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14 Feb 2012

Volume 136, Issue 6, Articles (06xxxx)

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J. Chem. Phys. 136, 064501 (2012); http://dx.doi.org/10.1063/1.3676408 (17 pages)

Florian Göltl and Jürgen Hafner
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Communication: Angle-resolved thermal dissociative sticking of CH4 on Pt(111): Further indication that rotation is a spectator to the gas-surface reaction dynamics

J. K. Navin, S. B. Donald, D. G. Tinney, G. W. Cushing, and I. Harrison

J. Chem. Phys. 136, 061101 (2012); http://dx.doi.org/10.1063/1.3685833 (4 pages)

Online Publication Date: 9 February 2012

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Effusive molecular beam measurements of angle-resolved thermal dissociative sticking coefficients for CH4 impinging on a Pt(111) surface, at a temperature of 700 K, are reported and compared to theoretical predictions. The reactivity falls off steeply as the molecular angle of incidence increases away from the surface normal. Successful modeling of the thermal dissociative sticking behavior, consistent with existent CH4 supersonic molecular beam experiments involving rotationally cold molecules, required that rotation be treated as a spectator degree of freedom.
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68.43.Mn Adsorption kinetics
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
37.20.+j Atomic and molecular beam sources and techniques
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Communication: Thermodynamics of condensed matter with strong pressure-energy correlations

Trond S. Ingebrigtsen, Lasse Bøhling, Thomas B. Schrøder, and Jeppe C. Dyre

J. Chem. Phys. 136, 061102 (2012); http://dx.doi.org/10.1063/1.3685804 (4 pages)

Online Publication Date: 14 February 2012

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We show that for any liquid or solid with strong correlation between its NVT virial and potential-energy equilibrium fluctuations, the temperature is a product of a function of excess entropy per particle and a function of density, T = f(s)h(ρ). This implies that (1) the system's isomorphs (curves in the phase diagram of invariant structure and dynamics) are described by h(ρ)/T = Const., (2) the density-scaling exponent is a function of density only, and (3) a Grüneisen-type equation of state applies for the configurational degrees of freedom. For strongly correlating atomic systems one has h(ρ) = ∑nCnρn/3 in which the only non-zero terms are those appearing in the pair potential expanded as v(r) = ∑nvnr−n. Molecular dynamics simulations of Lennard-Jones type systems confirm the theory.
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65.20.Jk Studies of thermodynamic properties of specific liquids
64.30.-t Equations of state of specific substances
81.30.Dz Phase diagrams of other materials
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Accurate thermochemistry from a parameterized coupled-cluster singles and doubles model and a local pair natural orbital based implementation for applications to larger systems

Lee M. J. Huntington, Andreas Hansen, Frank Neese, and Marcel Nooijen

J. Chem. Phys. 136, 064101 (2012); http://dx.doi.org/10.1063/1.3682325 (17 pages)

Online Publication Date: 8 February 2012

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We have recently introduced a parameterized coupled-cluster singles and doubles model (pCCSD(α, β)) that consists of a bivariate parameterization of the CCSD equations and is inspired by the coupled electron pair approximations. In our previous work, it was demonstrated that the pCCSD(−1, 1) method is an improvement over CCSD for the calculation of geometries, harmonic frequencies, and potential energy surfaces for single bond-breaking. In this paper, we find suitable pCCSD parameters for applications in reaction thermochemistry and thermochemical kinetics. The motivation is to develop an accurate and economical methodology that, when coupled with a robust local correlation framework based on localized pair natural orbitals, is suitable for large-scale thermochemical applications for sizeable molecular systems. It is demonstrated that the original pCCSD(−1, 1) method and several other pCCSD methods are a significant improvement upon the standard CCSD approach and that these methods often approach the accuracy of CCSD(T) for the calculation of reaction energies and barrier heights. We also show that a local version of the pCCSD methodology, implemented within the local pair natural orbital (LPNO) based CCSD code in ORCA, is sufficiently accurate for wide-scale chemical applications. The LPNO based methodology allows us for routine applications to intermediate sized (20–100 atoms) molecular systems and is a significantly more accurate alternative to MP2 and density functional theory for the prediction of reaction energies and barrier heights.
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31.15.bw Coupled-cluster theory
31.50.-x Potential energy surfaces
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Fm Bond strengths, dissociation energies
82.20.Kh Potential energy surfaces for chemical reactions
82.60.-s Chemical thermodynamics

Revised self-consistent continuum solvation in electronic-structure calculations

Oliviero Andreussi, Ismaila Dabo, and Nicola Marzari

J. Chem. Phys. 136, 064102 (2012); http://dx.doi.org/10.1063/1.3676407 (20 pages)

Online Publication Date: 8 February 2012

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The solvation model proposed by Fattebert and Gygi [J. Comput. Chem. 23, 662 (2002)10.1002/jcc.10069] and Scherlis et al. [J. Chem. Phys. 124, 074103 (2006)10.1063/1.2168456] is reformulated, overcoming some of the numerical limitations encountered and extending its range of applicability. We first recast the problem in terms of induced polarization charges that act as a direct mapping of the self-consistent continuum dielectric; this allows to define a functional form for the dielectric that is well behaved both in the high-density region of the nuclear charges and in the low-density region where the electronic wavefunctions decay into the solvent. Second, we outline an iterative procedure to solve the Poisson equation for the quantum fragment embedded in the solvent that does not require multigrid algorithms, is trivially parallel, and can be applied to any Bravais crystallographic system. Last, we capture some of the non-electrostatic or cavitation terms via a combined use of the quantum volume and quantum surface [M. Cococcioni, F. Mauri, G. Ceder, and N. Marzari, Phys. Rev. Lett. 94, 145501 (2005)10.1103/PhysRevLett.94.145501] of the solute. The resulting self-consistent continuum solvation model provides a very effective and compact fit of computational and experimental data, whereby the static dielectric constant of the solvent and one parameter allow to fit the electrostatic energy provided by the polarizable continuum model with a mean absolute error of 0.3 kcal/mol on a set of 240 neutral solutes. Two parameters allow to fit experimental solvation energies on the same set with a mean absolute error of 1.3 kcal/mol. A detailed analysis of these results, broken down along different classes of chemical compounds, shows that several classes of organic compounds display very high accuracy, with solvation energies in error of 0.3-0.4 kcal/mol, whereby larger discrepancies are mostly limited to self-dissociating species and strong hydrogen-bond-forming compounds.
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31.15.xv Molecular dynamics and other numerical methods
31.70.Dk Environmental and solvent effects
33.15.Fm Bond strengths, dissociation energies

A neural network potential-energy surface for the water dimer based on environment-dependent atomic energies and charges

Tobias Morawietz, Vikas Sharma, and Jörg Behler

J. Chem. Phys. 136, 064103 (2012); http://dx.doi.org/10.1063/1.3682557 (11 pages) | Cited 1 time

Online Publication Date: 9 February 2012

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Understanding the unique properties of water still represents a significant challenge for theory and experiment. Computer simulations by molecular dynamics require a reliable description of the atomic interactions, and in recent decades countless water potentials have been reported in the literature. Still, most of these potentials contain significant approximations, for instance a frozen internal structure of the individual water monomers. Artificial neural networks (NNs) offer a promising way for the construction of very accurate potential-energy surfaces taking all degrees of freedom explicitly into account. These potentials are based on electronic structure calculations for representative configurations, which are then interpolated to a continuous energy surface that can be evaluated many orders of magnitude faster. We present a full-dimensional NN potential for the water dimer as a first step towards the construction of a NN potential for liquid water. This many-body potential is based on environment-dependent atomic energy contributions, and long-range electrostatic interactions are incorporated employing environment-dependent atomic charges. We show that the potential and derived properties like vibrational frequencies are in excellent agreement with the underlying reference density-functional theory calculations.
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31.50.-x Potential energy surfaces
33.20.Tp Vibrational analysis
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
31.15.E- Density-functional theory
31.15.xv Molecular dynamics and other numerical methods

Coherent control and time-dependent density functional theory: Towards creation of wave packets by ultrashort laser pulses

Shampa Raghunathan and Mathias Nest

J. Chem. Phys. 136, 064104 (2012); http://dx.doi.org/10.1063/1.3682980 (6 pages)

Online Publication Date: 10 February 2012

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Explicitly time-dependent density functional theory (TDDFT) is a formally exact theory, which can treat very large systems. However, in practice it is used almost exclusively in the adiabatic approximation and with standard ground state functionals. Therefore, if combined with coherent control theory, it is not clear which control tasks can be achieved reliably, and how this depends on the functionals. In this paper, we continue earlier work in order to establish rules that answer these questions. Specifically, we look at the creation of wave packets by ultrashort laser pulses that contain several excited states. We find that (i) adiabatic TDDFT only works if the system is not driven too far from the ground state, (ii) the permanent dipole moments involved should not differ too much, and (iii) these results are independent of the functional used. Additionally, we find an artifact that produces fluence-dependent excitation energies.
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31.15.E- Density-functional theory
37.10.-x Atom, molecule, and ion cooling methods
32.80.Rm Multiphoton ionization and excitation to highly excited states

Transient-time correlation function applied to mixed shear and elongational flows

Remco Hartkamp, Stefano Bernardi, and B. D. Todd

J. Chem. Phys. 136, 064105 (2012); http://dx.doi.org/10.1063/1.3684753 (7 pages)

Online Publication Date: 10 February 2012

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The transient-time correlation function (TTCF) method is used to calculate the nonlinear response of a homogeneous atomic fluid close to equilibrium. The TTCF response of the pressure tensor subjected to a time-independent planar mixed flow of shear and elongation is compared to directly averaged non-equilibrium molecular dynamics (NEMD) simulations. We discuss the consequence of noise in simulations with a small rate of deformation. The generalized viscosity for planar mixed flow is also calculated with TTCF. We find that for small rates of deformation, TTCF is far more efficient than direct averages of NEMD simulations. Therefore, TTCF can be applied to fluids with deformation rates which are much smaller than those commonly used in NEMD simulations. Ultimately, TTCF applied to molecular systems is amenable to direct comparison between NEMD simulations and experiments and so in principle can be used to study the rheology of polymer melts in industrial processes.
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47.11.Mn Molecular dynamics methods
66.20.Ej Studies of viscosity and rheological properties of specific liquids
62.10.+s Mechanical properties of liquids

Critical lines for an unequal size of molecules in a binary gas-liquid mixture around the van Laar point using the combination of the Tompa model and the van der Waals equation

Mustafa Gençaslan and Mustafa Keskin

J. Chem. Phys. 136, 064106 (2012); http://dx.doi.org/10.1063/1.3683443 (7 pages)

Online Publication Date: 10 February 2012

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We combine the modified Tompa model with the van der Waals equation to study critical lines for an unequal size of molecules in a binary gas-liquid mixture around the van Laar point. The van Laar point is coined by Meijer and it is the only point at which the mathematical double point curve is stable. It is the intersection of the tricritical point and the double critical end point. We calculate the critical lines as a function of x1 and x2, the density of type I molecules and the density of type II molecules for various values of the system parameters; hence the global phase diagrams are presented and discussed in the density-density plane. We also investigate the connectivity of critical lines at the van Laar point and its vicinity and discuss these connections according to the Scott and van Konynenburg classifications. It is also found that the critical lines and phase behavior are extremely sensitive to small modifications in the system parameters.
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64.75.Cd Phase equilibria of fluid mixtures, including gases, hydrates, etc.
64.60.Kw Multicritical points

Calculations of nonlinear response properties using the intermediate state representation and the algebraic-diagrammatic construction polarization propagator approach: Two-photon absorption spectra

S. Knippenberg, D. R. Rehn, M. Wormit, J. H. Starcke, I. L. Rusakova, A. B. Trofimov, and A. Dreuw

J. Chem. Phys. 136, 064107 (2012); http://dx.doi.org/10.1063/1.3682324 (15 pages)

Online Publication Date: 10 February 2012

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An earlier proposed approach to molecular response functions based on the intermediate state representation (ISR) of polarization propagator and algebraic-diagrammatic construction (ADC) approximations is for the first time employed for calculations of nonlinear response properties. The two-photon absorption (TPA) spectra are considered. The hierarchy of the first- and second-order ADC/ISR computational schemes, ADC(1), ADC(2), ADC(2)-x, and ADC(3/2), is tested in applications to H2O, HF, and C2H4 (ethylene). The calculated TPA spectra are compared with the results of coupled cluster (CC) models and time-dependent density-functional theory (TDDFT) calculations, using the results of the CC3 model as benchmarks. As a more realistic example, the TPA spectrum of C8H10 (octatetraene) is calculated using the ADC(2)-x and ADC(2) methods. The results are compared with the results of TDDFT method and earlier calculations, as well as to the available experimental data. A prominent feature of octatetraene and other polyene molecules is the existence of low-lying excited states with increased double excitation character. We demonstrate that the two-photon absorption involving such states can be adequately studied using the ADC(2)-x scheme, explicitly accounting for interaction of doubly excited configurations. Observed peaks in the experimental TPA spectrum of octatetraene are assigned based on our calculations.
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33.80.Wz Other multiphoton processes

Markov processes follow from the principle of maximum caliber

Hao Ge, Steve Pressé, Kingshuk Ghosh, and Ken A. Dill

J. Chem. Phys. 136, 064108 (2012); http://dx.doi.org/10.1063/1.3681941 (5 pages)

Online Publication Date: 13 February 2012

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Markov models are widely used to describe stochastic dynamics. Here, we show that Markov models follow directly from the dynamical principle of maximum caliber (Max Cal). Max Cal is a method of deriving dynamical models based on maximizing the path entropy subject to dynamical constraints. We give three different cases. First, we show that if constraints (or data) are given in the form of singlet statistics (average occupation probabilities), then maximizing the caliber predicts a time-independent process that is modeled by identical, independently distributed random variables. Second, we show that if constraints are given in the form of sequential pairwise statistics, then maximizing the caliber dictates that the kinetic process will be Markovian with a uniform initial distribution. Third, if the initial distribution is known and is not uniform we show that the only process that maximizes the path entropy is still the Markov process. We give an example of how Max Cal can be used to discriminate between different dynamical models given data.
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05.70.Ce Thermodynamic functions and equations of state
02.50.Ga Markov processes
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion

An excited state paired interacting orbital method

Isao Kawata and Hiroya Nitta

J. Chem. Phys. 136, 064109 (2012); http://dx.doi.org/10.1063/1.3684233 (9 pages)

Online Publication Date: 13 February 2012

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A new method for analyzing and visualizing the molecular excited states, named “excited state paired interacting orbital (EPIO),” is proposed. The method is based both on the paired interacting orbital (PIO) proposed by Fujimoto and Fukui [J. Chem. Phys. 60, 572 (1974)] and the natural transition orbital (NTO) by Martin [J. Chem. Phys. 118, 4775 (2003)10.1063/1.1558471]. Within the PIO method, orbital interactions between the two fragmented molecules are represented practically only by a few pairs of fragment orbitals. The NTO method is a means of finding a compact orbital representation for the electronic transitions in the excited states. With the method, electronic transitions are expressed by a few particle-hole orbital pairs and a clear picture on the electronic transitions is obtained. EPIO method is designed to have both properties of the preceding two methods: electronic transitions in composite molecular systems can be expressed with a few pairs of EPIOs which are constructed with fragmented molecular orbitals (MOs). Excited state characters, such as charge transfer and local excitations, are analyzed by using EPIOs with their generation probabilities. Thus, the present method gives us clear information on the composition of MOs which play an important role in the molecular excitation processes, e.g., optical processes.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics
34.70.+e Charge transfer

Vibronic coupling simulations for linear and nonlinear optical processes: Simulation results

Daniel W. Silverstein and Lasse Jensen

J. Chem. Phys. 136, 064110 (2012); http://dx.doi.org/10.1063/1.3684235 (14 pages)

Online Publication Date: 13 February 2012

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A vibronic coupling model based on time-dependent wavepacket approach is applied to simulate linear optical processes, such as one-photon absorbance and resonance Raman scattering, and nonlinear optical processes, such as two-photon absorbance and resonance hyper-Raman scattering, on a series of small molecules. Simulations employing both the long-range corrected approach in density functional theory and coupled cluster are compared and also examined based on available experimental data. Although many of the small molecules are prone to anharmonicity in their potential energy surfaces, the harmonic approach performs adequately. A detailed discussion of the non-Condon effects is illustrated by the molecules presented in this work. Linear and nonlinear Raman scattering simulations allow for the quantification of interference between the Franck-Condon and Herzberg-Teller terms for different molecules.
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33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
31.15.E- Density-functional theory
31.50.Df Potential energy surfaces for excited electronic states
33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
31.15.bw Coupled-cluster theory

Vibronic coupling simulations for linear and nonlinear optical processes: Theory

Daniel W. Silverstein and Lasse Jensen

J. Chem. Phys. 136, 064111 (2012); http://dx.doi.org/10.1063/1.3684236 (13 pages) | Cited 1 time

Online Publication Date: 13 February 2012

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A comprehensive vibronic coupling model based on the time-dependent wavepacket approach is derived to simulate linear optical processes, such as one-photon absorbance and resonance Raman scattering, and nonlinear optical processes, such as two-photon absorbance and resonance hyper-Raman scattering. This approach is particularly well suited for combination with first-principles calculations. Expressions for the Franck-Condon terms, and non-Condon effects via the Herzberg-Teller coupling approach in the independent-mode displaced harmonic oscillator model are presented. The significance of each contribution to the different spectral types is discussed briefly.
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33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
32.80.Rm Multiphoton ionization and excitation to highly excited states
31.15.ag Excitation energies and lifetimes; oscillator strengths
33.20.Fb Raman and Rayleigh spectra (including optical scattering)

Density functional theory guided Monte Carlo simulations: Application to melting of Na13

Satya Bulusu and René Fournier

J. Chem. Phys. 136, 064112 (2012); http://dx.doi.org/10.1063/1.3684628 (7 pages)

Online Publication Date: 13 February 2012

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We present a density functional theory (DFT) based Monte Carlo simulation method in which a simple energy function gets fitted on-the-fly to DFT energies and gradients. The fitness of the energy function gets tested periodically using the classical importance function technique [R. Iftimie, D. Salahub, D. Wei, and J. Schofield, J. Chem. Phys. 113, 4852 (2000)]. The function is updated to fit the DFT energies and gradients of the most recent structures visited whenever it fails to achieve a preset accuracy. In this way, we effectively break down the problem of fitting the entire potential energy surface (PES) into many easier problems, which are to fit small local regions of the PES. We used the scaled Morse potential empirical function to guide a DFT Monte Carlo simulation of Na13 at various temperatures. The use of empirical function guide produced a computational speed-up of about 7 in our test system without affecting the quality of the results.
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64.70.dj Melting of specific substances
82.20.Kh Potential energy surfaces for chemical reactions

First-order phase transitions in repulsive rigid k-mers on two-dimensional lattices

P. M. Pasinetti, F. Romá, and A. J. Ramirez-Pastor

J. Chem. Phys. 136, 064113 (2012); http://dx.doi.org/10.1063/1.3678312 (8 pages) | Cited 1 time

Online Publication Date: 13 February 2012

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In a previous paper [F. Romá, A. J. Ramirez-Pastor, and J. L. Riccardo, Phys. Rev. B 72, 035444 (2005)], the critical behavior of repulsive rigid rods of length k (k-mers) on a square lattice at half coverage has been studied by using Monte Carlo (MC) simulations. The obtained results indicated that (1) the phase transition occurring in the system is a second-order phase transition for all adsorbate sizes k; and (2) the universality class of the transition changes from 2D Ising-type for monomers (k = 1) to an unknown universality class for k ≥ 2. In the present work, we revisit our previous results together with further numerical evidences, resulting from new extensive MC simulations based on an efficient exchange algorithm and using high-performance computational capabilities. In contrast to our previous conclusions (1) and (2), the new numerical calculations clearly support the occurrence of a first-order phase transition for k ≥ 2. In addition, a similar scenario was found for k-mers adsorbed on the triangular lattice at coverage k/(2k+1).
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64.60.De Statistical mechanics of model systems (Ising model, Potts model, field-theory models, Monte Carlo techniques, etc.)
64.60.F- Equilibrium properties near critical points, critical exponents
68.43.De Statistical mechanics of adsorbates

Survival of interacting Brownian particles in crowded one-dimensional environment

Artem Ryabov and Petr Chvosta

J. Chem. Phys. 136, 064114 (2012); http://dx.doi.org/10.1063/1.3684954 (11 pages)

Online Publication Date: 14 February 2012

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We investigate a diffusive motion of a system of interacting Brownian particles in quasi-one-dimensional micropores. In particular, we consider a semi-infinite 1D geometry with a partially absorbing boundary and the hard-core inter-particle interaction. Due to the absorbing boundary the number of particles in the pore gradually decreases. We present the exact analytical solution of the problem. Our procedure merely requires the knowledge of the corresponding single-particle problem. First, we calculate the simultaneous probability density of having still a definite number (N − k) of surviving particles at definite coordinates. Focusing on an arbitrary tagged particle, we derive the exact probability density of its coordinate. Second, we present a complete probabilistic description of the emerging escape process. The survival probabilities for the individual particles are calculated, the first and the second moments of the exit times are discussed. Generally speaking, although the original inter-particle interaction possesses a point-like character, it induces entropic repulsive forces which, e.g., push the leftmost (rightmost) particle towards (opposite) the absorbing boundary thereby accelerating (decelerating) its escape. More importantly, as compared to the reference problem for the non-interacting particles, the interaction changes the dynamical exponents which characterize the long-time asymptotic dynamics. Interesting new insights emerge after we interpret our model in terms of (a) diffusion of a single particle in a N-dimensional space, and (b) order statistics defined on a system of N-independent, identically distributed random variables.
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66.10.cd Thermal diffusion and diffusive energy transport
05.60.-k Transport processes
05.40.Jc Brownian motion
02.40.-k Geometry, differential geometry, and topology
02.50.Cw Probability theory
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion

Far-from-equilibrium processes without net thermal exchange via energy sorting

Jose M. G. Vilar and J. Miguel Rubi

J. Chem. Phys. 136, 064115 (2012); http://dx.doi.org/10.1063/1.3683441 (5 pages)

Online Publication Date: 14 February 2012

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Many important processes at the microscale require far-from-equilibrium conditions to occur, as in the functioning of mesoscopic bioreactors, nanoscopic rotors, and nanoscale mass conveyors. Achieving such conditions, however, is typically based on energy inputs that strongly affect the thermal properties of the environment and the controllability of the system itself. Here, we present a general class of far-from-equilibrium processes that suppress the net thermal exchange with the environment by maintaining the Maxwell-Boltzmann velocity distribution intact. This new phenomenon, referred to as ghost equilibrium, results from the statistical cancellation of superheated and subcooled nonequilibrated degrees of freedom that are autonomously generated through a microscale energy sorting process. We provide general conditions to observe this phenomenon and study its implications for manipulating energy at the microscale. The results are applied explicitly to two mechanistically different cases, an ensemble of rotational dipoles and a gas of trapped particles, which encompass a great variety of common situations involving both rotational and translational degrees of freedom.
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05.70.Ln Nonequilibrium and irreversible thermodynamics
05.20.-y Classical statistical mechanics

A generalized gradient approximation for exchange derived from the model potential of van Leeuwen and Baerends

Alex P. Gaiduk and Viktor N. Staroverov

J. Chem. Phys. 136, 064116 (2012); http://dx.doi.org/10.1063/1.3684261 (8 pages) | Cited 1 time

Online Publication Date: 14 February 2012

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The common way to obtain energies from Kohn-Sham exchange potentials is by using the Levy-Perdew virial relation. For potentials that are not functional derivatives (i.e., nearly all model exchange potentials in existence), this approach leads to energy expressions that lack translational and rotational invariance. We propose a method for constructing potential-based energy functionals that are free from these artifacts. It relies on the same line-integration technique that gives rise to the Levy-Perdew relation, but uses density scaling instead of coordinate scaling. The method is applicable to any exchange or correlation potential that depends on the density explicitly, and correctly recovers the parent energy functional from a functional derivative. To illustrate our approach we develop a properly invariant generalized gradient approximation for exchange starting from the model potential of van Leeuwen and Baerends.
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31.15.eg Exchange-correlation functionals (in current density functional theory)
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
33.20.Sn Rotational analysis

State-to-state reaction probabilities within the quantum transition state framework

Ralph Welsch, Fermín Huarte-Larrañaga, and Uwe Manthe

J. Chem. Phys. 136, 064117 (2012); http://dx.doi.org/10.1063/1.3684631 (11 pages)

Online Publication Date: 14 February 2012

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Rigorous quantum dynamics calculations of reaction rates and initial state-selected reaction probabilities of polyatomic reactions can be efficiently performed within the quantum transition state concept employing flux correlation functions and wave packet propagation utilizing the multi-configurational time-dependent Hartree approach. Here, analytical formulas and a numerical scheme extending this approach to the calculation of state-to-state reaction probabilities are presented. The formulas derived facilitate the use of three different dividing surfaces: two dividing surfaces located in the product and reactant asymptotic region facilitate full state resolution while a third dividing surface placed in the transition state region can be used to define an additional flux operator. The eigenstates of the corresponding thermal flux operator then correspond to vibrational states of the activated complex. Transforming these states to reactant and product coordinates and propagating them into the respective asymptotic region, the full scattering matrix can be obtained. To illustrate the new approach, test calculations study the D + H2(ν, j) → HD(ν′, j′) + H reaction for J = 0.
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82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.20.Db Transition state theory and statistical theories of rate constants
82.20.Ej Quantum theory of reaction cross section
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.20.Rp State to state energy transfer
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
back to top Advanced Experimental Techniques

Electromagnetically induced transparency spectroscopy

Asaf Eilam, Evgeny A. Shapiro, and Moshe Shapiro

J. Chem. Phys. 136, 064201 (2012); http://dx.doi.org/10.1063/1.3683159 (6 pages)

Online Publication Date: 14 February 2012

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We propose a method based on the electromagnetically induced transparency (EIT) phenomenon for the detection of molecules which exist as a small minority in the presence of a majority of absorbers. The EIT effect we employ effectively eliminates the absorption of the majority species in the spectral region where it overlaps with the absorption of the minority species. The method can also be used to enhance local-modes transitions which overlap spectrally with a background of other local-modes transitions of the same molecule. The general theory is applied to the case of sparse and congested background spectra within the same molecule and to the recording of the spectra of isotopomers (of chlorine and methanol) that are in minority relative to other isotopomers which constitute the majority of molecules present.
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31.30.Gs Hyperfine interactions and isotope effects
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Gas-phase structures of neutral silicon clusters

Marko Haertelt, Jonathan T. Lyon, Pieterjan Claes, Jorg de Haeck, Peter Lievens, and André Fielicke

J. Chem. Phys. 136, 064301 (2012); http://dx.doi.org/10.1063/1.3682323 (6 pages) | Cited 1 time

Online Publication Date: 9 February 2012

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Vibrational spectra of neutral silicon clusters Sin, in the size range of n = 6–10 and for n = 15, have been measured in the gas phase by two fundamentally different IR spectroscopic methods. Silicon clusters composed of 8, 9, and 15 atoms have been studied by IR multiple photon dissociation spectroscopy of a cluster-xenon complex, while clusters containing 6, 7, 9, and 10 atoms have been studied by a tunable IR-UV two-color ionization scheme. Comparison of both methods is possible for the Si9 cluster. By using density functional theory, an identification of the experimentally observed neutral cluster structures is possible, and the effect of charge on the structure of neutrals and cations, which have been previously studied via IR multiple photon dissociation, can be investigated. Whereas the structures of small clusters are based on bipyramidal motifs, a trigonal prism as central unit is found in larger clusters. Bond weakening due to the loss of an electron leads to a major structural change between neutral and cationic Si8.
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36.40.Mr Spectroscopy and geometrical structure of clusters
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Ea Infrared spectra
33.20.Lg Ultraviolet spectra
33.80.Gj Diffuse spectra; predissociation, photodissociation

Absorption by DNA single strands of adenine isolated in vacuo: The role of multiple chromophores

Lisbeth Munksgaard Nielsen, Sara Øvad Pedersen, Maj-Britt Suhr Kirketerp, and Steen Brøndsted Nielsen

J. Chem. Phys. 136, 064302 (2012); http://dx.doi.org/10.1063/1.3679444 (5 pages)

Online Publication Date: 10 February 2012

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The degree of electronic coupling between DNA bases is a topic being up for much debate. Here we report on the intrinsic electronic properties of isolated DNA strands in vacuo free of solvent, which is a good starting point for high-level excited states calculations. Action spectra of DNA single strands of adenine reveal sign of exciton coupling between stacked bases from blueshifted absorption bands (∼3 nm) relative to that of the dAMP mononucleotide (one adenine base). The bands are blueshifted by about 10 nm compared to those of solvated strands, which is a shift similar to that for the adenine molecule and the dAMP mononucleotide. Desolvation has little effect on the bandwidth, which implies that inhomogenous broadening of the absorption bands in aqueous solution is of minor importance compared to, e.g., conformational disorder. Finally, at high photon energies, internal conversion competes with electron detachment since dissociation of the bare photoexcited ions on the microsecond time scale is measured.
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87.15.Pc Electronic and electrical properties
36.20.Kd Electronic structure and spectra
87.14.gk DNA
87.15.M- Spectra of biomolecules

New determination of the adiabatic ionization potential of the BaOH radical from laser photoionization-molecular beam experiments and ab initio calculations

Maximiliano Rossa, Iván Cabanillas-Vidosa, Gustavo A. Pino, and Juan C. Ferrero

J. Chem. Phys. 136, 064303 (2012); http://dx.doi.org/10.1063/1.3682283 (8 pages)

Online Publication Date: 10 February 2012

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The adiabatic ionization potential of the BaOH radical, as generated in a laser vaporization-supersonic expansion source has been determined by laser photoionization experiments to be (4.55 ± 0.03) eV. This value supports the three lowest out of seven previous experimental estimates, the former ranging from 4.35 to 4.62 eV. The present result is compared to ab initio calculations, as performed using both quantum chemistry at different levels of theory and density functional theory, and trying several effective core potentials and their accompanying basis sets for Ba. The most satisfactory agreement is obtained for either the adiabatic or vertical ionization potentials that derive from post-Hartree-Fock [MP2 and CCSD(T)] treatments of electron correlation, along with consideration of relativistic effects and extensive basis sets for Ba, in both BaOH and BaOH+. Such conclusions extend to the results of related calculations on the Ba−OH dissociation energies of BaOH and BaOH+, which were performed to help in calibrating the present computational study. Bonding in BaOH/BaOH+, as well as possible sources of discrepancy with previous experimental determinations of the BaOH adiabatic ionization potential are discussed.
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33.80.Eh Autoionization, photoionization, and photodetachment
31.15.bw Coupled-cluster theory
31.15.xp Perturbation theory
31.15.xr Self-consistent-field methods
33.15.Fm Bond strengths, dissociation energies
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

B(1)1Π state of KCs: High-resolution spectroscopy and description of low-lying energy levels

I. Birzniece, O. Nikolayeva, M. Tamanis, and R. Ferber

J. Chem. Phys. 136, 064304 (2012); http://dx.doi.org/10.1063/1.3683218 (9 pages)

Online Publication Date: 13 February 2012

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The diode laser induced B(1)1Π → X1Σ+ fluorescence spectra of the KCs molecule were recorded by Fourier-transform spectrometer with resolution of 0.03 cm−1. Buffer gas Ar was used to facilitate appearance of rotation relaxation lines in the spectra, thus enlarging the B(1)1Π dataset, allowing one to determine the Λ-splitting constants and to reveal numerous local perturbations. A dataset was systematically obtained for B(1)1Π vibrational levels v′ ∈ [0; 5] nonuniformly covering rotational levels with J′ ∈ [7; 233]. For v′ ∈ [0; 3], the less-perturbed data of f-components were included in the fit. A pointwise potential energy curve (PEC) based on the inverted perturbation approach, as well as the Dunham coefficients, was obtained and compared with ab initio calculations; in particular, the energy of the PEC's minimum Te = 14 044.918(6) cm−1 was determined. Both approaches allowed us to reproduce the vast majority of data used in the fit with accuracy of 0.02 cm−1. Tentative molecular constants for several vibrational levels of the near lying C(3)1Σ+ state were estimated.
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33.50.Dq Fluorescence and phosphorescence spectra
31.15.A- Ab initio calculations
34.20.Cf Interatomic potentials and forces
31.50.-x Potential energy surfaces

Electronic spectroscopy of jet-cooled YbNH3

Nicola M. Tonge, Cassandra A. Rusher, Nitika Bhalla, Luigi Varriale, and Andrew M. Ellis

J. Chem. Phys. 136, 064305 (2012); http://dx.doi.org/10.1063/1.3683220 (6 pages)

Online Publication Date: 13 February 2012

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We report the first spectroscopic study of a complex consisting of a rare earth atom in combination with ammonia. Using two-color resonance-enhanced multiphoton ionization (REMPI) spectroscopy, the lowest energy electronic transition of YbNH3 has been found in the near-infrared. The spectrum arises from a spin-forbidden transition between the 1A1 ground electronic state and the lowest 3E excited electronic state. The transition is metal centered and approximately correlates with the Yb 6s6p 3P ← 6s2 1S transition. The observation of clear spin-orbit structure in the spectrum confirms the C3v symmetry of YbNH3. Vibrational structure is also observed in the REMPI spectrum, which is dominated by excitation of the Yb–N stretching vibration.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.20.Tp Vibrational analysis
31.50.Df Potential energy surfaces for excited electronic states
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