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28 Mar 2010

Volume 132, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

J. Chem. Phys. 132, 125101 (2010); http://dx.doi.org/10.1063/1.3358340 (5 pages)

R. B. Pandey and B. L. Farmer
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Spotlight on ionic liquids

Edward W. Castner and James F. Wishart

J. Chem. Phys. 132, 120901 (2010); http://dx.doi.org/10.1063/1.3373178 (9 pages) | Cited 45 times

Online Publication Date: 23 March 2010

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Ionic liquids are an emerging class of materials with a diverse and extraordinary set of properties. Understanding the origins of these properties and how they can be controlled by design to serve valuable practical applications presents a wide array of challenges and opportunities to the chemical physics and physical chemistry community. We highlight here some of the significant progress already made and future research directions in this exciting area.
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61.25.-f Studies of specific liquid structures
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Communications: The Metropolis Monte Carlo finite element algorithm for electrostatic interactions

Martial Mazars

J. Chem. Phys. 132, 121101 (2010); http://dx.doi.org/10.1063/1.3367886 (4 pages)

Online Publication Date: 25 March 2010

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The Metropolis Monte Carlo algorithm with the finite element method applied to compute electrostatic interaction energy between charge densities is described in this work. By using the finite element method to integrate numerically Poisson’s equation, it is shown that the computing time to obtain the acceptance probability of an elementary trial move does not, in principle, depend on the number of charged particles present in the system.
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41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems
02.50.Ng Distribution theory and Monte Carlo studies
02.70.Dh Finite-element and Galerkin methods
02.60.Lj Ordinary and partial differential equations; boundary value problems
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Communications: High-temperature water under pressure

Takashi Ikeda, Yoshinori Katayama, Hiroyuki Saitoh, and Katsutoshi Aoki

J. Chem. Phys. 132, 121102 (2010); http://dx.doi.org/10.1063/1.3374812 (4 pages) | Cited 1 time

Online Publication Date: 26 March 2010

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The effects of temperature and pressure upon structural, dynamical, and electronic properties of liquid H2O were systematically investigated via first principles molecular dynamics and in situ x-ray diffraction in the chosen isochore (1.00–1.61 g/cm3) and isotherm (300–900 K) conditions. Our study suggests that the crossover occurs between H-bonded and simple-liquidlike liquids by raising temperature in molecular liquid phase.
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61.20.Ne Structure of simple liquids
61.20.Ja Computer simulation of liquid structure
62.50.-p High-pressure effects in solids and liquids
61.25.Em Molecular liquids
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Communications: Hamiltonian regulated cell signaling network

Ge Wang and Muhammad H. Zaman

J. Chem. Phys. 132, 121103 (2010); http://dx.doi.org/10.1063/1.3357980 (4 pages)

Online Publication Date: 29 March 2010

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Cell signaling is fundamental to cell survival and disease progression. Traditional approaches to study these networks have focused largely on probabilistic approaches, with a large number of ad hoc assumptions. In this paper, we develop a linear Hamiltonian model to study the integrin signaling network. The integrin signaling network is central to cell adhesion, migration, and differentiation, but has not been studied in the same detail as other cell cycle networks. In this study, the integrin signaling network with 16 nodes in thermal fluctuations is analyzed through ensemble averages on the linear Hamiltonian model. This new and analytically rigorous approach offers a quick method to find out the dominant nodes in the complex network, which operate in the thermal noise regime. The robust on/off transitions due to the different initial inputs also reflect the inherent structure in the network, providing new insights into structure and function of the network.
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87.14.-g Biomolecules: types
87.17.-d Cell processes
87.18.-h Biological complexity
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Communications: Entanglement switch for dipole arrays

Qi Wei, Sabre Kais, and Yong P. Chen

J. Chem. Phys. 132, 121104 (2010); http://dx.doi.org/10.1063/1.3366522 (4 pages) | Cited 3 times

Online Publication Date: 29 March 2010

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We propose a new entanglement switch of qubits consisting of electric dipoles oriented along or against an external electric field and coupled by the electric dipole-dipole interaction. The pairwise entanglement can be tuned and controlled by the ratio of the Rabi frequency and the dipole-dipole coupling strength. Tuning the entanglement can be achieved for one, two, and three-dimensional arrangements of the qubits. The feasibility of building such an entanglement switch is also discussed.
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03.65.Ud Entanglement and quantum nonlocality (e.g. EPR paradox, Bell's inequalities, GHZ states, etc.)
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An efficient algorithm for classical density functional theory in three dimensions: Ionic solutions

Matthew G. Knepley, Dmitry A. Karpeev, Seth Davidovits, Robert S. Eisenberg, and Dirk Gillespie

J. Chem. Phys. 132, 124101 (2010); http://dx.doi.org/10.1063/1.3357981 (11 pages) | Cited 8 times

Online Publication Date: 22 March 2010

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Classical density functional theory (DFT) of fluids is a valuable tool to analyze inhomogeneous fluids. However, few numerical solution algorithms for three-dimensional systems exist. Here we present an efficient numerical scheme for fluids of charged, hard spheres that uses O(N log N) operations and O(N) memory, where N is the number of grid points. This system-size scaling is significant because of the very large N required for three-dimensional systems. The algorithm uses fast Fourier transforms (FFTs) to evaluate the convolutions of the DFT Euler–Lagrange equations and Picard (iterative substitution) iteration with line search to solve the equations. The pros and cons of this FFT/Picard technique are compared to those of alternative solution methods that use real-space integration of the convolutions instead of FFTs and Newton iteration instead of Picard. For the hard-sphere DFT, we use fundamental measure theory. For the electrostatic DFT, we present two algorithms. One is for the “bulk-fluid” functional of Rosenfeld [ Y. Rosenfeld, J. Chem. Phys. 98, 8126 (1993) ] that uses O(N log N) operations. The other is for the “reference fluid density” (RFD) functional [ D. Gillespie et al., J. Phys.: Condens. Matter 14, 12129 (2002) ]. This functional is significantly more accurate than the bulk-fluid functional, but the RFD algorithm requires O(N2) operations.
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66.10.Ed Ionic conduction
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Vibrational multiconfiguration self-consistent field theory: Implementation and test calculations

Sandra Heislbetz and Guntram Rauhut

J. Chem. Phys. 132, 124102 (2010); http://dx.doi.org/10.1063/1.3364861 (7 pages) | Cited 8 times

Online Publication Date: 22 March 2010

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A state-specific vibrational multiconfiguration self-consistent field (VMCSCF) approach based on a multimode expansion of the potential energy surface is presented for the accurate calculation of anharmonic vibrational spectra. As a special case of this general approach vibrational complete active space self-consistent field calculations will be discussed. The latter method shows better convergence than the general VMCSCF approach and must be considered the preferred choice within the multiconfigurational framework. Benchmark calculations are provided for a small set of test molecules.
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31.15.xr Self-consistent-field methods
31.50.-x Potential energy surfaces
33.20.Tp Vibrational analysis

Exciton scattering approach for branched conjugated molecules and complexes. IV. Transition dipoles and optical spectra

Hao Li, Sergey V. Malinin, Sergei Tretiak, and Vladimir Y. Chernyak

J. Chem. Phys. 132, 124103 (2010); http://dx.doi.org/10.1063/1.3366521 (9 pages) | Cited 1 time

Online Publication Date: 23 March 2010

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The electronic excitation energies and transition dipole moments are the essential ingredients to compute an optical spectrum of any molecular system. Here we extend the exciton scattering (ES) approach, originally developed for computing excitation energies in branched conjugated molecules, to the calculation of the transition dipole moments. The ES parameters that characterize contributions of molecular building blocks to the total transition dipole can be extracted from the quantum-chemical calculations of the excited states in simple molecular fragments. Using these extracted parameters, one can then effortlessly calculate the oscillator strengths and optical spectra of various large molecular structures. We illustrate application of this extended ES approach using an example of phenylacetylene-based molecules. Absorption spectra predicted by the ES approach show close agreement with the results of the reference quantum-chemical calculations.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Trace correcting density matrix extrapolation in self-consistent geometry optimization

Anders M. N. Niklasson, Matt Challacombe, C. J. Tymczak, and Károly Németh

J. Chem. Phys. 132, 124104 (2010); http://dx.doi.org/10.1063/1.3351785 (5 pages) | Cited 1 time

Online Publication Date: 23 March 2010

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A linear scaling trace correcting density matrix extrapolation method is proposed for accelerated self-consistency convergence in geometry optimization. The technique is based on nonorthogonal trace correcting purification and perturbation theory. Compared with alternative schemes, extrapolated total energies are often an order of magnitude closer to the self-consistent solution. For insulators, the computational cost is low and it scales linearly with the size of the perturbed region affected by the modified geometry, O(Npert). For local perturbations, the computational cost is therefore independent of the total size of the system and scales as O(1).
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31.15.xr Self-consistent-field methods
02.60.Ed Interpolation; curve fitting
31.15.xp Perturbation theory

Effect of removing the no-virtual pair approximation on the correlation energy of the He isoelectronic sequence. II. Point nuclear charge model

Yoshihiro Watanabe, Haruyuki Nakano, and Hiroshi Tatewaki

J. Chem. Phys. 132, 124105 (2010); http://dx.doi.org/10.1063/1.3359857 (7 pages) | Cited 4 times

Online Publication Date: 24 March 2010

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The correlation energies (CEs) of the He isoelectronic sequence Z = 2–116 with a point nuclear charge model were investigated with the four component relativistic configuration interaction method. We obtained CEs with and without the virtual pair approximation which are close to the values from Pestka et al.’s Hylleraas-type configuration interaction calculation. We also found that the uniform charge and point charge models for the nucleus differ substantially for Z ≥ 100.
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31.15.V- Electron correlation calculations for atoms, ions and molecules
31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure

Quantum grow—A quantum dynamics sampling approach for growing potential energy surfaces and nonadiabatic couplings

Oded Godsi, Michael A. Collins, and Uri Peskin

J. Chem. Phys. 132, 124106 (2010); http://dx.doi.org/10.1063/1.3364817 (8 pages) | Cited 4 times

Online Publication Date: 25 March 2010

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A quantum sampling algorithm for the interpolation of diabatic potential energy matrices by the Grow method is introduced. The new procedure benefits from penetration of the wave packet into classically forbidden regions, and the accurate quantum mechanical description of nonadiabatic transitions. The increased complexity associated with running quantum dynamics is reduced by using approximate low order expansions of the nuclear wave function within a Multi-configuration time-dependent Hartree scheme during the Grow process. The sampling algorithm is formulated and applied for three representative test cases, demonstrating the recovery of analytic potentials by the interpolated ones, and the convergence of a dynamic observable.
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31.15.xr Self-consistent-field methods
31.50.-x Potential energy surfaces
02.60.Ed Interpolation; curve fitting
12.20.Ds Specific calculations

Length and end group dependence of the electronic transport properties in carbon atomic molecular wires

Xiaoqing Deng, Zhenhua Zhang, Jicheng Zhou, Ming Qiu, and Guiping Tang

J. Chem. Phys. 132, 124107 (2010); http://dx.doi.org/10.1063/1.3363894 (5 pages) | Cited 3 times

Online Publication Date: 30 March 2010

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Carrying out theoretical calculations using the nonequilibrium Green’s function method combined with the density functional theory, the transport properties of functionalized atomic chains of carbon atoms with different lengths are investigated. The results show that the I-V evolution and rectifying performance can be affected by the length of wire when both ends of it is capped with the benzene-thiol attached with an amino group and the pyridine attached with nitro group. But when capped with the benzene-thiol attached with an amino group and the nitro group, we can observe a surprised result that different systems show similar I-V characteristics and their transport properties are almost independent of molecular length, which suggests that this is a favorable way to design more ideal molecular interconnecting wires with a high length-independent conductance behavior.
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85.65.+h Molecular electronic devices
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Predissociation and dissociative ionization of Rydberg states of Xe2 and the photodissociation of Xe2+

V. Alvin Shubert, Maria Rednic, and Stephen T. Pratt

J. Chem. Phys. 132, 124108 (2010); http://dx.doi.org/10.1063/1.3356040 (14 pages) | Cited 5 times

Online Publication Date: 30 March 2010

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The Rydberg states of Xe2 in the region between 76 000 and 84 000 cm−1 were studied by using a combination of two-photon excitation and velocity map ion imaging. The electronic states in this region are based on the Xe(1S0)+Xe 6p and 5d dissociation limits, and the large number of states leads to numerous curve crossings and distorted potentials. These Rydberg states can decay by predissociation or fluorescence or can be photoionized, dissociatively photoionized, or photodissociated by the absorption of a single additional photon. Furthermore, the molecular ion can be photodissociated as well. While numerous other techniques have been applied to this problem, velocity map ion imaging provides a high resolution approach to determine the operative processes. When combined with existing data obtained by other methods, the present experiments allow a more complete understanding of the assignment and behavior of these states.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
31.50.-x Potential energy surfaces
33.80.Eh Autoionization, photoionization, and photodetachment

Fluorescent resonant excitation energy transfer in linear polyenes

Mousumi Das and S. Ramasesha

J. Chem. Phys. 132, 124109 (2010); http://dx.doi.org/10.1063/1.3367896 (10 pages) | Cited 2 times

Online Publication Date: 31 March 2010

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We have studied the dynamics of excitation transfer between two conjugated polyene molecules whose intermolecular separation is comparable to the molecular dimensions. We have employed a correlated electron model that includes both the charge-charge, charge-bond, and bond-bond intermolecular electron repulsion integrals. We have shown that the excitation transfer rate varies as inverse square of donor-acceptor separation R−2 rather than as R−6, suggested by the Förster type of dipolar approximation. Our time-evolution study also shows that the orientational dependence on excitation transfer at a fixed short donor-acceptor separation cannot be explained by Förster type of dipolar approximation beyond a certain orientational angle of rotation of an acceptor polyene with respect to the donor polyene. The actual excitation transfer rate beyond a certain orientational angle is faster than the Förster type of dipolar approximation rate. We have also studied the excitation transfer process in a pair of push-pull polyenes for different push-pull strengths. We have seen that, depending on the push-pull strength, excitation transfer could occur to other dipole coupled states. Our study also allows for the excitation energy transfer to optically dark states which are excluded by Förster theory since the one-photon transition intensity to these states (from the ground state) is zero.
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34.50.Gb Electronic excitation and ionization of molecules
33.50.Dq Fluorescence and phosphorescence spectra
34.20.Gj Intermolecular and atom-molecule potentials and forces
31.15.vq Electron correlation calculations for polyatomic molecules
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Cross sections for the valence shell excitations of nitrous oxide studied by fast electron impact

You-Yan Wang, Jian-Min Sun, and Lin-Fan Zhu

J. Chem. Phys. 132, 124301 (2010); http://dx.doi.org/10.1063/1.3360311 (6 pages) | Cited 2 times

Online Publication Date: 24 March 2010

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The generalized oscillator strengths, differential cross sections, as well as the integral cross sections for electron impact excitation of the B 1Δ, C 1Π, and D 1Σ+ states of N2O have been determined at an incident electron energy of 2500 eV. A generalized oscillator strength analysis reveals that the B 1Δ←X 1Σ+ transition is dominated by the quadrupolar component. From the comparison to the previous experimental results, it is found that the first Born approximation is not satisfied for the C 1Π excitation while it is valid for the D 1Σ+ excitation at an incident electron energy of 200 eV. The BE-scaled integral cross section for the B 1Δ excitation from its threshold to 5000 eV was calculated based on its generalized oscillator strength, and the present integral cross sections for the excitation of the C 1Π and D 1Σ+ states are in good agreement with the calculations using the BEf-scaling approach.
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34.80.Gs Molecular excitation and ionization
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors

Enhanced magnetic moments of alkali metal coated Sc clusters: New magnetic superatoms

Kalpataru Pradhan, J. Ulises Reveles, Prasenjit Sen, and S. N. Khanna

J. Chem. Phys. 132, 124302 (2010); http://dx.doi.org/10.1063/1.3367722 (5 pages) | Cited 2 times

Online Publication Date: 25 March 2010

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It is shown that the magnetic moments of Sc atoms can be significantly enhanced by combining them with alkali atoms. We present results of first principles electronic structure calculations of ScNan (1 ≤ n ≤ 12) clusters that indicate that a ScNa12 cluster consisting of a Sc atom surrounded by 12 Na atoms forming a compact icosahedral structure has a spin magnetic moment of 3μB that is three times that of an isolated Sc atom. This unusual behavior is analyzed in terms of the filling of the supershells 1S, 1P,… controlled by the nature and size of the alkali atoms and the more localized Sc 3d orbitals that hybridize weakly with Na sp orbitals. It is shown that even larger magnetic moments could be attained by controlling the relative position of 1S, 1P, and 3d states. Indeed, our studies indicate large magnetic moment five times that of an isolated Sc atom in the ScK12 and ScCs12 clusters, in which the 3d orbitals of Sc adopt a half-filled configuration, while the clusters are stabilized by filled 1S2, 1P6, and 2S2 shells, the features making them as new magnetic superatoms.
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36.40.Cg Electronic and magnetic properties of clusters
31.15.A- Ab initio calculations
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

An experimental investigation on the performance of conical nozzles for argon cluster formation in supersonic jets

Haiyang Lu (卢海洋), Guoquan Ni (倪国权), Ruxin Li (李儒新), and Zhizhan Xu (徐至展)

J. Chem. Phys. 132, 124303 (2010); http://dx.doi.org/10.1063/1.3356024 (9 pages) | Cited 1 time

Online Publication Date: 25 March 2010

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This work intends to get a better understanding of cluster formation in supersonic nozzles of different geometries. The throat diameters d are within 0.26 mm ≤ d ≤ 0.62 mm, the half-opening-angle α within 4.2° ≤ α ≤ 11.3°, and the length L of the conical section is 17.5 mm (eight nozzles) or 12 mm (two nozzles). Thus the so-called “equivalent sonic-nozzle diameter deq” for these conical nozzle geometries, defined by deq = 0.74 d/tan α (for monatomic gases), is in the range of 1.59 mm ≤ deq ≤ 5.21 mm. Source temperature for the clustering experiments was T0 = 298 K, and the backing pressure P0 was between 0.5 and 30 bars. The (average) cluster sizes observed for these conical nozzles deviate from the predictions of the simple stream-tube-model. These deviations are accounted for by introducing the so-called “effective equivalent sonic-nozzle diameter deq∗,” defined as the product of the equivalent sonic-nozzle diameter deq and a new parameter δ, deq∗ = δdeq. The parameter δ serves to modify the equivalent diameters deq of the conical nozzles, which are applied in the idealized cases where the gas flows are suggested to be formed through free jet expansion. Then, δ represents the deviation of the performance in cluster formation of the practical conical nozzles from those predicted based on the idealized picture. The experimental results show that the values of δ can be described by an empirical formula, depending on the gas backing pressure P0 and the parameter deq of the conical nozzles. The degradation of the performance of the present conical nozzles was found with the increase in P0 and the larger deq. It was revealed that δ is inversely proportional to a fractional power ( ∼ 0.5–0.6) of the molecular density nmol in the gas flows under the present experimental conditions. The boundary layers effects are considered to be mainly responsible for the restriction of the performance of the conical nozzles in cluster formation.
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36.40.Vz Optical properties of clusters
47.40.Ki Supersonic and hypersonic flows
47.60.Kz Flows and jets through nozzles
33.20.Fb Raman and Rayleigh spectra (including optical scattering)

Rotationally resolved spectroscopy of the math 2A1←math 2B1 transition of H2S+ above the barrier to linearity using the mass-analyzed threshold ionization photofragment excitation technique

Songhee Han, Tae Yeon Kang, and Sang Kyu Kim

J. Chem. Phys. 132, 124304 (2010); http://dx.doi.org/10.1063/1.3358252 (12 pages)

Online Publication Date: 26 March 2010

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The math 2A1←math 2B1 transitions of H2S+ above the barrier to linearity have been investigated with the energy resolution high enough to identify individual rotational transition lines for the first time. The rotational cooling of the cation is achieved either by the direct ionization or mass-analyzed threshold ionization (MATI) technique employed in the vacuum-ultraviolet laser excitation of the jet-cooled H2S. Subsequent photoexcitation leads to the H2S+→H2+S+ dissociation and the S+ product yield taken as a function of the excitation energy gives the photofragment excitation (PHOFEX) spectra. The combined use of MATI and PHOFEX techniques greatly simplifies the spectrum allowing the accurate identification of the rotationally resolved bands which is otherwise a formidable task due to the intrinsic complexity of the math 2A1←math 2B1 transition. Highly excited states of math(0,7,0), math(0,8,0), and math(0,9,0) vibronic levels with different K quantum numbers which are located above the barrier to linearity are thoroughly investigated. The bent-to-quasilinear transition of H2S+ above the barrier to linearity shows the characteristics of the Renner–Teller effect, showing the large A rotational constant and strong intensity borrowing of the highly vibrationally excited ground levels such as math(0,23,0) or math(0,24,0) in the dipole-allowed excitation. Spectroscopic parameters of term values, rotational, and spin-orbit coupling constants are precisely determined in this work, providing the most quantitative spectroscopic structure of the H2S+ to date. Quantum-state dependent photodissociation dynamics are also discussed from spectral features of PHOFEX.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Gj Diffuse spectra; predissociation, photodissociation
33.15.Mt Rotation, vibration, and vibration-rotation constants

Al4− cluster anion: Electronic structure, excited states, and electron detachment

Thomas Sommerfeld

J. Chem. Phys. 132, 124305 (2010); http://dx.doi.org/10.1063/1.3366520 (6 pages)

Online Publication Date: 29 March 2010

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Full-valence complete-active-space self-consistent-field and coupled-cluster methods are used to investigate excitation and electron detachment energies of the Al4− cluster anion. Both, Al4 and Al4−, have electronic structures with many low-energy electron configurations and exhibit accordingly pronounced configuration mixing. The complete-active-space self-consistent-field calculations show that all low-energy states of the neutral and the cluster anion can nevertheless be characterized by a single configuration, and in contrast to Møller–Plesset perturbation theory, coupled-cluster methods are found to recover enough static correlation to describe these states accurately. Coupled-cluster methods are then used to find minimal-energy structures of four states of the anion and four states of the neutral cluster, the respective ground states are identified, and vertical and adiabatic detachment energies are computed. The computed vertical detachment energies suggest that the first peak in the experimental photoelectron spectrum consists of at least three different transitions, and the computed excitation energies corroborate the conclusions from the analysis of the recently observed delayed detachment from excited Al4− ions in an electrostatic trap.
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36.40.Cg Electronic and magnetic properties of clusters
36.40.Mr Spectroscopy and geometrical structure of clusters
31.15.bw Coupled-cluster theory
31.15.xr Self-consistent-field methods
32.80.Gc Photodetachment of atomic negative ions
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)

Stepwise hydration of the cyanide anion: A temperature-controlled photoelectron spectroscopy and ab initio computational study of CN−(H2O)n, n = 2–5

Xue-Bin Wang, Karol Kowalski, Lai-Sheng Wang, and Sotiris S. Xantheas

J. Chem. Phys. 132, 124306 (2010); http://dx.doi.org/10.1063/1.3360306 (10 pages) | Cited 7 times

Online Publication Date: 30 March 2010

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We report the study of microsolvated CN−(H2O)n (n = 1–5) clusters in the gas phase using a combination of experimental and computational approaches. The hydrated cyanide clusters were produced by electrospray and their structural and energetic properties were probed using temperature-controlled photoelectron spectroscopy (PES) and ab initio electronic structure calculations. Comparison between the low temperature (LT,T = 12 K) and the room-temperature (RT) spectra shows a 0.25 eV spectral blueshift in the binding energy of the n = 1 cluster and a significant spectral sharpening and blueshift for n = 2 and 3. The experimental results are complemented with ab initio electronic structure calculations at the MP2 and CCSD(T) levels of theory that identified several isomers on the ground state potential energy function arising from the ability of CN− to form hydrogen bonds with water via both the C and N ends. In all cases the N end seems to be the preferred hydration site for the water network. The excellent agreement between the low temperature measured PES spectra and the basis set- and correlation-corrected [at the CCSD(T) level of theory] calculated vertical detachment energies, viz., 3.85 versus 3.84 eV (n = 0), 4.54 versus 4.54 eV (n = 1), 5.20 versus 5.32 eV (n = 2), 5.58 versus 5.50 eV (n = 3), and 5.89 versus 5.87 eV (n = 4), allow us to establish the hydration motif of cyanide. Its microsolvation pattern was found to be similar to that of the halide anions (Cl−, Br−, and I−) as well as other diatomic anions having cylindrical symmetry such as NO−, resulting to structures in which the ion resides on the surface of a water cluster. The exception is CN−(H2O)2, for which one water molecule is bound to either side of the anion resulting in a quasilinear structure. For the n = 3 cluster the anion was found to freely “tumble” on the surface of a water trimer, since the inclusion of zero-point energy even at T = 0 K stabilizes the configuration of C3 symmetry with respect to the one having the anion tilted toward the water cluster. For n = 4 this motion is more restricted since the corresponding barrier at RT is 1.2 kcal/mol. It is also possible that at RT other isomers (lying within ∼ 0.6 kcal/mol above the global minima) are also populated, resulting in the further broadening of the PES spectra.
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36.40.Mr Spectroscopy and geometrical structure of clusters
33.60.+q Photoelectron spectra
33.15.Fm Bond strengths, dissociation energies
31.15.A- Ab initio calculations
33.70.Jg Line and band widths, shapes, and shifts
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
31.15.bw Coupled-cluster theory

Time-resolved photoelectron spectroscopy of wavepackets through a conical intersection in NO2

Yasuki Arasaki, Kazuo Takatsuka, Kwanghsi Wang, and Vincent McKoy

J. Chem. Phys. 132, 124307 (2010); http://dx.doi.org/10.1063/1.3369647 (10 pages) | Cited 10 times

Online Publication Date: 30 March 2010

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We report the results of theoretical studies of the time-resolved femtosecond photoelectron spectroscopy of quantum wavepackets through the conical intersection between the first two 2A′ states of NO2. The Hamiltonian explicitly includes the pump-pulse interaction, the nonadiabatic coupling due to the conical intersection between the neutral states, and the probe interaction between the neutral states and discretized photoelectron continua. Geometry- and energy-dependent photoionization matrix elements are explicitly incorporated in these studies. Photoelectron angular distributions are seen to provide a clearer picture of the ionization channels and underlying wavepacket dynamics around the conical intersection than energy-resolved spectra. Time-resolved photoelectron velocity map images are also presented.
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33.60.+q Photoelectron spectra
31.50.Bc Potential energy surfaces for ground electronic states
31.50.Df Potential energy surfaces for excited electronic states
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
31.15.A- Ab initio calculations

Finite temperature infrared spectroscopy of polycyclic aromatic hydrocarbon molecules: Path-integral molecular dynamics

F. Calvo, P. Parneix, and N.-T. Van-Oanh

J. Chem. Phys. 132, 124308 (2010); http://dx.doi.org/10.1063/1.3367719 (9 pages) | Cited 5 times

Online Publication Date: 31 March 2010

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The vibrational spectra of the naphthalene, pyrene, and coronene molecules have been computed in the 0–3500 cm−1 infrared range using classical and quantum molecular dynamics simulations based on a dedicated tight-binding potential energy surface. The ring-polymer molecular dynamics (RPMD) and partially adiabatic centroid molecular dynamics (CMD) methods have been employed to account for quantum nuclear effects. The contributions of quantum delocalization to the line shift and broadening are significant in the entire spectral range and of comparable magnitude as pure thermal effects. While the two methods generally produce similar results, the CMD method may converge slower at low temperature with increasing Trotter discretization number. However, and contrary to the CMD method, the RPMD approach suffers from serious resonance problems at high frequencies and low temperatures.
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33.20.Ea Infrared spectra
31.15.xv Molecular dynamics and other numerical methods
33.70.Jg Line and band widths, shapes, and shifts
31.50.-x Potential energy surfaces
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants

Electron collisions with α-D-glucose and β-D-glucose monomers

Romarly F. da Costa, Márcio H. F. Bettega, Márcio T. do N. Varella, and Marco A. P. Lima

J. Chem. Phys. 132, 124309 (2010); http://dx.doi.org/10.1063/1.3369646 (7 pages)

Online Publication Date: 31 March 2010

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The development of new alternative routes for production of second generation ethanol from sugarcane biomass poses a challenge to the scientific community. Current research in this field addresses the use of a plasma-based pretreatment of the lignocellulosic raw material. With the aim to provide a theoretical background for this experimental technique we investigate the role of low-energy electrons from the plasma in the rupture of the matrix of cellulosic chains. In this paper, we report calculated cross sections for elastic scattering of low-energy electrons by the α- and β-D-glucose monomers. The calculations employed the Schwinger multichannel method with pseudopotentials and were carried out at the static-exchange and static-exchange plus polarization levels of approximation. Through the comparison of the results obtained with inclusion of polarization effects we discuss the influence of the different conformations of the hydroxyl group linked to the anomeric carbon on the resonance spectra of these molecules. Resonant structures appearing at different energies for α- and β-glucose at the low-energy regime of impact energies can be understood as a fingerprint of an “isomeric effect” and suggest that distinct fragmentation mechanisms proceeding via σ∗ shape resonances may become operative depending on the glucose anomer under consideration. For energies above 15 eV the integral elastic cross sections are very similar for both monomers. Differential cross sections for the glucopyranose anomers considered in this work are typically dominated by a strong forward scattering due to the molecules’ large electric dipole moments and, for energies close to the resonances’ positions, they display particular features at the intermediate angular region, notably a pronounced f-wave scattering pattern, that are probably associated with the presence of those structures.
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34.80.Bm Elastic scattering
34.80.Gs Molecular excitation and ionization
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
33.15.Bh General molecular conformation and symmetry; stereochemistry

Electronic structure of LaO based on frozen-core four-component relativistic multiconfigurational quasidegenerate perturbation theory

Hiroko Moriyama, Yoshihiro Watanabe, Haruyuki Nakano, Shigeyoshi Yamamoto, and Hiroshi Tatewaki

J. Chem. Phys. 132, 124310 (2010); http://dx.doi.org/10.1063/1.3359854 (9 pages) | Cited 1 time

Online Publication Date: 31 March 2010

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The electronic structure of the LaO molecule is studied using frozen-core four-component multiconfigurational quasidegenerate perturbation theory. The ground state and nine experimentally observed excited states are examined. The ground state is 2Σ1/2+ and its gross atomic orbital population is La(5p5.766s0.836p0.14p∗0.21d∗1.17f∗0.26) O(2p4.63), where p∗, d∗, and f∗ are the polarization functions of La that form molecular spinors with O 2ps. We found that it is not necessary to consider the excitation from the O 2p electrons when analyzing the experimental spectra. This validates the foundation of the ligand field theory on diatomic molecules, including the La atom where only one electron is considered. The spectroscopic constants Re, ωe, and T0 calculated for the ground state and low-lying excited states A′(2Δ3/2), A′(2Δ5/2) A(2Π1/2), and A(2Π3/2) are in good agreement with the experimental values.
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31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
31.15.V- Electron correlation calculations for atoms, ions and molecules
31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
33.15.Fm Bond strengths, dissociation energies
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation

Characterization of iso-CF2I2 in frequency and ultrafast time domains

Patrick Z. El-Khoury, Lisa George, Aimable Kalume, Scott A. Reid, Bruce S. Ault, and Alexander N. Tarnovsky

J. Chem. Phys. 132, 124501 (2010); http://dx.doi.org/10.1063/1.3357728 (11 pages) | Cited 5 times

Online Publication Date: 22 March 2010

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The photolysis of diiododifluoromethane (CF2I2) in condensed phases was studied by a combination of matrix isolation and ultrafast time-resolved spectroscopy, in concert with ab initio calculations. Photolysis at wavelengths of 355 or 266 nm of CF2I2:Ar samples (1:5000) held at ∼ 8 K yielded iso-CF2I2 (F2C–I–I), a metastable isomer of CF2I2, characterized here for the first time. The infrared (IR) spectra of this isomer were recorded in matrix experiments, and the derived positions of the C–F stretching modes are in very good agreement with the predictions of high level ab initio calculations, which show that the iso-form is a minimum on the CF2I2 ground state potential energy surface. The formation of this isomer following 350 nm excitation of CF2I2 in room temperature CCl4 solutions was monitored through its intense C–F stretching mode by means of ultrafast time-resolved IR absorption. Together, matrix isolation and ultrafast IR absorption experiments suggest that the formation of iso-CF2I2 occurs via recombination of CF2I radical and I atom. Ultrafast IR experiments detect a delayed rise of iso-CF2I–I absorption, placing an upper limit of 400 fs for the C–I bond dissociation and primary geminate recombination processes. The product absorption spectrum recorded 1 ns after 350 nm excitation of CF2I2 in solution is virtually identical to the visible absorption spectrum of iso-CF2I2 trapped in matrix isolation experiments [with subtracted I2(X) absorption]. The formation of this isomer in solution at room temperature has direct dynamic implications for the ultrafast production of molecular iodine from electronically excited CF2I2.
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82.50.Bc Processes caused by infrared radiation
31.15.A- Ab initio calculations
31.50.Df Potential energy surfaces for excited electronic states
33.20.Ea Infrared spectra
82.20.Kh Potential energy surfaces for chemical reactions
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