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28 Oct 2011

Volume 135, Issue 16, Articles (16xxxx)

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J. Chem. Phys. 135, 164501 (2011); http://dx.doi.org/10.1063/1.3643417 (11 pages)

Samira Hezaveh, Susruta Samanta, Giuseppe Milano, and Danilo Roccatano
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Communication: A dynamical theory of homogeneous nucleation for colloids and macromolecules

James F. Lutsko

J. Chem. Phys. 135, 161101 (2011); http://dx.doi.org/10.1063/1.3657400 (4 pages) | Cited 3 times

Online Publication Date: 24 October 2011

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Homogeneous nucleation is formulated within the context of fluctuating hydrodynamics. It is shown that for a colloidal system in the strong damping limit the most likely path for nucleation can be determined by gradient descent in density space governed by a nontrivial metric. This is illustrated by application to low-density/high-density liquid transition of globular proteins in solution where it is shown that nucleation process involves two stages: the formation of an extended region with enhanced density followed by the formation of a cluster within this region.
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82.70.Dd Colloids
87.15.Zg Phase transitions
64.70.Ja Liquid-liquid transitions
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back to top Theoretical Methods and Algorithms

On the gauge invariance of nonperturbative electronic dynamics using the time-dependent Hartree-Fock and time-dependent Kohn-Sham

Feizhi Ding, Wenkel Liang, Craig T. Chapman, Christine M. Isborn, and Xiaosong Li

J. Chem. Phys. 135, 164101 (2011); http://dx.doi.org/10.1063/1.3655675 (11 pages)

Online Publication Date: 26 October 2011

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Nonperturbative electronic dynamics using the time-dependent Hartree-Fock (TDHF) and time-dependent Kohn-Sham (TDKS) theories with the adiabatic approximation is a powerful tool in obtaining insights into the interaction between a many-electron system and an external electromagnetic field. In practical applications of TDHF/TDKS using a truncated basis set, the electronic dynamics and molecular properties become gauge-dependent. Numerical simulations are carried out in the length gauge and velocity gauge to verify the extent of gauge-dependence using incomplete basis sets. Electronic dynamics of two many-electron systems, a helium atom and a carbon monoxide molecule in high-intensity linearly polarized radiation fields are performed using the TDHF and TDKS with two selected adiabatic exchange-correlation (xc) functionals. The time evolution of the expectation values of the dipole moment and harmonic spectra are calculated in the two gauges, and the basis set dependence on the gauge-invariance of these properties is investigated.
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31.30.jp Electron electric dipole moment
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
31.15.xr Self-consistent-field methods

Relaxation mode analysis of a peptide system: Comparison with principal component analysis

Ayori Mitsutake, Hiromitsu Iijima, and Hiroshi Takano

J. Chem. Phys. 135, 164102 (2011); http://dx.doi.org/10.1063/1.3652959 (15 pages) | Cited 1 time

Online Publication Date: 27 October 2011

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This article reports the first attempt to apply the relaxation mode analysis method to a simulation of a biomolecular system. In biomolecular systems, the principal component analysis is a well-known method for analyzing the static properties of fluctuations of structures obtained by a simulation and classifying the structures into some groups. On the other hand, the relaxation mode analysis has been used to analyze the dynamic properties of homopolymer systems. In this article, a long Monte Carlo simulation of Met-enkephalin in gas phase has been performed. The results are analyzed by the principal component analysis and relaxation mode analysis methods. We compare the results of both methods and show the effectiveness of the relaxation mode analysis.
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87.15.ak Monte Carlo simulations
87.15.B- Structure of biomolecules
87.15.H- Dynamics of biomolecules
02.50.-r Probability theory, stochastic processes, and statistics
87.15.Ya Fluctuations

Chemical reactions modulated by mechanical stress: Extended Bell theory

Sai Sriharsha M. Konda, Johnathan N. Brantley, Christopher W. Bielawski, and Dmitrii E. Makarov

J. Chem. Phys. 135, 164103 (2011); http://dx.doi.org/10.1063/1.3656367 (8 pages) | Cited 1 time

Online Publication Date: 27 October 2011

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A number of recent studies have shown that mechanical stress can significantly lower or raise the activation barrier of a chemical reaction. Within a common approximation due to Bell [Science 200, 618 (1978)], this barrier is linearly dependent on the applied force. A simple extension of Bell's theory that includes higher order corrections in the force predicts that the force-induced change in the activation energy will be given by –FΔR – ΔχF2/2. Here, ΔR is the change of the distance between the atoms, at which the force F is applied, from the reactant to the transition state, and Δχ is the corresponding change in the mechanical compliance of the molecule. Application of this formula to the electrocyclic ring-opening of cis and trans 1,2-dimethylbenzocyclobutene shows that this extension of Bell's theory essentially recovers the force dependence of the barrier, while the original Bell formula exhibits significant errors. Because the extended Bell theory avoids explicit inclusion of the mechanical stress or strain in electronic structure calculations, it allows a computationally efficient characterization of the effect of mechanical forces on chemical processes. That is, the mechanical susceptibility of any reaction pathway is described in terms of two parameters, ΔR and Δχ, both readily computable at zero force.
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82.20.Pm Rate constants, reaction cross sections, and activation energies
82.20.Db Transition state theory and statistical theories of rate constants
82.20.Hf Product distribution

Short-time self-diffusion coefficient of a particle in a colloidal suspension bounded by a microchannel: Virial expansions and simulation

Marcin Kȩdzierski and Eligiusz Wajnryb

J. Chem. Phys. 135, 164104 (2011); http://dx.doi.org/10.1063/1.3653941 (4 pages)

Online Publication Date: 27 October 2011

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Self-diffusion of colloidal particles confined to a cylindrical microchannel is considered theoretically and numerically. Virial expansion of the self-diffusion coefficient is performed. Two-body and three-body hydrodynamic interactions are evaluated with high precision using the multipole method. The multipole expansion algorithm is also used to perform numerical simulations of the self-diffusion coefficient, valid for all possible particle packing fractions. Comparison with earlier results shows that the widely used method of reflections is insufficient for calculations of hydrodynamic interactions even for small packing fractions and small particles radii, contrary to the prevalent opinion.
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66.10.cg Mass diffusion, including self-diffusion, mutual diffusion, tracer diffusion, etc.
82.70.Dd Colloids
82.70.Kj Emulsions and suspensions

Assessing weak hydrogen binding on Ca+ centers: An accurate many-body study with large basis sets

Wirawan Purwanto, Henry Krakauer, Yudistira Virgus, and Shiwei Zhang

J. Chem. Phys. 135, 164105 (2011); http://dx.doi.org/10.1063/1.3654002 (11 pages)

Online Publication Date: 28 October 2011

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Weak H2 physisorption energies present a significant challenge to even the best correlated theoretical many-body methods. We use the phaseless auxiliary-field quantum Monte Carlo method to accurately predict the binding energy of Ca+– 4H2. Attention has recently focused on this model chemistry to test the reliability of electronic structure methods for H2 binding on dispersed alkaline earth metal centers. A modified Cholesky decomposition is implemented to realize the Hubbard-Stratonovich transformation efficiently with large Gaussian basis sets. We employ the largest correlation-consistent Gaussian type basis sets available, up to cc-pCV5Z for Ca, to accurately extrapolate to the complete basis limit. The calculated potential energy curve exhibits binding with a double-well structure.
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61.50.Lt Crystal binding; cohesive energy
68.43.Fg Adsorbate structure (binding sites, geometry)
71.10.Hf Non-Fermi-liquid ground states, electron phase diagrams and phase transitions in model systems
71.15.Nc Total energy and cohesive energy calculations
71.20.Gj Other metals and alloys
82.20.Kh Potential energy surfaces for chemical reactions

Non-equilibrium spin-boson model: Counting statistics and the heat exchange fluctuation theorem

Lena Nicolin and Dvira Segal

J. Chem. Phys. 135, 164106 (2011); http://dx.doi.org/10.1063/1.3655674 (14 pages)

Online Publication Date: 31 October 2011

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We focus on the non-equilibrium two-bath spin-boson model, a toy model for examining quantum thermal transport in many-body open systems. Describing the dynamics within the noninteracting-blip approximation equations, applicable, e.g., in the strong system-bath coupling limit and/or at high temperatures, we derive expressions for the cumulant generating function in both the Markovian and non-Markovian limits by energy-resolving the quantum master equation of the subsystem. For a Markovian bath, we readily demonstrate the validity of a steady-state heat exchange fluctuation theorem. In the non-Markovian limit a “weaker” symmetry relation generally holds, a general outcome of microreversibility. We discuss the reduction of this symmetry relation to the universal steady-state fluctuation theorem. Using the cumulant generating function, an analytic expression for the heat current is obtained. Our results establish the validity of the steady-state heat exchange fluctuation theorem in quantum systems with strong system-bath interactions. From the practical point of view, this study provides tools for exploring transport characteristics of the two-bath spin-boson model, a prototype for a nonlinear thermal conductor.
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05.30.Jp Boson systems
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion
05.60.Gg Quantum transport
05.70.Ln Nonequilibrium and irreversible thermodynamics

Optimized hierarchical equations of motion theory for Drude dissipation and efficient implementation to nonlinear spectroscopies

Jin-Jin Ding, Jian Xu, Jie Hu, Rui-Xue Xu, and YiJing Yan

J. Chem. Phys. 135, 164107 (2011); http://dx.doi.org/10.1063/1.3653479 (9 pages)

Online Publication Date: 31 October 2011

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Hierarchical equations of motion theory for Drude dissipation is optimized, with a convenient convergence criterion proposed in advance of numerical propagations. The theoretical construction is on the basis of a Padé spectrum decomposition that has been qualified to be the best sum-over-poles scheme for quantum distribution function. The resulting hierarchical dynamics under the a priori convergence criterion are exemplified with a benchmark spin-boson system, and also the transient absorption and related coherent two-dimensional spectroscopy of a model exciton dimer system. We combine the present theory with several advanced techniques such as the block hierarchical dynamics in mixed Heisenberg-Schrödinger picture and the on-the-fly filtering algorithm for the efficient evaluation of third-order optical response functions.
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31.15.X- Alternative approaches
05.30.Jp Boson systems

Ab initio properties of Li-group-II molecules for ultracold matter studies

Svetlana Kotochigova, Alexander Petrov, Maria Linnik, Jacek Kłos, and Paul S. Julienne

J. Chem. Phys. 135, 164108 (2011); http://dx.doi.org/10.1063/1.3653974 (8 pages) | Cited 1 time

Online Publication Date: 31 October 2011

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We perform a systematic investigation of the electronic properties of the 2Σ+ ground state of Li-alkaline-earth dimers. These molecules are proposed as possible candidates for quantum simulation of lattice-spin models. We apply powerful quantum chemistry coupled-cluster method and large basis sets to calculate potential energies and permanent dipole moments for the LiBe, LiMg, LiCa, LiSr, and LiYb molecules. Agreement of calculated molecular constants with existing experimental data is better than or equal to 8%. Our results reveal a surprising irregularity in the dissociation energy and bond length with an increase in the reduced mass of the molecule. At the same time, the permanent dipole moment at the equilibrium separation has the smallest value between 0.01 a.u. and 0.1 a.u. for the heaviest (LiSr and LiYb) molecules and increases to 1.4 a.u. for the lightest (LiBe), where 1 a.u. is one atomic unit of dipole moment. We consider our study of the 2Σ+ molecules a first step towards a comprehensive analysis of their interactions in an optical trap.
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31.15.ae Electronic structure and bonding characteristics
31.30.jp Electron electric dipole moment
31.50.Bc Potential energy surfaces for ground electronic states
33.15.Dj Interatomic distances and angles
33.15.Fm Bond strengths, dissociation energies
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Geometry optimization of bimetallic clusters using an efficient heuristic method

Xiangjing Lai, Ruchu Xu, and Wenqi Huang

J. Chem. Phys. 135, 164109 (2011); http://dx.doi.org/10.1063/1.3656766 (7 pages)

Online Publication Date: 31 October 2011

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In this paper, an efficient heuristic algorithm for geometry optimization of bimetallic clusters is proposed. The algorithm is mainly composed of three ingredients: the monotonic basin-hopping method with guided perturbation (MBH-GP), surface optimization method, and iterated local search (ILS) method, where MBH-GP and surface optimization method are used to optimize the geometric structure of a cluster, and the ILS method is used to search the optimal homotop for a fixed geometric structure. The proposed method is applied to Cu38-nAun (0 ≤ n ≤ 38), Ag55-nAun (0 ≤ n ≤ 55), and Cu55-nAun (0 ≤ n ≤ 55) clusters modeled by the many-body Gupta potential. Comparison with the results reported in the literature indicates that the present method is highly efficient and a number of new putative global minima missed in the previous papers are found. The present method should be a promising tool for the theoretical determination of ground-state structure of bimetallic clusters. Additionally, some key elements and properties of the present method are also analyzed.
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36.40.Mr Spectroscopy and geometrical structure of clusters
31.15.xv Molecular dynamics and other numerical methods
33.15.Bh General molecular conformation and symmetry; stereochemistry

Dispersion, static correlation, and delocalisation errors in density functional theory: An electrostatic theorem perspective

Austin D. Dwyer and David J. Tozer

J. Chem. Phys. 135, 164110 (2011); http://dx.doi.org/10.1063/1.3653980 (6 pages)

Online Publication Date: 31 October 2011

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Dispersion, static correlation, and delocalisation errors in density functional theory are considered from the unconventional perspective of the force on a nucleus in a stretched diatomic molecule. The electrostatic theorem of Feynman is used to relate errors in the forces to errors in the electron density distortions, which in turn are related to erroneous terms in the Kohn-Sham equations. For H2, the exact dispersion force arises from a subtle density distortion; the static correlation error leads to an overestimated force due to an exaggerated distortion. For H2+, the exact force arises from a delicate balance between attractive and repulsive components; the delocalisation error leads to an underestimated force due to an underestimated distortion. The net force in H2+ can become repulsive, giving the characteristic barrier in the potential energy curve. Increasing the fraction of long-range exact orbital exchange increases the distortion, reducing delocalisation error but increasing static correlation error.
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34.20.Gj Intermolecular and atom-molecule potentials and forces
31.15.E- Density-functional theory
31.50.-x Potential energy surfaces

Extended Lagrangian free energy molecular dynamics

Anders M. N. Niklasson, Peter Steneteg, and Nicolas Bock

J. Chem. Phys. 135, 164111 (2011); http://dx.doi.org/10.1063/1.3656977 (11 pages)

Online Publication Date: 31 October 2011

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Extended free energy Lagrangians are proposed for first principles molecular dynamics simulations at finite electronic temperatures for plane-wave pseudopotential and local orbital density matrix-based calculations. Thanks to the extended Lagrangian description, the electronic degrees of freedom can be integrated by stable geometric schemes that conserve the free energy. For the local orbital representations both the nuclear and electronic forces have simple and numerically efficient expressions that are well suited for reduced complexity calculations. A rapidly converging recursive Fermi operator expansion method that does not require the calculation of eigenvalues and eigenfunctions for the construction of the fractionally occupied density matrix is discussed. An efficient expression for the Pulay force that is valid also for density matrices with fractional occupation occurring at finite electronic temperatures is also demonstrated.
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31.15.xv Molecular dynamics and other numerical methods
02.70.Ns Molecular dynamics and particle methods
31.15.at Molecule transport characteristics; molecular dynamics; electronic structure of polymers
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Solvation effects on angular distributions in H−(NH3)n and NH2−(NH3)n photodetachment: Role of solute electronic structure

Emily R. Grumbling and Andrei Sanov

J. Chem. Phys. 135, 164301 (2011); http://dx.doi.org/10.1063/1.3653232 (8 pages)

Online Publication Date: 24 October 2011

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We report 355 and 532 nm photoelectron imaging results for H−(NH3)n and NH2−(NH3)n, n = 0−5. The photoelectron spectra are consistent with the electrostatic picture of a charged solute (H− or NH2−) solvated by n ammonia molecules. For a given number of solvent molecules, the NH2− core anion is stabilized more strongly than H−, yet the photoelectron angular distributions for solvated H− deviate more strongly from the unsolvated limit than those for solvated NH2−. Hence, we conclude that solvation effects on photoelectron angular distributions are dependent on the electronic structure of the anion, i.e., the type of the initial orbital of the photodetached electron, rather than merely the strength of solvation interactions. We also find evidence of photofragmentation and autodetachment of NH2−(NH3)2−5, as well as autodetachment of H−(NH3)5, upon 532 nm excitation of these species.
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36.40.Cg Electronic and magnetic properties of clusters
36.40.Mr Spectroscopy and geometrical structure of clusters
33.80.Eh Autoionization, photoionization, and photodetachment
33.60.+q Photoelectron spectra

Photoelectron angular distributions in negative-ion photodetachment from mixed sp states

Emily R. Grumbling and Andrei Sanov

J. Chem. Phys. 135, 164302 (2011); http://dx.doi.org/10.1063/1.3653234 (7 pages)

Online Publication Date: 24 October 2011

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We describe an approach for constructing analytical models for the energy-dependence of photoelectron angular distributions in the one-electron, non-relativistic approximation. We construct such a model for electron emission from an orbital described as a superposition of s- and p-type functions, using linearly polarized light. In the limits of pure s or pure p electron photodetachment or photoionization, the model correctly reproduces the familiar Cooper–Zare formula. The model predictions are compared to experimental results for strongly solvated H− and NH2−, corresponding to predominantly s and predominantly p character parent states, respectively.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.60.+q Photoelectron spectra

A theoretical study of hydrogen- and lithium-bonded complexes of F–H/Li and Cl–H/Li with NF3, NH3, and NH2(CH3)

Sean A. C. McDowell and Janine A. S. St. Hill

J. Chem. Phys. 135, 164303 (2011); http://dx.doi.org/10.1063/1.3653476 (5 pages)

Online Publication Date: 25 October 2011

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Hydrogen- and lithium-bonded complexes of A−H/Li (A = F, Cl) with the amine analogues NF3, NH3, and NH2(CH3) were studied at the MP2/6-311++G(d,p) level of theory. Bond extensions and redshifts were obtained for the H-bonded complexes, while bond extensions and blueshifts were obtained for the Li-bonded species. The variation of these and other properties with the basicity of the amines was investigated and rationalized by comparing the ab initio results with predictions from a model derived from perturbation theory.
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33.15.Fm Bond strengths, dissociation energies
33.70.Jg Line and band widths, shapes, and shifts
31.15.ae Electronic structure and bonding characteristics
31.15.xp Perturbation theory

Control of vibronic excitation using quantum-correlated photons

Hisaki Oka

J. Chem. Phys. 135, 164304 (2011); http://dx.doi.org/10.1063/1.3654136 (5 pages)

Online Publication Date: 25 October 2011

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We theoretically investigate the two-step excitation of a molecular vibronic state using quantum-correlated photons with time delay in order to control the population of the vibronic excited state. A Morse oscillator having three sets of vibronic states, namely, the ground state, intermediate states, and excited states, is used to evaluate the efficiency of the two-step excitation process. We show that we can efficiently and selectively excite only a target state by using correlated photons and can control the excitation population of the target state by adjusting the delay time of the correlated photons. The potential of controlling a chemical reaction using correlated photons is also discussed.
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33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
42.50.-p Quantum optics
31.50.Bc Potential energy surfaces for ground electronic states
31.50.Df Potential energy surfaces for excited electronic states

Ab initio quantum dynamical study of photoinduced ring opening in furan

E. V. Gromov, C. Lévêque, F. Gatti, I. Burghardt, and H. Köppel

J. Chem. Phys. 135, 164305 (2011); http://dx.doi.org/10.1063/1.3653792 (11 pages)

Online Publication Date: 26 October 2011

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The nonadiabatic photoinduced ring opening occurring in the two lowest excited singlet states of furan is investigated theoretically, using wave-packet propagation techniques. The underlying multidimensional potential energy surfaces (PESs) are obtained from ab initio computations, using the equation-of-motion coupled cluster method restricted to single and double excitations (EOM-CCSD), reported in earlier recent work [E. V. Gromov, A. B. Trofimov, F. Gatti, and H. Köppel, J. Chem. Phys. 133, 164309 (2010)10.1063/1.3493451]. Up to five nuclear degrees of freedom are considered in the quantum dynamical treatment. Four of them represent in-plane motion for which the electronic states in question (correlating with the valence 1B2(V) and Rydberg 1A2(3s) states at the C2v ground-state molecular configuration) have different symmetries, A′ and A′′, respectively. The fifth mode, representing out-of-plane bending of the oxygen atom against the carbon-atom plane, leads to an interaction of these states, as is crucial for the photoreaction. The nonadiabatic coupling and conical intersection cause an electronic population transfer on the order of ∼10 fs. Its main features, and that of the wave-packet motion, are interpreted in terms of properties of the PES. The lifetime due to the ring-opening process has been estimated to be around 2 ps. The dependence of this estimate on the nuclear degrees of freedom retained in the computations is discussed.
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33.80.-b Photon interactions with molecules
31.15.ae Electronic structure and bonding characteristics
31.15.bw Coupled-cluster theory
31.50.Df Potential energy surfaces for excited electronic states
31.50.Gh Surface crossings, non-adiabatic couplings

Theoretical investigation of the photophysics of methyl salicylate isomers

Richard D. Massaro and Estela Blaisten-Barojas

J. Chem. Phys. 135, 164306 (2011); http://dx.doi.org/10.1063/1.3653969 (8 pages)

Online Publication Date: 26 October 2011

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The photophysics of methyl salicylate (MS) isomers has been studied using time-dependent density functional theory and large basis sets. First electronic singlet and triplet excited states energies, structure, and vibrational analysis were calculated for the ketoB, enol, and ketoA isomers. It is demonstrated that the photochemical pathway involving excited state intramolecular proton transfer (ESIPT) from the ketoB to the enol tautomer agrees well with the dual fluorescence in near-UV (from ketoB) and blue (from enol) wavelengths obtained from experiments. Our calculation confirms the existence of a double minimum in the excited state pathway along the O–H–O coordinate corresponding to two preferred energy regions: (1) the hydrogen belongs to the OH moiety and the structure of methyl salicylate is ketoB; (2) the hydrogen flips to the closest carboxyl entailing electronic rearrangement and tautomerization to the enol structure. This double well in the excited state is highly asymmetric. The Franck-Condon vibrational overlap is calculated and accounts for the broadening of the two bands. It is suggested that forward and backward ESIPT through the barrier separating the two minima is temperature-dependent and affects the intensity of the fluorescence as seen in experiments. When the enol fluoresces and returns to its ground state, a barrier-less back proton transfer repopulates the ground state of methyl salicylate ketoB. It is also demonstrated that the rotamer ketoA is not stable in an excited state close to the desired emission wavelength. This observation eliminates the conjecture that the near-UV emission of the dual fluorescence originates from the ketoA rotamer. New experimental results for pure MS in the liquid state are reported and theoretical results compared to them.
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33.20.Tp Vibrational analysis
33.50.Dq Fluorescence and phosphorescence spectra
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.70.Jg Line and band widths, shapes, and shifts
31.15.ee Time-dependent density functional theory
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)

Interpretation of the photoelectron spectra of superalkali species: Li3O and Li3O−

S. Zein and J. V. Ortiz

J. Chem. Phys. 135, 164307 (2011); http://dx.doi.org/10.1063/1.3636082 (9 pages)

Online Publication Date: 27 October 2011

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The present paper deals with the interpretation of the photoelectron spectrum of the Li3O−. After several failed attempts to attribute all of the observed peaks in the experimental spectrum to anionic species, neutral species were considered assuming a sequential two-photon absorption mechanism. We find that only two of the six observed peaks can be attributed to photodetachments and that all other observed features can be assigned to ionizations from the ground and excited states of the neutral. Nuclear distributions other than three lithium atoms surrounding the oxygen are not likely to be stable. The interpretation of the experimental peak located at about 1.2 eV remains challenging. It can either be attributed to the second electron detachment (involving the HOMO −1 orbital) energy from the anion's triplet C2v state or to higher excited states (involving HOMO +10, 11, 12… orbitals) of the neutral species. Furthermore, we have examined the influence of vibrational displacements on the location of the observed peaks. We find that this effect is smaller than 0.05 eV and, therefore, must be considered as negligible.
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33.60.+q Photoelectron spectra
33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.20.Tp Vibrational analysis
31.15.bw Coupled-cluster theory

Photoelectron spectroscopy of the molecular anions, Li3O− and Na3O−

Di Wang, Jacob D. Graham, Allyson M. Buytendyk, and Kit H. Bowen, Jr.

J. Chem. Phys. 135, 164308 (2011); http://dx.doi.org/10.1063/1.3657854 (4 pages)

Online Publication Date: 27 October 2011

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The molecular anions, Li3O− and Na3O− were produced by laser vaporization and studied via anion photoelectron spectroscopy. Li3O− and Na3O− are the negative ions of the super-alkali neutral molecules, Li3O and Na3O. A two-photon process involving the photodetachment of electrons from the Li3O− and Na3O− anions and the photoionization of electrons from the resulting Li3O and Na3O neutral states was observed. The assignment of the Li3O− photoelectron spectrum was based on computational results provided by Zein and Ortiz [J. Chem. Phys. 135, 164307 (2011)]10.1063/1.3636082.
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33.60.+q Photoelectron spectra
33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)

Ultrafast non-adiabatic dynamics of methyl substituted ethylenes: The π3s Rydberg state

Guorong Wu, Andrey E. Boguslavskiy, Oliver Schalk, Michael S. Schuurman, and Albert Stolow

J. Chem. Phys. 135, 164309 (2011); http://dx.doi.org/10.1063/1.3652966 (10 pages)

Online Publication Date: 28 October 2011

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Excited state unimolecular reactions of some polyenes exhibit localization of their dynamics at a single ethylenic double bond. Here we present studies of the fundamental photophysical processes in the ethylene unit itself. Combined femtosecond time-resolved photoelectron spectroscopy (TRPES) and ab initio quantum chemical calculations was applied to the study of excited state dynamics in cis-butene, trans-butene, trimethylethylene, and tetramethylethylene, following initial excitation to their respective π3s Rydberg states. The wavelength dependence of the π3s Rydberg state dynamics of tetramethylethylene was investigated in more detail. The π3s Rydberg to ππ* valence state decay rate varies greatly with substituent: the 1,2-di- and tri-methyl substituted ethylenes (cis-butene, trans-butene, and trimethylethylene) show an ultrafast decay (∼20 fs), whereas the fully methylated tetramethylethylene shows a decay rate of 2 to 4 orders of magnitude slower. These observations are rationalized in terms of topographical trends in the relevant potential energy surfaces, as found from ab initio calculations: (1) the barrier between the π3s state and the ππ* state increases with increasing methylation, and (2) the π3s/ππ* minimum energy conical intersection displaces monotonically away from the π3s Franck-Condon region with increasing methylation. The use of systematic methylation in combination with TRPES and ab initio computation is emerging as an important tool in discerning the excited state dynamics of unsaturated hydrocarbons.
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33.60.+q Photoelectron spectra
33.15.Fm Bond strengths, dissociation energies
31.50.Df Potential energy surfaces for excited electronic states
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
31.15.ae Electronic structure and bonding characteristics

Vibronic coupling in the A2Π and B2Σ+ electronic states of the NCS radical

Riccardo Tarroni

J. Chem. Phys. 135, 164310 (2011); http://dx.doi.org/10.1063/1.3655816 (8 pages)

Online Publication Date: 31 October 2011

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The spin-rovibronic energy levels of the A2Π and B2Σ+ electronic states of thiocyanate radical have been calculated variationally, using high-level ab initio coupled diabatic potential energy surfaces. Computations up to J = 7/2 have been performed, obtaining all levels with K ⩽ 3 (Σ½,math,math,math), for energies up to 2000 cm−1 above the A(000)2Π3/2 level. The available experimental data have been critically reviewed in the light of the theoretical findings.
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33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
31.50.-x Potential energy surfaces
31.15.ae Electronic structure and bonding characteristics
33.20.Vq Vibration-rotation analysis

New ab initio coupled potential energy surfaces for the Br(2P3/2, 2P1/2) + H2 reaction

Bin Jiang, Changjian Xie, and Daiqian Xie

J. Chem. Phys. 135, 164311 (2011); http://dx.doi.org/10.1063/1.3656242 (9 pages) | Cited 1 time

Online Publication Date: 31 October 2011

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The three lowest (1A′, 2A′, and 1A′′) adiabatic potential energy surfaces (PESs) for the Br(2P) + H2 reactive system have been computed based on the multi-reference configuration interaction (MRCI) method including the Davidson's correction with a large basis set. These three adiabatic PESs have been transformed to a diabatic representation, leading to four coupling potentials. In addition, the spin-orbit matrix elements were also obtained using the Breit-Pauli Hamiltonian and the unperturbed MRCI wavefunctions in the Br + H2 channel and the transition state region. Consequently, six coupling potentials were obtained and their characteristics were extensively discussed. Nonadiabatic quantum dynamics calculations for this system have been realized with these realistic diabatic potentials instead of previous semi-empirical diabatic potentials. Based on two-state model nonadiabatic calculations for the Br(2P3/2, 2P1/2) + H2 reaction, the Br(2P1/2) + H2 reaction was found to show less reactivity than the Br(2P3/2) + H2 reaction at collision energies beyond the threshold of the Br(2P3/2) + H2 reaction. Our results are consistent with the previous studies on the XH2 (X = F, Cl) system, which indicate that the adiabatically forbidden channel is dominant at low energies in the open-shell halogen atom plus H2 reactions.
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82.20.Kh Potential energy surfaces for chemical reactions
82.20.Db Transition state theory and statistical theories of rate constants

State-to-state quantum dynamics of the N(4S) + OH(X 2Π) → H(2S) + NO(X 2Π) reaction

Changjian Xie, Anyang Li, Daiqian Xie, and Hua Guo

J. Chem. Phys. 135, 164312 (2011); http://dx.doi.org/10.1063/1.3656243 (7 pages) | Cited 1 time

Online Publication Date: 31 October 2011

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Quantum state-to-state dynamics for the N(4S) + OH(X 2Π) → H(2S) + NO(X 2Π) reaction is reported on an accurate ab initio potential energy surface of the lowest triplet electronic state (a3A″) of HNO/HON. It was found that the reaction is dominated by long-lived resonances supported by the HNO and HON wells. Significant non-reactive scattering was observed, indicating substantial deviations from the statistical limit. Due to the large exothermicity of the reaction, the NO product has hot internal state distributions: its rotational state distribution is inverted and peaks near the highest accessible rotational level; and its vibrational state distribution extends to υ = 10 and decays monotonically with the vibrational quantum number. In particular, the predicted product vibrational distribution is in reasonably good agreement with experiment. The calculated differential cross section is dominated by scattering in both the forward and backward directions, consistent with the formation of reaction intermediates.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.20.Ej Quantum theory of reaction cross section
82.20.Kh Potential energy surfaces for chemical reactions
82.20.Pm Rate constants, reaction cross sections, and activation energies
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation

Structure and dynamics of 1,2-dimethoxyethane and 1,2-dimethoxypropane in aqueous and non-aqueous solutions: A molecular dynamics study

Samira Hezaveh, Susruta Samanta, Giuseppe Milano, and Danilo Roccatano

J. Chem. Phys. 135, 164501 (2011); http://dx.doi.org/10.1063/1.3643417 (11 pages) | Cited 1 time

Online Publication Date: 24 October 2011

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Herein, we report a comparative modelling study of 1,2-dimethoxyethane (DME) and 1,2-dimethoxypropane (DMP) at 298 K and 318 K in the liquid state, water mixtures, and at infinite dilution condition in water, methanol, carbon tetrachloride, and n-heptane. Both DME and DMP are united-atom models compatible with GROMOS/OPLS force fields. Calculated thermodynamic and structural properties of the pure DME and DMP liquids resulted in excellent agreement with the experimental data. In aqueous solutions, densities, diffusion coefficients, and concentration dependent conformers of DME, were in agreement with experimental data. The calculated free energy of solvation (ΔGhyd) at 298 K is equal to –22.1 ± 0.8 kJ mol−1 in good agreement with the experimental value of 20.2 kJ mol−1. In addition, the free energy of solvation of DME in non-aqueous solvents follows the trend methanol ≈ water < carbon tetrachloride < n-heptane, consistently with the dielectric constant of the solvents. On contrary, the presence of an extra methyl group on chiral carbon makes DMP less soluble than DME in water (ΔGhyd = −16.0 ± 1.1 kJ mol−1) but more soluble in non-polar solvents as n-heptane. Finally, for the DMP the chiral discrimination of the two enantiomers was calculated as solvation free energy difference of one DMP isomer in the solution of the other. The obtained value of ΔΔGRS = –3.7 ± 1.4 kJ mol−1 indicates a net chiral discrimination of the two enantiomers.
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61.20.Ja Computer simulation of liquid structure
82.30.Nr Association, addition, insertion, cluster formation
65.20.Jk Studies of thermodynamic properties of specific liquids
66.10.C- Diffusion and thermal diffusion
31.15.xv Molecular dynamics and other numerical methods
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