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7 Feb 2012

Volume 136, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

J. Chem. Phys. 136, 054301 (2012); http://dx.doi.org/10.1063/1.3675919 (9 pages)

J. Navarro, D. Mateo, M. Barranco, and A. Sarsa
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back to top Theoretical Methods and Algorithms

Quantum locality and equilibrium properties in low-temperature parahydrogen: A multiscale simulation study

R. Potestio and L. Delle Site

J. Chem. Phys. 136, 054101 (2012); http://dx.doi.org/10.1063/1.3678587 (7 pages)

Online Publication Date: 1 February 2012

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Parahydrogen is the spin-zero singlet state of molecular hydrogen, which at low temperature (between 14 and 25 K) is in a fluid state. A classical treatment of the system leads to unphysical freezing, and the inclusion of quantum delocalization of the molecule is then required to obtain a realistic description of its equilibrium properties. In the present work, we employ the classical-quantum adaptive resolution method AdResS to investigate the spatial extension of quantum delocalization effects in the bulk fluid at low temperature. Specifically, we simulate a small, spherical region of the system in full quantum detail: this region is coupled to a bulk of coarse-grained particles with classical, quantum-derived effective interactions obtained from quantum simulations. The two regions are interfaced through open boundaries and in conditions of thermodynamic equilibrium. Structural properties of the fluid, namely, pair distribution functions, are measured for different sizes of the quantum region. The results of this work show that, for the thermodynamic conditions corresponding to the range of temperature between 14 and 25 K, the bead-based, quantum structural properties of low-temperature parahydrogen are deemed local and do not require the support of an explicit quantum bulk.
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61.25.Em Molecular liquids
82.60.Hc Chemical equilibria and equilibrium constants
02.70.Ns Molecular dynamics and particle methods
61.20.Ja Computer simulation of liquid structure

Nuclear signatures on the molecular harmonic emission and the attosecond pulse generation

Liqiang Feng and Tianshu Chu

J. Chem. Phys. 136, 054102 (2012); http://dx.doi.org/10.1063/1.3681165 (7 pages) | Cited 1 time

Online Publication Date: 2 February 2012

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In this paper, we theoretically investigate the nuclear signatures effects, i.e., the initial vibrational state and the isotopic effects on the generations of the molecular high-order harmonics and the attosecond pulses when the model H2+/D2+ ions are exposed to a 5 fs/800 nm chirp pulse. The numerical solution of the time-dependent Schrödinger equation for these vibrating molecule ions shows that the intensities of the harmonic spectra are reinforced with the enhancement of the initial vibrational state. Moreover, through the investigation of the isotopic effect, we find that more intense harmonics are generated in the lighter nucleus. Furthermore, by optimizing the chirp pulse under the optimal initial vibrational state, an intense ultrabroad supercontinuum with a 325 eV bandwidth can be obtained. By properly superposing the harmonic spectrum, an attosecond pulse as short as 57 as (16 as) is generated without (with) phase compensation.
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33.20.Tp Vibrational analysis
31.15.X- Alternative approaches
31.30.Gs Hyperfine interactions and isotope effects

Fitting properties from density functional theory based molecular dynamics simulations to parameterize a rigid water force field

Jonàs Sala, Elvira Guàrdia, Jordi Martí, Daniel Spångberg, and Marco Masia

J. Chem. Phys. 136, 054103 (2012); http://dx.doi.org/10.1063/1.3679402 (10 pages)

Online Publication Date: 2 February 2012

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In the quest towards coarse-grained potentials and new water models, we present an extension of the force matching technique to parameterize an all-atom force field for rigid water. The methodology presented here allows to improve the matching procedure by first optimizing the weighting exponents present in the objective function. A new gauge for unambiguously evaluating the quality of the fit has been introduced; it is based on the root mean square difference of the distributions of target properties between reference data and fitted potentials. Four rigid water models have been parameterized; the matching procedure has been used to assess the role of the ghost atom in TIP4P-like models and of electrostatic damping. In the former case, burying the negative charge inside the molecule allows to fit better the torques. In the latter, since short-range interactions are damped, a better fit of the forces is obtained. Overall, the best performing model is the one with a ghost atom and with electrostatic damping. The approach shown in this paper is of general validity and could be applied to any matching algorithm and to any level of coarse graining, also for non-rigid molecules.
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61.25.Em Molecular liquids
31.15.E- Density-functional theory
33.20.Tp Vibrational analysis
61.20.Gy Theory and models of liquid structure
61.20.Ja Computer simulation of liquid structure

Dressed adiabatic and diabatic potentials to study conical intersections for F + H2

Anita Das, Tapas Sahoo, Debasis Mukhopadhyay, Satrajit Adhikari, and Michael Baer

J. Chem. Phys. 136, 054104 (2012); http://dx.doi.org/10.1063/1.3679406 (6 pages)

Online Publication Date: 2 February 2012

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We follow a suggestion by Lipoff and Herschbach [Mol. Phys. 108, 1133 (2010)10.1080/00268971003662912] and compare dressed and bare adiabatic potentials to get insight regarding the low-energy dynamics (e.g., cold reaction) taking place in molecular systems. In this particular case, we are interested to study the effect of conical intersections (ci) on the interacting atoms. For this purpose, we consider vibrational dressed adiabatic and vibrational dressed diabatic potentials in the entrance channel of reactive systems. According to our study, the most one should expect, in case of F + H2, is a mild effect of the (1, 2) ci on its reactive/exchange process−an outcome also supported by experiment. This happens although the corresponding dressed and bare potential barriers (and the corresponding van der Waals potential wells) differ significantly from each other.
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34.20.Gj Intermolecular and atom-molecule potentials and forces
31.15.A- Ab initio calculations
33.15.Mt Rotation, vibration, and vibration-rotation constants

Iterative diagonalization in the state-averaged multi-configurational time-dependent Hartree approach: Excited state tunneling splittings in malonaldehyde

Thorsten Hammer and Uwe Manthe

J. Chem. Phys. 136, 054105 (2012); http://dx.doi.org/10.1063/1.3681166 (17 pages) | Cited 1 time

Online Publication Date: 3 February 2012

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An iterative block Lanczos-type diagonalization scheme utilizing the state-averaged multi-configurational time-dependent Hartree (MCTDH) approach is introduced. Combining propagation in real and imaginary time and using a set of initial seed wavefunctions corresponding to excitations via the different components of the dipole moment vector, the scheme can favorably be used to selectively compute vibrational states which show high intensities in vibrational absorption spectra. Tunneling splitted vibrational states in double well systems can be described particularly efficient employing an increased set of seed wavefunctions which includes symmetric and anti-symmetric wavefunctions simultaneously. The new approach is used to study the tunneling splittings of the vibrationally excited states of malonaldehyde. Full-dimensional multi-layer MCTDH calculations are performed and results for the tunneling splittings of several excited vibrational states can be obtained. The calculated tunneling splittings agree reasonably well with available experimental data. Order of magnitude differences between tunneling splittings of different vibrationally excited states are found and interpreted.
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33.20.Tp Vibrational analysis
31.15.xr Self-consistent-field methods
31.15.xv Molecular dynamics and other numerical methods
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Effect of dimensionality on the continuum percolation of overlapping hyperspheres and hypercubes

S. Torquato

J. Chem. Phys. 136, 054106 (2012); http://dx.doi.org/10.1063/1.3679861 (16 pages)

Online Publication Date: 3 February 2012

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We show analytically that the [0, 1], [1, 1], and [2, 1] Padé approximants of the mean cluster number S for both overlapping hyperspheres and overlapping oriented hypercubes are upper bounds on this quantity in any Euclidean dimension d. These results lead to lower bounds on the percolation threshold density ηc, which become progressively tighter as d increases and exact asymptotically as d → ∞, i.e., ηc → 2−d. Our analysis is aided by a certain remarkable duality between the equilibrium hard-hypersphere (hypercube) fluid system and the continuum percolation model of overlapping hyperspheres (hypercubes). Analogies between these two seemingly different problems are described. We also obtain Percus-Yevick-like approximations for the mean cluster number S in any dimension d that also become asymptotically exact as d → ∞. We infer that as the space dimension increases, finite-sized clusters become more ramified or “branch-like.” These analytical estimates are used to assess simulation results for ηc up to 20 dimensions in the case of hyperspheres and up to 15 dimensions in the case of hypercubes. Our analysis sheds light on the radius of convergence of the density expansion for S and naturally leads to an analytical approximation for ηc that applies across all dimensions for both hyperspheres and oriented hypercubes. Finally, we describe the extension of our results to the case of overlapping particles of general anisotropic shape in d dimensions with a specified orientational probability distribution.
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02.50.Cw Probability theory
05.10.-a Computational methods in statistical physics and nonlinear dynamics

When does the non-variational nature of second-order Møller-Plesset energies manifest itself? All-electron correlation energies for open-shell atoms from K to Br

Shane P. McCarthy and Ajit J. Thakkar

J. Chem. Phys. 136, 054107 (2012); http://dx.doi.org/10.1063/1.3679969 (8 pages)

Online Publication Date: 3 February 2012

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All-electron correlation energies Ec are not very well known for open-shell atoms with more than 18 electrons. The complete basis-set (CBS) limits of second-order Møller-Plesset (MP2) perturbation theory energies are obtained for open-shell atoms by computations in large basis sets combined with a knowledge of the MP2/CBS limit for the next larger closed-shell atom with the same valence shell structure. Then higher-order correlation corrections are found by coupled-cluster calculations using basis sets that are not quite as large. The method is validated for the open-shell atoms from Al to Cl for which Ec is reasonably well established. Then, the method is used to obtain non-relativistic Ec values, probably accurate to 3%, for the open-shell atoms of the fourth period: K, Sc–Cu, and Ga–Br. These energies are compared with the predictions of 19 density functionals and may be useful for the parameterization of new ones. The results show that MP2 overestimates |Ec| for atoms heavier than Fe.
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31.15.V- Electron correlation calculations for atoms, ions and molecules
31.15.xp Perturbation theory
31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
31.15.eg Exchange-correlation functionals (in current density functional theory)
31.15.bw Coupled-cluster theory

Nonadiabatic excited-state molecular dynamics: Numerical tests of convergence and parameters

Tammie Nelson, Sebastian Fernandez-Alberti, Vladimir Chernyak, Adrian E. Roitberg, and Sergei Tretiak

J. Chem. Phys. 136, 054108 (2012); http://dx.doi.org/10.1063/1.3680565 (12 pages)

Online Publication Date: 3 February 2012

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Nonadiabatic molecular dynamics simulations, involving multiple Born-Oppenheimer potential energy surfaces, often require a large number of independent trajectories in order to achieve the desired convergence of the results, and simulation relies on different parameters that should be tested and compared. In addition to influencing the speed of the simulation, the chosen parameters combined with the frequently reduced number of trajectories can sometimes lead to unanticipated changes in the accuracy of the simulated dynamics. We have previously developed a nonadiabatic excited state molecular dynamics methodology employing Tully's fewest switches surface hopping algorithm. In this study, we seek to investigate the impact of the number of trajectories and the various parameters on the simulation of the photoinduced dynamics of distyrylbenzene (a small oligomer of polyphenylene vinylene) within our developed framework. Various user-defined parameters are analyzed: classical and quantum integration time steps, the value of the friction coefficient for Langevin dynamics, and the initial seed used for stochastic thermostat and hopping algorithms. Common approximations such as reduced number of nonadiabatic coupling terms and the classical path approximation are also investigated. Our analysis shows that, at least for the considered molecular system, a minimum of ∼400 independent trajectories should be calculated in order to achieve statistical averaging necessary for convergence of the calculated relaxation timescales.
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31.50.Df Potential energy surfaces for excited electronic states
31.15.xv Molecular dynamics and other numerical methods

Trajectory-guided configuration interaction simulations of multidimensional quantum dynamics

Scott Habershon

J. Chem. Phys. 136, 054109 (2012); http://dx.doi.org/10.1063/1.3681167 (8 pages)

Online Publication Date: 6 February 2012

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We propose an approach to modelling multidimensional quantum systems which uses direct-dynamics trajectories to guide wavefunction propagation. First, trajectory simulations are used to generate a sample of dynamically relevant configurations on the potential energy surface (PES). Second, the sampled configurations are used to construct an n-mode representation of the PES using a greedy algorithm. Finally, the time-dependent Schrödinger equation is solved using a configuration interaction expansion of the wavefunction, with individual basis functions derived directly from the 1-mode contributions to the n-mode PES. This approach is successfully demonstrated by application to a 20-dimensional benchmark problem describing tunnelling in the presence of coupled degrees of freedom.
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31.15.V- Electron correlation calculations for atoms, ions and molecules
03.65.Ge Solutions of wave equations: bound states
03.65.Xp Tunneling, traversal time, quantum Zeno dynamics
31.50.-x Potential energy surfaces

The sign problem and population dynamics in the full configuration interaction quantum Monte Carlo method

J. S. Spencer, N. S. Blunt, and W. M.C. Foulkes

J. Chem. Phys. 136, 054110 (2012); http://dx.doi.org/10.1063/1.3681396 (10 pages)

Online Publication Date: 6 February 2012

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The recently proposed full configuration interaction quantum Monte Carlo method allows access to essentially exact ground-state energies of systems of interacting fermions substantially larger than previously tractable without knowledge of the nodal structure of the ground-state wave function. We investigate the nature of the sign problem in this method and how its severity depends on the system studied. We explain how cancellation of the positive and negative particles sampling the wave function ensures convergence to a stochastic representation of the many-fermion ground state and accounts for the characteristic population dynamics observed in simulations.
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31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
31.15.ve Electron correlation calculations for atoms and ions: ground state
05.30.Fk Fermion systems and electron gas

Stochastic mapping of the Michaelis-Menten mechanism

Éva Dóka and Gábor Lente

J. Chem. Phys. 136, 054111 (2012); http://dx.doi.org/10.1063/1.3681942 (7 pages)

Online Publication Date: 6 February 2012

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The Michaelis-Menten mechanism is an extremely important tool for understanding enzyme-catalyzed transformation of substrates into final products. In this work, a computationally viable, full stochastic description of the Michaelis-Menten kinetic scheme is introduced based on a stochastic equivalent of the steady-state assumption. The full solution derived is free of restrictions on amounts of substance or parameter values and is used to create stochastic maps of the Michaelis-Menten mechanism, which show the regions in the parameter space of the scheme where the use of the stochastic kinetic approach is inevitable. The stochastic aspects of recently published examples of single-enzyme kinetic studies are analyzed using these maps.
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87.15.R- Reactions and kinetics
02.50.-r Probability theory, stochastic processes, and statistics

The multi-configuration electron-nuclear dynamics method applied to LiH

Inga S. Ulusoy and Mathias Nest

J. Chem. Phys. 136, 054112 (2012); http://dx.doi.org/10.1063/1.3682091 (6 pages)

Online Publication Date: 6 February 2012

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The multi-configuration electron-nuclear dynamics (MCEND) method is a nonadiabatic quantum dynamics approach to the description of molecular processes. MCEND is a combination of the multi-configuration time-dependent Hartree (MCTDH) method for atoms and its antisymmetrized equivalent MCTDHF for electrons. The purpose of this method is to simultaneously describe nuclear and electronic wave packets in a quantum dynamical way, without the need to calculate potential energy surfaces and diabatic coupling functions. In this paper we present first exemplary calculations of MCEND applied to the LiH molecule, and discuss computational and numerical details of our implementation.
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31.15.xr Self-consistent-field methods

Exploring the competition between localization and delocalization of the neutral soliton defect in polyenyl chains with the orbital optimized second order opposite spin method

Westin Kurlancheek, Rohini Lochan, Keith Lawler, and Martin Head-Gordon

J. Chem. Phys. 136, 054113 (2012); http://dx.doi.org/10.1063/1.3679658 (11 pages)

Online Publication Date: 6 February 2012

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Theory and implementation of the analytical nuclear gradient is presented for orbital optimized scaled opposite-spin perturbation theory (O2). Evaluation of the O2 analytical gradient scales with the 4th power of molecular size, like the O2 energy. Since the O2 method permits optimization of the orbitals in the presence of wavefunction-based electron correlation, it is suitable for problems where correlation effects determine the competition between localization and delocalization of an odd electron, or hole. One such problem is the description of a neutral soliton defect on an all-trans polyacetylene chain with an odd number of carbon atoms. We show that the results of the O2 method compare well to benchmark values for small polyenyl radicals. O2 is also efficient enough to be applied to longer chains where benchmark coupled cluster methods are unfeasible. For C41H43, unrestricted orbital O2 calculations yield a soliton length of about 9 carbon atoms, while other unrestricted orbital methods such as Hartree-Fock, and the B3LYP and ωB97X-D density functionals, delocalize the soliton defect over the entire chain. The O2 result is about half the width inferred experimentally.
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31.15.eg Exchange-correlation functionals (in current density functional theory)
31.15.am Relativistic configuration interaction (CI) and many-body perturbation calculations
05.45.Yv Solitons
31.15.xr Self-consistent-field methods
31.15.xp Perturbation theory

Quasi-variational coupled cluster theory

James B. Robinson and Peter J. Knowles

J. Chem. Phys. 136, 054114 (2012); http://dx.doi.org/10.1063/1.3680560 (12 pages)

Online Publication Date: 6 February 2012

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We extend our previous work on the construction of new approximations of the variational coupled cluster method. By combining several linked pair functional transformations in such a way as to give appropriately balanced infinite-order contributions, in order to approximate 〈mathmathmath〉L well at all orders, we formulate a new quantum chemical method, which we name quasi-variational coupled cluster. We demonstrate this method to be particularly robust in the regime of strong static electron correlation, improving significantly on our earlier approximate variational coupled cluster approach.
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31.15.bw Coupled-cluster theory
31.15.V- Electron correlation calculations for atoms, ions and molecules
31.15.xt Variational techniques

Search for a small hole in a cavity wall by intermittent bulk and surface diffusion

Alexander M. Berezhkovskii and Alexander V. Barzykin

J. Chem. Phys. 136, 054115 (2012); http://dx.doi.org/10.1063/1.3682243 (6 pages) | Cited 1 time

Online Publication Date: 7 February 2012

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We study the search of a small round hole in the wall of a spherical cavity by a diffusing particle, which can reversibly bind to the cavity wall and diffuse on the surface being in the bound state. There are two channels for the particle first passage to the hole, through the bulk, and through the surface. We propose a coarse-grained model of the search process and use it to derive simple approximate formulas for the mean time required for the particle to reach the hole for the first time and for the probability of the first passage to the hole through the bulk channel. This is done for two distributions of the particle starting point: (1) Uniform distribution over the cavity volume and (2) uniform distribution over the cavity wall. We check the accuracy of the approximate formulas by comparing their predictions with the corresponding quantities found by solving the mixed bulk-surface diffusion problem numerically by the finite difference method. The comparison shows excellent agreement between the analytical and numerical results.
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68.35.Fx Diffusion; interface formation

Quadrupole-bound anions: Efficacy of positive versus negative quadrupole moments

W. R. Garrett

J. Chem. Phys. 136, 054116 (2012); http://dx.doi.org/10.1063/1.3682465 (5 pages)

Online Publication Date: 7 February 2012

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A pseudopotential method is utilized to study the critical stability of model anions formed by long-range quadrupolar molecular potentials. Results indicate that critical quadrupole moments of simple point-charge triads do not serve well as predictors of real quadrupole-bound anions of systems with negative moments.
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33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
34.20.Gj Intermolecular and atom-molecule potentials and forces
back to top Advanced Experimental Techniques

Angle-resolved metastable fragment yields spectra of N2 and CO in K-edge excitation energy region

Tatsuo Gejo, Takashi Tamura, Kenji Honma, Eiji Shigemasa, Yasumasa Hikosaka, and Yusuke Tamenori

J. Chem. Phys. 136, 054201 (2012); http://dx.doi.org/10.1063/1.3680561 (7 pages)

Online Publication Date: 3 February 2012

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Angle-resolved metastable fragments yields spectra have been measured in the N 1s ionization region of the N2 and C 1s ionization region of CO. These spectra are compared with zero kinetic energy electron and photoelectron spectra. It has been shown that an isotropic metastable fragments yields spectra are almost identical with the ZEKE spectrum, whereas metastable fragments yields spectra with the Σ–Σ transition show similarity with photoelectron spectra. This means that these spectra clearly contain information about two shake-up mechanisms: conjugate and direct shake-up processes. All the peaks in the metastable photofragment spectra can be assigned as either satellite states or double/triple excitation states. Thus, it was shown that angle-resolved metastable photofragment spectroscopy could be used to help characterize multi-electron excitation states in general.
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33.80.Eh Autoionization, photoionization, and photodetachment
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry
FREE

Mg impurity in helium droplets

J. Navarro, D. Mateo, M. Barranco, and A. Sarsa

J. Chem. Phys. 136, 054301 (2012); http://dx.doi.org/10.1063/1.3675919 (9 pages) | Cited 1 time

Online Publication Date: 1 February 2012

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Within the diffusion Monte Carlo approach, we have determined the structure of isotopically pure and mixed helium droplets doped with one magnesium atom. For pure 4He clusters, our results confirm those of Mella et al. [J. Chem. Phys. 123, 054328 (2005)10.1063/1.1982787] that the impurity experiences a transition from a surface to a bulk location as the number of helium atoms in the droplet increases. Contrarily, for pure 3He clusters Mg resides in the bulk of the droplet due to the smaller surface tension of this isotope. Results for mixed droplets are presented. We have also obtained the absorption spectrum of Mg around the 3s3p 1P1 ← 3s2 1S0 transition.
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36.40.Mr Spectroscopy and geometrical structure of clusters

Low energy collisions of CN(X  2Σ+) with He in magnetic fields

Eryin Feng, Xi Shao, Chunhua Yu, Chunyan Sun, and Wuying Huang

J. Chem. Phys. 136, 054302 (2012); http://dx.doi.org/10.1063/1.3679869 (7 pages) | Cited 1 time

Online Publication Date: 1 February 2012

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See Also: RETRACTION

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A theoretical investigation of the He–CN(2Σ+) complex is presented. We perform ab initio calculations of the interaction potential energy surface and carry out accurate calculations of bound energy levels of the complex including the molecular fine structure. We find the potential has a shallow minimum and supports seven and nine bound levels in complex with 3He and 4He, respectively. Based on the potential the quantum scattering calculation is then implemented for elastic and inelastic cross sections of the magnetically trappable low-field-seeking state of CN(2Σ+) in collision with 3He atom. The cold collision properties and the influence of the external magnetic field as well as the effect of the uncertainty of interaction potential on the collisionally induced Zeeman relaxation are explored and discussed in detail. The ratios of elastic to inelastic cross sections are large over a wide range of collision energy, magnetic field, and scaling factor of the potential, suggesting helium buffer gas loading and cooling of CN in a magnetic trap is a good prospect.
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34.20.Gj Intermolecular and atom-molecule potentials and forces
33.15.Pw Fine and hyperfine structure
31.15.A- Ab initio calculations
33.57.+c Magneto-optical and electro-optical spectra and effects

Ultrafast ring opening in 1,3-cyclohexadiene investigated by simplex-based spectral unmixing

J. L. White, J. Kim, V. S. Petrović, and P. H. Bucksbaum

J. Chem. Phys. 136, 054303 (2012); http://dx.doi.org/10.1063/1.3681258 (8 pages)

Online Publication Date: 2 February 2012

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We use spectral unmixing to determine the number of transient photoproducts and to track their evolution following the photo-excitation of 1,3-cyclohexadiene (CHD) to form 1,3,5-hexatriene (HT) in the gas phase. The ring opening is initiated with a 266 nm ultraviolet laser pulse and probed via fragmentation with a delayed intense infrared 800 nm laser pulse. The ion time-of-flight (TOF) spectra are analyzed with a simplex-based spectral unmixing technique. We find that at least three independent spectra are needed to model the transient TOF spectra. Guided by mathematical and physical constraints, we decompose the transient TOF spectra into three spectra associated with the presence of CHD, CHD+, and HT, and show how these three species appear at different times during the ring opening.
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33.80.-b Photon interactions with molecules

Dynamics of H+ + CO at ELab = 30 eV

Christopher Stopera, Buddhadev Maiti, Thomas V. Grimes, Patrick M. McLaurin, and Jorge A. Morales

J. Chem. Phys. 136, 054304 (2012); http://dx.doi.org/10.1063/1.3678014 (13 pages)

Online Publication Date: 2 February 2012

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The astrophysically relevant system H+ + CO (vi = 0) → H+ + CO (vf) at ELab = 30 eV is studied with the simplest-level electron nuclear dynamics (SLEND) method. This investigation follows previous successful SLEND studies of H+ + H2 and H+ + N2 at ELab = 30 eV [J. Morales, A. Diz, E. Deumens, and Y. Öhrn, J. Chem. Phys. 103(23), 9968 (1995)10.1063/1.469886; C. Stopera, B. Maiti, T. V. Grimes, P. M. McLaurin, and J. A. Morales, J. Chem. Phys. 134(22), 224308 (2011)10.1063/1.3598511]. SLEND is a direct, time-dependent, variational, and non-adiabatic method that adopts a classical-mechanics description for the nuclei and a single-determinantal wavefunction for the electrons. A canonical coherent-states (CS) procedure associated with SLEND reconstructs quantum vibrational properties from the SLEND classical dynamics. Present SLEND results include reactivity predictions, snapshots of the electron density evolution, average vibrational energy transfers, rainbow angle predictions, total and vibrationally resolved differential cross sections (DCS), and average vibrational excitation probabilities. SLEND results are compared with available data from experiments and vibrational close-coupling rotational infinite-order sudden (VCC-RIOS) approximation calculations. Present simulations employ four basis sets: STO-3G, 6-31G, 6-31G**, and cc-pVDZ to determine their effect on the results. SLEND simulations predict non-charge-transfer scattering and CO collision-induced dissociation as the main reactions. SLEND/6-31G, /6-31G**, and /cc-pVDZ predict rainbow angles and total DCS in excellent agreement with experiments and more accurate than their VCC-RIOS counterparts. SLEND/6-31G** and /cc-pVDZ predict vibrationally resolved DCS for vf = 0–2 in satisfactory experimental agreement, but less accurate than their comparable H+ + CO VCC-RIOS and H+ + H2 and H+ + N2 SLEND results. SLEND/6-31G** and /cc-pVDZ predict qualitatively correct average vibrational excitation probabilities, which are quantitatively correct for vf = 2, but under(over)estimated for vf = 0(1). Discrepancies in some H+ + CO SLEND vibrational properties, not observed in H+ + H2 and H+ + N2 SLEND results, are attributed to the moderately overestimated SLEND vibrational energy through its effect upon the canonical CS probabilities. Correction of that energy to its experimental values produces a remarkable improvement in the average vibrational excitation probabilities. Ways to obtain more accurate vibrational properties with higher-level versions of electron nuclear dynamics are discussed.
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34.50.Ez Rotational and vibrational energy transfer
34.50.Gb Electronic excitation and ionization of molecules
31.15.xt Variational techniques
33.15.Mt Rotation, vibration, and vibration-rotation constants

Coupled-cluster, Möller Plesset (MP2), density fitted local MP2, and density functional theory examination of the energetic and structural features of hydrophobic solvation: Water and pentane

Yasaman Ghadar and Aurora E. Clark

J. Chem. Phys. 136, 054305 (2012); http://dx.doi.org/10.1063/1.3679933 (8 pages)

Online Publication Date: 2 February 2012

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The interaction potentials between immiscible polar and non-polar solvents are a major driving force behind the formation of liquid:liquid interfaces. In this work, the interaction energy of water–pentane dimer has been determined using coupled-cluster theory with single double (triple) excitations [CCSD(T)], 2nd order Möller Plesset perturbation theory (MP2), density fitted local MP2 (DF-LMP2), as well as density functional theory using a wide variety of density functionals and several different basis sets. The M05-2X exchange correlation functionals exhibit excellent agreement with CCSD(T) and DF-LMP2 after taking into account basis set superposition error. The gas phase water–pentane interaction energy is found to be quite sensitive to the specific pentane isomer (2,2-dimethylpropane vs. n-pentane) and relative orientation of the monomeric constituents. Subsequent solution phase cluster calculations of 2,2-dimethylpropane and n-pentane solvated by water indicate a positive free energy of solvation that is in good agreement with available experimental data. Structural parameters are quite sensitive to the density functional employed and reflect differences in the two-body interaction energy calculated by each method. In contrast, cluster calculations of pentane solvation of H2O solute are found to be inadequate for describing the organic solvent, likely due to limitations associated with the functionals employed (B3LYP, BHandH, and M05-2X).
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61.20.Qg Structure of associated liquids: electrolytes, molten salts, etc.
61.25.Em Molecular liquids
65.20.Jk Studies of thermodynamic properties of specific liquids
61.20.Ja Computer simulation of liquid structure

Cold collisions of complex polyatomic molecules

Zhiying Li and Eric J. Heller

J. Chem. Phys. 136, 054306 (2012); http://dx.doi.org/10.1063/1.3682982 (7 pages)

Online Publication Date: 6 February 2012

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We introduce a method for classical trajectory calculations to simulate collisions between atoms and large rigid asymmetric-top molecules. We investigate the formation of molecule-helium complexes in buffer-gas cooling experiments at a temperature of 6.5 K for molecules as large as naphthalene. Our calculations show that the mean lifetime of the naphthalene-helium quasi-bound collision complex is not long enough for the formation of stable clusters under the experimental conditions. Our results suggest that it may be possible to improve the efficiency of the production of cold molecules in buffer-gas cooling experiments by increasing the density of helium. In addition, we find that the shape of molecules is important for the collision dynamics when the vibrational motion of molecules is frozen. For some molecules, it is even more crucial than the number of accessible degrees of freedom. This indicates that by selecting molecules with suitable shape for buffer-gas cooling, it may be possible to cool molecules with a very large number of degrees of freedom.
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34.50.Lf Chemical reactions
33.15.Mt Rotation, vibration, and vibration-rotation constants

The electronic spectrum of the Cs-C11H3 radical

Dongfeng Zhao (赵东锋), Harold Linnartz, and Wim Ubachs

J. Chem. Phys. 136, 054307 (2012); http://dx.doi.org/10.1063/1.3681259 (8 pages)

Online Publication Date: 6 February 2012

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The electronic gas-phase absorption spectrum of the bent carbon-chain radical, HC4CHC6H with Cs symmetry, is recorded in the 595 nm region by cavity ring-down spectroscopy through an expanding hydrogen plasma. An unambiguous spectroscopic identification becomes possible from a systematic deuterium labeling experiment. A comparison of the results with recently reported spectra of the nonlinear HC4CHC4H and HC4C(C2H)C4H radicals with C2v symmetry provides a more comprehensive understanding of the molecular behavior of π-conjugated bent carbon-chain systems upon electronic excitation. We find that the electronic excitation in the bent carbon-chain HC4CHC2nH (n = 1–4) series exhibits a similar trend as in the linear HC2n+1H (n = 3–6) series, shifting optical absorptions towards longer wavelengths for increasing overall bent chain lengths. The π-conjugation in bent HC4CHC2nH (n = 1–4) chains is found to be generally smaller than in the linear HC2n+1H (n = 3–6) case for equivalent numbers of C-atoms. The addition of an electron-donating group to the bent chain causes a slight decrease of the effective conjugation.
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33.15.Bh General molecular conformation and symmetry; stereochemistry
33.20.Kf Visible spectra
33.20.Lg Ultraviolet spectra
33.70.Jg Line and band widths, shapes, and shifts

Nonadiabatic dynamics of O(1D) + N2(X1Σg+)→O(3P) + N2(X1Σg+) on three coupled potential surfaces: Symmetry, Coriolis, spin-orbit, and Renner-Teller effects

Paolo Defazio, Pablo Gamallo, and Carlo Petrongolo

J. Chem. Phys. 136, 054308 (2012); http://dx.doi.org/10.1063/1.3682467 (6 pages) | Cited 1 time

Online Publication Date: 6 February 2012

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We present the spin-orbit (SO) and Renner-Teller (RT) quantum dynamics of the spin-forbidden quenching O(1D) + N2(X1Σg+)→O(3P) + N2(X1Σg+) on the N2O math1A′, math3A″, and math3A′ coupled PESs. We use the permutation-inversion symmetry, propagate coupled-channel (CC) real wavepackets, and compute initial-state-resolved probabilities and cross sections σj0 for the ground vibrational and the first two rotational states of N2, j0 = 0 and 1. Labeling symmetry angular states by j and K, we report selection rules for j and for the minimum K value associated with any electronic state, showing that math3A″ is uncoupled in the centrifugal-sudden (CS) approximation at j0 = 0. The dynamics is resonance-dominated, the probabilities are larger at low K, σj0 decrease with the collision energy and increase with j0, and the CS σ0 is lower than the CC one. The nonadiabatic interactions play different roles on the quenching dynamics, because the math1A′−math3A′ SO effects are those most important while the math3A″−math3A′ RT ones are negligible.
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82.50.-m Photochemistry
82.33.Tb Atmospheric chemistry
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Kh Potential energy surfaces for chemical reactions
33.15.Mt Rotation, vibration, and vibration-rotation constants
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