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28 Jan 2013

Volume 138, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

J. Chem. Phys. 138, 044701 (2013); http://dx.doi.org/10.1063/1.4774376 (8 pages)

Simone Taioli, Giovanni Garberoglio, Stefano Simonucci, Silvio a Beccara, Lucrezia Aversa, Marco Nardi, Roberto Verucchi, Salvatore Iannotta, Maurizio Dapor, and Dario Alfè
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Communication: A vibrational study of titanium dioxide cation using the vacuum ultraviolet laser pulsed field ionization-photoelectron method

Yih-Chung Chang, Huang Huang, Zhihong Luo, and C. Y. Ng

J. Chem. Phys. 138, 041101 (2013); http://dx.doi.org/10.1063/1.4789792 (4 pages)

Online Publication Date: 24 January 2013

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We have successfully measured the vacuum ultraviolet (VUV) laser photoionization efficiency and pulsed field ionization-photoelectron (PFI-PE) spectra of cold titanium dioxide (TiO2) prepared by a supersonically cooled laser ablation source. The VUV-PFI-PE spectrum thus obtained exhibits long progressions of the v2+(a1) bending and the combination of v1+(a1) stretching and v2+(a1) bending vibrational modes of the TiO2+(math2B2) ion. The pattern of Franck-Condon factors observed indicates that the O–Ti–O bond angle of the TiO2+(math2B2) ion is significantly different from that of the TiO2(math1A1) neutral, whereas the change of the Ti–O bond distance is very minor upon the photoionization transition. The analysis of the PFI-PE bands has made possible the determination of the adiabatic ionization energy for TiO2, IE(TiO2) = 77215.9 ± 1.2 cm−1 (9.57355 ± 0.00015 eV), the harmonic vibrational frequencies, ω1+ = 829.1 ± 2.0 cm−1 and ω2+ = 248.7 ± 0.6 cm−1, and the anharmonic coefficients, χ11+ = 5.57 ± 0.65 cm−1, χ22+ = 0.08 ± 0.06 cm−1, and χ12+ = −4.51 ± 0.30 cm−1 for the TiO2+(math2B2) ground state.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.60.+q Photoelectron spectra
37.10.Mn Slowing and cooling of molecules
33.15.Dj Interatomic distances and angles
33.15.Mt Rotation, vibration, and vibration-rotation constants
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back to top Theoretical Methods and Algorithms

Resonance Raman spectra of ortho-nitrophenol calculated by real-time time-dependent density functional theory

Martin Thomas, Federico Latorre, and Philipp Marquetand

J. Chem. Phys. 138, 044101 (2013); http://dx.doi.org/10.1063/1.4776218 (8 pages)

Online Publication Date: 23 January 2013

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A new approach for the calculation of resonance Raman spectra is presented. The new method is based on dynamic polarizabilities from real-time time-dependent density functional theory, and its estimations are compared to two established techniques for the prediction of resonance Raman spectra. These established methods either use dynamic polarizabilities from linear-response time-dependent density functional theory or employ excited-state gradients. The three different ways to calculate resonance Raman spectra are investigated using the example of ortho-nitrophenol. The three methods give very similar results, respectively, for the four different exchange-correlation functionals applied. Thus, the new approach is validated for the calculation of resonance Raman intensities and advantages as well as disadvantages are discussed.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)
31.15.ee Time-dependent density functional theory
31.15.eg Exchange-correlation functionals (in current density functional theory)

An effective energy gradient expression for divide-and-conquer second-order Møller–Plesset perturbation theory

Masato Kobayashi and Hiromi Nakai

J. Chem. Phys. 138, 044102 (2013); http://dx.doi.org/10.1063/1.4776228 (11 pages) | Cited 1 time

Online Publication Date: 23 January 2013

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We recently proposed a linear-scaling evaluation scheme for the second-order Møller–Plesset perturbation (MP2) energy based on the divide-and-conquer (DC) method [M. Kobayashi, Y. Imamura, and H. Nakai, J. Chem. Phys. 127, 074103 (2007)10.1063/1.2761878]. In this paper, we propose an approximate but effective expression for the first derivative of the DC-MP2 energy. The present scheme evaluates the one- and two-body density matrices, which appear in the MP2 gradient formula, in the DC manner; that is, the entire matrix is obtained as the sum of subsystem matrices masked by the partition matrix. Therefore, the method requires solving only the local Z-vector equations. Illustrative applications to three types of systems, peptides, Si surface model, and delocalized polyenes, reveal the effectiveness of the present method.
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31.15.xp Perturbation theory

Simple electrolyte solutions: Comparison of DRISM and molecular dynamics results for alkali halide solutions

In Suk Joung, Tyler Luchko, and David A. Case

J. Chem. Phys. 138, 044103 (2013); http://dx.doi.org/10.1063/1.4775743 (15 pages)

Online Publication Date: 23 January 2013

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Using the dielectrically consistent reference interaction site model (DRISM) of molecular solvation, we have calculated structural and thermodynamic information of alkali-halide salts in aqueous solution, as a function of salt concentration. The impact of varying the closure relation used with DRISM is investigated using the partial series expansion of order-n (PSE-n) family of closures, which includes the commonly used hypernetted-chain equation (HNC) and Kovalenko-Hirata closures. Results are compared to explicit molecular dynamics (MD) simulations, using the same force fields, and to experiment. The mean activity coefficients of ions predicted by DRISM agree well with experimental values at concentrations below 0.5 m, especially when using the HNC closure. As individual ion activities (and the corresponding solvation free energies) are not known from experiment, only DRISM and MD results are directly compared and found to have reasonably good agreement. The activity of water directly estimated from DRISM is nearly consistent with values derived from the DRISM ion activities and the Gibbs-Duhem equation, but the changes in the computed pressure as a function of salt concentration dominate these comparisons. Good agreement with experiment is obtained if these pressure changes are ignored. Radial distribution functions of NaCl solution at three concentrations were compared between DRISM and MD simulations. DRISM shows comparable water distribution around the cation, but water structures around the anion deviate from the MD results; this may also be related to the high pressure of the system. Despite some problems, DRISM-PSE-n is an effective tool for investigating thermodynamic properties of simple electrolytes.
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82.30.Nr Association, addition, insertion, cluster formation
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Bh General molecular conformation and symmetry; stereochemistry
31.15.xv Molecular dynamics and other numerical methods
82.45.Gj Electrolytes

Accuracy of relativistic energy-consistent pseudopotentials for superheavy elements 111–118: Molecular calibration calculations

Tim Hangele and Michael Dolg

J. Chem. Phys. 138, 044104 (2013); http://dx.doi.org/10.1063/1.4776757 (7 pages) | Cited 1 time

Online Publication Date: 24 January 2013

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Relativistic energy-consistent pseudopotentials modelling the Dirac-Coulomb-Breit Hamiltonian with a finite nucleus model for the superheavy elements with nuclear charges 111–118 were calibrated in atomic and molecular calculations against fully relativistic all-electron reference data. Various choices for the adjustment of the f-potentials were investigated and an improved parametrization is recommended. Using the resulting pseudopotentials relativistic all-electron reference data can be reproduced at the self-consistent field level with average absolute (relative) errors of 0.0030 Å (0.15%) for bond lengths and 2.79 N m−1 (1.26%) for force constants for 24 diatomic test molecules, i.e., neutral or singly charged monohydrides, monofluorides, and monochlorides with closed-shell electronic structure. At the second-order Møller-Plesset perturbation theory level the corresponding average deviations are 0.0033 Å (0.15%) for bond lengths and 2.86 N m−1 (1.40%) for force constants. Corresponding improved f-potentials were also derived for the pseudopotentials modelling in addition the leading contributions from quantum electrodynamics.
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31.15.xp Perturbation theory
27.90.+b A ≥ 220
33.15.Dj Interatomic distances and angles

Simulating rare events using a weighted ensemble-based string method

Joshua L. Adelman and Michael Grabe

J. Chem. Phys. 138, 044105 (2013); http://dx.doi.org/10.1063/1.4773892 (13 pages)

Online Publication Date: 24 January 2013

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We introduce an extension to the weighted ensemble (WE) path sampling method to restrict sampling to a one-dimensional path through a high dimensional phase space. Our method, which is based on the finite-temperature string method, permits efficient sampling of both equilibrium and non-equilibrium systems. Sampling obtained from the WE method guides the adaptive refinement of a Voronoi tessellation of order parameter space, whose generating points, upon convergence, coincide with the principle reaction pathway. We demonstrate the application of this method to several simple, two-dimensional models of driven Brownian motion and to the conformational change of the nitrogen regulatory protein C receiver domain using an elastic network model. The simplicity of the two-dimensional models allows us to directly compare the efficiency of the WE method to conventional brute force simulations and other path sampling algorithms, while the example of protein conformational change demonstrates how the method can be used to efficiently study transitions in the space of many collective variables.
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87.14.E- Proteins
87.15.ap Molecular dynamics simulation
87.15.B- Structure of biomolecules
05.40.Jc Brownian motion
36.20.Ey Conformation (statistics and dynamics)

Improved constrained optimization method for reaction-path determination in the generalized hybrid orbital quantum mechanical/molecular mechanical calculations

Jaewoon Jung, Suyong Re, Yuji Sugita, and Seiichiro Ten-no

J. Chem. Phys. 138, 044106 (2013); http://dx.doi.org/10.1063/1.4775812 (10 pages) | Cited 1 time

Online Publication Date: 24 January 2013

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The nudged elastic band (NEB) and string methods are widely used to obtain the reaction path of chemical reactions and phase transitions. In these methods, however, it is difficult to define an accurate Lagrangian to generate the conservative forces. On the other hand, the constrained optimization with locally updated planes (CO-LUP) scheme defines target function properly and suitable for micro-iteration optimizations in quantum mechanical/molecular mechanical (QM/MM) systems, which uses the efficient second order QM optimization. However, the method does have problems of inaccurate estimation of reactions and inappropriate accumulation of images around the energy minimum. We introduce three modifications into the CO-LUP scheme to overcome these problems: (1) An improved tangent estimation of the reaction path, which is used in the NEB method, (2) redistribution of images using an energy-weighted interpolation before updating local tangents, and (3) reduction of the number of constraints, in particular translation/rotation constraints, for improved convergence. First, we test the method on the isomerization of alanine dipeptide without QM/MM calculation, showing that the method is comparable to the string method both in accuracy and efficiency. Next, we apply the method for defining the reaction paths of the rearrangement reaction catalyzed by chorismate mutase (CM) and of the phosphoryl transfer reaction catalyzed by cAMP-dependent protein kinase (PKA) using generalized hybrid orbital QM/MM calculations. The reaction energy barrier of CM is in high agreement with the experimental value. The path of PKA reveals that the enzyme reaction is associative and there is a late transfer of the substrate proton to Asp 166, which is in agreement with the recently published result using the NEB method.
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87.15.R- Reactions and kinetics
82.20.Rp State to state energy transfer
82.30.Qt Isomerization and rearrangement
82.39.Jn Charge (electron, proton) transfer in biological systems
87.14.ej Enzymes

Application of the scaled-opposite-spin approximation to algebraic diagrammatic construction schemes of second order

Caroline M. Krauter, Markus Pernpointner, and Andreas Dreuw

J. Chem. Phys. 138, 044107 (2013); http://dx.doi.org/10.1063/1.4776675 (12 pages)

Online Publication Date: 25 January 2013

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With the concept of scaled-opposite-spin (SOS), a pragmatic semi-empirical approximation has been introduced to the extended algebraic diagrammatic construction scheme of second order (ADC(2)-x) that leads to a significant saving in computational effort. The parameters included were fitted with respect to a benchmark set of electronically excited states in standard organic molecules that include some doubly-excited states, as well. Like the original, unscaled ADC(2)-x scheme it can be used to identify electronically excited states with high double excitation character, however at reduced computational cost. At the same time, it is possible to reduce the overestimation of doubly-excited configurations that is inherent to ADC(2)-x. Additionally, a scheme for the strict variant (ADC(2)-s) was derived directly from SOS-MP2 by application of the intermediate state formalism and compared to an existing version of SOS-ADC(2)-s.
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31.15.xp Perturbation theory
33.15.Bh General molecular conformation and symmetry; stereochemistry

The reduced dynamics of an exciton coupled to a phonon bath: A new approach combining the Lang-Firsov transformation and the perturbation theory

Vincent Pouthier

J. Chem. Phys. 138, 044108 (2013); http://dx.doi.org/10.1063/1.4789017 (10 pages)

Online Publication Date: 28 January 2013

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To go beyond the Born approximation, a new method is introduced for describing the reduced dynamics of an exciton coupled to a phonon bath. Two unitary transformations are applied for accounting for the exciton-phonon entanglement through a dual dressing mechanism affecting both the exciton and the phonons. In doing so, one obtains an analytical expression of the exciton reduced density matrix without integrating numerically any generalized master equation. Therefore, by using a quite simple model that can be solved exactly, it has been shown that the proposed method is particularly suitable for describing the exciton dynamics over a rather broad region in the parameter space. However, although the method shows many strengths, it also exhibits weaknesses and it accidentally breaks down owing to the occurrence of specific resonances.
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71.35.Gg Exciton-mediated interactions
63.20.kk Phonon interactions with other quasiparticles

Contraction of completeness-optimized basis sets: Application to ground-state electron momentum densities

Susi Lehtola, Pekka Manninen, Mikko Hakala, and Keijo Hämäläinen

J. Chem. Phys. 138, 044109 (2013); http://dx.doi.org/10.1063/1.4788635 (8 pages) | Cited 1 time

Online Publication Date: 28 January 2013

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Completeness-optimization is a novel method for the formation of one-electron basis sets. Contrary to conventional methods of basis set generation that optimize the basis set with respect to ground-state energy, completeness-optimization is a completely general, black-box method that can be used to form cost-effective basis sets for any wanted property at any level of theory. In our recent work [J. Lehtola, P. Manninen, M. Hakala, and K. Hämäläinen, J. Chem. Phys. 137, 104105 (2012)]10.1063/1.4749272 we applied the completeness-optimization approach to forming primitive basis sets tuned for calculations of the electron momentum density at the Hartree-Fock (HF) level of theory. The current work extends the discussion to contracted basis sets and to the post-HF level of theory. Contractions are found to yield significant reductions in the amount of functions without compromising the accuracy. We suggest polarization-consistent and correlation-consistent basis sets for the first three rows of the periodic table, which are completeness-optimized for electron momentum density calculations.
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31.15.xr Self-consistent-field methods

The generalized identification of truly interfacial molecules (ITIM) algorithm for nonplanar interfaces

Marcello Sega, Sofia S. Kantorovich, Pál Jedlovszky, and Miguel Jorge

J. Chem. Phys. 138, 044110 (2013); http://dx.doi.org/10.1063/1.4776196 (10 pages) | Cited 1 time

Online Publication Date: 28 January 2013

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We present a generalized version of the ITIM algorithm for the identification of interfacial molecules, which is able to treat arbitrarily shaped interfaces. The algorithm exploits the similarities between the concept of probe sphere used in ITIM and the circumsphere criterion used in the α-shapes approach, and can be regarded either as a reference-frame independent version of the former, or as an extended version of the latter that includes the atomic excluded volume. The new algorithm is applied to compute the intrinsic orientational order parameters of water around a dodecylphosphocholine and a cholic acid micelle in aqueous environment, and to the identification of solvent-reachable sites in four model structures for soot. The additional algorithm introduced for the calculation of intrinsic density profiles in arbitrary geometries proved to be extremely useful also for planar interfaces, as it allows to solve the paradox of smeared intrinsic profiles far from the interface.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
64.75.Bc Solubility

Optimized unrestricted Kohn–Sham potentials from ab initio spin densities

Katharina Boguslawski, Christoph R. Jacob, and Markus Reiher

J. Chem. Phys. 138, 044111 (2013); http://dx.doi.org/10.1063/1.4788913 (16 pages)

Online Publication Date: 29 January 2013

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The reconstruction of the exchange–correlation potential from accurate ab initio electron densities can provide insights into the limitations of the currently available approximate functionals and provide guidance for devising improved approximations for density-functional theory (DFT). For open-shell systems, the spin density is introduced as an additional fundamental variable in spin-DFT. Here, we consider the reconstruction of the corresponding unrestricted Kohn–Sham (KS) potentials from accurate ab initio spin densities. In particular, we investigate whether it is possible to reconstruct the spin exchange–correlation potential, which determines the spin density in unrestricted KS-DFT, despite the numerical difficulties inherent to the optimization of potentials with finite orbital basis sets. We find that the recently developed scheme for unambiguously singling out an optimal optimized potential [Ch. R. Jacob, J. Chem. Phys. 135, 244102 (2011)10.1063/1.3670414] can provide such spin potentials accurately. This is demonstrated for two test cases, the lithium atom and the dioxygen molecule, and target (spin) densities from full configuration interaction and complete active space self-consistent field calculations, respectively.
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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.ej Spin-density functionals
31.15.xr Self-consistent-field methods

Polaron formation: Ehrenfest dynamics vs. exact results

Guangqi Li, Bijan Movaghar, Abraham Nitzan, and Mark A. Ratner

J. Chem. Phys. 138, 044112 (2013); http://dx.doi.org/10.1063/1.4776230 (7 pages) | Cited 1 time

Online Publication Date: 31 January 2013

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We use a one-dimensional tight binding model with an impurity site characterized by electron-vibration coupling, to describe electron transfer and localization at zero temperature, aiming to examine the process of polaron formation in this system. In particular we focus on comparing a semiclassical approach that describes nuclear motion in this many vibronic-states system on the Ehrenfest dynamics level to a numerically exact fully quantum calculation based on the Bonca-Trugman method [J. Bonča and S. A. Trugman, Phys. Rev. Lett. 75, 2566 (1995)]10.1103/PhysRevLett.75.2566. In both approaches, thermal relaxation in the nuclear subspace is implemented in equivalent approximate ways: In the Ehrenfest calculation the uncoupled (to the electronic subsystem) motion of the classical (harmonic) oscillator is simply damped as would be implied by coupling to a Markovian zero temperature bath. In the quantum calculation, thermal relaxation is implemented by augmenting the Liouville equation for the oscillator density matrix with kinetic terms that account for the same relaxation. In both cases we calculate the probability to trap the electron by forming a polaron and the probability that it escapes to infinity. Comparing these calculations, we find that while both result in similar long time yields for these processes, the Ehrenfest-dynamics based calculation fails to account for the correct time scale for the polaron formation. This failure results, as usual, from the fact that at the early stage of polaron formation the classical nuclear dynamics takes place on an unphysical average potential surface that reflects the distributed electronic population in the system, while the quantum calculation accounts fully for correlations between the electronic and vibrational subsystems.
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71.38.-k Polarons and electron-phonon interactions
63.20.kd Phonon-electron interactions
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Semilocal and hybrid meta-generalized gradient approximations based on the understanding of the kinetic-energy-density dependence

Jianwei Sun, Robin Haunschild, Bing Xiao, Ireneusz W. Bulik, Gustavo E. Scuseria, and John P. Perdew

J. Chem. Phys. 138, 044113 (2013); http://dx.doi.org/10.1063/1.4789414 (8 pages)

Online Publication Date: 31 January 2013

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We present a global hybrid meta-generalized gradient approximation (meta-GGA) with three empirical parameters, as well as its underlying semilocal meta-GGA and a meta-GGA with only one empirical parameter. All of them are based on the new meta-GGA resulting from the understanding of kinetic-energy-density dependence [J. Sun, B. Xiao, and A. Ruzsinszky, J. Chem. Phys. 137, 051101 (2012)]10.1063/1.4742312. The obtained functionals show robust performances on the considered molecular systems for the properties of heats of formation, barrier heights, and noncovalent interactions. The pair-wise additive dispersion corrections to the functionals are also presented.
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31.15.E- Density-functional theory
82.60.Cx Enthalpies of combustion, reaction, and formation

Theory of reversible associative-dissociative diffusion-influenced chemical reaction. II. Bulk reaction

Alexey A. Kipriyanov and Alexander B. Doktorov

J. Chem. Phys. 138, 044114 (2013); http://dx.doi.org/10.1063/1.4779476 (17 pages)

Online Publication Date: 31 January 2013

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A many-particle homogeneous reacting system of reactants, where bulk reversible reaction A + B ↔ C takes place, is considered in the framework of the kinetic theory approach. The various forms of kinetic equations in the thermodynamic limit are obtained, and important relations between kinetic coefficients characterizing the course of bulk and the corresponding geminate reactions are established. Based on the kinetic equations derived, different results available in the literature have been analyzed. Universal long-term kinetic laws of the reaction course are deduced.
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82.30.Nr Association, addition, insertion, cluster formation
82.20.Fd Collision theories; trajectory models
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
back to top Advanced Experimental Techniques

Ion-pairing in aqueous CaCl2 and RbBr solutions: Simultaneous structural refinement of XAFS and XRD data

Van-Thai Pham and John L. Fulton

J. Chem. Phys. 138, 044201 (2013); http://dx.doi.org/10.1063/1.4775588 (13 pages)

Online Publication Date: 22 January 2013

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We present a new methodology involving the simultaneous refinement of both x-ray absorption and x-ray diffraction spectra (x-ray absorption/diffraction structural refinement, XADSR) to study the hydration and ion pair structure of CaCl2 and RbBr salts in concentrated aqueous solutions. The XADSR method combines the x-ray absorption fine structure (XAFS) spectral analysis of both the cation and anion as a probe of their short-range structure with an x-ray diffraction (XRD) spectral analysis as a probe of the global structural. Together they deliver a comprehensive picture of the cation and anion hydration, the contact ion pair (CIP) structure, and the solvent-separated ion pair (SSIP) structure. XADSR analysis of 6.0 m aqueous CaCl2 reveals that there are ∼0.26 Ca2+-Cl− CIP's separated by about 2.71 Å, while there are 3.4 SSIP's separated by about 4.98 Å. In contrast XADSR analysis of 6 m aqueous RbBr yields about 0.7 pair CIP at a bond length of 3.51 Å. The present work demonstrates a new approach for a direct co-refinement of XRD and XAFS spectra in a simple and reliable fashion, opening new opportunities for analysis in various disordered and crystalline systems.
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78.70.Dm X-ray absorption spectra
82.30.-b Specific chemical reactions; reaction mechanisms
61.66.Fn Inorganic compounds

A velocity map imaging photoelectron spectrometer for the study of ultrafine aerosols with a table-top VUV laser and Na-doping for particle sizing applied to dimethyl ether condensation

Bruce L. Yoder, Adam H. C. West, Bernhard Schläppi, Egor Chasovskikh, and Ruth Signorell

J. Chem. Phys. 138, 044202 (2013); http://dx.doi.org/10.1063/1.4788620 (12 pages)

Online Publication Date: 30 January 2013

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We present a new experimental configuration for the study of size-dependent, angle-resolved photoelectron and photoion spectra of weakly bound ultrafine aerosol particles targeted at particle sizes below ∼20 nm. It combines single photon ionization by a tunable, table-top vacuum ultraviolet laser at energies up to 18 eV with velocity map imaging detection and independent size determination of the aerosol particles using the Na-doping method. As an example, the size-dependence of the valence photoelectron spectrum of dimethyl ether clusters and ultrafine aerosols is investigated. Up to a mean particle diameter of ∼3–4 nm, the first ionization energy (value at band maximum) decreases systematically (up to ∼1 eV) and the corresponding band broadens systematically (up to a factor of ∼3) with increasing aggregate size. Plateau values for band positions and bandwidths are reached beyond a diameter of ∼3–4 nm. Experimental evidence for the dominance of the fast intermolecular proton transfer over monomer fragmentation reactions upon ionization is presented via photoion imaging.
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33.60.+q Photoelectron spectra
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.80.Eh Autoionization, photoionization, and photodetachment
34.20.Gj Intermolecular and atom-molecule potentials and forces
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.70.Rr Aerosols and foams
back to top Atoms, Molecules, and Clusters

Solvation at nanoscale: Alkali-halides in water clusters

Leena Partanen, Mikko-Heikki Mikkelä, Marko Huttula, Maxim Tchaplyguine, Chaofan Zhang, Tomas Andersson, and Olle Björneholm

J. Chem. Phys. 138, 044301 (2013); http://dx.doi.org/10.1063/1.4775586 (7 pages)

Online Publication Date: 22 January 2013

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The solvation of alkali-halides in water clusters at nanoscale is studied by photoelectron spectroscopy using synchrotron radiation. The Na 2p, K 3p, Cl 2p, Br 3d, and I 4d core level binding energies have been measured for salt-containing water clusters. The results have been compared to those of alkali halide clusters and the dilute aqueous salt solutions. It is found that the alkali halides dissolve in small water clusters as ions.
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36.40.Jn Reactivity of clusters
36.40.Mr Spectroscopy and geometrical structure of clusters
82.30.Nr Association, addition, insertion, cluster formation
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
33.60.+q Photoelectron spectra
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

Theoretical studies of the CO2–N2O van der Waals complex: Ab initio potential energy surface, intermolecular vibrations, and rotational transition frequencies

Limin Zheng, Soo-Ying Lee, Yunpeng Lu, and Minghui Yang

J. Chem. Phys. 138, 044302 (2013); http://dx.doi.org/10.1063/1.4776183 (9 pages)

Online Publication Date: 23 January 2013

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Theoretical studies of the potential energy surface and bound states were performed for the CO2–N2O van der Waals complex. A four-dimensional intermolecular potential energy surface (PES) was constructed from 11 466 ab initio data points which were calculated at the coupled-cluster single double (triple) level with aug-cc-pVTZ basis set supplemented with bond functions. Three co-planar local minima were found on this surface. They correspond to two equivalent isomers with a slipped parallel structure in which the O atom in N2O is near the C atom in CO2 and a T-shaped isomer in which the terminal N atom in N2O is closest to the C atom in CO2. The two slipped parallel isomers are energetically more stable than the T-shaped isomer by 178 cm−1. Four fundamental vibrational excited states for the slipped parallel isomers and two fundamental vibrational excited states (torsion and disrotation) for the T-shaped isomer were assigned via bound states calculations based on this PES. The theoretical vibrational frequencies are in good agreement with the available experimental values for the slipped parallel isomers. Rotational excitations (J = 0–6) for the ground vibrational state of the slipped parallel structure were calculated and the accuracy of the PES in the vicinity of minima is validated by the good agreement between the theoretical and experimental transition frequencies and spectroscopic parameters.
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31.15.A- Ab initio calculations
31.15.bw Coupled-cluster theory
31.50.Bc Potential energy surfaces for ground electronic states
31.50.Df Potential energy surfaces for excited electronic states
33.20.Tp Vibrational analysis
34.50.Ez Rotational and vibrational energy transfer

Multiscale approach combining nonadiabatic dynamics with long-time radiative and non-radiative decay: Dissociative ionization of heavy rare-gas tetramers revisited

Ivan Janeček, Tomáš Janča, Pavel Naar, René Kalus, and Florent Xavier Gadea

J. Chem. Phys. 138, 044303 (2013); http://dx.doi.org/10.1063/1.4775804 (12 pages)

Online Publication Date: 23 January 2013

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A multiscale approach is proposed to address short-time nonadiabatic dynamics and long-time decay. We show the role of both radiative and non-radiative processes in cluster decay mechanisms on examples of rare-gas cluster fragmentation after electron impact ionization. Nonadiabatic molecular dynamics is used as an efficient tool for theoretical study on femto- and picosecond scales and a multiscale approach based on kinetic rates of radiative as well as non-radiative transitions, both considered as parallel reaction channels, is used for the analysis of the long-time system relaxation spanning times over microseconds to infinity. While the radiative processes are typically slow, the system relaxation through non-radiative electronic transitions connected with electron-nuclear interchange of energy may, on the other hand, significantly vary in kinetic rates according to kinetic couplings between relevant adiabatic states. While the predictions of picosecond molecular dynamics themselves fail, the results of the multiscale model for the electron-impact post-ionization fragmentation of krypton and xenon tetramers are in agreement with experiment, namely, in leading to the conclusion that charged monomers prevail. More specifically, on microsecond and longer scales, mainly slow radiative processes are substantial for krypton cluster decay, while for xenon the radiative and slow non-radiative processes compete. In general, the role of slow decay processes through non-radiative transitions is comparable with the role of radiative decay mechanism. The novel multiscale model substantially improves theoretical predictions for the xenon tetramer decay and also further improves the good agreement between theory and experiment we reached previously for krypton.
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36.40.Wa Charged clusters
31.70.Hq Time-dependent phenomena: excitation and relaxation processes, and reaction rates
34.50.Gb Electronic excitation and ionization of molecules
36.40.Mr Spectroscopy and geometrical structure of clusters

Exploring electric field induced structural evolution of water clusters, (H2O)n [n = 9–20]: Density functional approach

Dhurba Rai, Anant D. Kulkarni, Shridhar P. Gejji, Libero J. Bartolotti, and Rajeev K. Pathak

J. Chem. Phys. 138, 044304 (2013); http://dx.doi.org/10.1063/1.4776214 (9 pages)

Online Publication Date: 24 January 2013

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Response of neutral water clusters (H2O)n, n = 9–20, to external uniform dipolar static electric fields is studied for some lowest-energy conformers for each “n” within an energy band of about 9 kcal mol−1 of their field-free counterparts. We perform density functional theory computations with B3LYP/6-311++G(2d,2p) model chemistry. Increasing the electric field destabilizes and distorts a cluster by elongating, hence weakening its hydrogen bonds, culminating into a catastrophic structural breakdown beyond a specific threshold field-strength. The electric field induced conformational transitions to extended structures stretched along the field direction to lower-energy configurations that appear as local minima on their potential energy surface are presented. It is observed that a typical structural transition of this type is always accompanied by an abrupt increase in the electric dipole moment of the cluster over and above its smooth increment with increasing applied field; the increase being phenomenal during breakdown. Interestingly, the HOMO-LUMO energy gap for a given conformer is found to diminish with increasing field strength, abruptly approaching zero at structural breakdown. In essence, the structural evolution traced through hydrogen-bond networks of the clusters reveals multiple enhancements in size by “opening up” of three-dimensional morphologies to form net-like structures with less number of hydrogen bonds. These clusters exhibit greater structural complexity than that encountered in the relatively small clusters reported previously.
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36.40.Mr Spectroscopy and geometrical structure of clusters
31.15.E- Density-functional theory
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Fm Bond strengths, dissociation energies
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
36.40.Ei Phase transitions in clusters

Absolute cross sections for dissociative electron attachment and dissociative ionization of cobalt tricarbonyl nitrosyl in the energy range from 0 eV to 140 eV

Sarah Engmann, Michal Stano, Peter Papp, Michael J. Brunger, Štefan Matejčík, and Oddur Ingólfsson

J. Chem. Phys. 138, 044305 (2013); http://dx.doi.org/10.1063/1.4776756 (7 pages)

Online Publication Date: 24 January 2013

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We report absolute dissociative electron attachment (DEA) and dissociative ionization (DI) cross sections for electron scattering from the focused electron beam induced deposition (FEBID) precursor Co(CO)3NO in the incident electron energy range from 0 to 140 eV. We find that DEA leads mainly to single carbonyl loss with a maximum cross section of 4.1 × 10−16 cm2, while fragmentation through DI results mainly in the formation of the bare metal cation Co+ with a maximum cross section close to 4.6 × 10−16 cm2 at 70 eV. Though DEA proceeds in a narrow incident electron energy range, this energy range is found to overlap significantly with the expected energy distribution of secondary electrons (SEs) produced in FEBID. The DI process, on the other hand, is operative over a much wider energy range, but the overlap with the expected SE energy distribution, though significant, is found to be mainly in the threshold region of the individual DI processes.
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34.80.Ht Dissociation and dissociative attachment
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
34.50.Gb Electronic excitation and ionization of molecules

Coherent control of radiationless transitions: Simultaneous excitation and decay of overlapping resonances

Timur Grinev, Moshe Shapiro, and Paul Brumer

J. Chem. Phys. 138, 044306 (2013); http://dx.doi.org/10.1063/1.4775808 (12 pages) | Cited 2 times

Online Publication Date: 24 January 2013

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We develop a simple analytical theory for the study of coherent control of radiationless transitions, and in particular, internal conversion leading to dissociation, in molecules possessing overlapping resonances. The method is applied to a model diatomic system. In contrast to previous studies, we consider here the control of a molecule that is allowed to decay during and after the preparation process. We use this theory to derive the shape of the laser pulse that creates the specific excited wave packet that best enhances or suppresses the radiationless transitions process. The results show the importance of resonance overlap in the molecule in order to achieve efficient coherent control over radiationless transitions via laser excitation. Specifically, resonance overlap is proven to be crucial in order to alter interference contributions to the controlled observable, and hence to achieve efficient coherent control by varying the phase of the laser field.
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33.50.Hv Radiationless transitions, quenching
33.80.Gj Diffuse spectra; predissociation, photodissociation

Elastic electron scattering from water vapor and ice at high momentum transfer

M. Vos, E. Weigold, and R. Moreh

J. Chem. Phys. 138, 044307 (2013); http://dx.doi.org/10.1063/1.4775810 (11 pages) | Cited 2 times

Online Publication Date: 24 January 2013

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We compare the area, peak separation, and width of the H and O elastic peak for light and heavy water, as observed in spectra of keV electrons scattered over large angles. Peak separation is well reproduced by the theory, but the O:H area ratio is somewhat larger than expected and is equal to the O:D area ratio. Thus no anomalous scattering from H was observed. Only minor differences are observed for scattering from a gaseous or a solid target. The extracted mean kinetic energy of H and D agreed within 5% with the calculated ones for ice. For the more difficult vapor measurements agreement was on a 12% level. A preliminary attempt to extract the O kinetic energy in ice agreed within 10% with the calculated values.
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34.80.Bm Elastic scattering
68.49.Jk Electron scattering from surfaces

Photofragmentations, state interactions, and energetics of Rydberg and ion-pair states: Resonance enhanced multiphoton ionization via E and V (B) states of HCl and HBr

Jingming Long, Huasheng Wang, and Ágúst Kvaran

J. Chem. Phys. 138, 044308 (2013); http://dx.doi.org/10.1063/1.4776260 (9 pages)

Online Publication Date: 25 January 2013

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(2 + n) resonance enhanced multiphoton ionization mass spectra for resonance excitations to diabatic E1Σ+ (v′) Rydberg and V 1Σ+ (v′) ion-pair states (adiabatic B1Σ+(v′) states) of HiCl (i = 35,37) and HiBr (i = 79,81) were recorded as a function of excitation wavenumber (two-dimensional REMPI). Simulation analyses of ion signal intensities, deperturbation analysis of line shifts and interpretations of line-widths are used to derive qualitative and quantitative information concerning the energetics of the states, off-resonance interactions between the E states and V states, closest in energy as well as on predissociation channels. Spectroscopic parameters for the E1Σ+ (v′)(v′ = 1) for H35Cl and v′ = 0 for H79Br states, interaction strengths for E − V state interactions and parameters relevant to dissociation of the E states are derived. An overall interaction and dynamical scheme, to describe the observations for HBr, is proposed.
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33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.15.Ta Mass spectra
33.70.Jg Line and band widths, shapes, and shifts
33.80.Gj Diffuse spectra; predissociation, photodissociation
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