243 ± 0.0078)  × 10−60 C3 m4 J−2. For dipolar molecules, the quadrupole moment is origin dependent, and the value reported here is referred to an origin called the effective quadrupole center. Comparison of this value with the center-of-mass quadrupole moment obtained from other experiments yields information about the dynamic dipole-quadrupole and dipole-magnetic dipole polarizabilities. The temperature-independent term, which contributes (7.0 ± 0.6)% to the EFGIB at room temperature, is by no means insignificant, and must necessarily be accounted for if the quadrupole moment is to be definitively established. The measured Θ and b′ are compared with the best available ab initio calculated values.
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33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.ap Polarizabilities and other atomic and molecular properties
33.20.Sn Rotational analysis

Coherent control of indirect photofragmentation in the weak-field limit: Control of transient fragment distributions

Chuan-Cun Shu and Niels E. Henriksen

J. Chem. Phys. 134, 164308 (2011); http://dx.doi.org/10.1063/1.3582928 (8 pages) | Cited 1 time

Online Publication Date: 27 April 2011

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We demonstrate theoretically that laser-induced coherent quantum interference control of asymptotic states of dissociating molecules is possible – even in the (one-photon) weak-field limit starting from a single vibrational eigenstate – when resonances are in play. This is illustrated for the NaI molecule, where it is shown that the probability of observing atomic fragments as well as the distribution of their relative momenta can be changed by a phase modulated pulse with a fixed bandwidth. This type of control is restricted to finite times during the indirect fragmentation.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
42.50.Wk Mechanical effects of light on material media, microstructures and particles

Molecular dynamics study on evaporation and condensation of n-dodecane at liquid–vapor phase equilibria

Bing-Yang Cao, Jian-Fei Xie, and Sergei S. Sazhin

J. Chem. Phys. 134, 164309 (2011); http://dx.doi.org/10.1063/1.3579457 (9 pages) | Cited 1 time

Online Publication Date: 28 April 2011

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Molecular dynamics simulations are performed to study the evaporation and condensation of n-dodecane (C12H26) at temperatures in the range 400–600 K. A modified optimized potential for liquid simulation model is applied to take into account the Lennard-Jones, bond bending and torsion potentials with the bond length constrained. The equilibrium liquid–vapor n-dodecane interface thickness is predicted to be ∼1.2–2.0 nm. It is shown that the molecular chains lie preferentially parallel to the interface in the liquid–vapor transition region. The predicted evaporation/condensation coefficient decreased from 0.9 to 0.3 when temperature increased from 400 to 600 K. These values can be used for the formulation of boundary conditions in the kinetic modeling of droplet heating and evaporation processes; they are noticeably different from those predicted by the transition state theory. We also present the typical molecular behaviors in the evaporation and condensation processes. The molecular exchange in condensation, typical for simple molecules, has never been observed for n-dodecane molecular chains.
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64.70.F- Liquid-vapor transitions
61.20.Ja Computer simulation of liquid structure
81.30.Dz Phase diagrams of other materials
68.15.+e Liquid thin films

Electronic spectra of GdF reanalyzed by decomposing state functions according to f-shell angular momentum

Shigeyoshi Yamamoto and Hiroshi Tatewaki

J. Chem. Phys. 134, 164310 (2011); http://dx.doi.org/10.1063/1.3583367 (11 pages)

Online Publication Date: 28 April 2011

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The electronic structure of the GdF molecule was studied by means of four-component relativistic configuration interaction (CI) calculations [S. Yamamoto, H. Tatewaki, and T. Saue, J. Chem. Phys. 129, 244505 (2008)10.1063/1.3039794]. To analyze the electronic spectra more accurately, the CI wave function is decomposed according to the angular momentum (Ωf) generated from the (4f)7 electrons. The weight of a specified Ωf is referred to as the “f-shell Omega component weight.” This Ωf plays a crucial role in classifying the strong electronic transitions from the upper states (0.7 eV–3.0 eV) to the lower states (∼0.55 eV). For these transitions, the upper and lower states have almost identical Ωf weights. This appears to be a necessary condition for a transition to be strong. The same condition is expected to hold for other lanthanide linear molecules. A point charge model is also studied, acting as a simplified model of GdF; it successfully reproduces the spectra of GdF, justifying studies based on ligand field theory.
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31.15.vn Electron correlation calculations for diatomic molecules
31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions

Discriminating the structure of exo-2-aminonorbornane using nuclear quadrupole coupling interactions

Patricia Écija, Emilio J. Cocinero, Alberto Lesarri, Judith Millán, Francisco Basterretxea, José A. Fernández, and Fernando Castaño

J. Chem. Phys. 134, 164311 (2011); http://dx.doi.org/10.1063/1.3583494 (8 pages)

Online Publication Date: 28 April 2011

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The intrinsic conformational and structural properties of the bicycle exo-2-aminonorbornane have been probed in a supersonic jet expansion using Fourier-transform microwave (FT-MW) spectroscopy and quantum chemical calculations. The rotational spectrum revealed two different conformers arising from the internal rotation of the amino group, exhibiting small (MHz) hyperfine patterns originated by the 14N nuclear quadrupole coupling interaction. Complementary ab initio (MP2) and DFT (B3LYP and M05–2X) calculations provided comparative predictions for the structural properties, rotational and centrifugal distortion data, hyperfine parameters, and isomerization barriers. Due to the similarity of the rotational constants, the structural assignment of the observed rotamers and the calculation of the torsion angles of the amino group were based on the conformational dependence of the 14N nuclear quadrupole coupling hyperfine tensor. In the most stable conformation (ss), the two amino N-H bonds are staggered with respect to the adjacent C-H bond. In the second conformer (st), only one of the N-H bonds is staggered and the other is trans. A third predicted conformer (ts) was not detected, consistent with a predicted conformational relaxation to conformer ss through a low barrier of 5.2 kJ mol−1.
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33.25.+k Nuclear resonance and relaxation
33.20.Bx Radio-frequency and microwave spectra
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
33.15.Bh General molecular conformation and symmetry; stereochemistry
31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
31.15.E- Density-functional theory

Conformer-specific vibronic spectroscopy and vibronic coupling in a flexible bichromophore: Bis-(4-hydroxyphenyl)methane

Chirantha P. Rodrigo, Christian W. Müller, Nathan R. Pillsbury, William H. James, III, David F. Plusquellic, and Timothy S. Zwier

J. Chem. Phys. 134, 164312 (2011); http://dx.doi.org/10.1063/1.3580901 (14 pages) | Cited 2 times

Online Publication Date: 28 April 2011

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The vibronic spectroscopy of jet-cooled bis-(4-hydroxyphenyl)methane has been explored using fluorescence excitation, dispersed fluorescence (DFL), UV–UV hole-burning, UV depletion, and fluorescence-dip infrared spectroscopies. Calculations predict the presence of three nearly isoenergetic conformers that differ in the orientations of the two OH groups in the para positions on the two aromatic rings (labeled uu, dd, and ud). In practice, two conformers (labeled A and B) are observed, with S0–S1 origins at 35 184 and 35 209 cm−1, respectively. The two conformers have nearly identical vibronic spectra and hydride stretch infrared spectra. The low-frequency vibronic structure is assigned to bands involving the phenyl torsions (T and math), ring-flapping (R and math), and butterfly (β) modes. Symmetry arguments lead to a tentative assignment of the two conformers as the C2 symmetric uu and dd conformers. The S0–S2 origins are assigned to bands located 132 cm−1 above the S0–S1 origins of both conformers. DFL spectra from the S2 origin of the two conformers display extensive evidence for vibronic coupling between the two close-lying electronic states. Near-resonant coupling from the S2 origin occurs dominantly to S1 math1 and S1 math1β1 levels, which are located –15 and +31 cm−1 from it. Unusual vibronic activity in the ring-breathing (ν1) and ring-deformation (ν6a) modes is also attributed to vibronic coupling involving these Franck–Condon active modes. A multimode vibronic coupling model is developed based on earlier theoretical descriptions of molecular dimers [Fulton and Gouterman, J. Chem. Phys. 35, 1059 (1961)] and applied here to flexible bichromophores. The model is able to account for the ring-mode activity under conditions in which the S2 origin is strongly mixed (60%/40%) with S1 math1 and math1 levels. The direct extension of this model to the T /math and R /math inter-ring mode pairs is only partially successful and required some modification to lower the efficiency of the S1/S2 mixing compared to the ring modes.
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33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.50.Dq Fluorescence and phosphorescence spectra
33.20.Ea Infrared spectra
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors

On the properties of X⋅⋅⋅N noncovalent interactions for first-, second-, and third-row X atoms

Steve Scheiner

J. Chem. Phys. 134, 164313 (2011); http://dx.doi.org/10.1063/1.3585611 (9 pages) | Cited 1 time

Online Publication Date: 29 April 2011

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In addition to a structure with a PH⋅⋅⋅N H-bond, a second complex of greater stability is formed when the PH3 is rotated such that its P-H bond is pointing away from the approaching N lone pair of NH3. Quantum calculations are applied to examine whether such a complex is characteristic only of P, or may occur as well for other atoms of the first, second, or third rows of the periodic table. The molecules PH3, H2S, HCl, AsH3, and NH3 are all paired with NH3 as electron donor. While NH3 will not engage in an N⋅⋅⋅N attraction, all the others do form a X⋅⋅⋅N complex. The energetics, geometries, and other properties of these complexes are relatively insensitive to the nature of the X atom. This uniformity contrasts sharply with the H-bonded XH⋅⋅⋅N complexes where a strong sensitivity to X is observed. The three-dimensional nature of the electrostatic potential, in conjunction with the striving for a linear H-X⋅⋅⋅N orientation that maximizes charge transfer, serves as an excellent tool in understanding both the shape of the potential energy surface and the proclivity to engage in a X⋅⋅⋅N interaction.
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31.50.-x Potential energy surfaces
34.70.+e Charge transfer
33.15.Fm Bond strengths, dissociation energies
33.15.Bh General molecular conformation and symmetry; stereochemistry
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation

Density functional theory of inhomogeneous liquids. IV. Squared-gradient approximation and classical nucleation theory

James F. Lutsko

J. Chem. Phys. 134, 164501 (2011); http://dx.doi.org/10.1063/1.3582901 (14 pages) | Cited 3 times

Online Publication Date: 25 April 2011

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The squared-gradient approximation to the modified-core Van der Waals density functional theory model is developed. A simple, explicit expression for the SGA coefficient involving only the bulk equation of state and the interaction potential is given. The model is solved for planar interfaces and spherical clusters and is shown to be quantitatively accurate in comparison to computer simulations. An approximate technique for solving the SGA based on piecewise-linear density profiles is introduced and is shown to give reasonable zeroth-order approximations to the numerical solution of the model. The piecewise-linear models of spherical clusters are shown to be a natural extension of classical nucleation theory and serve to clarify some of the nonclassical effects previously observed in liquid–vapor nucleation. Nucleation pathways are investigated using both constrained energy-minimization and steepest-descent techniques.
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71.15.Mb Density functional theory, local density approximation, gradient and other corrections
64.60.Q- Nucleation
64.70.F- Liquid-vapor transitions
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
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