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7 Jul 2011

Volume 135, Issue 1, Articles (01xxxx)

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J. Chem. Phys. 135, 015101 (2011); http://dx.doi.org/10.1063/1.3598473 (16 pages)

Alexander Barabanschikov, Alexander Demidov, Minoru Kubo, Paul M. Champion, J. Timothy Sage, Jiyong Zhao, Wolfgang Sturhahn, and E. Ercan Alp
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Announcement: New Advanced Experimental Techniques section in The Journal of Chemical Physics

Marsha I. Lester, Editor

J. Chem. Phys. 135, 010201 (2011); http://dx.doi.org/10.1063/1.3610377 (1 page)

Online Publication Date: 7 July 2011

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01.10.Cr Announcements, news, and awards
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Bx Radio-frequency and microwave spectra
33.80.Be Level crossing and optical pumping
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back to top Theoretical Methods and Algorithms

Direct selected multireference configuration interaction calculations for large systems using localized orbitals

Nadia Ben Amor, Fabienne Bessac, Sophie Hoyau, and Daniel Maynau

J. Chem. Phys. 135, 014101 (2011); http://dx.doi.org/10.1063/1.3600351 (14 pages) | Cited 1 time

Online Publication Date: 1 July 2011

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A selected multireference configuration interaction (CI) method and the corresponding code are presented. It is based on a procedure of localization that permits to obtain well localized occupied and virtual orbitals. Due to the local character of the electron correlation, using local orbitals allows one to neglect long range interactions. In a first step, three topological matrices are constructed, which determine whether two orbitals must be considered as interacting or not. Two of them concern the truncation of the determinant basis, one for occupied/virtual, the second one for dispersive interactions. The third one concerns the truncation of the list of two electron integrals. This approach permits a fine analysis of each kind of approximation and induces a huge reduction of the CI size and of the computational time. The procedure is tested on linear polyene aldehyde chains, dissociation potential energy curve, and reaction energy of a pesticide-Ca2+ complex and finally on transition energies of a large iron system presenting a light-induced excited spin-state trapping effect.
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36.20.Kd Electronic structure and spectra
31.50.Df Potential energy surfaces for excited electronic states
31.15.vq Electron correlation calculations for polyatomic molecules

Self-assembly behavior of ABA coil-rod-coil triblock copolymers: A Brownian dynamics simulation approach

Yongliang Li, Shaoliang Lin, Xiaohua He, Jiaping Lin, and Tao Jiang

J. Chem. Phys. 135, 014102 (2011); http://dx.doi.org/10.1063/1.3606396 (10 pages)

Online Publication Date: 5 July 2011

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The self-assembly behavior of ABA coil-rod-coil triblock copolymers in a selective solvent was studied by a Brownian molecular dynamics simulation method. It was found that the rod midblock plays an important role in the self-assembly of the copolymers. With a decrease in the segregation strength, ɛRR, of rod pairs, the aggregate structure first varies from a smecticlike disk shape to a long twisted string micelle and then to small aggregates. The influence of the block length and the asymmetry of the triblock copolymer on the phase behavior were studied and the corresponding phase diagrams were mapped. It was revealed that the variation of these parameters has a profound effect on microstructure. The simulation results are consistent with experimental results. Compared to rod-coil diblock copolymers, the coil-rod-coil triblock copolymers has a larger entropy penalty associated with the interfacial grafting density of the aggregate, leading to a higher ɛRR value for structural transitions.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
61.41.+e Polymers, elastomers, and plastics
61.43.Bn Structural modeling: serial-addition models, computer simulation
81.30.Dz Phase diagrams of other materials
82.70.Dd Colloids
64.75.Yz Self-assembly

Simple preconditioning for time-dependent density functional perturbation theory

Lauri Lehtovaara and Miguel A. L. Marques

J. Chem. Phys. 135, 014103 (2011); http://dx.doi.org/10.1063/1.3606467 (6 pages)

Online Publication Date: 6 July 2011

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By far, the most common use of time-dependent density functional theory is in the linear-reponse regime, where it provides information about electronic excitations. Ideally, the linear-response equations should be solved by a method that avoids the use of the unoccupied Kohn-Sham states — such as the Sternheimer method — as this reduces the complexity and increases the precision of the calculation. However, the Sternheimer equation becomes ill-conditioned near and indefinite above the first resonant frequency, seriously hindering the use of efficient iterative solution methods. To overcome this serious limitation, and to improve the general convergence properties of the iterative techniques, we propose a simple preconditioning strategy. In our method, the Sternheimer equation is solved directly as a linear equation using an iterative Krylov subspace method, i.e., no self-consistent cycle is required. Furthermore, the preconditioner uses the information of just a few unoccupied states and requires simple and minimal modifications to existing implementations. In this way, convergence can be reached faster and in a considerably wider frequency range than the traditional approach.
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31.15.ee Time-dependent density functional theory
31.15.xp Perturbation theory
34.50.Gb Electronic excitation and ionization of molecules
34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)

Simple orbital theory for the molecular electrician

Matthias Ernzerhof

J. Chem. Phys. 135, 014104 (2011); http://dx.doi.org/10.1063/1.3603444 (7 pages) | Cited 1 time

Online Publication Date: 6 July 2011

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Theories of molecular electronic devices (MEDs) are quite involved in general. However, various prominent features of MEDs can be understood drawing only on elementary quantum theory. To support this point of view, we provide a two component orbital theory that enables one to reproduce various important features of MEDs. In this theory, the device orbitals are divided into two components, each of which is obtained from simple rules. To illustrate our two-component model, we apply it to explain, among other things, the conductance suppression in cross-conjugated systems and the dependence of the conductance on the contact position in aromatic systems.
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85.65.+h Molecular electronic devices

QM:QM embedding using electronic densities within an ONIOM framework: Energies and analytic gradients

Hrant P. Hratchian, Aliaksandr V. Krukau, Priya V. Parandekar, Michael J. Frisch, and Krishnan Raghavachari

J. Chem. Phys. 135, 014105 (2011); http://dx.doi.org/10.1063/1.3603450 (13 pages) | Cited 1 time

Online Publication Date: 6 July 2011

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Accurate calculations of large systems remain a challenge in electronic structure theory. Hybrid energy techniques are a promising family of methods for treating such systems. Expanding on previous developments, we present a QM:QM electronic embedding model whereby the high-level region is polarized by the electron density of the low-level region within an ONIOM framework. A direct Coulomb embedding model as well a more computationally efficient model involving a density fitting expansion are considered. We also develop a generalized theory for the first derivatives of these classes of QM:QM electronic embedding schemes, which requires solution of a single set of self-consistent field response equations. Two initial test cases are presented and discussed.
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31.15.xr Self-consistent-field methods

Accurate explicitly correlated wave functions for two electrons in a square

Ilya G. Ryabinkin and Viktor N. Staroverov

J. Chem. Phys. 135, 014106 (2011); http://dx.doi.org/10.1063/1.3603451 (7 pages)

Online Publication Date: 6 July 2011

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An explicitly correlated linear-r12 variational method is developed for a system of two electrons confined to a two-dimensional square well with infinite walls. The wave function is written as an expansion in products of non-negative integer powers of the relative and center-of-mass electronic coordinates and powers of r12 restricted to 0 and 1. This form indirectly includes higher powers of the interelectronic distance and exhibits a much faster convergence than a similar expansion without r12-dependent terms. The method is implemented using high-precision floating-point arithmetic. Ground-state total energies are reported with at least 12 accurate significant figures for squares with sides from 1 to 50 bohrs. The method can be used “as is” for excited states and for two-dimensional rectangular wells. We also show that wave functions for two electrons in a square and in a rectangle have a higher symmetry than can be accounted for by the point group of the system.
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31.15.xt Variational techniques
31.15.ve Electron correlation calculations for atoms and ions: ground state
31.15.vj Electron correlation calculations for atoms and ions: excited states

Condensed phase molecular dynamics using interpolated potential energy surfaces with application to the resolvation process of coumarin 153

Jae Woo Park, Hyun Woo Kim, Chang-ik Song, and Young Min Rhee

J. Chem. Phys. 135, 014107 (2011); http://dx.doi.org/10.1063/1.3605302 (12 pages) | Cited 1 time

Online Publication Date: 6 July 2011

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Interpolated potential energy surfaces (PESs) have been used for performing reliable molecular dynamics (MD) simulations of small molecular reactions. In this article, we extend this method to MD simulations in condensed phase and show that the same scheme can also be feasibly used when it is supplemented with additional terms for describing intermolecular interactions. We then apply the approach for studying the resolvation process of coumarin 153 in a number of polar solvents. We find that the interpolated surface actually reproduces experimentally found features much better than the conventional force field based potential especially in terms of both dynamics Stokes shift in the short time limit and solute vibrational decoherence. This shows that the solute vibrational effect is important to some degree along the resolvation and should be modeled properly for accurate description of the related dynamics. The stability issue of trajectories on the interpolated PESs is also discussed, in regard to the goal of reliably performing long time simulations. Operational limitations of the present scheme are also discussed.
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82.20.Kh Potential energy surfaces for chemical reactions
82.20.Yn Solvent effects on reactivity
33.70.Jg Line and band widths, shapes, and shifts
34.20.Gj Intermolecular and atom-molecule potentials and forces
82.30.Nr Association, addition, insertion, cluster formation
31.15.xv Molecular dynamics and other numerical methods
31.50.-x Potential energy surfaces

An enhanced splined saddle method

S. Alireza Ghasemi and Stefan Goedecker

J. Chem. Phys. 135, 014108 (2011); http://dx.doi.org/10.1063/1.3605539 (13 pages) | Cited 1 time

Online Publication Date: 6 July 2011

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We present modifications for the method recently developed by Granot and Baer [J. Chem. Phys. 128, 184111 (2008)]10.1063/1.2916716. These modifications significantly enhance the efficiency and reliability of the method. In addition, we discuss some specific features of this method. These features provide important flexibilities which are crucial for a double-ended saddle point search method in order to be applicable to complex reaction mechanisms. Furthermore, it is discussed under what circumstances this methods might fail to find the transition state and remedies to avoid such situations are provided. We demonstrate the performance of the enhanced splined saddle method on several examples with increasing complexity, isomerization of ammonia, ethane and cyclopropane molecules, tautomerization of cytosine, the ring opening of cyclobutene, the Stone-Wales transformation of the C60 fullerene, and finally rolling a small NaCl cube on NaCl(001) surface. All of these calculations are based on density functional theory. The efficiency of the method is remarkable in regard to the reduction of the total computational time.
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82.20.Ln Semiclassical theory of reactions and/or energy transfer
82.20.Hf Product distribution
82.30.Qt Isomerization and rearrangement
82.20.Kh Potential energy surfaces for chemical reactions

Polarization justified Fukui functions: The theory and applications for molecules

Ludwik Komorowski, Józef Lipiński, Paweł Szarek, and Piotr Ordon

J. Chem. Phys. 135, 014109 (2011); http://dx.doi.org/10.1063/1.3603449 (8 pages)

Online Publication Date: 7 July 2011

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The Fukui functions based on the computable local polarizability vector have been presented for a group of simple molecules. The necessary approximation for the density functional theory softness kernel has been supported by a theoretical analysis unifying and generalizing early concepts produced by the several authors. The exact relation between local polarizability vector and the derivative of the nonlocal part of the electronic potential over the electric field has been demonstrated. The resulting Fukui functions are unique and represent a reasonable refinement when compared to the classical ones that are calculated as the finite difference of the density in molecular ions. The new Fukui functions are strongly validated by their direct link to electron dipole polarizabilities that are reported experimentally and by other computational methods.
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33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.E- Density-functional theory
31.15.xf Finite-difference schemes

Bifurcations of dividing surfaces in chemical reactions

Manuel Iñarrea, Jesús F. Palacián, Ana Isabel Pascual, and J. Pablo Salas

J. Chem. Phys. 135, 014110 (2011); http://dx.doi.org/10.1063/1.3600744 (10 pages) | Cited 1 time

Online Publication Date: 7 July 2011

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We study the dynamical behavior of the unstable periodic orbit (NHIM) associated to the non-return transition state (TS) of the H2 + H collinear exchange reaction and their effects on the reaction probability. By means of the normal form of the Hamiltonian in the vicinity of the phase space saddle point, we obtain explicit expressions of the dynamical structures that rule the reaction. Taking advantage of the straightforward identification of the TS in normal form coordinates, we calculate the reaction probability as a function of the system energy in a more efficient way than the standard Monte Carlo method. The reaction probability values computed by both methods are not in agreement for high energies. We study by numerical continuation the bifurcations experienced by the NHIM as the energy increases. We find that the occurrence of new periodic orbits emanated from these bifurcations prevents the existence of a unique non-return TS, so that for high energies, the transition state theory cannot be longer applied to calculate the reaction probability.
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82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.20.Bc State selected dynamics and product distribution
82.20.Db Transition state theory and statistical theories of rate constants

On the effect of electron correlation on the static second hyperpolarizability of π conjugated oligomer chains

Peter A. Limacher, Qingxu Li, and Hans P. Lüthi

J. Chem. Phys. 135, 014111 (2011); http://dx.doi.org/10.1063/1.3603967 (4 pages) | Cited 2 times

Online Publication Date: 7 July 2011

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In this article, we report on the ab initio calculation of the static longitudinal second hyperpolarizability (γ) of π conjugated unsaturated oligomer chains using polyacetylene and polyyne as model compounds. The common observation is that the electron correlation enhances γ in these systems. The present study reveals that for extended chain lengths the opposite appears to be true: Electron correlation may have a damping effect on this property. For double-zeta basis sets, a negative contribution from electron correlation to γ is found within the range of chain lengths investigated. For triple-zeta basis sets, the same behavior must be anticipated at larger chain lengths based on extrapolation schemes. The analysis of the excitation energies and transition moments shows that transition moments between excited states as predicted by the Hartree-Fock and coupled cluster methods have a different response to chain length extension. There also are indications that higher order correlation effects will enhance γ.
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31.15.ap Polarizabilities and other atomic and molecular properties
31.15.eg Exchange-correlation functionals (in current density functional theory)
31.15.vj Electron correlation calculations for atoms and ions: excited states
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.50.Df Potential energy surfaces for excited electronic states
31.15.xr Self-consistent-field methods

Dimension reduction by balanced truncation: Application to light-induced control of open quantum systems

Boris Schäfer-Bung, Carsten Hartmann, Burkhard Schmidt, and Christof Schütte

J. Chem. Phys. 135, 014112 (2011); http://dx.doi.org/10.1063/1.3605243 (13 pages)

Online Publication Date: 7 July 2011

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In linear control, balanced truncation is known as a powerful technique to reduce the state-space dimension of a system. Its basic principle is to identify a subspace of jointly easily controllable and observable states and then to restrict the dynamics to this subspace without changing the overall response of the system. This work deals with a first application of balanced truncation to the control of open quantum systems which are modeled by the Liouville-von Neumann equation within the Lindblad formalism. Generalization of the linear theory has been proposed to cope with the bilinear terms arising from the coupling between the control field and the quantum system. As an example we choose the dissipative quantum dynamics of a particle in an asymmetric double well potential driven by an external control field, monitoring population transfer between the potential wells as a control target. The accuracy of dimension reduction is investigated by comparing the populations obtained for the truncated system versus those for the original system. The dimension of the model system can be reduced very efficiently where the degree of reduction depends on temperature and relaxation rate.
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42.50.Wk Mechanical effects of light on material media, microstructures and particles

Analytical Hessian of electronic excited states in time-dependent density functional theory with Tamm-Dancoff approximation

Jie Liu and WanZhen Liang

J. Chem. Phys. 135, 014113 (2011); http://dx.doi.org/10.1063/1.3605504 (8 pages) | Cited 1 time

Online Publication Date: 7 July 2011

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We present the analytical expression and computer implementation for the second-order energy derivatives of the electronic excited state with respect to the nuclear coordinates in the time-dependent density functional theory (TDDFT) with Gaussian atomic orbital basis sets. Here, the Tamm-Dancoff approximation to the full TDDFT is adopted, and therefore the formulation process of TDDFT excited-state Hessian is similar to that of configuration interaction singles (CIS) Hessian. However, due to the replacement of the Hartree-Fock exchange integrals in CIS with the exchange-correlation kernels in TDDFT, many quantitative changes in the derived equations are arisen. The replacement also causes additional technical difficulties associated with the calculation of a large number of multiple-order functional derivatives with respect to the density variables and the nuclear coordinates. Numerical tests on a set of test molecules are performed. The simulated excited-state vibrational frequencies by the analytical Hessian approach are compared with those computed by CIS and the finite-difference method. It is found that the analytical Hessian method is superior to the finite-difference method in terms of the computational accuracy and efficiency. The numerical differentiation can be difficult due to root flipping for excited states that are close in energy. TDDFT yields more exact excited-state vibrational frequencies than CIS, which usually overestimates the values.
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31.15.eg Exchange-correlation functionals (in current density functional theory)
31.15.xr Self-consistent-field methods

A multigrid method for N-component nucleation

Dennis S. van Putten, Simon P. Glazenborg, Rob Hagmeijer, and Cornelis H. Venner

J. Chem. Phys. 135, 014114 (2011); http://dx.doi.org/10.1063/1.3605658 (8 pages)

Online Publication Date: 7 July 2011

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A multigrid algorithm has been developed enabling more efficient solution of the cluster size distribution for N-component nucleation from the Becker-Döring equations. The theoretical derivation is valid for an arbitrary number of condensing components, making the simulation of many-component nucleating systems feasible. A steady state ternary nucleation problem is defined to demonstrate its efficiency. The results are used as a validation for existing nucleation theories. The non-steady state ternary problem provides useful insight into the initial stages of the nucleation process. We observe that for the ideal mixture the main nucleation flux bypasses the saddle point.
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64.60.qe General theory and computer simulations of nucleation
64.70.F- Liquid-vapor transitions
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Collision-induced dipole polarizability of helium dimer from explicitly correlated calculations

Wojciech Cencek, Jacek Komasa, and Krzysztof Szalewicz

J. Chem. Phys. 135, 014301 (2011); http://dx.doi.org/10.1063/1.3603968 (7 pages) | Cited 1 time

Online Publication Date: 1 July 2011

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Large expansions in basis sets of explicitly correlated Gaussian functions and the variation-perturbation technique were used to calculate the static dipole polarizability of the helium dimer at 16 different internuclear separations from 1.0 to 9.0 bohrs. The convergence towards the complete basis set limit was analyzed in order to estimate uncertainties of all the calculated values. The results are significantly more accurate than literature data. Asymptotically correct analytic fits for the trace and anisotropy of collision-induced polarizability were obtained.
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33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.xt Variational techniques
31.15.xp Perturbation theory

The binding energies of NO–Rg (Rg = He, Ne, Ar) determined by velocity map imaging

Heather L. Holmes-Ross and Warren D. Lawrance

J. Chem. Phys. 135, 014302 (2011); http://dx.doi.org/10.1063/1.3601924 (6 pages) | Cited 1 time

Online Publication Date: 6 July 2011

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We report velocity map imaging measurements of the binding energies, D0, of NO–Rg (Rg = He, Ne, Ar) complexes. The math state binding energies determined are 3.0 ± 1.8, 28.6 ± 1.7, and 93.5 ± 0.9 cm−1 for NO–He, –Ne, and –Ar, respectively. These values compare reasonably well with ab initio calculations. Because the math–math transitions were unable to be observed for NO–He and NO–Ne, values for the binding energies in the math state of these complexes have not been determined. Based on our math state value and the reported math–math origin band position, the math state binding energy for NO–Ar was determined to be 50.6 ± 0.9 cm−1.
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31.15.ae Electronic structure and bonding characteristics
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Fm Bond strengths, dissociation energies
31.15.bw Coupled-cluster theory

Kinetics and dynamics of the NH3 + H → NH2 + H2 reaction using transition state methods, quasi-classical trajectories, and quantum-mechanical scattering

Jose C. Corchado, Joaquin Espinosa-Garcia, and Minghui Yang

J. Chem. Phys. 135, 014303 (2011); http://dx.doi.org/10.1063/1.3605242 (9 pages) | Cited 1 time

Online Publication Date: 6 July 2011

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On a recent analytical potential energy surface developed by two of the authors, an exhaustive kinetics study, using variational transition state theory with multidimensional tunneling effect, and dynamics study, using both quasi-classical trajectory and full-dimensional quantum scattering methods, was carried out to understand the reactivity of the NH3 + H → NH2 + H2 gas-phase reaction. Initial state-selected time-dependent wave packet calculations using a full-dimensional model were performed, where the total reaction probabilities were calculated for the initial ground vibrational state and for four excited vibrational states of ammonia. Thermal rate constants were calculated for the temperature range 200–2000 K using the three methods and compared with available experimental data. We found that (a) the total reaction probabilities are very small, (b) the symmetric and asymmetric N–H stretch excitations enhance the reactivity, (c) the quantum-mechanical calculated thermal rate constants are about one order of magnitude smaller than the transition state theory results, which reproduce the experimental evidence, and (d) quasi-classical trajectory calculations, which were performed with the main goal of analyzing the influence of the zero-point energy problem on the final dynamics results, reproduce the quantum scattering calculations on the same surface.
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82.20.Db Transition state theory and statistical theories of rate constants
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
33.20.Tp Vibrational analysis
82.20.Kh Potential energy surfaces for chemical reactions

Theoretical study of radiative and non-radiative decay processes in pyrazine derivatives

Chunmei Deng, Yingli Niu, Qian Peng, Anjun Qin, Zhigang Shuai, and Ben Zhong Tang

J. Chem. Phys. 135, 014304 (2011); http://dx.doi.org/10.1063/1.3606579 (8 pages)

Online Publication Date: 7 July 2011

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Aggregation-induced emission (AIE) phenomenon has attracted much attention in recent years due to its potential applications in optoelectronic devices, fluorescence sensors, and biological probes. Restriction of intramolecular rotation has been proposed as the cause of this unusual phenomenon. Rational design of AIE luminogens requires quantitative descriptions of its mechanism. 2,3-dicyano-5,6-diphenylpyrazine (DCDPP) with “free” phenyl rings is an AIE active compound, whereas 2,3-dicyanopyrazino [5,6-9,10] phenanthrene (DCPP) with “locked” phenyl rings is not. Quantum chemistry calculations coupled with our thermal vibration correlation function formalism for the radiative and non-radiative decay rates reveal that the radiative decay rates for both DCPP and DCDPP are close to each other for all the temperatures, but the non-radiative decay processes are very different. For DCDPP, the low-frequency modes originated from the phenyl ring twisting motions are strongly coupled with the electronic excited state, which dissipate the electronic excitation energy through mode-mixing (Duschinsky rotation effect), and the non-radiative decay rate strongly increases with temperature. For DCPP, however, such mode-mixing effect is weak and the non-radiative decay rate is insensitive to temperature. These findings rationalize the fact that DCDPP is AIE active but DCPP is not, and are instructive to further development of AIE luminogens.
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33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
31.15.-p Calculations and mathematical techniques in atomic and molecular physics

Full-dimensional time-dependent wave packet dynamics of H2 + D2 reaction

Hongwei Song, Yunpeng Lu, and Soo-Y Lee

J. Chem. Phys. 135, 014305 (2011); http://dx.doi.org/10.1063/1.3607965 (10 pages) | Cited 1 time

Online Publication Date: 7 July 2011

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Collision induced dissociation (CID), four center reaction (4C), and single exchange reaction (SE) in H2 (v1 = high) + D2 (v2 = low) were studied by means of time-dependent wave packet approach within a full-dimensional model. Initial state-selected total reaction probabilities for the three competitive processes have been computed on two realistic global potential energy surfaces of Aguado-Suárez-Paniagua and Boothroyd-Martin-Keogh-Peterson (BMKP) with the total angular momentum J = 0. The role of both vibrationally excited and rotationally excited reagents was examined by varying the initial vibrational and rotational states. The vibrational excitation of the hot diatom gives an enhancement effect on the CID process, while the vibrational excitation of the cold diatom gives an inhibition effect. The rotational excitation of both reagents has a significant effect on the reaction process. The 4C and SE probabilities are at least one order of magnitude smaller than the CID probabilities over the energy range considered. Isotope substitution effects were also studied by substituting the collider D2 by H2 and HD on the BMKP potential energy surfaces. The CID process is most efficient for the H2 + D2 combination and least efficient for the H2 + H2 combination and is different for the 4C and SE processes.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
33.20.Sn Rotational analysis
33.20.Tp Vibrational analysis
82.20.Kh Potential energy surfaces for chemical reactions
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)

The products of the thermal decomposition of CH3CHO

AnGayle Vasiliou, Krzysztof M. Piech, Xu Zhang, Mark R. Nimlos, Musahid Ahmed, Amir Golan, Oleg Kostko, David L. Osborn, John W. Daily, John F. Stanton, and G. Barney Ellison

J. Chem. Phys. 135, 014306 (2011); http://dx.doi.org/10.1063/1.3604005 (5 pages) | Cited 1 time

Online Publication Date: 7 July 2011

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We have used a heated 2 cm × 1 mm SiC microtubular (μtubular) reactor to decompose acetaldehyde: CH3CHO + Δ → products. Thermal decomposition is followed at pressures of 75–150 Torr and at temperatures up to 1675 K, conditions that correspond to residence times of roughly 50–100 μs in the μtubular reactor. The acetaldehyde decomposition products are identified by two independent techniques: vacuum ultraviolet photoionization mass spectroscopy (PIMS) and infrared (IR) absorption spectroscopy after isolation in a cryogenic matrix. Besides CH3CHO, we have studied three isotopologues, CH3CDO, CD3CHO, and CD3CDO. We have identified the thermal decomposition products CH3 (PIMS), CO (IR, PIMS), H (PIMS), H2 (PIMS), CH2CO (IR, PIMS), CH2=CHOH (IR, PIMS), H2O (IR, PIMS), and HC≡CH (IR, PIMS). Plausible evidence has been found to support the idea that there are at least three different thermal decomposition pathways for CH3CHO; namely, radical decomposition: CH3CHO + Δ → CH3 + [HCO] → CH3 + H + CO; elimination: CH3CHO + Δ → H2 + CH2=C=O; isomerization/elimination: CH3CHO + Δ → [CH2=CH–OH] → HC≡CH + H2O. An interesting result is that both PIMS and IR spectroscopy show compelling evidence for the participation of vinylidene, CH2=C:, as an intermediate in the decomposition of vinyl alcohol: CH2=CH–OH + Δ → [CH2=C:] + H2O → HC≡CH + H2O.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.30.Qt Isomerization and rearrangement
82.20.Hf Product distribution
82.20.Tr Kinetic isotope effects including muonium
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
82.80.Gk Analytical methods involving vibrational spectroscopy

Characterisation of H2S⋯CuCl and H2S⋯AgCl isolated in the gas phase: A rigidly pyramidal geometry at sulphur revealed by rotational spectroscopy and ab initio calculations

Nicholas R. Walker, David P. Tew, Stephanie J. Harris, David E. Wheatley, and Anthony C. Legon

J. Chem. Phys. 135, 014307 (2011); http://dx.doi.org/10.1063/1.3598927 (10 pages) | Cited 3 times

Online Publication Date: 7 July 2011

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Pure rotational spectra of the ground vibrational states of eight isotopologues of H2S⋯CuCl and twelve isotopologues of H2S⋯AgCl have been analysed allowing rotational constants and hyperfine coupling constants to be determined. The molecular structures have been determined from the measured rotational constants and are presented alongside the results of calculations at the CCSD(T) level. Both molecules have Cs symmetry at equilibrium and are pyramidal at the sulphur atom. The chlorine, metal, and sulphur atoms are collinear while the local C2 axis of the hydrogen sulphide molecule intersects the axis defined by the heavy atoms at an angle, ϕ = 74.46(2)° for Cu and ϕ = 78.052(6)° for Ag. The molecular geometries are rationalised using simple rules that invoke the electrostatic interactions within the complexes. Centrifugal distortion constants, ΔJ, and nuclear quadrupole coupling constants, χaa(Cu) and χaa(Cl) for H2S⋯CuCl are presented for the first time. The geometry of H2S⋯AgCl is determined with fewer assumptions and greater precision than previously.
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33.20.Sn Rotational analysis
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.30.Gs Hyperfine interactions and isotope effects
31.15.bw Coupled-cluster theory
31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure

Multimode calculations of rovibrational energies and dipole transition intensities for polyatomic molecules with torsional motion: Application to H2O2

Stuart Carter, Amit R. Sharma, and Joel M. Bowman

J. Chem. Phys. 135, 014308 (2011); http://dx.doi.org/10.1063/1.3604935 (10 pages)

Online Publication Date: 7 July 2011

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We report rigorous calculations of rovibrational energies and dipole transition intensities for hydrogen peroxide using a new version of MULTIMODE as applied to molecules with torsional (reaction path) motion. The key features which permit such calculations for moderately sized polyatomic molecules of this general type are briefly described. A previous, accurate potential energy surface and a new high-level ab initio dipole moment surface are employed in these calculations. Detailed comparisons are made with high-resolution experimental spectral intensities from the HITRAN database.
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34.50.Ez Rotational and vibrational energy transfer
31.50.-x Potential energy surfaces
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.A- Ab initio calculations
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation

Resummed thermodynamic perturbation theory for central force associating potential. Multi-patch models

Y. V. Kalyuzhnyi, H. Docherty, and P. T. Cummings

J. Chem. Phys. 135, 014501 (2011); http://dx.doi.org/10.1063/1.3604819 (12 pages) | Cited 1 time

Online Publication Date: 1 July 2011

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A resummed thermodynamic perturbation theory for associating fluids with multiply bondable central force associating potential is extended for the fluid with multiple number of multiply bondable associating sites. We consider a multi-patch hard-sphere model for associating fluids. The model is represented by the hard-sphere fluid system with several spherical attractive patches on the surface of each hard sphere. Resummation is carried out to account for blocking effects, i.e., when the bonding of a particle restricts (blocks) its ability to bond with other particles. Closed form analytical expressions for thermodynamical properties (Helmholtz free energy, pressure, internal energy, and chemical potential) of the models with arbitrary number of doubly bondable patches at all degrees of the blockage are presented. In the limiting case of total blockage, when the patches become only singly bondable, our theory reduces to Wertheim's thermodynamic perturbation theory (TPT) for polymerizing fluids. To validate the accuracy of the theory we compare to exact values, for the thermodynamical properties of the system, as determined by Monte Carlo computer simulations. In addition we compare the fraction of multiply bonded particles at different values of the density and temperature. In general, predictions of the present theory are in good agreement with values for the model calculated using Monte Carlo simulations, i.e., the accuracy of our theory in the case of the models with multiply bondable sites is similar to that of Wertheim's TPT in the case of the models with singly bondable sites.
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31.15.xp Perturbation theory
33.15.Fm Bond strengths, dissociation energies

Fluctuation theory of molecular association and conformational equilibria

Yuanfang Jiao and Paul E. Smith

J. Chem. Phys. 135, 014502 (2011); http://dx.doi.org/10.1063/1.3601342 (13 pages) | Cited 1 time

Online Publication Date: 5 July 2011

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General expressions relating the effects of pressure, temperature, and composition on solute association and conformational equilibria using the fluctuation theory of solutions are provided. The expressions are exact and can be used to interpret experimental or computer simulation data for any multicomponent mixture involving molecules of any size and character at any composition. The relationships involve particle-particle, particle-energy, and energy-energy correlations within local regions in the vicinity of each species involved in the equilibrium. In particular, it is demonstrated that the results can be used to study peptide and protein association or aggregation, protein denaturation, and protein-ligand binding. Exactly how the relevant fluctuating properties may be obtained from experimental or computer simulation data are also outlined. It is shown that the enthalpy, heat capacity, and compressibility differences associated with the equilibrium process can, in principle, be obtained from a single simulation. Fluctuation based expressions for partial molar heat capacities, thermal expansions, and isothermal compressibilities are also provided.
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82.30.Nr Association, addition, insertion, cluster formation
33.15.Bh General molecular conformation and symmetry; stereochemistry
87.15.B- Structure of biomolecules
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