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7 Aug 2010

Volume 133, Issue 5, Articles (05xxxx)

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J. Chem. Phys. 133, 054302 (2010); http://dx.doi.org/10.1063/1.3455431 (9 pages)

Jianyi Ma, Shi Ying Lin, Hua Guo, Zhigang Sun, Dong H. Zhang, and Daiqian Xie
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Communication: The influence of line tension on the formation of liquid bridges

F. Dutka and M. Napiórkowski

J. Chem. Phys. 133, 051101 (2010); http://dx.doi.org/10.1063/1.3469770 (4 pages) | Cited 1 time

Online Publication Date: 6 August 2010

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The formation of liquid bridges between planar and conical substrates is analyzed macroscopically taking into account the line tension. Depending on the value of the line tension coefficient τ and geometric parameters of the system one observes two different scenarios of liquid bridge formation upon changing the fluid state along the bulk liquid-vapor coexistence. For τ>τ∗ (τ∗<0) there is a first-order transition to a state with infinitely thick liquid bridge. For τ<τ∗ the scenario consists of two steps: First there is a first-order transition to a state with liquid bridge of finite thickness, which upon further increase of temperature is followed by continuous growth of the thickness of the bridge to infinity. In addition to constructing the relevant phase diagram we examine the dependence of the width of the bridge on thermodynamic and geometric parameters of the system.
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68.03.Cd Surface tension and related phenomena
81.30.Dz Phase diagrams of other materials
64.70.Ja Liquid-liquid transitions
05.70.Np Interface and surface thermodynamics
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back to top Theoretical Methods and Algorithms

A semiclassical correction for quantum mechanical energy levels

Alexey L. Kaledin, C. William McCurdy, and William H. Miller

J. Chem. Phys. 133, 054101 (2010); http://dx.doi.org/10.1063/1.3464318 (6 pages) | Cited 1 time

Online Publication Date: 2 August 2010

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We propose a semiclassical method for correcting molecular energy levels obtained from a quantum mechanical variational calculation. A variational calculation gives the energy level (i.e., eigenvalue) as the expectation value of the molecular Hamiltonian 〈ϕ|math|ϕ〉, where |ϕ〉 is the trial wave function. The true (i.e., exact) eigenvalue E can thus be expressed as this variational result plus a correction, i.e., E = 〈ϕ|math|ϕ〉+ΔE, the correction being due to the lack of exactness of the trial wave function. A formally exact expression for ΔE is usually given (via Löwdin partitioning methodology) in terms of the Greens function of the Hamiltonian projected onto the orthogonal complement of |ϕ〉. Formal treatment of this expression (using Brillouin–Wigner perturbation theory to infinite order) leads to an expression for ΔE that involves matrix elements of the Greens function for the unprojected, i.e., full molecular Hamiltonian, which can then be approximated semiclassically. (Specifically, the Greens function is expressed as the Fourier transform of the quantum mechanical time evolution operator, math, which in turn is approximated by using an initial value representation of semiclassical theory.) Calculations for several test problems (a one dimensional quartic potential, and vibrational energy levels of H2O and H2CO) clearly support our proposition that the error in the total eigenvalue E arises solely due to the semiclassical error in approximating ΔE, which is usually a small fraction of the total energy E itself.
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31.10.+z Theory of electronic structure, electronic transitions, and chemical binding
31.15.xt Variational techniques
03.65.Sq Semiclassical theories and applications
03.65.Db Functional analytical methods
03.65.Fd Algebraic methods

Unidirectional hopping transport of interacting particles on a finite chain

Mario Einax, Gemma C. Solomon, Wolfgang Dieterich, and Abraham Nitzan

J. Chem. Phys. 133, 054102 (2010); http://dx.doi.org/10.1063/1.3463000 (12 pages) | Cited 2 times

Online Publication Date: 2 August 2010

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Particle transport through an open, discrete one-dimensional channel against a mechanical or chemical bias is analyzed within a master equation approach. The channel, externally driven by time-dependent site energies, allows multiple occupation due to the coupling to reservoirs. Performance criteria and optimization of active transport in a two-site channel are discussed as a function of reservoir chemical potentials, the load potential, interparticle interaction strength, driving mode, and driving period. Our results, derived from exact rate equations, are used in addition to test a previously developed time-dependent density functional theory, suggesting a wider applicability of that method in investigations of many particle systems far from equilibrium.
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05.50.+q Lattice theory and statistics (Ising, Potts, etc.)
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion
05.60.-k Transport processes

Theoretical studies of surface enhanced hyper-Raman spectroscopy: The chemical enhancement mechanism

Nicholas Valley, Lasse Jensen, Jochen Autschbach, and George C. Schatz

J. Chem. Phys. 133, 054103 (2010); http://dx.doi.org/10.1063/1.3456544 (8 pages) | Cited 5 times

Online Publication Date: 3 August 2010

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Hyper-Raman spectra for pyridine and pyridine on the surface of a tetrahedral 20 silver atom cluster are calculated using static hyperpolarizability derivatives obtained from time dependent density functional theory. The stability of the results with respect to choice of exchange-correlation functional and basis set is verified by comparison with experiment and with Raman spectra calculated for the same systems using the same methods. Calculated Raman spectra were found to match well with experiment and previous theoretical calculations. The calculated normal and surface enhanced hyper-Raman spectra closely match experimental results. The chemical enhancement factors for hyper-Raman are generally larger than for Raman (102−104 versus 101−102). Integrated hyper-Raman chemical enhancement factors are presented for a set of substituted pyridines. A two-state model is developed to predict these chemical enhancement factors and this was found to work well for the majority of the molecules considered, providing a rationalization for the difference between hyper-Raman and Raman enhancement factors.
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31.15.E- Density-functional theory

Link atom bond length effect in ONIOM excited state calculations

Marco Caricato, Thom Vreven, Gary W. Trucks, and Michael J. Frisch

J. Chem. Phys. 133, 054104 (2010); http://dx.doi.org/10.1063/1.3474570 (10 pages) | Cited 1 time

Online Publication Date: 5 August 2010

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We investigate how the choice of the link atom bond length affects an electronic transition energy calculation with the so-called our own N-layer integrated molecular orbital molecular mechanics (ONIOM) hybrid method. This follows our previous paper [ M. Caricato et al., J. Chem. Phys. 131, 134105 (2009) ], where we showed that ONIOM is able to accurately approximate electronic transition energies computed at a high level of theory such as the equation of motion coupled cluster singles and doubles (EOM-CCSD) method. In this study we show that the same guidelines used in ONIOM ground state calculations can also be followed in excited state calculations, and that the link atom bond length has little effect on the ONIOM energy when a sensible model system is chosen. We also suggest further guidelines for excited state calculations which can help in checking the effectiveness of the definition of the model system and controlling the noise in the calculation.
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31.50.Bc Potential energy surfaces for ground electronic states
33.15.Dj Interatomic distances and angles
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
31.15.ee Time-dependent density functional theory
31.15.bw Coupled-cluster theory

Steady-state current transfer and scattering theory

Vered Ben-Moshe, Dhurba Rai, Spiros S. Skourtis, and Abraham Nitzan

J. Chem. Phys. 133, 054105 (2010); http://dx.doi.org/10.1063/1.3466876 (9 pages) | Cited 1 time

Online Publication Date: 6 August 2010

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The correspondence between the steady-state theory of current transfer and scattering theory in a system of coupled tight-binding models of one-dimensional wires is explored. For weak interwire coupling both calculations give nearly identical results, except at singular points associated with band edges. The effect of decoherence in each of these models is studied using a generalization of the Liouville–von Neuman equation suitable for steady-state situations. An example of a single impurity model is studied in detail, leading to a lattice model of scattering off target that affects both potential scattering and decoherence. For an impurity level lying inside the energy band, the transmission coefficient diminishes with increasing dephasing rate, while the opposite holds for impurity energy outside the band. The efficiency of current transfer in the coupled wire system decreases with increasing dephasing.
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73.63.-b Electronic transport in nanoscale materials and structures
05.50.+q Lattice theory and statistics (Ising, Potts, etc.)
71.55.-i Impurity and defect levels
73.23.-b Electronic transport in mesoscopic systems

Optimal design strategies for electrostatic energy storage in quantum multiwell heterostructures

Ilya Grigorenko and Herschel Rabitz

J. Chem. Phys. 133, 054106 (2010); http://dx.doi.org/10.1063/1.3469984 (5 pages)

Online Publication Date: 6 August 2010

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We study physical principles of optimal design of a nanoscale multiwell heterostructure functioning as an electrostatic energy storage device. We performed numerical optimization of the multiwell trapping potential for electrons in the nanostructure with the goal to obtain the maximum possible static polarizability of the system. The response of the heterostructure is modeled microscopically using nonlocal linear response theory within the random phase approximation. Three main design strategies are identified which lead to the maximization of the stored energy. We found that the efficiency of each strategy crucially depends on the temperature and the broadening of electron levels. The stored energy for optimized heterostructures can exceed the nonoptimized ones by a factor of 450. These findings provide a theoretical basis for the development of new nanoscale capacitors with high energy density storage capabilities.
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84.60.-h Direct energy conversion and storage
84.32.Tt Capacitors
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

About the collapse of the 3.3 μm CH stretching band with ionization in polycyclic aromatic hydrocarbons: Configuration interaction and quantum Monte Carlo studies of the CH fragment

Françoise Pauzat, Julien Pilmé, Julien Toulouse, and Yves Ellinger

J. Chem. Phys. 133, 054301 (2010); http://dx.doi.org/10.1063/1.3465552 (6 pages) | Cited 3 times

Online Publication Date: 2 August 2010

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The puzzling difference between the IR spectra of polycyclic aromatic hydrocarbons (PAHs) and those of the corresponding positive ions (PAHs+) is a well documented fact, although the basic reason for it is far from clear. In this report, the CH fragment, in its neutral and ionized forms is taken as a case study for investigating the collapse of the CH stretching vibration with ionization. A comprehensive study of the dipole moment function around the equilibrium geometries of the fragments using large scale configuration interaction and quantum Monte Carlo methods shows very different variations with the CH distance: a marked decrease for neutral CH(2Π) and a perfect stability for ionized CH+(1Σ+). These results are consistent with strong/weak intensities of the CH vibrations in the neutral/ionized PAHs, the key point being the presence, or not, of a hole in the π shell. A topological analysis of the electronic densities shows that the collapse of the CH stretching with ionization is directly linked to the compensation between the internal charge transfer contribution and the distortion of the electronic density within the CH bond.
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34.50.Gb Electronic excitation and ionization of molecules
31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
02.70.Uu Applications of Monte Carlo methods
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
34.70.+e Charge transfer

State-to-state quantum dynamics of the O(3P)+OH(2Π)→H(2S)+O2(3Σg−) reaction

Jianyi Ma, Shi Ying Lin, Hua Guo, Zhigang Sun, Dong H. Zhang, and Daiqian Xie

J. Chem. Phys. 133, 054302 (2010); http://dx.doi.org/10.1063/1.3455431 (9 pages) | Cited 2 times

Online Publication Date: 2 August 2010

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The authors report a detailed quantum mechanical study of the state-to-state dynamics of the O+OH(vi = 0, ji = 0)→H+O2(vf,jf) reaction on an accurate HO2(X2A″) potential energy surface. The scattering dynamics was treated using a reactant coordinate based Chebyshev real wavepacket method with full Coriolis coupling. A total of 84 partial waves were calculated in order to achieve convergence up to the collision energy of 0.17 eV. The differential cross section is near forward-backward symmetric, consistent with the complex-forming mechanism. The O2 product was found to have a monotonically decaying vibrational distribution and highly excited and inverted rotational distributions, also consistent with the formation of the HO2 intermediate. These quantum mechanical results were compared with those obtained in earlier quasiclassical trajectory and statistical studies and it is shown that the statistical theory gives a reasonably good description of the product state distributions despite its inability to predict the total reaction cross section.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Ej Quantum theory of reaction cross section
82.20.Fd Collision theories; trajectory models
82.20.Hf Product distribution
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.20.Rp State to state energy transfer

Toward a realistic density functional theory potential energy surface for the H5+ cluster

Patricia Barragán, Rita Prosmiti, Octavio Roncero, Alfredo Aguado, Pablo Villarreal, and Gerardo Delgado-Barrio

J. Chem. Phys. 133, 054303 (2010); http://dx.doi.org/10.1063/1.3466763 (10 pages) | Cited 4 times

Online Publication Date: 2 August 2010

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The potential energy surface of H5+ is characterized using density functional theory. The hypersurface is evaluated at selected configurations employing different functionals, and compared with results obtained from ab initio CCSD(T) calculations. The lowest ten stationary points (minima and saddle-points) on the surface are located, and the features of the short-, intermediate-, and long-range intermolecular interactions are also investigated. A detailed analysis of the surface’s topology, and comparisons with extensive CCSD(T) results, as well as a recent ab initio analytical surface, shows that density functional theory calculations using the B3(H) functional represent very well all aspects studied on the H5+ potential. These include the tiny energy difference between the minimum at 1-C2v configuration and the 2-D2d one corresponding to the transition state for the proton transfer between the two equivalent C2v minima, and also the correct asymptotic behavior of the long-range interactions. The calculated binding energy and dissociation enthalpies compare very well with previous benchmark coupled-cluster ab initio data, and with experimental data available. Based on these results the use of such approach to perform first-principles molecular dynamics simulations could provide reliable information regarding the dynamics of protonated hydrogen clusters.
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31.15.E- Density-functional theory
31.50.-x Potential energy surfaces
31.15.A- Ab initio calculations
36.40.Cg Electronic and magnetic properties of clusters
34.20.Gj Intermolecular and atom-molecule potentials and forces
31.15.bw Coupled-cluster theory

A-band methyl halide dissociation via electronic curve crossing as studied by electron energy loss spectroscopy

H. Kato, H. Masui, M. Hoshino, H. Cho, O. Ingólfsson, M. J. Brunger, P. Limão-Vieira, and H. Tanaka

J. Chem. Phys. 133, 054304 (2010); http://dx.doi.org/10.1063/1.3464483 (7 pages) | Cited 1 time

Online Publication Date: 3 August 2010

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Excitation of the A-band low-lying electronic states in the methyl halides, CH3I, CH3Br, CH3Cl, and CH3F, has been investigated for the (n→σ∗) transitions, using electron energy loss spectroscopy (EELS) in the range of 3.5–7.5 eV. For the methyl halides, CH3I, CH3Br, and CH3Cl, three components of the Q complex (3Q1, 3Q0, and 1Q1) were directly observed, with the exception of methyl fluoride, in the optically forbidden EELS experimental conditions of this investigation. The effect of electronic-state curve crossing emerged in the transition probabilities for the 3Q0 and 1Q1 states, with spin-orbit splitting observed and quantified against results from recent ab initio studies.
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34.80.Ht Dissociation and dissociative attachment
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors

H2 production from reactions between water and small molybdenum suboxide cluster anions

David W. Rothgeb, Jennifer E. Mann, and Caroline Chick Jarrold

J. Chem. Phys. 133, 054305 (2010); http://dx.doi.org/10.1063/1.3463413 (10 pages) | Cited 3 times

Online Publication Date: 3 August 2010

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Reactions between molybdenum suboxide cluster anions, MoxOy− (x = 1–4;y ≤ 3x), and water (H2O and D2O) have been studied using mass spectrometric analysis of products formed in a high-pressure, fast-flow reactor. Product distributions vary with the number of metal atoms in the cluster. Within the MoOy− oxide series, product masses correspond to the addition of one water molecule, as well as a H/D exchange with MoO4H−. Within the Mo2Oy− oxide series, product evolution and distribution suggest sequential oxidation via Mo2Oy−+H2O/D2O→Mo2Oy+1−+H2/D2 reactions for y<5, while for Mo2O5−, Mo2O6H2/D2− is produced. Mo2O6− does not appear to be reactive toward water. For the Mo3Oy− oxide series, sequential oxidation similarly is suggested for y<5, while Mo3O5− reactions result in Mo3O6H2/D2− formation. Mo3O6− appears uniquely unreactive. Mo3O7− and Mo3O8− react to form Mo3O8H2/D2− and Mo3O9H2/D2−, respectively. Lower mass resolution in the Mo4Oy− mass range prevents unambiguous mass analysis, but intensity changes in the mass spectra do suggest that sequential oxidation with H2/D2 evolution occurs for y<6, while Mo4Oy+1H2/D2− addition products are formed in Mo4O6− and Mo4O7− reactions with water. The relative rate constants for sequential oxidation and H2O/D2O addition for the x = 2 series were determined. There is no evidence of a kinetic isotope effect when comparing reaction rates of H2O with D2O, suggesting that the H2 and D2 losses from the lower-oxide/hydroxide intermediates are very fast relative to initial reaction complex formation with H2O or D2O. The rate constants determined here are two times higher than those determined in identical reactions between W2Oy−+H2O/D2O.
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84.60.-h Direct energy conversion and storage
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.20.Tr Kinetic isotope effects including muonium

A perfectly matched layer applied to a reactive scattering problem

Anna Nissen, Hans O. Karlsson, and Gunilla Kreiss

J. Chem. Phys. 133, 054306 (2010); http://dx.doi.org/10.1063/1.3458888 (11 pages) | Cited 3 times

Online Publication Date: 4 August 2010

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The perfectly matched layer (PML) technique is applied to a reactive scattering problem for accurate domain truncation. A two-dimensional model for dissociative adsorbtion and associative desorption of H2 from a flat surface is considered, using a finite difference spatial discretization and the Arnoldi method for time-propagation. We compare the performance of the PML to that of a monomial complex absorbing potential, a transmission-free complex absorbing potential, and to exterior complex scaling. In particular, the reflection properties due to the numerical treatment are investigated. We conclude that the PML is accurate and efficient, especially if high accuracy is of significance. Moreover, we demonstrate that the errors from the PML can be controlled at a desired accuracy, enabling efficient numerical simulations.
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34.35.+a Interactions of atoms and molecules with surfaces
34.80.Ht Dissociation and dissociative attachment

Dynamics of highly excited barium atoms deposited on large argon clusters. I. General trends

A. Masson, L. Poisson, M.-A. Gaveau, B. Soep, J.-M. Mestdagh, V. Mazet, and F. Spiegelman

J. Chem. Phys. 133, 054307 (2010); http://dx.doi.org/10.1063/1.3464489 (13 pages) | Cited 2 times

Online Publication Date: 4 August 2010

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Ba(Ar) ≈ 750 clusters were generated by associating the supersonic expansion and the pick-up techniques. A femtosecond pump (266.3 nm)-probe (792 or 399.2 nm) experiment was performed to document the dynamics of electronically excited barium within the very multidimensional environment of the argon cluster. Barium was excited in the vicinity of the 6s9p 1P state and probed by ionization. The velocity imaging technique was used to monitor the energy distribution of photoelectrons and photoions as a function of the delay time between the pump and the probe pulses. A complex dynamics was revealed, which can be interpreted as a sequence/superposition of elementary processes, one of which is the ejection of barium out of the cluster. The latter has an efficiency, which starts increasing 5 ps after the pump pulse, the largest ejection probability being at 10 ps. The ejection process lasts at a very long time, up to 60 ps. A competing process is the partial solvation of barium in low lying electronic states. Both processes are preceded by a complex electronic relaxation, which is not fully unraveled here, the present paper being the first one in a series.
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36.40.Cg Electronic and magnetic properties of clusters
36.40.Mr Spectroscopy and geometrical structure of clusters
33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.60.+q Photoelectron spectra

Optimized basis sets for the calculation of indirect nuclear spin-spin coupling constants involving the atoms B, Al, Si, P, and Cl

Patricio F. Provasi and Stephan P. A. Sauer

J. Chem. Phys. 133, 054308 (2010); http://dx.doi.org/10.1063/1.3465553 (10 pages) | Cited 1 time

Online Publication Date: 6 August 2010

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The aug-cc-pVTZ-J series of basis sets for indirect nuclear spin-spin coupling constants has been extended to the atoms B, Al, Si, P, and Cl. The basis sets were obtained according to the scheme previously described by Provasi et al. [J. Chem. Phys. 115, 1324 (2001)] . First, the completely uncontracted correlation consistent aug-cc-pVTZ basis sets were extended with four tight s and three tight d functions. Second, the s and p basis functions were contracted with the molecular orbital coefficients of self-consistent-field calculations performed with the uncontracted basis sets on the simplest hydrides of each atom. As a first illustration, we have calculated the one-bond indirect spin-spin coupling constants in BH4−, BF, AlH, AlF, SiH4, SiF4, PH3, PF3, H2S, SF6, HCl, and ClF at the level of density functional theory using the Becke three parameter Lee–Yang–Parr and the second order polarization propagator approximation with coupled cluster singles and doubles amplitudes.
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31.15.xr Self-consistent-field methods
33.25.+k Nuclear resonance and relaxation
31.15.E- Density-functional theory
31.15.bw Coupled-cluster theory

Resonant two-photon ionization spectroscopy of jet-cooled tantalum carbide, TaC

Olha Krechkivska and Michael D. Morse

J. Chem. Phys. 133, 054309 (2010); http://dx.doi.org/10.1063/1.3464486 (8 pages) | Cited 1 time

Online Publication Date: 6 August 2010

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The optical spectrum of diatomic TaC has been investigated for the first time, with transitions recorded in the range from 17 850 to 20 000 cm−1. Six bands were rotationally resolved and analyzed to obtain ground and excited state parameters, including band origins, upper and lower state rotational constants and bond lengths, Fermi contact parameter bF for the ground state, and lambda doubling parameters for the excited states. The ground state of TaC was found to be X 2Σ+, originating from the 1σ22σ21π43σ1 electronic configuration, in which only the valence orbitals arising from the Ta(5d+6s) and C(2s+2p) orbitals are listed. All of the rotationally resolved and analyzed bands were found to originate from the ground state, giving B0″ = 0.489 683(83) cm−1, r0″ = 1.749 01(15) Å, and bF″ = 0.131 20(36) cm−1 (1σ error limits) for 181Ta 12C. Comparison of the Fermi contact parameter to the atomic value shows that the 3σ orbital is approximately 75% Ta 6s in character. The other group 5 transition metal carbides, VC and NbC, have long been known to have 1σ22σ21π41δ1, 2Δ ground states, with low-lying 1σ22σ21π43σ1, 2Σ+ excited states. The emergence of a different ground state in TaC, as compared to VC and NbC, is due to the relativistic stabilization of the 6s orbital in Ta. This lowers the energy of the 6s-like 3σ orbital in TaC, causing the 1σ22σ21π43σ1, 2Σ+ state to fall below the 1σ22σ21π41δ1, 2Δ state.
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33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.15.Dj Interatomic distances and angles
31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
33.15.Mt Rotation, vibration, and vibration-rotation constants

Rovibronically selected and resolved two-color laser photoionization and photoelectron study of nickel carbide cation

Yih Chung Chang, Xiaoyu Shi, Kai-Chung Lau, Qing-Zhu Yin, H. T. Liou, and C. Y. Ng

J. Chem. Phys. 133, 054310 (2010); http://dx.doi.org/10.1063/1.3464488 (10 pages) | Cited 2 times

Online Publication Date: 6 August 2010

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We have performed a two-color laser photoionization and photoelectron study of nickel carbide (NiC) and its cation (NiC+). By preparing NiC in a single rovibronic level of an intermediate vibronic state via visible laser excitation prior to ultraviolet laser photoionization, we have measured the photoionization efficiency spectrum of NiC near its ionization threshold, covering the formation of NiC+(X 2Σ+;v+ = 0–3). We have also obtained well-resolved rotational transitions for the v+ = 0 and 1 vibrational bands of the NiC+(X 2Σ+) ground state. The assignment of rotational transitions observed between the neutral NiC intermediate state and the NiC+ ion ground state has allowed the direct determination of a highly precise value for the ionization energy of NiC, IE(NiC) = 67 525.1±0.5 cm−1 (8.372 05±0.000 06 eV). This experiment also provides reliable values for the vibrational spacing [ΔG(1/2) = 859.5±0.5 cm−1], rotational constants (Be+ = 0.6395±0.0018 cm−1 and αe+ = 0.0097±0.0009 cm−1), and equilibrium bond distance (re+ = 1.628 Å) for the NiC+(X 2Σ+) ground state. The experimental results presented here are valuable for benchmarking the development of more reliable ab initio quantum computation procedures for energetic and spectroscopic calculations of transition metal-containing molecules.
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32.80.Fb Photoionization of atoms and ions
31.15.ap Polarizabilities and other atomic and molecular properties
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.60.+q Photoelectron spectra
33.80.Eh Autoionization, photoionization, and photodetachment
33.15.Mt Rotation, vibration, and vibration-rotation constants
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation

Trading sensitivity for information: Carr–Purcell–Meiboom–Gill acquisition in solid-state NMR

Krishna K. Dey, Jason T. Ash, Nicole M. Trease, and Philip J. Grandinetti

J. Chem. Phys. 133, 054501 (2010); http://dx.doi.org/10.1063/1.3463653 (10 pages) | Cited 1 time

Online Publication Date: 2 August 2010

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The Carr–Purcell–Meiboom–Gill (CPMG) experiment has gained popularity in solid-state NMR as a method for enhancing sensitivity for anisotropically broadened spectra of both spin 1/2 and half integer quadrupolar nuclei. Most commonly, the train of CPMG echoes is Fourier transformed directly, which causes the NMR powder pattern to break up into a series of sidebands, sometimes called “spikelets.” Larger sensitivity enhancements are observed as the delay between the π pulses is shortened. As the duration between the π pulses is shortened, however, the echoes become truncated and information about the nuclear spin interactions is lost. We explored the relationship between enhanced sensitivity and loss of information as a function of the product Ω 2τ, where Ω is the span of the anisotropic lineshape and 2τ is the π pulse spacing. For a lineshape dominated by the nuclear shielding anisotropy, we found that the minimum uncertainty in the tensor values is obtained using Ω 2τ values in the range Ω 2τ ≈ 12−1+6 and Ω 2τ ≈ 9−3+3 for ηs = 0 and ηs = 1, respectively. For an anisotropic second-order quadrupolar central transition lineshape under magic-angle spinning (MAS), the optimum range of Ω 2τ ≈ 9−2+3 was found. Additionally, we show how the Two-dimensional One Pulse (TOP) like processing approach can be used to eliminate the cumbersome sideband pattern lineshape and recover a more familiar lineshape that is easily analyzed with conventional lineshape simulation algorithms.
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76.60.Lz Spin echoes

On the paradoxical relation between the melting temperature and forbidden energy gap of nanoparticles

K. K. Nanda

J. Chem. Phys. 133, 054502 (2010); http://dx.doi.org/10.1063/1.3466920 (4 pages) | Cited 1 time

Online Publication Date: 2 August 2010

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We comment on the paradox that seems to exist about a correlation between the size-dependent melting temperature and the forbidden energy gap of nanoparticles. By analyzing the reported expressions for the melting temperature and the band gap of nanoparticles, we conclude that there exists a relation between these two physical quantities. However, the variations of these two quantities with size for semiconductors are different from that of metals.
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73.22.-f Electronic structure of nanoscale materials and related systems
64.70.dj Melting of specific substances

Two-photon resonances in femtosecond time-resolved four-wave mixing spectroscopy: β-carotene

V. Namboodiri, M. Namboodiri, G. Flachenecker, and A. Materny

J. Chem. Phys. 133, 054503 (2010); http://dx.doi.org/10.1063/1.3466750 (6 pages) | Cited 2 times

Online Publication Date: 3 August 2010

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Femtosecond time-resolved pump-degenerate four-wave mixing (pump-DFWM) spectroscopy has been used to study the ultrafast dynamics of β-carotene involving several electronic and vibrational states. An initial pump pulse, resonant with the S0-to-S2 transition, excites the molecular system and a DFWM process, resonant with the S1-to-Sn transition, is used to probe the relaxation pathways. The transient shows a peculiar decay behavior, which is due to the contributions of resonant DFWM signal of the excited S1 state, nonresonant DFWM signal of the ground S0 state and vibrational hot S0∗ state, and the two-photon resonant DFWM signal of the ground S0 state. We have used a kinetic model including all the signal contributions to successfully fit the transient. The time constants extracted are in very good agreement with the known values for β-carotene. For comparison, a two-pulse pump-probe experiment was performed measuring the transient absorption at the wavelength of the DFWM experiment.
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87.15.M- Spectra of biomolecules
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
87.64.K- Spectroscopy
82.50.-m Photochemistry
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Mesoscale spatial distribution of electron spins studied by time-resolved small-angle and ultrasmall-angle neutron scattering with dynamic nuclear polarization: A case of 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) doped in high-density polyethylene

Takayuki Kumada (熊田高之), Yohei Noda (能田洋平), Satoshi Koizumi (小泉智), and Takeji Hashimoto (橋本竹治)

J. Chem. Phys. 133, 054504 (2010); http://dx.doi.org/10.1063/1.3460923 (7 pages) | Cited 2 times

Online Publication Date: 3 August 2010

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We carried out time-resolved small-angle neutron scattering (SANS) and ultrasmall-angle neutron scattering (USANS) studies of dynamically polarized high-density polyethylene (HDPE) doped with 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) persistent free radicals. We observed a remarkable enhancement of the scattering intensity shortly after a switching of microwave frequency from positive (negative) to negative (positive) dynamic nuclear polarization (DNP). The enhancement was found to be due to spatially heterogeneous proton-spin polarization generated as a result of heterogeneously distributed TEMPO in the HDPE sample. The spatial fluctuation of the polarization ranged up to the length-scale of ≥ 100 nm. This result strongly suggests that the TEMPO free radicals are localized more in nonfibrils but less in fibrils of HDPE. In this way, we propose that the time-resolved DNP-SANS and DNP-USANS be general techniques to determine mesoscale spatial distribution of electron spins in dielectric materials.
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75.30.Cr Saturation moments and magnetic susceptibilities
76.70.Fz Double nuclear magnetic resonance (DNMR), dynamical nuclear polarization

Hydrogen vibrational modes on graphene and relaxation of the C–H stretch excitation from first-principles calculations

Sung Sakong and Peter Kratzer

J. Chem. Phys. 133, 054505 (2010); http://dx.doi.org/10.1063/1.3474806 (8 pages) | Cited 3 times

Online Publication Date: 5 August 2010

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Density functional theory (DFT) calculations are used to determine the vibrational modes of hydrogen adsorbed on graphene in the low-coverage limit. Both the calculated adsorption energy of a H atom of 0.8 eV and calculated C–H stretch vibrational frequency of 2552 cm−1 are unusually low for hydrocarbons, but in agreement with data from electron energy loss spectroscopy on hydrogenated graphite. The clustering of two adsorbed H atoms observed in scanning tunneling microscopy images shows its fingerprint also in our calculated spectra. The energetically preferred adsorption on different sublattices correlates with a blueshift of the C–H stretch vibrational modes in H adatom clusters. The C–H bending modes are calculated to be in the 1100 cm−1 range, resonant with the graphene phonons. Moreover, we use our previously developed methods to calculate the relaxation of the C–H stretch mode via vibration-phonon interaction, using the Born–Oppenheimer surface for all local modes as obtained from the DFT calculations. The total decay rate of the H stretch into other H vibrations, thereby creating or annihilating one graphene phonon, is determined from Fermi’s golden rule. Our calculations using the matrix elements derived from DFT calculations show that the lifetime of the H stretch mode on graphene is only several picoseconds, much shorter than on other semiconductor surfaces such as Ge(001) and Si(001).
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63.20.-e Phonons in crystal lattices
61.48.Gh Structure of graphene
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.-m Methods of electronic structure calculations
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
79.20.Uv Electron energy loss spectroscopy
68.43.Mn Adsorption kinetics
88.30.R- Hydrogen storage

Dynamically skewed lines: Rotations in superfluid helium

Marie N. van Staveren and V. A. Apkarian

J. Chem. Phys. 133, 054506 (2010); http://dx.doi.org/10.1063/1.3469816 (4 pages)

Online Publication Date: 6 August 2010

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Dynamically skewed spectral lines arise for chirped damped oscillators. We extend this to the chirped damped rotor and apply it to treat the rovibrational line shapes of small molecules isolated in superfluid helium. The simple analysis generates valuable physical insights on the prevailing dynamics of a rotor coupled to its environment.
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67.25.D- Superfluid phase
33.20.Vq Vibration-rotation analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.70.Jg Line and band widths, shapes, and shifts

The covariant dissipation function for transient nonequilibrium states

Denis J. Evans, Debra J. Searles, and Stephen R. Williams

J. Chem. Phys. 133, 054507 (2010); http://dx.doi.org/10.1063/1.3463439 (5 pages) | Cited 1 time

Online Publication Date: 6 August 2010

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It has recently become apparent that the dissipation function, first defined by Evans and Searles [J. Chem. Phys. 113, 3503 (2000)] , is one of the most important functions in classical nonequilibrium statistical mechanics. It is the argument of the Evans–Searles fluctuation theorem, the dissipation theorem, and the relaxation theorems. It is a function of both the initial distribution and the dynamics. We pose the following question: How does the dissipation function change if we define that function with respect to the time evolving phase space distribution as one relaxes from the initial equilibrium distribution toward the nonequilibrium steady state distribution? We prove that this covariant dissipation function has a rather simple fixed relationship to the dissipation function defined with respect to the initial distribution function. We also show that there is no exact, time-local, Evans–Searles nonequilibrium steady state fluctuation relation for deterministic systems. Only an asymptotic version exists.
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05.20.Dd Kinetic theory
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion
05.70.Ln Nonequilibrium and irreversible thermodynamics
back to top Surfaces, Interfaces, and Materials

Multiple coherent states semiclassical initial value representation spectra calculations of lateral interactions for CO on Cu(100)

Michele Ceotto, David Dell’Angelo, and Gian Franco Tantardini

J. Chem. Phys. 133, 054701 (2010); http://dx.doi.org/10.1063/1.3462242 (10 pages) | Cited 2 times

Online Publication Date: 3 August 2010

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Lateral interactions between carbon monoxide molecules adsorbed on a copper Cu(100) surface are investigated via semiclassical initial value representation (SC-IVR) molecular dynamics. A previous analytical potential is extended to include long-range dipole interactions between coadsorbed molecules and preliminary classical simulations were performed to tune the potential parameters. Then, the spectra for several coadsorbed molecules are calculated using the multiple coherent states approximation of the time-averaging representation of the SC-IVR propagator. Results show strong resonances between coadsorbed molecules as observed by past experiments. Resonances turn into dephasing when isotopical substitutions are performed.
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68.43.Mn Adsorption kinetics
82.20.Kh Potential energy surfaces for chemical reactions
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
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