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14 Jun 2011

Volume 134, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

J. Chem. Phys. 134, 225101 (2011); http://dx.doi.org/10.1063/1.3592712 (11 pages)

Jianhui Tian and Angel E. García
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back to top Theoretical Methods and Algorithms

Construction of CASCI-type wave functions for very large active spaces

Katharina Boguslawski, Konrad H. Marti, and Markus Reiher

J. Chem. Phys. 134, 224101 (2011); http://dx.doi.org/10.1063/1.3596482 (13 pages)

Online Publication Date: 8 June 2011

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We present a procedure to construct a configuration-interaction expansion containing arbitrary excitations from an underlying full-configuration-interaction-type wave function defined for a very large active space. Our procedure is based on the density-matrix renormalization group (DMRG) algorithm that provides the necessary information in terms of the eigenstates of the reduced density matrices to calculate the coefficient of any basis state in the many-particle Hilbert space. Since the dimension of the Hilbert space scales binomially with the size of the active space, a sophisticated Monte Carlo sampling routine is employed. This sampling algorithm can also construct such configuration-interaction-type wave functions from any other type of tensor network states. The configuration-interaction information obtained serves several purposes. It yields a qualitatively correct description of the molecule's electronic structure, it allows us to analyze DMRG wave functions converged for the same molecular system but with different parameter sets (e.g., different numbers of active-system (block) states), and it can be considered a balanced reference for the application of a subsequent standard multi-reference configuration-interaction method.
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31.15.V- Electron correlation calculations for atoms, ions and molecules

Alternative single-reference coupled cluster approaches for multireference problems: The simpler, the better

Francesco A. Evangelista

J. Chem. Phys. 134, 224102 (2011); http://dx.doi.org/10.1063/1.3598471 (13 pages) | Cited 1 time

Online Publication Date: 10 June 2011

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We report a general implementation of alternative formulations of single-reference coupled cluster theory (extended, unitary, and variational) with arbitrary-order truncation of the cluster operator. These methods are applied to compute the energy of Ne and the equilibrium properties of HF and C2. Potential energy curves for the dissociation of HF and the BeH2 model computed with the extended, variational, and unitary coupled cluster approaches are compared to those obtained from the multireference coupled cluster approach of Mukherjee et al. [J. Chem. Phys. 110, 6171 (1999)] and the internally contracted multireference coupled cluster approach [F. A. Evangelista and J. Gauss, J. Chem. Phys. 134, 114102 (2011)10.1063/1.3559149]. In the case of Ne, HF, and C2, the alternative coupled cluster approaches yield almost identical bond length, harmonic vibrational frequency, and anharmonic constant, which are more accurate than those from traditional coupled cluster theory. For potential energy curves, the alternative coupled cluster methods are found to be more accurate than traditional coupled cluster theory, but are three to ten times less accurate than multireference coupled cluster approaches. The most challenging benchmark, the BeH2 model, highlights the strong dependence of the alternative coupled cluster theories on the choice of the Fermi vacuum. When evaluated by the accuracy to cost ratio, the alternative coupled cluster methods are not competitive with respect to traditional CC theory, in other words, the simplest theory is found to be the most effective one.
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31.15.bw Coupled-cluster theory
31.50.-x Potential energy surfaces
33.15.Dj Interatomic distances and angles
33.15.Mt Rotation, vibration, and vibration-rotation constants

The nature of electron correlation in a dissociating bond

Joshua W. Hollett, Laura K. McKemmish, and Peter M. W. Gill

J. Chem. Phys. 134, 224103 (2011); http://dx.doi.org/10.1063/1.3599937 (5 pages)

Online Publication Date: 10 June 2011

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We have constructed the unrestricted Hartree-Fock (UHF), restricted Hartree-Fock (RHF), and full configuration interaction (FCI) position and momentum intracules and holes for H⋅⋅⋅H at bond lengths R from 1 to 10 bohrs. We trace the recently discovered inversion of the UHF position hole at intermediate R to over-localization of the spin-orbitals, and support this by a correlation energy component analysis. The RHF and UHF momentum holes are found to be more complicated; however their features are explained through decomposition of electron correlation effects. The UHF momentum hole is also found to invert and exhibits interesting behavior at large R. The RHF (but not UHF) and FCI momentum intracules exhibit Young-type interference patterns related to recent double photoionization experiments. Our analyses yield the most comprehensive picture to date of the behavior of the electrons during homolytic bond fission.
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31.15.V- Electron correlation calculations for atoms, ions and molecules
33.15.Dj Interatomic distances and angles
34.80.Ht Dissociation and dissociative attachment

Some comments and corrections regarding the calculation of electrostatic potential derivatives using the Ewald summation technique

Joakim Stenhammar, Martin Trulsson, and Per Linse

J. Chem. Phys. 134, 224104 (2011); http://dx.doi.org/10.1063/1.3599045 (5 pages)

Online Publication Date: 13 June 2011

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A review of the literature on the calculation of electrostatic potentials, fields, and field gradients in systems consisting of charges and dipoles using the Ewald summation technique is presented. Discrepancies between the previous formulas are highlighted, and an error in the derivation of the reciprocal contributions to the electrostatic field and field gradient is corrected. The new formulas for the field and field gradient are shown to exhibit a termwise identity with the ones for the electrostatic energy.
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41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems

Molecular association of heteronuclear vibrating square-well dumbbells in liquid-vapor phase equilibrium

Gustavo A. Chapela, Fernando de Río, and José Alejandre

J. Chem. Phys. 134, 224105 (2011); http://dx.doi.org/10.1063/1.3598480 (12 pages)

Online Publication Date: 14 June 2011

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Molecular aggregates are formed by heteronuclear vibrating square-well dumbbells. In a recent article [G. A. Chapela and J. Alejandre, J. Chem. Phys., 132(10), 104704 (2010)], it is shown that heteronuclear vibrating square-well dumbbells with a diameter ratio between particles of 1/2 and interacting potential ratio of 4 form micelles of different sizes and shapes which manifest themselves in both the liquid and vapor phases, up to and above the critical point. This means that micellization and phase separation are present simultaneously in this simple model. These systems present a maximum in the critical temperature when plotted against the potential well depth of the second particle ε2. In the same publication, it was speculated that the formation of micelles was responsible for the appearance of the maximum. A thorough study on this phenomena is presented here and it is found that there is a threshold on the size of the second particle and its corresponding depth of interaction potential, where the micelles are formed. If the diameter and well depth of the second particle are small enough for the first and deep enough for the second, micelles are formed. For σ2/σ1 between 0.25 and 0.65 and ε2/ε1 larger than 5.7, micelles are formed up to and above the critical temperature. Outside these ranges micelles appear only at temperatures lower than the critical point. There is a strong temperature dependence on the formation and persistence of the aggregates. For the deepest wells and large enough second particles, a gel interconnected aggregate is obtained. In this work, the micelles are formed at temperatures as low as the triple point and as high as the critical point and, in some cases, persist well above it. The presence of these maxima in critical temperatures Tc when plotted against ε2 as follows. At lower values of ε2, an increase of Tc is obtained as is expected by the increase of the attractive volume as indicated by the principle of corresponding states. As ε2 increases further, the formation of molecular aggregates produce a saturation effect of the deepening of the potential well by encapsulating the particles of the second kind inside the micelles, so the resulting Tc represents a new poly disperse system of molecular aggregates and not the original heteronuclear vibrating square-well dumbbells. The surface tension is also analyzed for these systems, and it is shown that decreases with increasing attraction due to the formation of molecular aggregates.
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82.30.Nr Association, addition, insertion, cluster formation
82.70.Dd Colloids
82.70.Gg Gels and sols
82.20.Kh Potential energy surfaces for chemical reactions

Generalized Kubo relations and conditions for anomalous diffusion: Physical insights from a mathematical theorem

Gerald R. Kneller

J. Chem. Phys. 134, 224106 (2011); http://dx.doi.org/10.1063/1.3598483 (7 pages) | Cited 1 time

Online Publication Date: 14 June 2011

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The paper describes an approach to anomalous diffusion within the framework of the generalized Langevin equation. Using a Tauberian theorem for Laplace transforms due to Hardy, Littlewood, and Karamata, generalized Kubo relations for the relevant transport coefficients are derived from the asymptotic form of the mean square displacement. In a second step conditions for anomalous diffusion are derived for the asymptotic forms of the velocity autocorrelation function and the associated memory function. Both spatially unconfined and confined diffusion processes are considered. The results are illustrated with semi-analytical examples.
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05.60.-k Transport processes
02.30.Uu Integral transforms
02.30.Hq Ordinary differential equations

The multiscale coarse-graining method. VII. Free energy decomposition of coarse-grained effective potentials

Lanyuan Lu and Gregory A. Voth

J. Chem. Phys. 134, 224107 (2011); http://dx.doi.org/10.1063/1.3599049 (10 pages)

Online Publication Date: 14 June 2011

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The potential of mean force (PMF) with respect to coarse-grained (CG) coordinates is often calculated in order to study the molecular interactions in atomistic molecular dynamics (MD) simulations. The multiscale coarse-graining (MS-CG) approach enables the computation of the many-body PMF of an atomistic system in terms of the CG coordinates, which can be used to parameterize CG models based on all-atom configurations. We demonstrate here that the MS-CG method can also be used to analyze the CG interactions from atomistic MD trajectories via PMF calculations. In addition, MS-CG calculations at different temperatures are performed to decompose the PMF values into energetic and entropic contributions as a function of the CG coordinates, which provides more thermodynamic information regarding the atomistic system. Two numerical examples, liquid methanol and a dimyristoylphosphatidylcholine lipid bilayer, are presented. The results show that MS-CG can be used as an analysis tool, comparable to various free energy computation methods. The differences between the MS-CG approach and other PMF calculation methods, as well as the characteristics and advantages of MS-CG, are also discussed.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics
33.15.Bh General molecular conformation and symmetry; stereochemistry
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

The isotropic spectrum of the CO2 Raman 2ν3 overtone: A line-mixing band shape analysis at pressures up to several tens of atmospheres

I. A. Verzhbitskiy, A. P. Kouzov, F. Rachet, and M. Chrysos

J. Chem. Phys. 134, 224301 (2011); http://dx.doi.org/10.1063/1.3596750 (6 pages)

Online Publication Date: 9 June 2011

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A line-mixing shape analysis of the isotropic remnant Raman spectrum of the 2ν3 overtone of CO2 is reported at room temperature and for densities, ρ, rising up to tens of amagats. The analysis, experimental and theoretical, employs tools of non-resonant light scattering spectroscopy and uses the extended strong collision model (ESCM) to simulate the strong line mixing effects and to evidence motional narrowing. Excellent agreement at any pressure is observed between the calculated spectra and our experiment, which, along with the easy numerical implementation of the ESCM, makes this model stand out clearly above other semiempirical models for band shape calculations. The hitherto undefined, explicit ρ-dependence of the vibrational relaxation rate is given. Our study intends to improve the understanding of pressure-induced phenomena in a gas that is still in the forefront of the news.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.20.Tp Vibrational analysis
33.70.Jg Line and band widths, shapes, and shifts
33.15.Mt Rotation, vibration, and vibration-rotation constants

Unveiling the nonadiabatic rotational excitation process in a symmetric-top molecule induced by two intense laser pulses

Daeyul Baek, Hirokazu Hasegawa, and Yasuhiro Ohshima

J. Chem. Phys. 134, 224302 (2011); http://dx.doi.org/10.1063/1.3598962 (10 pages)

Online Publication Date: 10 June 2011

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We experimentally investigate the nonadiabatic rotational excitation process of a symmetric-top molecule, benzene, in the electronic ground state irradiated by intense nonresonant ultrafast laser fields. The initial rotational-state distribution was restricted mostly to the five lowest levels with different nuclear spin modifications by an extensive adiabatic cooling with the rotational temperature well below 1 K, and distributions after the interaction with a femtosecond double-pulse pair (3–5 TW/cm2 each with 160 fs duration) with time delays were probed in a quantum-state resolved manner by employing resonant enhanced multiphoton ionization via the S1 ← S0 601 vibronic transition. Populations of 10 rotational levels with J ranging from 0 to 4 and K from 0 to 3 were examined to show an oscillatory dependence on the time delay between the two pulses. Fourier analysis of the beat signals provides the coupling strengths between the constituent levels of the rotational wave packets created by the nonadiabatic excitation. These data are in good agreement with the results from quantum mechanical calculations, evidencing stepwise excitation pathways in the wave packet creation with ΔJ = 2 in the K = 0 stack while ΔJ = 1 and 2 in the K > 0 stacks.
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33.80.Wz Other multiphoton processes
33.80.Eh Autoionization, photoionization, and photodetachment
33.20.Sn Rotational analysis
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
42.50.Wk Mechanical effects of light on material media, microstructures and particles

On the correlation between bond-length change and vibrational frequency shift in halogen-bonded complexes

Weizhou Wang, Yu Zhang, Baoming Ji, and Anmin Tian

J. Chem. Phys. 134, 224303 (2011); http://dx.doi.org/10.1063/1.3599050 (5 pages) | Cited 1 time

Online Publication Date: 10 June 2011

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The C-Hal (Hal = Cl, Br, or I) bond-length change and the corresponding vibrational frequency shift of the C-Hal stretch upon the C-Hal ⋯Y (Y is the electron donor) halogen bond formation have been determined by using density functional theory computations. Plots of the C-Hal bond-length change versus the corresponding vibrational frequency shift of the C-Hal stretch all give straight lines. The coefficients of determination range from 0.94366 to 0.99219, showing that the correlation between the C-Hal bond-length change and the corresponding frequency shift is very good in the halogen-bonded complexes. The possible effects of vibrational coupling, computational method, and anharmonicity on the bond-length change-frequency shift correlation are discussed in detail.
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31.15.E- Density-functional theory
33.15.Dj Interatomic distances and angles
33.20.Tp Vibrational analysis
FREE

All-boron analogues of aromatic hydrocarbons: B17− and B18−

Alina P. Sergeeva, Boris B. Averkiev, Hua-Jin Zhai, Alexander I. Boldyrev, and Lai-Sheng Wang

J. Chem. Phys. 134, 224304 (2011); http://dx.doi.org/10.1063/1.3599452 (11 pages) | Cited 3 times

Online Publication Date: 10 June 2011

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We have investigated the structural and electronic properties of the B17− and B18− clusters using photoelectron spectroscopy (PES) and ab initio calculations. The adiabatic electron detachment energies of B17− and B18− are measured to be 4.23 ± 0.02 and 3.53 ± 0.05 eV, respectively. Calculated electron detachment energies are compared with experimental data, confirming the presence of one planar C2v (1A1) isomer for B17− and two nearly isoenergetic quasi-planar C3v (2A1) and Cs (2A′) isomers for B18−. The stability and planarity/quasi-planarity of B17− and B18− are ascribed to σ- and π-aromaticity. Chemical bonding analyses reveal that the nature of π-bonding in B17− and B18− is similar to that in the recently elucidated B162− and B19− clusters, respectively. The planar B17− cluster can be considered as an all-boron analogue of naphthalene, whereas the π-bonding in the quasi-planar B18− is reminiscent of that in coronene.
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36.40.Mr Spectroscopy and geometrical structure of clusters
32.80.Fb Photoionization of atoms and ions
31.15.ae Electronic structure and bonding characteristics
32.80.Gc Photodetachment of atomic negative ions
36.40.Cg Electronic and magnetic properties of clusters

Intramolecular proton transfer in malonaldehyde: Accurate multilayer multi-configurational time-dependent Hartree calculations

Thorsten Hammer and Uwe Manthe

J. Chem. Phys. 134, 224305 (2011); http://dx.doi.org/10.1063/1.3598110 (11 pages) | Cited 5 times

Online Publication Date: 13 June 2011

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Full-dimensional (multilayer) multi-configurational time-dependent Hartree calculations studying the intramolecular proton transfer in malonaldehyde based on a recent potential energy surface (PES) [Wang et al., J. Chem. Phys. 128, 224314 (2008)10.1063/1.2937732] are presented. The most accurate calculations yield a ground state tunneling splitting of 23.8 cm−1 and a zero point energy of 14 678 cm−1. Extensive convergence tests indicate an error margin of the quantum dynamics calculations for the tunneling splitting of about 0.2 cm−1. These results are to be compared with the experimental value of the tunneling splitting of 21.58 cm−1 and results of Monte Carlo calculations of Wang et al. on the same PES which yielded a zero point energy of 14 677.9 cm−1 with statistical errors of 2 − 3 cm−1 and a tunneling splitting of 21.6 cm−1. The present data includes contributions resulting from the vibrational angular momenta to the tunneling splitting and the zero point energy of 0.2 cm−1 and 2.4 cm−1, respectively, which have been computed using a perturbative approach.
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31.15.xr Self-consistent-field methods
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
33.20.Tp Vibrational analysis
31.50.Bc Potential energy surfaces for ground electronic states
31.15.xp Perturbation theory
82.20.Kh Potential energy surfaces for chemical reactions
FREE

Designing organic spin filters in the coherent tunneling regime

Carmen Herrmann, Gemma C. Solomon, and Mark A. Ratner

J. Chem. Phys. 134, 224306 (2011); http://dx.doi.org/10.1063/1.3598519 (9 pages)

Online Publication Date: 13 June 2011

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Spin filters, that is, systems which preferentially transport electrons of a certain spin orientation, are an important element for spintronic schemes and in chemical and biological instances of spin-selective electronic communication. We study the relation between molecular structure and spin filtering functionality employing a theoretical analysis of both model and stable organic radicals based on substituted benzene, which are bound to gold electrodes, with a combination of density functional theory and the Landauer–Imry–Büttiker approach. We compare the spatial distribution of the spin density and of the frontier central subsystem molecular orbitals, and local contributions to the transmission. Our results suggest that the delocalization of the singly occupied molecular orbital and of the spin density onto the benzene ring connected to the electrodes, is a good, although not the sole indicator of spin filtering functionality. The stable radicals under study do not effectively act as spin filters, while the model phenoxy-based radicals are effective due to their much larger spin delocalization. These conclusions may also be of interest for electron transfer experiments in electron donor–bridge–acceptor complexes.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.65.+h Molecular electronic devices

Gas phase analogs of stable sodium-tin Zintl ions: Anion photoelectron spectroscopy and electronic structure

W.-J. Zheng, O. C. Thomas, J. M. Nilles, K. H. Bowen, A. C. Reber, and S. N. Khanna

J. Chem. Phys. 134, 224307 (2011); http://dx.doi.org/10.1063/1.3597604 (9 pages)

Online Publication Date: 13 June 2011

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Mass spectrometry and photoelectron spectroscopy together with first principles theoretical calculations have been used to study the electronic and geometric properties of the following sodium-tin, cluster anion/neutral cluster combinations, (NanSn4)−/(NanSn4), n = 0–4 and (NaSnm)−/(NaSnm), m = 4–7. These synergistic studies found that specific Zintl anions, which are known to occur in condensed Zintl phases, also exist as stable moieties within free clusters. In particular, the cluster anion, (Na3Sn4)− is very stable and is characterized as (Na+)3(Sn4)−4; its moiety, (Sn4)−4 is a classic example of a Zintl anion. In addition, the cluster anion, (NaSn5)− was the most abundant species to be observed in our mass spectrum, and it is characterized as Na+(Sn5)2−. Its moiety, (Sn5)2− is also known to be present as a Zintl anion in condensed phases.
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31.15.ae Electronic structure and bonding characteristics
33.60.+q Photoelectron spectra
33.15.Ta Mass spectra
36.40.Cg Electronic and magnetic properties of clusters
36.40.Mr Spectroscopy and geometrical structure of clusters
36.40.Qv Stability and fragmentation of clusters

Dynamics of H+ + N2 at ELab = 30 eV

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

J. Chem. Phys. 134, 224308 (2011); http://dx.doi.org/10.1063/1.3598511 (11 pages) | Cited 1 time

Online Publication Date: 14 June 2011

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The H+ + N2 system at ELab = 30 eV, relevant in astrophysics, is investigated with the simplest-level electron nuclear dynamics (SLEND) method. SLEND is a time-dependent, direct, variational, non-adiabatic method that employs a classical-mechanics description for the nuclei and a single-determinantal wavefunction for the electrons. A canonical coherent-states procedure, intrinsic to SLEND, is used to reconstruct quantum vibrational properties from the SLEND classical mechanics. Present simulations employ three basis sets: STO-3G, 6-31G, and 6-31G**, to determine their effect on the results, which include reaction visualizations, product predictions, and scattering properties. Present simulations predict non-charge-transfer scattering and N2 collision-induced dissociation as the main reactions. Average vibrational energy transfer, H+ energy-loss spectra, rainbow angle, and elastic vibrational differential cross sections at the SLEND/6-31G** level agree well with available experimental data. SLEND/6-31G** results are comparable to those calculated with the vibrational close-coupling rotational infinite-order sudden approximation and the quasi-classical trajectory method.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.20.Wt Computational modeling; simulation
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.20.Fd Collision theories; trajectory models

Application of parametric equations of motion to study the laser induced multiphoton dissociation of H2+ in intense laser field

Dhruba J. Kalita, Akshay Rao, Ishir Rajvanshi, and Ashish K. Gupta

J. Chem. Phys. 134, 224309 (2011); http://dx.doi.org/10.1063/1.3598516 (6 pages)

Online Publication Date: 14 June 2011

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We have applied parametric equations of motion (PEM) to study photodissociation dynamics of H2+. The resonances are extracted using smooth exterior scaling method. This is the first application of PEM to non-Hermitian Hamiltonian that includes resonances and the continuum. Here, we have studied how the different resonance states behave with respect to the change in field amplitude. The advantage of this method is that one can easily trace the different states that are changing as the field parameter changes.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
31.50.Df Potential energy surfaces for excited electronic states

Theoretical modeling of ionization energies of argon clusters: Nuclear delocalization effects

Pavla Svrčková, Aleš Vítek, František Karlický, Ivana Paidarová, and René Kalus

J. Chem. Phys. 134, 224310 (2011); http://dx.doi.org/10.1063/1.3599052 (6 pages) | Cited 1 time

Online Publication Date: 14 June 2011

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Temperature dependence of vertical ionization energies is modeled for small argon clusters (N ⩽ 13) using classical parallel-tempering Monte Carlo methods and extended interaction models based on the diatomics-in-molecules approach. Quantum effects at the zero temperature are also discussed in terms of zero-point nuclear vibrations, either at the harmonic approximation level or at the fully anharmonic level using the diffusion Monte Carlo calculations. Both approaches lead to a considerable improvement of the theoretical predictions of argon clusters ionization energies and represent a realistic way of modeling of ionization energies for weakly bound and floppy complexes in general. A thorough comparison with a recent electron-impact experiment [O. Echt et al., J. Chem. Phys. 123, 084313 (2005)] is presented and a novel interpretation of the experimental data is proposed.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics
33.20.Tp Vibrational analysis
02.70.Uu Applications of Monte Carlo methods
36.40.-c Atomic and molecular clusters
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
34.80.Gs Molecular excitation and ionization

The 15Πg state of C2

Timothy W. Schmidt and George B. Bacskay

J. Chem. Phys. 134, 224311 (2011); http://dx.doi.org/10.1063/1.3599933 (4 pages)

Online Publication Date: 14 June 2011

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We report ab initio spectroscopic constants for the recently identified 15Πg state of C2 [P. Bornhauser, Y. Sych, G. Knopp, T. Gerber, and P. P. Radi, J. Chem. Phys. 134, 044302 (2011)]. The calculations are performed at the multi-reference configuration interaction level of theory with Davidson's correction using aug-cc-pV6Z basis sets and include core-valence correlation and relativistic corrections obtained with quadruple-zeta bases. Such treatment accurately reproduces the experimentally observed constants of the a3Πu and other states. Thus, we expect our calculated ωe value for the 15Πg state to be within a few  cm−1, and rotational constants to be within 0.1% of experiment. Agreement with available spectroscopic data is excellent, with the calculations strongly suggesting that the 15Πg vibrational level observed by Bornhauser et al. is v = 0.
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31.15.aj Relativistic corrections, spin-orbit effects, fine structure; hyperfine structure
31.30.js Corrections to bound-electron g factor
33.20.Sn Rotational analysis
33.20.Tp Vibrational analysis
back to top Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation

On the mechanism of the highly viscous flow

U. Buchenau

J. Chem. Phys. 134, 224501 (2011); http://dx.doi.org/10.1063/1.3598506 (7 pages)

Online Publication Date: 10 June 2011

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The asymmetry model for the highly viscous flow postulates thermally activated jumps from a practically undistorted ground state to strongly distorted, but stable structures, with a pronounced Eshelby backstress from the distorted surroundings. The viscosity is ascribed to those stable distorted structures which do not jump back, but relax by the relaxation of the surrounding viscoelastic matrix. It is shown that this mechanism implies a description in terms of the shear compliance, with a viscosity which can be calculated from the cutoff of the retardation spectrum. Consistency requires that this cutoff lies close to the Maxwell time. The improved asymmetry model compares well with experiment.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.dj Poisson's ratio
62.20.de Elastic moduli
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Renormalization-group analysis of the RI − RV rotator phase transition

Prabir K. Mukherjee

J. Chem. Phys. 134, 224502 (2011); http://dx.doi.org/10.1063/1.3599051 (6 pages) | Cited 1 time

Online Publication Date: 10 June 2011

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A model for coupled tilt angle and lattice distortion parameter is proposed to describe the RI − RV transition in n-alkane. The model is treated in the framework of a Landau mean-field theory and renormalization-group theory. The influence of gauche conformations and molecular flexibility on the RI − RV transition is discussed within the mean-field theory. The fluctuations on the RI − RV transition are discussed by the renormalization-group theory. Renormalization-group theory predicts that the RI − RV transition can be driven first order by fluctuations and becomes second order at a tricritical point. Available experimental data are consistent with our model.
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64.60.ae Renormalization-group theory
61.66.Hq Organic compounds
64.70.K- Solid-solid transitions

Time-resolved luminescence spectroscopy of self-trapped excitons in ladder type Br-bridged Pt complexes

T. Suemoto, H. Nakao, M. Nakajima, and H. Kitagawa

J. Chem. Phys. 134, 224503 (2011); http://dx.doi.org/10.1063/1.3595264 (6 pages)

Online Publication Date: 10 June 2011

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The out-of-phase and in-phase ladder type Br-bridged Pt complexes are investigated by time-resolved luminescence spectroscopy in pico- and femtosecond time regions. The observed luminescence spectra have peaks at 0.87 and 0.94 eV in out-of-phase and in-phase materials, respectively, and are assigned to self-trapped excitons. The wave-packet oscillations in self-trapped excitons (STE) are observed in both materials. The time-evolution curves are analyzed in terms of the secondary radiation theory of strongly coupled electron-phonon system. The period and dephasing time of oscillations as well as the lifetime and spectral shape of the STE luminescence are determined. The fast dephasing or cooling of the wave-packet motion observed in the in-phase type complex is ascribed to inter-chain interactions within the ladder.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
63.20.kd Phonon-electron interactions
78.47.jd Time resolved luminescence
71.35.-y Excitons and related phenomena
71.38.-k Polarons and electron-phonon interactions
78.55.Kz Solid organic materials

Simulation of multiple ordered phases in C23 n-alkane

Nathaniel Wentzel and Scott T. Milner

J. Chem. Phys. 134, 224504 (2011); http://dx.doi.org/10.1063/1.3589417 (11 pages) | Cited 1 time

Online Publication Date: 13 June 2011

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Normal alkanes display multiple ordered phases, including an orthorhombic crystal (X) and two partially ordered rotator phases (RI and RII). The rotator phase transitions X–RI and RI–RII are of interest because they are weakly first-order, and because experiments suggest that crystalline polyethylene may nucleate via a metastable rotator phase. We have performed heating and cooling scans of all-atom NσT (isothermal, isostress) simulations of a pure C23 solid. We find a sequence of phases, transition temperatures, structural and thermodynamic properties, all reasonably consistent with experiment, except that a monoclinic crystal is more stable in our simulations than the experimental orthorhombic structure. We find that the RI phase is well described as an orthorhombic crystal disordered by random ±90° rotations of molecules about their stem axis, and the RII phase can be represented as a loose hexagonal packing of parallel chain stems, which tend to orient with the in-plane projection of C-C bonds pointing between neighbors. To measure local orthorhombic, RI, or RII order, we define Potts- and Ising-like order parameters, from which global order parameters and correlation functions can be computed. We observe modest pretransitional fluctuations of local RI order in the RII phase near TRI-RII, characteristic of this weakly first-order transition.
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64.60.My Metastable phases
64.60.Q- Nucleation
61.50.Ks Crystallographic aspects of phase transformations; pressure effects
81.40.Gh Other heat and thermomechanical treatments
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions

Intermediate vibronic coupling in charge transfer states: Comprehensive calculation of electronic excitations in sexithiophene crystal

Anna Stradomska, Waldemar Kulig, Michał Slawik, and Piotr Petelenz

J. Chem. Phys. 134, 224505 (2011); http://dx.doi.org/10.1063/1.3597607 (12 pages) | Cited 1 time

Online Publication Date: 13 June 2011

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A comprehensive theory of linear vibronic coupling in a coupled manifold of Frenkel and charge-transfer states in an infinite molecular crystal is presented and applied for sexithiophene. The approach, valid in the intermediate-coupling regime, includes up to three-particle terms of the Philpott expansion, with the vibronic wavefunctions represented in the Lang-Firsov basis. As a stringent test, the scheme is used to reproduce the complete set of available sexithiophene absorption and electroabsorption spectra within a unified theoretical framework. The input is based primarily on independent calculations and to some extent on independent experiments, with explicit fitting contained within the limits set by the estimated inherent errors of a priori parameter estimates. Reasonably good quantitative agreement with experimental spectra is achieved. The results resolve some existing interpretational ambiguities and expose some peculiarities of electric field effect on vibronic eigenstates of Frenkel parentage, highlighting the role of charge-transfer interactions.
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63.20.kk Phonon interactions with other quasiparticles
71.35.-y Excitons and related phenomena
78.20.Jq Electro-optical effects

CO2 solvation free energy using quasi-chemical theory

Dian Jiao and Susan B. Rempe

J. Chem. Phys. 134, 224506 (2011); http://dx.doi.org/10.1063/1.3598470 (9 pages)

Online Publication Date: 14 June 2011

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Accumulation of greenhouse gases, especially carbon dioxide, is believed to be the key factor in global climate change. To develop effective ways to remove CO2 from the atmosphere, it is helpful to understand the mechanism of CO2 solvation first. Here we investigate the thermodynamics of CO2 hydration using quasi-chemical theory. Two approaches for estimating hydration free energy are carried out. Both agree reasonably well with experimental measurements. Analysis of the free energy components reveals that the weak hydration free energy results from a balance of unfavorable molecular packing and favorable chemical association.
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82.33.Tb Atmospheric chemistry
92.60.Sz Air quality and air pollution
82.20.-w Chemical kinetics and dynamics
82.30.Nr Association, addition, insertion, cluster formation
82.60.Lf Thermodynamics of solutions

Increased fraction of low-density structures in aqueous solutions of fluoride

Iradwikanari Waluyo, Congcong Huang, Dennis Nordlund, Thomas M. Weiss, Lars G. M. Pettersson, and Anders Nilsson

J. Chem. Phys. 134, 224507 (2011); http://dx.doi.org/10.1063/1.3597606 (7 pages)

Online Publication Date: 14 June 2011

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X-ray absorption spectroscopy (XAS) and small angle x-ray scattering (SAXS) were utilized to study the effect of fluoride (F−) anion in aqueous solutions. XAS spectra show that F− increases the number of strong H-bonds, likely between F− and water in the first hydration shell. SAXS data show a low-Q scattering intensity increase similar to the effect of a temperature decrease, suggesting an enhanced anomalous scattering behavior in F− solutions. Quantitative analysis revealed that fluoride solutions have larger correlation lengths than chloride solutions with the same cations but shorter compared to pure water. This is interpreted as an increased fraction of tetrahedral low-density structures in the solutions due to the presence of the F− ions, which act as nucleation centers replacing water in the H-bonding network and forming stronger H-bonds, but the presence of the cations restricts the extension of strong H-bonds.
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78.70.Dm X-ray absorption spectra
78.70.Ck X-ray scattering
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